bluuebunny/crossref_metadata_2025 huggingface dataset:
Abstraction of chemisorbed bromine from the Si(111) surface by incident hydrogen atoms
Authors: McEllistrem Marcus , Buehler Emily J. , Itchkawitz Bruce S. , Boland John J.
Published: July 2002

The abstraction of bromine atoms from the Si(111) surface has been studied by scanning tunneling microscopy (STM). Vacant dangling bond (DB) sites created by H-atom abstraction of surface Br are identified as are the subsequent reaction of these DB sites with atomic hydrogen. The kinetics of Br abstraction and the H-atom–DB reaction are shown to be dependent on the local surface structure. Bromine abstraction rates on the 1×1 regions of the surface are about twice that of the 7×7 regions. Surprisingly, we also find that the DB reaction rate is significantly different on the two regions of the surface: reaction on the 7×7 regions being about six times more efficient than on the 1×1 regions. In substantial agreement with earlier studies we find an abstraction-to-DB reaction ratio for H atoms of about 0.2 for the 1×1 regions of the surface. This ratio is much smaller (about 0.01) for the 7×7 regions of the surface, suggesting different types of H-atom–surface interactions in these regions. Abstraction of chemisorbed hydrogen is about 50 times more efficient than abstraction of chemisorbed bromine. Although the low reaction barrier (∼1 kcal/mol) we find is consistent with a direct Eley–Rideal mechanism, this mechanism cannot readily account for the structural sensitivity observed. The possibility of a hot-atom precursor mechanism is discussed. At large exposures definite evidence for an etching reaction is presented, which precludes analysis of the data over a wide exposure range.
Anomalous conformational behavior of poly(ethylene oxide) oligomers in aqueous solutions. A molecular dynamics study
Authors: Bedrov Dmitry , Smith Grant D.
Published: July 2002

Molecular dynamics simulations of 1,2-dimethoxyethane (DME) CH3(OCH2CH2)OCH3 and diglyme CH3(OCH2CH2)2OCH3 in aqueous solution have been performed for several solution compositions. Conformational analysis of these systems shows that the g population of the O–C—C–O dihedral increases with increasing water content. For DME solutions, this increase is monotonic with a tendency to saturate in the extremely dilute (water-rich) regime. For diglyme solutions a distinct maximum in the g population of the O–C—C–O dihedral was observed at mole fraction Xdiglyme=0.03. More detailed analysis of the composition dependence of diglyme conformational populations reveals that the decrease in the O–C—C–O g population in extremely dilute solutions is due to a decrease in the tgt population of the C–O—C—C—O–C conformational triad. This in turn can be related to a decrease in a single conformer of diglyme, namely tgttgt. This conformer is unique in its nearly perfect antiparallel alignment of large triad dipoles. Finally, the anomalous conformational behavior of diglyme at extreme dilution is found to disappear at higher temperature.
Patterns due to quintic kinetics in a diffusion-reaction system with global interaction
Authors: Sheintuch Moshe , Nekhamkina Olga
Published: July 2002

We study the process of pattern selection in a catalytic ribbon or disk subject to global interaction. The diffusion-reaction system, xt−Δx=f(x,y)−〈f(x,y)〉; yt=ε(−αx−y), with a quintic source function f(x,y)=−x(x2−1)(x2−a2)+y, qualitatively describes the behavior of catalytic or electrochemical oscillations subject to control or gas-phase mixing and the kinetics describes a system with two simultaneous or consecutive reactions. This model shows a richer class of solutions than the extensively studied one with a cubic source function (f=−x3+x+y) since f(x)=0 is tristable and for a wide separation of time scales the system admits, without global interaction, coexistence of a stable and oscillatory states. Also the reaction-diffusion equation with a quintic source may admit one large and two small fronts and their domains of existence and stability are mapped. Under global interaction the system exhibits all the patterns unveiled with the “cubic kinetics,” along with multifront patterns and new patterns at the border of instability of the large front.
Coupling of a Jahn–Teller pseudorotation with a hindered internal rotation in an isolated molecule: 9-hydroxytriptycene
Authors: Furlan Alan , Leutwyler Samuel , Riley Mark J.
Published: July 2002

The irregular vibronic structure in the S1←S0 resonant two-photon ionization (R2PI) spectrum of supersonically cooled triptycene is a result of a classic E⊗e Jahn–Teller effect [A. Furlan et al., J. Chem. Phys. 96, 7306 (1992)]. This is well characterized and can be used as an effective probe of intramolecular perturbations. Here we examine the S1←S0 R2PI spectrum of 9-hydroxytriptycene and the fluorescence from various excited state vibronic levels. In this system the pseudorotation of the Jahn–Teller vibration is strongly coupled to the torsional motion of the bridgehead hydroxy group. This torsional motion results in a tunneling splitting in both the ground and excited states. The population of the upper level in the ground electronic state results in additional vibronic transitions becoming symmetry allowed in the R2PI spectrum that are forbidden in the bare triptycene molecule. The assignment of the R2PI and fluorescence spectra allows the potential energy surfaces of these vibrational modes to be accurately quantified. The full C3v vibronic point group must be used to interpret the spectra. The time scale of the internal rotation of the–OH group and the butterfly flapping of the Jahn–Teller pseudorotation are of similar magnitude. The tunneling between the nine minima on the three dimensional potential energy surface is such that the Jahn–Teller pseudorotation occurs in concert with the–OH internal rotation. The Berry phase that is acquired during this motion is discussed. The simple physical picture emerges of the angle between two of the three benzene moieties opening in three equivalent ways in the S1 electronic state. This geometry follows the position of the hydroxy group, which preferentially orients itself to point between these two rings.
Quantum dynamics of chirped excitation of multimode systems
Authors: Yuan J. M. , Liu W.-K. , Hayashi M. T. , Lin S. H.
Published: July 2002

We investigate the effectiveness of chirped laser pulses in exciting a multimode system, where a vibrational mode is coupled to a large number of bath modes. We solve the Liouville equation for this model numerically to investigate the roles played by laser frequency, laser intensity, pulse width, frequency sweeping rate, and bath relaxation times in inducing vibrational excitation. We investigate the range of parameters for which chirping excitation is efficient for multimode systems. In addition, we study constant-frequency excitations using the present model, revealing the special effects of phase relaxation time and the phenomenon of molecular bistability. Furthermore, we present results on quantum decoherence and assess the validity of an effective Hamiltonian method.
Undulational instabilities of smectic thin films on heterogeneous patterned surfaces under positive and negative strain: The case of diblock copolymers
Authors: Pereira G. G. , Williams D. R. M.
Published: July 2002

We consider the problem of a thin smectic film placed on a periodically striped solid surface, with stripe width λ, and with the upper surface free. The striped surface–smectic fluid interfacial energy induces the lamellae to align perpendicularly to the surface. We show that in many cases both the bulk liquid and the free upper surface will undulate to relieve the frustration caused by the stripes. In marked contrast to the traditional Helfrich–Hurault instability we show that this new instability occurs under both extension and compression. As a concrete example we consider a symmetric diblock copolymer thin film melt, with bulk equilibrium AB–BA bilayer spacing L2. When L2<2λ these undulations will be enhanced while for L2>2λ they will be diminished.
A formal method for solving the stationary BBGKY hierarchy for a classical inhomogeneous fluid
Authors: Paine Gregory H.
Published: July 2002

A methodology is developed for finding a formal solution to the entire stationary Bogoliubov, Born, Green, Kirkwood, Yvon (BBGKY) hierarchy for a classical inhomogeneous fluid in thermal equilibrium. The method is unique in that neither a closure relationship nor a restriction on the density or the temperature of the fluid is required. The decisive step in the analysis is the creation of a more general system of coupled integrodifferential equations through the introduction of a coupling parameter. Recognizing that the coupling parameter can also act as an expansion parameter, series solutions to the generalized hierarchy can be obtained through the application of regular perturbation theory. At the end of the calculation, a formal solution to the original BBGKY hierarchy can be recovered by setting the coupling parameter to unity.
Response to “Comment on ‘Improving protein circular dichroism calculations in the far-ultraviolet through reparameterizing the amide chromophore’ ” [J. Chem. Phys. 111, 2844 (1999)]
Authors: Hirst Jonathan D. , Besley Nicholas A.
Published: July 2002

In response to Woody and Sreerama’s Comment that they have realized significant improvements in calculations of the circular dichroism of proteins over those reported by Hirst previously, we report the simultaneous and independent achievement of comparably accurate calculations. Our calculations are based on parameters from ab initio wave functions, in contrast to the combination of experimental data and semiempirical wave functions used by Woody and Sreerama.
Strong amplification of sidebands in a strongly driven three-level atomic system. II. Classical description of the laser field
Authors: Mavroyannis Constantine
Published: July 2002

The fluorescent spectra arising from the interaction of a three-level atom with a strong pump field and a weak signal field have been studied simultaneously. The atom consists of an upper excited state ‖2〉 and two lower ground states ‖3〉 and ‖1〉, which arise by removing the degeneracy of the ground state by applying internal or external fields. The laser field depletes the metastable state ‖3〉 by bringing the electrons into the excited state ‖2〉 from where the electrons emit photons and decay into the lower states through the transitions ‖2〉 → ‖3〉 and ‖2〉 → ‖1〉, which are described by the signal field. Using a classical description of the laser field, where in the model Hamiltonian the laser–atom interaction is treated classically while the free and interacting electron and signal fields are quantized, the decay process ‖2〉 ↔ ‖1〉 of the signal field is considered by evaluating the appropriate Green’s function of the system. The spectral function for the ‖2〉 ↔ ‖1〉 transition of the signal field describes one-photon, three-photon, and two-photon Raman processes, respectively. The one-photon spectra consist of the main peak at the signal frequency and a pair of sidebands, which are symmetrically located from the position of the main peak. The intensity of the main peak is positive while that of the sidebands is negative indicating that the signal is attenuated and is amplified at the corresponding frequencies, respectively. The three-photon and two-photon Raman spectra are described by a doublet, respectively, whose intensities are always negative, implying amplification of the signal field. The computed spectra are presented graphically and compared with those derived in a recent study, where the laser field is quantized and photon–photon correlations are taken into consideration in the limit of high photon densities of the laser field. A detailed discussion of both treatments is given for the processes under investigation.
Quantum line bundles on S2 and method of orbits for SUq(2)
Authors: Šťovíček Pavel
Published: July 2002

The quantum sphere is covered by two quantum complex planes. Quantum line bundle on S2 is introduced by specifying a transition function. The structure of the quantum complex planes enables one to construct representations of SUq(2) acting in spaces of holomorphic sections. In the quantum case, dressing transformation replaces coadjoint action.
Metrics and pairs of left and right connections on bimodules
Authors: Da̧browski Ludwik , Hajac Piotr M. , Landi Giovanni , Siniscalco Pasquale
Published: July 2002

Properties of metrics and pairs consisting of left and right connections are studied on the bimodules of differential 1-forms. Those bimodules are obtained from the derivation based calculus of an algebra of matrix valued functions, and an SLq(2,C)-covariant calculus of the quantum plane at a generic q and the cubic root of unity. It is shown that, in the aforementioned examples, giving up the middle-linearity of metrics significantly enlarges the space of metrics. A metric compatibility condition for the pairs of left and right connections is defined. Also, a compatibility condition between a left and right connection is discussed. Consequences entailed by reducing to the center of a bimodule the domain of those conditions are investigated in detail. Alternative ways of relating left and right connections are considered.
Metastable states, spin–reorientation transitions, and domain structures in planar hexagonal antiferromagnets
Authors: Bogdanov A. N. , Dragunov I. E.
Published: July 2002

Equilibrium states are calculated for a planar hexagonal antiferromagnet in a magnetic field oriented in the basal plane. As the field is rotated in the basal plane, a number of first-order phase transitions accompanied by magnetization jumps are observed in the range of metastable states in the system. The range and equilibrium parameters of the thermodynamically stable domain structure formed in the vicinity of such transitions are determined. Magnetization curves in RbMnCl3 are analyzed.
Approach of a gas-focusing system to steady state
Authors: Horowitz Eric J. , Chernin David , Reiser Martin
Published: July 2002

A computational model in one dimension (radius) has been developed that simulates the time evolution of a low-energy H− beam propagating through a gas-focusing channel. The simulation starts from charge neutralization and proceeds to steady state. It is found that the time to steady state (ts) relative to the neutralization time (tN) depends only on the radial profile of the beam. All physical parameters such as the beam density, beam current, ionization cross section, electron temperature, neutral gas density, and all particle masses scale out. Results relating the time to steady state to the shape of the beam are discussed.
Kelvin–Helmholtz instability in collisionless space plasmas
Authors: Pu Zu-yin
Published: July 2002

The drift kinetic approximation (DKA) is developed by combining the macro- and microdynamics of guiding center plasmas. It is shown that the DKA provides a better description for collisionless processes in plasmas than the Chew–Goldberger–Low approximation. A new theory of the Kelvin–Helmholtz instability (KHI) in collisionless space plasmas is established. Calculations show that the general pattern of the growth rate of the KHI versus flow velocity in the DKA is similar to that in compressional magnetohydrodynamics. However, the critical velocity decreases if pressure is anisotropic, and the growth rate and energy flux are reduced in the presence of wave–particle interactions.
Magnetohydrodynamic channel flow study
Authors: Ramos J. I. , Winowich N. S.
Published: July 2002

A finite-difference study of a steady, incompressible, viscous, magnetohydrodynamic (MHD) channel flow which has direct application to dc electromagnetic pumps is presented. The study involves the numerical solution of the coupled Navier–Stokes and Maxwell equations at low magnetic Reynolds numbers. It is shown that the axial velocity profiles have a characteristic M shape as the fluid approaches and passes the electrode. The electric potential varies almost linearly from the channel centerline to the channel wall. The current shows a steep gradient near the electrodes. Comparison between the finite-difference solution and a quasi-one-dimensional approach are presented. The two-dimensional numerical calculations predict a larger pressure rise, a smaller net current, and a smaller pump efficiency than the quasi-one-dimensional model.
Stabilization of flute modes by finite-Larmor-radius and surface effects
Authors: Caponi Maria Zales , Cohen Bruce I. , Freis Robert P.
Published: July 2002

The combination of finite-ion-Larmor-radius effects and surface stabilization by contact with a lateral wall or with a line-tied cold-plasma blanket can stabilize interchange modes at low plasma beta (beta=plasma pressure/magnetic pressure) in axisymmetric mirror devices. This is illustrated analytically in a simple one-dimensional radial model and numerically with a two-dimensional stability code for anisotropic mirror plasmas and parameters appropriate to the TRW symmetric tandem mirror experiment [Phys. Fluids 28, 1503 (1985)].
The energy dissipation function for turbulence closure theory
Authors: Therry Gérard , André Jean-Claude , Debar Roger
Published: July 2002

Approximations for the substantial derivative of the eddy kinetic energy dissipation rate are discussed and compared to those previously proposed, particularly with respect to equilibrium solutions.
Deep-water gravity wave instabilities at large steepness
Authors: Kharif Christian , Ramamonjiarisoa Alfred
Published: July 2002

An extension of earlier computations on deep-water gravity wave instabilities up to a wave steepness of 0.434 is performed to compare the relative strength of class I versus class II instabilities. The three-dimensional class II, m=1 instabilities are still predominant. However, as the steepness increases, the difference between the growth rates of two-dimensional and three-dimensional perturbations decreases rapidly and becomes negligible around a 0.43 wave steepness.
Framework of parametric instabilities in the presence of space-time fluctuations in homogeneous and inhomogenous plasmas. I. Theory
Authors: Lu Liang
Published: July 2002

The problem of parametric instabilities in the presence of space-time fluctuation in homogeneous or inhomogeneous plasmas can be cast into the problem of finding an effective Hamiltonian Heff of the linear stochastic equation. For the Kubo–Anderson–random-phase model (RPM) [J. Math. Phys. 15, 524 (1974); Phys. Rev. Lett. 29, 565 (1972); J. Phys. Soc. Jpn. 9, 316 (1954)], Heff is generally found to be of the form H0+ΔωH1, where H0 represents all the coherent effects and ΔωH1 represents the finite bandwidth modification. It is shown that H1 is a trivial constant matrix for all parametric processes. A method called frame transformation is introduced to treat all kinds of group velocities in a unified fashion. The theory can be used to calculate average amplitude as well as average power. Importantly, the theory is not limited to wide bandwidths.
Enhancement of optical nonlinearity in p-type semiconductor quantum wells due to confinement and stress
Authors: Chang Yia-Chung
Published: July 2002

It is shown that large values of the third-order nonlinear susceptibility χ(3) can be obtained in p-type semiconductor quantum wells (e.g., GaInAs-AlInAs) due to strong valence-band nonparabolicity. The strong nonparabolicity in valence bands arises from the mixing of heavy and light hole states via quantum well potential. It is further shown that stress can modify χ(3) substantially.
Very thin gold films produced with ion plating for improved transparent infrared reflectors
Authors: Smith G. B.
Published: July 2002

Semitransparent gold films under 10 nm thick were produced with ion plating onto glass and were shown to give improvements, depending on thickness, for either solar control or transparent heat-mirror applications relative to conventional deposits. Film inhomogeneities, modified gold optical constants, and ion-beam assisted onset of film coalescence all play an important role. An anomalously large frequency dependence of conduction electron relaxation time was identified in a continuous film from a Drude analysis.
Platinum gettering in silicon by phosphorus
Authors: Falster Robert
Published: July 2002

The gettering capture of certain metallic impurities (especially Au) is known to be associated with enhanced solubility in the presence of high concentration phosphorus. Platinum is a metal whose diffusion characteristics closely resemble that of gold. It is likewise a deep acceptor in n-type silicon. One might therefore expect its gettering behavior also to be similar. Experiments described here show this not the case. Platinum was indeed found to be gettered effectively by phosphorus though on nonsubstitutional sites at the sample surface. This is explained to be a supersaturation of silicon self-interstitials induced by the diffusion of phosphorus which kicks platinum onto high mobility, low solubility interstitial sites. The possible relevance of this solubility supression mechanism for Au gettering is discussed.
CO2 laser-induced dislocations and other damage in tellurium single crystals
Authors: Quang N. V. , Shih I. , Zhang S. K. , Champness C. H.
Published: July 2002

Etching experiments were performed on (0001) oriented tellurium single crystal samples irradiated with a CO2 laser beam to reveal the localized induced dislocations in the crystals. It was found that the tellurium surface is very sensitive to the laser beam. Under low illumination intensity, visible defects were not found but the dislocation density was greatly increased. Under high illumination intensity, visible damage on the surface was observed; the surface was found to be locally remelted by the laser beam to result in a hole with many cracks around it.
Composition of amorphous (Si,Ge):H films from nuclear elastic scattering of 12 MeV protons
Authors: Schwarz R. , Wagner S. , Kouzes R. T. , Wieting R. D.
Published: July 2002

Nuclear elastic scattering of 12 MeV protons was employed for the first time to study the composition of thin films of hydrogenated amorphous Si-Ge alloys. The concentrations of H, Si, and Ge were measured simultaneously. The detection limit is about 25 ppm for a 10-min run. Free-standing films or films on a flat substrate with a total thickness of up to 20 μm can be analyzed.
Growth of a novel InAs-GaAs strained layer superlattice on InP
Authors: Tamargo M. C. , Hull R. , Greene L. H. , Hayes J. R. , Cho A. Y.
Published: July 2002

Strained layer superlattice structures with ultrathin, alternating InAs and GaAs layers have been grown on buffer layers lattice matched to InP. Low angle x-ray scattering and transmission electron microscopy studies were used to characterize the layers.
Electrodynamic explosions in liquids
Authors: Graneau Peter , Graneau P. Neal
Published: July 2002

This letter reports experimental results which show that electric arc currents through salt water produce explosions by electrodynamic forces rather than by the thermal expansion of gases generated in the arc column. The explosive phenomena can be explained with the aid of longitudinal Ampere forces but not with traditional Lorentz forces. This represents the first experimental evidence indicating that Ampere’s force law may be valid for dense arc plasmas.
Redistribution of Cr in GaAs:Cr and of V in GaAs:V after implantation of Si, Be, or B and annealing in a controlled atmosphere
Authors: Kütt W. , Bimberg D. , Maier M. , Kräutle H. , Köhl F. , Tomzig E.
Published: July 2002

The redistribution of V in V-doped and Cr in Cr-doped semi-insulating GaAs substrates after implantation with Si, Be, B and subsequent controlled atmosphere annealing at 840 °C for 20 min is determined using secondary ion mass spectrometry. Both V and Cr show accumulation into zones of high defect densities at ∼Rp+ΔRp of the Si, Be, or B implantation profile, respectively, and a depletion which extends beyond that zone to ∼2–4×Rp. Some surface accumulation has also been observed. For all three cases studied, the V redistribution is much smaller than the Cr redistribution. It is therefore concluded that from thermal stability point of view semi-insulating GaAs:V should be a better substrate material for implantation type devices than is GaAs:Cr.
Electrical transport properties of tungsten silicide thin films
Authors: Li B. Z. , Aitken R. G.
Published: July 2002

The electrical transport properties of cosputtered tungsten silicide films were investigated. The microstructure of the annealed film was determined by x-ray diffraction. Both resistivity and Hall coefficients for the WSi2 films were measured in the temperature range 80–300 K. The current carriers in tungsten disilicide were found to be positive holes. The carrier concentration determined from this experiment is ∼1×1022 cm−3 which does not change with either annealing process or measuring temperature. The resistivity of the WSi2 film in the measured temperature range increases approximately linearly with temperature. The carrier mobility and its temperature dependence were also studied.
Effect of phase separation on the electrical properties of the interface between Ni-Ta thin films and GaAs substrate
Authors: Lahav A. , Eizenberg M.
Published: July 2002

The dependence of Schottky barrier height (φB) derived from current-voltage measurements on annealing temperature of thin films of Ni, Ta, Ni/Ta, and Ta/Ni bilayers, and Ni60Ta40 alloy on n-type (100) GaAs substrate was determined. Variations in the measured φB values have been related to the appearance of different phases at the interface with GaAs resulting from chemical reactions between the metal films and the GaAs substrate. Both Ni and Ta form with n-GaAs rectifying contacts with barrier height higher for Ni than for Ta; at a certain temperature related to compound formation (550 °C for Ni and 650 °C for Ta) the contacts become ohmic. For the bilayers and alloyed films the presence of Ni phases (Ni2GaAs at 350 °C and NiGa at 550 °C at the interface with GaAs due to phase separation during annealing determines the electrical properties of the contact (rectifying up to 350 °C and ohmic at 550 °C). The φB measurements were proved to be very sensitive to the initial stages of interfacial reactions. The phase separation can be potentially used for formation of shallow contacts to n-GaAs.
Polymer-polypyrrole alloy films as semitransparent organic conductors
Authors: Niwa Osamu , Hikita Makoto , Tamamura Toshiaki
Published: July 2002

The electrochemical polymerization of pyrrole on a polymer-coated electrode produces an electrically conducting polymer-polypyrrole alloy film. The surface resistance and the optical transmission of the alloy film can be controlled by the polymerization conditions, and semitransparent conducting films with a transmittance of 60% and a conductivity of 2/Ω cm can be realized.
Etching of deep grooves for the precise positioning of cleaves in semiconductor lasers
Authors: Bowers J. E. , Hemenway B. R. , Wilt D. P.
Published: July 2002

Photoelectrochemical etching of InP is used to etch deep (80 μm), narrow (20 μm) grooves. The grooves are used to precisely position cleaves in semiconductor lasers and to demonstrate the first wafer processing of long/short cleaved-coupled-cavity (C3) lasers. Large numbers of low threshold C3 lasers wth very similar cavity lengths were obtained.
High output power characteristics in broad-channeled substrate inner stripe lasers
Authors: Yamamoto S. , Miyauchi N. , Maei S. , Morimoto T. , Yamamoto O. , Yano S. , Hijikata T.
Published: July 2002

A high output power AlGaAs laser is newly developed in the spectral range of 770–780 nm. The laser has a double-depth channel on the p-GaAs substrate which forms a built-in optical waveguide having a double effective refractive index/loss step. This novel waveguide is effective to make the fundamental lateral mode extremely stable; that is, up to 60 mW when the reflectivity of the front facet (Rf) is 0.12, and 100 mW when Rf is 0.04. cw threshold currents are 35–45 mA and external differential efficiencies are 0.6–0.8 mW/mA. Also, an astigmatic distance below 3 μm is obtained when Rf is more than 0.10.
Local oxygen diffusion induced in Ca-doped yttrium iron garnet films by laser annealing
Authors: Antonini B. , Paroli P. , Salustri C.
Published: July 2002

Local inward and outward oxygen diffusion induced in Ca-doped yttrium iron garnet films by laser annealing in controlled atmospheres is reported for the first time. This allows changing locally and reversibly the concentration of Fe4+ ions, which control the electrical and infrared optical properties of the material. The effects of laser annealing were investigated by measuring in the irradiated regions the optical absorption and the magnetic circular dichroism in the near infrared. The possibility of small scale maskless treatments and the short times involved make this technique interesting for several device applications.
Spectral sensitivity of resist by x-ray excited ion mass analysis
Authors: Mochiji Kozo , Kimura Takeshi , Obayashi Hidehito
Published: July 2002

A measurement technique of spectral sensitivity for x-ray resist is developed. Sensitivity is evaluated from the yield of gaseous fragment of resist during exposure to monochromatized synchrotron radiation. Using this technique named x-ray excited ion mass analysis, the spectral sensitivity of x-ray resist, poly-2-methylpentene-1-sulfone, is evaluated. The sensitivity is found to be enhanced at shorter wavelengths despite a low absorption coefficient. This measurement technique promises to improve the spectral sensitivity analysis in the soft x-ray region.
1/f frequency fluctuations in quartz acoustic resonators
Authors: Parker T. E.
Published: July 2002

The level of 1/f frequency fluctuations has been measured on numerous quartz surface acoustic wave resonators. When these results are combined with existing data for quartz bulk acoustic wave resonators it becomes clear that the 1/f process is essentially the same in both types of devices. Furthermore, the power spectral density of frequency fluctuations shows a clear power law dependence that is very close to 1/Q4u , where Qu is the unloaded Q. However, the observed dependence on loaded Q is weak.
Minority-carrier lifetime study of the pressure induced Γ-X crossover in GaAs
Authors: Leroux M. , Pelous G. , Raymond F. , Verie C.
Published: July 2002

Room-temperature continuous and time-resolved (on a nanosecond scale) photoluminescence experiments have been performed on p-type GaAs. Observation of indirect luminescence in GaAs above 4 GPa allowed a direct determination of the room-temperature pressure coefficient of the Xc1 valleys. A new set of pressure dependence parameters for both Γ and X energy gaps in GaAs has been determined. These pressure coefficients, together with the intensity of luminescence as a function of pressure, yielded an estimate of the electron lifetime ratio confirmed by subsequent time-resolved experiments. A threefold enhancement of electron lifetime is observed above the Γ-X crossover.
Low pressure chemical vapor deposition of titanium silicide
Authors: Tedrow P. K. , Ilderem V. , Reif R.
Published: July 2002

The low pressure chemical vapor deposition (LPCVD) of titanium silicide is reported here for the first time. X-ray diffraction spectra show that the as-deposited films are polycrystalline and TiSi2 is the predominant phase. The as-deposited films had resistivities of 22 to 39 μΩ cm with film thicknesses ranging from 2000 to 15 500 Å, and Si/Ti ratios of 1.8 to 2.3 as determined by Rutherford backscattering spectroscopy. Auger analyses did not detect any impurities such as oxygen and carbon in these films. The LPCVD system consists of a cold wall reactor with the wafer being heated externally by infrared lamps. The reactor is capable of sequential deposition of polycrystalline silicon (polysilicon) and silicide films; moreover, the final annealing step, if necessary, can be performed in situ. Care has been taken to provide a clean environment by using a turbomolecular pump which is capable of keeping the base pressure of the reactor ≤10−7 Torr. We have deposited in situ sequential films of polysilicon and titanium silicide in this system. The silicide films were deposited by reacting SiH4 with TiCl4.
Microwave intensity and frequency modulation of heteroepitaxial-ridge-overgrown distributed feedback lasers
Authors: Bowers J. E. , Tsang W. T. , Koch T. L. , Olsson N. A. , Logan R. A.
Published: July 2002

The intensity and frequency modulation response of heteroepitaxial-ridge-overgrown distributed feedback lasers are characterized as a function of modulation frequency from 0.2 to as high as 17 GHz. Small-signal intensity modulation measurements show a −3 dB frequency of 7.1 GHz. Efficient frequency modulation (>0.1 GHz/mA) is demonstrated for modulation frequencies up to 13 GHz. A new standard for comparing semiconductor lasers, the chirp to modulated power ratio, is suggested as a means of comparing semiconductor lasers and as an aid to understanding the interaction of FM and IM in a semiconductor laser.
Stimulated emission from a Cd1−xMnxTe-CdTe multilayer structure
Authors: Bicknell R. N. , Giles-Taylor N. C. , Schetzina J. F. , Anderson N. G. , Laidig W. D.
Published: July 2002

In this letter we report the first observation of stimulated emission from an optically pumped Cd1−xMnxTe-CdTe multilayer structure. This new laser structure was grown by molecular beam epitaxy and consists of an active superlattice (SL) region containing 25 CdTe quantum wells (Lz∼150 Å) alternating with 24 Cd1−xMnxTe (x∼0.45) barriers (LB∼50 Å). The SL is sandwiched between thicker Cd1−xMnxTe cladding layers. The substrate consists of a 2-μm-thick buffer layer of CdTe on GaAs. The Cd1−xMnxTe-CdTe SL lasers operate at 763–766 nm when optically pumped at ∼25 K with a cavity-dumped argon ion laser which emits 4-ns light pulses (514.5 nm) at a repetition rate of 3.8 MHz. The onset of laser action occurs at a peak pump power density of about 1.35×104 W/cm2. The mode spacing of the emitted laser radiation is in reasonable agreement with the spacing expected from measured cavity dimensions of the Cd1−xMnxTe-CdTe multilayer.
High accuracy noncontact laser-optical method for measuring surface acoustic wave velocity and attenuation
Authors: Burov J. I. , Branzalov K. P. , Ivanov D. V.
Published: July 2002

A high accuracy noncontact laser-optical method for measuring surface acoustic wave (SAW) velocity and attenuation is described. The accuracy depends on the power of the two lasers, used for generation and probe of SAW and on bandwidth of the intensity modulation. The method is applicable to all acoustic materials including the nonpiezoelectrical ones.
Radiometric crack detection in fast moving surfaces
Authors: Kaufman Irving , Choudhury Ashish K.
Published: July 2002

Cracks in the surfaces of metal shafts rotating up to 3200 rpm were detected by passive, radiometric sensing of the 8–12-μm thermal radiation emitted. This detection is possible because the effective crack emissivity approaches that of a black body, while the metal itself has a much lower emissivity. By the use of signal storage and signal subtraction, the technique is expected to permit ‘‘on-line’’ monitoring of the development of cracks, even in the presence of surface blemishes.
Lateral photodetectors on semi-insulating InGaAs and InP
Authors: Diadiuk V. , Groves S. H.
Published: July 2002

A new type of high-performance lateral PIN photodector has been formed by alloying p-type and n-type metallic contacts onto semi-insulating InGaAs or InP without a separate junction fabrication step. Low dark current (<1 nA), high external quantum efficiency (40% at λ=1.24 μm, without antireflection coating), and high speed (full width at half-maximum <50 ps) have been obtained with reverse bias of 10 V. These characteristics, plus the simplicity of fabrication and the planar lateral configuration, make these devices attractive for monolithic integration with field-effect transistors and for photodetector arrays.
Observation of electron transport in polyethylene terephthalate and the radiation hardening of dielectrics
Authors: Kurtz S. R.
Published: July 2002

Electron-induced conductivity measurements were performed on polyethylene terephthalate to compare electron and hole contributions to the radiation-induced conductivity. The electron mobility in this material was found to be ≳102 times that of the holes. This result explains an earlier observation that the radiation-induced conductivity of polyethylene terephthalate can be radically reduced by chemically doping this dielectric with electron acceptor molecules.
Uniform and thermally stable AuGeNi ohmic contacts to GaAs
Authors: Callegari A. , Pan E.T-S. , Murakami M.
Published: July 2002

An in situ rf sputter precleaning of the GaAs substrate before AuGeNi ohmic metal deposition yields contact resistance Rc=0.11 Ω mm at a peak doping of ∼1018/cm3. Excellent uniformity and thermal stability are achieved across the wafer. The contacts do not deteriorate appreciably after themal treatment at 410 °C for 57 h.
Molecular beam epitaxially grown circular U-groove barrier transistor
Authors: Chang C. Y. , Wang Y. H. , Liu W. C. , Liao S. A. , Cheng K. Y.
Published: July 2002

A new version of simple GaAs n+-n-δ(p+)-n-n+ ultrathin base transistor with U-groove base contact is demonstrated by molecular beam epitaxy which possesses a circular mesa etched base. The potential barrier height can be directly modulated by the applied base voltage and thus the current can traverse over the barrier by thermionic emission. It is a voltage-controlled device. Its transconductance increases with increasing collector-emitter and base-emitter voltage. The collector current density of the present device is larger than 1.5 kA/cm2 and the transconductance is larger than 200 mS/mm, which are larger than those of the previously reported V-groove device.
Evidence of chemical ordering in amorphous hydrogenated silicon carbide
Authors: Tafto J. , Kampas F. J.
Published: July 2002

Amorphous Si0.68C0.32:H prepared by radio frequency glow discharge from a mixture of methane and silane was studied by means of the complementary techniques of electron energy-loss spectroscopy and electron diffraction. The experimental results are consistent with Si and C forming a tetrahedral network with nearest neighbor distances similar to those in crystalline Si and crystalline SiC. There is evidence that the C atoms tend to be surrounded by four Si atoms rather than a random distribution of C and Si on the tetrahedral network.
Effects of substrate temperatures on the doping profiles of Si in selectively doped AlGaAs/GaAs/AlGaAs double-heterojunction structures
Authors: Inoue Kaoru , Sakaki Hiroyuki , Yoshino Junji , Yoshioka Yoshiaki
Published: July 2002

Electrical properties of selectively doped double heterojunctions with a thin GaAs layer (≤300 Å) grown by molecular beam epitaxy are known to depend significantly on the substrate temperatures during growth. Although samples grown at 530 °C show high electron mobilities and reasonable electron concentrations, much lower mobilities and rather high electron concentrations have been obtained for those grown at 630 °C. Secondary ion mass spectrometry studies have been performed and have revealed that the degraded electrical properties are caused mainly by the surface migration of Si and the subsequent incorporation of Si into the undoped GaAs layer of the quantum well.
Laser writing on a novel bilayer resist structure
Authors: Li Kin , Oprysko Modest M.
Published: July 2002

Laser and bilayer resist techniques have been combined to produce a new lithographic process. An argon ion laser operating at 514.5 nm is used to write a mask on the top layer of a novel resist structure. The laser writing process is based on a thermal decomposition mechanism. Flood exposure with deep ultraviolet light is used to replicate the laser generated patterns on the bottom layer, polymethyl methacrylate (PMMA). The bilayer resist structure is insensitive to ambient light and eliminates the interfacial problems usually encountered in photoresist-on-PMMA structures. The process results in clean and well defined features smaller than 2 μm.
Variable frequency picosecond optical pulse generation from laser diodes by electrical feedback
Authors: Izadpanah S. H. , Paslaski J. , Rav-Noy Z. , Margalit S. , Yariv A.
Published: July 2002

High repetition rate picosecond optical pulse generation is achieved by providing electrical feedback (with and without external gain) to a self-pulsating laser diode. The feedback improves pulsation short-term stability (<25-kHz frequency jitter) and narrows the laser pulses (14 ps).
High resolution infrared measurements of the OH− bands in KTiOPO4
Authors: Theis William M. , Norris George B. , Porter Marc D.
Published: July 2002

High resolution infrared transmission measurements were performed at 10–300 K on KTiOPO4 crystals grown by hydrothermal or flux methods. The previously reported low resolution OH− band at 2.8 μm resolved into more than 100 lines. The strongest line was identified as a pure OH− stretch which broadened as T2, whereas lines which broadened as T1 were attributed to combinations with librations or other vibrational transitions. Although the integrated OH− related absorption strengths for several crystals were equivalent (±10%), the relative absorption strengths for various groups of lines scaled together and correlated with frequency doubling efficiencies; this indicated the possible occupation of several nonequivalent OH− sites in the lattice. Thus, only a portion of the OH− impurity was detrimental to the nonlinear polarizability.
Single-crystal n-InAs coupled Josephson junction
Authors: Kawakami Tsuyoshi , Takayanagi Hideaki
Published: July 2002

A high electron mobility single-crystal n-InAs coupled Josephson junction with refractory metal Nb electrodes has been fabricated. Josephson current has been obtained for devices with electron carrier concentrations of 1016–1018 cm−3 and with Nb electrode spacings longer than 0.5 μm. The devices have a planar geometry with implicit potential for gate control. The rf sputter cleaning of the InAs surface prior to Nb deposition is found to have significant effects on the performance of the devices. The device characteristics are explained by the proximity effect theory.
Photochemical generation and deposition of copper from a gas phase precursor
Authors: Jones C. R. , Houle F. A. , Kovac C. A. , Baum T. H.
Published: July 2002

The photochemical generation and deposition of copper metal from a volatile copper coordination complex are described. Pulsed and cw ultraviolet light sources were used to induce deposition. The chemical compositions of the films are compared for all methods.
Calorimetric interferometry using pulsed Nd-glass laser for measurement of small absorption coefficient at 1.06 μm
Authors: Yoon Jae Sun , Lee Sang Soo
Published: July 2002

A new calorimetric interferometry using a pulsed high power Nd-glass laser was developed to determine small absorption coefficients of the order of 10−3 cm−1 or less at the wavelength of 1.06 μm. The absorption coefficients of the liquid specimens, C6H6, C6H5Cl, 0-C6H4Cl2, and 1,2,4-C6H3Cl3, were determined by the fast acquisition of an interferogram, accurate microcalorimetry, and the measurement of the laser beam radius.
Coherence and focusing properties of unstable resonator semiconductor lasers
Authors: Mittelstein M. , Salzman J. , Venkatesan T. , Lang R. , Yariv A.
Published: July 2002

The emission characteristics of unstable resonator semiconductor lasers were measured. The output of an 80-μm-wide laser consists of a diverging beam with a virtual source 5 μm wide located 50 μm behind the laser facet. A high degree of spatial coherence of the laser output was measured, indicating single lateral mode operation for currents I≲3 Ith.
Mercury zinc telluride, a new narrow-gap semiconductor
Authors: Sher Ariel , Eger D. , Zemel A.
Published: July 2002

For the first time the growth of single crystal solid solutions of Hg1−xZnxTe is demonstrated. Layers with compositions of x=0.16 and 0.23 having transmission cut-on wavelengths of 9.1 and 4.1 μm at 80 K, respectively, were grown by liquid phase epitaxy on CdTe substrates. The optical and electrical characteristics of the epilayers are similar to those obtained for Hg1−xCdxTe alloys.
High performance photovoltaic infrared devices in Hg1−xCdxTe on sapphire
Authors: Reidel R. A. , Gertner E. R. , Edwall D. D. , Tennant W. E.
Published: July 2002

A combination of organometallic vapor phase epitaxy and liquid phase expitaxy (LPE) has been used to grow CdTe on sapphire. The resultant heterostructure has been used as a substrate for LPE growth of Hg0.7Cd0.3Te. Photodiodes in the HgCdTe show excellent properties. Typical R0A products are ≥106 Ω cm at 77 K for Hg1−xCdxTe layers with cut-off wavelengths of 4.8–5.2 μm at 77 K. The backside-illuminated spectral response was broadband with quantum efficiencies typically >80% (without antireflection coating).
Effects of Be and Si on disordering of the AlAs/GaAs superlattice
Authors: Kawabe Mitsuo , Shimizu Norisato , Hasegawa Fumio , Nannichi Yasuo
Published: July 2002

Effects of Be doping and the interaction of Be and Si on the disordering of 15-nm AlAs/15-nm GaAs superlattices were studied. Be doping of more than 4×1019 cm−3 causes the intermixing of Al and Ga during epitaxial growth and the effect of Be surface accumulation is observed at the growth temperature of 540 °C, while after incorporation of Be in the crystal the annealing of 750 °C, 2 h does not cause any remarkable change in the superlattice structure. Be doping in the Si-doped superlattice shows remarkable suppression of the disordering of superlattice when the Be doping level exceeds that of Si.
Impurity-disordered, coupled-stripe AlxGa1−xAs-GaAs quantum well laser
Authors: Gavrilovic P. , Meehan K. , Epler J. E. , Holonyak N. , Burnham R. D. , Thornton R. L. , Streifer W.
Published: July 2002

Continuous room-temperature operation of impurity-disordered, coupled-stripe AlxGa1−xAs-GaAs quantum well heterostructure lasers is described. Silicon (donor) diffusion at 850 °C is used to produce layer disordering and index guiding, in addition to providing carrier confinement in a ten-stripe coupled array (8-μm-wide stripes on 10-μm centers).
Rare-earth metal Schottky-barrier contacts to GaAs
Authors: Waldrop J. R.
Published: July 2002

The electrical properties and interface chemistry of ideal (no interfacial oxide) rare-earth metal contacts to GaAs are investigated by using x-ray photoemission spectroscopy (XPS), current-voltage (I-V), and capacitance-voltage (C-V) techniques. The contacts were formed (in ultrahigh vacuum) by evaporation of Tb, Dy, and Er onto clean, n-type GaAs (100) surfaces. For each metal a substantial interface chemical reaction occurs in which GaAs is dissociated and a rare-earth arsenide is formed that results in a>12-Å-thick interface layer. The Schottky-barrier height, measured with I-V and C-V methods at the same interfaces characterized by XPS, for these rare-earth metals is 0.85 eV. By a comparison to selected other materials, the results for rare-earth metals emphasize that the Schottky-barrier height for ideal contacts to GaAs is independent of the contact work function, electronegativity, and interface chemical reactivity.
Capacitance decrease due to stress in a Cu-doped, n-type Si Schottky diode
Authors: Tōyama Naotake
Published: July 2002

In Au n-type Si Schottky diodes heavily doped with copper, a remarkable decrease in the depletion layer capacitance is frequently observed by applying stress. It was found that the capacitance decrease due to stress was attributed to the change of the copper substitutional species (CuI) dissolved in silicon into other different copper-associated species (CuII) in accordance with a stress level. Since the capacitance decrease due to stress becomes conspicuous, too, as the signal frequency of measurement is increased, we can expect an application as a stress-sensitive capacitor.