bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-assisted low temperature processing of Pb(Zr, Ti)O3 thin film
Authors: Zhu Yongfei , Zhu Jinsong , Song Yoon J. , Desu S. B.
Published: July 2002

A method for lowering the processing temperature of PbZr1−xTixO3 (PZT) films was developed utilizing a laser-assisted two-step process. In the first step, perovskite phase was initiated in the PZT films to a furnace anneal at low temperatures in the range of 470–550 °C, depending on the Zr/Ti ratio. Later, the films were laser annealed (using KrF excimer laser) at room temperature to grow the perovskite phase, and to improve microstructure and ferroelectric properties. It was found that this two-step process was very effective in producing excellent quality ferroelectric PZT films at low temperatures. It should be noted that although laser annealing of amorphous and/or pyrochlore films directly (one-step process) produced perovskite phase, the ferroelectric properties of these films, irrespective of the composition, were rather unattractive. Some possible reasons for the ineffectiveness of the one-step process were discussed.
Nanometer-scale patterning of self-assembled monolayer films on native silicon oxide
Authors: Inoue A. , Ishida T. , Choi N. , Mizutani W. , Tokumoto H.
Published: July 2002

A nanoscale-patterning method on silicon oxide using a self-assembled monolayer (SAM) was developed. The silicon surface with native oxide was additionally oxidized locally in dry nitrogen atmosphere by the field-induced oxidation (FIO) technique using an atomic force microscope with a conductive cantilever, and then immersed in octadecyltrichlorosilane (OTS) solution. The contact angle and topography image revealed that the OTS layer was formed only on the native oxide. In contrast, when FIO was performed under the humidity of 88%, OTS SAM was formed on both FIO and native oxide. These results indicate that SAM formation on silicon oxides can be locally suppressed by FIO in a dry environment. By using this technique, we could fabricate a line structure of OTS SAM as narrow as 22 nm.
Microguns with 100-V electron beams
Authors: Binh Vu Thien , Semet V. , Guillot D. , Legagneux P. , Pribat D.
Published: July 2002

The microgun is a combination of a nanotip and a microlens which is composed of two planar micron-size bore electrodes and a coplanar four-pole deflector microfabricated on the same Si chip. The focusing and deflection characteristics of the microgun, working as an immersion lens at 100 V, have been studied both experimentally and by numerical simulations. Results show unique electron optics properties due mainly to the coherence of the electron beam emitted from the nanotip and to the noninteraction of the incident electrons with the different microelectrodes. The focus spot can reach nanometric dimensions with minimum aberrations and a deflection amplitude of ∼2.5 mrad/V.
1.1 W continuous-wave, narrow spectral width (<1 Å) emission from broad-stripe, distributed-feedback diode lasers (λ=0.893 μm)
Authors: Earles T. , Mawst L. J. , Botez D.
Published: July 2002

By etching a distributed-feedback grating directly into the Al-free optical confinement region of a 100 μm stripe InGaAs/InGaP/GaAs diode laser, 1.1 W cw front-facet output power has been obtained at 0.893 μm with a spectral full width at half maximum of 0.9 Å. These devices have 1 mm long cavities and shallow gratings with a coupling coefficient, κ∼7 cm−1. The combination of long device length and low grating coupling results in both efficient operation as well as a longitudinally uniform field profile. As a result, all excited lateral modes oscillate at the same longitudinal cavity resonance to high power levels. Using shallow gratings etched in an InGaP upper confinement layer permits the growth of a high-quality cladding layer over the grating surface yielding excellent device performance. Facet-coated (5%/95%) devices demonstrate external differential quantum efficiencies of 51% and peak wallplug efficiencies of 32% at 1.1 W cw output power.
Adjustable x-ray phase plate and phase modulator
Authors: Polikarpov Igor
Published: July 2002

Diffractive birefringence of a crystal in the x-ray region is shown to be adjustable by high-frequency ultrasonic waves (USWs). An increase in diffractive birefringence can be used for fine tuned transformation of linearly polarized synchrotron radiation into circular polarized x rays by a quarter-wave plate. For a stationary USW, x-ray polarization changes with the ultrasound frequency, providing the design parameters for an x-ray phase modulator.
Microwave power handling in engineered YBa2Cu3O7−δ grain boundaries
Authors: Habib Y. M. , Oates D. E. , Dresselhaus G. , Dresselhaus M. S. , Vale L. R. , Ono R. H.
Published: July 2002

Microwave-frequency (rf) power-dependence measurements performed on thin-film YBa2Cu3O7−δ grain boundaries engineered on sapphire bicrystal substrates with misorientation angles of θ=2°, 5°, 10°, and 24° are presented. The data are compared to measurements on films grown on single-crystal substrates. A stripline-resonator measurement technique is employed. The rf results are compared to dc measurements performed on a four-point test structure on the same substrate as the resonator. The measurements demonstrate that low-angle grain boundaries (θ⩽10°) have little effect on the rf power handling, while the high-angle grain boundaries (θ=24°) cause large nonlinear losses due to Josephson vortices created by rf currents.
In situ ultrasonic monitoring of photoresist development
Authors: Morton Susan L. , Degertekin F. Levent , Khuri-Yakub B. T.
Published: July 2002

We have developed an in situ method to measure the change in thickness of photoresist during development. The phase of a high frequency ultrasound signal is monitored as it is reflected from the silicon/photoresist interface during resist development. The method was tested using a 1.5 μm film of Shipley 1811 resist. The total phase change during development of 19° was consistent with theoretical calculations at 280 MHz, and this change was used to obtain the resist thickness during development. The method was used to find the development rate of this positive-tone resist as a function of exposure dose in the 20–68 mJ/cm2 range. As expected, there was an increase in development rate as the exposure time increased; this continued up to about 40 s of exposure, beyond which the rates were essentially unchanged. Measurements on a wafer with microelectronic devices ranging in topography from 0.10 to 1.0 μm show that the method is applicable to wafers with typical circuit topography.
Te substitution in disordered dilute Se1−xTex alloys
Authors: Bhatnagar A. K. , Srivastava Vipin , Reddy K. V.
Published: July 2002

Photoacoustic absorption measurements at room temperature are reported for Se1−xTex alloys in both crystalline and amorphous states for 0<x⩽0.3. The optical energy gap thus measured shows two features: (a) the gap decreases linearly as x increases with a change of slope at x=0.1 for both crystalline and amorphous alloys; and (b) the difference in the gaps corresponding to the amorphous and crystalline phase remains remarkably constant over the entire range of x(0–0.3) studied here. We attribute the result (a) to the onset of “quantum percolation” at x=0.1, and deduce from (b) that introduction of Te apparently does not affect the structural disorder. The results are argued to yield vital information about the restrictive nature of Te substitution into host Se.
Impact of the free electron distribution on the random telegraph signal capture kinetics in submicron n-metal–oxide–semiconductor field-effect transistors
Authors: Lukyanchikova N. B. , Petrichuk M. V. , Garbar N. P. , Simoen E. , Claeys C.
Published: July 2002

In this letter, the role of the free electron distribution on the capture kinetics of repulsive random telegraph signals in deep submicron n-channel metal–oxide–semiconductor field-effect transistors is studied. The inversion layer density and profile is varied by changing simultaneously the substrate and the gate bias of the transistor which is in linear operation at a constant drain current I. Detailed results are obtained for a class of repulsive trap centers when charged by an electron, which show a I−m variation of the capture time constant, with m>1. Such a nonstandard behavior can be understood in the framework of the Coulomb blockade model, whereby the image charge of the trapped carrier is stored on the gate electrode and in the inversion and depletion layer in the silicon substrate. As is shown here the capture time constant is a unique function of the ratio of the inversion layer surface density and the squared thickness of the inversion layer.
Fluorine diffusion and accumulation in Si step-doped InAlAs layers
Authors: Wakejima A. , Onda K. , Fujihara A. , Mizuki E. , Kanamori M.
Published: July 2002

The quantitative relation between fluorine (F) accumulation and Si donor concentration in n-InAlAs layers on InP substrate was investigated for several kinds of step-doped InAlAs samples using secondary ion mass spectroscopy. From the depth profile of F and Si donors in a periodic i-/n-InAlAs sample, we found that F accumulates only in n-InAlAs layers, passing through i-InAlAs layers. We also found that the amount of F accumulation in an n-InAlAs layer depends on the Si doping concentration. The experimental results can be explained by considering two states of F. In one state, F is bound to a Si donor and immobile, and in the other it is free and can diffuse.
On the synthesis and magnetic properties of Nd(Fe,Mo,Ti)12
Authors: Cheng Q. M. , Lin J. H. , Su M. Z.
Published: July 2002

NdFe 10+x Mo 2−2x Ti x and NdFe10+xMo2−x (0⩽x⩽1.0) have been synthesized by using a reduction-diffusion process with superfine precursor particles as starting materials. The easy direction of magnetization of the NdFe10+xMo2−2xTix system has been determined by ac susceptibility and x-ray diffraction of the aligned samples. By comparison with NdFe12+xMo2−x, a magnetic phase diagram of the NdFe10+xMo2−2xTix system has been proposed.
Two different domains in a cubic boron nitride (111) surface observed by friction force microscopy
Authors: Takami Tomohide , Kusunoki Isao , Suzuki Katsunori , Loh Kian Ping , Nishitani-Gamo Mikka , Sakaguchi Isao , Taniguchi Takashi , Ando Toshihiro
Published: July 2002

A single-crystalline cubic boron nitride (c-BN) (111) surface has been studied by atomic force microscopy with simultaneous measurements of normal atomic force (constant height mode and constant force mode) and lateral (friction) force in air. On the friction force mode the different two domains observed can be attributed to the termination of the surface; boron (A side) or nitrogen (B side). 2.6 Å periodicity corresponding to the 1×1 surface unit cell as of c-BN (111) (as=a0/√=2.56 Å, where a0 is the lattice constant, 3.62 Å) has been observed also on the friction force mode, which is in agreement with our low-energy electron diffraction measurement.
Effect of twinning on the grain shape of crystallized amorphous Si0.7Ge0.3 thin films on SiO2
Authors: Kim Hong Seung , Lee Jeong Yong
Published: July 2002

The grain morphology of Si0.7Ge0.3 depends on the number of the primary noncoplanar twin variants formed at the early stage of solid-phase crystallization. The grain with major twin bands of a single twin variant parallel to a {111} plane develops an elongated shape, owing to the preferential growth in a 〈112〉 direction along twins. When the grain has major twin bands of two or more noncoplanar twin variants, the growth front between noncoplanar twin bands develops as fast as the 〈112〉 direction along twins propagates, because such a growth front is formed from a {111} ledge. As results, the grain becomes more or less equiaxed due to the increasing number of primary, noncoplanar twin variants.
Deposition of transition metal carbide superlattices using C60 as a carbon source
Authors: Norin Lars , Högberg Hans , Lu Jun , Jansson Ulf , Malm Jan-Olle
Published: July 2002

Epitaxial films of TiC and VC can be deposited at low temperatures on Mg(001) substrates by coevaporation of the metals with C60 in a ultrahigh vacuum system. This process was used to deposit TiC/VC (001) superlattices on MgO(001) at 400 °C. The superlattice structure was characterized with low electron energy diffraction, x-ray diffraction, and transmission electron microscopy (TEM). Cross-sectional high-resolution TEM showed good registry between the different carbide layers.
Photoluminescence and band edge alignment of C-induced Ge islands and related SiGeC structures
Authors: Schmidt O. G. , Eberl K.
Published: July 2002

Growth of less than 2 monolayers Ge on a submonolayer amount of predeposited C on Si results in the formation of very small Ge quantum islands. In a photoluminescence study, we compare these C-induced Ge (CGe) dots with carefully chosen reference structures incorporating the same total amount of C and Ge but with different deposition orders and with varied C distribution below the Ge islands. Our investigations imply that the special combination of pregrown low surface mobility C and post-grown high surface mobility Ge constitutes a distinct microstructure within the SiGeC material system, causing dot formation at a very early stage and showing particularly intense photoluminescence signal. Moreover, structures combining CGe dots with Si1−yCy quantum wells are well explained by the model of spatially indirect type-II recombination within the CGe islands.
Bistability of charge accumulated in low-temperature-grown GaAs
Authors: Brounkov P. N. , Chaldyshev V. V. , Suvorova A. A. , Bert N. A. , Konnikov S. G. , Chernigovskii A. V. , Preobrazhenskii V. V. , Putyato M. A. , Semyagin B. R.
Published: July 2002

Capacitance–voltage characteristics were studied at various temperatures for Schottky barriers formed on n-GaAs/low-temperature-grown (LT)-GaAs/n-GaAs sandwich structures. Charge accumulation at deep traps in the LT-GaAs layer was observed. At room temperature, the C–V characteristics were found to be step-like with a wide plateau originated from emission of electrons accumulated in the LT-GaAs layer. At the temperature below 100 K, the electron emission from the LT-GaAs layer was completely suppressed. At intermediate temperatures (150–200 K), an effect of charge bistability was observed, which manifested itself as a hysteresis in the capacitance under sweeping the reverse dc bias. We suppose that the phenomenon takes place when the sweeping rate is higher than the electron emission rate but lower than the electron capture rate by the deep traps in the LT-GaAs layer.
The role of lead component in second-harmonic generation in lead silica by electron-beam irradiation
Authors: Qiu Mingxin , Pi F. , Orriols G.
Published: July 2002

It is found that the second-order nonlinearity induced in lead silica by electron-beam irradiation increases linearly with the lead percentage of the glass and a value of 4 pm/V has been estimated for ZF7 lead silica. The electrostatic field created under the glass surface increases with the lead percentage, which can be explained by the theory of stopping collisions of fast electrons. The layer depth is found proportional to the inverse square root of the lead percentage. The accumulative effect of electron irradiation for inducing the nonlinearity appears limited by the breakdown threshold in the charged layer. An optimum total electron charge per unit of scanned area of 0.29 C/m2 has been determined for SF2 glass. Nonlinearity layer depths of 1.9–4.1 μm have been estimated by chemical etching for different lead silica and electron voltages, and the coefficients of the Bohr–Bethe penetration formula have been determined for SF2 glass.
Efficient contour generation and tracking of a moving object with a rhodium-doped BaTiO3 crystal working in the near infrared
Authors: Mathey Pierre , Jullien Pierre , Rytz Daniel
Published: July 2002

The depletion efficiencies and their corresponding constant times are investigated in four differently doped barium titanate crystals at the near-infrared wavelength of 854 nm. It is shown that the rhodium-doped crystal offers the best results. Satisfactory motion tracking and edge enhancement are demonstrated with an optical photorefractive novelty filter.
Interaction of vacuum-arc-generated macroparticles with a liquid surface
Authors: Anders André
Published: July 2002

The concept of trapping vacuum-arc-generated macroparticles by a liquid is introduced. Experiments have been performed using a pulsed vacuum arc plasma source operating with a carbon cathode. Vacuum pump oil was used as the trapping liquid in vacuum. It was experimentally shown that trapping did not work as anticipated: a substantial number of particles experienced elastic reflection from the liquid surface. With simplified energy and momentum balances it is shown that the liquid behaves increasingly like a solid when the approaching particle is fast. A significant portion of its kinetic energy is transformed into deformation energy which can reappear as kinetic energy of the reflected particle. Particle reflection is likely to be additionally supported by a Leidenfrost-type effect: a thin oil vapor layer of relatively high pressure can be formed between the liquid surface and the macroparticle caused by the macroparticle’s high temperature.
Multistable antiferroelectric liquid-crystal optical modulator
Authors: Vorflusev Valery , Kumar Satyendra
Published: July 2002

An electro-optical element based on antiferroelectric liquid crystal (AFLC) has been prepared by photopolymerization-induced anisotropic phase separation of a solution of an AFLC and a prepolymer. It consists of two adjacent layers, one comprised of the isotropic polymer and the other of the AFLC aligned by surface treatment of the adjacent substrate. The electro-optical properties show that these devices are either optically monostable or multistable (at zero field) with maximum memory angle of ∼15°. A qualitative model to describe the origin of memory in these AFLC/polymer composites is discussed.
Sub-5 nm gold dot formation using retarding-field single ion deposition
Authors: Hori M. , Woodham R. G. , Ahmed H.
Published: July 2002

Gold dots of 2.5 nm mean diameter and 0.8 nm standard deviation have been fabricated successfully on chromium oxide (CrOx) thin films. The CrOx thin films were deposited on Si substrates by sputtering and gold dots were subsequently deposited by a retarding-field single ion deposition (RSID) technique. The formation of gold dots has been investigated systematically with landing energies from 100 to 900 eV and doses from 10 to 40 C/m2. The dot diameter and density could be controlled by varying the landing energy and dose of gold ions arriving on the surface. The formation of single electron devices, quantum dots, nanopillars, and other nanoscale device structures is proposed using the RSID technique.
Evidence on the formation of a heavily Ge-doped layer in Pd/Ge-based ohmic contact to pseudomorphic high electron mobility transistor
Authors: Lee Jong-Lam , Kim Yi-Tae
Published: July 2002

Microstructural evidence on the formation of a heavily Ge-doped layer below Pd/Ge-based ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was obtained. The contact resistivity is decreased by two orders of magnitude as InGaAs channel is intermixed. This originates from the formation of Au2Al and Au7Ga2 compounds below the contacts during annealing, via production of group III vacancies. The vacancies play a role in producing free electrons by the incorporation of Ge atoms, resulting in intermixing of InGaAs as well as reduction of contact resistivity.
Simultaneous phase separation and basal-plane atomic ordering in InxGa1−xN
Authors: Shimotomai Michio , Yoshikawa Akihiko
Published: July 2002

Reported discrepancy of phase separation in InxGa1−xN films between experimental studies and theoretical calculations based on the usual regular solution model is discussed from the standpoint of phase diagram. The inclusion of higher-order pairwise interactions in the theoretical model may allow the system to undergo a spinodal decomposition in an asymmetrical manner as revealed by experiments. It is suggested that basal-plane atomic ordering in the In-rich precipitates should accompany the decomposition.
Electroabsorption spectroscopy study of an azopolymer film fabricated by electrostatic adsorption
Authors: Yang Ke , Balasubramanian Srinivasan , Wang Xiaogong , Kumar Jayant , Tripathy Sukant
Published: July 2002

Electroabsorption spectroscopy measurements are reported on a multilayer thin film of a prototypical azopolymer. The sample was prepared by sequentially dipping the substrate into aqueous solutions containing the polycation poly(diallyl dimethyl ammonium chloride) and the polyanion CH-1A-NS, an epoxy based polymer with azobenzene chromophore. The measured ratio of χ3333(3) to χ1133(3) for the electrostatically assembled film is 4, which indicates that the chromophores in this film are oriented preferentially perpendicular to the film plane instead of an isotropic distribution in three-dimensional space. For comparison, a spin coated film of CH-1A-NS was studied by the same method. The ratio of χ3333(3) to χ1133(3) for the spin coated film is found to be 1.9, indicating that the same chromophores in the spin coated film are oriented preferentially in the film plane. These results imply that the process of electrostatic layer-by-layer adsorption leads to a preferred orientation of the chromophores, perpendicular to the film plane, while the same chromophores in the spin coated film lie predominately in the plane of the substrate.
Transient thermochromism during ArF excimer laser ablation of poly(3-dodecylthiophene) films
Authors: Tsunoda Katsunori , Kakinuma Keiko , Yajima Hirofumi , Ishii Tadahiro
Published: July 2002

The photothermal effects involved in ArF (193 nm) laser ablation of poly(3-dodecylthiophene) (PDT) films, which have the characteristics of fusibility and thermochromism, were studied using atomic force microscopy and transient absorption spectroscopy. A molten layer was observed in the irradiated region of the PDT films. The behavior of the transient absorption spectra corresponding to the thermochromism showed a rapid increase in temperature during laser duration. A heating rate of approximately 5×109 deg/s was obtained. The obtained findings reveal that photothermal effects are significantly involved in the ablation process.
Observation of wire width fluctuations in the optical spectra of GaAs–AlGaAs V-groove quantum wires
Authors: Tribe W. R. , Steer M. J. , Forshaw A. N. , Schumacher K. L. , Mowbray D. J. , Whittaker D. M. , Skolnick M. S. , Roberts J. S. , Hill G.
Published: July 2002

Optical spectroscopy of a single GaAs–AlGaAs V-groove quantum wire is reported. Photoluminescence spectra are recorded over a five order-of-magnitude variation of incident laser power. With decreasing laser power, a continuous transition is observed from multiple wire subband occupancy to single subband occupancy through to the observation of the recombination of excitons localized by discrete potential fluctuations. The effect of single monolayer wire thickness fluctuations on the subband transitions is calculated using a finite difference technique which includes the Luttinger Hamiltonian description of the valence band states. These calculations indicate that the main contribution to the exciton localization potential is probably monolayer fluctuations of the wire thickness.
Current-induced persistent capacitance in Au/n-In0.08Ga0.92As0.51P0.49 Schottky contacts
Authors: Kwon Ho Ki , Kim Y. , Lim H.
Published: July 2002

The zero-bias capacitance of a Schottky diode formed on a nominally undoped In0.08Ga0.92As0.51P0.49 is found to be persistently increased after a high current injection at low temperatures. The increment of capacitance grows as the amplitude or duration of the current pulse is increased. When a high current is injected at low temperatures before the deep level transient spectroscopy measurements, the concentration of the so-called ET1 defects is decreased. It is discussed that all these results are related to the hole injection from the Schottky contact and the charge-state controlled stability of the ET1 defects.
Charge-ring model for the charge-induced confinement enhancement in stacked quantum-dot transistors
Authors: Rudin A. M. , Guo L. J. , Glazman L. I. , Chou S. Y.
Published: July 2002

A model is proposed to explain the charge-induced confinement enhancement observed in a stacked quantum-dot transistor that has a floating dot on top of a channel quantum dot. The model assumes that the charge on the floating dot distributes on its rim, forming a ring and creating a confinement potential that squeezes the electrons in the channel dot toward its center. The charge on the floating dot can be calculated from the device geometry and from the measured threshold voltage difference before and after the charging. Given the charge on the floating dot, the spatial confinement and the energy level spacing increase induced by the charging can be obtained. The calculation based on the model agrees with the observed increase of the energy level spacing.
Monolithic integration of a SiGe/Si modulator and multiple quantum well photodetector for 1.55 μm operation
Authors: Li Baojun , Li Guozheng , Liu Enke , Jiang Zuimin , Qin Jie , Wang Xun
Published: July 2002

The monolithic integration of a SiGe/Si rib waveguide modulator and multiple quantum well photodetector prepared by molecular beam epitaxy is achieved. The low dark current of 49.8 nA at −5 V reverse bias is measured and a modulation depth of 90% at 2.8 V modulation bias is obtained. The external quantum efficiency at λ=1.55 μm is estimated to be 18.2%.
Interfacial origin of inverse magnetoresistance in uncoupled Fe/Si/Fe/Ru sandwiches
Authors: Dinia A. , Guth M.
Published: July 2002

Experimental evidence of inverse magnetoresistance for ferromagnetic layers separated by a Si layer is reported. A series of Fe/Si sandwiches have been prepared by ion-beam sputtering at room temperature onto a glass substrate with the following nomenclature: glass/Si20 nm/Fe5 nm/Six nm/Fe5 nm/Ru2 nm. Magnetization measurements have been performed at 300 K and show no evidence of antiferromagnetic exchange coupling. However, the magnetoresistance curves recorded at 300 K are very interesting and show a reversed magnetoresistance for sandwiches with Si spacer layer thicknesses between 1.2 and 1.5 nm. Indeed, the resistivity is smaller at zero field than at saturation. This reversed magnetoresistance is due to the superparamagnetic interfaces and finds its origin in the difference of the electronic nature of the Fe/Si interfaces and Fe/Ru interfaces. Indeed, iron silicide Fe1−ySiy at Fe/Si interfaces have scattering spin asymmetry ratios (α=ρ↓/ρ↑) larger than 1, whereas, Fe with Ru impurities at the Fe/Ru interfaces present scattering spin asymmetry ratios lower than 1.
Miniature high-sensitivity quartz tuning fork alternating gradient magnetometry
Authors: Todorovic M. , Schultz S.
Published: July 2002

We present a high-sensitivity alternating gradient magnetometer. It uses inexpensive, commercially available, piezoelectric quartz tuning fork resonators as vibration amplitude sensors of a vibrating magnetic sample in an alternating gradient field. The technique exploits the high quality factor, high resonant frequency, and small spring constant of the quartz tuning fork. The instrument also utilizes miniature gradient coils, which allow for large field gradients to be applied to the sample while minimizing the diamagnetic background signal. An instrument noise floor of ∼1×10−12 emu/(Hz) has been achieved at room temperature in vacuum. Hysteresis loop measurements on micron sized magnetic samples are demonstrated.
Complete suppression of boron transient-enhanced diffusion and oxidation-enhanced diffusion in silicon using localized substitutional carbon incorporation
Authors: Carroll M. S. , Chang C-L. , Sturm J. C. , Büyüklimanli T.
Published: July 2002

In this letter, we show the ability, through introduction of a thin Si1−x−yGexCy layer, to eliminate the enhancement of enhanced boron diffusion in silicon due to an oxidizing surface or ion implant damage. This reduction of diffusion is accomplished through a low-temperature-grown thin epitaxial Si1−x−yGexCy layer which completely filters out excess interstitials introduced by oxidation or ion implant damage. We also quantify the oxidation-enhanced diffusion (OED) and transient-enhanced diffusion (TED) dependence on substitutional carbon level, and further report both the observation of carbon TED and OED, and its dependence on carbon levels.
Observation of incident angle dependent phonon absorption in hydrogenated amorphous silicon nitride thin films
Authors: Li Tong , Kanicki Jerzy
Published: July 2002

We have demonstrated the existence of longitudinal- and transverse-like optical modes of Si–N bond in vibrational absorption spectrum of hydrogenated amorphous silicon nitride thin films. One of the longitudinal-like optical resonances coincides with the transverse-like mode of Si–O bond, and the other closely neighbors the bending mode of N–H bond. We have also shown that the conventionally assigned asymmetric stretching mode of Si–N bond is merely a transverse-like mode of the bond. The microstructures of both longitudinal- and transverse-like modes can well be apprehended by a p-polarized beam at an oblique incidence light, especially at Brewster angle incidence. The spectrum distortion induced by interference fringes can be eliminated at this condition.
Electronic transport properties of (001)/(110) oriented La2/3MnO3−δ thin films
Authors: Chen Chun-Che , de Lozanne Alex
Published: July 2002

We report the unusual transport properties found in La2/3MnO3−δ thin films on Al2O3 (11̄02). Powder x-ray diffraction shows that the film has a mixture of perpendicular (110) and (001) crystal orientations. Unlike epitaxial or polycrystalline La1−xMnO3−δ samples, in which the peak resistance temperature Tp shifts toward a higher temperature under the influence of magnetic field, the Tp of this particular film remains almost the same even in fields up to 5 T. The film becomes insulating at a low temperature Tm(∼45 K), but the trend is reversed by the applied magnetic field.
Electronic and transport properties of N-P doped nanotubes
Authors: Esfarjani Keivan , Farajian Amir A. , Hashi Yuichi , Kawazoe Yoshiyuki
Published: July 2002

Electronic properties of a doped zigzag nanotube are investigated by a self-consistent tight-binding method. We propose that a doped nanotube with donor atoms on one side and acceptors on the other can function as a nano diode. It is shown that a potential step in the tube, created by two different types of doping in this case, causes the nonlinear rectifying effect.
Depth profile and lattice location analysis of Sb atoms in Si/Sb(δ-doped)/Si(001) structures using medium-energy ion scattering spectroscopy
Authors: Kobayashi T. , McConville C. F. , Dorenbos G. , Iwaki M. , Aono M.
Published: July 2002

Medium-energy coaxial impact-collision ion scattering spectroscopy has been used to study the depth profile and lattice location of Sb atoms in Si/Sb(δ-doped)/Si(001) structures prepared by solid phase epitaxy. The Sb atoms are observed to diffuse into the Si capping layer at concentrations much higher than the solubility limit in a Si crystal. In addition, the concentration of diffused Sb atoms does not show a monotonic decrease with increasing distance from the δ-layer plane. The lattice locations of the diffused Sb atoms are found to be strongly dependent on the distance from the location of the original Sb δ layer.
Local coordination of Ga impurity in hydrogenated amorphous germanium studied by extended x-ray absorption fine-structure spectroscopy
Authors: Dalba G. , Fornasini P. , Grisenti R. , Rocca F. , Comedi D. , Chambouleyron I.
Published: July 2002

The local structure of Ga-doped a-Ge:H films has been investigated by extended x-ray absorption fine-structure (EXAFS) fluorescence for impurity concentrations ranging from 1.5×1018 atoms cm−3 to 4.5×1020 atoms cm−3. The mean-coordination number of Ga atoms changes from around 4 (1.5×1018–1.5×1019 cm−3) to below 3 (1.5×1020–4.5×1020 cm−3) with rising concentration. The change from fourfold to threefold coordination occurs in a rather narrow impurity concentration range. The variance of the distance distribution function decreases with increasing Ga content, suggesting that well-ordered sites are present at high-impurity concentration. From EXAFS phase analysis the first Ga–Ge shell distance has been found to be 0.03 Å larger in the amorphous network than in Ga-doped crystalline Ge.
Extended x-ray absorption fine structure study on the cerium(IV)-induced DNA hydrolysis: Implication to the roles of 4f orbitals in the catalysis
Authors: Shigekawa Hidemi , Ishida Masahiko , Miyake Koji , Shioda Ryu , Iijima Yoshitoki , Imai Takamitsu , Takahashi Hideyuki , Sumaoka Jun , Komiyama Makoto
Published: July 2002

At various Ce(IV)/DPP (DPP: diphenyl phosphate) molar ratios, the structure of Ce clusters in aqueous solutions was studied by extended x-ray absorption fine structure measurements. Although the Ce–Ce bond was strong in the absence of DPP, the corresponding signal was significantly reduced when the Ce(IV)/DPP molar ratio was 1. The result indicates the existence of a strong interaction between Ce(IV) ions and DPP, and suggests the formation of a Ce–DPP structure in solution. With an increase in the molar ratio, the signal of Ce–Ce bonds increased again, and exceeded that observed in the absence of DPP, suggesting the formation of a Ce–Ce–DPP structure. Ce(IV) ions in the complexes were found to have ∼0.67 4f electrons. On the other hand, no measurable charge transfer was observed in the case of Ce(III) ions. These results demonstrate the role of the 4f orbital of Ce(IV) ions for its enormous activity for DNA hydrolysis.
Sm(Co, Cu, Ni) thin films with giant coercivity
Authors: Prados C. , Hadjipanayis G. C.
Published: July 2002

Nanostructured Sm(Co, Ni, Cu) thin films have been obtained by heat treating as-deposited sputtered amorphous films. The room-temperature coercivity increases from less than 100 Oe in the amorphous state to 42 kOe in a SmCo2Cu3 sample annealed 30 min at 550 °C. Structural data in the optimum samples suggest a particle size around 10 mn. Magnetic viscosity measurements indicated that the switching volume is of the same order as the crystallite size. Remanence measurements showed that interparticulate interactions are magnetizing and rather independent of the crystallization stage. These data indicate that the huge coercivity enhancement is due to domain-wall pinning at high anisotropy Sm–Co precipitates.
Effects of high magnetic field on the morphology of carbon nanotubes and selective synthesis of fullerenes
Authors: Yokomichi Haruo , Sakima Hiroyuki , Ichihara Masaki , Sakai Fumiko , Itoh Kikuo , Kishimoto Naoki
Published: July 2002

Carbon nanotubes and fullerenes were synthesized by arc discharge in a He gas atmosphere under a high magnetic field up to 10 T. Morphology and the yield of these nanotubes were investigated by scanning electron microscopy and transmission electron microscopy (TEM). The yield and type of fullerenes were also evaluated by ultraviolet visual spectroscopy. TEM images revealed that thin collapsed nanotubes having larger curvature were synthesized under a high magnetic field, in particular at 10 T. Furthermore, the ratio of C70 to C60 concentration was found to vary depending on the magnitude of the magnetic field during arc discharge. Based on these results, the effects of magnetic field on the synthesis of carbon nanotubes and fullerenes are discussed.
Pattern formation and shadow instability in collimated energetic molecular beam growth of silicon
Authors: Roadman S. E. , Levine S. W. , Zheng Y.-J. , Clancy P. , Engstrom J. R.
Published: July 2002

Epitaxial silicon thin films were deposited on Si(100) substrates at variable angles of incidence using well-collimated supersonic molecular beams of disilane, Si2H6. The resulting thin-film surface topology has been examined using atomic force microscopy. Rough surface morphology is observed as the beam angle of incidence is increased above ∼60°. Thin films deposited at substrate temperatures ⩽600 °C exhibit anisotropic features, which are elongated in a direction perpendicular to the incident beam. Increasing the substrate temperature leads to films with increased root-mean-square roughness and larger characteristic features, maintaining a nearly constant feature aspect ratio. Analysis indicates that the film feature size is controlled by a competition between roughening driven by the shadow instability and smoothening driven by surface mass transport.
Fabrication of nano-structural arrays by channeling pulsed atomic beams through pulsed-laser standing-waves under off-resonant condition
Authors: Zhu X. D.
Published: July 2002

We show that it is feasible to produce one- and two-dimensional nano-structure arrays by passing microsecond pulsed atomic beams through microsecond laser standing-wave patterns under completely off-resonant condition. This method enables fabrication of vertically heterogeneous nanostructures such as multilayers with one pulsed laser system.
Noncontact continuous wavefront/diffractive acoustic elements for Rayleigh wave control
Authors: Clark M. , Sharples S. D. , Somekh M. G.
Published: July 2002

A laser is used to excite Rayleigh waves on a sample. The optical distribution of the laser energy as it strikes the sample is controlled using a computer generated hologram—this optical distribution determines the initial acoustic wavefront and hence the acoustic amplitude distribution. In this letter, we present two designs of acoustic elements which use diffraction of the Rayleigh waves as a means of controlling the acoustic amplitude distribution.
X-ray diffraction study of chalcopyrite ordering in epitaxial ZnSnP2 grown on GaAs
Authors: Francoeur S. , Seryogin G. A. , Nikishin S. A. , Temkin H.
Published: July 2002

We report on the structural characterization of epitaxial ZnSnP2 grown on GaAs (001). Ordering of Zn and Sn atoms in the cation sublattice is observed by high-resolution x-ray diffraction. By varying the growth conditions, samples with two distinct structures were obtained: one showing chalcopyrite ordering with the tetragonal axis oriented along the growth direction and the other showing no evidence of ordering. Chalcopyrite ordering was determined unambiguously by observing several characteristic reflections uniquely identifying this structure.
Negative capacitance in forward biased hydrogenated amorphous silicon p+-i-n+ diodes
Authors: Lemmi F. , Johnson N. M.
Published: July 2002

We present experimental results and a physical explanation for the negative values of the small-signal capacitance of forward biased hydrogenated amorphous silicon (a-Si:H) p+-i-n+ diodes. The device capacitance varies with the probe signal frequency. In the low frequency range the measured capacitance shows large negative values if the diode is sufficiently forward biased. Higher forward bias voltages shift this effect to higher frequencies. Time domain response of the device to a small voltage step and a Fourier transform of the resulting transient current provide a verification of the results. The time domain data also suggest the physical mechanism responsible for the overall dispersive behavior: separate and delayed trapping processes for holes and electrons at the interfaces with the two doped layers.
Reflection high-energy electron diffraction intensity oscillation during layer-by-layer oxidation of Si(001) surfaces
Authors: Watanabe Heiji , Baba Toshio , Ichikawa Masakazu
Published: July 2002

We have studied initial layer-by-layer oxidation of Si(001)-2×1 surfaces by using reflection high-energy electron diffraction (RHEED). We observed an intensity oscillation and a change in the streaky profile of a specular reflection spot in RHEED patterns during initial oxidation. These results indicate that layer-by-layer oxidation of Si surfaces is promoted by nucleation and lateral growth of two-dimensional oxide islands. We have also confirmed that a 1-monolayer-thick oxide has an ordered structure originating from the initial 2×1 reconstruction.
High-efficiency p–i–n detectors for the visible spectral range based on ZnSTe–ZnTe superlattices
Authors: Faschinger W. , Ehinger M. , Schallenberg T. , Korn M.
Published: July 2002

We demonstrate that ZnSTe–ZnTe superlattices, which are grown lattice matched on GaAs substrates by molecular-beam epitaxy, are well suited as a material for light detection in the visible spectral range. Due to their type-II band alignment, these superlattices have a small band gap compared to ZnSe and allow light detection for photon energies between 2.1 and 3.2 eV. In combination with ZnMgSSe, the response curve of the diodes shows a strong dependence on the applied reverse bias, so that they can be used as two-color devices. The obtained external quantum efficiencies are as high as 70%, and dark currents as low as 10−12 A/mm2 were obtained.
Direct measurement of the destruction of charge quantization in a single-electron box
Authors: Duncan David S. , Livermore Carol , Westervelt Robert M. , Maranowski Kevin D. , Gossard Arthur C.
Published: July 2002

We report here direct measurements of the destruction of charge quantization in a single-electron box, the first over the full range of box-to-lead conductance values from G≅0 to the conductance quantum GQ=2e2/h, using a sensitive single-electron transistor (SET) electrometer. The sensitivity of the electrometer is measured to be δq≅6×10−5e/√Hz and its superiority to conductance measurements of charge fluctuations is clearly demonstrated. As the rate of quantum mechanical tunneling from the box to its lead is increased, the quantization of charge is destroyed, disappearing entirely at G=GQ in agreement with theory.
Imaging of current paths and defects in Al and TiSi interconnects on very-large-scale integrated-circuit chips using near-field optical-probe stimulation and resulting resistance change
Authors: Nikawa K. , Saiki T. , Inoue S. , Ohtsu M.
Published: July 2002

The optical-beam-induced resistance-change-detection (OBIRCH) method has been improved by using a near-field optical probe as the heat source instead of a laser beam. The near-field OBIRCH method has two advantages over the conventional one: (1) its spatial resolution is higher (50 vs 400 nm) and (2) the optical-probe-induced resistance change caused by heating can be observed using a metallized probe without interference from a photocurrent created by electron–hole-pair generation. In the conventional-OBIRCH method, the laser beam creates not only a resistance change, but also a photocurrent that can mask the resistance change signals.
Optimal geometry for electron emission from a metallic grating
Authors: Haddad B. , Schächter L.
Published: July 2002

Field emission from a rectangular metallic grating is considered, ignoring space-charge effects. It is shown that there is an optimal geometry of the grooves for extraction of maximum current or current density.
CaF
2
:Yb
3+
+Pr
3+
codoped waveguides grown by molecular beam epitaxy for 1.3 μm applications
Authors: Lahoz F. , Daran E. , Lifante G. , Balaji T. , Muñoz-Yagüe A.
Published: July 2002

CaF 2 :Yb 3+ +Pr 3+ codoped thin films grown by molecular beam epitaxy have been studied in order to determine their ability to be used for optical amplification in telecommunication devices. The guiding behavior of the layers has been demonstrated and an increase in the refractive index has been measured for increasing Pr3+ and Yb3+ doping levels. Energy transfer between Yb3+ and Pr3+ ions has also been observed with different pump wavelengths. Room temperature 1.3 μm emission of Pr3+ ions has been detected when pumping in the absorption band of Yb3+, where high performance laser diodes already exist.
Polarization dynamics in vertical-cavity surface-emitting lasers with optical feedback through a quarter-wave plate
Authors: Masoller C. , Abraham N. B.
Published: July 2002

Square-wave switching of the intensities of the orthogonal linearly polarized components of the output of a vertical-cavity surface-emitting laser (VCSEL) found previously in experiments with polarization-changing optical feedback, is not found in rate equation models incorporating only birefringence and gain anisotropy, but is found in the model for VCSELs developed by San Miguel, Feng, and Moloney [M. San Miguel, Q. Feng, and J. V. Moloney, Phys. Rev. A 52, 1729 (1995)]. The dynamics is sensitive to both the feedback strength and the relaxation rate of the magnetization in the quantum well sublevels.
A 200 nm×2 mm array of organic light-emitting diodes and their anisotropic electroluminescence
Authors: Suganuma Naotoshi , Adachi Chihaya , Koyama Toshiki , Taniguchi Yoshio , Shiraishi Hiroshi
Published: July 2002

We demonstrated the fabrication of a 200 nm×2 mm array of organic light-emitting diodes (OLEDs) on a glass substrate. The photolithographic technique using an optical phase shift mask allowed us to construct a super-fine resolution patterning of OLEDs. A single organic electroluminescent (EL) layer composed of an inert poly(methylmethacrylate) polymer binder and tetraphenylbendidine and tris(8-quinolinol) aluminum molecules was fabricated on a fine-resolution photoresist patterning by a spin coating method. The lines and spaces of the photoresist patterning were 200 nm. The emitting area was well confined by the regular array of residual photoresist resin walls. Finally, a MgAg cathode layer was uniformly deposited on the organic layer. We observed anisotropic EL spectra between the directions perpendicular and parallel to the patterning of OLED arrays. Furthermore, we observed a large difference of EL intensities between them. We assume that the anisotropic EL characteristics are caused by the confinement effect of photons inside the submicrometer-sized OLED array.
Exchange biasing in ferromagnetic amorphous wires: A controllable micromagnetic configuration
Authors: Freijo J. J. , Hernando A. , Vázquez M. , Méndez A. , Ramanan V. R.
Published: July 2002

Nonmagnetostrictive Co-rich amorphous wires, 130 μm in diameter, were stress annealed to induce a transverse anisotropy. The resultant structure consists of a circular-magnetization single domain except in a thin core, 2 μm in diameter, where magnetization is axially oriented. The wall interconnecting the outer shell with the core magnetization induces a local helical anisotropy during the annealing. As a consequence, a strong link between the magnetization directions in both regions appears. It is shown that direct current axial fields produce remarkable shifts of the circular hysteresis loops.
On the sensitivity of the x-ray excited optical luminescence to the local structure of the luminescent Si sites of porous silicon
Authors: Dalba G. , Fornasini P. , Grisenti R. , Daldosso N. , Rocca F.
Published: July 2002

X-ray excited optical luminescence (XEOL) has been recorded in a wide x-ray energy range to obtain the extended x-ray absorption fine structure (EXAFS) at the Si K edge of porous silicon. A comparison between EXAFS measurements carried out simultaneously in photoluminescence yield (PLY) mode and in total electron yield (TEY) mode on red and orange porous silicon samples is presented. Experimental results suggest that TEY provides average structural information on all luminescent and nonluminescent Si sites. On the contrary, PLY is able to probe the local structure near the light emitting sites, and to monitor the modifications induced by current density changes during the sample preparation. PLY–EXAFS shows that the luminescent Si nanostructures are smaller and more disordered than the average structures of the porous layer probed by TEY, suggesting that the luminescent sites are located at the surface of the nanostructures.