bluuebunny/crossref_metadata_2025 huggingface dataset:
Cathodoluminescence and annealing study of plasma-deposited polycrystalline diamond films
Authors: Ruan J. , Choyke W. J. , Partlow William D.
Published: July 2002

We have measured the cathodoluminescence spectra of microwave plasma-assisted chemical-vapor deposited (CVD) polycrystalline diamond films at 77 K over the spectral range of 2300–8000 Å. Annealing studies of these spectra have been carried out at 500, 800, 1000, 1200, and 1350 °C. Rich spectra are observed. Many of them are stable up to the highest annealing temperature. Two peaks at 3.188 and 2.638 eV and the 5RL lines are destroyed, while other lines at 3.57 and 3.462 eV appear, after a 1200 °C anneal. The two neighboring peaks at 2.330 and 2.320 eV are probably responsible for the broadness of the often observed peak at 2.328 eV in CVD diamond films. We also compare some of the annealing behavior of the CVD diamond films with those of natural single-crystal diamond, and conclude that while most of the annealing characteristics of plasma-deposited diamond films are similar with those which have been reported for single-crystal natural diamonds, some of the annealing behaviors are different for these two types of materials.
Induced magnetic anisotropy in Sm(Fe,Co)2 compounds
Authors: Mushnikov N. V. , Korolyov A. V. , Gaviko V. S. , Raevski Ye. I. , Pareti L.
Published: July 2002

Intermetallic Sm(Fe1−xCox)2 compounds having the cubic MgCu2-type structure absorb a small quantity of hydrogen from the atmosphere under normal conditions. A magnetic annealing of such samples leads to the induction of a gigantic magnetic uniaxial anisotropy, which is linked to the ordered distribution of hydrogen into interstitial sites of the lattice. In this paper the induced magnetic anisotropy and spontaneous lattice distortions are studied as a function of both composition and hydrogen content. It is shown that the induced uniaxial anisotropy which adds to the initial cubic anisotropy gives rise to the occurrence of first-order magnetization processes (FOMP). In the temperature range where spin reorientation transitions take place a peculiar behavior of the FOMP is observed.
Mechanism for zinc diffusion in n-type gallium arsenide
Authors: Kahen K. B. , Spence J. P. , Rajeswaran G.
Published: July 2002

A model is presented that is able to account successfully for the Zn diffusion profiles in n+-GaAs. The model is based on a previously developed formalism whose basis is the retarding of the interstitial Zn diffusivity because of Coulomb pairing between interstitial and substitutional Zn. By extending the model to include Coulomb pairing of interstitial Zn with all acceptors present during diffusion, the resulting theoretical profiles are shown to be in very good agreement with the data while using only one adjustable parameter.
Phonon scattering and quantum mechanical reflection at the Schottky barrier
Authors: Lee E. Y. , Schowalter L. J.
Published: July 2002

Motivated by the recently developed experimental capability of ballistic-electron-emission microscopy (BEEM), we study the effect of phonon scattering and quantum mechanical reflection on the ballistic transport across the Schottky barrier from the metal into the semiconductor. We argue that, for the Schottky barrier formed by a metal overlayer on a semiconductor substrate, one can typically expect the quantum mechanical transmission probability to have an E1/2 dependence, where E is the electron kinetic energy in the final state. We make a distinction between the metallurgical metal/semiconductor interface and the Schottky barrier energy maximum resulting from image potential, and calculate the optical phonon scattering rate between the interface and the maximum. We compute the combined effect of optical phonon scattering and quantum mechanical scattering on the ballistic transport for an initially isotropic velocity distribution of electrons in the metal, and we show that the two scattering processes combine to give a much weaker energy dependence than for either effect alone for cases of the Au/Si and Au/GaAs at both 300 K and 77 K. We use our model to show that the magnitude of the BEEM current for Au/Si should be roughly 5 times larger than for Au/GaAs and that decreasing the temperature from 300 K to 77 K should increase the magnitude of the BEEM current for Au/GaAs by a factor of about 3. There is fairly good agreement between our predictions and the available experimental evidence.
Optical energy-gap variation and deformation potentials in CuInTe2
Authors: Quintero M. , Gonzalez J. , Woolley J. C.
Published: July 2002

Values of optical energy gap E0 as a function of pressure P up to 3 GPa at room temperature, and as a function of temperature T in the range 10–300 K at atmospheric pressure were obtained by optical-absorption measurements on samples of CuInTe2. It was shown that in this pressure range, E0 varies linearly with P, dE0/dP having a value of 2.2×10−2 eV/GPa. The variation of E0 with T was fitted well by a simple Manoogian–Leclerc equation of the form E0(0) − E0(T) = UT + Vφ (coth φ/2T−1). Both dE0/dP and U can be related to (dE0/dT)2, the lattice dilation contribution to the variation of the energy gap with temperature, and the values obtained in the two cases showed good agreement. The Vφ term can be related to (dE0/dT)1, the energy-gap variation due to electron-phonon interaction. From the values of (dE0/dT)1 and (dE0/dT)2, values were determined for the acoustic deformation potentials of the conduction band Ce and of the valence band Ch.
Relationship among shock-wave velocity, particle velocity, and adiabatic exponent for dry air
Authors: Kim In Ho , Hong Sang Hee , Jhung Kyu Soo , Oh Ki-Hwan , Yoon Yo Kil
Published: July 2002

Based on detailed equation-of-state calculations, it is shown that the relationship between the shock-wave velocity Us and the particle velocity Up for shock-compressed dry air can be represented accurately by the linear relation Us = a(P0) + b(P0)Up in a wide range of Up (2≤Up≤9 km/s) and initial pressure P0 (10−6≤P0≤1 atm) where a and b are given by the cubic polynomials of log10P0. An accurate analytic expression for the adiabatic exponent is derived by utilizing the linear relation.
Structural and optical properties of Al0.48In0.52As layers grown on InP by molecular beam epitaxy: Influence of the substrate temperature and of a buffer layer
Authors: Tournié E. , Zhang Y.-H. , Pulsford N. J. , Ploog K.
Published: July 2002

We have studied the crystalline and optical properties of AlyIn1−yAs ternary alloys grown by molecular beam epitaxy on InP substrates. We obtain Al0.48In0.52As layers with both high structural quality and excellent optical performance by growing (i) at high substrate temperature (600 °C), (ii) on a high-quality GaxIn1−xAs/AlyIn1−yAs short-period superlattice buffer, (iii) or on a high-quality GaxIn1−xAs buffer layer, as attested by double-crystal x-ray diffraction and photoluminescence measurements. In addition the experimental results indicate a significant reduction of the clustering level in these samples which is interpreted in terms of a smoothing of the growth front, a thermodynamically controlled growth mode, and the interplay between In segregation and In desorption. Our investigations further show that the improvement of the structural quality and of the optical performance are strongly correlated. Finally, we report the first evidence of excitonic features in photoluminescence excitation spectra of the AlyIn1−yAs ternary alloy.
Thickness and substrate dependence of the magneto-optical Kerr effect of thin magnetic films
Authors: Zhai H. R. , Xu Y. B. , Lu M. , Miao Y. Z. , Hogue K. L. , Naik H. M. , Ahmad M. , Dunifer G. L.
Published: July 2002

Different thickness dependencies of the magneto-optical Kerr effect of the magnetic (Co, Ni, and Fe)/nonmagnetic (air, glass, Cu, and W) bilayer structures were studied experimentally and theoretically, showing the complicated influence of the dielectric constants of the underlying substrate.
Near-edge study of gold-substituted YBa2Cu3O7−δ
Authors: Ruckman Mark W. , Hepp Aloysius F.
Published: July 2002

The valence of Cu and Au in YBa2Au0.3Cu2.7O7−δ was investigated using x-ray absorption near-edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide (Au2O3) and monovalent potassium gold cyanide (KAu(CN)2) and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au—O bond in YBa2Au0.3Cu2.7O7−δ than in trivalent gold oxide.
Optical properties of oxygen-deficient centers in silica glasses fabricated in H2 or vacuum ambient
Authors: Awazu Koichi , Kawazoe Hiroshi , Muta Ken-ichi
Published: July 2002

Silica soots were sintered under a reducing ambient to study the generation mechanism of the oxygen-deficient-type defects in silica glasses. Glasses sintered under H2/He gas mixtures or vacuum were prepared with an intent to produce oxygen-deficient centers. Two optical-absorption bands were generated in the silica glasses sintered under the H2/He gas mixtures. One was 5.17-eV absorption band and the other was an absorption tail near the Urbach tail of silica glasses. Both absorptions were attributed to the silicon lone pair center (SLPC). On the other hand, the other type of reduced silica glasses were prepared in the vacuum ambient. Three kinds of absorption bands could be detected clearly: one was peaking at 5.17 eV, another showed only its shoulder near the Urbach tail, (both were also attributed to the SLPC) and the third was peaking at 6.7 eV and was attributed to a SiSiSi structure. Fabricated in higher volatile ambient under vacuum, the color of the sample showed a smoky black and generated broad absorption band peaking at 5.1 eV. This band is tentatively attributed to the optical absorption due to excitation from the inner shell of silicon.
Bound to continuum superlattice miniband long wavelength GaAs/AlxGa1−xAs photoconductors
Authors: Gunapala S. D. , Levine B. F. , Chand Naresh
Published: July 2002

We have measured and theoretically analyzed the optical absorption and hot electron transport physics of a new long wavelength (λ=5–9 μm) infrared miniband photoconductor based on a GaAs/AlxGa1−x superlattice. The optical absorption photoexcites an electron from the lowest miniband below the barriers to the excited state which is designed to be above the top of the barriers. This bound to continuum absorption leads to more than an order of magnitude improvement in electron transport and detector performance, compared with previous bound state miniband photoconductors.
Analytic approach to glow discharge theory: The physical model
Authors: Pai S. T.
Published: July 2002

On the basis of fluid approximation, a physical model in analytic form for dc glow discharge is presented. The model has yielded a variety of analytic expressions for the physical quantities concerned. These analytic expressions are functional, self-consistent, and satisfy all the governing equations as well as the real boundary conditions. With the builtin feature of mode indexing, the model may be employed for a wide range of applications. Several physically significant points which have not been reported previously were revealed from the present model.
Analytic approach to glow discharge theory: Result and analysis
Authors: Pai S. T. , Guo X. M.
Published: July 2002

Using the analytic expressions given in the preceding article, S. T. Pai [J. Appl. Phys. 71, 5820 (1992)] the concerned physical quantities n, N, V, Ez, Γ−, Γ+, and Jz and many others for dc glow discharges were calculated and systematically analyzed under various conditions. Several physically significant points have been brought forward via the analysis. Comparisons between the present results and the corresponding ones obtained by previous investigators showed similarities between them in many aspects. Such similarities signify the wide range applicability of the present model. The builtin feature of mode indexing in the model has been quantitatively demonstrated. Results yielded from such a demonstration are consistent with the corresponding physical situations.
Adsorption of benzene on porous amorphous hydrogenated carbon films
Authors: Yin Y. , Collins R. E. , Pailthorpe B. A.
Published: July 2002

The annealing effect on porosity of amorphous hydrogenerated carbon thin films was studied using a quartz crystal microbalance. As-prepared films show a mesoporous structure and a low adsorption capacity which is proportional to film thickness. Porosity of the as-prepared film is estimated at about 0.15. Baking in vacuum changes the film to be highly microporous and significantly increases the porosity of the films to over 0.40, depending annealing history. Outgassing during the annealing process plays an important role in the formation of porosity. Heat treatment first opens micropores in the slightly mesoporous film. Further heating increases the number and size of micropores, and also produces mesopores. With prolonged heating at high temperatures, further outgassing occurs, resulting in collapsing of the films.
Growth of epitaxial C54 TiSi2 on Si(111) substrate by in situ annealing in ultrahigh vacuum
Authors: Kim Kun Ho , Lee Jeoung Ju , Seo Dong Ju , Choi Chi Kyu , Hong Sung Rak , Koh Jeoung Dae , Kim Sung Chul , Lee Jeong Yong , Nicolet Marc A.
Published: July 2002

The growth of Ti and the formation of epitaxial Ti silicide on Si(111)-7×7 were investigated by using reflection high-energy electron diffraction (RHEED) and high-resolution transmission electron microscopy (HRTEM). The growth mode of Ti is Stransky–Krastanov type when the substrate temperature is room temperature (RT). On the other hand, it is Volmer–Weber type when the substrate temperature is ∼550 °C. The HRTEM lattice image and transmission electron diffraction pattern show that C54 TiSi2 is grown epitaxially on a Si substrate when 160 ML of Ti is deposited on a Si(111)-7×7 surface at RT followed by in situ annealing at 750 °C for 10 min in ultrahigh vacuum (UHV). The TiSi2/Si interface is somewhat incoherent, but the developed TiSi2 crystallites are single crystal with matching face relationships of TiSi2(111)∥Si(111), TiSi2(311)∥Si(111), and TiSi2(022)∥Si(111). A thin single-crystal Si overlayer with [111] direction is grown on the TiSi2 surface when TiSi2/Si(111) is annealed at ∼900 °C in UHV, which is confirmed by observing the Si(111)-7×7 RHEED pattern.
A Franz-Keldysh model for photoreflectance from GaAs/GaAlAs heterojunction structures
Authors: Batchelor R. A. , Hamnett A.
Published: July 2002

A model is described for the simulation of photoreflectance spectra from GaAs/GaAlAs heterojunctions. The Franz-Keldysh theory is used to obtain the field-induced modulation of optical properties within the structure, and a transfer matrix method is applied to calculate the modulation of reflectance in the presence of heterojunctions and spatially varying electric fields. The photoreflectance results of Sydor et al. [J. Appl. Phys. 67, 7423 (1990)] on structures of GaAlAs layers grown on GaAs and capped with GaAs were interpreted with this approach. It is shown that in the presence of a 3 μm GaAlAs layer, rapid interference oscillations are both predicted and observed in the spectrum from the lower GaAs layer, preventing easy characterization of internal electric fields. However, comparison of simulated spectra with experimental results does allow estimates of the dc electric fields in the two layers to be made, and also enables the strength of the ac modulation in the two layers to be compared. Photoreflectance from a high electron mobility transistor structure has also been modeled. Calculations reveal, in addition, that electro- and photoreflectance spectra from multilayer structures can be very sensitive to the angle of incidence used in measurements, the presence or absence of cap layers, and the optical properties of the component semiconductors.
Epitaxial regrowth of n+ and p+ polycrystalline silicon layers given single and double diffusions
Authors: Williams J. D. , Ashburn P.
Published: July 2002

This article investigates the epitaxial regrowth of n-type and p-type polycrystalline silicon (polysilicon) layers deposited on silicon, which are subjected to either a single emitter diffusion or consecutive base and emitter diffusions. A wide range of diffusion conditions is considered, covering both rapid thermal and furnace diffusion in the temperature range 950–1200 °C. The sheet resistances of single-diffused n-type polysilicon layers are significantly higher than those of double diffused layers for rapid-thermal emitter diffusions in the temperature range 1025–1125 °C. This is explained by the epitaxial regrowth of the polysilicon during the emitter diffusion, caused by the partial break-up of the interfacial oxide during the base diffusion. In contrast the sheet resistances of single- and double-diffused p-type polysilicon layers are found to be similar. Rutherford backscattering spectra are presented which show that the structures of the single- and double-diffused polysilicon layers are similar. This is explained by the effect which fluorine, incorporated into the polysilicon during the BF2 emitter implant, has in accelerating the break-up of the interfacial oxide during the early part of the emitter diffusion. Estimates are made of the time to break up the interfacial oxide layer and the time to vertically epitaxially align the polysilicon at different temperatures, and activation energies of 4.9 and 4.7 eV, respectively obtained. In n-type polysilicon, the epitaxial regrowth is dominated by the time to break up the interfacial oxide layer, whereas in BF2 implanted p-type polysilicon it is dominated by the time to vertically epitaxially align the polysilicon. A vertical epitaxial alignment rate of 1000 Å/s is obtained for n-type polysilicon at 1050 °C, compared with 240 Å/s for p-type polysilicon at 1100 °C.
A study of group-V desorption from GaAs and GaP by reflection high-energy electron diffraction in gas-source molecular beam epitaxy
Authors: Liang B. W. , Tu C. W.
Published: July 2002

Desorption behaviors of arsenic on GaAs and phosphorus on GaP surfaces have been studied by the specular-beam intensity change of reflection high-energy electron diffraction when the group-V cracker shutter is closed in gas-source molecular beam epitaxy. We obtained an activation energy of 58 kcal/mol for arsenic desorption from GaAs. Compared with arsenic on GaAs, phosphorus on GaP has a large desorption rate constant, and the activation energy of phosphorus desorption is 43 kcal/mol. These activation energies are comparable to the heats of vaporation of As2 and P2.
Stress dependent low-frequency electrical noise in carbon fibers
Authors: Patel Dinesh , Dumont Yves , Spain I. L.
Published: July 2002

Low-frequency (10–60 Hz) electrical noise has been measured for the first time in carbon fibers while they were subjected to tensile stress. The measurements were performed at room temperature. In all the fibers, a minimum in the noise was observed with applied stress. Low-modulus ex-PAN (polyacrylonitrile) fibers showed three times the increase in noise at the highest stress compared to the higher modulus fiber. Measurements were also made on vapor grown carbon fibers (VGCFs) both as-grown and annealed. The highly graphitized VGCF showed the smallest increase in the noise with stress among the fibers studied. Our noise results can be related to the microstructure of the fibers. The fiber microstructure becomes better aligned with applied stress. Therefore, the noise would be expected to decrease. Our results, however, indicate that stress dependent noise in these fibers is caused by a combination of parameters such as fibril alignment and electronic characteristics.
Studies on recombining Al-plasma using 1.06, 0.532, 0.355, and 0.266 μm laser radiation
Authors: Tambay Rekha , Singh Ranjit , Thareja R. K.
Published: July 2002

We report studies on the emission spectra of Al-plasma produced by Nd:YAG laser and its harmonics. The electron temperature estimated using relative intensities of Al II lines is between 0.8 and 4.0 eV. The electron density measurement using Stark width broadened transition shows density of the order of 2×1016 cm−3. An estimate of plasma expansion velocity from temporal behavior at various distances from the target is also reported.
Spatial variation of the critical current density of the high T
c superconducting thin films
Authors: Feng Y. J. , Cheng Q. H. , Wu P. H. , Liu H. M.
Published: July 2002

Low-temperature scanning electron microscopy (LTSEM) is a promising measuring technique for probing the spatial distribution of the superconducting properties of high Tc thin films. In the presented article we have given some experimental observations on the spatial variation of the critical current density of two kinds of high Tc thin films using a LTSEM. The results show that in the polycrystalline TlBaCaCuO film prepared by dc magnetron sputtering, the maximum local critical current density is about 3–4 times greater than the minimum local critical current density. The microstructure analysis implies that the strong inhomogeneous critical current density distribution in the TlBaCaCuO film is due to its granular structures and the existence of several structural phases. For c-axis oriented epitaxial YBaCuO thin film deposited in situ by laser ablation, the results indicate a less inhomogeneous critical current density distribution. The maximum local critical current density is less than 1.5 times the minimum local critical current density in the epitaxial thin film.
Structural studies on highly ordered and highly conductive thin films of pentacene
Authors: Minakata Takashi , Imai Hideaki , Ozaki Masaru , Saco Kentaro
Published: July 2002

Structural studies on highly conductive thin films of pentacene (PEN) were carried out by x-ray and electron diffraction methods. The ultrathin film before and after doping with iodine was confirmed to consist of single crystalline domains, and the lattice parameters were determined. Drastic elongation along the c axis as a result of doping was observed, while the a-b plane did not change during doping. The intercalation of iodine molecules between molecular layers of PEN was confirmed.
Numerical computation of higher-order chromatic aberrations for rotationally symmetric electrostatic lenses
Authors: Liu Zhixiong , Ximen Jiye
Published: July 2002

In the present paper third order chromatic aberrations have been computed for an immersion lens and an einzel lens based on canonical aberration theory. The electron trajectories with up to third order chromatic aberrations have been compared with the real trajectories. They are in good agreement, and the computational errors are believed to be about 0.2%. Therefore, the canonical theory of higher order chromatic aberration has been verified. As a practical application, for a typical electrostatic lens, the first, third order chromatic aberrations and the third order geometric aberrations, which are functions of the object side beam half-angle, have been presented in detail. It is expected that the results are useful for designing and optimizing a low chromatic aberration electrostatic lens.
Definition, resolution, and contrast in photothermal imaging
Authors: Friedrich K. , Haupt K. , Seidel U. , Walther H. G.
Published: July 2002

Photothermal imaging can be described quantitatively by means of a point spread function (PSF), which represents the image of a buried thermal point defect. From this PSF conclusions can be drawn about amplitude and phase contrast, half-width, and resolution of photothermal imaging. The theoretical findings are stated by measurements from an appropriately designed model sample.
A sensitive YBaCuO thin film bolometer with ultrawide wavelength response
Authors: Dwir B. , Pavuna D.
Published: July 2002

We have constructed two types of high-temperature superconducting (HTSC) bolometers, whose performance is essentially wavelength independent from λ∼0.6 to 450 μm: The first is a microbridge, of dimensions 20×20 μm, and the second is a meander, covering a region of ∼1 mm2. Both were fabricated by photolithography of a superconducting YBaCuO thin film on SrTiO3. The bolometers are current biased, and the ac voltage induced by the chopped radiation is measured using lock-in detection. Operating optimally in the vicinity of the transition temperature (90 K), the first bolometer shows responsivity S∼1 mV/(W/cm2), while the second gives S∼800 V/W. The response of the first bolometer for various chopping frequencies is basically S∼1/√f, which makes it usable at frequencies up to ≥50 kHz, while the second bolometer has a chopping-frequency response that is basically S∼1/f, with a cutoff frequency near 0.01 Hz.
Mechanically alloyed 1:12 nitrides and carbides
Authors: Gong Wei , Hadjipanayis G. C.
Published: July 2002

Nd10Fe90−yMoyNx(y=8,12,15) nitrides and Nd10Fe75Mo15Cx carbides have been prepared by mechanical alloying. The experimental results show that both Tc and Ms increase from 310 to 355 °C and from 84.5 to 108.8 emu/g, respectively, when the Mo content is reduced from 15 to 8 at. %. However, the coercivity of the lower Mo content Nd10Fe90−yMoyNx compounds is decreased with a value of Hc=4.0–4.5 kOe for y=8. An increase in coercivity by 2–3 kOe was obtained after an addition of 1.5 at. % Dy in the Nd8.5Dy1.5Fe82Mo8Nx compound. Al-bonded magnets were made with mechanically alloyed powders using Al contents from 5 to 40 wt % and bonding temperatures in the range of 600–680 °C. The coercivity of the bonded magnets was found to increase by about 1–2 kOe. The best results are obtained on a 10 wt % Al sample, bonded at 660 °C with Hc=9.5 kOe. Both the nitrides and carbides had very high coercivities (Hc≳22 kOe) at low temperatures.
Preparation of YBa2Cu3O7−x films and YBa2Cu3O7−x/Y2O3 multilayers using coevaporation and atomic oxygen
Authors: Hudner J. , Östling M. , Ohlsén H. , Stolt L. , Nordblad P. , Ottosson M. , Villegier J.-C. , Moriceau H. , Weiss F. , Thomas O.
Published: July 2002

Thin layers of YBa2Cu3O7−x (YBCO) deposited on LaAlO3 substrates have been prepared in situ by coevaporation of Y, Ba, and Cu. Incorporation of oxygen was accomplished by an atomic oxygen beam source with high cracking efficiency. The total oxygen flow at the substrate could be kept low enough to permit the use of a quadrupole mass spectrometer for evaporation rate monitoring. Films were strongly c-axis oriented with rocking curve full width at half-maximum values of 0.6°. Transport measurements on patterned films yielded critical current densities of 6×106 A/cm2 at 77 K. The deposition method was demonstrated to be feasible for preparation of Y2O3/YBCO heterostructures.
The majority carrier mobility of n-type and p-type Hg0.78Cd0.22Te liquid phase epitaxial films at 77 K
Authors: Chen M. C. , Colombo L.
Published: July 2002

The dependence of majority carrier mobility on carrier concentration at 77 K in Hg0.78Cd0.22Te has been studied by Hall measurements on about 190 n-type and 360 p-type liquid phase epitaxial films. The n-type films were indium doped with the carrier concentration varying from 1×1014 to 2×1016 cm−3. The measured electron mobility changed from 2×105 to 8×104 cm2/V s. The p-type films were undoped (Hg vacancy) with the carrier concentration varying from 2×1015 to 3×1017 cm−3. The measured hole mobility changed from 600 to 200 cm2/V s. By comparing calculated mobility curves with the experimental data, we found that the major scattering mechanisms for electron mobility in n-type materials were polar optical phonon, ionized impurity, and alloy disorder scatterings. These three scattering mechanisms also dominate the hole mobility in p-type materials at 77 K. It was also found that a model with Hg vacancy as doubly ionized shallow acceptors fitted very well the hole mobility versus carrier concentration data.
Frequency-dependent complex permeability in rare earth-substituted cobalt/nonmagnetic transition metal soft ferromagnetic amorphous thin films
Authors: Russat J. , Suran G. , Ouahmane H. , Rivoire M. , Sztern J.
Published: July 2002

Using radio frequency (rf) sputtering, we have prepared in presence of a static magnetic field, ferromagnetic thin films of composition (Co93Zr7)100−yREy(RE=Nd,Pr,Dy,Tb... a magnetic rare earth element). This study was performed for small amounts of RE substitution (0<y<3). These films exhibit attractive soft magnetic properties similar to CoZr alloys: low coercivity (Hc∼1 Oe), and a high saturation induction (4πMs≳10 kG). A low in-plane uniaxial anisotropy Hk was induced, whose magnitude depends upon the composition and the preparation parameters. Substitution by RE atoms affects essentially the μ frequency-response. Depending on the nature, the concentration of RE atoms and on the value of Hk, a high relative rotational permeability μ (μ′∼500–3000 at frequencies up to 500 MHz) was obtained. Also depending on RE and on y, high μ″ (μ″∼400–3000 at ν∼1 GHz) distributed over a very broad frequency range (Δν∼500–2500 MHz) could be measured.
Spontaneous and field induced spin reorientation transitions of DyFe11Ti single crystal
Authors: García L. M. , Bartolomé J. , Algarabel P. A. , Ibarra M. R. , Kuz’min M. D.
Published: July 2002

The spontaneous and field induced spin reorientation transitions (SRT) have been studied in the DyFe11Ti compound, using different experimental techniques as: ac magnetic susceptibility, magnetization, and electric resistivity. From these measurements, the thermal dependence of the easy magnetization direction has been undoubtedly determined from 4.2 to 300 K, range in which two SRT take place (at ∼69 and 187 K). We have checked the continuous character of the SRT at 187 K. On the other hand, it has been established that the SRT at 69 K under an applied magnetic field (H≥2 kOe) becomes of first order.
Electronic energy levels of quantum-well wires
Authors: Sánchez-Dehesa J. , Porto J. A. , Agulló-Rueda F. , Meseguer F.
Published: July 2002

An efficient variational method to solve the two-dimensional Schrödinger equation using a basis set of cubic B splines is introduced. The method, which uses the effective mass theory and the envelope function approximation, is applied to find the energy levels of quantum-well wires of different shapes. Finally, for rectangular wires a very simple method based on a special decomposition of the V(x,y) potential is used to reduce the problem to two one-dimensional equations. This gives very good results even for very narrow wires, where the conventional decomposition V(x,y)=V(x)+V(y) fails.
Spin polarized neutron reflectivity study of a Co/Cu superlattice
Authors: Schreyer A. , Zeidler Th. , Morawe Ch. , Metoki N. , Zabel H. , Ankner J. F. , Majkrzak C. F.
Published: July 2002

We present spin polarized neutron reflectivity data on a Co/Cu(111) superlattice and show how not only the magnitude but also the orientation of the average magnetic moment of each layer can be extracted by analyzing the polarization of the reflected beam. This method allows more detailed conclusions about the exchange coupling of magnetic layers across nonmagnetic interlayers and the magnetic in-plane anisotropy in such systems. We present a theoretical fit to the spin-flip and non-spin-flip data which leads to quantitative conclusions about the spin structure. These spin polarized neutron reflectivity results coincide well with the macroscopic magnetic properties which were measured using the magneto-optic Kerr effect revealing a newly discovered uniaxial anisotropy in this system.
Pattern sensitivity of selective Si1−xGex chemical vapor deposition: Pressure dependence
Authors: Kamins T. I.
Published: July 2002

The thickness dependence of selectively deposited Si1−xGex on the oxide pattern defining the deposition is a strong function of the total system operating pressure. The pattern sensitivity is much greater for atmospheric-pressure deposition than for reduced-pressure (10–80 Torr) deposition. Within the reduced-pressure regime, the pattern sensitivity decreases as the pressure is reduced, either for the same GeH4 mole fraction or for the same Ge content in the deposited layer. The observed behavior is consistent with the easier lateral transport of reactive species in the gas phase at lower pressure. Higher HCl mole fractions also decrease the pattern sensitivity.
Sensitive bolometers using high-T
c superconducting thermometers for wavelengths 20–300 μm
Authors: Verghese S. , Richards P. L. , Sachtjen S. A. , Char K.
Published: July 2002

Two types of sensitive high-Tc bolometer have been fabricated on 20-μm-thick sapphire substrates with YBa2Cu3O7−δ thin film transition edge thermometers. The sensitivity of both devices is superior to commercially available, room temperature pyroelectric detectors. A 1×1 mm bolometer with a radiation absorber of gold black smoke has a noise equivalent power NEP=2.4×10−11 W/Hz1/2 at 10 Hz and has useful sensitivity over wavelengths 20–100 μm. A 3×3 mm bolometer with a Bi film radiation absorber has NEP=3.6×10−10 W/Hz1/2 at 10 Hz and has useful sensitivity over wavelengths 100–300 μm. Water vapor transmittance spectra were measured to demonstrate the sensitivity of both devices.
Compressibility of SiC up to 68.4 GPa
Authors: Bassett W. A. , Weathers M. S. , Wu T.-C. , Holmquist T.
Published: July 2002

A diamond anvil cell was used with synchrotron radiation to measure the compressibility of the 6H polytype of SiC (moissanite) up to 68.4 GPa. NaCl was used as the pressure medium, and Au was used as the pressure calibrant. The effect of pressure gradient was minimized by using a very small x-ray beam (0.015 mm diam), and uniaxial stress was minimized by using three times as much volume of NaCl as SiC. The 101 and 102 peaks of SiC were measured as a function of pressure, and the molar volumes based on them were in excellent agreement. Pressure was calculated from the 111, 200, and 220 peaks of Au. The data when fit to the Birch–Murnaghan equation yield a bulk modulus of K0=230.2±4.0 GPa if the K′0 is set at 4. These values are in good agreement with earlier unpublished measurements (K0=234.3±4.9 GPa; K′0=4) made by us in which NaCl was used as the pressure calibrant. Our compression measurements appear to indicate a stiffer behavior than those based on shock measurements.
GeAs as a novel arsenic dimer source for n-type doping of Ge grown by molecular beam epitaxy
Authors: Kawanaka M. , Iguchi N. , Fujieda S. , Furukawa A. , Baba T.
Published: July 2002

GeAs is successfully applied as a new arsenic dimer source for efficient n-type doping of Ge grown by molecular beam epitaxy. The arsenic fluxes emanating from GeAs Knudsen cells are not composed of arsenic tetramers, but only of arsenic dimers. High electron concentrations of up to 1.1×1020 cm−3 are achieved with GeAs, which is much larger than any ever obtained in antimony-doped Ge. The electron concentration in the arsenic-doped Ge films depends on the GeAs cell temperature with an activation energy of 2.5 eV, which coincides with that of the arsenic dimer beam flux generated from GeAs. Moreover, it is found that the electron and arsenic concentrations in the arsenic-doped Ge layer are identical. These results indicate that arsenic atoms are incorporated into Ge from the arsenic dimer beam, and that a very high electrical activation of the incorporated arsenic atoms is obtained.
Strong blue light emission from an oxygen-containing Si fine structure
Authors: Morisaki H. , Hashimoto H. , Ping F. W. , Nozawa H. , Ono H.
Published: July 2002

A photoluminescence study has been made on an oxygen-containing Si fine structure fabricated by a gas evaporation technique. Transmission electron micrographs have shown that the fine structure is composed of nonspherical particles aggregated together in chain-like or cluster-like structures. The luminescence from the samples after oxidation treatment is bright blue as viewed with the naked eye, the spectra having a peak at about 470 nm or shorter wavelength. A peculiar temperature dependence of the emission peak indicates that the emission is strongly correlated with some structural change in the fine structure.
Shallow Si p+-n junctions fabricated by focused ion beam Ga+ implantation through thin Ti and TiSi2 layers
Authors: Mogul H. C. , Steckl A. J. , Novak S. W.
Published: July 2002

Focused ion beam Ga+ implantation through Ti metal (ITM) and TiSi2 (ITS) layers, followed by rapid thermal annealing (RTA), has been investigated for application in self-aligned silicide technology. The Ga+ energy was varied from 25 to 50 keV at doses of 1×1013 and 1×1015 cm−2 followed by RTA at 600 °C for 30 s. Depth profiles of the Ga implants were obtained by performing secondary-ion mass spectrometry. It was observed that higher-energy and higher-dose implants yielded good quality p+-n junction characteristics. Diodes were fabricated to obtain the electrical properties of these silicided junctions. At higher implant energies (≥40 keV) and all doses, I-V characteristics of ITS diodes showed 100 times lower leakage currents (Ir) than ITM diodes. For low-energy (<40 keV)/high-dose implantation the ITS diodes showed a slight improvement in Ir over the ITM diodes, whereas for low-energy/low-dose implantation the same Ir was observed.
Determination of the crystal orientation of CuInSe2 by Raman spectroscopy
Authors: Tanino H. , Fujikake H. , Maeda T. , Nakanishi H.
Published: July 2002

We have developed a new method for the determination of the crystal orientation of CuInSe2 by Raman spectroscopy. The single crystal of CuInSe2 has a (112) natural surface. On this surface we often observe slip lines, which construct a triangular shape. However, it is difficult to identify which corner is the projection of the c axis. We established a new method to identify the c direction by using Raman spectroscopy. This method is also effective for small single crystals down to the size of 1 μm.
Epitaxial growth of CoSi2 on both (111) and (100) Si substrates by multistep annealing of a ternary Co/Ti/Si system
Authors: Liu Ping , Li Bing-Zong , Sun Zhen , Gu Zhi-Guang , Huang Wei-Ning , Zhou Zu-Yao , Ni Ru-Shan , Lin Cheng-Lu , Zou Shi-Chang , Hong Feng , Rozgonyi G. A.
Published: July 2002

Formation of CoSi2 films by the reaction of ternary Co/Ti/Si system has been investigated. Ti and Co films were sequentially deposited on Si substrates by ion beam sputtering. It succeeded in the growth of epitaxial single-crystalline CoSi2 films on both Si(111) and Si(100) substrates through a multistep annealing process with temperatures from 550 to 900 °C in a nitrogen environment. A thin layer of TiN was formed on top of the epitaxial CoSi2. The values of Rutherford backscattering spectrometry/channeling minimum yield χmin for the epitaxial CoSi2 films were in the range of 10%–14%. The epitaxial CoSi2 grown on Si(111) was found to be composed of type B.
Investigation of compensation defects in CdTe:Cl samples grown by different techniques
Authors: Eiche C. , Maier D. , Sinerius D. , Weese J. , Benz K. W. , Honerkamp J.
Published: July 2002

A detailed analysis of the photoinduced current transients of differently grown CdTe:Cl samples was performed in the 100–140 K range in order to investigate the influence of different growth techniques (sublimation, Bridgman method, and traveling heater method) on compensation defects. While studying the experimental results the analysis of the transients turned out to be a crucial point. With the conventional two-gate technique only one trap with misleading trap parameters could be identified in each sample. Analyzing the transients with the regularization method proposed recently [C. Eiche, D. Maier, M. Schneider, D. Sinerius, J. Weese, K. W. Benz, and J. Honerkamp, J. Phys. Condens. Matter 4, 6131 (1992)], three traps could be identified in each sample. Only one of these traps leads to an activation energy and a cross section approximately the same for the different samples. The other two traps of each sample depend on the growth technique.
Influence of applied torsion on the bistable behavior of CoSiB amorphous wire
Authors: Blanco J. M. , Aragoneses P. , Irurieta E. , González J. , Kulakowski K.
Published: July 2002

Experimental results are reported on the torsion dependence of bistability of CoSiB amorphous alloys. Switching field and remanence magnetization are measured with applied torsion up to 20π rad/m for as-quenched wire as well as for stress-annealed wire, with and without preannealing. Measurements are performed both for Mz-Hz and Mz-Hφ hysteresis loop. The results show that the bistability of Co-rich amorphous wire strongly depends on the torsion-induced helical anisotropy.
Low-temperature characterization of the magnetic properties of MnBiAl thin films
Authors: Wierman K. W. , Shen J. X. , Kirby R. D. , Sellmyer D. J.
Published: July 2002

The magnetic properties of thin-film samples of MnBi0.8Alx with aluminum concentrations of x=0.0, 0.4, 0.6, and 0.8 were systematically studied over a temperature range of 20 to 300 K. The as-deposited films are amorphous and nonmagnetic, but highly textured polycrystalline films that are ferromagnetic are formed by annealing at 350 °C. Our measurements show that the coercivity of such films rapidly decreases, then approaches a constant value (4 kOe for x=0.4) with increasing annealing time. Magnetic measurements show that both anisotropy and coercivity decrease with decreasing temperature. Unlike bulk MnBi, our MnBi0.8Alx thin films do not have a spin reorientation transition at low temperatures. This may be due to impediment of the lattice contraction by the Al atoms doped into the interstitial sites of the MnBi lattice.
Phase transformation induced by gas phase reaction in RFe10SiCx alloys
Authors: Singleton E. W. , Hadjipanayis G. C. , Papaefthymiou V. , Hu Z. , Yelon W. B.
Published: July 2002

A new series of rare-earth iron intermetallic carbide compounds has been prepared by the reaction of powders with methane gas. The alloys prior to the methane heat treatment had the 2:17-type structure, R2(Fe,Si)17 (R=Y, Ce, Pr, Nd, and Sm). After heat treatment in temperatures up to 873 K the alloys absorb carbon and retain their original structure with a volume expansion over the carbon-free unit cell. For higher heat treatment temperatures (973–1073 K), a phase transformation occurs leading to the BaCd11-type structure. These compounds have a lower Curie temperature than those with the Th2Zn17-type structure, in the range of 453–495 K. Rietveld analysis of neutron diffraction data on NdFe10SiCx with the BaCd11-type structure are reported. In addition, the average hyperfine parameters determined by Mössbauer spectroscopy are reported for the Nd compounds.
Indirect-band-gap transition in strained GaInAs/InP quantum-well structures
Authors: Härle V. , Bolay H. , Lux E. , Michler P. , Moritz A. , Forner T. , Hangleiter A. , Scholz F.
Published: July 2002

Using photoluminescence (PL) and time-resolved measurements, the valence-band structure of tensile strained GaInAs quantum wells has been evaluated. From temperature-dependent PL, LO-phonon-assisted transitions at energies of about 32 meV below the band gap transition were observed. In addition, a hundredfold increase in the carrier lifetime of tensile strained quantum wells compared to unstrained layers was measured. Both findings are strong indications that the maximum of the valence band in k space is shifted away from the center of the Brillouin zone in tensile strained quantum wells near a critical composition, where the lowest heavy-hole and light-hole levels cross each other, thus giving rise for indirect optical transitions as predicted by theory.
Time behavior of currents in ZnS:Mn metal-insulator-semiconductor-insulator-metal structures
Authors: Goldenblum A. , Oprea A. , Bogatu V.
Published: July 2002

An experimental and theoretical investigation is made on the current pulse evolution, from a very low amplitude toward the steady-state shapes, if a sequence of alternative voltage pulses is applied to a ZnS:Mn metal-insulator-semiconductor-insulator-metal structure. The influence on this evolution of the voltage pulse maximum amplitude, of its rising slope, of pulse shape, and of the frequency is investigated. A quantitative model is developed which explains the current pulse evolution taking into account the competition between the multiplication of the carriers in the ZnS layer, and their recombination involving deep hole traps. The model describes the shapes of current pulse evolution and their peculiarities corresponding to different experimental conditions.
Thermodynamics and crystallographic mechanism of metastable phase formation in Nb-Fe, Nb-Co, and Nb-Ni systems by ion mixing
Authors: Zhang Z. J. , Liu B. X.
Published: July 2002

Two metastable crystalline phases, i.e., hcp and fcc, were formed in Nb-rich Nb-Fe, Nb-Co, and Nb-Ni multilayered films by room temperature 200 keV xenon ion mixing. The experimental results revealed that the formation sequence was first hcp and then fcc through an abnormal two-step phase transition of bcc→hcp→fcc. To give insight into the phase formation, Gibbs free-energy diagrams of the systems were constructed by the calculation method proposed by Alonso, Gallego, and Somozar [Nuovo Cimento, 12, 587 (1990)]. Besides, steady-state thermal annealing experiments of the corresponding as-deposited multilayers were conducted and the results confirmed the existence as well as the energetic sequence of the hcp and fcc phases predicted by the calculated free-energy diagram. Concerning the growth kinetics of the two metastable crystalline phases, the two-step phase transition was determined to be a shearing plus sliding mechanism.
Microvoids in diamond-like amorphous silicon carbide
Authors: Carreño M. N. P. , Pereyra I. , Fantini M. C. A. , Takahashi H. , Landers R.
Published: July 2002

The correlation between composition, microstructure, and optical properties of a-Si1−xCx:H thin films with different stoichiometries was established. The alloys were deposited by radio frequency glow discharge under ‘‘starving’’ plasma conditions from mixtures of SiH4 and CH4. The samples were characterized by small angle x-ray scattering, ultraviolet-visible and infrared spectrometry, and Auger electron spectroscopy. The results showed the presence of microvoids with sizes between ≂3 Å and ≂8 Å. The relative microvoid volume fraction displayed a maximum for x around 55 at. % and decreased for higher values of x. High carbon content alloys (x≂70 at. %) not only have a lower relative microvoid volume fraction, but show optical gaps as high as 3.7 eV, high resistivity, and very low refractive index, indicating the presence of a diamond-like C-C structure. These remarkable results are attributed to the deposition under ‘‘starving’’ plasma conditions.
Measurement and theory of the pressure dependence of zero-dispersion wavelength for communications fibers
Authors: Kim K. S. , Quigley A. I. , LaParre D. , Lines M. E.
Published: July 2002

The pressure dependencies of the zero-dispersion wavelength λ0 for dispersion-shifted fiber on the spool and in a submarine lightwave (SL) cabled sample were measured using pressures P up to 10 kpsi. The spool results showed a mean zero-dispersion shift dλ0/dP of close to +0.04 nm/kpsi. The corresponding shift for the SL cabled fiber was much smaller (less than 0.01 nm/kpsi) and the results were much less reproducible. This was believed to be due to the pressure-shielding effect of the cable structure. A theoretical calculation of dλ0/dP has been carried out for the unshielded fiber using a two-term (electronic and lattice) Sellmeier formalism. Assuming the dominant effect to be of fiber material (rather than waveguide design) origin, we find that the electronic and lattice contributions are of opposite sign with a resultant that agrees with experiment to within the combined accuracy of the experiment and theory.