bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of a model molecular-electronic rectifier with an evaporated Ti–metal top contact
Authors: Chang Shun-Chi , Li Zhiyong , Lau Chun Ning , Larade Brian , Williams R. Stanley
Published: October 2003

Molecular-electronic devices are usually fabricated by sandwiching organic monolayers between electrodes. Questions arise about whether the molecules react with a deposited metal. We investigated a self-assembled monolayer (SAM) of alkoxynaphthalene thiol (I) on Pt before and after Ti film deposition. The SAM on Pt was highly ordered. Ti deposition resulted in some reaction with the alkyl chains and disordering, but the napthelenes remained intact. Pinhole free films of the monolayers were characterized by current–voltage measurements, revealing that a rectification ratio as high as 5×105 was achieved.
Red, green, and blue simultaneous generation in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ nonlinear channel waveguides
Authors: Cantelar E. , Torchia G. A. , Sanz-Garcı́a J. A. , Pernas P. L. , Lifante G. , Cussó F.
Published: October 2003

In this work, continuous-wave broadly tunable simultaneous generation of red (650–690 nm), green (520–575 nm), and blue (425–495 nm) light in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ channel waveguides is reported after Ti:sapphire excitation in the 850–990 nm range. The red and green emissions arise from energy transfer and upconversion mechanisms between Yb3+ and Er3+ ions, while the blue light with a maximum efficiency of 0.04% W−1 cm−1 is produced by quasi-phase matching processes.
Active photonic crystals based on surface acoustic waves
Authors: de Lima M. M. , Hey R. , Santos P. V.
Published: October 2003

An active photonic crystal (PC) based on the modulation of a one-dimensional cavity resonator by electrically-generated surface acoustic waves is described. The high nonthermal population of surface modes combined with the enhanced Brillouin scattering in the cavity increases the intensity of the scattered light to values comparable to the excitation intensity. This process is employed to switch and modulate light beams in PCs.
Grazing-incidence small angle x-ray scattering studies of phase separation in hafnium silicate films
Authors: Stemmer Susanne , Li Youli , Foran Brendan , Lysaght Patrick S. , Streiffer Stephen K. , Fuoss Paul , Seifert Soenke
Published: October 2003

Grazing-incidence small-angle x-ray scattering (GISAXS) and high-resolution transmission electron microscopy (HRTEM) were used to investigate phase separation in hafnium silicate films after rapid thermal annealing between 700 and 1000 °C. 4-nm-thick Hf–silicate films with 80 and 40 mol % HfO2, respectively, were prepared by metalorganic vapor deposition. Films of the two compositions showed distinctly different phase-separated microstructures, consistent with two limiting cases of microstructural evolution: nucleation/growth and spinodal decomposition. Films with 40 mol % HfO2 phase separated in the amorphous by spinodal decomposition and exhibited a characteristic wavelength in the plane of the film. Decomposition with a wavelength of ∼3 nm could be detected at 800 °C. At 1000 °C the films rapidly demixed with a wavelength of 5 nm. In contrast, films with 80 mol % HfO2 phase separated by nucleation and growth of crystallites, and showed a more random microstructure. The factors determining specific film morphologies and phase separation kinetics are discussed.
Pattern-induced alignment of silicon islands on buried oxide layer of silicon-on-insulator structure
Authors: Ishikawa Yasuhiko , Imai Yasuhiro , Ikeda Hiroya , Tabe Michiharu
Published: October 2003

Alignment control of Si islands thermally agglomerated on a buried SiO2 layer of a silicon-on-insulator (SOI) structure is reported. As a starting structure, a line-shaped (001) SOI layer is prepared using an electron beam lithography and a selective oxidation technique. Annealing in an ultrahigh vacuum, SOI line structure having submicron width and thickness of ∼3 nm is deformed into island arrays aligned along two edges of the line pattern. This pattern-induced alignment occurs independent of in-plane crystalline directions of the line pattern, while we have previously reported for unpatterned SOI that the island alignment is commonly observed along the 〈310〉 directions. It is indicated that the linewidth and the SOI thickness play key roles in changing alignment behavior from the crystalline directions to the line pattern directions.
Optoelectrical properties of four amorphous silicon thin-film transistors 200 dpi active-matrix organic polymer light-emitting display
Authors: Hong Yongtaek , Nahm Jeong-Yeop , Kanicki Jerzy
Published: October 2003

We report on opto-electrical properties of a current-driven 200 dpi active-matrix organic polymer red light-emitting display (AM–PLED) based on four hydrogenated amorphous silicon thin-film transistor pixel electrode circuits. The AM–PLED luminance and effective light-emission efficiency were 30 cd/m2 and 0.3 cd/A, respectively, at the data current equal to 25 mA. The display electroluminescent spectrum has a peak located at and the full width at half maximum value of 644 and 95 nm, respectively, and Commission Internationale de l’Eclairage color coordinates of (0.66,0.33).
How to estimate the Green’s function of a heterogeneous medium between two passive sensors? Application to acoustic waves
Authors: Derode Arnaud , Larose Eric , Campillo Michel , Fink Mathias
Published: October 2003

The exact Green’s function of a heterogeneous medium can be retrieved from the crosscorrelation of the fields received by two passive sensors. We propose a physical interpretation based on time-reversal symmetry. We address the issue of causality and show the role of multiple scattering for the reconstruction of the Green’s function. Ultrasonic experimental results are presented to illustrate the argument. Applications to geophysics and ocean acoustics are discussed.
Semiconducting nanocrystalline iron disilicide thin films prepared by pulsed-laser ablation
Authors: Yoshitake T. , Yatabe M. , Itakura M. , Kuwano N. , Tomokiyo Y. , Nagayama K.
Published: October 2003

Amorphous iron silicide was reported to be semiconducting as well as β-FeSi2, and it has received considerable attention from both the physical and engineering points of view. However, there have been few studies and its basic properties are still unknown. We could grow the semiconducting nanocrystalline iron disilicide thin films by pulsed-laser deposition using an FeSi2 target. They consist of crystallites with diameters ranging from 3 to 5 nm. The carrier density and the mobility at 300 K were 1.5×1019 cm−3 and 35 cm/V s, respectively.
Room-temperature epitaxial growth of GaN on conductive substrates
Authors: Ohta J. , Fujioka H. , Oshima M.
Published: October 2003

We have grown GaN films on (Mn,Zn)Fe2O4 (111) substrates by pulsed-laser deposition at room temperature and investigated their structural properties using reflection high-energy electron diffraction, atomic force microscopy, grazing-incidence x-ray reflectivity, and grazing-incidence x-ray diffraction (GIXD). We have found that GaN (0001) grows epitaxially even at room temperature. The room-temperature growth of GaN starts with the two-dimensional mode followed by the three-dimensional mode, which indicates that the precursors of GaN have large energy enough to migrate on the surface. GIXD measurements showed that the in-plane epitaxial relationship is GaN [11-20] // (Mn,Zn)Fe2O4 [01-1] and approximately 90% of the lattice mismatch is released at the interface. These results indicate that the present technique solves one of the two major problems with epitaxial growth of GaN (mismatch in the thermal expansion coefficients) and alleviates the other problem (mismatch in the lattice constants).
Effect of intrinsic point defects on copper precipitation in large-diameter Czochralski silicon
Authors: Xi Zhenqiang , Yang Deren , Xu Jin , Ji Yujie , Que Duanlin , Moeller H. J.
Published: October 2003

Effect of intrinsic point defects on copper precipitation in large-diameter Czochralski silicon annealed at 1100 °C under air cooling was studied by means of scanning infrared microscopy (SIRM), optical microscopy (OM), and transmission electron microscopy (TEM). The SIRM images showed that, in the A-defect zone of the Cu-contaminated silicon wafers, the copper-precipitate colonies with larger size were observed, while in the D-defect zone almost no copper precipitates could be observed. However, the OM results revealed that the density of etching pits in the D-defect zone was higher than that in the A-defect zone, indicating that the copper precipitates with smaller size and higher density formed in the D-defect zone. The TEM investigation showed that the size of copper precipitate colonies in the A-defect zone was about 300 nm, while that in the D-defect zone was about 50 nm. It is considered that as-grown vacancies in the D-defect zone enhanced the nucleation of copper precipitates but hindered their growth, whereas the role of as-grown interstitial silicon on copper precipitation was inverse.
Liquid gallium ball/crystalline silicon polyhedrons/aligned silicon oxide nanowires sandwich structure: An interesting nanowire growth route
Authors: Pan Zheng Wei , Dai Sheng , Beach David B. , Lowndes Douglas H.
Published: October 2003

We demonstrate the growth of silicon oxide nanowires through a sandwich-like configuration, i.e., Ga ball/Si polyhedrons/silicon oxide nanowires, by using Ga as the catalyst and SiO powder as the source material. The sandwich-like structures have a carrot-like morphology, consisting of three materials with different morphologies, states, and crystallographic structures. The “carrot” top is a liquid Ga ball with diameter of ∼10–30 μm; the middle part is a Si ring usually composed of about 10 μm-sized, clearly faceted, and crystalline Si polyhedrons that are arranged sequentially in a band around the lower hemisphere surface of the Ga ball; the bottom part is a carrot-shaped bunch of highly aligned silicon oxide nanowires that grow out from the downward facing facets of the Si polyhedrons. This study reveals several interesting nanowire growth phenomena that enrich the conventional vapor-liquid-solid nanowire growth mechanism.
A molecular picture of hydrophilic and hydrophobic interactions from ab initio density functional theory calculations
Authors: Meng Sheng , Wang E. G. , Gao Shiwu
Published: October 2003

A molecular picture of hydrophilic and hydrophobic interactions, which ubiquitously exist in nature, has been proposed based on ab initio density functional study of water at two prototype metal (Pt and Au) surfaces. We demonstrate that the hydrophilicity–hydrophobicity can be characterized by the water–surface coupling and the strength of the hydrogen bond at the interfaces. From this picture, Pt is found to be hydrophilic while Au is hydrophobic, in agreement with experiment. The effect of the charge transfer and the long-ranged electron polarization of water on these interactions are also elaborated.
Measurement of the average size and density of clusters in a gas jet
Authors: Kim K. Y. , Kumarappan V. , Milchberg H. M.
Published: October 2003

We present an all-optical method for measurement of the average size and density of clusters produced by high-pressure gas jet flow. The technique employs Rayleigh scattering imaging combined with interferometry. The cluster size and density in a gas jet under the irradiation of intense laser fields plays a critical role in the laser–cluster coupling dynamics.
160-A bulk GaN Schottky diode array
Authors: Baik K. H. , Irokawa Y. , Kim Jihyun , LaRoche J. R. , Ren F. , Park S. S. , Park Y. J. , Pearton S. J.
Published: October 2003

Pt Schottky rectifier arrays were fabricated on 200-μm-thick, freestanding GaN layers. Even with the reduced dislocation density in these layers (∼105 cm−2) relative to conventional GaN on sapphire (>108 cm−2), rectifiers fabricated on the freestanding GaN show a strong dependence of reverse breakdown on contact diameter. We show that by interconnecting the output of many (∼130) smaller (500 μm×500 μm) rectifiers, we can achieve high total forward output current (161 A at 7.12 V), low forward turn-on voltage of ∼3 V, and maintain the reverse breakdown voltage. The on/off ratio of the rectifier array was ∼8×107 at 5 V/−100 V.
High-resolution Fourier transform x-ray spectroscopy
Authors: Tamasaku Kenji , Ishikawa Tetsuya , Yabashi Makina
Published: October 2003

Fourier transform spectroscopy was extended to the x-ray region using an intensity correlation technique and a separate crystal design of an x-ray Michelson interferometer capable of a large path difference. A demonstration was presented measuring the bandwidth of Si 0 6 14 back diffraction as narrow as 12.8 attometers at a wavelength of 71.3 pm. Insensitivity of the resolution to the crystal perfection would open up ultrahigh-resolution spectroscopy beyond 10−9.
Frequency entrainment for micromechanical oscillator
Authors: Zalalutdinov M. , Aubin K. L. , Pandey M. , Zehnder A. T. , Rand R. H. , Craighead H. G. , Parpia J. M. , Houston B. H.
Published: October 2003

We demonstrate synchronization of laser-induced self-sustained vibrations of radio-frequency micromechanical resonators by applying a small pilot signal either as an inertial drive at the natural frequency of the resonator or by modulating the stiffness of the oscillator at double the natural frequency. By sweeping the pilot signal frequency, we demonstrate that the entrainment zone is hysteretic and can be as wide as 4% of the natural frequency of the resonator, 400 times the 1/Q∼10−4 half-width of the resonant peak. Possible applications are discussed based on the wide range of frequency tuning and the power gain provided by the large amplitude of self-oscillations (controlled by a small pilot signal).
Photoresist-free printing of amorphous silicon thin-film transistors
Authors: Miller Scott M. , Troian Sandra M. , Wagner Sigurd
Published: October 2003

Conventional fabrication of amorphous silicon thin-film transistors (a-Si TFTs) requires patterning numerous photoresist layers, a subtractive process that is time consuming and expensive. This letter describes transistor fabrication by a photoresist-free approach in which polymer etch masks are letterpress printed from flexible polyimide stamps. Pattern registration is achieved through optical alignment since the printed masks are thin and optically transparent. This modified fabrication scheme produces transistor performance equivalent to conventionally fabricated a-Si TFTs. The ability to directly print etch masks onto nonhomogeneous substrates brings one step closer the realization of flexible, large-area, macroelectronic fabrication.
Highly sensitive transverse load sensing with reversible sampled fiber Bragg gratings
Authors: Shu Xuewen , Chisholm Karen , Felmeri Ian , Sugden Kate , Gillooly Andrew , Zhang Lin , Bennion Ian
Published: October 2003

We present the implementation of optical load sensors utilizing mechanically induced reversible sampled fiber Bragg gratings (SFBGs). The load is measured by the reflectivity of the first-order Fourier component of the induced SFBGs. The theoretical and experimental characterization indicates that such SFBGs can be tailored to realize load sensors with high sensitivity of near-linear response and free of influence from environmental and system noises.
Strain relaxation in stacked InAs/GaAs quantum dots studied by Raman scattering
Authors: Ibáñez J. , Patanè A. , Henini M. , Eaves L. , Hernández S. , Cuscó R. , Artús L. , Musikhin Yu. G. , Brounkov P. N.
Published: October 2003

We report a Raman scattering investigation of InAs vibrational modes in multiple layers of InAs self-assembled quantum dots in a GaAs matrix. The Raman peak associated with quantum-dot phonons shows a downward frequency shift as the interlayer spacing decreases. We attribute this frequency shift to the relaxation of the elastic strain in the stacked quantum-dot layers. From the phonon frequency shift, we estimate the magnitude of the strain in the quantum dot layers, which we relate to the energy of the photoluminescence emission of the dots.
Reliable strain determination method for InGaAsN/GaAs quantum wells using a simple photoluminescence measurement
Authors: Kim N. J. , Jang Y. D. , Lee D. , Park K. H. , Jeong Weon G. , Jang J. W.
Published: October 2003

We present a reliable method for determining the strain in InGaAsN quantum wells. The method uses the fact that the splitting between heavy hole and light hole energy levels depends mostly on the strain. We also found that the strain was largely relaxed in an In0.34Ga0.66As/GaAs quantum well, but recovered when a small amount of nitrogen was added to the In0.34Ga0.66As layer.
Temperature-dependent Cl2/Ar plasma etching of bulk single-crystal ZnO
Authors: Lim W. T. , Baek I. K. , Lee J. W. , Lee E. S. , Jeon M. H. , Cho G. S. , Heo Y. W. , Norton D. P. , Pearton S. J.
Published: October 2003

The etch rate of bulk ZnO in Cl2/Ar high density plasmas was found to be thermally activated with an activation energy of ∼0.31 eV at <300 °C. The rate-limiting step appears to be the ion-assisted desorption of the ZnClX etch products. The threshold ion energy for etching ZnO at 150 °C in Cl2/Ar is ∼170 eV, obtained by fitting to a model of ion-enhanced sputtering by a collision-cascade process. The amount of residual chlorine on the ZnO surface decreases with increasing etch temperature, but there is a tendency for the surface to become Zn-rich and roughen at elevated temperatures (>200 °C).
Effect of the Ca content on the electronic structure of Pb1−xCaxTiO3 perovskites
Authors: Jan J. C. , Krishna Kumar K. P. , Chiou J. W. , Tsai H. M. , Shih H. L. , Hsueh H. C. , Ray S. C. , Asokan K. , Pong W. F. , Tsai M.-H. , Kuo S. Y. , Hsieh W. F.
Published: October 2003

This study performs O K- and Ti L3,2-edge x-ray absorption near-edge structure (XANES) measurements and first-principles pseudopotential calculations for the electronic structures of ABO3-type Pb1−xCaxTiO3 (x=0–1) perovskites. The features in the O K-edge XANES spectra are found to be contributed primarily by hybridization between O 2p and Ti 3d, Pb 6p, and Ca 3d orbitals. The O K-edge XANES spectra reveal that partial substitution of A cations, Pb, by Ca not only decreases O 2p–Pb 6p but also O 2p–Ti 3d hybridization. The Ti L3,2-edge measurements find that the off-center displacement of Ti, and hence, ferroelectricity persist up to a Ca concentration between 0.3 and 0.4.
Room-temperature light emission from a highly strained Si/Ge superlattice
Authors: Zakharov N. D. , Talalaev V. G. , Werner P. , Tonkikh A. A. , Cirlin G. E.
Published: October 2003

We discuss the formation of a Si/Ge-superlattice (SL) generated by molecular beam epitaxy. Specific growth parameter were chosen to optimize the periodic structure of vertically stacked Ge islands. Optimized SLs show a strong photoluminescence at a wavelength in the region of 1.55 μm up to room temperature. The luminescence is explained by a recombination of electrons in a miniband and holes localized in the Ge islands. The morphology and the crystal structure of the SL, which are influenced by the growth parameters, were analyzed by transmission electron microscopy techniques. It is demonstrated that doping of the SL structure by antimony improves both structural and optical properties.
Electronic structure of acceptor-donor complexes in silicon
Authors: Atoro E. , Ohama Y. , Hayafuji Y.
Published: October 2003

The electronic structure of trimer acceptor-donor complexes in silicon Si clusters is studied using the ab initio discrete variational-Xα molecular-orbital (MO) method. The trimer complexes In2D (D=phosphorus P, arsenic As, antimony Sb, or bismuth Bi) consist of two indium In acceptor elements and a centered donor element D from the group V elements. Calculations are performed under the assumption that the three atoms are arranged in the nearest neighbor substitutional trimer configuration. Results indicate that the trimer complexes act as shallower acceptors having smaller ionization activation energies than In acceptor. The potential of In2D as an acceptor in Si is then discussed and In2D is proposed as a promising acceptor for the formation of channels and source/drains in ultralarge scaled integration.
Nitrogen effects on lowering specific junction resistance and suppressing Mn diffusion in a magnetic tunnel junction
Authors: Shim Heejae , Cho B. K. , Kim Jin-Tae , Choi J. W. , Park Y.
Published: October 2003

We investigated the annealing effects of a magnetic tunnel junction on the Fe bottom pinned layer, of which the top surface was exposed to nitrogen plasma for a few tens of seconds prior to the deposition of the Al layer. The nitrogen-treated junction shows a lower magnetoresistance (MR) ratio and specific junction resistance (RA) than the untreated normal junction. However, after annealing at 230 °C, the MR ratio of the nitrogen-treated junction recovers to optimal values of the normal junction, while the RA remains lower than that of the normal junction. Furthermore, the nitrogen-treated junction shows less reduction of MR ratio and RA value with annealing at 270 °C for 3 h than the normal junction. From x-ray photoelectron spectroscopy and auger electron spectroscopy depth profiles, it is found that the nitrogen, which was initially at an interface between Al and Fe, diffuses into both the Al and FeMn layers after annealing at 230 °C. It seems that the nitrogen plays an important role in reducing Mn diffusion, as well as in improving the junction properties.
Activation and diffusion studies of ion-implanted p and n dopants in germanium
Authors: Chui Chi On , Gopalakrishnan Kailash , Griffin Peter B. , Plummer James D. , Saraswat Krishna C.
Published: October 2003

We have demonstrated symmetrically high levels of electrical activation of both p- and n-type dopants in germanium. Rapid thermal annealing of various commonly implanted dopant species were performed in the temperature range of 600–850 °C in germanium substrates. Diffusion studies were also carried out by using different anneal times and temperatures. T-SUPREM™ simulations were used to fit the experimental profiles and to extract the diffusion coefficient of various dopants.
Dynamics of the O(1D)+CO2 oxygen isotope exchange reaction
Authors: Perri Mark J. , Van Wyngarden Annalise L. , Boering Kristie A. , Lin Jim J. , Lee Yuan T.
Published: October 2003

The O1(D1)+CO2 oxygen isotope exchange reaction has been studied using a crossed molecular beam apparatus at a collision energy of 7.7 kcal/mol. Two different reaction channels are observed, both proceeding via a relatively long-lived CO3 complex. Electronic quenching of O(1D) is the major channel, accounting for 68% of all isotope exchange, while 32% occurs without quenching. These results are the first experimental evidence that isotope exchange can occur through a long-lived CO3 intermediate without subsequent crossing to the triplet surface, and could prove important for atmospheric models of oxygen isotope exchange between CO2 and O3.
Efficient wavelength-selective optical waveguiding in a silica layer containing Si nanocrystals
Authors: Khriachtchev Leonid , Räsänen Markku , Novikov Sergei
Published: October 2003

The optical properties of a silica layer containing Si nanocrystals deposited onto fused quartz are studied with emphasis on optical waveguiding (WG) of the photoluminescence (PL). The WG layer was estimated to be 4.3 μm thick with a refractive index of 1.67. We observed efficient (long-distance) propagation of the PL light in the layer, the losses being below 1 cm−1 at 1000 nm. Efficient narrowing of the PL spectrum (down to 8 meV) was detected demonstrating spectral filtering by the waveguide.
Two-photon optical absorption in PbO-SiO2 glasses
Authors: Tanaka K. , Yamada N. , Oto M.
Published: October 2003

One- and two-photon absorption spectra in PbO-SiO2 glasses have been studied comparatively as a function of the PbO content. The two spectra show different composition dependence, which can be accounted for by taking related electronic wave functions and the densities-of-states into account. This interpretation can be extended to understand high optical nonlinearity in heavy-metal oxide glasses.
β
-phase tungsten nanorod formation by oblique-angle sputter deposition
Authors: Karabacak Tansel , Mallikarjunan Anupama , Singh Jitendra P. , Ye Dexian , Wang Gwo-Ching , Lu Toh-Ming
Published: October 2003

We report the creation of an unusual simple cubic β-phase W(100) nanorods with a pyramidal tip having four (110) facets using an oblique-angle sputter deposition technique with substrate rotation (also known as glancing-angle deposition). During the oblique-angle deposition, both β-phase W(100) and α-phase W(110) islands exist at the initial stages of growth. The β-phase W(100) islands grow taller due to the lower adatom mobility on these islands. The taller islands survive in the competition and form isolated nanorods in the later stages of growth. This is in contrast to the sputter deposition at normal incidence, where only the thermodynamically stable bcc α-phase W(110) polycrystalline films were formed when the film grows to a certain thickness.
Electrically tunable mid-infrared electroluminescence from graded cascade structures
Authors: Vasilyev Yu. B. , Solov’ev V. A. , Meltser B. Ya. , Semenov A. N. , Ivanov S. V. , Kop’ev P. S. , Ulbrich N. , Abstreiter G. , Amann M.-C. , Schmult S. , Wegscheider W.
Published: October 2003

Mid-infrared electroluminescence (EL) is observed from multiperiod bilayer type-II InAs/AlGaSb structures with the effective interlayer separation controlled by bias. The emission with powers in the microwatt range is characterized by a linear dependence of the photon energy on the bias. By measuring the temperature and current dependence of EL, we find evidence that the EL emission results from recombination of holes in AlGaSb quantum wells (QWs) with electrons occupying two different quantum states in InAs QWs.
Effect of nanoparticles on critical heat flux of water in pool boiling heat transfer
Authors: You S. M. , Kim J. H. , Kim K. H.
Published: October 2003

The present study is to enhance the critical heat flux (CHF) in pool boiling from a flat square heater immersed in nanofluid (water mixed with extremely small amount of nanosized particles). The test results show that the enhancement of CHF was drastic when nanofluid is used as a cooling liquid instead of pure water. The experiment was performed to measure and compare pool boiling curves of pure water and nanofluid at the pressure of 2.89 psia (Tsat=60 °C) using 1×1 cm2 polished copper surfaces as a boiling surface. The tested nanofluid contains alumina (Al2O3) nanoparticles dispersed in distilled and deionized water. Tested concentrations of nanoparticles range from 0 g/l to 0.05 g/l. The measured pool boiling curves of nanofluids saturated at 60 °C have demonstrated that the CHF increases dramatically (∼200% increase) compared to pure water case; however, the nucleate boiling heat transfer coefficients appear to be about the same.
High Curie temperature piezocrystals in the BiScO3-PbTiO3 perovskite system
Authors: Zhang Shujun , Randall Clive A. , Shrout Thomas R.
Published: October 2003

Perovskite ferroelectric single crystals in the (1−x)BiScO3-xPbTiO3 (BSPT) system were grown using a flux method. The Curie temperature of rhombohedral BSPT(43/57) crystals was found to be about 404 °C, with a rhombohedral–tetragonal phase transition temperature (Tr−t) around 350 °C. The coercive field (Ec) was found to be 13.7 kV/cm for 〈001〉-oriented crystals, while the coupling factor k33 was determined to be ∼90% at room temperature and was nearly temperature independent until 330 °C. High piezoelectric properties together with a high Curie temperature and coercive field make rhombohedral BSPT crystals promising candidates for the next generation of high-performance, high-temperature actuators and transducers.
Design, fabrication, and characterization of coupling-strength-controlled directional coupler based on two-dimensional photonic-crystal slab waveguides
Authors: Sugimoto Y. , Tanaka Y. , Ikeda N. , Yang T. , Nakamura H. , Asakawa K. , Inoue K. , Maruyama T. , Miyashita K. , Ishida K. , Watanabe Y.
Published: October 2003

A directional coupler (DC) with a coupling-strength control defect (CCD) based on a two-dimensional photonic-crystal slab waveguide is numerically and experimentally studied. The structure consists of two parallel-coupled single-defect waveguides separated by a triple-line air-hole array, with some missing air holes in the middle of the triple line. Using a two-dimensional finite-difference time-domain method, a 50% coupler was designed and almost 50% coupling performance was experimentally confirmed at a wavelength of ∼1.3 μm with a coupling length of about 7 μm, about 1/3 in length as compared to the DC without the CCD.
Silicon substrate integrated high Q-factor parallel-plate ferroelectric varactors for microwave/millimeterwave applications
Authors: Vorobiev A. , Rundqvist P. , Khamchane K. , Gevorgian S.
Published: October 2003

Parallel-plate Ba0.25Sr0.75TiO3 (BST) varactors with a record high Q factor are fabricated on Si substrate. At 45 GHz the Q factor is about 40, and the tuneability at 25 V is more than 40% in the measured frequency range 0.045–45 GHz. The improvement in the Q factor is achieved by using a thick bottom electrode consisting of Pt (50 nm)/Au (0.5 μm) allowing us to reduce the microwave losses associated with metal layers. The BST films exhibit relatively high permittivity (150) at zero bias and high resistivity (1010 Ω cm) at fields up to 700 kV/cm.
Burn-in effect on GaInP heterojunction bipolar transistors
Authors: Mimila-Arroyo J.
Published: October 2003

The burn-in effect in metalorganic chemical vapor deposition grown GaInP/GaAs heterojunction bipolar transistors is explained as due to the passivation of hydrogen-related recombination centers in the emitter. Results show that the diffusion base current contribution is dominated by the recombination in the emitter neutral region. The recombination centers are deactivated through the capture of electrons, available under forward bias, increasing the hole diffusion length and decreasing the diffusion contribution of the base current producing the observed current gain increase. These processes produce an independent behavior of the diffusion ideality factors for holes and electrons at each side of the emitter junction.
Influence of image force and many-body correction on electron mobility in ultrathin double gate silicon on insulator inversion layers
Authors: Gámiz F. , Cartujo-Cassinello P. , Jiménez-Molinos F. , Carceller J. E. , Cartujo P.
Published: October 2003

We study the influence of the image and exchange-correlation effects in double-gate silicon-on-insulator (DGSOI) devices, in the calculation of both charge distribution and electron mobility. The image and exchange correlation potentials produce a greater confinement of the carriers and, according to the uncertainty principle, a greater phonon scattering rate, which produces a decrease in electron mobility. Moreover, the influence of image and exchange-correlation potentials on electron mobility, while almost negligible for bulk silicon inversion layers, becomes increasingly important as the silicon thickness decreases, due to the effect of volume inversion in DGSOI inversion layers. These effects must then be taken into account in order to achieve a correct evaluation of the charge distribution and of mobility in DGSOI inversion layers.
Observation of huge nonlinear absorption enhancement near exciton resonance in GaN
Authors: Lin Kung-Hsuan , Chern Gia-Wei , Huang Yin-Chieh , Keller Stacia , DenBaars Steven P. , Sun Chi-Kuang
Published: October 2003

Huge excitonic enhancement of two-photon absorption near the exciton-transition energy was observed in the GaN system. The peak value of the nonlinear absorption coefficient is at least 1500 cm/GW, corresponding to an enhancement factor of >100. The room temperature exciton dephasing time is also obtained based on a spectral analysis to be ∼150 fs in bulk GaN, which is close to the exciton ionization time.
Origin of nondetectable x-ray diffraction peaks in nanocomposite CuTiZr alloys
Authors: Jiang J. Z. , Kato H. , Ohsuna T. , Saida J. , Inoue A. , Saksl K. , Franz H. , Ståhl K.
Published: October 2003

Microscopic structures of Cu60Ti10+xZr30−x (x=0 and 10) alloys have been investigated by transmission electron microscopy, x-ray diffraction (XRD) and differential scanning calorimeter (DSC). In the Cu60Ti10Zr30 samples annealed at 708 K for times ranging from 0 to 130 min, where the enthalpy of the first exothermic peak decreases by 80%, the corresponding XRD patterns still look similar to that for the as-prepared sample. However, the simulated XRD patterns for the pure Cu51Zr14 phase, which is the crystalline phase formed during the first exothermic reaction, with small grain sizes and defects clearly show a broadened amorphous-like feature. This might be the reason that no diffraction peaks from the nanocrystalline component were detected in the XRD patterns recorded for the as-cast or as-spun Cu60Ti10+xZr30−x (x=0 and 10) alloys and for the alloys annealed at lower temperatures, in which the enthalpy of the first exothermic peak has a significant reduction. The second exothermic peak found in DSC curves is due to the formation of another hexagonal phase, spacing group P63/mmc (194) and lattice parameters a=5.105 Å and c=8.231 Å.
Ultrabroadband terahertz radiation from low-temperature-grown GaAs photoconductive emitters
Authors: Shen Y. C. , Upadhya P. C. , Linfield E. H. , Beere H. E. , Davies A. G.
Published: October 2003

Terahertz radiation was generated with a biased and asymmetrically excited low-temperature-grown GaAs photoconductive emitter, and characterized with a 20-μm-thick ZnTe crystal using free-space electro-optic sampling. Using a backward collection scheme, we obtained terahertz radiation with frequency components over 30 THz, the highest ever observed for photoconductive emitters. We present spectra over the whole frequency range between 0.3 and 20 THz, demonstrating the use of this source for ultrabroadband THz spectroscopy.
Metalorganic vapor-phase epitaxial growth and characterization of vertical InP nanowires
Authors: Bhunia S. , Kawamura T. , Watanabe Y. , Fujikawa S. , Tokushima K.
Published: October 2003

Highly dense and free-standing InP nanowire structures of vertical orientation were grown by the metalorganic vapor-phase epitaxial technique using colloidal Au nanoparticles as the catalyst. Scanning electron microscopy and transmission electron microscopy showed that the nanowires were single crystalline with 〈111〉 growth direction and of uniform length of about 700 nm, and most of them had diameter in the range of 20–25 nm. Photoluminescence measurements, carried out at room temperature as well as at 77 K, showed a significant blueshift in the peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires. The successful growth of these nanowires opens up the possibility of realizing various nanoscale devices on the wafer scale in the bottom-up approach.
Electric-field switching of orbital order in layered manganites
Authors: Hatsuda K. , Kimura T. , Tokura Y.
Published: October 2003

We have investigated the electric-field effect on the orbital-ordered state of eg electrons for layered manganites Nd1−xSr1+xMnO4 near the phase boundary between antiferro d3x2−r2/d3y2−r2 and ferro d3x2−r2 orbital-ordered phases. By means of a polarization microscope in crossed-Nicol configuration, we can distinguish these two orbital-ordered phases, and observed the electric-field switching between the two phases. This indicates that the electric-field can affect the directional order of orbital, and the system with the two competitive orbital-ordered states bears the orbital analog of the liquid-crystal functionality.
Thermal expansion coefficient of hydrogenated amorphous carbon
Authors: Marques F. C. , Lacerda R. G. , Champi A. , Stolojan V. , Cox D. C. , Silva S. R. P.
Published: October 2003

The coefficient of thermal expansion (CTE) of hydrogenated amorphous carbon (a-C:H) was investigated as a function of the concentration of sp2 hybridization. The CTE, determined using the thermally induced bending technique, depends on the concentration of sp2 bonded carbon, increasing to the value of graphite as the sp2 concentration approaches 100%. By using a combination of the thermally induced bending technique and nanohardness measurements, we extract separately the Young’s modulus and Poisson’s ratio of the a-C:H films as function of the sp2 concentration.
Hybrid organic-inorganic photoconductive diode
Authors: Wang Qi , Shaheen Sean E. , Williams Evan L. , Jabbour Ghassan E.
Published: October 2003

A hybrid organic-inorganic diode has been fabricated by hot-wire chemical vapor deposition of low process temperature (<140 °C) hydrogenated amorphous silicon (a-Si:H) onto a spin-coated layer of poly(N-vinylcarbazole) (PVK). The hybrid device was found to be a photoconductive diode with a high photosensitivity of near 700, a high photogain of over 100, and a response time of 500 μs. The high photosensitivity of the a-Si:H intrinsic layer and the large barrier for carrier injection at the PVK/a-Si:H interface are responsible for the good performance.
Morphology of femtosecond-laser-ablated borosilicate glass surfaces
Authors: Ben-Yakar Adela , Byer Robert L. , Harkin Anthony , Ashmore Jacqueline , Stone Howard A. , Shen Mengyan , Mazur Eric
Published: October 2003

We study the morphology of borosilicate glass surface machined by femtosecond laser pulses. Our observations show that a thin rim is formed around ablated craters after a single laser pulse. When multiple laser pulses are overlapped, the crater rims also overlap and produce a surface roughness. The rim appears to be a resolidified splash from a molten layer generated during the ablation process. We estimate that this molten layer is a few micrometers thick and exists for a few microseconds. During this melt lifetime, forces acting on the molten layer move it from the center to the edge of the crater.
Tensile stress in hard metal films
Authors: Janssen G. C. A. M. , Dammers A. J. , Sivel V. G. M. , Wang W. R.
Published: October 2003

Thin films on substrates are usually in a stressed state. An important, but trivial, contribution to that stress stems from the difference in thermal expansion coefficient of substrate and film. Much more interesting are the intrinsic stresses, resulting from the growth and/or microstructure of the film. Intrinsic compressive stress was explained by d’Heurle in 1970. Intrinsic tensile stress for recrystallizing metal films was treated succesfully by Doljack and Hoffman in 1972. In the present letter we explain the occurrence of tensile stress in nonrecrystallizing metal films. The explanation is based on modern grain growth models and accurate stress measurements. The key ingredient to the explanation is the proof of the existence of a stress gradient in nonrecrystallizing metal films.
Structuring nanodiamond cone arrays for improved field emission
Authors: Zhang W. J. , Wu Y. , Wong W. K. , Meng X. M. , Chan C. Y. , Bello I. , Lifshitz Y. , Lee S. T.
Published: October 2003

A structuring method capable of producing uniform, large-area cone arrays of diamond films was developed. The technique employs bias-assisted reactive ion etching and is applicable to any structure of diamond films ranging from microcrystalline to nanocrystalline. Variation of the etching conditions enables control of the cone density, geometry, and height. Surface nanostructuring of cone arrays significantly improves the field emission properties of diamond films of all kinds. The turn on field is reduced to 6 and 10 V/μm for nanodiamond and microdiamond films, respectively, (compared to >25 V/μm for as deposited surfaces). Lower cone density yields better field electron emission (lower turn-on electrical field) due to the screening in high-density cone arrays. The field emission properties are determined by both the enhancement factor of the cone array and the emitting properties of the material. The field electron emission properties of nanodiamond arrays are better than cone arrays of single crystalline diamond with a similar cone density and cone geometry.
Magnetic moment compensation in exchange-biased trilayers with antiparallel spin alignment
Authors: Fan Yang-Hsiung , Brückl Hubert
Published: October 2003

Trilayers consisting of ferromagnetic rare earth and transition metals show an antiparallel exchange coupling of the individual layers. Thus, they can be exploited as hardmagnetic electrodes in spin valve stacks and magnetic tunnel junctions for sensors or memories. Magnetic tunnel junctions consisting of IrMn exchange-biased NiFe/Gd/NiFe trilayers show a compensation of the total magnetic moment at an appropriate choice of the individual layer thicknesses and temperature. This stack setup allows a sixfold enhancement of the exchange-bias field and a strong reduction of the Néel and edge stray field coupling in patterned elements. Therefore, such trilayers are proposed as an alternative for artificial ferrimagnets in the relevant devices.
Pillar-lattice-assisted stress-free silicon-on-insulator
Authors: Haisma Jan
Published: October 2003

Standard silicon-on-insulator (SOI) technology is hampered by dilatation mismatch between silicon and its thermal oxide: the thin silicon top-layer is subjected to tensile stress. However, by combining three advanced technologies: covalent bonding, nanoimprint lithography, and Smart-Cut thinning, an insulating, pillar-lattice-structured, and bonded intermediate layer can be created to relieve the dilatation-determined tensile stress. The insulated silicon top-layer properties of this so-called lattice-SOI resemble those of bulk silicon. The layer optimizes the electrical characteristics, shows no warp, no stress-corrosion, and can be upgraded to a zero defect density by annealing. This proposal of lattice-SOI technology should have an important impact on the SOI quality level against bulk silicon in comparison with standard SOI.
Evidence of second-order nonlinear susceptibility sign reversal in thermally poled samples
Authors: Kudlinski A. , Quiquempois Y. , Zeghlache H. , Martinelli G.
Published: October 2003

Thin layers of silica have been removed from thermally poled samples using a hydrofluoric acid etching. After each etching, the second-harmonic signal generated within the remaining glass has been recorded by means of a Maker fringes experiment. Evidence of a sign reversal within the nonlinear distribution is pointed out for 10-min poled Infrasil™ samples.
Organic light-emitting diodes driven by pentacene-based thin-film transistors
Authors: Kitamura M. , Imada T. , Arakawa Y.
Published: October 2003

Integrated circuits with an organic light-emitting diode (OLED) and a thin-film transistor (TFT) based on small molecules were fabricated on a glass substrate. The field-effect mobility and the current on/off ratio of the integrated TFTs with a pentacene layer deposited at room temperature were 0.12 cm2/V s and higher than 103, respectively. The OLEDs had a multilayer structure containing tris-(8-hydroxyquinoline) aluminum doped with coumarin 6 to obtain high luminance efficiency. The luminance was controlled in the range of up to approximately 1000 by applying the gate voltage of 10 to −10 V. The value of the luminance is sufficient for conventional displays.
Transmission electron microscopy investigation of dislocations in forward-biased 4H-SiC p–i–n diodes
Authors: Zhang Ming , Pirouz Pirouz , Lendenmann Heinz
Published: October 2003

When a 4H-SiC p–i–n diode is operated under forward biasing, it rapidly degrades, and the degradation is accompanied by the generation of a high density of stacking faults in the active region of the device. In this letter, the partial dislocations bounding the stacking faults have been investigated by transmission electron microscopy. They are found to be in the form of single leading partial half-loops with a 13〈101̄0〉 Burgers vector that bound triangular-shaped stacking faults. Two sides of each faulted loop are bound by two partial dislocation segments lying along different 〈12̄10〉 directions, while the other edge of the triangular stacking fault is a surface (or interfacial) step. The core nature of the two segments has been determined by the technique of large-angle, convergent-beam electron diffraction, and found to be different: one has a silicon core, while the other has a carbon core.
Active silicon-based two-dimensional slab photonic crystal structures based on erbium-doped hydrogenated amorphous silicon alloyed with carbon
Authors: Choi Yong-Seok , Sung Joo Yeon , Kim Se-Heon , Shin Jung H. , Lee Yong-Hee
Published: October 2003

Two-dimensional (2D) slab photonic crystals based on Er-doped hydrogenated amorphous silicon alloyed with carbon (a-Si:H:C) are proposed and realized. Freestanding and oxide-cladding slab structures are fabricated and compared. 2D slab active photonic crystal structures show enhanced extraction of the trivalent erbium ion (Er3+) luminescence independent of the pump intensity. Temperature-insensitive light extraction efficiency with negligible surface-related nonradiative recombination was experimentally observed. The maximum enhancement became eightfold in freestanding slab structures.
Stretching of megabase-sized deoxyribonucleic acid molecules by tuning electric-field frequency
Authors: Kaji Noritada , Ueda Masanori , Baba Yoshinobu
Published: October 2003

Despite the technical difficulties of dealing with chromosome deoxyribonucleic acid (DNA) molecules, over a megabase pair (Mbp) in size, yeast chromosome DNA molecules, over hundreds of micrometers in length, were stretched from random coil conformation within a few minutes by careful tuning of the ac field frequency in a 1% agarose gel. This rapid and efficient stretching method was accomplished by a combination of optimal conditions for the stretching process and maintenance of stretched conformation. In the stretching process, Mbp DNA gets easily trapped in gel fibers. So achieving a stretched conformation without the trapping was accomplished by tuning the field frequency according to the conformation at the moment. Once stretched out, any sized DNA could be maintained in a stretched conformation under a 10 Hz ac field. As compared with shorter DNA, longer DNA existed in stretched conformation under a wide range of ac field frequencies.
Pressure effect on glass transition in a Zr65Al7.5Cu27.5 metallic glass
Authors: Jin H. J. , Wen P. , Lu K.
Published: October 2003

By means of the enthalpy recovery experiments in a Zr65Al7.5Cu27.5 metallic glass, the glass transition process was found to correlate with an obvious variation of enthalpy change with the annealing temperature. With this correlation, we developed an approach to determine the pressure effect on the glass transition temperature (Tg), and a drastic increment of Tg up to 50 K was observed in this glass when a hydrostatic pressure of 5 GPa was applied. It is much smaller than that observed in nonmetallic glasses, which is attributed to smaller activation volume of the relaxation in metallic glasses.
Electron spin resonance observation of trapped electron centers in atomic-layer-deposited hafnium oxide on Si
Authors: Kang A. Y. , Lenahan P. M. , Conley J. F.
Published: October 2003

We observed two paramagnetic defects in thin films of HfO2 on silicon with electron spin resonance. Both appear after photoinjecting electrons into the dielectric. Strong spectroscopic evidence links one spectrum to an O2− defect. A second spectrum is likely due to an Hf+3 related defect.