bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of melting and stability of ice 1h: Molecular-dynamics simulations of the SPC/E model of water
Authors: Gay S. C. , Smith E. J. , Haymet A. D. J.
Published: July 2002

Ice 1h is studied by molecular-dynamics simulations using the SPC/E model of water. The simulations were carried out in the constant stress, constant temperature ensemble, over a range of temperature and external pressure. By heating the system at 10 K intervals every 100 ps, we establish an upper bound for the stability of the ice 1h structure at 1 atmosphere to be below 260 K for the SPC/E model. The shape of the crystal lattice does not change significantly from the ideal hexagonal structure of ice 1h, even close to the melting transition. This is significant for future investigations of the ice–water interface using molecular simulations.
Copper precipitates in silicon: Precipitation, dissolution, and chemical state
Authors: McHugo Scott A. , Mohammed A. , Thompson A. C. , Lai B. , Cai Z.
Published: July 2002

The precipitation and dissolution of copper impurities at oxygen precipitates and stacking faults in silicon were studied using thermal budgets commensurate with standard integrated circuit processing. Additionally, in order to develop a better understanding of the dissolution process, we have obtained results on the chemical state of the copper precipitates. The goal of this work was to determine the feasibility of removing and maintaining copper impurities away from the active device region of an integrated circuit device by use of oxygen precipitates and stacking faults in the bulk of the material. Based on our results, we provide a basis for a predictive understanding of copper precipitation and dissolution in silicon and we discuss the feasibility of copper impurity control in silicon integrated circuit devices.
Direct method for monitoring two-beam coupling in photorefractive materials
Authors: Hall Jeffrey E. , Higgins Daniel A.
Published: July 2002

A method for directly monitoring two-beam coupling (2BC) in photorefractive materials is presented. This method allows accurate measurement of the gain and loss in the probe and pump beams, respectively, even in situations where substantial power is diffracted into higher order beams (i.e., for large grating spacings). Modulation of the pump beam at a frequency significantly greater than the grating decay rate, coupled with synchronous detection of the modulated probe beam signal, provides this information, automatically correcting for diffractive losses. The probe beam gain and pump beam loss are obtained without further correction. 2BC measurements are made on dye-doped photorefractive polymer-supported liquid crystal films to demonstrate the advantages of this method. The measurements are made for small grating spacings, in which little high-order diffraction is observed, and for large grating spacings for which there are several diffraction orders.
Passivation of defects at the SrTiO3/Si interface with H and H2
Authors: Browne R. J. , Ogryzlo E. A. , Eisenbeiser K. , Yu Z. , Droopad R. , Overgaard C.
Published: July 2002

A silicon surface covered with ∼150 Å of strontium titanium oxide was exposed to both atomic and molecular hydrogen at temperatures between 20 and 300 °C. A rf probe was used to continuously monitor changes in charge-carrier recombination centers at the SrTiO3/Si interface by following the steady-state photogenerated carrier concentration in the silicon. Independent passivation of interfacial defects was observed by both atomic and molecular hydrogen.
Creation and suppression of point defects through a kick-out substitution process of Fe in InP
Authors: Zhao Y. W. , Dong H. W. , Chen Y. H. , Zhang Y. H. , Jiao J. H. , Zhao J. Q. , Lin L. Y. , Fung S.
Published: July 2002

Indium antisite defect InP-related photoluminescence has been observed in Fe-diffused semi-insulating (SI) InP. Compared to annealed undoped or Fe-predoped SI InP, there are fewer defects in SI InP obtained by long-duration, high-temperature Fe diffusion. The suppression of the formation of point defects in Fe-diffused SI InP can be explained in terms of the complete occupation by Fe at indium vacancy. The InP defect is enhanced by the indium interstitial that is caused by the kick out of In and the substitution at the indium site of Fe in the diffusion process. Through these Fe-diffusion results, the nature of the defects in annealed undoped SI InP is better understood.
Study of light emission from GaN/AlGaN quantum wells under power-dependent excitation
Authors: Łepkowski S. P. , Suski T. , Perlin P. , Ivanov V. Yu. , Godlewski M. , Grandjean N. , Massies J.
Published: July 2002

We have performed a study of excitation power-dependent spectra of GaN/AlGaN single quantum wells (QWs). First, the experimental “blueshift” of the emission energy, due to screening of internal piezoelectric fields, was compared with the model calculations based on self-consistent solution of Schroedinger and Poisson equations. We found that, even for the highest applied levels of excitation power (2.5 MW/cm2), only 0.5×1012 cm−2 carriers were present in the QW layers. Second, we analyzed the evolution of power-dependent spectra of two single QW having different widths. For the thinner QW (2.1 nm), the peak corresponding to a QW photoluminescence (PL) emission dominates the entire spectrum in the whole range of the used excitation power. In the case of the wider QW (4.4 nm), for sufficiently high excitation power, we observe the effect of PL quenching. Using the rate equation model we show that the observed effect of the PL quenching can be associated with the reduction of exciton binding energy due to the many body interactions in the QW.
Low-temperature integration of lead-based ferroelectric capacitors on Si with diffusion barrier layer
Authors: Liu B. T. , Maki K. , Aggarwal S. , Nagaraj B. , Nagarajan V. , Salamanca-Riba L. , Ramesh R. , Dhote A. M. , Auciello O.
Published: July 2002

Ferroelectric lead zirconate titanate thin films have been integrated on silicon substrates using Ti–Al-based conducting diffusion barriers produced by sputter deposition. The microstructure of the Ti–Al barrier layer was systematically altered through changes in the sputtering conditions, specifically the power density and deposition pressure. We find that the crystallinity of the Ti–Al film strongly correlates with sputtering power density and ambient i.e., it is amorphous at low power density and/or high deposition pressure, and polycrystalline at high power density and/or low deposition pressure. Electron energy loss spectroscopy studies demonstrate that the amorphous Ti–Al (a-Ti–Al) films contain a higher concentration of dissolved oxygen than crystalline Ti–Al. A low temperature sol–gel process has been used to prepare Pb(Zr,Ti)O3 PZT films at 450 °C on conducting Si wafers with a-Ti–Al conducting barrier layer and La–Sr–Co–O top and bottom electrodes. The excellent ferroelectric properties obtained with the a-Ti–Al barrier provide a promising approach for integration of PZT-based capacitors with silicon transistor technology for the fabrication of nonvolatile ferroelectric memories.
Nonlinear characteristics of a cylindrical Cherenkov laser at millimeter wavelengths
Authors: Hirata A. , Yuse Y. , Shiozawa T.
Published: July 2002

Nonlinear characteristics of a cylindrical Cherenkov laser, which is composed of a dielectric-loaded coaxial waveguide and a hollow relativistic electron beam, are investigated with the use of particle simulation. The results obtained in this paper are compared with those for parallel plate and rectangular models. Numerical results show that, in the cylindrical Cherenkov laser, the electromagnetic (EM) wave grows exponentially in the longitudinal direction and reaches saturation, as is the case with the parallel plate and rectangular models. However, the efficiency of energy transfer from the electron beam to the EM wave in the cylindrical model is not in good agreement with that for the parallel plate model, especially for the case of a small radius of the inner conductor. Thus, we propose a modified parallel plate model whose growth characteristics are the same as those for the cylindrical model. With the use of the corresponding modified parallel plate model, one can calculate growth characteristics for the cylindrical model at a particular frequency more easily.
High spatial resolution grain orientation and strain mapping in thin films using polychromatic submicron x-ray diffraction
Authors: Tamura N. , MacDowell A. A. , Celestre R. S. , Padmore H. A. , Valek B. , Bravman J. C. , Spolenak R. , Brown W. L. , Marieb T. , Fujimoto H. , Batterman B. W. , Patel J. R.
Published: July 2002

The availability of high brilliance synchrotron sources, coupled with recent progress in achromatic focusing optics and large area two-dimensional detector technology, has allowed us to develop an x-ray synchrotron technique that is capable of mapping orientation and strain/stress in polycrystalline thin films with submicron spatial resolution. To demonstrate the capabilities of this instrument, we have employed it to study the microstructure of aluminum thin film structures at the granular and subgranular levels. Due to the relatively low absorption of x-rays in materials, this technique can be used to study passivated samples, an important advantage over most electron probes given the very different mechanical behavior of buried and unpassivated materials.
Simulation studies of the coplanar electrode and other plasma display panel cell designs
Authors: Veronis G. , Inan U. S.
Published: July 2002

A two-dimensional self-consistent simulation model is used to study the effect of the geometric parameters on the operating voltages and ultraviolet (UV) efficiency of a coplanar-electrode plasma display panel cell. It is found that in the standard coplanar-electrode geometry there is a tradeoff between high UV efficiency and low operating voltages as the electrode gap, or the parameters of the upper dielectric are varied, while variation of the sustain electrode width has no significant effect on either the operating voltages or UV efficiency. It is also found that wider discharge area results in higher efficiency. In addition, the effect of the insertion of floating electrodes in the upper dielectric is investigated. When floating electrodes are used, UV light is emitted in a more confined area, thus limiting cross talk with adjacent cells, while efficiency decreases by ∼8%. Finally, a self-erase discharge sustaining waveform is studied. Use of this waveform results in ∼17% increase in the UV efficiency.
The O(1D)+H2 reaction at 56 meV collision energy: A comparison between quantum mechanical, quasiclassical trajectory, and crossed beam results
Authors: Aoiz F. J. , Bañares L. , Castillo J. F. , Herrero V. J. , Martı́nez-Haya B. , Honvault P. , Launay J. M. , Liu X. , Lin J. J. , Harich S. A. , Wang C. C. , Yang X.
Published: July 2002

Quantum mechanical and quasiclassical trajectory reactive scattering calculations have been performed for the O(1D)+H2 (v=0,j=0) reaction on the Dobbyn–Knowles ab initio 1 1A′ and 1 1A″ potential energy surfaces (PES) at the mean collision energy Ecol=56 meV (1.3 kcal/mol) of a crossed beam experimental study based on H-atom Rydberg “tagging” time-of-flight detection. Novel data from this latter experiment are presented and compared with the theoretical results at the level of state-resolved integral and differential cross sections and product recoil energy distributions. A good overall agreement with small discrepancies is found between the experimental data and the results of the two theoretical approaches. The main conclusion of the present work is that the contribution of the ground state 1 1A′ PES to the global reactivity accounts for the experimental observations and that, at the title collision energy, the participation of the 1 1A″ PES in the reaction is negligible for all practical purposes.
Reduction of intensity from coatings on cathodoluminescent phosphors: MgO or Al2O3 on Y2O3:Eu or Y2SiO5:Tb
Authors: Thomes W. J. , Seager C. H. , Holloway P. H.
Published: July 2002

Coatings of MgO and Al2O3 were deposited on Y2O3:Eu and Y2SiO5:Tb field emission display phosphors by pulsed laser deposition. Steady-state and pulsed cathodoluminescence (CL) data were collected over a range of electron beam energies up to 4 keV. The reduced CL intensities from coated phosphors are consistent with a reduction in the energy of the incoming primary electrons. This energy loss can be attributed to inelastic collisions between the incident electron and the electrons of atoms in the coating layer. Monte Carlo simulations were used to verify the modeled results.
Control and analysis of ion species in N2 inductively coupled plasma with inert gas mixing
Authors: Bai K. H. , Lee D. S. , Chang H. Y. , Uhm H. S.
Published: July 2002

We control the ion density ratio of [N+]/[N2+] and investigate the relation between the ion ratio and the plasma parameters in inductively coupled plasma. We measure the electron energy distribution functions and the ion ratio in a N2/He,Ar,Xe mixture system as a function of mixing ratio. We can control the ion ratio from 0.002 to 1.4, and the ion ratio is a strong function of electron temperature. We can calculate the ion ratio using a simple model, and the obtained results agree well with the measured values in N2/He,Ar, but there is a large discrepancy in the N2/Xe discharge. The non-Maxwellian structure of the electron energy distribution functions may be the reason for the discrepancy.
Abnormal lattice effect on magnetic/transport phase diagram in La0.7−xLuxSr0.3MnO3 perovskites
Authors: Huang Yun-Hui , Luo Feng , Li Yong , Wang Zhe-Ming , Liao Chun-Sheng , Yan Chun-Hua
Published: July 2002

An anomalous dependence of the average ion radius 〈rA〉 on Curie temperature (TC) and metal-insulator (M-I) transition is obtained in La0.7−xLuxSr0.3MnO3 compared with the phenomenon observed by Hwang et al. [Phys. Rev. Lett. 75, 914 (1995)]. Little variation in TC is found when x⩽0.4; whereas a sharp drop in TC only occurs at x>0.4. Meanwhile, the M-I transition occurs at a much lower temperature than TC when x varies from 0.1 to 0.4. X-ray diffraction patterns show coexistence of rhombohedral and hexagonal lattice symmetry for the Lu-substituted manganites. We suggest that a magnetic inhomogeneity caused by different local distortion of the lattice around La3+ and Lu3+ ions should be responsible for the magnetic/transport abnormality.
Electrical properties of carbon nitride films on silicon
Authors: Konofaos N. , Evangelou E. K. , Logothetidis S. , Gioti M.
Published: July 2002

Carbon nitride (CNx) films grown onto n-type Si by rf magnetron sputtering at room temperature were studied by electrical measurements in order to identify the effects of nitrogen concentration on the electrical characteristics of the films. The CNx films, developed with various nitrogen concentrations in the plasma, showed very good insulating properties. The bulk-trapped charge was calculated, showing a dependence on the nitrogen content, indicating the existence of free charges inside the bulk. The dielectric constant of the films and the loss factor (tan δ) were examined as a function of frequency and found to differ with the relative increase of the nitrogen concentration. The examination showed that the films were suitable for use as insulators in metal-insulator-semiconductor devices.
Film structure and ferroelectric properties of vanadium-doped Sr0.8Bi2.3Ta2O9 thin films
Authors: Chen San-Yuan , Lan Bang-Chiang , Taso Chang-Sheng
Published: July 2002

Vanadium-doped strontium bismuth tantalate Sr0.8Bi2.3(Ta2−xVx)O9 (SBTV) (x=0–0.8) have been prepared on Pt/Ti/SiO2/Si substrates using a metalorganic decomposition method. Well-crystallized and dense SBTV films can be obtained at an annealing temperature as lower as 650–700 °C that can be attributed to the enhanced densification due to the addition of vanadium. With partial substitution of tantalum by vanadium up to x=0.15, a larger remanent polarization (2Pr) of 30.5 μC/cm2 can be obtained for the Sr0.8Bi2.3Ta1.85V0.15O9 film at 800 °C that is attributed to the larger grain size and increased “rattling space.” Furthermore, the vanadium substitution for tantalum ion can effectively reduce the leakage current density as lower as 5×10−8 A/cm2 at an applied electric field of 100 kV/cm because of the reduced mobility of charge carriers. However, the incorporation of vanadium does not cause appreciable negative effect on the fatigue endurance of Sr-deficient Sr0.8Bi2.3Ta2O9 films until more than 20 mol % (x=0.2) vanadium was added.
Magnetic resonance diffraction using the magnetic field from a ferromagnetic sphere
Authors: Barbic Mladen
Published: July 2002

The theory of magnetic resonance diffraction is developed for the case of a crystal in close proximity of a ferromagnetic sphere. Distinct spectral peaks in the magnetic resonance signal are discovered for the specific ferromagnetic sphere and magnetic field configurations, and the appearance of the peaks is a direct signature of the presence of discrete atomic sites in the crystal lattice. The positions of the spectral peaks are sensitive to the crystal unit-cell size, thereby providing a method for determination of the basic parameters of the crystal at the atomic scale. The appearance of the spectral peaks is explained, and the dependence of the magnetic resonance spectra on the sphere size and the angle of the sphere magnetization with respect to the sample surface is analyzed. Applications to the studies of crystals, thin films, and crystallites are reviewed, and potential measurement methods for the confirmation of the diffraction theory are proposed. The analysis suggests that the long-desired goal of detecting atomic resolution magnetic resonance diffraction is well within reach of current experimental techniques.
Luminescence of laterally ordered Ge islands along 〈100〉 directions
Authors: Vescan L. , Stoica T.
Published: July 2002

The optical properties of coherently strained, self-ordered Ge islands are analyzed in connection with their size distribution. The ordering was achieved by depositing Ge on Si mesas oriented parallel to 〈100〉 directions and grown by selective epitaxy on Si(001) using low pressure chemical vapor deposition. The spontaneous ordered nucleation of Ge islands along mesa edges is driven by the presence of tensile strain at the periphery of the mesas. All photoluminescence peaks of the islands as well as of the wetting layer are well resolved. The emission peaks of ordered islands could be separated from the emission of randomly distributed islands on the (001) plane by varying the width of the straight mesa lines. The peaks of ordered islands are narrower than from random islands in agreement with the atomic force microscopy analysis. This effect is due to the strong island–island interaction in the one-dimensional row. The emission is governed at low temperature by hole transfer from the wetting layer to the islands, and at higher temperature by hole transfer from the islands to the wetting layer.
The role of the OH species in high-k/polycrystalline silicon gate electrode interface reactions
Authors: Gougousi Theodosia , Kelly M. Jason , Parsons Gregory N.
Published: July 2002

In this letter, reactions occurring at the interface between polycrystalline silicon (poly-Si) and LaSiOx high-dielectric-constant (high-k) insulating layers are characterized using x-ray photoelectron spectroscopy. Dielectrics were formed by sputter deposition of metal on silicon, followed by oxidation at 900 °C. Amorphous silicon was deposited on top by plasma-enhanced chemical vapor deposition from silane, followed by anneal at 650–1050 °C. We show that if the dielectric layer is exposed to sufficient water vapor before polysilicon deposition, annealing at 1050 °C for 10 s is sufficient to completely oxidize ∼25 Å of deposited silicon. Minimal reaction is observed without deliberate water exposure. This demonstrates the importance of the dielectric surface condition in determining reactivity of high-k/polysilicon interfaces.
Cardiac arrhythmias and circle maps−A classical problem
Authors: Glass Leon
Published: July 2002

The periodic forcing of nonlinear oscillations can often be cast as a problem involving self-maps of the circle. Consideration of the effects of changes in the frequency and amplitude of the periodic forcing leads to a problem involving the bifurcations of circle maps in a two-dimensional parameter space. The global bifurcations in this two-dimensional parameter space is described for periodic forcing of several simple theoretical models of nonlinear oscillations. As was originally recognized by Arnold, one motivation for the formulation of these models is their connection with theoretical models of cardiac arrhythmias originating from the competition and interaction between two pacemakers for the control of the heart.
Recognition and classification of nonlinear chaotic signals
Authors: Wright Jon , Schult R. L.
Published: July 2002

We propose a method of identifying and classifying signals generated by nonlinear, chaotic processes even when there are other signals and noise present. The method compares probability densities constructed from signals with a library of known densities. We note that there are many different invariant densities that can be constructed and that the characteristic functional of these densities factorizes into a product of characteristic functionals. Each member of the product is the characteristic functional of one of the signals present. This factorization provides a means of identifying the presence of a particular signal. Simple examples are given to demonstrate the method.
Turbulent decomposition of chemical waves by spontaneously induced hydrodynamic oscillation
Authors: Miike H. , Müller S. C.
Published: July 2002

The dynamic evolution of a chemical reaction–diffusion pattern and its interaction with hydrodynamic flow is investigated by two-dimensional velocimetry and spectrophotometry based on microscope video imaging techniques. Oscillatory deformation and turbulent decomposition of chemical wave fronts are observed which are induced by a pronounced oscillatory flow excited spontaneously in a Belousov–Zhabotinsky solution layer with a free surface.
Monitoring changes in time of chaotic nonlinear systems
Authors: Wright Jon
Published: July 2002

We extend our method for classifying signals from chaotic nonlinear dynamical systems to the problem of monitoring chaotic nonlinear dynamical systems with the goal of detecting that the state of a system has changed. One potential application would be to systems where the changes are not easily detectable by spectral analysis or other linear techniques. The method is expected to be most useful in comparison to other techniques when there are other signals or noise present, some of which have a broad band frequency spectrum, and the signal of interest is associated with either a low dimensional dynamical system or a low dimensional chaotic attractor. The method is applied to data from a laboratory model of a fluidized bed reactor and to data from a gyroscope as well as to numerically generated signals from mathematical models. For the dynamical systems considered in the paper, the proposed method provides significantly better discrimination than spectral analysis.
A simple model of chaotic advection and scattering
Authors: Stolovitzky Gustavo , Kaper Tasso J. , Sirovich Lawrence
Published: July 2002

In this work, we study a blinking vortex-uniform stream map. This map arises as an idealized, but essential, model of time-dependent convection past concentrated vorticity in a number of fluid systems. The map exhibits a rich variety of phenomena, yet it is simple enough so as to yield to extensive analytical investigation. The map’s dynamics is dominated by the chaotic scattering of fluid particles near the vortex core. Studying the paths of fluid particles, it is seen that quantities such as residence time distributions and exit-vs-entry positions scale in self-similar fashions. A bifurcation is identified in which a saddle fixed point is created upstream at infinity. The homoclinic tangle formed by the transversely intersecting stable and unstable manifolds of this saddle is principally responsible for the observed self-similarity. Also, since the model is simple enough, various other properties are quantified analytically in terms of the circulation strength, stream velocity, and blinking period. These properties include: entire hierarchies of fixed points and periodic points, the parameter values at which these points undergo conservative period-doubling bifurcations, the structure of the unstable manifolds of the saddle fixed and periodic points, and the detailed structure of the resonance zones inside the vortex core region. A connection is made between a weakly dissipative version of our map and the Ikeda map from nonlinear optics. Finally, we discuss the essential ingredients that our model contains for studying how chaotic scattering induced by time-dependent flow past vortical structures produces enhanced diffusivities.
Communication with chemical chaos in the presence of noise
Authors: Dolnik Milos , Bollt Erik M.
Published: July 2002

We use control of chaos to encode information into the oscillations of the Belousov-Zhabotinsky reaction. An arbitrary binary message is encoded by forcing the chaotic oscillations to follow a specified trajectory. The information manipulating control requires only small perturbations to vary the binary message. In this paper we extend our recent theoretical work [Bollt and Dolnik, Phys. Rev. E 64, 1196 (1990)] by introducing a new and simplified encoding technique which can be utilized in the presence of experimental noise. We numerically and theoretically study several practical aspects of controlling symbol dynamics including: modeling noisy time-series, learning underlying symbol dynamics, and evaluation of derivatives for control by observing system responses to an intelligent and deliberate sequence of input parameter variations. All of the modeling techniques incorporated here are ultimately designed to learn and control symbol dynamics of experimental data known only as an observed time-series; the simulation assumes no global model. We find that noise affects reliability of encoding information and may cause coding errors. But, if the level of noise is confined to relatively small values, which are achievable in experiments, the control mechanism is robust to the noise. Thus we can still produce a desired symbolic code. However, scarce errors in encoding may occur due to rare but large fluctuations. These errors may be corrected during the decoding process by a variation of the filtering technique suggested by Rosa et al. [Phys. Rev. Lett. 78, 1247 (1997)].
A method to Fourier filter textured images
Authors: Hoffman David K. , Gunaratne Gemunu H. , Zhang D. S. , Kouri Donald J.
Published: July 2002

An algorithm is introduced to extract an underlying image from a class of textures. It is assumed that the image is bandwidth limited and the noise is broad-band. The initial step of the algorithm extends the signal to a larger periodic image using “Distributed Approximating Functionals.” The second step introduces a low-pass filter which allows the identification and elimination of the high-frequency components of the noise. The periodicity of the resulting image allows it to be Fourier filtered without aliasing. The feasibility of the algorithm is demonstrated on several noisy patterns generated in experiments and model systems.
Electronic contribution to the recrystallization growth velocity asymmetry in doped silicon
Authors: Mosley L. E. , Paesler M. A.
Published: July 2002

We have examined the regrowth rate of single implants of electrically active elements in silicon in terms of a model of crystallization that considers the diffusion of charged dangling bonds. An asymmetry in the regrowth velocity as a function of dopant concentration is explained in terms of differences in the shifts of the Fermi level on the amorphous (a-) and crystalline (c-) sides of the a-c interface. This effect is consistent with an increased shift in the Fermi level in the a- layer at the a-c interface. The increased shift is in turn suggested to be produced by an increased concentration of charged dangling bonds resulting from the dopant concentration gradient.
Point contact diode at laser frequencies
Authors: Evenson K. M. , Inguscio M. , Jennings D. A.
Published: July 2002

Dramatic improvements in the stability of the metal-insulator-metal point contact diode has been achieved by the use of blunter whisker tips. The optimum values for tip radius and diode resistance were experimentally determined. Both sensitivity and high-speed response of W-NiO-Ni point contact diodes were investigated at different laser frequencies and mixing orders as a function of tip radius, resistance, and coupling. The tip radii were changed by more than an order of magnitude, and surprisingly, the sensitivity and the harmonic generation up to 88 THz were not significantly affected. A conical antenna was found to be superior to the conventional long-wire antenna at wavelengths shorter than 10 μm. Responsivity measurements as a function of the diode resistance showed evidence for two different physical mechanisms responsible for the operation of the diode.
Plasma production by laser-driven explosively heated thin metal films
Authors: Mayer F. J. , Busch Gar. E.
Published: July 2002

A simple method of producing a relatively large volume of metal vapor for laser-plasma interaction studies is described. The method uses the explosive removal of a thin metal film from a glass substrate with a low-intensity laser pulse.
Magneto-optical effect in anodized Al2O3 film with micropores electrodeposited with Co
Authors: Abe M. , Gomi M. , Yokoyama F.
Published: July 2002

We have electrodeposited Co into the micropores of an anodic Al2O3 coating on Al, making Co rods of about 120 Å in diameter and 0.3–1 μm in length. The Al2O3 is amorphous, while the Co is crystalline (hexagonal form) with no preferred orientation exhibiting saturation magnetization 80% of that of bulk Co. The composite Al2O3/Co film shows prominent magnetic anisotropy perpendicular to the surface due to the shape anisotropy of the Co rods, having coercive force of ∼1.2 kOe. The Kerr rotation and the reflectivity of the films at λ=0.63 μm, Θ̂k =±15′ to ±50′, and R=5 to 15% varied from sample to sample due to interference effect of light in the films. The values of θk and R change irreversibly when heated above ∼150 °C. Stripping the Al2O3-Co film from the Al substrate by dissolving the Al, we have measured the Faraday effect and light transmittance. They increase linearly with increasing rod length, giving Θ̂f(rotation) =−0.41 deg/μm, Ψ̂f(ellipticity) =1.14 deg/μm, and α̂(absorption coefficient)=1.1 μm−1. These values conform with what is expected from the effective dielectric tensor, including off-diagonal elements, which we [Jpn. J. Appl. Phys. 23, 1580 (1984)] have formulated for composite materials containing magnetic fine particles or rods.
Investigation of magnetism at surfaces by polarized neutron reflection (invited)
Authors: Felcher G. P. , Felici Roberto , Kampwirth R. T. , Gray K. E.
Published: July 2002

It is shown that the spin-dependent reflectivity of a cold neutron beam from magnetically active surfaces, measured as a function of the neutron wavelength, can provide the magnetic depth profile of the material. Following the construction of a prototype instrument at the Intense Pulsed Neutron Source at Argonne, studies were made of the magnetic disturbances at the surface of superconductors. The results obtained, and discussed here, pertain to the penetration depth in a superconductor (niobium and lead) below the critical flux entry field Hc1, and the surface superconductivity of an incipient type II superconductor (lead-bismuth alloy) below Hc3. The prospects for this technique, with particular regard to the study of the surface critical phenomena of ferromagnets, are also discussed.
Apparent spin-glass nature of an anisotropic ferromagnet
Authors: Griffith G. , Volkening F. A. , Claus H.
Published: July 2002

Low-field ac and dc magnetization measurements on a Pd-0.4 at. %Fe sample in two metallurgical states are presented. In a well-annealed state the sample responds like an ideal soft ferromagnet. After plastic deformation the sample has essentially the same ordering temperature and saturation magnetization, however, its low-field response looks more like that of a spin glass. Magnetic isotherms in this latter state look like those of a ferromagnet with infinite susceptibility but zero spontaneous magnetization.
Grid-controlled plasma cathodes
Authors: Humphries S. , Coffey S. , Savage M. , Len L. K. , Cooper G. W. , Woodall D. M.
Published: July 2002

Experiments are described on a plasma cathode with biased grids to prevent entry of ions into the electron extraction gap. The cathode has potential applications to the generation of high-current pulsed electron beams. Operation at 20 A/cm2 is theoretically possible. The source combines the low average power consumption of a plasma cathode with many of the attractive features of thermionic cathodes, such as space-charge-limited extractor gap electron flow, fast turn-on, and no diode closure. Initial experiments are reported at the 2 A/cm2 level for pulse lengths to 160 μs.
Dark current transport mechanism of p-i-n hydrogenated amorphous silicon diodes
Authors: Matsuura Hideharu , Matsuda Akihisa , Okushi Hideyo , Tanaka Kazunobu
Published: July 2002

The dark current-voltage characteristics of p-i-n hydrogenated amorphous silicon diodes with various thicknesses of the intrinsic layer (i-layer) (770–9300 Å) are systematically investigated. The magnitude of the forward current is found to be independent of thickness of the i layer, which is obviously against the simple conventional junction theory. It has been demonstrated through various experiments that the forward current of amorphous p-i-n diodes is limited by a layer thinner than 770 Å, possibly being the p/i interface or a narrow zone of the i layer.
Propagation profile of ablation front driven by a nonuniform UV laser beam
Authors: Matsushima Isao , Tanimoto Mitsumori , Kasai Takeshi , Yano Masaaki
Published: July 2002

Spatial profile of ablation front is observed under the irradiation of spatially modulated 0.27-μm laser beam. Propagation depth of the ablation front is derived by means of various methods which detect x-ray radiation from aluminum substrates overcoated with polyethylene layers of different thicknesses. A higher mass ablation rate is observed for the UV laser than the longer wavelength lasers. However, observation with an x-ray television camera shows that the spatial nonuniformity in the laser beam is projected on the ablation front surface without substantial smoothing.
Experimental study of laser-induced cavitation bubbles
Authors: Giovanneschi Pia , Dufresne Daniel
Published: July 2002

The focused beam from a Nd:YAG laser (λ=0.532 μm) is used to generate cavitation bubbles in water. Optics of short focal length have been shown to be the most suitable for producing a single bubble in a definite place. Some typical photographs of bubbles obtained are presented. These prove that the laser is a useful tool for the study of simulated cavitation in the laboratory.
Ion implantation of Si by 12C, 29Si, and 120Sn: Amorphization and annealing effects
Authors: Wang Kou-Wei , Spitzer William G. , Hubler Graham K. , Sadana Devendra K.
Published: July 2002

Several Cr-doped, low carrier density (10–20 Ω cm), (111)-oriented wafers of Si were ion implanted at room temperature and ∼90 K with various doses of 12C, 29Si, and 120Sn. The ion energy was 380 keV except for 12C at 90 K where 150 keV was used. Infrared reflection as a function of frequency and cross-sectional transmission electron microscopy measurements were made for both as-implanted and thermally annealed (400 °C for 2 h) samples. The results of these measurements demonstrate the following: (i) The previously reported pair of metastable amorphous states are observed, a-Si-I for high-dose as-implanted material and a-Si-II for anneal-stabilized material; (ii) interface positions and microstructural properties show good consistency between the two types of measurements; (iii) the measurements are consistent with the view that the implanted material can be a heterogeneous mixture of undamaged, damaged, and amorphous regions. By using an effective medium approximation and a damage cascade overlap model one concludes that no overlap is required for 120Sn to create amorphous zones, while a large number is necessary for a light ion, 14 for 12C implantations at room temperature; (iv) from several different approximation methods, average values for the critical amorphization energy are obtained, i.e., in units of 1021 keV/cm3, 1.4 for 120Sn, 2.0 for 29Si, and 13.0 for 12C (all for room-temperature implantations) and 0.5 for all ions for 90 K implantations; (v) the measurements show that the annealing-induced recrystallization behavior of incomplete or mixed amorphous layers is very different from that for complete or homogeneous layers which crystallized by planar epitaxial regrowth; (vi) samples were cycled between the a-Si-I and a-Si-II states and it was observed that the energy required for a-Si-II→a-Si-I is about an order of magnitude smaller than the critical amorphization energy (c-Si→a-Si-I) for 29Si implantations at room temperature.
Hard amorphous carbon studied by ellipsometry and photoluminescence
Authors: Wagner J. , Lautenschlager P.
Published: July 2002

Plasma-deposited hard amorphous carbon films were studied by ellipsometry and photoluminescence. Both techniques are suited for the optical characterization of films on transparent as well as on opaque substrates. From the ellipsometric data the complex dielectric function was deduced for the energy range 1.8–5.6 eV for the as-grown as well as for thermally annealed films. In the photoluminescence spectrum both peak energy and emission intensity were found to increase (the latter by four orders of magnitude) when going from hard, strongly cross-linked films to softer, polymerlike layers.
High-resolution imaging with the stigmatic ion microscope
Authors: Bernius Mark T. , Ling Yong-Chien , Morrison George H.
Published: July 2002

An exposition of the lateral image resolution specific to the ion optics in the stigmatic ion microscope (based on ion sputtering mass spectrometry) is presented, with emphasis on investigations leading to the current level of understanding of high-resolution operation. Modifications are presented for the CAMECA IMS-3f ion microscope which extends instrumental magnifications to over 2000 diameters and smallest resolvable distances in undistorted images to 0.1 μm. This is necessary to keep pace with the increasingly stringent requirements for the analysis of the shrinking features in fabricated very-large-scale integration devices. Conditions for ensuring the formation of undistorted images are given, and the performance of the instrument under these conditions is evaluated. The current concerns of ion microscopic image analysis are then presented and discussed.
(ArO)+ and (ArO2)+ ions in rf sputter deposition discharges
Authors: Aita Carolyn Rubin , Lad Robert J.
Published: July 2002

Glow discharge mass spectrometry was used to study the occurrence of argon–oxygen ions in rf-diode sputter deposition discharges. The results show that (ArO)+ and (ArO2)+ ions are formed over an extensive range of Ar–O2 sputtering gas mixtures. The populations of these ions are independent of whether a ZnO or Au target is used and coupled in a manner that indicates (ArO2)+ is formed first then dissociates to form (ArO)+. An associative ionization reaction between an Ar atom in a highly excited long-lived Rydberg state and ground state O2 is proposed to be responsible.
The logarithmic response of palladium-gate metal-insulator-silicon field-effect transistors to hydrogen
Authors: Robins I. , Ross J. F. , Shaw J. E. A.
Published: July 2002

The response characteristics of palladium-gate metal-insulator-silicon field-effect transistor (MISFET) structures to hydrogen are shown to be logarithmically related to the partial pressure of the gas. It is proposed that these palladium-gate MIS structures should be considered as electrochemical devices where the metal/insulator structure behaves as a gas electrode. The results presented were obtained for hydrogen in air and therefore relate directly to the use of these devices as sensors for use in the ambient environment.
Determination of high-density interface state parameters in metal-insulator-semiconductor structures by deep-level transient spectroscopy
Authors: Murray F. , Carin R. , Bogdanski P.
Published: July 2002

The interpretation of experimental results concerning insulator-semiconductor interface states in metal-insulator-semiconductor structures obtained with the deep-level transient spectroscopy (DLTS) techniques, particularly in the case of high-density interface states continuously distributed in the energy band gap (larger than 5×1011 eV−1 cm−2), is reconsidered. It is shown that the ‘‘saturating pulse’’ condition, which allows a classical treatment of the DLTS spectra, corresponds to a filling pulse amplitude which rapidly increases with the average density of the traps located at the interface. The use of large or small pulses is discussed. The determination of the profile of interface state density Nss(E) can only be derived for high densities from a simulation of the DLTS signal ΔC(T), since the classical relation between Nss and ΔC is no more valid in this case. A simplified simulation is proposed. It allows us to justify the results reported in this paper and to fit experimental results previously obtained on Al–Si3N4–GaAs structures with interface state densities about 1013 eV−1 cm−2.
Quantitative x-ray spectroscopy of neon Z-pinch plasmas
Authors: Mehlman G. , Burkhalter P. G. , Stephanakis S. J. , Young F. C. , Nagel D. J.
Published: July 2002

Spatially resolved soft x-ray spectra were collected for neon plasmas produced by imploding hollow annular gas puffs with MA level driving currents. The Z-pinch imploded plasmas were studied for different risetime currents produced with or without the use of a plasma erosion opening switch (PEOS). Selected spectrograms were processed and analyzed to obtain absolute energies for the radiation emitted in the Ne ix and Ne x discrete transitions, as well as for total emission over the spectral range 900–1600 eV. The neon plasmas radiate 1–2.5 kJ in this energy range predominantly in the α transitions of both ions. The plasma uniformity inferred from spatially resolved spectral lines improves significantly using a faster rise-time driving current.
Eddy current calculations using half-space Green’s functions
Authors: Bowler J. R.
Published: July 2002

A simple scalar representation is used to describe the electromagnetic field in the quasi-static limit for an arbitrary time-harmonic source current above an imperfectly conducting half-space. Solutions are given in terms of half-space scalar and dyadic Green’s functions. The general results are then used to derive analytical expressions for the fields arising from circular filaments and extended sources whose axes of symmetry are parallel to the surface of the conductor. These tangent coil solutions have applications in the theory of inductive sensors, particularly for eddy current nondestructive testing.
Measurements of ion transverse-velocity distribution in the gap of an ion-beam diode
Authors: Maron Y. , Coleman M. D. , Hammer D. A. , Peng H. S.
Published: July 2002

We have measured the distributions of ion transverse velocities in the acceleration gap of a magnetically insulated ion diode. The measurement is based on observing the spectral profile of the Doppler-broadened spontaneous line emission from accelerating ions. The velocity distributions of C++ and Al++ ions were peaked at zero transverse velocity and symmetric with respect to the directions parallel and antiparallel to the magnetic-field lines. The mean transverse velocities for both of the ion species corresponded to energies of about 200 eV in experiments with a gap potential difference of 260–330 kV. The divergence angles observed for both of the ion species are significantly smaller than previously observed for protons outside the diode.
Alignment of thermal donors in Si by uniaxial stress
Authors: Wagner P. , Gottschalk H. , Trombetta J. , Watkins G. D.
Published: July 2002

Thermal donors generated in Czochralski-Si by heat treatment at around 450 °C can be preferentially aligned by applying a large uniaxial stress during their formation process. This alignment is clearly observed by a polarization of the optical transitions of the thermal donors and a corresponding effect for the paramagnetic NL8 centers. Thus a strong correlation between thermal donors and NL8 is again demonstrated, as well as the extended defectlike nature of such defects. The g3 value of the g tensor and the 2p0 dipole oscillator are found to be oriented preferentially perpendicular to the stress direction, a result which seems to disagree with some of the presently discussed thermal donor models.
The capture barrier of the D
X center in Si-doped AlxGa1−xAs
Authors: Mooney P. M. , Caswell N. S. , Wright S. L.
Published: July 2002

We report measurements of the capture barrier for the DX center in Si-doped AlxGa1−xAs as a function of the alloy composition. A model of the capture process which requires a distribution of capture barrier heights has been fit to the data for samples with x=0.35. A simple technique is used to extract the average capture barrier height from data for samples with AlAs mole fraction ranging from x=0.27 to x=0.55. The barrier height varies strongly with the composition and has a minimum at x=0.35. The implications of these results are discussed.
Reversible structural relaxation in Fe-Ni-B-Si metallic glasses
Authors: Brüning R. , Altounian Z. , Ström-Olsen J. O.
Published: July 2002

Reversible structural relaxation has been studied in (Fe1−xNix)80B10Si10 by differential scanning calorimetry and x-ray diffraction. It is found that surface crystallization plays a major role in inhibiting reversibility. In consequence, previously published data have presented a misleading picture about the composition dependence of the reversible effect in Fe-Ni-B-Si, which simply increases monotonically with Ni composition. There is no evidence that chemical short-range order plays any role in reversibility, and the data have been quantitatively modeled by simply assuming that reversible relaxation is caused by the thermal repopulation of excited structural states.
Novel microstructures for the i
n s
i
t
u measurement of mechanical properties of thin films
Authors: Mehregany Mehran , Howe Roger T. , Senturia Stephen D.
Published: July 2002

This paper discusses microfabricated structures designed for the in situ measurement of the mechanical properties of thin films under residual tensile stress. The film is deposited and patterned on a (100) silicon substrate in which 5-μm-thick diaphragms have been fabricated. When the silicon diaphragm is etched from the backside in an SF6 plasma, the microstructures are released and deform under the residual tension. Measurement of this deformation in conjunction with appropriate mechanical models determines the mechanical properties of interest. We have used these structures to study benzophenonetetracarboxylicdianhidride-oxydianiline/metaphenylene-diamine polyimide films. Typical value for the residual stress to modulus ratio in this case was determined to be 0.011±0.001 while the ultimate strain at break was found to be 4.5% for 5.5-μm-thick films. For thicker films (8.5 μm), the film did not fail until 8% strain was reached.