bluuebunny/crossref_metadata_2025 huggingface dataset:
Lamb-wave electroacoustic voltage sensor
Authors: Palma A. , Palmieri L. , Socino G. , Verona E.
Published: July 2002

The effect of a bias electric field on the phase velocity of Lamb waves propagating in a piezoelectric plate has been investigated in order to develop an electroacoustic voltage sensor. Experiments were performed on YX and YZ LiNbO3 Lamb-wave delay lines, used as the stabilizing element in the feedback loop of an oscillator, by measuring the fractional frequency change produced by a bias electric field normal to the plate surfaces. The results obtained have shown that Lamb-wave sensors can exhibit a higher sensitivity and a better linearity than the corresponding Rayleigh-wave devices.
Heat-resisting and efficient indium oxide/indium phosphide heterojunction solar cells
Authors: Ito K. , Nakazawa T.
Published: July 2002

Indium oxide/indium phosphide heterojunction solar cells have been fabricated in which the transparent conductive n-type indium oxide films were deposited in two steps by reactive evaporation of indium on the p-type InP single-crystal substrates. The cells were heat resisting up to 500 °C in air and had a solar power conversion efficiency of 16.3% without antireflection coatings.
Magnetically sensitive InSb films prepared on SiO layers using hot-wire recrystallization
Authors: Isai Masaaki , Ohshita Masahide
Published: July 2002

Magnetically sensitive InSb films have been prepared by hot-wire recrystallization. A room-temperature magnetoresistance (MR) value of ΔR/R0=155%/1 T was obtained at 1 T with length to width ratio (L/W)=0.4. Samples were prepared by sequential deposition of In, InSb, and SiO onto unheated mica substrates. They were placed mica side toward the nichrome wire heater. The crystal properties of these films were investigated with a transmission electron microscope (TEM). The TEM investigations showed that single-crystal InSb films were grown from the SiO layer. This preparation technique is useful because effective MR elements with large area (20×30 mm) can be prepared without a complicated process and huge cost.
Lamb wave interaction with light
Authors: Alippi A. , Diodati P. , Maccari D. , Socino G.
Published: July 2002

The interaction of light with Lamb waves propagating in transparent plates has been investigated. The analytical study has been done by considering a three-step interaction, at the limiting surfaces and within the propagation medium. Experimental data are given, relative to isotropic crystal plates in the MHz frequency regions and compared with theory.
Organic-on-GaAs contact barrier diodes
Authors: Forrest S. R. , Kaplan M. L. , Schmidt P. H. , Parsey J. M.
Published: July 2002

Thin films of the organic compound 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) were deposited on n- and p-type GaAs substrates, and were found to form high contact barriers. Barrier energies of 0.64 eV on n-type substrates and 0.75 eV on p-type material yielded organic-on-inorganic (OI) contact barrier diodes characterized by exponentially increasing forward current with voltage, and a reverse dark current leakage limited by generation and recombination of carriers in the GaAs bulk. The Fermi level does not appear to be pinned at the OI interface, contrary to what is commonly observed in metal/GaAs Schottky barrier diodes. In addition, we have made OI contact barriers using N,N′-dimethyl 3,4,9,10-perylenetetracarboxylic diimide (DIME-PTCDI) deposited on n- and p-type GaAs. These devices have contact barriers of 0.85 eV for substrates of either majority-carrier-type. The n values obtained from the forward biased characteristics of the GaAs/DIME-PTCDI structures are n=1.19, and are the lowest obtained to date for OI devices.
Thermal stability of magneto-optic quadrilayers
Authors: Anthony T. C. , Brug J. , Naberhuis S. , Birecki H.
Published: July 2002

The thermal stability of sputtered TbFeCo thin films in magneto-optic quadrilayer structures containing Si3N4, SiO, and SiO2 dielectrics has been examined. The observed changes in coercivity upon annealing are attributed to two parallel mechanisms: structural relaxation in the amorphous magnetic alloy and preferential oxidation of Tb at the TbFeCo/SiO and TbFeCo/SiO2 interfaces. Kinetic modeling has revealed that a spectrum of activation energies is required to explain the relaxation data, whereas a single activation energy of 1.65 eV describes the oxidation process.
Evaluation of dielectric relaxation parameters from the ionic thermocurrent spectrum
Authors: Prakash Jai , Rahul  , Nishad A. K.
Published: July 2002

A method is developed to evaluate the dielectric relaxation parameters from the ionic thermocurrent spectrum. The suggested method is found to be convenient and easier in comparison to Bucci, Fieschi, and Guidi’s (BFG) method. The total charge released in the ITC measurement helps in the evaluation of the dielectric relaxation parameters. The accuracy of the evaluated parameters depends essentially on the extent to which the total released charge is estimated exactly. The method has been successfully applied in a number of cases. The evaluated parameters are found to be in very good agreement with those obtained following BFG method.
Angular dispersion of ‘‘backward’’ Raman scattering: Absorbing III-V semiconductors (GaAs)
Authors: Anastassiadou A. , Raptis Y. S. , Anastassakis E.
Published: July 2002

A previously developed model for the angular dispersion of Raman scattering power from the surface of absorbing centrosymmetric cubic materials is extended to absorbing materials of the zinc blende type. Independent expressions have been obtained which give the scattered power due to the longitudinal and transverse long-wavelength optical phonons as a function of external scattering geometry parameters; from these calculations, it has been found that the ratio of the scattered powers shows significant dependence on the angles of incidence and detection. These results provide a quantitative method in assessing the effects of choosing an approximate rather than the exact backward scattering geometry. Experimental results obtained from GaAs are in very good agreement with the predictions of the model. Examples of physical situations are given where angular dispersion corrections become necessary.
The number of third-order elastic constants of an icosahedral solid
Authors: Chen L. C. , Ebalard S. , Goldman L. M. , Ohashi W. , Park B. , Spaepen F.
Published: July 2002

An icosahedral solid has 20 nonzero third-order elastic constants, four of which are independent.
Laser-induced fluorescence measurement and analytical model for the reaction probability of CF2 on Si
Authors: Thoman J. W. , Suzuki K. , Kable S. H. , Steinfeld J. I.
Published: July 2002

We investigate an analytical model for concentration profiles of reactive gas-phase species adjacent to surfaces, as determined by optical probe techniques. The model is illustrated with measurements of CF2, detected by laser-induced fluorescence, above silicon and other substrates. Conditions under which the model is applicable are discussed.
Schottky barrier degradation of the W/GaAs system after high-temperature annealing
Authors: Yu Kin Man , Cheung S. K. , Sands T. , Jaklevic J. M. , Cheung N. W. , Haller E. E.
Published: July 2002

W/GaAs diodes annealed at temperatures ranging from 100 to 900 °C were investigated with current voltage (I-V) and capacitance voltage (C-V) techniques, Rutherford backscattering spectrometry, scanning electron microscopy, and transmission electron microscopy. Improvements in the diode characteristics were observed after annealing at temperatures below 600 °C. Noticeable degradation in the rectifying behavior of the diodes occurred after annealing at temperatures >600 °C. Correlations between the electrical degradation and the interdiffusion of W and GaAs at the interface were found. Our results strongly suggest that the in-diffusion of W leads to the formation of a diffused, highly resistive region near the W/GaAs interface. The high resistance of this region is believed to be caused by the compensation of the substrate dopants by tungsten acceptors. Annealing the diodes at temperatures >850 °C resulted in reactions between W and GaAs. The W-GaAs reaction leads to islands of W2As3 at the W/GaAs interface, resulting in physical breakdown of the W/GaAs diode.
More on focus wave modes in Maxwell equations
Authors: Hillion P.
Published: July 2002

New solitary electromagnetic wave solutions of Maxwell’s equations are obtained. Brittingham [J. Appl. Phys. 54, 1179 (1983)] calls them focus wave modes.
A new rutile structure solid-solution phase in the LiNb3O8-TiO2 system, and its role in Ti diffusion into LiNbO3
Authors: Rice C. E. , Holmes R. J.
Published: July 2002

An extensive range of solid solubility was found in the LiNb3O8-TiO2 system. The solid-solution phase has the undistorted rutile structure for 0.40≤x≤1.0 in (Li0.25Nb0.75O2)1−x (TiO2)x. A member of this series, with x≊0.58, is proposed to be the intermediate phase formed during Ti indiffusion in LiNbO3 during optical waveguide formation, rather than Ti0.65Nb0.35O2 as was previously postulated. This assignment agrees with the experimental results of previous studies of Ti indiffusion into LiNbO3 single crystals, and is consistent with a Ti diffusion mechanism based on defect chemistry studies. The preparation and structural characterization of the LiNb3O8-TiO2 solid-solution phase is discussed.
Nanosecond surface discharge development using the computer simulation method
Authors: Tanaka Masahito , Murooka Yoshihiro , Hidaka Kunihiko
Published: July 2002

The authors have analytically studied the experimental results of the nanosecond surface discharge by using a simulation model. The results used were obtained using the dust figure technique with a nanosecond square pulse generator under the following conditions: an applied voltage of 5–20 kV, a pulse width of 3, 5, 8,..., 920 ns, and a gas pressure of 50, 100, 150,..., 760 Torr. Three kinds of simulation models were used: the first was based on the continuity equations together with the Poisson’s equation, without any photoionization effects; the second examined the gas photoionization effect on the first model; and the third considered further the photoelectric effect on the insulation surface. From a series of computations, it was found that by using the third simulation model, the experimental results such as the developing length of the corona streamer and its velocity were roughly confirmed, and the field intensity at the streamer tip was also obtained. Finally, the photoelectric emission coefficient θm at the insulation surface was evaluated.
Magnetic properties of single-crystal Fe films grown on ZnSe epilayers by molecular-beam epitaxy
Authors: Krebs J. J. , Jonker B. T. , Prinz G. A.
Published: July 2002

We report the magnetic properties of single-crystal α-Fe films grown by molecular-beam epitaxy (MBE) on both (110) and (001)ZnSe epilayers. These ZnSe layers were grown by MBE on GaAs substrates with (110) or (001) surfaces and a final ZnSe layer protected the Fe from oxidation. The samples were characterized by vibrating sample magnetometry and in-plane FMR in addition to x-ray fluorescence and the usual in situ surface analysis tools. Film thicknesses ranged from 140 to 3100 Å. The coercive forces are significantly smaller for these films than for similar films grown directly on GaAs substrates and the FMR linewidths indicate much smaller microwave losses. Except for the thinnest film studied, the 4πM and K1 (cubic anisotropy) values are similar to bulk Fe. The origin of the uniaxial in-plane anisotropy found in thicker (110)Fe/ZnSe and (110)Fe/GaAs films is attributed to the combination of magnetostriction and lattice mismatch-induced strain originating at the Fe/substrate interface.
Moment distribution in amorphous magnetic ribbons by Mössbauer measurements
Authors: Melamud M. , Swartzendruber L. J. , Bennett L. H. , Cullen J. , Wun-Fogle M.
Published: July 2002

Mössbauer effect measurements were obtained on smooth-surface Fe78B13Si9 amorphous ribbons annealed in a transverse magnetic field at high temperature. Absorption spectra were obtained with the ribbon plane tilted at several angles with respect to the direction of the γ rays, in an external field ranging from 0 to 10 Oe. Intensity ratios were analyzed to obtain the magnetization as a function of field. A large zero-field spread was deduced and excess scatter near the anisotropy field was observed.
Impedance control of Applied-B ion diodes
Authors: Slutz S. A. , Mehlhorn T. A. , Maenchen J. E. , Ruiz C. , Woodworth J. R.
Published: July 2002

We present a device to control the rapidly decreasing impedance that has been observed with Applied-B ion diodes. This device, which we call an impedance limiter, is a protrusion at the midplane of the anode. Its purpose is to reduce the electron space charge near the anode emission surface. Electromagnetic particle-in-cell simulations show that the impedance characteristics of an Applied-B diode can be favorably modified by using this device. Preliminary experimental results on the particle beam fusion accelerator I for an Applied-B ion diode using an impedance limiter show promise.
Charge density excitations in semiconductor superlattices
Authors: Kushwaha Manvir S.
Published: July 2002

The dispersion relations are derived for collective (bulk and surface) excitations of model type-II semi-infinite semiconductor superlattices using Maxwell’s equations and appropriate boundary conditions. In the nonretarded limit (c→∞), the dispersion relation, for bulk excitations, is identical to the one obtained by Quinn and co-workers using a somewhat more complicated method. It is interesting to note that the dispersion relation for the surface-plasmon polaritons is found to be independent of the decay parameter (or inverse penetration depth). The general dispersion relations for type-II superlattices have been generalized, with appropriate conditions, to those for type-I superlattices. The numerical calculations establish the existence of the surface plasmon modes with an exotic characteristic of being free from Landau damping.
Kinetics and oxide composition for thermal oxidation of cadmium telluride
Authors: Wang Fang , Schwartzman Alan , Fahrenbruch Alan L. , Sinclair Robert , Bube Richard H. , Stahle Carl M.
Published: July 2002

Thermal oxidation of single-crystal p-type CdTe has been carried out in dry and wet oxygen. The thickness of the oxide varies as the square root of oxidation time, implying a diffusion controlled process. The activation energy for thermal oxidation is 1.2 eV. Examination of the oxide by Auger electron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy shows that the composition of thick layers is CdTeO3; thin layers less than 100 Å thick may differ slightly in composition. An oxygen gradient is detected in as-grown thin oxides, but with storage in air at room temperature the oxygen gradient disappears. Values of chemical shift of the x-ray photoelectron spectroscopy peaks for the cadmium-tellurium-oxygen ternary system are clarified.
A simple formula for diffusion calculations involving wall reflection and low density
Authors: Chantry P. J.
Published: July 2002

Diffusion theory is often employed to calculate the effects of wall destruction on the local concentration of an active species immersed in a scattering gas. In many situations the spatial dependence of the concentration is given to a good approximation by the fundamental diffusion mode, and the local loss frequency can be calculated using the container’s fundamental mode diffusion length Λ. The additional assumption that the density of the active species may be taken to be zero at the container boundaries gives a value of Λ=Λ0 which depends only on the container dimensions, but use of Λ0 can be seriously in error if the diffusion mean free path λm is comparable to the dimensions, or if the particle reflection coefficient R becomes of significance. An improved boundary condition may be written simply in terms of the linear extrapolation length λ, whose inverse is the logarithmic gradient of the particle density at the boundary. The equation λ=2(1+R)λm/3(1−R) allows the representation of the full range of possible values of the particle reflection coefficient, 0<R<1, and extends the usefulness of the diffusion approximation to low scatterer densities. In the collisionless limit, the predicted particle loss frequency is identical to that predicted from the average chord length. Using this boundary condition, the dependence of Λ on λ/Λ0 has been computed for a range of simple container shapes, by solving the transcendental equations involved. This has allowed the identification of a dimensionless scaling variable, l0λ/Λ20, where l0 is the ratio of the container volume to its surface area. For all cases considered the simple empirical approximation Λ2=(Λ20+l0λ) is accurate when λ is very large or very small compared to Λ0, and disagrees most with the numerical solutions in the region where λ and Λ0 are comparable, with the worst case error being 11%.
Optical probing of magnetostatic forward volume waves in thin film yttrium-iron-garnet
Authors: Vlannes Nickolas P.
Published: July 2002

An optical probe system has been developed that uses magneto-optic effects to examine the microwave magnetization of microwave magnetostatic waves propagating in thin ferrite films. The optical probe uses light from a 45 mW, 1.15 μm He-Ne laser which is focused upon a ferrite for localized probing. An effective spatial resolution of 100 μm was achieved with the optical probe. Experiments to examine linear and nonlinear magnetostatic forward volume waves (MSFVW) were conducted with the probe. MSFVW, with microwave frequency from 1 to 2 GHz, were launched in the [21̄1̄] direction of a thin film of liquid-phase-epitaxy (LPE) yttrium-iron-garnet (YIG). The LPE-YIG thin film was 47.4 μm thick, and deposited on a 1-in. disk of gadolinium-gallium-garnet with the [111] direction perpendicular to the surface of the disk. The nonlinear microwave MSFVW effects were characterized by a MSFVW power saturation and then a decline as input power to the MSFVW was increased. Localized optical probing of nonlinear effects, along the propagation path of the MSFVW, showed that a monotonic increase in MSFVW modulation of light with increasing microwave input power does not always occur. Optical probing of linear MSFVW examined the evolution of a MSFVW profile, transverse to the phase-propagation direction, as the MSFVW traveled from its launching antenna.
Alkali reactions with wall coating materials used in atomic resonance cells
Authors: Camparo J. C. , Frueholz R. P. , Jaduszliwer B.
Published: July 2002

It is well known that the chemisorption of various chlorosilane materials on glass atomic storage vessel walls results in surface coatings which inhibit electronic- and nuclear-spin relaxation. In the present study the chemical reaction of rubidium, and by analogy other alkali metals, with dichlorodimethylsilane-treated glass surfaces has been studied. We find evidence that rubidium reacts with a freshly prepared coating to produce H2 and a volatile silicon-containing species. The most reasonable reaction process is postulated to be rubidium reacting with residual silanol groups (Si-OH) found on the surface. As the reaction proceeds these groups would disappear, thus reducing the spin-relaxation rate associated with the surface. We believe that this reaction results in the ‘‘curing’’ of wall coatings reported by other investigators. Concurrently, the gaseous reaction products become impurities within the system. The spin-relaxation cross section of the silicon-containing species is expected to be less than 1×10−17 cm2.
Effective dipole moment of intersecting conducting spheres
Authors: Jones T. B.
Published: July 2002

In this paper the effective dipole moment of two intersecting, electrically conducting spheres is calculated by using the method of electrical inversion. By invoking the constraint that the volume of the body formed by the two intersecting spheres must be fixed and equal to the original volume of the two spheres, a simple model for fusing biological cells, coalescing liquid droplets, etc., is developed. With this volume-constrained effective dipole moment, the net dielectrophoretic force on merging particles may be calculated as a function of their center-to-center spacing.
Molecular-beam epitaxy of (100) InSb for CdTe/InSb device applications
Authors: Williams G. M. , Whitehouse C. R. , Martin T. , Chew N. G. , Cullis A. G. , Ashley T. , Sykes D. E. , Mackey K. , Williams R. H.
Published: July 2002

Interest in InSb and InSb-based heterostructures has recently been renewed in view of their important potential applications in infrared, logic, and novel quantum-well devices. Our work to date has concentrated on the growth of CdTe/InSb multilayer structures in which the properties of the InSb constituent layers have a very significant influence on subsequent device performance. The present paper describes data obtained during a systematic investigation of the growth, using molecular-beam epitaxy (MBE), of (100) InSb homoepitaxial layers, specifically for CdTe/InSb device applications. Modulated-beam mass spectrometry experiments have shown that polycrystalline InSb can be used as an MBE source of antimony, and the properties of InSb epilayers grown using either elemental antimony or polycrystalline InSb as the group-V source are compared. Cross-sectional transmission electron microscope analysis indicates that very high structural quality layers can be produced and has also identified the mechanisms which give rise to structural breakdown in layers grown under nonoptimum conditions. All unintentionally doped InSb layers grown to date have exhibited n-type conductivity (n≳3×1015 cm−3) and secondary ion mass spectrometry data has indicated the presence of tellurium, sulfur, and selenium contamination. The mechanisms by which tellurium and sulfur become incorporated in the grown layers are identified.
A method for improved short-wavelength response in hydrogenated amorphous silicon-based solar cells
Authors: Catalano A. , Wood G.
Published: July 2002

Amorphous silicon p-i-n devices show a diminished short-wavelength response as the boron concentration of the p-layer increases. A reactive flush with NF3 between p- and i-layer deposition improves the short-wavelength response. Secondary ion mass spectroscopy profiles, however, do not reveal a significant boron tail into the i layer as anticipated suggesting that excess boron in the p layer is associated with interface recombination and is responsible for the effect.
Influence of photoexcitation on hopping conduction in neutron-transmutation-doped GaAs
Authors: Satoh M. , Kawahara H. , Kuriyama K. , Kawakubo T. , Yoneda K. , Kimura I.
Published: July 2002

The nature of the tunneling-assisted hopping conduction in neutron-transmutation-doped GaAs has been studied under photoexcitation with a photon energy of 1.32 eV. It is found that the dopants activated by annealing around 400 °C provide the electrons to the defect levels originating the hopping conduction even when under photoexcitation. The hopping conduction under photoexcitation is affected by quenching in photoconductance below 120 K concerned with the main electron trap (EL2) and/or the As antisite defect (AsGa) induced by the neutron irradiation. The photoconductance of the samples with a lower radiation damage, AsGa≤1×1018 cm−3, consists of the coexistence of the hopping and band conductions.
Conduction in n+-i-n+ thin-film polycrystalline/silicon devices in relation to the film deposition conditions
Authors: Dimitriadis C. A. , Papadimitriou L. , Stoemenos J. , Economou N. A. , Meakin D. B. , Coxon P. A.
Published: July 2002

The electrical conduction in n+-i-n+ thin-film polycrystalline/silicon devices, in relation to the deposition conditions of the low-pressure chemically vapor deposited film, is investigated. Transmission electron microscopy study showed the following: (i) By decreasing the growth pressure from 180 to 80 mTorr, the mean grain size increases by a factor of 3. (ii) In the material grown at 180 mTorr, there is a mean dilatation for the d111 lattice plane amounting to 2.7%, while in the material grown at 80 mTorr, the systematic dilatation previously observed is absent. The current-voltage characteristics show a linear behavior in a voltage region and a nonlinear behavior at higher voltages attributed to Joule heating within the sample. The energy gap of the material grown at 80 mTorr is 1.12 eV, while for the material grown at 180 mTorr, it decreases to 0.96 eV. The shrinkage of the energy gap could be due to the high density of ‘‘tail states’’ close to the conduction or valence band.
Analytical investigation of the junction space-charge region properties of heterojunction semiconductor devices: Application to n-AlzGa1−zAs/p-GaAs system
Authors: Mohammad S. Noor
Published: July 2002

An analytical investigation of the space-charge region junction properties of heterojunction semiconductor devices from heavily doped and degenerate semiconductors has been carried out. On the basis of a new formula for Fermi–Dirac integral of order (1)/(2) theoretical formulas for junction boundary conditions, minority-carrier concentrations at the edges of space-charge region and excess minority-carrier concentrations at the edges of space-charge region have been derived. All of these formulas take the spatial dependence of band structures, carrier degeneracy, and band-gap narrowing into account. Under special conditions the formulas reduce to the well-known standard formulas for homojunction devices from both degenerate and nondegenerate semiconductors. The new relation for Fermi–Dirac integral is very highly accurate. Numerical calculations performed on an n-AlzGa1−zAs/p-GaAs (z=0.1) diode indicate that all these parameters significantly influence the junction properties of heterojunction semiconductor devices, and without which theoretical modeling of heterojunction devices with spatially dependent and heavily doped semiconductor regions are likely to involve errors.
Toward an algorithm to make cuts for magnetic scalar potentials in finite element meshes
Authors: Kotiuga P. R.
Published: July 2002

Kotiuga [J. Appl. Phys. 61, 3916 (1987)] showed that the integral (co)homology groups of a region Ω in R3 are torsion free and that cuts for magnetic scalar potentials can be realized by embedded orientable submanifolds which represent generators of the homology group H2(Ω,∂Ω;Z). The present paper makes these formal results intuitive by appealing to concepts familiar from electromagnetics and clarifies several issues relating to an algorithm for finite element meshes. Sufficiency conditions for the intersection of different cuts show that when several cuts are required it may not be possible to avoid intersections. This in turn clarifies the question of what data must necessarily be given in order for an algorithm to work.
Magnetic moment suppression in rapidly solidified Co-TE-B alloys
Authors: Ghemawat A. Mitra , McHenry M. E. , O’Handley R. C.
Published: July 2002

Amorphous alloys in the series Co80MoxB20−x and Co80ZrxB20−x have been produced through melt spinning. The magnetic moment per Co atom has been measured as a function of early transition metal (TE) addition and compared with earlier data on the Co80NbxB20−x. The influence of the TE additions are understood through the split band model though quantitative differences exist due to the influence of B–Te p-d hybrid bonding and its competition with Co-TE interactions in moment suppression.
Magnetic properties and film structures of Fe/C multilayers
Authors: Kobayashi Toshio , Nakatani Ryoichi , Ootomo Shigekazu , Kumasaka Noriyuki
Published: July 2002

The magnetic properties and film structures of Fe/C multilayers (period: 5–50 nm) formed by ion beam sputtering are studied. The coercivity in the easy axis direction is decreased from 380 A/m (=4.8 Oe) to 25 A/m (=0.3 Oe) by reducing the period from 50 to 5 n. The relative permeability increases to a maximum of approximately 3000 with increasing C layer thickness. Cross-sectional transmission electron microscopy and Auger electron spectroscopy show that Fe layers are clearly separated by C layers, resulting in small Fe crystallites.
Chemical treatment and Fermi-level pinning of CuInS2 and InP photocathodes
Authors: Lewerenz H. J. , Goslowsky H.
Published: July 2002

The photovoltage variation with redox potential ERed is investigated on p-InP and p-CuInS2 for various surface treatments. Etching and ion chemisorption are shown to successively improve CuInS2 photovoltages VPh resulting in a slope of ∼1 of VPh vs ERed. The respective densities of states are determined using a model calculation yielding Ds ≊6×1011 states cm−2 eV−1 and Ds ≊1.2×1014 states cm−2 eV−1 for the unpinned and pinned situation, respectively. Good agreement between the calculated voltage drop in the Helmholtz layer due to CuInS2 Fermi-level pinning (FLP) and the missing photovoltage is obtained in a simple model calculation based on the surface state charge density. InP photocathodes show a VPh vs ERed dependence in the dark, depending on pretreatment which is attributed to a chemical reaction that inhibits Fermi level equilibration. Positive from −0.4 V (SCE) VPh is independent of ERed for polished and etched surfaces. The independence is explained assuming a dynamic equilibrium between semiconductor and solution without band-edge shifting. At the potential where p-InP solar cells are operated (−0.47 V vs SCE), the electrodes behave as unpinned.
Study of molecular-beam epitaxially grown GexSi1−x/Si layers by Raman scattering
Authors: Chang S. J. , Kallel M. A. , Wang K. L. , Bowman R. C. , Chow Peter
Published: July 2002

The strain distribution of a GexSi1−x/Si strained layer superlattice (SLS) as a function of the distance from the superlattice/substrate interface has been studied by Raman spectroscopy. A small-angle bevel was made by angle lapping on a given thick GexSi1−x/Si SLS so that it is possible to probe the structure at different thicknesses. The Raman spectrum as a function of the distance from interface is then obtained. The results indicate that, as we move away from the substrate interface, the compression strain in the alloy layers decreases while the tensile strain in the Si layers increases. From linewidth measurement of the Raman peaks, it appears that there is an improved crystal quality and a lower concentration of defects going away from the substrate interface.
Soft magnetic properties of Fe-C/Ni-Fe multilayered films
Authors: Kobayashi Toshio , Nakatani Ryoichi , Ootomo Shigekazu , Kumasaka Noriyuki , Shiiki Kazuo
Published: July 2002

The paper examines soft magnetic properties and film structures of Fe-C/Ni-Fe multilayers formed by the dual ion-beam sputtering method. The following results are obtained. (1) The addition of C to Fe improves the soft magnetic properties of Fe, making its magnetostriction constant zero while keeping its high saturation magnetic flux density. (2) The insertion of Ni-Fe intermediate layers between Fe-C layers further improves the soft magnetic properties to a relative permeability of 3000, with a saturation magnetic flux density of 2.0 T. (3) The improvements in the soft magnetic properties are due to reductions in the magnetic anisotropy dispersions and the mean anisotropy field, which in turn are due to reduction of crystallite diameter.
The measurement of narrow domain-wall widths in SmCo5 using differential phase contrast electron microscopy
Authors: Morrison G. R. , Gong H. , Chapman J. N. , Hrnciar V.
Published: July 2002

Differential phase contrast imaging in a scanning transmission electron microscope has been used to measure very narrow domain walls in the ferromagnetic alloy SmCo5. This technique provides a more accurate and direct measurement of domain-wall structure than is possible with more conventional methods, and has allowed, for the first time, an experimental test of the predicted wall widths in highly anisotropic material.
Surface heat transfer coefficient, heat efficiency, and temperature of pulsed solid-state lasers
Authors: Mann K. , Weber H.
Published: July 2002

The temperature of solid-state lasers is a critical parameter. Efficiency and output power are strongly influenced by it. The two parameters which determine the temperature are the heat generation efficiency (HGE) and the surface heat transfer coefficient (SHTC) of the laser rod. These parameters allow the scaling of the rod temperature up to high pumping powers. Moreover, from the temperature inside the rod, the temperature gradients and the mechanical stress can be evaluated. Using transient temperature measurements, the SHTC and the HGE were determined for air- and water-cooled Nd:YAG and alexandrite lasers. The SHTC can be confirmed by theoretical considerations.
Properties of Nd-Fe-B anisotropic powder prepared from rapidly solidified materials
Authors: Eshelman L. J. , Young K. A. , Panchanathan V. , Croat J. J.
Published: July 2002

Anisotropic Nd-Fe-B permanent magnets can be prepared by consolidation and hot forming of melt-spun ribbon material; energy products to 45 MGOe have been obtained by this method. One feature of this type of magnet is that they can be converted into stable powders for subsequent processing into anisotropic resin-bonded magnets. The stability of this powder contrasts markedly with that prepared by grinding conventional ‘‘sintered’’ magnets, a factor attributed to the much smaller crystallite size of the rapidly solidified materials. In this work the properties of the anisotropic powder are presented along with preliminary properties of bonded magnets; energy products of 15–17 MGOe have been achieved by compression molding techniques and energy product as high as 20 MGOe are believed to be readily achievable.
Three-dimensional transient thermal analysis for laser chemical vapor deposition on uniformly moving finite slabs
Authors: Kar A. , Mazumder J.
Published: July 2002

A mathematical model for heat transfer in the substrate during laser chemical vapor deposition (LCVD) is presented. The results of this study are applicable to the LCVD of pure titanium obtained from the thermal decomposition of titanium tetrabromide on stainless steel (S.S. 304), because the absorptivity of the substrate is determined from the optical properties of titanium tetrabromide, pure titanium, and S.S. 304. The three-dimensional and transient heat conduction equation is solved for a slab of finite dimension by considering both convective and radiative losses of energy at the surfaces of the slab. Thermal analysis such as this can provide information on the variation of film width with laser power and scanning speed, and the upper and lower limits of the operating scanning speed for LCVD processes. It is found that for a given laser power, the peak temperature varies linearly with the operating scanning speed of the laser beam on the log-log scale. Also, the peak temperature is found to vary linearly with the laser power on the linear scale for a given scanning speed of the laser beam. Finally a method of determining the optical properties at high temperatures from the low-temperature data is presented.
Multiple-quantum-well vertical light guide switch
Authors: Chmielowski Marek , Langer Dietrich W.
Published: July 2002

The performance efficiency of optoelectronic couplers which change the intensity distribution of light propagating in two waveguides by the application of an electric field can be improved by several orders of magnitude by the use of multiple-quantum-well material and by positioning the guides vertically in consecutively deposited planes, separated by a coupling layer. The optical properties of such a vertical wave guide coupler were numerically calculated including the effects of absorption in the quantum-well guide.
Properties of hydrogenated amorphous germanium nitrogen alloys prepared by reactive sputtering
Authors: Honma I. , Kawai H. , Komiyama H. , Tanaka K.
Published: July 2002

Hydrogenated amorphous germanium-nitrogen alloys (a-GeNx:H) were synthesized as a new group of amorphous semiconductors by rf(13.56 MHz) reactive sputtering of a Ge target in a gas mixture of Ar+N2+H2 under a variety of deposition conditions such as gas ratio, rf-discharge power, and substrate temperature. Structural, optical, and electrical properties of those a-GeNx:H alloys were systematically measured and are discussed in relation to their preparation conditions. The optical band gap E04 of a-GeNx:H alloys could be continuously controlled in the range from 1.1 eV to 3.3 eV primarily depending on the atomic N/Ge ratio in the film. The role of hydrogen and nitrogen in the optical and electrical properties of the material is also crucially demonstrated.
Arsenic-rich melt effect on threshold voltage scattering for Si-implanted GaAs metal-semiconductor field-effect transistor
Authors: Saito Y.
Published: July 2002

The microscopic electrical activation efficiency of implanted Si atoms in undoped, liquid-encapsulated Czochralski-grown GaAs substrates was investigated by means of the threshold voltage (Vth) of implanted metal-semiconductor field-effect transistors as a function of stoichiometry and impurities, especially of carbon as determined by Fourier transform infrared (FT-IR) spectroscopy (≤2.5×1016 cm−3). The Vth scattering, which is related to the electrical activation efficiency dispersion, was small for an As-rich substrate grown from an As-rich melt, whether or not there existed a horizontal 3400-Oe magnetic field. The smallest amplitude of the Vth scattering occurred for the As-rich melt and did not vary with magnetic field. The Vth scattering with magnetic field was independent of carbon concentration (≤2.5×1016 cm−3). However, without magnetic field, an effect clearly appeared at low carbon concentration (nearly nondetectable). It seems that the Vth scattering or the electrical activation efficiency dispersion is dominated by the dispersion of stoichiometry, that is, composition, of the GaAs substrate because the electrical activation efficiency depends on the ratio of the Ga vacancy concentration and As vacancy concentration and the magnitude of their concentrations at the annealing temperature for the Si-implanted GaAs substrate. Therefore small Vth scattering means that the dispersion of the composition (Ga and As) is small. The composition dispersion for the most As-rich melt is small because the solidification is controlled by the straight As-rich side solidus line of the Ga:As composition-temperature phase diagram, and thus temperature variations of the GaAs melt in the pyrolytic boron nitride crucible are not as important. Also, there was no correlation between Vth scattering and dislocation density.
Spatially and temporally resolved laser-induced fluorescence measurements of CF2 and CF radicals in a CF4 rf plasma
Authors: Booth J. P. , Hancock G. , Perry N. D. , Toogood M. J.
Published: July 2002

Laser-induced fluorescence has been used to examine the temporal behavior of ground-state CF2 and CF radicals in a CF4 plasma etching reactor. We also report the measured spatial dependencies of the radical concentrations, and develop a rigorous model for their interpretation. The results indicate that for CF2 and CF, wall removal processes are dominant at low pressures of the order of 50 mTorr, and that CF is not produced by electron impact dissociation of CF2.
Structural studies and magnetic properties of Fe/Ag superlattices
Authors: Xiao J. Q. , Gavrin A. , Xiao Gang , Childress J. R. , Bryden W. A. , Chien C. L. , Edelstein A. S.
Published: July 2002

Fe(110)/Ag(111) superlattices with Ag layer thicknesses of 30 or 60 Å and various Fe layer thicknesses have been fabricated by high-rate sputtering and studied by x-ray diffraction magnetometries, and Mössbauer spectroscopy. A slightly enhanced magnetic moment and hyperfine field, and a reduced Tc have been observed in samples with thin Fe layers. The magnetization exhibits a BT3/2 dependence with very large values of B.
Thermal and spectral dependence of low-frequency oscillations in semi-insulating GaAs:In
Authors: Johnson D. A. , Puechner R. A. , Maracas G. N.
Published: July 2002

We have investigated the thermal dependence of low-frequency current oscillations in the range of 140–400 K for semi-insulating (SI) GaAs resistor structures illuminated with sub-band-gap light. We have also investigated the spectral dependence of the low-frequency current oscillations in SI GaAs for illumination in the range of 0.85–1.25 μm. We find that the oscillation frequency is proportional to the carrier concentration. The thermal and the spectral measurement results both support the hypothesis that the low-frequency oscillations are caused by carriers interacting with the EL2 level and that the presence of holes can significantly alter the oscillation frequency. The behavior of the oscillations can be qualitatively described by a simple empirical expression with the assumption that EL2 exhibits field-enhanced capture from the Γ valley, although the exact behavior of the enhanced capture is not fully understood.
Target strength of ceramic materials for high-velocity penetration
Authors: Forrestal M. J. , Longcope D. B.
Published: July 2002

We derived equations for the target-strength term used in the modified hydrodynamic model that describes long rod penetration into ceramic targets. Since ceramics have tensile strengths that are usually an order of magnitude lower than their compressive strength, this model allows for tensile cracking. In addition, our model includes the effect of pressure-dependent shear strength.
X-ray diffraction determination of the effect of various passivations on stress in metal films and patterned lines
Authors: Flinn Paul A. , Chiang Chien
Published: July 2002

Direct x-ray diffraction determination of elastic strain and stress in aluminum and aluminum-silicon films and patterned lines has been used to investigate the effect of various passivations. Passivation over uniform metal films has very little effect. Passivation over patterned metal results in substantial triaxial tensile stress. Contrary to the conventional wisdom, high compressive stress in the passivation does not result in additional tensile stress in the metal. The deleterious effects of highly compressive silicon nitride on metal is probably due to the effect of excess hydrogen in the silicon nitride.
An experimental estimation of silicon interstitial diffusivity
Authors: Wijaranakula W.
Published: July 2002

A relatively simple experimental method to estimate a diffusivity of silicon interstitials is described. In the low-temperature range between 460 and 500 °C, oxygen thermal donors are used as a monitor for silicon interstitials. The estimated diffusivity of silicon interstitials at oxygen-donor-formation temperatures is fitted to previously-published results from oxidation-enhanced and retarded-diffusion experiments at temperatures above 950 °C. In the temperature range between 460 and 1200 °C, the diffusivity of silicon interstitials is described by the Arrhenius equation, Di=3.35×10−1 exp(−1.86/kT) cm2/s.
Focused ion beam stimulated deposition of aluminum from trialkylamine alanes
Authors: Gross M. E. , Harriott L. R. , Opila R. L.
Published: July 2002

Focused ion beam stimulated deposition of aluminum from trimethylamine alane, a white solid, and triethylamine alane, a colorless liquid, is reported. Initiation of growth on Si and SiO2 substrates is enhanced by in situ sputter cleaning of the surface with the Ga+ beam prior to introduction of the metallo-organic. Alternatively gas phase chemical activation with a silane coupling agent can enhance nucleation. Uniform nucleation on Al surfaces does not require any pretreatment. The Al features are electrically conducting, but incorporation of C and N from the amines leads to a resistivity approximately 300 times that of bulk Al. A qualitative model is presented that describes the balance condition for net material deposition as opposed to sputtering in terms of precursor flux and sticking probability as well as ion beam current density and beam scanning parameters. Film morphology and composition are also discussed.
The effects of F2 concentration on discharge pumped KrF laser characteristics
Authors: Lou Qihong , Yagi Takashi , Igarashi Kaoru , Saito Hideaki
Published: July 2002

The F2 concentration , laser output power , laser pulse duration, and laser beam patterns of discharge pumped KrF excimer laser are measured at high repetition rate during long-term operation. The effects of the F2 concentration on the laser output characteristics are analyzed.
Growth and characterization of reactively sputtered thin-film platinum oxides
Authors: McBride J. R. , Graham G. W. , Peters C. R. , Weber W. H.
Published: July 2002

Thin-film oxides of platinum have been prepared by reactive sputtering and characterized primarily by x-ray diffraction (XRD) and Raman scattering. Different phases of the Pt-O system were obtained by adjusting sputtering parameters such as gas composition, deposition rate, and substrate temperature. Optimum conditions for producing crystalline α-PtO2 and PtO were identified. Raman spectra of α-PtO2 films show two sharp lines at 514 and 560 cm−1, in agreement with those from commercially available powders. XRD and high-resolution scanning electron microscopy (HRSEM) analyses indicate that these samples have a poorly crystallized structure with lack of order along the c axis. The Raman spectra from PtO show two broad peaks at 438 and 657 cm−1, close to the lines seen in PdO, which has the same structure as PtO. Estimates from XRD line broadening and HRSEM photographs indicate mean crystallite sizes on the order of 300 Å. Infrared reflectivity spectra yield two of the three ir-active phonons, and along with scanning tunneling microscopy measurements suggest that PtO is a semiconductor. Thermoelectric measurements show that the predominant carriers are p-type, and ir reflectivity data indicate a carrier concentration of ∼4×1018 cm−3.
Magnetic susceptibility and order parameter of nematic liquid crystals as determined by a high-temperature SQUID magnetometer
Authors: Dries Th. , Fuhrmann K. , Fischer E. W. , Ballauff M.
Published: July 2002

The design and operation of a high-temperature measuring cell for SQUID magnetometers is described. It is demonstrated this device is well suited for precision measurements of magnetic susceptibility up to approximately 600 K. Thus, the SQUID method can be employed for the study of phase transitions of most thermotropic liquid crystals and LC polymers. To access the influence of molecular biaxiality on the determination of the order parameter, measurements were performed on a homologous series of four nematic oxybenzoate trimers varying in shape. Since the conformation of those model compounds is well known, the molecular susceptibility can be calculated by the incremental scheme devised by Flygare [Chem. Rev. 74, 653 (1974)]. Data obtained therefrom compare favorably with the values of the molecular susceptibility as extrapolated according to the Haller [Prog. Solid State Chem. 10, 103 (1975)] method.
Quasi-one-dimensional antiferromagnetism in MnCl2⋅H2O
Authors: Lukin J. A. , Friedberg S. A. , DeFotis G. C.
Published: July 2002

Recent magnetic susceptibility measurements on polycrystalline MnCl2⋅H2O indicate that it behaves like a quasi-one-dimensional antiferromagnet. The heat capacity of this compound has now been measured between ∼0.5 and 80 K in a liquid-3He-cooled vacuum calorimeter. Cp exhibits a large, sharp λ-type peak at TN = 2.18 ± 0.01 K marking the onset of long-range spin order. The critical entropy S(TN) is found to be ∼0.40R ln 6, confirming the short-range, low-dimensional nature of most of the spin ordering. An anisotropic elastic continuum model has been used to calculate the contribution of lattice vibrations to Cp. The data above ∼3 K are well represented by this model (with suitable choice of three parameters) plus the theoretical heat capacity of the 1D Heisenberg antiferromagnet with S =5/2 and exchange constant J/k=−0.45 K. Below ∼ 0.7TN, the magnetic part of Cp is well described by an anisotropic 3D spin-wave model with Jz/k = J/k = −0.45 K, Jx/k = Jy/k = −0.015 K, and an anisotropy field HA ≊ 3.3 kOe. The intra- and interchain exchange constants agree well with those inferred from χM. 