bluuebunny/crossref_metadata_2025 huggingface dataset:
Alpha‐1B adrenergic receptor knockout mice are protected against methamphetamine toxicity
Authors: Battaglia Giuseppe , Fornai Francesco , Busceti Carla Letizia , Lembo Giuseppe , Nicoletti Ferdinando , De Blasi Antonio
Published: February 2004

The psychostimulant methamphetamine (MA) is toxic to nigro‐striatal dopaminergic terminals in both experimental animals and humans. In mice, three consecutive injections of MA (5 mg/kg, i.p. with 2 h of interval) induced a massive degeneration of the nigro‐striatal pathway, as reflected by a 50% reduction in the striatal levels of dopamine (DA) and 3,4‐dihydroxyphenylacetic acid (DOPAC), by a substantial reduction in striatal tyrosine hydroxylase and high‐affinity DA transporter immunostaining, and by the development of reactive gliosis. MA‐induced nigro‐striatal degeneration was largely attenuated in mice lacking α1b‐adrenergic receptors (ARs). MA‐stimulated striatal DA release (measured by microdialysis in freely moving animals) and locomotor activity were also reduced in α1b‐AR knockout mice. Pharmacological blockade of α‐adrenergic receptors with prazosin also protected wild‐type mice against MA toxicity. These results suggests that α1b‐ARs may play a role in the toxicity of MA on nigro‐striatal DA neurons.
Increased survival and neuroprotective effects of BN82451 in a transgenic mouse model of Huntington's disease
Authors: Klivenyi Peter , Ferrante Robert J. , Gardian Gabrielle , Browne Susan , Chabrier Pierre‐Etienne , Beal M. Flint
Published: February 2004

There is substantial evidence that excitotoxicity and oxidative damage may contribute to Huntington's disease (HD) pathogenesis. We examined whether the novel anti‐oxidant compound BN82451 exerts neuroprotective effects in the R6/2 transgenic mouse model of HD. Oral administration of BN82451 significantly improved motor performance and improved survival by 15%. Oral administration of BN82451 significantly reduced gross brain atrophy, neuronal atrophy and the number of neuronal intranuclear inclusions at 90 days of age. These findings provide evidence that novel anti‐oxidants such as BN82451 may be useful for treating HD.
Statistical evaporation of rotating clusters. III. Molecular clusters
Authors: Calvo F. , Parneix P.
Published: February 2004

Unimolecular evaporation of weakly bound clusters made of rigid molecules is considered from the points of view of statistical theories and molecular dynamics simulations. We explicitly work out expressions for the kinetic energy released and product angular momentum distributions within the sphere+sphere and sphere+linear rigid body assumptions of phase space theory (PST). Various approximations are investigated, including the shape of the interaction potential between the two fragments and the anharmonicity of the vibrational density of states. The comparison between phase space theory and simulation for nitrogen and methane clusters shows a quantitative agreement, thereby suggesting that PST is accurate in predicting statistical observables in a wide range of systems under various physical conditions.
Electron affinity of the sodium atom within the coupled-channel hyperspherical approach
Authors: De Groote J. J. , Masili Mauro
Published: February 2004

We present a nonadiabatic calculation, within the hyperspherical adiabatic approach, for the ground state energy of the alkali–metal negative ions. An application to the sodium negative ion (Na−) is considered. This system is treated as a two-electron problem in which a model potential is used for the interaction between the Na+ core and the valence electrons. Potential curves and nonadiabatic couplings are obtained by a direct numerical calculation, as well as the channel functions. An analysis of convergence is made and comparisons of the electron affinity with results of prior work of other authors are given.
Double-quantum homonuclear correlation magic angle sample spinning nuclear magnetic resonance spectroscopy of dipolar-coupled quadrupolar nuclei
Authors: Mali Gregor , Fink Gerhard , Taulelle Francis
Published: February 2004

A double-quantum homonuclear correlation nuclear magnetic resonance experiment for dipolar-coupled half-integer quadrupolar nuclei in solids is presented. The experiment is based on rotary resonance dipolar recoupling and uses bracketed spin-lock pulses to excite double-quantum coherence and later to convert it to the zero-quantum one. A central-transition-selective π pulse at the beginning of the t1 evolution period differentiates coherence transfer pathways of double-quantum coherences arising from coupled spins and from a single spin, so that the latter can be efficiently filtered out by phase cycling. The experiment was tested on an aluminophosphate molecular sieve AlPO4-14, a material with a variety of aluminum quadrupolar coupling constants, isotropic chemical shifts and homonuclear distances. In a two-dimensional spectrum aluminum dipolar couplings with internuclear distances between 2.9 and 5.5 Å were resolved. Although the experiment requires an application of weak radio-frequency fields, frequency offsets did not affect its performance crucially.
Mode-switching and nonlinear effects in compressible flow over a cavity
Authors: Kegerise Michael A. , Spina Eric F. , Garg Sanjay , Cattafesta Louis N.
Published: February 2004

Multiple distinct peaks of comparable strength in unsteady pressure autospectra often characterize compressible flow-induced cavity oscillations. It is unclear whether these different large-amplitude tones (i.e., Rossiter modes) coexist or are the result of a mode-switching phenomenon. The cause of additional peaks in the spectrum, particularly at low frequency, is also unknown. This article describes the analyses of unsteady pressure data in a cavity using time-frequency methods, namely the short-time Fourier transform (STFT) and the continuous Morlet wavelet transform, and higher-order spectral techniques. The STFT and wavelet analyses clearly show that the dominant mode switches between the primary Rossiter modes. This is verified by instantaneous schlieren images acquired simultaneously with the unsteady pressures. Furthermore, the Rossiter modes experience some degree of low-frequency amplitude modulation. An estimate of the modulation frequency, obtained from the wavelet analysis, matches the low-frequency peak seen in the autospectrum. Higher-order spectral methods were employed to investigate potential quadratic nonlinear interactions between the Rossiter modes and to determine if they are responsible for the low-frequency mode present in the autospectrum. In turn, this low-frequency mode could interact with the Rossiter modes to modulate their amplitude. Significant nonlinearities, in the form of sum and difference frequencies of the Rossiter modes, are present in the l/d=2 cavity at M∞=0.4, while nonlinear effects are much smaller in the l/d=4 at M∞=0.6. The bispectral analysis indicates that quadratic interactions between Rossiter modes in the near-field pressure are not responsible for the observed low-frequency peak in the pressure autospectrum. Furthermore, the low-frequency mode does not exhibit a strong nonlinear coupling with the Rossiter modes.
Coupled numerical and theoretical study of the flow transition between a rotating and a stationary disk
Authors: Serre Eric , Tuliszka-Sznitko Ewa , Bontoux Patrick
Published: February 2004

Both direct numerical simulation and theoretical stability analysis are performed together in order to study the transition process to turbulence in a flow between a rotating and a stationary disk. This linear stability analysis considers the complete rotor-stator flow and then extends the results of Lingwood [J. Fluid Mech. 299, 17 (1995); 314, 373 (1996)] obtained in a single disk case. The present linear analysis also extends the former two-disk computations of Itoh [ASME FED 114, 83 (1991)], only limited to a hydrodynamic spatial instability analysis. Moreover, in the present work, this approach is completed by discussing the effects of buoyancy-driven convection on the flow stability and by absolute/convective analysis of the flow. Coupled with accurate numerical computations based on an efficient pseudo-spectral Chebyshev–Fourier method, this study brings new insight on the spatio-temporal characteristics of this flow during the first stages of transition. For instance, an exchange of stability from a steady to a periodic flow with spiral structures is observed for the first time numerically in such cavity of large aspect ratio. The nature of the first bifurcation is discussed as well as the influence on it of disturbances coming from the end-wall boundary layer. Annular and spiral patterns are observed in the unstable stationary disk layer with characteristic parameters agreeing very well with the present theoretical results. Then, these structures are interpreted in terms of type I and type II generic instabilities. Moreover, the absolute instability regions which are supposed to be strongly connected with the turbulent breakdown process are also identified and the critical Reynolds numbers of the convective/absolute transition in both Ekman and Bödewadt layers are given.
Velocity slip and temperature jump coefficients for gaseous mixtures. II. Thermal slip coefficient
Authors: Sharipov Felix , Kalempa Denize
Published: February 2004

The thermal slip coefficient was calculated for a binary gaseous mixture on the basis of the McCormack kinetic model of the Boltzmann equation, which was solved by the discrete velocity method. The calculations were carried out for the three mixtures of noble gases: neon–argon, helium–argon, and helium–xenon. A strong influence of the potential of intermolecular interaction upon the thermal slip coefficient was observed by comparing the results based on the model of rigid spheres with those obtained for a realistic potential. An example of application of the thermal slip coefficient is given.
Transmission electron microscopy and Raman measurements of the misfit stress in a Si tensile strained layer
Authors: Cabié M. , Ponchet A. , Rocher A. , Paillard V. , Vincent L.
Published: February 2004

A tensile-strained Si layer grown on a Si0.8Ge0.2 pseudo substrate with a nominal lattice mismatch of −0.76% has been studied by transmission electron microscopy using a curvature method and Raman scattering in order to determine experimentally the in-plane component of the epitaxial stress. The stress is obtained by measuring the curvature and the thickness on different areas of a thinned sample. Experimental values of the stress given by the two methods are in good agreement and are close to the nominal one.
Weakly nonlinear cubic interactions between surface waves and interfacial waves: An analytic solution
Authors: Hill D. F.
Published: February 2004

A set of third-order equations describing the interactions between surface waves and interfacial waves is presented. The specific interaction studied is that of exact subharmonic resonance of two interfacial waves by a single surface wave. The coupled amplitude evolution equations are solved analytically in terms of Jacobian elliptic functions. Upon specification of the initial conditions, the minimum and maximum amplitudes attained by the surface and interfacial waves, along with the nonlinear interaction period, are obtained. The results from the third-order theory are contrasted with those from second-order theory and highlight the importance of the cubic interactions.
Optical and structural properties of SixSnyGe1−x−y alloys
Authors: Aella P. , Cook C. , Tolle J. , Zollner S. , Chizmeshya A. V. G. , Kouvetakis J.
Published: February 2004

Single-phase SixSnyGe1−x−y alloys (x⩽0.25,y⩽0.11) were grown on Si using chemical vapor deposition. First principles simulations predict that these materials are thermodynamically accessible and yield lattice constants as a function of Si/Sn concentrations in good agreement with experiment. An empirical model derived from experimental SixGe1−x and SnyGe1−y binary data also provides a quantitative description of the composition dependence of the lattice parameters. Spectroscopic ellipsometry of selected samples yields dielectric functions indicating a band structure consistent with highly crystalline semiconductor materials of diamond symmetry. Incorporation of Si into SnyGe1−y leads to an additional reduction of the E2 critical point, as expected based on the E2 values of Si and Ge.
Cubic optical nonlinearity in nanostructured SnO2:SiO2
Authors: Clementi A. , Chiodini N. , Paleari A.
Published: February 2004

Nonlinear self-focusing and absorption effects were investigated in nanostructured SnO2:SiO2 by means of z-scan techniques. The results show electronic nonlinearity with the real part of the cubic susceptibility ranging between 0.5 and 2.3×10−20 m2/V2. Nonlinear dissipative effects appear to be caused by two-photon absorption involving localized states at the cluster interfaces, controlled by oxygen nonstoichiometry. As a result, synthesis can be optimized to give a wide-band-gap semiconductor-doped glass with good figure of merit for nonlinear directional couplers.
Very fast YbxY1−xAlO3 single-crystal scintillators
Authors: Nikl M. , Solovieva N. , Pejchal J. , Shim J. B. , Yoshikawa A. , Fukuda T. , Vedda A. , Martini M. , Yoon D. H.
Published: February 2004

Scintillation, radioluminescence, photoluminescence, and thermoluminescence characteristics of Czochralski-grown YbxY1−xAlO3 single crystals for x=0.02–0.45 are described. Under x-ray excitation, the intensity of Yb3+ charge-transfer luminescence is increasing with x and reaches at room temperature more than 11% of Bi4Ge3O12 (BGO) for x=0.45, while at 80 K it is over 170% of BGO for x⩾0.3. At room temperature, scintillation decay shows a dominant decay time of 0.8–0.9 ns for x⩾0.3 and no significant slow components were detected. The photoluminescence decay time is tuned by temperature and Yb concentration from tens of nanoseconds at 80 K down to about 0.8 ns at 295 K. Thermoluminescence glow curve below room temperature evidences very low concentration of shallow traps compared to the Ce-doped YAlO3 scintillator.
Enhancement of 1.54 μm photoluminescence observed in Al-doped β-FeSi2
Authors: Terai Yoshikazu , Maeda Yoshihito
Published: February 2004

We present photoluminescence (PL) properties of impurity (Al, Mn, Co)-doped β-FeSi2 produced by ion-beam synthesis. The β-Fe(Si1−xAlx)2 sample showed an increase of both the PL intensity and activation energy (Ea) for a nonradiative recombination path. On the contrary, the β-(Fe1−xMnx)Si2 and the β-(Fe1−xCox)Si2 samples reduced the PL intensity and Ea. We found that the doping of Al atoms occupying the Si sites in β-FeSi2 is effective to enhance the 1.54 μm photoluminescence.
Simulation of rapid startup in microwave magnetrons with azimuthally varying axial magnetic fields
Authors: Jones M. C. , Neculaes V. B. , White W. , Lau Y. Y. , Gilgenbach R. M.
Published: February 2004

A method is proposed whereby the startup of a magnetron may be hastened. For a N-cavity magnetron operating in the pi mode, the formation of the N/2 electron spokes is much more rapid when an azimuthally varying axial magnetic field of N/2 periodicity is employed. Electromagnetic particle-in-cell code simulations are presented that show electron prebunching by the azimuthally varying axial magnetic field, long before the pi mode is excited.
Polar-surface dominated ZnO nanobelts and the electrostatic energy induced nanohelixes, nanosprings, and nanospirals
Authors: Kong Xiang Yang , Wang Zhong Lin
Published: February 2004

We report the controlled synthesis of free-standing ZnO nanobelts whose surfaces are dominated by the large polar surfaces. The nanobelts grow along the a axis, their large top/bottom surfaces are the ±(0001) polar planes, and the side surfaces are (011̄0). Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated ±(0001) surfaces, respectively, the nanobelts form multiloops of nanohelixes/nanosprings/nanospirals for the sake of reducing electrostatic energy introduced by the polar surfaces as well as balancing the difference in surface tension. The polar surface dominated ZnO nanobelts are likely to be an ideal system for understanding piezoelectricity and polarization induced phenomena at nanoscale.
Determination of anisotropic dipole moments in self-assembled quantum dots using Rabi oscillations
Authors: Muller A. , Wang Q. Q. , Bianucci P. , Shih C. K. , Xue Q. K.
Published: February 2004

By investigating the polarization-dependent Rabi oscillations using photoluminescence spectroscopy, we determined the respective transition dipole moments of the two excited excitonic states |Ex〉 and |Ey〉 of a single self-assembled quantum dot that are nondegenerate due to shape anisotropy. We find that the ratio of the two dipole moments is close to the physical elongation ratio of the quantum dot.
In situ observations of carbon nanotube formation using environmental transmission electron microscopy
Authors: Sharma Renu , Iqbal Zafar
Published: February 2004

Environmental transmission electron microscope is used for in situ observations of the growth mechanism and reaction conditions of carbon nanotubes. Chemical vapor deposition was performed by flowing propylene or acetylene gas (precursor) over Ni or Co catalyst heated to 450 °C and 700 °C. We are reporting the in situ observations of the growth process of carbon nanotubes. Multi-wall nanotubes formed at temperatures as low as 450 °C while only single-wall carbon nanotubes formed at higher temperatures (700 °C and above). At lower temperatures, a cubic phase was also observed to form on the walls of the multi-wall carbon nanotubes.
Energetic of nitrogen incorporation reactions in SiO2
Authors: Orellana Walter
Published: February 2004

We study using first-principles calculations the energetic, structural and electronic properties of nitrogen incorporation in SiO2. We consider NO, NH, N2 and atomic N as the nitriding species interacting with a Si–Si bond of an otherwise perfect SiO2 network in order to simulate the nitrogen incorporation near Si–SiO2 interface regions. We find that all the species react with the Si–Si bond forming bridge structures with the Si atoms without dissociating, where NH and atomic N form the most stable structures. Concerning the electronic properties, our results show that incorporated NH is the only structure which does not introduce trapping center at the interface. The structures involving NO and atomic N are acceptors, whereas that involving N2 may be either a donor or an acceptor. The hydrogen passivation of the electrically active centers is also discussed.
Resonant Raman scattering in nanoscale pentacene films
Authors: He Rui , Dujovne Irene , Chen Liwei , Miao Qian , Hirjibehedin Cyrus F. , Pinczuk Aron , Nuckolls Colin , Kloc Christian , Ron Arza
Published: February 2004

Resonant Raman scattering intensities from nanoscale films of pentacene display large resonant enhancements that enable observation of vibrational modes in monolayer cluster films. The resonant enhancements occur when the outgoing photon energy overlaps the free exciton optical transitions observed in luminescence. The results point to the significant potential of resonant Raman methods in the characterization of nanoscale structures of organic molecular semiconductors.
NEAR BAND EDGE OPTICAL ABSORPTION PRODUCED BY ION IMPLANTATION IN GaAs
Authors: Borders J. A.
Published: February 2004

Ion implantation of 400-keV Se+ and Xe+ in GaAs at room temperature has been found to induce a strong optical absorption in the photon energy range 0.5 eV ≤ hv ≤ Eg. This absorption is used as a measure of the ion-bombardment damage in GaAs and is similar to that seen in neutron-damaged GaAs. The fluence dependence and annealing of the damage are presented and compared to previous work. An annealing stage is seen near 230 °C and corresponds to the annealing observed in radiation-damaged GaAs.
5PbO·3GeO2 CRYSTAL; A NEW FERROELECTRIC
Authors: Iwasaki Hiroshi , Sugii Kiyomasa , Yamada Tomoaki , Niizeki Nobukazu
Published: February 2004

Dielectric constants and refractive indices of a 5PbO · 3GeO2 crystal, which was grown from the melt by by the Czochralski method, were measured as a function of temperature. The crystal was identified as a new type of ferroelectric with spontaneous polarization Ps = 0.046 C/m2, coercive field Ec ∼ 2.3 × 106 V/m at room temperature, and Tc = 177°C.
PLASMA ELECTRON HEATING BY ABSORPTION OF COLD ELECTRONS
Authors: MacKenzie K. R. , Taylor R. J. , Cohn D. , Ault E. , Ikezi H.
Published: February 2004

The electron temperature of a quiescent plasma in a metal discharge chamber, where the walls serve as the anode, can be raised by introducing a second anode consisting of 0.0025-cm-diam tungsten wires held at potentials as high as 100 V with respect to the walls. Hot electrons orbit the wires and return to the plasma. Cold electrons are absorbed. Smooth temperature variation, without introduction of noise, has been achieved between 0.5 and 4.0 eV.
PASSIVE MODE LOCKING OF A HIGH-PRESSURE CO2 LASER WITH A CO2 SATURABLE ABSORBER
Authors: Gibson A. F. , Kimmitt M. F. , Rosito C. A.
Published: February 2004

Passive mode locking of a transversely excited CO2 laser has been obtained using CO2 at 350°C as a saturable absorber. Pulses with a half-width of 4-nsec duration have been observed.
FORMATION OF OPTICAL WAVEGUIDES IN PHOTORESIST FILMS
Authors: Ostrowsky D. B. , Jacques A.
Published: February 2004

We have demonstrated that photoresist films on glass substrates can act as optical waveguides. Coupling to these guides can be accomplished by inscription of a grating in the guide material itself. Approximately 50% coupling efficiencies have been observed. Waveguide effects can considerably alter the behavior of holograms and gratings inscribed on such structures.
SCANNING ELECTRON MICROSCOPY OF RESONATING QUARTZ CRYSTALS
Authors: Gerdes R. J. , Wagner C. E.
Published: February 2004

SL- and AT-cut quartz crystal resonators which are commonly used in frequency control devices were examined in the scanning electron microscope. The quartz slices were resonated at frequencies ranging from 455 kHz to 15 MHz. Variations in surface charges which were produced during resonance strongly affected secondary electron emission. Therefore, micrographs could be obtained which were characteristic of the various modes of motion of the resonators. From displacements of topographical features during resonance approximate values for the amplitudes of face and thickness shear were obtained.
EXPLANATION OF PLASMA DENSITIES HIGH ABOVE CRITICAL DENSITY IN A CYLINDER EXCITED BY AN rf HELIX
Authors: Aubert A. E. , Messiaen A. M. , Vandenplas P. E.
Published: February 2004

We show that the density characteristics of plasmas created by an rf helix are completely determined by the low-power resonance features of the bounded system, which is constituted by the plasma column and the surrounding helix of finite axial length. Whether a magnetic field is present or not, plasma densities high above critical density are obtained in agreement with the general philosophy previously developed. Experiments already performed without magnetic field support the theoretical predictions.
LIQUID PHASE EPITAXIAL GROWTH OF UNIAXIAL GARNET FILMS; CIRCUIT DEPOSITION AND BUBBLE PROPAGATION
Authors: Shick L. K. , Nielsen J. W. , Bobeck A. H. , Kurtzig A. J. , Michaelis P. C. , Reekstin J. P.
Published: February 2004

Magnetically uniaxial epitaxial films of Eu2Er1Ga0.7Fe4.3O12 and Er2Eu1Ga0.7Fe4.3O12 5–20 μm thick have been grown free of cracks from PbO · B2O3 solutions on (110) and (111) Gd3Ga5O12 substrates, respectively. Bubble propagating T-bar and Y-bar circuits of nickel-cobalt-phosphorus were electrolessly deposited on these films. Operation in excess of 100 steps has been achieved in T-bar and Y-bar bubble domain shift registers. Details of the growth procedure, magnetic properties, and circuit preparation are presented.
EFFECT OF ULTRASOUND ON A NEMATIC LIQUID CRYSTAL
Authors: Mailer H. , Likins K. L. , Taylor T. R. , Fergason J. L.
Published: February 2004

The effects of ultrasound on the optical properties of an aligned layer of nematic liquid crystal are described. It was observed that the birefringence of a normally oriented nematic liquid crystal was a function of the acoustic energy, and that with sufficient incident acoustic energy, a scattering phenomenon similar to dynamic scattering occurred.
PIEZOELECTRIC ACOUSTIC SURFACE WAVES FOR A FILM ON SUBSTRATE
Authors: Solie L. P.
Published: February 2004

A computer program has been written for calculating the dispersion curves of acoustic waves for the film-on-substrate problem where both materials may be arbitrarily anisotropic and piezoelectric. The electromechanical coupling factor Δv/v is calculated for nonpiezo-electric films on LiNbO3 showing a marked increase over its value without the film. Velocity curves are shown for fused quartz on LiNbO3, and Δv/v is shown for ZnO on a sapphire substrate predicting a maximum value of 0.019.
SINGLE-MODE OPERATION AND MODE LOCKING OF HIGH-PRESSURE CO2 LASERS BY MEANS OF SATURABLE ABSORBERS
Authors: Nurmikko A. , DeTemple T. A. , Schwarz S. E.
Published: February 2004

Single-longitudinal-mode operation of pulsed, high-pressure, transversely excited CO2 lasers has been obtained by means of a saturable absorber (SF6) cell placed inside the laser cavity. Eighty percent of the multimode ouput power is obtained in the single-mode output. Single-mode operation has been verified by means of a scanning Fabry-Perot interferometer. Pressure broadening of the saturable absorber by a buffer gas has been found to cause multimode mode-locked operation of the laser.
NOVEL HELICAL-PATH SURFACE WAVE DELAY LINE
Authors: Lewis M. F. , Patterson E.
Published: February 2004

A surface acoustic wave delay line has been constructed on quartz in which the path of the wave is approximately a helix. The line operated at 102 MHz and gave delays up to about 50 μsec at room temperature.
SPECTRAL BEHAVIOR, CARRIER LIFETIME, AND PULSED AND cw LASER OPERATION (77 °K) OF In1−xGaxP
Authors: Burnham R. D. , Holonyak N. , Keune D. L. , Scifres D. R.
Published: February 2004

The spontaneous and laser spectral behavior of high-quality In1−x Gax P grown slowly from an In solution in a small temperature gradient is described. The band-to-band carrier decay times are measured below (2.3 nsec, 77°K) and above (0.85 nsec) laser threshold by an optical phase shift technique and indicate low bulk and surface losses (s≤104 cm/sec). Continuous laser operation of a thin In1−x Gax P sample is demonstrated at a photoexcitation level of ∼103 W/cm2 (hνpump =1.96 eV).
LOW-TEMPERATURE MIGRATION OF SILICON IN THIN LAYERS OF GOLD AND PLATINUM
Authors: Hiraki A. , Nicolet M-A. , Mayer J. W.
Published: February 2004

The backscattering method is employed to obtain microscopic information about solid-solid reactions of Si with thin layers (500–2000 Å) of both vacuum-evaporated Au and sputtered Pt. A remarkable observation is the migration of Si atoms into Au and Pt at relatively low temperatures (150 and 350 °C, respectively). Migration of Si in Pt induces first the formation of Pt2Si-like compounds and then PtSi. In the Au–Si system, on the other hand, Si moves through and accumulates on the Au surface in the form of SiO2 under an oxidizing heat-treatment atmosphere.
POWER AND LINEWIDTH OF TUNABLE STIMULATED FAR-INFRARED EMISSION IN LiNbO3
Authors: Johnson B. C. , Puthoff H. E. , SooHoo J. , Sussman S. S.
Published: February 2004

The power-versus-wavelength characteristic for a high-power, continuously tunable far-infrared source has been experimentally determined and compared with theory. Utilizing a Q-switched ruby laser as the pump and stimulated polariton scattering in the crystal LiNbO3 as the scattering mechanism, peak powers outside the crystal of ∼ 3 W at 200 μ are observed without crystal damage. Linewidth measurements indicate a bandwidth of < 0.5 cm−1 for the radiation over the observed tuning range 66–200 μ.
TRANSIENT CHARACTERISTICS OF SEMICONDUCTING GLASS DIODES
Authors: Homma K.
Published: February 2004

The transient characteristic of a semiconducting glass diode is analyzed on the basis of a model in which a filamentary plasma with high conductivity travels through the diode from one electrode to the other. The switching mechanism is well explained in terms of the travel of this injected plasma. The predicted characteristics of the model exhibit good agreement with experimental results in a Ge2SeTe7 amorphous semiconductor.
APPLICATION OF AN IMAGE ORTHICON CAMERA TUBE TO X-RAY DIFFRACTION TOPOGRAPHY UTILIZING THE DOUBLE-CRYSTAL ARRANGEMENT
Authors: Hashizume Hiroo , Kohra Kazutake , Yamaguchi Tomoyori , Kinoshita Kojiro
Published: February 2004

A video imaging system utilizing a high sensitive image orthicon camera tube has been set up and applied to x-ray diffraction topography using the double-crystal arrangement of parallel setting. The system gives a video signal of S/N 20 dB for incident 3 × 104 x-ray photons sec−1 mm−2. The resolution of the system is 300 μ for 70% of the modulation transfer function, limited presently by the resolution of the x-ray phosphor. As an example, long-range elastic strains in an Sb-doped silicon crystal have been studied.
AUGER ELECTRON SPECTROSCOPY MADE QUANTITATIVE BY ELLIPSOMETRIC CALIBRATION
Authors: Vrakking J. J. , Meyer F.
Published: February 2004

Auger electron spectroscopy has been calibrated for various atoms absorbed on clean silicon surfaces by using ellipsometry. The Auger peak heights, measured as the first derivative of the energy distribution, were found to be proportional to surface coverage up to 1.5 monoatomic layer. The advantages of this particular combination of techniques are discussed.
A NEW HIGH-FIELD SUPERCONDUCTOR, V2HfxZr1−x
Authors: Inoue Kiyoshi , Tachikawa Kyōji , Iwasa Y.
Published: February 2004

C-15 type structure V2HfxZr1−x shows a high resistive critical field exceeding 200 kOe at 4.2°K whenever x>0.3. The highest transition temperature, 10.1°K, and critical field, 230 kOe, are achieved with the composition V2Hf0.5Zr0.5. For this material the critical current density at 4.2°K and 130 kOe is as high as 1×105 A/cm2, which should make it of interest for practical use at high fields.
COLD-CATHODE ELECTRON EMISSION FROM SILICON
Authors: Kohn Elliott S.
Published: February 2004

Cold-cathode electron emission has been obtained from forward-biased silicon p-n junctions whose surfaces were activated to a state of negative electron affinity. Currents as high as 7.3 mA were obtained with current densities in excess of 1 A/cm2. Efficiencies as high as 2% were measured, and currents of tens of microamperes were drawn for several hours.
LINEAR AND NONLINEAR OPTICAL PROPERTIES OF ZnGeP2 AND CdSe
Authors: Boyd G. D. , Buehler E. , Storz F. G.
Published: February 2004

The refractive indices of ZnGeP2, point group 4̄2m, have been determined from 0.64 to 12 μ. ZnGeP2 has positive birefringence with reasonable temperature tunability and a band gap in the visible. Its nonlinear optical coefficient d14 for second harmonic generation (SHG) measured relative to d14 of GaAs is 0.83 ± 15%. The birefringence of ZnGeP2 is not large enough to allow phase-matched SHG, but nondegenerate phase-matched three-frequency mixing is possible and the parametric oscillator threshold power is calculated for several situations. A redetermination of the coefficient d31 in CdSe is made and the materials compared. It is concluded that ZnGeP2 may be a most promising material for parametric generation in the 0.8– to 12-μ region.
DEGRADATION AND PASSIVATION OF GaP LIGHT-EMITTING DIODES
Authors: Hartman R. L. , Schwartz B. , Kuhn M.
Published: February 2004

Degradation of GaP red electroluminescent diodes has been significantly reduced by a chemical passivation of the surface. Chemical passivation was accomplished by heating the completed diodes in a solution of hydrogen peroxide which was shown to produce a native oxide surface film which is believed to be principally an amorphous form of hydrated gallium oxide. The degradation of the external electroluminescent quantum efficiency of passivated diodes at elevated temperatures has been studied and yields a predicted room-temperature half-life of 108–109 h. The results suggest that this native oxide film can act as a getter for impurities and as a barrier against the transport of impurities into the bulk material.
POCKELS READOUT OPTICAL MEMORY USING Bi12SiO20
Authors: Hou S. L. , Oliver D. S.
Published: February 2004

The Pockels Readout Optical Memory using Bi12SiO20 single crystals is described. Devices have a built-in capability to optically read out a positive or a negative image from a single stored image. The stored information also can be selectively erased. Application of 650 V across the crystal wafer introduces a retardation of 30°. The read-in and dark decay mechanisms, which include sensitivity, resolution, and response time, are discussed. The sensitivity is better than most of the previously reported reusable optical memories. The resolution is 10 μm. The read-in response time is 5×10−6 sec. The storage time is 50 min under a constant illumination of 0.4 μW/cm2 at 633 nm and is 2 h in the dark. The dark resistivity of Bi12SiO20 after complete dark adaptation is likely to be ∼1015 Ω cm.
LINEAR AND NONLINEAR OPTICAL PROPERTIES OF TRIGONAL SELENIUM
Authors: Day G. W.
Published: February 2004

Measurement of the second-order nonlinear optical susceptibility of trigonal selenium yielded d11 = (9.7 ± 2.5) × 10−11 m/V. This value was obtained by cw SHG with a 10.6-μm CO2 laser at a phase-matching angle of 5.5° ± 0.3° to the optic axis. Factors affecting this measurement are discussed along with data on absorption, optical activity, and birefringence.
LONG-WAVELENGTH PHOTOEMISSION FROM Ga1 − xInxAs ALLOYS
Authors: Fisher D. G. , Enstrom R. E. , Williams B. F.
Published: February 2004

We have activated epitaxial layers of vapor-deposited Ga1−xInxAs alloys in the bandgap range 0.96–1.18 eV with Cs and O2. The Cs–O was determined to be ∼1 monolayer thick. For each sample the photothreshold energy was approximately equal to the bandgap energy. A long-wavelength limit of approximately 1.3 μm was determined for valence-band emission. There was no evidence of an internal barrier which might have decreased this limit. Spectral yield data were analyzed to give a surface escape probability versus bandgap plot.
An Infrared Spectroscopic Study on TbF3 in Solid Nitrogen and on Electroluminescent Thin Films of ZnS:TbF3
Authors: Krupka D. C. , Rochkind M. M.
Published: February 2004

A search was carried out for the infrared spectrum of the TbF3 molecule in thin films of ZnS: TbF3 which form the active layers in efficient electroluminescent structures. The vibrational spectrum of a TbF3 molecule and an estimate of the oscillator strength were first obtained by trapping the molecule in solid nitrogen near 20°K employing matrix isolation techniques. Using the information so obtained, appropriate samples of ZnS : TbF3 were prepared by coevaporating ZnS and TbF3 onto CsI and Si, and a search was made for the TbF3 vibrational spectrum anticipating some solvent shift. The search proved unsuccessful. It is concluded that the ionic bond between the terbium and fluorine ions is significantly modified by embedding the molecule in the rather ionic ZnS lattice. This result is contrasted with the examples of OH− and CN− in the alkali halide lattices where the covalent bond of the molecule is little affected by the host.
Evidence for Reverse Photoelectrons in Laser-Induced Current
Authors: Ahmad S. Rafi
Published: February 2004

Strong experimental evidence has been obtained for the significant contribution of ``reverse photoelectrons'' in the production of current signals induced by focusing laser light onto a metal target and biasing the collector negative with respect to the target. Reverse photoelectrons are essentially normal photoelectrons from the collector region. The source of these photons is the laser-produced hot spot on the target.
Theory of High-Temperature Breakaway of Dislocations from a Row of Randomly Placed Pinning Agents
Authors: Blair D. G.
Published: February 2004

This paper discusses the decrement, at temperature T, of a sound wave of stress amplitude σ0 due to the breakaway of dislocations from pinning agents placed at random along a line. Attention is confined to the high-temperature low-amplitude region; then many pins are involved in the saddle configuration for breakaway. This region is found to consist of two regions P and Q of qualitatively different behavior. For each region, an expression is obtained for the dominant (exponential) factor in the decrement; the same expression is also the dominant factor in the modulus defect and in the fraction of dislocations breaking away during one cycle. In region Q, the decrement varies as exp(− A/σ0 + BT), where A and B are approximately independent of both σ0 and T at sufficiently low amplitudes. This approximate behavior has been found previously in experimental results.
Analysis of Thermal Induction Plasmas between Coaxial Cylinders
Authors: Eckert H. U.
Published: February 2004

A previously derived approximate solution of the one-dimensional energy-balance equation for steady thermal induction plasmas is applied to the case of an annular plasma contained between coaxial cylinders. It is assumed that heat conduction is the only loss mechanism and that both walls are at zero temperature. Charted material is presented to facilitate determination of heat loads to either wall and calculation of temperature distributions across the gap. Results for an atmospheric-pressure argon discharge are compared with both exact numerical calculations and with experimental data. With the former, agreement is fair to good; with the latter it is poor. The disagreement is shown to be caused by electron diffusion which leads to overpopulation near the walls and suggests erroneously high temperatures when Saha equilibrium is assumed. The experimental temperature profiles are reproduced with excellent accuracy from a diffusion profile for the electrons which takes into account the nonuniformity of the induced electric field.
Scattering Effects in Photoelectric Emission from PbTe Films
Authors: Pong W.
Published: February 2004

The escape length of the photoelectrons in PbTe films was determined by measuring the quantum yield as a function of film thickness. The data indicate that the escape length of the electrons excited by photons of energies 7.7–11 eV is approximately 20–40 Å. The results are shown to be useful in estimating the mean free path for electron-electron scattering in PbTe.
Acoustical holography with a scanned linear array
Authors: Knollman G. C. , Weaver J. L.
Published: February 2004

A mechanically scanned linear detector array is analyzed for acoustical holography applications in which the sound transmitter is stationary. The theory of hologram formation is extended to include linear and nonlinear scanning as well as temporal reference phase. Both linear translatory scan and oscillatory mirror (cylindrical) scan are treated theoretically and experimentally. A rotating linear array is noted as yet another mechanical scanning technique. Emphasis is placed on an electronically simulated reference wave for the linear array under translatory and oscillating mirror scan. Attention centers on simulation of a plane reference wave for cylindrical scan by means of a temporal reference phase. The electronic reference technique is broadened to include curvilinear arrays. A rectilinear array for hydroacoustic holography receives particular mention; typical linear and cylindrical holograms obtained with this system are presented. Also shown are holograms occurring with a simulated plane reference wave for cylindrical scan. Applications of a scanned linear array in aeroacoustic and hydroacoustic holography, medical ultrasonics, and nondestructive testing are specifically mentioned.
Theory of the measurement of thickness and conductivity of cylindrical shells by an inductive method
Authors: Callarotti R. C. , Schmidt P. , Arqué H.
Published: February 2004

We consider the case of a solid cylinder of arbitrary conductivity, covered by a thin shell of conductivity σs. The coated cylinder is assumed to be located inside a primary exciting coil, and also inside a secondary detection coil. A time-varying current in the primary induces currents in the sample, and these currents are reflected at the secondary. We derive expressions for the time constants of the decay of the secondary voltage. We relate the dominant time constant to the conductivity and the thickness of the shell. If the conductivity of the shell is known, then the simple measurement of a time constant allows the determination of the thickness of the shell. The special case where the conductivity of the inner cylinder is zero is analyzed in detail. The method of measuring the thickness of the shell by induction is shown to be of practical importance in the case of thin metallic films deposited on a cylindrical substrate. We show that the dominant time constant for this case depends linearly on the thickness of the film. Thus measurements on a cylindrical shell are shown to be more convenient than measurements on flat films, where the dominant time constant is proportional to the square of the thickness of the film.
Radiation from an electric dipole in anisotropic media
Authors: Sundaram A. K.
Published: February 2004

Based on the single-fluid theory of magnetohydrodynamics (MHD), the investigation deals with a comparative study on the radiation characteristics of an electric dipole in homogeneous anistropic media of infinite extent with a uniform magnetostatic field. Attention is specifically focussed on the excitation of waves in a frequency range below the ion cyclotron frequency. In the asymptotic evaluation of the far fields, critical cases of the dispersion curves having points of inflexion or unbounded branches are briefly considered. The normalized power density as a function of the polar angle θ (being measured from the axis of the magnetic field) is calculated, and it is shown that both compressibility and Hall effects enhance the angular zone of radiation for increasing values of the parameters χ and λ.
Propagation of the mutual coherence of optical waves in a random medium
Authors: Torrieri Don J.
Published: February 2004

The propagation of the mutual coherence function of optical waves is investigated, with the following new results: (a) Sufficient conditions for the conservation of the transverse mutual coherence function are obtained, that is, it is determined under what conditions the transverse coherence propagates unchanged from plane to plane. (b) The usual analysis is generalized to include a treatment of the full three-dimensional mutual coherence function; also, general homogeneous boundary conditions, not just plane-wave conditions, are assumed. (c) The mathematical analysis by means of the Born approximation is made more rigorous, and the physical interpretation of the required approximations is clarified.
Laser excitation processes in the cathode region of a glow discharge through metal-vapor-rare-gas mixtures
Authors: Palmer A. J. , McGowan J. Wm.
Published: February 2004

An experimental investigation of the spectral characteristics of the cathode region in a glow discharge through He–Cd and He–Zn mixtures is undertaken from the point of view of evaluating the feasibility of achieving laser action in the Crookes region. Observations reveal the existence of distinctly shaped spatial profiles of the intensity, in spontaneous emission, from lines in He–Zn indicative of charge-transfer excitation in the Crookes region. A quenching behavior with increasing metal-vapor concentration similar to that which occurs in the positive column was also observed and precluded any laser action in the Crookes region. Theoretical models are presented which allow qualitative interpretation of these observations.
Limitation imposed by field clamping on the efficiency of high-field ac electroluminescence in thin films
Authors: Chen Y. S. , Krupka D. C.
Published: February 2004

In a series of experiments we have found that the field in the ZnS layer of an ac-operated thin-film high-field electroluminescent device becomes clamped at values ranging from 2.1×106 to 3×106 V/cm. The device is fabricated as a sandwich with the following layers from top to bottom: thin metal; ZnS:Tb3+; Ta1.98Mo0.02O5 and Ta0.99Mo0.01. Since the electroluminescence is expected to be very strongly field dependent because the excitation proceeds via direct impact of the Tb3+ ions by hot carriers, the observed field clamping may impose a serious limitation on the efficiency that one can obtain from such structures. Evidence for field clamping is obtained by measuring as a function of peak-to-peak applied voltage the following: (i) Tb3+ emission intensity, (ii) the ratio of emissions originating in two different Tb3+ levels and (iii) the magnitude of a pulsed photocurrent. In addition, the clamped field may be determined quantitatively through the use of a novel technique which permits the measurements of the current-field relationship in the active layer. The value of the clamped field depends only slightly on the method of preparation of the ZnS layer and is insensitive to the type of metal contact used, to the Tb concentration, and to temperature. Several mechanisms which could give rise to the steep current-field relationship responsible for field clamping are considered. One of these, multiplication by impact ionization, is ruled out by the pulsed photocurrent measurements; Frenkel-Poole emission and Schottky emission are too temperature dependent and do not exhibit sufficiently steep current-field characteristics. It is concluded that field emission at the contacts must be responsible although it is not entirely clear why it is so insensitive to the contact materials.
Quantum yield of metal-semiconductor photodiodes
Authors: Li Sheng S. , Lindholm Fredrik A. , Wang C. T.
Published: February 2004

A theoretical expression for the quantum yield of metal-semiconductor photodiodes is derived that takes into account the effects of the presence of an inversion region. This expression predicts a sharp decrease of the quantum yield in the short wavelength regime, in contrast with previous theoretical predictions. Applied to a Au-nSi Schottky-barrier photodiode, our theory displays the functional dependence with which the quantum yield increases with increasing doping densities for short wavelengths and decreases with increasing doping densities for long wavelengths. Excellent agreement is demonstrated between theoretical predictions and experimental data in the short-wavelength regime (i.e., for 0.4<λ<0.6 μm).
The graded-gap Alx Ga1 − x As–GaAs heterojunction
Authors: Womac J. F. , Rediker R. H.
Published: February 2004

The electrical properties of n-n (AlGa)As–GaAs heterojunctions and the photoresponse of n-p and p-n (AlGa)As–GaAs heterojunctions, all grown by liquid-epitaxy techniques, are explained in terms of a graded-gap model of the heterojunction interface. This model, in which the grading occurs over a few hundred angstroms now makes possible a consistent explanation of the operation of double-heterostructure lasers in contrast to the abrupt model of the heterojunction which predicts a series resistance due to reverse biasing of the n-n heterojunction. Most n-n heterojunctions measured were Ohmic with the percentage of non-Ohmic (rectification ratio ∼ 5 : 1) junctions decreasing with increasing growth temperature. The grading and its statistical nature are explained in terms of the initial nonequilibrium growth condition in liquid-phase epitaxy when the (AlGa)As melt is placed in contact with a GaAs solid rather than the (AlGa)As solid alloy determined from the equilibrium phase diagram. The measured photoresponse of the n-p junction extends from the (AlGa)As band energy to the GaAs band energy as predicted by the graded-gap model and is not consistent with previous abrupt models in which there is a spike in the conduction band.