bluuebunny/crossref_metadata_2025 huggingface dataset:
A semiempirical model for liquid-crystal refractive index dispersions
Authors: Wu Shin-Tson
Published: July 2002

A single-band model and a three-band model which consists of one σ→σ* and two major π→π* electronic transitions were developed for understanding the refractive index dispersions of uniaxial liquid crystals. This information is particularly important for liquid-crystal-display applications. By comparing the three-band model with experimental results of 5CB and 7CB (two cyanobiphenyl homologs), the contribution of each band to both refractive indices and birefringence is evaluated quantitatively. It is found that the σ→σ* band makes the primary contribution to refractive indices, but its contribution to birefringence is not as significant. Conversely, the π→π* bands make the primary contribution to birefringence, but their contribution to refractive indices is not comparable to the σ→σ* band. These characteristics originate from the differences in transition wavelength, intensity, and absorption anisotropy of the σ→σ* and π→π* bands.
Stresses in silicon substrates near isolation trenches
Authors: Chidambarrao D. , Peng J. P. , Srinivasan G. R.
Published: July 2002

We describe a methodology for obtaining stresses near isolation trenches in silicon considering the entire trench forming process. A two-dimensional plane strain finite element stress analysis is performed for a trench with a thermal SiO2 sidewall and polysilicon ‘‘fill’’ which includes the cumulative stresses from the superposition of (i) residual stresses from the thermal oxidation step, (ii) the intrinsic stress from the polysilicon deposition, and (iii) stresses due to the coefficient of thermal expansion mismatch between SiO2 and silicon during the temperature cycles involved in the process. The thermal oxidation step is simulated using a two-dimensional nonlinear viscoelastic program novel [in Proceedings of the Second International Symposium on Process Physics and Modeling in Semiconductor Technology, edited by G. R. Srinivasan, J. D. Plummer, and S. T. Pantelides (Electrochemical Society, Pennington, NJ, 1991), p. 772], that produces the oxide shape and stress at the oxide-silicon interface which is converted into equivalent nodal forces on the finite element grid. We have also made a three-dimensional finite element analysis of the thermal mismatch stresses between a parallelopipedic oxide inclusion in silicon with anisotropic properties and have compared these results with the analytical results [J. Appl. Phys. 66, 2741 (1989); 67, 1092 (1990)] in which the oxide and silicon are assumed to have identical isotropic elastic properties.
Raman scattering and stress measurements in Si1−xGex layers epitaxially grown on Si(100) by ion-beam sputter deposition
Authors: Meyer F. , Zafrany M. , Eizenberg M. , Beserman R. , Schwebel C. , Pellet C.
Published: July 2002

Si1−xGex thin films have been grown on silicon substrates by ion-beam sputter deposition (IBSD). Film stress has been determined from the change in deflection curvature of the substrate after deposition and strain has been investigated by using Raman scattering spectroscopy. These properties have been studied as a function of different parameters: growth temperature, layer thickness, and annealing conditions. Raman and stress results are in close correspondence with regard to effects of deposition temperature. Si-rich films (0≤x≤0.3) were compressively strained for all deposition temperatures. A compressive to tensile stress change was observed in the Ge-rich alloys (x=0.6) when the growth temperature reached Tg ≊ 500 °C. In addition, the strain as a function of depth from the surface has been studied by changing the laser wavelength. The strain has been shown to increase from the surface to the interior of the film. The origin of the stress observed in IBSD films is discussed and we show that this stress is due to the effect of the bombardment of the growing film by energetic sputtered atoms and can be understood by using the atomic peening model.
A grain consolidation model for the critical or percolation volume fraction in conductor-insulator mixtures
Authors: McLachlan D. S.
Published: July 2002

The critical volume fraction, at which the conducting component in conductor-insulator mixtures first becomes continuous or percolates, plays a very important role in both percolation theory and the generalized effective-media equation. The growth mechanism, by which very low (≤0.05) critical volume fractions for nearly spherical conducting powders in insulating hosts, such as polymers, are obtained, is not well understood. In this paper a simple model, based on the computer-generated model of Roberts and Schwartz [Phys. Rev. B 31, 5990 (1985)] for grain consolidation in porous media, for the very low critical volume fractions observed in some conductor-insulator mixtures is proposed.
Structural and magnetic properties of Fe/Ni and Fe/Co multilayers
Authors: Krishnan R. , Gupta H. O. , Lassri H. , Sella C. , Kaabouchi M.
Published: July 2002

Fe/Ni and Fe/Co multilayers (ML) have been deposited by dc triode sputtering, with a layer thickness (t) in the range 1–10 nm. For t≳4 nm both metals are in crystalline form (bcc Fe, fcc Ni, hcp Co). For t<2 nm one has a single-phase structure (fcc in Fe/Ni ML, bcc in Fe/Co ML) which can be explained by assuming the presence of a 1-nm-thick mixed layer at the interfaces. This interfacial mixing affects the magnetic properties. The basic difference between the two systems is the fact that while Fe-Ni interfacial alloys are magnetically soft those of Fe-Co are hard which leads to different magnetic behavior. Furthermore, the Fe layers are better crystallized in our samples than those prepared by rf magnetron or ion-beam sputtering.
Magnetic anisotropies in single and multilayered structures (invited)
Authors: Heinrich B. , Celinski Z. , Cochran J. F. , Arrott A. S. , Myrtle K.
Published: July 2002

Ultrathin magnetic metallic structures provide a variety of systems in which unique magnetic properties can be engineered. The investigation of magnetic anisotropies in ultrathin structures has brought exciting results to the basic studies of magnetism in systems with reduced dimensionality and to the engineering of new magnetic materials. Molecular-beam epitaxy (MBE) techniques turned out to be particularly useful in the formation of new stable and metastable structures whose sharply defined interfaces, lattice relaxations, and lattice reconstructions have resulted in a wide range of interesting magnetic properties. In this presentation the present authors’ recent studies of single and multilayered structures composed of bcc Fe(001), bcc Cu(001), lattice-expanded Pd(001), fcc Co(001), and fcc Cu(001) will be summarized. Besides presenting their interesting magnetic properties the following techniques will be highlighted: reflection high-energy electron diffraction (RHEED) and ferromagnetic resonance (FMR). RHEED patterns and RHEED intensity oscillations were used to monitor the MBE growths. It will be shown that RHEED studies provide an effective way to characterize the quality of growth which can then be correlated with the observed magnetic properties. It will be shown that the FMR technique is extremely useful in determining all of the basic magnetic parameters. The role of interfaces, lattice relaxations, and proximity effects on the in-plane fourfold and perpendicular uniaxial anisotropies will be discussed.
An analytical model for organic-based thin-film transistors
Authors: Horowitz Gilles , Delannoy Philippe
Published: July 2002

A model describing the current-voltage characteristics of organic thin-film transistors (TFTs) is presented. The model is based on the trap distribution deduced from temperature-dependent current-voltage measurements on Au/alpha-sexithienyl (α6T)/Au symmetrical structures, which comprises a dominant single shallow trap level located near the valence-band edge. Numerical and approximate analytical derivations of the saturation current density as a function of the gate voltage have been made. From these calculations, the dependence of the threshold voltage on the parameters of the trap level (density and energy) is deduced. It appears that the threshold voltage corresponds to the filling of traps, and is a surface equivalent of the trap-filled limit voltage in bulk space-charge-limited current. The model is in good agreement with experimental data on α6T TFTs. The energy of the trap level compares well with that obtained from the temperature-dependent conductivity. However, the mobility is much lower in the TFT than in a bulk structure. This is tentatively explained by the strong influence of the state of the insulator-semiconductor interface on the characteristics of a TFT.
Effects of hydrogen on the Schottky barrier of Ti/n-GaAs diodes
Authors: Jin S. X. , Wang L. P. , Yuan M. H. , Chen J. J. , Jia Y. Q. , Qin G. G.
Published: July 2002

Having been exposed to hydrogen plasma, Te-doped GaAs wafers were deposited with metal Ti, to form Ti/n-GaAs Schottky barrier diodes (SBD). It was found that due to hydrogenation the Schottky barrier height (SBH) of the SBD decreases from 0.76 to 0.58 eV and the effective Richardson constant A** decreases from 11 to 0.03 A/cm2/K2. Annealing the hydrogenated SBD at different reverse biases at 100 °C produces SBHs that have a one-to-one correlation with the biases of reverse-bias annealing (RBA), i.e., the SBH can be controlled, within the range 0.58–0.74 eV, by the bias of RBA. When the reverse bias is equal to or larger than 3 V, the SBH and the effective Richardson constant of the hydrogenated SBDs after RBA are very near to those of SBDs without hydrogenation. This means that a RBA with a bias higher than a critical value, 3 V in our case, can remove the effects of hydrogenation, but if the SBD is annealed again without a bias at 100 °C for 1 h or more, its SBH and effective Richardson constant recover their hydrogenated values. The main experimental facts can be explained qualitatively by a simple theoretical model.
Defect levels in H+-, D+-, and He+-bombarded silicon
Authors: Palmetshofer L. , Reisinger J.
Published: July 2002

Defect levels produced by H+, D+, and He+ bombardment of silicon with different phosphorus doping and oxygen content were investigated using transient capacitance spectroscopy. After He+ implantation only pure damage defect levels occur, whereas after H+ and D+ implantation additional hydrogen-related defects are observed. For vacancy-related defects both the peak concentration and the halfwidth of the profiles depend only on the Fermi energy. The profiles were found to be broader than the theoretical vacancy distribution. The broadening which increases with decreasing doping level is explained by a model based on electric-field-enhanced diffusion. The production behavior of the defects shows a linear dependence of the sheet concentration on the ion dose for vacancy-related defects and a quadratic dependence for the hydrogen related defect E(0.30). This defect is tentatively identified as the (H-V) pair.
Multi-Tesla permanent magnet field sources
Authors: Leupold Herbert A. , Tilak Anup S. , Potenziani Ernest
Published: July 2002

Both cylindrical (‘‘magic ring’’) and spherical (‘‘magic sphere’’) dipolar permanent magnet field sources are capable of providing arbitrarily high fields in their interior cavities. However, since the obtainable field increases only logarithmically with the structural radius, fields above about 2.5 T necessitate excessively massive and costly structures if working volumes of more than a few cm3 are desired. The present work shows how for some cavity shapes the structures can be modified to produce fields up to 4.0 T with only about one fifth the mass and bulk of the conventional structures. Possible applications which would be impractical with the unmodified field sources are cited.
Spin-polarized photoemission study of epitaxial Gd(0001) films on W(110)
Authors: Tang H. , Walker T. G. , Hopster H. , Pang A. W. , Weller D. , Scott J. C. , Chappert C. , Pappas D. P. , Dessau D. S.
Published: July 2002

Surface magnetic properties of epitaxial Gd(0001) films grown on W(110) were studied with spin-polarized resonant 4f photoemission. Films grown at room temperature and subsequently annealed to 550 °C show 66% polarization at 150 K, whereas films grown at 400 °C show only 46% polarization. Both types of films exhibit surface enhanced magnetic order, with the highest observed surface critical temperature exceeding the bulk value by as much as 60 K. For the first time, a rich variety of novel surface magnetic phenomena, i.e., sizeable perpendicular polarization component and unusual temperature hysteresis in the spin polarization, are observed, demonstrating that surface magnetic reconstruction is present in Gd(0001) films.
Orientation ratio and microstructure of magnetic recording disks
Authors: Wang Po-Wen
Published: July 2002

Microstructures of magnetic CoPtCr/Cr/NiP/Al thin-film disks were studied by conventional and grazing-incidence x-ray diffraction (GI XRD) and correlated with the mechanism of the orientation ratio (OR). The OR is defined as the ratio of circumferential and radial coercivity on a circumferentially textured disk. Due to the severe overlap of the Co(002), Cr(110), and Al(200) peaks superimposed on the amorphous NiP, the conventional XRD patterns showed only limited information. However, the grazing-incidence method is able to remove the interfering effect of the amorphous NiP and AlMg substrate. As a result, the GI XRD intensity of Co(100) is observed to be stronger in the circumferential direction as compared to the radial direction when the OR is greater than 1. Also, the intensity ratio of Co(100):Co(101) is constantly higher in the circumferential direction than the radial direction. An isotropic distribution of Co(100) and Co(101) is observed in all directions when the OR is close to 1. However, in this study, the strain effect on the OR from the chromium underlayer is not observed [A. Kawamoto and F. Hikami, J. Appl. Phys. 69, 5151 (1991); R. Nishikawa, T. Hikosaka, K. Igarashi, and M. Kanamaru, IEEE Trans. Magn. 25, 3890 (1989)].
Interface magnetism and superparamagnetism of Co/Cu multilayers
Authors: Shan Z. -S. , Nafis S. , Woollam John , Liou S. H. , Sellmyer D. J.
Published: July 2002

The magnetic properties of Co/Cu multilayers were investigated from 5 to 380 K and analyzed in terms of the interface magnetism and mean-field model. The interface, which is about 1.2 Å thick, is nonmagnetic at room temperature and becomes magnetic at 5 K with the average magnetization of 40% of the pure Co magnetization. The samples of X Å Co/10 Å Cu behaved superparamagnetically as X ranged from 4 to 6.5 Å and did not show superparamagnetic behavior for thinner or thicker Co layer thickness.
Microstructure and MO enhancement in Ni-substituted Ba ferrite films prepared by sputtering (abstract)
Authors: Gomi M. , Shimai K. , Cho J. , Abe M.
Published: July 2002

Sputtered Ba ferrite films are promising media for magneto-optical (MO) recording because they have strong perpendicular magnetic anisotropy. However, MO activity of the Ba ferrites is low, which makes the feasibility as a practical medium poor. The MO activity is reported to be prominently enhanced by specific ions such as Bi3+, Co2+, and light rare earth ions in garnet ferrites, while, in Ba ferrites, the MO enhancement ions except Co2+ have not yet been known. We have recently found that Ni2+ substitution also enhances Faraday rotation in the visible region around hν=2.5 eV. In this paper we describe MO properties as well as microstructures of Ba1−xMxFe12−xNixO19 (M=La, Pr, x=0, 0.3, 0.6) films prepared by rf sputtering. The films were deposited on Gd3Ga5O12 (GGG) single crystal substrates at substrate temperature (Ts) of 400–600 °C by the conventional rf diode sputtering. When Ts≥550 °C for the incident rf power over 19 W/cm2, the films in situ crystallized in Ba–ferrite single phase. They had c-crystal axis well oriented normal to the film plane. The SEM and TEM observations revealed that the grain size in the films increases from several nm to ∼300 nm with increasing the incident power. The films with larger grains showed higher saturation magnetization and lower coercivity. Faraday rotation of the films was clearly enhanced in the visible around 2.5 eV with increasing Ni2+ substitution, though they showed rather complicated spectral structure inherent to the Ba ferrites. The enhancement factor of specific Faraday rotation at 2.5 eV was as large as 2×104 deg/x, independent of the kind of the rare earth ion substituted for Ba2+ for charge compensation. This implies that the substitution of the rare earth ion itself enhances no Faraday rotation in Ba ferrites. Thus, the MO enhancement around 2.5 eV may be attributed to the octahedrally coordinated Ni2+.
Passivation of GaAs (100) using selenium sulfide
Authors: Kuruvilla Beena Annie , Ghaisas S. V. , Datta A. , Banerjee S. , Kulkarni S. K.
Published: July 2002

The chemical and electronic aspects of a GaAs (100) surface passivated by selenium sulfide (SeS2) have been investigated by x-ray photoelectron spectroscopy and photoluminescence. It has been observed that this treatment gives rise to an arsenic selenide (As2Se3) terminated surface. No S—GaAs bonds were observed. The remarkable electronic properties and the formation of the chemically and thermally stable As2Se3 phase reveals the successful passivation. Passivation of GaAs in single step and identification of a single selenium species on the surface are considered to be the major advantages of using SeS2.
Photoluminescence study of liquid phase electroepitaxially grown GaInAsSb on (100)GaSb
Authors: Iyer S. , Hegde S. , Bajaj K. K. , Abul-Fadl Ali , Mitchel W.
Published: July 2002

Low-temperature (4.5 K) photoluminescence (PL) spectra of liquid phase electroepitaxially grown GaSb and GaInAsSb have been examined. The excitonic transitions observed in GaSb and GaInAsSb layers of compositions close to the GaSb corner of the phase diagram indicate an excellent quality of the grown layers. A systematic trend in the low-temperature PL spectra is observed with the change in the alloy composition. The overall PL emission efficiency decreases and the number of excitonic transitions are fewer with the shift in the composition towards the lower band gap. Shift in the PL peak energy corresponding to the band to band transition with temperature was determined. The linear part of the shift above 100 K exhibits a slope of −0.3 meV/K.
Scanning Hall microprobe measurements of magnetization profiles in YBa2Cu3O7−y single crystals
Authors: Brawner D. A. , Ong N. P.
Published: July 2002

A scanning Hall microprobe technique has been developed to measure the magnetic field around superconductors, and to make precision measurements of the ‘‘critical state’’ profiles in single crystals of YBa2Cu3O7−y. The field around a superconducting crystal has been calculated for the Meissner state and for the remanent state. This enables a quantitative analysis of the critical state profiles, and a novel method to determine JC. The invasion of magnetic flux above HC1 was examined and this provides direct evidence for the existence of a surface barrier to the entry of magnetic flux lines. The temperature dependence of JC was also measured and compared with that of the low TC material Nb0.5Ti0.5.
Relaxation of interface states and positive charge in thin gate oxide after Fowler–Nordheim stress
Authors: El Hdiy A. , Salace G. , Petit C. , Jourdain M. , Meinertzhagen A.
Published: July 2002

Fowler–Nordheim (F.N.) tunneling of electrons from the gate into thin thermally grown SiO2 under high electrical field stress has been performed with polycrystalline Si-SiO2-Si capacitors and relaxation of both interface state densities and flat-band voltage investigated during several months after F.N. stress at room temperature. It has been found that the relaxation behavior of surface states and positive charge densities follow fractional power laws in time.
Behavior of disordered Co-Pd, Co-Ag, and Co-Mo alloys in multilayer interfaces
Authors: Shan Z. -S. , He Ping , Moore C. , Woollam John , Sellmyer D. J.
Published: July 2002

Local environment effects are important for understanding interfacial magnetism in artificially structured multilayers. For this reason, stable and/or metastable disordered alloys CoXM1−X (M=Pd, Ag, Mo) were fabricated in a dc cosputtering system. The magnetization as a function of composition and temperature were measured and analyzed in terms of a mean-field model. The local environment effect on the Co moment from its Ag (or Mo) neighbors and the Pd moment from its Co neighbors are studied. It is found that the polarized Pd moment increases linearly with an increasing number of nearest Co neighbors and the Co moment is destroyed by only two Mo neighbors.
Hybrid boundary-volume Galerkin’s method for solution of magnetostatic problems with hysteresis
Authors: Friedman G. , Ahya D.
Published: July 2002

This article describes a method for the solution of magnetostatic problems with hysteresis. A time-stepping technique is employed to accumulate field history. At each time step, the magnetostatic problem is formulated using a constitutive law determined from the accumulated history and the vector Preisach hysteresis model. The field problem at each time step is reduced to coupled boundary-volume Galerkin’s forms. The finite-element discretization is used in the interior regions, while harmonic basis functions are used in the exterior regions. A globally convergent iterative technique is proposed for the solution of discretized hybrid boundary-volume Galerkin’s forms. The solution method is illustrated on 2D magnetostatic problems.
Raman spectroscopic and Hall effect analysis of the free electron concentration in GaAs with ultrahigh silicon doping
Authors: Ramsteiner M. , Wagner J. , Hiesinger P. , Köhler K. , Rössler U.
Published: July 2002

Heavily silicon-doped GaAs grown by molecular beam epitaxy has been studied by combined coupled plasmon-phonon mode Raman spectroscopy and Hall effect measurements. Free electron concentrations up to 2×1019 cm−3 have been achieved with the dopant atoms being incorporated dominantly on Ga sites (≥90%) as measured by local vibrational mode Raman spectroscopy. To extract quantitative information from the plasmon-phonon Raman spectra, these spectra have been fitted using the temperature-dependent Lindhard–Mermin dielectric function including the nonparabolicity of the conduction band and wave vector nonconservation due to the absorption of the incident and scattered light. The excellent agreement found between Hall effect and Raman measurements demonstrates that consistent data on dopant incorporation and activation can be obtained, if band structure effects are accounted for appropriately in the analysis of the Raman spectra.
Third-order nonlinear optical properties of processable polyazine thin films
Authors: Nalwa Hari Singh , Kakuta Atsushi , Mukoh Akio
Published: July 2002

The third-order nonlinear optical susceptibility χ(3)(−3ω;ω,ω,ω) of propylmethylpolyazine thin films as measured by the third harmonic generation is reported. The χ(3)(−3ω;ω,ω,ω) values of propylmethylpolyazine that possess statistically alternating methyl and propyl substituents on the carbon atoms along the conjugated chain were found to be 8.0×10−12 esu off resonance at 1.5 μm fundamental radiation. The interesting third-order nonlinear properties presumably originate from the unique periodicity of the main π-electron-conjugated polyazine backbone.
Growth of gallium nitride thin films by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy
Authors: Eddy C. R. , Moustakas T. D. , Scanlon J.
Published: July 2002

We report on optimization studies for the growth of GaN films by the electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (ECR-MBE) method on the R plane of sapphire. The films were grown by the reaction of Ga vapor with ECR-activated molecular nitrogen and their growth kinetics were found to depend strongly on the distance between the ECR condition and the substrate. Single crystalline films with their α plane (112̄0) parallel to the R plane of sapphire (101̄2) were grown with the substrate held at 400–700 °C. All films were found to be n type with carrier concentrations varying between 1017 and 1019 cm−3. Films grown at 600 °C were found to have the smallest amount of strain and the highest electron mobility, suggesting that strain might be one of the sources of compensating defects.
Low-temperature mixing in Cu/W superlattices irradiated with light and heavy ions
Authors: Pacaud J. , Gladyszewski G. , Jaouen C. , Naudon A. , Goudeau Ph. , Grilhé J.
Published: July 2002

Ion irradiation effects, induced at low temperature in Cu/W superlattices prepared by ion sputtering, were studied and compared using in situ resistivity measurements and x-ray diffraction. The influence of the particle mass was particularly investigated in order to measure the role of spike effects in this immiscible system. It is shown that a more important mixing can be obtained with light-ion irradiation. Nevertheless, the contribution of ‘‘thermally’’ activated jumps opposing ballistic effects is significant even when small and weakly energetic cascades are formed. A dependence of the microstructural state and of the compositional substructure on the irradiating particle is also evidenced. Light-ion irradiation favors grain growth, restores grain texture, and preserves the composition modulation.
Trap-assisted conduction in nitrided-oxide and re-oxidized nitrided-oxide n-channel metal-oxide-semiconductor field-effect transistors
Authors: Fleischer S. , Lai P. T. , Cheng Y. C.
Published: July 2002

The off-state leakage characteristics of n-channel metal-oxide-semiconductor field-effect transistors with pure oxide, low-partial pressure nitrided (LPN) oxide, re-oxidized LPN, and nitrogen-annealed LPN oxide as the gate insulator, were investigated over the temperature range 300–400 K. In the high-field region (above 7 MV/cm), the gate-induced drain leakage was found to be due to band-to-band tunneling for all samples. Low-field conduction was determined to be due to a gate current which was many orders of magnitude higher than the Fowler–Nordheim current observed in capacitors on the same wafers. A trap-assisted tunneling model was employed, using a trap energy of 0.7 eV determined from the activation data, in order to explain the low-field gate current. The most likely cause of this enhanced conduction is oxide degradation in the gate-to-drain overlap region created during the source/drain implant.
Optical limitation and bistability in fullerene
Authors: Lin Fucheng , Zhao Jiran , Luo Ting , Jiang Minghua , Wu Zhengliang , Xie Yanyan , Qian Qiuming , Zeng Heping
Published: July 2002

Efficient optical limitation is demonstrated in the toluene solution of C60 based on the reverse saturable absorption. The highly nonlinear absorption can be used to smooth a spike-like pulse in the nanosecond region. Optical bistability is obtained in a nonlinear Fabry–Perot cavity filled with a thin layer of polystyrene doped with C60/C70. A smooth pulse with 25 ns width (full width at half-maximum) is compressed to 15 ns and a spike-like pulse is subjected a wave form distortion by this device. The light limitation effect in this polystyrene layer 0.3 mm thick was demonstrated at the wavelength of 532 nm and the threshold about 20 mJ/cm2.
Selective growth of diamond using an iron catalyst
Authors: Shimada Yoshihito , Machi Yoshio
Published: July 2002

Selective growth of diamond was carried out on the silicon substrate with patterned iron films, using the radio frequency plasma chemical vapor deposition method. Iron film was used to increase the nucleation density of diamond. Although the density of diamond particles on the silicon substrate exposed in CF4 plasma was on the order of 103 cm−2, the iron film enhanced the density up to the order of 108 cm−2. In the photolithography process for patterning the iron film, the formation of iron carbide (Fe-C) was caused by carbon atoms diffused from the photoresist film onto the iron film during baking of the photoresist film. It was confirmed that the presence of Fe-C was effective in enhancing diamond nucleation.
Comment on ‘‘Surface acoustic wave studies on single crystal nickel using Brillouin scattering and scanning acoustic microscope’’ [J. Appl. Phys. 71, 2830 (1992)]
Authors: Kim Jin O. , Weglein Rolf D.
Published: July 2002

The authors comment sequentially on several statements in the paper by M. Mendik, S. Sathish, A. Kulik, G. Gremaud, and P. Wachter, J. Appl. Phys. 71, 2830 (1992) and suggest a more reliable technique to determine the elastic constants of a {100}-oriented cubic crystal.
Transmission electron microscopy study of B-site cation configurations in perovskite-structured Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics
Authors: Furuya M. , Mori T. , Ochi A.
Published: July 2002

Configurations of B-site cations in the perovskite-structured ternary system Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 (PMW-PNN-PT) of interest for multilayer ceramic capacitors were studied by transmission electron microscopy. The evaluated specimens were four PMW/PNN/PT compositions: 10/30/60, 30/30/40, 50/30/20, and 70/30/0 on a compositional line with 30 mol % PNN content. A ‘‘core-shell-type’’ microstructure was seen in the 10/30/60 specimen composition, which has a ‘‘normal’’ ferroelectric characteristic, along with typical ferroelectric domain structures. The B-site cation ordering in the 10/30/60 composition was not detectable in the selected-area electron diffraction pattern. On the other hand, an ‘‘island-type’’ microstructure, consisting of clusters (∼1–2 nm) with B-site cations 1:1 ordered, was observed in the 30/30/40, 50/30/20, and 70/30/0 compositions, which have relaxor-type characteristics. In the 70/30/0 composition, larger stripe-shaped ordered regions (∼20–200 nm) were also observed. These ordered regions extended from the center of the grain to the boundary. On the basis of the results obtained, origins of the dielectric behaviors for this system, that is, a ‘‘normal’’ ferroelectric, a relaxor ferroelectric, and an antiferroelectric, were discussed from the point of view of the B-site cation configurations. The PMW component plays two roles in this ternary system, corresponding to its content. When the PMW content is low, Mg and W ions are disordered in the B-site sublattice, and interrupt the ferroelectricity. With increasing PMW content, small ordered clusters (∼1–2 nm) are formed, which are believed to localize superparaelectric potentials effectively and dominate a degree of a diffuse phase transition in the solid-solution system.
Effect of thickness on the transverse thermal conductivity of thin dielectric films
Authors: Griffin A. J. , Brotzen F. R. , Loos P. J.
Published: July 2002

The transverse thermal conductivities of SiO2 thin films are determined as a function of film thickness. The results indicate that the apparent thermal conductivities of SiO2 thin films are much lower than the thermal conductivity of bulk SiO2. In addition, a slight decrease in the thermal conductivity is observed as the average temperature within the dielectric film increases. The average transverse thermal conductivity decreases drastically as the film thickness is reduced. This strong thickness dependence is explained in terms of an interfacial thermal resistance that develops at the SiO2/Si interface. The experimentally determined value for the interfacial thermal resistance, Rint, is 2.05 mm2 °C W−1.
A Mössbauer effect study of the microscopic magnetic properties of Th2Fe17 and its nitride, Th2Fe17N2.6
Authors: Long Gary J. , Pringle O. A. , Grandjean F. , Jacobs T. H. , Buschow K. H. J.
Published: July 2002

The Mössbauer spectra of Th2Fe17 and Th2Fe17N2.6 have been measured at various temperatures between 85 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Th2Fe17, the 85 K weighted average isomer shift increases from 0.037 to 0.156 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. The nonmagnetic thorium in Th2Fe17N2.6 yields an easy axis of magnetization which, in contrast to magnetic rare earths in R2Fe17 and R2Fe17Nx, is in a general basal direction and not oriented along one of the basal axes. The isomer shift and its temperature dependence for both Th2Fe17 and its nitride are very similar to those observed in related rare-earth R2Fe17 compounds and their nitrides. Upon nitrogenation of Th2Fe17, the 85 K weighted average hyperfine field increases from 256.3 to 336.5 kOe. However, the increases on the 6c and 18f sites are smaller than those observed on the 9d and 18h sites; changes which are in agreement with changes in the magnetic moments observed by neutron diffraction and calculated for the nitrogenation of Nd2Fe17, Gd2Fe17, and Y2Fe17.
Determination of the valence-band discontinuity in Be-doped GaAs/Al0.3Ga0.7As multiple-quantum wells using admittance spectroscopy
Authors: Smith S. R. , Szmulowicz F. , Brown G. J.
Published: July 2002

Admittance spectroscopy has been used to determine the value of the valence-band discontinuity in a p-type GaAs/Al0.3Ga0.7As multiple-quantum-well system. The structures were multiple quantum wells grown by molecular-beam epitaxy on semi-insulating GaAs substrates. Three Be-doped (p-type) GaAs wells, 30, 35, and 40 Å wide, were used in these measurements. The barriers were undoped. Based on our measurements and a Fermi-level determination from an 8×8 envelope function approximation calculation of the valence electronic structure of the GaAs/AlGaAs system, the valence-band discontinuity, ΔEv, was found to be 0.165 eV. Using established relations, the band-gap difference in the GaAs/AlGaAs system ΔEg for xAl=0.3 was calculated to be 0.429 eV, which, together with the valence-band offset determined in this work, gives the ratio of the conduction–to–valence-band offsets as 60:40. These values are in excellent agreement with those determined by capacitance-voltage profiling, thus confirming the utility of the admittance spectroscopic technique for determining the band discontinuities in band-gap-engineered materials.
Structural and magnetic properties of Nd2(Fe,Ti)19
Authors: Cadogan J. M. , Li Hong-Shuo , Davis R. L. , Margarian A. , Collocott S. J. , Dunlop J. B. , Gwan P. B.
Published: July 2002

Alloys with the composition Nd2(Fe,Ti)19 can exist in two crystal structures depending on the preparation technique. Melt-spun material has a hexagonal TbCu7-type structure (a=4.902 Å, c=4.248 Å) for a range of quenching speeds. Alloys prepared by arc melting, annealing at 1373 K and then water quenching have a complex monoclinic structure derived from a TbCu7 superlattice (a=10.644 Å, b=8.585 Å, c=9.755 Å, β=96.92°) and related to those of other intermetallics such as tetragonal Nd(Fe,Ti)12 and rhombohedral Nd2Fe17. Magnetic ordering temperatures for annealed (monoclinic) and melt-spun (hexagonal) Nd2(Fe,Ti)19 are 411 and 454 K, respectively. 57Fe Mössbauer spectroscopy at 295 K demonstrates that the local environments of the Fe atoms in the two structural modifications of Nd2(Fe,Ti)19 are similar. The average 57Fe magnetic hyperfine fields at 295 K for the monoclinic and hexagonal Nd2(Fe,Ti)19 are 20.8 and 22.3 T, corresponding to average Fe magnetic moments of 1.33 and 1.43μB, respectively.
Experimental study on opening compensation for magnetic shields by current superposition
Authors: Sasada I. , Oonaka Y.
Published: July 2002

A new method is studied experimentally by which magnetic fields coming in through an opening of a magnetic shield can be compensated. The horizontal component of the earth’s field is targeted as an external magnetic field to be compensated by the method, in which a single figure-eight coil is used. A cylindrical shielding case is developed for this study using a Permalloy cylindrical case (outer diameter=68 cm, length=180 cm) with an opening at an end and Metglas 2705M amorphous ribbons, which are wound helically on the outer surface of the Permalloy case by 16 layers. A magnetic shaking field of 200 Hz is applied to only the amorphous layers by a toroidal shaking coil of 36 turns. The size of the figure-eight coil used is 74 cm in diameter with 30 turns. Residual magnetic field measured by a flux gate magnetometer in the horizontal center plane of the shielding case shows that the area where the amplitude of the residual magnetic field is within ±0.15 mG is extended by about 30 cm toward the opening.
Magnetic behavior of the amorphous wires covered by glass
Authors: Chiriac Horia , Pop Gheorghe , Barariu Firuta , Vázquez Manuel
Published: July 2002

Magnetic properties are presented of amorphous wires covered by glass, with the compositions Fe65B15Si15C5, Fe60B15Si15Cr10, and Fe40Ni40P14B6, which were prepared by melting the alloy in glass tubes and drawing fibers from the softened glass. The magnetization, the remanence, and the coercive force of the samples covered by glass, and of those obtained after removing the glass cover, were measured at a field of 2054 A/m. These amorphous wires have a square-shaped hysteresis loop, a value of the coercive force ranging between 255 and 462 A/m and an axial magnetization of 0.21–0.32 T for different compositions. The glass removal leads to an increase in magnetization and a decrease in the coercive force. The influence of a passing dc current through the wire during measurements has also been studied, influence that is much pronounced in the case of the wires obtained after removing the glass cover. The observed different magnetic properties of the amorphous magnetostrictive wires are attributed to the difference in internal stress distribution produced during preparation of the samples.
Calculations of plasma wavelength in highly doped III-V semiconductor alloys
Authors: Stiens J. , Vounckx R.
Published: July 2002

A detailed study of the dependence of the plasma wavelength on the doping concentration in ternary and quaternary III-V semiconductor alloys has been made. The band-structure properties are included in the calculations by applying the triple-band effective-mass equations to an extended Drude formula. The results show that for high doping levels the plasma wavelengths of the considered materials (InAsxSb1−x, GaxIn1−xSb, GaAs1−xSbx, In1−xGaxAs, In1−xGaxAsyP1−y, and AlxGayIn1−x−yAs) saturate into the 10-μm-wavelength region (the smaller the band gap, the larger the saturation wavelength). The optimal material group for the realization of the plasma resonance for 10.6 μm (CO2 lasers) seems to be In0.53Ga0.47As. Numerical fits for the plasma wavelength and the optical effective mass are provided.
Polarized-cathodoluminescence study of stress for GaAs grown selectively on patterned Si(100)
Authors: Tang Y. , Rich D. H. , Lingunis E. H. , Haegel N. M.
Published: July 2002

The spatial variation of stress tensor in selective-area metalorganic chemical-vapor- deposition-grown GaAs on Si substrate by using a linearly polarized cathodoluminescence (CL) technique has been examined. The polarized CL technique enables a precise determination of the energy positions for the strain-split j=3/2 valence-band excitonic contributions to the luminescence by a simultaneous deconvolution of two CL spectra that are each taken under different polarization detection conditions; this procedure enables a mapping of the stress tensor. The biaxial in-plane stress (σ∥=σ⊥; where ∥ and ⊥ denote parallel and perpendicular, respectively, to a 〈110〉-oriented mesa edge) is found to decrease from ∼2.2 to 0.5 kbar as the square pattern size is decreased from 1 mm to 10 μm. Patterns having smaller dimension are found to have an increased luminescence efficiency, indicating a reduction in thermal stress induced dislocation density. The stress decay in the vicinity of edges and corners is found to be modeled well with a bimetal thin-film model, showing an approximately exponential decay in stress. A residual tensile stress (comprised of nonzero σ⊥, shear and peeling stress terms) of 0.5–1.0 kbar is found to exist at the edges and corners of the square GaAs mesas; this result agrees qualitatively with an elastic finite-element analysis. The CL results show that the decay length of stress relief near a pattern edge essentially increases with increasing mesa size. The maximum biaxial stress and residual stress near the mesa edges and corners is found to increase with increasing pattern size. Polarized CL imaging is observed to be sensitive to local deviations from biaxial stress and can be used to map the boundaries of stress contours near mesa edges and defects.
InAlAs/InP heterostructures: Influence of a thin InAs layer at the interface
Authors: Vignaud D. , Wallart X. , Mollot F.
Published: July 2002

InAlAs lattice matched on InP heterostructures with a thin InAs layer of variable thickness intentionally added at the interface has been grown by molecular-beam epitaxy and characterized by photoluminescence. Radiative transitions, the position of which is correlated with the InAs thickness, are systematically observed, even in samples without any added InAs layer. This shows that, even in the latter case, type-I transitions are observed at the interface. Following this result, it is proposed that a transition around 1.2 eV, previously assigned to type-II transitions, results in fact from type-I recombinations in a quantum well at the interface. The spatially indirect type-II transitions would occur at ≊1.3 eV, and could be observed up to now only for reverse interfaces (InP grown on InAlAs).
Straightened voltage effect in high-T
c superconductors
Authors: Grishin A. , Niska J. , Loberg B. , Weber H.
Published: July 2002

A new effect called ‘‘ac-current straightening’’ has been observed in ceramic (Bi,Pb)-2223 slabs carrying ac current Idc+Iac cos(ωt). The current-voltage (I-V) characteristics of the ceramic were measured at 77 K at frequencies ranging from 50 to 20 000 Hz. A spectrum analyzer showed a series of high harmonics in the voltage signal as well as a constant voltage drop. The full set of experimental data has been explained theoretically using the Bean–Kim critical state model with a magnetic field dependent critical current jc(H)=jc(0)/(1+H/H0). A low transport ac current gives a voltage linearly proportional to the frequency and quadratically proportional to the ac-current amplitude Iac. It consists of odd harmonics only. If a bias dc current is switched on, then even harmonics and a dc-voltage drop appear. Their amplitudes are proportional to the small parameter Iac/cH0 and depend on the Idc/Iac ratio.
Magnetic and magnetotransport properties of granular Cu85Fe15 prepared by mechanical alloying
Authors: Saxena Siddharth S. , Tang Jinke , Lee Young-Sook , O’Connor Charles J.
Published: July 2002

The magnetic and magnetotransport properties of granular Cu85Fe15 prepared by mechanical alloying have been investigated. The sample was prepared by grinding fine powders of copper and iron in a high energy ball mill. Zero field cooled and field cooled susceptibilities showed a behavior that is typical of a superparamagnet. The blocking temperature TB of 20 K was determined from ac susceptibility. The magnetoresistance reached 5.5% at 4.5 K in a field of 5 T. It was increased to 7.6% after the sample was annealed at 300 °C for 20 min. The hysteresis loop was measured for both magnetization and magnetoresistance. There was a clear correlation between the two. The magnetoresistance is due to the scattering associated with iron nanoparticles present in the samples and its dependence on particle size is discussed.
Uniaxial magnetic anisotropy in Fe-rich 2:17 compounds with sp substitutions
Authors: Dunlap R. A. , Wang Z. , Foldeaki M.
Published: July 2002

The magnetic properties of single-phase 2:17 compounds of the composition Sm2Fe17−x−yCoyMx with M=Al and Ga and x and y in the range 0–5 are reported. The Curie temperature is found to increase for the y=0 samples with increasing x up to a maximum at x=3 for M=Al and x=4 for M=Ga and a monotonic increase with increasing y for all x and M. Samples with x<2 showed an easy-plane magnetic anisotropy at room temperature while samples with x≳2 showed a single-phase uniaxial anisotropy. The addition of Co is seen to increase the saturation magnetization and the anisotropy field.
Hydrogen ion interactions with silicon carbide and the nucleation of diamond thin films
Authors: Lannon J. M. , Gold J. S. , Stinespring C. D.
Published: July 2002

Ultrahigh-vacuum surface studies of hydrogen ion interactions with silicon carbide thin films were performed to provide new insights into the mechanisms of diamond thin-film nucleation. These experiments were carried out at room temperature using hydrogen ions with energies of 10, 100, 500, and 2000 eV. In situ analyses using Auger electron spectroscopy indicated that silicon atoms were removed from the surface and near-surface layers of the film, and the resulting carbon-rich layers were converted to a mixture of sp2 and sp3 carbon. The relative amounts of sp2 and sp3 species formed were strongly dependent upon ion energy. The highest concentration of sp3 carbon was obtained using 500 eV ions. Theoretical considerations suggest this behavior was the result of both chemical and energy transfer effects.
Physical vapor deposition of highly oriented fullerene C60 films on amorphous substrates
Authors: Xiao Rong-Fu , Ho Wai-ching , Chow Lai-yee , Fung Kwok Kwong , Zheng Jiaqi
Published: July 2002

Crystalline films of fullerene C60 have been grown on amorphous substrates by a physical vapor deposition technique. X-ray diffraction has shown that these C60 films are highly oriented in either (111)/(glass substrate) or (220)/(fused silica substrate) orientations. The explanation for such growth behavior is that the orientation of C60 crystals can be adjusted during growth by the rotation of individual C60 molecules at elevated temperatures.
Investigation of the high temperature behavior of strained Si1−yCy /Si heterostructures
Authors: Fischer G. G. , Zaumseil P. , Bugiel E. , Osten H. J.
Published: July 2002

We report on x-ray diffraction measurements of the substitutional carbon content y in pseudomorphic Si1−yCy (y<0.02) layers grown on (100)-oriented silicon substrate. The samples were grown by molecular beam epitaxy and investigated during post growth annealing in situ by an x-ray powder diffractometer. Despite the tensile strain in the 100-nm-thick layers and the high carbon supersaturation, the samples were stable up to 800 °C. Beyond this temperature range, the substitutional carbon content decreased exponentially during isothermal annealing. This effect can be explained by the precipitation of the carbon and the nucleation and diffusion limited growth of SiC nanocrystals. Since no strain relief by the introduction of misfit dislocations was detectible, we conclude that contrary to the mechanism of strain relief in Si1−xGex, in comparably strained Si1−yCy epilayers, the main high temperature process is precipitation.