bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical properties of AlN epitaxial thin films in the vacuum ultraviolet region
Authors: Yamashita H. , Fukui K. , Misawa S. , Yoshida S.
Published: February 2003

Optical absorption of AlN thin films shows a ’’knee’’ structure at 6.2 eV and an intense band at 7.8 eV. The structure at 6.2 eV is interpreted as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV. Dichroism observed at the absorption edge indicates that the transition Γ1v–Γ1c (E∥c) is of lower energy than the transition Γ6v–Γ1c (E⊥c). Strong dichroism in the 7–8-eV region is thought to cause the birefringence of AlN.
Predictions of the Onsager theory based on an exponential distribution of electron-hole separation distances
Authors: Borsenberger P. M. , Ateya A. I.
Published: February 2003

An analytic expression for the free-carrier photogeneration efficiency is derived which is based on the Onsager theory of geminate recombination. The expression assumes that the initial distribution of thermalized electron-hole pairs is described by the function g (r) = (1/4πr2b)  exp(−r/b), where r is the electron-hole separation distance and b is a dispersion parameter. An evaluation of the electric field and temperature dependences of the photogeneration efficiency is described. A comparison of results obtained with exponential and δ function distributions is presented and discussed.
High-efficiency thin-film polycrystalline-silicon solar cells
Authors: Chu T. L. , Chu Shirley S. , Lin C. L. , Abderrassoul R.
Published: February 2003

The deposition of a silicon film containing a p-n junction on a metallurgical silicon substrate has been used for the preparation of thin-film silicon solar cells. The substrate was prepared by the unidirectional solidification of purified metallurgical silicon on a graphite plate, and the silicon film was deposited by the thermal reduction of trichlorosilane with hydrogen containing appropriate dopants. Solar cells of the p+/n/n+-metallurgical silicon/graphite configuration have been prepared, and the AM1 efficiencies of 9–10 cm2 area cells are up to 9.5%
On the diffusivity of holes in silicon
Authors: Nava F. , Canali C. , Reggiani L. , Gasquet D. , Vaissiere J. C. , Nougier J. P.
Published: February 2003

The longitudinal diffusion coefficient of holes in Si has been measured with time-of-flight and noise techniques at 300 K for field strengths ranging from about 0.5 up to 40 kV/cm. As the electric field increases, the diffusion coefficient decreases to about 0.3 of its Ohmic value much more sharply than results previously reported in literature. The experimental results are interpreted by a Monte Carlo simulation which includes warping and nonparabolicity effects of the heavy-hole band.
Nonalloyed and i
n s
i
t
u Ohmic contacts to highly doped n-type GaAs layers grown by molecular beam epitaxy (MBE) for field-effect transistors
Authors: DiLorenzo J. V. , Niehaus W. C. , Cho A. Y.
Published: February 2003

MBE was used to grow n-type GaAs layers doped with tin to approximately 5×1019 cm−3. Au/Ge Ohmic contacts were formed on the heavily doped layers without exceeding the eutectic temperature, thereby producing a nonalloyed Ohmic contact. In an in situ metallization experiment, tin was deposited on a freshly grown n++ layer. The deposited contact (without any heating) has linear current-voltage characteristics. Power GaAs FET’s were fabricated with nonalloyed Au/Ge contacts which showed excellent rf and dc characteristics. The combination of MBE n++ layer growth and the technology presented here may have potential for microwave devices and GaAs integrated circuits.
Study of the Ge surface segregation in superconducting sputter-deposited Nb3Ge films using Auger electron spectroscopy
Authors: Buitrago R. H. , Toth L. E. , Goldman A. M.
Published: February 2003

Auger electron spectroscopy (AES) has been used to diagnose the nature of Ge enrichment in the top atomic layers of sputter-deposited films of superconducting Nb3Ge. In films with high Tc’s, there is a small oxygen-rich layer of 5–10 Å followed by a layer about 60–70 Å thick in which a pronounced Ge enrichment exists. This segregation layer is much thicker than comparable layers found in other binary alloys and this suggests that thermodynamic considerations are not the only cause of the enrichment. Beneath the layers, the Nb3Ge film is chemically homogeneous as a function of depth with constant Nb/Ge ratio existing up to the interface with the substrate where a Nb enrichment occurs. In films with low Tc’s, however, there is a smaller oxygen-rich layer and a thinner Ge-rich layer existing at the top surface. Very thin films sputter deposited under otherwise optimum conditions for producing high transition temperatures have low Tc’s and an incompletely formed Ge-rich surface layer. Additional experiments have established that the Ge-rich layer forms during the sputter deposition and its thickness is a function of deposition time. The data have serious implications for the fabrication of tunneling junctions for the purposes of probing the physics of superconductivity in Nb3Ge because the thickness of the Ge-rich layer is about the same as the coherence length. Methods to remove the Ge-rich layer without damaging the underlying film were also investigated, as was the effect of oxidation on the layer. One interesting sidelight of the interpretation of the data is that the Ge-rich layer may stabilize the growth of the high-Tc metastable phase.
ac cataphoresis measurements
Authors: Sery George E. , Chanin L. M.
Published: February 2003

Light spectrometric investigations of ac-excited binary noble-gas mixtures show ac cataphoretic phenomena. Time-averaged and discrete-time analysis techniques are used in studies of He-Ne, Ne-Ar, and Kr-Xe mixtures. Enhancement of the readily ionized gas component can occur either at the discharge tube ends or at the center. Time-dependent analyses indicate the importance of ionization waves when ac cataphoretic segregation is detected. The dependence of enhancement on various discharge parameters is reported.
Study of plasma expansion in a vacuum diode by the spectroscopic method
Authors: Wei P. S. P. , Adamski J. L. , Beymer J. R.
Published: February 2003

New results on the plasmas produced by an e-beam in a vacuum diode are presented. In the near-uv range, we measure the plasma expansion speeds by the Doppler-shift and by the time-of-flight methods. The maximum observed speed of 2.4×107 cm/sec for the C+3 ions leads us to estimate the electric field which is probably in the range of 1–6 kV/cm and may exist for tens of nsec. Some aspects of the spectral characteristics, the collective field effect, and the partition of the discharge energy are discussed in connection with recent literature.
Cyclotron maser instability for intense solid electron beams
Authors: Uhm Han S. , Davidson Ronald C.
Published: February 2003

The cyclotron maser instability for a solid relativistic electron beam propagating parallel to a uniform axial magnetic field B0?z is investigated. The stability analysis is carried out within the framework of the linearized Vlasov-Maxwell equations. It is assumed that ν/?≪1, where ν is Budker’s parameter and ?mc2 is the electron energy. Stability properties are investigated for the choice of equilibrium distribution function in which all electrons have the same value of total perpendicular energy, the same value of axial velocity, and a step-function distribution in canonical angular momentum. The instability growth rate is calculated including a determination of the optimum value of the beam radius R0 for maximum growth. It is found that the maximum growth rate for a solid beam is comparable to the maximum growth rate for a hollow beam.
The multiplier-assisted discharge: A new type of cold cathode
Authors: Catanese C. A. , Endriz J. G.
Published: February 2003

A multiplier-assisted discharge is a new type of electron source obtained by operating a high-gain electron multiplier in the presence of a feedback mechanism. At sufficient multiplier gain such a closed feedback loop results in self-sustaining currents. In one such feedback configuration—called ion feedback—the multiplier is operated in a background gas pressure of 10−6–10−4 Torr. At this pressure, and with multiplier gains of ?105, positive ions that are created by electron-gas collisions are accelerated to the multiplier input and produce sufficient secondary electron emission to sustain exponential current buildup. The operation of a nonlinear mechanism, most notably electron space charge, serves to ’’saturate’’ the current at a stable dc level. A second feedback mechanism, optical feedback, is obtained by operating a multiplier with a photocathode at the input that is spectrally matched to a phosphor at the output. The feedback mechanism in this case consists of that part of the phosphor emission that reaches the photocathode and causes photoelectrons that enter the multiplier. Again, space charge acts to saturate the currents to a stable dc level. Both theoretical expressions and experimental measurements were obtained for the operating parameters and the dynamic characteristics of feedback cells. For ion feedback, the relation that was developed between the multiplier gain and the pressure required for sustained emission was found to agree with the experimental values over the range of rare gases from helium to xenon. Current rise times were measured for this range of gases and agreed with predictions; exponential rise times as short as 26 nsec are available in cells using helium as background gas. Space-charge effects, in the form of both cell saturation due to electrons and neutralization due to the positive currents, were observed; the latter effect showed the dependence on pressure and gas species that is expected on the basis of simple theory. There was also measured the production and decay rates of metastable atoms, which are created along with positive ions as a result of electron-gas collisions. A similar correlation of theory with experiment was achieved for optical feedback. Particularly noteworthy in the optical feedback case is the very fast—1.5 nsec—rise time available with a short-time-constant phosphor such as cerium-doped LaPO4.
Impurity-peak formation during proton-enhanced diffusion of phosphorus and boron in silicon
Authors: Akutagawa W. , Dunlap H.L. , Hart R. , Marsh O. J.
Published: February 2003

The formation of a phosphorus or boron impurity peak in silicon has been observed following irradiation with monoenergetic protons. In this study we used a sample temperature of 700 °C, proton-beam energies of 50–140 keV, proton-beam current densities of ∼1 μA/cm2, and proton-bombardment times of 3 min to 3 h. The resultant impurity profiles were obtained using Schottky-barrier differential C-V techniques.
Pulsed-electron-beam annealing of ion-implantation damage
Authors: Greenwald A. C. , Kirkpatrick A. R. , Little R. G. , Minnucci J. A.
Published: February 2003

Short-duration high-intensity pulsed electron beams have been used to anneal ion-implantation damage in silicon and to electrically activate the dopant species. Lattice regrowth and dopant activation were determined using 4He+ backscattering, SEM, TEM, and device performance characteristics as diagnostic techniques. The annealing mechanism is believed to be liquid-phase epitaxial regrowth initiating from the substrate. The high-temperature transient pulse produced by the electron beam causes the dopant to diffuse rapidly in the region where the liquid state is achieved.
Rayleigh scattering of elastic waves from cracks
Authors: Gubernatis J. E. , Domany E.
Published: February 2003

We discuss apparent characteristic features of Rayleigh scattering of elastic waves from cracks. Interpreting these features, we suggest a procedure that in some experimental situations may be useful to distinguish generally shaped cracks from volume defects and to determine for elliptically shaped cracks the orientation, shape, and size.
Epitaxial growth of Al/GaAlAs films on (100) GaAs by hot vacuum deposition
Authors: Christou A. , Davey J. E. , Day H. M. , Macpherson A. C.
Published: February 2003

Epitaxial growth of (100) GaAlAs and Al was achieved on (100) n-GaAs substrates using vacuum deposition in an ultrahigh vacuum system. In situ Auger electron analysis, microspot Auger electrospectroscopy, LEED, and reflection electron diffraction was used to characterize the films. Regions of GaAlAs and Al were identified. Electrical measurements indicated the presence of a stable Schottky barrier with a barrier height of 0.76 eV.
Some unique aspects on ThO2-doped SnO2 exposed to H2 gas
Authors: Kanefusa Shinji , Nitta Masayoshi , Haradome Miyoshi
Published: February 2003

In ThO2-doped SnO2 exposed to H2 gas, the remarkable phenomenon like the increase of sample resistivity has been found in spite of n-type semiconductors. This phenomenon depends on the gas concentration, the sample temperature, and also the history of the samples. In samples sintered at 600 °C, it appears remarkably at the sample temperature below 240 °C and above 250 ppm of the gas concentration.
Core-level spectra of chromium and nickel atoms on polystyrene
Authors: Burkstrand James M.
Published: February 2003

Nickel and chromium atoms which were vapor deposited on clean surfaces of polystyrene were characterized with x-ray photoemission spectroscopy. For nickel coverages less than 0.01 monolayer the nickel atoms form isolated clusters. As the nickel coverage increases, these islands gradually coalesce into larger islands. The chromium undergoes the same coverage-dependent behavior beginning at about 0.02 monolayer. A comparison of the nickel and chromium data with the corresponding data for copper indicates that the mobility of copper on the polystyrene is less than that of either nickel or chromium. Finally, we did not find a nickel or chromium surface site with an unusually low core-electron binding energy similar to the copper site previously observed.
Comment on ’’A systematic experimental and theoretical investigation of the grain-boundary resistivities of n-doped BaTiO3 ceramics’’
Authors: Hoffmann B.
Published: February 2003

In a recent paper Ihrig and Puschert reported on measurements of the current-voltage characteristics and the temperature dependence of the effective zero resistivity of n-type ceramic BaTiO3. They described their results using Heywang’s potential-barrier model. In contradiction to other authors they denied a need to modify this model. It is shown here that the experimental results of Ihrig and Puschert are not detailed enough to warrant such a decision. The effect of an intergranular layer of a second phase on the grain-boundary resistance of ceramic BaTiO3 is briefly discussed.
Thin-film CdS/Cu2S heterojunctions: Dark I-V characteristcs and heat treatment
Authors: Amith A.
Published: February 2003

The temperature dependence of I-V curves of thin-film polycrystalline CdS/Cu2S heterojunctions was investigated as a function of heat treatment applied to them. Prior to any heat treatment, the space charge in the CdS is narrow enough so that electrons can tunnel from the bottom of its conduction band and the tunneling current is temperature independent. Considerable Ohmic shunting is caused by thin layers of Cu2S which had formed along the grain boundaries. After heat treatment, the space charge in the CdS widened due to diffusion of Cu from the Cu2S, so that electrons in CdS now require an activation energy to tunnel, and this results in a temperature-dependent tunneling current. Furthermore, the thin layers of Cu2S disappeared from the grain boundaries, thus eliminating the shunting paths which had existed prior to the heat treatment.
The relation of the yield stress of high-pressure anvils to the pressure attained at yielding and the ultimate attainable pressure
Authors: Panda Prakash C. , Ruoff Arthur L.
Published: February 2003

Using a sensitive microprofilometer, the onset of yielding in the anvils of a supported opposed anvil device can readily be determined. If the pressure at which yielding occurs is measured, the yield stress of the anvil material can be obtained. This is illustrated for 3% cobalt cemented tungsten carbide. The reverse is also true and can be used as the basis for obtaining the transition pressures of a material that transforms to a conducting phase at a pressure near which yielding of the anvil material commences. This is illustrated for the gallium phosphide transition which is found to be near 18 GPa based on the commencement of yielding in boron carbide anvils. Moreover, the yield stress or Knoop hardness can be used as the basis for obtaining the ultimate attainable pressures in supported opposed anvil devices. Based on the measured yield stress of a maraging steel, and the experimental observation that the bismuth transition is near or at the ultimate attainable pressure of this steel in a supported opposed anvil device, the III–V transition is found to be near 7.7 GPa. Based on the Knoop hardness and the previously mentioned observation, this transition is found to be near 7.5 GPa. Based on the measured yield stress of a 3% cobalt cemented tungsten carbide anvil, the ultimate pressure attainable in a supported opposed anvil device is found to be about 18 GPa and in any case less than 19 GPa. Inasmuch as the gallium phosphide transition occurs near the limit of the ultimate attainable pressure with such tungsten carbide pistons, the transition pressure of gallium phosphide to a conducting phase under the stress state present there is near 18 GPa. Based on the ultimate attainable pressure in boron carbide pistons the completion of the transition of sulfur to a conducting phase is found to be less than 33 GPa. The yielding of supported opposed diamond anvils with dislocation densities of ∼5×104/cm2 or more is expected to be in the neighborhood of 50 GPa. The onset of this yielding could be used as the basis for determining approximately the transition pressure of silicon carbide to a conducting phase at an estimated value of 64 GPa.
Isotope separation by jet-background interaction
Authors: Delgow T. L. , Muntz E. P.
Published: February 2003

Separation measurements have been made for neon isotopes penetrating a nitrogen jet over a broad range of flow regimes. The products of the jet-background interaction were collected by molecular probes which projected through the jet orifice from the plenum into the background chamber. The separation profiles are in excellent agreement with a very simple physical model of the penetration process. This model can be used to predict the performance of any isotopic separation experiment and has been shown to agree with another investigator’s argon and SF6 data. The amount of separation is adjustable, does not appear to be limited, and thus can be arbitrarily large. The apparatus required is particularly simple to construct.
Evaluation of beam distribution parameters in an electron storage ring
Authors: Chao Alexander W.
Published: February 2003

The motion of a charged particle in a linear electromagnetic device can often be analyzed by using the transport matrices. For an electron storage ring, this technique has been applied to yield fruitful results such as the trajectory of the particle distribution center and the beam sizes and shapes in phase space. Coupling effects among the horizontal, vertical, and longitudinal motions are included in a straightforward manner.
Measurement of the width of the inverted Lamb dip in H2CO at 3.51 μm
Authors: Ohtsu Motoichi , Tako Toshiharu
Published: February 2003

The width of the inverted Lamb dip in H2CO at 3.51 μm [51,5 (ground state) →60,6(v5=1)] was measured by using a low-noise He-Xe laser in an axial magnetic field as the light source. To measure the dip width it was necessary to determine first the range of the magnetic field strength and the maximum frequency deviation of the laser frequency modulation. Based on these results, the power-broadening characteristics were measured. Finally, the relation between the dip width free from the power broadening and the pressure of H2CO was obtained. The dip width (HWHM) was Δνh= (123±24)+(155±31) PF (kHz), where PF represents the H2CO pressure expressed in Pascal.
An ultrahigh-Q isotropically sensitive optical filter employing atomic resonance transitions
Authors: Marling J. B. , Nilsen J. , West L. C. , Wood L. L.
Published: February 2003

A new resonance principle in optical filters has been utilized to simultaneously permit realization of wide field-of-view (∼2π sr) and very narrow acceptance bandwidths, approaching 0.01 Å. A light signal is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, resulting in a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filter. The outer and inner bandpass filters have no common transmission band, resulting in complete blockage of all optical signals (background noise) that are not resonantly shifted in wavelength by the intervening atomic vapor. This ’’resonance filter’’ principle is experimentally verified, and system parameters are discussed for filters utilizing potassium, rubidium, or cesium vapor at nine wavelengths between 420 and 532 nm.
Rotational population transfer in HF
Authors: Hinchen J. J. , Hobbs R. H.
Published: February 2003

Population transfer in HF by both collisional and radiative processes was measured by ir-laser double-resonance experiments. In three kinds of experiments populations pumped to a specific rotational level were followed: out of the pumped level, to the levels above, and to the levels below. The rates of loss from the pumped level and transfer to the lower levels were strongly affected by lasing between rotational levels. Data for gain and laser intensity were incorporated into a kinetic rate model to evaluate transfer rates.
On the stress-induced electrical properties of point defects in the sphalerite structure. II. The piezoresistance effect
Authors: Booyens H. , Vermaak J. S.
Published: February 2003

It is shown that point defects in a crystal of the sphalerite structure can give rise to spatial variations in the tensor conductivity around them due to the piezoresistance effect. The expressions for these conductivity variations are derived for a general crystal of the sphalerite structure and are then applied to the particular case of n-type GaSb.
Effects of surface condition on the infrared absorptivity of 304 stainless steel
Authors: Wieting T. J. , DeRosa J. L.
Published: February 2003

The absorptivity of 304 stainless steel at 10.6 μm has been obtained between room temperature and 1000 °C by laser calorimetry. Highly polished specimens have been compared with as-received and rough-polished specimens in order to determine the effects of surface condition on the absorptivity. When the surfaces are well annealed, the calorimetry data show that the absorptivities of the highly polished surface and the rougher surfaces are nearly the same over the entire range of temperature. No influence of grain size on the absorptivity has been observed, despite the substantial growth of the grain boundaries at elevated temperatures. When the surfaces are deformed by cold rolling or rough polishing, the absorptivity at room temperature increases by 22–27% due to increased scattering from nonplanar defects within the surface layer. The absorptivity data on damage-free surfaces of stainless steel have been found to agree closely with the predictions of generalized Drude theory, applied to disordered alloys. The calorimetry data have also been used to calculate the hemispherical emissivity of 304 stainless steel between 400 and 1000 °C.
Photoluminescence in ZnSe grown by liquid-phase epitaxy from Zn-Ga solution
Authors: Fujita Shigeo , Mimoto Haruhiko , Noguchi Toru
Published: February 2003

Photoluminescence has been studied of epitaxial ZnSe layers grown from a pure Zn or a Zn-Ga alloy solution on ZnSxSe1−x (0⩽x⩽1) single-crystalline substrates. Intense blue emission bands at room temperature have been observed in the layers grown from a Zn-Ga alloy solution. The spectrum of the layer at 4.2 K generally consists of a strong emission line due to radiative recombination of excitons bound to the neutral donor, I2, an associated donor-acceptor pair emission band with LO-phonon replicas, and a deep-level emission, i.e., the so-called SA emission band. The effect of Ga on the emission spectrum is to greatly increase the intensity of the blue part of the spectrum. On the basis of the comparison between the experimental results and theoretical calculations, it is tentatively proposed that the blue emisison bands at room temperature originate from the radiative recombination due to band-to-band transition.
Energy deposition functions in electron resist films on substrates
Authors: Parikh Mihir , Kyser David F.
Published: February 2003

A Monte Carlo simulation of electron scattering in the resist and substrate of a target in electron lithography was used to obtain the spatial distribution of energy deposition in the resist. Analytical approximations were subsequently obtained by a least-squares fit of Gaussian functions to the forward- and backward-scattered components of these distributions. The parameters in the analytical functions were deduced and a compendium of values are tabulated for a variety of resist thicknesses, incident electron energies, and substrates. The parameters were found to agree with other parameters that can be physically correlated with electron-scattering processes and with available experimental data. These approximations and parameters provide quantitative guidelines for understanding and compensating of electron-scattering and proximity effects in electron-beam lithography.
High-power tunable 385-μm D2O vapor laser optically pumped with a single-mode tunable CO2 TEA laser
Authors: Woskoboinikow P. , Praddaude H. C. , Mulligan W. J. , Cohn D. R. , Lax B.
Published: February 2003

We demonstrate a 2-GHz tunability of the 385-μm stimulated Raman transition of D2O vapor optically pumped by the 9R (22) transition of a tunable single-mode CO2 TEA laser. Power levels of up to 800 kW in 100-nsec pulses and conversion efficiency of CO2 laser energy to D2O laser energy at 385 μm of up to 0.4% have been obtained with a D2O oscillator cavity. The TEA CO2 pump laser, which consists of a grating and étalon tuned oscillator followed by an amplifier chain, produced 25-J 100-nsec single-mode pulses and was tunable ±1 GHz around the 9R (22) line center. The present results indicate that tunable single-mode pump lasers are necessary in order to optimize high-power optically pumped laser systems and to produce narrow-linewidth spectral characteristics.
Potential flow in a region with sharp change of boundary
Authors: Hays W. P. , LaCasce E. O. , Stone W. A.
Published: February 2003

A series solution is developed for the problem of potential flow in a region with sudden change of boundary. The boundary and continuity conditions are applied directly to the velocity potential; no ambiguities arise. The resulting linear equations for the amplitudes in the eigenfrequency expansion can be solved using the Gauss-Seidel approximation method. This method allows the velocities to be computed accurately even near the transition region. Its convergence is closely connected with the physical properties of the solution. A simplified approximation for a river flowing into a harbor is the rectangular model given in the paper. In the course of applying Yeh’s method to this model for a comparison with experimental observations of the flow pattern, we discovered this extension of Yeh’s method.
Magnetoresistive determination of the anisotropy energy and its strain dependence in thin Permalloy films
Authors: Mazumdar P. , Juretschke H. J.
Published: February 2003

The variation of longitudinal magnetoresistance with angle and strength of an applied field is used to determine the anisotropy energy and its strain dependence in 80-20 and 90-10 Permalloy films. The results can usually be interpreted in terms of single-domain theory. Measurements for applied strains at angles other than parallel or normal to the easy axis give information about the anisotropy of the strain dependence, and an applied strain bisecting these directions is a preferred orientation for finding the strain sensitivity for an isotropic planar strain.
Magnetic properties of inter-rare-earth alloys at low temperatures in high magnetic fields
Authors: Amin Ali Y.
Published: February 2003

The effects of low concentrations of the weakly magnetic rare earths Sm(0–16.23 at.%) and Eu(0–1.08 at.%) on the strongly ferromagnetic rare-earth metals Ho, Dy, and Gd have been studied through measurements of magnetization at temperatures from 4.2 to 300 K in magnetic fields up to 50 kOe in polycrystalline samples. Samples of Ho-Sm alloys with concentrations of 1–6 at.% Sm show a definite increase in magnetic induction over the value for pure Ho metal under identical conditions, the magnetic induction of the alloy decreasing linearly with increasing Sm concentration. In contrast, the addition of 1.0 at.% Eu to Ho, Dy, or Gd does not change the magnetic properties of the host metal. The magnetic moment per atom and the temperature dependance of the magnetization were determined.
Characterization of domain-wall nucleation sites in SmCo5 single crystals
Authors: Searle C. W. , Maartense I.
Published: February 2003

Domain-wall nucleation fields in several single crystals of SmCo5 have been measured. These results, together with a model for magnetization reversal, were used to determine the domain-wall gradients and local demagnetizing factors at specific nucleation sites. Exposing the samples to hydrogen led to a degradation of permanent magnet properties.
Structural dependence of the Seebeck effect of thin tellurium films
Authors: Ozkaplan H. , Dinno M. A. , Schwartz M.
Published: February 2003

The thermoelectric emf, Seebeck coefficient, and electrical conductivity of thin tellurium films were determined for temperature differences up to almost 80 °C with one end of the film held at about 24 °C under nonannealed, quenched, and annealed conditions. The first two factors were greatest for the nonannealed film and smallest for the annealed film, whereas the conductivity was greatest for the annealed film and smallest for the nonannealed film. The results suggest the charge carrier concentration as the dominant factor in the first two cases, in contrast to the mobility as the dominant factor in the last case.
Effect of wall pinning on bubble motion
Authors: Magnin J. , Jouve H. , Barbara B.
Published: February 2003

Detailed measurements have been performed at small drive fields in SmYGa garnet bubble material. The results show the existence of an irreversible initial jump of the order of 0.2 μm. The minimum drive-field amplitude needed to achieve a net bubble motion is shown to be dependent on the pulse duration. This dependence is formulated in terms of a thermal-activation law.
Magnetic properties and thermal stability of Fe-B amorphous films
Authors: Shimada Y. , Kojima H.
Published: February 2003

Magnetic properties of Fe1−xBx sputtered films were investigated in the range 0.09<x<0.49. Due to the large magnetostrictions already reported for rapidly quenched ribbons, the films are very sensitive to the annealing process. Change of internal stress by annealing was measured. The stress is tensile in the as-deposited samples and it continues to increase with successive annealing on fused-quartz substrates but decreases on substrates with a larger thermal expansion coefficient. This decrease of tensile stress and a shape anisotropy of a columnar structure develop a perpendicular anisotropy to the film plane and increase Hc. However, a thermally stable composition was found, where the films maintain magnetic softness up to near the crystallization temperature, irrespective of different thermal propeties of the substrates.
Heat treatment of silicon and the nature of thermally induced donors
Authors: Rijks H. J. , Bloem J. , Giling L. J.
Published: February 2003

Silicon, heat treated to temperatures above 1000 °C followed by a rapid quench, shows a donor activity due to the so called thermally induced donors (TID’s). In this paper it is shown that for samples treated in this way the TID effect and the behavior of the resistivity as a function of time after quenching is exactly the same as for similar samples which have been deliberately doped with iron. Hall measurements reveal the same donor levels at Ev+0.40 eV in both cases indicating that unintentional Fe contamination may have taken place in the former samples during high-temperature treatment. An extra argument in favor of the opinion that TID’s do not originate from an intrinsic effect but are due to unwanted doping is given by the fact that the entire TID effect can be eliminated by treating the samples in a H2 flow containing a few percent HCl and 100 ppm O2. This mixture, which has no etching capacity, has a strong gettering effect for Fe because of the high volatility of the iron chlorides in the gas phase. Samples heated in this gas mixture and quenched rapidly remain completely free of TID’s and show no other donor activity within the accuracy of the measurements.
Influence of impurities and crystalline defects on electron mobility in heavily doped silicon
Authors: Finetti M. , Galloni R. , Mazzone A. M.
Published: February 2003

Mobility measurements have been carried out at room temperature on phosphorus-doped silicon samples. The desired concentration of dopant, varying in the range 1019–1020 atoms/cm3, was obtained in three different ways: homogeneously during growth of the crystal, by ion implantation, and by thermal diffusion. Significant differences have been observed. A theoretical analysis, based on scattering due to dopant impurities, dislocations, and point defects, has been found to be in reasonable agreement with the results obtained from mobility measurements and from transmission electron microscopy and x-ray analysis performed on the samples.
The effect of SiO2 precipitation in Si on generation currents in MOS capacitors
Authors: Patrick W. J. , Hu S. M. , Westdorp W. A.
Published: February 2003

Silicon substrates of various oxygen contents were heat treated to cause SiO2 precipitation. Generation currents in pulse-depleted MOS capacitors made on these substrates were measured. In substrates from the seed section of the crystal, SiO2 precipitation began during growth of the MOS oxide, and the generation currents were very low for all the anneal cycles used. In substrates from the tail section of the crystal, where the SiO2 precipitated more slowly, the generation currents decreased with anneal time and finally leveled off at a very low value. MOS capacitors were also formed on substrates in which the precipitates extended to the surface. Such MOS capacitors all showed extremely high generation currents. The conclusion that ’’internal gettering’’ by SiO2 precipitates in the bulk reduces generation currents was cross-checked with intentional copper decoration.
Influence of preparation conditions on forward-bias currents of amorphous silicon Schottky diodes
Authors: Deneuville A. , Brodsky M. H.
Published: February 2003

We report on the open-circuit voltage Voc and the forward-current–voltage characteristic, J=Js(expqV/nKT−1), of Schottky diodes obtained by evaporation of platinum onto hydrogenated amorphous silicon (a-Si :H) fabricated by glow-discharge decomposition of silane. The diode characteristics were studied as a function of several preparation parameters, namely, silane pressure, substrate temperature, silane flow rate, annealing temperature. Rectifying behavior was obtained only for substrate temperatures between 200 and 300°C. Within this constraint, the preparation parameters have only a small effect on Voc but have large influences on n and Js. The factor n decreases towards ideality (n=1) as the silane pressure decreases, as the substrate temperature increases and with annealing of the Pt contact. The corresponding decrease of the concentration of polyhydride H sites with similar variations in the preparation parameters suggests that the recombination center responsible for nonideal value of n are associated with the polyhydride sites. We argue that the nearly constant value of Voc and therefore of the potential barrier probably originates from the crossing of the Fermi level with deep levels near the interface rather than from a previously proposed interface state. Although we were unable to use a sufficiently low temperature to choose between the thermionic emission and diffusion theories for the forward-current-voltage relationship, we point out that carrier injection in the metal base transistor structure favors a thermionic emission model. Assuming thermionic emission the value deduced for the Richardson constant is of the same order of magnitude as found for crystal Si Schottky barriers.
Non-steady-state studies on MOS devices subject to a linear voltage ramp
Authors: Nassibian A. G. , Faraone L. , Simmons J. G.
Published: February 2003

Experimental studies of MOS capacitors subject to linear voltage ramps so as to drive the devices into the non-steady-state are presented. The resulting current-voltage characteristics, which are extremely rich in structure, are shown to be strongly dependent on temperature and voltage sweep rate. Furthermore, the characteristics, which are related to electron-hole pair generation in the depletion region of the silicon, correlate extremely well with the appropriate theoretical curves over a wide range of temperatures and sweep rates. Consequently, the technique is shown to be a sensitive means of determining information on the trap parameters of generation centers present in the silicon bulk.
Surface-state studies of nonparabolic band semiconductors using MIS structures
Authors: Leonard W. F. , Michael M.
Published: February 2003

Capacitance (C-V) and capacitance derivative (C′-V) measurements have been taken on MIS Hg0.8Cd0.2Te-ZnS devices. The surface-state distributions are determined from a digital simulation program describing the characteristics of an MIS structure with a semiconductor having a nonparabolic conduction band and a parabolic valence band. A combination of a nonuniform acceptor surface-state distribution centered at the conduction band edge and a nonuniform donor surface-state distribution centered at the valence band edge is necessary to fit the experimental C-V and C′-V data. From flat-band voltage versus insulator thickness plots, the work function for Hg0.8Cd0.02Te is 4.23±0.67 eV. The immobile trapped charge density in the samples studied has an average value of 1.66×1012 cm−2.
Physical processes in ’’implanted-disk’’ magnetic bubble devices
Authors: Callen Herbert
Published: February 2003

Calculations of domain wall energies, effective threefold anisotropy, and graphical solutions of the equilibrium magnetization directions are carried out for a (111) implantation layer in the implanted-disk bubble configuration. Comparison is made with the observations of Lin, Dove, Schwarzl, and Shir.
The oscillation of domain-wall motion detected by a dynamic bubble-collapse experiment
Authors: Honda Shigeo , Fukushima Yasukiyo , Fukuda Nobuo , Kusuda Tetsuzo
Published: February 2003

The wall velocity of a nonimplanted garnet film is measured carefully by the collapse method for the drive field higher than the Walker critical field. The wall displacements (ΔR) were plotted as a function of the pulse width (τ) or the pulse field strength (Hp). The data (ΔR versus τ) show that the discontinuous phenomena continue from the fast-velocity region I to the saturation-velocity region III via the oscillatory region II. For region II, the periodic time (T) of the oscillatory motion indicates the relation T= (2π/γ)(1/Hp) (γ=1.3×107 rad/sec Oe) versus the drive field Hp. The others (ΔR versus Hp) demonstrate clearly also the oscillatory mode and the relation H̃= (2π/γ)(1/τ) between the oscillation period for field strength (H̃) and the pulse width (τ) for region II. We say the ’’2π-mode’’ oscillation for the mode of region II. This 2π-mode oscillation can be explained neither by Walker model for the untwisted wall nor by the horizontal Bloch line model for the twisted wall. Here, we propose a hypothesis: the coherent precession of spins in the wall occurs with maintaining the twisted structure of the static state by applying the drive field pulse sufficiently higher than the critical field (regions I and II), and then the mode changes to the incoherent precession mode (region III).
On the magnetic behavior of iron in ternary gadolinium-yttrium compounds
Authors: Burzo E. , Ursu I.
Published: February 2003

We present the results of the magnetic measurements on (GdxY1−x)Fe2 compounds between 4.2 and 1300 K. For x≳0 typical magnetization curves characteristic of ferrimagnetic ordering are evidenced. The reciprocal susceptibility follows a Néel-type relation. The composition dependence of the magnetic interactions in the system is analyzed. The iron moment scales linearly with the exchange field acting on Fe atoms. The correlation between the Fe57 hyperfine field and the electronic moment MFe at the iron site in a number of rare-earth (yttrium) compounds is presented. A simple linear relation is found. Based on the above data a comparison between the thermal variation of iron magntization, calculated using the Néel model, and that deduced from the hyperfine field is made. The data evidence that the molecular field model describes rather well the magnetic behavior of these systems. The results of ferromagnetic-resonance measurements in X and K bands are presented. The data are analyzed using the Vangsness relation. Finally, the magnetic behavior of iron atoms in these compounds is discussed.
Thermally stimulated depolarization (TSD) currents in adsorbed phases on silica
Authors: Ehrburger Françoise , Donnet Jean-Baptiste
Published: February 2003

The low-temperature (LT) TSD spectra of water and methyl alcohol adsorbed on Aerosil have been experimentally resolved. The variation of the area under the peaks with relative pressure (partial dielectric isotherms) have been studied and correlated with the adsorption isotherms. The relationship between the peak areas and the adsorbed amount suggest peaks I, II, and III be attributed to the dipolar polarization of the water or methyl alcohol molecules H bonded to the surface OH groups. The lengthening of the relaxation times as compared with that of the bulk liquid is explained in terms of entropy change on adsorption. In contrast, peaks IV and IV* are probably due to the dielectric polarization into small-size molecular aggregates. The fine structure of the TSD spectrum of adsorbed water on Aerosil is also compared with hertzian spectra of water adsorbed on silica.
The application of a dipolar theory to the piezoelectricity in vinylidene fluoride–co-tetrafluoroethylene polymers
Authors: Stefanou Harry
Published: February 2003

The piezoelectric activity of eight vinylidene fluoride–co-tetrafluoroethylene polymers was studied to further our understanding of this phenomenon. Film compliance, density, degree of crystallinity, and piezoelectric activity were measured in this study. It is shown that the piezoelectric d constant is calculable from a molecular dipole theory where the polarization is derived using a cavity reaction field.
Temperature dependence of the optical properties of silicon
Authors: Weakliem H. A. , Redfield D.
Published: February 2003

The spectral dependence of the absorption coefficient of silicon for photon energies up to 2.7 eV was determined for several temperatures in the range 298–473 K. The effect of a temperature increase appears as a red shift of the absorption spectrum. The magnitude of the shift is larger than that of the fundamental energy gap, increases with increasing photon energy in the range 1.1–1.7 eV, and is constant for energies greater than 1.7 eV. A phenomenological expression deduced by analysis of the data may be used to calculate α (E) at elevated temperature, given α (E) at room temperature. The reflectance was also measured at 299, 413, and 516 K in the photon energy range 2.5–3.8 eV.
Visualization of thick specimens using a reflection acoustic microscope
Authors: Nongaillard B. , Rouvaen J. M. , Bridoux E. , Torguet R. , Bruneel C.
Published: February 2003

A reflection acoustic microscope may be used to image structural details under the apparent surface of a thick sample. To design such an apparatus, the geometrical parameters of the acoustic lenses must be carefully defined. The acoustic field distribution has been computed in the previous structure for this purpose. Some preliminary experimental results are also reported here.
Optical pumping of a dense Na+He+N2 system: Application as an rf spectrum analyzer
Authors: Tam A. C.
Published: February 2003

An rf wave applied to an optically pumped Na vapor in a high-density He+N2 buffer gas, situated in a magnetic field gradient, can produce localized bright fringes due to local rf magnetic resonance. We examine in this paper the features of optical pumping in a dense alkali-helium-nitrogen vapor mixture, and investigate how such systems can be optimized for use as a simple real-time rf spectrum analyzer (for broadcast rf waves) with a wide frequency range (dc to several GHz). We derive the optimum values of the optical pumping rate, helium density, sodium density, and nitrogen density which are necessary in order to produce sharp, high-contrast, and bright fringes, and have accurate and unambiguous rf frequency spectra determinations with fast dynamic response. Samples of observed rf frequency spectra are presented, and the observed spectrum of a sinusoidal FM wave compares satisfactorily with the theoretical spectrum. The observed rf resolution bandwidth is about equal to the optical pumping rate, which is about 1 kHz in this study (rf frequency ∼1 MHz). Similar resolution can be obtained in the microwave range.
Analysis of the CO2 laser transverse mode-medium instability
Authors: Hunter II Allen M.
Published: February 2003

Large-scale temporal oscillations are observed in the output of high-energy flowing cw CO2 lasers, causing appreciable reduction in power output and optical-beam quality. The modulation is linked to wavelike disturbances in the optical cavity which propagate either along the flow axis or transverse to both optical and flow axes. These waves, caused by an unstable interaction between the radiation field and the laser medium, are referred to as the mode-medium instability. The present analysis examines transverse waves that are associated with interactions between optical resonator modes and acoustic resonator modes. The modes interact through fluctuations in gain and refractive gradients due to the heat release during lower-laser-level collisional deactivation. This can lead to unstable acoustic wave growth. Two important propagation numbers, k0 and km, emerge from the analysis. They define a region of unstable wave growth for k between k0 and km. The instability growth rate is maximum near km and is zero at k0. It appears possible to minimize the instability by adjusting the laser parameters so that k0 and km coincide.
Antireflection coatings on metal layers for photolithographic purposes
Authors: van den Berg H. A. M. , van Staden J. B.
Published: February 2003

The image formation in photoprojection and contact printing systems is frustrated by the existence of standing waves in the photosensitive resist layer, and the reflections will cause blurring of the image. This problem is most severe for coherent illuminated systems and for realization of patterns in highly conducting substrates such as metals. A number of materials which can be used as spacers to reduce the reflected wave in the resist are theoretically investigated and experimentally tested. The use of a spacer reduces exposure time and increases the edge sharpness of the resist’s intensity profile.