bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoair-bridged lateral overgrowth of GaN on ordered nanoporous GaN template
Authors: Wang Y. D. , Zang K. Y. , Chua S. J. , Tripathy S. , Chen P. , Fonstad C. G.
Published: December 2005

We report the growth of high-quality GaN epilayers on an ordered nanoporous GaN template by metalorganic chemical vapor deposition. The nanopores in GaN template were created by inductively coupled plasma etching using anodic aluminum oxide film as an etch mask. The average pore diameter and interpore distance is about 65 and 110nm, respectively. Subsequent overgrowth of GaN first begins at the GaN crystallite surface between the pores, and then air-bridge-mediated lateral overgrowth leads to the formation of the continuous layer. Microphotoluminescence and micro-Raman measurements show improved optical properties and significant strain relaxation in the overgrown layer when compared to GaN layer of same thickness simultaneously grown on sapphire without any template. Similar to conventional epitaxial lateral overgrown GaN, such overgrown GaN on a nanopatterned surface would also serve as a template for the growth of ultraviolet-visible light-emitting III-nitride devices.
Larger polarization and weak ferromagnetism in quenched BiFeO3 ceramics with a distorted rhombohedral crystal structure
Authors: Zhang S. T. , Lu M. H. , Wu D. , Chen Y. F. , Ming N. B.
Published: December 2005

Single-phase insulating BiFeO3 ceramics have been synthesized by a simple but effective method that conventional solid state reaction is followed immediately by quenching processing. At room temperature, the ceramics show a metastable, distorted rhombohedral phase and the refined structure parameters are presented based on x-ray diffraction. It is revealed that the formations of Fe2+ and oxygen deficiency are greatly suppressed by the quenching processing. A well-saturated ferroelectric hysteresis loop with a large remnant polarization (2Pr=23.5μC∕cm2) is observed with an applied field of 155kV∕cm. Temperature-dependent magnetic property is investigated and weak ferromagnetism with a remnant magnetization of 4×10−6μB∕Fe at 10K is established. These results may have implications for further studies on multiferroics.
Self-assembly of steps and vacancy lines during the early stages of Ge∕Si(001) heteroepitaxy
Authors: Tambe D. T. , Ciobanu C. V. , Shenoy V. B.
Published: December 2005

The wetting layer formed during the early stages of Ge∕Si(001) growth has been found in recent experiments to undergo a roughening process, where the SA surface steps affect the spatial organization of vacancy lines (VLs) by increasing (stretching) or decreasing (squeezing) their average spacing. Using a combination of atomistic simulations and elastic theory of surface defects, we have computed the interaction energy of the SA steps and VLs for each of the observed defect configurations. We find that the repulsive SA-VL interactions lead to an increase in the spacing of the VLs in the “stretch” arrangement, but do not significantly affect the VL spacing in the “squeeze” configuration, providing an explanation for the observed correlations in the wetting layer roughness.
Grain boundary migration as rotational deformation mode in nanocrystalline materials
Authors: Gutkin M. Yu. , Ovid’ko I. A.
Published: December 2005

Stress-induced grain boundary migration is theoretically described as a new mode of rotational plastic deformation in nanocrystalline materials. We have calculated the strain energy change due to migration of a grain boundary that carries rotational plastic flow. It is shown that, depending on the stress level, the grain boundary can either be immobile or mobile, and in the latter case it can migrate in either a stable or unstable regime. The critical stress values, which correspond to the transitions between these migration regimes, are estimated and discussed.
Crystal orientation dependence of the electro-optic effect in epitaxial lanthanum-modified lead zirconate titanate films
Authors: Sato Keisuke , Ishii Masatoshi , Kurihara Kazuaki , Kondo Masao
Published: December 2005

Lanthanum-modified lead zirconate titanate epitaxial films with (100), (101), and (111) orientations were grown on (100), (101), and (111) niobium lending conductivity strontium titanate using chemical solution deposition, respectively. We investigated the changes in the refractive index induced by the electric field in these films using the prism coupling method. Birefringence was observed in the (101)- and (111)-oriented epitaxial films induced by the electric field. However, no birefringence was observed in the (100) epitaxial film. This crystal orientation dependence of the electrooptic effect can be explained by the rotation of the refractive indicatrix that accompanies the switching of the polar clusters.
Thermal stability of a slab waveguide implemented by α particles implantation in potassium lithium tantalate niobate
Authors: Gumennik Alexander , Agranat Aharon J. , Shachar Igal , Hass Michael
Published: December 2005

A slab waveguide was fabricated in a potassium lithium tantalate niobate crystal by the implantation of He2+ ions at 2.26 MeV. The waveguide profile and loss were evaluated by measuring the dark mode TE spectrum using the prism coupling method at λ=1.3μm. The implantation generated amorphous cladding layer 5μm below the surface of the crystal with a refractive index lower by 3.9% then that of the substrate. The propagation loss of the waveguided modes was found to be 0.1–0.2dB∕cm. Thermal stability of the waveguide was obtained by isothermal annealing at 351 and 446 °C. Following the annealing the waveguide index profile remained unchanged when subjected to annealing at 150 °C for one week.
Observation of exciton molecule consisting of two different excitons in coupled quantum dots
Authors: Goshima Keishiro , Yamauchi Shohgo , Komori Kazuhiro , Morohashi Isao , Sugaya Takeyoshi
Published: December 2005

We propose and experimentally investigate an exciton molecule consisting of two different excitons in coupled quantum dots (QDs). Quantum mechanical coupling between double QDs leads to the creation of bonding and antibonding states and should yield an exciton molecule consisting of two excitons that originate from these two states. We prepared a quantum mechanically coupled QD system and succeeded in observing a single exciton molecule in a single pair of coupled QDs by means of a two-color excitation photoluminescence measurement.
Soft mode behavior and phase transition in BaxSr1−xTiO3
Authors: Wu H. , Shen W. Z.
Published: December 2005

We present a clear picture for soft mode behavior and ferroelectric phase transition in BaxSr1−xTiO3 throughout the concentration range (x from 0 to 1), by proposing a simple way to quantitatively explain all the experimental data in the literature. The approach was realized through combining the transverse-field Ising model with the Lyddane-Sachs-Tell relation, cell volume effect, and ferroelectric distortion. It is found that, with the increase of impurity concentration, the soft mode softens in the paraelectric phase, and stiffens in the ferroelectric one, where the phase transition will change from the second order to the first order at high concentration (x⩾0.57). We have further shown the quantum effect on the soft mode in BaxSr1−xTiO3 with the concentration below 0.10.
Single-electron tunneling at room temperature in TixSi1−xO2 nanocomposite thin films
Authors: Sarkar D. K. , Brassard D. , El Khakani M. A. , Ouellet L.
Published: December 2005

Titanium silicate (TixSi1−xO2) nanocomposite thin films containing dispersed TiO2 nanocrystallites have been grown by means of an optimized sol-gel process. The size of the TiO2 nanoprecipitates was varied from ∼1to22nm by controlling the content of the TiO2 component of the films. For the Ti0.40Si0.60O2 film composition, which contains TiO2 nanoparticles of ∼1nm diameter, regular oscillations are observed in their conductance-voltage characteristics in the mid-to-high-fields range. This abnormal behavior can be interpreted by single-electron tunneling at room temperature between the TiO2 nanocrystallites separated by the wider band-gap amorphous TixSi1−xO2 phase.
Applicability of Born’s stability criterion to face-centered-cubic crystals in [111] loading
Authors: Milstein Frederick , Zhao Jianhua , Chantasiriwan Somchart , Maroudas Dimitrios
Published: December 2005

The applicability of Born’s criterion for the assessment of structural stability of perfect crystals under mechanical loading is examined for the case of face-centered-cubic (fcc) crystals subjected to uniaxial [111] loading. The analysis is based on the results of lattice-statics calculations and isostress molecular-dynamics simulations of the mechanical response of model fcc metallic crystals to applied loading. Born’s criterion is found to provide a good predictor of loss of stability under tension, in conjunction with “universal” characteristics of the strain dependent elastic moduli.
Strain relaxation in patterned strained silicon directly on insulator structures
Authors: Lei R. Z. , Tsai W. , Aberg I. , O’Reilly T. B. , Hoyt J. L. , Antoniadis D. A. , Smith Henry I. , Paul A. J. , Green M. L. , Li J. , Hull R.
Published: December 2005

Strain relaxation is studied in strained silicon directly on insulator (SSDOI) substrates patterned with nanoscale features. Using interference lithography, biaxially strained SSDOI substrates with 30nm thick strained Si on insulator films were patterned into grating structures with 90nm wide stripes, and arrays of 80nm×170nm pillars. The strain profiles of these patterned structures were examined by ultraviolet Raman spectroscopy. Raman analysis of the SSDOI gratings indicates strain relaxation in the 90nm wide stripes, compared to the strain measured in unpatterned portions of the SSDOI wafer. Three-dimensional finite-element modeling of the stress distributions in the grading structures predicts that 95% of the strain is maintained in the direction along the length of the stripes. These simulations are used to decouple the strain components along the width and length of the SSDOI grating structure, inferred from Raman measurements. The results are consistent with substantial stress relaxation across the width of the stripes and very little stress relaxation along the length of the stripes.
Carrier relaxation dynamics in annealed and hydrogenated (GaIn)(NAs)∕GaAs quantum wells
Authors: Hantke K. , Heber J. D. , Chatterjee S. , Klar P. J. , Volz K. , Stolz W. , Rühle W. W. , Polimeni A. , Capizzi M.
Published: December 2005

We measured time-resolved photoluminescence on as-grown, annealed, as well as annealed and hydrogenated (Ga0.7In0.3)(N0.006As0.994)∕GaAs quantum-well structures. The postgrowth treatment changes not only the photoluminescence decay time but also the intensity of photoluminescence directly after excitation. This initial luminescence intensity is determined by a competition between relaxation of electrons into nitrogen related potential fluctuations in the conduction band and their capture by deep traps. In contrast, the decay of the photoluminescence is mainly determined by the competition between radiative and nonradiative recombination, which are both influenced by localization. Annealing decreases localization effects and nonradiative recombination. Hydrogenation also reduces localization effects but increases nonradiative recombination.
Highly efficient tunable tapered-polymer-fiber lasers
Authors: Peng Qinjun , Wang Guiling , Bo Yong , Guo Xinjun , Geng Aicong , Xu Zuyan , Ren Liyong , Zhang Yani , Wang Yishan , Zhao Wei , Wang Lili
Published: December 2005

A highly efficient tunable tapered-polymer-fiber (TPF) laser was demonstrated by use of a compound parabolic TPF doped with Rhodamine-6G (R6G) dye. The tuning ranges over 40nm at the visible region for laser output with the maximum output energy of 600μJ at 570nm and the optical-optical conversion efficiency of 23% were achieved by a prism as a spectrally selective element. Moreover, the coupling efficiency for the taper exceeded 90%. Compared to traditional polymer fibers with a micrometer-size core diameter, the taper allows for a higher pump to be launched without damaging the fiber endfaces, and it can efficiently couple the light into the fiber and alleviate the alignment difficulty. So, the TPF laser not only possesses all of the advantages of traditional polymer-fiber lasers, and it can also obtain higher output energy and higher efficiency. Additionally, it is insensitive to geometrical displacements.
Effect of Cl2∕Ar dry etching on p-GaN with Ni∕Au metallization characterization
Authors: Hsueh Kuang-Po , Hsu Hung-Tsao , Wang Che-Ming , Huang Shou-Chian , Hsin Yue-Ming , Sheu Jinn-Kong
Published: December 2005

This work investigates the effect of Cl2∕Ar dry etching on p-GaN. The root-mean-square (rms) surface roughness is measured, and the depth display (Bearing analysis) is monitored. The current-voltage characteristics of etched p-GaN with Ni(20nm)∕Au(20nm) metallization are studied. Experimental results indicate that the etching rate does not increase significantly with the Cl2 flow rate at a constant power or chamber pressure. The Bearing ratio data exhibit a much stronger variation with etch conditions, the rms displays the same trend but to a lesser extent.
Strong and stable ultraviolet emission from porous silicon prepared by photoetching in aqueous KF solution
Authors: Tomioka Katsuhiro , Adachi Sadao
Published: December 2005

A new method of fabricating porous silicon emitting in the ultraviolet (UV) spectral region is presented. This method uses photoetching in an aqueous salt (KF) solution. Strong UV photoluminescence is observed at ∼3.3eV with a full width at a half maximum of ∼0.1eV, which is much narrower than those reported previously. Fourier transform infrared spectroscopy suggests that the surface oxide produced during photoetching plays an important role in the UV emission of the KF-prepared PSi.
All optically tunable wavelength-selective reflector consisting of coupled polymeric microring resonators
Authors: Scheuer Jacob , Paloczi George T. , Yariv Amnon
Published: December 2005

We present an all optically tunable wavelength-selective reflector for planar lightwave technology based on coupled microring resonators. By employing the Vernier effect, we demonstrate narrow-band reflection and strong side-lobe suppression in an optical polymer device fabricated by soft lithography. Wide and simple tuning of the reflection peak using an external control beam is demonstrated.
Temperature dependence of the return current in Bi2Sr2CaCu2Ox stacks fabricated by self-planarizing process
Authors: Okanoue K. , Hamasaki K.
Published: December 2005

We investigated the temperature variation of the return currents of stacked Bi2Sr2CaCu2Ox (Bi-2212) intrinsic Josephson junctions fabricated using self-planarizing process. In this process, the Bi-2212 crystal around the junction window was changed to an insulator by soaking it into the solution of dilute hydrochloric acid. The current-voltage characteristics of the stacks with areas as large as 30×40μm2 exhibited large hystereses and multiple branches at 4.2K, which can be explained by a series connection of highly capacitive Josephson junctions. At higher temperatures than 40K, we found that the return current Ir of the intrinsic junction depended strongly on the temperature, T. We analyzed the Ir-T characteristics using simple resistively and capacitively shunted junction model in view of the temperature dependence of the c-axis resistance of the stack.
Optical properties of nanocluster-assembled ZnO thin films by nanocluster-beam deposition
Authors: Zhao Z. W. , Tay B. K. , Chen J. S. , Hu J. F. , Sun X. W. , Tan S. T.
Published: December 2005

Nanocluster-assembled ZnO thin films have been synthesized by nanocluster-beam deposition, and the films exhibit a band-gap energy at 323.7nm (3.84eV) and ultraviolet (UV) light emission at 373nm (3.32eV) with an average particle size of 6nm. A comparison of the optical properties of the annealed films with that of as-grown one is presented. It is found that, after the film is annealed, the shoulder in the absorbance spectra turns steeper and the intensity of UV light emission band becomes stronger. Moreover, blueshifts of band-gap energy and a UV emission band are both observed as decreasing the annealing temperature and ascribed to the quantum-confinement effect.
Time-resolved analysis of the set process in an electrical phase-change memory device
Authors: Kang Dae-Hwan , Cheong Byung-ki , Jeong Jeung-hyun , Lee Taek Sung , Kim In Ho , Kim Won Mok , Huh Joo-Youl
Published: December 2005

An experimental investigation was carried out on the kinetic nature of the set process in a phase change memory device by combined analyses of set voltage wave forms and time-resolved low-field resistances. As it turned out, the progress of a set process may be measured in terms of three characteristic times in sequence i.e., threshold switching time tth, incubation time for crystallization tinc, and complete set time tset. These characteristic times are supposed to demarcate, in some measure, different stages of crystallization in the memory material during a set process. Each of these times has a strong dependence on input pulse voltage and particularly threshold switching time tth was found to have an exponentially decaying dependence. The latter may be related to the decreasing capacitance of an amorphous phase-change material with approaching threshold switching.
Investigation of local ordering and electronic structure in Si- and hydrogen-doped tetrahedral amorphous carbon thin films
Authors: Abbas G. A. , Papakonstantinou P. , McLaughlin J. A.
Published: December 2005

This work investigates the CK-edge near-edge x-ray absorption fine structure (NEXAFS) and x-ray reflectivity spectra of Si- and hydrogen-incorporated tetrahedral amorphous carbon (ta-C:Si:H) films. The CK-edge NEXAFS spectra indicate that the sp2∕sp3 hybridization ratio increases with the amount of tetramethylsilane vapor precursor introduced during deposition. This suggests that Si addition enhances sp2- and reduces sp3-bonding configurations. The increase in sp2 sites correlates well with the decrease in hardness, mass density, and thermal stability. The comparison of angle-dependent NEXAFS spectra of nondoped and Si-doped ta-C films at the K edge reveals significant dopant-induced local ordering in πCC* and σC–H* orbitals. In contrast to the highly oriented pyrolytic graphite, the πCC* orbitals lie parallel to the surface.
Effect of local ordering on the decomposition of an amorphous Cu–Zr–Ti alloy
Authors: Kovács Zs. , Révész Á
Published: December 2005

We present free-energy calculations based on the random solution model. These calculations support the fact that the Cu-based solid solution observed to form during decomposition in amorphous Cu60Zr30Ti10 alloy is an ordered metastable L12 Cu3(Zr,Ti) phase which can nucleate due to its small unit cell and high mixing preference of Zr with Cu atoms.
Optical gain from InAs nanocrystal quantum dots in a polymer matrix
Authors: Chen Gang , Rapaport Ronen , Fuchs Dan T. , Lucas Leah , Lovinger Andrew J. , Vilan Sahar , Aharoni Assaf , Banin Uri
Published: December 2005

We report on the observation of optical gain from InAs nanocrystal quantum dots which emit at 1.55microns and are imbedded in a novel polymer platform. The measurements are based on a three-beam time resolved pump-probe technique, which enables extracting the intrinsic gain cross section, lifetime, and recovery time. These experiments are another step toward the realization of active optical devices based on InAs nanocrystals.
Electronegativity model for barrier formation at metal/organic interfaces
Authors: Tang J. X. , Lee C. S. , Lee S. T.
Published: December 2005

An electronegativity model is proposed to characterize the variation of charge injection barrier heights at metal/organic interfaces. In contrast to the traditionally used metal work function, barrier heights at interfaces are shown to be linearly dependent on metal electronegativity for a wide range of organic materials. The physical basis for the better suitability of electronegativity than work function to describe barrier heights is discussed. While barrier formation is caused by charge transfer between metals and organic semiconductors, the variation of the barrier height is related to the electronegativity difference of metals. The applicability of the electronegativity model to compound or alloy electrodes, such as indium tin oxide having no defined electronegativity, is also exemplified.
Polarization switching in epitaxial BiFeO3 films
Authors: Zavaliche F. , Shafer P. , Ramesh R. , Cruz M. P. , Das R. R. , Kim D. M. , Eom C. B.
Published: December 2005

Ferroelectric domain structure and polarization switching in an epitaxial BiFeO3 film grown on a 0.8° miscut SrTiO3(001) substrate were studied by piezoelectric force microscopy. The film shows a two-domain stripe pattern, with the polarization vectors oriented along two ⟨111⟩ axes which form an angle of 71°. Polarization switching was investigated by locally poling the film. By combining the perpendicular and in-plane piezoresponse data we found that polarization rotates by 71° and 109°, while 180° switching is mainly observed at low fields.
Enhanced quantum efficiency of high-purity silicon imaging detectors by ultralow temperature surface modification using Sb doping
Authors: Blacksberg Jordana , Hoenk Michael E. , Elliott S. Tom , Holland Stephen E. , Nikzad Shouleh
Published: December 2005

A low temperature process for Sb doping of silicon has been developed as a backsurface treatment for high-purity n-type imaging detectors. Molecular beam epitaxy (MBE) is used to achieve very high dopant incorporation in a thin, surface-confined layer. The growth temperature is kept below 450°C for compatibility with Al-metallized devices. Imaging with MBE-modified 1k×1k charge coupled devices (CCDs) operated in full depletion has been demonstrated. Dark current is comparable to the state-of-the-art process, which requires a high temperature step. Quantum efficiency is improved, especially in the UV, for thin doped layers placed closer to the backsurface. Near 100% internal quantum efficiency has been demonstrated in the ultraviolet for a CCD with a 1.5nm silicon cap layer.
Optical spectroscopy of trivalent chromium in sol-gel lithium niobate
Authors: Krebs J. K. , Happek U.
Published: December 2005

We report on the characterization of sol-gel derived lithium niobate via trivalent chromium probe ions, a study that is motivated by recent reports on the synthesis of high quality sol-gel lithium niobate (LiNbO3). In order to assess the quality of sol-gel derived LiNbO3, we incorporate Cr3+ during the hydrolysis stage of the sol-gel process. A comparison of the Cr3+ emission and photoexcitation data on both sol-gel and melt-grown LiNbO3 shows that the sol-gel derived material is highly stoichiometric.
Longitudinal profiles of plasma parameters in a laser-ignited capillary discharge and implications for laser wakefield accelerator applications
Authors: Levin M. , Pukhov A. , Hubbard R. F. , Kaganovich D. , Gordon D. F. , Sprangle P. , Ting A. , Hafizi B. , Zigler A.
Published: December 2005

The evolution of longitudinal electron density and temperature profiles in plasma channel produced by a low-current Plexiglas capillary discharge with laser ignition was investigated by spectroscopic methods. The plasma was produced by an electric discharge using a 0.5mm diameter, 15mm long Plexiglas capillary. The electron density measured in near-outlet region was found to be lower by 30%. Simulations show that this variation of the plasma density near the entrance of the capillary can pose substantial difficulties for external injection of electrons for laser wakefield accelerator applications.
Photodegradation and wavelength dependency of blue polymer light-emitting diode devices
Authors: Colditz H. J. O. , Kurt R. , Büchel M.
Published: December 2005

A systematic study of the wavelength dependency of the photodegradation of blue polymer light-emitting diodes is reported. Clearly two different regions can be distinguished, inside the absorption band, where the strongest and permanent photodegradation is found, and at wavelengths above the edge of absorption, where at least partially reversible photodegradation is observed. Irradiation experiments on samples with and without a cathode show the effect of the cathode-polymer interface and its contribution to the degradation mechanisms involved.
Chirality- and size-dependent elastic properties of single-walled carbon nanotubes
Authors: Chang Tienchong , Geng Jingyan , Guo Xingming
Published: December 2005

An analytical molecular mechanics model is established to relate the chirality- and size-dependent elastic properties of a single-walled carbon nanotube to its atomic structure. Properties at different length scales are directly connected by the derived closed-form expressions. The effects of tube chirality and tube diameter are investigated. The present analytical results are helpful to the understanding of elastic properties of carbon nanotubes, and thus are important for the application of carbon nanotubes as building blocks of nanomechanical devices.
Refractive index changes by electrically induced domain reversal in a c-cut slab of LiNbO3
Authors: Gao Feng , Xu Jingjun , Yan Boxia , Yao Jianghong , Fu Bo , Wang Zhenhua , Qi Jiwei , Tang Baiquan , Rupp Romano A.
Published: December 2005

Refractive index changes caused by electrically induced domain reversal are investigated by light diffraction from domains in periodically poled LiNbO3. Light diffraction from this type of refractive index modulation is calculated theoretically thus providing an effective and damage-free technique to characterize periodically poled materials. Examplarily, the refractive index modulation and the duty cycle are determined. The refractive index modulation obtained by electrically induced domain reversal is in the magnitude of 10−5.
Absorption of short duration pulses by small, scalable, tapered granular chains
Authors: Sokolow Adam , Pfannes Jan M. M. , Doney Robert L. , Nakagawa Masami , Agui Juan H. , Sen Surajit
Published: December 2005

Making shock proof layers is an outstanding challenge. Elastic spheres are known to repel softer than springs when gently squeezed but develop strong repulsion upon compression and the forces between adjacent spheres lead to ballistic-like energy transfer between them. Here we demonstrate that a small alignment of progressively shrinking spheres of a strong, light-mass material, placed horizontally in an appropriate casing, can absorb ∼80% (∼90%) of the incident force (energy) pulse. The system can be scaled down in size. Effects of varying the size, radius shrinkage and restitutive losses are shown via computed “dynamical phase diagrams.”
Noise-voltage mapping by a quantum-Hall electrometer
Authors: Kawano Y. , Okamoto T.
Published: December 2005

We have developed a scanning type of noise sensor system, which utilizes the detection of local voltage fluctuations with a quantum Hall effect (QHE) electrometer. This technique has enabled us to produce the first image of a noise-voltage distribution in a QHE sample. The experimental data clearly reveal that a large amount of noise occurs in the lower magnetic field region of a QHE plateau of Landau-level-filling factor 2 and that it is concentrated in a high-potential edge region of the Hall bar sample. These findings can be reasonably explained as originating from unstable electron transfer taking place when the nonequilibrium edge state equilibrates with the bulk state. These results identify our sensor system as a unique probe of nonequilibrium edge states in QHE systems.
Spatial fluctuation of dielectric properties in Hf-based high-k gate films studied by scanning capacitance microscopy
Authors: Naitou Y. , Ando A. , Ogiso H. , Kamiyama S. , Nara Y. , Nakamura K. , Watanabe H. , Yasutake K.
Published: December 2005

Scanning capacitance microscopy using a self-sensing probe has been applied to the quantification of local dielectric properties in Hf-based high-k films grown by an atomic layer deposition method. Local capacitance spectroscopy revealed distinctive contrasts in dC∕dV and dC∕dZ images originating from the spatial distribution of fixed charges in the films. We also found that the HfSiON film shows better performance than HfSiO and HfO2, in terms of flat-band voltage (VFB) shift and spatial fluctuation. In every sample, the spatial fluctuations of gate capacitance (COX) are less than 3%. Considering VFB shift and COX fluctuations, HfSiON was found to be a promising candidate for gate dielectric applications.
Tin doped indium oxide transparent conducting thin films containing silver nanoparticles by sol-gel technique
Authors: Houng Boen
Published: December 2005

Tin doped indium oxide films (ITO) with embedded silver nanoparticles were prepared by a sol-gel spin coating method. Delafossite structure of tin doped AgInO2 was found at lower annealing temperatures in all compositions and decomposed into ITO and Ag as annealing temperatures were increased. The interconnected network of Ag phases provides effective conducting paths that reduced the electrical resistivity of the films to 8.2×10−5Ωcm. The optical transmissions of the films are greater than 80% in visible wavelength and show an absorption band towards longer wavelength at higher Ag concentrations.
High upper critical field and irreversibility field in MgB2 coated-conductor fibers
Authors: Ferrando V. , Orgiani P. , Pogrebnyakov A. V. , Chen J. , Li Qi , Redwing J. M. , Xi X. X. , Giencke J. E. , Eom Chang-Beom , Feng Qing-Rong , Betts J. B. , Mielke C. H.
Published: December 2005

We report on structural and superconducting properties of round MgB2 coated-conductor fibers deposited by hybrid physical-chemical vapor deposition on SiC fibers. The coating is polycrystalline and composed of elongated crystallites with dimensions less than 1μm in length and 0.2μm in width. The pure MgB2 fiber shows a zero-resistance Tc of 39.3 K. The carbon-alloyed fibers show a high upper critical field of 55 T at 1.5 K and a high irreversibility field of 40 T at 1.5 K. The result demonstrates great potential of MgB2 coated conductors for superconducting magnets.
Visible luminescence from octadecylsilane monolayers on silica surfaces: Time-resolved photoluminescence characterization
Authors: Sagawa Natsuko , Uchino Takashi
Published: December 2005

We have found that the adsorption of octadecyltrichlorosilane (OTS) monolayers on nanometer-sized silica particles yields a broad blue photoluminescence (PL) with a time scale of nanoseconds. The observed PL intensity increases after curing at temperatures from ∼100 to ∼300°C, suggesting that condensations between adjacent OTS molecules on the silica surface are related to the PL. The PL decay curve of the cured samples remains unchanged from 77 to 450 K, whereas the time-integrated PL intensity shows a monotonous decrease with increasing temperature. From these experimental results, a model of radiative and nonradiative process associated with the PL is presented.
Characterization of nanoporous Si thin films obtained by Al–Si phase separation
Authors: Fukutani Kazuhiko , Ishida Youhei , Aiba Toshiaki , Miyata Hirokatsu , Den Tohru
Published: December 2005

Nanoporous silicon films of ultrahigh pore densities and large surface areas have been fabricated by sputtering an Al–Si target and subsequent removal of the deposited film’s Al regions by etching in a sulfuric acid solution. The resulting nanoporous films are mainly composed of amorphous silicon and have cylindrical pores with an average pore density exceeding 1016pores∕m2. These nanoporous films can be crystallized by thermal annealing in a H2 atmosphere to improve their electrical properties. The electrical properties of the crystallized nanoporous films, which behave as p-type semiconductors, are very similar to those of electrochemically etched porous Si.
Organic double-gate field-effect transistors: Logic-AND operation
Authors: Chua Lay-Lay , Friend Richard H. , Ho Peter K. H.
Published: December 2005

A unipolar double-gate field-effect transistor (DG-FET) with AND logic functionality is demonstrated. This operation regime arises through a symmetric electrostatic coupling of two conduction channels via the intrinsic semiconductor layer. According to simulation, this mode of operation is general and not limited to organic devices. These DG-FETs provide for two-signal modulation in a single device of a shared active region, and are thus versatile building blocks for logic, memories, sensing, data transmission and light-emitting FETs. When the two gates are tied together somewhat reminiscent of Si FinFETs, these devices can achieve considerably deeper gate modulation than possible with single gating.
Role of Ti in the formation of Zr–Ti–Cu–Ni–Al glasses
Authors: Kim T. H. , Gangopadhyay A. K. , Xing L. Q. , Lee G. W. , Shen Y. T. , Kelton K. F. , Goldman A. I. , Hyers R. W. , Rogers J. R.
Published: December 2005

It has been widely reported that glass formation improves in Zr62Cu20Ni8Al10 alloys when small amounts of Ti are substituted for Zr. Glasses containing greater than 3 at. % Ti crystallize to a metastable icosahedral phase, suggesting that Ti enhances icosahedral short-range order in the liquid/glass, making crystallization more difficult during cooling. However, based on containerless solidification and in situ high-energy synchrotron diffraction studies of electrostatically levitated supercooled liquids of these alloys, we demonstrate that Ti inhibits surface crystallization but neither increases the icosahedral short-range order nor improves glass formation.
12.5 nm base pseudomorphic heterojunction bipolar transistors achieving fT=710GHz and fMAX=340GHz
Authors: Hafez Walid , Snodgrass William , Feng Milton
Published: December 2005

The pseudomorphic collector structure is known to allow enhanced collector transport, facilitating higher current cutoff frequencies at lower current densities and junction temperatures compared to traditional single heterojunction structures. The performance of a 0.25×3μm2 pseudomorphic heteojunction bipolar transistors achieves peak fT of 710 GHz (fMAX=340GHz) at a collector current density of 20mA∕μm2. The same device achieves a fT∕fMAX of 540∕407GHz at a reduced current density of 7.5mA∕μm2. The epitaxial structure employs a 12.5 nm strained InGaAs base and 55 nm InGaAs collector, and exhibits a β of 115 and breakdown voltage of BVCEO=1.75V.
Performance of HfO2∕TiN gate stacks with in situ grown and O3 chemical interfacial oxide layers
Authors: Park Chang Seo , Moumen Naim , Sim Jang Hoan , Barnett Joel , Lee Byoung Hun , Bersuker Gennadi
Published: December 2005

Electrical properties of the gate stacks with atomic-layer-deposited HfO2 dielectric on either a HF-last cleaned Si substrate or chemical oxide grown by an O3∕de-ionized water clean have been evaluated. The properties of the oxide layers formed at the interface between the high-k dielectric and the substrate in both types of gate stacks are similar as they exhibit identical equivalent oxide thickness and comparable gate leakage current values. However, the gate stack formed on the HF-last cleaned surface shows higher intrinsic mobility and transient charge trapping, which may be explained by the oxygen deficiency model.
Gold nanoparticles via alloy decomposition and their application to nonvolatile memory
Authors: Chandra A. , Clemens B. M.
Published: December 2005

A technique for fabricating Au-rich nanoparticles via phase separation and subsequent oxidation of amorphous Au25Si75 sputtered thin films is presented. Nanoparticles formed in this manner are surrounded by SiO2 and have an average diameter of 2.88nm with an aerial density of 1.9×1012cm−2. Au-rich nanoparticles are incorporated into capacitor structures and the capacitance-voltage behavior is characterized. Significant hysteresis is observed and the flat-band voltage shift is attributed to charge storage due to the presence of the metal nanoparticles.
Mechanism for stamp collapse in soft lithography
Authors: Zhou W. , Huang Y. , Menard E. , Aluru N. R. , Rogers J. A. , Alleyne A. G.
Published: December 2005

Mechanical collapse of recessed features of relief on elastomeric elements for soft lithography represents an important phenomena for this lithographic technology. By comparing computed and measured shapes of partially collapsed structures, we show that the dominant mechanism for collapse is surface adhesion between the elastomer and substrate, for typical materials and processing conditions. In particular, the shapes obtained using models that account for surface adhesion agree well with the experimentally measured shapes. Electrostatic forces may contribute to this process, but they do not dominate. The weight of the elastomer has essentially no effect.
Dual localizations for second-harmonic generations using left-handed materials
Authors: Chen Jing , Ren Fang-Fang , Li Rui , Shen Nian-Hai , Fan Ya-Xian , Ding Jianping , Wang Hui-Tian
Published: December 2005

We show that dual localized modes can be achieved in defective one-dimensional photonic crystals containing left-handed materials. By inserting a nonlinear defect into a photonic crystal formed by stacked alternating left-handed materials and air layers, defective modes for fundamental wave and second-harmonic signal inside the zero-n¯ gap and a Bragg gap are formed, respectively. We present a theory in designing the whole structure, and show that a giant enhancement of second-harmonic generation is achieved. The merits and character of such a scheme comparing with that in ordinary photonic crystals are discussed.
Coded excitation of broadband terahertz using optical rectification in poled lithium niobate
Authors: Buma T. , Norris T. B.
Published: December 2005

We demonstrate coded excitation of broadband terahertz for imaging applications. The encoded transmitter uses optical rectification of femtosecond laser pulses in poled lithium niobate patterned with a 53-bit binary phase code. The terahertz wave forms are detected by electro-optic sampling in zinc telluride. A digital pulse compression filter decodes the binary wave forms, producing broadband pulses at 1.0THz. A two-dimensional imaging experiment shows comparable performance between the encoded transmitter and a zinc telluride emitter.
Nitride-mediated epitaxy of self-assembled NiSi2 nanowires on (001)Si
Authors: Chen S. Y. , Chen L. J.
Published: December 2005

Self-assembled NiSi2 nanowires with a high-aspect ratio have been fabricated by combining the methods of reactive deposition epitaxy and nitride-mediated epitaxy (NME). Both types of epitaxial NiSi2 nanowires, which are parallel and twin related to the substrates, were formed with the length/width aspect ratios increased by a factor of 8 with the effect of NME. One type of nanowire was successfully grown with a high-aspect ratio despite the four-fold symmetric epitaxial relationship between NiSi2 and Si with very small mismatch. The use of NME method effectively diminished the flux of Ni atoms and allowed sufficient time for the strain to be released by means of shape transition during the island growth at elevated temperatures.
Lattice distortion in nanostructured porous silicon
Authors: Pascual L. , Martín-Palma R. J. , Landa-Cánovas A. R. , Herrero P. , Martínez-Duart J. M.
Published: December 2005

High-resolution transmission electron microscopy in combination with image analysis was used to perform a detailed analysis of the lattice structure of the Si nanocrystals that compose porous silicon (PS) as a function of depth. It has been observed that the morphology, crystallinity, and orientation of porous silicon change strikingly from that of Si depending on depth. In addition to misalignment produced by the formation process, a nonsymmetrical distortion of the Si cell away from cubic has been found. Thus, the resulting lattice structure of porous silicon could be triclinic and partially nonperiodic. These effects become more prominent with distance away from the Si∕PS interface.
Improvement in bias instabilities of Hf-silicate by dilute hydrochloric acid (500:1) post-deposition rinsing and its effect after high-pressure H2 anneal
Authors: Akbar Mohammad S. , Moumen Naim , Barnett Joel , Lee Byoung Hun , Lee Jack C.
Published: December 2005

We report that post-deposition rinsing of metalorganic-chemical-vapor-deposited Hf-silicate dielectric with HCl (500:1) improves mobility, bias instabilities, and stress-induced leakage current of metal-oxide-semiconductor field-effect transistors. Reduction of bulk charge trapping has primarily been attributed to this improvement. High-pressure H2 anneal improved interface states significantly, with no effect on bulk trapping characteristics. HCl post-treatment did not show any apparent effect on interface state properties.
High critical current densities in YBa2Cu3O7−x films grown at high rates by hybrid liquid phase epitaxy
Authors: Kursumovic A. , Evetts J. E. , MacManus-Driscoll J. L. , Maiorov B. , Civale L. , Wang H. , Jia Q. X. , Foltyn S. R.
Published: December 2005

Liquid-mediated growth of YBa2Cu3O7−x has the potential to be high rate and low cost. However, the reported critical current densities (Jc) are generally lower than for films deposited by physical vapor deposition processes. We report the deposition of thick high-Jc films (1.2MAcm−2 in self-field) on (001) SrTiO3 by high-rate hybrid liquid phase epitaxy, and show angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy.
Superior high-field current density in slightly Mg-deficient MgB2 tapes
Authors: Jiang C. H. , Nakane T. , Kumakura H.
Published: December 2005

A series of Fe-clad MgxB2 tapes with x varying from 0.5 to 1.2 was prepared by the in situ powder-in-tube method. Slightly Mg-deficient samples showed higher Jc in high magnetic fields, whereas samples with stoichiometric Mg or a slight excess of Mg exhibited better Jc in the low-field region. The sample with x=0.9 showed the best Jc in the applied magnetic field. The MgB2 core was porous in Mg-deficient tapes but with smaller grain sizes than the samples with a slight Mg excess due to insufficient grain growth. Some fine nanometer size grains were also observed in the B-rich samples. The enhanced grain boundary pinning due to the smaller grain size may explain the superior high-field Jc property of the slightly Mg-deficient MgB2 tapes. Our results indicate that preparing MgB2 samples with a slight excess of Mg may not be advantageous when developing devices for high-field applications.
Structure investigation of low-temperature-grown GaAsSb, a material for photoconductive terahertz antennas
Authors: Sigmund J. , Sydlo C. , Hartnagel H. L. , Benker N. , Fuess H. , Rutz F. , Kleine-Ostmann T. , Koch M.
Published: December 2005

The formation of precipitates after an annealing process in low-temperature-grown GaAs0.6Sb0.4 is observed. We use high-resolution transmission electron microscopy for a detailed structure investigation and demonstrate the functionality of the material, which has a band gap of 0.86 eV, for ultrafast optical switches. The average diameter of the clusters is 5.7 nm in the bulk region, while larger clusters are observed near the interface to a 1.3% lattice mismatched Al0.77In0.23As buffer layer. After an annealing treatment, the sheet resistance is increased by five orders of magnitude to 1.7×108Ω/sq, which is sufficiently high to enable Auston switch operation. We report terahertz (THz) emission from the material measured in a THz time-domain spectroscopy setup. THz generation is demonstrated by using a six interdigital finger metal-semiconductor-metal structure at the feed-point of a log-periodic antenna.
Comparison of measured and calculated specific resistances of Pd∕Pt interfaces
Authors: Olson S. K. , Loloee R. , Theodoropoulou N. , Pratt W. P. , Bass J. , Xu P. X. , Xia Ke
Published: December 2005

We compare specific resistances (AR=areaAtimes resistanceR) of sputtered Pd∕Pt interfaces measured in two different ways with no-free-parameter calculations. One way gives 2ARPd∕Pt=0.29±0.03fΩm2 and the other 2ARPd∕Pt=0.17±0.13fΩm2. From these we derive a “best estimate” of 2ARPd∕Pt=0.28±0.06fΩm2, which overlaps with no-free-parameters calculations: 2ARPd∕Pt(predicted)=0.30±0.04fΩm2 for flat, perfect interfaces, or 0.33±0.04fΩm2 for interfaces composed of 2 monolayer (ML) of a 50%–50% PdPt alloy. These results support three prior examples of agreement between calculations and measurements for pairs of metals having the same crystal structure and the same lattice parameter to within 1%. We also estimate the spin-flipping probability at Pd∕Pt interfaces as δPd∕Pt=0.13±0.08.
Single electrospun regioregular poly(3-hexylthiophene) nanofiber field-effect transistor
Authors: Liu Haiqing , Reccius Christian H. , Craighead H. G.
Published: December 2005

We report on a single nanofiber field-effect transistor made from electrospun regioregular poly(3-hexylthiophene). Nanofibers, with diameters of 100–500 nm, were deposited by electrospinning from chloroform solution onto electrodes on a SiO2∕Si substrate. The transistor exhibited a hole field-effect mobility of 0.03cm2∕Vs in the saturation regime, and a current on/off ratio of 103 in the accumulation mode. Electrospinning offers a simple means of fabricating one-dimensional polymer transistors.
Intense thermal field electron emission from room-temperature stable electride
Authors: Toda Yoshitake , Kim Sung Wng , Hayashi Katsuro , Hirano Masahiro , Kamiya Toshio , Hosono Hideo , Haraguchi Takeshi , Yasuda Hiroshi
Published: December 2005

Thermal field emission (TFE) from a flat surface of 12CaO∙7Al2O3 (C12A7) electride was examined at temperatures up to 900°C and applied external voltages of 0–6kV in a 10−5Pa vacuum. TFE started to occur at ∼650°C and steeply increased at ∼900°C to reach ∼80μA (∼1.5Acm−2) when an extraction field of 105Vcm−1 (an extraction voltage of 6kV) was applied. The work function estimated from the Richardson–Dushman equation was ∼2.1eV, which is rather smaller than that of LaB6 (∼2.7eV). It is experimentally confirmed that the emission with a current of ∼50μA (from a 80μm diameter area) was stably sustained for more than 90h. The efficient and stable emission at relatively low temperature in a moderate vacuum atmosphere strongly suggests that the C12A7 electride has high potential for TFE applications.
Role of substrate and transparent conducting oxide in impurity evolvement in polycrystalline thin-film devices
Authors: Emziane M. , Durose K. , Halliday D. P. , Bosio A. , Romeo N.
Published: December 2005

A comparison of as-grown and processed CdTe∕CdS solar cell structures deposited on sapphire substrate has been undertaken with those grown on glass. The device structures were depth-profiled using quantitative secondary ion mass spectrometry. It was shown that while Si concentration profiles are similar to those for structures grown on glass, Na was more than one order of magnitude lower when sapphire was used instead of glass, showing that Na diffused from the glass. It was also found that there was no measurable diffusion of Sn from the SnO2 layer into CdTe, and that the former played an important role in preventing the diffusion of In from In-containing transparent conducting oxide layer. Cl, O, Br, and F species were also investigated and while Cl and O were found to be independent of the nature of the substrate used, Br and F were shown to be affected by the processing.
Response to anions of AlGaN∕GaN high-electron-mobility transistors
Authors: Alifragis Y. , Georgakilas A. , Konstantinidis G. , Iliopoulos E. , Kostopoulos A. , Chaniotakis N. A.
Published: December 2005

The response of AlGaN∕GaN electrolyte-gate high-electron-mobility transistors to various concentrations of the potassium salts KCl, KBr, KNO3, and KSCN in an aqueous solution has been investigated. The transistors’ drain-source current decreased with increasing concentration of potassium salts. This indicates that the potential at the gate becomes more negative with respect to the channels’ potential, suggesting a selective anion adsorption onto the GaN gate surface area.