bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanometer-size InAs/AlSb quantum wires: Fabrication and characterization of Aharonov–Bohm quantum rings
Authors: Cheng K. A. , Yang C. H. , Yang M. J.
Published: July 2002

We report a fabrication method for laterally confining the two-dimensional electrons in InAs/AlSb single quantum wells into artificially patterned conducting wires. The minimum wire width is demonstrated to be ∼30 nm, among the smallest reported to date. The confining potential is approximately square and abrupt, and that makes the electron’s spatial distribution in the transverse direction the same as the physical width of the wire. The conducting electrons have close proximity to the surface charges, thus there is always a reduction in the elastic mean free path when the wire width decreases. Despite the reduction in mean free path, we find that the phase coherence length is approximately 1 μm at 2.2 K, a factor of 30 larger than the minimum feature size.
Forward Raman scattering by quasilongitudinal optical phonons in GaN
Authors: Azuhata T. , Ono M. , Torii K. , Sota T. , Chichibu S. F. , Nakamura S.
Published: July 2002

Quasilongitudinal optical phonons in wurtzite GaN have been studied by Raman spectroscopy in the forward scattering geometry with annular apertures. It is demonstrated that the geometry is simple and powerful for determining frequency variation of quasilongitudinal optical phonons in a relatively wide range of their propagation directions, over which the quasilongitudinal optical phonon frequency changes remarkably. Good agreement is obtained between experimental and theoretical results. Discussion is also given on selection rules for quasilongitudinal optical phonons, which are used to interpret polarized Raman signals.
Investigation of deep electronic centers in low-temperature grown GaAs using extremely thin layers
Authors: Pfeiffer K.-F. G. , Tautz S. , Kiesel P. , Steen C. , Malzer S. , Döhler G. H.
Published: July 2002

We report on an approach to investigate the deep electronic defect centers in low-temperature grown GaAs (LT-GaAs). Using an extremely thin LT-GaAs layer (comparable with the penetration depth of an electric field in bulk material) incorporated in the i layer of a p-i-n diode, we are able to charge or to deplete the deep centers in the energy gap by applying a reverse bias. The corresponding space charge is monitored by the field changes across the LT-GaAs layer, both optically by Franz–Keldysh experiments and electrically by n-channel conductance changes. From our results, we derive a deep trap density of 1018 cm−3 centered at around 500–700 meV below the conduction band.
Polycrystallization and surface erosion of amorphous GaN during elevated temperature ion bombardment
Authors: Kucheyev S. O. , Williams J. S. , Jagadish C. , Zou J. , Li G.
Published: July 2002

The effects of elevated-temperature ion bombardment of wurtzite GaN films preamorphized by ion implantation are studied by Rutherford backscattering/channeling spectrometry and transmission electron microscopy. Amorphous layers annealed in vacuum at 500 °C exhibit polycrystallization. Bombardment of amorphous layers with 2 MeV Cu+63 ions at elevated temperatures leads to anomalous erosion of GaN (with a sputtering yield of ∼102 at 500 °C), rather than to ion-beam-induced epitaxial crystallization. Temperature dependence of the erosion rate suggests that such a large sputtering yield results from a two-step process of (i) thermally- and ion- beam-induced material decomposition and (ii) ion beam erosion of a highly N-deficient near-surface layer of GaN. This study shows that amorphization during ion implantation should be avoided due to the present inability to epitaxially recrystallize amorphous layers in GaN.
Amplification of picosecond optical pulses in midinfrared intersubband semiconductor optical amplifiers
Authors: Tang J. M. , Spencer P. S. , Shore K. A.
Published: July 2002

A comprehensive theoretical model describing the amplification of picosecond optical pulses in midinfrared intersubband semiconductor optical amplifiers is developed, taking into account gain dispersion, short carrier relaxation time and ultrafast nonlinear refraction. It is shown that these factors are extremely important in determining the amplified optical pulse characteristics in both the time and frequency domains. The calculations also indicate that gain dispersion can be significantly enhanced by fast carrier relaxations, short pulse widths, and high pulse energies.
Annealing effect on electron field-emission properties of diamond-like nanocomposite films
Authors: Ding Xing-zhao , Mao Dong-sheng , Tay B. K. , Lau S. P. , Shi J. R. , Li Y. J. , Sun Z. , Shi X. , Tan H. S. , Zhang Fu-min , Liu Xiang-huai
Published: July 2002

The field-emission properties of a Si–O bond-containing diamond-like nanocomposite (DLN) film were investigated as a function of annealing temperature (Ta). It was found that with increasing Ta the emission threshold voltage decreased gradually. After annealing at Ta=500 °C, the emission current decreased significantly. At Ta=700 °C, however, the field-emission properties of the DLN film improved greatly, the threshold field became very low (∼1.5 V/μm), and the emission current rather high (e.g., ∼2.3 μA/mm2 at an electric field of 22 V/μm). The structural variation of the film after annealing at different temperatures was monitored by ultraviolet Raman spectroscopy, spectroscopic ellipsometry, atomic-force microscopy, and electrical resistivity measurements. By using a three-step model: (i) electron injection from the substrate, (ii) electron transport through the film, and (iii) electron emission at the film surface, the annealing effect on field-emission properties of the DLN film were qualitatively interpreted. It is believed that the threshold electric field is determined by the local electron affinity on the film surface, while the emission current is mainly limited by electron injection and transport processes.
A trochoidal analyzer to measure the electron beam energy distribution in a traveling wave tube
Authors: Guyomarc’h D. , Doveil F.
Published: July 2002

The trochoidal monochromator is commonly used to produce a monoenergetic electron beam in an axial magnetic field. By adding a retarding electric field system at the entrance and a Faraday cup at the exit of the monochromator, such a dispersive device can be used to measure the energy distribution of an electron beam. This device is used in a traveling wave tube in order to study wave particle interactions.
A triply differentially pumped supersonic beam target for high-resolution collision studies
Authors: Götte S. , Gopalan A. , Bömmels J. , Ruf M.-W. , Hotop H.
Published: July 2002

A Campargue-type source of an intense, triply differentially pumped supersonic beam of atoms (He, Ne, Ar) and molecules (N2) for use in high-resolution collision experiments is described. Using stagnation pressures of (1–10) bar, nozzle diameters of (0.05–0.25) mm, and skimmer diameters of (0.5–1.0) mm, the center-line intensity and collimated target density are quantitatively characterized by electron impact ionization in conjunction with total ion collection. Optimum densities in a target plane, located about 160 mm from the nozzle, range from 1012 cm−3 (N2) to 8×1012 cm−3 (He) at background densities which are about 1% of the beam densities. The results are compared with values calculated for ideal supersonic expansions.
Effects of prewells on transport in p-type resonant tunneling diodes
Authors: Lewis R. M. , Wei H. P. , Lin S. Y. , Klem J. F.
Published: July 2002

We investigate the transport of holes through AlAs/In0.10Ga0.90As resonant tunneling diodes which utilize InxGa1−xAs prewells in the emitter with x=0, 0.10, and 0.20. The data show an increase in peak current and bias at resonance and a concurrent increase in the peak-to-valley ratio with increasing x. We explain this enhancement in tunneling as due to confinement (or localization) of charges in the prewell and the formation of direct heavy (light) hole to heavy (light) hole conduction channels as a consequence.
Ultrafast optical dynamics of excitons in J-aggregates
Authors: Lee Jin-Ho , Min Chang-Ki , Joo Taiha
Published: July 2002

Time evolution of the coherence properties of excitons in J-aggregates of an organic molecule is studied by femtosecond transient absorption and three-pulse stimulated photon echo peak shifts. The exciton energy correlation function decays to zero by 120 fs single exponential, manifesting an ultrafast rupture of the coherent wave packet motion and the absence of inhomogeneity beyond the 100 fs time scale. Insensitivity of the correlation function to the isotopic substitution of the solvent suggests that the phonon modes of the molecular chain are responsible for the ultrafast dynamics.
Computational method of many-electron integrals over explicitly correlated Cartesian Gaussian functions
Authors: Saito Shiro L. , Suzuki Yoshi-ichi
Published: July 2002

Derivation of recurrence formulas for general many-electron overlap, nuclear attraction, and electron repulsion integrals over explicitly correlated Cartesian Gaussian functions is presented. The recurrence formulas are derived in a similar way as the derivation of molecular two-electron integrals over Cartesian Gaussian functions by Obara and Saika. As a result, the formulas expressing the many-electron integrals of higher angular momentum as a linear combination of those of lower angular momentum are obtained. An algorithm for computation of the general many-electron integrals by means of the recurrence formulas is also shown.
Compact parameter set for fast estimation of proton transfer rates
Authors: Lill Markus A. , Helms Volkhard
Published: July 2002

Several proton transfer systems were studied by quantum chemical calculations in the presence of further ligand waters. The calculated proton transfer barriers are fitted by an analytical expression, which allows for fast calculation of proton transfer rates between common donor–acceptor pairs in biological systems under the influence of surrounding chemical groups. The only information required is the chemical nature of the donor and acceptor, the distance between donor and acceptor, and the environmental influence in the acceptor and donor bound states. The quantum nature of the transferred proton is approximated at the level of an effective zero-point energy along the reaction coordinate. The approach presented allows efficient calculation of transfer rates and allows to include proton hopping events between titratable sites in classical molecular dynamics simulations.
Dielectric control of electrostatic barriers for molecular electronics
Authors: Kane C. L. , Mele E. J.
Published: July 2002

We describe an approach for controlling electrostatic barriers in molecular electronics devices which uses anisotropic dielectric material to modify the analytic form of the effective electrostatic interactions within the device. We study the one-dimensional geometry relevant to interfaces between carbon nanotubes and find that the bound charge induced in a uniaxial dielectric can replace the bare electrostatic interaction between charges with separation z by an effective −log(z) interaction or a confining |z| interaction. We use these models to study the depletion region formed at heterojunctions between segments of doped carbon nanotubes.
Simulating the dynamic strength of molecular interactions
Authors: Galligan Eoin , Roberts Clive J. , Davies Martyn C. , Tendler Saul J. B. , Williams Philip M.
Published: July 2002

It has been demonstrated that the force at which an interaction will break depends on the rate at which force is applied. Here, we present a strategy for the modeling of the forced dissociation of a ligand–receptor interaction, using the streptavidin–biotin complex as an example, over a range of loading rates that are outside those attainable by current all-atom simulation techniques. The method adopted is a combination of traditional reaction coordinate mapping and Brownian dynamics. Our simulations predict a dynamic force spectrum for the streptavidin–biotin interaction of similar form to recent experimental results. In this study we confirm the logarithmic dependence of a rupture force on the loading rate, highlight the barriers that are probed at the loading rates attainable by the atomic force microscope, and discuss how these barriers transform under loading. Furthermore, it is confirmed that additional information obtained from the distribution of rupture forces can be used to complement dynamic force spectroscopy data and should be used in experimental studies to verify the results obtained.
Resonant and phase-mixed magnetohydrodynamic waves in the solar atmosphere
Authors: Goossens Marcel , De Groof Anik
Published: July 2002

The magnetic field in the solar atmosphere is not uniformly distributed but organized in typical configurations: e.g., intense flux tubes in the photosphere, magnetic loops in the corona, plumes in the solar wind. Each of these magnetic configurations can support magnetohydrodynamic (MHD) waves and observations show that this is indeed the case. The intrinsic inhomogeneity of the magnetic configurations enables local (slow and) Alfvén waves to exist on individual magnetic surfaces. These local Alfvén waves provide a means for dissipating wave energy which is far more efficient in a weakly dissipative plasma than classical resistive or viscous MHD wave damping in a uniform plasma. This property has inspired a lot of work on the dissipation of driven Alfvén waves and wave heating in the solar atmosphere by resonant absorption and phase mixing. This review concentrates on the interaction between fast magnetosonic waves, local Alfvén waves and quasimodes and discusses recent results on the time evolution of phase mixing of resonant waves driven by footpoint motions.
Two-dimensional profiling and size effects on the transient enhanced diffusion of ultralow-energy B implants in Si
Authors: Giannazzo Filippo , Priolo Francesco , Raineri Vito , Privitera Vittorio
Published: July 2002

Two-dimensional profiles of ultralow-energy B implants in Si after diffusion have been studied in detail by scanning capacitance microscopy in connection with a double beveling technique to enhance depth and lateral resolution. Implants have been made into patterned wafers with different feature sizes ranging from 0.8 to 5 μm. It is demonstrated that the B transient enhanced diffusion is strongly reduced with decreasing feature size below about 2 μm. This effect is related to the increasing effect of interstitial lateral out-diffusion under the SiO2 mask. The implication for the formation of ultrashallow junctions in device structures is discussed.
Effect of microstructure on the magnetoresistive properties of NiFe/Co(CoFe)/Al(Ta)–oxide/Co(CoFe) tunnel junctions
Authors: Kyung H. , Ahn H. S. , Yoon C. S. , Kim C. K. , Song Ohsung , Miyazaki T. , Ando Y. , Kubota H.
Published: July 2002

The microstructure of the NiFe/Co(CoFe)/Al(Ta)-oxide/Co(CoFe) ferromagnetic tunnel junction was investigated using cross-sectional transmission electron microscopy (TEM). The effect of the insulating layer on the magnetoresistive (MR) properties of the junction was studied. The multilayer junction was formed using magnetron sputtering and the insulating layer was created by plasma oxidation of the deposited metal film. TEM analysis showed that the MR ratio was highly dependent on the insulating layer. For the NiFe/Co/Al-oxide/Co junction, when the Al2O3 layer was 13 Å, the oxide layer was flat and the highest MR ratio of 15% was attained. As the Al2O3 thickness increased, the interface roughness rapidly increased, and the MR ratio also markedly dropped. In contrast, NiFe/CoFe/Al-oxide/CoFe junction showed a comparatively flatter interface and recorded a higher MR ratio. The Ta-oxide insulating layer remained flat regardless of the thickness; however, the largest MR ratio of only 9% was obtained within a narrow thickness range. We have demonstrated that there exists a direct correlation between the microstructure of the oxide layer and the MR ratio of the junction, which could be utilized to optimize the electrical properties of the ferromagnetic tunneling junction.
In situ laser light scattering studies on the influence of kinetics on surface morphology during growth of In0.2Ga0.8As/GaAs
Authors: González M. U. , González Y. , González L. , Calleja M. , Sánchez-Gil J. A.
Published: July 2002

Using real-time in situ laser light scattering we study, in this work, the influence of growth kinetics on the initial development of the crosshatched morphology and its subsequent evolution. The crosshatched morphology is characteristic of relaxed low strained layers (ε< 2%) and has been traditionally related to the plastic relaxation process driven by generation and multiplication of dislocations. However we have observed that, if the growth rate is slow enough, the onset of crosshatch formation takes place at a layer thickness in which the dislocation formation and multiplication processes have not appeared yet. This reveals that the stress field generated by the small density of misfit dislocations formed by bending of the dislocations preexisting in the substrate is strong enough to affect the evolution of the growth front morphology. Our results also show that the starting point and evolution of this characteristic morphology depend on the growth rate in such a way that when the growth rate is lower the crosshatched morphology starts to develop at a smaller thickness and shows a faster evolution rate.
Boundary-layer thickness and instabilities in Bénard convection of a liquid with a temperature-dependent viscosity
Authors: Manga Michael , Weeraratne Dayanthie , Morris S. J. S.
Published: July 2002

New and published experimental measurements of spatial and temporal aspects of variable-viscosity convection are compared with boundary layer models. Viscosity μ is assumed to decrease with increasing temperature T so that convection occurs beneath a relatively stagnant layer. Of particular interest to applications involving asymptotically large viscosity variations, is the result that both the temperature difference across the hot thermal boundary layer and the frequency of thermal formation scale with the rheological temperature scale −(d log μ/dT)−1. Measurements indicate that for large Rayleigh numbers, viscosity varies by less than a factor of ≈37 across the actively convecting region.
Fast through-bond diffusion of nitrogen in silicon
Authors: Schultz Peter A. , Nelson Jeffrey S.
Published: July 2002

We report first-principles total energy calculations of interaction of nitrogen in silicon with silicon self-interstitials. Substitutional nitrogen captures a silicon interstitial with 3.5 eV binding energy forming a 〈100〉 split interstitial ground-state geometry, with the nitrogen forming three bonds. The low-energy migration path is through a bond bridge state having two bonds. Fast diffusion of nitrogen occurs through a pure interstitialcy mechanism: the nitrogen never has less than two bonds. Near-zero formation energy of the nitrogen interstitialcy with respect to the substitutional rationalizes the low solubility of substitutional nitrogen in silicon.
Enhanced copper K-alpha radiation from a low-energy plasma focus
Authors: Zakaullah M. , Alamgir K. , Shafiq M. , Hassan S. M. , Sharif M. , Waheed A.
Published: July 2002

A low-energy (2.3 kJ) plasma focus is operated in an enhanced Cu Kα line emission mode. The emission is dominated by the interaction of electrons in the current sheath with the anode tip. The Cu Kα line radiation of 0.4 J/sr is recorded in the side-on direction, which steadily increases in the end-on direction and attains the value of 0.8 J/sr. It is estimated about 40 J of energy is radiated as x rays, out of which 8 J is in the form of Cu Kα lines in 4π geometry. The radiation yield represents a system efficiency of 1.7% for overall x-ray emission, and 0.35% for the Cu Kα line.
Influence of intermolecular distance on optical property in polydiacetylene crystalline films
Authors: Kondo T. , Ishii A. , Manabe H. , Munekata H.
Published: July 2002

Optical absorption spectrum of polydiacetylene (PDA) crystalline films shifts toward higher energies as irregularity in molecular ordering is increased. We view this behavior in terms of the reduced overlap of conjugated π-electron wave function among one-dimensional PDA molecular wires. This point is further discussed by using the Kronig–Penney model, in which the influence of irregularity in molecular ordering is assessed in terms of a change in the intermolecular distance which in turn shifts the fundamental absorption edge.
Emission properties of an amorphous AlN:Cr3+ thin-film phosphor
Authors: Caldwell M. L. , Martin A. L. , Dimitrova V. I. , Van Patten P. G. , Kordesch M. E. , Richardson H. H.
Published: July 2002

Chromium-doped aluminum nitride (AlN:Cr) films were grown on p-doped silicon (111) by rf magnetron sputtering in a nitrogen atmosphere at a pressure of 10−4 Torr. Film thickness was typically 200 nm. After growth, the films were “activated” at ∼1300 K for 30 min in a nitrogen atmosphere. Films activated in this manner exhibit intense cathodoluminescence and photoluminescence emission. Spectral evidence demonstrates conclusively that the luminescent centers are Cr3+ ions.
Domain formation in a one-dimensional superlattice
Authors: Mourokh Lev G. , Horing Norman J. M. , Smirnov Anatoly Yu.
Published: July 2002

The dynamics of the temporal formation of high electric field domains in a one-dimensional superlattice miniband subject to inelastic phonon scattering is analyzed here. Our formulation is based on the derivation of equations of motion for generating functions of electron momentum fluctuations which take account of electron scattering by acoustic phonons, facilitating the determination of analytical expressions for both the electron drift velocity and the diffusion coefficient as functions of the applied bias voltage. The speed of domain formation and the minimum carrier concentration required are determined explicitly.
Diffusion of chloroaluminum phthalocyanine on MoS2 surface detected by photoemission electron microscopy and metastable electron emission microscopy
Authors: Yasufuku H. , Ibe T. , Okumura M. , Kera S. , Okudaira K. K. , Harada Y. , Ueno N.
Published: July 2002

Diffusion of a large organic semiconductor molecule, chloroaluminum phthalocyanine (ClAlPc), on a cleaved MoS2 surface was detected using photoemission electron microscopy (PEEM) and metastable electron emission microscopy (MEEM). The PEEM and MEEM images showed that a micropattern of ClAlPc ultrathin film prepared on the MoS2 surface by vacuum deposition shrinks with time and finally disappears even at room temperature at which the molecules do not evaporate. The results indicate that control of molecular diffusion is necessary for the preparation of stable micro or nanostructure of organic thin films.
Planar p-on-n HgCdTe heterostructure infrared photodiodes
Authors: Bahir G. , Garber V. , Rosenfeld D.
Published: July 2002

We report on a simple process to fabricate planar Hg1−yCdyTe/Hg1−xCdxTe (x<y) heterostructure photodiodes with p-on-n configuration. The material used for this demonstration was a double-layer p-on-n heterostructure that was grown by a liquid-phase-epitaxy technique. The p-on-n planar devices consisted of an arsenic-doped p-type epilayer (y=0.28) on top of a long-wavelength infrared n-type epilayer (x=0.225, λ=10 μm). The ion-beam-milling p-to-n type conversion effect was used in order to delineate the active device element, and to isolate the planar device. Detailed analysis of the current–voltage characteristics of these diodes as a function of temperature show that they have high performance and that their dark current is diffusion limited down to 60 K. The results show that the R0A values are close to the theoretical limit over a wide range of cutoff wavelengths.
Strain and composition dependence of the E1(TO) mode in hexagonal Al1−xInxN thin films
Authors: Kasic A. , Schubert M. , Off J. , Scholz F.
Published: July 2002

Infrared spectroscopic ellipsometry is used to study the influence of strain and composition on the transverse-optical phonon mode of E1 symmetry in hexagonal Al1−xInxN films for 0.12⩽x⩽0.21. The 0.1–0.2-μm thick films were grown on slightly compressively strained hexagonal GaN buffer layers, or directly on [0001] sapphire by metalorganic vapor phase epitaxy. The Al1−xInxN E1(TO) phonon shows a one-mode behavior in contrast to recent theoretical predictions [H. Grille, C. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Films grown on GaN reveal the influence of strain on the phonon mode frequencies due to pseudomorphic film growth. Al1−xInxN deposited directly on sapphire possesses phonon modes which indicate fully relaxed film growth.
Semiclassical molecular dynamics computation of spontaneous light emission in the condensed phase: Resonance Raman spectra
Authors: Ovchinnikov M. , Apkarian V. A. , Voth Gregory A.
Published: July 2002

The three-time correlation function that describes resonance Raman (RR) spectra is computed directly using the Herman–Kluk semiclassical propagator. The trace expression for this correlation function {C(t1,t2,t3)=Tr[e−βĤe−iĤg(t1+t2)e−iĤet3e+iĤg(t2+t3)e+iĤet1]} allows forward–backward time propagation of trajectories over closed time-circuits, leading to efficient convergence in multidimensional systems. A local harmonic approximation is used to derive an expression for the density operator in the coherent state representation (〈p1 q1|e−βĤ|p2 q2〉). This allows efficient sampling of phase space as well as simulations at arbitrary temperatures and in arbitrary coordinates. The resulting method is first analyzed for a one-dimensional problem, where the results are shown to be in excellent agreement with exact quantum calculations. The method is then applied to the problem of RR scattering of iodine in the condensed phase. The RR spectrum of an I2 molecule in a xenon fluid at 230 K is calculated and also found to be in excellent agreement with experiment.
On thermally induced separation of laminar free-convection flows
Authors: Exner Alfred , Kluwick Alfred
Published: July 2002

The influence of a short cooled wall region on the laminar free-convection flow along a semi-infinite constantly heated vertical flat plate is investigated in the limit of large Grashof number. A double-deck structure is shown to emerge in an asymptotically correct description of the flow. Two different flow regimes have to be distinguished depending on the spatial extent and the intensity of cooling. For short-scale, strong disturbances we present a numerical investigation of the resulting interaction problem as well as analytic solutions of a linear perturbation analysis. For disturbances which are longer and weaker compared to interaction scales the phenomenon of marginal separation comes into play and the lower and upper decks can be treated independently. In this case the field quantities can be described by regular asymptotic expansions which are found to be in good agreement with a numerical solution of the boundary-layer equations.
Optical parameters of a magnetized semiconductor plasma with nonparabolic band structure
Authors: Sharma Giriraj , Ghosh S.
Published: July 2002

The optical parameters (linear and nonlinear) and dispersion characteristics of a III–V compound semiconductor plasma subjected to a strong transverse magnetic field have been investigated theoretically. The nonlinearity induced in the medium has been attributed to heating of the carriers by the pump that results in modification of the electron effective mass in a nonparabolic conduction band and the momentum transfer collision frequency of electrons. The external magnetic field is found to have two consequences: (a) increasing the nonlinearity of the medium and (b) modifying the dispersion characteristics and determining the direction of energy flow between the pump and the generated waves. The plasma frequency ωp is found to enhance the magnitude of the optical parameters as usual. For a typical n-InSb semiconductor, linear refractive index and nonlinear refractive index coefficients are found maximum (nl=5.3, nnl=2×10−10 m2 V−2) whereas absorption coefficients al (linear) and anl (nonlinear) are found to vanish when ωo resonates with ωc(=1.138×1014 s−1). The present study once again establishes the device potentials of n-InSb.
Piezoelectric contributions to pulsed degenerate four-wave mixing
Authors: Biaggio Ivan
Published: July 2002

The existence of geometry and pulse-length-dependent piezoelectric contributions to pulsed degenerate four-wave mixing is demonstrated experimentally. These effects must be taken into account when measuring third-order susceptibilities in noncentrosymmetric materials.
Ab initio electronic structure of HCN− and HNC− dipole-bound anions and a description of electron loss upon tautomerization
Authors: Skurski Piotr , Gutowski Maciej , Simons Jack
Published: July 2002

The binding of an excess electron to HCN and HNC was studied at the coupled cluster level of theory with single, double, and noniterative triple excitations and with extended basis sets to accommodate the loosely bound excess electron. The HCN molecule, with a dipole moment of 3.05 Debye, binds an electron by 10 cm−1, whereas the HNC tautomer possesses a similar dipole moment (3.08 Debye) and binds the electron by 43 cm−1. The electronic stability of the anionic system along the minimum energy HCN→HNC tautomerization path has been investigated, and it was concluded that the excess electron autodetaches during the tautomerization. Unusually large electron correlation energy contributions to the total electron binding energy were found and are discussed.
Electroluminescence at silicon band gap energy from mechanically pressed indium–tin–oxide/Si contact
Authors: Lin Ching-Fuh , Chen Miin-Jang , Chang Shu-Wei , Chung Peng-Fei , Liang Eih-Zhe , Su Ting-Wien , Liu C. W.
Published: July 2002

Room temperature electroluminescence (EL) corresponding to Si band gap energy is observed from mechanically pressed indium–tin–oxide (ITO)/Si contact. The intensity of luminescence is pressure dependent and highly related to the current–voltage characteristics. Increasing pressure simultaneously reduces the rectification property and the luminescence. The physical reason for EL is attributed to the formation of an air gap between the ITO and the Si substrate. The role of the air gap is similar to the oxide layer in the metal–oxide–semiconductor structure. The influence of surface quality of the Si substrate on the luminescence spectrum is also studied, and found to be significant.
Miura map between lattice Kadomtsev–Petviashvili and its modification is canonical
Authors: Liu Q. P.
Published: July 2002

We consider the Miura map between the lattice Kadomtsev–Petviashvili hierarchy and the lattice modified KP hierarchy and prove that the map is canonical not only between the first Hamiltonian structures, but also between the second Hamiltonian structures.
Integration of n-type and p-type quantum-well infrared photodetectors for sequential multicolor operation
Authors: Dupont E. , Gao M. , Wasilewski Z. , Liu H. C.
Published: July 2002

A multicolor infrared photodetector based on the epitaxial integration of an n-type with a p-type GaAs/AlGaAs quantum-well stack is experimentally demonstrated. Additionally, a quantum-well GaAs light-emitting diode is inserted between the stacks to achieve up-conversion of mid-infrared radiation to near-infrared signal. This device shows a remarkable selectivity on wavelength: depending on the bias voltage the peak wavelength detection can be switched on and off between 9.1 and 4.85 μm.
Wave equations with point interactions in finite energy spaces
Authors: Bertini Massimo , Noja Diego , Posilicano Andrea
Published: July 2002

Given the abstract wave equation φ̈−Δαφ=0, where Δα is the Laplace operator with a point interaction of strength α, we define and study W̄α, the associated wave generator in the phase space of finite energy states. We prove the existence of the phase flow generated by W̄α, and describe its most relevant properties with a particular emphasis on the associated symplectic structure and scattering theory.
Hexagonal growth spirals on GaN grown by molecular-beam epitaxy: Kinetics versus thermodynamics
Authors: Parkhomovsky A. , Dabiran A. M. , Benjaminsson B. , Cohen P. I.
Published: July 2002

GaN grown by molecular-beam epitaxy on Ga-polar GaN templates prepared by metal organic chemical vapor deposition shows a variety of morphologies that depend on defects and growth conditions. We measured the mean terrace widths of hexagonal growth spirals or hillocks versus ammonia and Ga fluxes and substrate temperature. The measurements were compared to a near equilibrium model of the growth. The results indicate that under excess Ga growth conditions, Ga-polar GaN(0001) has a mean step-edge energy of 0.27 eV/Å.
Ion-beam-induced deoxyribose nucleic acid transfer
Authors: Anuntalabhochai S. , Chandej R. , Phanchaisri B. , Yu L. D. , Vilaithong T. , Brown I. G.
Published: July 2002

We report our observations of the interaction of energetic ions with bacterial cells, inducing direct deoxyribose nucleic acid (DNA) transfer into Escherichia coli (E. coli). Argon- and nitrogen-ion beams were used to bombard the bacteria E. coli in a vacuum with energy of 26 keV and fluence in the range 0.5–4×1015 ions/cm2. Three DNA plasmids, pGEM2, pGEM-T easy, and pGFP, carrying different marker genes, were subsequently transferred (separately) into the appropriately ion-bombarded bacteria and successfully expressed. The results of this study indicate that ion beams with an energy such that the ion range is approximately equal to the cell envelope thickness, at a certain range of fluence, are able to generate pathways for macromolecule transfer through the envelope without irreversible damage.
SrTiO
3
-based metal–insulator–semiconductor heterostructures
Authors: Pallecchi Ilaria , Grassano Giuseppe , Marré Daniele , Pellegrino Luca , Putti Marina , Siri Antonio Sergio
Published: July 2002

We explored the feasibility of employing strontium titanate (SrTiO3) as semiconducting material in field-effect metal–insulator–semiconductor epitaxial heterostructures. This idea was suggested by the observation of a dramatic effect of the oxygen deficiency on SrTiO3−δ transport properties, which brings about metallic behavior with low-temperature mobility values comparable with those commonly found for silicon. By pulsed-laser deposition, we realized patterned field-effect devices, showing a resistance enhancement up to 90%. This promising result could open perspectives for crystalline-oxide electronics.
Modifications of the magnetic properties of ferrites by swift heavy ion irradiations
Authors: Costantini Jean-Marc , Studer Francis , Peuzin Jean-Claude
Published: July 2002

Single crystal plates of ferrimagnetic yttrium iron garnet (111)-YIG:Si (Y3Fe4.94Si0.06O12) and barium hexaferrite (00.1)-BaM (BaFe12O19) or (00.1)-BaM:Co,Ti (BaFe9.1Co1.4Ti1.5O19) are irradiated with swift heavy ions (3.8 GeV Xe129 or 6.0 GeV Pb208) in the electronic slowing down regime, above the threshold (≈20 keV nm−1) of formation of continuous and homogeneous cylindrical amorphous tracks. The modifications of the magnetic properties are studied by Fe57 Mössbauer spectroscopy and ac magnetic permeability measurements versus ion fluence. In the doped crystals having a planar magnetic anisotropy (YIG:Si and BaM:Co,Ti), the room-temperature Mössbauer spectra show that the magnetization is flipped perpendicularly to the sample plane at a critical amorphous fraction around 30% in both compounds. This corresponds to a 90% drop of the measured in-plane magnetic permeability. No such effect is seen in the undoped BaM samples with the axial [00.1] anisotropy. These data are interpreted by a magnetomechanical effect generated by the stress field induced by the amorphous tracks in the sample plane which flips the magnetization along the track-axis direction when the stress-induced anisotropy constant surpasses the pristine crystal anisotropy constant at the critical amorphous fraction. In the case of YIG:Si single crystal, a track-induced anisotropy field around 0.1 T is deduced from the Mössbauer spectra under a magnetic field applied in the sample (111) plane which rotates the magnetization back to the easy 〈111〉 magnetization axis lying near the sample (111) plane in a reversible manner. The magnetic ordering of amorphous YIG:Si below 70 K is also studied by Mössbauer spectroscopy under high magnetic field (5 T). A two-dimensional Bruggeman model used for the calculation of the permeability of the crystal+amorphous track composites yields track-core radii larger by about 40% than the values previously obtained for both compounds by Mössbauer spectroscopy. We think that such discrepancies show that the samples cannot be treated like standard two-phase composites since the undamaged crystal undergoes a variable stress field depending on the damaged fraction.
RTT relations, a modified braid equation and noncommutative planes
Authors: Chakrabarti A.
Published: July 2002

With the known group relations for the elements (a,b,c,d) of a quantum matrix T as input a general solution of the RTT relations is sought without imposing the Yang–Baxter (YB) constraint for R or the braid equation for R̂=PR. For three biparametric deformatios, GL(p,q)(2), GL(g,h)(2), and GL(q,h)(1/1), the standard, the nonstandard, and the hybrid one, respectively, R or R̂ is found to depend, apart from the two parameters defining the deformation in question, on an extra free parameter K, such that R̂(12)R̂(23)R̂(12)−R̂(23)R̂(12)R̂(23)=[(K/K1)−1][(K/K2)−1](R̂(23)−R̂(12)) with (K1,K2)=(1,p/q),(1,1), and (1,1/q), respectively. Only for K=K1 or K=K2 one has the braid equation. Arbitray K corresponds to a class (conserving the group relations independent of K) of the MQYBE or modified quantum YB equations studied by Gerstenhaber, Giaquinto, and Schack. Various properties of the triparametric R̂(K;p,q), R̂(K;g,h), and R̂(K;q,h) are studied. In the larger space of the modified braid equation (MBE) even R̂(K;p,q) can satisfy R̂2=1 outside the braid equation (BE) subspace. A generalized, K-dependent, Hecke condition is satisfied by each three-parameter R̂. The role of K in noncommutative geometries of the (K;p,q), (K;g,h), and (K;q,h) deformed planes is studied. K is found to introduce a “soft symmetry breaking,” preserving most interesting properties and leading to new interesting ones. Further aspects to be explored are indicated.
A measurement method of absolute hydrogen atom density in plasmas by (2+1)-photon laser-induced fluorescence spectroscopy
Authors: Sasaki K. , Nakamoto M. , Kadota K.
Published: July 2002

A technique of (2+1)-photon laser-induced fluorescence (LIF) spectroscopy has been developed for measuring hydrogen atom density in plasmas. In this method, the following two-step excitation scheme is employed to excite ground-state H atoms to the 4p state. In the first step, H atoms at the ground (1s) state are excited to the 2s state by two photons at a wavelength of 243 nm. Subsequently, the 2s state is excited to the 4p state by the third photon at 486 nm in the second step. Fluorescence emission at 486 nm (4p→2s, Hβ line) is detected to determine the H atom density at the ground state. Since the wavelength used in the first-step excitation is the half of the wavelength used in the second-step excitation, one tunable laser with a system for second harmonic generation can be utilized in the measurement. The absolute density was evaluated by comparing the intensity of LIF emission from H with that from Xe at a known gas pressure. The present method is suitable for diagnostics of reactive plasmas since optical dissociation of molecules and radicals can be avoided because of the low photon energy of the laser radiation.
Double tuned Na 123H nuclear magnetic resonance birdcage for application on mice in vivo
Authors: Lanz Titus , Ruff Jan , Weisser Alexander , Haase Axel
Published: July 2002

The design and the characterization of a double tuned nuclear magnetic birdcage resonator is presented. It abandons quadrature drive and uses the two orthogonal modes of the birdcage for two different frequencies. In order to tune the birdcage to frequencies that are far apart, the number of legs is reduced to only four. This limits the homogeneity of the rf field, but enables the birdcage to be tuned to very different frequencies without further B1 field distortions. Following a brief explanation of the theory of the coil design, a Na 123H four leg birdcage for in vivo measurements on mice is presented. The performance of the coil is demonstrated in experiments on both a phantom and a mouse.
Adsorption of a polydisperse soft-sphere fluid in a slit pore
Authors: Kim Soon-Chul
Published: July 2002

A fundamental-measure theory for a soft-sphere fluid has been extended to the study of the adsorption for a polydisperse soft-sphere fluid within a slit pore. The preferred species in a slit pore depends on the pore size and softness of a polydisperse soft-sphere fluid, but does not depend on the bulk packing fraction of a polydisperse soft-sphere fluid. For a fixed slit pore, the pore average mole fraction is nearly independent from the density development of a confined polydisperse soft-sphere fluid. The pore average mole fraction for small particles decreases linearly with increasing the pore size. The local relative concentration oscillates with a spatial period close to the diameter of a large particle the same way as the equilibrium particle density distribution.
The equilibrium structure of the ammonium radical Rydberg ground state
Authors: Sattelmeyer Kurt W. , Schaefer Henry F. , Stanton John F.
Published: July 2002

The equilibrium structure of the ammonium radical is determined by an extrapolation procedure of large [up to CCSD(T)/aug-cc-pV5Z] coupled cluster calculations and analysis of experimental rotational constants corrected for effects of rotation–vibration interaction. These approaches yield re values of 1.0367 and 1.0363 Å, respectively. The small difference serves as a valuable internal consistency check and suggests that re in NH4 lies in the range 1.0365±0.0005 Å.
A theory for the magnetic hyperfine interactions in the microwave spectrum of NO–HF
Authors: Dennis C. R. , Whitham C. J. , Howard B. J.
Published: July 2002

A theory is presented for the fine and hyperfine interactions in the Π2 state open shell complexes like NO–HF containing remote magnetic nuclei. The nitrogen hyperfine Hamiltonian is based on the conventional Frosch and Foley treatment for diatomic radicals. An alternative treatment has been developed for the intermolecular hydrogen and fluorine magnetic hyperfine interactions based on a dipolar model for both electron spin and orbital magnetic moments.
Surface induced ordering in thin film diblock copolymers: Tilted lamellar phases
Authors: Tsori Y. , Andelman D.
Published: July 2002

We investigate the effect of chemically patterned surfaces on the morphology of diblock copolymers below the order–disorder transition. Profiles for lamellar phases in contact with one surface, or confined between two surfaces are obtained in the weak segregation limit using a Ginzburg–Landau expansion of the free energy, and treating it with mean-field theory. The periodically patterned surface induces a tilt of the lamellae in order to match the surface periodicity. The lamellae relax from the constrained periodicity close to the surface to the bulk periodicity far from it. The phases we investigate are a generalization to the mixed (perpendicular and parallel to the surface) lamellar phases occurring when the two surfaces are homogeneous. A special case when the surface pattern has a period equal to the bulk lamellar period showing “T-junction” morphology is examined. Our analytic calculation agrees with previous computer simulations and self-consistent field theories.
Fabrication of strain-balanced Si0.73Ge0.27/Si distributed Bragg reflectors on Si substrates
Authors: Kawaguchi K. , Koh S. , Shiraki Y. , Zhang J.
Published: July 2002

Strain-balanced Si0.73Ge0.27/Si distributed Bragg reflectors (DBRs) which were designed to overcome the limitation of the number of pairs originating from the strain accumulation were fabricated. Raman spectra of Si0.73Ge0.27/Si DBRs with 11 and 25 mirror pairs showed that SiGe and Si layers were under compressive and tensile strain on SiGe virtual substrates as designed. A record reflectivity of 80% was achieved at 1.44 μm in SiGe/Si DBRs with 25 pairs. The surface roughness of the 25 pair sample, however, was increased to about 46 nm compared with 6.3 nm of the 11 pair sample.
Interstitial oxygen loss and the formation of thermal double donors in Si
Authors: Lee Young Joo , von Boehm J. , Nieminen R. M.
Published: July 2002

The combination of first-principles total energy calculations and a general kinetic model, which takes into account all processes of association, dissociation, and restructuring, is used to study the kinetics of thermal double donors (TDDs) in silicon over the temperature range of 300–650 °C. A strong correlation is found between the formation rate of TDDs and the loss rate of interstitial oxygen atoms. Also, a close agreement with experiments is obtained. It is found that TDDs grow via consecutive reactions where fast diffusing oxygen dimers and all TDDs capture interstitial oxygen atoms.
Mechanism of proton transfer in ice. II. Hydration, modes, and transport
Authors: Kobayashi Chigusa , Saito Shinji , Ohmine Iwao
Published: July 2002

The mechanism of the excess-proton transfer in ice is investigated by analyzing the potential energy surface, the normal modes, and the interaction between the excess proton and defects. It is found that the solvation from water molecules in long-distance shells is essential for the smooth transport of the proton. The solvation shells up to, for example, about the 18th shell are needed to attain a convergence of the excess-proton solvation energies. The potential energy surface of the excess-proton transfer calculated with including these distant hydration shells is very smooth even for a long distance proton transport. Normal modes are calculated along the reaction paths of the proton transfer. An analysis is done to find how the character of these normal modes changes along the proton transfer. The structure and energetics of hydronium ion and L-defect complex are also examined to explain the temperature dependence of the proton transport.
Control of nanocrystalline orientation using the application of a stress field in an amorphous alloy
Authors: Ogura A. , Tarumi R. , Shimojo M. , Takashima K. , Higo Y.
Published: July 2002

Precipitation of nanocrystals in a Ni–P amorphous alloy film during application of a stress field has been investigated. Microsized cantilever-beam-type specimens were prepared from the film by focused-ion-beam machining and bending stress was applied to the specimen using a mechanical testing machine for microsized specimens. Transmission electron microscopy observation in the plane strain deformed region has revealed that the deformation induces the precipitation of nanocrystalline Ni particles, and a (111) plane of all crystalline particles is aligned parallel to the side surface of the specimen. This suggests that control of the nanocrystalline orientation in amorphous alloys would be possible using the application of a stress field.
Enhanced magneto-optical Kerr effects and decreased Curie temperature in Co–Mn ferrite thin films
Authors: Zhou Biao , Zhang Ya-Wen , Liao Chun-Sheng , Cheng Fu-Xiang , Yan Chun-Hua , Chen Liang-Yao , Wang Song-You
Published: July 2002

Co–Mn ferrite thin films were prepared on a monocrystalline silicon substrate by a sol–gel process, and the influences of Mn3+ on the microstructure, magnetism, and polar magneto-optical Kerr effects of the as-deposited films were examined. The results reveal that doping of Mn3+ ions could effectively lower the TC of Co ferrite, and the Mn3+ substitution caused enhanced Kerr rotations due to the migration of Co2+ from the octahedral site to the tetrahedral site. A maximum rotation of 2.7° was produced by the stress in the metastable cubic structure of CoFe0.6Mn1.4O4 films.