bluuebunny/crossref_metadata_2025 huggingface dataset:
An energy functional for surfaces
Authors: Mattsson Ann E. , Kohn Walter
Published: July 2002

We propose a simple way of correcting general gradient and local density approximation surface energies for errors of these approximations intrinsic to surfaces by the appropriate use of reference systems with an exponential surface potential veff(z)∝e(z/a). A test of this approach applied to general gradient and local density approximation surface exchange energies for half jellium systems removes most of the surface-intrinsic errors and yields excellent results. We suggest that the same procedure would also be successful for surface correlation effects. We conclude with some general remarks about future directions of density functional theory.
Piezoresistivity of AlxGa1−xN layers and AlxGa1−xN/GaN heterostructures
Authors: Eickhoff M. , Ambacher O. , Krötz G. , Stutzmann M.
Published: July 2002

The piezoresistivity of wurtzite AlxGa1−xN layers with different Al contents and electron concentrations grown by plasma induced molecular beam epitaxy is investigated. A strong increase of the piezoresistivity with increasing Al content and decreasing carrier density is observed. The corresponding piezoresistive gauge factor is negative and its absolute value increases from 3.5 to 25.8 if the Al concentration is increased from x=0 to 0.35. The dependence of the piezoresistive effect on the free electron concentration in the epitaxial layers is calculated by a model which compares the strain induced piezoelectric field to an externally applied gate voltage in field effect transistors. In addition, the strain dependence of the channel conductivity in pseudomorphic, undoped AlGaN/GaN high electron mobility transistors containing a polarization induced two-dimensional electron gas close to the heterointerface, is measured. A remarkably high gauge factor of −85 is observed for these devices.
Hall detection of magnetic resonance
Authors: Boero Giovanni , Besse Pierre-André , Popovic Radivoje
Published: July 2002

We propose a detection method for magnetic resonance experiments based on the use of a Hall effect device. To demonstrate its feasibility, we have measured the quasistatic and radio-frequency magnetic fields generated by the unpaired electrons contained in a (50 μm)3 grain of diphenylpicrylhydrazil, excited into magnetic resonance in a 10 mT static magnetic field. The proposed technique has the same versatility of the conventional inductive method but, potentially, allows one to perform magnetic resonance spectroscopy and imaging studies with submicron spatial resolution.
Formation of location-controlled crystalline islands using substrate-embedded seeds in excimer-laser crystallization of silicon films
Authors: van der Wilt Paul Ch. , van Dijk B. D. , Bertens G. J. , Ishihara R. , Beenakker C. I. M.
Published: July 2002

Single-crystal thin-film transistors on nonrefractory materials such as glass can be realized if monocrystalline islands of sufficient sizes can be grown at a predetermined position. By artificially controlling the super-lateral growth phenomenon observed in excimer-laser crystallization, this could be achieved. In this letter, we present such a method in which the silicon filling of a very small indentation fabricated in the substrate will act as a seed for lateral growth of large grains. When the melt is deep in these indentations, lateral growth is preceded by a vertical growth phase during which grains become occluded, so that a high yield of monocrystalline islands is obtained.
Thickness dependence of exciton and polariton spectra from ZnSe films grown on GaAs substrates
Authors: Wang Xingjun , Huang Daming , Sheng Chuangxiang , Yu Gencai
Published: July 2002

ZnSe films with thicknesses from 0.05 to 1.45 μm were grown on GaAs substrates by molecular beam epitaxy. Low temperature photoluminescence (PL) and reflectance spectra are presented to show the thickness dependence of the exciton and polariton properties in the films. In addition to sharp PL peaks from free and donor bound excitons, an acceptor bound exciton peak was observed in the thin films and its intensity decreases rapidly with the film thickness. The PL characteristics show the acceptor centers being the defect states near the ZnSe/GaAs interface. The classical theory of exciton–polaritons was used to calculate the reflectance spectra and compared to the measured results. The comparison reveals the effects of strain, surface, and interface on the reflectance spectra from both heavy- and light-hole excitons. In addition to the strain-induced light- and heavy-hole splitting, the light-hole excitons show a larger damping and less sensitivity to the surface dead layer than the heavy-hole excitons. When the film thickness increases, the interference effects become more important and the contribution from the excited exciton states to the reflectance spectra may no longer be negligible.
Centrifugal instability of Couette flow over a wavy wall
Authors: Floryan J. M.
Published: July 2002

Linear stability of Couette flow over a wavy wall is considered. It is shown that centrifugal effects may create an instability that leads to the formation of streamwise vortices. The conditions leading to the onset of the instability depend on the amplitude and the wavelength of the waviness and can be expressed in terms of the critical Reynolds number. The global critical conditions describing the minimum critical Reynolds number and the associated wave number of wall waviness required to create the instability for the specified amplitude of the waviness are also given.
Strained Ge channel p-type metal–oxide–semiconductor field-effect transistors grown on Si1−xGex/Si virtual substrates
Authors: Lee Minjoo L. , Leitz C. W. , Cheng Z. , Pitera A. J. , Langdo T. , Currie M. T. , Taraschi G. , Fitzgerald E. A. , Antoniadis Dimitri A.
Published: July 2002

We have fabricated strained Ge channel p-type metal–oxide–semiconductor field-effect transistors (p-MOSFETs) on Si0.3Ge0.7 virtual substrates. The poor interface between silicon dioxide (SiO2) and the Ge channel was eliminated by capping the strained Ge layer with a relaxed, epitaxial silicon surface layer grown at 400 °C. Ge p-MOSFETs fabricated from this structure show a hole mobility enhancement of nearly eight times that of co-processed bulk Si devices, and the Ge MOSFETs have a peak effective mobility of 1160 cm2/V s. These MOSFETs demonstrate the possibility of creating a surface channel enhancement-mode MOSFET with buried channel-like transport characteristics.
Crystal growth of vanadium doped YAlO3, LaGaO3, and CaYAlO4 crystals and spectroscopic studies of vanadium valence states
Authors: Noginov M. A. , Loutts G. B. , Jones D. E. , Turney V. J. , Rakhimov R. R. , Herbert L. , Truong A.
Published: July 2002

V 4+ doped YAlO3, LaGaO3, and CaYAlO4 crystals (3d1 ion in octahedral coordination) have been grown and characterized as potential broadband laser materials using optical and electron paramagnetic resonance techniques. The effect of charge compensation on the vanadium valence state and spectroscopic properties of the materials are discussed.
High emissivity of a rough Pr2NiO4 coating
Authors: Rousseau B. , Chabin M. , Echegut P. , Sin A. , Weiss F. , Odier P.
Published: July 2002

A rough and thick film of doped praseodymium nickel oxide (Pr2NiO4+δ) has been obtained by combining the spray pyrolysis deposition technique with rapid thermal annealing process. The precursors are nitrate solutions. Spectral emissivity measurements from the far infrared up to the midinfrared region at T=1000 K show the strong black body character of the film. This feature is well suited to the thermal efficiency of an industrial infrared ceramic radiant plate.
Peristaltically induced motion in a closed cavity with two vibrating walls
Authors: Yi Mingqiang , Bau Haim H. , Hu Howard
Published: July 2002

We consider incompressible, viscous fluid confined in a rectangular cavity. Both the bottom and top walls are made of thin membranes. Traveling waves with the same amplitude and frequency but opposite phase are transmitted in these membranes and induce peristaltic motion in the fluid. The induced velocity profiles are determined analytically for small-amplitude waves (ε) and numerically for waves of any amplitude. The analysis consists of a perturbation expansion in terms of the wave amplitude (ε) up to O(ε2). Solutions for large-amplitude oscillations are obtained through the use of a finite element code that employs a moving grid. The numerical code is verified by critically comparing the simulations’ predictions with analytical results.
Cross-field blob transport in tokamak scrape-off-layer plasmas
Authors: D’Ippolito D. A. , Myra J. R. , Krasheninnikov S. I.
Published: July 2002

Recent measurements show that nondiffusive, intermittent transport of particles can play a major role in the scrape-off-layer (SOL) of fusion experiments. A possible mechanism for fast convective plasma transport is related to the plasma filaments or “blobs” observed in the SOL with fast cameras and probes. In this paper, physical arguments suggesting the importance of blob transport [S. I. Krasheninnikov, Phys. Lett. A 283, 368 (2001)] have been extended by calculations using a three-field fluid model, treating the blobs as coherent propagating structures. The properties of density, temperature and vorticity blobs, and methods of averaging over ensembles of blobs to get the average SOL profiles, are illustrated. The role of ionization of background neutrals in sustaining the density blob transport is also discussed. Many qualitative features of the experiments, such as relatively flat density profiles and transport coefficients increasing toward the wall, are shown to emerge naturally from the blob transport paradigm.
Inverse scattering theory of the heat equation for a perturbed one-soliton potential
Authors: Boiti M. , Pempinelli F. , Pogrebkov A. K. , Prinari B.
Published: July 2002

The inverse scattering theory of the heat equation is developed for a special subclass of potentials nondecaying at space infinity—perturbations of the one-soliton potential by means of decaying two-dimensional functions. Extended resolvent, Green’s functions, and Jost solutions are introduced and their properties are investigated in detail. The singularity structure of the spectral data is given and then the inverse problem is formulated in an exact distributional sense.
High field ferromagnetic resonance measurements of the anisotropy field of longitudinal recording thin-film media
Authors: Oates C. J. , Ogrin F. Y. , Lee S. L. , Riedi P. C. , Smith G. M. , Thomson T.
Published: July 2002

The average value of the magnetocrystalline anisotropy field, Hk, is an important parameter for the characterization of magnetic recording media but is difficult to measure accurately due in part to the effect of interactions between the grains. In order to evaluate Hk we have studied two model CoCrPtTa magnetic films using a number of complementary techniques: high field ferromagnetic resonance (FMR) (35.0–45.0 kOe), low field (<20 kOe) vector vibrating-sample magnetometry and torque magnetometry. The FMR measurements were performed at a number of discrete frequencies in the range 75–93 GHz using a new quasi-optical spectrometer developed at the University of St. Andrews. The values of Hk derived by FMR (10.8 kOe) are approximately 10% greater than those obtained from conventional magnetometry (9.6 kOe). This difference is believed to be due to the presence of intergranular exchange coupling which reduces the measured value of anisotropy when the applied field is not sufficiently large to completely align the magnetic moments.
Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films
Authors: Preble E. A. , Tracy K. M. , Kiesel S. , McLean H. , Miraglia P. Q. , Nemanich R. J. , Davis R. F. , Albrecht M. , Smith David J.
Published: July 2002

Schottky contacts of Pt(111) and Au(111) were deposited on chemical-vapor-cleaned, n-type GaN(0001) thin films. The growth mode of the deposition, as determined by x-ray photoelectron spectroscopy analysis, followed the two-dimensional Frank–van der Merwe growth model. The resulting as-deposited metal films were monocrystalline and epitaxial with a (111)//(0002) relationship with the GaN. Selected samples were annealed for three minutes at 400 °C, 600 °C or 800 °C. The rectifying behavior of both contacts degraded at 400 °C; they became ohmic after annealing at 600 °C (Au) or 800 °C (Pt). High-resolution transmission electron micrographs revealed reactions at the metal/GaN interfaces for the higher temperature samples. X-ray diffraction results revealed an unidentified phase in the Pt sample annealed at 800 °C. A decrease in the room temperature in-plane (111) lattice constant for both metals, ranging from −0.1% to −0.5%, was observed as the annealing temperature was increased from 400 to 800 °C. This plastic deformation was caused by tensile stresses along the [111] direction that exceeded the yield strength as a result of the large differences in the coefficients of thermal expansion between the metal contacts and the GaN film.
Spectroscopic properties of Sm3+(4f 5) in GaN
Authors: Gruber John B. , Zandi Bahram , Lozykowski H. J. , Jadwisienczak W. M.
Published: July 2002

We have analyzed the cathodoluminescence spectra of Sm3+ ions implanted and annealed in GaN epilayers. High-resolution emission spectra were obtained at 11 K between 350 and 1050 nm, representing transitions from the G45/2 to the H4J and F6J manifolds of Sm3+(4f5). Emission lifetimes were determined at various temperatures between 7 and 320 K for transitions from G45/2 to G45/2, G67/2, and G69/2. Lattice-sum calculations were carried out to determine the crystal-field splitting of the multiplet manifolds. With individual Stark levels and corresponding wave functions identified, the matrix elements for both electric–dipole and magnetic–dipole transitions were calculated between levels. Radiative lifetimes were calculated and compared with experimental lifetimes. High quantum efficiencies are reported. The calculated branching ratios for transitions from G45/2 to F6J and F6J manifolds indicate that transitions to H65/2, H67/2, and H69/2 account for 80% of the total observed emission.
Oriented Y-type hexaferrites for ferrite device
Authors: Obol M. , Zuo X. , Vittoria C.
Published: July 2002

We have developed a technique to orient particles of Y-type hexaferrite in which the c axis of the particles is oriented perpendicular to a plane. Disks of oriented Ba2MnZnFe12O22 particles were characterized in static and dynamic field excitations and exhibited the following properties: 4πMs=2300 G, Ha=9500 G, 4πMeff=4πMs+Ha=11800 G, and Hc=60 Oe. The ferrimagnetic resonance linewidth at 27 GHz measured to be 350 Oe and the g factor approximately equal to 2. The magnetic parameters of the oriented particles were very similar to the bulk parameters previously published.
Phase transitions in solutions of semiflexible polyelectrolytes
Authors: Ghosh K. , Carri G. A. , Muthukumar M.
Published: July 2002

Using a mean-field model, we have studied the phase behavior of a collection of semiflexible polyelectrolytes with electrostatic and anisotropic excluded volume interactions. The interference between the second-order critical phenomenon in the flexible limit and the first-order isotropic-nematic phase transition in the rod limit is found to be richly dependent on the intrinsic chain stiffness, polymer concentration, salt concentration, and temperature through the Flory–Huggins χ parameter. For intrinsic chain stiffness below a critical value, there exists only a critical point and a coexistence curve between two isotropic phases. For smaller values of stiffness, but above the critical value, we have found a triple point corresponding to the coexistence of two isotropic phases and one anisotropic phase. As the chain stiffness is increased progressively, the triple point moves towards lower polyelectrolyte concentration and approaches the critical point. If the chain stiffness is increased even more, another triple point emerges corresponding the coexistence of one isotropic phase and two anisotropic phases.
Low-temperature dependence of midinfrared optical constants of lead–germanium–telluride thin film
Authors: Li Bin , Jiang Jinchun , Zhang Su-ying , Zhang Feng-shan
Published: July 2002

The design and manufacture of diode lasers for gas analysis or multilayer thin-film optical devices used at low-temperature require the refractive index and the temperature coefficient of IV–VI compound over a significant temperature range. In this article, the refractive index and the absorption coefficient of Pb0.94Ge0.06Te thin film have been determined from transmission spectra measured at temperature between 80 and 300 K in the spectral range of 2.5–8.5 μm by fitting based on a Lorentz-oscillator model. It is found that the maximum refractive index occurs at 150 K, which corresponds to the structural phase transition from rocksalt to rhombohedrally distorted structure and reflects an increase of lattice polarizability. The value of the index of refraction is 5.350–6.000 in the spectral range of 4.0–8.5 μm for all measured temperatures, which reveals that Pb1−xGexTe is a highly refractive infrared material. The temperature coefficient of refractive index, dn/dT, is found to be −0.006–0.002 K−1 in the spectral range of 3.0–8.5 μm for all measured temperature. An empirical formula that fits the temperature coefficient in the spectral range of 4.0-8.5 μm is presented. The dependence of the transmission and absorption spectra on decreasing temperature can be explained by the modification of the energy-band structure due to rhombohedral distortions. The conclusion can be drawn that anomalies corresponding to the ferroelectric phase transition occur in both refractive index and absorption coefficient of Pb1−xGexTe alloy.
Study of intermixing in a GaAs/AlGaAs quantum-well structure using doped spin-on silica layers
Authors: Fu L. , v. d. Heijden R. W. , Tan H. H. , Jagadish C. , Dao L. V. , Gal M.
Published: July 2002

The effect of two different dopants, P and Ga, in spin-on glass (SOG) films on impurity-free vacancy disordering (IFVD) in GaAs/AlGaAs quantum-well structures has been investigated. It is observed that by varying the annealing and baking temperatures, P-doped SOG films created a similar amount of intermixing as the undoped SOG films. This is different from the results of other studies of P-doped SiO2 and is ascribed to the low doping concentration of P, indicating that the doping concentration of P in the SiO2 layer is one of the key parameters that may control intermixing. On the other hand, for all the samples encapsulated with Ga-doped SOG layers, significant suppression of the intermixing was observed, making them very promising candidates with which to achieve the selective-area defect engineering that is required for any successful application of IFVD.
Effect of the number of wells on optical and structural properties in InGaN quantum well structures grown by metalorganic chemical vapor deposition
Authors: Yuh H.-K. , Yoon E. , Shee S. K. , Lam J. B. , Choi C. K. , Gainer G. H. , Park G. H. , Hwang S. J. , Song J. J.
Published: July 2002

High-quality InGaN quantum well (QW) structures with one, two, three, five, and seven wells were grown by metalorganic chemical vapor deposition. The effect of the number of InGaN QWs on the structural and optical properties was studied by high-resolution x-ray diffraction (HRXRD), atomic force microscopy, low excitation density photoluminescence (PL), high excitation density pulsed PL, and PL excitation (PLE). The 10 K PLE band edge of all the samples is almost same, but the 10 K PL peaks of the InGaN QWs initially blueshifts, and then redshifts as the number of wells increases. HRXRD reciprocal space mapping and high excitation pulsed PL show that this anomalous peak shift is due mainly to potential fluctuations, rather than the piezoelectric field. The degree of potential fluctuations varies with dislocation density, which could be affected by growth interruption, the deposition of strained layers, and the accumulated strain energy in InGaN QW structures.
Study on requirements for shielded current perpendicular to the plane spin valve heads based on dynamic read tests
Authors: Matsuzono Atsushi , Terada S. , Ono H. , Furukawa A. , Sone T. , Sasaki S. , Kakihara Y. , Takeda Y. , Chiyokubo N. , Matsuki H.
Published: July 2002

Shielded current perpendicular to the plane (CPP) spin valve heads with about 20 Gbit/in.2 dimensions were fabricated and tested both quasistatically and dynamically. Dual synthetic spin valves with 2.3 mΩ μm2 of resistivity change and area product (dRA) was used. Quasistatic tests were conducted to determine the current efficiency loss caused by the specific CPP head structure. Dynamic tests were performed to examine the flux efficiency of the readback process in the spin valve element, in order to confirm the calculation results which take into account the increase of effective anisotropy field caused by the circular sense current field. Output voltage of about 260 μV (peak to peak) was successfully obtained from the dynamic tests. Finite element modeling analysis of current distribution and temperature rise, together with degradation experiments with excessive sense current, was conducted to predict the maximum allowable current density in the 200 Gbit/in.2 dimension, where read track width and stripe height are assumed to be 100 nm. With these results, requirements of spin valve material properties (dRA, RA) and the CPP structure was predicted. Essential issues to satisfy the requirements and possible solutions are also discussed.
Maximization of the output of shielded current perpendicular to the plane spin valve heads by optimum sense current and hard bias
Authors: Furukawa A. , Ishii S. , Matsuzono A. , Hashimoto M.
Published: July 2002

The head efficiency of shielded current perpendicular to the plane (CPP) spin valve heads of 20 and 200 Gbpsi dimension has been computed and analyzed by an analytical approach utilizing the transmission line model (TLM), and a numerical approach using micro magnetic simulation. For the TLM, the effect of the circular current field was taken into account by incorporating the distribution of the effective permeability of the free layer. Both results showed higher head efficiency for the configuration where sense current field cancels the hard bias field at the front side (air-bearing side) of the free layer. The difference of efficiency by sense current direction was significant at higher sensor height and stronger hard bias. The effect was also observed experimentally on transfer curves from CPP spin valve heads of 20 Gbpsi dimension.
Front speed enhancement in cellular flows
Authors: Abel M. , Cencini M. , Vergni D. , Vulpiani A.
Published: July 2002

The problem of front propagation in a stirred medium is addressed in the case of cellular flows in three different regimes: slow reaction, fast reaction and geometrical optics limit. It is well known that a consequence of stirring is the enhancement of front speed with respect to the nonstirred case. By means of numerical simulations and theoretical arguments we describe the behavior of front speed as a function of the stirring intensity, U. For slow reaction, the front propagates with a speed proportional to U1/4, conversely for fast reaction the front speed is proportional to U3/4. In the geometrical optics limit, the front speed asymptotically behaves as U/ln U.
Solvation of formic acid and proton transfer in hydrated clusters
Authors: Wei Dongqing , Truchon Jean-Francois , Sirois Suzanne , Salahub Dennis
Published: July 2002

In this paper we report detailed theoretical studies of formic acid–water clusters using a Gaussian implementation of Kohn–Sham density functional theory (DFT). Some MP2 calculations were made when necessary to make comparison. The newly developed Laplacian-dependent (LAP) functionals are extensively used although calculations with other traditional gradient-corrected functionals were also made for comparison. To assess our techniques we studied first the formic acid dimer. Good results for structures, vibrational frequencies and proton transfer barrier heights were achieved by the LAP functionals in contrary to other DFT methods, which usually give extremely low barrier heights. We obtained optimized structures of the formic acid–water clusters with up to 4 waters with many possible minimum energy states. The vibrational frequencies, successive hydration energy as well as the corresponding enthalpy were calculated. The interaction energy between formic acid and water was found to be larger than that of water–water. Ring-type structures are among the lowest in energy. Transition states were located for formic acid–water with various solvation patterns to study the effect of hydration on the proton transfer barrier. The transition state structures are of two fundamental types, i.e., a formic acid anion bound to H3O+- and H5O2+-centered structures, respectively. The proton transfer barrier is reduced by proper solvation of the transition states, notably to full and proper solvation of the hydrated proton units.
The CH+H reaction studied with quantum-mechanical and classical trajectory calculations
Authors: van Harrevelt Rob , van Hemert Marc C. , Schatz George C.
Published: July 2002

The CH+H→C+H2 reaction is studied with quantum-mechanical wave packet calculations and quasiclassical trajectory calculations using a CH2 ground-state potential energy surface. Although quantum tunneling is important for direct hydrogen abstraction, the dominance of the complex formation mechanism ensures the reliability of quasiclassical calculations. Most collisions (≈80%) are nonreactive, because of a too-weak excitation of the CH vibration after a H–CH collision with H approaching CH with HCH angles larger than 60 deg. In this aspect the reaction differs from reactions such as the well-studied O(1D)+H2 reaction, where the H–H vibration in the triatomic complex is strongly excited. Also presented is the rate constant for a temperature range between 50 and 2000 K, obtained from quasiclassical cross-section results for collision energies between 0.0005 and 0.3 eV. The role of the excited triplet and singlet states of CH2 on the reaction dynamics is discussed.
A presentation of pulsed nuclear magnetic resonance with full quantization of the radio frequency magnetic field
Authors: Jeener J. , Henin F.
Published: July 2002

We show that there is excellent quantitative agreement between the usual semiclassical predictions for nuclear magnetic resonance experiments (quantized spins interacting with a classical radio frequency magnetic field, including radiation damping), and the predictions of a fully quantized description of the same experiment. We also propose a pictorial description of the relevant dynamical quantum states, which helps to lead the intuition towards the same conclusion. Our model ignores spin relaxation, and simulates the equivalent damping resistor of the sample circuit by a very long piece of lossless coaxial cable. The classical rf field (pulses and free induction decay) is described quantum mechanically by means of Glauber’s “coherent” or “quasiclassical” states.
Field-effect-assisted photoconductivity in PbS films deposited on silicon dioxide
Authors: Pintilie L. , Pentia E. , Matei I. , Pintilie I. , Ozbay E.
Published: July 2002

Lead sulfide (PbS) thin films were deposited from a chemical bath onto SiO2/Si (n-type) substrates. Pseudo-metal–oxide–semiconductor devices were obtained by evaporating source and drain gold electrodes on a PbS surface and aluminum gate electrode on a Si substrate. Field-effect-assisted photoconductivity in the PbS layer was investigated at room temperature, in the 800–2700-nm-wavelength domain for different values and polarities of the drain and gate voltages. The best results were obtained for a positive gate, when both semiconductors are in depletion. An enhancement of about 25% of the photoconductive signal is obtained compared with the case when the gate electrode is absent or is not used. A simple model is proposed that explains the behavior of the dark current and photoconductive signal in PbS film with changing the gate voltage.
Nucleation of copper on TiN and SiO2 from the reaction of hexafluoroacetylacetonate copper(I) trimethylvinylsilane
Authors: Ma P. F. , Schroeder T. W. , Engstrom J. R.
Published: July 2002

The nucleation of copper on TiN and SiO2 surfaces has been investigated using a collimated molecular beam of hexafluroacetylacetonate copper(I) trimethylvinylsilane in ultrahigh vacuum. The Cu thin film precursor was delivered using a bubbler with H2 as the carrier gas and the substrate temperature was varied from 150 to 260 °C. Ex situ analysis of thin film morphology and microstructure has been conducted using scanning electron microscopy. On SiO2 surfaces the Cu nuclei density reaches a maximum near 5×1010 cm−2, nearly independent of substrate temperature. In contrast, on TiN surfaces the maximum nuclei density is strongly dependent on temperature, varying nearly two orders of magnitude from 150 to 260 °C. On TiN the nucleation process is described well by established kinetic models where a maximum in nuclei density (Nmax) is predicted with respect to the time, and where this quantity exhibits an Arrhenius dependence on substrate temperature.
Phase space Feynman path integrals
Authors: Albeverio S. , Guatteri G. , Mazzucchi S.
Published: July 2002

A rigorous mathematical formulation of the “phase space Feynman path integral” is given in a general setting. This is then applied to yield a representation of solutions of the Schrödinger equation with potential depending both on the position and momentum variables.
Photoluminescence of silanone and dioxasilyrane groups in silicon oxides: A theoretical study
Authors: Zyubin A. S. , Mebel A. M. , Lin S. H. , Glinka Yu. D.
Published: July 2002

The photoluminescence (PL) properties of silanone, =Si=O, and dioxasilyrane, =Si(O2), in substoichiometric silicon oxide layers have been investigated by high-level ab initio calculations. The calculated 2.3 and 1.6 eV PL energies are evidenced to correspond to transitions from two lowest excited singlet states in silanone. Additional broadening of the PL bands is due to an involvement of the ground-state =Si=O stretching and bending vibrations with frequencies of ∼1300 and ∼360 cm−1, respectively. As dioxasilyrane group is excited to the S2 (21A1) states, five excited states 11B2, 21A1, 11A2, 31A1, and 11B1 are involved in radiationless and radiative relaxation. The excitation initiates a rupture of the O–O bond and the deexcitation process drives through the activation of O–O stretching vibrations in the ground state (∼630 cm−1). The radiative 31A1→11A1 transition contributes to PL in the range from 2.05 to 2.3 eV, while the 31A1→11B2 and 11B1→11A1 transitions can produce PL bands at 1.7–1.8 eV. The calculated results are compared with green PL bands experimentally observed for a wide range of nanoscale silicon and silicon oxide materials.
Switch-on voltage in disordered organic field-effect transistors
Authors: Meijer E. J. , Tanase C. , Blom P. W. M. , van Veenendaal E. , Huisman B.-H. , de Leeuw D. M. , Klapwijk T. M.
Published: July 2002

The switch-on voltage for disordered organic field-effect transistors is defined as the flatband voltage, and is used as a characterization parameter. The transfer characteristics of the solution processed organic semiconductors pentacene, poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) are modeled as a function of temperature and gate voltage with a hopping model in an exponential density of states. The data can be described with reasonable values for the switch-on voltage, which is independent of temperature. This result also demonstrates that the large threshold voltage shifts as a function of temperature reported in the literature constitute a fit parameter without a clear physical basis.
Influence of biasing stresses on the propagation of surface waves
Authors: Sinha B. K. , Tanski W. J. , Lukaszek T. , Ballato A.
Published: July 2002

It is known that the propagation characteristics of elastic waves are influenced by the nature of biasing stress distributions in the propagating medium. A knowledge of the magnitude of such effects plays an important role in improving the performance and long term aging characteristics of surface acoustic wave (SAW) devices. Generally, SAW devices employ thin platelike structures as the propagating medium of surface waves. The biasing deformation of such structures due to externally applied forces can be decomposed into extensional and flexural deformations which can have substantially different effects on the change in the time delay between two observations points. This paper describes a study of the fractional change in the time delay of surface waves due to the stress components in terms of which a general deformation can be expressed. The information on the biasing state of thin disks has been employed in a previously reported perturbation procedure for equations of motion for small dynamic field superposed on a static bias. Computational results have been obtained for fractional changes in the time delay of surface waves in crystalline quartz of various orientations and propagation directions due to many simple stress systems in thin disks. We have considered the cases of flexural deformation of rectangular plates due to cylindrical bending and disks subjected to normal pressures, as well as extensional deformation due to a pair of forces acting diametrically on a circular disk along various azimuthal angles. Experimental results have been obtained for the moment-frequency effect on circular ST-cut quartz disks and the force-frequency effects on both singly, as well as doubly rotated quartz disks. Good agreement has been obtained between the theoretical predictions and experimental measurements.
A novel x-ray photoelectron spectroscopy study of the Al/SiO2 interface
Authors: Hecht M. H. , Vasquez R. P. , Grunthaner F. J. , Zamani N. , Maserjian J.
Published: July 2002

We report on the first nondestructive measurement of the chemical and physical characteristics of the interface between bulk SiO2 and thick aluminum films. Both x-ray photoelectron spectroscopy (XPS) and electrical measurements of unannealed, resistively evaporated Al films on thermal SiO2 indicate an atomically abrupt interface. Post metallization annealing (PMA) at 450 °C induces reduction of the SiO2 by the aluminum, at a rate consistent with the bulk reaction rate. The XPS measurement is performed from the SiO2 side after the removal of the Si substrate with XeF2 gas and thinning of the SiO2 layer with HF:ETOH. This represents a powerful new approach to the study of metal-insulator and related interfaces.
Differential scanning calorimetry studies of amorphous Zr2PdHx and Zr3RhHx
Authors: Wagner J. E. , Bowman R. C. , Cantrell J. S.
Published: July 2002

The effects of hydrogen concentration and crystal structure on thermal stability of amorphous Zr2PdHx and Zr3RhHx samples were studied with differential scanning calorimetery (DSC). Samples showing endothermic irreversible transitions are a-Zr2PdHx [x=1.91 (powder and foil)/2.7] and a-Zr3RhHx (x=3.7/4.1/5.0/5.1/5.2). Samples showing exothermic irreversible transitions are a-Zr2Pd alloy, a-Zr2PdH1.91 (powder and foil), a-Zr3Rh alloy, and a-Zr3RhHx (x=3.7/4.1/5.0/5.1). Powder x-ray diffraction methods suggest that crystalline Zr2PdHx, ZrHx, and ZrPd are decomposition products from the Zr2PdHx system, that depend upon experimental conditions. The a-Zr3RhHx hydrides decomposed into ZrHx phases and Rh metal. The effect of DSC heating on the products, the heats of transition, and the activation energies are the thermal data that are presented.
Photoluminescent properties of n-GaAs electrodes: Simultaneous determination of depletion widths and surface hole-capture velocities in photoelectrochemical cells
Authors: Burk A. A. , Johnson Phelps B. , Hobson William S. , Ellis Arthur B.
Published: July 2002

Steady-state photoluminescence measurements performed on n-GaAs electrodes used in photoelectrochemical cells (PEC’s) employing a stabilizing, aqueous telluride electrolyte yield values for the electrode’s depletion width W and surface hole-capture velocity S. Between −1.0 V (a potential near short circuit) and −1.5 V vs an SCE reference electrode (a potential near open circuit at the photon flux of 1×1015 photons/s cm2 employed), the interface behaves ideally: virtually all of the applied potential appears in the semiconductor space-charge region. Over this potential regime S is determined to be constant to within 10% and has a value, using literature values for hole lifetime and diffusion length, of approximately 2×105 cm/s for n-GaAs electrodes having carrier concentrations of (1–4)×1017 cm−3. Similar values of S obtained in air and in the PEC suggest a common rate-limiting mechanism for hole consumption in the two media.
Diffusion of Cu into rf-sputtered iron oxide films
Authors: Ishii Osamu
Published: July 2002

Diffusion of Cu into iron oxide films sputter deposited on Cu substrates is studied. After heating in H2 at 200 °C and in air at 300 °C, iron-free Cu oxide layers are formed on the film surfaces. X-ray diffraction method and magnetic measurement show that the Cu atoms diffuse in the iron oxide films without forming CuFe2O4. The crystal-grain size of the reduced and reoxidized films are 20 and 25 nm, respectively. Such fine crystal grains, which are favorable for low noise magnetic disk media application, are attributed to the peculiar Cu interdiffusion in the iron oxide films.
Electrochromic properties of sputtered nickel-oxide films
Authors: Yamada Shoji , Yoshioka Tatsuo , Miyashita Masatoshi , Urabe Kazuo , Kitao Michihiko
Published: July 2002

Electrochromic properties of nickel-oxide films have been investigated. Films were prepared by rf sputtering from a compressed powder NiO target in an atmosphere of an Ar-O2 mixture. The deposition rate of the nickel oxide decreased when the total pressure of the sputtering atmosphere was increased, but was independent of the oxygen content. The films obtained can be electrochemically colored and bleached in a 1-N NaOH electrolyte solution, and are colored anodically. The colored film is dark brown, and the bleached one is transparent and colorless. The maximum coloration efficiency is obtained with the films prepared at the total pressure of 0.04 Torr, and is 36 cm2/C at a wavelength of 640 nm. Coloration efficiency is independent of oxygen content in the sputtering atmosphere.
Thermal and ion-induced, metastable-cubic Al3M phases in Al-Ti and Al-Hf thin films
Authors: Hong Q. Z. , Lilienfeld D. A. , Mayer J. W.
Published: July 2002

Thermal and ion-induced reactions in codeposited, multilayer and bilayer Al-Ti and Al-Hf structures were studied by transmission electron microscopy and Rutherford backscattering. A metastable Al3 M (M being Ti or Hf) phase was found by both ion beam mixing and thermal annealing. The metastable phases have a cubic structure with lattice parameters a=3.98±0.01 Å and 4.08±0.01 Å for Al-Ti and Al-Hf, respectively, at a composition of Al3M. The metastable phase transforms to the tetragonal equilibrium compound at annealing temperatures approximately 400 °C. The effectiveness of ion beam mixing is demonstrated by its lower formation temperatures and faster reaction rates. The thermally induced metastable phase formation is ascribed to a lower nucleation barrier than that of the equilibrium phase.
Pressure measurements correlated with electrical explosion of metals in water
Authors: Lee W. M. , Ford R. D.
Published: July 2002

Time profiles of underwater shock wave pressure, current, and voltage were measured for exploding aluminum, aluminum-lithium alloy, and copper wire in water when an inductive energy store was discharged through the wire. A linear relationship existed between the peak voltage across exploding wire and the underwater shock wave pressure generated by the wire. The aluminum-lithium alloy reached a highly resistive state more quickly than pure aluminum wire at the same heating rate. The chemical reaction between the exploding wire material and the surrounding water plays a small role in the generation of detonation wave.
Influence of the temperature-dependent spontaneous birefringence in the electro-optic measurements of LiNbO3
Authors: Aillerie M. , Fontana M. D. , Abdi F. , Carabatos-Nedelec C. , Theofanous N. , Alexakis G.
Published: July 2002

In spite of the large utilization of LiNbO3 in optical devices, its electro-optic coefficients are not perfectly known. We show in the present paper that not taking into account the temperature dependence of the linear spontaneous birefringence can lead to an erroneous determination of the electro-optic coefficients. The electro-optic coefficient rc of LiNbO3 has been determined by an accurate technique issued from the Sénarmont method. At room temperature, rc=19.9×10−12 m/V, with an estimated error of ±5%. The measurements are performed for values of the dc applied electric field as a function of the temperature around room temperature. We point out the drastic influence on the electro-optic response of the spontaneous birefringence variation due to the temperature. Accurate and reproducible values of the electro-optic coefficients are obtained only if this dependence is taken into account.
Crystallographic characteristics and electrical properties of Al-doped ZnO thin films prepared by ionized deposition
Authors: Kuroyanagi Akio
Published: July 2002

Aluminum-doped ZnO thin films were prepared by ionized deposition on glass substrates. The crystallinity and electrical properties of Al-doped ZnO films prepared by ionized evaporation depend on the deposition conditions. The c-lattice constant of ZnO films increases with ionization current and acceleration voltage. The spacing distribution of c-lattice planes varies inversely with the orientation distribution of the c axis, when deposition conditions such as ionization current, acceleration voltage, and substrate temperature are changed; the line width B002 of a (002) diffraction peak increases while the FWHM of rocking curve ΔΘ50 decreases. These changes of crystallographic characteristics cause a decrease in Hall mobility, and defects in the film resulting from ion bombardment cause a decrease in carrier concentration. Therefore, an increase in resistivity is observed in Al-doped ZnO films grown by ionized deposition. Ion bombardment during deposition must be minimized to avoid degradation of Al-doped ZnO films, because the properties of Al-doped ZnO films are significantly changed by ion bombardment of the film surface.
Acceleration instability in elastic-plastic solids. I. Numerical simulations of plate acceleration
Authors: Swegle J. W. , Robinson Allen C.
Published: July 2002

Acceleration instability occurs when a body is accelerated by surface tractions. This situation resembles classic Rayleigh–Taylor instability, but differs due to the temporal and spatial variation of the stress field in the accelerated body caused by wave propagation and the time dependence of the accelerating forces. These factors produce phenomena in acceleration instability which are without precedent in classical Rayleigh–Taylor analyses. An extensive numerical study of acceleration instability using a Lagrangian finite-difference wavecode has determined the influence of various parameters including amplitude and wavelength of initial surface perturbations, material yield strength, and time dependence of the driving force. The nature of the criteria determining stability or instability is established, and the fundamental physical quantity controlling perturbation growth at an interface is shown to be the local stress gradient.
Dielectric and pyroelectric properties of the morphotropic phase boundary lead barium niobate (PBN) single crystals at low temperature (10–300 K)
Authors: Guo R. , Bhalla A. S. , Randall C. A. , Cross L. E.
Published: July 2002

Low-temperature (10–300 K) dielectric and pyroelectric properties of morphotropic-phase-boundary lead-barium-niobate tungsten-bronze ferroelectric single crystals have been investigated. Strong ‘‘Debye-like’’ dielectric dispersion, along a nonpolar direction (perpendicular to the polarization direction), has been observed and characterized by dielectric spectrum techniques. A direct charge measurement method has been used to study the low-temperature pyroelectric properties in polar and nonpolar directions. A ‘‘frozen-in’’ polarization component in a nonpolar direction is also reported. The low-temperature relaxation effects are explained by the internal reorientation polarization perturbation and a thermally agitated local dipole fluctuation model.
Ge redistribution in solid-phase Ge/Pd/GaAs ohmic contact formation
Authors: Palmstro/m C. J. , Schwarz S. A. , Yablonovitch E. , Harbison J. P. , Schwartz C. L. , Florez L. T. , Gmitter T. J. , Marshall E. D. , Lau S. S.
Published: July 2002

A backside secondary ion mass spectrometry technique is employed to examine elemental redistribution in the Ge/Pd/GaAs ohmic contact as a function of annealing conditions. Dilute Al containing marker layers (Ga1−x Alx As) in the GaAs permit precise calibration and alignment of the elemental depth profiles. Double etch-stop thinning yields high depth resolution. The onset of ohmic behavior is found to occur when Ge is detected at the GaAs surface. Good ohmic behavior is observed when an interfacial layer of reacted Pd4GaAs is dispersed and complete coverage of Ge occurs. The Ge/GaAs interface is abrupt with the Ge concentration dropping by over three orders of magnitude within 100 Å. About 40 Å of GaAs is found to be consumed during the ohmic contact formation. Degradation of the ohmic contacts, as a result of further heat treatment, was found to correlate with Ge in-diffusion into the GaAs. The results place strict limitations on doping and heterointerface models of ohmic behavior for this contact.
An i
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i
t
u observation of the growth kinetics and stress relaxation Pd2Si thin films on Si(111)
Authors: White G. E. , Chen Haydn
Published: July 2002

The growth of the Pd2Si thin fllms on Si(111) substrates has been monitored by an in situ x-ray diffraction technique in vacuum and in helium atmosphere from 160 to 250 °C. A familiar parabolic growth rate was found, confirming the diffusion-controlled film growth process. The activation energies were found to be 1.34 and 1.37 eV for the measurements performed in vacuum and helium environment, respectively. Stress relaxation in the growing Pd2Si fllm was observed when the reaction temperature exceeds 200 °C. The relaxed films showed a higher degree of texture as evidenced by the rocking curve measurements.
High-temperature stability of platinum silicide associated with fluorine implantation
Authors: Tsai Jiunn-Yann , Tsui Bing-Yue , Chen Mao-Chieh
Published: July 2002

High-temperature stability of the F+- or BF+2 -implanted PtSi thin film was investigated. For the PtSi films that received F+ implantation, the film characteristics remain unchanged even after annealing at 800 °C for 90 min, while for those without F+ implantation, the film properties begin to degrade after annealing at 750 °C as observed by scanning electron microscopic inspection, Auger electron spectroscopy analysis, Rutherford backscattering spectroscopy analysis, and sheet resistance measurement. The secondary ion mass spectroscopy analysis indicates that the fluorine atoms are segregated to the PtSi/Si interface. A fluorine barrier model is proposed to explain the absence of Pt in-diffusion induced deterioration for the F+-implanted PtSi film.