bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic evidence for reduction of unoccupied states in the band gap of GaP(001) by H2S passivation
Authors: Fukuda Y. , Shimomura M. , Sanada N. , Nagoshi M.
Published: July 2002

Clean and H2S-adsorbed GaP(001) surfaces have been studied by inverse and ultraviolet photoemission spectroscopy (IPES) and (UPS) and by high-resolution electron energy loss spectroscopy. H2S is found to be dissociated on the surface, leaving only sulfur on it, which is consistent with UPS results. IPES spectra show strong reduction in intensity at 1.5 and 4.5 eV above the Fermi level upon sulfur adsorption. The reduction in the former indicates tremendous decrease of unoccupied states, which correspond to dangling bonds of surface gallium atoms, in the band gap by H2S passivation.
Investigation of strain-symmetrized and pseudomorphic SimGen superlattices by x-ray reciprocal space mapping
Authors: Koppensteiner E. , Bauer G. , Kibbel H. , Kasper E.
Published: July 2002

Double-crystal and triple-axis x-ray diffractometry was used to characterize in detail the strain and composition of short period Si6Ge4, Si8Ge8, Si9Ge6, and Si17Ge2 strained-layer superlattices (SLSs), grown by molecular-beam epitaxy. Nominally strain-symmetrized superlattices, intended to be free standing from underlying buffer layers and the substrate, grown on rather thin (20 nm thick) SiGe alloy buffers with constant Ge content (Si6Ge4 and Si8Ge8) are compared to those grown on 1.3-μm-thick step-graded SiGe alloy buffers (Si6Ge4 and Si9Ge6). Due to the much higher instrumental resolution offered by triple-axis diffractometry (Δ2Θ=12 arcsec) buffer and SLS peaks are clearly separated from each other, which overlap in corresponding double-crystal-diffractometry measurements (Δ2Θ in the range of 180 arcsec to 2°). The lattice constants parallel and perpendicular to the [001] growth direction are determined independently from each other and thus precise strain data of the buffers and the SLS constituting layers were extracted from two-dimensional reciprocal space maps around (004) and (224) reciprocal lattice points (RELPs). The only fitting parameter in a dynamical simulation of conventional rocking curves is then the relative thickness ratio of the Si and Ge layers in the superlattice. The strain relaxation process and the principle of tailoring the strain status in the electronically active layers are shown to be different in structures with single-step and step-graded buffers. For these superlattice samples the RELPs originating from the zeroth-order SLS reflection show significant mosaic broadening (full width at half-maximum of 1100–1300 arcsec perpendicular to the ω/2Θ scan direction in reciprocal space). In contrast, the corresponding RELPs from a pseudomorphic SLS with a much higher average Si content (Si17Ge2), but consisting just of 10 periods, which was grown directly on a Si buffer layer deposited on (001)-oriented Si substrate, are not broadened (full width at half-maximum of 14 arcsec). Besides the determination of strain and composition, examples for the interpretation of diffuse x-ray scattering are given, conveniently measured by reciprocal space mapping.
Photothermal deflection and photoluminescence studies of CdS and CdSe quantum dots
Authors: Yuang Yu-Shen , Chen Yang-Fang , Lee Yang-Yao , Liu Li-Chi
Published: July 2002

We report on the observation of the quantum confinement effect by using photothermal deflection spectroscopy (PDS) experiment and the time dependence of optically induced degradation in CdS and CdSe semiconductor-doped glasses. The observed absorption peaks in the PDS experiment, together with a simple model, were used to evaluate the average radius of semiconductor microcrystals. It is found that the estimated average radii of quantum dots are consistent with that obtained from other methods. This result demonstrates that the PDS technique provides an alternative tool for the study of the optical properties of semiconductor microscrystals. The time dependence of the luminescence degradation of the impurity band, which is attributed to the process of Auger ionization, follows a stretched-exponential function. The inconsistency with the previously proposed exponential relaxation may be due to the size distribution of CdS and CdSe microcrystals.
Stress annealing in Fe73.5Cu1Ta3Si13.5B9 amorphous alloy: Induced magnetic anisotropy and variation of the magnetostriction constant
Authors: González J. , Murillo N. , Blanco J. M. , González J. M. , Kulik T.
Published: July 2002

The effect of Joule heating anneals, carried out with the simultaneous application of a mechanical stress (stress-current annealing), on the anisotropy and magnetostriction of Fe73.5Cu1Ta3Si13.5B9 amorphous samples is investigated. As a result of these thermal treatments an uniaxial in-plane magnetic anisotropy, characterized by the constant Kσ, was induced in the samples. The dependence of Kσ on the annealing temperature shows a maximum around 450 °C which can be connected to the first stages of the crystallization process. From the measurement of the stress dependence of the magnetization work Wm, the magnetostriction constant λs of the as-quenched and thermally treated samples was also evaluated. The results obtained show how the presence of two phases in the partially crystallized material determines the magnetoelastic behavior of these samples.
Extension of the tuning range of a femtosecond Ti:sapphire laser amplifier through cascaded second-order nonlinear frequency conversion processes
Authors: Petrov V. , Seifert F. , Kittelmann O. , Ringling J. , Noack F.
Published: July 2002

The article presents single step and cascade methods for converting the femtosecond radiation from a 1 kHz repetition rate Ti:sapphire regenerative amplifier to the near-infrared (1.2–1.5 μm and 1.6–2.2 μm), visible (554–593 nm), and for the first time to our knowledge to the vacuum ultraviolet spectral region well below 190 nm. Using only solid state materials (nonlinear optical crystals) femtosecond pulses are generated through phase-matched mixing processes down to 172.7 nm. The developed scheme for femtosecond parametric conversion provides nearly bandwidth limited femtosecond pulses, whose duration is comparable or even shorter than that of the pump pulses. The temporal gain narrowing in the optical parametric amplifier is identified as a pulse compression mechanism on the femtosecond time scale leading to generation of infrared light pulses as short as ≊50 fs. As a whole our all-solid state laser complex provides independently tunable and synchronized sub-200 fs light pulses simultaneously at several wavelengths and practically without relative jitter.
Origin of giant magnetoresistance effect in granular thin films
Authors: Maeda Atsushi , Kume Minoru , Oikawa Satoru , Kuroki Kazuhiko
Published: July 2002

Though the demagnetization process of granular Co-Ag films became steep by adding permalloy layer, slow saturation in the magnetoresistance (MR) curves was maintained. In addition, the MR characteristics of granular Fe-Ag films prepared under a magnetic field, in which strong magnetic anisotropy was induced, were isotropic. The disagreement between the MR and magnetic characteristics implies that ferromagnetic granules are not responsible for the giant MR (GMR) effect. The MR ratio of the granular Fe-Ag films considerably increased at thicknesses less than 20 nm. In such ultrathin films, the features of the MR curves corresponded well with those of the magnetization curves with slow saturation and no hysteresis. These results suggest that the GMR effect in the granular systems is attributable to superparamagnetism.
Bragg reflection in periodically segmented KTiOPO4 waveguides
Authors: Oron M. , Katz M. , Zussman A. , Eger D. , Shahna A.
Published: July 2002

Distributed Bragg reflection spectra in segmented waveguides of KTiOPO4 are studied both theoretically and experimentally. Regular period and super period structures are analyzed. The reflectivity is found to be strongly dependent on the unit cell structure. High reflectivity values, in excess of 90%, are obtained in relatively short 3.8 mm waveguides.
Magnetism of α ″-Fe16N2 (invited)
Authors: Metzger Robert M. , Bao Xiaohua , Carbucicchio Massimo
Published: July 2002

The metastable α″-Fe16N2 phase may have a magnetic moment up to 50% higher than that of pure bulk α-Fe. This article addresses the following issues. (i) Can epitaxial films of α″-Fe16N2 be prepared phase pure? Yes, but there are some doubts. (ii) Can powders of α″-Fe16N2 be prepared phase pure? Not yet. (iii) Is the Mössbauer spectrum due to α″-Fe16N2, to martensite, or to something else? Most assign it to α″-Fe16N2. (iv) What is the specific saturation magnetic moment of α″-Fe16N2? Some claim it is close to that of α-Fe, most claim that it is much larger. (v) Is the high moment due to α″-Fe16N2, or to some other phase?
Light-induced metastable states in amorphous organic polysilanes
Authors: Naito Hiroyoshi , Zhang Shenchu , Okuda Masahiro , Dohmaru Takaaki
Published: July 2002

Ultraviolet (UV) light-induced metastable states of transient hole transport in amorphous polymethylphenylsilane (PMPS) have been investigated with a time-of-flight technique. No change in the hole drift mobility is detected after UV light soaking, while the hole lifetime is reduced by UV light irradiation because of the increase in silicon (Si) dangling bond density. The photoscission of Si backbone chain is enhanced by the application of electric field to PMPS during UV light exposure. The origin of this enhancement is discussed. The annealing behavior of the light-induced metastable state has also been investigated at various temperatures. The light soaking and annealing behavior of PMPS is found to be similar to that of hydrogenated amorphous Si.
Enhancement of the Stark effect in AlInAs/GaInAs coupled quantum wells and their application to tunable midinfrared photodetectors
Authors: Huang Yimin , Lien Chenhsin
Published: July 2002

A tunable midinfrared photodetector using 1→4 intersubband Stark shift in the four-level AlInAs/GaInAs coupled quantum wells (CQWs) is proposed. The operation of this device is based on the infrared absorption by the electrons in the ground state transited from the ground-state subband E1 of the CQWs to the third-excited-state subband E4. A large variation of eigenenergy spacing ΔE41 between E1 and E4 under an applied electric field can be achieved for the proposed AlInAs/GaInAs CQW system. Since the infrared radiation is absorbed via the intersubband resonance absorption (ℏω=E4−E1), the detected infrared wavelength can be tuned by the spacing ΔE41 which can be adjusted by an applied electric field. The tunability of these AlInAs/GaInAs CQWs have been studied theoretically. Based on theoretical calculations, tuning ranges from 3 to 3.9 and 2.9 to 4.2 μm are predicted for the proposed asymmetric CQW structure and compositionally asymmetric CQW structure, respectively. This tuning capability is achieved by varying the applied electric field in the 90 to −90 kV/cm range.
Residual stresses in amorphous alumina films synthesized by ion beam assisted deposition
Authors: Parfitt L. , Goldiner M. , Jones J. W. , Was G. S.
Published: July 2002

A set of experiments was conducted to determine the origin of residual stresses in amorphous Al2O3 films formed by ion beam assisted deposition. Samples were deposited during bombardment by Ne, Ar, or Kr over a narrow range of energies, E, and a wide range of ion-to-atom arrival rate ratios, R. Films were characterized in terms of composition, thickness, density, crystallinity, microstructure, and residual stress. Film composition was independent of ion beam parameters and residual stress was independent of thickness over the range 200–1200 nm. Stress varied strongly with ion beam parameters and gas content. Residual stress and gas content saturated at a normalized energy of ∼20 eV/atom or an R of ∼0.05. Where residual stress varied linearly with RE1/2, results are consistent with an atom peening model, but saturation at high R or RE1/2 is inconsistent with such a model. Stress due to gas pressure in existing voids explains neither the functional dependence on gas content nor the magnitude of the observed stress. A probable explanation for the behavior of stress is gas incorporation into the matrix, where the amount of incorporated gas is controlled by trapping.
Optical and magnetic resonance study of impurity ions in undoped and cerium-doped Sr0.61Ba0.39Nb2O6
Authors: Giles N. C. , Wolford J. L. , Edwards G. J. , Uhrin R.
Published: July 2002

Single crystals of strontium barium niobate (Sr0.61Ba0.39Nb2O6), normally referred to as SBN:61, have been investigated using optical absorption, micro-Raman, photoluminescence, and electron paramagnetic resonance (EPR) techniques. Both undoped and cerium-doped (nominally 0.01 to 0.10% Ce) samples were included in the study. A broad optical absorption band centered near 490 nm and extending to the band edge near 380 nm is observed at room temperature in the Ce-doped crystals. Additional absorption, which we assign to iron, occurs just below the band edge in some of the samples. Photoluminescence data were taken at room temperature. Sharp emission bands at 545 and 650 nm are assigned to Er3+, an emission band at 755 nm is assigned to Ho3+, and a broader emission band extending from 700 to 850 nm is assigned to Cr3+. The SBN:61 crystals strongly absorb 9.4 GHz microwaves. To minimize the effect of these microwave losses, the EPR data were taken near 7 K. A broad isotropic EPR line due to Ce3+ ions is observed at g=0.9 in the Ce-doped samples. Additional isotropic EPR lines due to Fe3+ ions are observed at g=9.35 and g=4.10.
Formation and kinetics of ion-induced yttrium silicide layers
Authors: Alford T. L.
Published: July 2002

Yttrium layers on amorphous or crystalline silicon substrates were irradiated with 600 keV Ar++, Kr++, and Xe++ ions between liquid-nitrogen temperatures and 265 °C. Ion-induced YSi1.7 formed in those samples irradiated above 205 °C and fluence ≥1×1015 ions/cm2. The growth rates were monitored as a function of fluence and nuclear energy deposition at the Y/Si interface. For each ions species investigated, the growth rate varied linearly with the square root of fluence. The apparent activation energy was determined to be 0.6±0.1 eV. The experimental growth rates also exhibited a linear dependence on the nuclear energy deposition. This finding agrees qualitatively with the premise of nonoverlapping subcascades.
Improvement of selectivity during diamond growth utilizing a new process
Authors: Chen Chia-Fu , Chen Sheng-Hsiung , Hong Tsao-Ming , Tsai Ming-Hsing
Published: July 2002

A new process, which employs the photoresist or SiO2 as a mask, the CH4-CO2 gas mixtures as the gas source of diamond deposition, and the HF:HNO3:H2O (1:1.1:10) solution as etching solution after the first step deposition, has been developed to improve the selective growth of diamond films. The longer etching time would result in increasing the selectivity during the following step of diamond film growth. The diamond nuclei growth on the undesired region would be removed and a thin SiO2 layer would be formed using the above solution, therefore, increasing the selectivity. Scanning electron microscopy and electron spectroscopy for chemical analysis were used to examine the selective loss and morphological change for the as-grown diamond films.
Effect of cumulative ablation on the ejection of particulates and molecular species from YBa2Cu3O7−x targets
Authors: Kumuduni W. K. A. , Nakata Y. , Sasaki Y. , Okada T. , Maeda M. , Kisu T. , Takeo M. , Enpuku K.
Published: July 2002

Effects of cumulative ablation on the ejection of particulates and molecular species in pulsed-laser deposition are studied by Mie scattering and laser-induced fluorescence spectroscopy, respectively. When a fresh target is ablated, a large amount of particulates are ejected during several initial shots and rapidly decreased within the first ten shots of ablation. This is due to the ejection of powder residues which are struck on the target surface during the polishing process. After this period, ejection of particulates increased gradually and almost saturated after 200 shots. The saturation characteristic is empirically formulated as a function of the number of cumulative ablations. On the other hand, ejection of molecular species rapidly decreases during the initial 500 ablations and afterwards decreases more slowly with further ablation. The effects of cumulative ablation on the particle ejection are discussed in conjunction with the structural modification of the ablated surface observed by the scanning electron microscope.
On degradation of ZnSe-based blue-green diode lasers
Authors: Hovinen M. , Ding J. , Salokatve A. , Nurmikko A. V. , Hua G. C. , Grillo D. C. , He Li , Han J. , Ringle M. , Gunshor R. L.
Published: July 2002

The degradation mechanism of ZnMgSSe/ZnSSe/ZnCdSe separate confinement heterostructure laser diodes is studied under continuous wave and pulsed operation at room temperature. The degradation of the active quantum well is caused by formation of optically inactive areas which nucleate at paired stacking faults. These ‘‘dark defects’’ are identified as areas of dislocation network and point defect segregation.
Cathodoluminescence from fractured surfaces of ZnO varistors
Authors: Tanaka Shigeru , Takahashi Ken , Sekiguchi Takashi , Sumino Koji , Tanaka Junzo
Published: July 2002

The fractured surfaces of Bi-doped and Bi, Co-doped ZnO varistors were investigated by means of cathodoluminescence. Three peaks were observed for the Bi-doped ZnO varistor. The 378 and 389 nm peaks in intragrains were intense compared to those at grain boundaries. On the other hand, the 526 nm peak was strong at grain boundaries and ascribed to deep levels formed at grain boundaries. In the case of further Co doping, the luminescence was extinct.
A magnetic, neutron-diffraction, and Mössbauer spectral study of the Ce2Fe17−xSix solid solutions
Authors: Middleton D. P. , Mishra S. R. , Long Gary J. , Pringle O. A. , Hu Z. , Yelon W. B. , Grandjean F. , Buschow K. H. J.
Published: July 2002

The magnetic properties of a series of Ce2Fe17−xSix solid solutions with x equal to 0.0, 0.23, 0.4, 0.6, 0.8, 1.02, 1.98, and 3.20 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. An x-ray-diffraction study indicates that the compounds adopt the rhombohedral Th2Zn17-type structure. The substitution of silicon for iron in Ce2Fe17 leads to a contraction of the a axis by 0.2%, an expansion of the c axis by 0.2%, and a consequent reduction of the unit-cell volume by about 0.2% per substituted silicon. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 455 K for Ce2Fe14Si2. Powder neutron-diffraction results, obtained at 295 K, indicate both that the silicon atoms preferentially occupy the 18h sites and that the iron moments increase with increasing silicon content, an increase which is related to the increase in Curie temperature. The Mössbauer spectra have been fit with a binomial distribution of the near-neighbor environments in terms of a maximum hyperfine field Hmax for an iron with zero silicon near neighbors, and a decremental field ΔH per silicon near neighbor. The compositional independence of both the weighted average maximum hyperfine field and of the decremental field indicates that the silicon acts as a magnetic hole, a hole which does not perturb the magnetic moments at the iron sites. The compositional dependence of the weighted average isomer shift is explained in terms of an interband mixing of the iron 4s and silicon 2p bands, due to the reduction of the iron 18h bond lengths. This interband mixing affects the charge but not the spin distribution at the iron sites.
Spot-size-dependent bifurcation of laser-ablated plumes
Authors: Witanachchi S. , Mukherjee P.
Published: July 2002

An ion probe investigation of an excimer-laser-ablated plume from a high-Tc superconducting YBa2Cu3O7−x (YBCO) target in an oxygen ambient revealed a significant alteration of the propagating plume as the laser spot size on the target was changed. For larger spot sizes, the time-resolved ion signals showed a bifurcation of the laser plume into two distinct components with increasing spot size. The faster component of the plume showed free expansion behavior, while the slow component corresponded to a highly collisional regime that represented the onset of a shock wave. Similar plume characteristics have been seen for laser-generated plumes expanding in high-pressure ambient gases. The YBa2Cu3O7−x films grown under the conditions that produced a high degree of plume bifurcation yielded high-quality superconducting films. Implications of these findings toward superconducting film growth are discussed.
Highly anisotropic etching of submicrometer features on tungsten
Authors: Bounasri F. , Gat E. , Chaker M. , Moisan M. , Margot J. , Ravet M. F.
Published: July 2002

We have investigated the anisotropic etching of submicrometer features (0.2–1 μm) on tungsten at substrate temperatures varying from −45 to +15 °C in a newly developed magnetoplasma reactor operated with SF6. In contrast to earlier reports, we have achieved such ultrafine pattern etching without external biasing, hence with low-energy ions, thus reducing possible damage to the substrate. We have observed highly anisotropic microscopically uniform etching at pressures lower than a threshold value which depends on the substrate temperature; above this threshold, the anisotropy decreases and the microscopic nonuniformity depends on linewidth and space pattern.
Interaction characteristics of dislocations in strained epitaxial layers
Authors: Shintani K.
Published: July 2002

In connection with nucleation and multiplication processes of misfit dislocations in epitaxial layers, elastic interactions of some configurations of dislocation surface half-loops and angular dislocations are investigated. By using the programme code produced by Gosling and Willis [J. Mech. Phys. Solid 42, 1199 (1994)], which calculates the image stresses of a straight dislocation half-line in a half-space and enables one to construct the stress field of any configuration of dislocation loops, the interaction energy of two surface half-loops is obtained. With the change of the relative positions of the two half-loops, the sign of the interaction energy varies from minus to plus, in accordance with which the interaction force between the two half-loops varies from an attractive force to a repulsive one. The interaction forces exerted on threading segments are also estimated for two angular dislocations, and their effects on the Matthews and Blakeslee equilibrium are discussed.
Dispersion relation, electron and hole effective masses in InxGa1−xAs single quantum wells
Authors: Oettinger K. , Wimbauer Th. , Drechsler M. , Meyer B. K. , Hardtdegen H. , Lüth H.
Published: July 2002

We report on optical and electrical properties of modulation doped InxGa1−xAs/InP single quantum wells in the composition range 0.56≤x≤0.79. Cyclotron resonance, contactless Shubnikov–de Haas and magnetophotoluminescence experiments are used to obtain two dimensional carrier densities, effective masses of electrons and holes and scattering times. We present data which give evidence for zero magnetic field spin splitting. The dispersion relation for electrons and holes is presented.
Two-band analysis of hole mobility and Hall factor for heavily carbon-doped p-type GaAs
Authors: Kim B. W. , Majerfeld A.
Published: July 2002

We solve a pair of Boltzmann transport equations based on an interacting two-isotropic-band model in a general way first to get transport parameters corresponding to the relaxation time. We present a simple method to calculate effective relaxation times, separately for each band, which compensate for the inherent deficiencies in using the relaxation time concept for polar optical–phonon scattering. Formulas for calculating momentum relaxation times in the two-band model are presented for all the major scattering mechanisms of p-type GaAs for simple, practical mobility calculations. In the newly proposed theoretical framework, first-principles calculations for the Hall mobility and Hall factor of p-type GaAs at room temperature are carried out with no adjustable parameters in order to obtain direct comparisons between the theory and recently available experimental results. In the calculations, the light-hole-band nonparabolicity is taken into account on the average by the use of energy-dependent effective mass obtained from the k⋅p method and valence-band anisotropy is taken partly into account by the use the Wiley’s overlap function.. The calculated Hall mobilities show a good agreement with our experimental data for carbon-doped p-GaAs samples in the range of degenerate hole densities. The calculated Hall factors show rH=1.25–1.75 over hole densities of 2×1017–1×1020 cm−3.
Electron and γ irradiation effects in InP assessed by photoluminescence
Authors: Souza P. L. , Ribas P. R. , Bellini J. V. , Mendes W. M.
Published: July 2002

Different InP samples were exposed to electron and γ radiation at 300 and 77 K, respectively. The effects of the exposure to high energy radiation were investigated by photoluminescence. A major reduction in the photoluminescence signal from all samples was observed due to the defects introduced. In the case of γ-irradiated samples, the photoluminescence characteristics were recovered after room temperature aging while for the electron irradiated ones a heat treatment either at 473 or 673 K was required for annealing out the radiation-induced defects. The different roles played by the amphoteric dopant Sn and the n dopant S in the changes in the photoluminescence near band-edge spectra are addressed.
Correlation between magnetovolume and giant magnetoresistance effects in doped La2/3Ca1/3MnO3 perovskites
Authors: De Teresa J. M. , Blasco J. , Ibarra M. R. , García J. , Marquina C. , Algarabel P. , del Moral A.
Published: July 2002

La0.62Tb0.05Ca0.33MnO3 and La0.6Y0.07Ca0.33MnO3 have been studied in order to probe into the mechanisms responsible for the giant magnetoresistance ratios observed in this kind of compound. The experiments have shown a strong connection between the magnetotransport and magnetovolume properties. A large volume effect appears above Tc which collapses with applied magnetic field or when the long range magnetic order sets in. Above Tc the magnetostriction and magnetoresistance isotherms are highly correlated. Charge localization with local distortion appears to be responsible for the transport and volume properties at zero field. Charge mobility and a more normal volume dependence on temperature are restored by applying high enough magnetic fields.
High density recorded patterns observed by high-resolution Bitter scanning electron microscope method
Authors: Kitakami O. , Sakurai T. , Shimada Y.
Published: July 2002

We have developed a new and versatile method for observation of fine domain structures in ferromagnetic specimens. In this method, which we call here the high-resolution Bitter scanning electron microscope (HRBS) method, ferromagnetic fine particles as small as 20 nm are fabricated by sputtering, and are subsequently deposited on the surface of ferromagnetic samples to be investigated. The particles form very faithful domain patterns reflecting the leakage field distribution from the samples. We have applied this method to several magnetic and magneto-optic high density recording media, and have successfully observed the bit patterns at a recording density of 300 kFCI (bit length ∼80 nm). Moreover, we have confirmed that the HRBS method is also effective in investigating the magnetized states within each recording bit.
Site affinity of substituents in Nd2Fe17−xTx (T=Cu,Zr,Nb,Ti,V) alloys
Authors: Yelon W. B. , Hu Z. , James W. J. , Marasinghe G. K.
Published: July 2002

In order to understand the magnetic properties of the substituted rare-earth-iron alloys, it is especially important to know the location of the substitutional atoms within the iron lattice. The site distributions of some nontransition-metal substituents in the substituted Nd2Fe17−xTx alloys have previously been reported. Here we report the site distributions of some transition-metal substituents (Cu,Zr,Nb,Ti,V) in the Nd2Fe17−xTx alloys and compare them with those of the nontransition-metal substituted compounds. Rietveld analysis of neutron powder diffraction data indicates that the nontransition-metal substituents show very similar site affinity at low substituent content. For example Al, Ga, and Si all prefer the 18h sites. The transition-metal substituents show a more complex site affinity. Ti and V atoms strongly prefer the 6c sites, Cu atoms prefer the 9d and 18f sites, Nb atoms prefer the 6c and 18h sites, and Zr atoms prefer 6c and 18f sites. It was also noted that the site affinity can change if carbon is included in the melting procedure of the sample preparation. The superconducting quantum interference device measurements show that all the substituted compounds have a Curie temperature higher than the unsubstituted parent compound. The relationship between the site distribution of substituents and the magnetic properties of the substituted Nd2Fe17−xTx alloys is discussed.
4 Gbit/in.2 inductive write heads using high moment FeAlN poles
Authors: Jayasekara W. P. , Wang S. , Kryder M. H.
Published: July 2002

Thin film inductive write heads incorporating 2-μm-thick single and multilayer FeAlN/SiO2 poles were fabricated. The poles were trimmed to 1 μm trackwidth using focused ion beam etching from the air bearing surface of the sliders. Tests on 2950 Oe media show satisfactory media saturation. Overwrite in excess of −43 dB and hard transition peak shift <2 nm were measured for wide trackwidth heads with 0.2 μm gap lengths. Tracks written using a 1 μm track width head were imaged using magnetic force microscopy, showing well defined transitions at linear densities up to 6600 flux changes per millimeter. A written track width of approximately 1.1 μm and a side erase band of less than 0.1 μm were observed. Assuming a coding scheme with a density ratio of 1.33, these heads promise a recording density of over 4 Gbit/in.2
Simultaneous molecular and spin dynamics: Quasiclassical approximation and quantum effects
Authors: Antropov V. P. , Harmon B. N.
Published: July 2002

We sketch the derivation of a set of equations of motion for the simultaneous treatment of both molecular and spin dynamics. The equations can be extended through the concept of imaginary time density functional theory, to describe the penetration of classically forbidden regions.
Optical and electrical investigations of indium oxide thin films prepared by thermal oxidation of indium thin films
Authors: Das V. Damodara , Kirupavathy Shahil , Damodare Laxmikant , Lakshminarayan N.
Published: July 2002

Indium oxide thin films have been prepared by thermal oxidation of vacuum-deposited indium thin films in air in an open furnace at about 600 K. These indium oxide thin films prepared by thermal oxidation have been examined for optical transparency by measuring their optical absorbance as a function of wavelength. From the optical absorption data, optical band gap and the nature of the forbidden energy gap in the indium oxide thin films have been determined. Electrical conductivity measurements have also been carried out on the above oxide films as a function of temperature during heating and cooling cycles in vacuum. It is found that after the first heating, electrical conductivity increases to a significant extent due to removal of point defect clusters due to annealing which contribute to both carrier generation and scattering. From the thermoelectric power measurements carried out, it has been concluded that electrons are the majority carriers in these indium oxide thin films.
Stationary carbon cathodic arc: Plasma and film characterization
Authors: Chhowalla M. , Davis C. A. , Weiler M. , Kleinsorge B. , Amaratunga G. A. J.
Published: July 2002

The plasma characteristics of a new arc mode on carbon referred to as the ‘‘stationary cathodic arc’’ are reported. Particularly, optical emission spectroscopy, probe and ion energy distribution measurements are used to compare the properties of the stationary arc with the normal ‘‘random cathodic arc’’ on carbon. The measurements revealed that the plasma properties of both arc modes are similar. In addition, we have correlated the plasma characteristics to the film properties. Carbon films deposited using the stationary arc were found to have a surface particle density equivalent to those deposited using the filtered cathodic vacuum arc. The macro-particle free films were found to be highly tetrahedral and compressively stressed. Both the sp3 fraction and stress values were strongly dependent on the ion energy with maximum values of 85% and 9.4 GPa, respectively, occurring at ≊50 eV.
Transmission electron microscopy and cathodoluminescence of tensile-strained GaxIn1−xP/InP heterostructures. I. Spatial variations of the tensile stress relaxation
Authors: Cléton F. , Sieber B. , Lefebvre A. , Bensaada A. , Masut R. A. , Bonard J. M. , Ganière J. D. , Ambri M.
Published: July 2002

We have investigated the optical and structural properties of tensile-strained GaxIn1−xP/InP heterojunctions by cathodoluminescence (CL) in the scanning electron microscope and by transmission electron microscopy (TEM). The lattice mismatch of the samples is ranging from 0.4% (x=5.5%) to 0.84% (x=11.8%). We show, in agreement with previous studies, that the relaxation of tensile-strained epilayers occurs by the emission of partial and perfect dislocations. The numerous twins and stacking faults which are found in the epilayers act as efficient recombination centers for electron-hole pairs and appear as dark line defects (DLDs) in CL images. ‘‘Ladderlike’’ configurations of these defects are found both by TEM and CL in samples with a lattice mismatch larger than 0.5%. We also demonstrate that DLDs are contaminated by impurities. Areas with networks of perfect dislocations are found between the DLDs. The analysis of the dislocation types allows us to suggest that the growth of low-mismatched samples is two dimensional, and that it is three dimensional in highly mismatched samples. Finally, the spatial variations of the strain relaxation throughout the samples are studied by 77-K CL spectroscopic measurements and it is shown that these variations can be correlated with the various types of structural defects.
Transient device modeling using the Lei-Ting hydrodynamic balance equations
Authors: Lee C. C. , Cui H. L. , Cai J. , Lenzing E. , Pastore R. , Rhodes D. , Perlman B. S.
Published: July 2002

A transient semiconductor device simulation model based on the recently developed Lei-Ting hydrodynamic balance equations is presented. Unlike other hydrodynamic models, where the various relaxation rates are imported from Monte Carlo calculations or simply assumed to be constant, our model calculates these relaxation rates within the simulation process, as functions of the electron drift velocity, electron temperature, as well as the electron density. Without any complicated mathematics, a decoupled method with a relatively large time step has been applied to the transient simulation on a one-dimensional ballistic diode.
Thermal wave imaging of electrically heated microstructures
Authors: Voigt P. , Hartmann J. , Reichling M.
Published: July 2002

The thermoreflectance technique is applied for imaging electric current distributions and thermal transfer in a temperature reference resistor heated by an alternating current. High-frequency scans (30 kHz) allow imaging of the current density distribution in conducting strips of the resistor while scans of amplitude and phase of the surface temperature variation at lower frequencies reveal plane, cylindrical, and spherical thermal waves. We investigate wave dimensionality as a function of heating geometry and thermal length, and present a simple method allowing a quantitative thermal analysis by exploiting the phase profile of cylindrical thermal waves.
Bonding structure and characteristics of defects of near-stoichiometric silicon nitride films
Authors: Hasegawa S. , Ikeda M. , Inokuma T. , Kurata Y.
Published: July 2002

Amorphous SiNx:H films having nitrogen content x greater than 1.3 were deposited at 300 °C by varying the ammonia-to-monosilane flow-rate ratio RN, using plasma-enhanced chemical- vapor-deposition. The characteristics of defects in the films subjected to UV illumination and anneal treatments were investigated by electron-spin-resonance (ESR) measurements. The paramagnetic Si dangling bonds (DBs) with three N atom neighbors, called the K0 center, were observed for an as-deposited film with RN of 5, and the density was favorably enhanced by exposing the film to UV light or by the UV illumination subsequent to its annealing. The K0 density decreased as the film was annealed at 550 °C after the UV illumination. The mechanisms of creation and disappearance of the K0 centers by the illumination and the annealing, respectively, were interpreted in terms of the potential fluctuation model. The K0 density in as-deposited films decreased with RN, and a new three-line spectrum was observed as RN exceeds 7. Origins of this new spectrum are discussed. The ESR spectra due to N DBs were observed for only the films subjected to the anneal/illumination sequence, and the densities of both N DBs and K0 centers decreased with increasing the annealing time before the illumination.
Electroluminescence and photovoltaic effects of anodically fabricated metal/porous Si/Si sandwich structures based on n-type ultraviolet-porous Si
Authors: Ünal B. , Bayliss S. C.
Published: July 2002

The electroluminescence and photosensitive surface effects from metal/porous silicon/Si sandwich structures based on n-type ultraviolet-porous silicon were investigated in this study. Contacts were made by bonding to semitransparent coatings of Au (deposited by a novel technique of thermal evaporation) via Al electrodes. In the case of electroluminescence, studied by applying a current across the electrodes, orange light is emitted beneath the semitransparent gold film, and a reversible avalanche breakdown was observed at the interface at a reverse bias of around 22 V. The photosensitivity of the surface, which was coated with a thin gold film having an initial transmission of less than 60%, was observed to get worse when the above process was repeated several times. Furthermore, the avalanche breakdown voltage shifted slightly to higher values, possibly because of both structural fluctuations in the porous networks and/or Schottky conductive changes in between the metal-porous silicon interface resulting from the high current passed at breakdown and causing excess heat inside the device. Photovoltaic effects at the Schottky metal/porous Si barrier were also observed under a number of different types of illumination in the range from UV to visible, and under white light of different powers. The current–voltage characteristics of various sandwich structures operating as solar cells were measured, along with the power efficiency of the solar cells under a calibrated tungsten bulb, this being over 0.35% under an illumination power of 12 mW/cm2. The power efficiency (=−a+bPin) is found to increase linearly with increasing illumination power up to a saturation value that depends simply on preparation conditions.
Precisely tuned emission from porous silicon vertical optical cavity in the visible region
Authors: Araki Minoru , Koyama Hideki , Koshida Nobuyoshi
Published: July 2002

The operating peak energy of a porous silicon (PS) cavity can be completely controlled over a wide range of 1.5–2.2 eV, using a PS-based Fabry–Perot resonator composed of a light-emitting active PS layer and two high-reflectivity mirrors. When the PS devices are excited by a uv laser, quite narrow spectra (10–40 meV in full width at half-maximum) are observed without any significant signs of side mode. The central photon energy is precisely and continuously tuned simply by changing the anodization parameters. The key issues of the controlled device operation are adjustment of the optical thickness of the active PS layer to an appropriate value and fabrication of the quarter-wavelength multilayered PS mirror with a high reflectivity. The spectral qualities of the emitted light are also discussed by theoretical analyses on the basis of a simplified model. These results suggest that the PS devices operate as sharp band-pass optical filter and the PS materials are available for novel silicon-based microphotonics.
Lattice vibrations in In1−x−yGaxAlyAs quaternary alloys
Authors: Ramam A. , Chua S. J.
Published: July 2002

We report here Raman observations due to lattice vibrations in the InGaAlAs quaternary alloy grown on an InP substrate by molecular-beam epitaxy. The variation with doping, alloy composition, and lattice mismatch are presented. The dominant bands observed in the spectra are of the three binaries, namely, the GaAs-, InAs-, and AlAs-like optical phonon vibrations. The relative intensity of the peaks and the Raman shifts are related to the alloy composition in the band-gap engineered quaternary material.
Electronic density of state in metal/polyimide Langmuir–Blodgett film interface and its temperature dependence
Authors: Itoh Eiji , Iwamoto Mitsumasa
Published: July 2002

Surface potentials of heat-treated polyimide (PI) Langmuir–Blodgett (LB) films deposited on Au, Cr, and Al electrodes were measured in a dark vacuum vessel at various temperatures as a function of the number of deposited layers. The potential depended on the thickness of PI LB films and the work function of base metal electrode. The spatial charge distribution in PI LB films on various electrodes was determined from the relationship between the surface potential and the number of deposited layers. Based on this result, distribution of the density of electronic state in PI LB films was determined. It was experimentally shown that the electrostatic phenomena in PI LB films at the metal/film interface were explained taking account of surface states which exist within the range of ∼1 nm from the interface and molecular–ion states which exist in the entire range. Further, it was found that distribution of electronic density in states of polyimides was broadened with the increment of temperature.
Linear in-plane uniaxial stress effects on the device characteristics of AlGaAs/GaAs modulation doped field effect transistors
Authors: Fung A. K. , Cong L. , Albrecht J. D. , Nathan M. I. , Ruden P. P. , Shtrikman H.
Published: July 2002

The current voltage relationships of AlGaAs/GaAs modulation doped field effect transistors (MODFETs) were measured as a function of applied uniaxial stress. Stresses in the [110] and [11̄0] directions on MODFETs that were grown on a (001) substrate produced threshold shifts of opposite sign. Stresses in [110] and [11̄0] directions resulted in threshold voltage pressure coefficients of −15 and 64 mV/Kbar, respectively. The asymmetric shifts in the threshold voltages are attributed to piezoelectric effects. In addition, stress induced changes in the slopes of the transconductance versus gate-to-source voltage relationships were also measured. For stresses in the [110] and [11̄0] directions, the dependencies were 0.4 and −0.7 mS/(VKbar), respectively.
A two-dimensional analysis for space–charge fields in anisotropic photorefractive materials
Authors: Solymar L. , Aguilar Marı́a , Limeres J. , Agulló-López F.
Published: July 2002

A two-dimensional time-dependent analysis is presented to describe photorefractive recording in a film with anisotropic transport parameters. The solution of the rate equations together with suitable boundary conditions on the film faces has been obtained by numerical methods for a parallel recording geometry. The recording curves very markedly depend on the anisotropy ratio ai=μz/μx (z being the axis perpendicular to the film faces), the grating period, and the ratio between film and buffer permittivities. For ai=1, the solution coincides with that previously obtained using an analytical approach. Approximate analytical solutions for ai≠1 have also been worked out and compared to the numerical results.
The Fermi level effect in III–V intermixing: The final nail in the coffin?
Authors: Jafri Z. H. , Gillin W. P.
Published: July 2002

We have shown that doping InGaAs/GaAs quantum well materials with 1019 Si/cm3 causes a time and temperature dependent diffusion process, which can be correlated with group III vacancy formation. This process can be modeled and shown to accurately fit other data in the literature. Samples with silicon doping concentrations below this value have no enhanced interdiffusion, in contradiction to the results of the Fermi level model. These results are shown to be comparable to data for AlGaAs/GaAs interdiffusion with doping concentrations between 5×1017 cm−3 and 1018 cm−3. We have shown that the position of the Fermi level plays no role in III–V intermixing.
Band gap modification in Ne+-ion implanted In1−xGaxAs/InP and InAsyP1−y/InP quantum well structures
Authors: Wan J. Z. , Simmons J. G. , Thompson D. A.
Published: July 2002

Band gap modification in Ne+-ion implanted In1−xGaxAs/InP (x=0.25, 0.33, 0.40, 0.47, 0.54, 0.61, 0.69) and InAsyP1−y/InP (y=0.32) quantum well structures has been studied by low temperature (12 K) photoluminescence spectra. The maximum usable high temperature anneal for inducing the compositional intermixing using an InP proximity cap is found to be ∼700 °C for 13 s. A second low-temperature (300 °C) anneal, following the high-temperature (700 °C) anneal, is found to induce greater band gap changes than the simple one-step anneal at 700 °C. The changes are found to be approximately proportional to the difference of bandgap energy between the well and the barrier materials; the proportionality coefficient increases with ion dose and reaches a maximum at a dose of ∼2×1013 cm−2. At higher doses, the proportionality coefficient decreases. The band gap changes are explained qualitatively based on the InGaAsP binary composition diagram.
Spin wave resonances of cobalt based multilayers
Authors: Wongsam M. A. , Chantrell R. W. , Haycock P. W.
Published: July 2002

A formulation of micromagnetics based on equations of motion in the Hamiltonian form is applied to the simulation of ferromagnetic resonance in Cobalt based magnetic/nonmagnetic multilayers. A two-peak feature in the field swept FMR absorption curve recently observed experimentally is reproduced. A semiclassical micromagnetic spin wave theory is presented and used to calculate the dispersion curves and amplitude spectra of the multilayers at various values of the external field. It is found that uniform precession dominates all in-plane modes, and that the features in the FMR absorption curve coincide with the sudden excitation of the first spin wave mode in the perpendicular direction.
Magnetic behavior of MnBi0.47Al0.15 alloy films
Authors: Shang C. H. , Wang Y. J. , Chen L. Y. , Zhang H. , Liu J. P.
Published: July 2002

MnBiAl films were prepared by vacuum interdiffusion alloying. We report on the magneto-optical properties and low temperature magnetization of this material. By eliminating the Faraday contribution from the glass substrates, a remanant Kerr rotation of 3.22° at 632.8 nm is measured at room temperature. At a wavelength of 376 nm, the remanent Kerr rotation is 2.25°. Superconducting quantum interference device magnetometer examination showed that there is no spin transition at low temperature for the MnBiAl films. By decreasing the temperature from 280 to 5 K, the perpendicular remanant magnetization of the MnBi0.47Al0.15 films remains along the c axis and increases about 12% in magnitude, while MnBi changes its easy axis from the c axis to the base plane at around 84 K. This suggests that both the lattice shrinkage and chemical interactions among Mn, Bi, and Al atoms play important roles in the magnetic properties of MnBi0.47Al0.15 alloy films.