bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain relaxation by directionally aligned precipitate nanoparticles in the growth of single-crystalline Gd-doped ceria thin films
Authors: Huang D. X. , Chen C. L. , Chen L. , Jacobson A. J.
Published: January 2004

Transmission electron microscopy has been used to investigate the microstructure and epitaxial behavior of gadolinium-doped ceria (Ce0.8Gd0.2O2−δ) thin films on single crystal (001) LaAlO3. The results show that the films have single-crystal cubic structure and a sharp interface with an interface relationship of (001)film∥(001)sub and [100]film∥[110]sub. Accompanying the high film crystallinity, a directionally aligned, precipitated nanoparticle structure has been observed. The precipitated particles have an average size of ∼4 nm, a Ga-rich composition of Ce0.7Gd0.3O2−δ, a rhombic shape with mainly {111} facets, and are uniformly distributed over the entire film area. The nanoparticles contribute a uniform tensile strain to the film that effectively compensates the compressive film strain induced by the substrate, and also leads to a uniform relaxation of the residual film strain by generating misfit dislocations at the film/particle interfaces. The high film crystallinity is believed to result from this uniform film strain relaxation mechanism.
Enhanced thermal stability of high-dielectric Gd2O3 films using ZrO2 incorporation
Authors: Cho M.-H. , Moon D. W. , Park S. A. , Rho Y. S. , Kim Y. K. , Jeong K. , Chang C. H. , Gu J. H. , Lee J. H. , Choi S. Y.
Published: January 2004

The thermal stability of Gd2O3 films, containing added Zr, was investigated using various techniques. The structural characteristics of epitaxial Gd2O3 are maintained on the Si(111) substrate when the Zr is codeposited along with Gd. The incorporation of ZrO2 into Gd2O3 improves the crystallinity of the film and no interfacial layers were observed. In particular, the structural stability with no deformation is greatly enhanced, and silicate formation is drastically suppressed, up to an annealing temperature of 800 °C. The interfacial defects caused by extensive interactions between Gd and Si are also minimized.
Measurement of the band offsets between amorphous LaAlO3 and silicon
Authors: Edge L. F. , Schlom D. G. , Chambers S. A. , Cicerrella E. , Freeouf J. L. , Holländer B. , Schubert J.
Published: January 2004

The conduction and valence band offsets between amorphous LaAlO3 and silicon have been determined from x-ray photoelectron spectroscopy measurements. These films, which are free of interfacial SiO2, were made by molecular-beam deposition. The band line-up is type I with measured band offsets of 1.8±0.2 eV for electrons and 3.2±0.1 eV for holes. The band offsets are independent of the doping concentration in the silicon substrate as well as the amorphous LaAlO3 film thickness. These amorphous LaAlO3 films have a bandgap of 6.2±0.1 eV.
Parallel dip-pen nanolithography with arrays of individually addressable cantilevers
Authors: Bullen David , Chung Sung-Wook , Wang Xuefeng , Zou Jun , Mirkin Chad A. , Liu Chang
Published: January 2004

In dip-pen nanolithography (DPN), nanoscale chemical patterns are created by directly transferring chemical molecules from the tip of an atomic force microscope probe to a surface. We report the development of a thermally actuated probe array for DPN applications. The array consists of ten thermal bimorph actuated probes, each 300 μm long, with a lateral spacing of 100 μm. The probes are actuated by passing dc current through a heater embedded in the probe base. The array is demonstrated by using it to simultaneously write ten different octadecanethiol patterns on a gold surface.
Colossal magnetoresistive manganite-based ferroelectric field-effect transistor on Si
Authors: Zhao T. , Ogale S. B. , Shinde S. R. , Ramesh R. , Droopad R. , Yu J. , Eisenbeiser K. , Misewich J.
Published: January 2004

An all-perovskite ferroelectric field-effect transistor with a ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) gate and a colossal magnetoresistive La0.8Ca0.2MnO3 (LCMO) channel has been successfully fabricated by pulsed-laser deposition on Si. A clear and square channel resistivity hysteresis loop, commensurate with the ferroelectric hysteresis loop of PZT, is observed. A maximum modulation of 20% after an electric field poling of 1.5×105 V/cm, and 50% under a magnetic field of 1 T, are achieved near the metal-insulator transition temperature of the LCMO channel. A data retention time of at least one day is measured. The effects of electric and magnetic fields on the LCMO channel resistance are discussed within the framework of phase separation scenario.
Nanoscale domain patterning of lead zirconate titanate materials using electron beams
Authors: Ferris J. H. , Li D. B. , Kalinin S. V. , Bonnell D. A.
Published: January 2004

The interactions of electron beams (e− beam) with ferroelectric oxides based on lead zirconate titanate have been quantified. The beam energy and dose dependencies of surface charge have been manipulated to influence local polarization orientation. The mechanism of ferroelectric domain polarization of 100 nm grains in lead zirconate titanate is discussed in terms of electron–solid interactions and the relative number of secondary electrons emitted to trapped electrons. Both positive and negative perpendicular polarization can be realized with e− beam exposure. The consequent nanoscale domain patterning is characterized with piezoforce microscopy.
High transmission and single-mode operation in low-index-contrast photonic crystal waveguide devices
Authors: Augustin M. , Fuchs H.-J. , Schelle D. , Kley E.-B. , Nolte S. , Tünnermann A. , Iliew R. , Etrich C. , Peschel U. , Lederer F.
Published: January 2004

We investigate photonic crystal films made of low-index glass materials. Polarization-sensitive waveguiding and single-mode operation (with losses as low as 1.7 dB/mm) have been observed in wide multimode photonic crystal waveguides after propagation of some millimeters. Furthermore, single-mode operation and transmission as high as about 50% per bend has been observed experimentally in low-index photonic crystal waveguide bends.
Importance of electron-impurity scattering for electron transport in terahertz quantum-cascade lasers
Authors: Callebaut Hans , Kumar Sushil , Williams Benjamin S. , Hu Qing , Reno John L.
Published: January 2004

Using an ensemble Monte Carlo simulation, including both electron–electron and electron–phonon scattering as well as electron-impurity scattering, the current density, population inversion, electron temperature, and gain in two THz quantum-cascade structures are investigated and compared to measurements. We find that the inclusion of electron-impurity scattering in the calculations is crucial when modeling the intersubband transport dynamics in these devices. However, the calculated gain is higher than inferred from experiments. This can be attributed to wavefunction localization caused by dephasing scattering, which is unaccounted for in the present model.
Molecular dynamics study of dislocation formation in a [001] face-centered-cubic epitaxial island under tensile stress
Authors: Liu P. , Zhang Y. W. , Fox B. , Lu C.
Published: January 2004

Dislocation formation in homoepitaxial pyramidal [001] Cu islands under tensile stress is studied using molecular dynamics simulations. It is found that 90° Shockley partial dislocations are dominant in the island strain relaxation. For a low-aspect-ratio island, the dislocations are nucleated from the island surface and propagate downwards to form misfit dislocations. For a high-aspect-ratio island, a pair of the dislocations on the same slip plane are simultaneously nucleated respectively from the two island edges, propagate inwards, and react to form a 90° Shockley misfit partial dislocation. These dislocations can form sequentially and cooperatively.
Controlled orientation of ellipsoidal fullerene C70 in carbon nanotubes
Authors: Khlobystov Andrei N. , Scipioni Roberto , Nguyen-Manh Duc , Britz David A. , Pettifor David G. , Briggs G. Andrew D. , Lyapin Sergey G. , Ardavan Arzhang , Nicholas Robin J.
Published: January 2004

Density functional theory calculations predict two orientations for ellipsoidal C70 fullerenes inside single-walled carbon nanotubes (SWNTs) of different sizes: transverse orientation for C70 in (11,11) nanotubes (d=14.9 Å) and longitudinal orientation for C70 in (10,10) nanotubes (d=13.6 Å). SWNTs with these diameters have been prepared and filled with the C70 fullerenes, and characterized by Raman spectroscopy and high-resolution transmission electron microscopy, showing the orientations predicted by theory.
Low temperature InP/Si wafer bonding
Authors: Tong Q.-Y. , Gan Q. , Hudson G. , Fountain G. , Enquist P.
Published: January 2004

An oxide-free, covalently bonded interface of InP/silicon wafer pairs has been realized at low temperature by B2H6 plasma treatment of bonding surfaces in the reactive ion etch mode followed by a HF dip and room temperature bonding in air. The bonding energy reaches InP fracture surface energy of 630 mJ/m2 at 200 °C. A total B-doped amorphous layer of about 15 Å with peak concentration of ∼2×1020 cm−3 was detected at the bonding interface. The release of hydrogen at low temperature from B–H complexes and subsequent absorption of the atomic hydrogen by the amorphous layer at the bonding interface is most likely responsible for the enhanced bonding energy.
Power-law load dependence of atomic friction
Authors: Fusco C. , Fasolino A.
Published: January 2004

We present a theoretical study of the dynamics of a tip scanning a graphite surface as a function of the applied load. From the analysis of the lateral forces, we extract the friction force and the corrugation of the effective tip-surface interaction potential. We find both the friction force and potential amplitude to have a power-law dependence on applied load with exponent ∼1.6. We interpret these results as characteristic of sharp undeformable tips in contrast to the case of macroscopic and elastic microscopic contacts.
Silicidation-induced band gap shrinkage in Ge epitaxial films on Si
Authors: Liu Jifeng , Cannon Douglas D. , Wada Kazumi , Ishikawa Yasuhiko , Jongthammanurak Samerkhae , Danielson David T. , Michel Jurgen , Kimerling Lionel C.
Published: January 2004

Ge epitaxial films on Si grown at high temperatures show a shrinkage in the direct band gap EgΓ as a result of the tensile strain accumulated during the cooling process after growth, making it a promising candidate for effective photon detection in L-band telecommunications. However, because of strain relaxation at temperatures >750 °C, only about 0.20% tensile strain can be accumulated at most. This leads to a direct band gap of 0.773 eV, corresponding to 1605 nm and is not enough to cover the whole L band (1561–1620 nm). In this letter, we report the strain enhancement in epitaxial Ge films induced by the formation of C54TiSi2 on the backside of the Si wafers. The backside C54-TiSi2 layer not only forms a good electric contact, but also increases the tensile strain of the Ge film on the front side from 0.20% to 0.24% and a further direct band gap shrinkage from 0.773 to 0.765 eV, corresponding to 1620 nm, which covers the whole L band. Since the silicidation process is compatible with Si complementary metal-oxide-semiconductor technology, this technique is promising to achieve low cost L-band photon detection completely with tensile strained Ge on Si.
GaInP
2
overgrowth and passivation of colloidal InP nanocrystals using metalorganic chemical vapor deposition
Authors: Hanna M. C. , Mićić O. I. , Seong M. J. , Ahrenkiel S. P. , Nedeljković J. M. , Nozik A. J.
Published: January 2004

We have used metalorganic chemical vapor deposition to deposit thin GaInP2 passivating films on both isolated and close-packed arrays of colloidal InP/GaInP2 core-shell nanocrystals. Conformal GaInP2 layers of 10–20 nm were grown on the nanocrystals after organic capping molecule removal by a thermal annealing treatment. We show that the InP nanocrystals retain their crystallinity, shape and luminescence efficiency after being exposed to growth temperatures of 600 °C. The GaInP2 nanocrystal composite showed strong photoluminescences indicating effective passivation of surface states. In close-packed nanocrystal arrays, the emission band is redshifted compared to films of isolated nanocrystals indicating electron coupling between dots embedded in GaInP2.
Air-bridged lateral growth of crack-free Al0.24Ga0.76N on highly relaxed porous GaN
Authors: Fareed R. S. Qhalid , Adivarahan V. , Chen C. Q. , Rai S. , Kuokstis E. , Yang J. W. , Khan M. Asif , Caissie J. , Molnar R. J.
Published: January 2004

We report on the strain reduction in AlGaN layers grown on porous GaN (P-GaN) by metalorganic chemical vapor deposition (MOCVD). The P-GaN was obtained by ultraviolet radiation-enhanced electroless wet chemical etching of thick hydride vapor phase epitaxial grown GaN (HVPE-GaN) templates over (001) sapphire substrates. By optimizing the growth conditions, lateral growth of AlGaN was enhanced resulting in air-bridge formation between the P-GaN and the AlGaN layers. X-ray diffraction studies showed significant strain relaxation in AlGaN layers primarily due to the strain sharing between P-GaN and the AlGaN layers. This allowed us to grow crack-free good optical quality layers with thickness exceeding the critical limits for AlGaN deposition on the conventional MOCVD GaN or HVPE-GaN. The obtained results demonstrate the potential of this approach for the development of efficient ultraviolet light emitters.
Improved technique to determine second-order optical nonlinearity profiles using two different samples
Authors: Ozcan A. , Digonnet M. J. F. , Kino G. S.
Published: January 2004

An improved inverse Fourier transform Maker fringe (MF) technique is described to retrieve the nonlinearity profile of thin films. It involves measuring the MF curve of two sandwich structures made by combining a pair of different nonlinear samples in two configurations. A simple algorithm is developed to process this data and retrieve the profile of both samples. Compared to our previous technique, which involves a single sandwich structure made of two identical samples, this technique is more flexible, it is insensitive to differences between the samples, and data processing is simpler and much faster. After a sample has been initially characterized by this technique, it can be used as a reference to characterize any other unknown sample using a single MF measurement. Experimental verification is demonstrated with a pair of thermally poled silica wafers.
Excitons and surface luminescence of CdS nanoribbons
Authors: Ip K. M. , Wang C. R. , Li Quan , Hark S. K.
Published: January 2004

The morphology and optical properties of CdS nanoribbons were studied by transmission electron microscopy and photoluminescence spectroscopy. The wurtzite-structured nanoribbons have a uniform rectangular cross section and grow along the [120] crystallographic direction. They are enclosed by small indice surfaces and have a highly perfect crystalline interior, free of extended defects. Luminescence peaks assigned to free and bound excitons were observed from these nanoribbons at low temperatures. In addition, a surface related luminescence band was also identified, showing that the proximity of unpassivated surfaces does not lead to dissociation of excitons in CdS nanoribbons of high purity and structural quality, even when their thickness is around 20 nm.
Measurement of the scattering and absorption cross sections of the human body
Authors: Conti Stéphane G. , Roux Philippe , Demer David A. , de Rosny Julien
Published: January 2004

Presented here are absolute measurements of the acoustic intensity scattered and absorbed by humans. The total scattering and absorption cross sections, σT and σa, were obtained for individual humans walking randomly in a room, using long-duration acoustic reverberation. Within the audible range, the sound scattering spectra of the human body is similar to that of a hard ellipsoid with same volume (dimensions proportional to the mass to the one-third power). Moreover, increasing amounts of clothing have little effect on scattering while absorption is greatly increased.
Conductor microstructures by laser curing of printed gold nanoparticle ink
Authors: Chung Jaewon , Ko Seunghwan , Bieri Nicole R. , Grigoropoulos Costas P. , Poulikakos Dimos
Published: January 2004

The laser-based curing of printed nanoparticle ink to create microlines (resistors) of electrical resistivity approaching that of bulk gold was investigated. The present work relies on laser absorption in both the nanoparticle ink and the sintered gold layer, as well as the transport of thermal energy in the substrate and the resulting solvent vaporization and nanoparticle deposition and sintering. The morphology and electrical properties of the gold line can be controlled by modulating the spatial distribution of the laser beam intensity. Based on the understanding of the underlying physics, a process that circumvents a serious drawback on the functionality of cured gold microlines is produced. Microconductors with resistivity approaching that of bulk gold are produced, while loss of gold nanoparticles and cross sectional nonuniformities are avoided.
On factors inducing the (101̄0) texture of hexagonal-close-packed Co63Cr31Mn6 layers in magnetic recording media
Authors: Song Hajung , Kwon Soon-Ju , Shin Kyung-Ho
Published: January 2004

We investigate factors affecting the movement of sputtered species and the (101̄0) texture formation of hexagonal-close-packed Co63Cr31Mn6 (CoCrMn) layers in magnetic recording media. Deposition conditions and underlayers rendering high mobility of the sputtered species promote the (101̄0) texture of the CoCrMn film. Elemental effects are studied by substituting manganese with a series of 3d transition elements (Ti, V, Cr, Fe, Ni, and Cu) in the CoCrMn films. The results suggest that the chemical characteristics of manganese, the preference of bonding with different elements (especially with cobalt), is important in the texture formation of CoCrMn films.
Boron alloying in GaN
Authors: Escalanti Laurian , Hart Gus L. W.
Published: January 2004

Using first-principles calculations in the local density approximation, we studied effects of adding up to 6% boron to zinc-blende GaN. We found that the band gap increases monotonically with boron incorporation, in agreement with experiment. A composition-independent band-gap bowing parameter of 4.30 eV was determined, and proved to be large compared to bowing for other mixed cation systems. The formation enthalpy of mixing, ΔH, was determined for BxGa1−xN, BxGa1−xAs, and GaAs1−xNx. A comparison of enthalpies indicates that the production of BxGa1−xN films with boron concentrations of at least 5% may be possible.
Two-dimensional extremely thin single-crystalline α-Si3N4 microribbons
Authors: Hu J. Q. , Bando Y. , Sekiguchi T. , Xu F. F. , Zhan J. H.
Published: January 2004

Two-dimensional extremely thin single-crystalline α-Si3N4 microribbons have been achieved in bulk via a thermal decomposition nitridation. The α-Si3N4 microribbons have small thicknesses of ∼10–20 nm, large widths of ∼10–25 μm and long lengths ranging from several hundred micrometers to the order of millimeters, and have the same growth direction of [101̄0] crystallographic orientation and are enclosed by ±(0001) and ±(21̄1̄0) facets. Room temperature cathodoluminescence from individual ribbons shows one intensive UV emission peak at ∼305 nm, and two weak and broad emission peaks at ∼540 and ∼735 nm, respectively. The form of α-Si3N4 is expected not only to possess many interesting mechanical properties, but also to have different optical properties.
Effect of quantum confinement on shallow acceptor transitions in δ-doped GaAs/AlAs multiple-quantum wells
Authors: Zheng W. M. , Halsall M. P. , Harmer P. , Harrison P. , Steer M. J.
Published: January 2004

We have investigated the effect of confinement on the shallow acceptor transitions in δ-doped GaAs/AlAs multiple-quantum wells with well widths ranging from 30 to 200 Å. A series of Be δ-doped GaAs/AlAs multiple-quantum wells with doping at the well center and a single epilayer of GaAs uniformly Be doped were grown by molecular beam epitaxy. Photoluminescence spectra were measured at 4, 20, 40, 80, 120, and 200 K, respectively. Two-hole transitions of the acceptor-bound exciton from the ground state, 1S3/2(Γ6), to the excited state, 2S3/2(Γ6), were clearly observed. It is found that the acceptor transition energy increases with a decrease in quantum well width.
Tunable microdisk resonators vertically coupled to bus waveguides using epitaxial regrowth and wafer bonding techniques
Authors: Choi Seung June , Peng Zhen , Yang Qi , Choi Sang Jun , Dapkus P. Daniel
Published: January 2004

We demonstrate two different types of tunable microdisk resonators vertically coupled to bus waveguides: a microdisk resonator coupled to air-guided rib bus waveguides and the other one built on buried heterostructure bus lines, respectively. The latter type contacts the substrate without relying on an extra supporting structure, which affords more reliable conductive paths toward the substrate. A planarized epitaxial regrowth technology combined with wafer bonding is used to fabricate the structure. The measured transmission spectra indicate improved tuning capability of buried-bus-coupled microdisks, but the overall device performance is limited by optical leakage through the substrate.
Contact issues in electroluminescent devices from ruthenium complexes
Authors: Gorodetsky Alon A. , Parker Sara , Slinker Jason D. , Bernards Daniel A. , Wong Man Hoi , Malliaras George G. , Flores-Torres Samuel , Abruña Héctor D.
Published: January 2004

We report on the temporal evolution of the current, radiance and efficiency of electroluminescent devices based on films of [Ru(bpy)3]2+(PF6−)2 (bpy is 2,2′-bipyridyl) with various electrodes. Under forward bias (with the bottom electrode wired as the anode) the device characteristics were independent of the electrodes used. The situation was different under reverse bias, where differences were observed in the steady-state as well as in the transient characteristics of devices with different electrodes. The origin of this asymmetry is discussed.
Cr
2
O
3
surface layer and exchange bias in an acicular CrO2 particle
Authors: Zheng R. K. , Liu Hui , Wang Y. , Zhang X. X.
Published: January 2004

It has been found by electron diffraction and high-resolution transmission electron microscopy that each commercial CrO2 particle is enclosed by an epitaxial Cr2O3 layer ∼2.5 nm thick. The epitaxial relationships of Cr2O3 layers on CrO2 particles have been identified. Magnetic hysteresis loops measured at different temperatures (5–300 K), after the sample was cooled from 350 K with a 50 kOe field, were found to be perfectly symmetrical, i.e., no exchange bias was observed, which is unexpected for ferromagnetic/antiferromagnetic core/shell structured particles. To gain a deeper understanding of the phenomenon, the “as-received” commercial CrO2 particles were annealed at 600 °C in air for 1 h to thicken the Cr2O3 shells. Exchange bias was clearly observed in the annealed particles with thicker Cr2O3 shells. At 5 K, the exchange bias field reached 220 Oe. These experimental observations can be explained well within the framework of the random field model.
Design of white light-emitting diodes using InGaN/AlInGaN quantum-well structures
Authors: Xiao D. , Kim K. W. , Bedair S. M. , Zavada J. M.
Published: January 2004

Based on the Rashba–Sheka–Pikus Hamiltonian in the vicinity of the Γ point, and taking into consideration spontaneous and piezoelectric polarization, the optical intensity of nitride-based quantum-well light-emitting diodes has been calculated. It is found that strain substantially alters the subband structure and thus the output intensity of these nitride-biased quantum-well light-emitting diodes. A design that uses AlInGaN as the quantum barrier is proposed to realize efficient red emission, which is hard to achieve if GaN is used as the barrier. In the proposed design, three different InGaN/AlInGaN quantum-well structures emit red, green, and blue light of similar intensity. Also, to achieve high efficiency, important factors related to the oscillator strength are discussed in detail.
Erbium-doped waveguide amplifiers fabricated using focused proton beam writing
Authors: Liu K. , Pun E. Y. B. , Sum T. C. , Bettiol A. A. , van Kan J. A. , Watt F.
Published: January 2004

Buried channel waveguides were fabricated in Er3+–Yb3+ codoped phosphate glasses using focused proton beam writing. Proton ion doses in the range of 1014–1015 ions/cm2 and 2.0 MeV energy were used. The waveguides were located 38 μm below the substrate surface and are in excellent agreement with the transport and range of ions in matter simulation. The waveguide properties were measured, and the fluorescence spectra and optical gain of the waveguides were characterized. The maximum net gain of the waveguide amplifiers at 1.534 μm wavelength was measured to be ∼1.72 dB/cm with 100 mW pump power at 975 nm wavelength.
Parallel plate THz transmitter
Authors: Coleman S. , Grischkowsky D.
Published: January 2004

A THz transmitter that directly excites the guided wave modes of a dielectric filled parallel plate waveguide is demonstrated. When coupled to free space, the transmitter yields a large peak time-domain THz signal. The device yields significant signal amplitudes with varying output spectra with and without a bias field applied. This transmitter provides powerful direct excitation of guided wave modes and is the next step toward an integrated guided wave transverse-electromagnetic mode THz bandwidth device.
Thermally assisted recording beyond traditional limits
Authors: Hamann Hendrik F. , Martin Yves C. , Wickramasinghe H. Kumar
Published: January 2004

This work demonstrates that current magnetic storage density limitations due to superparamagnetic effects can be overcome by thermally assisted writing. Specifically, we write magnetization patterns on thin magnetic films that correspond to storage densities of ∼400 Gbit/in.2. Simple thermal diffusion considerations predict potential storage densities of >1 Tbit/in.2 accompanied by recording speeds of >1 GHz.
Optically detected heavy- and light-hole anti-crossing in GaAs quantum wells under pulsed magnetic fields
Authors: Kim Yongmin , Lee Kyu-Seok , Perry C. H.
Published: January 2004

We report magneto-photoluminescence studies of two undoped GaAs–Al0.3Ga0.7As single quantum well (SQW) samples (120 and 60 Å) in pulsed magnetic fields up to ∼65 T. Both samples exhibit exciton transitions due to the ground-state (1s) electron-heavy-hole recombination which undergoes diamagnetic energy shifts at low fields and has a liner dependence at high fields. The 120 Å SQW shows the electron-light-hole exciton transition at zero magnetic field. However at about 30 T, the electron-heavy-hole and the electron-light-hole transitions intersect and show an anti-crossing behavior. The 60 Å SQW shows a similar behavior but the splitting between the heavy- and light-hole excitons can only be observed in the anti-crossing region at about 35 T. The results indicate that the valence band mixing plays a significant role at high magnetic fields.
Magnetic properties of Mn doped ZnO tetrapod structures
Authors: Roy V. A. L. , Djurišić A. B. , Liu H. , Zhang X. X. , Leung Y. H. , Xie M. H. , Gao J. , Lui H. F. , Surya C.
Published: January 2004

ZnO tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn diffusion doping was performed at two different temperatures (600 and 800 °C). The samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray fluorescence, x-ray diffraction (XRD), superconducting quantum interference device magnetometer, and photoluminescence. Diffusion doping resulted in the increase of the size of tetrapods, but no new peaks were found in XRD spectrum. Mn doped ZnO tetrapod structures were found to be ferromagnetic with Curie temperature ∼50 K, and showed large coercive field (∼3500 Oe for 800 °C sample, ∼5500 Oe for 600 °C sample).
Low temperature deposited Ba0.96Ca0.04Ti0.84Zr0.16O3 thin films on Pt electrodes by radio frequency magnetron sputtering
Authors: Cramer N. , Philofsky Elliot , Kammerdiner Lee , Kalkur T. S.
Published: January 2004

Ba 0.96 Ca 0.04 Ti 0.84 Zr 0.16 O 3 films acceptor doped with Sc were deposited on Pt/TiO2/SiO2/Si substrates using radio frequency magnetron sputtering. Substrate temperatures throughout the fabrication process remained at or below 450 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. In addition, this process made no use of oxygen in the sputter gas or in annealing atmospheres and thus it remains compatible with easily oxidized materials. A relative dielectric constant of 166 was achieved along with a loss tangent of 1.9% at 100 kHz. Leakage current densities of 1.6×10−8 A/cm2 were observed at 300 K with 300 kV/cm of applied electric field.
Nuclear reactions in copper induced by protons from a petawatt laser-foil interaction
Authors: Yang J. M. , McKenna P. , Ledingham K. W. D. , McCanny T. , Shimizu S. , Robson L. , Clarke R. J. , Neely D. , Norreys P. A. , Wei M.-S. , Krushelnick K. , Nilson P. , Mangles S. P. D. , Singhal R. P.
Published: January 2004

High-intensity (>1019 W cm−2) laser-plasma interactions have been shown to produce large quantities of protons with energies up to several tens of MeV. A range of laser-driven proton-induced reactions in copper have been investigated and the observed reactions quantified. The energy spectrum of the accelerated protons was determined from the reactions in a single thin copper foil and found to be in agreement with that deduced from (p,n) reactions measured in a stack of copper foils. The potential applications of this diagnostic technique are discussed.
Direct observation of contact and channel resistance in pentacene four-terminal thin-film transistor patterned by laser ablation method
Authors: Yagi Iwao , Tsukagoshi Kazuhito , Aoyagi Yoshinobu
Published: January 2004

We established a dry-etching patterning process for the channel formation of pentacene thin-film transistor, and fabricated a four-terminal device equipped with a gate electrode. The four-terminal device enabled us to divide two-terminal source–drain resistance into two components of contact resistance and pentacene channel resistance. We obtained direct evidence of a gate-voltagedependent contact resistance change: the gate-induced charge significantly reduced the contact resistance and increased source–drain current. Furthermore, the temperature dependence of the device clearly indicated that the contact resistance was much higher than the channel resistance and was dominated in the two-terminal total resistance of the device below 120 K. An observed activation energy of 80 meV for contact resistance was higher than that of 42 meV for pentacene channel resistance.
Uniaxial magnetic anisotropy tuned by nanoscale ripple formation: Ion-sculpting of Co/Cu(001) thin films
Authors: Sekiba D. , Moroni R. , Gonella G. , Buatier de Mongeot F. , Boragno C. , Mattera L. , Valbusa U.
Published: January 2004

We have investigated the growth of surface nanostructures on a Co/Cu(001) film and the growth of Co films on a nanostructured Cu(001) substrate as well as the effect of nanoscale pattern formation on the film magnetic properties. Here we demonstrate by scanning tunneling microscopy measurements and magneto-optic Kerr effect hysteresis curves that low-temperature grazing-incidence ion sputtering can be used to induce the formation of nanoscale ripples which reduce the four-fold symmetry of the Co film to two-fold, thus generating a strong in-plane uniaxial magnetic anisotropy. The nanostructures and the associated uniaxial magnetic anisotropy were found to be stable up to room temperature.
Manganese-doped ZnO nanobelts for spintronics
Authors: Ronning C. , Gao P. X. , Ding Y. , Wang Z. L. , Schwen D.
Published: January 2004

Zinc oxide (ZnO) nanobelts synthesized by thermal evaporation have been ion implanted with 30 keV Mn+ ions. Both transmission electron microscopy and photoluminescence investigations show highly defective material directly after the implantation process. Upon annealing to 800 °C, the implanted Mn remains in the ZnO nanobelts and the matrix recovers both in structure and luminescence. The produced high-quality ZnO:Mn nanobelts are potentially useful for spintronics.
Total reflection amorphous carbon mirrors for vacuum ultraviolet free electron lasers
Authors: Steeg B. , Juha L. , Feldhaus J. , Jacobi S. , Sobierajski R. , Michaelsen C. , Andrejczuk A. , Krzywinski J.
Published: January 2004

Sputter-deposited amorphous carbon coatings of high optical quality and very high radiation stability will be used as reflecting optical elements for free electron laser (FEL) applications in the vacuum ultraviolet (VUV) and soft x-ray spectral regions. Their reflectivity at grazing angles of 2° is typically 94–96% for photon energies between 50 and 250 eV. Using the focused radiation (λ=98 nm) of the VUV FEL at Deutsches Elektronen-Synchrotron DESY the damage threshold of such coatings was determined to 0.07 J/cm2. Ripples with a spatial period of 76 nm were found on the surfaces damaged by the FEL radiation.
Lock-in thermography and nonuniformity modeling of thin-film CdTe solar cells
Authors: Shvydka Diana , Rakotoniaina J. P. , Breitenstein O.
Published: January 2004

We present the lock-in thermography study of thin-film CdTe/CdS solar cells. Several major features of thermal signal are identified, such as much higher intensity for cells under illumination, considerable inhomogeneity, and a bright contour line corresponding to the higher intensity at the cell edge. Light soak stress is shown to increase the device lateral nonuniformity. We model the solar cell as a two-dimensional system of random diodes connected in parallel through a resistive electrode. The simulated current distribution maps are consistent with the thermography data.
Individually addressed large-scale patterning of conducting polymers by localized electric fields
Authors: Su Ming , Fu Lei , Wu Nianqiang , Aslam Mohammed , Dravid Vinayak P.
Published: January 2004

A scaleable and site-specific patterning approach with individual addressability is demonstrated via an electropolymerization process within the gap of electrodes. The method can pattern conducting polymer structures by applying a bias between desired electrodes in a monomer vapor. The reaction is proposed to happen in a thin water film condensed inside the electrode gap at ambient environment. It is possible to pattern different conducting polymers on the same substrate by exposing to different monomers. Proof-of-concept experiments on pyrrole and thiophene have shown the generality of this simple and robust method, which enables the real-time monitoring of the resistance and deposition of the conducting polymers. Finally, chemical sensing of the patterned polypyrrole structures to ethanol vapor and ammonia gas are presented.
Calibration procedure for temperature measurements by thermoreflectance under high magnification conditions
Authors: Dilhaire S. , Grauby S. , Claeys W.
Published: January 2004

We show that, in thermoreflectance measurements under high focusing conditions, the signal is not only due to the surface temperature variations. Indeed, the reflected light from the device under test interferes with the incoming one, making a parasitic Fabry-Pérot. Besides, the motion of the sample surface induced, for example, by Joule heating, can produce an additional signal superimposed on the thermoreflectance one. Consequently, reliable thermoreflectance measurements under high focusing conditions, and particularly their calibration, demand a control of the distance between the objective and the sample. Using a servo loop to maintain the distance between the objective and the device constant, thermoreflectance measurements have been made in transient regime on an electronic device and the thermoreflectance coefficient of gold has been deduced.
Isolated nickel impurities in diamond: A microscopic model for the electrically active centers
Authors: Larico R. , Assali L. V. C. , Machado W. V. M. , Justo J. F.
Published: January 2004

We present a theoretical investigation on the structural and electronic properties of isolated nickel impurities in diamond. The atomic structures, symmetries, formation and transition energies, and hyperfine parameters of isolated interstitial and substitutional Ni were computed using ab initio total energy methods. Based on our results, we ultimately propose a consistent microscopic model which explains several experimentally identified nickel-related active centers in diamond.
Lattice-strain-driven ferromagnetic ordering in La0.8Sr0.2MnO3 thin films
Authors: Lee Y. P. , Park S. Y. , Prokhorov V. G. , Komashko V. A. , Svetchnikov V. L.
Published: January 2004

The effects of lattice strain on the magnetic and the transport properties of La0.8Sr0.2MnO3 films grown on an (001) LaAlO3 substrate and on a La0.8Ca0.2MnO3 layer have been studied. It was observed that the metal-insulator and the ferromagnetic transitions turn out to be at higher temperatures for the film deposited on La0.8Ca0.2MnO3 layer with respect to that on LaAlO3. The dependence of Curie temperature on the bulk and the Jahn–Teller strains has also been determined.
Improved dielectric properties and tunability of multilayered thin films of (Ba0.80Sr0.20)(Ti1−xZrx)O3 with compositionally graded layer
Authors: Wang Can , Cheng B. L. , Wang S. Y. , Lu H. B. , Zhou Y. L. , Chen Z. H. , Yang G. Z.
Published: January 2004

Multilayered thin films of (Ba0.80Sr0.20)(Ti1−xZrx)O3 (BSTZ) with compositionally graded layer (CGL) have been fabricated by pulsed laser deposition on Pt/TiO2/SiO2/Si substrate. In each CGL, four individual layers of BSTZ with x=0.36, 0.18, 0.08 and 0 are grown in series with equal thickness. Three kinds of thin-film CGL samples comprising one, two or four CGLs have been elaborated with the final same thickness, and the thickness of each CGL is accordingly varied in different samples to achieve the gradients of composition. The crystalline structures of the CGL thin films are successively characterized using x-ray diffraction and their electrical properties such as ac dielectric properties and polarizations are investigated. Improved dielectric properties and tunability of permittivity have been observed in the multilayered CGL films compared to single-layer BSTZ films prepared in the identical condition. Furthermore, with increasing gradients of compositions in the CGL multilayered films, the dielectric permittivity and its tunability increase, and the hysteresis loop of the thin films disappears. The results show that the internal stress produced by the gradient of composition could be a dominant factor to influence the dielectric properties. The improved dielectric properties and tunability for the applications of tunable devices can be obtained by the manipulation of the gradient of compositions in the multilayered films.
Systematic study of the magnetization reversal in patterned Co and NiFe Nanolines
Authors: Uhlig W. Casey , Shi Jing
Published: January 2004

We report a universal dependence of switching field of patterned magnetic nanolines as a function of the linewidth for Co and NiFe films of various thicknesses. This dependence is shown to be consistent with a nucleation picture in which the magnetization reversal is controlled only by a small nucleus equivalent to a particle with an aspect ratio of 1.25, which spreads across the width of the nanoline. Micromagnetic simulation, taking into account of the edge roughness, agrees well with the observed results.
GaN quantum dot density control by rf-plasma molecular beam epitaxy
Authors: Brown J. , Wu F. , Petroff P. M. , Speck J. S.
Published: January 2004

We report on the growth of GaN quantum dots and the control of their density in the Stranski–Krastanov mode on AlN (0001) by rf-plasma molecular beam epitaxy at 750 °C. After depositing the equivalent of 2–3 ML GaN coverage, as limited by N fluence under Ga-droplet growth conditions, excess Ga was desorbed and Stranski–Krastanov islands formed under vacuum. We present the dependence of island density as a function of GaN coverage (for two growth rates: 0.10 and 0.23 ML/s), as estimated from atomic force microscopy and cross-sectional transmission electron microscopy. With a GaN growth rate of 0.23 ML/s, the island density was found to vary from less than 3.0×108–9.2×1010 cm−2 as the GaN coverage was varied from 2.2 (critical thickness) to 3.0 ML. For a GaN growth rate of 0.10 ML/s, the island density varied from 2.0×1010 to 7.0×1010 cm−2 over a GaN coverage range of 2.0–3.0 ML. For each growth rate, the GaN islands were found to be of nearly uniform size, independent of the quantum dot density.
Comparison of the field emissions between highly ordered carbon nanotubes with closed and open tips
Authors: Yoon Seon Mi , Chae Joseok , Suh Jung Sang
Published: January 2004

We have studied the field emission from the closed and open tips of highly ordered carbon nanotubes fabricated on porous anodic aluminum oxide templates by changing the tube height. Due to the field-screening effect provoked by the proximity of the neighboring tubes, the field emission from both kinds of the tips was critically affected by the tube height that protruded from the surface. The field emission optimizes when the tube height is similar to the intertube distance for both kinds of tips. The field emission from the closed tips is much more efficient than that from the open ones.
Enhancement of evanescent waves in waveguides using metamaterials of negative permittivity and permeability
Authors: Qing De-Kui , Chen Gang
Published: January 2004

Electromagnetic waves in waveguides consisting of metamaterials with negative permittivity and permeability are analyzed. It is found that metamaterials can enhance the intensity of the evanescent waves in the cladding without altering the propagation constant of the waveguide for both TE and TM modes. This is a unique property of metamaterials. The enhancement factor increases with the increasing of the thickness of the metamaterial and saturates when complete surface polaritons were established at the interface between the metamaterial and the cladding. The enhancement effect can improve the performance of evanescent-wave-based waveguide devices.
Role of soft dielectric energy in poling crystals or ceramics and in domain average engineering
Authors: Marvan M. , Erhart J. , Fousek J.
Published: January 2004

Poling process is essential for ferroelectric ceramics and crystals. It is traditionally assumed that the one of PS vectors allowed by symmetry is energetically preferred which is closest to the direction of applied field. It is shown that because of the role of the soft energy this may not be the case. Theoretical results for crystals and ceramics of the m3̄m→4mm species show that regions of field directions, which induce PS of a given orientation, depend on the field magnitude. In crystals the situation can even arise when spontaneous polarization is directed against the field. Experiments could demonstrate practical consequences of this theory.
A 50-nm-gate-length erbium-silicided n-type Schottky barrier metal-oxide-semiconductor field-effect transistor
Authors: Jang Moongyu , Kim Yarkyeon , Shin Jaeheon , Lee Seongjae , Park Kyoungwan
Published: January 2004

The theoretical and experimental current–voltage characteristics of 50-nm-gate-length erbium-silicided n-type Schottky barrier metal-oxide-semiconductor field-effect transistors (SB-MOSFETs) are discussed. The manufactured 50-nm-gate-length n-type SB-MOSFET shows large on/off current ratio with low leakage current less than 10−4 μA/μm. The saturation current is 120 μA/μm when drain and gate voltage is 1 and 3 V, respectively. The experimental current–voltage characteristics of 50-nm-gate-length n-type SB-MOSFET are fitted using newly developed theoretical model. From the theoretical analysis, the off- and on-current is mainly attributed to the thermionic and tunneling current, respectively. The decrease of tunneling distance at silicon/silicide Schottky junction with the increase of drain voltage gives the increase of tunneling current. This phenomenon is explained by using drain-induced Schottky barrier thickness thinning effect.
Visible spectrum (645 nm) transverse electric field laser operation of InP quantum dots coupled to tensile strained In0.46Ga0.54P quantum wells
Authors: Walter G. , Elkow J. , Holonyak N. , Heller R. D. , Zhang X. B. , Dupuis R. D.
Published: January 2004

Data are presented that demonstrate the continuous wave room-temperature transverse-electric field (TE) visible-spectrum (645 nm) heterostructure laser operation of single-layer compressively strained 3.75 monolayer equivalent InP quantum dots (QDs) coupled to 60 Å wide tensile-strained In0.46Ga0.54P quantum wells (QWs). The simple stripe geometry (200 μm×4 μm) InP QD+InGaP QW heterostructure laser is capable of high performance despite the coupling of two competing recombination systems. The InP QD+InGaP QW laser exhibits low threshold (∼31 mA), high quantum efficiency (72%, ∼1.38 mW/mA), a relatively high characteristic temperature T0 of 69 K, and a shift in wavelength at temperature of 0.19 nm/°C.
Intense blue–white luminescence from carbon-doped silicon-rich silicon oxide
Authors: Seo Se-Young , Cho Kwan-Sik , Shin Jung H.
Published: January 2004

The effect of carbon doping on the enhancement of visible luminescence from silicon-rich silicon oxide (SRSO), which consists of Si nanoclusters embedded inside a SiO2 matrix, is investigated. C-doped SRSO films were fabricated by electron cyclotron resonance-plasma enhanced chemical vapor deposition method using SiH4, O2, and CH4 source gases followed by a high-temperature anneal. Intense blue-white visible luminescence, visible to the naked eye under daylight conditions, was observed from the film with a nearly equal amount of C and excess Si (∼16 at. %) after an anneal at 950 °C. Furthermore luminescence could be tuned from 1.8 to 2.5 eV by controlling the C to excess Si ratio, the C content, and the anneal temperature. Taken together with the infrared absorption spectra, these results indicate that the luminescence is attributed to exciton recombination in C-incorporated Si nanoclusters.
Automated array-based genomic profiling in chronic lymphocytic leukemia: Development of a clinical tool and discovery of recurrent genomic alterations
Authors: Schwaenen Carsten , Nessling Michelle , Wessendorf Swen , Salvi Tatjana , Wrobel Gunnar , Radlwimmer Bernhard , Kestler Hans A. , Haslinger Christian , Stilgenbauer Stephan , Döhner Hartmut , Bentz Martin , Lichter Peter
Published: January 2004

B cell chronic lymphocytic leukemia (B-CLL) is characterized by a highly variable clinical course. Recurrent chromosomal imbalances provide significant prognostic markers. Risk-adapted therapy based on genomic alterations has become an option that is currently being tested in clinical trials. To supply a robust tool for such large scale studies, we developed a comprehensive DNA microarray dedicated to the automated analysis of recurrent genomic imbalances in B-CLL by array-based comparative genomic hybridization (matrix–CGH). Validation of this chip in a series of 106 B-CLL cases revealed a high specificity and sensitivity that fulfils the criteria for application in clinical oncology. This chip is immediately applicable within clinical B-CLL treatment trials that evaluate whether B-CLL cases with distinct chromosomal abnormalities should be treated with chemotherapy of different intensities and/or stem cell transplantation. Through the control set of DNA fragments equally distributed over the genome, recurrent genomic imbalances were discovered: trisomy of chromosome 19 and gain of the
MYCN
oncogene correlating with an elevation of
MYCN
mRNA expression.