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1

Digitale Medien

Applicability of effective medium theory to ferroelectric/ferrimagnetic composites with composition and frequency-dependent complex permittivities and permeabilities (1996)

Mantese, Joseph V. ; Micheli, Adolph L. ; Dungan, Dennis F. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 1655-1660

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: High-frequency (1 MHz–1 GHz) transmission line measurements were used to determine the composition and frequency-dependent complex permittivities and complex permeabilities of ferroelectric/ferrimagnetic (barium titanate and a magnesium-copper-zinc ferrite) composites. The effective medium rules of Maxwell–Garnett give both lower and upper bounds for the effective permittivities and permeabilities and yield accurate estimates of the bulk electric and magnetic properties at low volume fill fraction of either component provided the proper host matrix is chosen. Bruggeman theory yielded the best predictive values for the permittivity and permeability over the entire composition range. In all cases these complex quantities were shown to be constrained by Bergman–Milton bounds. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.361010

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2

Digitale Medien

Surface modification during scanning tunneling microscope measurements on YBa2Cu3O7 thin films (1994)

Geyer, Ulrich ; von Minnigerode, Gunther ; Krebs, Hans-Ulrich

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 7774-7777

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: During scanning tunneling microscopy measurements on YBa2Cu3O7 thin films with positive sample bias voltages, different kinds of surface modifications appear. While in the topography condition no surface modification occurs, the cleaning and etching conditions irreversibly change the surface topography. In the deformation condition a strong elastic deformation of the tip and/or the surface is observed. It is shown that field evaporation of material from the surface to the tip is responsible for the observed surface modification. In consequence, the tip is contaminated with different oxides. Localized states in the oxides make resonant tunneling of electrons through the oxide layer possible. The configuration of these localized states determines the kind of surface modification by the scanning tunneling microscope. © 1994 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.357955

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3

Digitale Medien

Optical deflection setup for stress measurements in thin films (1998)

Bicker, M. ; von Hülsen, U. ; Laudahn, U. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 69 (1998), S. 460-462

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: We demonstrate an optical two-beam deflection setup for in situ stress measurements in thin films. By using improved position sensitive photodetectors we reach a resolution of better than 10−4 m−1 for substrate curvature measurement at a bandwidth of 1 kHz, with a relatively short optical path of 0.53 m and without employing a lock-in technique. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1148721

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4

Digitale Medien

Decomposition and nanocrystallization in reactively sputtered amorphous Ta–Si–N thin films (2001)

Pinnow, C. U. ; Bicker, M. ; Geyer, U. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 90 (2001), S. 1986-1991

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The nanocrystallization process of reactively sputtered thin amorphous Ta–Si–N films is investigated by anomalous small angle x-ray scattering (ASAXS) and x-ray diffraction (XRD). Changes in the microstructure in Ta40Si14N46 films, density variations in the amorphous matrix, decomposition, formation, and growth of nanocrystals after vacuum anneals at different temperatures in the range between 800 and 1000 °C are observed and the results of the different techniques are compared. From a Fourier analysis of ASAXS intensities the nanostructure of the investigated ternary system is derived using a model of hard spheres according to Guinier and Fournet. ASAXS investigations indicate that the noncrystalline samples can be described by a monophase fit and the crystallized samples by a bimodal-phase fit, the latter results being consistent with XRD which identifies TaN and Ta5Si3 phases. Detailed analysis shows that TaN nanograins of approximately 2 nm size develop after a decomposition process. Larger grains of Ta5Si3 are observed in addition to the TaN grains if annealing is performed at temperatures higher than 950 °C. The aim of these investigations is to give a generally applicable explanation of the barrier failure mechanism for Ta–Si–N diffusion barriers, which is actually observed at temperatures below the crystallization temperature if the films are used in contact with Cu or Al. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1388173

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5

Digitale Medien

Defect characterization in amorphous silicon based solar cells by subband-gap spectroscopy with constant photocurrent measurements (1991)

Frammelsberger, W. ; Rübel, H. ; Lechner, P. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 58 (1991), S. 2660-2662

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We used the constant photocurrent method to characterize a-Si:H based pin cells in order to discuss the correlation between the device characterizing quantity, the fill factor (FF), and the number of defects which is related to the quantity αD (subbandgap optical absorption constant). We show that the changes in the i layer due to the creation of metastable defects after light soaking or current injection−characterized by αD−directly correlate with the changes in solar cell performance (FF). We are able to show that other reasons than an increased defect density can lead to a reduction of the fill factor. Further we try to quantify αD in terms of a defect density of states.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.104799

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6

Digitale Medien

Spectra and structure of small ring compounds. XLVIII. Conformational stability of methylcyclobutane from low frequency Raman data of the gas (1987)

Durig, J. R. ; Geyer, T. J. ; Little, T. S. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 86 (1987), S. 545-551

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The low frequency (500–80 cm−1) Raman spectra of gaseous methylcyclobutane, c-C4H7CH3, and methyl-d3-cyclobutane have been recorded. A series of Q branches beginning at 161 cm−1 for the light molecule and 154 cm−1 for the d3 compound with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fitted to an asymmetric potential function of the form: V(cm−1)=(4.78±0.10)×105X4−(3.08±0.04)×104X2 +(2.18±0.1)×104X3 with an assumed reduced mass of 160 amu for the light compound. Utilizing this potential the difference between the puckering angles for the two conformers was calculated to be 4.3° with the equatorial conformer having the larger value of 20.7°. A similar potential was obtained for the d3 molecule. The energy difference between the equatorial and axial forms was found to be 247±20 cm−1 (706 cal/mol) and a barrier of 641±20 cm−1 (1.83 kcal/mol) was found for the interconversion. Experimental values for the ΔH of both the liquid (354±179 cm−1) and gas (295±75 cm−1) from relative intensities of different Raman band pairs over 85 and 37 °C temperature ranges, respectively, were found to be consistent with the value obtained from the potential function. These results are compared to the corresponding quantities for similar molecules.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.452305

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7

Digitale Medien

The osp(1,2)-covariant Lagrangian quantization of irreducible massive gauge theories (1999)

Geyer, B.

College Park, Md. : American Institute of Physics (AIP)

Journal of Mathematical Physics 40 (1999), S. 674-698

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ISSN: 1089-7658

Quelle: AIP Digital Archive

Thema: Mathematik , Physik

Notizen: The osp(1,2)-covariant Lagrangian quantization of general gauge theories is formulated which applies also to massive fields. The formalism generalizes the Sp(2)-covariant Batalin–Lavrov–Tyutin (BLT) approach and guarantees symplectic invariance of the quantized action. The dependence of the generating functional of Green's functions on the choice of gauge in the massive case disappears in the limit m→0. Ward identities related to osp(1,2) symmetry are derived. Massive gauge theories with closed algebra are studied as an example. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.532681

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8

Digitale Medien

The osp(1,2)-covariant Lagrangian quantization of reducible massive gauge theories (1999)

Geyer, B.

College Park, Md. : American Institute of Physics (AIP)

Journal of Mathematical Physics 40 (1999), S. 6189-6208

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ISSN: 1089-7658

Quelle: AIP Digital Archive

Thema: Mathematik , Physik

Notizen: The osp(1,2)-covariant Lagrangian quantization of irreducible gauge theories is generalized to L-stage reducible theories. The dependence of the generating functional of Green's functions on the choice of gauge in the massive case is discussed and Ward identities related to osp(1,2) symmetry are given. Massive first-stage theories with closed gauge algebra are studied in detail. The generalization of the Chapline–Manton model and topological Yang–Mills theory to the case of massive fields are considered as examples. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.533086

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9

Digitale Medien

Superspace formulation of general massive gauge theories and geometric interpretation of mass-dependent Becchi–Rouet–Stora–Tyutin symmetries (2000)

Geyer, B.

College Park, Md. : American Institute of Physics (AIP)

Journal of Mathematical Physics 41 (2000), S. 7304-7332

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ISSN: 1089-7658

Quelle: AIP Digital Archive

Thema: Mathematik , Physik

Notizen: A superspace formulation is proposed for the osp(1,2)-covariant Lagrangian quantization of general massive gauge theories. The superalgebra osp(1,2) is considered as subalgebra of the superalgebra sl(1,2)∼osp(2,2) which may be considered as the algebra of generators of the conformal group in a superspace with two anticommuting coordinates. The mass-dependent (anti)Becchi–Rouet–Stora–Tyutin symmetries of proper solutions of the quantum master equations in the osp(1,2)-covariant formalism are realized in that superspace as invariance under translations combined with mass-dependent special conformal transformations. The Sp(2) symmetry—in particular the ghost number conservation—and the new ghost number conservation are realized in the superspace as invariance under symplectic rotations and dilatations, respectively. The new ghost number conservation is generally broken by the choice of a gauge. The transformations of the gauge fields and the full set of necessarily required (anti)ghost and auxiliary fields under the superalgebra sl(1,2) are determined both for irreducible and first-stage reducible theories with closed gauge algebra. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1288496

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10

Digitale Medien

Internal interfaces and intrinsic stress in thin amorphous Cu-Ti and Co-Tb films (1998)

Geyer, U. ; von Hülsen, U. ; Kopf, H.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 83 (1998), S. 3065-3070

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A combined investigation of intrinsic stress formation by in situ substrate curvature measurements and of surface morphology evolution by scanning tunneling microscopy during the growth of amorphous Cu-Ti and Co-Tb films is reported. Intrinsic tensile stress and surface morphology are clearly correlated: all films that show intrinsic tensile stress formation in the late growth stages exhibit a cluster-like surface morphology and vice versa. Both the magnitude of the intrinsic tensile stress and the cluster size at the surface depend systematically on the reduced substrate temperature during film preparation. This dependence fits Hoffman's model for tensile stress formation in thin films. Thus, the observed surface clusters are probably the top domes of growth columns, and the atomic mismatch at the column boundaries gives rise to tensile stress formation. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.367061

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