bluuebunny/crossref_metadata_2025 huggingface dataset:
SiC/SiO
2
interface states observed by x-ray photoelectron spectroscopy measurements under bias
Authors: Sakurai Takeaki , de Vasconcelos Elder A. , Katsube Teruaki , Nishioka Yasushiro , Kobayashi Hikaru
Published: July 2002

Energy distribution of interface states at an ultrathin SiO2/SiC interface is obtained by means of x-ray photoelectron spectroscopy (XPS) under bias. The substrate Si 2p peak shows a reversible energy shift by the application of a bias voltage to SiC with respect to the Pt layer of the 〈Pt/SiO2/6H–SiC(0001)〉 structure, and the analysis of the shift clarifies that an interface state peak is present near the midgap. The analysis of the current–voltage curves shows that in the entire bias region, the interface states communicate with conduction and/or valence bands under x-ray irradiation, and consequently, despite the wide-gap semiconductor, interface states in the whole band-gap region are observable by this method.
Lamb wave devices using capacitive micromachined ultrasonic transducers
Authors: Yaralioglu G. G. , Badi M. H. , Ergun A. S. , Cheng C. H. , Khuri-Yakub B. T. , Degertekin F. L.
Published: July 2002

Lamb wave devices based on capacitive micromachined ultrasonic transducers (CMUTs) have been built on 500-μm-thick silicon wafers for frequencies in the vicinity of 1 MHz. CMUTs have been used to both excite and detect Lamb waves in the substrate. This configuration eliminates the need for piezoelectric materials, which are not compatible with the existing integrated circuit (IC) fabrication techniques, and allows easy integration of Lamb wave devices and electronics on the same wafer. Finite element analysis of the devices shows that the lowest order antisymmetric Lamb wave (A0) is the dominant mode in the substrate in this frequency range. This result is also confirmed by demonstration experiments.
Correlation consistent valence basis sets for use with the Stuttgart–Dresden–Bonn relativistic effective core potentials: The atoms Ga–Kr and In–Xe
Authors: Martin Jan M. L. , Sundermann Andreas
Published: July 2002

We propose large-core correlation-consistent (cc) pseudopotential basis sets for the heavy p-block elements Ga–Kr and In–Xe. The basis sets are of cc-pVTZ and cc-pVQZ quality, and have been optimized for use with the large-core (valence-electrons only) Stuttgart–Dresden–Bonn (SDB) relativistic pseudopotentials. Validation calculations on a variety of third-row and fourth-row diatomics suggest them to be comparable in quality to the all-electron cc-pVTZ and cc-pVQZ basis sets for lighter elements. Especially the SDB-cc-pVQZ basis set in conjunction with a core polarization potential (CPP) yields excellent agreement with experiment for compounds of the later heavy p-block elements. For accurate calculations on Ga (and, to a lesser extent, Ge) compounds, explicit treatment of 13 valence electrons appears to be desirable, while it seems inevitable for In compounds. For Ga and Ge, we propose correlation consistent basis sets extended for (3d) correlation. For accurate calculations on organometallic complexes of interest to homogenous catalysis, we recommend a combination of the standard cc-pVTZ basis set for first- and second-row elements, the presently derived SDB-cc-pVTZ basis set for heavier p-block elements, and for transition metals, the small-core [6s5p3d] Stuttgart–Dresden basis set-relativistic effective core potential combination supplemented by (2f1g) functions with exponents given in the Appendix to the present paper.
Stimulated emission depletion microscopy with an offset depleting beam
Authors: Klar T. A. , Dyba M. , Hell S. W.
Published: July 2002

We demonstrate that an offset stimulated emission depletion (STED) beam breaks the diffraction barrier of fluorescence microscopy in both the lateral and the axial directions. A 2.5-fold axial reduction of the focal spot is accomplished through the ear-shaped lobes of the diffraction maximum of the STED beam. The effect of the minima and side maxima of the STED beam on the lateral and axial resolution is shown to be in remarkable agreement with theory. Conditions are given for which a regular STED beam reduces the axial extent of a confocal spot from 490±36 to 175±18 nm, and simultaneously from 183±12 to 70±8 nm along the direction of the offset. The latter establishes the lowest reported value in far-field fluorescence microscopy.
Enhanced tunnel current through thin oxide due to single-defect scattering
Authors: Fu Y. , Willander M. , Lundgren P. , Aderstedt E.
Published: July 2002

We have studied the conduction current from an n-silicon substrate to n+-polycrystalline-silicon gate through an ultrathin oxide layer. Carrier transmission through the thin oxide layer is enhanced by the presence of an ionized impurity in the oxide layer. In addition to the normal direct tunnel current, the Coulomb potential of the ionized impurity provides extra conduction channels for carriers in the n-silicon substrate to transmit to the polycrystalline-silicon gate. It has been found that the ratio between the conduction current through the extra conduction channels and the direct tunnel current can be as large as 1.9. The exact value of the ratio depends on the location of the charge in the oxide layer.
Study of single-cycle pulse propagation inside a terahertz near-field probe
Authors: Mitrofanov O. , Harel R. , Lee M. , Pfeiffer L. N. , West K. , Wynn J. D. , Federici J.
Published: July 2002

Propagation of 0.5 THz single cycle pulses inside an aperture-type near-field probe is studied. The E-field amplitude attenuation is experimentally measured at various distances from the aperture. Numerical simulations based on a two-dimensional model illustrate the pulse waveform transformation and the spectral blueshift, which is experimentally observed. The study shows that the sensitivity of such a near-field probe can be improved by more than a factor of 10 by decreasing the aperture-to-detector separation without reduction of the spatial resolution.
Anomalous oxygen annealing effects on La0.7Ca0.3MnO3 films grown on MgO substrates
Authors: Choi H. S. , Kim W. S. , Nam B. C. , Hur N. H.
Published: July 2002

Epitaxial La0.7Ca0.3MnO3 thin films were grown on MgO (001) substrates by pulsed laser deposition. The as-grown films exhibit a metal–insulator transition at temperatures ranging from 200 to 230 K. Surprisingly, the transition temperature of postannealed films under O2 at 900 °C decreases by more than 100 K, featured with the colossal magnetoresistance. The O2 annealed films also show thermal hysteresis in resistivity and nonlinear I–V behavior. These results are interpreted in terms of Mn deficiency induced by large structural difference between film and substrate, and also discussed in viewpoint of a percolative phase transition.
Evidence for an additional noise source modifying conventional 1/f frequency dependence in sub-μm metal–oxide–semiconductor field-effect transistors
Authors: Ueno H. , Kitamura T. , Matsumoto S. , Okagaki T. , Miura-Mattausch M. , Abe H. , Hamasaki T.
Published: July 2002

Flicker noise measurements for n-metal–oxide–semiconductor field-effect transistors have been carried out under a wide range of bias conditions. The experiments show excess noise over an ideal 1/f noise spectrum at around 1–10 kHz frequency range, which is independent of the drain voltage. The origin of the additional noise is the Shockley–Read–Hall generation–recombination process occurring near the drain in the channel. Monte Carlo device simulations confirmed the excess noise origin as well as the observed reduction of its magnitude with increasing gate voltage.
Variable-temperature scanning capacitance microscopy: A way to probe charge traps in oxide or semiconductor
Authors: Kim C. K. , Yoon I. T. , Kuk Y. , Lim H.
Published: July 2002

The spatial distribution of carriers and an energy level of charge traps are measured with a newly built variable-temperature scanning capacitance microscope (VTSCM). The system has the spatial resolution of ∼20 nm, and the good energy resolution enough to measure the energy level and the capture cross section of electron or hole traps. By operating the VTSCM in an isothermal transient mode of capacitance spectroscopy, a hole trap that lies about 0.40 eV above the valence band maximum is identified in a SiO2/p-Si sample, and the result is compared to that taken with a conventional deep level transient spectroscopy.
Imaging layers for 50 kV electron beam lithography: Selective displacement of noncovalently bound amine ligands from a siloxane host film
Authors: Dressick W. J. , Chen M.-S. , Brandow S. L. , Rhee K. W. , Shirey L. M. , Perkins F. K.
Published: July 2002

We report the development of an imaging layer technology for 50 kV electron-beam lithography based upon the displacement of noncovalently bound amine ligands from a siloxane host film. The patterned films were used as templates for the selective deposition of an electroless nickel film resulting in a positive tone imaging mechanism. The deposited nickel was sufficiently robust to function as an etch mask for pattern transfer by reactive ion etching. Metallized and etched patterns with linewidths to approximately 40 nm are demonstrated using an exposure dose of 500 μC/cm2.
Effects of the morphologies and structures of light-emitting layers on the performance of organic electroluminescent devices
Authors: Qin D. S. , Li D. C. , Wang Y. , Zhang J. D. , Xie Z. Y. , Wang G. , Wang L. X. , Yan D. H.
Published: July 2002

Organic electroluminescent devices with a structure of ITO/ploy (9-vinylcarbazole)/tris (8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag are fabricated at different substrate temperatures (77, 298, and 438 K) during Alq3 deposition. It is found that the surface morphologies of Alq3 thin films greatly affect the I–V characteristics of the devices by the contact area between metal cathode and light-emitting layer. There is an increase in the luminous efficiency of the devices in the order 77 K<298 K<438 K. We attribute this trend to different structures of Alq3 thin films.
Passively Q-switched Ho3+:Y3Al5O12 laser using a PbSe-doped glass
Authors: Malyarevich A. M. , Prokoshin P. V. , Demchuk M. I. , Yumashev K. V. , Lipovskii A. A.
Published: July 2002

Saturable absorber Q switching of Ho3+:Y3Al5O12 laser at 2.1 μm using PbSe-doped phosphate glass was demonstrated. Q-switched pulses of 22 mJ in energy and 85 ns in duration were obtained.
High-performance quantum cascade lasers (λ∼11 μm) operating at high temperature (T ⩾425 K)
Authors: Tahraoui A. , Matlis A. , Slivken S. , Diaz J. , Razeghi M.
Published: July 2002

We report record-low threshold current density and high output power for λ∼11 μm Al0.48In0.52As/Ga0.47In0.53As quantum cascade lasers operating up to 425 K. The threshold current density is 1.1, 3.83, and 7.08 kA/cm2 at 80, 300, and 425 K, respectively, for 5 μs pulses at a 200 Hz repetition rate. The cavity length is 3 mm with a stripe width of 20 μm. The maximum peak output power per facet is 1 W at 80 K, 0.5 W at 300 K, and more than 75 mW at 425 K. The characteristic temperature of these lasers is 174 K between 80 and 300 K and 218 K in the range of 300–425 K.
Newton’s rings in near-field optics
Authors: Goldner Lori S. , Hwang Jeeseong , Bryant Garnett W. , Fasolka Michael J. , Absil P. P. , Hryniewicz J. V. , Johnson F. G. , Shen H. , Ho P.-T.
Published: July 2002

We show how Newton’s rings manifest themselves in near-field scanning optical microscopy and discuss how this effect can be used with topographic imaging to measure correlated roughness of thin films. In conventional optics, transmission through a thin nonabsorbing film depends on film thickness when multiple reflections from the film boundaries are coherent. Measurements and modeling of the transmission through thin films illuminated by a near-field probe show that these oscillations are present despite the large distribution of transverse wave vectors needed to describe light from the probe.
Structure and melting of two-dimensional dust crystals
Authors: Totsuji Hiroo
Published: July 2002

Dust particles in plasmas confined near the boundary between the plasma bulk and the sheath form a two-dimensional system when appropriate conditions are satisfied. To keep dust particles from running away horizontally, the electrostatic potential is usually applied to the electrode surrounding these dusty plasmas and we have finite two-dimensional systems of dust particles. Adopting the Yukawa model for the interaction between dust particles, structures of finite two-dimensional Yukawa systems at low temperatures have been analyzed both by molecular dynamics simulations and variational methods. The effect of the correlation energy between dust particles is shown to play an important role in the formation of the one-body distribution in these systems. Molecular dynamics simulations of large systems typically with 103 to 104 particles have been performed and the behavior of the mean square displacement is obtained for various combinations of characteristic parameters. The results are discussed in relation to the melting transition on the basis of the theoretical analysis on static structures.
Single-electron charging in a parallel dot structure
Authors: Wang T. H. , Aoyagi Y.
Published: July 2002

A parallel dot structure, which is not conductively coupled but capacitively coupled, is fabricated. Both of the respective single dots show clear Coulomb blockade oscillations (CBOs) as their gate voltages are scanned. Single-electron charging in one dot causes oscillations of the current through another dot, even in the regime of more negative gate voltages where the CBOs cannot be observed due to a too weak current. In addition, information on the energy levels in one dot can be obtained.
Vaporization of heated materials into discharge plasmas
Authors: Keidar Michael , Fan Jing , Boyd Iain D. , Beilis Isak I.
Published: July 2002

The vaporization of condensed materials in contact with high-current discharge plasmas is considered. A kinetic numerical method named direct simulation Monte Carlo (DSMC) and analytical kinetic approaches based on the bimodal distribution function approximation are employed. The solution of the kinetic layer problem depends upon the velocity at the outer boundary of the kinetic layer which varies from very small, corresponding to the high-density plasma near the evaporated surface, up to the sound speed, corresponding to evaporation into vacuum. The heavy particles density and temperature at the kinetic and hydrodynamic layer interface were obtained by the analytical method while DSMC calculation makes it possible to obtain the evolution of the particle distribution function within the kinetic layer and the layer thickness.
Electronically controlled microwave band gap filter structures
Authors: Hill Michael J. , Ziolkowski Richard W. , Papapolymerou John
Published: July 2002

Microwave band gap structures (MBG) utilizing fixed defects have received much interest because of their ability to operate as narrow band filters. With the recent interest in reconfigurable wireless devices, the need for electronically controllable narrow band filters is on the rise. By altering the defects in an MBG crystal, the transmission properties of the crystal can be changed. Using this concept, two controllable defect structures have been studied. Microwave band gap crystals utilizing single and dual p–i–n diode defect structures have been simulated, fabricated, and tested. Through the control of the p–i–n diode bias current, the transmission effects caused by the crystal defects can be altered. Experiments demonstrating contrasts of more than 30 dB between the diode-on and diode-off states are presented along with the corresponding finite difference time domain simulation results.
Fourier transform infrared emission spectroscopy of VCl
Authors: Ram R. S. , Bernath P. F. , Davis S. P.
Published: July 2002

The high resolution spectrum of VCl has been observed in emission in the 3000–9400 cm−1 region using a Fourier transform spectrometer. The bands were excited in a high temperature carbon tube furnace from the reaction of vanadium metal vapor and a trace of BCl3 and the spectra were recorded at a resolution of 0.05 cm−1. The new bands observed in the 6000–8000 cm−1 interval have been attributed to VCl. The bands having R heads near 6176, 6589, 7004, 7358, and 7710 cm−1 have been assigned as the 0–2, 0–1, 0–0, 1–0, and 2–0 bands, respectively, of the [7.0]5Δ–X 5Δ electronic transition. A rotational analysis of the Δ15–Δ15, Δ25–Δ25, and Δ35–Δ35, subbands of the 0–1 and 0–0 vibrational bands has been obtained and molecular constants have been extracted. The remaining two of the five subbands could not be analyzed because of severe overlapping from neighboring subbands. The principal molecular constants for the X 5Δ state obtained from the present analysis are: ΔG(1/2)=415.26(113) cm−1, Be=0.165 885(250) cm−1, αe=0.000 586(84) cm−1, and re=2.213 79(170) Å. Our work represents the first observation of this near infrared electronic transition of VCl.
Absorption of nonequilibrium acoustic phonons by low-mobility electrons in GaN
Authors: Stanton N. M. , Akimov A. V. , Kent A. J. , Cheng T. S. , Foxon C. T.
Published: July 2002

We report direct phonon absorption experiments in n-type GaN epitaxial layers grown by molecular beam epitaxy. Nonequilibrium phonons with characteristic energies up to 15 meV (3.5 THz) are injected from a constantan heater. They propagate ballistically through the sapphire substrate, reach the GaN layer, and are absorbed by the degenerate three-dimensional electron gas. The phonon absorption is studied as a function of heater temperature through the effects of phonon induced changes of the device resistivity. The experimental results lead us to the conclusion that in low-mobility GaN, the momentum conservation cutoff for electron-phonon transitions is shifted to higher energy than predicted by standard theory.
Properties of surface waves determined via bistatic terahertz impulse ranging
Authors: Reiten M. T. , Grischkowsky D. , Cheville R. A.
Published: July 2002

A bistatic terahertz impulse ranging system has permitted the full isolation and direct measurements of the surface wave loss and dispersion for terahertz frequencies on a dielectric cylinder. This system permits ranging investigations with variable bistatic angles between the source and detector. Direct, frequency dependent comparisons of surface wave loss and propagation velocity are compared to Mie theory and previous measurements of surface wave propagation over a 1 THz bandwidth. The observed radiation from the surface waves is seen to depend on the path of the radiation in and along the scatterer.
Initial stages of molecular-beam epitaxy growth of GaN on 6H-SiC(0001)
Authors: Lu J. , Haworth L. , Westwood D. I. , Macdonald J. E.
Published: July 2002

We studied the atomic H etching of 6H-SiC substrates and the initial stages of GaN/6H-SiC molecular-beam epitaxy growth. Atomic H etched 6H-SiC(0001)Si and (0001̄)C surfaces show a (∛×∛)−R30° and a (1×1) reconstruction respectively, with 0.7±0.2 monolayers of remnant O on both surfaces. GaN/6H-SiC(0001)Si growth is initiated by the formation of islands that develop into flat-top terraces through coalescence. Growth steps of one or integer numbers of the GaN atomic bilayer height are observed. GaN grown on 6H-SiC(0001̄)C is rougher with islands of irregular shape. X-ray photoemission spectroscopy studies show that Si 2p and C 1s photoelectron inelastic mean free paths in GaN are 22±1 and 20±1 Å, respectively.
Continuous-wave InGaN multiple-quantum-well laser diodes on copper substrates
Authors: Wong William S. , Kneissl Michael , Mei Ping , Treat David W. , Teepe Mark , Johnson Noble M.
Published: July 2002

Continuous-wave (cw) indium-gallium nitride multiple-quantum-well laser diodes (LDs) were transferred from sapphire onto copper substrates using a two-step laser lift-off process. Reduced threshold currents and increased differential quantum efficiencies were measured for LDs on Cu due to a 50% reduction of the thermal impedance. Light output for LDs on Cu was three times greater than comparable LDs on sapphire with a maximum output of 30 mW. CW operation was possible up to heatsink temperatures of 90 °C for LDs on Cu.
Atomic force microscopy detects transient frictional contrasts in apoptotic cells induced by deprivation of interleukin-3
Authors: Girasole M. , Cricenti A. , Generosi R. , Silvestri I. , Gazzaniga P. , Pozzi D. , Aglianò A. M.
Published: July 2002

The morphological changes of murine hematopoietic 32D Cl3-A cell line, in which apoptosis was induced by deprivation of interleukin-3 (IL-3) from the culture medium, were studied through air operating atomic force microscopy. The subtraction of IL-3 determines the appearing of blebs on plasma membrane and cell fragmentation in several residual bodies. Areas of strong contrast in the friction images, which are nearly absent in control and necrotic cells, were detected with percentage that peaks at 6 h of IL-3 deprivation. These are the results revealing that transient modification of the plasma membrane accompanies the first steps of apoptosis pathway.
Origin of the domain contrast on a Si(001)-2×1 surface imaged by secondary electrons
Authors: Watanabe Heiji , Ichikawa Masakazu , Kawamura Takaaki
Published: July 2002

Secondary electron (SE) imaging of alternating domains on Si(001)-2×1 surfaces was studied. We experimentally investigated the relationship between the domain contrast and the incident electron-beam angles, and found that the domain contrast between alternating 2×1 terraces is reversed by changing the incident-beam-angle conditions. And we theoretically show that the intensity of electron waves near the surface changes drastically and reverses according to the incident beam conditions. Both these experimental and theoretical results indicate that the domain contrast in SE images does not originate from anisotropic SE emission from the reconstructed surface but from the difference between the SE excitation on the 2×1 terrace and that on the 1×2 terrace.
Ionization and fragmentation dynamics of benzene in intense laser fields by tandem mass spectroscopy
Authors: Itakura Ryuji , Watanabe Jun , Hishikawa Akiyoshi , Yamanouchi Kaoru
Published: July 2002

Using a tandem time-of-flight mass spectrometer, benzene cations produced by the resonantly enhanced multiphoton ionization are mass separated and are exposed to intense laser fields (∼2×1016 W/cm2) at λ∼790 and 395 nm with the pulse duration of ∼50 fs. Comparing the yields of the product ions with those obtained from neutral benzene molecules, the ionization and dissociation dynamics of benzene in intense laser fields is investigated. At λ∼790 nm, the formation of parent benzene ions is a dominant process irrespective of the initial charge states, i.e., major products obtained when starting from neutral benzene are benzene cations and dications and those obtained when starting from benzene cation are benzene dications. On the other hand, at λ∼395 nm, the fragmentation processes to produce C4Hi+(i=2–4) and C3Hj+(j=1–3) dominate over further ionization to the benzene dication for both cases starting from neutral benzene and benzene cation, indicating the population trapping occurs by the efficient confinement in the light-dressed mixture of the C̃ and X̃ states of benzene cations assisted by the ultrafast intramolecular decay process.
Infrared extinction coefficient of LiNbO3 at temperatures to 1150 °C: Semiconductor behavior of a metal oxide at high temperature
Authors: Marı́n C. , Ostrogorsky A. G. , Foulon G. , Jundt D. , Motakef S.
Published: July 2002

The temperature dependence (up to 1150 °C) of transmittance of LiNbO3 in the 1.2–25-μm-wavelength range was measured and the extinction coefficient calculated. The transmittance of LiNbO3 in the 1.2–3.8-μm-transparent region decreases with increasing temperature. This reduction is explained through a semiconductor model, and related to the temperature dependence of intrinsic carriers in the conduction band. A simple equation is provided for the extinction coefficient dependence on temperature and wavelength.
Roughening transition and solid-state diffusion in short-period InP/In0.53Ga0.47As superlattices
Authors: Gerling M. , Gustafsson A. , Rich D. H. , Ritter D. , Gershoni D.
Published: July 2002

We have examined the structural properties of InP/In0.53Ga0.47As superlattices grown by metalorganic molecular beam epitaxy by varying the periodicity and the total thickness. We observed a roughening transition, which involves the formation of wavy interfaces, when the period and total thickness of the superlattice exceeded critical values. Interface roughening in the wake of the growth front reveals that solid state diffusion in subsurface layers can be induced by surface stresses associated with surface roughening.
The generalized star product and the factorization of scattering matrices on graphs
Authors: Kostrykin V. , Schrader R.
Published: July 2002

In this article we continue our analysis of Schrödinger operators on arbitrary graphs given as certain Laplace operators. In the present article we give the proof of the composition rule for the scattering matrices. This composition rule gives the scattering matrix of a graph as a generalized star product of the scattering matrices corresponding to its subgraphs. We perform a detailed analysis of the generalized star product for arbitrary unitary matrices. The relation to the theory of transfer matrices is also discussed.
Effect of annealing time and temperature on the formation of threading and projected range dislocations in 1 MeV boron implanted Si
Authors: Jones K. S. , Jasper Craig , Hoover Allen
Published: July 2002

The effect of annealing temperature and time on the formation of threading dislocations was investigated for high energy boron implants into silicon. 1 MeV B+ was implanted at a dose of 1×1014/cm2 into 〈100〉 Si wafers. The wafers were subsequently annealed in either a rapid thermal annealing (RTA) furnace or a conventional furnace for times between 1 s and 1 h at temperatures between 700 and 1150 °C. Following this anneal the wafers were put through a standard complementary metal-oxide-semiconductor (CMOS) process. After processing, the threading dislocation density and projected range dislocation density were studied using etch pit density counts and transmission electron microscopy (TEM). The results show that annealing (either RTA or furnace) at temperatures above 1000 °C prior to CMOS processing reduced the high density of threading dislocations by 1–2 orders of magnitude. Quantitative plan-view TEM studies show that the mechanism for defect reduction is different for the RTA versus furnace annealing and may be ramp rate dependent.
Nanoscale p-n junction fabrication in silicon due to controlled dopant electromigration
Authors: Chernyak Leonid , Klimov Mikhail
Published: July 2002

An external electric field (up to 106 V/cm) was used for nanoscale p-n junction fabrication in Si doped with Li (Si:Li) in situ in a scanning probe microscope. Creation of nano-p-n junctions was ascribed to the thermally assisted electromigration of Li+ ions. Tunneling I–V spectroscopy provided evidence for a conversion of the electrical conductivity type from p to n. A local temperature increase during an electric field-induced p-n junction fabrication was estimated to be up to 160 °C.
Hydrogen passivation and activation of oxygen complexes in silicon
Authors: Rashkeev S. N. , Di Ventra M. , Pantelides S. T.
Published: July 2002

We report first-principles calculations in terms of which we describe the role of hydrogen in passivating or activating oxygen complexes in Si. In particular we find that attaching H to a pre-existing oxygen cluster can change the electric activity of the cluster. Furthermore, the addition of a hydrogen atom in the core structure of thermal donors can account for the NL10 electron-paramagnetic-resonance signal. The interaction of H with the thermal-donor-like defects at the Si–SiO2 is also discussed.
High-frequency eddy-current technique for thickness measurement of micron-thick conducting layers
Authors: Sakran F. , Golosovsky M. , Goldberger H. , Davidov D. , Frenkel A.
Published: July 2002

We demonstrate a reflection-mode eddy-current technique operating in the 100 MHz to 5 GHz range. It allows contactless measurement of the thickness of conducting layers (Ag, Al, Cu, W, etc.) 0.1–1 μm thick with the spatial resolution of 1–2 mm.
High-resolution spectral hole burning in CdSe/ZnS core/shell nanocrystals
Authors: Palinginis Phedon , Wang Hailin
Published: July 2002

We report studies of the homogeneous linewidth in CdSe/ZnS core/shell nanocrystals by means of high-resolution spectral hole burning under low excitation levels. The hole burning spectrum reveals a sharp spectral hole as well as clearly resolved acoustic phonon sidebands. Homogeneous linewidths as narrow as 32 μeV were obtained. At low temperature, the temperature dependence of the homogeneous linewidth deviates from the usual linear dependence, reflecting the effects of phonon quantization.
Observation of the flexoelectric effect in relaxor Pb(Mg1/3Nb2/3)O3 ceramics
Authors: Ma Wenhui , Cross L. Eric
Published: July 2002

The relationship between elastic strain gradient and electric polarization was investigated in the relaxor ferroelectric lead magnesium niobate ceramic. Experimental studies indicated that flexoelectric polarization is linearly proportional to the applied strain gradient, and the flexoelectric coefficient μ12 is calculated to be 4×10−6 C/m, which is much higher than the early phenomenological estimations.
Generation of streams of highly charged Ag ions by picosecond laser
Authors: Badziak J. , Makowski J. , Parys P. , Wołowski J. , Woryna E. , Vankov A. B.
Published: July 2002

The results of the investigation of ion emission from a Ag target irradiated with high-intensity (up to 5×1016 W/cm2) 1 ps laser pulse are presented. It is shown that using a picosecond subjoule laser a production of intense streams of highly charged (charge state z>20), high-energy (up to hundreds of kilo-electron-volts) Ag ions is possible. Some properties of the ion streams are discussed.
In situ analysis of the room-temperature epitaxial growth of CeO2 ultrathin films on Si (111) by coaxial impact-collision ion scattering spectroscopy
Authors: Furusawa M. , Tashiro J. , Sasaki A. , Nakajima K. , Takakura M. , Chikyow T. , Ahmet P. , Yoshimoto M.
Published: July 2002

The room-temperature epitaxial growth of CeO2 films on Si(111) substrates was examined in situ by combined use of a coaxial impact-collision ion scattering spectroscopy (CAICISS) and the laser molecular beam epitaxy (laser MBE). It was found that the crystal quality of CeO2 ultrathin films (∼3 nm thick) as-grown in UHV (∼10−9 Torr) could be improved remarkably by a few minutes of O2 gas exposure (∼10−5 Torr) at room temperature. A three-fold symmetry in the Ce signal intensity of azimuth rotational CAICISS spectra, which exhibited the type-B epitaxial growth ([1̄10]CeO2‖[11̄0]Si), was observed for the films thicker than about 1 nm.
Terahertz-sideband generation in a semiconductor optical amplifier
Authors: Citrin D. S. , Hughes S.
Published: July 2002

We show that in a semiconductor optical amplifier irradiated by a strong terahertz electromagnetic field, terahertz-sideband generation can be substantial. Applications for frequency-shifting devices for wavelength-division-multiplexed optical systems are discussed.
Si/SiGe/Si:Er:O light-emitting transistors prepared by differential molecular-beam epitaxy
Authors: Du Chun-Xia , Duteil Fabrice , Hansson Göran V. , Ni Wei-Xin
Published: July 2002

Si/SiGe/Si:Er:O heterojunction bipolar transistor (HBT) type light-emitting devices with Er3+ ions incorporated in the collector region have been fabricated using a layered structure grown by differential molecular-beam epitaxy. Electroluminescence measurements on processed light-emitting HBTs can be performed in either constant driving current mode or constant applied bias mode, which is an important advantage over conventional Si:Er light-emitting diodes. Intense room-temperature light emission at the Er3+ characteristic wavelength of 1.54 μm has been observed at low driving current density, e.g., 0.1 A cm−2, and low applied bias, e.g., 3 V, across the collector and emitter.
Magnetic field induced luminescence spectra in a quantum cascade laser
Authors: Apalkov V. M. , Chakraborty Tapash
Published: July 2002

We report on our study of the luminescence spectra of a quantum cascade laser in the presence of an external magnetic field tilted from the direction perpendicular to the electron plane. The effect of the tilted field is to allow novel optical transitions because of the coupling of intersubband-cyclotron energies. We find that by tuning the applied field, one can get optical transitions at different energies that are as sharp as the zero-field transitions.
Near infra-red radiation squeezing through 20 nm voids in obliquely deposited metal films
Authors: Smith G. B. , Hossain A. K. M. , Gentle A.
Published: July 2002

Obliquely deposited metal films which are nearly continuous, displaying several unexpected solar optical properties. Transmittance intensity, spectral character, preferred direction of incidence, and polarization sensitivity, infer processes which effective-medium models based solely on “interior” properties cannot describe. Amplified transmittance through voids around 20 nm wide involving near surface excitations can explain the data.
Field emission from polymer-converted carbon films by ultraviolet radiation
Authors: Sun Z. , Huang S. M. , Lu Y. F. , Chen J. S. , Li Y. J. , Tay B. K. , Lau S. P. , Chen G. Y. , Sun Y.
Published: July 2002

A polymer, poly(phenylcarbyne) (PPC), was converted to carbon film by ultraviolet pulsed-laser (KrF, λ=248 nm) irradiation in nitrogen atmosphere at room temperature. The irradiated PPC consisted of fine graphitic carbon particles of several tens of nm in size, and exhibited good field emission properties. Low turn-on emission field of 2 V/μm (at 1 nA/cm2), high emission current density of 20 mA/cm2 (at 12 V/μm), and high emission luminescent spots density of 104/cm2 were observed for the polymer film irradiated by a pulsed-laser fluence of 40 mJ/cm2. We demonstrate multiple-lines and 2×5 array field emission patterns using the laser irradiation of PPC.
Low-temperature scanning probe microscopy of surface and subsurface charges
Authors: Vogel Markus , Stein Bernhard , Pettersson Håkan , Karrai Khaled
Published: July 2002

The operation of a cryogenic scanning force microscope is demonstrated with a sensitivity of about 50 fN/Hz at 5 kHz modulation. This microscope is used as an electrometer in noncontact mode in order to map the local electrostatic forces and capacitance of several nanostructures at 4.2 K. Capacitance imaging of nanostructured surfaces with subatto-Farad resolution is demonstrated.
Wavelength tuning in InGaAs/InGaAsP quantum well lasers using pulsed-photoabsorption-induced disordering
Authors: Ong T. K. , Chan Y. C. , Lam Y. L. , Ooi B. S.
Published: July 2002

Pulsed-laser irradiation followed by rapid thermal annealing was used to induce layer disordering of an InGaAs/InGaAsP laser structure. A band gap shift larger than 160 nm was achieved using energy densities of about 3.9 mJ mm−2 with 4800 pulses of laser irradiation. Transmission electron microscopy and photoluminescence were used to understand the possible effect of the laser irradiation on the material structure. Band gap-tuned lasers exhibiting blueshift up to 82 nm were obtained. This approach offers the prospect of a powerful and relatively simple postgrowth process for integrating multiple-wavelength lasers for wavelength-division-multiplexing applications.
Selectivity of nanocavities and dislocations for gettering of Cu and Fe in silicon
Authors: Stritzker B. , Petravic M. , Wong-Leung J. , Williams J. S.
Published: July 2002

The selectivity of interstitial-based extended defects (loops) and nanocavities for the gettering of Cu and Fe in Si has been studied. Controlled amounts of Cu and Fe were introduced by ion implantation into wafers containing pre-existing nanocavities and/or dislocations. Results show that Cu has a strong preference for gettering to open volume defects, even when high concentrations of interstitial-based loops are present in close proximity. However, the gettering of Fe in samples containing both vacancy- and interstitial-type defects is more complex, with Fe accumulation at all regions in the sample which contain defects, whether they are vacancy- or interstitial-like in character.
Ordered stretching of single molecules of deoxyribose nucleic acid between microfabricated polystyrene lines
Authors: Klein D. C. G. , Gurevich L. , Janssen J. W. , Kouwenhoven L. P. , Carbeck J. D. , Sohn L. L.
Published: July 2002

A technique for creating arrays of parallel, stretched single molecules of deoxyribose nucleic acid (DNA) on an arbitrary substrate for high-resolution scanning-probe imaging is discussed. The technique consists of lithographically patterning polystyrene lines on a substrate which then provide attachment sites for the ends of individual DNA molecules. Molecular combing is performed to stretch DNA from one polystyrene line to the other. Scanning-tunneling and atomic-force microscope images of single molecules of bacteriophage-lambda DNA are shown to demonstrate the advantages of this technique. Several applications, from high-resolution genomics to molecular electronics, are discussed.
Asymmetric switching of antiferroelectric liquid-crystal cells
Authors: Otón J. M. , Pena J. M. S. , Quintana X. , Gayo J. L. , Urruchi V.
Published: July 2002

Antiferroelectric liquid-crystal cells usually show symmetric electro-optic switching response from the antiferroelectric state to two opposite ferroelectric states. Intermediate transmission levels (analog gray scale) can be stabilized, applying a constant dc bias voltage after switching. Modifying the manufacturing process and using narrow dynamic-range antiferroelectric materials, a fully asymmetric response has been achieved. This asymmetric switching allows the antiferroelectric cell to be driven as a ferroelectric cell, reducing or eliminating the bias voltage, and ultimately leading to analog optical multistability, i.e., devices whose optical transmission may be arbitrarily set and maintained without power supply.
Analytical solution of the diffusion-controlled precipitation problem
Authors: Anestiev L. , Froyen L.
Published: July 2002

The understanding of the mechanisms and processes taking place during the production of metal matrix composites, especially of in situ produced composites, is of crucial importance for the properties of the composite. An analytical solution of the equations governing the kinetics of diffusion-controlled precipitation of TiB2 is proposed. The solution allows to predict the concentration profiles and the volume fraction distribution of the reinforcements that are in situ formed along the specimen. The influence of the physicochemical parameters is also taken into account in the proposed solution.
Characterization of the surface irregularities of cubic GaN using micro-Raman spectroscopy
Authors: Liu Ming S. , Prawer Steven , Bursill Les A. , As D. J. , Brenn R.
Published: July 2002

The surface irregularities of molecular-beam-epitaxy-grown cubic GaN on GaAs substrates were characterized by micro-Raman spectroscopy. Some surface irregularities are found to be the result of the mixed phases of cubic (zinc-blende) and hexagonal (wurtzite) GaN, while others originate from the alloying of GaN with the GaAs substrate. The polarization scattering of the surface irregularities suggests that misoriented wurtzite GaN clusters sit on or are imbedded in the cubic GaN layer. It is revealed that the crystalline defects created during the growth of cubic GaN induce a growth of hexagonal GaN and, therefore, the surface irregularities consist of a phase mixture of cubic and hexagonal GaN polytypes.
Residual arsenic site in oxidized AlxGa1−xAs (x=0.96)
Authors: Cheong S.-K. , Bunker B. A. , Shibata T. , Hall D. C. , DeMelo C. B. , Luo Y. , Snider G. L. , Kramer G. , El-Zein N.
Published: July 2002

X-ray absorption fine-structure spectroscopy is used to determine the site of residual As in wet-oxidized Al0.96Ga0.04As. In a ∼0.5-μm-oxide film removed from its GaAs substrate, the remaining As atoms are found to be coordinated with oxygen in the form of amorphous-As oxides, with a mixture of ∼80% As3+ and ∼20% As5+ sites that are locally similar to As2O3 and As2O5. No evidence of interstitial or substitutional As, As precipitates, or GaAs is seen, implying that less than 10% of the As atoms are in these forms.
Quasioptic dielectric tetrahertz cavity: Coupled through optical tunneling
Authors: Zhang Weili , Zhang Jiangquan , Grischkowsky D.
Published: July 2002

We report the observation of the well defined oscillation of a picosecond tetrahertz (ps THz) pulse within a dielectric concentric cylindrical cavity, which is coupled to an incoming focused beam of ps THz pulses by the optical tunneling effect of frustrated total internal reflection. The tunneling barrier is an 18-μm-thick air slab, situated between the plane surfaces of a hyperhemicylindrical focusing lens and the cavity. The output of the quasioptic cavity consists of a train of ps THz pulses with a frequency spectrum from 0.1 to 1.0 THz. Good agreement between experiment and theory is obtained in both the time and frequency domains.
Inversion domains in GaN layers grown on (111) silicon by molecular-beam epitaxy
Authors: Sánchez A. M. , Pacheco F. J. , Molina S. I. , Garcia R. , Ruterana P. , Sánchez-Garcı́a M. A. , Calleja E.
Published: July 2002

Transmission electron microscopy is used to investigate GaN layers grown on Si(111) substrates by plasma-assisted molecular-beam epitaxy. These layers were grown on top of different AlN buffer layers. Multiple-beam dark-field techniques applied to both cross-sectional and planar-view samples show the presence of inversion domains. These domains grow directly from the interface with the Si(111) substrate. Such observations are related, as in the case of growth on sapphire, to the symmetry difference between wurtzite and diamond.
Anisotropies in magnetron sputtered carbon nitride thin films
Authors: Hellgren Niklas , Johansson Mats P. , Broitman Esteban , Hultman Lars , Sundgren Jan-Eric
Published: July 2002

Carbon nitride CNx (0⩽x⩽0.35) thin films, deposited by reactive dc magnetron sputtering in Ar/N2 discharges have been studied with respect to microstructure using electron microscopy, and elastic modulus using nanoindentation and surface acoustic wave analyses. For growth temperature of 100 °C, the films were amorphous, and with an isotropic Young’s modulus of ∼170–200 GPa essentially unaffected by the nitrogen fraction. The films grown at elevated temperatures (350–550 °C) show anisotropic mechanical properties due to a textured microstructure with standing basal planes, as observed from measuring the Young’s modulus in different directions. The modulus measured in the plane of the film was ∼60–80 GPa, while in the vertical direction the modulus increased considerably from ∼25 to ∼200 GPa as the nitrogen content was increased above ∼15 at. %.
Analysis of tip–sample interaction in tapping-mode atomic force microscope using an electrical circuit simulator
Authors: Sahin O. , Atalar A.
Published: July 2002

We present a mechanical model for the atomic force microscope tip tapping on a sample. The model treats the tip as a forced oscillator and the sample as an elastic material with adhesive properties. It is possible to transform the model into an electrical circuit, which offers a way of simulating the problem with an electrical circuit simulator. Also, the model predicts the energy dissipation during the tip–sample interaction. We briefly discuss the model and give some simulation results to promote an understanding of energy dissipation in a tapping mode.
Low temperature specific heat of bulk glassy and crystalline Zr41Ti14Cu12.5Ni10Be22.5 alloys
Authors: Bai Hai Yang , Luo Jian Lin , Chen Zhao Jia , Wang Wei Hua
Published: July 2002

The low temperature specific heat of Zr41Ti14Cu12.5Ni10Be22.5 alloys in glassy and crystalline states has been investigated. The glassy state of the alloy shows much larger specific heat than that of the crystalline state. The density of states at the Fermi level and Debye temperatures, θD of the alloys are determined. It is found that the density of states at the Fermi level for the glassy state is higher than that for crystalline state, the phenomenon is interpreted by localization of electrons in the glassy alloy. A much smaller value of θD in the glassy state indicates marked soften transverse phonons compared to its corresponding crystalline state.
One-dimensional cuprate as a nonlinear optical material for ultrafast all-optical switching
Authors: Ashida M. , Ogasawara T. , Tokura Y. , Uchida S. , Mazumdar S. , Kuwata-Gonokami M.
Published: July 2002

We examine the feasibility of ultrafast all-optical switching utilizing a one-dimensional cuprate Sr2CuO3 operable within the optical fiber communication window at room temperature by using the pump-probe spectroscopy and Z-scan measurements. The strength of the interband two-photon absorption in Sr2CuO3 is much larger than that of conventional semiconductors, and is comparable to the largest reported values in π-conjugated polymers. The intensity-dependent refractive index, however, is considerably larger than that of polymeric materials. We further show that the recovery of optical transparency after the photoinjection of carriers lies within picosecond time scale. Large nonlinearity, ultrafast response, and high damage threshold make the one-dimensional cuprate a potential material for multiterabits/second rate all-optical switch.
Consequence of isovalent rare earth substitution to magnetic irreversibility in cation-stoichiometric CuBa2RECu2O6.93±0.01
Authors: Yasukawa Yukiko , Nakane Takayuki , Yamauchi Hisao , Karppinen Maarit
Published: July 2002

For a series of CuBa2RECu2O7−δ (Cu−1(Ba)2RE12; RE= rare earth element) single-phase cation-stoichiometric samples with a fixed oxygen content, δ=0.07±0.01, a clear dependence of the Hirr characteristics on the ionic radius of RE is revealed. With decreasing ionic radius of RE, the Hirr characteristics are remarkably enhanced such that the samples containing heavy REs exhibit very high Hirr values. This result implies that through isovalent cation substitution alone carrier-density distribution and thereby the superconductivity characteristics may be controlled.
Systematics of elasticity: Ab initio study in B1-type alkaline earth oxides
Authors: Tsuchiya T. , Kawamura K.
Published: July 2002

The elastic properties and their pressure dependence of four B1-type alkaline earth oxides, MgO, CaO, SrO, and BaO, are calculated using the ab initio full-potential linear muffin-tin-orbital (FP-LMTO) generalized gradient approximated (GGA) method to elucidate their systematics. The calculated results agree quite well with the comparable experimental data. The large pressure dependence of c11 and c44 of MgO observed over 25 GPa is not predicted as well as the previous local-density approximation (LDA) calculations. It is inferred that the high-pressure measurement of elastic constant is quite sensitive to nonhydrostaticity. The deviation from the Cauchy relation and the elastic anisotropy are investigated. It is found that the interatomic interaction in SrO is nearest to the two-body force and the many-body contribution is largest in MgO. The elastic anisotropy in SrO and BaO are almost the same and only MgO has a large positive anisotropy under low pressure. The normalized elastic constants cij′ are introduced for more detail analysis. It is found that while there is no substantial difference in c11′ and c12′ of the four oxides, only c44′ and its pressure dependence vary systematically. The difference in the Cauchy deviation and elastic anisotropy of alkaline earth oxides under pressure is characterized by c44.