bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of pressure on the α relaxation in glycerol and xylitol
Authors: Paluch M. , Casalini R. , Hensel-Bielowka S. , Roland C. M.
Published: July 2002

The effect of pressure on the dielectric relaxation of two polyhydroxy alcohols is examined by analysis of existing data on glycerol, together with new measurements on xylitol. The fragility, or Tg-normalized temperature dependence, changes with pressure for low pressures, but becomes invariant above 1 GPa. When compared at temperatures for which the α-relaxation times are equal, there is no effect of pressure (<1 GPa) on the shape of the α dispersion at higher temperatures. However, nearer Tg, pressure broadens the α peak, consistent with the expected correlation of fragility with the breadth of the relaxation function. We also observe that the α-relaxation peaks for both glycerol and xylitol show an excess intensity at higher frequencies. For xylitol, unlike for glycerol, at lower temperatures this wing disjoins to form a separate peak. For both glass formers, elevated pressure causes the excess wing to become more separated from the peak maximum; that is, the properties of the primary and excess intensities are not correlated. This implies that the excess wing in glycerol is also a distinct secondary process, although it cannot be resolved from the primary peak.
Cerium-ion-doped yttrium aluminum garnet nanophosphors prepared through sol-gel pyrolysis for luminescent lighting
Authors: Lu Chung-Hsin , Jagannathan R.
Published: July 2002

Luminescent Y3Al5O12: Ce3+ [yttrium aluminum garnet (YAG):Ce3+] nanoceramics (5–50 nm) have been prepared through a facile sol-gel pyrolysis route. A blueshift of about 720 cm−1 in the reflectance spectra near the absorption edge can be observed for YAG:Ce3+ nanoparticles (having an average particle size around 5 nm) with respect to the submicron powders (∼0.9 μm). Furthermore, the scope of application for this important luminescent system can be extended by isostructural substitution with heavier cations such as Ba2+. This substitution giving rise to an oxygen-vacancy defect complex, that exhibits certain size-sensitive exciton-impurity energy-transfer property in YAG:Ce3+ nanoparticles.
Resonant Raman scattering measurements of strains in ZnS epilayers grown on GaP
Authors: Yu Young-Moon , Hyun M.-H. , Nam S. , Lee D. , O Byungsung , Lee K.-S. , Yu Pyeong Yeol , Choi Yong Dae
Published: July 2002

The relaxation of strain in the ZnS epilayers grown on (100) GaP was investigated with resonant Raman scattering measurement. The single LO phonon resonant Raman shift and the intensity increased but the full width at half maximum decreased with the increasing ZnS epilayer thickness. These were attributed to the relaxation of the biaxial tensile strain with the generating misfit dislocations. Finally, the critical thickness of ZnS/GaP epilayer was found to be around 35 nm.
Characterization of metal-oxide-semiconductor transistors with very thin gate oxide
Authors: Hung K. K. , Cheng Y. C.
Published: July 2002

Metal-oxide-semiconductor field-effect transistors with very thin (100–400 Å) gate oxides are fabricated. With improved procedures for extracting the various physical parameters from the capacitance-voltage curves and carefully controlled experiments, it is confirmed that the fixed oxide charge density increases inversely with the oxide thickness. The surface mobilities at both room temperature and 77 K are also characterized. It is found that the mobility in general decreases as the oxide thickness is reduced. The mobility results are interpreted in terms of the coulomb and surface roughness scattering. A plausible model explaining the correlation of oxide thickness, growth condition, and the above physical parameters is also proposed.
Characterization of optically active sites in CaF2:Ce,Mn from optical spectra
Authors: McKeever S. W. S. , Brown M. D. , Abbundi R. J. , Chan H. , Mathur V. K.
Published: July 2002

In this work we study CaF2:Ce,Mn and use optical absorption, photoluminescence (excitation and emission), and x-ray-induced luminescence to characterize the role played by Ce in various lattice sites during these processes. The data indicate that energy transfer takes place from Ce to Mn, predominantly from Ce3+ in tetragonal sites (i.e., Ce3+-F−int centers with C4v symmetry). There is also some evidence of transfer from higher-order clusters of these defects. In contrast, however, we note that there is no evidence of energy transfer in x-ray-excited luminescence; an increase in the Ce concentration causes a decrease in the Mn2+ emission. It appears from the present investigations that, during x-ray excitation, nonlocally compensated Ce3+ ions of cubic symmetry compete with Mn2+ ions for free electrons released during irradiation. Thus, the data indicate that tetragonal Ce3+ sites are dominant during UV excitation and give rise to energy transfer to Mn2+, whereas cubic Ce3+ sites are dominant during irradiation with high-energy ionizing radiations and no energy transfer takes place.
Properties of Fe single-crystal films grown on (100)GaAs by molecular-beam epitaxy
Authors: Krebs J. J. , Jonker B. T. , Prinz G. A.
Published: July 2002

Single-crystal (100)Fe films 90–330 Å thick have been grown on etch-annealed (100)GaAs substrates by molecular-beam-epitaxy techniques. Ferromagnetic resonance data indicate that the two in-plane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases. The inequivalence is attributed to the nature of the interface bonding at a (100) zinc-blende surface. The decreased magnetization is attributed to the formation of Fe2As microclusters in the film due to As diffusion which is supported by Auger and electron diffraction studies. In general, the Fe films grown to date on etch-annealed (100)GaAs substrates are significantly inferior to those grown on (110)GaAs.
A second-order planar gradiometer composed of concentric superconductive loops
Authors: Kuriki S. , Isobe Y. , Mizutani Y.
Published: July 2002

A planar gradiometer composed of three concentric superconductive loops is analyzed. The gradiometer performs the second derivative with a rotational symmetry in a form of ∂2Bz/∂r2, where r2=x2+y2. In response to the biomagnetic field generated by a current dipole, an isoflux line distribution which resembles well the magnetic field distribution is obtained. The location and the strength of the current-dipole source can readily be estimated from the isoflux pattern. Reduction of the magnetic field noise from distant sources with respect to the signal of a near source is calculated to be comparable with that of conventional axial gradiometers.
Irreversible evolution in the topology of magnetic domains (invited)
Authors: Molho P. , Porteseil J. L. , Souche Y. , Gouzerh J. , Levy J. C. S.
Published: July 2002

Hysteresis does not vanish in materials essentially free from defects and domain wall pinning. It arises from the existence of many geometrically different domain structures separated by intrinsic energy barriers. Although generally metastable, these states can nevertheless be explored by suitable excursion in the manifold of domain structures, along which irreducible irreversibility is present. This idea is illustrated by experiments performed on garnet layers with uniaxial anisotropy (bubble material). Cooling the layer from T>Tc in a field H normal to it results in various states: parallel stripes (H=0), bubbles of increasing diameters and mixtures of bubbles and stripes (H<52 Oe), and mazes of convoluted stripes with defects (forks, dead ends). Cycling the applied field at constant temperature also causes evolution of the structure. For example, starting from parallel stripes the structure evolves toward a maze with intermediate steps corresponding to stripe folding, and then there is the onset of defects (forks, dead ends). We classify these various structures in a kind of phase diagram, depending on the following parameters: current field H, maximum field Hmax previously applied, and memory temperature Tm at which the domain structure is nucleated. The relations and irreversible paths between various structures are precised. We also discuss mechanisms for topological evolution linked with changes in the equlibrium period of the structure. Irreversibility arises from asymmetric processes of domain collapse and nucleation. The first stages in the processes leading from bubbles to stripes, or from parallel stripes to mazes, can be analyzed respectively in terms of elliptical and folding instabilities, the latter being similar to the undulation instability of smectic A liquid crystals.
Analytical relationship for the oxidation of silicon in dry oxygen in the thin-film regime
Authors: Massoud Hisham Z. , Plummer James D.
Published: July 2002

The oxidation of silicon in dry oxgen is characterized by an initial stage where the growth rate is larger than predicted by the Deal–Grove linear-parabolic general oxidation relationship. This growth-rate enhancement has been studied in the 800–1000 °C range by using in situ ellipsometry, and its dependence on the oxidation parameters has been analyzed. In this paper, the rate enhancement in the thin-film regime is analyzed as a function of oxidation time and is found to fit two terms which decay exponentially with time. These results yield an analytical relationship between the oxide thickness and the oxidation time that describes SiO2 growth beyond the native oxide. The nature of the additional oxidation mechanisms and their decay with time is discussed.
Growth and characterization of Si1−xGex and Ge epilayers on (100) Si
Authors: Baribeau J. M. , Jackman T. E. , Houghton D. C. , Maigné P. , Denhoff M. W.
Published: July 2002

Two approaches to the growth of high-quality epitaxial Ge epilayers on (100) Si have been investigated. The first consisted of compositional-grading Si1−xGex layers and the use of strained-layer superlattices as dislocation filters. In general, this method produced unsatisfactory results, due to the difficulty in achieving good epitaxial growth in the Ge concentration interval 30%−70%. The second approach consisted of simply depositing pure Ge directly on (100) Si. Excellent epitaxial films with dislocation densities of less than 107 cm−2 and smooth morphology were obtained after optimization of the growth parameters. The initial growth temperature and post-growth annealing were found to be critical in obtaining good epitaxial material.
An electron paramagnetic resonance study of electron injected oxides in metal-oxide-semiconductor capacitors
Authors: Trombetta L. P. , Gerardi G. J. , DiMaria D. J. , Tierney E.
Published: July 2002

Electron paramagnetic resonance, in conjuction with electrical measurements, has been used to study Si-SiO2 interface defects produced as a result of negative bias, high-field electron injection into the SiO2 layer of metal-oxide-semiconductor capacitors. In particular, a search was made for Pb centers, previously identified as a source of interface traps in unannealed SiO2 on Si, and for E′ centers, which have been associated with trapped holes in SiO2. The results of the EPR experiments show no change in the density of Pb centers following injection, despite the presence of interface traps as indicated by the electrical measurements. Further, no E′ centers are detected in samples for which an analysis of the current-voltage and capacitance-voltage data suggest the presence of 5×1012 cm−2 positively charged centers. We conclude that interface traps generated in the present samples are not of the same microscopic nature as those found in unannealed SiO2 on Si, and that positive charging under the present conditions is not due to trapped holes. It is suggested that the source of positive charge is the so-called ‘‘anomalous positive charge’’ (APC) center. The microscopic nature of the present defects has not been identified.
The interdiffusion of Si, P, and In at polysilicon/GaAs interfaces
Authors: Kavanagh K. L. , Magee C. W. , Sheets J. , Mayer J. W.
Published: July 2002

Gallium arsenide (GaAs) encapsulated at 450 °C with thin films of amorphous silicon has been annealed at temperatures up to 1050 °C and the resulting polysilicon (poly-Si)/GaAs interfaces investigated with secondary ion mass spectroscopy, Rutherford backscattering, and transmission electron microscopy. Little or no interdiffusion is detected at undoped Si/GaAs interfaces whereas Si diffuses from P- or As-doped Si to depths as great as 550 nm in the GaAs after 10 s at 1050 °C. The flux of Si into the GaAs is correlated with the flux of Ga and As into the Si and both increase with increases in the dopant concentration of the Si. The diffusion of other Si dopants into the GaAs, including P and In, is also detected. This enhanced diffusivity of Si, P, and In in GaAs results from the diffusion of point defects into the GaAs created by the diffusion of the Ga and As into the encapsulant. Numerical simulations using position-dependent impurity diffusion coefficients predict that Si, P, and In diffusivities in GaAs at doped poly-Si interfaces are enhanced by factors of 104 above their respective intrinsic bulk equilibrium diffusivities, where known.
The study of mechanical properties of a-C:H films by Brillouin scattering and ultralow load indentation
Authors: Jiang X. , Zou J. W. , Reichelt K. , Grünberg P.
Published: July 2002

In this study diamondlike a-C:H films have been prepared by different methods: In our first experiment a-C:H films were deposited by plasma decomposition of methane at different bias voltages. In the second experiment a-C:H films with high hardness were implanted with 400-keV C+ ions and different doses between 1013 and 1017 ions/cm2 . Subsequently, the following mechanical properties of the films were measured: The shear modulus μ by the frequency of the surface phonon (Rayleigh wave), the stiffness S by an ultralow load indentation of diamond. The Young’s modulus and the Poisson’s ratio were calculated from μ and S. The internal stress σ was determined with the bending beam method. From the Young’s modulus E and the internal stress σ, the average strain ε of the films has been calculated. From the behavior of ε it was concluded that a phase transition from amorphous diamondlike to amorphous graphitelike a-C:H films occurred with increasing substrate bias voltage.
A master-oscillator-driven phase-locked vircator array
Authors: Sze H. , Price D. , Harteneck B. , Cooksey N.
Published: July 2002

Phase locking of a vircator array driven by a relativistic magnetron in a pure master–slave configuration has been achieved. A single high voltage pulse drives the relativistic magnetron and the vircator array in series. Phase locking occurs for ∼40 ns. The time required to lock is ≂10 ns. the peak array power is ≂1 GW. The injection ratio, ρ, and allowable frequency difference, Δf, relationship required for phase locking is examined. The results suggest that the Adler’s inequality, ρ≳(Q/Δf) f, is a necessary, but not sufficient condition to predict phase locking. A hybrid configuration in which the driven vircators are also mutually connected together has also been attempted. Phase locking is observed with better phase stability than in the pure master–slave configuration.
Determining thin film properties by fitting optical transmittance
Authors: Klein J. D. , Yen A. , Cogan S. F.
Published: July 2002

The optical transmission spectra of rf sputtered tungsten oxide films on glass substrates were modeled to determine absorption edge behavior, film thickness, and index of refraction. Removal of substrate reflection and absorption phenomena from the experimental spectra allowed direct examination of thin film optical characteristics. The interference fringe pattern allows determination of the film thickness and the dependence of the real index of refraction on wavelength. Knowledge of the interference fringe behavior in the vicinity of the absorption edge was found essential to unambiguous determination of the optical band gap. In particular, the apparently random deviations commonly observed in the extrapolation of as-acquired data are eliminated by explicitly considering interference fringe phenomena. The multivariable optimization fitting scheme employed allows air-film-substrate reflection losses to be compensated without making reflectance measurements.
Recombination mechanism and carrier lifetimes of semi-insulating GaAs:Cr
Authors: Papastamatiou M. J. , Papaioannou G. J.
Published: July 2002

The recombination process has been investigated in semi-insulating GaAs Cr. The theoretical model was based on the Shockley–Read statistics considering two traps, the HL1 (Cr) and EL2, respectively. The trap concentrations and the carrier lifetimes have been determined from the dependence of both the photomagnetoelectric effect short-circuit current and the photoconductance on the illumination intensity.
Mössbauer study of Fe-substituted Co-Zr and Cu-Zr metallic glasses
Authors: Michaelsen C. , Meyer M. , Freyhardt H. C.
Published: July 2002

The structure of pseudobinary Co-Zr and Cu-Zr metallic glasses, where Co and Cu were substituted by Fe, was studied by means of  57Fe-Mössbauer spectroscopy. The resulting spectra can be divided into two different classes: (1) For Zr concentrations larger than 67 at. %, the structure of the glass, as derived from Mössbauer spectroscopy, is nearly independent from a substitution, leading to only small changes of the average isomer shifts and quadrupole splittings. These small variations of hyperfine parameters can be ascribed to charge transfer effects. (2) For lower Zr contents, pronounced systematic changes of hyperfine parameters occur upon Co or Cu substitution. Beyond changes of the average hyperfine values, the corresponding quadrupole-splitting distributions become dependent on the degree of substitution, i.e., there is a concentration dependent splitting into two peaks. For the amorphous binary Zr-Fe system, these two peaks have been connected to two amorphous phases with concentrations near Zr2Fe and ZrFe2. At least for the Fe-doped Cu-Zr metallic glasses it could be demonstrated that Fe does not substitute the Cu sites but rather creates preferred environments.
Novel Ce magnetism in CeDipnictide and Di-Ce pnictide structures
Authors: Canfield P. C. , Thompson J. D. , Fisk Z.
Published: July 2002

Results of electrical resistance and magnetic susceptibility measurements on Ce2Bi, Ce2Sb, CeScGe, CeScSi and CeSb2 are presented. Ce2Bi and Ce2Sb have antiferromagnetic transitions at low temperatures, while CeSb2, CeScGe and CeScSi have ferromagnetic transitions, CeScGe having a Tc = 46 K. The data are analyzed with respect to the similarities of the two crystal structure groups that these materials fall into: CeSb2 having the LaSb2 structure and the other materials all having the La2Sb structure.
Models for hydrogen permeation in metals
Authors: Andrew P. L. , Haasz A. A.
Published: July 2002

Hydrogen transport in metals is affected by processes occurring in the bulk, the surface/bulk, and gas/surface interfaces. Several models have been proposed to explain the permeation process. Here the development of the various models is discussed and the similarities and differences among them are highlighted. By considering the limiting case of high pressure, it is shown that the dissociative chemisorption model of Wang [Proc. Cambridge Philos. Soc. 32, 657 (1936)] is sufficient to explain the observed experimental results.
Electrical characterization of ITO/p-InP heterostructures
Authors: Thomas H. , Luo J. K.
Published: July 2002

An analysis of current-voltage, capacitance-voltage properties of ITO/p-InP solar cell structures has been carried out. I-V-T properties of ITO/p-InP structures show that the conduction of diodes is dominated by defect-assisted tunnelling at low bias, and by thermionic emission at high bias similar to Schottky diodes. Experimental results gave an increased barrier height from thermionic-emission, an anomalously large intercept from 1/C2 vs VB plots on the bias axis and a near-surface depletion of carriers. Such anomalies could be removed by thermal annealing at temperatures, TA≥200 °C, or by etching a thin InP surface layer. All these results demonstrate the existence of a near surface n-type layer, which is a result of process-induced donor-like defects, and the ITO/InP junction is more likely a buried n/p junction.
The magnetostrictive laser diode magnetometer for personal magnetic field dosimetry (abstract)
Authors: Chung R. , Weber R. , Jiles D. C.
Published: July 2002

This paper reports on the completion of a new type of magnetometer for personal magnetic field dosimetry.1,2 The instrument is a small 15 cm×10 cm×2.5 cm device which can be worn by the user. It utilizes the magnetostrictive response of a Tb–Dy–Fe sensor to measure the prevailing ac magnetic field amplitude. The results are stored using an on-board microprocessor which then integrates the field values to determine the total exposure ∫ Hmax(ω) dt over a given time period. The performance of this new device is reported for a range of ac field frequencies from 10 Hz to 30 kHz. It has been found that the sensitivity of the device is greatly enhanced by using a localized 16 kA/m dc bias field to operate the sensor at the condition of highest dλ/dH. The device can detect fields down the 5 μ T range, and by suitable signal processing, has been designed to give an output signal in both field amplitude and frequency. The device contains a rugged laser diode interferometer of the type used in compact disk audio systems, an AlNiCo permanent magnet to provide the bias field and a Tb0.3Dy0.7Fe1.9 magnetostrictive alloy sensors with strain amplitudes up to 1000 ppm.
Surface damage in a Mn-Zn ferrite induced by laser chemical etching
Authors: Lu Yong-Feng , Takai Mikio
Published: July 2002

Surface damage induced by laser etching of a Mn-Zn ferrite has been investigated by Rutherford backscattering spectrometry and proton-induced x-ray emission measurements. It is found that laser-induced etching of the Mn-Zn ferrite in both CCl4 gas and H3PO4 could cause surface damage that is much less than that induced by mechanical polishing. The laser-induced surface damage is distributed in a thin surface layer with a thickness of 50 nm. It is also found that the surface damage is caused by thermally activated lattice dislocation and impurity doping due to the laser irradiation instead of the chemical reactions between etchant chemicals and the ferrite surface. There are two different sources of damage: one is the interstitial atoms from the ferrite substrates; another is from interstitial impurity atoms resulting from the etching process. The study also indicates that the surface damage could reduce the magnetization of the substrate surface.
Study of SiO2-Si and metal-oxide-semiconductor structures using positrons
Authors: Leung T. C. , Asoka-Kumar P. , Nielsen B. , Lynn K. G.
Published: July 2002

Studies of SiO2-Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO2-Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown.
SiO2 films deposited on Si substrates studied by monoenergetic positron beams
Authors: Uedono A. , Wei L. , Tanigawa S. , Suzuki R. , Ohgaki H. , Mikado T. , Fujino K.
Published: July 2002

Variable-energy positron beams were utilized to study SiO2 films grown on Si substrates. Annihilation characteristics of positrons in the SiO2 films were found to be dominated by the formation probability of positronium (Ps). For the SiO2 film grown by wet oxidation, a high formation probability of Ps was found by measurements of Doppler broadening profiles of the annihilation radiation and those of lifetime spectra. For SiO2 films grown by an atmospheric-pressure chemical vapor deposition technique using tetraethylorthosilicate and ozone, however, the formation probability of Ps drastically decreased. The inhibition of the Ps formation was attributed to interactions between positrons and –OH bonds.
Peculiarities of catastrophic optical damage in single quantum well InGaAsP/InGaP buried-heterostructure lasers
Authors: Yoo Jae S. , Lee Sang H. , Park Gueorgui T. , Ko Yong T. , Kim Taeil
Published: July 2002

For investigation of the catastrophic optical damage (COD) of InGaAsP material systems emitting at 0.8 μm, separate-confinement-heterostructure single-quantum-well structures grown on (100) GaAs substrate by liquid-phase epitaxy were mesa-etched for buried heterostructure (BH) laser diodes. The single mode InGaAsP/InGaP diodes were cw operated at room temperature. The measured COD level of a BH InGaAsP/InGaP laser with a cavity length of 470 μm was 8.6±0.7 (MW/cm2). Particularly, we could not observe COD in the long cavity InGaAsP/InGaP lasers, but they showed thermal saturation which is reversible. Also, InGaAsP lasers were found to sustain high current injection three times more strongly than AlGaAs counterparts.
The magnetic and structural properties of pulsed laser deposited epitaxial MnZn–ferrite films
Authors: Williams C. M. , Chrisey D. B. , Lubitz P. , Grabowski K. S. , Cotell C. M.
Published: July 2002

The magnetic and structural properties of pulsed laser deposited MnZn–ferrite films have been examined. The results show that the uniaxial anisotropy, ferromagnetic resonance linewidth and coercive force are strongly influenced by the microstructure of the films, and the saturation magnetization and first-order magnetocrystalline anisotropy constant depend on intrinsic properties such as composition and cation site occupation. A comparison of bulk and film magnetic properties shows that the magnetic properties of the films are comparable to the bulk, which makes pulsed laser deposition ferrite films a prime candidate for thin film high-frequency microwave device applications.
Magnetic properties of two new compounds: Gd2Ni3Si5 and Sm2Ni3Si5
Authors: Mazumdar Chandan , Nagarajan R. , Gupta L. C. , Vijayaraghavan R. , Godart C. , Padalia B. D.
Published: July 2002

The formation of two new materials, Sm2Ni3Si5 and Gd2Ni3Si5, of the rare-earth series R2M3Si5 (R denotes rare earth and Y) and their magnetic and transport properties are reported here. These materials crystallize in the orthorhombic U2Co3Si5-type structure (space group Ibam). The magnetic susceptibility of Gd2Ni3Si5 follows a Curie–Weiss behavior with an effective magnetic moment 8.1μB/Gd ion. The material orders antiferromagnetically at ≊15 K. The magnetic susceptibility of Sm2Ni3Si5 exhibits a deviation from the Curie–Weiss behavior which is attributed to the low-lying excited state of Sm3+ ions and also to crystal-field effects. This material also orders antiferromagnetically, but at ≊11 K. This value of the ordering temperature does not seem to follow the de Gennes scaling with respect to that of Gd2Ni3Si5.
Reflection and transmission of electromagnetic waves by a dielectric medium moving in an arbitrary direction
Authors: Huang Yao-Xiong
Published: July 2002

The problem of reflection and transmission of an electromagnetic wave by a dielectric medium moving uniformly in an arbitrary direction is analyzed in detail. The expressions for wave four vectors, the modified law of reflection and Snell’s law, the reflected and transmitted wave field vectors, and the reflection and transmission coefficients are presented as the general solution for the problem. These expressions cover all the cases of arbitrary velocities of the moving medium and reduce to the results given previously by other authors for the particular cases of v=vx, v=vy, v=vz, and v=vxx̂+vyŷ.
Miniature electrical filters for single electron devices
Authors: Vion D. , Orfila P. F. , Joyez P. , Esteve D. , Devoret M. H.
Published: July 2002

In experiments on single electron devices, the electromagnetic noise from parts of the apparatus at temperatures higher than that of the device can dramatically increase the tunnel rates out of the Coulomb-blocked state and therefore increase the device error rate. The electrical lines must therefore be filtered adequately. We derive simple expressions for calculating the required attenuation coefficient. We describe a wide-band miniature dissipative filter functioning at cryogenic temperatures. The effective thermalization of an experiment at 30 mK can be obtained by placing four of these filters in series at temperatures ranging from 4 K to 30 mK.
Morphological evolution of the low-temperature oxidation of silicon with a gold overlayer
Authors: Chen C. R. , Chen L. J.
Published: July 2002

Low-temperature oxidation of silicon with a gold overlayer has been studied by in situ reflected high-energy electron diffraction, Auger electron spectroscopy, and transmission electron microscopy. In nonultrahigh vacuum (non-UHV) deposited (001) samples, wet oxidation was found to proceed more rapidly than that of UHV deposited (001) samples. In samples annealed at 220 °C, an oxide layer was found to rapidly develop between a two-layer structure of Au films. Au globules were observed to disperse in the oxide layer after an extended period of oxidation. The difference in the oxidation behavior between UHV and non-UHV samples is attributed to the absence and presence of empty channels between the Au grains. In UHV deposited (111) samples wet oxidized at 220–250 °C for various periods of time, the oxide was found to grow initially on top of the Au layer. Both the thickness of the oxide layer and the unevenness of the Au layer were found to increase with annealing time. The presence of highly textured Au/Si interface in (111) samples led to the retardation of oxidation process. The morphological evolution observed in the present study is used to explain the dependence of maximum oxide thickness on starting Au layer as well as the termination of oxide growth.
Conversion efficiencies from laser-produced plasmas in the extreme ultraviolet regime
Authors: Spitzer R. C. , Orzechowski T. J. , Phillion D. W. , Kauffman R. L. , Cerjan C.
Published: July 2002

The conversion efficiency of spectral emission from laser-irradiated solid targets was investigated for short wavelength source development. The plasma brightness was quantified using absolutely calibrated detectors for 20 materials and spectra were obtained between 50 and 200 Å. Laser parameters such as wavelength, pulse length, intensity, and spot size were systematically varied to establish a comprehensive database for source optimization. Qualitative differences in the underlying dominant emission features as a function of atomic number and laser wavelength were observed that accounted for the relatively high spectral conversion efficiencies produced. In the specific case of Sn, a conversion efficiency greater than 0.8%/eV has been observed in the technologically important region of λ=134.0 Å using a laser intensity of 1–2×1011 W/cm2.
Effects of V/III ratio on ordering in GaInP: Atomic scale mechanisms
Authors: Chun Y. S. , Murata H. , Hsu T. C. , Ho I. H. , Su L. C. , Hosokawa Y. , Stringfellow G. B.
Published: July 2002

Ga0.5In0.5P layers have been grown by organometallic vapor-phase epitaxy using various values of input V/III ratio for two phosphorus precursors, phosphine, the conventional precursor, and tertiarybutylphosphine (TBP), a newly developed, less-hazardous precursor. For growth on nominally (001) GaAs substrates misoriented by 3° (and in some cases by 0° or 6°) to produce [110] steps on the surface at a growth temperature of 620 °C, the Cu–Pt-type ordering is found to be strongly affected by the input flow rate of the phosphorus precursor (V/III ratio). For decreasing input partial pressures below 3 Torr for PH3 and 0.75 Torr for TBP the low-temperature photoluminescence (PL) peak energy increases indicating a lower degree of order. This is confirmed by transmission electron diffraction results. The decrease in the degree of order corresponds to a decrease in the concentration of [1̄10]-oriented P dimers on the surface, as indicated by surface photoabsorption spectroscopy results. These data indicate that the reduction in ordering is caused by the loss of the (2×4) reconstructed surface during growth. The difference in the behavior for PH3 and TBP is interpreted as due to the lower pyrolysis efficiency of PH3. The surface structure measured using high-resolution atomic force microscopy indicates that the [110] steps produced by the intentional misorientation of the substrate are bunched to produce supersteps approximately 30–40 Å in height for the lowest V/III ratios. The step height decreases markedly as the input phosphorus partial pressure increases from 0.4 to 0.75 Torr for TBP and from 1 to 3 Torr for PH3. This corresponds to a change from mainly monolayer to predominantly bilayer steps in the vicinal regions between bunched supersteps. Stabilization of the bilayer steps is interpreted as due to formation of the (2×2) reconstruction on the (111)B step edges. The degree of order is an inverted U-shaped function of the flow rate of the phosphorus precursor. Thus, use of very high input V/III ratios is also found to reduce the degree of order in the Ga0.5In0.5P layers. These high input phosphorus flow rates are found to result in a monotonic increase in the density of [1̄10]-oriented P dimers on the surface. This decrease in order is believed to be related to a change in the structure of kinks on the [110] steps at high V/III ratios.
Effect of precipitate coherency strains on acoustic harmonic generation
Authors: Cantrell John H. , Yost William T.
Published: July 2002

A model is presented of the dependence of acoustic harmonic generation in polycrystalline solids on the coherency strains resulting from the lattice mismatch at the interface between the matrix material and a precipitated second phase in the matrix material. The acoustic nonlinearity parameter (a quantitative measure of acoustic nonlinearity) is shown to depend on the second, third, and fourth order elastic constants of the material, the precipitate-matrix lattice misfit parameter, and the volume fraction of precipitates. The model is applied to the artificial aging of aluminum alloy 2024 from the T4 to the T6 temper. Experimental measurements on samples of Al 2024 taken at various heat treatment times not only confirm the predictions of the model but together with the model provide a basis for assessing the influence of precipitate phase transformations on the aging process.
On the origin of failure waves in glass
Authors: Bourne Neil , Millett Jeremy , Rosenberg Zvi
Published: July 2002

The compressive failure of soda-lime glass under uniaxial shock loading has been the subject of much recent discussion. Evidence of failure occurring behind a traveling boundary that follows a shock front has been accumulated and verified in several laboratories. Such a boundary has been called a failure wave. The variations in material properties across this front include complete loss of tensile strength, reduction in shear strength, lowered acoustic impedance and sound speed, and opacity to light. It in many ways resembles a phase boundary. While these observations are generally held to be true, there is no universally agreed mechanism for the process or processes that gives rise to the failure. It is the object of this work to present the results of plate impact experiments that aim to identify the mechanism by which the failure wave propagates. The experiments indicate that the failure is nucleated by the shock wave at surfaces, and that deliberately introducing flaws by roughening the surface speeds the fracture of the material leading to a failure wave close to the shock front.
Fractional-dimensional space and applications in quantum-confined semiconducting heterostructures
Authors: de Dios-Leyva M. , Bruno-Alfonso A. , Matos-Abiague A. , Oliveira L. E.
Published: July 2002

We present a systematic study of excitonic and impurity states in semiconducting quantum wells within a fractional-dimensional space approach, in which the Schrödinger equation is solved in a noninteger-dimensional space where the interactions are assumed to occur in an isotropic effective environment. In this scheme, the fundamental quantity is the parameter D which defines the fractional dimension associated to the effective medium, and to the degree of anisotropy of the interactions. A direct procedure for determining the fractional dimensionality of the isotropic effective space is proposed in which one may obtain a reliable solution for the energies of the actual physical system under consideration. Explicit calculations of the fractional-dimensional D parameter are made in the case of excitons and impurities in infinite-barrier quantum wells, with exciton and impurity binding energies found in excellent agreement with previous variational results. Calculations are also performed for exciton binding energies in finite-barrier quantum wells with good agreement with recent experimental results.
Optical and electrical properties of undoped ZnO films grown by spray pyrolysis of zinc nitrate solution
Authors: Studenikin S. A. , Golego Nickolay , Cocivera Michael
Published: July 2002

Undoped ZnO films were deposited by spray pyrolysis using aqueous zinc nitrate solution at different substrate temperatures. The effect of the growth temperature on the structural, optical, electrical, and relaxation properties has been studied. It was found that there was a critical temperature Tc=180 °C below which the thermal decomposition to ZnO did not occur or was incomplete. Films grown above Tc showed strong preferred orientation of polycrystals along the c-axis, while the films grown at Tc or below showed a powder-like, non-oriented polycrystalline structure when they were converted afterwards to zinc oxide by annealing. A slight increase of the optical band gap was observed for as-prepared films as the substrate temperature was decreased near the critical temperature. Annealing brought all the samples to the same band gap 3.30 eV measured at a half height of the maximum absorption. After illumination, the steady-state photoconductivity decayed very slowly with a time constant of about a week for as-grown samples. The steady-state photoconductivity in daylight was very close to saturation. Steady-state photoconductivity in the daylight can be as much as four orders in magnitude larger than the dark value. Annealing in nitrogen at 400 °C brought all samples to the same conductivity of 10−3  (Ω cm)−1 in daylight and 10−4  (Ω cm)−1 in the dark. The photoconductivity transients were complicated and changed from a power law to multiexponential time dependence after annealing. The data are discussed on the basis of model in which hole traps located at the grain boundaries play the major role.
Modification of the mechanical and optical properties of a polycarbonate by 50 keV Ar+ and H+ ion implantation
Authors: Yap E. , McCulloch D. G. , McKenzie D. R. , Swain M. V. , Wielunski L. S. , Clissold R. A.
Published: July 2002

The effects of 50 keV H+ and Ar+ ions on the mechanical properties and ultraviolet-visible absorption of the polymer CR39 were investigated. It was found that the H+ implantation produced a yellow–brown material with optical properties similar to amorphous hydrogenated carbon, whereas Ar+ implantation produced a material with optical properties more like evaporated amorphous carbon. The mechanical properties of the implanted material were measured using a nanoindentation technique and increases in both the elastic modulus and hardness (maximum sustainable contact pressure) were observed following irradiation with both ion species. Compared to Ar+ implantation, H+ implantation of CR39 was found to produce a more transparent material at an equivalent maximum sustainable contact pressure and therefore H+ ions were found to be more desirable than Ar+ ions for the treatment of CR39 optical components.
Improved SrTiO3 multilayers for microwave application: Growth and properties
Authors: Petrov Peter Kr. , Carlsson Erik F. , Larsson Peter , Friesel Milan , Ivanov Zdravko G.
Published: July 2002

Au/SrTiO 3 (STO), Au/YBa2Cu3O7−x (YBCO)/STO, Au/STO/CeO2/STO, and Au/STO/MgO/STO multilayer structures on LaAlO3 substrates have been fabricated. Their properties are investigated at 1 MHz and at microwave frequencies (40 MHz–40 GHz) as a function of applied voltage, and in the temperature range between 20 and 300 K. The STO thin films showed comparatively high values of dielectric constant (up to 1800 at 50 K) with low measured film losses, tan δ<0.005, (limit of the measurement setup), at 20 GHz and 20 K, indicating their applicability for microwave devices. The dielectric constant is shown to be independent of frequency to at least 40 GHz, while the losses exhibit no or weak frequency dependence. Relaxation of the STO film in oxygen atmosphere before deposition of YBCO is shown to reduce interactions between the YBCO and STO films. After an “ex situ” high-temperature (900 °C) treatment in flowing oxygen a reduction of the STO dielectric constant as well as tan δ has been observed. Using cerium dioxide as a sublayer in a multilayer STO structure gives rise to an additional (110) STO peak. Substituting the CeO2 layer with a MgO layer drastically reduces this peak, but the lattice distortion increases, with increased dielectric constant and higher controllability as a result. Multilayers with eight intermediate oxygen relaxations during the STO film deposition showed the lowest losses and highest dielectric constant with 25% tunability of the effective dielectric constant at 20 K and with an applied electric field of 19 kV/cm.
Analysis of current distribution in magnetic film inductors
Authors: Gromov A. , Korenivski V. , Haviland D. , van Dover R. B.
Published: July 2002

We have extended our electromagnetic model for high-frequency magnetic film inductors [A. Gromov, V. Korenivski, K. V. Rao, R. B. van Dover, and P. M. Mankiewich, IEEE Trans. Magn. 34, 1246 (1998)] to account for driving current redistribution in structures where the conductor and the magnetic film are in direct electrical contact. We consider a stripe conductor of a rectangular cross section enclosed in a magnetic film. A potential difference of fixed amplitude is applied to both the conductor and the magnetic film. Maxwell’s equations for this geometry are solved analytically, and a simple expression for the impedance is obtained. The inductance at low frequencies is practically unchanged compared to the case where the magnetic film is insulated from the conductor. However, the maximum achievable quality factor is found to be higher than that for the insulated case, even when a significant portion of the driving current flows through the magnetic film. Magnetic film inductors without insulation layers are simple in fabrication and promise large technological advantages.
Colossal magnetoresistance in cluster glass-like insulator La0.67Sr0.33(Mn0.8Ni0.2)O3
Authors: Wang Zhi-Hong , Shen Bao-Gen , Tang Ning , Cai Jian-Wang , Ji Tian-Hao , Zhao Jian-Gao , Zhan Wan-Shan , Che Guang-Chan , Dai Shou-Yu , Ng Dickon H. L.
Published: July 2002

Substitution of Ni for Mn in La0.67Sr0.33MnO3 (LSMO) lowers the Curie temperature TC from 365 K for LSMO to 194 K for La0.67Sr0.33(Mn0.8Ni0.2)O3, which exhibits a cluster glass-like state. The oxide is insulating under both zero field and 60 kOe, but application of the magnetic field induces colossal magnetoresistance (CMR) especially at low temperature. Far below TC, the compound’s field dependence of resistivity has a very similar shape with that of metallic perovskite manganite at relatively high temperature when the spin fluctuation grows stronger. The results indicate that the ferromagnetic superexchange between Ni and Mn, is helpful for the overall ferromagnetic exchange components just overcoming the generic antiferromagnetic exchange components, which leads to the presence of the cluster glass-like state. The reduction of the magnetic disorder and the suppression of the spin fluctuation in Mn–O layer by the external magnetic field are suggested to explain the CMR effect in this insulating compound
Enhancement of coercivity in nanometer-size CoPt crystallites
Authors: Liou S. H. , Huang S. , Klimek E. , Kirby R. D. , Yao Y. D.
Published: July 2002

In this study, we showed that a magnetic coercivity (Hc) as high as 37 kOe was obtained in a CoPt thin film that contains separated nanometer-size CoPt crystallites. We prepared CoPt thin films with thicknesses of 5 and 175 nm by magnetron sputtering. After annealing in an Ar/H2 atmosphere at temperatures from 650 to 750 °C for 3–12 h, we measured the magnetic properties and found that magnetic Hc relates to annealing temperature, annealing time and film thickness. From atomic force microscopy and magnetic force microscopy studies, the magnetic single domain size of CoPt is in the range of 100–200 nm. The high Hc is likely due to the well-separated nanometer-size crystallites and the well-ordered fct phase of CoPt alloy.
Ion-implantation in bulk semi-insulating 4H–SiC
Authors: Rao Mulpuri V. , Tucker Jesse B. , Ridgway M. C. , Holland O. W. , Papanicolaou N. , Mittereder J.
Published: July 2002

Multiple energy N (at 500 °C) and Al (at 800 °C) ion implantations were performed into bulk semi-insulating 4H–SiC at various doses to obtain uniform implant concentrations in the range 1×1018–1×1020 cm−3 to a depth of 1.0 μm. Implant anneals were performed at 1400, 1500, and 1600 °C for 15 min. For both N and Al implants, the carrier concentration measured at room temperature for implant concentrations ⩽1019 cm−3 is limited by carrier ionization energies, whereas for the 1020 cm−3 implant, the carrier concentration is also limited by factors such as the solubility limit of the implanted nitrogen and residual implant damage. Lattice quality of the as-implanted and annealed material was evaluated by Rutherford backscattering spectroscopy measurements. Residual lattice damage was observed in the implanted material even after high temperature annealing. Atomic force microscopy revealed increasing deterioration in surface morphology (due to the evaporation of Si containing species) with increasing annealing temperature. The surface damage is in the form of long furrows running in one direction across the wafer to a depth of ∼25 nm from the surface for samples annealed at 1600 °C for 15 min. We measured room temperature sheet resistivities of ∼70 and 1.2×104 Ω/sq., respectively, for 2×1019 cm−3 N (1500 °C annealing) and 1×1020 cm−3 Al (1600 °C annealing) implanted samples.