bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverse-bias leakage current reduction in GaN Schottky diodes by electrochemical surface treatment
Authors: Miller E. J. , Schaadt D. M. , Yu E. T. , Waltereit P. , Poblenz C. , Speck J. S.
Published: February 2003

An electrochemical surface treatment has been developed that decreases the reverse-bias leakage current in Schottky diodes fabricated on GaN grown by molecular-beam epitaxy (MBE). This treatment suppresses current flow through localized leakage paths present in MBE-grown GaN, while leaving other diode characteristics, such as the Schottky barrier height, largely unaffected. A reduction in leakage current of three orders of magnitude was observed for Schottky diodes fabricated on the modified surface compared to diodes fabricated on the unmodified surface for reverse-bias voltages as large as −20 V. In addition to suppressing reverse-bias leakage, the surface treatment was found to improve substantially the ideality factor of the modified surface diodes compared to that of unmodified surface diodes, suggesting that such a surface modification process could be useful for a variety of GaN-based electronic devices.
Longitudinal-shock-wave compression of Nd2Fe14B high-energy hard ferromagnet: The pressure-induced magnetic phase transition
Authors: Shkuratov Sergey I. , Talantsev Evgueni F. , Dickens James C. , Kristiansen Magne , Baird Jason
Published: February 2003

A study of a magnetic phase state of Nd2Fe14B high-energy hard ferromagnets subjected to longitudinal-shock-wave compression (where the shock wave propagates along magnetization vector M) has been performed. The results of the investigation show that longitudinal-shock-wave compression of Nd2Fe14B at 28–38 GPa causes a magnetic phase transition terminated by practically complete demagnetization of Nd2Fe14B. Due to this phase transition all electromagnetic energy stored in Nd2Fe14B is released and can be transformed into pulsed power. Explosive-driven autonomous sources of primary power utilizing this effect are capable of producing high-current pulses [current amplitude of 1.0 kA, full width at half maximum (FWHM) of 165 μs] and high-voltage pulses (peak voltage of 13.4 kV, FWHM of 8.2 μs).
Numerical modeling of linear drift-tearing mode stability
Authors: Yu Q. , Günter S. , Scott B. D.
Published: February 2003

Numerical modeling results of the linear drift tearing modes are presented. The present model is based on the two-fluids equations, and the perturbed bootstrap current is also included. The electron temperature and the density perturbations are self-consistently calculated by solving the two-dimensional transport equations. It is found that, with the inclusion of the electron perpendicular heat transport, which is neglected in the previous theory, the behavior of the drift tearing mode becomes significantly different, and a new type of tearing mode instability appears. This mode is driven unstable by a sufficiently large electron temperature gradient in a certain range of the electron diamagnetic drift frequency ω*e. The stability of the drift tearing mode is found to be mainly determined by ω*e. The parallel ion flow driven by the parallel pressure gradient is found to be stabilizing for the drift tearing modes, while the perturbed bootstrap current is destabilizing for large or small ω*e but can be stabilizing for a certain range of ω*e.
Observation of chaos caused by flute instability excited in electron cyclotron resonance plasma
Authors: Koga Mayuko , Kawai Yoshinobu
Published: February 2003

The behavior of the fluctuation observed in an electron cyclotron resonance plasma was investigated. The amplitude of the fluctuation increased with increasing the incident microwave power and decreasing the gas pressure. The characteristics of the fluctuation indicated that it was excited by the flute instability. From chaos analysis using time series data, it was found that the fluctuation was in turbulent state in the high microwave power region and chaotic state in the low microwave power region. Furthermore, when the multicusped fields were applied, the system transited from a chaotic state to a periodic one.
Physical and electronic structure of p-sexiphenyl on Au(111)
Authors: France C. B. , Parkinson B. A.
Published: February 2003

The electronic structure, adsorption energies, and molecular ordering of p-sexiphenyl (p-6P) films on Au(111) have been investigated with ultraviolet photoemission spectroscopy, temperature programmed desorption (TPD), and scanning tunneling microscopy (STM). Films up to 50 Å of p-6P were studied and a substantial interface dipole was measured (0.73 eV). Two distinct p-6P binding environments with heats of adsorption of 126 and 143 kJ/mol were observed using TPD. An unusual surface structure that contains alternating face and edge-on p-6P molecules was observed using STM. A model similar to the bulk p-6P structure with alternating face and edge-on interactions is proposed.
Metallic percolation in La0.67Ca0.33MnO3 thin films
Authors: Chen S. F. , Lin P. I. , Juang J. Y. , Uen T. M. , Wu K. H. , Gou Y. S. , Lin J. Y.
Published: February 2003

Phase separation in La0.67Ca0.33MnO3 thin films was investigated by scanning tunneling microscopy. The correlation between the grain structure and the spatial distribution of the coexisting metallic and insulating phases was evidently established. At temperatures not far below the metal–insulator transition, the spatial variation of the coexisting metallic and insulating phases is susceptible to magnetic field in an irreversible manner. The irreversibility suggests that the metallic percolation paths can be affected randomly by magnetic field. However, the variation becomes insensitive to magnetic field at lower temperatures.
Theory of spin relaxation in magnetic resonance force microscopy
Authors: Mozyrsky D. , Martin I. , Pelekhov D. , Hammel P. C.
Published: February 2003

We study relaxation of a spin in magnetic resonance force microscopy (MRFM) experiments. We evaluate the relaxation rate for the spin caused by high-frequency mechanical noise of the cantilever under the conditions of adiabatic spin inversion. We find quantitative agreement between the obtained relaxation time and the experimental results of B. C. Stipe, H. J. Mamin, C. S. Yannoni, T. D. Stowe, T. W. Kenny, and D. Rugar [Phys. Rev. Lett. 87, 277602 (2001)]. Based on our analysis, we propose a method for improving the MRFM sensitivity by engineering cantilevers with reduced tip positional fluctuations.
Magnetic domain wall trapping by in-plane surface roughness modulation
Authors: Swerts J. , Temst K. , Van Bael M. J. , Van Haesendonck C. , Bruynseraede Y.
Published: February 2003

Using the influence of surface roughness on the coercivity of thin magnetic films, we have produced an artificially modulated magnetic domain configuration in a chemically homogeneous polycrystalline thin magnetic film. This is achieved by evaporating a thin Fe film on top of a smooth substrate that was previously covered with an array of considerably rougher Ag lines. Magneto-optical Kerr effect measurements revealed the presence of two distinct switching fields in the hysteresis loops. In the intermediate state, a stable magnetic domain configuration of antiparallel aligned domains is achieved. Magnetic force microscopy images indicate that interacting cross-tie domain walls are separating the magnetic domains.
Fluid detection with photonic crystal-based multichannel waveguides
Authors: Topol’ančik J. , Bhattacharya P. , Sabarinathan J. , Yu P.-C.
Published: February 2003

A simple fluid detection scheme, based on light propagation through linear defect waveguides in photonic crystals, is demonstrated with isopropanol and xylene. The two-channel photonic crystal waveguide sensor is made from a GaAs-based heterostructure. The preferential channeling of light is controlled by the change in the refractive index of the corresponding waveguide branch due to the presence of the inserted fluid in the guide regions only.
Origin of the efficient light emission from inversion domain boundaries in GaN
Authors: Fiorentini Vincenzo
Published: February 2003

Intentionally produced inversion domain boundaries in GaN have been reported to be highly efficient shallow recombination centers. This letter report a rationale for this phenomenon based on ab initio density-functional calculations. A model is also proposed, based on the existence of polarization in GaN, of the observation that a domain boundary acts as a rectifying junction under voltage applied between the two opposite-polarity surfaces.
Nitrogen-induced decrease of the electron effective mass in GaAs1−xNx thin films measured by thermomagnetic transport phenomena
Authors: Young D. L. , Geisz J. F. , Coutts T. J.
Published: February 2003

Thin films of GaAs1−xNx were grown on insulating GaAs substrates and subjected to temperature-dependent resistivity, Hall, Seebeck, and Nernst coefficient measurements. Density of states, effective-mass values, which are calculated from the transport data, decrease from 0.084me to 0.029me as x increases from 0 to 0.004.
Stabilization of ion temperature gradient mode by small-scale zonal flows
Authors: Li Jiquan , Kishimoto Y.
Published: February 2003

Interaction between large-scale turbulence and small-scale sheared flows is a new issue in magnetized plasmas. In this work, the key interaction mechanism is explored by sampling the large-scale ion temperature gradient (ITG) mode and the small-scale zonal flows driven by the electron temperature gradient turbulence. It is analytically found that the small-scale zonal flows lead to a radially nonlocal mode coupling of ITG fluctuations. It can mediate to transfer the fluctuating free energy of an unstable mode in the longer wavelength region to the stable or damped components at shorter wavelengths. Then, the ITG mode is stabilized. Three-dimensional gyrofluid ITG simulations with an initial value code have confirmed the analytical results very well. The spectral analysis also shows a distinctive feature that this kind of interaction can deform the radial decaying spectrum of ITG fluctuation in the short wavelength region. It may be expected to modulate the turbulent ion heat transport in ITG turbulence.
Energy balance in a low pressure capacitive discharge driven by a double-saddle antenna
Authors: Charles C. , Boswell R. W. , Lieberman M. A.
Published: February 2003

A radio frequency (rf) plasma is created at low pressure (∼1 mTorr) in the source tube of a “helicon” excited diffusion system in the absence of a dc magnetic field. The coupling is capacitive for the low source power of 160 W at 13.56 MHz considered here. Temperature measurements of the glass source tube yield a plasma power deposition of ∼35 W. The plasma parameters (density, potential, electron temperature) were measured using a retarding field energy analyzer. An analytical model based on the measured plasma parameters and on additional external parameters measured in the matching box (rf voltages and phase, rf current) is developed. The model takes into account the geometry of the double saddle rf antenna. It is found that the inside of the glass wall adjacent to the antenna wire charges negatively. Ion acceleration into the glass along the antenna and fast electrons escaping the plasma account for most of the power deposition to the walls (∼16.8 W). Secondary electrons liberated by ions impinging onto the glass along the antenna contribute a power of ∼4.6 W. Adding the power of 3.7 W deposited to the part of the tube not affected by the antenna, the total power deposition responsible for the temperature rise of the tube is found to be about 25 W. The model shows that the power deposition is strongly nonuniform along the tube as a result of the antenna geometry. An estimate of the power deposited into the electrons by stochastic heating yields ∼1.4 W, compared to an estimate of 5.8 W for the measured power loss from electrons.
Strong low-frequency turbulence observed in presheaths
Authors: Nakamura Y. , Sato S.
Published: February 2003

A noise whose frequency is from 0 to ωpi/10, where ωpi is the ion plasma frequency, is observed in presheaths in both sides of a plane stainless-steel mesh grid immersed in a uniform and unmagnetized plasma. To excite the noise, a negative dc voltage lower than −20 V is applied to the grid. The frequency spectrum of the noise is expressed with the Lorenz distribution a/(f2+fo2), where f is the frequency and a and fo are constants. The noise is found to propagate away from the grid with the speed of one-fifth of the ion-sound velocity. The noise is considered to be excited in the presheaths by counter-streaming ion-beams whose velocity are slower than the ion-acoustic velocity. The kinetic dispersion relation is solved numerically and results are compared with experimental findings.
Ferromagnetic Ga1−xMnxAs produced by ion implantation and pulsed-laser melting
Authors: Scarpulla M. A. , Dubon O. D. , Yu K. M. , Monteiro O. , Pillai M. R. , Aziz M. J. , Ridgway M. C.
Published: February 2003

We demonstrate the formation of ferromagnetic Ga1−xMnxAs films by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of x≈0.03. A remanent magnetization persisting above 85 K has been observed for samples with x≈0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in Ga1−xMnxAs is rather robust to the presence of structural defects.
Large conductance switching and memory effects in organic molecules for data-storage applications
Authors: Bandyopadhyay Anirban , Pal Amlan J.
Published: February 2003

We have observed a large electrical conductance switching (ON:OFF ratio=105) in single-layer sandwich structures based on organic molecules at room temperature. The switching devices showed an associated memory effect for data-storage applications. We could write or erase a state and read it for many cycles. In switching devices, the active semiconductor retained its high conducting state until a reverse voltage erased it. A high conducting state arose due to restoration of conjugation in the molecule via electroreduction. Such a high ON–OFF ratio in a single layer sandwich structure, as compared to contemporary switching devices, is due to low off-state leakage current. The concept of conjugation restoration has been verified in supramolecular structures by adding donor groups to the molecule, which resulted in increased off-state current and hence lower ON–OFF ratio. Our work set a generalized example of selecting organic molecules to obtain higher ON–OFF ratio in molecular switching devices.
In situ measurements of GaN nucleation layer decompostion
Authors: Koleske D. D. , Coltrin M. E. , Allerman A. A. , Cross K. C. , Mitchell C. C. , Figiel J. J.
Published: February 2003

GaN nucleation layer (NL) decomposition was measured using optical reflectance over a wide range of pressure P, temperature T, and H2/NH3 gas mixture. The GaN NLs show measurable decomposition above 800 °C and do not significantly roughen until above 960 °C. The NL decomposition rates increase with increasing P, increasing T, and decreasing NH3 flow. An activation energy EA of 2.68 eV was measured (from 820 to 960 °C) for NL decomposition and an EA of 2.62 eV was measured (from 900 to 1075 °C) for decomposition of thick, high-T bulk GaN films. Depending on P, the pre-exponential factor A0 was four to nine times larger for NL decomposition compared to bulk GaN decomposition. The EA measured for both NL and bulk GaN decomposition in mixed H2 and NH3 flows is similar to the EA for Ga desorption, suggesting that the rate-limiting step for both NL and bulk GaN decomposition is Ga desorption.
Annealing of InGaAlAs digital alloy studied with scanning-tunneling microscopy and filled-states topography
Authors: Offermans P. , Koenraad P. M. , Wolter J. H. , Song J. D. , Kim Jong Min , Bae Seong Ju , Lee Yong Tak
Published: February 2003

We have investigated the structural properties of as-grown and annealed (750 and 800 °C) digital alloy InGaAlAs (λ=1.3 μm) laser structures by cross-sectional scanning-tunneling microscopy. We show that it is possible to resolve the digital alloy period in the as-grown sample and the 750 °C annealed sample. The 800 °C annealed sample did not show the digital alloy period because of intermixing of the digital alloy. The 750 °C annealed sample showed only slight intermixing. The barrier/well interface roughness for the as-grown and the 750 °C annealed samples was the same. Annealing at 800 °C showed large barrier/well interface roughness and lateral composition modulation due to the phase separation of InGaAs/InAlAs alloys.
Why are arsenic clusters situated at dislocations in gallium arsenide?
Authors: Lei H. , Leipner H. S. , Engler N.
Published: February 2003

The interaction of arsenic with dislocations in gallium arsenide has been studied. By performing molecular dynamics simulations with a Tersoff-type interaction potential and simulating the microscopic diffusion–drift–aggregation process based on the kick-out mechanism, we obtained that arsenic clusters are preferably situated at dislocations from energetic and kinetic reasons. This formation of arsenic clusters explains why the radius of the cylinder with an increased free electron concentration around dislocations in n-type sulfur-doped gallium arsenide extends up to about 10 μm, as revealed by Raman scattering.
High-pressure measurements of mid-infrared electroluminescence from InAs light-emitting diodes at 3.3 μm
Authors: Choulis S. A. , Andreev A. , Merrick M. , Adams A. R. , Murdin B. N. , Krier A. , Sherstnev V. V.
Published: February 2003

The spontaneous electroluminescence emission of InAs light-emitting diodes (LEDs) operating at 3.3 μm was studied as a function of applied hydrostatic pressure. An enhancement of a factor of almost four in radiative efficiency at room temperature was observed in the range 0 to 10 kbar. Analysis of the dependence of electroluminescence emission intensity on hydrostatic pressure at constant current reveals that nonradiative Auger recombination dominates the quantum efficiency of these LEDs.
Kinetics-limited surface structures at the nanoscale
Authors: Huang Hanchen , Woo C. H. , Wei H. L. , Zhang X. X.
Published: February 2003

This letter presents the evolution of kinetics-limited nanoscale structures during copper thin film deposition. We first calculate the three-dimensional Ehrlich–Schwoebel (3D ES) kinetic barrier of copper using the molecular dynamics/statics method. Based on this calculation, the dimension of {111} facets, under typical sputtering deposition conditions, is estimated to be 700 nm if the 3D ES barrier is effective, in contrast to 70 μm without it. Accompanying the calculations, we deposit copper 〈111〉 columns using the magnetron sputtering technique, and characterize their structures using scanning electron microscopy and x-ray diffraction techniques. The observed facets of pure copper films are on the order of 200 nm in dimension, confirming that surface structure is controlled by the 3D ES kinetic barrier. When indium is introduced as surfactant, the facet dimension increases, leading to conformal films; this is attributed to reduction of the 3D ES barrier.
AlGaN/GaN heterostructure field-effect transistors on single-crystal bulk AlN
Authors: Hu X. , Deng J. , Pala N. , Gaska R. , Shur M. S. , Chen C. Q. , Yang J. , Simin G. , Khan M. A. , Rojo J. C. , Schowalter L. J.
Published: February 2003

We report on the performance of AlGaN/GaN/AlN heterostructure field-effect transistors (HFETs) grown over slightly-off c-axis, single-crystal, bulk AlN substrates. Dc and rf characteristics of these devices were comparable to HFETs grown on semi-insulating SiC. The obtained results demonstrate that bulk AlN substrates are suitable for fabricating high-power microwave AlGaN/GaN transistors.
Implantation site of rare earths in single-crystalline ZnO
Authors: Wahl U. , Rita E. , Correia J. G. , Alves E. , Araújo J. P. , Collaboration The ISOLDE
Published: February 2003

The lattice location of rare-earth Er167m in single-crystalline hexagonal ZnO was studied by means of the emission channeling technique. Following 60-keV, room-temperature implantation of the precursor isotope Tm167 at doses of 1.3–2.8×1013 cm−2 and annealing up to 900 °C, the angular distribution of conversion electrons emitted by the radioactive isotope Er167m was measured by a position-sensitive electron detector. The conversion electron emission patterns from Er167m around the [0001], [1_102], [1_101], and [2_113] directions give direct evidence that the large majority of Er atoms (75%–90%) occupies substitutional Zn sites.
Negative temperature dependence of electron multiplication in In0.53Ga0.47As
Authors: Yee M. , Ng W. K. , David J. P. R. , Houston P. A. , Harrison C. N.
Published: February 2003

Electron multiplication in In0.53Ga0.47As has been determined from photomultiplication measurements over the temperature range of 20 to 400 K for a series of p–i–n diodes. A negative temperature dependence is observed in the electron multiplication of In0.53Ga0.47As at electric fields over 200 kV/cm, contrary to the positive temperature dependence of collector multiplication previously observed in InP/In0.53Ga0.47As heterojunction bipolar transistors. The results also showed that the breakdown voltage for In0.53Ga0.47As is comparable to GaAs at room temperature, and has a weaker temperature dependence.
Time-dependent reconnection for anisotropic pressure
Authors: Mühlbachler S. , Ivanova V. V. , Semenov V. S. , Biernat H. K. , Langmayr D. , Vogl D. F.
Published: February 2003

An analysis of the reconnection process which extends the famous solution obtained by Petschek for the steady-state case to incorporate the effects of unsteady reconnection in an anisotropic plasma is presented. The case of so-called switch-off shocks, where the Alfvén discontinuity and the slow shock degenerate to one discontinuity and the downstream magnetic field vanishes in lowest order, so that the plasma is isotropic in the field reversal region is studied. It is shown that the plasma anisotropy can essentially modify the plasma acceleration, the magnetic field intensity, and the shape of the moving slow shocks. Characteristics of reconnection in several limits, such as the isotropic limit and extreme pressure anisotropy cases corresponding to the fire hose and the mirror instability are analyzed.
Oscillons at a plasma surface
Authors: Stenflo L. , Yu M. Y.
Published: February 2003

The theory for nonlinear electrostatic surface waves on a cold semi-infinite plasma is generalized to include an external driving force. An oscillon solution is found.
High-speed focused-ion-beam patterning for guiding the growth of anodic alumina nanochannel arrays
Authors: Liu N. W. , Datta A. , Liu C. Y. , Wang Y. L.
Published: February 2003

Long-range ordered arrays of anodic alumina nanochannels are grown by anodizing an aluminum covered with a patterned layer of polymethylmethacrylate (PMMA) resist. The two-dimensional hexagonal-closed-packed pattern is created by focused ion beam (FIB) exposure of the PMMA and transferred onto the aluminum surface by phosphoric acid etching. The required exposure time per channel is only ∼20 μs, more than two orders of magnitude reduction in comparison with the previous method employing FIB direct sputtering of the aluminum surface.
Direct measurements of grain boundary sliding in yttrium-doped alumina bicrystals
Authors: Matsunaga K. , Nishimura H. , Muto H. , Yamamoto T. , Ikuhara Y.
Published: February 2003

The behavior of grain boundary sliding in pure and yttrium-doped Al2O3 was directly measured at a high temperature, using bicrystal experiments. For this purpose, we fabricated Al2O3 bicrystals containing a random grain boundary with or without yttrium ions. High-resolution transmission electron microscopy observations and energy dispersive x-ray spectroscopy analyses showed that bicrystals were successfully joined at an atomic scale, and doped yttrium ions segregated along the grain boundaries. It was found by compressive creep tests that the grain boundary sliding rate was restrained by two orders of magnitude due to yttrium addition, as compared to that of undoped bicrystals.
Raman-spectroscopic determination of inhomogeneous stress in submicron silicon devices
Authors: Dietrich B. , Bukalo V. , Fischer A. , Dombrowski K. F. , Bugiel E. , Kuck B. , Richter H. H.
Published: February 2003

We present the deconvolution of measurements of inhomogeneous mechanical stress in silicon device structures obtained by UV micro-Raman spectroscopy. Due to the very small UV penetration depth of only 12 nm, averaging of stress over the depth is almost eliminated. Only the averaging of stress over the area of the laser spot remains. By deconvolution of the spectra and comparison with finite element simulations, it is now possible to extract information on mechanical stress from areas as small as 200 nm. Oppositely stressed regions in submicroscopic dimensions can be detected, which could not be detected in previous visible light measurements due to averaging.
Femtosecond laser aperturless near-field nanomachining of metals assisted by scanning probe microscopy
Authors: Chimmalgi A. , Choi T. Y. , Grigoropoulos C. P. , Komvopoulos K.
Published: February 2003

Ultrashort pulsed-laser radiation is an effective method for precision materials processing and surface nano-/micromodification because of minimal thermal and mechanical damage. This study demonstrates that controllable surface nanomachining can be achieved by femtosecond laser pulses through local field enhancement in the near-field of a sharp probe tip. Nanomachining of thin gold films was accomplished by coupling 800-nm femtosecond laser radiation with a silicon tip in ambient air. Finite-difference time-domain numerical predictions of the spatial distribution of the laser field intensity beneath the tip confirmed that the observed high spatial resolution is due to the enhancement of the local electric field. Possible structuring mechanisms and factors affecting this process are discussed. The present process provides an intriguing means for massive nanofabrication due to the flexibility in the substrate material selection, high spatial resolution of ∼10 nm (not possible with standard nanomachining techniques), and fast processing rates achievable through simultaneous irradiation of multiarray tips.
Low-cost, low-loss microlens arrays fabricated by soft-lithography replication process
Authors: Kunnavakkam Madanagopal V. , Houlihan F. M. , Schlax M. , Liddle J. A. , Kolodner P. , Nalamasu O. , Rogers J. A.
Published: February 2003

This letter describes a soft lithographic approach for fabricating low-cost, low-loss microlens arrays. An accurate negative reproduction (stamp) of an existing high-quality lens surface (master) is made by thermally curing a prepolymer to a silicone elastomer against the master. Fabricating the stamp on a rigid backing plate minimizes distortion of its surface relief. Dispensing a liquid photocurable epoxy loaded to high weight percent with functionalized silica nanoparticles into the features of relief on the mold and then curing this material with UV radiation against a quartz substrate generates a replica lens array. The physical and optical characteristics of the resulting lenses suggest that the approach will be suitable for a range of applications in micro and integrated optics.
Diffusion-limited transport in the off-state of amorphous Si thin-film transistors
Authors: Lee J. U. , Possin G. E.
Published: February 2003

An analytic solution is derived to model the transient off-state transport in amorphous silicon thin-film transistors. The solution is based on a diffusion equation with a generation term to account for the emission from deep states. A characteristic diffusion time is calculated that depends on the channel length. For times much greater than the diffusion time, the transport current is proportional to the generation rate from approximately uniform density of states in the band gap. For shorter times, diffusion limits the transport of channel carriers to the contacts. As a result, a substantially different off-state transient behavior is observed. The analytic solution is compared with measured results from different channel length devices.
Structural and electrical properties of silicon dioxide layers with embedded germanium nanocrystals grown by molecular beam epitaxy
Authors: Kanjilal A. , Hansen J. Lundsgaard , Gaiduk P. , Larsen A. Nylandsted , Cherkashin N. , Claverie A. , Normand P. , Kapelanakis E. , Skarlatos D. , Tsoukalas D.
Published: February 2003

A sheet of spherical, well-separated, crystalline Ge nanodots embedded in SiO2 on top of a p-(001)Si wafer was fabricated by molecular beam epitaxy (MBE) combined with rapid thermal processing and characterized structurally and electrically. The average size of the Ge nanodots was estimated to be 4.5 nm with an average aerial density of 3×1011 cm−2, situated at 4.4 nm in average away from the Si/SiO2 interface. Significant charge storage effects were observed through capacitance–voltage measurements of metal–oxide–semiconductor capacitors.
Tuning the onset voltage of resonant tunneling through InAs quantum dots by growth parameters
Authors: Hapke-Wurst I. , Zeitler U. , Keyser U. F. , Haug R. J. , Pierz K. , Ma Z.
Published: February 2003

We investigated the size dependence of the ground-state energy in self-assembled InAs quantum dots embedded in resonant tunneling diodes. Individual current steps observed in the current–voltage characteristics are attributed to resonant single-electron tunneling via the ground state of individual InAs quantum dots. The onset voltage of the first step observed is shown to decrease systematically from 200 mV to 0 with increasing InAs coverage. We relate this to a coverage-dependent size of InAs dots grown on AlAs. The results are confirmed by atomic force micrographs and photoluminescence experiments on reference samples.
Cables of BN-insulated B–C–N nanotubes
Authors: Golberg D. , Dorozhkin P. S. , Bando Y. , Dong Z.-C. , Grobert N. , Reyes-Reyes M. , Terrones H. , Terrones M.
Published: February 2003

Nanotubular ropes composed of aligned multiwalled nanotubes having electrically insulating BN-rich outer shells and semiconducting B–C–N inner shells were synthesized through the reaction of aligned CNx (x⩽0.1) nanotube mats with boron oxide and nitrogen at ∼2000–2110 K. The atomic structure and chemical composition of the ropes were analyzed by high-resolution transmission and energy-filtered (Omega filter) electron microscopy. Individual ropes display perfect insulating performance of BN-rich outer layers and excellent field emission and thus conductive properties of inner B–C–N layers. A semiconducting nanometer-scale cable with built-in electrical insulation has thus been realized.
Quantitative studies of spin-momentum-transfer-induced excitations in Co/Cu multilayer films using point-contact spectroscopy
Authors: Rippard W. H. , Pufall M. R. , Silva T. J.
Published: February 2003

We have measured current-induced magnetic excitations in a variety of exchange-coupled Co/Cu multilayers using point-contact spectroscopy. A step in the dc resistance and corresponding peak in dV/dI are observed at a critical current Ic whose value depends linearly on applied magnetic field Bapp′ in agreement with Slonczewski’s theory. These features are observed for both in- and out-of-plane fields. Excitations in ferromagnetically coupled films occur even without an applied field. The spin transfer efficiency is determined from the slope and intercept of Ic vs Bapp and varied from contact to contact. For out of plane magnetized samples, the deduced spin transfer efficiency values are in good agreement with the predictions of Slonczewski.
CoSi
2
surface phase separation into self-assembled lateral multilayers
Authors: Goldfarb I.
Published: February 2003

CoSi 2 was grown on the Si(001) surface by solid-phase reaction. Its transformation from elemental Co/Si(001) was complete after a 700 °C anneal, as followed from the reflection high-energy electron diffraction analysis. Scanning tunneling microscopy observations of the resulting surface revealed a variety of atomic reconstructions, some apparent only under bias-dependent imaging conditions. Particularly striking was the appearance of alternating (3√2×2√2)-R45° and (4√2×2√2)-R45° surface domains arranged in long parallel stripes. Plausible reasons for such a phase separation are discussed.
One-shot-laser-pulse-induced demagnetization in rubidium manganese hexacyanoferrate
Authors: Tokoro Hiroko , Ohkoshi Shin-ichi , Hashimoto Kazuhito
Published: February 2003

We report on the photomagnetic effect in Rb0.91Mn1.05[Fe(CN)6]⋅0.6H2O ferromagnet. Magnetization of this system was reduced by irradiation with only one-shot of laser pulse (532 nm) at 3 K. This photodemagnetization was observed only when the laser power density (P) was above 9.3 mJ cm−2 pulse−1. The quantum yield was above one and reached 4.5 at P=43 mJ cm−2 pulse−1, showing that this phenomenon is driven by a cooperative effect such as the photoinduced domino effect. Infrared spectra before and after the irradiation indicated that this photomagnetic effect was caused by a photoinduced phase transition from the Fe(II)–CN–Mn(III) phase to the Fe(III)–CN–Mn(II) phase.
Direct observation of nonlinear effects in a one-dimensional photonic crystal
Authors: Inouye Hideyuki , Kanemitsu Yoshihiko
Published: February 2003

A total-reflection one-dimensional photonic crystal with a gold nanoparticles dispersed layer as a defect structure is fabricated and defect mode shifts induced by strong localization of light are demonstrated. It is found that the defect mode shift can be attributed to the Kerr effect inside the defect structure. Nonlinear optical effects inside the photonic crystal with the defect structure are also discussed.
Blueshifted Kerr effects and enhanced reflectivity in nanocrystalline CoFe2−xAlxO4 thin films
Authors: Zhou Biao , Zhang Ya-Wen , Liao Chun-Sheng , Yu Yue-Jun , Yan Chun-Hua , Chen Liang-Yao , Wang Song-You
Published: February 2003

The doping effects of Al3+ on the microstructure, magnetism, polar magneto-optical Kerr effects, and optical property of the sol-gel derived nanocrystalline CoFe2−xAlxO4 (x=0–1.0) thin films on silicon substrate were investigated. Doping of Al3+ not only led to the existence of two Kerr rotation peaks at 620 and 550 nm associated with the crystal-field transition, but also aroused the blueshifting of another peak at 540 nm correlated with the intervalence charge transfer transition. On the other hand, the reflectivity of as-deposited films increased with the Al3+ content x (except x=0.2) due to the decreased light scatter and absorptivity of Al3+ in substitution of Fe3+. Both the blueshifted Kerr effects and enhanced reflectivity in these films are of much benefit to magneto-optical recording.
Clusters and magnetism in epitaxial Co-doped TiO2 anatase
Authors: Chambers S. A. , Droubay T. , Wang C. M. , Lea A. S. , Farrow R. F. C. , Folks L. , Deline V. , Anders S.
Published: February 2003

We show that under certain conditions, highly Co-enriched TiO2 anatase clusters nucleate on epitaxial TiO2 anatase grown on LaAlO3(001) by oxygen plasma assisted molecular beam epitaxy. In the most extreme cases, virtually all incident Co segregates to the clusters, yielding a nanoscale ferromagnetic phase that is not ferromagnetic in homogeneous films of the same Co concentration. The nucleation of this phase simultaneous with continuous epitaxial film growth must be carefully monitored in order to avoid drawing false conclusions about the film structure.
Design and test of noncrosshybridizing oligonucleotide building blocks for DNA computers and nanostructures
Authors: Deaton Russell , Kim Jin-Woo , Chen Junghuei
Published: February 2003

DNA oligonucleotides that anneal to form duplexes in specific, planned configurations are a basic construction material for DNA-based computers and nanotechnology. Unplanned duplex configurations introduce errors in computations and defects in structures, and thus, the sequences must be designed to minimize these effects. A software design tool has been developed that uses thermodynamic models of DNA duplex thermal stability and algorithms from graph theory to select good sets of oligonucleotides. An example set was tested in the laboratory, and the designed sequences formed no unplanned duplexes and had no detectable secondary structure.
Electron pump by a combined single-electron/field-effect- transistor structure
Authors: Ono Yukinori , Takahashi Yasuo
Published: February 2003

A silicon-based single-electron pump that operates at much higher temperatures than previous pumps is fabricated on a silicon-on-insulator substrate. The pump consists of one single-electron transistor (SET) and two ultrasmall metal-oxide-semiconductor field-effect transistors (MOSFETs). We exploit, for the operation, the extremely high off-resistance of the MOSFETs. The high resistance enables us to prevent the unwanted injection (emission) of electrons into (from) the SET nearly perfectly and to make the SET work as a pump. The operation is confirmed at 25 K at the pumping frequency of ∼1 MHz.
Thermodynamic analysis of temperature-graded ferroelectrics
Authors: Alpay S. P. , Ban Z.-G. , Mantese J. V.
Published: February 2003

A Landau–Ginzburg thermodynamic model is constructed and used to develop a methodology for analyzing temperature-graded ferroelectrics. Spatial nonuniformities in temperature are shown to give rise to nonuniformities in polarization with corresponding spatial variations. The magnitude and the sign of the polarization gradients are shown to depend on the imposed temperature gradient. The polarization gradients result in asymmetric hysteresis responses with “up” or “down” charge offsets. The theoretical analysis presented here not only predicts the general trends associated with the hysteresis offsets observed from temperature-graded ferroelectrics, but is also in excellent quantitative agreement with the experimental data reported in the literature [W. Fellberg, J. V. Mantese, N. W. Schubring, and A. L. Micheli, Appl. Phys. Lett. 78, 524 (2001)].
Effects of Zn addition and thermal annealing on yield phenomena of CdTe and Cd0.96Zn0.04Te single crystals by nanoindentation
Authors: Pang M. , Bahr D. F. , Lynn K. G.
Published: February 2003

Mechanical yield phenomena in CdTe and CdZnTe single crystals for use as radiation detectors were studied by nanoindentation, since dislocations can act as electrically active levels that would impact device performance. The initial deformation behavior prior to yielding is elastic for as-grown crystals, indicating that rapid dislocation nucleation is the controlling mechanism for the observed yield point. Zn doping increases the stress required for initiating plastic deformation from 0.76 GPa in CdTe to 1.29 GPa in CdZnTe, and increases the flow stress of the material from solid solution hardening. Thermal annealing leads to plastic loading at very low loads, suggesting that annealing CdZnTe generates a low but increased density of dislocations in the bulk material.
Two photon absorption and photo-induced polymerization in partially polymerized crystals of polydiacetylene poly[4,6-dodecadiyn-1, 10-diol-bis(n-butoxycarbonylmethylurethane)]
Authors: Polyakov Sergey , Pauchard Thomas , Stegeman George , Berréhar Jeanne , Schott Michel
Published: February 2003

We investigated the validity of noninteracting molecular chain theories for fully polymerized polydiacetylene crystals by measuring the two photon absorption spectrum of poly[4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane)] chains isolated in their monomer matrix and comparing the results to those obtained previously from polydiacetylene single crystals. Data were taken over 800–940 nm using Z-scan and the measurements were found to be consistent with previously measured results in polydiacetylene single crystal poly[bis(p-toluene sulfonate) of 2,4-hexadiyne-1,6-diol], indicating the validity of the isolated molecule theoretical approach. We also report a low photo-induced polymerization threshold.
Lateral confinement of image electron wave function by an interfacial dipole lattice
Authors: Dutton Gregory , Pu Jingzhi , Truhlar Donald G. , Zhu X.-Y.
Published: February 2003

Image-potential states on Cu(111) surfaces covered by thin films of C60 fullerene have been characterized by angle-resolved two-photon photoemission spectroscopy. Metal-to-molecule electron transfer within the first layer creates a 4×4 superlattice of surface dipoles. We show that such a surface dipole lattice provides lateral confinement of image-electron wave functions. Measurements of parallel dispersion indicate that the n=1 image state is localized in the presence of one monolayer of C60 but becomes delocalized by the addition of a second layer. Quantum mechanical calculations explain this in terms of the screening of the dipole potential, thus, restoring the free-electron behavior parallel to the surface. These results show that a surface dipole lattice can effectively control the interfacial electronic structure.
Integrated optic broadband duplexer made by ion exchange
Authors: Ghibaudo E. , Broquin J.-E. , Benech P.
Published: February 2003

The development of optical amplification and bidirectional traffic in local and wide area networks requires broadband multiplexers which are able to treat the signal of an entire telecommunication window. A device made by ion exchange and answering to these needs is proposed in this letter. Its working principle, based on a leaky structure is first explained. An experimental result confirming a good broadband spectral behavior is then presented. Its spectral response displays two duplexing bands of at least 100 nm.
Anomalous power and spectrum dependence of terahertz radiation from femtosecond-laser-irradiated indium arsenide in high magnetic fields up to 14 T
Authors: Ohtake Hideyuki , Murakami Hidetoshi , Yano Takayuki , Ono Shingo , Sarukura Nobuhiko , Takahashi Hiroshi , Suzuki Yuji , Nishijima Gen , Watanabe Kazuo
Published: February 2003

We report on the terahertz radiation from femtosecond-laser-irradiated indium arsenide in high magnetic fields up to 14 T. It is found that the radiation power exhibits anomalous magnetic-field dependence, including saturation, decrease, and recovery up to 14 T. Moreover, the radiation spectrum possesses a clear periodic structure over 6 T.
Electroreflectance of hexagonal gallium nitride at the fundamental and E1 spectral regions
Authors: Al-Kuhaili M. F. , Glosser R. , Wickenden A. E. , Koleske D. D. , Henry R. L.
Published: February 2003

We have measured the room-temperature electroreflectance (ER) of hexagonal gallium nitride. Our measurements were obtained at the fundamental optical gap and at the E1 critical point regions. The measurements were performed using front contact ER. In the fundamental region, the ER spectra were found to be of excitonic nature and in the low field regime. In the E1 region, the ER spectra were also in the low field regime, but were fitted with two-dimensional critical points.
Formation of LaAlO3 films on Si(100) substrates using molecular beam deposition
Authors: Park Byung-Eun , Ishiwara Hiroshi
Published: February 2003

Lanthanum aluminate (LaAlO3) films were deposited on Si(100) substrates by a molecular beam deposition method with an electron beam gun and annealed typically in N2 atmosphere at 800 °C for 1 min. Reflection high-energy electron diffraction observation as well as x-ray diffraction analysis showed that the crystalline quality of the LaAlO3 films was amorphous, even after annealing at 800 °C. It was also found from x-ray fluorescence measurements that the ratio of La-to-Al for LaAlO3 films was almost 1:1. The dielectric constant of LaAlO3 films was estimated to be 20–25 and the leakage current density was improved by about eight orders of magnitude in maximum after the annealing process.
Dynamical mean-field theory for inhomogeneous polymeric systems
Authors: Ganesan Venkat , Pryamitsyn Victor
Published: February 2003

We propose and demonstrate a new computational approach which enables the simulation of the dynamics and rheology in inhomogeneous phases of multicomponent polymeric systems. Our approach generalizes Doi’s dynamical mean-field theory of rodlike polymers by combining single chain Brownian dynamics algorithms with phenomenological prescriptions for the dynamics of coarse-grained field variables. We provide a general overview of the technique and illustrate its applicability by our results in the context of a symmetric A+B polymer blend.
Real-time characterization of free-carrier absorption during epitaxial Si p-layer growth
Authors: Fujiwara Hiroyuki , Kondo Michio , Matsuda Akihisa
Published: February 2003

We have applied IR attenuated total reflection spectroscopy (ATR) to characterize free-carrier absorption during epitaxial Si p-layer growth by plasma-enhanced chemical vapor deposition. In the early stage of the growth, there are no detectable free carriers in the epitaxial p-layer, whereas we find a drastic increase in free-carrier concentration after terminating the plasma for the growth. We attribute this effect to a reduction in surface defects present during the epitaxial growth. The carrier concentration and mobility for the Si p-layer deduced from an ATR analysis were in excellent agreement with those estimated by Hall measurement. The results demonstrate the feasibility of real-time ATR to characterize the dynamics of carrier generation during doped semiconductor growth.
Observation of inductively coupled-plasma-induced damage on n-type GaN using deep-level transient spectroscopy
Authors: Choi Kyoung Jin , Jang Ho Wan , Lee Jong-Lam
Published: February 2003

The effects of inductively coupled plasma (ICP) etching on electrical properties of n-type GaN Schottky contacts were investigated by observing ion damage using deep-level transient spectroscopy. An electron trap, not previously seen, localized near the contact, as well as a pre-existing trap, was observed in the ICP-etched sample. The ICP-etched surface was found to be N-deficient, which means that N vacancies (VN) were produced by ICP etching. From these, the origin of the ICP-induced electron trap was suggested to be VN or a VN-related complex of point defects. The ICP-induced traps provided a path for the transport of electrons, leading to the reduction of Schottky barrier height and increase of gate leakage current.
Simulations of nanometric optical circuits based on surface plasmon polariton gap waveguide
Authors: Tanaka Kazuo , Tanaka Masahiro
Published: February 2003

Nanometric optical waveguides can be made by using the dependence of surface plasmon polaritons on the gap-width between two parallel metallic plates. This waveguide can be called surface plasmon polariton gap waveguide (SPGW). The H-plane and E-plane optical circuits that consist of SPGWs have been considered. Three-dimensional numerical simulations have been performed for the nanometric optical circuits that consist of straight and branched bend SPGWs. Results show that optical circuits considered in this letter can perform guiding, branching, and bending functions of optical waves in the nanometric device.
A carbon-nanotube-based nanorelay
Authors: Kinaret J. M. , Nord T. , Viefers S.
Published: February 2003

We investigate the operational characteristics of a nanorelay based on a conducting carbon nanotube placed on a terrace in a silicon substrate. The nanorelay is a three-terminal device that acts as a switch in the gigahertz regime. Potential applications include logic devices, memory elements, pulse generators, and current or voltage amplifiers.