bluuebunny/crossref_metadata_2025 huggingface dataset:
Brightness measurements of nanometer-sized field-emission-electron sources
Authors: Qian W. , Scheinfein M. R. , Spence J. C. H.
Published: July 2002

The brightness of nanometer-sized field-emission-electron sources have been measured experimentally. Ultrasharp tungsten (111) single-crystal tips were fabricated in situ using Ne sputtering and field evaporation, and monitored using field ion microscopy. The average brightness of single-atom-terminated nanotips was found to be 3.3×108 A cm−2 sr−1 at 470 V, or 7.7×1010 A cm−2 sr−1 when extrapolated to 100 kV. These results show an improvement of about two orders of magnitude in source brightness over existing cold field-emission-electron sources, and produce a beam with greater particle flux per unit energy than those obtainable using current synchrotron/wiggler/undulator devices.
Hole traps of metastable iron-boron pairs in silicon
Authors: Nakashima H. , Sadoh T. , Tsurushima T.
Published: July 2002

Hole traps of configurationally metastable iron-boron pairs in p-type silicon are studied using deep level transient spectroscopy, thermally stimulated capacitance, and single shot techniques combined with minority-carrier injection. Two levels at EV+0.53 and 0.48 eV are observed as the metastable pairs after the injection at 150 K. The level at 0.53 eV consists of two traps vanishing with different decay rates at around 220 K, while the level at 0.48 eV annihilates with simple exponential form. The decay rate for each trap has a thermal activation energy of ∼0.7 eV and shows a single jump process of interstitial iron from one configuration to another. These new traps of iron-born pairs are discussed with the aid of configuration-coordinate description within the framework of the simple ionic model.
Germanium blocked-impurity-band detector arrays: Unpassivated devices with bulk substrates
Authors: Watson Dan M. , Guptill Matthew T. , Huffman James E. , Krabach Timothy N. , Raines S. Nicholas , Satyapal Shobita
Published: July 2002

We have fabricated and characterized six-element monolithic arrays of Ge:Ga blocked- impurity-band detectors, with threshold wavelength 220 μm, peak quantum efficiency 14%, detective quantum efficiency 9%, dark current 300 e− s−1, and response uniformity better than 4%. The devices are described very well by the standard model of blocked-impurity-band detectors, and appear to satisfy many of the requirements of low-background astronomical instruments.
Two-dimensional ion velocity distribution functions in electron cyclotron resonance plasma under a divergent magnetic field
Authors: Okuno Yoshihiro , Ohtsu Yasunori , Fujita Hiroharu
Published: July 2002

Two-dimensional ion velocity distribution functions are measured in electron cyclotron resonance (ECR) argon plasmas under a divergent magnetic field configuration using a directional analyzer. Ions produced in the ECR source grow to a beam in the downstream region inside an allowed angle, while the distribution function is almost isotropic outside the angle. The beam energy corresponds to the potential difference between the ECR source and downstream locations. The ion beam is almost parallel to an applied magnetic field, the beam being deflected along the divergent magnetic field lines. The energy spread and the temperature of the ion beam, and the temperature of the bulk ions are also shown as a function of the distance from the ECR source or of the gas pressure. The validity of the directional analyzer measurements is discussed by considering the motion of an ion in a sheath in front of the analyzer.
Micromagnetic model for the influence of biaxial stress on hysteretic magnetic properties
Authors: Sablik M. J. , Riley L. A. , Burkhardt G. L. , Kwun H. , Cannell P. Y. , Watts K. T. , Langman R. A.
Published: July 2002

A micromagnetic formulation has been developed for modeling the effect of biaxial stress on magnetoelastic processes in polycrystalline steels. In particular, the formulation employs the Schneider–Cannell–Watts model and involves substitution of an effective stress equal to one of the deviatoric (i.e., distortional) normal stress components, depending on whether the field is parallel to a tensile or compressive axis or to the third axis perpendicular to the plane of biaxial stress. Computer results are compared to experimental results on the effects of biaxial stress on magnetic properties in mild steel and in SAE-4130 steel. Good qualitative agreement is found in almost all cases, in that in going from one biaxial stress case to the next, the same kinds of changes are seen magnetically. It is also shown from the model and the data that a method can be formulated to nondestructively determine the difference in biaxial stresses.
Resonant ultrasound measurements of elastic constants in melt-spun R2Fe14B compounds (R=Ce, Pr, Nd, Er)
Authors: Fuerst C. D. , Herbst J. F. , Sarrao J. L. , Migliori A.
Published: July 2002

Measurements are reported of the longitudinal and transverse elastic moduli of the R2Fe14B compounds having rare-earth component R=Ce, Pr, Nd, and Er. A resonant ultrasound technique was used to determine the elastic constants on hot-pressed, melt-spun samples which are essentially isotropic, polycrystalline specimens of the four compounds. The results for Nd2Fe14B, which agree well with previous studies, and Er2Fe14B exhibit clear signatures of the spin reorientations which occur in those compounds. No such signature appears in the data for Pr2Fe14B, consistent with the fact that no spin reorientation occurs in that material. The ultrasonic attenuation of each sample has also been measured and it has been found that it shows features in the vicinity of spin reorientations (Nd2Fe14B, Er2Fe14B) and the Curie point (Ce2Fe14B).
Lateral carrier diffusion and surface recombination in InGaAs/AlGaAs quantum-well ridge-waveguide lasers
Authors: Hu S. Y. , Corzine S. W. , Law K.-K. , Young D. B. , Gossard A. C. , Coldren L. A. , Merz J. L.
Published: July 2002

We measured the increase in threshold currents due to lateral carrier diffusion in InGaAs/AlGaAs quantum-well ridge-waveguide laser diodes. The ridge stripes were fabricated by using both in situ monitored pure Cl2 reactive ion etching and selective wet etching to completely eliminate the spreading current in the conductive upper cladding layer while keeping the ridge sidewalls straight. After comparing the threshold data with a theoretical model, the ambipolar diffusion coefficient is found to be 22 cm2/s in the population-inverted InGaAs layer. This model is based on the calculated optical gain curve and the ambipolar carrier transport in the quantum-well and waveguiding layers. The dependence of carrier lifetime on the local carrier concentration is included in the calculation. Moreover, from another set of devices with the portions of the active layer outside the ridge stripes etched away, the surface recombination velocity is found to be around 1–2×105 cm/s.
Grain growth in laser dehydrogenated and crystallized polycrystalline silicon for thin film transistors
Authors: Mei P. , Boyce J. B. , Hack M. , Lujan R. , Ready S. E. , Fork D. K. , Johnson R. I. , Anderson G. B.
Published: July 2002

Selective dehydrogenation and crystallization are realized by a three-step incremental increase in laser energy density. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those after a conventional one-step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few micrometers. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated to the material properties, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors. Our structure simplifies fabrication of both high quality amorphous and polycrystalline thin film transistors on the same glass substrate. We discuss the application of this process for producing hybrid amorphous and polycrystalline silicon thin film transistors from hydrogenated amorphous silicon on glass substrates.
Optical mixing of laser light in a plasma and electron acceleration by relativistic electron plasma waves
Authors: Ebrahim N. A.
Published: July 2002

Experimental results are presented to demonstrate the principle of electron acceleration by relativistic electron plasma waves driven by the optical mixing of laser light in a plasma. Electrons injected at 12.5 MeV have been accelerated to 29.0 MeV over a plasma length of approximately 1 cm. This corresponds to an effective accelerating electric field gradient of approximately 1.7 GeV/m.
1/f noise produced by the random motion of the carriers crossing potential barriers in semiconductors
Authors: Yoshida Hiromichi , Yoshida Masanori , Shinoda Tsutomu , Saito Ihoe
Published: July 2002

A new model for 1/f noise is discussed. When carriers in a semiconductor are separated by a potential barrier into two groups, some of the carriers climb over the barrier and move into the other group as a series of random events. If one group is in a trap, the number of the carriers in the trap varies with time. The probability of the occurrence of the first return to the initial state is in inverse proportion to the cube root value of the number of random events. The number of carriers is proportionate to the electric charge. The charge induces change in the resistance in the local area near the trap. The area is so small that the semiconductor shows the small resistance change of a square wave form. The distribution of the random square wave is represented by the Poisson distribution and its autocorrelation function has a Lorentzian spectrum. The characteristic of first return to the initial state shows that the probability of the Lorentzian spectrum is in inverse proportion to the wavelength. A 1/f spectrum is obtained by the superposition of the spectra.
Thermal reduction of KTiOPO4 single crystals
Authors: Martín M. J. , Bravo D. , Solé R. , Díaz F. , López F. J. , Zaldo C.
Published: July 2002

KTiOPO4 (KTP) samples heated in vacuum at temperatures in the 400–650 °C range show a broad optical absorption similar to that observed by H2 reduction. The position of the maximum depends on the reduction degree. The transparency of the sample is recovered by heating in air at high temperature (600 °C). Vacuum annealing leads to the reduction of Ti4+ to Ti3+ and also to the reduction of Fe, W, and Rh impurities present in the samples, as inferred from electron paramagnetic resonance measurements. X-ray irradiation at 15 K induces an optical absorption peaking at 585 nm. This absorption has been ascribed to the superposition of the 2T2→2E transition of Ti3+ in the two different Ti sites of the lattice. It is suggested that the absorption observed in vacuum-reduced samples consists of the overlapping of the latter contribution and a charge transfer band of Fe-Ti pairs. A loss of K and P ions has been observed after the annealing of KTP in vacuum at 800 °C forming a surface layer that scatters light. Moreover, the K and P loss decreases the optical absorption induced at lower temperature (T<650 °C).
High-resolution lifetime mapping using modulated free-carrier absorption
Authors: Glunz Stefan W. , Warta Wilhelm
Published: July 2002

Modulated free-carrier absorption (MFCA) is introduced as a novel contactless lifetime mapping technique with high spatial resolution. The advantages of MFCA mapping as compared to other methods are discussed. Examples of lifetime maps on multicrystalline silicon are presented. Solar cells fabricated from identical wafers have been investigated using light beam induced current mapping. Excellent agreement between structures obtained in the measured lifetime and in the current maps was observed. In addition, a quantitative comparison with diffusion lengths determined by local internal quantum efficiency evaluations is presented.
Effect of energetic particle bombardment during sputter deposition on the properties of exchange-biased spin-valve multilayers
Authors: Kools J. C. S.
Published: July 2002

The effect of energetic particle bombardment during sputter deposition on the physical (magnetoresistance and interlayer coupling) and microstructural (roughness and interface thickness) properties of exchange-biased spin-valve multilayers is investigated. An increasing pressure leads, through enhanced stopping of energetic particles by collisions with the background gas, to a decrease of the interfacial intermixing by collisions during growth, and to a more rough, void-rich structure. These microstructural changes lead to an increase of the transmissivity of the interfaces for conduction electrons, as well as to an increase of the ferromagnetic interlayer coupling with increasing pressure.
A reflectance anisotropy spectroscopy study of molecular sulfur adsorption on the GaAs(100) surface
Authors: Hughes G. , Springer C. , Resch U. , Esser N. , Richter W.
Published: July 2002

The interaction of molecular sulfur with the GaAs(100) surface has been investigated by reflectance anisotropy spectroscopy (RAS). The use of arsenic-capped GaAs(100) surfaces provided a means to study the interaction of sulfur with both the arsenic-rich (2×4) and gallium-rich (4×1) surface reconstructions. A sulfur flux was generated in ultra-high-vacuum (UHV) by the thermal decomposition of silver sulfide. The room-temperature deposition of a 1–2 monolayer saturation coverage of sulfur on both arsenic- and gallium-rich surfaces produces a (1×1) low-energy electron-diffraction pattern. This surface displays a strongly anisotropic optical response with RAS spectra which contain two clear features at 3.5 and 5.2 eV. These features become more pronounced as the sulfur-covered surface is annealed up to 500 °C where the surface displays a (2×1) reconstruction. The origin of these spectral features is believed to be due to optical transitions related to the sulfur dimers which are formed on this surface. The extent of the reduction in surface band bending induced by the sulfur coverage can be monitored by measuring the magnitude of the linear electro-optic feature which appears prominently in the RAS spectra of high-doped GaAs samples.
The role of texture in the electromigration behavior of pure aluminum lines
Authors: Knorr D. B. , Rodbell K. P.
Published: July 2002

The effects of microstructure on electromigration behavior were evaluated in three nominally 1 μm thick pure aluminum films, which were tested at temperatures from 423 to 523 K. The three Al films had essentially the same grain structure but different variants of an 〈111〉 texture. Texture had a very strong effect on the electromigration behavior in ∼2 μm wide polycrystalline lines, where both a reduced fraction of randomly oriented grains and a tighter 〈111〉 distribution increased the electromigration lifetime. The apparent activation energy for electromigration decreased as the texture strengthened. The near bamboo microstructure of 0.5 μm narrow lines showed extensive orientation clustering with an unusually high proportion of low angle boundaries in the most strongly 〈111〉 textured film. The electromigration damage in both 2 and 0.5 μm wide lines was correlated with the types of flux divergence sites in each film. The texture impacts the character of the grain boundaries and interfaces which control the mass transport during electromigration. A weaker texture has more juxtaposed ‘‘fast’’ and ‘‘slow’’ diffusivity grain boundaries and interfaces, which results in faster mass transport, more flux divergence sites, and a more rapid accumulation of damage.
Physics of high-intensity nanosecond electron source: Charge limit phenomenon in GaAs photocathodes
Authors: Herrera-Gómez A. , Vergara G. , Spicer W. E.
Published: July 2002

GaAs negative electron affinity cathodes are used as high-intensity, short-time electron source at the Stanford Linear Accelerator Center. When the cathodes are illuminated with high-intensity laser pulses draw peak currents that are extremely high, typically of tens of Amperes. Because of the high currents, some nonlinear effects are present. Very noticeable is the so-called charge limit (CL) effect, which consists of a limit on the total charge in each pulse; that is, the total bunch charge stops increasing as the light pulse intensity increases. The CL effect is directly related to a photovoltage built up in the surface as a consequence of the photoelectrons coming from the bulk. We discuss possible ways to minimize the formation of the surface photovoltage.
A model of impact ionization due to the primary hole in silicon for a full band Monte Carlo simulation
Authors: Kunikiyo Tatsuya , Takenaka Masahiro , Morifuji Masato , Taniguchi Kenji , Hamaguchi Chihiro
Published: July 2002

The rate of impact ionization due to the primary hole in silicon is numerically derived from pseudo-wave-functions and realistic energy band structure based on a nonlocal empirical pseudopotential method including the spin-orbit interaction. The calculated impact-ionization rate SII [s−1] is well fitted to an analytical formula with a power exponent of 3.4, indicating a soft threshold of the impact ionization rate: SII [s−1]=1.14×1012 [s−1 eV−3.4]×(ε [eV]−1. 49 [eV])3.4, where ε [eV] is the energy of the primary hole relative to the valence band edge. The soft threshold originates from the complexity of the silicon band structure. The calculated impact-ionization rate shows strong anisotropy at low hole energies (ε<3 eV), while it becomes isotropic at high hole energies, indicating the isotropy of the joint density of states at high energies. Numerical calculation also makes it clear that average energies of secondary generated carriers ε̄ depend linearly on primary hole energies at the moment of their generation. The calculated average energies of secondary generated holes ε̄(hole) [eV] and electrons ε̄(electron) [eV] are well fitted to linear functions of primary hole energy ε [eV]: ε̄(hole) [eV]=3.75×10−1 ε [eV]−4.76×10−1 [eV],ε̄(electr on) [eV]=−3.14×10−1 ε [eV]−8.60×10−1 [eV]. The standard deviations of secondary generated carriers are also presented.
Efficiency of TiN diffusion barrier between Al and Si prepared by reactive evaporation and rapid thermal annealing
Authors: Gagnon G. , Currie J. F. , Brebner J. L. , Darwall T.
Published: July 2002

TiN layers prepared by reactive evaporation and rapid thermal annealing were tested as diffusion barrier between Al and Si. First, Rutherford backscattering spectroscopy (RBS) analysis of Al/Ti(N)/Ti/Si and Al/Ti(N)/Si multilayer structures showed that Si does not diffuse out up to a sintering temperature of 550 °C. However, as the temperature increases beyond 450 °C, Al starts to react with TiN. This reaction leaves less than half the TiN original thickness after a 30 min anneal at 550 °C. The RBS results indicate that TiN, crystallized at a temperature around 850 °C, forms a good barrier between Al and Si. Electrical measurements on various microelectronic devices were performed to verify this. Annealing of Ti(N) at 900 °C leads to a breakdown of p-MOS (metal–oxide–semiconductor) devices while n-MOS devices still work properly. Annealing at 800 °C gives good results on both MOS types except that the contact resistance of a p-type resistor is higher than desired. The electrical circuit failure is mainly due to dopant loss from the active area of the device into the titanium silicide which forms during the rapid thermal annealing at 800 or 900 °C of the deposited Ti(N) layers.
The Si/Pd ohmic contact to n-GaP based on the solid phase regrowth principle
Authors: Park Moon-Ho , Wang L. C. , Dufner D. C. , Deng Fei , Lau S. S. , Tan I. H. , Kish F.
Published: July 2002

A Si/Pd ohmic contact scheme to n-GaP (n∼5×1017 cm−3) was investigated using Rutherford backscattering spectrometry, transmission electron microscopy, energy dispersive x-ray spectrometry, and the Cox–Strack measurement. Contact resistivities of ∼2×10−4Ω cm2 are obtained for annealing temperatures ranging from 350 to 650 °C. This contact is thermally stable at 550 °C. The ohmic contact formation mechanism is rationalized in terms of the solid phase regrowth of an n+ layer and the solid phase epitaxy of a Si layer.
Evidence of local lattice distortions in La1−xSrxMnO3 provided by pulsed neutron diffraction
Authors: Louca Despina , Egami T.
Published: July 2002

The pulsed neutron powder diffraction study of La1−xSrxMnO3 reveals that the local atomic structure is significantly different from the long range structure, and these differences are important in understanding their properties. Even though the crystal structure suggests that the Jahn–Teller (JT) distortion disappears quickly with Sr doping, the analysis by the pair distribution function technique indicates that locally JT distortions are always present. Doped charge carriers induce local anti-JT distortions and disrupt the long range JT distortion. In the paramagnetic phase, such anti-JT distortions are represented by Mn4+ ions, corresponding to small polarons. Below Tc charge carriers are delocalized, but still induce local lattice distortions, giving rise to an inhomogeneous metallic state. The effects of these local distortions are discussed.
Stress in dc sputtered TiN/B–C–N multilayers
Authors: Fayeulle S. , Nastasi M.
Published: July 2002

Stress in crystalline TiN/amorphous B–C–N multilayered thin films has been determined by the substrate curvature technique. It is established that the total stress is dependent on the number of deposited bilayers and on the bilayer repeat length. The linear relationship between the stress and the inverse of the bilayer repeat length allows calculation of the value of the interface stress. It is found to be compressive with a value between 1.79 and 2.46 J/m2, depending on the calculation method. An apparent dependence between the interface stress and the total thickness of the multilayer film is observed. It is interpreted as an additional relaxation due to an increase of the roughness of the interfaces when the number of deposited bilayers is increased.
Size quantization and interfacial effects on a novel γ-Fe2O3/SiO2 magnetic nanocomposite via sol-gel matrix-mediated synthesis
Authors: Zhang Lei , Papaefthymiou George C. , Ying Jackie Y.
Published: July 2002

Novel isolated magnetic single-domain γ-Fe2O3 nanoclusters have been prepared by coprecipitation of ferrous and ferric salts encapsulated within sol-gel derived silica (SiO2). The nonmagnetic SiO2 coating formed by hydrolysis and polycondensation of tetraethoxysilane on the surface of the Fe2O3 nanoclusters provides a means for thermally stable dispersion of Fe2O3 clusters. The precipitated particles coated with SiO2 are spherical with 4–5 nm diameters. Surface and strain effects played a critical role in determining the overall magnetic behavior of the spherical single-domain particles. Superparamagnetic behavior was observed by superconducting quantum interference device magnetometry and Mössbauer spectroscopy. Superparamagnetic barrier energies and the low-temperature coercivities were modified through cluster/support interface microstructure manipulation. The optical studies showed the absorption edge of the nanocomposites to be slightly blue shifted in the UV–VIS spectrum range when compared to that of bulk γ-Fe2O3. This was attributed to the combined effects of the quantum confinement of the nanocrystalline γ-Fe2O3 clusters and the stress present at the particle/support interface. The magnetic properties can be manipulated via the matrix microstructure, synthesis conditions and thermal treatment.
Nitridation of fine grain chemical vapor deposited tungsten film as diffusion barrier for aluminum metallization
Authors: Chang Kow-Ming , Yeh Ta-Hsun , Deng I-Chung
Published: July 2002

A novel tungsten nitride (WNx) film for diffusion barrier applications has been prepared by nitridation of a fine grain chemical vapor deposited tungsten (CVD-W) film. The fine grain CVD-W is deposited at 300 °C in a low pressure chemical vapor deposition reactor with a SiH4/WF6 flow rate of 12.5/5 sccm under a total gas pressure of 100 mTorr. The subsequent nitridation process is executed in nitrogen plasma at 300 °C without breaking vacuum. The thickness of WNx layer as examined by secondary ion mass spectroscopy is 50 nm after 5 min exposure to nitrogen plasma. X-ray photoelectron spectroscopy spectra shows that the atomic ratio of tungsten to nitrogen in WNx layer is 2:1. According to the analysis by Auger electron spectroscopy and the measurement of n+p junction leakage current, the Al/WNx/W/Si multilayer maintains excellent interfacial stability after furnace annealing at 575 °C for 30 min. The effectiveness of W2N barrier is attributed to stuffing grain boundaries with nitrogen atoms which eliminates the rapid diffusion paths in fine grain CVD-W films.
SmCo/Cr bilayer films for high-density recording media
Authors: Takei S. , Shomura S. , Morisako A. , Matsumoto M. , Haeiwa T.
Published: July 2002

The magnetic properties of a SmCo layer on a Cr underlayer, which was prepared by various Ar gas pressure (PAr), were studied. A single line appeared in each X-ray diffraction diagram and its intensity became strong when PAr was decreased from 1.06 to 0.13 Pa. The microstructure observed by using atomic force microscopy showed that the surface morphological structure of Cr underlayers depended on PAr and the surface of the Cr underlayer became smoother as PAr was decreased, while the surface and the grain of the SmCo layer on the Cr underlayer were independent of PAr. The grain size of SmCo layers was as small as 30 nm with the surface roughness of about 1 nm. The coercivity, the squareness ratio, and the coercivity squareness ratio of the SmCo layer on the Cr underlayer prepared at 0.13 Pa were 155 kA/m, 0.92 and 0.92, respectively. Those values suggest that an easy axis of magnetization for the SmCo layer is in plane and the switching field distribution is very small. Although the crystal structure of the SmCo layer has not been clarified yet, it was found that the magnetic properties of SmCo layers can be controlled by the crystal structure of the Cr underlayer and SmCo/Cr bilayer films are promising materials for the ultrahigh density recording media.
Two layer model for photothermal radiometry applied on semiconducting thin films
Authors: Nestoros M. , Karmiotis Y. , Christofides C.
Published: July 2002

A two layer model has been developed in order to study the dependence of the photothermal radiometric signal on the optoelectronic and thermophysical properties of a two layer semiconducting sample. In the following theoretical analysis, both thermal and electronic contributions have been used in order to interpret the infrared emission of a semiconducting sample under the influence of a pump modulated laser beam. The potential of the above model towards a quantitative analysis of photothermal radiometric experimental data, for the extraction of thermal and electronic parameters of the semiconducting thin film and substrate, has been examined. Experimental evidence of the quality of this model has also been presented.
Yttrium oxide films prepared by pulsed laser deposition
Authors: Zhang Shaoqiang , Xiao Rongfu
Published: July 2002

Yttrium oxide, Y2O3, films were prepared by pulsed laser deposition in the presence of oxygen (O2) gas. The microstructures of these films were found to be highly dependent on the deposition temperature and the amount of O2 gas used during the deposition process. X-ray diffraction (XRD) analysis showed that the Y2O3 films transformed from amorphous to polycrystalline form when the deposition temperature was increased to 350 °C at an O2 pressure of 0.01 mbar, and an extremely strong XRD peak originated from Y2O3(111) orientation was observed when the deposition temperature was increased above 400 °C. However, during the deposition at a fixed temperature (650 °C), the Y2O3 films became amorphous when the O2 pressure was successively increased. For the films deposited on either fused silica or silicon substrate between 150 and 650 °C, very smooth surface morphologies with an average surface roughness of 0.4–19 nm have been observed by an atomic force microscopy. UV/Visible spectrometer and Fourier transform infrared analysis have shown that the as-grown Y2O3 films are highly transparent from the UV (with a band gap 5.6 eV) to the middle infrared region (∼15 μm). The refractive index of the Y2O3 films measured by a spectroscopic ellipsometer changed from 1.9 to 2.15 with decreasing wavelength. Furthermore, a good waveguiding property has been observed in the as-grown Y2O3 films. The dielectric constant of these Y2O3 films measured by a standard ferroelectric test system is between 11 and 18 depending on the film thickness. A C–V measurement has confirmed that these Y2O3 films are indeed good for metal-insulator-semiconductor device applications.
Domain-wall motion in random potential and hysteresis modeling
Authors: Pasquale M. , Basso V. , Bertotti G. , Jiles D. C. , Bi Y.
Published: July 2002

Two different approaches to hysteresis modeling are compared using a common ground based on energy relations, defined in terms of dissipated and stored energy. Using the Preisach model and assuming that magnetization is mainly due to domain-wall motion, one can derive the expression of magnetization along a major loop typical of the Jiles–Atherton model and then extend its validity to cases where mean-field effects and reversible contributions are present.
High coercivity SmCo based films made by pulsed laser deposition
Authors: Cadieu F. J. , Rani R. , Qian X. R. , Chen Li
Published: July 2002

Films of SmCo based materials exhibiting high intrinsic coercivities and smooth hysteresis loops have been prepared by pulsed laser deposition (PLD) onto moderately heated substrates. Films directly crystallized from SmCo5 targets onto 375 °C substrates exhibited a maximum Hc=11.3 kOei at a pulse repetition rate of 10 Hz with lower coercivities for both lower and higher pulse repetition rates. In the present case the films were deposited onto polycrystalline substrates. The films exhibited a very small grain size of less than 1 μm diameter, were mirrorlike, and shadow deposited films were relatively particulate free under scanning electron microscope examination. Shadowed PLD deposition was used for the best films. Laser wavelengths of 193 and 248 nm were used with pulse repetition rates from 5 to 50 Hz. Films grown without shadowing exhibited a great deal of particulate contamination. The hysteresis loops of such nonshadowed films were constricted and exhibited drops in the 4πM values upon demagnetization. To our knowledge this is the first reporting of high coercive force SmCo based films deposited by PLD exhibiting single phase type hysteresis loops.
Behavior of soft piezoelectric ceramics under high sinusoidal electric fields
Authors: Kugel V. D. , Cross L. E.
Published: July 2002

The behavior of piezoelectric, dielectric, and elastic characteristics of soft piezoelectric lead zirconate titanate (PZT) ceramics was investigated under sinusoidal electric field E applied along the poling direction and under mechanical stress-free conditions for a frequency range 10 Hz–10 kHz. Electrical displacement D3 along the poling direction, mechanical strain S1 in the direction perpendicular to the poling direction, and the resonant frequency νr of electromechanically uncoupled bending vibrations of polarized plates were measured. Commercial ceramics PZT5H, 3203HD, and PKI550 with chemical composition near the morphotropic phase boundary were used in the study. It was found that the amplitude and phase of the first harmonic of the relative strain S1(1)/Em and of the relative electrical displacement D3(1)/Em increase similarly with increasing amplitude Em of the electric field if the amplitude is less than coercive field. The corresponding increase in the square of the resonant frequency is more moderate. The dependencies are described well by linear functions except for low electric fields. The functions S1m(1)/Em and D3m(1)/Em demonstrate frequency dispersion as well. Relative amplitude of the second harmonic of the electrical displacement, D3m(2)/D3m(1), which is polar, also increases almost linearly with increasing Em. The relative third harmonic D3m(3)/D3m(1) demonstrates saturationlike behavior. By means of the electric pulse technique, it was found that irreversible changes in the remnant polarization take place even at electric fields much smaller that the coercive field. A mathematical model of a hysteretic transducer, describing the electric field dependence of electromechanical properties of soft piezoelectric PZT ceramics, was suggested. According to this approach, the response depends not only on the instantaneous magnitude of the input signal (e.g., electric field) but also on its past extreme values. It was shown that the experimental Rayleigh law is a particular case of the suggested approach. The model relates directly electric field dependencies of complex piezoelectric coefficient d31(Em) and S1(1)/Em, of complex dielectric permittivity ε33T(Em) and D3(1)/Em, and of the amplitude of elastic compliance s11E(Em) and νr2. Application of the model to experimental data showed that the model describes well the first three complex harmonics of D3 and the irreversible change in the remnant polarization. Physical causes of the observed behavior were analyzed. As an alternative to the model based on the 90° polarization reorientation and tetragonal/rhombohedral phase boundary motion, a new approach was suggested. In this model, the observed hysteretic changes in the electromechanical properties are assumed to be caused by the electric field dependency of the mechanical stress acting at interdomain boundaries in the partly constrained crystallites of these ceramics.
The detailed balance principle and the reciprocity theorem between photocarrier collection and dark carrier distribution in solar cells
Authors: Rau Uwe , Brendel Rolf
Published: July 2002

It is shown that a recently described general relationship between the local collection efficiency of solar cells and the dark carrier concentration (reciprocity theorem) directly follows from the principle of detailed balance. We derive the relationship for situations where transport of charge carriers occurs between discrete states as well as for the situation where electronic transport is described in terms of continuous functions. Combining both situations allows to extend the range of applicability of the reciprocity theorem to all types of solar cells, including, e.g., metal-insulator-semiconductor-type, electrochemical solar cells, as well as the inclusion of the impurity photovoltaic effect. We generalize the theorem further to situations where the occupation probability of electronic states is governed by Fermi–Dirac statistics instead of Boltzmann statistics as underlying preceding work. In such a situation the reciprocity theorem is restricted to small departures from equilibrium.
Identification of the relation between the material parameters in the Preisach model and in the Jiles–Atherton hysteresis model
Authors: Dupré Luc R. , Van Keer Roger , Melkebeek Jan A. A.
Published: July 2002

In this article the relation between the material parameters appearing in the Preisach model and those entering the Jiles-Atherton model is discussed. Emphasis is on the variation of the anhysteretic curve and on the magnetization dependency of the pinning parameter, when changing the Preisach distribution function. The discussion rests upon the consideration of the shape of the MH loop on the one hand and upon the identification of the instantaneous loss dissipation on the other hand. The techniques outlined are applied to silicon iron alloys and are compared with results from measurements.
Ferromagnetic resonance in granular thin films
Authors: Kakazei G. N. , Kravets A. F. , Lesnik N. A. , Pereira de Azevedo M. M. , Pogorelov Yu. G. , Sousa J. B.
Published: July 2002

A theoretical analysis has been done of the effects of granule size, shape, orientation, and concentration and the temperature effects on the ferromagnetic resonance (FMR) field Hr in granular thin films. The granular CoxAg1−x thin films with 0.2<x<0.85 (the volumetric filling factor 0.17<f<0.83) were prepared by electron-beam oblique coevaporation. Our room temperature FMR data show an abrupt change in the Hr(f) dependence at f=fp≈0.3, the percolation point for this system (as evidenced from the magnetization and magnetoresistance measurements). This change is associated to the development of great clusters [ferromagnetic (FM) phase] beside single granules [superparamagnetic (SPM) phase] at f>fp. For the Co–Ag system, persistence of a considerable SPM fraction is revealed by the superconducting quantum interference device data up to the highest f, and the effect at f=fp consists in a discontinuous jump of the Hr(f) slope. Otherwise, the FMR data for granular Fe–SiO2 films reveal a discontinuous jump in Hr itself at f≈0.28. The latter can indicate a 1st kind-like magnetic percolation transition in that material. Thus FMR studies can effectively probe the internal structural processes in granular magnetic systems.
Thermal stability of sintered and bonded rare-earth magnets
Authors: Kato Yoshio
Published: July 2002

One of most important issues of magnets for automobiles is thermal stability. The aim of the present work is to make clear the available temperature limit of sintered and bonded magnets for automobile applications. Thermal stability was determined by the critical temperature of 3% irreversible flux loss (T−3%φ) under thermal cycles. For instance, the T−3%φ of sintered NdFeB magnets (Pc=0.5) with the intrinsic coercivity of 1600, 1920, and 2240 kA/m, were 393, 423, and 453 K, respectively. On the other hand, the T−3%φ of HDDR-NdFeB (HcJ=960 kA/m) and SmFeN (HcJ=560 kA/m) bonded magnets (Pc=2) were about 353 K.
Effect of underlayer thickness on magnetic properties of SmCo film
Authors: Takei Shigeto , Morisako Akimitsu , Matsumoto Mitsunori
Published: July 2002

It is well known that the Cr underlayer plays significant role in the magnetic properties of Co alloy film. In this study, the effects of the underlayer materials such as Cr, Mo, W, W/Cr, and Al and their thickness on the magnetic properties of SmCo films were studied. In the x-ray diffraction diagrams of the SmCo/Cr film and the SmCo/Mo film, only (110) line of body-centered-cubic crystal structure was observed, while diffraction lines from SmCo phase could not be observed. The oval shaped grains were observed on the surface of Cr underlayer and the Mo underlayer when the thickness was thicker than 100 nm. The coercivity of the SmCo/Cr film and the SmCo/Mo film with thickness over 100 nm was higher than 3 kOe and the squareness ratio and the coercivity squareness ratio was above 0.8 and 0.9, respectively. These results indicate the Cr underlayer and the Mo underlayer are suitable for SmCo layers in order to increase the coercivity and the SmCo/Cr film and the SmCo/Mo film are good candidates for high density recording media.
Ferromagnetic resonance investigation of surface anisotropy distribution in amorphous glass-covered wires
Authors: Chiriac H. , Colesniuc C. N. , Óvári T.-A. , Castano F. J.
Published: July 2002

The distribution of the magnetic anisotropy in the surface region of amorphous glass-covered wires with positive and nearly zero magnetostriction is analyzed by means of microwave absorption ferromagnetic resonance (FMR). The surface layer of as-cast positive magnetostrictive amorphous glass-covered wires displays an axial anisotropy, which changes to radial after partial or complete removal of the glass cover. The as-cast nearly zero magnetostrictive amorphous glass-covered wires display a circumferential anisotropy in their surface layer, its direction being maintained even after partial or complete glass removal, but its strength slightly increases with glass removal. The results are explained by taking into account the most recent results on the domain structure of these wires, as well as the skin effect that occurs at microwave frequencies.
Local current distribution in a ferromagnetic tunnel junction measured using conducting atomic force microscopy
Authors: Ando Y. , Kameda H. , Kubota H. , Miyazaki T.
Published: July 2002

The local electrical properties were measured simultaneously with the topography for a Ta(50 Å)/Fe20Ni80(50 Å)/IrMn(150 Å)/Co(50 Å)/Al(13 Å)-oxide junction. The electrical image showed the contrast with around a few nm lateral size and a strong correlation with the topographical image was not observed. In the local current–voltage characteristics, data within the bias voltage of ±1.5 V were fitted well to Simmon’s equation and we obtained the barrier height Φ=1.9 eV and the thickness d=12 Å. On the other hand, data with the bias voltages higher than 3 V were fitted well to Fowler–Nordheim equation. The histogram of current density was calculated by taking into consideration a Gaussian distribution of the barrier thickness and the height. The distribution of the barrier height can explain the experimental result realistically.
Spectroscopic studies of nickel and iron clusters at 12 K
Authors: Nour E. M. , Alfaro-Franco C. , Gingerich K. A. , Laane J.
Published: July 2002

The electronic and far-infrared spectra of nickel and iron clusters trapped in argon matrices at 12 K are reported. The ν3 antisymmetric stretching frequencies for Ni3 and Fe3 were observed for the first time at 198 and 180 cm−1, respectively. The fr and frr force constants for Ni3 are calculated to be 0.80 and 0.13 mdyn/Å, respectively. For Fe3 these are 0.67 and 0.13 mdyn/Å.
Temperature dependence of the Raman spectrum of ammonia solid I
Authors: Nye C. L. , Medina F. D.
Published: July 2002

The Raman spectrum of ammonia solid I in the lattice and intramolecular regions has been studied at temperatures between 93.6 and 213.5 K. The three most intense lines in the lattice region, one librational and two translational modes, have frequencies and linewidths whose temperature dependence can be explained by anharmonic interactions. In the intramolecular region, all bending modes studied have unusually large decreases in frequency with temperature. However, there is no indication in support of the recently reported critical-like behavior of the compressibility near the melting line.
Deposition of mass selected silver clusters in rare gas matrices
Authors: Harbich W. , Fedrigo S. , Meyer F. , Lindsay D. M. , Lignieres J. , Rivoal J. C. , Kreisle D.
Published: July 2002

We report on the successful ‘‘soft landing’’ of size selected silver dimers and trimers in solid krypton matrices. Silver cluster cations, produced by sputtering, were mass selected in a quadrupole mass filter and then codeposited with krypton on a cooled sapphire or CaF2 window in the presence of low energy electrons. Neutralized cluster samples were interrogated in situ by excitation and fluorescence spectroscopy. Deposition of slow (≤20 eV) silver dimer cations gave rise to strong excitation bands (centered at λ=275 and 390 nm) from Ag2 plus the characteristic triplet signal of the atom. The spectra imply that fewer than 25% of the dimers were fragmented during the neutralization and deposition steps. In similar experiments with Ag3 we were able to assign trimer absorption bands at 331, 364, 402, 421, 458, and 514 nm and identify characteristic emission features at 381, 560, and 626 nm.
Equation-of-state, shock-temperature, and electrical-conductivity data of dense fluid nitrogen in the region of the dissociative phase transition
Authors: Nellis W. J. , Radousky H. B. , Hamilton D. C. , Mitchell A. C. , Holmes N. C. , Christianson K. B. , van Thiel M.
Published: July 2002

The dissociative phase transition of fluid nitrogen at pressures in the range 30–110 GPa (0.3–1.1 Mbar), temperatures in the range 4000–14 000 K, densities up to 3.5 g/cm3, and internal energies up to 1 MJ/mol was investigated by shock compression. Equation-of-state, shock-temperature, and electrical-conductivity experimental data are presented and analyzed in detail.
On obtaining interatomic potentials from multiproperty fits to experimental data
Authors: Keil Mark , Danielson Laurie J. , Dunlop Peter J.
Published: July 2002

High-resolution differential cross section (DCS) and accurate new limiting diffusion measurements for all the unlike-pair He+rare-gas systems are combined in constructing new multiproperty interatomic potentials. The new potentials predict most properties available for these systems, including independent high-resolution DCS measurements. Remaining discrepancies with earlier multiproperty potentials for HeKr and HeXe are attributed to incompatibilities among data sets used in the multiproperty fitting procedure. It is also shown that the 5% difference in well depths between two recently proposed potentials for HeXe is due to some of the data used in constructing these potentials, and that the DCS measurements of those studies are mutually consistent. Finally, the present potentials are refined slightly for agreement with high-energy cross section measurements. At the present level of reliability for DCS and dilute-gas data, it seems likely that high-resolution DCS and accurate (limiting) diffusion measurements will assist in determining He+molecule potentials. These two properties are particularly useful because they are independent of uncertainties in the corresponding molecule+molecule potentials.
Molecular dynamics simulation of adsorption of ions from aqueous media onto charged electrodes
Authors: Glosli James N. , Philpott Michael R.
Published: July 2002

Molecular dynamics simulation of 216 water molecules (ST2 model) between charged flat electrodes 2.362 nm apart showed layering with a few molecules at each surface that broke H bonds with the bulk and oriented their charges towards the electrode. Compared to uncharged electrodes, the atomic and molecular distributions were unsymmetric. When a lithium and an iodide ion were substituted at random for two water molecules, the iodide ion contact adsorbed on the anode with no water molecules between it and the electrode. The iodide ion appeared weakly solvated on the solution side to water molecules that preferred to engage in hydrogen bonding with the network of the bulk solvent. In contrast, the lithium ion adsorbed without losing its primary solvation shell of six water molecules and was never observed further than two water molecules removed from the electrode. Its average position corresponded to an ion supported on a tripod of three waters. The average solvation number was not changed upon adsorption in this configuration. These qualitative observations and some quantitative results afford striking confirmation on the one hand and new insight on the other of some aspects of the standard model of the adsorption of ions on electrode surfaces. Time durations for simulations were generally between 200 and 800 ps with a basic integration time step of 2 fs.
Theoretical aspects of higher-order truncations in solid-state nuclear magnetic resonance
Authors: Goldman M. , Grandinetti P. J. , Llor A. , Olejniczak Z. , Sachleben J. R. , Zwanziger J. W.
Published: July 2002

Recent experimental developments of high-resolution NMR in solids (for example, double rotation and dynamic-angle spinning) address the reduction of second-order line broadening effects, particularly in systems involving quadrupolar nuclei such as 23Na, 17O, 27Al, and 14N. However, some aspects of the theoretical description of these systems have not been clearly understood; in particular, the various procedures available to truncate the interactions give incompatible results. We present a general framework, based on static perturbative methods, which provides a natural procedure to derive the correct Hamiltonian for higher-order effects in irreducible tensor form. Applications of this method to coherent averaging techniques (sample motion or radio-frequency irradiation) are described and compared to previous treatments based on average Hamiltonian theory.