bluuebunny/crossref_metadata_2025 huggingface dataset:
UV irradiation effects in Al chemical vapor deposition on titanium nitride
Authors: Nitta Toshinari , Hanabusa Mitsugu
Published: July 2002

UV irradiation effects on Al chemical vapor deposition on titanium nitride (TiN) was investigated by using dimethylaluminum hydride at 150 °C. Al films grew thermally at a rate of 6.3 nm/min, while the UV light generated by a deuterium lamp reduced the rate to 5.2 nm/min. When TiN surfaces were oxidized, Al films started to grow only under UV irradiation. Using x-ray photoelectron spectroscopy (XPS), we showed that the adsorbates formed on the oxidized surfaces could be dissociated only when the UV light was irradiated. The XPS results also suggested involvement of photoinduced desorption in reducing the growth rate.
Degrees of visible determinism in crystal growth striations as a measure of crystal quality
Authors: Miyano Takaya , Morita Hiroshi , Shintani Akira , Kanda Tadashi
Published: July 2002

A diagnostic test based on the parallelism of neighboring trajectories generated from a time series in phase space for visible determinism is applied to characterizing complexities in growth striations of Czochralski silicon crystals. Change in the structure of the striations by crystal annealing is examined in terms of degrees of randomness in growth striations.
Self-texturing of nitrogenated amorphous carbon thin films for electron field emission
Authors: Silva S. R. P. , Amaratunga Gehan A. J. , Barnes J. R.
Published: July 2002

The electron field-emission process for nitrogenated amorphous carbon (a-C:H:N) thin films deposited using a magnetically confined hydrocarbon plasma is examined. The morphology of the films obtained using an atomic force microscope is compared to the field-emission properties. Beyond a chemical composition of 14 at. % nitrogen, the mirror smooth a-C:H:N films become self-texturing, and multiple “domelike” cathodes of nanometer scale are observed. The dimensions of these “domelike” cathodes varies with time, and after a 15 min deposition have dimensions of approximately 50 nm base diameter and 20 nm in height. When the electronic field emission of these textured films (N content 15 at. %) are measured, there is an enhancement in the emitted current density of ∼2 orders of magnitude at an electric field of 20 V/μm, in comparison to the untextured films with a nitrogen content of 11 at. %.
Control of liquid crystal alignment by polyimide surface modification using atomic force microscopy
Authors: Pidduck A. J. , Haslam S. D. , Bryan-Brown G. P. , Bannister R. , Kitely I. D.
Published: July 2002

Atomic force microscopy (AFM) has been used to modify a polyimide surface to give controlled liquid crystal (LC) alignment, and to examine the modification produced. Strong LC azimuthal anchoring was observed typically for normal forces >300 nN and line densities >5 μm−1, and optically diffracting LC elements were fabricated by repeatedly overpatterning the same area along different directions. Atomic force microscopy images showed little sign of topographic modification such as grooving, whereas lateral force images showed locally increased friction. Estimated contact pressures, 0.08–0.3 GPa, suggest shear-yielding occurs within a surface layer, causing polymer chain alignment. The AFM micromechanical interaction is compared with that occurring during the conventional cloth-rubbing LC alignment process.
Epitaxially stacked lasers with Esaki junctions: A bipolar cascade laser
Authors: Garcia J. Ch. , Rosencher E. , Collot Ph. , Laurent N. , Guyaux J. L. , Vinter B. , Nagle J.
Published: July 2002

We present a two-color (956 and 985 nm) InGaAs/AlGaAs laser structure epitaxially stacked through a low-resistance (10−5–10−4 Ω cm2) Esaki junction, exhibiting two threshold characteristics. It is shown that this structure can be considered as a bipolar cascade laser.
Nanoparticle morphology in a granular Cu–Co alloy with giant magnetoresistance
Authors: Wang Wendong , Zhu Fengwu , Weng Jun , Xiao Jimei , Lai Wuyan
Published: July 2002

The morphology of nanometer-sized cobalt granules in a granular Cu88Co12 alloy was directly determined utilizing an atom probe-field ion microscope. The granules are spherical in shape, and exhibit a size distribution. Giant magnetoresistance (GMR) was observed in alloys with an average granule size ranging from 1.5 to 6 nm in diameter. A well-known theoretical model of general GMR behavior in magnetic granular systems was confirmed based on measurement of size distribution of the granules.
Photoluminescence and structural defects in erbium-implanted silicon annealed at high temperature
Authors: Sobolev N. A. , Gusev O. B. , Shek E. I. , Vdovin V. I. , Yugova T. G. , Emel’yanov A. M.
Published: July 2002

The behavior of luminescence spectra and structural defects in single crystal Czochralski silicon after erbium implantation at 1 MeV energy and 1×1013 cm−2 dose with subsequent annealing at 1100 °C for 0.25–3 h in an argon or chlorine-containing ambience was studied by photoluminescence (PL), transmission electron microscopy, and chemical etching/Nomarski microscopy. We have found that annealing in the chlorine-containing ambience gives rise to dislocation loops and pure edge dislocations with dominant dislocation-related lines in the PL spectrum. Pure edge dislocations are responsible for the appearance of the lines. The Er-related lines due to the intra-4f shell transitions in the rare-earth ions dominate in the PL spectra and no structural defects are observed after annealing in argon. The observed differences in the optical and structural properties of Si:Er are associated with intrinsic point defects generated during the implantation and annealing.
Beam quality enhancement for a radio-frequency excited annular CO2 laser
Authors: Lapucci A. , Ciofini M. , Mascalchi S. , Di Fabrizio E. , Gentili M.
Published: July 2002

We report the preliminary experimental results obtained from an annular radio-frequency excited CO2 laser with a Talbot cavity and a phase correcting mirror external to the cavity. The Talbot cavity is adopted in order to reduce the number of oscillating azimuthal modes. The use of the external profile-modulated mirror is aimed at reducing the beam phase modulation and thus increasing the amount of fundamental annular mode energy content. The beam quality results to be sensibly increased.
Molecular doping of gallium nitride
Authors: Pankove J. I. , Torvik J. T. , Qiu C.-H. , Grzegory I. , Porowski S. , Quigley P. , Martin B.
Published: July 2002

Photoconductivity experiments were made on bulk GaN doped with Mg and O and grown using high pressures and high temperature. The bulk GaN:Mg,O was insulating, indicating compensation. The photoconductive response to photons above the energy band gap was comparable to that of epitaxially grown GaN:Mg samples. However, the UV-to-visible rejection ratio (solar blindness) was three orders of magnitude larger in the bulk GaN:Mg,O than for other epitaxially grown GaN samples. The dramatically improved visible rejection ratio is tentatively attributed to molecular doping by paired donors (O) and acceptors (Mg). Vacuum UV reflectance was performed to verify if MgO critical point transitions could be found in the GaN:Mg,O. A reflectance peak at 6.7 eV was found in both MgO and GaN:Mg,O.
DX centers in GaAs/Si-δ/AlAs heterostructure
Authors: Miwa R. H. , Schmidt T. M.
Published: July 2002

Microscopic mechanisms of impurity spreading in GaAs/Si-δ/AlAs heterostructure have been investigated using an ab initio pseudopotential total energy calculation. Our results showed that silicon atoms can move from the δ-doped plane occupying interstitial positions, favored by the high doped concentration, forming DX centers. The silicon impurity position, out of the δ plane in the AlAs layers, presents an energetically stable configuration, and in the GaAs layers, presents a metastable configuration. As a consequence a silicon doping limit is reached due to the presence of localized deep states inside the band gap, when silicon atoms are in interstitial positions.
Suppression of temperature sensitivity of interband emission energy in 1.3-μm-region by an InGaAs overgrowth on self-assembled InGaAs/GaAs quantum dots
Authors: Mukai Kohki , Sugawara Mitsuru
Published: July 2002

We found that the temperature sensitivity of interband emission energy was suppressed significantly in 1.3-μm-emitting self-assembled InGaAs/GaAs quantum dots by an InGaAs overgrowth on the dots. Transmission electron microscopy measurements indicated that lattice distortion was enhanced on dots in a 10-nm-thick InxGa1−xAs overgrowth layer. Photoluminescence spectra showed that the emission energy shift with increasing temperature was nearly negligible above 150 K when x⩾0.25. The shift between 4.2 and 200 K was less than half that of bulk GaAs when x=0.3. The results reveal the potential of InGaAs-covered dots in realizing temperature-insensitive lasing wavelength of laser diodes by manipulating the three-dimensional strain distribution.
Electrochemical formation of GaAs/Bi Schottky barriers
Authors: Vereecken Philippe M. , Searson Peter C.
Published: July 2002

Bismuth layers have been deposited electrochemically on (100) n- and p-type GaAs. The electrical properties of junctions on n-GaAs were dependent on the bismuth deposition potential. Bismuth films deposited at −0.2 V (Ag/AgCl) were compact, continuous, and exhibited good adhesion; the n-GaAs/Bi junctions exhibited an average barrier height of 0.83 eV. Films deposited at ⩽−0.3 V were porous and the barrier heights exhibited an aging effect decreasing to 0.73 eV after several days under ambient conditions. Bismuth films deposited on p-GaAs exhibited barrier heights of 0.57 eV. The sum of the barrier heights for n- and p-type junctions correspond to 1.40 eV, close to the band gap of GaAs consistent with Fermi-level pinning.
Strain relaxation mechanism for hydrogen-implanted Si1−xGex/Si(100) heterostructures
Authors: Trinkaus H. , Holländer B. , Rongen St. , Mantl S. , Herzog H.-J. , Kuchenbecker J. , Hackbarth T.
Published: July 2002

A mechanism of strain relief of H+ ion implanted and annealed pseudomorphic Si1−xGex/Si(100) heterostructures grown by molecular beam epitaxy is proposed and analyzed. Complete strain relaxation was obtained at temperatures as low as 800 °C and the samples appeared free of threading dislocations within the SiGe layer to the limit of transmission electron microscopy analysis. In our model, H filled nanocracks are assumed to generate dislocation loops, which glide to the interface where they form strain relieving misfit segments. On the basis of this assumption, the conditions for efficient strain relaxation are discussed.
Theory of Langmuir wave generation in the presence of Alfvén wave turbulence in an electron-positron plasma: Case III
Authors: Kakati H. , Goswami K. S. , Bujarbarua S.
Published: July 2002

The plasma maser interaction of a test Langmuir wave in the presence of Alfvén wave turbulence is studied theoretically in a magnetized electron-positron (e-p) plasma, where the turbulence is produced by both electron and positron temperature anisotropies. Langmuir waves are generated without the necessity of an electron or positron beam component. The growth takes place in the direction of propagation of the Alfvén waves.
Coherent elastic and rotationally inelastic scattering of N2, O2, and CH4 from a 10 K Cu(111) surface
Authors: Andersson T. , Althoff F. , Linde P. , Hassel M. , Persson M. , Andersson S.
Published: July 2002

We report observations of coherent elastic and rotationally inelastic scattering of N2, O2, and CH4 from a 10 K Cu(111) surface, kept clean by pulsed laser heating. The related sharp features in the measured angular distributions decrease drastically in intensity at elevated target temperatures. At low temperature rotational transitions reduce the elastic scattering probability by about an order of magnitude. This effect is weak for D2 at the impact conditions of concern. Quantum scattering calculations for N2 and D2 show that this difference is primarily caused by the large difference in rotational constants and the associated rotational transition energies of these molecules.
Simulation studies of heavy ion heating by current-driven instabilities
Authors: Toida M. , Maeda T. , Shiiba I. , Sugishima A. , Ohsawa Y.
Published: July 2002

Nonlinear evolution of current-driven instabilities and associated energy transport among different particle species are studied by means of a two-dimensional, electrostatic, particle simulation code with full ion and electron dynamics. The plasma is assumed to consist of hydrogen (H) and helium (He) ions and electrons with the electron temperature larger than the ion temperatures; the electrons drift along a uniform magnetic field with an initial speed equal to the thermal speed. Then, simulations show that after the development of ion acoustic waves and fundamental H cyclotron waves, second harmonic waves are destabilized due to the change in the electron velocity distribution function parallel to the magnetic field, fe(v∥). Even though the linear theory based on the initial conditions predicts that the second harmonics are only marginally unstable, they eventually grow to the largest amplitudes and heat He ions more significantly than H ions. The instabilities of these three kinds of modes with different phase velocities give rise to flattening of fe(v∥) over a region larger than the thermal speed.
The AlCO− and Al(CO)2− anions: Matrix isolation infrared spectra and density functional theory studies
Authors: Zhang Luning , Dong Jian , Zhou Mingfei , Qin Qizong
Published: July 2002

After deposition of laser ablated aluminum with CO in excess argon at 11 K, distinct IR bands at 1682.3, 1803.9, and 1741.0 cm−1 have been observed in addition to the absorptions of neutral AlCO and Al(CO)2. With the aid of CO13 isotope enriched experiments and density functional calculations, the band at 1682.3 cm−1 has been assigned to the C–O stretch vibration of the AlCO− anion. Absorptions at 1803.9 and 1741.0 cm−1 have been assigned to the symmetric and antisymmetric C–O stretching vibrations of the Al(CO)2− anion, respectively. Vertical detachment energies of AlCO− and Al(CO)2− as well as the electron affinities of AlCO and Al(CO)2 have been calculated. The properties of MCO− anions (M=B, Ga, and In) have also been predicted for comparison with those of AlCO−.
Reduced multireference coupled cluster method: Ro-vibrational spectra of N2
Authors: Li Xiangzhu , Paldus Josef
Published: July 2002

The reduced multireference (RMR) coupled cluster method with singles and doubles (CCSD), relying on four- and eight-dimensional reference spaces, is employed to generate the potential energy curve for the nitrogen molecule, using both the correlation-consistent polarized valence-triple-zeta (cc-pVTZ) and atomic natural orbital basis sets. The resulting potentials are then used to compute the ro-vibrational term values, which are compared with the available experimentally determined values. Moreover, a direct comparison with the measured spectral line frequencies, for both the fundamental rotational Raman band and the vibrationally excited Q branches, is also carried out. Comparisons with the single reference CCSD, as well as with the corresponding multireference configuration interaction results that serve as the external source for RMR CCSD, are also made. An excellent performance of RMR CCSD, and its systematic improvement with the increasing dimension of the reference space employed, is demonstrated for the cc-pVTZ basis set. The fundamental Raman band frequencies are computed with an error of less than 1 cm−1, while for the vibrationally excited bands a systematic deviation of about 7 cm−1 is found.
Beam of metastable krypton atoms extracted from a rf-driven discharge
Authors: Chen C. Y. , Bailey K. , Li Y. M. , O’Connor T. P. , Lu Z.-T. , Du X. , Young L. , Winkler G.
Published: July 2002

A rf-driven discharge is used to produce a beam of metastable krypton atoms at the 5s(3/2)2 level with an angular flux density of 4×1014 s−1 sr−1 and most probable velocity of 290 m/s, while consuming 7×1016 krypton atoms/s. When operated in a gas-recirculation mode, the source consumes 2×1015 krypton atoms/s with the same atomic-beam output.
Hydrogenic impurities in spherical quantum dots in a magnetic field
Authors: Corella-Madueño A. , Rosas R. , Marı́n J. L. , Riera R.
Published: July 2002

The ground state and binding energies for a hydrogenic impurity in a spherical quantum dot within a uniform magnetic field, are calculated through the variational method in the frame of the effective-mass approximation. The trial wave functions used in the calculation are flexible enough to treat the cases of on-center, off-center, or edge impurities. Overall results show reasonable agreement when compared with other calculations. Interestingly enough, in the case of an off-center impurity, a critical point from which bulk states evolve to surface or edge states is also found. The dependence of this point on the magnetic field strength is discussed and interpreted.
Crystallization of amorphous Cu47Ti34Zr11Ni8
Authors: Glade S. C. , Löffler J. F. , Bossuyt S. , Johnson W. L. , Miller M. K.
Published: July 2002

The results of a study on the crystallization of amorphous Cu47Ti34Zr11Ni8 with the use of differential scanning calorimetry, transmission electron microscopy (TEM), x-ray diffraction, field ion microscopy, atom probe tomography (APT), and small-angle neutron scattering (SANS) are presented. These experimental techniques were used to characterize as-prepared samples and specimens heat treated at different temperatures around the glass transition temperature. APT and SANS show that the alloy decomposes into copper-enriched and titanium-enriched regions prior to nucleation and growth of a crystalline phase. TEM shows that the primary nucleating phase has a face centered cubic structure.
Polyisoprene local dynamics in solution: Comparison between molecular dynamics simulations and high order diffusion theory
Authors: La Penna Giovanni , Carbone Paola , Carpentiero Rita , Rapallo Arnaldo , Perico Angelo
Published: July 2002

The local dynamics of a cis-1,4-polyisoprene of ten monomer units in dilute toluene solution is approached by deterministic molecular dynamics (MD) simulations and by a high-order mode-coupling diffusion theory. The first- and second-rank orientation autocorrelation functions for virtual bonds connecting the repeat units are calculated from the theory and compared to the same quantities calculated directly from the MD trajectory. The equilibrium statistical averages needed in the theory are calculated from a time average along the same MD trajectory. The correlation functions from the simulation are found to be almost coincident when significant contributions to high orders in the mode-coupling expansion are considered. Even the first-order diffusion theory represents a good approximation to the MD result. Alternatively, when the statistics are obtained by substituting the trajectory in the explicit solvent with a suitable trajectory in the vacuum, the local dynamics is still well-approximated by the diffusion theory. The study addresses the relationship between correlation functions of different rank, which has been shown to be universal for chains undergoing a first-order Gaussian random process.
Nonoptically probing near-field microscopy for the observation of biological living specimens
Authors: Kawata Yoshimasa , Murakami Manabu , Egami Chikara , Sugihara Okihiro , Okamoto Naomichi , Tsuchimori Masaaki , Watanabe Osamu , Nakamura Osamu
Published: July 2002

We present the observation of living specimens with subwavelength resolution by using the nonoptically probing near-field microscopy we have developed recently. In the near-field microscope, the optical field distributions near the specimens are recorded as the surface topography of a photosensitive film, and the topographical distributions are readout with an atomic-force microscopy. Since the near-field microscope does not require the scanning of a probe tip for illumination or detection or scattering of light, it is possible to observe moving biological specimens and fast phenomena. We demonstrate the observation of a moving paramecium and euglena gracilis with subwavelength resolution. The observation of the nucleus inside a euglena cell was also demonstrated.
Effect of correlating core orbitals in calculations of nuclear spin–spin couplings
Authors: Lantto Perttu , Vaara Juha
Published: July 2002

Electron correlation effects on nuclear spin–spin coupling tensors arising from core-valence interaction were investigated with ab initio calculations based on multiconfigurational self-consistent field (MCSCF) reference states, an adequate basis set, and large restricted active spaces. Calculations of first and second-row hydrides were performed to examine the effect of including the core and semicore orbitals in the active molecular orbital space. The effects of using a multireference wave function instead of a single-reference one, as well as different numbers of electrons in the virtual orbitals, were considered. In second-row hydrides, the inclusion of semicore orbitals is found to be necessary for accurate calculations of spin–spin couplings involving the heavy nucleus. A smaller but nonnegligible effect is observed also for the hydrogen–hydrogen coupling. Comparison is made with nuclear shielding and electric field gradient, for which the effect is considerably smaller. Recommendations for wave functions for calculations of spin–spin couplings are given.
Humidity sensor using porous tape cast alumina substrate
Authors: Chatterjee Suman , Basu Santanu , Chattopadhyay Debdas , Mistry Kalyan Kr. , Sengupta Kamalendu
Published: July 2002

Moisture sensors based on porous alumina were designed and fabricated to detect and measure the concentration of moisture in gases. In the thin alumina disks taken, the surface and penetration effect has been considered during the process of adsorption and absorption of water molecules through pores and grain boundaries. Three different fabrication techniques, the tape casting technique, pelletization, and porous thick film, have been tried to achieve the desired moisture-sensing property of the samples. Different types of electrode structures and designs were also investigated and optimized to obtain maximum sensitivity. Electrodes were formed by screen printing the samples with thick film conductive pastes. The planar porous alumina sensor so obtained is found to be sensitive in the range of the 100–1000 ppmv level of moisture. The response time of the sensor in the ppmv range is approximately 2 min, and at higher concentrations of moisture it shows quasilinear dependency on the moisture content.
Mode coupling theory of self and cross diffusivity in a binary fluid mixture: Application to Lennard-Jones systems
Authors: Ali Sk. Musharaf , Samanta Alok , Ghosh Swapan K.
Published: July 2002

A microscopic approach has been developed for the self as well as cross diffusivity of a binary fluid mixture based on the concepts of mode coupling theory. Illustrative numerical results calculated for a Lennard-Jones fluid mixture are presented and are shown to be in good agreement with the available computer simulation results. The effects of mass, composition, interaction strength, and sizes of the components on the diffusivities are studied in order to obtain insight into the role of different modes in the diffusion process. The mass dependence of diffusivity is found to be weak with a power law behavior in contrast to the Enskog theory prediction of strong mass dependence. Also the mass and concentration of one component are found to have significant and interesting effects on the diffusivity of the other component. The new expressions derived here are shown to predict positive values for the cross diffusion constant over the various parameter ranges considered, which is consistent with the simulation results but unpredicted by other commonly used models. It is also found that the cross diffusion is significant in liquid Lorentz–Berthelot mixture for size ratio unity, strong interaction potential, and intermediate composition range.
Monitoring penetration of ethanol in a porous silicon microcavity by photoluminescence interferometry
Authors: Gaburro Z. , Daldosso N. , Pavesi L. , Faglia G. , Baratto C. , Sberveglieri G.
Published: July 2002

A photoluminescent porous silicon microcavity is exposed to saturated vapor of ethanol. The ethanol substitutes the air inside the pores giving rise to a progressive monotonic redshift of the interference pattern of the photoluminescence spectrum. On the other hand, the photoluminescence intensity of the cavity peak oscillates in time. Both effects can be explained in terms of a very simple model based on the progressive change of the effective refractive index of single layers of the cavity. The change is due to the difference between the index of refraction of air and ethanol. The result suggests that a porous silicon microcavity can be a tool to study the dynamics of gas penetration into porous silicon since it allows a monitoring of the depth reached by the ethanol at any given time.
A reduced dimensionality, six-degree-of-freedom, quantum calculation of the H+CH4→H2+CH3 reaction
Authors: Wang Dunyou , Bowman Joel M.
Published: July 2002

A reduced dimensionality, time-dependent wave-packet calculation is reported for the H+CH4→H2+CH3 reaction in six degrees of freedom and for zero total angular momentum, employing the Jordan–Gilbert potential energy surface. Reaction probabilities for seven initial vibrational states of nonrotating “CH4,” and for the three lowest energy vibrational states and numerous initial rotational states are presented. Excitation of the C–H stretch, and the bending of H–CH3, enhances the reaction probability more than excitation of the umbrella mode. The six-degree-of-freedom cumulative reaction probability (CRP) for zero total angular momentum is obtained by direct summation over initial state-resolved reaction probabilities. An approximate full-dimensional CRP for zero total angular momentum is obtained using the energy-shift approximation to account for the contribution of degrees of freedom missing in the reduced dimensionality calculations. Then J–K shifting is applied to this CRP to obtain the thermal rate constant which is compared with previous calculations.
Dislocation glide and blocking kinetics in compositionally graded SiGe/Si
Authors: Leitz C. W. , Currie M. T. , Kim A. Y. , Lai J. , Robbins E. , Fitzgerald E. A. , Bulsara M. T.
Published: July 2002

The effects of growth temperature, substrate offcut, and dislocation pileup formation on threading dislocation density (TDD) in compositionally graded SiGe buffers are explored. To investigate dislocation glide kinetics in these structures, a series of identical samples graded to 30% Ge were grown at temperatures between 650 and 900 °C on (001)-, (001) offcut 6° towards an in-plane 〈110〉-, and (001) offcut 6° towards an in-plane 〈100〉-oriented Si substrates. The field threading dislocation density (field TDD) in the on-axis samples varied exponentially with temperature, from 3.7×106 cm−2 at 650 °C to 9.3×104 cm−2 at 900 °C. The activation energy for dislocation glide in this series, calculated from the evolution of field TDD with growth temperature, was 1.38 eV, much lower than the expected value for this composition. This deviation indicates that strain accumulating during the grading process at low growth temperatures is forcing further dislocation nucleation, resulting in a deviation from pure glide-limited relaxation. The TDD of samples grown on offcut substrates exhibited a more complicated temperature dependence, likely because films grown on offcut substrates have an increased tendency towards saturation in dislocation reduction reactions at high temperature. Dislocation reduction processes were further explored by initiating compositional grading up to 15% Ge at 650 °C and continuing the grade to 30% Ge at 900 °C. The low temperature portion of this growth provided an excess concentration of threading dislocations which could subsequently be annihilated during the high temperature portion of the growth, enabling a comparison of reduction rates for different substrate offcuts. Combining these results with threading dislocation densities in a variety of other samples, a complete picture of strain relaxation kinetics in compositionally graded SiGe/Si emerges. Generally, strain relaxation in these structures is limited by dislocation glide, and threading dislocation densities are independent of final Ge content. However, we theorize that dislocation pileup formation inhibits the strain relaxation process and is therefore accompanied by a rise in field threading dislocation density. Based on these results, we now have a predictive model for TDD in compositionally graded SiGe/Si over a wide range of growth conditions.
Can ordinary single-reference coupled-cluster methods describe potential energy surfaces with nearly spectroscopic accuracy? The renormalized coupled-cluster study of the vibrational spectrum of HF
Authors: Piecuch Piotr , Kucharski Stanisław A. , Špirko Vladimir , Kowalski Karol
Published: July 2002

The recently proposed renormalized (R) and completely renormalized (CR) CCSD(T) and CCSD(TQ) methods, which remove the failing of the standard CCSD(T) and CCSD(TQf) approaches at large internuclear separations, have been used to obtain the potential energy function and the vibrational spectrum of the HF molecule. The vibrational term values obtained in the renormalized and completely renormalized CCSD(T) and CCSD(TQ) calculations have been found to be in a better agreement with the experimental [Rydberg–Klein–Rees (RKR)] data than than the results of the expensive full CCSDT calculations. The simple R-CCSD(T) method gives <10 cm−1 errors for the vibrational energies up to ∼41 000 cm−1. The CR-CCSD(T) and CR-CCSD(TQ) methods reduce the ∼300 cm−1 errors in the full CCSDT results for the high-lying states near dissociation to 100–200 cm−1.
Investigation of direct and indirect band gaps of [100]-oriented nearly strain-free β-FeSi2 films grown by molecular-beam epitaxy
Authors: Takakura Ken-ichiro , Hiroi Noriyoshi , Suemasu Takashi , Chichibu Shigefusa F. , Hasegawa Fumio
Published: July 2002

Optical absorption (OA) spectra of [100]-oriented, nearly strain-free β-FeSi2 continuous films grown by molecular-beam epitaxy were investigated. Although the film is a multidomain epilayer, the OA spectra of the annealed film were fitted well by the sum of the contributions from both direct and indirect absorption transitions for a wide range of temperatures from 77 to 300 K. The indirect absorption edge of 0.78 eV obtained at 77 K agreed with the effective band gap energy obtained from temperature dependence of the carrier density.
Comparative study of stripe magnetic domains in epitaxial Ni(111) and Co(0001) films
Authors: Naik R. , Hameed S. , Talagala P. , Wenger L. E. , Naik V. M.
Published: July 2002

The evolution of stripe magnetic domain structures observed by magnetic force microscopy on epitaxial Ni(111) and Co(0001) films as a function of film thickness is successfully explained by a periodic one-dimensional model with tilted partial flux closure domains. The model predicts a sizable fraction of the magnetization not being parallel to the film’s normal, which consequentially results in an in-plane magnetization in agreement with the experimentally observed magnetization for these films.
Modified physical properties by ion-beam mixing of Fe–Si multilayered films
Authors: Park J. S. , Kim C. O. , Lee Y. P. , Kudryavtsev Y. V. , Dubowik J. , Szymański B. , Rhee J. Y.
Published: July 2002

We investigated the effect of ion-beam mixing (IBM) on the physical properties of Fe–Si multilayerd films (MLF). By the magnetic, magneto-optical, optical and structural studies, it was found that the IBM results in a formation of metastable B2-phase Fe2Si wih a perfect crystalline structure, a low coercivity and a Curie temperature of about 550 K. An annealing at 720 K of the ion-beam mixed Fe–Si MLF further destroys the layered structure at the bottom and also decomposes Fe2Si to form a metastable magnetically-hard Fe5Si3 phase and, presumably, Fe3Si.
The effect of gate metal and SiO2 thickness on the generation of donor states at the Si-SiO2 interface
Authors: Fischetti M. V. , Weinberg Z. A. , Calise J. A.
Published: July 2002

Two experimental observations are reported concerning the degradation of the Si–SiO2 interface during electron injection in metal-oxide-semiconductor structures. First, the generation of the interfacial positive charge during avalanche injection can be strongly inhibited by employing magnesium, instead of aluminum, as gate metal, or enhanced by employing gold. This correlates with the different work functions of the metals. Second, during negative bias high-field injection in Al-gate capacitors with thin oxides (≲100 Å), a threshold in gate voltage, of 7–8 V, is found for the generation of the positive charge. Both observations are consistent with a model which assumes that holes generated in the anode by hot electrons, via emission of surface plasmons, are injected into the SiO2 and are subsequently trapped at the Si–SiO2 interface. Other possible mechanisms are also discussed.
Monte Carlo simulations of amorphous hydrogenated silicon thin-film growth
Authors: Gleason K. K. , Wang K. S. , Chen M. K. , Reimer J. A.
Published: July 2002

Monte Carlo simulations of amorphous hydrogenated silicon thin-film growth are carried out to examine the effects of film growth reactions, etching reactions, and surface diffusion on three-dimensional film structure. Although a simulated film contains 1000 silicon atoms or less, the hydrogen content and density can be extrapolated to bulk values. The predicted bulk values of the hydrogen content, 11–44 at. %, and density, 1.8–2.0 g/cm3, are consistent with experimental results. The surface diffusion of silicon-containing species is found to have the most significant effect on the final film properties. A knowledge of the specific chemical mechanism leading to film growth is not assumed.
Beam end erosion
Authors: Faltens A. , Lee E. P. , Rosenblum S. S.
Published: July 2002

The time evolution of the line charge density and energy at the ends of an initially rectangular ion bunch due to the space charge of the bunch are measured and found to be in good agreement with a one-dimensional dynamical theory. The ends erode at the space-charge wave speed into the bunch, and the end particles move at twice that speed away from the bunch.
Generation of the ninth, eleventh, and fifteenth harmonics of iodine laser radiation
Authors: Wildenauer J.
Published: July 2002

Results of experiments to produce coherent radiation in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) by high-order optical nonlinearities in rare gases are described. Frequency conversion into the third and fifth harmonics was used to obtain pulses at 146.1 and 87.7 nm. VUV pulses at 146.1 and 119.6 nm were directly generated from infrared radiation by generating the ninth and eleventh harmonics of 1.315-μm iodine laser pulses. Frequency conversion into the eleventh harmonic is the highest-order nonlinear process of this kind reported to date.
Laser-induced chemical vapor deposition of hydrogenated amorphous silicon. I. Gas-phase process model
Authors: Meunier M. , Flint J. H. , Haggerty J. S. , Adler D.
Published: July 2002

In the laser-induced chemical vapor deposition (LICVD) process, a CO2 laser beam impinges on a gas mixture parallel to the substrate upon which the film is deposited. Since heating of the reactant gases is accomplished only via the absorption of infrared photons, the reaction zone can be controlled precisely. The LICVD technique is a cold-wall thermal process allowing independent control of both the gas and substrate temperatures. In this paper, we propose a model for LICVD of silane (SiH4) and growth of hydrogenated amorphous silicon (a-Si:H) thin films in which the film growth is controlled by gas-phase homogeneous thermal decomposition of the SiH4. The peak gas temperature Tg depends on many process parameters, namely, gas partial pressures, laser power, substrate temperature, and cell geometry. Due to the extreme sensitivity of the growth rate G to the values of the partial pressures and laser power, these parameters must be fixed to within ±1% variation in order to control G to ±50% and prevent powder formation. LICVD gas-phase chemistry involves the production of SiH2 for the thermal decomposition of SiH4 and higher polysilanes (Si2H6, Si3H8, etc.) resulting from reactions between SiH2 and SiH4. SiH2 and possibly higher diradicals produced in the laser beam then diffuse to the substrate and react with the surface layer, thus inducing growth of the a-Si:H film and the concomitant elimination of H2.
Threshold in electron-beam end-pumped II-VI lasers
Authors: Colak S. , Khurgin J. , Seemungal W. , Hebling A.
Published: July 2002

Electron-beam end-pumped lasers from different bulk grown II-VI compounds have been experimentally studied and compared under similar preparation and excitation conditions. The reasons for the lasing threshold variations are discussed. The first results on e-beam pumped CdMnTe lasers and end-pumped CdTe lasers are reported. The order of lowest to highest threshold is found to be from CdSe, ZnCdSe, CdS, CdTe, CdMnTe, and ZnSe. The comparisons between lasing conditions are used to evaluate the contribution of the intrinsic semiconductor parameters to lasing threshold. Experiments with a large number of samples indicate that the influence of intrinsic and extrinsic parameters on lasing threshold are in most cases comparable. Therefore, for most bulk II-VI lasers, the average threshold pump power density reductions with the elimination of extrinsic factors are expected to be less than several times. These findings are further supported by our threshold and relative slope efficiency measurements on lasers with different output mirror couplings.
Effect of free surface and interface on thermal annealing of dislocation loops in silicon
Authors: Narayan J. , Jagannadham K.
Published: July 2002

The denuded zones free from dislocation loops formed near a free surface or an interface in ion-implanted specimens subjected either to rapid thermal annealing or annealing in a furance were studied. The point defects cluster to form dislocation loops. Smaller dislocation loops coalesce by glide and climb processes to form bigger loops. Free surfaces and interfaces give rise to interaction with the dislocation loops, thus exerting an image force. Transmission electron microscopy observations in the annealed specimens are presented to show that dislocation loops situated within twice the diameter from the free surface are annealed out, thus creating a denuded zone. In order to explain the formation of denuded zones, we have analyzed the forces of interaction between a square dislocation loop and either a free surface or a second phase with a planar interface including the Poisson’s ratio effects. The elastic field of a square loop is a reasonable approximation to represent the actually observed circular loop. Analytical closed-form expressions for the stress and displacement fields associated with a square dislocation loop in a two-phase medium are used to calculate the image force acting on the dislocation loop. Further considerations of the equilibrium of the dislocation loop under the action of the image force exerted by the free surface and the opposing lattice frictional stress at the annealing temperature enable us to determine the dimensions of the denuded zone that are found to be in agreement with the experimental results. These results further show that a soft second phase (over layer) attracts the dislocation loops whereas a hard second phase repels them.
Ultrahigh vacuum studies of Pd metal-insulator-semiconductor diode H2 sensors
Authors: Rye R. R. , Ricco A. J.
Published: July 2002

Hydrogen sensitive Pd metal/insulator/semiconductor diodes provide an ambient temperature, low power electronic sensor for hydrogen as a result of hydrogen trapping at the Pd/insulator interface. Current kinetic models consider the rate limiting step to be adsorption at the Pd surface followed by rapid transport to the interface. We have obtained both steady-state and kinetic results for diodes with clean Pd surfaces over hydrogen pressures ranging from 10−10 to 10−1 Torr. The sensitivity limit (equivalent to <1011 total H2 impacts/cm2 at the Pd surface) is set by our vacuum capabilities, and is at least seven orders of magnitude greater than that obtained for devices with contaminated surfaces. These results clearly show that the kinetic and sensitivity limitations reported for such devices are a result of surface contamination. For diodes with a clean Pd surface, analysis of the steady-state results requires at least two binding states (9 and 6.8 kcal/mol of H relative to H2(g)) for H at the Pd/SiO2 interface. The kinetics of the diode response to H2 are inconsistent with direct transfer to the bulk exclusively through strong chemisorbed surface states, but suggest with a ‘‘precursor’’ mechanism in which the initial step is adsorption into a weakly bound precursor state from which branching steps populate both strongly bound chemisorbed surface states and bulk states. The surface states act in part as traps for hydrogen in competition with transfer to the bulk (and therefore to the electronically active interface).
Magnetic anisotropy induced by magnetic field cooling in Ni3Mn alloys
Authors: Yamauchi T. , Miyajima H. , Chikazumi S.
Published: July 2002

The magnetic anisotropy of Ni3Mn alloys with various degrees of atomic order has been investigated by a torque magnetometry. By cooling down from 300 to 80 K in a magnetic field of 10 kOe, a unidirectional anisotropy Kd with a period of 360° was induced. The temperature dependence of this anisotropy can be expressed by exp(Q/T) from 50 to 20 K and by log(T) below 20 K. The magnitude of Kd was increased by a factor of 100 during cooling down from 50 to 4.2 K. Furthermore, the hysteresis loop at 4.2 K for a disordered alloy was shifted such that the easy direction of magnetization is that of the cooling magnetic field. They are discussed in terms of exchange anisotropy and the size distribution of clusters with antiferromagnetic coupling.
Magneto-optic nonreciprocal phase shift in (YLa)3 (FeGa)5O12 single-mode channel waveguides
Authors: Inuzuka H. , Okamura Y. , Yamamoto S.
Published: July 2002

We have investigated characteristics of the nonreciprocal guided-wave phase shifter, which is one of the key elements in integrated optic isolators and circulators. Based on the external magnetic field independence of the horizontally polarized mode, we measured the nonreciprocal phase shift of the vertically polarized mode using a straight waveguide instead of the complicated interferometric structures employed in previous works. It was revealed that the nonreciprocal phase shift varies remarkably with a thickness of the waveguide and there exists the optimum film thickness for the nonreciprocal phase shifter.
Formation and characterization of grain-oriented VO2 thin films
Authors: De Natale J. F. , Hood P. J. , Harker A. B.
Published: July 2002

Grain-oriented films of VO2 have been prepared to characterize the effects of film orientation on electrical and optical switching performance. This oriented growth has been achieved by lattice matching to (0001) sapphire, and results in intergranular structures favorable to rapid propagation of the monoclinic-tetragonal phase transformation. The electrical and optical property changes across this transition are strongly affected by film microstructure, with the oriented structures favoring rapid switching and narrow hysteresis.
Laser-induced iodine desorption from impregnated polystyrene
Authors: Torres-Filho A. , Leite N. F. , Miranda L. C. M. , Stempniak R. A.
Published: July 2002

The Ar+ laser-stimulated desorption of iodine molecules from an impregnated polystyrene film was investigated. The photoprocess induces a color change (from red to the transparent) and leaves in the film a marked print, which is related to the laser beam characteristics. The experimental data was fitted using a set of differential equations relating the time dependence of the film temperature and absorption coefficient. At low-power levels (<25 mW), the time evolution of the laser transmitted power could be well matched to the experimental data. The wavelength dependence of the marking process was also studied and the relative contribution of photodissociative and photothermal processes was inferred.
High-power Nd:glass laser transmission through optical fibers and its use in acceleration of thin foil targets
Authors: Trott Wayne M. , Meeks Kent D.
Published: July 2002

Measurements on commercially available fused silica fibers and fiber tapers have shown that Nd:glass laser pulses of irradiance >3.5 GW cm−2 can be transmitted without bulk or surface damage. Optical energy at the fiber output can be used for efficient acceleration of thin metal foils. For 0.025-mm-thick aluminum coupled to a 0.2-mm-diam fiber, target foil velocities up to 2.3 km s−1 have been achieved with very modest laser energies (<25 mJ).
The structure and properties of phthalocyanine films grown by the molecular-beam epitaxy technique. II. Ultraviolet/visible spectroscopic study
Authors: Hoshi Hajime , Dann Anthony J. , Maruyama Yusei
Published: July 2002

Ultrathin films of F-bridged Al-phthalocyanine polymer, (AlPcF)n, grown by the molecular-beam epitaxy technique show unusual spectroscopic properties which can be described by the possibility of pseudomorphic layer formation at the thin-film/substrate interface. A change in the electronic structure of the molecules of this layer is presumed to occur. The existence of the layer is directly related to the degree of epitaxy.
Fabrication of ferromagnetic and antiferromagnetic chromium oxides by organometallic chemical vapor deposition
Authors: Dowben P. A. , Kim Yoon Gi , Baral-Tosh S. , Ramseyer G. O. , Hwang Chanyong , Onellion M.
Published: July 2002

We have been able to fabricate CrO2 and Cr2O3 from ultraviolet photolytic and plasma-assisted decomposition of Cr(CO)6 in an oxygen carrier gas. The composition of these films is uniform in composition and contains little contamination. Using magneto-optic Kerr effect measurements, we have been able to demonstrate that the CrO2 films are ferromagnetic.
Admittance spectroscopy measurement of band offset in GaAs-GaAlAs multiquantum well
Authors: Letartre X. , Stievenard D. , Lannoo M. , Lippens D.
Published: July 2002

We report measurements of the conduction-band offset in GaAs-Ga1−xAlxAs multiquantum wells. Admittance spectroscopy is used to measure the activation energy for thermionic emission of electrons over GaAlAs barriers and we discuss the validity of the technique in the presence of a low electric field. We show that the usual approximation in calculating the position of the Fermi level at 0 K can lead to significant error in the determination of the band offset. For an alloy composition x=0.39, we found a conduction-band offset of 303 meV.
Interface properties and capacitance-voltage behavior of indium phosphide metal-insulator-semiconductor prepared by plasma-assisted oxidation
Authors: Lim H. , Baglio J. A. , DeCola N. , Park H. L. , Lee J. I. , Kang K. N.
Published: July 2002

A remote plasma-enhanced oxidation method, with two different reactant gases of N2O and POCl3, is used to grow stable insulating layers on an InP substrate. The compositional profile of the oxide grown with N2O reactant was very similar to that of thermally grown oxide. The hysteresis of capacitance-voltage (C-V) characteristics in this system was relatively small and determined by the compensative effects of mobile charges in the oxide and the capture of electrons at the interface. The very unstable nature of the C-V characteristics in the metal-insulator-semiconductor (MIS) diode prepared with POCl3 reactant seems to be related to the gradual nature of the interface and/or the P-oxide deficiency at the interface. Even if a stable oxide layer of InPO4 can be grown by POCl3 plasma, the very poor nature of the transition region must be overcome to achieve a good MIS structure.