bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial growth of group III nitrides on silicon substrates via a reflective lattice-matched zirconium diboride buffer layer
Authors: Tolle J. , Roucka R. , Tsong I. S. T. , Ritter C. , Crozier P. A. , Chizmeshya A. V. G. , Kouvetakis J.
Published: April 2003

Growth of metallic and reflecting ZrB2 films is conducted on Si(111) substrates at 900 °C using a single-source unimolecular precursor Zr(BH4)4 in a molecular beam epitaxy chamber. Epitaxial growth of ZrB2(0001) is accomplished despite the very large lattice mismatch between ZrB2 and Si(111). High-resolution cross-sectional transmission electron microscopy images of the sharp ZrB2/Si(111) interface show a heteroepitaxial relationship involving a “magic mismatch” of coincidence lattices. The GaN films grown on the ZrB2/Si(111) template is virtually homoepitaxy because of the very small lattice mismatch, 0.6%, between the in-plane lattice parameters of ZrB2(0001) and GaN(0001).
Extended Arrhenius law of time-to-breakdown of ultrathin gate oxides
Authors: Xu Mingzhen , Tan Changhua , Li MingFu
Published: April 2003

A stress-induced double-donor conductivity model is proposed to investigate the temperature dependence of time-to-breakdown in ultrathin gate oxides. The permittivity-to-breakdown is defined as the product of conductivity and time-to-breakdown. The breakdown of oxides occurs when the permittivity-to-breakdown reaches a critical value. This model shows that the overall temperature dependence of time-to-breakdown can be described in terms of the extended Arrhenius law. In this case, there exist three temperature regions with different activation energies, where Arrhenius behavior still holds in each region.
Hot-phonon bottleneck in the photoinjected plasma in GaN
Authors: Vasconcellos A. R. , Luzzi R. , Rodrigues C. G. , Freire V. N.
Published: April 2003

The evolution on the picosecond scale of the macroscopic (nonequilibrium thermodynamic) state of a highly excited photoinjected plasma in bulk GaN is analyzed. We present the equations of evolution for the quasitemperature (level of excitation) of the hot carriers and of the optical phonons. A hot-phonon temperature overshoot is evidenced, as well as a preferential production of phonons in excess of equilibrium in a reduced off-center region of the Brillouin zone. A comparative analysis of the influence of the length of the exciting laser pulse is also performed.
An experimental investigation of the near-field flow development in coaxial jets
Authors: Sadr Reza , Klewicki Joseph C.
Published: April 2003

The near-field region of a coaxial jet having inner to outer diameter ratio di/do=0.39 is investigated experimentally for four ratios of annular to central jet velocities of η=0.18, 0.48, 0.8, and 1.11. Measurements were acquired nonintrusively using molecular tagging velocimetry at downstream distances up to six inner jet diameters. High spatial-resolution profiles of mean axial velocity, axial turbulent intensity, skewness, kurtosis, radial gradients of mean velocity, and velocity gradient fluctuations are presented and discussed. In the near-exit region of the inner mixing layer, evidence suggests the existence of two trains of vortices shed from the inner jet wall for velocity ratios η>0.18. The results also indicate that for the flow configuration examined the length of the annular potential core is a function of the velocity ratio. Turbulence characteristics of the flow appear to be influenced by both the velocity ratio and absolute velocity of the annular jet. Integral length and Taylor microscales in the inner shear layer are shown to grow monotonically with downstream distance, with their ratio reaching a constant value. It is concluded that the turbulence structure in the inner mixing layer is highly anisotropic and that the levels of anisotropy are a relatively strong function of the velocity ratio.
Bottom-up approach for carbon nanotube interconnects
Authors: Li Jun , Ye Qi , Cassell Alan , Ng Hou Tee , Stevens Ramsey , Han Jie , Meyyappan M.
Published: April 2003

We report a bottom-up approach to integrate multiwalled carbon nanotubes (MWNTs) into multilevel interconnects in silicon integrated-circuit manufacturing. MWNTs are grown vertically from patterned catalyst spots using plasma-enhanced chemical vapor deposition. We demonstrate the capability to grow aligned structures ranging from a single tube to forest-like arrays at desired locations. SiO2 is deposited to encapsulate each nanotube and the substrate, followed by a mechanical polishing process for planarization. MWNTs retain their integrity and demonstrate electrical properties consistent with their original structure.
Simulating collective magnetic dynamics in nanodisk arrays
Authors: Bennett A. J. , Xu J. M.
Published: April 2003

We study the magnetostatic interactions in planar arrays of single domain, magnetic disk nanostructures. We derive equations for the time evolution of magnetization and energy, and use these results to simulate the relaxation of these systems with a Monte-Carlo model. Our model confirms that relaxation of a one-dimensional array into one of its ground states occurs by propagating the inversion site along the line. A two-dimensional honeycomb array enters a metastable state of frustrated spiral domains due to the availability of low-energy configurational states. This model has potential application in the design of magnetic nanostructure systems for data storage and data processing applications.
Spin engineering of CoPd alloy films via the inverse piezoelectric effect
Authors: Lee Jeong-Won , Shin Sung-Chul , Kim Sang-Koog
Published: April 2003

The spin engineering of CoxPd1−x alloy films on Pb(Zr0.52Ti0.48)O3 substrates was studied by measuring the polar Kerr rotation hysteresis loops and their electric field dependencies. The electric field dependence of polar Kerr rotation strongly depends on the composition of the CoPd alloys. This is especially so in the case of Co0.25Pd0.75 alloy film where the hysteresis loop of magnetic remanence with respect to voltage applied is nearly squared, i.e., the direction of magnetization maintains its initial state even when the voltage applied is turned off. This spin engineering in a ferromagnetic/piezoelectric hybrid system is possible mainly due to a combination of the magnetostrictive effect and the inverse piezoelectric effect. The results are applicable to future nonvolatile memory devices.
Study of interfacial reaction and its impact on electric properties of Hf–Al–O high-k gate dielectric thin films grown on Si
Authors: Lee P. F. , Dai J. Y. , Wong K. H. , Chan H. L. W. , Choy C. L.
Published: April 2003

Amorphous thin films of Hf–Al–O (with atomic ratio of Al/Hf of about 1.4) were deposited on (100) p-Si substrates by pulsed-laser deposition using a HfO2 and Al2O3 composite target. Transmission electron microscopy was employed for a detailed study of the interfacial reaction between the Hf–Al–O films and the Si substrates. Islands of Hf silicide formed from interfacial reaction were observed on the surface of the Si substrate. The formation of Hf silicide is attributed to the presence of Al oxide in the films that triggers the reaction between Hf atoms in the amorphous Hf–Al–O films and Si under an oxygen deficient condition. The impact of silicide formation on the electrical properties was revealed by high-frequency capacitance–voltage (C–V) measurements on metal–oxide–semiconductor capacitors. The observed abnormal C–V curve due to interfacial reaction was discussed.
Effects of interlayer electrode thickness in Nb/(MoSi2/Nb)N stacked Josephson junctions
Authors: Chong Yonuk , Dresselhaus P. D. , Benz S. P. , Bonevich J. E.
Published: April 2003

Dense, vertically stacked Josephson junction arrays are being developed for voltage metrology applications. We present measurements of the uniformity and reproducibility of Nb/(MoSi2/Nb)N vertically stacked junctions that clarify the superconducting properties of the middle Nb superconducting electrode. Middle electrode thicknesses down to 20 nm have shown minimal suppression of the superconducting order parameter as measured through the critical current density. Even with a middle electrode thickness of 5 nm, excellent junction uniformity has been observed as demonstrated by the measurement of large Shapiro steps when the arrays are biased with microwaves. We also discuss the role of the superconducting coherence length in these arrays of high-density junctions.
Early self-assembled stages in epitaxial SrRuO3 on LaAlO3
Authors: Vasco E. , Dittmann R. , Karthäuser S. , Waser R.
Published: April 2003

The stress-induced self-assembled growth of SrRuO3 on LaAlO3 was studied by atomic force microscopy and x-ray diffraction. SrRuO3 epitaxially grown on LaAlO3 by pulsed laser deposition shows two types of out-of-plane arrangements and four in-plane matches. The lattice mismatch (stress) produced by these arrangements was estimated and correlated with the SrRuO3 growth dynamics. After 1 nm, the SrRuO3 film surface exhibits a ripple structure, which serves as a template for the development of a nanopattern of flat islands. These islands coalesce anisotropically resulting in a regular array of “infinite” wires. The wire coalescence for the 12–20 nm thick film nullifies the surface symmetry, while SrRuO3 keeps growing in three dimensions.
In(Ga)As self-assembled quantum ring formation by molecular beam epitaxy
Authors: Granados Daniel , Garcı́a Jorge M
Published: April 2003

The effect of growth conditions on the morphological properties of InAs/GaAs(001) quantum dots covered by a thin (<3 nm) GaAs cap has been studied by atomic force microscopy. Each dot turns into an elongated nanostructure at 540 °C upon deposition of the cap in As4 atmosphere, while structures with two humps are obtained when capping at 500 °C. The use of As2 atmosphere instead of As4 at 500 °C leads to the formation of quantum rings. Photoluminescence spectroscopy and polarization photoluminescence (PL) at 15 K show dramatic changes due to the different kinds of confinement. This allows the possibility of tailoring PL emission by controlling the size and shape.
Effect of stress-induced phase transformation on nanomechanical properties of sputtered amorphous carbon films
Authors: Lu W. , Komvopoulos K.
Published: April 2003

The nanomechanical properties of radio-frequency sputtered ultrathin carbon films measured by surface force microscopy were correlated to the carbon bonding structures analyzed by x-ray photoelectron and Auger electron spectroscopy. The films consisted of amorphous carbon (a-C) comprising both trigonal (sp2) and tetrahedral (sp3) carbon hybridizations. The sp3 carbon content in the a-C materials of films with nanohardness of 19–40 GPa was found to be in the range of 22%–28%. From variations of the binding energy of Ar 2p electrons and the sp3 carbon content with the film Ar content, a stress-induced phase transformation from sp2 to sp3 carbon was determined at compressive residual stress of about 14 GPa. Film hardening occurs due to material densification, which is controlled by the intensity of the energetic Ar+ bombardment and the flux ratio of incoming C atoms and Ar+ ions during film growth. The results of this study elucidate the underlying hardening mechanism in ultrathin sputter-deposited carbon films.
Self-assembled molecular chains formed by selective adsorption of lead–phthalocyanine on InSb(100)-(4×2)/c(8×2)
Authors: Papageorgiou N. , Ferro Y. , Layet J. M. , Giovanelli L. , Mayne A. J. , Dujardin G. , Oughaddou H. , Le Lay G.
Published: April 2003

We study the structure of ultra thin lead–phthalocyanine (PbPc) overlayers deposited on the indium terminated InSb(100)-(4×2)/c(8×2) reconstructed surface by low-energy electron diffraction and scanning tunneling microscopy. The diffraction pattern for the PbPc monolayer grown on this surface corresponds to a 4×3 structure. We show that this structure is induced by a selective adsorption of the PbPc molecules on the indium stripes of the InSb(100) substrate. The adsorption is dominated by the interaction between the central lead atom of the molecule and the topmost indium atoms of the surface.
One-step formation of aligned carbon nanotube field emitters at 400 °C
Authors: Shiratori Y. , Hiraoka H. , Takeuchi Y. , Itoh S. , Yamamoto M.
Published: April 2003

Fabrication of field emitters by the radio-frequency plasma-enhanced chemical vapor deposition of vertically aligned carbon nanotubes (CNT) on soda-lime glass is reported. CNT was produced at 400 °C by the control of the collision energy of carbonic cations to a substrate through a dc bias voltage. The CNTs produced in this work were of a cup-stacked type and had catalyst particles on the top. The CNT emitters formed by our method were integrated into triode-type microcathodes and showed field-emission properties suitable for display applications.
Rapid-thermal-annealing effect on lateral charge loss in metal–oxide–semiconductor capacitors with Ge nanocrystals
Authors: Kim Jae Kwon , Cheong Hea Jeong , Kim Yong , Yi Jae-Yel , Bark Hong Jun , Bang S. H. , Cho J. H.
Published: April 2003

The rapid-thermal-annealing effect on lateral charge loss in metal–oxide–semiconductor capacitors with Ge nanocrystals is investigated by means of capacitance-voltage (C–V) and capacitance decay measurements. The C–V curves show the hysteresis indicating the charge storage effect in Ge nanocrystals. The hysteresis width shows strong annealing temperature dependence and shows the maximum at 700 °C meaning the maximum nanocrystal density. Capacitance decay experiment at flat-band voltage shows that the decay is dominated by two decay mechanisms. The initial fast discharge is more significant for samples annealed at lower temperatures. The cross-sectional transmission electron microscopic observations show the quasi-continuous Ge layer with Ge nanocrystals and Ge-rich amorphous regions for samples annealed at lower temperatures. Therefore, the fast discharging is attributed to lateral charge loss of insufficiently localized nanocrystals. On the other hand, the slow discharge is attributed to tunneling out of the stored charges in completely localized Ge nanocrystals via the tunneling barrier.
Enhanced cathodoluminescent properties of ZnO encapsulated ZnS:Ag phosphors using an electrochemical deposition coating
Authors: Choi Han-Ho , Ollinger M. , Singh R. K.
Published: April 2003

An electrochemical deposition coating method was developed to encapsulate the surface of micron-sized ZnS:Ag particulates with nanosized ZnO particles. The particle size of the as-synthesized ZnO particles was estimated to be below 10 nm from x-ray powder diffraction and transmission electron microscopy. The thickness of coating layer was measured to be from a few nm to about 100 nm using transmission electron microscopy. X-ray photoelectron spectroscopy analysis demonstrated the presence of ZnO particle layers on the surface of ZnS:Ag particulates. With the use of this ZnO coating layer, the cathodoluminescent lifetime of ZnS:Ag phosphors was dramatically improved.
Tensile yielding of multiwall carbon nanotubes
Authors: Wei Chenyu , Cho Kyeongjae , Srivastava Deepak
Published: April 2003

The tensile yielding of multiwall carbon nanotubes (MWCNTs) has been studied using molecular-dynamics simulations and a transition state theory based model. We find a strong dependence of the yielding on the strain rate. A critical strain rate has been predicted above/below which yielding strain of a MWCNT is larger/smaller than that of the corresponding single-wall carbon nanotubes (CNTs). At an experimentally feasible strain rate of 1%/h and T=300 K, the yield strain of a MWCNT is estimated to be about 3%–4% higher than that of an equivalent single-wall CNT. This is in good agreement with recent experimental observations.
Theoretical verification of the backward displacement of waves reflected from an interface having superimposed periodicity
Authors: Declercq Nico F. , Degrieck Joris , Briers Rudy , Leroy Oswald
Published: April 2003

Experiments are reported by Breazeale and Torbett [Appl. Phys. Lett. 29, 456 (1976)] that visualize ultrasonic backward beam displacement due to the excitation of surface waves by means of diffraction. The authors have simulated these experiments using the concept of inhomogeneous waves. Such waves have proven to be well suited in predicting beam displacements on plane interfaces. It is now found that inhomogeneous waves are even capable of predicting the experimentally observed displacement phenomena on periodic rough surfaces.
Low-temperature layer splitting of (100) GaAs by He+H coimplantation and direct wafer bonding
Authors: Radu I. , Szafraniak I. , Scholz R. , Alexe M. , Gösele U.
Published: April 2003

The present letter introduces a low-temperature GaAs layer splitting approach by He+H coimplantation which—in combination with direct wafer bonding—enables monolithic integration of GaAs with different substrates. The influence of He+H coimplantation on blistering and layer splitting of GaAs is studied and the optimum coimplantation conditions are determined. Thin GaAs layers are transferred onto Si after bonding of He+H coimplanted GaAs and Si substrates via a spin-on glass intermediate layer and subsequent annealing at only 225 °C for 14 h. Cross-sectional transmission electron microscopy investigations show a high quality of the GaAs/SOG bonding interface.
2.5 Gbit/s polycrystalline germanium-on-silicon photodetector operating from 1.3 to 1.55 μm
Authors: Masini Gianlorenzo , Colace Lorenzo , Assanto Gaetano
Published: April 2003

We report on a fast polycrystalline germanium-on-silicon heterojunction photodetector for the near-infrared. The device exhibits a pulse response faster than 200 ps, allowing operation at 2.5 Gbit/s as testified by open eye diagrams. This polycrystalline device, with responsivities of 16 and 5 mA/W at 1.3 and 1.55 μm, respectively, and dark currents of 1 mA/cm2, is entirely integrable on standard silicon electronics and is an appealing low-cost candidate for fiber-to-the-home communication networks.
Parametrically driven first-order Suhl instability and nonlinearities in bismuth-substituted yttrium iron garnet films
Authors: Elezzabi A. Y. , Irvine S. E.
Published: April 2003

We have demonstrated the enhancement of spin-wave nonlinearities in a bismuth-substituted yttrium iron garnet (Bi-YIG) film by parametrically exciting the first-order Suhl instability at the difference frequency of two simultaneous driving frequencies. The results show that parametric excitation of spin waves can cause this instability to grow at low threshold powers, which, in turn, channels power to other nonlinear spin-wave modes. Multiple interactions between spin waves lead to the enhancement of nonlinear processes.
Simple and efficient method for carbon nanotube attachment to scanning probes and other substrates
Authors: Hall A. , Matthews W. G. , Superfine R. , Falvo M. R. , Washburn S.
Published: April 2003

We present a fast, high yield, low cost method for the production of scanning probes with aligned carbon nanotubes protruding from the ends. The procedure is described and images of undercut films are used to demonstrate the improved probe quality for topography measurements. A magnetophoretic model of the attachment and alignment processes is discussed.
Characterization of porosity and dielectric constant of fluorocarbon porous films synthesized by using plasma-enhanced chemical vapor deposition and solvent process
Authors: Takahashi Kazuo , Mitamura Takashi , Ono Kouichi , Setsuhara Yuichi , Itoh Atsushi , Tachibana Kunihide
Published: April 2003

Fluorocarbon films obtained in plasma-enhanced chemical vapor deposition with a C4F8 compound were composed of a carbon cross-linked network and unlinked species encapsulated in the network [J. Appl. Phys. 89, 893 (2001)]. The unlinked species were effectively removed from the films. Then, the network probably containing the pore of the species was extracted on wafers when the films were dipped into tetrahydrofran (THF) solvent. The fact implied that fluorocarbon porous films with a low-dielectric constant might be formed by using dry and wet processes. In the present study, x-ray analyses showed that the THF-treated films actually became porous in the dipping process. The dielectric constant of the THF-treated films was consistently low (<1.9) and reduced by 10% from that of as-deposited films. The fluorocarbon network as a porous medium may be applied to interlayer dielectrics for ultralarge-scale integrated circuits.
AlGaN/GaN metal–oxide–semiconductor high electron mobility transistors using Sc2O3 as the gate oxide and surface passivation
Authors: Mehandru R. , Luo B. , Kim J. , Ren F. , Gila B. P. , Onstine A. H. , Abernathy C. R. , Pearton S. J. , Gotthold D. , Birkhahn R. , Peres B. , Fitch R. , Gillespie J. , Jenkins T. , Sewell J. , Via D. , Crespo A.
Published: April 2003

We demonstrated that Sc2O3 thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, IDS, reaches a value of over 0.8 A/mm and is ∼40% higher on Sc2O3/AlGaN/GaN transistors relative to conventional HEMTs fabricated on the same wafer. The metal–oxide–semiconductor HEMTs (MOS–HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that Sc2O3 retains a low surface state density on the AlGaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to +6 V of gate voltage. In particular, Sc2O3 is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO.
Quantum screening effects on occurrence scattering time for elastic collisions in electron–positron plasmas
Authors: Jung Young-Dae
Published: April 2003

Quantum screening effects on the occurrence time advance or delay for elastic collisions in electron-positron plasmas are investigated using the corrected Kelbg potential taking into account the classical effect as well as the quantum-mechanical effect. The eikonal method is applied to obtain the scattering amplitudes for electron–electron, positron–positron, and electron–positron elastic collisions in electron–positron plasmas. The results show that the occurrence time delay for electron–electron and positron–positron collisions increases with increasing plasma temperature. However, it is found that the occurrence time advance for electron–positron collisions has the maximum value at the temperature kBT≈4.5 eV and decreases with increasing the plasma temperature.
L1
0
ordering of off-stoichiometric FePt (001) thin films at reduced temperature
Authors: Seki T. , Shima T. , Takanashi K. , Takahashi Y. , Matsubara E. , Hono K.
Published: April 2003

We have investigated the effect of extensive compositional change on the structure and magnetic properties of FePt sputtered films deposited at a substrate temperature of 300 °C. The Fe concentration in the FePt films was varied from 19 to 68 at. %. In the x-ray diffraction patterns, (001) and (003) superlattice peaks were observed at a Pt-rich composition range, indicating the formation of a L10 ordered structure. A L10 ordered Fe38Pt62 film exhibited perpendicular magnetization with a large uniaxial magnetic anisotropy of Ku=1.8×107 erg/cm3.
Structural and optical properties of near-surface GaInNAs/GaAs quantum wells at emission wavelength of 1.3 μm
Authors: Liu H. F. , Peng C. S. , Pavelescu E.-M. , Karirinne S. , Jouhti T. , Valden M. , Pessa M.
Published: April 2003

X-ray diffraction, x-ray-induced photoelectron emission, and low-temperature photoluminescence have been used to investigate structural and optical properties of near-surface Ga1−xInxNyAs1−y/GaAs double quantum wells. The evolution of x-ray diffraction fringes, due to post-growth annealing, provides evidence for In/Ga interdiffusion at elevated temperatures. Photoelectron spectra indicate that indium tends to re-evaporate from the surface. Photoluminescence exhibits a strong feature, as part of the GaInNAs/GaAs material system. This feature is assigned to a hybridized state that is created by an interaction between surface states and quantum-confined states of the near-surface quantum well.
Free-space focused-beam characterization of left-handed materials
Authors: Li Kin , McLean S. J. , Greegor R. B. , Parazzoli C. G. , Tanielian M. H.
Published: April 2003

We used a broadband, free-space, focused-beam system to measure the transmission and reflection in left-handed-material (LHM) slabs. The samples were made of alternating patterns of copper wires and split-ring resonators on Rogers 5880 substrates separated by Rohacell™ spacers. The measured data show very good agreement with numerical simulations. The measured insertion loss of this structure was −1.1 dB/cm at the LHM pass band. Simulations suggest that the loss may be attributable to the finite conductivity of the copper patterns.
Metal layer Bragg–Fresnel lenses for diffraction focusing of hard x-rays
Authors: Li Youli , Yasa Mario , Pelletier Olivier , Safinya Cyrus R. , Caine Ernie , Hu Evelyn E. , Fernandez Patricia
Published: April 2003

A thin-film Bragg–Fresnel lens (BFL) was developed for diffractive focusing of hard x-rays into submicron to nanometer spots for scanning x-ray spectromicroscopy. The lens is made of metal-layer Fresnel zones deposited on an x-ray reflective substrate. The use of a high-density lens structure reduces the thickness of the lens and simplifies the fabrication process. Linear and elliptical lenses made of a 200-nm-thick Au film were fabricated using e-beam lithography and a metal deposition process. The focusing capabilities of the Au layer BFLs were demonstrated at the Advanced Photon Source.
Sub-Poissonian shot noise in molecular wires
Authors: Dallakyan S. , Mazumdar S.
Published: April 2003

We investigate the transport behavior of polyene molecules sandwiched between two metallic contacts using the nonequilibrium Green’s function formalism. We calculate both current and noise power as a function of applied voltage and show that they decrease with increasing size of the polyene molecules. We find that even with symmetric connection to metallic contacts, current-versus-voltage curves can be asymmetric for asymmetrically substituted polyenes. Most importantly, we demonstrate a crossover from Poissonian to sub-Poissonian behavior in the shot noise as a function of applied voltage. The algorithm for noise power calculation can be used for designing molecules with low noise.
Relaxed silicon–germanium-on-insulator substrates by oxygen implantation into pseudomorphic silicon germanium/silicon heterostructure
Authors: An Zhenghua , Wu Yanjun , Zhang Miao , Di Zengfeng , Lin Chenglu , Fu Ricky K. Y. , Chen Peng , Chu Paul K. , Cheung W. Y. , Wong S. P.
Published: April 2003

We have developed a modified separation-by-implantation-of-oxygen (SIMOX) process for fabricating relaxed silicon–germanium-on-insulator (SGOI) substrates without using thick graded SiGe buffer structures. Oxygen ions are implanted into a pseudomorphically grown 115 nm Si0.86Ge0.14 layer, with the implant peak located slightly below the heterostructure interface. Following two annealing processes (∼800+1350 °C) instead of conventional one-step annealing (∼1350 °C) in traditional SIMOX, a buried silicon dioxide layer is created near the original SiGe/Si interface, resulting in a fully relaxed SGOI structure. Our results show that an annealing step at a moderate temperature (∼800 °C) leads to less Ge loss.
Finite-size effect on highly dispersive photonic-crystal optical components
Authors: Ye Yong-Hong , Jeong D.-Y. , Mayer Theresa S. , Zhang Q. M.
Published: April 2003

This letter describes using the large near band edge dispersion in the effective refractive index (neff) of photonic crystals (PCs) to design PC lenses with focal lengths that are very sensitive to small differences in incident wavelength. Our calculations show that practical PCs of finite thickness exhibit an neff with a thickness dependent oscillatory behavior. This results in broadening of the focal spot size along the optical axis when the number of periods in the PC lens is small, which limits the wavelength sensitivity of the lens. These results demonstrate the importance in accounting for the finite-size effect when designing high performance optical devices or components that use the highly dispersive properties of PCs.
Thermally bandwidth-controllable reflective polarizers from (polymer network/liquid crystal/chiral dopant) composites
Authors: Yang Huai , Mishima Kenji , Matsuyama Kiyoshi , Hayashi Ken-Ichiro , Kikuchi Hirotsugu , Kajiyama Tisato
Published: April 2003

A (polymer network/nematic liquid crystal/chiral dopant) composite exhibiting a chiral nematic (N*) phase at room temperature has been developed. Because the helical twisting power of the chiral dopant increases with increasing temperature and the polymer network affects the molecular rearrangement of the liquid crystal, the bandwidth of the selective reflection spectrum of the N* phase becomes wider and narrower reversibly with increasing and decreasing temperature, respectively.
Morphological instability of GaInNAs quantum wells on Al-containing layers grown by metalorganic vapor-phase epitaxy
Authors: Sundgren P. , Asplund C. , Baskar K. , Hammar M.
Published: April 2003

We report on the optical and structural integrity of metalorganic vapor-phase epitaxy-grown GaInNAs/GaAs single quantum wells on AlGaAs/GaAs distributed Bragg reflectors (DBRs). Photoluminescence and surface morphology as measured by atomic force microscopy were investigated for different numbers of DBR periods and different DBR-growth temperatures. An increasing number of DBR periods may severely degrade the quantum well surface morphology and photoluminescence. Surface secondary-ion mass spectroscopy revealed surface segregation of an Al-containing species. Decreasing the DBR-growth temperature lowers the surface concentration of Al and improves the GaInNAs quantum-well morphology.
Electrical properties of thermally oxidized p-GaN metal–oxide–semiconductor diodes
Authors: Nakano Yoshitaka , Kachi Tetsu , Jimbo Takashi
Published: April 2003

We report on the electrical properties of thermally oxidized p-GaN metal–oxide–semiconductor (MOS) diodes with n+ source regions fabricated on sapphire substrates. The n+ regions were selectively produced in Mg-doped GaN by Si+N coimplantation and subsequent annealing at 1300 °C, and then 100-nm-thick β-Ga2O3 was grown by dry oxidation at 880 °C for 5 h. Capacitance–voltage measurements at room temperature display a surface inversion feature with an onset voltage of ∼2.5 V and show an extremely low interface trap density less than 1×1010 eV−1 cm−2. These results suggest that the thermally grown β-Ga2O3/p-GaN MOS structure is a promising candidate for inversion-mode MOS field-effect transistors.
Ferromagnetic resonant tunneling diodes as spin polarimeters
Authors: Giazotto Francesco , Taddei Fabio , Fazio Rosario , Beltram Fabio
Published: April 2003

A method for measuring the degree of spin polarization of magnetic materials based on spin-dependent resonant tunneling is proposed. The device we consider is a ballistic double-barrier resonant structure consisting of a ferromagnetic layer embedded between two insulating barriers. A simple procedure, based on a detailed analysis of the differential conductance, allows one to accurately determine the polarization of the ferromagnet. The spin-filtering character of such a system is furthermore addressed. We show that a 100% spin selectivity can be achieved under appropriate conditions. This approach is believed to be well suited for the investigation of diluted magnetic semiconductor heterostructures.
Optical absorption of intersubband transitions in In0.3Ga0.7As/GaAs multiple quantum dots
Authors: Pattada B. , Chen Jiayu , Zhou Qiaoying , Manasreh M. O. , Hussein M. L. , Ma W. , Salamo G. J.
Published: April 2003

Fourier-transform infrared spectroscopy technique was employed to investigate the optical absorption coefficient of intersubband transitions in Si-doped In0.3Ga0.7As/GaAs multiple quantum dot structures. Waveguides with 45° polished facets were fabricated from molecular beam epitaxy grown wafers with different quantum dot size. The measured maximum optical absorption coefficient was found to be in the order of 1.10×104 cm−3. The peak position energy of the intersubband transition was observed to shift toward lower energy when the quantum dot size is increased as expected. The photoluminescence spectra were also measured for different samples with different quantum dot size. The internal quantum efficiency was estimated to be in the order of 58% for a sample with 40 periods of 6 nm dot size.
Er
3+
-doped multicomponent sol-gel-processed silica glass for optical signal amplification at 1.5 μm
Authors: Biswas A. , Maciel G. S. , Kapoor R. , Friend C. S. , Prasad P. N.
Published: April 2003

We have developed a multicomponent K–Er codoped silica-based sol-gel glass that presents high luminescence quantum yield (∼100 times larger than that of an Er-doped silica sol-gel glass) and long emission lifetime at 1.54 μm (17 ms). The glass was heat treated to melting temperature with the optical properties of the system remaining practically unchanged. The IR absorption data shows that the hydroxyl content of this multicomponent glass is drastically reduced to a few tens of parts per million by using optimized compositions. The maximum gain coefficient expected for this glass is ∼4.5 dB/cm at 1.5 μm.
Photonic crystal microcavities for cavity quantum electrodynamics with a single quantum dot
Authors: Vučković Jelena , Yamamoto Yoshihisa
Published: April 2003

We propose a planar photonic crystal microcavity design specially tailored for cavity quantum electrodynamics with a single quantum dot emitter embedded in semiconductor. With quality factor up to 45 000, mode volume smaller than a cubic optical wavelength in material, and electric field maximum located in the high-refractive index region at the cavity center, this design can enable both strong coupling and lasing with a single quantum dot exciton. The achievable range of the quality factor to mode volume ratios and the feasible fabrication of the proposed structure make it favorable to other semiconductor microcavities.
Switching and regulation of a pulsed discharge channel in a coplanar plasma tetrode
Authors: Sakai Osamu , Hashimoto Satoshi , Hatano Akitsugu
Published: April 2003

Control of a pulsed coplanar discharge by two-dimensional potential tailoring is investigated experimentally in a flat tetrode configuration. One pair of electrodes generates a coplanar discharge, and the other electrodes play roles of switching and controlling the discharge current by changing their electrical potential, where their electrical isolation from the discharge channel is kept without an insulator layer. All the electrodes are cold and arranged on a completely flat plate immersed in discharge gas with the pressure which is in the region to the right of and near the minimum sparking voltage condition.
Coherent optical phonon oscillations in cubic ZnSe
Authors: Lim Yong-Sik , Yoon Seok-Chan , Yee Ki-Ju , Ahn Yeong-Hwan , Oh E. , Lee Jai-Hyung
Published: April 2003

We report the observation of coherent optical phonon oscillations in cubic bulk ZnSe(001). With a photon energy far below the band gap, the generation mechanism of the coherent longitudinal optical phonon mode is revealed to be the impulsive stimulated Raman scattering. Dephasing of the coherent longitudinal optical phonon modes by electron-phonon interaction and anharmonic processes is studied by investigating excitation intensity and temperature dependence of the dephasing rates.
Blue organic electrophosphorescence using exothermic host–guest energy transfer
Authors: Holmes R. J. , Forrest S. R. , Tung Y.-J. , Kwong R. C. , Brown J. J. , Garon S. , Thompson M. E.
Published: April 2003

We demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of N,N′-dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic). By examining the temperature dependence of the radiative lifetime and the photoluminescence of a film of mCP doped with FIrpic, we confirm the existence of exothermic energy transfer in contrast to the endothermic transfer characteristic of the N,N′-dicarbazolyl-4-4′-biphenyl and FIrpic system. In employing exothermic energy transfer between mCP and FIrpic, a maximum external electroluminescent quantum efficiency of (7.5±0.8)% and a luminous power efficiency of (8.9±0.9)lm/W are obtained, representing a significant increase in performance over previous endothermic blue electrophosphorescent devices.
Designing the refractive indices by using magnetic fluids
Authors: Horng H. E. , Hong Chin-Yih , Yang S. Y. , Yang H. C.
Published: April 2003

Magnetic fluid is a type of colloid consisting of magnetic nanoparticles dispersed in liquid carriers with the aid of surfactants and Brownian motion. Thus, the optical properties of magnetic fluids can be manipulated through the careful selection of magnetic particles and carriers. In this work, we give an example by designing a refractive index by using magnetic fluids composed of various carriers and particles, around 1.465 at 1.557 μm wavelength, which plays an important role in optical fiber communication. In addition, we also show how to achieve a desired flexibility in the tunable refractive index with externally varying fields by adopting suitable magnetic fluid films. These results reveal the feasibility of developing index-match or index-tunable devices using magnetic fluids.
Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes
Authors: Kneissl Michael , Treat David W. , Teepe Mark , Miyashita Naoko , Johnson Noble M.
Published: April 2003

We demonstrate ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes operating under continuous-wave (cw) conditions. The laser diodes were grown on sapphire substrates by metalorganic chemical vapor deposition. Under pulsed bias conditions, we have achieved threshold current densities as low as 5 kA/cm2 for laser diodes with emission wavelengths between 368 nm and 378 nm and have demonstrated lasing at 363.2 nm at room temperature, the shortest wavelength yet reported for a semiconductor laser diode. The cw operation up to a heat sink temperature of 40 °C was demonstrated on a series of narrow ridge-waveguide devices processed with chemically assisted ion beam etched mirrors and high reflective coating on both facets. The shortest wavelength emission under cw operation conditions was 373.5 nm with output powers of more than 1 mW.
1.3 μm wavelength vertical cavity surface emitting laser fabricated by orientation-mismatched wafer bonding: A prospect for polarization control
Authors: Okuno Yae L. , Geske Jon , Gan Kian-Giap , Chiu Yi-Jen , DenBaars Steven P. , Bowers John E.
Published: April 2003

We propose and demonstrate a long-wavelength vertical cavity surface emitting laser (VCSEL) which consists of a (311)B InP-based active region and (100) GaAs-based distributed Bragg reflectors (DBRs), with an aim to control the in-plane polarization of output power. Crystal growth on (311)B InP substrates was performed under low-migration conditions to achieve good crystalline quality. The VCSEL was fabricated by wafer bonding, which enables us to combine different materials regardless of their lattice and orientation mismatch without degrading their quality. The VCSEL was polarized with a power extinction ratio of 31 dB.
Field emission from aligned carbon nanofibers grown in situ by hot filament chemical vapor deposition
Authors: Chen Chia-Fu , Lin Chien-Liang , Wang Chi-Ming
Published: April 2003

Aligned high-aspect-ratio carbon nanofibers were grown in situ using modified hot filament chemical vapor deposition. The field-emission properties were then studied. An Fe–Cr wire filament acted as a catalytic source and a heat source. Carbon nanofibers were deposited on a Si substrate with CO2 as a carrier gas through ethanol. The experimental results indicate that the flow in the horizontal direction to the substrate produces carbon nanofibers with diameters of less than 10 nm. The field-emission current of 2 V/μm was 0.54 mA/cm2; the turn-on field of the sample was 1.1 V/μm.
Temperature-dependent photoinduced third-harmonic-generation variation in azo-homopolymer and azo-doped polymer thin films
Authors: Hsu Chia-Chen , Lin Jian-Hung , Huang Tzer-Hsiang , Harada Kenji
Published: April 2003

The temperature effect on the variation of photoinduced third-harmonic generation (THG) of an azo-polyurethane homopolymer and an azo guest–host polymer is studied at several different temperatures. At higher temperatures, both angular hole burning and molecule angular redistribution motions weaken, due to the decreases of cis-to-trans thermal relaxation time and the cis population and the increase of orientational diffusion coefficient. Smaller photoinduced THG variation is observed in both samples at higher temperatures. Results from the THG recovery experiment show that polyurethane homopolymer thin films pumped at a high temperature have the best photoinduced THG variation stability after turning off the pump beam.
Switching field phase diagram of Co nanoring magnets
Authors: Yoo Y. G. , Kläui M. , Vaz C. A. F. , Heyderman L. J. , Bland J. A. C.
Published: April 2003

We have studied the magnetic switching behavior of arrays of Co ring elements as a function of film thickness (2⩽t⩽32 nm), ring width (0.15⩽w⩽0.7 μm), and external diameter (0.5⩽D⩽2.0 μm), using magneto-optical Kerr effect magnetometry. For thick rings, two stable magnetic states are observed, a high remanence state (called the “onion” state) and a low remanence state (called the vortex state). The switching field for the transition from the onion to the vortex state increases with increasing thickness t and external diameter D, and with decreasing width w. In particular, for thin rings, the switching occurs between the two oppositely magnetized onion states, i.e., no vortex states develop during the reversal process. The transition between these two regimes depends on the diameter and width of the rings, and phase diagrams for the dependence of the switching behavior on the geometric parameters are presented. The switching behavior is discussed in terms of the competition between the exchange and magnetostatic energy terms.
Temperature dependence of the ionic conductivity in Li3xLa2/3−xTiO3: Arrhenius versus non-Arrhenius
Authors: Rivera A. , Santamarı́a J. , León C. , Blochowicz T. , Gainaru C. , Rössler E. A.
Published: April 2003

We report on the temperature dependence of the ionic conductivity at low temperatures in the crystalline lithium ionic conductor Li0.18La0.61TiO3. Time domain measurements of the electric modulus have been performed to investigate ion dynamics in the frequency range 10−5–102 Hz and for conductivity values in the range 10−14–10−8 S/cm. Ionic conductivity shows an Arrhenius temperature dependence below 300 K and down to 120 K, in contrast to the non-Arrhenius behavior found at higher temperatures, demonstrating that the temperature dependence of ionic conductivity in Li0.18La0.61TiO3 cannot be described by a Vogel–Fulcher–Tamman law.
The G protein-coupled receptor repertoires of human and mouse
Authors: Vassilatis Demetrios K. , Hohmann John G. , Zeng Hongkui , Li Fusheng , Ranchalis Jane E. , Mortrud Marty T. , Brown Analisa , Rodriguez Stephanie S. , Weller John R. , Wright Abbie C. , Bergmann John E. , Gaitanaris George A.
Published: April 2003

Diverse members of the G protein-coupled receptor (GPCR) superfamily participate in a variety of physiological functions and are major targets of pharmaceutical drugs. Here we report that the repertoire of GPCRs for endogenous ligands consists of 367 receptors in humans and 392 in mice. Included here are 26 human and 83 mouse GPCRs not previously identified. A direct comparison of GPCRs in the two species reveals an unexpected level of orthology. The evolutionary preservation of these molecules argues against functional redundancy among highly related receptors. Phylogenetic analyses cluster 60% of GPCRs according to ligand preference, allowing prediction of ligand types for dozens of orphan receptors. Expression profiling of 100 GPCRs demonstrates that most are expressed in multiple tissues and that individual tissues express multiple GPCRs. Over 90% of GPCRs are expressed in the brain. Strikingly, however, the profiles of most GPCRs are unique, yielding thousands of tissue- and cell-specific receptor combinations for the modulation of physiological processes.
Striking variation in the sex ratio of pups born to mice according to whether maternal diet is high in fat or carbohydrate
Authors: Rosenfeld Cheryl S. , Grimm Kristie M. , Livingston Kimberly A. , Brokman Angela M. , Lamberson William E. , Roberts R. Michael
Published: April 2003

In female mammals, it remains controversial whether maternal diet and particularly the source and availability of energy can influence sex of offspring born. Outbred female mice were fed ad libitum from 30 days to ≈45 wk of age on defined, complete diets that differed only in their relative content of fat and carbohydrate to determine whether calorie source influenced litter size and sex ratio of pups. Diet 1 (very high in saturated fat, VHF) provided 60% of calories as fat, mainly lard. Diet 2 (low in saturated fat, LF) was low in fat (10% of calories) but high in carbohydrate. Mice delivered four litters of pups, resulting in a total of 1,048 young born over 108 pregnancies. Gestation length and litter size did not differ between VHF and LF groups and did not change as mice aged. Sex ratio of pups (fraction male) born to mothers on VHF diet was unusually high (0.67) and to mothers on LF diet very low (0.39) over litters 2, 3, and 4. This skewing of sex ratio was related to diets fed and not to body mass of mothers. Age of mothers was an important variable, however. Mice that were first bred at 10 wk of age delivered similar numbers of sons and daughters, whereas virgin mice bred later than 20 wk of age produced litters that were skewed toward males or females according to diet. The data show that the source of calories provided in a nutritionally complete diet to mature female mice can influence sex of offspring born.
Inhibition of calcineurin facilitates the induction of memory for sensitization inAplysia: Requirement of mitogen-activated protein kinase
Authors: Sharma Shiv K. , Bagnall Martha W. , Sutton Michael A. , Carew Thomas J.
Published: April 2003

The induction of both synaptic plasticity and memory is thought to depend on the balance between opposing molecular regulatory factors, such as protein kinases and phosphatases. Here we show that inhibition of protein phosphatase 2B (calcineurin, CaN) facilitates the induction of intermediate-term memory (ITM) and long-term memory (LTM) for tail shock-induced sensitization inAplysiawithout any effect on short-term memory. To identify the molecular cascade underlying the improvement of memory by inhibition of CaN, we examined the role of extracellular signal-regulated kinase 1/2/mitogen-activated protein kinase (MAPK). Molecular experiments revealed that one pulse of serotonin, which by itself does not activate MAPK, leads to significant MAPK activation in the sensory neurons of the pleural ganglia when CaN is inhibited. Extending these observations, behavioral experiments showed that the facilitated induction of ITM and LTM produced by CaN inhibition depends on MAPK activity. These results demonstrate: (i) that CaN acts as an inhibitory constraint in the formation of long-lasting phases of memory, and (ii) that facilitated induction of ITM and LTM by CaN inhibition requires MAPK activity.