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  • 1
    Electronic Resource
    Electronic Resource
    Adsorption dynamics of CO on the polar surfaces of ZnO (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6334-6343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of initial adsorption probabilities, S0, as well as the coverage dependence of the adsorption probability, S(aitch-thetaCO), of CO on Zn–ZnO [ZnO(0001)] and O–ZnO [ZnO(0001¯)] are presented. The samples have been characterized by He atom scattering, He atom reflectivity measurements, LEED, and XPS. Samples with different densities of defects were examined, either by investigating different samples with identical surface termination (for O–ZnO) or by inducing defects by ion sputtering at low temperatures (for Zn–ZnO). The influence of kinetic energy and impact angle (for Zn–ZnO) as well as adsorption temperature on the adsorption dynamics have been studied. For both polar surfaces the shape of the coverage dependent adsorption probability curves are consistent with a precursor mediated adsorption mechanism. Adsorbate assisted adsorption dominates the adsorption dynamics for high impact energies and low adsorption temperatures, especially for Zn–ZnO. The He atom reflectivity measurements point to the influence of an intrinsic precursor state. In contrast to the Zn–ZnO surface, for O–ZnO a weak thermal activation of the CO adsorption was observed. Total energy scaling is obeyed for Zn–ZnO. The heat of adsorption for CO on both polar faces varies between 7 kcal/mol (low coverage) and 5 kcal/mol (high coverage). A comparison of He atom reflectivity with S(aitch-thetaCO) curves demonstrates that CO initially populates defect sites on both surfaces. For O–ZnO an increase in S0 with decreasing density of defects was observed, whereas for the Zn-terminated surface S0 was independent of the defect density within the range of parameters studied. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1309131
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  • 2
    Electronic Resource
    Electronic Resource
    Photoinitiated H2CO unimolecular decomposition: Accessing H+HCO products via S0 and T1 pathways (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2752-2761 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoinitiated unimolecular decomposition of formaldehyde via the H+HCO radical channel has been examined at energies where the S0 and T1 pathways both participate. The barrierless S0 pathway has a loose transition state (which tightens somewhat with increasing energy), while the T1 pathway involves a barrier and therefore a tight transition state. The product state distributions which derive from the S0 and T1 pathways differ qualitatively, thereby providing a means of discerning the respective S0 and T1 contributions. Energies in excess of the H+HCO threshold have been examined throughout the range 1103≤E†≤2654 cm−1 by using two complementary experimental techniques; ion imaging and high-n Rydberg time-of-flight spectroscopy. It was found that S0 dominates at the low end of the energy range. Here, T1 participation is sporadic, presumably due to poor coupling between zeroth-order S1 levels and T1 reactive resonances. These T1 resonances have small decay widths because they lie below the T1 barrier. Alternatively, at the high end of the energy range, the T1 pathway dominates, though a modest S0 contribution is always present. The transition from S0 dominance to T1 dominance occurs over a broad energy range. The most reliable value for the T1 barrier (1920±210 cm−1) is given by the recent ab initio calculations of Yamaguchi et al. It lies near the center of the region where the transition from S0 dominance to T1 dominance takes place. Thus, the present results are consistent with the best theoretical calculations as well as the earlier study of Chuang et al., which bracketed the T1 barrier energy between 1020 and 2100 cm−1 above the H+HCO threshold. The main contribution of the present work is an experimental demonstration of the transition from S0 to T1 dominance, highlighting the sporadic nature of this competition. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480849
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  • 3
    Electronic Resource
    Electronic Resource
    Design and performance of a versatile, cost-effective microwave electron cyclotron resonance plasma source for surface and thin film processing : The 8th international conference on ion sources (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1177-1180 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A plasma source has been developed, which makes use of electron cyclotron microwave resonance conditions without cost-intensive tuning or other active elements. A magnetron typical of domestic microwave ovens is coupled to a cylindrical resonator of fixed dimensions. A high density plasma is maintained with permanent magnets. Sources have been designed for both high vacuum and ultrahigh vacuum environments. In the latter, microwaves are conducted by a coaxial feedthrough from the resonator to a ceramic plasma cup inside the vacuum chamber. This permits shorter working distances, resulting in higher beam densities at the sample. Ions are extracted from the plasma by grid assemblies. Beam energies are in the range from 30 to 2000 eV, with densities from a few μA/cm2 up to 10 mA/cm2, respectively. Predominantly neutral species are emitted using a specially designed, ceramic grid. Operating with O2 gas, a flux of neutral monomers of 2×1016/cm2 s has been measured by the oxidation of Ag films. The performance of the source is demonstrated in various surface and thin film processes, like ion beam sputtering, reactive ion beam deposition, as well as sputter cleaning and reactive etching of semiconductor materials. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150420
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  • 4
    Electronic Resource
    Electronic Resource
    Imaging of liquid crystals using a new scanning near-field optical microscope with microfabricated tips and shear force detection (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2759-2764 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report results obtained with a scanning near-field optical microscope which was developed, recently. The scanning head of the device is mounted on an inverted polarizing microscope. The sample is illuminated through a microfabricated tip which is mounted on a single-mode optical wave-guiding fiber. The light transmitted through the sample is collected in the far field by a microscope lens. The distance between the tip and the sample is controlled by shear force detection, using a nonconventional setup. We applied this new equipment successfully in order to investigate birefringent and dichroic liquid crystal films, using polarization modulation or fluorescence detection, respectively. An optical resolution down to (approximate)200 nm was obtained on the sample of a cholesteric liquid crystal for a wavelength of 488 nm. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150688
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  • 5
    Electronic Resource
    Electronic Resource
    Concurrent measurement of adhesive and elastic surface properties with a new modulation technique for scanning force microscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2765-2771 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The combination of two well-established dynamic scanning force microscopy (SFM) modes is incorporated for SFM in combined dynamic X mode or CODY Mode® SFM. A vertical modulation of low frequency and large amplitude is superimposed with a second vertical modulation of high frequency and low amplitude leading to a combination of pulsed force mode SFM, force modulation, and phase sensitive SFM. SFM in the new mode allows the simultaneous mapping of a number of physical surface properties including adhesive force and elasticity over one scan. The new SFM technique is nondestructive and alteration or even destruction of the sample surface is reduced to a minimum. A polymer blend (two homopolymers spin coated on silicon from a tetrahydrofuorane solution of a mixture of poly-2-vinylpyridin and polytertbutylmethacrylate) was used as a sample for comparative measurements between pulsed force mode, force modulation mode and the new SFM mode. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150689
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  • 6
    Electronic Resource
    Electronic Resource
    Radio frequency power deposition in a high-density helicon discharge with helical antenna coupling (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4308-4319 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A high-density helicon discharge (ne≤1020 m−3) produced through a new m=1 helical antenna is investigated. Various diagnostics are applied to measure the discharge parameters and the radio frequency (rf) quantities like the plasma resistance and the rf field distribution. Special attention is paid to the axial asymmetry of the discharge, which is characteristic for helicon devices with helical antennas. The axial profiles of the rf wave fields, as well as the energy deposition profiles, reveal that the rf power is mainly transferred and absorbed via the m=+1 helicon mode traveling in the positive magnetic-field direction. The experimental findings are compared with numerical results obtained from a fully electromagnetic model, which takes into account the rf current distribution of the launching antenna, as well as the finite size of the plasma column. The antenna–plasma coupling, as well as the total rf power deposited in the plasma, can be explained satisfactorily if the measured profiles are taken in the computations. In particular, the axial asymmetry of the helicon discharge can be understood in terms of the radial inhomogeneity of the plasma column. Furthermore, the calculations show that the small-scale Trivelpiece–Gould waves may be excited near the plasma edge. These waves would carry a considerable fraction of the absorbed rf power and may thus be important for the rf power coupling. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288399
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum kinetic equations for nonideal plasmas: Bound states and ionization kinetics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 59-67 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, nonequilibrium properties of strongly coupled plasmas are considered. Usually, such problems are dealt with using Boltzmann– or Lenard–Balescu-type equations. However, for the application to strongly coupled plasmas, these equations exhibit several shortcomings. So, it is not possible (i), to describe the short time kinetics, (ii), to recover the correct (energy) conservation laws and thermodynamics, and, (iii), to account for the formation or destruction of bound states. Therefore, the kinetics of strongly coupled plasmas is considered starting from the Kadanoff–Baym equations, which are known to overcome the above limitations. This is demonstrated by a numerical solution of the two-time Kadanoff–Baym equations in second Born approximation. To be able to discuss approximations which are physically more interesting, it is advantageous to proceed to the time diagonal Kadanoff–Baym equations. In first order gradient expansion, generalizations of the Boltzmann and of the Lenard–Balescu kinetic equations are derived accounting for the bound state problem, too. Thus, the shortcomings (i)–(iii) mentioned above are overcome. Finally, the kinetic equations are applied to the problem of ionization kinetics. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873781
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  • 8
    Electronic Resource
    Electronic Resource
    Diagnostics and modeling of a macroscopic plasma display panel cell (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3905-3913 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A macroscopic plasma display discharge cell has been designed in order to more easily study the plasma evolution in dielectric barrier discharges occurring in the much smaller commercial ac plasma display panels (PDPs). The electrodes in the macrocell can be arranged in matrix or coplanar configurations. The dimensions of the cell are 100 times larger than those of typical PDP cells and the gas pressure is 100 times smaller. Although some of the properties of the discharge pulse obviously do not follow the classical similarity laws, we find that the macrocell is a very useful tool for improving our understanding of the discharge in a PDP cell. The large dimensions of the cell and the longer time scale because of the smaller pressure make the plasma diagnostics easier than in a real PDP cell. The results are presented here for discharges in pure neon at 5 Torr. Measurements of the time evolution of the current and imaging of the plasma with an intensified charge coupled device (ICCD) camera are presented in matrix electrode configurations and are compared with previously developed models. The experiment confirms the large power deposition in electron impact excitation of the gas atoms while the plasma spreads over the dielectric surface above the anode. The images obtained with the ICCD camera also show the existence of striations of the plasma near the dielectric surface which were not predicted by the models. Measured and calculated duration and shape of the current pulse are in reasonable agreement. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308094
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  • 9
    Electronic Resource
    Electronic Resource
    Local structure of In0.5Ga0.5As from joint high-resolution and differential pair distribution function analysis (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 665-672 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High resolution total and indium differential atomic pair distribution functions (PDFs) for In0.5Ga0.5As alloys have been obtained by high energy and anomalous x-ray diffraction experiments, respectively. The first peak in the total PDF is resolved as a doublet due to the presence of two distinct bond lengths, In–As and Ga–As. The In differential PDF, which involves only atomic pairs containing In, yields chemical specific information and helps ease the structure data interpretation. Both PDFs have been fit with structure models and the way in that the underlying cubic zinc-blende lattice of In0.5Ga0.5As semiconductor alloy distorts locally to accommodate the distinct In–As and Ga–As bond lengths present has been quantified. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373718
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  • 10
    Electronic Resource
    Electronic Resource
    On the origin of stress in magnetron sputtered TiN layers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6332-6345 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recently proposed model has been used to describe the state of stress in magnetron sputtered TiN layers in which the stresses are believed to be caused by atomic peening. The state of stress in the layer is described by a combination of: (i) a hydrostatic state of stress, caused by the introduction of the misfitting atoms, and (ii) a biaxial state of stress induced by the equalization of the lateral dimensions of the substrate and the layer, dilated due to the misfitting atoms and the thermal misfit due to the cooling down of the layer/substrate assembly to room temperature. The implications of the thus obtained total state of stress on x-ray diffraction measurements have been clarified and a quantitative elaboration of the growth stress as a function of the amount and type of misfitting particles has been given. It has been deduced that the growth stresses are caused by about 1 wt % Ti atoms on nitrogen sites in the TiN lattice. By comparing x-ray diffraction results of layers of different thickness, deposited simultaneously on two different substrates, it has been concluded that the growth stress in the layers depends on the layer thickness, whereas the thermal stress is equal for all layers on a given substrate. The observed layer thickness dependence of the growth stress has been associated with a (macro)strain depth profile in the layers. The distinct diffraction line broadening observed for all layers cannot be due to smallness of crystallite size and the macrostrain-depth profiles, it is ascribed to (localized) lattice defects as dislocations and low angle grain boundaries. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319973
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