bluuebunny/crossref_metadata_2025 huggingface dataset:
BGaInAs alloys lattice matched to GaAs
Authors: Geisz J. F. , Friedman D. J. , Olson J. M. , Kurtz Sarah R. , Reedy R. C. , Swartzlander A. B. , Keyes B. M. , Norman A. G.
Published: July 2002

We report the epitaxial growth of zinc-blende BxGa1−x−yInyAs and BxGa1−xAs on GaAs substrates with boron concentrations (x) up to 2%–4% by atmospheric-pressure metalorganic chemical vapor deposition. The band gap of BxGa1−xAs increases by only 4–8 meV/%B with increasing boron concentration in this concentration range. We demonstrate an epitaxial BxGa1−x−yInyAs layer deposited on GaAs with a band gap of 1.34 eV that is significantly less strained than a corresponding Ga1−yInyAs layer with the same band gap.
On the band gap anomaly in I–III–VI2, I–III3–VI5, and I–III5–VI8 families of Cu ternaries
Authors: Wasim S. M. , Rincón C. , Marı́n G. , Delgado J. M.
Published: July 2002

The experimentally observed energy band gap difference (ΔE1) between the I–III3–VI5 and I–III–VI2 and the energy band gap difference (ΔE2) between the I–III5–VI8 and I–III–VI2 phases of Cu–In–Se, Cu–Ga–Se, Cu–In–Te, and Cu–Ga–Te systems is explained in terms of the relative shift of the conduction band minimum (CBM) and the valence band maximum (VBM) caused due to the presence of the ordered VCu and [In(Ga)Cu+2+2 VCu−1] defect pair and to the effect of the p–d hybridization. The nearly linear variation of ΔE1 and ΔE2 with p–d hybridization of the corresponding I–III–VI2 phase suggests that in selenides the lowering of the VBM predominates over that of the CBM. In the case of the Cu–In–Te system, they are very near the same magnitude, whereas in Cu–Ga–Te the lowering of the CBM predominates over that of the VBM.
Significant improvement of the emission property of Spindt-type platinum field emitters by operation in carbon monoxide ambient
Authors: Gotoh Y. , Nozaki D. , Tsuji H. , Ishikawa J. , Nakatani T. , Sakashita T. , Betsui K.
Published: July 2002

The emission property of a Spindt-type platinum field emitter was greatly improved by operating in carbon monoxide ambient with appropriate operating parameters. After sufficient aging, the emitter was operated in carbon monoxide ambient up to 10−3 Pa, at the emission current of 1 μA. The emission current first decreased in accordance with the gas introduction, but turned to show rapid increase when the gas pressure was increased to 10−3 Pa. The current stability, as well as the operating voltage, was improved by this treatment. The apex of the emitter was examined with the Seppen–Katamuki analysis technique, in which detailed information on the emission area and effective work function can be read from the diagram plotted with the intercept and slope of a Fowler–Nordheim plot. The analysis suggested reduction of the effective work function is a major reason for the improvement of the emission property.
On-wafer characterization of thermomechanical properties of dielectric thin films by a bending beam technique
Authors: Zhao Jie-Hua , Ryan Todd , Ho Paul S. , McKerrow Andrew J. , Shih Wei-Yan
Published: July 2002

A bending beam technique has been developed for on-wafer characterization of thermomechanical properties of dielectric thin films including Young’s modulus (E), the coefficient of thermal expansion (CTE), and the Poisson ratio (ν). The biaxial modulus E/(1−ν) and CTE were determined by measuring the thermal stresses of the dielectric film as a function of temperature on two different substrates. The Poisson ratio and Young’s modulus were determined by measuring the temperature dependence of the thermal stress of periodic line structures of the dielectric film. Three dielectric thin films were selected for this study, consisting of silica made from tetraethylorthosilane (TEOS), hydrogen silsesquioxane (HSQ), and biphenyltetracarboxylic dianhydride-p-phenylene diamine (BPDA-PDA). The deduced biaxial modulus and CTE are 77 GPa and 1.0 ppm/°C for TEOS, 7.07 GPa and 20.5 ppm/°C for HSQ, and 11.1 GPa and 3.4 ppm/°C for BPDA-PDA. The Poisson ratio is determined to be 0.24 and Young’s modulus is 59 GPa for the TEOS film. The error limit and the valid range of E/(1−ν) and CTE for applying this technique are also discussed.
All-solid-state electrochromic reflectance device for emittance modulation in the far-infrared spectral region
Authors: Franke E. B. , Trimble C. L. , Schubert M. , Woollam J. A. , Hale J. S.
Published: July 2002

All-solid-state electrochromic reflectance devices for thermal emittance modulation were designed for operation in the spectral region from mid- to far-infrared wavelengths (2–40 μm). All device constituent layers were grown by magnetron sputtering. The electrochromic (polycrystalline WO3), ion conductor (Ta2O5), and Li+ ion-storage layer (amorphous WO3), optimized for their infrared (IR) optical thicknesses, are sandwiched between a highly IR reflecting Al mirror, and a 90% IR transmissive Al grid top electrode, thereby meeting the requirements for a reversible Li+ ion insertion electrochromic device to operate within the 300 K blackbody emission range. Multicycle optical switching and emittance modulation is demonstrated. The measured change in emissivity of the device is to 20%.
Photoluminescence of undoped and neutron-transmutation-doped InSe
Authors: Homs A. A. , Marı́ B.
Published: July 2002

Photoluminescence (PL) spectra of undoped and neutron-transmutation-doped InSe samples at 15 K are reported. The undoped InSe PL spectrum clearly shows the free exciton line and an exciton-neutral acceptor complex recombination. A structure of partially resolved transitions is observed between 1.315 and 1.330 eV, whose nature is discussed. An exciton bound to the native donor of ED=19 meV is also reported. Neutron-transmutation doping attenuates the excitonic transitions and increases the intensity of lower energy bands. This behavior is interpreted in terms of defects remaining after the annealing. A native acceptor level 40 meV above the valence band and two donor-acceptor pair transitions are identified.
On nonlinear effects in inductively coupled plasmas
Authors: Smolyakov A. , Godyak V. , Duffy A.
Published: July 2002

Nonlinear current and potential oscillations in low pressure inductively coupled plasmas are analyzed within the framework of electron magnetohydrodynamics. It is shown that both current and potential oscillations can be attributed, respectively, to the solenoidal and potential components of nonlinear Lorentz and inertial forces. Scaling of the nonlinear force with the phase shift between the electric current and the electric field is analyzed. It is demonstrated that the solenoidal part of the force that provides a source of nonlinear current vanishes in neglect of collisions and collisionless absorption, while oscillations of the electrostatic potential remain finite. It is shown that these oscillations are the result of plasma polarization due to Hall drifts.
Raman spectra of rhodium trimers in argon matrices
Authors: Fang Li , Shen Xiaole , Chen Xiaoyu , Lombardi John R.
Published: July 2002

Resonance Raman spectra of rhodium trimers (Rh3) in argon matrices have been obtained for the first time. Our samples are prepared by neutralizing a mass-filtered beam of trimer ions. Although the absorption spectrum of our optically thin samples failed to show any obvious transitions, a rich Raman spectrum was found for laser excitation wavelengths between 545 nm and 593 nm. Three fundamentals, corresponding to normal modes of a bent (C2v) molecule can be assigned with up to four overtones in the symmetric stretch. Using standard techniques, we obtained for this mode ωe=322.4(6) cm−1, with ωexe=0.49(10) cm−1. The resulting stretching force constant is ke=2.10±0.01 mdyn/Å. Assuming a Morse potential governs the symmetric stretching normal coordinate, we obtain an atomization energy of De=6.6±1.4 eV. The asymmetric stretch and bend are found at 259 cm−1 and 247.9(8) cm−1, respectively. A line at 400 cm−1 is observed, which does not fit the normal mode scheme of the ground state. This is assigned as the origin of a low lying electronic state.
Reduction of the hydrogen degradation in SrBi2(Ta1−xNbx)2O9 by TiN barrier metal
Authors: Furuya Akira , Cuchiaro J. D.
Published: July 2002

The use of ferroelectric SrBi2(Ta1−xNbx)2O9 (SBTN) as a mainstream form of nonvolatile memory requires that the degradation of its electrical qualities that is caused by annealing in a hydrogen atmosphere be reduced. Titanium nitride (TiN) is a candidate for use as a barrier-metal layer against hydrogen diffusion. The relationship between the degradation in the qualities of SBTN and the quality of the TiN barrier metal has been investigated. TiN when sputtered onto SBTN capacitors creates a good barrier under all sputtering conditions, and maintains the electrical characteristics of the SBTN through annealing in an atmosphere of H2. Higher density TiN films provide more effective protection. The characteristics of the degraded capacitor were investigated in terms of its current-voltage characteristic. Remanent polarization can be recovered from, at least partially, by applying a series of bipolar pulses. This rejuvenation of the electrical qualities indicates that degradation arises from a combination of electrical and structural faults.
High-temperature optical gain of 980 nm InGaAs/AlGaAs quantum-well lasers
Authors: Beffa Federico , Jäckel Heinz , Achtenhagen Martin , Harder Christoph , Erni Daniel
Published: July 2002

The optical modal gain of ridge-waveguide single-quantum-well InGaAs/AlGaAs diode lasers with an emission wavelength of 980 nm were measured up to a temperature of 250 °C. Comparisons of the obtained gain curves with a simple semiclassical model based on the single-band envelope function theory allows straightforward curve fitting of the gain as it is used, e.g., in numeric models. As a result a simple temperature dependence of the line shape function has been deduced.
Pinning of size-selected Ag clusters on graphite surfaces
Authors: Carroll S. J. , Pratontep S. , Streun M. , Palmer R. E. , Hobday S. , Smith R.
Published: July 2002

We have explored the deposition of size-selected AgN+ clusters (N=50–200) onto the graphite surface (at room temperature) over the impact energy range of 250–2500 eV, via a combination of scanning tunneling microscopy experiments and molecular dynamics simulations. We show that the clusters are pinned to the surface when the impact energy exceeds a critical value, which is proportional to the cluster size, N, via the formation of a point defect at the impact site. This prevents lateral diffusion of the clusters even at room temperature.
Lorentz transmission electron microscopy of focused ion beam patterned magnetic antidot arrays
Authors: Toporov A. Yu. , Langford R. M. , Petford-Long A. K.
Published: July 2002

A focused-ion beam has been used to pattern magnetic antidot arrays containing different sized antidots and spacings in Ni80Fe20 films. Their magnetic domain structure has been studied using Lorentz transmission electron microscopy, which has shown that the edges of the antidots pin the domain walls during magnetization reversal. The remanent domain structure was found to depend strongly on the antidot size and spacing, from domains pinned between the corners of adjacent rows of antidots for large sizes to domains pinned between the edges of adjacent antidots for small sizes. The relevance of such structures for high density recording is discussed.
Optical modeling of a-Si:H solar cells with rough interfaces: Effect of back contact and interface roughness
Authors: Zeman M. , van Swaaij R. A. C. M. M. , Metselaar J. W. , Schropp R. E. I.
Published: July 2002

An approach to study the optical behavior of hydrogenated amorphous silicon solar cells with rough interfaces using computer modeling is presented. In this approach the descriptive haze parameters of a light scattering interface are related to the root mean square roughness of the interface. Using this approach we investigated the effect of front window contact roughness and back contact material on the optical properties of a single junction a-Si:H superstrate solar cell. The simulation results for a-Si:H solar cells with SnO2:F as a front contact and ideal Ag, ZnO/Ag, and Al/Ag as a back contact are shown. For cells with an absorber layer thickness of 150–600 nm the simulations demonstrate that the gain in photogenerated current density due to the use of a textured superstrate is around 2.3 mA cm−2 in comparison to solar cells with flat interfaces. The effect of the front and back contact roughness on the external quantum efficiency (QE) of the solar cell for different parts of the light spectrum was determined. The choice of the back contact strongly influences the QE and the absorption in the nonactive layers for the wavelengths above 650 nm. A practical Ag back contact can be successfully simulated by introducing a thin buffer layer between the n-type a-Si:H and Ag back contact, which has optical properties similar to Al, indicating that the actual reflection at the n-type a-Si:H/Ag interface is smaller than what is expected from the respective bulk optical parameters. In comparison to the practical Ag contact the QE of the cell can be strongly improved by using a ZnO layer at the Ag back contact or an ideal Ag contact. The photogenerated current densities for a solar cell with a 450 nm thick intrinsic a-Si:H layer with ZnO/Ag and ideal Ag are 16.7 and 17.3 mA cm−2, respectively, compared to 14.4 mA cm−2 for the practical Ag back contact. The effect of increasing the roughness of the contact interfaces was investigated for both superstrate and substrate types of solar cells. Increasing the roughness of the carrier electrode, i.e., the rough electrode on which the silicon cell structure is deposited, up to 35 nm leads to a strong increase in the photogenerated current density; for higher values of the interface roughness the photogenerated current density tends to saturate.
Low-temperature ordering of L1–CoPt thin films promoted by Sn, Pb, Sb, and Bi additives
Authors: Kitakami O. , Shimada Y. , Oikawa K. , Daimon H. , Fukamichi K.
Published: July 2002

We have studied the effect of additional elements of Sn, Pb, Sb, and Bi on the ordering of L10–CoPt films. All of these additives are demonstrated to be very effective to promote the ordering and developing of a very large coercivity of the samples annealed at 400 °C. It is worth noting that this annealing temperature for ordering is 200 °C lower than that of pure CoPt. The crystallographic and chemical analyses have revealed that these additives easily diffuse and segregate onto the film surfaces by postannealing because of their very low surface free energy and extremely low solubility in Co. Therefore, it seems reasonable to conclude that the ordering in the CoPt film is significantly promoted at much lower temperature by the aid of a lot of defects produced by the additives excreted by postannealing.
Molecular-beam-epitaxy-grown ZnMgS ultraviolet photodetectors
Authors: Sou I. K. , Wu Marcus C. W. , Sun T. , Wong K. S. , Wong G. K. L.
Published: July 2002

Epitaxial growth of Zn1−xMgxS alloy thin films on GaP(100) substrates was carried out using the molecular-beam-epitaxy technique. In situ reflection high-energy electron diffraction studies show that the alloys can be grown with a stable zinc-blende structure up to x around 30%. For x>30%, a structural transition will occur at a critical thickness which is sensitively dependent on the x composition. A near-band-edge peak with a full width at half maximum of about 10 nm was observed in room-temperature photoluminescence measurements made on as-grown alloy thin films. Several Zn1−xMgxS-based Schottky barrier photodetectors were fabricated. Room-temperature photoresponse measurements were performed on these detectors and abrupt long-wavelength cutoffs covering 325, 305, 295, and 270 nm were achieved for devices with Mg composition of 16%, 44%, 57%, and 75%, respectively. The response curve of the Zn0.43Mg0.57S device offers a close match to the erythemal action spectrum that describes human skin sensitivity to UV radiation.
A picosecond time-resolved photoluminescence microscope with detection at wavelengths greater than 1500 nm
Authors: Smith J. M. , Hiskett P. A. , Gontijo I. , Purves L. , Buller G. S.
Published: July 2002

We describe a picosecond resolution time-resolved photoluminescence microscope with high detection sensitivity at wavelengths extending beyond 1500 nm. The instrument performs time-correlated single photon counting using an InGaAs/InP single photon avalanche diode as a detector, and provides temporal resolution of less than 300 ps (full width at half maximum) and spatial resolution down to 4 μm at a sample temperature between 4 and 300 K. Analysis of noise characteristics indicates the ability to measure the excess carrier lifetimes of semiconductor devices with excited carrier densities of less than 1014 cm−3.
High precision scanning angle ellipsometry
Authors: van Duijvenbode R. C. , van der Zeeuw E. A. , Koper G. J. M.
Published: July 2002

A home-built computer-controlled scanning angle ellipsometer setup is presented, together with a detailed method to derive the ellipsometric parameters ψ and Δ by applying null ellipsometry. The high positioning accuracy obtained with the stepper motors and the long path length make it possible to assess various alignment methods. Some of the methods proposed in the literature do not give enough accuracy to apply high precision measurements. As a reflectometer, levels of reflection amplitudes as low as 10−4.5 can be determined. In ellipsometry, null intensity is located using a simplex algorithm including corrections for angular beam deviations caused by component imperfections. With the presented method maximum accuracy is only achieved with four-zone averaging measurements, with the compensator fast axis fixed at 45°. The four polarizer and compensator combinations in the different zones lead to variations in Δ up to 20° for incidence angles close to the Brewster angle. With a first-order analysis of component imperfection effects on the ellipsometric parameters, it is shown that these large deviations are related to window birefringence, that contributes to the phase difference with a cot 2ψ dependency. Because in a four-zone average the window imperfections do not contribute significantly, values for the zone averaged values 〈ψ〉 and 〈Δ〉 are accurate within 0.01° and 0.1°, respectively.
Modification of oxidation resistance of copper films by shallow implantation
Authors: Zhao X. Q. , Han Y. F. , Liu B. X.
Published: July 2002

Using a metal vapor vacuum arc ion source with high current, a study has been made of the modification of copper thin films by implantation. It was found that a shallow implantation of Cr, Al, and Mg could effectively enhance the oxidation resistance of copper films, but not have significant influence on their conductivity since the implanted species just concentrate on the surfacial layer of the films. By x-ray diffraction, Rutherford back-scattering, and scanning electron microscopy, the effects of Cr ion implantation on the evolution of structures and morphologies of copper oxides on the copper films were presented.
Intertwined isospectral potentials in an arbitrary dimension
Authors: Kuru Ş. , Teğmen A. , Verçin A.
Published: July 2002

The method of intertwining with n-dimensional (nD) linear intertwining operator L is used to construct nD isospectral, stationary potentials. It has been proven that the differential part of L is a series in Euclidean algebra generators. Integrability conditions of the consistency equations are investigated and the general form of a class of potentials respecting all these conditions have been specified for each n=2, 3, 4, 5. The most general forms of 2D and 3D isospectral potentials are considered in detail and construction of their hierarchies is exhibited. The followed approach provides coordinate systems which make it possible to perform separation of variables and to apply the known methods of supersymmetric quantum mechanics for 1D systems. It has been shown that in choice of coordinates and L there are a number of alternatives increasing with n that enlarge the set of available potentials. Some salient features of higher dimensional extension as well as some applications of the results are presented.
Magnetochromatics of the magnetic fluid film under a dynamic magnetic field
Authors: Horng Herng-Er , Yang S. Y. , Lee S. L. , Hong Chin-Yih , Yang H. C.
Published: July 2002

The structure and the corresponding magnetochromatics of homogeneous magnetic fluid films under dynamic magnetic fields perpendicular to the film surfaces are investigated in this letter. During the application of a magnetic field from 0 up to 200 Oe, the structure in the magnetic fluid film evolves from a monodispersed state to a disordered-column state, and then to an ordered hexagonal structure. The column spacing for the instant hexagonal structure during the dynamic process was measured and found to vary from 2.41 to 1.83 μm when the field strength was raised from 60 to 200 Oe. Within this range, the hexagonal structure diffracts the visible light like an optical grating. Due to the dynamic variation of the column spacing with the increasing field strength, the color of the diffracted light changed unceasingly from red to blue when observed from a fixed point above the film. The results strongly suggest the possibility that optical devices may be developed by utilizing the magnetochromatics of magnetic fluid films under dynamic magnetic fields.
Numerical simulations of sound radiated from an axisymmetric premixed reacting jet
Authors: Zhao Wei , Frankel Steven H.
Published: July 2002

The sound radiated by an axisymmetric (two-dimensional) premixed reacting free jet was studied using direct numerical simulation. The jet was injected into cold combustion products. A narrow (in radial extent) high temperature pulse was specified at the jet inlet to stabilize the reacting jet. The computational domain included both the near-field flow and far-field acoustic regions. Both reacting and nonreacting cases were considered. The heat release associated with the reacting jet had a significant effect on the vortical structure, as well as the sound radiation level and pattern, within the jet. The sound radiation pattern and the source terms in Lighthill’s equation were used to identify apparent sound source locations. Within the context of the assumptions of the present simulations, the results showed that the effect of heat release was to: (1) Stabilize the jet, (2) enhance sound radiation levels due to an increase in the entropy source, and (3) shift the frequency of the most unstable mode to lower values, resulting in a broader sound spectrum.
Two-dimensional electrical modeling of asymmetric radio-frequency discharges for geometry effect analysis. Comparison with experiments
Authors: Radouane K. , Despax B. , Yousfi M. , Couderc J. P. , Klusmann E. , Meyer H. , Schulz R. , Schulze J.
Published: July 2002

A self-consistent two-dimensional particle model coupled to the external circuit equations was developed in an asymmetrical configuration for the self-bias voltage calculation and the reactor design study. An intermediate modeling was performed in one and two symmetrical geometries. The one-dimensional model is used to optimize the computing time which is reduced by a factor of 10 by using some optimization techniques. It is also used to validate the charged particle and basic data choices. We have shown that the consideration of only two charged particle species (electron and H3+ positive ion) is sufficient in the present hydrogen radio-frequency discharge modeling. Computational results (i.e., power density and self-bias voltage) are in good agreement with experimental results. A strong gradient of the plasma parameters (such as electric field, potential, charged particle densities and energies) was observed in the periphery of the driven electrode. Furthermore, the present two-dimensional asymmetric model shows that the interelectrode distance increase (from 1.7 up to 3.7 cm) can lead to reducing the plasma heterogeneity due to the geometrical electric field.
Investigation of Li-doped ferroelectric and piezoelectric ZnO films by electric force microscopy and Raman spectroscopy
Authors: Ni H. Q. , Lu Y. F. , Liu Z. Y. , Qiu H. , Wang W. J. , Ren Z. M. , Chow S. K. , Jie Y. X.
Published: July 2002

We have grown Li-doped ZnO films on silicon (100) using the rf planar magnetron sputtering method. The surface charges induced piezoelectrically by defect and by polarization can be observed by electric force microscopy. The Li-doped ZnO films have been proven to be ferroelectric. The Raman spectra of ZnO and Li-doped ZnO films have been measured.
Charge transfer and “band lineup” in molecular electronic devices: A chemical and numerical interpretation
Authors: Xue Yongqiang , Datta Supriyo , Ratner Mark A.
Published: July 2002

We present first-principles based calculation of charge transfer and “band lineup” in molecular electronic devices using as an example the device formed by a phenyldithiolate molecule bridging two gold electrodes and local-spin-density-functional theory with a Gaussian-type orbital basis. We show that significant charge transfer from the metal to the molecule occurs, reflecting the partially ionic character of the sulfur–gold bond and localized in the interfacial region. Such charge transfer increases the electrostatic potential in the molecule which changes the molecular energy level structures. The interaction between the molecular orbitals under the self-consistent potential and the surface metal states determines the lineup of molecular levels relative to the metal Fermi level. We also discuss the implications of our work on device engineering at the molecular scale.
Three-dimensional instability during vortex merging
Authors: Meunier Patrice , Leweke Thomas
Published: July 2002

The interaction of two parallel vortices of equal circulation is observed experimentally. For low Reynolds numbers (Re), the vortices remain two dimensional and merge into a single one, when their time-dependent core size exceeds approximately 30% of the vortex separation distance. At higher Re, a three-dimensional (3-D) instability is discovered, showing the characteristics of an elliptic instability of the vortex cores. The instability rapidly generates small-scale turbulent motion, which initiates merging for smaller core sizes and produces a bigger final vortex than for laminar 2-D flow.
Electronic structure of noncrystalline transition metal silicate and aluminate alloys
Authors: Lucovsky G. , Rayner G. B. , Kang D. , Appel G. , Johnson R. S. , Zhang Y. , Sayers D. E. , Ade H. , Whitten J. L.
Published: July 2002

A localized molecular orbital description (LMO) for the electronic states of transition metal (TM) noncrystalline silicate and aluminate alloys establishes that the lowest conduction band states are derived from d states of TM atoms. The relative energies of these states are in agreement with the LMO approach, and have been measured by x-ray absorption spectroscopy for ZrO2–SiO2 alloys, and deduced from an interpretation of capacitance–voltage and current–voltage data for capacitors with Al2O3–Ta2O5 alloy dielectrics. The LMO model yields a scaling relationship for band offset energies providing a guideline for selection of gate dielectrics for advanced Si devices.
Observation of heat flow at transition temperature in La1−xCaxMnO3+δ Oxides
Authors: Zhang Y. B. , Li S. , Sun C. Q. , Gao W. , Dou S. X. , Hing P.
Published: July 2002

Heat-flow changes of La1−xCaxMnO3+δ (x=0.25, 0.33, and 0.375) magnetoresistive oxides at their Curie temperatures have been detected using differential scanning calorimetry in the temperature range from 173 to 293 K. However, the transition does not occur in the samples of x=0.125 and 0.5. It was found that the heat flow reflected the transition behavior and the enthalpy change of the transition decreased as the transition temperature increased. These results indicate that the La1−xCaxMnO3+δ oxides (x=0.25, 0.33, and 0.375) undergo an endothermic phase transition from a low-temperature ferromagnetic metal to a high-temperature paramagnetic insulator. It is assumed that the transition is strongly associated with a local structure change, which is correlated with the metal–insulator transition.
Optical parameters and luminescent properties of Nd:GdVO4 crystals
Authors: Xia H. R. , Jiang H. D. , Zheng W. Q. , Lu G. W. , Meng X. L. , Zhang H. J. , Liu X. S. , Zhu L. , Wang J. Y.
Published: July 2002

Based on the quantum electrodynamics and using Einstein’s coefficient and Planck’s energy density, the stimulated emission cross section was given. The measured absorption of 0.5 at. % Nd-doped Nd:GdVO4 crystal was compared to the Judd–Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric–dipole transitions of rare-earth ions on noncentrosymmetric site lacking inversion symmetry demonstrates good agreement. An absorption band around 808 nm is suitable to match laser diode pumping. The branching ratio of the fluorescence emission and stimulated emission cross section at the emissive wavelength of 1064 nm are of great advantage to produce a laser output.
Laser expulsion of an organic molecular nanojet from a spatially confined domain
Authors: Goto Masashiro , Zhigilei Leonid V. , Hobley Jonathan , Kishimoto Maki , Garrison Barbara J. , Fukumura Hiroshi
Published: July 2002

Functional organic molecules have been manipulated into fluorescent features as small as 450 nm on a polymer film using a method derived from laser ablation and laser implantation. The technique utilizes a piezodriver to position a pipette, having a 100 nm aperture and doped at the tip with organic molecules, tens of nanometers above a polymer film. The pipette is subsequently irradiated using 3 ns (full width at half maximum) laser pulses guided down to the tip by a fiber optic. This method of ablation confinement gives fine spatial control for placing functional organic molecules in a designated region and will have applications in optoelectronics. It could also be applied to drug delivery or biotechnology, because in principle, different molecules of diverse function can be manipulated in the same way for various purposes.
Electrical effects of plasma enhanced chemical vapor deposition of SiNx on GaAs Schottky rectifiers
Authors: Luo B. , Johnson J. W. , Ren F. , Baik K. H. , Pearton S. J.
Published: July 2002

The diode ideality factor, reverse breakdown voltage, and forward current characteristic were used to measure the effect on electric performance of GaAs rectifiers deposited with thin films of SiNx. Over a broad range of deposition conditions there were minimal changes (<10%) in breakdown voltage and the cause was hydrogen passivation of Si dopants in the GaAs. Ion-induced damage did not appear to play a significant role in the results. The ideality factors and forward leakage currents were essentially unchanged by the SiNx deposition indicating that the plasma exposure did not create defects states around the periphery of the Schottky contact.
X-ray induced persistent photoconductivity in Si-doped Al0.35Ga0.65As
Authors: Soh Yeong-Ah , Aeppli G. , Zimmermann Frank M. , Isaacs E. D. , Frenkel Anatoly I.
Published: July 2002

We demonstrate that x-ray irradiation can be used to induce an insulator–metal transition in Si-doped Al0.35Ga0.65As, a semiconductor with DX centers. The excitation mechanism of the DX centers into their shallow donor state was revealed by studying the photoconductance along with fluorescence. The photoconductance as a function of incident x-ray energy exhibits an edge both at the Ga and As K edge, implying that core–hole excitation of Ga and As are efficient primary steps for the excitation of DX centers. A high quantum yield (≫1) suggests that the excitation is indirect and nonlocal, due to secondary electrons, holes, and fluorescence photons.
Yield strength and dislocation mobility in plastically deformed bulk single-crystal GaN
Authors: Yonenaga Ichiro , Motoki Kensaku
Published: July 2002

The mechanical strength of bulk single-crystal wurtzite-GaN grown by the hydride vapor phase epitaxy technique is investigated at elevated temperatures by means of compressive deformation. The yield stress of GaN in the temperature range 900–1000 °C is around 100–200 MPa, i.e., similar to that of 6H-SiC and much higher than those of Si and GaAs. From the temperature dependence of the yield stress an activation energy for dislocation motion in the GaN is estimated to be 2–2.7 eV.
Three-dimensional phase field microelasticity theory and modeling of multiple cracks and voids
Authors: Jin Y. M. , Wang Y. U. , Khachaturyan A. G.
Published: July 2002

It is proved that the stress-free strain distribution minimizing the strain energy of the homogeneous modulus body fully determines the elasticity of the discontinuous body. This result is used as a basis for the proposed three-dimensional phase field microelasticity theory and model of a discontinuous body with cracks and voids in elastically anisotropic crystal under applied stress. The elastic equilibrium and spontaneous evolution of these defects are described by the Ginzburg–Landau kinetic equation. Examples of computations of elastic equilibrium and evolutions of systems with cracks and/or voids are considered.
Nanowires of four epitaxial hexagonal silicides grown on Si(001)
Authors: Chen Yong , Ohlberg Douglas A. A. , Williams R. Stanley
Published: July 2002

Epitaxial self-assembled silicide nanowires can be grown on Si (001) if the magnitude of the lattice mismatch between epilayer and substrate is large along one crystal axis and small along the perpendicular axis. This phenomenon is illustrated with four examples: ScSi2, ErSi2, DySi2, and GdSi2, which have lattice mismatches of −4.6%, 6.3%, 7.6%, and 8.9%, respectively, along one of the Si 〈110〉 directions and mismatches of 0.8%, −1.6%, −0.1%, and 0.8%, respectively, along the perpendicular Si〈110〉 direction. The resulting self-assembled nanowires have widths and heights in the range of 3–11 and 0.2–3 nm, depending on the lattice mismatches. The average lengths of the nanowires are in the range 150–450 nm, and are determined primarily by kinetic issues. The epitaxial growth of silicide nanowires should prove interesting to those studying quasi-one- dimensional systems.
Internal gravity wave emission from a pancake vortex: An example of wave–vortex interaction in strongly stratified flows
Authors: Plougonven R. , Zeitlin V.
Published: July 2002

At small Froude numbers the motion of a stably stratified fluid consists of a quasisteady vortical component and a propagating wave component. The vortical component is organized into layers of horizontal motions with well-pronounced vertical vorticity and often takes the form of so-called “pancake” vortices. An analytical model of such a vortex that is a solution of the Euler–Boussinesq equations at a vanishing Froude number is constructed as a superposition of horizontal two-dimensional Kirchhoff elliptic vortices. This vortex is nonstationary and internal gravity waves are, therefore, excited by its motion. The radiation properties are studied by matching the vortex field with the far internal gravity wave field according to the procedure applied in acoustics to determine vortex sound. The structure of the gravity wave field is completely quantified. By calculating energy and angular momentum fluxes carried by outgoing waves and attributing them to the adiabatic change of the vortex parameters, we calculate the backreaction of the internal gravity waves radiation and show that, as in the case of acoustic radiation by the Kirchhoff vortex, this adiabatic evolution leads to an elongation of the vortex, and its eventual destabilization.
Mechanism of fatigue in micron-scale films of polycrystalline silicon for microelectromechanical systems
Authors: Muhlstein C. L. , Stach E. A. , Ritchie R. O.
Published: July 2002

Reported nearly a decade ago, cyclic fatigue failure in silicon thin films has remained a mystery. Silicon does not display the room-temperature plasticity or extrinsic toughening mechanisms necessary to cause fatigue in either ductile (e.g., metals) or brittle (e.g., ceramics and ordered intermetallics) materials. This letter presents experimental evidence for the cyclic fatigue of silicon via a conceptually different mechanism termed reaction-layer fatigue. Based on mechanical testing, electron microscopy, and self-assembled monolayers, we present direct observation of fatigue-crack initiation in polycrystalline silicon, the mechanism of crack initiation, and a method for altering fatigue damage accumulation.
The real geometry of holomorphic four-metrics
Authors: Robinson D. C.
Published: July 2002

The real geometry of holomorphic four-metrics is investigated. The almost product and complex structures, associated with the real eight-metrics corresponding to the real and imaginary parts of the holomorphic metrics, are studied. It is shown that half-flat holomorphic metrics, and the corresponding real eight-metrics, are associated with integrable almost product, complex and hyper-Kähler structures. Real and complex local coordinate descriptions are presented.
Two families of superintegrable and isospectral potentials in two dimensions
Authors: Demircioğlu B. , Kuru Ş. , Önder M. , Verçin A.
Published: July 2002

As an extension of the intertwining operator idea, an algebraic method which provides a link between supersymmetric quantum mechanics and quantum (super)integrability is introduced. By realization of the method in two dimensions, two infinite families of superintegrable and isospectral stationary potentials are generated. The method makes it possible to perform Darboux transformations in such a way that, in addition to the isospectral property, they acquire the superintegrability preserving property. Symmetry generators are second and fourth order in derivatives and all potentials are isospectral with one of the Smorodinsky–Winternitz potentials. Explicit expressions of the potentials, their dynamical symmetry generators, and the algebra they obey as well as their degenerate spectra and corresponding normalizable states are presented.
Spatially resolved electron temperatures, species concentrations, and electron energy distributions in inductively coupled chlorine plasmas, measured by trace-rare gases optical emission spectroscopy
Authors: Donnelly V. M. , Schabel M. J.
Published: July 2002

Determining the spatial dependence of charged and neutral species concentrations and energies in inductively coupled plasmas (ICP) is important for understanding basic plasma chemistry and physics, as well as for optimizing the placement of the wafer with respect to the ICP source to maximize properties such as etching rate uniformity, while minimizing charging-induced damage and feature profile anomalies. We have determined the line-integrated electron temperature (Te) and Cl-atom number density (nCl) as a function of the axial distance (z) from the wafer in a chlorine ICP, using trace rare gases optical emission spectroscopy (TRG-OES). By selecting rare gas lines that are either (a) excited mostly from the ground states, or (b) excited mainly from the metastable states we were also able to obtain approximate electron energy distributions functions (EEDFs). The gap between the wafer and the window adjacent to the flat coil inductive source was fixed at 15 cm. The pressure was 2, 10, or 20 mTorr (95% Cl2, 1% each of He, Ne, Ar, Kr, Xe) and the inductive mode source power was 340 or 900 W. Te measured by TRG-OES, mostly characteristic of the high-energy (>10 eV) part of the EEDF, peaked near the source under all conditions except 2 mTorr and 900 W, where a maximum Te of 5.5 eV was observed at midgap. The falloff in this high-electron-energy Te away from the source is mainly due to a preferential loss of high-energy electrons, which can be explained by an increasingly depleted (with increasing energy) EEDF, combined with the nonlocal effect: electrons lose kinetic energy as they approach the higher potential energy regions of lower electron density near the wafer. At 20 mTorr and 340 W, the mean free path for inelastic scattering by high-energy electrons becomes comparable to the reactor dimensions, causing added cooling of the EEDF near the wafer. TRG-OES EEDFs measured at a distance of 3 cm from the wafer and 900 W are in excellent agreement with previous Langmuir probe measurements. nCl increased with power and was highest at 900 W in the region between midgap and the ICP window, reaching a level corresponding to a high degree of dissociation of Cl2.
Persistent spectral hole burning in chalcohalide glasses doped with Eu3+
Authors: Chung Woon Jin , Heo Jong
Published: July 2002

Efficient persistent spectral hole burning in Eu3+-doped sulfide glasses was observed with the addition of CsBr or KBr. Holes in these glasses showed high initial growth rates, thermal barrier heights, and low relaxation rates. It was also possible to form independent multiholes on the inhomogeneously broadened absorption spectrum. One-photon absorption of the burning light and corresponding reduction of Eu3+ into Eu2+ via interaction with local conduction (or charge transfer) bands are the main processes for hole burning.
Control of wave packet dynamics in quantum wells: Effects of Coulomb interactions
Authors: Shuford Kevin L. , Krause Jeffrey L.
Published: July 2002

We present a theoretical investigation of the effects of Coulomb interactions on the control of wave packets in quantum wells. In particular, we consider the attractive interactions between electrons and holes in an asymmetric double-quantum well. The goal of this work is to clarify the extent to which this interaction affects the controllability of wave packets in quantum-well structures. We find that significant control is attained using simple, experimentally feasible laser pulses. The optimal fields in the presence and absence of the Coulomb interaction are quite similar. The primary effect of the Coulomb interaction is to modify the energy splittings, which induces a small change in the oscillation period and eigenstate composition of the wave packet. Our results indicate that the electron–hole interaction does not substantially affect the controllability of the system dynamics, and that small adjustments in laser parameters can compensate for the interaction.
Determination of the space-charge field in polymeric photorefractive material
Authors: Joo Won-Jae , Kim Nam-Jun , Chun Hyunaee , Moon In Kyu , Kim Nakjoong , Oh Cha-Hwan
Published: July 2002

We proposed a method for measuring the magnitude of the space-charge field of the polymeric photorefractive materials. In the case of polymeric photorefractive material with low glass transition temperature, optically anisotropic chromophores are known to be reoriented under space-charge field. Simply by adding a pair of crossed polarizer units to a conventional degenerated four wave mixing setup, we could measure the birefringence of the photorefractive materials induced by a newly formed space-charge field. Since the birefringence of a given material is governed by the applied electric field, the space-charge field can be determined from the variation of birefringence using the oriented gas model.
Elastic and anelastic properties of Fe-doped InP films on silicon cantilevers
Authors: Klose F. B. , Harms U. , Neuhäuser H. , Bakin A. , Behrens I. , Peiner E. , Wehmann H.-H. , Schlachetzki A. , Rösler J.
Published: July 2002

The effect of Fe doping on the elastic and anelastic properties of heteroepitaxial InP films on microfabricated silicon cantilevers has been investigated by the vibrating-reed technique (typical frequencies 100 Hz to 10 kHz) with strain amplitudes in the range of 10−6 to 10−3 and in the temperature interval from 113 to 508 K. A matter of particular interest has been the effect of iron doping on the motion and multiplication of dislocations which are known to restrict the application of the material for instance in optoelectronic devices. For this purpose, the amplitude dependence of damping as well as internal friction as a function of temperature, thermal treatment, and frequency have been investigated and are discussed in terms of the present knowledge about twins and dislocations in InP. In addition, Young’s modulus as well as film stress have been measured as a function of temperature, which permits an estimate of the thermal expansion coefficient.
Thermal oxidation of Si (001) single crystal implanted with Ge ions
Authors: Terrasi A. , Scalese S. , Re M. , Rimini E. , Iacona F. , Raineri V. , La Via F. , Colonna S. , Mobilio S.
Published: July 2002

The thermal oxidation of Ge-implanted Si single crystals has been investigated for different Ge doses (3×1015 cm−2 and 3×1016 cm−2) and different oxidation processes (in wet ambient at 920 °C for 30, 60, and 120 min, or dry ambient at 1100 °C for 30 min). The oxide roughness, the oxidation rate, the Ge diffusion, precipitation, and clustering, have been monitored by several experimental techniques: atomic force microscopy, transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray absorption spectroscopy. We found that the surface roughness is related to the segregation of Ge at the oxide/substrate interface, occurring when the oxidation rate is faster than the Ge diffusion, in particular at the higher implanted dose (3×1016 cm−2) when processed in a wet ambient. For these conditions, we also observed an oxidation rate enhancement with respect to pure Si, and a strong indication that pure Ge clusters were formed. When a critical Ge concentration at the interface is reached, the oxidation mechanisms change and the oxidation rate is reduced, along with Ge diffusion into the substrate and a consequent reduction of the Ge fraction at the interface. Nevertheless, the oxide roughness still increases despite the Ge concentration reduction, resulting from the initial nucleation of precipitates.
Study of superalloy topography during ultrahigh intensity nanosecond ultraviolet laser ablation
Authors: Wu Qihong , Jie Jiansheng , Ma Yurong , Yu Qingxuan , Miao Bin , Wang Guanzhong , Liao Yuan , Fang Rongchuan , Chen Xiangli , Wang Kelvin
Published: July 2002

We report on the topography of holes ablated by an ultrahigh intensity 355 and 266 nm laser with 8 ns pulse width in Ni-base superalloy Inconel 718. The origin of droplets, micropores, and microcracks on the surface of hole is identified. Qualitative differences in the characteristics of microcracks indicate that the dominant continuous microcracks result from thermal effects in 355 nm laser ablation, and the dominant island-chain microcrack result from photochemical effects in 266 nm laser ablation. In ultrahigh intensity laser ablation (>200 GW/cm2), the mechanical load on the surface is very significant to the resulting topography, and the grain boundary plays an important role in the origin of the micropores.
Generation of positive and negative charges under Fowler–Nordheim injection and breakdown
Authors: Ushizaka Hironori
Published: July 2002

Characteristics shifts and time to breakdown of metal–oxide–semiconductor devices due to the Fowler–Nordheim current were investigated. The characteristics shifts were changed by holes and electrons generated in the gate oxides. Distribution of the holes and electrons shows injections of holes from anode electrodes into the gate oxide and uniform generation of electron traps except for tunneling distance of the Fowler–Nordheim current. Moreover, correlations between magnitude of gate electric fields calculated from the distribution and the time to breakdown show the breakdown occurring without impact ionizations in the gate oxide.