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  • Artikel  (106)
  • Finite elements  (43)
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  • 2015-2019
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 58 (1994), S. 121-127 
    ISSN: 1432-0630
    Schlagwort(e): 07.85 ; 68.55 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The importance of collecting the distribution of scattered X-rays in two dimensions with the “right probe” will be addressed. The data-collection method will be briefly covered and how this greatly assists the interpretation of structural features giving rise to the distributed X-ray scattering. The combination of diffraction-space mapping with multiple crystal topography will also be presented to show how any region of scattering can be related to lateral structural changes or crystal imperfections. The simulation of the diffraction profiles of structures with defects will be addressed as well as the interpretation of “unusual and strange” diffraction features observed in high resolution, which yield further useful information on the materials under study.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 58 (1994), S. 191-195 
    ISSN: 1432-0630
    Schlagwort(e): 42.40 ; 78.20 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Holograms may be recorded in photorefractive LiNbO3:Cu with pulsed infrared light (wavelength λ=1064 nm, Q-switched Nd:YAG laser), if the crystals are previously or simultaneously illuminated with a green (λ=532 nm) light pulse. We study refractive index changes and time constants of as-grown and thermally treated crystals with different copper concentrations. A model explaining this effect is discussed.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 59 (1994), S. 163-168 
    ISSN: 1432-0630
    Schlagwort(e): 78.70. Bj ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Samples of the near equiatomic NiSb compound were irradiated by 3 MeV electrons at 20 K or quenched from 1103 K and 1333 K and subsequently annealed isochronally. The behaviour of defects created by quench or irradiation were studied by the positron annihilation technique. Only one recovery stage was found around 425 K for quenched specimens, but two distinct stages (100 K and 425 K) were observed after irradiation. The 425 K stage is ascribed to the migration of Ni vacancies giving dislocation loops. The recombination of mobile interstitials with vacancies after irradiation is assumed to occur between 100 K and 250 K. Doppler broadening and lifetime variations of positrons as a function of the measuring temperature in these irradiation samples are discussed.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 59 (1994), S. 193-197 
    ISSN: 1432-0630
    Schlagwort(e): 73.20 ; 81.60 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The evaluation of the surface state distribution of differently HF-treated Si(111) surfaces during the native-oxide growth in air is investigated by the large-signal field-modulated photovoltage technique. The surface state distribution consisting of intrinsic and extrinsic Si dangling bond defects is directly related to the state of oxidation of the Si surface. It is shown that the kind of HF treatment strongly influences the concentration of extrinsic defects with a lower state of oxidation. Special HF preparations for H termination of the Si(111) surface result in a nearly intrinsic surface state distribution. During the oxidation process three typical phases can be distinguished each characterized by specific defect structures. It was found that native-oxide growth is highly sensitive to the concentration of extrinsic defects directly after HF treatment.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 59 (1994), S. 563-567 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 72.40 ; 78.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Photoconductivities and photovoltaic currents of ruthenium-doped KNbO3 are orders of magnitude larger than that of undoped and ion-doped crystals. KNbO3:Ru is very sensitive for holographic recording with red light and the photovoltaic current increases sublinearly with light intensity.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 59 (1994), S. 295-297 
    ISSN: 1432-0630
    Schlagwort(e): 81.60 ; 82.65 ; 82.80
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A multilayered structure of GaAs and AlGaAs was depth profiled using the technique of digital etching. A single excimer laser (KrF) was used to control the etch rate and to identify each layer by monitoring the Ga ions generated during the desorption process. The Ga ions were the only ions observed and were only generated when the photon flux was in the GaAs layer. The etch rate, 0.9 monolayers (2.5 Å) per pulse, was constant with depth. The overall layer recognition resolution was 45 monolayers.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 59 (1994), S. 245-251 
    ISSN: 1432-0630
    Schlagwort(e): 71.00 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract An electron trap having an energy level of 0.14 eV from the conduction band edge was found in the bulk of copper-diffused VPE-grown n-GaAs0.6P0.4 by conventional DLTS measurements and by pulse-duration dependent capacitance amplitude measurements. The capture cross section at room temperature is about 1.0×10−21 cm2 and has a weak temperature dependence. These properties are attributed to a non-repulsive center having a capturing mechanism which involves multiphonon emission processes with hardly any lattice relaxation. Evolution of the spatial distributions of the traps with time under junction electric field were studied. The results suggest that the trap is positively charged and has a high diffusivity under electric field. The center can thus be identified as positively charged interstitial copper ion rather than some form of copper complexes.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1432-0630
    Schlagwort(e): 68.55 ; 61.70 ; 74.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Ultrathin epitaxial films of YBa2Cu3O7−δ on SrTiO3 prepared by Direct Current (DC) sputtering and pulsed laser deposition were imaged by Atomic Force Microscopy (AFM) to follow the different stages of growth of the thin films. Series of films with thicknesses between 1.2 nm and 12 nm (1–10 monolayers of YBa2Cu3O7−δ) were prepared under identical conditions, optimized with respect to electrical and structural properties, to obtain information on the mechanisms responsible for the formation of growth spirals which are commonly observed in films having a thickness of several 10 nm or more. It could be shown that few layers are formed by a layered growth mode where material is attached laterally to 2D islands which are only one c-axis unit cell in height. In a later stage of growth when about 8–10 layers have been formed, the growth process changes to a mode which is mediated by growth spirals. This could be directly monitored in the AFM images where different defect structures like vertically sheared growth fronts and dendrite-like terraces of stacked islands as well as the resulting growth spirals could be identified.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 59 (1994), S. 289-293 
    ISSN: 1432-0630
    Schlagwort(e): 42.55 ; 81.40 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Structure formation upon 500 fs 248 nm KrF-laser irradiation of PolyEthylene Terephthalate (PET) and PolyImide (PI) has been investigated. The results obtained with fs pulses have been compared to those with ns pulses.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 18 (1994), S. 1021-1060 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Shallow water equations ; Boundary conditions ; Dispersion analysis ; Spurious modes ; Wave equation ; Primitive equations ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Finite element solutions of the primitive equation (PE) form of the shallow water equations are notorious for the severe spurious 2Δx modes which appear. Wave equation (WE) solutions do not exhibit these numerical modes. In this paper we show that the severe spurious modes in PE solutions are strongly influenced by essential normal flow boundary conditions in the coupled continuity-momentum system of equations. This is demonstrated through numerical examples that avoid the use of essential normal flow boundary conditions either by specifying elevation values over the entire boundary or by implementing natural flow boundary conditions in the weak weighted residual form of the continuity equation. Results from a series of convergence tests show that PE solutions are of nearly the same quality as WE solutions when spurious modes are suppressed by alternative specification of the boundary conditions. Network intercomparisons indicate that varying nodal support does not excite spurious modes in a solution, although it does enhance the spurious modes introduced when an essential normal flow boundary condition is used.Dispersion analysis of discrete equations for interior and boundary nodes offers an explanation of the observed solution behaviour. For certain PE algorithms a mixed situation can arise where the boundary nodes exhibit a monotonic (noise-free) dispersion relationship and the interior nodes exhibit a folded (noisy) dispersion relationship. We have found that the mixed situation occurs when all boundary nodes are specified elevation nodes (which are enforced as essential conditions in the continuity equation) or when specified flow boundary nodes are treated as natural boundary conditions in the continuity equation. In either case the effect is to generate a solution that is essentially free of noise. Apparently, the monotonic dispersion behaviour at the boundaries suppresses the otherwise noisy behaviour caused by the folded dispersion relation on the interior.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 11
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 19 (1994), S. 513-525 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Incompressible viscous flow ; Streamfunction-vorticity ; Vorticity boundary conditions ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The streamfunction-vorticity equations for incompressible two-dimensional flows are uncoupled and solved in sequence by the finite element method. The vorticity at no-slip boundaries is evaluated in the framework of the streamfunction equation. The resulting scheme achieves convergence, even for very high values of the Reynolds number, without the traditional need for upwinding. The stability and accuracy of the approach are demonstrated by the solution of two well-known benchmark problems: flow in a lid-driven cavity at Re ≤ 10,000 and flow over a backward-facing step at Re = 800.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 499-505 
    ISSN: 1432-0630
    Schlagwort(e): 68.55 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The adsorption of CO on a Ni(100) surface has been studied by FT-IRAS in the temperature range from 85 K to 300 K. At 300 K and for Θ=0.5, the CO molecules are predominantly adsorbed in on-top sites with only a minor fraction located at two-fold bridge sites. Measurements on a Ni(100) surface pre-covered with sulphur, oxygen and carbon indicate that the occupation of bridge sites may be caused by small amounts of surface impurities. The relative broadness of the infrared bands is explained by CO molecules occupying intermediate positions at domain walls. Upon lowering the temperature, the bridge sites are increasingly occupied at the expense of terminal sites. This process is completely reversible and is explained by a contribution of the hindered translations of the adsorbed CO molecules to the entropy. At 85 K and for low initial coverages, we observe an unusual high CO stretching frequency at 2205 cm−1 which cannot be explained at present.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 437-440 
    ISSN: 1432-0630
    Schlagwort(e): 78.20 ; 61.70 ; 72.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Holograms recorded under suitable conditions in photorefractive BaTiO3 exhibit an unusual dark build-up. The diffraction efficiency increases by some orders of magnitude after the recording beams are switched off, and then steadily decreases afterwards. An interpretation of this effect in terms of a two-center charge transport model is given.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 561-566 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 68.35 ; 81.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The laser-induced solid-state explosive nucleation in amorphous media is studied analytically. The shapes of the temperature switching wave and that of the nucleation front as well as the formula for the front velocity are derived considering also self-consistent medium deformation. Two conditions of explosive nucleation reflecting the roles of latent heat emission and of deformation are formulated. It is shown that, in explosive nucleation, the rate of internal heat emission is proportional to the square of the latent crystallization heat (“superemission”) in analogy to photon superradiance in initially inverted two-level atomic systems.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 367-374 
    ISSN: 1432-0630
    Schlagwort(e): 82.65 ; 82.50 ; 42.10
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract UV-laser ablation is described in terms of a two-level system in which the excitation energy is dissipated via stimulated emission, thermal relaxation, and activated desorption of excited species. For thermal relaxation times t T〉10−9 s and ΔE* ≪ ΔE (activation energies for excited-state and ground-state species) the model predicts high ablation rates at moderate surface temperatures, typically below 2000° C.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 377-383 
    ISSN: 1432-0630
    Schlagwort(e): 07.80 ; 61.70 ; 81.10 ; 85.30
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract High-resolution transmission electron microscopy (HREM) allows to study a wide range of device-relevant topics in heteroepitaxial layer structures. Quantitative HREM may be used to obtain chemical information on a near-atomic scale from interfacial transition zones. The physical background is described and demonstrated on several examples in the Al x Gal1−x As/GaAs system. The HREM contrast of antiphase boundaries in InP grown on Si was studied by image simulations and has been compared to experimental images. Silicon carbide precipitates were identified by HREM at the homoepitaxial Si/Si interface. They stem from carbon contamination prior to Si layer growth.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 56 (1993), S. 69-72 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 73.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A computer simulation study of the capacitance of a surface space charge layer in undoped n-GaAs grown by metalorganic vapour phase epitaxy is presented. The effect of the deep donor level EL2 on the surface capacitance of epilayers with an ideal free surface is estimated. In order to approach the as-grown layer surface the model used is extended considering MIS and Schottky-barrier structures and their voltage-capacitance curves are analysed. The theoretical C-V dependences are compared with experimental C-V curves of a real structure including N+-GaAs substrate, undoped n-GaAs epitaxial layer containing EL2 levels and thin native oxide. Conditions are determined at which the EL2 levels as well as the native oxide film may influence the capacitance characteristics.
    Materialart: Digitale Medien
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  • 18
    ISSN: 1432-0630
    Schlagwort(e): 68.35 ; 82.20 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The influence of surface reconstruction on the kinetics of adsorption-desorption processes is studied through a simple two-position model by means of Monte Carlo simulation. Effects due to constraints on the translational motion of activated complexes and to heterogeneity are particularly investigated. Heterogeneity emerges as the most important factor to explain the huge variation of the preexponential Arrhenius parameter with coverage observed in the H/W(001) system. In the present model it is conjectured that heterogeneity originates from additional interactions of H with surface or sub-surface W atoms when hydrogen is adsorbed on sites where surface W atoms are farther apart due to reconstruction.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 449-455 
    ISSN: 1432-0630
    Schlagwort(e): 82.65 ; 82.50 ; 42.10
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The stability of a planar surface upon pulsed UV-laser irradiation is studied with special emphasis on polymer ablation. Here, we consider a two-level system in which the excitation energy is dissipated via stimulated emission, non-radiative transitions, and activated desorption of excited species. With thermal relaxation times t T≥10−10 s the ablation front turns out to become stable. This could explain the smooth surfaces obtained after pulsed UV-laser ablation of pure and stress free organic polymers. The situation is quite different for materials, for example metals, where fast thermal relaxation of the excitation energy within times, typically, t T〈10−11 s, gives rise to instabilities which result in surface roughening.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 57 (1993), S. 507-511 
    ISSN: 1432-0630
    Schlagwort(e): 68.35 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract PhotoEmission Electron Microscopy (PEEM) enables imaging a surface via its work function. If a CO covered Pt(100) surface is exposed to oxygen patches are formed which appear dark in the PEEM image due to their high work function. As the surface is heated to temperatures above 650 K we observe the conversion of these dark islands into very bright ones with work functions much lower than even that of the clean surface. These findings are attributed to a change in the dipole moment of the adsorbed oxygen induced by their migration beneath the surface. A total work-function decrease of up to 1.2 eV has been evaluated independently using a Scanning Photoemission Microscope (SPM). The properties of this new kind of oxygen were also further investigated with thermal desorption spectroscopy and with Auger-electron spectroscopy.
    Materialart: Digitale Medien
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  • 21
    ISSN: 1432-0630
    Schlagwort(e): 68.55 ; 81.15 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Heteroepitaxial diamond growth has been attempted on mirror-polished monocrystalline (001), (111), and (110) silicon substrates by microwave plasma CVD. The surface morphology and the crystallographic properties of the films were characterized by means of Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray diffraction, and X-ray and Raman pole-figure analysis. The results demonstrate epitaxial growth of diamond on both (001) and (111) oriented silicon substrates. Preliminary results give strong evidence for substrate-induced orientation of the diamond crystallites also on (110) oriented silicon substrate. The heteroepitaxy can be assigned to the oriented covalent bonding across the interface between diamond and silicon.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 56 (1993), S. 323-327 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 75.50
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Measurements of the magnetic after-effect in magnetite have been made in the temperature range 200 to 600 K. Important relaxation peaks have been observed in the temperature range 250 to 350 K (peak III) and 400 to 550 K (peak I). A study of both the dynamics and the parameters of the defects are consistent with an interpretation of peak III and peak I in magnetite as a combined after-effect due to octahedrally coordinated vacancies.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 56 (1993), S. 343-348 
    ISSN: 1432-0630
    Schlagwort(e): 81.40 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Laser-induced maskless etching of III–V compound semiconductors (InSb, GaAs, and InP) in a KOH aqueous solution by irradiation with a focused argon-ion laser has been investigated to obtain high etching rates and aspect ratios of etched grooves. The etching rate at low laser power was found to depend on the carrier density of the sample and its type. With the increase of the laser power, the etching reaction becomes primarily a thermochemical reaction. High etching rates and aspect ratios have been achieved with a single scan of the laser beam. The damage induced by laser wet etching is less than that by laser dry etching, and the damage at the etched side wall is less than that at the etched bottom. Grooves with locally controlled depth and slab structures have been fabricated for application.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 56 (1993), S. 417-423 
    ISSN: 1432-0630
    Schlagwort(e): 42.60 ; 82.65 ; 73.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Ablation of the surface of a polyimide (Kapton™) film by single pulses of 248 nm or 308 nm radiation (∼20 ns) or 9.17 μm laser radiation (∼170 ns) was studied by photographing the emergence of the blast wave and the plume by a pulse (〈1 ns; 596 nm) of visible laser light. The dynamics of the blast wave was similar in the ultraviolet and in the infrared but the composition of the plume was obviously different. A mass of opaque solid material was ejected for as long as 2.6 μs following the IR pulse in contrast to the minute amount of solids that are seen in the ablation by UV laser pulses of ns duration. UV laser pulses of 50–400 μs duration interact with polyimide surfaces in a manner that is similar to IR laser pulses of ns duration or longer. Chemical analysis of the ablation products that are obtained under various conditions of ablation when compared to the known modes of thermal degradation of polyimide show that the reaction is a thermal process when IR laser pulses or UV laser pulses of long (〉10 μs) duration are employed. Ablation by ns UV laser pulses differs fundamentally in the chemistry of the products from all of the cases mentioned above.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 56 (1993), S. 571-574 
    ISSN: 1432-0630
    Schlagwort(e): 78.30 ; 68.55 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Macroscopic defects of the GaAs surface grown by molecular beam epitaxy (MBE) have been investigated by using a micro-probing method of Raman spectroscopy. Especially, the oval defects, the most common macroscopic defects in MBE GaAs, were focused in this study. In Raman spectroscopy for the oval defect on the (100)GaAs surface, TO phonon mode of the 269 cm−1 peak was observed. This indicates that the oval defects can include the (111) growth direction or the amorphized surface. The TO/LO intensity ratios for the defects are in the range from 0.3 to 1.0. In the sample grown under the condition that the substrate temperature is 580° C with the As/Ga ratio of 20, the density of the oval defects is about 200 cm−2 at a growth thickness of 5 μm. With increasing thickness of the epilayer, the density and the size of the α-tye oval defect increased, while the TO/LO ratio decreased. From the spatial measurement by Raman spectroscopy for the α-type oval defect, it is supposed that the α-type oval defect remains in a rather good crystalline state and its orientation along the (100) growth direction is much closer to the (111) direction, but the growth direction of the defect might tend toward the (100) direction with a thicker layer.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Journal of computer-aided materials design 1 (1993), S. 85-96 
    ISSN: 1573-4900
    Schlagwort(e): Finite elements ; Brownian dynamics ; Colloidal dispersion ; Plane Couette flow ; Simulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary We present a novel method for the numerical calculation of the flow of particulate fluid systems and apply it to the flow of a colloidal dispersion. This method is based on the CONNFFESSIT (Calculation Of Non-Newtonian Flow: Finite Element and Stochastic Simulation Technique) [Laso and Öttinger, J. Non-Newtonian Fluid Mech., 47 (1993) 1]. It couples microscopic dynamic simulations (Brownian Dynamics, BD) with macroscopic Finite Element (FE) methods as traditionally used in the calculation of viscoelastic flow. The standard continuum-mechanical form of the momentum transport equation is closed by microscopic BD simulations. The coupling between the macroscopic FE formulation for the velocity field and the microscopic simulation is effected through the stress tensor, which is obtained as an ensemble average over BD trajectories. This combination of microscopic simulations with macroscopic FE methods obviates the need for a rheological constitutive equation (strain history-stress relationship) to describe the fluid system. It is therefore possible to solve flow problems for very general fluid systems, for which no exact constitutive equation can be derived. The method is applied to the start-up of plane Couette flow of an electrostatically stabilized colloidal dispersion. The calculation of the inhomogeneous start-up of Couette flow for a colloidal dispersion undergoing a disorder-order transition has remained intractable up to now, due to the difficulty of deriving a constitutive equation for the interacting colloidal dispersion in order to close the equation of motion. Besides giving the evolution of the velocity field, the combination of BD and FE techniques provides a fully detailed, time-dependent, dynamic and structural description of the colloidal dispersion. During inhomogeneous start-up, the colloidal dispersion undergoes a disorder-order phase transition as in the homogeneous case. However, depending on the ratio of the characteristic time for the phase transition and the transit time for a velocity disturbance, either the transition can occur simultaneously throughout the fluid or a moving front separating ordered and disordered regions can appear.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 16 (1993), S. 29-42 
    ISSN: 0271-2091
    Schlagwort(e): 3D extrusion ; Moving boundaries ; Die design ; Remeshing ; Finite elements ; Free surfaces ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Let us call a direct extrusion problem (DEP) the problem of finding the shape of the extrudate coming out of a die of prescribed shape. An implicit finite element formulation of the DEP which is geometrically general and for which a Newton-Raphson technique can be implemented has recently been proposed by Legat and Marchal. However, the problem posed to the die designer is frequently the inverse extrusion problem (IEP), i.e. finding the die shape which produces an extrudate of prescribed shape. This paper presents an extension of our original method for solving the IEP which avoids the ‘trial-and-error’ iteration on the die geometry itself.The advantage of the formulation lies in its capability to handle complex geometrics and in its low cost, because the CPU time and memory required to solve the IEP are almost identical to those of the DEP. We present benchmark results for squares and rectangles and new results obtained for geometries involving multiple corners. For an octagonal shape we also consider the case of a power-law fluid.For all results presented in this paper, surface tension has not been included.
    Zusätzliches Material: 13 Ill.
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  • 28
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 16 (1993), S. 217-230 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Moist atmosphere ; Convection ; Computation ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A computer simulation is made of cellular convection in a moist atmosphere in an endeavour to obtain a computer model which more closely approximates the observed modes of convection. A finite element Galerkin technique, with Taylor approximation and Crank-Nicolson, is employed and comparisons are made with the author's earlier finite element models of convection in an absolutely unstable atmosphere and with finite difference models. It is found that the inclusion of the moisture effects alters the structure of a cell to that of a narrow ascending region and a wider descending region with the former of larger velocities than the latter, and also alters the preferred mode of convection by increasing the aspect ratio. This more closely resembles that which is observed in the atmosphere.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 16 (1993), S. 613-627 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Aeroacoustics ; Propellers ; Sheared flow ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The recent interest in propeller noise generation, stimulated by development of new propeller types for commerical propjets, has generated a need for the ability of measure the noise characteristics of propellers. However, wind tunnel noise measurements are affected by reflections from the wind tunnel walls. Computer codes predicting the free-field noise of a propeller and its noise field in a circular wind tunnel allow validating the use of wind tunnel measurements to predict free-field noise characteristics. A wind tunnel contains flow which is uniform in the duct axial direction, but can vary in the radial direction. It can be shown that a third-order differential equation governs the acoustic pressure field for such a duct containing radially sheared subsonic flow. This third-order problem is then posed as a coupled pair of equations which are second-order in terms of acoustic density and first-order in terms of an artificial variable which represents the effects of the flow being sheared. It is shown that this form of the problem allows a natural extension of the existing numerical solution techniques for non-sheared flow. The sheared flow problem is presented, and a finite element method is developed to yield a solution for propeller-type acoustic forces. The finite element code and method are refined with numerical experiments, and results are presented for a specific propeller and duct geometry. Good agreement is shown between this method and an alternate approach to the sheared flow problem using a piecewise constant representation of the velocity in the boundary layer. This validates both the numerical methods.
    Zusätzliches Material: 15 Ill.
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  • 30
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 955-974 
    ISSN: 0271-2091
    Schlagwort(e): Advection-dispersion equation ; Finite elements ; Iterative methods ; Non-symmetric linear systems ; Conjugate gradients ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Seven leading iterative methods for non-symmetric linear systems (GMRES, BCG, QMR, CGS, Bi-CGSTAB, TFQMR and CGNR) are compared in the specific context of solving the advection-dispersion equation by a classic approach: The space derivatives are approximated by linear finite elements while an implicit scheme is used to integrate the time derivatives. Convergence formulas that predict the behaviour of the iterative methods as a function of the discretization parameters are developed and validated by experiments. It is shown that all methods converge nicely when the coefficent matrix of the linear system is close to normal and the finite element approximation of the advection-dispersion equation yields accurate results.
    Zusätzliches Material: 7 Ill.
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  • 31
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 943-953 
    ISSN: 0271-2091
    Schlagwort(e): Viscoelastic ; Least squares ; Finite elements ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Viscoelastic flows remain a demanding class of problems for approximate analysis, particularly at increasing Weissenberg numbers. Part of the difficulty stems from the convective behavior and in the treatment of the stress field as a primary unknown. This latter aspect has led to the use of higher-order piecewise approximations for the stress approximation spaces in recent finite element research. The computational complexity of the discretized problem is increased significantly by this approach but at present it appears the most viable technique for solving these problems. Motivated by recent success in treating mixed systems and convective problems, we formulate here a least squares finite element method for the viscoelastic flow problem. Numerical experiments are conducted to test the method and examine its strengths and limitations. Some difficulties and open issues are identified through the numerical experiments. We consider the use of high degree elements (p refinement) to improve performance and accuracy.
    Zusätzliches Material: 5 Ill.
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  • 32
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 995-1002 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Turbomachinery flow ; Optimal design ; Decomposition method ; Potential flow ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A method of optimal design of Francis turbine tongue and wicket gate angle for given spiral casing is proposed. The potential flow in the doubly connected domain is decomposed into basic and circulation flows. The intensity of circulation is then calculated by the least-squares method minimizing the error function equal to the sum of squares of differences between given and calculated circumferential velocities in the outflow boundary nodes. It is shown that the error function has a sharp minimum, which qualifies the proposed method as well defined. For given numerical example, the variations in the outflow velocity angles are much smaller for optimal than for already used non-optimal design. A finite element method is used, with originally developed pre- and post-processor and frontal solver suited for personal computers.
    Zusätzliches Material: 6 Ill.
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  • 33
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 16 (1993), S. 953-966 
    ISSN: 0271-2091
    Schlagwort(e): Curvilinear co-ordinate system ; Incompressible viscous flow ; Finite elements ; Penalization and reduced integration ; Streamline upwind artificial viscosity ; Algebraic model of turbulence ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This paper discusses the calculation of quasi-three-dimensional incompressible viscous flow by FEM. The Reynolds-averaged Navier-Stokes equations are solved in curvilinear co-ordinates by the reduced integration and penalty method (RIP). Streamline upwind artificial viscosity (SUAV) and the Baldwin-Lomax algebraic model of turbulence are used. Time discretization is by the general implicit θ-method.
    Zusätzliches Material: 11 Ill.
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  • 34
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 349-364 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Velocity correction method ; Flow past a cylinder ; Navier-Stokes equations ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A finite element solution of the two-dimensional incompressible Navier-Stokes equations has been developed. The present method is a modified velocity correction approach. First an intermediate velocity is calculated, and then this is corrected by the pressure gradient which is the solution of a Poisson equation derived from the continuity equation. The novelty, in this paper, is that a second-order Runge-Kutta method for time integration has been used. Discretization in space is carried out by the Galerkin weighted residual method. The solution is in terms of primitive variables, which are approximated by polynomial basis functions defined on three-noded, isoparametric triangular elements. To demonstrate the present method, two examples are provided. Results from the first example, the driven cavity flow problem, are compared with previous works. Results from the second example, uniform flow past a cylinder, are compared with experimental data.
    Zusätzliches Material: 20 Ill.
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  • 35
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 463-475 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Streamline upwind ; Quadratic elements ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A direct streamline upwind method has been developed for convection-dominated flow problems utilizing quadratic elements. The approach presented retains the curve-sidedness feature offered by these elements. This facilitates the use of boundary conforming elements in domains that possess extreme curvature such as turbomachinery bladed components, for which the method is particularly suited. Three test cases are solved to evaluate the stability and diffusive characteristics of the numerical solution. The results presented clearly demonstrate that the proposed method does not exhibit any non-physical spatial oscillations, nor does it suffer from the traditional problem of excessive numerical diffusion.
    Zusätzliches Material: 15 Ill.
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Meccanica 27 (1992), S. 119-130 
    ISSN: 1572-9648
    Schlagwort(e): Finite elements ; Time integration ; Dynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Beschreibung / Inhaltsverzeichnis: Sommario Due differenti formulazioni agli elementi finiti nel tempo sono presentate in questo lavoro quali casi particolari di una formulazione generale a tre campi: la prima è una formulazione agli spostamenti, mentre la seconda è una formulazione mista dove i campi indipendenti sono costituiti da spostamenti e momenti cinetici. Dopo aver sviluppato la linearizzazione e l'approssimazione agli elementi finiti delle forme, viene discussa una tecnica per il trattamento di vincoli di olonomia ed anolonomia. Le principali caratteristiche numeriche dei due metodi vengono infine evidenziate facendo anche ricorso ad esempli semplici ma significativi.
    Notizen: Abstract Very general weak forms may be developed for dynamic systems, the most general being analogous to a Hu-Washizu three-field formulation, thus paralleling well-established weak methods of solid mechanics. In this work two different formulations are developed: a pure displacement formulation and a two-field mixed formulation. With the objective of developing a thorough understanding of the peculiar features of finite elements in time, the relevant methodologies associated with this approach for dynamics are extensively discussed. After having laid the theoretical bases, the finite element approximation and the linearization of the resulting forms are developed, together with a method for the treatment of holonomic and nonholonomic constraints, thus widening the horizons of applicability over the vast world of multibody system dynamics. With the purpose of enlightening on the peculiar numerical behavior of the different approaches, simple but meaningful examples are illustrated. To this aim, significant parallels with elastostatics are emphasized.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Meccanica 27 (1992), S. 3-11 
    ISSN: 1572-9648
    Schlagwort(e): Elliptic PDEs ; Finite elements ; Mixed elements ; Differential geometry ; Whitney forms ; Tonti diagrams ; Complementarity ; Duality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Beschreibung / Inhaltsverzeichnis: Sommario Gli elementi misti sono elementi finiti speciali per campi vettoriali le cui funzioni di interpolazione non sono necessariamente continue in tutte le componenti; tali elementi vengono usati nell'ambito delle formulazioni ‘a due campi’, per esempio quando si calcolano simultaneamente spostamento e tensione in elasticità. In questo articolo viene presentata una famiglia di elementi finiti che traggono origine da un costrutto di geometria differenziale che in apparenza non ha alcun nesso con l'analisi numerica (le forme di Whitney): vengono illustrate le proprietà strutturali complessive di tale famiglia. Questa presentazione getta una nuova luce sugli elementi misti, sotto la quale essi acquistano un carattere più naturale.
    Notizen: Abstract Mixed elements are special finite elements for vector fields, whose shape functions are not necessarily continuous in all their components. They are used in connection with ‘two-field’ formulations, for instance when one tries simultaneously to compute displacement and stress in elasticity. We present here a family of finite elements which originate from a chapter of differential geometry apparently unconnected with numerical analysis (Whitney forms) and insist on the structural properties of this family considered as a whole. This sheds a new light on mixed elements, under which they acquire a more natural character than in previous presentations.
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  • 38
    ISSN: 1432-0630
    Schlagwort(e): 81.40 ; 61.70 ; 61.80
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Extended lattice damage created by implantation of 3.6 MeV Au2+ ions has been investigated using transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). Systematic observations of damage for Au2+ ions implanted with varying doses into silicon are explained in terms of a model. The origin of two distinct bands of extended defects is explained in terms of annealing of the central region of implant-damage, during the course of the implantation. Two distinct bands of Au precipitates are observed in high-dose implanted samples. This observation is explained as being the result, in part, of segregation of gold in front of a recrystallizing front, and in part, of gettering of dopant-atoms to nodes in a dislocation network. The network arises as a result of dynamic annealing of damaged crystalline silicon.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 54 (1992), S. 221-224 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 64 ; 72.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The thermal evolution of monoclinic SiAs precipitates at 1050° C in silicon samples implanted with 1 and 1.5×1017 As/cm2 was followed by transmission electron microscopy (TEM) and secondary neutral mass spectrometry (SNMS). These experiments show, for the first time, the coexistence of two different states of As in silicon, i.e., the electrically active and the inactive mobile dopant, in equilibrium with monoclinic SiAs precipitates. Moreover, they provide, for the saturation concentration of As in silicon, which includes both these states, a value of 3×1021 cm−3 at 1050° C.
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 54 (1992), S. 265-269 
    ISSN: 1432-0630
    Schlagwort(e): 68.55 ; 61.16D ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract We have used STM to study the surface morphology of thin epitaxial Ge films grown on Si(001) in the presence of the “surfactant” As. The surfactant forces layer-by-layer growth up to 12 ML Ge coverage which could partly be explained by the geometrical surface arrangement of the growing film. Beyond 12 ML coverage we observed a network of trenches which decorate the earlier described V-shaped defects inside the film. Overgrowth of such defects is studied and a mechanism discussed.
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 54 (1992), S. 517-519 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 62.20.Fe ; 64.70.−p
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A theoretical model is proposed which treats the diffusion-induced decay of fragment boundary disclinations as being a micromechanism for the solid state amorphization in mechanically alloyed materials. Within the framework of the suggested model the kinetics of amorphous-phase nucleation centres (spread cores of the decayed disclinations) is studied. In doing so, kinetic equations are suggested and solved, which describe the evolution of the radius of the amorphous core of the decayed disclination.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 55 (1992), S. 161-166 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 81.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The electron-deformation-thermal theory of pulsed laser-induced point defect generation in strongly absorbing semiconductors is developed. The theoretical results obtained are in a good agreement with the results of experiments carried out in Ge, GaAs, and GaP.
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 55 (1992), S. 269-273 
    ISSN: 1432-0630
    Schlagwort(e): 42.60 ; 82.65 ; 73.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Continuous wave laser radiation from an argonion laser in the wavelength range 275–330 nm can be used to etch polyethylene terephthalate (PET) films with as little thermal damage as from a pulsed, ultraviolet laser (248 nm or 308 nm) provided the beam is focussed to a spot of 10–100 kW/cm2 of power density and is moved over the surface at speeds at which the transit time over its own diameter (which can be looked upon as a “pulse width”) is on the order of 10–200 μs. In contrast to results which had been obtained previously on the photokinetic etching of polyimide and doped polymethyl methacrylate films under similar conditions, the sensitivity of PET to etching is 〉5-fold greater than either of these polymers and increases steadily with increasing pulse width. There is lateral thermal damage as the pulse widths increase to 〉200 μs. The material that is removed is vaporized in part. More than 20% is probably ejected in a molten state and resolidifies at the edge of the cut. There is no acoustic report similar to that seen in ablative photodecomposition. The process appears to be largely thermal in nature.
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  • 44
    ISSN: 1432-0630
    Schlagwort(e): 02.50 ; 81.60.c ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Si surfaces covered with up to a monolayer of chlorine by exposure to a low chlorine pressure have been irradiated with nanosecond excimer-laser pulses at a fluence just large enough to melt the surface. Angle-resolved time-of-flight (TOF) distributions and surface temperatures have been measured as a function of chlorine dose between laser pulses. The TOF distributions can be fitted well by Maxwell-Boltzmann (MB) distributions for all coverages and at all desorption angles. With increasing coverage, the intensity and kinetic energy distributions become increasingly peaked along the surface normal. Monte-Carlo simulations of the effect of post-desorption collisions, occurring when many molecules are desorbed within a very short time, reproduce the experimental results quite well. It is shown that just a few collisions per molecule are sufficient to convert any initial desorption distribution into a MB one.
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  • 45
    ISSN: 1432-0630
    Schlagwort(e): 61.10 ; 61.70 ; 68.55
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The structure of Si implanted with high doses of yttrium has been investigated by varying implantation doses and energies. As implantation doses increase into the low 1017 cm−2 range, silicide precipitates form. The precipitates are thin and long and lie parallel to {111} planes in the Si matrix. As dopant concentrations increase, the precipitates themselves become more equiaxed, aspect ratios decrease, and precipitates densities increase until the precipitates coalesce to form a continuous buried layer of yttrium silicide within the Si matrix. The layer thickness is relatively uneven. As implant doses increase to ∼ 4×1017 cm−2, the layer thicknesses become more uniform although there are still defects present. As the implant doses increase further, the precipitate bands on either side of the continuous layer decrease due to gettering of yttrium to the layer. As the energy of the implant is increased, the appearance of the sample is similar to that of the lower energy implants except that the layer is buried deeper in the Si matrix. Observations of the silicide are consistent with its having the AlB2 structure with ordered vacancies on the Si sublattice.
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  • 46
    ISSN: 1432-0630
    Schlagwort(e): 81.40 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Laser-induced direct writing of silver lines on a ferrite surface from a silver acetate (CH3COOAg) thin layer has been investigated. The deposition is a thermochemical process and the threshold temperature for thermal decomposition of CH3COOAg is about 380° C. About 100% of Ag in the deposited lines has been achieved. The width of the deposited Ag-lines increased with the increase in laser power, and it can be accurately estimated by the temperature profile induced by laser irradiation within the power region below the melting point of ferrite. A line thickness of micron order can be formed both on a ferrite surface and on a deposited SiO2 surface, whereas the line width decreased with the increase in beam dwell time due to the vaporization of both CH3COOAg precursor and deposited Ag material.
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  • 47
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 47-69 
    ISSN: 0271-2091
    Schlagwort(e): Partial differential equations ; Non-linear equations ; Coupled system ; Numerical methods ; Finite elements ; Adaptive grid ; Flow in porous media ; Groundwater contamination ; Multiphase flow ; Immiscible flow ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This paper presents numerical examples for the moving grid finite element algorithm derived in Part Ito solve the non-linear coupled set of PDEs governing immiscible multiphase flow in porous media in one dimension. Examples include single- and double-front simulations for two- and three-phase flow regimes and incorporating a mass sink. The modelling approach is shown to achieve significant savings in computation time and memory allocation when compared with fixed grid solutions of equivalent accuracy. This work includes sensitivity analyses for the parameters which are incorporated in the grid adaptation method, including the curvature weights, artificial viscosity and artificial repulsive force. It is found that the curvature weights are exponential functions of the negative ratio of the square root of the domain length to the number of discrete nodes. These weighting parameters are also shown to depend upon the shape of the front. On the basis of the examined simulations, it is recommended that artificial viscosity be neglected in the solution of the coupled non-linear set of PDEs governing multiphase flow in porous media. Similarly, use of a repulsive force is found to be unnecessary in simulations involving the migration of two liquid phases. For multiphase flows incorporating a gas phase it is recommended to use a non-zero value for the repulslive force to avoid development of an ill-conditioned nodal distribution matrix. An equation to evaluate the repulsive force under these circumstances is suggested.
    Zusätzliches Material: 13 Ill.
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  • 48
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 609-625 
    ISSN: 0271-2091
    Schlagwort(e): 3D extrusion ; Moving boundaries ; Kinematic condition ; Remeshing ; Finite elements ; Free surfaces ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This paper presents a numerical technique for solving three-dimensional free surface problems in extrusion applications. The method is fully implicit in the sense that a Newton-Raphson scheme is applied on all variables, and geometrically general. In particular, the die section shape may be complex and contains multiple corners: very few restrictions apply on the mesh generation because the method does not require the nodes to be located on straight lines (spines). A clear distinction is introduced between the directions associated with the kinematic condition and the remeshing rules. As a difference with respect to earlier publications, these concepts are handled separately. Only Stokes problems are solved in this paper and we have not introduced surface tension. Therefore corners in the die section propagate discontinuities in the extrudate shape, an a method for relocating corners without losing the quadratic convergence of the scheme is presented. Data structures used for the implementation are briefly discussed.We present results on the extrusion of various profiles, including a rectangular die (a benchmark problem) and various complex sections containing multiple corners.
    Zusätzliches Material: 15 Ill.
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  • 49
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 15 (1992), S. 1073-1118 
    ISSN: 0271-2091
    Schlagwort(e): Space-time ; Finite elements ; Incompressible flows ; Galerkin/least-squares ; Deforming spatial domain ; Oscillating cylinder ; Pitching aerofoil ; Clustered element-by-element ; GMRES ; Vortex shedding ; Vortex-induced oscillations ; Lock-in ; Hysteresis ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: We present our numerical results for certain unsteady flows past oscillating cylinders and aerofoils. The computations are based on the stabilized space-time finite element formulation. The implicit equation systems resulting from the space-time finite element discretizations are solved using iterative solution techniques.One of the problems studied is flow past a cylinder which is forced to oscillate in the horizontal direction. In this case we observe a change from an unsymmetric mode of vortex shedding to a symmetric one. An extensive study was carried out for the case in which a cylinder is mounted on lightly damped springs and allowed to oscillate in the vertical direction. In this case the motion of the cylinder needs to be determined as part of the solution, and under certain conditions this motion changes the vortex-shedding pattern of the flow field significantly. This non-linear fluid-structure interaction exhibits certain interesting behaviour such as ‘lock-in’ and ‘hysteresis’, which are in good agreement with the laboratory experiments carried out by other researchers in the past. Preliminary results for flow past a pitching aerofoil are also presented.
    Zusätzliches Material: 39 Ill.
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  • 50
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 15 (1992), S. 967-974 
    ISSN: 0271-2091
    Schlagwort(e): Permeable walls ; Bulk friction ; Time-dependent ; Incompressible Navier-Stokes ; Pressure correction ; Projection ; Semi-implicit ; Finite elements ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Computer simulations may contribute significantly to the optimal design of air-conditioning systems. To capture the effects of partially permeable walls such as bookshelves on the movement of air and heat, it is necessary to extend the density-dependent Navier-Stokes equations by an additional friction term. The finite element technique is convenient to approximate the extended equations in spatial co-ordinates. For the time co-ordinate a recently proposed semi-implicit finite difference method is very efficient in terms of accuracy and computational complexity. A pressure correction approach is most appropriate to decouple the primitive variables in the extended Navier-Stokes equations. The resulting algorithm has the interesting feature that small symmetric positive definite systems of equations can be solved sequentially for each of the primitive variables. Iterative solution of the systems of equations with preconditioned conjugate gradients combined with a compressed storage scheme allows fine grid computations at affordable costs. As an example a two-dimensional version of the code was applied to an enclosure which was heated from the side and contained a porous wall. The time-dependent computational results are compared with measurement data.
    Zusätzliches Material: 2 Ill.
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  • 51
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 25-45 
    ISSN: 0271-2091
    Schlagwort(e): Partial differential equations ; Non-linear equations ; Coupled system ; Numerical methods ; Finite elements ; Adaptive grid ; Flow in porous media ; Groundwater contamination ; Multiphase flow ; Immiscible flow ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A straightforward moving grid finite element method is developed to solve the one-dimensional coupled system of non-linear partial differential equations (PDEs) governing two- and three-phase flow in porous media. The method combines features from a number of self-adaptive grid techniques. These techniques are the equidistribution, the moving grid finite element and the local grid refinement/coarsening methods. Two equidistribution criteria, based on solution gradient and curvature, are employed and nodal distributions are computed iterativcly. Using the developed approach, an intermingle-free nodal distribution is guaranteed. The method involves examination of a single representative gradient to facilitate the application of moving grid algorithms to solve a non-linear coupled set of PDEs and includes a feature to limit mass balance error during nodal redistribution. The finite element part of the developed algorithm is verified against an existing finite difference model. A numerical simulation example involving a single-front two-phase flow problem is presented to illustrate model performance. Additional simulation examples are given in Part 2 of this paper. These examples include single and double moving fronts in two- and three-phase flow systems incorporating source/sink terms. Simulation sensitivity to the moving grid parameters is also explored in Part 2.
    Zusätzliches Material: 8 Ill.
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  • 52
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 817-841 
    ISSN: 0271-2091
    Schlagwort(e): Mixed convection ; Finite elements ; CVD ; Iterative methods ; Preconditioning ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An algorithm is presented for the finite element solution of three-dimensional mixed convection gas flows in channels heated from below. The algorithm uses Newton's method and iterative matrix methods. Two iterative solution algorithms, conjugate gradient squared (CGS) and generalized minimal residual (GMERS), are used in conjunction with a preconditioning technique that is simple to implement. The preconditioner is a subset of the full Jacobian matrix centered around the main diagonal but retaining the most fundamental axial coupling of the residual equations. A domain-renumbering scheme that enhances the overall algorithm performance is proposed on the basis of and analysis of the preconditioner. Comparison with the frontal elimination method demonstrates that the iterative method will be faster when the front width exceeds approximately 500. Techniques for the direct assembly f the problem into a compressed sparse row storage format are demonstrated. Elimination of fixed boundary conditions is shown to decrease the size of the matrix problem by up to 30%. Finally, fluid flow solutions obtained with the numerical technique are presented. These solutions reveal complex three-dimensional mixed convection fluid flow phenomena at low Reynolds numbers, including the reversal of the direction of longitudinal rolls in the presence of a strong recirculation in the entrance region of the channel.
    Zusätzliches Material: 10 Ill.
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  • 53
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 1367-1376 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Viscoelastic flow ; Convergence failure ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This paper presents an algorithm for two-dimensional Steady viscoelastic flow Simulation in which the Solution of the momentum and continuity equations is decoupled from that of the constitutive equations. The governing equations are discretized by the finite element method, with 3 × 3 element subdivision for the stress field approximation. Non-consistent Streamline upwinding is also used. Results are given for flow through a converging channel and through an abrupt planar 4:1 contraction.
    Zusätzliches Material: 4 Ill.
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  • 54
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 1377-1382 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Viscoelastic flow ; Convergence failure ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: We present the results of some numerical experiments which were carried out in order to investigate the general characteristics of the algorithm described in Part I of this paper.
    Zusätzliches Material: 4 Ill.
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  • 55
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 1407-1419 
    ISSN: 0271-2091
    Schlagwort(e): Adaptive mesh refinement ; Finite elements ; Compressible flow ; Transient problems ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An adaptive finite element scheme for transient problems is presented. The classic h-enrichment/coarsening is employed in conjunction with a tetrahedral finite element discretization in three dimensions. A mesh change is performed every n time steps, depending on the Courant number employed and the number of ‘protective layers’ added ahead of the refined region. In order to simplify the refinement/coarsening logic and to be as fast as possible, only one level of refinement/coarsening is allowed per mesh change. A high degree of vectorizability has been achieved by pre-sorting the elements and then performing the refinement/coarsening groupwise according to the case at hand. Further reductions in CPU requirements arc realized by optimizing the identification and sorting of elements for refinement and deletion. The developed technology has been used extensively for shock-shock and shock-object interaction runs in a production mode. A typical example of this class of problems is given.
    Zusätzliches Material: 4 Ill.
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  • 56
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 14 (1992), S. 343-360 
    ISSN: 0271-2091
    Schlagwort(e): Free surfaces ; Extrusion ; Conjugate gradients ; Finite elements ; Three-dimensional free surfaces ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In order to reduce the cost of large three-dimensional calculations of steady state free surfaces, we have combined a time-dependent approach, a decoupling algorithm and a conjugate gradient solver along the lines introduced earlier by Gresho and Chan. The free surface is calculated separately by applying the kinematic condition to a number of faces defined on the undeformed surface. For the pseudo-time-marching technique we show that it is economical to adopt different time steps for the free surface calculation and the other fields. The accuracy of the method is tested on the well-known circular die problem; the method is then used to reveal the effects of inertia and shear thinning on square and rectangular dies.
    Zusätzliches Material: 15 Ill.
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  • 57
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 52 (1991), S. 218-221 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 61.70Ph
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Various dislocations on Ag(111) were imaged with a scanning tunneling microscope, e.g. screw dislocations, Lomer-Cottrell locks and stacking fault tetrahedron. The distortion field near a screw dislocation was measured.
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  • 58
    ISSN: 1432-0630
    Schlagwort(e): 73.30 ; 61.70 ; 81.15C
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Magnetron-sputtered CoSi2 and TiSi2 Schottky barriers on n- and p-type GaP were investigated. Their hitherto unknown barrier heights were determined to be 0.98 eV (for CoSi2/n-GaP and CoSi2/p-GaP), 0.91 eV (for TiSi2/n-GaP), and 0.90 eV (for TiSi2/p-GaP). It was found that magnetron-sputtering induced a compensated layer near the surface, both for n- and p-type GaP, with a thickness of about 0.05 μm. As the dependence of the shift of the Mott-Schottky intercept with the V-axis on the substrate dopant concentration obeyed some specific law, we proposed that the defects are neutral complexes of dopant ions and sputter-induced native defects. These native defects were assumed to depend on the Fermi level position, namely the PGa antisite and the VP vacancy for p-GaP and the VGa vacancy for n-GaP. The conversion between these defects occurs by nearest neighbour hopping of a phosphorus atom. The Schottky barrier heights obtained on p-GaP could be explained by Fermi level pinning at the surface due to the PGa defects. This could not be confirmed by n-GaP as the energy level position of the VGa was not available. The defects could be annealed out between 200° C and 300° C and the associated change of the Schottky barrier height corroborated the proposed model.
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  • 59
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 52 (1991), S. 445-447 
    ISSN: 1432-0630
    Schlagwort(e): 82.65 ; 36.40 ; 73.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Desorption of K atoms by laser-excitation of surface plasmons in small K particles is reported. The desorption rate has been measured for different laser wavelengths and particle sizes. Time-of-flight measurements reveal a kinetic energy of the desorbed atoms of Ekin=0.13(3) eV. From the experimental data it is concluded that the desorption mechanism is non-thermal in nature. Comparison of the results reported here with our earlier work on Na desorption is made.
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 339-342 
    ISSN: 1432-0630
    Schlagwort(e): 68.55.G ; 82.50.-m ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Large area excimer laser induced deposition of titanium on fused silica from TiCl4 is studied with an emphasis on process modeling. We show that several TiCl4 monolayers can be adsorbed if the surface is adequately prepared and that the Ti thin film growth occurs through the photodecomposition of this adsorbed TiCl4 layer. We propose two growth regimes. During an initiation phase, up to 3 nm in thickness, the adsorbed layer is photochemically decomposed giving a growth rate of ∼ 0.015 nm/pulse. In a second phase, the deposition rate increases to between 2 and 7 nm/pulse due to the laser heating of the preceding photochemically deposited titanium film. Between consecutive pulses, TiCl4 molecules primarily from the adsorbed layer diffuse to the reaction zone leading to a new adsorbed layer ready to be transformed to solid titanium.
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  • 61
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 8-19 
    ISSN: 1432-0630
    Schlagwort(e): 82.45 ; 61.70 ; 68.45
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A number of interesting and still not fully understood phenomena occur if silicon is used as an electrode in an electrochemical cell. Effects include porous silicon layer (PSL) formation with features on a nanometer scale, surface roughening on a micrometer scale, quantum efficiencies for light generated currents much larger than 1, preferential etching of defects, electropolishing, and voltage or current oscillations. It is shown that despite the complexities of chemical reactions involved, a basic understanding of the electrode behavior is possible from a semiconductor physics point of view and that it can be advantageous to use the silicon — electrolyte junction for analytical purposes. Topics such as defect characterization, measurements of minority carrier diffusion length, or surface recombination velocities can be addressed in unique ways by taking advantage of particular properties of the silicon — hydrofluoric acid system. Based on the general description of the Si — electrolyte junction given in this paper, strengths and limitations of some electrochemical methods are discussed in some detail and illustrated by examples.
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  • 62
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 179-184 
    ISSN: 1432-0630
    Schlagwort(e): 81.15.C ; 79.20.N ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract We studied the angular distributions of silicon and nitrogen atoms emitted from a Si target subjected to reactive sputtering by N 2 + ions at primary energies of 0.5 and 2keV. The composition of the deposited material does not depend strongly on the substrate position. From a comparison with nonreactive sputtering, we show that the observed shift of the Si angular distribution is mainly due to the contribution of collision events occurring in the first monolayer. Contrary to the case of noble gas ions, the sharpness of the Si distribution depends on the N 2 + energy. The behavior of the differential sputtering yield of silicon indicates that this effect is likely to be due to a loss of recoil atoms out of the preferential direction. A possible explanation of the observed phenomena consists in assuming an anisotropic emission of Si x N y radicals. This hypothesis is very attractive as it could satisfactorily explain the similarity we observed between the angular distributions of silicon and nitrogen.
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  • 63
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 189-193 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 81.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The electrical activity of interfacial misfit dislocations in silicon has been examined using the electron beam induced current technique (EBIC) in a scanning electron microscope. “Clean” misfit dislocations, i.e. no EBIC contrast, formed during high-temperature Si(Ge) chemical vapor epitaxy were studied. These defects were subsequently decorated with known metallic impurities (Au and Ni) by diffusion at 400° C to 1130° C from a back-side evaporated layer. Qualitative analysis of the electrical activity in relation to the energy levels anticipated for the clean or decorated dislocations is presented. Of particular interest is the case of defect-induced conductivity type inversion which occurred both at the top surface and at the buried dislocated interfaces of the multilayer. The prospects for using dislocations in a beneficial manner as active elements in electronic devices are discussed.
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 388-402 
    ISSN: 1432-0630
    Schlagwort(e): 68.35 ; 61.16 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Low-energy ion backscattering and scanning tunneling microscopy (STM) have been used in combination to get better insight into the field of surface crystallography. The synergic effectiveness resulting from the complementing character of the two methods has been exemplified at clean NiAl(111) and for oxygen and nitrogen adsorption on Cu(110). The position of the atom cores is accessible by the low-energy noble gas impact collision ion scattering spectroscopy with neutral detection (NICISS). As a technique averaging over a macroscopic area of the sample, NICISS is better suited to supply information on features of completely developed phases, either on clean or adsorbate saturated surfaces. Additional information, on the other hand, can be gained by scanning tunneling microscopy (STM), which as a powerful local probe may be used to image surfaces with atomic resolution and to monitor defects, steps and the growth kinetics of e.g. adsorption-induced phase changes.
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  • 65
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 81-86 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 72.40 ; 78.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Measurements of photoconductivity and light-induced absorption in KNbO3: Fe are performed at different light intensities and crystal temperatures. The results are interpreted in terms of a two-center charge transport model. Different model parameters may be evaluated from the experimental data. A complete set of parameters is suggested explaining the dependences of photoconductivity and light-induced absorption on light intensity and temperature for the KNbO3: Fe crystal investigated.
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 332-338 
    ISSN: 1432-0630
    Schlagwort(e): 42.55P ; 81.40Z ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The results of the numerical analysis of the effects induced by pulsed Nd:YAG and ruby laser on Hg0.8Cd0.2Te are presented. The proposed model facilitates the planning of HgCdTe laser processing and the choice of the processing parameters such as: melt depth, melt duration of the surface layer and melt front velocity, as well as the irradiation parameters. The influence of the optical parameters and the temperature dependence of the HgCdTe thermal parameters on the results of laser irradiation are specially analyzed.
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  • 67
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 765-783 
    ISSN: 0271-2091
    Schlagwort(e): Radiation boundary conditions ; Open boundary conditions ; Wave equation ; Finite elements ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: On the basis of the dispersion relation of the generalized linear wave equation we derive a radiation boundary condition (RBC) that explicitly incorporates the physical parameters of the governing equation into the form of the boundary condition. Using finite element techniques we investigate the properties of the generalized RBC by examining forced and unforced solutions to the telegraph and Klein-Gordon equations in one dimension. The results show that within the limits of the physical parameters of the problem the generalized RBC is an improvement over the Sommerfeld RBC when the governing equation contains additional terms that influence the propagation. These gains are achieved without introducing any computational overhead. A two-dimensional example suggests that the 1D findings can generalize to higher dimensions.
    Zusätzliches Material: 11 Ill.
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  • 68
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 507-533 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Hydrodynamics ; Three-dimensional hydrodynamics ; Non-linear hydrodynamics ; Tidal hydrodynamics ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The development and application of a non-linear 3D hydrodynamic model are described. The model is based on the wave equation rearrangement of the primitive 3D shallow water equations with a general eddy viscosity formulation for the vertical shear. A Galerkin procedure is used to discretize these on simple sixnode elements: linear triangles in the horizontal with linear variations in the vertical. Resolution of surface, bottom and interfacial boundary layers is facilitated and total flexibility is preserved for specifying spatial and temporal variations in the vertical viscosity and density fields. A semi-implicit time-stepping algorithm allows the solutions for elevation and velocity to be uncoupled during each time step. The elevation solution is essentially a 2D wave equation calculation with a stationary sparse matrix representing the gravity waves. With nodal quadrature the subsequent velocity calculation is achieved by factoring only a tridiagonal diffusion matrix representing the vertical viscous terms. As a result the overall calculation scales computationally as only a 2D problem but provides the full 3D solution. Application to field-scale problems is illustrated for the English Channel/Southern Bight system and the Lake Maracaibo system.
    Zusätzliches Material: 19 Ill.
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  • 69
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 343-367 
    ISSN: 0271-2091
    Schlagwort(e): Stokes waves ; Non-linear waves ; Second order waves ; Wave diffraction ; Finite elements ; Wave loading ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A new finite-element based method of calculating non-linear wave loads on offshore structures in extreme seas is presented in this paper. The diffraction wave field is modelled using Stokes wave theory developed to second order. Wave loads and free surface elevations are obtained for fixed surface-piercing structures by solving a boundary value problem for the second-order velocity potential. Special attention has been given to the radiation condition for the second-order diffraction field. Results are presented for three test examples, the vertical cylinders of Kim and Yue and of Chakrabarti, and an elliptic cylinder. These results demonstrate that early problems with the application of second-order theory arising from inadequate radiation conditions have been overcome.
    Zusätzliches Material: 10 Ill.
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  • 70
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 12 (1991), S. 559-576 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Quasi-three-dimensional ; Numerical oceanography ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A quasi-three-dimensional numerical model is presented and applied to some test problems with constant density. The numerical technique is based on a finite element formulation and the three-dimensional problem is factorized into one- and two-dimensional subproblems. The non-linear advection is treated by use of a weak formulation of the characteristics method and the equations are transformed to ‘sigma’ coordinates.
    Zusätzliches Material: 14 Ill.
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  • 71
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 33-48 
    ISSN: 0271-2091
    Schlagwort(e): Laminar mixed convection ; Parabolic flow ; Finite elements ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A generally applicable finite element procedure for the prediction of laminar mixed convection in horizontal straight ducts of arbitrary cross-section is presented. The procedure, based on the parabolized simplification of the complete Navier-Stokes equations and on the Boussinesq approximation of the buoyancy terms, is validated through comparisons of computed results with the available literature data for mixed convection in the entrance region of a rectangular duct of aspect ratio a=2. Uniform heating at different sides is considered as the thermal boundary condition, although the proposed formulation allows specification of most thermal boundary conditions of practical interest.
    Zusätzliches Material: 11 Ill.
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  • 72
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 145-165 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Meshing ; Adaptivity ; Navier-Stokes ; Power law ; Error estimation ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An adaptive strategy for the finite element solution of three-dimensional viscous flow problems is defined and implemented. The solution strategy is based on an advancing front mesh generator making use of binary data structures for fast geometrical data handling. The error is estimated a posteriori with a residual-type bound. The error estimate is shown to exhibit proper convergence for tetrahedral elements. Its combination with the mesh generator and an interpolation scheme for unstructured meshes is shown to generate adaptive meshes and to reduce the solution cost for a given error level, as illustrated by the isothermal flow of a shear-thinning fluid.
    Zusätzliches Material: 19 Ill.
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  • 73
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 1251-1265 
    ISSN: 0271-2091
    Schlagwort(e): Singular basis functions ; Finite elements ; Stick-slip problem ; Die-swell problem ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: We further develop a new singular finite element method, the integrated singular basis function method (ISBFM), for the solution of Newtonian flow problems with stress singularities. The ISBFM is based on the direct subtraction of the leading local solution terms from the governing equations and boundary conditions of the original problem, followed by a double integration by parts applied to those integrals with singular contributions. The method is applied to the stick-slip and the die-swell problems and improves the accuracy of the numerical results in both cases. In the case of the die-swell problem it considerably accelerates the convergence of the free surface profile with mesh refinement. The advantages and disadvantages of the ISBFM when compared to other singular methods are also discussed.
    Zusätzliches Material: 9 Ill.
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  • 74
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 545-549 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 66.30
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The primary species in both solid-state conduction and heterogeneous electrocatalysis of solid oxide electrolytes is the anion vacancy. The nature and effect of the local environment on anion vacancies in 10 m/o yttria stabilized zirconia (YSZ) and 20 m/o erbia stabilized bismuth oxide (ESB) was studied using uv-visible absorption and fluorescence spectroscopy. Partial reduction of YSZ and ordering of the oxygen sublattice in ESB is discussed. The species common to both of these phenomena, anion vacancies, was found to be luminescent and the absorption and fluorescence spectra attributable to F-center type defects is described.
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 385-396 
    ISSN: 1432-0630
    Schlagwort(e): 42.5 ; 68 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Reaction rates, particle densities, and temperature distribution in pyrolytic (photothermal) laser-induced microchemical processing are investigated with respect to temperature and concentration-dependent transport coefficients, and with respect to the effect of thermal diffusion. While the model employed is particularly suitable for laser-induced chemical vapor deposition (LCVD), it can also be applied to many cases of laser-induced surface modification and dry-etching.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 151-156 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 17.55
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Electrically active deep levels related to zinc in silicon are investigated in n- and p-type silicon using Deep-Level Transient Fourier Spectroscopy (DLTFS) measurements. While in n-type silicon a level at E C−0.49 eV is observed, the main zinc-related levels in p-type silicon are determined to be E V+0.27 eV and E V+0.60 eV. The latter are associated with zinc situated on regular silicon lattice sites. The emission rate of these centers exhibits a field dependence which cannot be quantitatively explained with the Poole-Frenkel model. On the other hand, a shallow level at E V+0.09 eV is observed only in boron-doped silicon which may be related to a zinc-boron complex. Other zinc-related levels are found at E V+0.23 eV and E V+0.33 eV, their concentration depending on that of zinc on substitutional sites. In addition, the evaluation of depth profiles and the analysis of the field dependence of the emission rate based on the DLTFS method is presented.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 77
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 273-286 
    ISSN: 1432-0630
    Schlagwort(e): 85.30 ; 72.20 ; 73.40 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The reproducible, mass production of almost ideal silicon p-n junctions has allowed two new phenomena to be discovered: a pure generation without recombination, and a slow capacitance-free current transient. Our present knowledge of these phenomena is reviewed and speculations about the centres responsible for them are discussed; these centres seem to be connected to ultimate, unavoidable properties of the silicon p-n junction rather than to unwanted impurities.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 78
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 271-280 
    ISSN: 1432-0630
    Schlagwort(e): 36.40 ; 79.20 ; 82.65 ; 68.45
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Desorption induced by electronic excitation with laser light is discussed. Emphasis is placed on nonthermal desorption where surface plasma excitation in small particles precedes the rupture of the surface chemical bond. A scenario for the mechanism underlying such a process is proposed. In this context, calculations of the electronic spectra of small sodium particles are presented and the influence of different multipole orders of the collective electron oscillation, of different shapes of the clusters and of the substrate are outlined. Furthermore, manipulation of the size distribution of metal particles on supports is described as an application of the effect. This allows the preparation of very special surfaces with novel physical and chemical properties. Methods to characterize such adsorbate-substrate combinations, especially by use of the optical spectra of the particles, are also discussed. Finally, prospects for future experiments in this field are outlined.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 79
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 349-352 
    ISSN: 1432-0630
    Schlagwort(e): 68.55 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A quantitative treatment of the crystallization kinetics in MBE growth of vicinal surfaces results the relation l 2=2D sτK between the surface diffusion coefficient D s, the time τ for a monolayer deposition and the interstep distance l at which the RHEED intensity oscillations disappear. The correction factor K depends on the size and the energy of the two-dimensional critical nucleus and it is estimated to be smaller than 10−2. The currently used interpretation of the RHEED intensity oscillations ignores the correction factor K and, therefore, the calculated values of D s are several orders of magnitude smaller than its real values. The surface transport during the time of growth interruption is discussed in connection with the tendency to three dimensional growth at every second interface (where a deposition of the material with strong intermolecular bonds starts) of a small period superlattice.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 80
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 13-17 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 72.40 ; 78.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A charge transport model including deep and shallow traps explains both the nonlinear relation between photoconductivity and light intensity and the light-induced absorption in BaTiO3. A correlation between measurements of photoconductivity and light-induced absorption as a function of temperature yields parameters for the shallow center, among them thermal activation energy and generation rate.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 81
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 215-220 
    ISSN: 1432-0630
    Schlagwort(e): 68.55 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Simple models for the thermally activated dissociation reaction of silane and silicon growth on a polycrystalline silicon surface are presented. The models are fitted to recent experimental molecular beam scattering data for the low-pressure reactive sticking coefficient. Thermally activated few-step models fit the data reasonably well, and thus, we are able to explain the temperature and pressure dependencies of the observed deposition rate.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 82
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 531-540 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 78.55 ; 78.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Two attractive methods for materials characterization are applied and discussed: (a) light scattering topography for fast and nondestructive testing of structural perfection, and (b) photoluminescence topography for evaluating the light emission characteristics of photoluminescent materials. Among the examples presented are semiconductor substrates and films of silicon, silicon-on-insulators of different kind, and III–V materials.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 498-507 
    ISSN: 1432-0630
    Schlagwort(e): 42.5 ; 68 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The influence of counterdiffusion on the reaction rate in non-equimolecular laser-induced gas-phase processing is investigated.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 84
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 107-109 
    ISSN: 1432-0630
    Schlagwort(e): 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A method is proposed for the determination of dislocation density depth profiles in the thin surface layers comparable to the penetration depth of X-rays, with no need to remove the surface layers by chemical or electrolytic polishing. The dislocation density depth profile is modelled mathematically and the parameters determining the profile can be evaluated from the Fourier transform of the X-ray diffracted profiles with various wavelengths of radiation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 85
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 131-139 
    ISSN: 1432-0630
    Schlagwort(e): 81.60 ; 82.65 ; 42.60
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The present status of experimental and theoretical work on continuous wave laser-assisted reaction of metals with oxygen is presented. Differences between this and normal isothermal oxidation of metals are emphasized. Available theoretical models are discussed. They deal with roles of thermal history, feedback effects between optical absorption and reaction rate. The nature of so-called “non-purely thermal” effects is discussed. Hints for further research are presented.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 86
    ISSN: 1432-0630
    Schlagwort(e): 81.60 ; 82.50 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract We present experimental data for vanadium and copper oxidation by cw CO2 laser light in an external electric field. Direct influence of the external field on the crystallisation process has been demonstrated in both vanadium and copper cases; the oxidation rate and surface morphology depend sensitively on the sign and strength of the external field.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 87
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 197-205 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 66.30
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Gold diffusion in silicon is investigated using Rapid Optical Annealing at temperatures in the range of 800°C to 1200°C and annealing times from 300 s down to 1 s. The resulting content of substitutional gold is determined by spreading resistance measurements and analyzed by comparison with extensive numerical simulations. The profiles obtained show a broader spectrum as compared to the U-shapes after long time diffusion. The cooling process affects the profiles significantly, since they depend on the wafer thickness. An unexpected penetration depth was found after 1200°C diffusion in thick wafers, which are subject to small cooling rates. This phenomenon is due to a special combination of reverse kick-out, deep diffusion of highly supersaturated interstitial gold, and again an incorporation in lattice sites, termed the RDI effect. Numerical calculations allow us to reproduce the experimentally observed profiles only if a sensitive balance between the different temperature dependencies is obeyed. These investigations, therefore, yield new information about the equilibrium concentration and diffusion of silicon interstitials. A best set of parameters is presented. The time constant of the kick-out process is quantified for the first time.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 88
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 340-343 
    ISSN: 1432-0630
    Schlagwort(e): 81.40 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Maskless etching of n-type GaAs in a KOH aqueous solution by irradiation of an argonion laser has been investigated to obtain high etching rates and aspect-ratios of etched grooves. High etching rates of up to 805 μm/s and an aspect ratio of 8 have been achieved by a single scan of a laser beam. Microprobe photoluminescence (PL), Raman scattering, and Auger electron spectroscopy (AES) measurements were carried out on the trench surface to characterize damage induced by laser wet etching.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 89
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 281-288 
    ISSN: 1432-0630
    Schlagwort(e): 68.35 ; 73.20 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The present theoretical understanding of imaging clean and adsorbate covered metal surfaces in scanning tunneling microscopy is examined with special emphasis on a possible theoretical foundation for the observed unexpectedly large corrugation on close-packed metal surfaces. Several suggestions for explaining these experimental findings are investigated. Resonance tunneling via tip d-orbitals might be a possible mechanism of amplifying small lateral structure of electronic or elastic origin. Two complementary theoretical methods are applied. The first one concentrates on a realistic description of the potential and wave functions of the sample surface whereas the second one attempts to model a more realistic transition metal tip. In the first approach the tip is represented by a Gaussian protrusion on an otherwise planar free-electron metal surface. The sample surface is built from muffin-tin potentials accounting for the atomic structure and the d-electrons. The spatial current distribution near the tip region is obtained by summing the contributions of all scattered waves. The method has been applied to study the current to Al(111) and Pd(100) surfaces. The corrugation obtained is rather small and cannot explain the experimental observations. The second approach studies two transition metal tips consisting of a single tungsten atom adsorbed on a flat W(110) surface and on a group of four other W atoms. The cluster of four W atoms is coupled to a flat W(110) surface by using an embedding method. The basis set on the W atoms includes 6s-, 6p-, and 5d-orbitals. The electronic structure of the tip exhibits a 5 d 2-resonance near the Fermi level. The effects of tip d-orbitals and resonance tunneling on the lateral contrast in STM are analyzed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 90
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 479-484 
    ISSN: 1432-0630
    Schlagwort(e): 61.70T ; 79.20D ; 42.60K ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract UV excimer lasers have been used to dope semiconductors by a one-step process in which the laser serves both to melt a controlled thickness of a sample placed in dopant ambient and to photodissociate the dopant molecules themselves. Here we report the boron doping of silicon by means of an ArF (193 nm) excimer laser. Dopant atoms are obtained by photolysis of BCl3 or pyrolysis of BF3 molecules. The doping is performed both in gas ambient and using only an adsorbed layer. We have investigated the dependence of doping parameters such as laser pulse repetition and gas pressure on the subsequent boron impurity profiles and the dopant incorporation rate. These results indicate that the laser doping process is dopant-flux limited for BF3 and externally rate limited for BCl3.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 91
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 609-615 
    ISSN: 1432-0630
    Schlagwort(e): 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A quartz crystal microbalance (QCM) has been used to study the KrF* excimer laser-induced etching of titanium by bromine-containing compounds. The experiment consists of focusing the pulsed UV laser beam at normal incidence onto the surface of a quartz crystal coated with 1 μm of polycrystalline titanium. The removal of titanium from the surface is monitored in real time by measuring the change in the frequency of the quartz crystal. The dependence of the etch rate on etchant pressure and laser fluence was measured and found to be consistent with a two-step etching mechanism. The initial step in the etching of titanium is reaction between the etchant and the surface to form the etch product between laser pulses. The etch product is subsequently removed from the surface during the laser pulse via a laser-induced thermal desorption process. The maximum etch rate obtained in this work was 6.2 Å-pulse−1, indicating that between two and three atomic layers of Ti can be removed per laser pulse. The energy required for desorption of the etch product is calculated to be 172 kJ-mole−1, which is consistent with the sublimation enthalpy of TiBr2 (168 kJ-mole−1). The proposed product in the etching of titanium by Br2 and CCl3Br is thus TiBr2. In the etching of Ti by Br2, formation of TiBr2 proceeds predominantly through the dissociative chemisorption of Br2. In the case of etching with CCl3Br, TiBr2 is formed via chemisorption of Br atoms produced in the gas-phase photodissociation of CCl3Br.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 61-63 
    ISSN: 1432-0630
    Schlagwort(e): 81.60 ; 82.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The etching of n-GaAs in aqueous solutions of hydroxides stimulated by HeNe and HeCd laser light was studied. It was found that at low laser-power densities (5–10 W · cm−2) the etched depths do not depend on the wavelength of the incident light. This conclusion is related to the concentration of the photogenerated holes on the semiconductor surface. The diffusion length and absorption depths for HeNe and HeCd lasers are compared.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 51 (1990), S. 141-145 
    ISSN: 1432-0630
    Schlagwort(e): 78.70 Bj ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Positron lifetime measurements have been made in quenched or irradiated pure Pb and in quenched Pb(Ag) alloys. From positron investigation of annealing behaviour, the precipitation of silver atoms in dilute alloys should be understood in terms of (Ag-Pb) interstitially migrating pairs. The presence of di-interstitials (Ag-Ag) or complexes [Ag(S)-V] as mobile defects responsible for the Ag transport process in concentrated alloys is discussed.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 50 (1990), S. 241-247 
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 78.30
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The resistivity of boron-doped silicon can be significantly increased by polishing such material with an appropriate amine- and copper-containing slurry. This effect is ascribed to a passivation of the boron acceptors by a defect produced or introduced by the polishing process. Three new, so far unknown localized vibrational modes at 691, 720, and 1038 cm−1 are observed in highly boron-doped silicon samples after such a polishing treatment. Two of these localized modes can be identified as due to a boron-containing defect. High concentrations of copper found in the samples after appropriate polishing indicate a participation — either directly or indirectly — of this metal in the passivation process.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 327-351 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Taylor-Galerkin algorithm ; Fractional step method ; Cavity flow ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In this paper the development and behaviour of a new finite element algorithm for viscous incompressible flow is presented. The stability and background theory are discussed and the numerical performance is considered for some benchmark problems. The Taylor-Galerkin approach naturally leads to a time-stepping algorithm which is shown to perform well for a wide range of Reynolds numbers (1 ≤ Re ≤ 400).A conventional definition for Re is assumed. Various modifications to the algorithm are investigated, particularly with respect to their effects on stability and accuracy.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 651-681 
    ISSN: 0271-2091
    Schlagwort(e): Porous media ; Two-phase flow ; Oil recovery ; Finite elements ; Preconditioning ; Conjugate gradients ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The equations governing immiscible, incompressible, two-phase, porous media flow are discretized by generalized streamline diffusion Petrov-Galerkin methods in space and by implicit differences in time. Systems of non-linear algebraic equations are solved by Newton-Raphson iteration employing ILU-preconditioned conjugate-gradient-like methods to the non-symmetric matrix system in each iteration. The resulting solution methods are robust, enable complex grids with irregular nodal orderings and allow capillary effects.Several numerical formulations are tested and compared for one-, two- and three-dimensional flow cases, with emphasis on problems involving saturation shocks, heterogeneous media and curved boundaries. For reservoirs consisting of multiple rock types with differing capillary pressure properties, it is shown that traditional Bubnov-Galerkin methods give poor results and the new Petrov-Galerkin formulations are required. Investigations regarding the behaviour of several preconditioned conjugate-gradient-like methods in these type of problems are also reported.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 849-865 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Navier-stokes ; Rotating cylinders ; Viscous dissipation ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A computational study of viscous flow between two eccentrically rotating cylinders is presented in which the effect of viscous dissipation is taken into account. The space discretization is based on piecewise linear finite elements with velocity stabilization, while the method of characteristics is used for time integration. Numerical results illustrate the efficiency of the adopted approach.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 661-675 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Navier-Stokes ; Velocity-vorticity ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A velocity-vorticity formulation of the Navier-Stokes equations is presented as an alternative to the primitive variables approach. The velocity components and the vorticity are solved for in a fully coupled manner using a Newton method. No artificial viscosity is required in this formulation. The pressure is updated by a method allowing natural imposition of boundary conditions. Incompressible and subsonic results are presented for two-dimensional laminar internal flows up to high Reynolds numbers.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 209-226 
    ISSN: 0271-2091
    Schlagwort(e): Finite elements ; Atmospheric flow ; Petrov-Galerkin ; Staggered grids ; Hybrid scheme ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Different finite element schemes are investigated with respect to their application in numerical weather prediction. Different methods of staggering of variables are considered. The tests concern the accuracy of a Rossby wave prediction and the generation of noise in a geostrophic adjustment process. Theoretical results concerning the noise level of different schemes are confirmed by computations with a one-dimensional model. Favourable results were obtained by hybrid schemes, using different Galerkin treatments for different terms of the dynamic equations.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 11 (1990), S. 1075-1095 
    ISSN: 0271-2091
    Schlagwort(e): Inexact Newton methods ; Global convergence ; Finite elements ; Full potential equation ; Damping strategies ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In computational fluid dynamics, non-linear differential equations are essential to represent important effects such as shock waves in transonic flow. Discretized versions of these non-linear equations are solved using iterative methods. In this paper an inexact Newton method using the GMRES algorithm of Saad and Schultz is examined in the context of the full potential equation of aerodynamics. In this setting, reliable and efficient convergence of Newton methods is difficult to achieve. A poor initial solution guess often leads to divergence or very slow convergence. This paper examines several possible solutions to these problems, including a standard local damping strategy for Newton's method and two continuation methods, one of which utilizes interpolation from a coarse grid solution to obtain the initial guess on a finer grid. It is shown that the continuation methods can be used to augment the local damping strategy to achieve convergence for difficult transonic flow problems. These include simple wings with shock waves as well as problems involving engine power effects. These latter cases are modelled using the assumption that each exhaust plume is isentropic but has a different total pressure and/or temperature than the freestream.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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