bluuebunny/crossref_metadata_2025 huggingface dataset:
Field dependence of the soliton contribution to the dynamic correlation function of a classical Heisenberg antiferromagnet
Authors: Subbaraman Kala , Zaspel Craig E. , Drumheller John E.
Published: July 2002

Recent theoretical and experimental work confirm the existence of solitons in the nearly classical two-dimensional (2D) Heisenberg antiferromagnet. Previous ac susceptibility measurements on (n-propyl ammonium)2MnCl4 or (PAMC), a 2D spin 5/2 antiferromagnet AFM shows that the susceptibility is strongly dependent on a weak magnetic field (≈0.2 Oe) at temperatures below TC. These data provided the motivation for a calculation of the field dependence of the static soliton structure factor. This is done by assuming the small field dependent term as a perturbation around the static soliton solution. The dynamic part of the correlation function is assumed to result from soliton–magnon scattering in the Born approximation. These field-dependent and dynamic results are combined to obtain the dynamic field-dependent correlation function.
Lateral structure of (TiSe2)n(NbSe2)m superlattices
Authors: Noh Myungkeun , Shin Hyun-Joon , Jeong Kwangho , Spear Jennifer , Johnson David C. , Kevan Stephen D. , Warwick Tony
Published: July 2002

The structures of a series of (TiSe2)n(NbSe2)m superlattices grown through controlled crystallization of designed multilayer reactants have been studied. X-ray diffraction of the data of the superlattices after crystallization show considerable preferred orientation, with the basal plane of the dichalcogenide structure parallel to the substrate to within 0.1°. Lattice refinement using the observed (00ℓ) diffraction maxima yields lattice parameters along the c axis that are consistent with those expected based on the target superlattices and lattice parameters of the binary constituents. These (00ℓ) diffraction data, however, contain no information about the crystalline structure in the ab plane of the superlattice associated with the preferred c-axis orientation. Off-specular x-ray diffraction (XRD), scanning electron microscopy, and scanning transmission x-ray microscopy (STXM) were used to explore the structure and homogeneity of the superlattices in the ab plane. XRD results rule out preferred long-range orientational order of the ab plane. Between grains, both the backscattered electron images and STXM images show grain domain structure in the ab plane with a characteristic grain domain size of approximately 50 μm. X-ray absorption microscopy in the STXM mode obtained at the Ti L2,3 edge shows that the titanium in the superlattices is present as both octahedral Ti consistent with the TiSe2 structure and metallic Ti. A comparison of the data obtained from these techniques highlights chemical information, which can be deduced on a submicrometer range from the space resolved spectra obtained using STXM.
Magnetic properties and switching volumes of nanocrystalline SmFeSiC films
Authors: Zhang S. Y. , Shan Z. S. , Liu Y. , Zhao T. Y. , Zhao J. G. , Shen B. G. , Zhan W. S. , Sellmyer D. J.
Published: July 2002

Systematic studies of the effects of Si addition on the magnetic and magnetization reversal properties of SmFeSiC films are presented. The magnetic switching volume and other magnetic parameters (e.g., coercivity) are strongly dependent upon the Si content. Correlations between switching volume, coercivity, and the intergrain interactions are discussed.
Nuclear magnetic resonance study of the Nd2Co17Ax(A=N,H) compounds
Authors: Kapusta Cz. , Riedi P. C. , Tomka G. J. , Mycielski R.
Published: July 2002

The 145Nd, 143Nd, and 59Co nuclear magnetic resonance (NMR) spin-echo spectra and echo decays for Nd2Co17 and its interstitial nitride, Nd2Co17N3 and hydride Nd2Co17H3.6 at 4.2 and 77 K at zero field and in applied fields of up to 5 T are reported. The Nd quadrupole splitting of 3.88 MHz for 145Nd in Nd2Co17 is reduced to 0.37 MHz for Nd2Co17N3. The value for Nd2Co17H3.6 is 3.66 MHz. The reduction of quadrupole splitting for Nd2Co17N3 as compared to the host Nd2Co17 is 50% larger than for the isostructural Nd2Fe17N3 and is assigned to a huge increase in the magnitude of the lattice electric field gradient at the Nd site and, thus to a huge rise of magnetocrystalline anisotropy caused by neighboring N atoms, whereas H atoms have only a slight influence on both quantities. The 59Co spectrum of the nitride is much different from that of the host compound indicating a large influence of N neighbors on Co hyperfine fields, whereas only minor changes are observed after hydriding.
In situ measurement of magnetoresistive head transfer curves on a spin stand tester (abstract)
Authors: Zhu Jian-Gang , Lam Terence , Ding Juren , Luo Yansheng , Wang Haiyun
Published: July 2002

An in situ method of measuring the magnetoresistive (MR) head transfer curves directly on a spin-stand tester is presented. We define the MR head transfer curve as the MR output voltage amplitude versus the magnitude of magnetic flux arising from transitions. To obtain adjustable transition flux magnitude on a spin stand tester, isolated transitions are recorded with write current level varied from zero to saturation. Adjusting the write current level varies the magnetization level difference across a recorded transition, thereby varying the magnetic flux generated by the transitions. At each write current level, the magnitude of the magnetic flux arising from the recorded transitions is measured by the thin film (TF) writer whose response is linear with respect to magnetic flux. At the same time, the MR head output is also measured. By plotting the MR head output as a function of the TF head output, a transfer curve is obtained. The experiments were performed using a film disk (Disk A) of MrT=2 memu/cm2, and a biased MR head. In order to confirm the validity of this method, a thin film disk (Disk B) with magnetic layer thickness gradually varying from one portion of the disk to another was fabricated by adding a shutter in the film deposition process. The MrT value of the film disk fabricated changes from zero to 2 memu/cm2 along a recording track within a revolution. Figure 1 shows the measured outputs of both the MR and TF writer as a function of write current using Disk A. At high write current level, the normalized MR output becomes smaller than the TF output due to head nonlinearity. The MR output as a function of TF output gives the MR head transfer curve. An MR transfer curve can also be measured by the quasistatic dc applied field method, and it has been shown to have good agreement with the medium transition excitation method.1 Using the three different methods, namely the varying write current, varying MrT, and varying dc-field methods, three MR transfer curves are measured and plotted in Fig. 2. Comparing the three transfer curves, excellent agreement is found among these methods in terms of the shape of the transfer curve which reflects amplitude asymmetry and nonlinearity.
Diamond growth by injecting thermally decomposed chlorine atoms into methane/hydrogen mixture
Authors: Wu Jih-Jen , Hong Franklin Chau-Nan
Published: July 2002

Crystalline diamond has been successfully deposited by injecting thermally decomposed Cl atoms into CH4/H2 in a hot-tube system at an extremely high flow velocity (in the convection-dominant mass transport region). Diamond growth rate increased with increasing the total flow rate, suggesting the increase of [Cl]/[H] ratio near the growth surface. Film quality also improved with increasing the total flow rate as well as reducing the reactor pressure. Both the quality and film growth rate were enhanced as the inlet [Cl2] increased, due to the increase of total radical concentration. Two distinct growth activation energies were measured ranging from 3.6 kcal/mol in the substrate temperature range of 600–750 °C to 7.9 kcal/mol in the temperature range of 400–600 °C. Owing to the extremely short residence time and low gas temperature, carbon species near the growth surface remained almost the same as the input carbon source. By employing almost pure CH4 or C2H2 near the substrate surface, the CH3 radical was shown to be a more efficient diamond growth precursor than C2H2. With almost pure C2H2 near the surface, diamond deposition was negligible in a wide range of conditions on either silicon or diamond surfaces.
Junction characteristics of electron-irradiated Ga0.5In0.5P n+-p diodes and solar cells
Authors: Reinhardt K. C. , Yeo Y. K. , Ostdiek P. H. , Hengehold R. L.
Published: July 2002

The effects of 1 MeV electron irradiation on n+-p mesa diodes and solar cells fabricated from metalorganic chemical vapor deposition grown Ga0.5In0.5P on GaAs have been studied. Upon electron irradiation, Ga0.5In0.5P n+-p junction dark current increased by more than one order of magnitude, but it could be reduced by about 75% after annealing at 250 °C for 10 min. The increase in junction dark current was mainly attributed to reductions in minority carrier lifetimes. It was also found that Ga0.5In0.5P solar cell open-circuit voltage, short-circuit current, fill factor, and air-mass zero conversion efficiency were all reduced on the average by 11%, 18%, 8%, and 33%, respectively, following exposure to 1016 electrons/cm2. However, a significant improvement in the electron-irradiated Ga0.5In0.5P solar cell efficiency was observed via thermal annealing at 250 °C, demonstrating good potential for a longer solar cell lifetime in space through on-orbit thermal annealing. The degradation in solar cell conversion efficiency following 1 MeV electron irradiation was smaller than that observed in Si and GaAs, but greater than that in InP solar cells.
Ab initio study of biquadratic coupling in Fe/Cr multilayers (abstract)
Authors: Shi Zhu-Pei , Wang Yang , Stocks G. M.
Published: July 2002

Magnetic coupling in multilayer materials is a fascinating phenomenon that manifests itself in a wide range of effects, including novel magnetic arrangements and anomalous transport properties. We employ the locally self-consistent multiple scattering method,1 which has recently been extended to treat general noncollinear magnetic systems,2 to study interlayer magnetic coupling in Fe/Cr(100) multilayer structures. The direction and magnitude of magnetization of each monolayer in a magnetic multilayer with 10 monolayer (ML) Fe layers separated by a 5 ML Cr spacer are obtained. We found that the Fe layers are nearly 90° coupled, and the Cr spacer is in spiral magnetic configuration. We attribute this biquadratic coupling in Fe/Cr multilayers to the nature of itinerant antiferromagnetism of the Cr spacer. These results will be discussed in connection with recent experiments.
Preparation of c-axis-oriented barium ferrite thin films with small crystallite size
Authors: Hoshi Y. , Kubota Y. , Ikawa H.
Published: July 2002

BaM thin films were deposited on thermally oxidized silicon wafer substrates at temperatures near 580 °C by using a dc facing-target sputtering system. The crystallite size of films 200 nm thick was greater than 200 nm, and it decreased monotonically with decreasing film thickness, reaching a value below 30 nm in films 30 nm thick. Further decreases in film thickness led to a degradation of the crystallinity of the film, causing the saturation magnetization and coercive force of the film to decrease significantly. Growth of BaM crystallites in films deposited on a SiO2/Si substrate was significantly suppressed when the films were deposited on a thin initial layer deposited beforehand under a substrate bias of −50 V.
New mechanical grinding process for anisotropic Sm2Fe17Nx powder with a nanocrystalline structure
Authors: Majima K. , Ito M. , Katsuyama S. , Nagai H.
Published: July 2002

A new mechanical grinding (MG) process in NH3 and subsequent nitriding in N2 without a crystallization treatment was developed for synthesizing Sm2Fe17Nx powders. This process features a shorter MG time compared to conventional MG to prevent amorpharization of the alloy structure and to avoid hydrogen in the ground powders which promotes a diffusion of nitrogen atoms into their particles. The Sm2Fe17Nx powder with x=3.2 prepared by grinding for 10 h and subsequent nitriding at 723 K for 6 h showed magnetic anisotropy and its magnetic properties were Ir=1.00 T, Hc=0.61i MA m−1, and (BH)max=129 kJ m−3 (16.1 MGOe).
Improved model of radiation damage to silicon solar cells
Authors: Taylor S. J. , Yamaguchi M. , Imaizumi M. , Ito T.
Published: July 2002

We have carried out modeling of the evolution of silicon solar cell performance following irradiation with high energy protons and electrons. Using the traditional semiempirical expression the solar cell output parameters of a given cell structure could be predicted for various particle energies by expressing the particle fluence as a displacement damage dose. We discuss the extent to which the evolution of different silicon solar cell structures in a radiation environment can be predicted using the software package PC-1D by taking account of the degradation of the minority carrier lifetime and majority carrier concentration in the cell.
Quantum dots under electric and magnetic fields: Impurity-related electronic properties
Authors: Ribeiro F. J. , Latgé A. , Pacheco M. , Barticevic Z.
Published: July 2002

A systematic study of the ground-state binding energies of a hydrogenic impurity in quantum dots subjected to external electric and magnetic fields is presented. The quantum dot is modeled by superposing a lateral parabolic potential and a square-well potential and the energies are calculated via a variational approach within the effective-mass approximation. The interplay between the confinement effects due to the applied fields and the quantum-size confinements on the binding energies is analyzed. The role played by the impurity position along the well direction on the impurity energies is also discussed. We have shown that by changing the strength of the external electric and magnetic fields, a large spread in the range of the donor binding energy may be obtained, for a particular choice for the lateral confinement. The presented results could be used to tailor energy states in optoelectronic devices.
Oxidation of hydrogen-passivated silicon surfaces by scanning near-field optical lithography using uncoated and aluminum-coated fiber probes
Authors: Madsen S. , Bozhevolnyi S. I. , Birkelund K. , Müllenborn M. , Hvam J. M. , Grey F.
Published: July 2002

Optically induced oxidation of hydrogen-passivated silicon surfaces using a scanning near-field optical microscope was achieved with both uncoated and aluminum-coated fiber probes. Line scans on amorphous silicon using uncoated fiber probes display a three-peak profile after etching in potassium hydroxide. Numerical simulations of the electromagnetic field around the probe–sample interaction region are used to explain the experimental observations. With an aluminum-coated fiber probe, lines of 35 nm in width were transferred into the amorphous silicon layer.
A comparison of surface roughness as measured by atomic force microscopy and x-ray scattering
Authors: Munkholm A. , Brennan S. , Carr E. C.
Published: July 2002

We compare measurements of the roughness of silicon(001) wafers cleaned by several methods. The roughness values were obtained using crystal truncation rod (CTR) scattering and atomic force microscopy. Although they do not yield identical results, both methods show the same relative roughness for the different cleans. CTR scattering is sensitive to roughness on lateral length scales down to atomic dimensions. The quantitative differences in roughness can be explained by the different wavelength spectrum of roughness probed by the two techniques. CTR measurements were also performed after a 60 Å thermal oxide was grown on the wafers. The roughness trends are the same after oxidation, but we also find that the oxidation process has significantly reduced the interfacial roughness.
The potential formation of O2− on an oxidizing porous silicon surface a source of oxygen atoms
Authors: Gole James L. , Dudel Frank P.
Published: July 2002

Evidence is presented for the formation of O2− on a porous silicon surface. The O2− present on a porous silicon surface may contribute to the infrared spectrum of air oxidized surfaces in the range encompassing ∼1100–1150 cm−1. The presence of O2− suggests its possible role as a precursor for oxygen atom formation.
Magnetostatic critical-point phenomena of Fe
Authors: Tanaka Toshiro , Miyatani Kazuo
Published: July 2002

The magnetostatic critical-point phenomena of a highly pure polycrystalline Fe sphere (99.999% pure) have been first investigated by a vibrating sample magnetometer for the applied field from 0 to 8 kOe. The kink point locus was observed for the whole critical region. The critical temperature, the spontaneous magnetization, and the zero-field susceptibility were determined without data extrapolations. The Curie temperature and the critical indices were obtained to be: Tc=1042.98±0.02 K, β=0.352±0.005 for ε=4×10−5–6×10−3, γ=1.269±0.005 for ε=2×10−4–2×10−2, and δ=4.20±0.05. γ neither agrees with the 3d Ising model nor with the 3d Heisenberg model, and β fits between the two models. These indices satisfy the Griffith’s inequality, γ′⩾β(δ−1). The critical equation of state was given by the same form as that for Ni.
X-ray diffraction studies of the effects of N incorporation in amorphous CNx materials
Authors: Walters J. K. , Kühn M. , Spaeth C. , Dooryhee E. , Newport R. J.
Published: July 2002

The effects of nitrogen incorporation on the atomic-scale structure of amorphous CNx samples have been studied for 0, 5, 20, and 30 at. % N concentration, by x-ray diffraction. Significant differences in the structure are observed on the incorporation of only 5 at. % N, and the changes in structure continue as further N is added. From the experimental data, we are able to obtain directly the average bond distances and then calculate the average bond angles for each of the samples. The average first neighbor distance shows a gradual decrease from 1.55 Å for 0 at. % N, to 1.44 Å for 30 at. % N, and a similar trend is observed in the position of the second neighbor peak. This gives a corresponding increase in the average bond angle from 108° to 114°. The results show an increase in the fraction of sp2 bonded carbon atoms with increasing N concentration, and there is evidence for the presence of significant numbers of C≡N and C=N bonds. These results are also consistent with stress, hardness, and optical gap measurements for these samples.
Spin reorientation transition due to thickness ratio variation in EuBi2Fe5O12/Y3Fe5O12 multilayer films—ferrimagnetic resonance studies
Authors: Lofland S. E. , Bhagat S. M. , Srinivasu V. V. , Ramesh R. , Simion B. M. , Thomas G.
Published: July 2002

We present the results of an investigation into ferrimagnetic resonance at room temperature in superlattice heterostructures with alternating layers of Y3Fe5O12 and EuBi2Fe5O12 grown by pulsed-laser deposition. We find that in the Y3Fe5O12 layer, the spins always prefer to lie in the plane. In the EuBi2Fe5O12 layer, on the other hand, the spin direction switches from normal to the film plane to in-plane as its thickness falls below that of the Y3Fe5O12 layer.
Optical study of silicon-containing amorphous hydrogenated carbon
Authors: Zhang X. , Weber W. H. , Vassell W. C. , Potter T. J. , Tamor M. A.
Published: July 2002

Silicon-containing amorphous hydrogenated carbon films deposited by a plasma-enhanced chemical vapor deposition process were studied using both Raman and ellipsometry spectroscopies. Analyses of the experimental data from both these techniques yielded valuable information about the microstructure of the films. The silicon incorporation in amorphous hydrogenated carbon breaks down large size sp2 carbon clusters and enhances sp3 bonding. The reduction of large sp2 graphitic defects, the enhancement of sp3 bonding, and the associated microstructure changes are responsible for the desired properties of silicon-containing amorphous hydrogenated carbon.
Orientation dependence of strained ZnSe/ZnS(h11) single quantum well luminescence
Authors: Tomasini P. , Arai K. , Lu F. , Zhu Z. Q. , Sekiguchi T. , Suezawa M. , Yao T. , Shen M. Y. , Goto T. , Yasuda T. , Segawa Y.
Published: July 2002

Pseudomorphic ZnSe/ZnS single quantum well (SQW) structures have been grown on GaP substrates with high Miller indices. Samples with different crystallographic axis, grown under similar experimental conditions, exhibit different thicknesses, since the growth rate of a crystal facet is axis dependent. The optical properties of ZnSe/ZnS(h11) single quantum wells have been successfully related to the axis orientation through a finite square well potential model. Optical transitions in ZnSe SQWs are dominated by the axis dependence of the heavy-hole effective masses. Furthermore, calculations concerning the piezoelectric effect show that the quantum confined Stark effect is almost negligible for 1–2 monolayers thick wells.
Polarization properties of light emitted by a bent optical fiber probe and polarization contrast in scanning near-field optical microscopy
Authors: Mitsuoka Yasuyuki , Nakajima Kunio , Homma Katsunori , Chiba Norio , Muramatsu Hiroshi , Ataka Tatsuaki , Sato Katsuaki
Published: July 2002

This article describes the polarization properties of light emitted by a bent optical fiber probe which is used for scanning near-field optical microscopy operated in atomic force mode (SNOM/AFM). SNOM/AFM can be applied to the observation of magnetic domains by imaging polarization contrast in transmission mode. A bent optical fiber probe with a subwavelength aperture is vibrated vertically as a cantilever for atomic force microscopy. Plane polarized light with an extinction ratio of better than 70:1 was emitted by the aperture by controlling the polarization state of incident light to the probe. A particular transverse polarization component of light transmitting a sample is selected by a polarization analyzer and detected. We obtained clear polarization contrast images of 0.7 μm length bits written with a conventional method using a focused laser beam on a bismuth-substituted dysprosium-iron-garnet film.
Analysis of thermally stimulated Maxwell-displacement current across organic monolayers
Authors: Iwamoto Mitsumasa , Wu Chen-Xu , Mizutani Yoshinobu
Published: July 2002

Dielectric relaxation processes in organic monolayer films during heating are analyzed on the basis of the rotational Debye–Brownian motion equation. Theoretical formula for the thermally stimulated current (TSC) is obtained. The polar orientational disordering of polarized and nonpolarized monolayers is examined by taking into account the dielectric relaxation time τ of monolayers. TSCs across phospholipid monolayers of L-α-dimyristoyl, phosphatidylcholine are discussed on the basis of the analysis developed here.
Residual defects in low energy and low dose antimony ion-implanted silicon
Authors: Uesugi F. , Kikuchi Y. , Watanabe K. , Hoshimoto I.
Published: July 2002

The residual defects in medium energy (40 keV) and low dose (5.0×1014/cm2) Sb ion-implanted Si after annealing at 1000 °C for 10 and 30 min have been investigated by several advanced transmission electron microscopy techniques and secondary ion mass spectroscopy. These annealing conditions give rise to the formation of two new types of residual defects: irregular shape defects with amorphous structure, and rod-shaped defects surrounded by four {1 1 1} planes which are extended to 〈1 1 0〉 directions on both sides of an initial amorphous-crystalline interface, as well as well known hexagonal Sb precipitates, depending on annealing time. It seems likely that a rod-shaped defect is grown from an irregular shape defect as a result of long annealing.
Reflection and transmission characterization of a hexagonal photonic crystal in the mid infrared
Authors: Rowson S. , Chelnokov A. , Lourtioz J.-M. , Carcenac F.
Published: July 2002

We report on the fabrication of a hexagonal photonic crystal of air cylinders in silicon and its characterization in the mid infrared. The structure was obtained in electrochemically etched macroporous silicon. Simultaneous reflection and transmission measurements were undertaken for the two main crystal orientations and two polarizations. The first four orders of photonic band gaps were identified by transmission attenuations and reflection peaks. A complete photonic band gap was observed at 5.8 μm, in good agreement with numerical calculations. The measured reflection characteristics of the crystal demonstrate the application possibilities of photonic crystals.
Thermoelectric power in porous silicon
Authors: Mathur R. G. , Mehra R. M. , Mathur P. C.
Published: July 2002

Thermoelectric power measurements have been made on macroporous (pore width >500 Å°) porous silicon samples prepared by an anodic dissolution technique. The sign of thermopower is found to be negative indicating that conduction takes place due to electrons in the conduction band. The conduction mechanism is found to be due to variable range hopping near the Fermi level for temperatures below 150 K. At higher temperatures the conduction is due to the tunneling of carriers in the localized states in the band edges. It was concluded that these localized states are formed because the nanocrystallites in porous silicon are randomly distributed in size and orientation leading to fluctuations in band gap. This results in the constitution of a disordered system on a macroscopic scale.
Spin fluctuations and thermal expansion of La(NixAl1−x)13 amorphous alloys
Authors: Fujita A. , Fukamichi K.
Published: July 2002

The influences of spin fluctuations on the magnetization M and thermal expansion for La(NixAl1−x)13 amorphous alloys have been investigated. The spontaneous magnetization obeys a M2–ξT4/3 relation and the coefficient ξ is concerned with the dynamical spin fluctuation spectrum. The spontaneous volume magnetostriction in the ferromagnetic state appears due to the thermal variation of the local spin amplitude. The change in the linear thermal expansion coefficient in paramagnetic temperature regions is caused by the saturation of amplitude of the spin fluctuations.
Magnetization and magnetostriction of dendritic [112] TbxDyyHozFe1.95 (x+y+z=1) rods under compressive stress
Authors: Wun-Fogle M. , Restorff J. B. , Clark A. E. , Lindberg J. F.
Published: July 2002

The field dependencies of the magnetization and magnetostriction of the Laves phase pseudobinary TbxDyyHozFe1.95 (x+y+z=1) compounds were measured as a function of compressive stress T (10 MPa<|T|<70 MPa) and applied magnetic field H (0<H<135 kA/m). Values of x, y, and z were chosen to obtain minimum magnetic anisotropy and easy magnetization axis rotation near room temperature. At a compressive stress of 34 MPa, the addition of Ho to the binary Tb1−xDyxFe1.95 compound reduced the width of the strain versus magnetic field hysteresis curves in Tb0.28Dy0.57Ho0.15Fe1.95 and Tb0.26Dy0.54Ho0.2Fe1.95 by 23% and 54%, respectively, compared to the original alloy, while the strains were reduced by only 7% and 10%.
Dielectric properties of oriented thin films of PbZrO3 on Si produced by pulsed laser ablation
Authors: Chattopadhyay Soma , Ayyub Pushan , Palkar V. R. , Multani M. S. , Pai S. P. , Purandare S. C. , Pinto R.
Published: July 2002

PbZrO 3 is an antiferroelectric perovskite with TC≈230 °C. We have deposited single phase, perfectly c-axis oriented thin films of PbZrO3 on Si(100) substrates by pulsed laser ablation at 700 °C. The growth conditions (substrate temperature, ambient oxygen pressure, and laser energy density) have been optimized and the morphology of the films studied by scanning electron microscopy and atomic force microscopy. From a study of the dielectric hysteresis of the films and a measurement of the temperature dependence of their capacitance, we find that films thicker than ≈300 nm are antiferroelectric, while thinner films (<300 nm) appear to exhibit ferroelectric behavior.
Photoconductivity and electronic transport in tetrahedral amorphous carbon and hydrogenated tetrahedral amorphous carbon
Authors: Ilie A. , Conway N. M. J. , Kleinsorge B. , Robertson J. , Milne W. I.
Published: July 2002

The photoconductivity of tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H) has been studied as a function of temperature, photon energy, and light intensity in order to understand the transport and recombination processes. ta-C and ta-C:H are found to be low mobility solids with μτ products of order 10−11–10−12 cm2/V at room temperature because of their relatively high defect densities. Deep defects tend to be the dominant recombination centers, but at high and moderate temperatures only a fraction of these centers or even tail states can act as recombination centers because the carrier demarcation levels do not always span the gap. For excitation by high energy UV photons, a peak in the photoconductivity is found at 200 K, similar to the thermal quenching effect found in a-Si:H, and attributed to competitive recombination between two classes of centers with very different capture cross sections.
Spatially and temporally resolved temperature measurements of plasma generated in percussion drilling with a diode-pumped Nd:YAG laser
Authors: Ii M. , Duffey T. P. , Mazumder J.
Published: July 2002

Results of spectroscopic temperature measurements of the laser-induced plasma generated during percussion drilling with a high power diode-pumped, pulsed Nd:YAG laser are presented. SAE 52100 steel was drilled with varying average powers. Helium and oxygen were each used as the shield gas. Emission spectra were collected with a monochrometer and an intensified charge coupled detector connected to the optical multichannel analyzer. The plasma electron temperatures were calculated from the relative intensities of the spectral lines. The spatial and temporal temperature distributions are presented. Both drilling times and spatial distributions indicate energy absorption by the plasma.
On the origin of 1/f noise in polysilicon emitter bipolar transistors
Authors: Deen M. Jamal , Rumyantsev S. L. , Schroter M.
Published: July 2002

Low frequency noise in polysilicon emitter bipolar transistors (BJT) with different emitter areas (AE) was studied. In BJTs with submicron emitter area, random telegraph signals of different amplitudes and frequencies were found. Averaging of noise spectra from different submicron BJTs gives 1/f noise of the same level (normalized to the emitter area) as 1/f noise found in transistors with large emitter areas. The sheet density of traps (NT) located within the polysilicon–crystalline silicon interfacial layer and responsible for 1/f noise was estimated to be ⩾3×108 cm−2.
Effect of erase bands on high tracks per inch applications
Authors: Chue J. M. , Baral D. , Dunbar G.
Published: July 2002

To meet the areal density growth (∼60% compound annual growth rate) challenge in the disk drive industry, track density (tracks per inch, TPI) has been increasing at ∼30% rate. As the track density increases, the size of the erase band, unless controlled, becomes a significant portion of the written track. In this work, special equipment was developed to study (i) the size of erase bands, (ii) the effect of pole trimming on erase band and hooks, (iii) the effect of disk anisotropy on erase bands and hooks, and (iv) the effect of hooks and erase bands at high TPI. We demonstrated servo pattern writing and reading capability (through the drive preamp and channel) on a spin stand level, showing that for properly trimmed pole heads, hook and erase band size becomes insignificant. With untrimmed pole heads, isotropic disks showed smaller hooks compared to oriented disks. From this work, we concluded that at higher TPI, erase bands must be scaled so that the servo Gray code signal-to-noise ratio is not unduly degraded.
Effects of a magnetic field on the germination of plants
Authors: Hirota Noriyuki , Nakagawa Jun , Kitazawa Koichi
Published: July 2002

The effects of a nonuniform magnetic field on the germination of plants were studied. When a 10 T magnetic field was applied at the center of a superconducting magnet, a cucumber shoot germinating in a horizontal bore leaned towards the field center. In contrast, the root grew in the direction opposite the shoot. The observed result seemed to have occurred as a result of the magnetic force influencing the geotaxis of the cucumber. This idea was supported qualitatively by analysis results of the experimental data. Knowledge obtained in this study will be helpful for the evaluation of the effect of the magnetic field on living bodies and suggests the possibility of applying magnetic fields in other areas of research.
Magnetization reversal and magnetoresistance in a lateral spin-injection device
Authors: Lee W. Y. , Gardelis S. , Choi B.-C. , Xu Y. B. , Smith C. G. , Barnes C. H. W. , Ritchie D. A. , Linfield E. H. , Bland J. A. C.
Published: July 2002

We have investigated the magnetization reversal and magnetoresistance (MR) behavior of a lateral spin-injection device. The device consists of a two-dimensional electron gas (2DEG) system in an InAs quantum well and two ferromagnetic (Ni80Fe20) contacts: an injector (source) and a detector (drain). Spin-polarized electrons are injected from the first contact and propagating through InAs are collected by the second contact. By engineering the shape of the permalloy film distinct switching fields (Hc) from the injector and the collector have been observed by scanning Kerr microscopy and MR measurements. Magneto-optic Kerr effect (MOKE) hysteresis loops demonstrate that there is a range of magnetic field (20–60 Oe), at room temperature, over which magnetization in one contact is aligned antiparallel to that in the other. The MOKE results are consistent with the variation of the magnetoresistance in the spin-injection device.
The effects of hydrogen bonds on the adhesion of inorganic oxide particles on hydrophilic silicon surfaces
Authors: Wu X. , Sacher E. , Meunier M.
Published: July 2002

Hydrogen bonds have a dominant effect on the adhesion of inorganic oxide particles, such as SiO2 and Al2O3, to hydrophilic silicon surfaces. An analysis of adhesion forces due to hydrogen bonds between particle and substrate surfaces has been carried out, and is used to interpret the efficiencies of removing polystyrene latex, SiO2, and Al2O3 particles from a hydrophilic silicon surface by laser cleaning. Evidence of the dominant effect of hydrogen bonding was confirmed by using alcohol instead of water during particle deposition.
Structural defects in 3C–SiC grown on Si by supersonic jet epitaxy
Authors: Long C. , Ustin S. A. , Ho W.
Published: July 2002

3C–SiC thin films have been grown on Si(001) and Si(111) substrates by supersonic jet epitaxy. Cross-sectional high resolution scanning transmission electron microscopy (STEM) is used to study the SiC/Si interface structure and defects in the films. The occurrence of twins is evident in the selected area electron diffraction pattern taken from a SiC/Si(111) heterostructure. A 39° angle between twinned and untwinned {111} planes in the [11̄0] projection is confirmed by x-ray pole figure. Twinning is attributed to the growth on the {111} planes. Pure edge misfit dislocations are found at the interface to accommodate the extreme lattice mismatch in SiC/Si(001) heterostructures. A schematic model of the STEM image reveals that a pair of 60° dislocations intersect to form an edge misfit dislocation. A large number of stacking faults and microtwins are present in SiC thin films grown on both Si(001) and Si(111) substrates. The formation of planar defects is attributed to the coalescence of individual three-dimensional islands. Possible methods for the reduction of the planar defects are discussed.
Strains and stresses in multilayered elastic structures: The case of chemically vapor-deposited ZnS/ZnSe laminates
Authors: Klein Claude A. , Miller Richard P.
Published: July 2002

Solid structures consisting of layers of different materials created at elevated temperatures usually exhibit substantial residual stresses. These stresses are caused by intrinsic strains in addition to thermal strains, and originate from the bonding of the layers, which generates internal forces and moments that must be balanced to achieve mechanical equilibrium. It is shown that the solution proposed by Townsend et al. [P. Townsend, D. Barnett, and T. Brunner, J. Appl. Phys. 62, 4438 (1987)] for describing elastic interactions in multilayered, elastically isotropic structures provides a powerful tool for evaluating the strains, the normal stresses off the edges, and the curvature of chemically vapor-deposited (CVD) laminates. The residual stresses acting in each layer are best expressed as follows: σi(z)=Ei′[(εi,0−ε0¯)+(zN−z)K], where z measures the distance from the bottom surface, Ei′ is the biaxial modulus of the layer, (εi,0−ε0¯) characterizes the strain mismatch prior to any mechanical relaxation, and (zN−z)K defines the bending contribution, which depends linearly on the distance from the neutral plane and stems from the curvature K. For bilayered structures the curvature can be expressed in a relatively simple form. In conjunction with the proper expression for the average stress in the coating, it is seen that Stoney’s equation holds for thickness ratios much larger than expected in the context of the thin-film approximation. The case of CVD laminates made of ZnS on ZnSe illustrates how the theory can be applied for designing structures that minimize the deformation and, thus, for obtaining optically desirable configurations. The stresses acting in bilayered ZnS/ZnSe structures are controlled by the strain differential Δε0=εcintr.+(αc¯−αs¯)ΔT, where εcintr. represents the intrinsic strain of the ZnS coating, and (αc¯−αs¯)ΔT defines the contribution originating from the thermal expansion mismatch. For ZnS deposited at 670 °C, measurements of the curvature yield Δε0≃−5.53×10−4; upon evaluating available information on the thermal expansion of ZnS and ZnSe we conclude that the intrinsic strain of CVD ZnS is compressive and amounts to about 1 or 2×10−4, for thicknesses ranging from 1 to 4 mm.
Schottky barrier studies on single crystal ZnTe and determination of interface index
Authors: Bhunia S. , Bose D. N.
Published: July 2002

Detailed studies on metal-(111) p-ZnTe Schottky barriers have been carried out using In, Ag, Al, and Cu as barrier metals. Weak dependence of barrier height on metal work function was observed. The highest and lowest barrier heights of 0.99 and 0.80 eV were found for In and Cu respectively which had lowest and highest work functions. The ideality factor n was found to vary between 1.84 for In and 2.13 for Al contacts. The Fermi level was found to be pinned effectively by interface states, the density of which was calculated to be 4.7×1013 states/cm2/eV. From the current–voltage characteristics measured between 250 and 350 K, the effective Richardson constant A** was determined to be 72±6 A/cm2/K2. This agrees very well with the theoretically calculated value of A** for a hole effective mass mh*=0.6m0. The temperature variation of barrier height was also determined from the capacitance–voltage characteristics. The interface index a parameter used to describe the pinning strength of semiconductors was found to be 0.34 for ZnTe.
Curie point written magnetoresistive memory
Authors: Beech R. S. , Anderson J. A. , Pohm A. V. , Daughton J. M.
Published: July 2002

Memory cells have been fabricated and tested to demonstrate storage in the pinned layer of a giant magnetoresistance (GMR) spin valve film. The spin valve was top pinned with a FeMn film and gave about 4% GMR ratio. The memory cell consisted of an oblong, 0.6 μm×7.0 μm GMR bit with first metal contacts at each end and a perpendicular first and second metal word line passing over the bit. Joule heating due to current pulses through both the memory cell and the word line raised the temperature of the FeMn pinning layer above its Néel point. The magnetic field generated by the word line current switched the pinning direction, depending on the polarity of the word line current. Sense line currents up to 5 mA provided a half select without disturbing the bit. In combination with a 5 mA sense current, the bit was written with a word current pulse of 190 mA. The improved thermal stability of the pinned storage layer memory cell is shown to become necessary as the size of a magnetoresistive memory cell drops below about 0.1 μm×0.4 μm.
Ferromagnetic resonance studies of exchange biasing in Ni81Fe19/Pt10Mn90 bilayers
Authors: Xi Haiwen , Mountfield Keith R. , White Robert M.
Published: July 2002

In-plane ferromagnetic resonance (FMR) has been used to study exchange anisotropy in Ni81Fe19/Pt10Mn90 bilayers at room temperature. A theoretical calculation for the FMR resonance field was carried out based on a simple model of the exchange bias in a polycrystalline bilayer that incorporates reversible as well as irreversible behavior of the antiferromagnetic layer. In addition to the expected cos φH contribution to the resonance field, where φH is the direction of the applied field, there is a negative shift of the resonance field. It is argued that the negative shift of the resonance related to the irreversible behavior of the antiferromagnetic moments is not isotropic. The linewidth broadening of in-plane resonance for the exchange biased bilayers is also discussed.
The oxidation of methanol on Cu(100)
Authors: Ryberg R.
Published: July 2002

Different aspects of the catalytic oxidation of methanol on Cu(100) have been investigated. CH3O is a surface intermediate formed in the reaction and infrared spectroscopy has been used to study its vibrational modes. For the C–O stretch mode there is a large coverage dependent shift of the vibration frequency caused by the dipole–dipole interaction between the molecules. In order to study the reaction mechanisms the vibration frequency was used as a measure of the CH3O coverage, which then indicated the probability for a methanol molecule to react with a surface oxygen atom under various conditions. LEED was used for structural studies and showed that the CH3O could form both a c(2×2) and a hexagonal structure. A model for the oxidation of methanol on Cu(100) is proposed, stressing the structural aspects. The model implies that the reaction can only occur if there exist empty nearest neighbor adsorption sites adjacent to the oxygen atom and that the reaction can be prevented by the presence of an excess of oxygen atoms or highly mobile CH3O molecules on the surface. The dehydrogenation of CH3O to H2CO was shown to proceed via the adsorption of a hydrogen atom on the surface during a thermally excited bend motion. Finally, it is reported that the infrared absorption peak width of the C–H stretch modes of CH3O is caused by inhomogeneous broadening and is not a measure of the vibrational damping, as previously assumed.
Rotational isomeric model of the coil stretching transition of semiflexible polymers in elongational flow
Authors: Henyey F. S. , Rabin Y.
Published: July 2002

A simple rotational isomeric-type model of polymers in elongational flows is developed and used to analyze the coil stretching and chain retraction as a function of polymer and flow parameters. The results are in agreement with available experimental data on dilute polymer solutions in strong elongational flows.
Self-broadening and self-shifting of ammonia lines in the 2ν2 band around 16 μm
Authors: Baldacchini G. , Marchetti S. , Montelatici V. , Buffa G. , Tarrini O.
Published: July 2002

We have measured the pressure broadening and shift of several transition lines of ammonia, 14NH3, in the 2ν2 band around 16 μm. Satisfactory agreement is found between the experimental results and a slightly modified version of the Anderson theory. A comparison between the theory and measurements of other authors has also been made.
Solvent isotope effect on ion mobility in water at high pressure. Conductance and transference number of potassium chloride in compressed heavy water
Authors: Nakahara M. , Zenke M. , Ueno M. , Shimizu K.
Published: July 2002

Limiting molar conductances of the K+ and Cl− ions in heavy and light water have been determined at 25 °C as a function of pressure up to 2 kbar from the measured conductances and transference numbers of KCl. The residual friction coefficients (Δζ) are obtained for the cation and the anion in D2O and H2O by using the determined limiting conductance and the bulk viscosity of solvent and compared with the corresponding values predicted by applying the Hubbard–Onsager (HO) dielectric friction theory at various pressures below 1 kbar. At atmospheric and high pressures Δζ of the K+ ion in D2O is larger than that in H2O just as predicted by the HO theory, but Δζ of the Cl− ion in D2O is smaller than that in H2O on the contrary to the theoretical prediction. The reverse solvent isotope effect on Δζ(Cl−) suggests that a microscopic viscosity in the vicinity of the relatively large ion is smaller than the bulk viscosity used in the continuum theory.
A theoretical analysis of the overtone-induced isomerization of methyl isocyanide
Authors: Miller James A. , Chandler David W.
Published: July 2002

A master-equation formalism is applied to the problem of overtone-induced isomerization of CH3NC to CH3CN. The results are compared to the experiments of Reddy and Berry, who measured the yield of isomerization as a function of pressure after excitation to the fourth and fifth overtones of the CH stretching mode. The master-equation model predicts the yield and the curvature in the yield−1 vs pressure plots observed in the experiments. For the lower overtone (5←0) the results are consistent with a simple strong-collider model. However, even under strong-collider conditions the yield is very sensitive to the parameters in the master equation. For the upper overtone (6←0) the data do not fit a strong collider model and multistep deactivation dominates. We are able to determine from the data the average energy transferred in a collision by assuming a particular form for the energy-transfer function. In addition, the effect of changing the shape of the energy-transfer function is investigated.
Nuclear spin relaxation due to order director fluctuations in the smectic A phase
Authors: Vilfan M. , Kogoj M. , Blinc R.
Published: July 2002

The frequency dispersion and anisotropy of nuclear spin relaxation caused by order director fluctuations in the smectic A phase are calculated. Dispersion of (T−11)OF at low frequencies, which departs from the nematic-like behavior, is examined in detail and the influence of the wave vector dependent viscosity coefficients on relaxation is commented. The deviation from the nematic-like relaxation behavior drastically changes the angular dependence of (T−11ρ)OF.
Vibronic coupling in polyenes and their derivatives. Interpretation of the absorption and emission spectra of a derivative of dodecahexaene
Authors: Zerbetto F. , Zgierski M. Z. , Orlandi G. , Marconi G.
Published: July 2002

It is shown that unusual frequency differences of the totally symmetric C=C bond stretching vibration in the S1(2Ag) state between 2,12-dimethyltridecahexaene and two of its derivatives N-(2,4,6,8,10-dodecapentaenylidine) butylamine (12SB) and dodecapentaenal (12R), result from vibronic coupling between the S1(2Ag) and S2(1Bu) electronic states via totally symmetric vibrations in 12SB and 12R. The vibronic coupling matrix elements between the lower ππ* electronic states of the three molecules are evaluated by CNDO/S+CISD calculations in a floating atomic orbital basis set. The resulting adiabatic frequencies of the Franck–Condon active totally symmetric vibrations in the S0(1Ag) and S1(2Ag) electronic states are in good agreement with experiment. High-resolution fluorescence and fluorescence excitation spectra of 12SB are successfully interpreted in terms of the vibronic coupling between the S1(2Ag) and S2(1Bu) electronic states via the totally symmetric C=C and C–C bond stretching vibrations. The analysis of these spectra provides values of the displacement parameters for these vibrations in the S1(2Ag) and S2(1Bu) states.