bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatially selective materials deposition by hydrogen-assisted laser-induced transfer
Authors: Toet D. , Smith P. M. , Sigmon T. W. , Thompson Michael O.
Published: July 2002

Si and Al lines were deposited on glass substrates using a transfer technique based on the explosive release of hydrogen from a hydrogenated amorphous Si film melted by a laser pulse. The Si lines have a minimum width of 4.5 μm and are well defined, while the Al lines are wider and less uniform. Analysis of time-resolved infrared transmission signals reveals that the lines do not break into droplets upon ejection, in contrast to the behavior of unpatterned films. This difference is attributed to the escape of hydrogen through the sides of the molten lines into the adjacent material.
A simple system of thermal control and frequency stabilization of solitary diode lasers
Authors: Andreoni E. , Xu J. H. , Cartaleva S. , Celli R. M. , Mango F. , Gozzini S.
Published: July 2002

A temperature controller using the photodiode of a free-running laser as a heater element is described. Its use can improve substantially the stabilization on a spectroscopic line and avoids the need of sink temperature controller at the millidegrees kelvin level. The long term stability of the system has been tested in performing a detailed study of the splitting of the dark lines in rubidium vapors.
Resonant-cavity InGaN quantum-well blue light-emitting diodes
Authors: Song Y.-K. , Diagne M. , Zhou H. , Nurmikko A. V. , Schneider R. P. , Takeuchi T.
Published: July 2002

We describe progress in blue resonant-cavity light-emitting diodes, based on InGaN/GaN quantum-well heterostructures. We have fabricated vertical-microcavity devices in which either one or both mirrors forming the cavity are patterned, high-reflectivity dielectrics Bragg reflectors. The results suggest that a blue vertical-cavity diode laser may be feasible by this approach.
Light-induced long-range hydrogen motion in hydrogenated amorphous silicon at room temperature
Authors: Cheong Hyeonsik M. , Lee Se-Hee , Nelson Brent P. , Mascarenhas Angelo , Deb Satyen K.
Published: July 2002

We present evidence for long-range hydrogen motion in hydrogenated amorphous silicon (a-Si:H) under room-temperature illumination, by monitoring the changes in the Raman spectrum of an a-WO3 overlayer with illumination. We observe that illumination causes hydrogen to diffuse out of the a-Si:H layer into the a-WO3 layer. This hydrogen motion is observed to saturate after about 30 min when the a-Si:H is illuminated with 15 W/cm2 of the 514.5 nm laser line at room temperature. The amount of hydrogen that diffuses out of the a-Si:H layer is estimated semiquantitatively to be approximately 9×10−4 at. %.
Experimental evidence of Si–H bond energy variation at SiO2–Si interface
Authors: Cheng Kangguo , Lee Jinju , Lyding Joseph W.
Published: July 2002

The threshold energy barrier for hydrogen desorption from the SiO2–Si interface has been assumed to be the Si–H bond energy with the value of 3.6 eV. Based on the uniform Si–H bond energy and diffusion-limited degradation, the time-dependent hot-carrier degradation of metal–oxide–semiconductor (MOS) devices has been described by the so-called power law. In this letter, by investigating the degradation of submicron n-channel MOS devices at various stress conditions and over a large time scale (0.01–10000 s), we present experimental evidence that contradicts the uniform bond energy theory and supports the bond energy variation theory proposed recently by Hess and co-workers [Appl. Phys. Lett. 75, 3147 (1999); Physica B 272, 527 (1999)]. We find that, instead of a constant power factor of n=0.5 predicted by the uniform bond/diffusion-limited energy theory, n varies from ∼0.8 at the initial stress stage to ∼0.2 at the final stress stage consistent with the bond energy variation theory.
Spin-Hamiltonian and density functional theory descriptions of spin exchange interactions
Authors: Dai Dadi , Whangbo Myung-Hwan
Published: July 2002

For a general spin dimer that has different numbers of unpaired electrons at the two spin sites, we examined the relationship between the spin exchange parameter J and the energy difference between the broken-symmetry and highest-spin states of the spin dimer on the basis of the spin-Hamiltonian Ĥ=−JŜ1⋅Ŝ2. The resulting relationship was shown to be a generalization of Noodleman’s formulas derived from the broken-symmetry method within density functional theory. We proposed a new method of calculating spin exchange parameters J within density functional theory on the basis of Slater’s transition state concept. The intrachain J values of magnetic solids A2MnF5 (A=Rb, Cs, NH4, Na, Li) were calculated by using the “transition-state” and Noodleman’s methods. The J values calculated by the transition-state method are in much better quantitative agreement with experiment.
Room-temperature random telegraph noise in luminescence from macroscopic InGaN clusters
Authors: Aoki Takao , Nishikawa Yukie , Kuwata-Gonokami Makoto
Published: July 2002

We report on photoluminescence properties of individual macroscopically sized InGaN clusters that were formed in InGaN multiple quantum wells. Phase separation in InGaN results in the formation of clusters with a size of 1–2 μm with three different indium compositions. A small fraction (one in 100–1000) of the clusters shows random telegraph noise in luminescence at room temperature. Superlinear dependence of the luminescence switching rate on excitation intensity indicates that the switching is induced by the cooperation of multiple carriers.
Radial compression and inward transport of positron plasmas using a rotating electric field
Authors: Greaves R. G. , Surko C. M.
Published: July 2002

It has recently been demonstrated that positron plasmas confined in a Penning-Malmberg trap can be compressed radially by applying a rotating electric field [Phys. Rev. Lett. 85, 1883 (2000)]. A more complete description of the original experiments is presented, together with the results of new measurements. Good coupling of the rotating electric field is observed over a broad range of frequencies. The heating caused by the rotating field is counteracted by cooling using a polyatomic gas. Rapid compression rates ṅ/n∼15 s−1 can be achieved, with central density increases of a factor of 20 or more. The good coupling and high compression rates can be explained in terms of excitation of heavily damped Trivelpiece–Gould modes, or alternatively as coupling directly to particle bounce resonances. Potential improvements and applications are discussed, including the production of high-density positron plasmas and brightness-enhanced positron beams.
Natural oxides on air-exposed and chemically treated InGaP surfaces grown by metalorganic vapor phase epitaxy
Authors: Hashizume Tamotsu , Saitoh Toshiya
Published: July 2002

Chemical properties of natural oxides on air-exposed and chemically treated In0.49Ga0.51P surfaces grown by metalorganic vapor phase epitaxy were systematically investigated by x-ray photoelectron spectroscopy. An air-exposed sample exhibited a highly In-rich surface which included a large amount of natural oxides. From the valence-band spectra and energy separations between core levels, it was found that the InPO4-like chemical phase was dominant in natural oxides of air-exposed InGaP surfaces. Chemical surface treatments in HCl and HF solutions were effective in reducing natural oxide and in recovering the surface stoichiometry.
Enhancement of second-harmonic generation in a one-dimensional semiconductor photonic band gap
Authors: Dumeige Y. , Vidakovic P. , Sauvage S. , Sagnes I. , Levenson J. A. , Sibilia C. , Centini M. , D’Aguanno G. , Scalora M.
Published: July 2002

We demonstrate significant enhancement of second-order nonlinear interactions in a one-dimensional semiconductor Bragg mirror operating as a photonic band gap structure. The enhancement comes from a simultaneous availability of a high density of states, thanks to high field localization, and the improvement of effective coherent length near the photonic band edge.
Separation of vacancy and interstitial depth profiles in ion-implanted silicon: Experimental observation
Authors: Pellegrino P. , Lévêque P. , Wong-Leung J. , Jagadish C. , Svensson B. G.
Published: July 2002

An experimental concept of studying shifts between concentration-versus-depth profiles of vacancy and interstitial-type defects in ion-implanted silicon is demonstrated. This concept is based on deep level transient spectroscopy measurements where the filling pulse width is varied. The vacancy profile, represented by the vacancy-oxygen center, and the interstitial profile, represented by the substitutional carbon–interstitial carbon pair, are obtained at the same sample temperature and can be recorded with a high relative depth resolution. For 6 MeV B11 ions, the peak of the interstitial profile is displaced by ∼0.5 μm towards larger depths compared to that of the vacancy profile, which is primarily attributed to the preferential forward momentum of recoiling Si atoms.
The treatment of classically forbidden electronic transitions in semiclassical trajectory surface hopping calculations
Authors: Jasper Ahren W. , Hack Michael D. , Truhlar Donald G.
Published: July 2002

A family of four weakly coupled electronically nonadiabatic bimolecular model photochemical systems is presented. Fully converged quantum mechanical calculations with up to 25 269 basis functions were performed for full-dimensional atom–diatom collisions to determine the accurate scattering dynamics for each of the four systems. The quantum mechanical probabilities for electronically nonadiabatic reaction and for nonreactive electronic deexcitation vary from 10−1 to 10−5. Tully’s fewest-switches (TFS) semiclassical trajectory surface-hopping method (also called molecular dynamics with quantum transitions or MDQT) is tested against the accurate quantal results. The nonadiabatic reaction and nonreactive deexcitation events are found to be highly classically forbidden for these systems, which were specifically designed to model classically forbidden electronic transitions (also called frustrated hops). The TFS method is shown to systematically overestimate the nonadiabatic transition probabilities due to the high occurrence of frustrated hops. In order to better understand this problem and learn how to best minimize the errors, we test several variants of the TFS method on the four new weakly coupled systems and also on a set of three more strongly coupled model systems that have been presented previously. The methods tested here differ from one another in their treatment of the classical trajectory during and after a frustrated hopping event. During the hopping event we find that using a rotated hopping vector results in the best agreement of semiclassical and quantal results for the nonadiabatic transition probabilities. After the hopping event, we find that ignoring frustrated hops instead of reversing the momentum along the nonadiabatic coupling vector results in the best agreement with the accurate quantum results for the final vibrational and rotational moments. We also test the use of symmetrized probabilities in the equations for the TFS hopping probabilities. These methods systematically lead to increased error for systems with weakly coupled electronic states unless the hopping probabilities are symmetrized according to the electronic state populations.
Electrical characterization of nanocrystalline carbon–silicon heterojunctions
Authors: Hastas N. A. , Dimitriadis C. A. , Tassis D. H. , Logothetidis S.
Published: July 2002

Nanocrystalline carbon (nc-C) films were grown by magnetron sputtering on n-type Si substrates at room temperature and at substrate bias voltage −200 V. The electrical transport properties of nc-C/n-Si heterojunctions are investigated by current–voltage measurements at various temperatures and capacitance–voltage measurements at room temperature. The results indicate that the forward conduction is determined by thermionic emission over a potential barrier of height 0.3 eV at temperatures above 180 K. At lower temperatures and low currents, multistep tunneling current dominates. At low reverse voltages, the reverse conduction is dominated by current generated within the depletion region, while at higher voltages the current is due to Poole–Frenkel emission.
Enhancement of dielectric constant and associated coupling of polarization behavior in thin film relaxor superlattices
Authors: Corbett M. H. , Bowman R. M. , Gregg J. M. , Foord D. T.
Published: July 2002

Thin film capacitor structures in which the dielectric is composed of superlattices of the relaxors [0.2Pb(Zn1/3Nb2/3)O3–0.8BaTiO3] and Pb(Mg1/3Nb2/3)O3 have been fabricated by pulsed laser deposition. Superlattice wavelength (Λ) was varied between ∼3 and ∼600 nm, and dielectric properties were investigated as a function of Λ. Progressive enhancement of the dielectric constant was observed on decreasing Λ, and, in contrast to previous work, this was not associated with the onset of Maxwell–Wagner behavior. Polarization measurements as a function of temperature suggested that the observed enhancement in dielectric constant was associated with the onset of a coupled response. The superlattice wavelength (Λ=20 nm) at which coupled functional behavior became apparent is comparable to that found in literature for the onset of coupled structural behavior (between Λ=5 nm and Λ=10 nm).
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A single, conductive-oxide buffer layer for the development of YBa2Cu3O7−δ coated conductors
Authors: Aytug T. , Paranthaman M. , Kang B. W. , Sathyamurthy S. , Goyal A. , Christen D. K.
Published: July 2002

Coated conductor applications in power technologies require stabilization of the high-temperature superconducting (HTS) layers against thermal runaway. Conductive La0.7Sr0.3MnO3 (LSMO) has been epitaxially grown on biaxially textured Ni substrates as a single buffer layer. The subsequent epitaxial growth of YBa2Cu3O7−δ (YBCO) coatings by pulsed laser deposition yielded self-field critical current densities (Jc) of 0.5×106 A/cm2 at 77 K, and provided good electrical connectivity over the entire structure (HTS+conductive-buffer+metal substrate). Property characterizations of YBCO/LSMO/Ni architecture revealed excellent crystallographic and morphological properties. These results have demonstrated that LSMO, used as a single, conductive buffer layer, may offer potential for use in fully stabilized YBCO coated conductors.
Effects of shapes and orientations of scatterers and lattice symmetries on the photonic band gap in two-dimensional photonic crystals
Authors: Wang Rongzhou , Wang Xue-Hua , Gu Ben-Yuan , Yang Guo-Zhen
Published: July 2002

The photonic band structures of two-dimensional photonic crystals consisting of lattices with different symmetries and scatterers of various shapes, orientations, and sizes are studied numerically. Specifically, four types of lattices (triangular, hexagonal, square, and rectangular) and five different shapes of scatterers (hexagon, circle, square, rectangle, and ellipse) are considered. The scatterers are either dielectric rods in air, or air rods in dielectric media. The lattice symmetry and all these properties of the scatterers can affect the band gap size. Given a lattice symmetry, the largest absolute photonic band gap is achieved by selecting a scatterer of the same symmetry; e.g., hexagonal rods in triangular or honeycomb lattices, square rods in square lattices, and rectangular rods in rectangular lattices. The band gap can be further maximized by adjusting the orientation and size of the scatterers; but no simple, systematic rules can be drawn.
Suppression of 1/f noise by permanent magnetic field in ion-implanted HgCdTe photodiodes
Authors: Khait Yu. L. , Garber V. , Bahir G. , Snapiro I.
Published: July 2002

A brief report on the experimental evidence and theoretical explanation of substantial effects of a permanent magnetic field (PMF) of B=0–2 T on 1/f noise in HgCdTe n+−p high performance planar photodiodes (HPPD) is presented. It is shown that the PMF suppresses 1/f noise in the HPPD at lower frequencies fLf0. These PMF effects follow from the earlier proposed nanoscopic stochastic theory of 1/f noise in solids. The proposed theoretical model is in good agreement with observations.
Raman microscopy determination of phase composition in polyfluorene composites
Authors: Stevenson R. , Arias A. C. , Ramsdale C. , MacKenzie J. D. , Richards D.
Published: July 2002

Confocal Raman spectroscopy with a spatial resolution of ⩽1 μm is used to determine the composition of binary polyfluorene composites with micro- and mesoscale phase separation. The phases are found to contain significant proportions of both constituents, implying that exciton dynamics such as charge and energy transfer may occur within a particular phase. The results presented here provide an insight into thin-film phase separation of conjugated polymer blends of interest for optoelectronic device applications. In particular, in this letter the high degree of intraphase mixing is discussed in relation to the relatively high efficiency of photovoltaic devices fabricated from these blends.
High-radiation-resistant InGaP, InGaAsP, and InGaAs solar cells for multijuction solar cells
Authors: Dharmarasu Nethaji , Yamaguchi Masafumi , Khan Aurangzeb , Yamada Takashi , Tanabe Tatsuya , Takagishi Shigenori , Takamoto Tatsuya , Ohshima Takeshi , Itoh Hisayoshi , Imaizumi Mitsuru , Matsuda Sumio
Published: July 2002

The radiation response of 3 MeV proton-irradiated InGaP, InGaAsP and InGaAs solar cells was measured and analyzed in comparison with those of InP and GaAs. The degradation of the minority-carrier diffusion length was estimated from the spectral response data. The damage coefficient KL for the 3 MeV proton-irradiated InGaP, InGaAsP and InGaAs was also determined. The radiation resistance increases with an increase in the fraction of In–P bonds in InGaP, InGaAsP and InGaAs. Differences in the radiation resistance of InGaP, InGaAs and InGaAs materials are discussed. Minority-carrier injection under forward bias is found to cause partial recovery of the degradation on irradiated InGaP and InGaAsP cells.
Low-temperature growth of SiCAlN films of high hardness on Si(111) substrates
Authors: Roucka Radek , Tolle John , Smith David J. , Crozier Peter , Tsong I. S. T. , Kouvetakis John
Published: July 2002

Thin films of metastable SiCAlN solid solution were deposited on Si(111) substrates at 550–750 °C, considerably below the miscibility gap of SiC and AlN phases at 1900 °C. Our low-temperature growth was based upon thermally activated reactions between a unimolecular precursor H3SiCN and Al atoms from an evaporative cell in a molecular-beam-epitaxy chamber. Characterization of deposited films by spectroscopic and microscopic techniques yielded near-stoichiometric composition throughout the columnar wurtzite structure with lattice parameters very close to those of 2H–SiC and hexagonal AlN. An average hardness of 25 GPa was measured for the SiCAlN films, comparable to that measured for sapphire.
Strain-induced piezoelectric field effects on light emission energy and intensity from AlInGaN/InGaN quantum wells
Authors: Aumer M. E. , LeBoeuf S. F. , Moody B. F. , Bedair S. M.
Published: July 2002

We report on the effects of the piezoelectric field and well width on the transition energy and intensity for InGaN quantum well structures with GaN or AlInGaN quaternary barriers. It was found that the emission energy of compressively strained GaN/In0.08Ga0.92N quantum wells exhibits a strong well width dependence not accounted for by quantum confinement subband energy shifting alone. However, for unstrained quantum well layers with quaternary barriers, no emission energy dependence on width was observed due to the elimination of the piezoelectric field, which was measured to be at least 0.6 MV/cm for the strained quantum wells. Furthermore, the unstrained quantum wells demonstrated a higher intensity than their strained counterparts for all quantum well widths investigated. The current data will help clarify the origin of emission in InGaN quantum wells.
Barium–strontium–titanate thin films for application in radio-frequency-microelectromechanical capacitive switches
Authors: Kirchoefer S. W. , Cukauskas E. J. , Barker N. S. , Newman H. S. , Chang W.
Published: July 2002

In this letter we report the application of barium–strontium–titanate (BST) thin film oxides as the dielectric layer in radio-frequency-microelectromechanical system (rf-MEMS) capacitive switches. BST thin films deposited at ambient temperature by off-axis sputtering have been employed for application in rf-MEMS switches. Their dielectric properties have been characterized in the frequency range from 1 to 20 GHz both on magnesium oxide and on gold metal films. Switches have been fabricated which demonstrate promising on-state capacitance and good dielectric breakdown properties. Dielectric breakdown in excess of 400 kV/cm has been measured on switches cycled in excess of 2000 times during testing.
Temperature-dependent photoluminescence of high-quality GaInNAs single quantum wells
Authors: Shirakata Sho , Kondow Masahiko , Kitatani Takeshi
Published: July 2002

Temperature dependence of the near-bandedge photoluminescence (PL) was studied on a 10-nm Ga0.68In0.32N0.01As0.99/GaAs single quantum well (SQW) prepared by molecular-beam epitaxy for both the as-grown and the rapid-thermal-annealed (RTA) samples. Full width at half maximum (FWHM) value was 18–26 meV (for 80–280 K) and 11–19 meV (for 8–280 K) for the as-grown and the RTA samples, respectively. The FWHM of the RTA sample is the smallest among the samples prepared before and those reported so far. At low temperature (8–50 K), a PL peak due to the localized level was observed for the as-grown sample. However, no such peak was observed for the RTA sample. The PL intensity of the RTA sample was about 10–100 times larger than that of similar SQWs grown previously. These results indicate that the crystal quality of the RTA GaInNAs SQW used in this study is both outstanding and comparable with that of the corresponding GaInAs SQW.
Direct observation of Ga-rich microdomains in crack-free AlGaN grown on patterned GaN/sapphire substrates
Authors: Riemann T. , Christen J. , Kaschner A. , Laades A. , Hoffmann A. , Thomsen C. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I.
Published: July 2002

The strong three-dimensional modulation of the optical and structural properties due to the self-organized formation of Ga-rich AlGaN microdomains is directly imaged by spectrally and spatially resolved cathodoluminescence microscopy. The 5-μm-thick, crack-free AlGaN was grown on patterned GaN/sapphire templates periodically structured into trenches and terraces. During initial AlGaN overgrowth, the modulation of the local AlGaN stochiometry results in marble-like striations of Ga accumulation clearly reflecting the pattern periodicity. In contrast, after subsequent overgrowth, a homogeneous emission wavelength, i.e., a homogeneous aluminum content, is found near the sample surface. However, the strong rise of quantum efficiency directly above the trenches indicates a drastic improvement of material quality.
Hyperfine structure of the 13Δg, 2 3Πg, and 33Σg+ states of Li6Li7
Authors: Li Li , Lazoudis Angelos , Yi Peng , Liu Yaoming , Huennekens John , Field Robert W. , Lyyra A. Marjatta
Published: July 2002

The hyperfine splittings of the 1 3Δg, 2 3Πg, and 3 3Σg+ states of Li6Li7 have been resolved by sub-Doppler, continuous wave, perturbation facilitated optical–optical double resonance excitation spectroscopy through newly identified A 1Σu+ (vA′=5, J′=24)∼b 3Πu (vb′=12, N′=23, J′=24) mixed window levels. The 3 3Σg+ and 1 3Δg states follow the case bβS coupling scheme. The Fermi contact interaction between the Li7 nucleus and the electron spin is the dominant term for the observed hyperfine splittings. The Fermi contact constants for the Li7 nucleus in the Li6Li7 molecule have been determined to be 110 MHz for the 3 3Σg+ state and 107 MHz for the 1 3Δg state. The 2 3Πg state has doubly excited character and its hyperfine coupling is different from that of the 3 3Σg+ and 1 3Δg states. The Fermi contact constants of triplet Rydberg states of Li6Li7 versus Li27 are discussed, and insights into the physical basis for case bβS coupling are illustrated.
Strong reduction of thermally activated flux jump rate in superconducting thin films by nanodot-induced pinning centers
Authors: Crisan A. , Badica P. , Fujiwara S. , Nie J. C. , Sundaresan A. , Tanaka Y. , Ihara H.
Published: July 2002

From frequency-dependent ac susceptibility studies of (Cu,T1)BaSrCa2Cu3Oy superconducting thin films, with and without nanodot-induced artificial pinning centers, we estimated the activation energy of flux jumps. The result was that, in the film with nanodots, the pinning potential is several times higher, leading to a probability of thermally activated flux jumps several orders of magnitude lower than in the film without artificial pinning centers. We suggest that our no cost straightforward method for creating extended defects can be successfully employed for the reduction of thermal noise in superconducting electronic devices.
Tunable photonic strength in porous GaP
Authors: Rivas J. Gómez , Lagendijk A. , Tjerkstra R. W. , Vanmaekelbergh D. , Kelly J. J.
Published: July 2002

The light-scattering properties of porous gallium phosphide, prepared by electrochemical etching, are investigated. We show that the photonic strength of the porous semiconductor can be tuned from weak to extremely strong. This tunability is related to the density and size of the pores, which are controlled by the dopant density of the GaP crystals, and the etching potential. Moreover, electrochemical etching does not introduce any significant optical absorption, which makes porous GaP suitable for many photonic applications.
Appearance of the superconducting phase transition of solders in magnetoresistance measurements
Authors: Buij A. W. , Schleijpen H. M. A. , Blom F. A. P.
Published: July 2002

We have examined the influence of the superconducting phase transition in the solder materials Rose-metal (Bi-52.5%, Pb-32%, Sn-15.5%), CdIn alloy (Cd-50%, In-50%), and indium on magnetoresistance measurements of (Cd1−xMnx)3As2 . The superconducting phase transition of these solders takes place within the temperature and magnetic field ranges where quantum oscillations of magnetoresistance usually are observed. The appearance of the generated anomalous signals may lead to misinterpretation, in terms of anomalous oscillations of the magnetoresistance or quantization of the surface impedance. We have found a correlation between the magnitude of the anomalous signals and the resistivity ratio of solder and sample material.
Current drift associated with surface recombination current in InGaAsP/InP optical devices
Authors: Fukuda Mitsuo
Published: July 2002

The current drift associated with surface recombination current is confirmed in InGaAsP/InP double heterostructure diodes and a model of the current drift is proposed. Moreover, the electrical behavior of the surface in InGaAsP/InP double heterostructure devices under low voltage bias is discussed through the model.
Stability of metallic CsCl-structured alloys under ion irradiation
Authors: Nastasi M. , Lilienfeld D. , Johnson H. H. , Mayer J. W.
Published: July 2002

The ion irradiation stability of the CsCl phases CoAl, IrAl, SiRu, and AuZn has been investigated. Thin-film (∼500-Å-thick) transmission electron microscopy samples were irradiated with Xe to a maximum dose of 4×1015 ions/cm2 at room temperature. Irradiation-induced transformations in the compound samples were examined by transmission electron diffraction. The alloys CoAl, IrAl, and AuZn remained crystalline while SiRu became amorphous. Analysis of our findings and other previously reported experimental results indicate that CsCl compound stability under ion irradiation is strongly correlated with atomic mobilities.
InGaAsP superlattices grown by liquid-phase epitaxy
Authors: Benchimol J. L. , Slempkes S. , N’Guyen D. C. , LeRoux G. , Bresse J. F. , Primot J.
Published: July 2002

The liquid-phase epitaxy of InGaAsP periodic structures is reported. A conventional horizontal sliding boat or a computer-controlled rotating crucible was used to grow two types of structures. Stacks of thin layers grown from the same melt showed high-quality x-ray diffraction profiles, which are shown to allow a precise determination of layer thickness; supersaturation was found to significantly influence layer thickness for short growth times. In superlattices such as InP/InGaAsP or InGaAsP/InGaAs, good composition and thickness reproductibility throughout the structure was verified by Auger sputtering. The presence of satellite peaks in x-ray diffraction profiles clearly proved that periodicity was well achieved in these structures. Quantum effects were observed by photoluminescence in sufficiently small wells.
A new connection rule of wave functions at a heterointerface and band discontinuity between GaAs and AlGaAs
Authors: Ishibashi A. , Mori Y. , Kaneko K. , Watanabe N.
Published: July 2002

A new connection rule of wave functions at a heterointerface was developed. This connection rule satisfies the conservation of probability current and contains a nonparabolic effective mass of carriers as a natural consequence of the theory. The subband energies in a GaAs/AlGaAs quantum well calculated using our new connection rule are in excellent conformity with a wide range of experimental results with band discontinuity of 85% and an effective mass for hole of 0.34m0.
Exact solution of three-dimensional transport problems using one-dimensional models
Authors: Misiakos K. , Lindholm F. A.
Published: July 2002

Several parameters of certain three-dimensional semiconductor devices including diodes, transistors, and solar cells can be determined without solving the actual boundary-value problem. The recombination current, transit time, and open-circuit voltage of planar diodes are emphasized here. The resulting analytical expressions enable determination of the surface recombination velocity of shallow planar diodes. The method involves introducing corresponding one-dimensional models having the same values of these parameters.
Electron flow and impedance of an 18-blade frustum diode
Authors: Sanford T. W. L. , Lee J. R. , Halbleib J. A. , Quintenz J. P. , Coats R. S. , Stygar W. A. , Clark R. E. , Faucett D. L. , Webb D. , Heath C. E. , Spence P. W. , Kishi J. , Schlitt L. G. , Morton D.
Published: July 2002

A new, large-area, high-uniformity, flash x-ray source that efficiently couples electrical energy to photon energy has been successfully constructed and tested on the 1-MV, 2-MA electron accelerator SPEED (short pulse experimental electron device). The source employs 18 individual blade diodes arranged in the configuration of a frustum. Each blade was magnetically isolated on the real-cathode side of an anode foil, but not on the virtual-cathode side. The operation of the diode was heavily diagnosed using 24 Rogowski coils, a vacuum voltage monitor, p-i-n diode detectors, an 80-element TLD array, and a fast-framing x-ray pinhole carnera. The individual blade diodes were found to exhibit line pinching, end-to-end pinching, and minimal electron reflexing through the Ta anode foil, with a radiation yield that agreed with Monte Carlo simulations. The end-to-end pinch location could be controlled by tapering the anode–cathode gap. The impedance depended on only the smallest spacing, and was independent of pinch location.
Thermal, fracture, and laser-induced decomposition of pentaerythritol tetranitrate
Authors: Ng W. L. , Field J. E. , Hauser H. M.
Published: July 2002

This paper describes a study of the decomposition of pentaerythritol tetranitrate (PETN) using a high-resolution time-of-flight mass spectrometer. The decomposition was induced by fracturing single crystals and by laser irradiation. In the fracture experiments, the energy input was varied from the lowest level necessary to produce smooth cleavage surfaces to high-energy loading which produced rough conchoidal fracture surfaces. In the laser experiments, a ruby laser was used in both normal and Q-switched modes, and again the energy input was varied. For all the various experiments, the reaction products were analyzed and reaction schemes are proposed. It is shown that low-energy fracture causes decomposition which follows the same reaction pathway as that induced thermally, with initial failure at the RO-NO2 bond. However, high-energy fracture results in the breaking of the C-C bonds. Two reaction pathways were observed with the laser irradiation. The first is the normal thermal process, but evidence was also found for failure at the R-ONO2 bond. The reaction continued for several milliseconds after the end of the laser pulse, suggesting a ‘‘partial’’ ignition of the explosive. In other experiments, the conditions for laser initiation of PETN in vacuum were investigated. Explosion occurred when Q-switched pulses of 1 J energy were applied to a molten layer of PETN.
Radiative transfer in multilayered random medium with laminar structure: Green’s function approach
Authors: Karam M. A. , Fung A. K.
Published: July 2002

For a multilayered random medium with a laminar structure a Green’s function approach is introduced to obtain the emitted intensity due to an arbitrary point source. It is then shown that the approach is applicable to both active and passive remote sensing. In active remote sensing, the computed radar backscattering cross section for the multilayered medium includes the effects of both volume multiple scattering and surface multiple scattering at the layer boundaries. In passive remote sensing, the brightness temperature is obtained for arbitrary temperature profiles in the layers. As an illustration the brightness temperature and reflectivity are calculated for a bounded layer and compared with results in the literature.
Kinetics of nuclear super-radiance
Authors: Baldwin G. C. , Feld Michael S.
Published: July 2002

We derive the minimum requirements for super-radiant gamma-ray emission by applying the semiclassical theory of coherent spontaneous emission to the case of nuclear transitions in a crystal host. We find that, if a pure sample of a storage isomer can be rapidly transferred into an inverted population for a recoilless transition, less than 1013 nuclei should suffice for an experimental demonstration of nuclear super-radiance.
Temperature dependence of two-dimensional hole gas in modulation-doped p-AlxGa1−xAs/GaAs heterojunctions
Authors: Oe Kunishige , Tsubaki Kotaro
Published: July 2002

Temperature dependence of transport properties of the two-dimensional hole gas (2DHG) at p-AlxGa1−xAs/GaAs heterostructures grown by molecular-beam epitaxy (MBE) was investigated. A phenomenon in which the 2DHG vanishes at low temperatures is found in the samples that were grown in an insufficient outgassing condition and unintentionally highly doped with carbon. It is peculiar to the 2DHG system because of two reasons; one is that the effective mass of the holes is much larger than that of electrons, which results in the Fermi level of the system being more dependent on the acceptors in GaAs. The second is that the acceptor level in GaAs is deeper than the donor level in GaAs and holes are more easily trapped by the acceptor levels at low temperatures. To prevent the 2DHG disappearance, two methods were successfully applied; one is to reduce acceptors in unintentionally doped GaAs, and the other is to dope more Be acceptors in the AlxGa1−xAs layer. By outgassing the MBE apparatus sufficiently, a mobility of 83500 cm2/V s at 4.2 K has been achieved at hole concentrations of ps=2.0×1011 cm−2 in the 2DHG sample. The persistent photoconductivity (PPC) effect was also found in the sample whose 2DHG vanishes at 4.2 K. This fact shows that the carbon acceptor level works as a PPC center in GaAs.
Silicon autocompensation in GaAs grown by molecular-beam epitaxy
Authors: Ballingall J. M. , Morris B. J. , Leopold D. J. , Rode D. L.
Published: July 2002

A systematic study has been made of silicon dopant compensation in GaAs grown by molecular-beam epitaxy. The compensation ratio is derived from Hall measurements for a number of samples grown under identical conditions except for silicon dopant flux. Results are compared with low-temperature (4.2 K) photoluminescence measurements. The donor and acceptor concentrations are both related to the silicon effusion cell temperature by Arrhenius relations; however, each is fitted with a different activation energy. This leads to increasing compensation with increasing dopant flux.
Monte Carlo scattering calculations of 24.8-MeV electrons through C, Al, Cu, and Pb foils
Authors: Antolak A. J. , Williamson W.
Published: July 2002

The absorption and scattering (reflection plus transmission) energy spectra of normally incident 24.8-MeV electrons on C, Al, Cu, and Pb foils have been calculated using an updated version of the relativistic Monte Carlo electron/photon transport code sandyl. The theoretical results are compared with recent experimental data and good agreement is found.
Tunable multiline and single-line operations on a pulsed transversely excited atmospheric pressure CO2 laser by means of an intracavity CO2 gas absorber
Authors: Kim Chil-Min , Park Song Chan , Kim Yongduk
Published: July 2002

The operating rotational-vibrational transition lines are observed in a pulsed transversely excited atmospheric pressure CO2 laser with a separated intracavity CO2 gas absorber. The laser operates a dominant 10.6-μm P-20 and P-18 line in a low pressure of CO2 cell and a single-line operation of P-20 line at more high pressure. In a high pressure, the laser does not operate the 10.6-μm P-20 and P-18, but it operates the single-line operation of 10.6-μm R-14, R-18, P-22, and 9.4-μm R-12, and in multiline oscillation, of various combinations of these lines and 10.6-μm R-16, according to the temperature of this gas absorber. The results are attributed to the absorbing mechanism of the CO2 gas.
Structural and optical properties of CoxIn2S3+x thin films grown by spray pyrolysis method
Authors: Kim Wha-Tek , Yun Chang-Sun , Jeong Hae-Mun , Kim Chang-Dae
Published: July 2002

CoxIn2S3+x thin films with various relative compositions were grown on thoroughly cleaned glass plates by the spray pyrolysis method. The substrate temperature during growth was maintained at 270 °C and the film then annealed in a vacuum chamber at 2×10−5 Torr at 500 °C for 30 min. The grown CoxIn2S3+x thin films, which had a composition of x=0.0–0.6, showed the tetragonal structure of In2S3, but above x=0.6 the films were amorphous. The energy gap for these films decreased with increasing x composition, and the impurity absorption spectra in near infrared region, ascribed to Co2+ ions, were observed at 13 333, 5970, and 4166 cm−1, which are the 4A2(F)−4T1(P), 4A2(F)−4T1(F), and 4A2(F)−4T2(F) transitions, respectively.
Effect of organic additives to a nitrogen laser
Authors: Kumar S. V. Krishna , Mitra S. K.
Published: July 2002

Contrary to recent predictions, it has been observed that the addition of small quantities of hydrogen, ethanol, and benzene to nitrogen reduce the output power of a nitrogen laser. N,N-dimethylaniline enhances the output power of the laser by 25%. A Penning ionization process is proposed as a mechanism for quenching the B 3Πg state of nitrogen.
Influence of NH3 plasma pretreatment on the properties of plasma-enhanced chemical-vapor-deposited SiON on GaAs interface
Authors: Wu C. Y. , Lin M. S.
Published: July 2002

Interface properties of plasma-enhanced chemical-vapor-deposited dielectric SiON on GaAs systems pretreated by NH3 plasma were studied. The effects of the process parameters in the NH3 plasma pretreatment, such as total pressure, radio-frequency power, substrate temperature, NH3 flow rate and pretreatment time, were investigated by the measurements of Auger electron spectroscopy, Raman spectroscopy, current-voltage, and capacitance-voltage characteristics. The transient region width and the surface strain field, surface leakage current, hysteresis, and degree of Fermi-level pinning evidently related to interface properties, are increased with increasing total pressure, decreased with increasing radio-frequency power, substrate temperature, and pretreatment time, and independent of NH3 flow rate. The physical and electrical properties of SiON/GaAs interface have been significantly improved under an optimum NH3 plasma pretreatment condition. The correlation of these parameters in pretreatment process with the interface properties including interdiffusion, surface strain field, surface leakage current, hysteresis, and Fermi-level pinning are discussed.
Release behavior of shock loaded commercial alumina
Authors: Rosenberg Z. , Yeshurun Y.
Published: July 2002

Plate impact experiments were conducted on AD-85 alumina specimens (manufactured by Coors) in the low shock stress region. The experimental configuration consisted of impacting a thin flyer disc (either copper or alumina) on a relatively thick specimen disc (the target). A thin manganin stress gauge was placed at the back face of the specimen supported by a thick polymethylmethacrylate disc. After recording the initial shock at the specimen-PMMA interface, the gauge showed an unusually fast compressional wave preceding the main release wave which originates at the flyer’s back surface. This wave appeared for all the shots with copper flyers and impact velocities resulting shock stresses in the 0–30 kb range. They did not appear when alumina flyers were used. Our explanation for the origin of this fast compressional wave is based on the possible occurrence of dilatancy in the specimen upon stress unloading.
Optimization and insight by geometric programming
Authors: Duffin R. J. , Peterson E. L.
Published: July 2002

The main ideas of geometric programming are introduced via elementary examples drawn from engineering design, operations research, chemical equilibrium, entropy maximization, and statistical inference.
High-spectral-resolution pulsed photoluminescence study of molecular-beam-epitaxy-grown GaAs/AlxGa1−xAs multi-quantum-well structures using a very-low-power tunable pulsed dye laser
Authors: Naganuma M. , Song J. J. , Kim Y. B. , Masselink W. T. , Morkoç H. , Vreeland T.
Published: July 2002

Ultralow-power, high-resolution, pulsed-laser photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies were carried out in molecular-beam-epitaxial GaAs/AlxGa1−xAs multi-quantum-well structures at 5 K. Fine structures were observed for the first time in the PLE spectra, both in the heavy-hole and light-hole excitonic regions. Most of the fine structures are considered to arise from monolayer fluctuations in the thicknesses of the GaAs wells. Dramatic changes in the line shapes and the peak positions of the PL and PLE spectra were observed by applying selective PL detection and excitation spectroscopic techniques.
Application of the electrostatic energy analyzer to cluster size measurement
Authors: Yano K. , Be S. H.
Published: July 2002

An electrostatic energy analyzer with a deflection angle of 90° and a resolving power of about 4% up to 200 keV was used to analyze the distribution from a cluster ion source. The experiments were carried out with cluster-ion beams of nitrogen extracted from a specially designed cluster ionizer for controlling the cluster sizes. It is shown that the cluster size as large as ∼105 atoms/cluster is measurable with this energy analyzer.
Charge transfer in the Al–Mg alloy
Authors: Park Chong-yun , Sagawa Takasi
Published: July 2002

The edge shift at the threshold in the L2,3 soft x-ray emissions spectra of Al and Mg in the γ-phase Al–Mg alloy was measured with a 2-m grazing incidence spectrometer of high resolution under ultrahigh vacuum (UHV). The work function of metallic Al, Mg, and Al–Mg alloy were measured by ultraviolet photoemission spectroscopy in UHV (5×10−10 Torr). The measured work function has shown that charge transfer from Mg to Al takes place on alloying and that the edge shift of the L2,3 soft x-ray emission spectrum in Al–Mg alloy is caused by such a charge transfer.
Effects of dislocations on axial channeling radiation from positrons
Authors: Pathak Anand P. , Balagari Prasanna K. John
Published: July 2002

The effects of a moderate concentration of noninteracting dislocations on the axial channeling radiation due to MeV positrons are analytically calculated. The axial potential due to all the six strings surrounding a 〈110〉 axial channel in diamond structure is first obtained which is exact up to quartic terms in distance from the central axis of the channel. The particle oscillation period and hence the radiation frequency depends upon the oscillation amplitude. The effects of dislocations are manifested through the modification in the oscillation amplitude of the channeled particle. We have suggested some suitable experiments to test the results.
Measurement of properties of the n layer in hydrogenated amorphous silicon solar cells
Authors: Sanchez-Sinencio F. , Williams Richard
Published: July 2002

By measuring flat-band voltage as a function of light intensity it is possible to get information about the transport properties of an intact solar cell. We illustrate different kinds of behavior and show how these are related to solar cell performance.
Capture-emission process in double Poole–Frenkel well traps: Theory and experiments
Authors: Chang C. Y. , Hsu W. C. , Wang S. J. , Hau S. S.
Published: July 2002

The field-dependent capture-emission process has been studied for double Poole–Frenkel well traps compared with that of single Poole–Frenkel well trap. The emission rate increases with increasing field strength for a single trap. However, for a double trap, it increases to a maximum then decreases with further increasing field due to the barrier lowering and interstate interactions between these two wells. Experimental capacitance deep-level transient spectroscopic data of GaAs samples grown by molecular-beam epitaxy show that when there is a delay in the capacitance transient then there always appear two levels, namely, 0.4 and 0.5 eV. In addition, for both levels, the emission rate increases first to a maximum and then decreases with increasing electric field.
Transient transport measurement on ion-implanted polymers
Authors: Wasserman B. , Dresselhaus M. S. , Wolf M. , Wnek G. E. , Woodhouse J. D.
Published: July 2002

Current transient measurements are carried out on ion-implanted polymers to provide new information on the mechanism for the implantation-induced conductivity. Using metal-oxide-semiconductor field-effect transistor devices in which implanted polymer films form part of the metal-oxide-semiconductor structure, the dispersion parameter α is measured as a function of ion fluence and temperature. The fluence dependent measurements provide evidence for trapping sites and support a trap-controlled hopping mechanism for ion-implanted polymers. The temperature-dependence measurements favor conduction by hopping between traps in the defect band in the mobility gap rather than between traps in the mobility edges. New results are also presented on the dc conductivity of polymers implanted at low temperature (77 K), the same samples as were used for the current transient measurements.
Field-effect density of states in a-(Si,Ge):H films
Authors: Singh P. , Fagen E. A.
Published: July 2002

We report field-effect measurements of the density-of-states (DOS) distribution in the last-deposited surface of undoped glow-discharge a-(Si,Ge):H alloy films containing up to 15% Ge. Over the energy range investigated (Ef≤E≤Ef+0.4 eV) the DOS exhibits a peak approximately 0.7 eV below Ec, and the total number of midgap states increases monotonically by a factor of 2 with Ge content. No structure specifically attributable to Ge defect states is seen. These results are interpreted in terms of a diphasic microstructural model of the alloy films.