bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-resolved carrier recombination dynamics of 1.3–1.8 μm broadband light emitting diode structures
Authors: Wang Li , Lin Shawn-Yu , Hafich M. J. , Fritz I. J.
Published: July 2002

We present a time-resolved study of carrier recombination dynamics of broadband light emitting diode structures comprised of a series of InGaAs/InGaAlAs digital pseudoalloy short period superlattices fabricated by molecular beam epitaxy. The structure consists of three quantum wells equally spaced in emission energy over the 1.3–1.8 μm range. We performed a time-resolved study of carrier recombination process for each quantum well using optical pumping. Experimental results show that carrier tunneling across adjacent wells plays a major role in the overall carrier population distribution across the three wells. By tailoring the thicknesses of barriers and wells of the structure, uniform spectral emission covering 1.3–1.8 μm range can be achieved.
Electron spin resonance identification of a methyl associated organic radical in irradiated amorphous SiO2
Authors: Austin Wm. R. , Leisure R. G.
Published: July 2002

An electron spin resonance (ESR) signal comprised of three resolved lines of equal 19.3 Gauss separation (3×19.3 G), but unequal amplitude, is observed in x-irradiated amorphous silicon dioxide. The radical appears exclusively in silica samples which also exhibit the methyl radical, a familiar indicator of trace carbon and hydrogen contamination. The 3×19.3 G signal is observed to grow most rapidly versus irradiation dose when methyl radical concentration is near maximum. This evidence suggests that the ESR signal is due to a radiolytic, organic radical which evolves after the methyl radical and, like the methyl radical, is trapped and stabilized in the amorphous silica network. Experimental methods of radical generation are presented, followed by discussion of models for the chemical structure of the 3×19.3 G radical.
Impurity dependence of oxide defects in Czochralski silicon
Authors: Itsumi Manabu , Akiya Hideo , Tomita Masato , Ueki Takemi , Yamawaki Masataka
Published: July 2002

Octahedral cavities have recently been found in the Czochralski silicon (CZ-Si) substrate surface layer just under oxide defects. We investigate the effect that adding HCl to oxygen during oxidation has on the oxide defect density. The effect of intentionally introducing impurities onto a Si surface on the oxide defect density is also examined. Our experimental results suggest that impurities are closely related to the generation of oxide defects. A model is presented in which impurities are incorporated into the growing octahedral cavities during Si crystal growth, and then introduced into the growing oxides during thermal oxidation. These impurities in the oxides then act as a conductive path (oxide defects) in the insulator on the CZ-Si.
Improved modeling of grain boundary recombination in bulk and p-n junction regions of polycrystalline silicon solar cells
Authors: Edmiston S. A. , Heiser G. , Sproul A. B. , Green M. A.
Published: July 2002

This article provides a theoretical investigation of recombination at grain boundaries in both bulk and p-n junction regions of silicon solar cells. Previous models of grain boundaries and grain boundary properties are reviewed. A two dimensional numerical model of grain boundary recombination is presented. This numerical model is compared to existing analytical models of grain boundary recombination within both bulk and p-n junction regions of silicon solar cells. This analysis shows that, under some conditions, existing models poorly predict the recombination current at grain boundaries. Within bulk regions of a device, the effective surface recombination velocity at grain boundaries is overestimated in cases where the region around the grain boundary is not fully depleted of majority carriers. For vertical grain boundaries (columnar grains), existing models are shown to underestimate the recombination current within p-n junction depletion regions. This current has an ideality factor of about 1.8. An improved analytical model for grain boundary recombination within the p-n junction depletion region is presented. This model considers the effect of the grain boundary charge on the electric field within the p-n junction depletion region. The grain boundary charge reduces the p-n junction electric field, at the grain boundary, enhancing recombination in this region. This model is in agreement with the numerical results over a wide range of grain boundary recombination rates. In extreme cases, however, the region of enhanced, high ideality factor recombination can extend well outside the p-n junction depletion region. This leads to a breakdown of analytical models for both bulk and p-n junction recombination, necessitating the use of the numerical model.
Negative electron affinity observed in boron-doped p-type diamond films by scanning field emission spectroscopy
Authors: Wang W. N. , Fox N. A. , Steeds J. W. , Lin S. R. , Butler J. E.
Published: July 2002

Field emission properties of boron-doped diamond films were studied by combined scanning tunneling microscopy/spectroscopy and scanning field emission spectroscopy. A detailed spatial correlation between field emission sites and diamond morphology, surface work function, and diamond quality can be established by this technique. A possible indication of negative electron affinity of the (111) faces near the (111)/(111) and (111)/(100) grain boundaries and high defect sites of boron doped p-type diamond films were observed by field emission I–V (current–voltage) measurement.
Structural, magnetic, and magnetotransport properties of NiFe/Ag as-deposited multilayers for variable NiFe and Ag layer thickness
Authors: Christides C. , Stavroyiannis S. , Niarchos D.
Published: July 2002

Superstructure refinement analyses of x-ray-diffraction data, magnetotransport, and hysteresis loop measurements were performed in Ni81Fe19/Ag ultrathin multilayers. A ferromagnetic coupling and oscillations of coercivity Hc and residual magnetization Mr at 5 K have been observed as a function of Ag layer thickness. The observed residual stresses in NiFe layers which induce preferable magnetic easy-axes distributions along the strain direction are related with bulk spin-dependent scattering in individual layers for this type of giant magnetoresistive systems.
Electrical characteristics and deep-level admittance spectroscopies of low-temperature grown GaAs p-i-n structures
Authors: Chen J. F. , Chen N. C. , Wang P. Y. , Tsai M. H.
Published: July 2002

The properties of low-temperature grown GaAs are studied via the electrical characterization of p-i-n structures with part of the intrinsic layer grown at 300 °C. Comparisons are made between the low-temperature and normally grown samples. The current of the low-temperature sample is about two orders of magnitude higher than that of the normally grown sample in both forward and reverse bias. From temperature-dependent analysis, the leakage current of the low-temperature sample is contributed by the recombination current through defect levels around the midgap, from which a recombination lifetime of 9.4×10−12 s was obtained. By using admittance spectroscopy we observed a dominant electron level at 0.60 eV with a corresponding capture cross section of 1.0×10−13 cm2 that was not observed in the normally grown sample; thus it is believed to be introduced by the As-rich low-temperature layer.
Harmonic thermal waves in materials with thermal memory
Authors: Novikov I. A.
Published: July 2002

A topic of great present interest is the investigation of heat transfer in materials with memory (HTMM). The correct description of different experimental heat transfer phenomena (in liquid helium, in dielectrics at helium temperature, in organic liquids, etc.) is conducted on the framework of HTMM theory. Also, new physical effects have been predicted in HTMM theory. The most important problem for HTMM theory and practical applications is analyzed—the propagation of harmonic thermal waves in an infinite plate from material with thermal memory. It is shown that in such materials there are appreciable effects produced by the interference of thermal waves, similar to multibeam interference of electromagnetic waves in optics.
Investigation on the color center distribution in LiF thin films
Authors: Jacobsohn Luiz Gustavo , Nunes Raul Almeida , Scavarda do Carmo Luiz Carlos
Published: July 2002

The F2 center depth distribution in LiF thin films irradiated by 15 and 30 keV electron beams was obtained experimentally by means of optical absorption measurements of multilayered LiF/KBr films. Monte Carlo simulations of the incidence of electron beams in LiF were also carried out to provide the dissipated energy and the fluor ionization depth profiles for comparison with the experimental data. The ionization and the dissipated energy profiles have essentially the same shape, with their maxima at a depth of 41±5% of the electron range. The F2 distributions could be described by Gaussian distributions centered at depths of 1.5 and 1.6 μm for 15 and 30 keV irradiation, respectively.
Comparison between direct current and sinusoidal current stressing of gate oxides and oxide/silicon interfaces in metal–oxide–silicon field-effect transistors
Authors: Trabzon L. , Awadelkarim O. O. , Werking J. , Bersuker G. , Chan Y. D.
Published: July 2002

It was recently reported that plasma process-induced damage to metal–oxide–silicon field-effect transistors (MOSFETs) comprises a damage mechanism that involves alternating-current (ac) stressing of the oxide and the oxide/silicon interface. The study reported herein is aimed at establishing signatures of MOSFET damage induced by ac stressing applied at conditions that emulate plasma processing environment. We apply sinusoidal ac voltage stress signals to 0.5 μm n-channel or p-channel MOSFETs with 90-Å-thick gate oxides. We assess damage on MOSFETs by measuring transconductance, threshold voltage, and subthreshold swing. We find that the onset of damage to devices subjected to ac stressing occurs at voltage amplitudes as low as 4 V, whereas in dc stressing, applied for the same time, damage becomes significant only at dc voltages larger than 10 V. We also show that damage from ac stressing attains a maximum at frequencies in the range 1–100 kHz and decreases at frequencies above 5 MHz. It is proposed that carrier hopping is primarily responsible for oxide current and, hence, device damage observed following the ac stress. This hopping current is insignificant during high-field dc stress when Fowler–Nordheim tunneling becomes the dominant conduction mechanism.
Formation of a graded-index waveguide in UV exposed polyimide
Authors: Sarkisov Sergey , Teague Zedric , Venkateswarlu Putcha , Abdeldayem Hossin , Frazier Donald , Adamovsky Grigory
Published: July 2002

We report on the formation of a graded-index waveguide in a photocrosslinkable fluorinated polyimide upon its photodarkening with the spectral line 313 nm of a mercury arc lamp at exposures exceeding 5 J/cm2. Photodarkening prevents the UV radiation from penetration deep into the polymer and finally sets the region with increased refractive index near the top surface. A theoretical model based on this concept reconstructs the refractive index profile of the waveguide in agreement with the phase integral calculations based on waveguide mode spectrum.
Quantum derivation of overall free-electron laser gain dependence on photon energy
Authors: Gim Sǒngho M.
Published: July 2002

The quantum electrodynamic perturbation technique is used to derive the overall dependence of photon amplification on photon wavelength by an electron beam through a transverse wiggler magnetic field without any additional assumptions such as of virtual photons or of virtual Compton scattering. In this simplified model we show that over the broad range of photon energy, from infrared through hard X ray, the overall net gain decreases as the inverse square root of the photon frequency in a fixed period of the magnetic wiggler array, which is in agreement with the classical result.
Single mode integrated-optical wide-band channel waveguides and junction splitters in KTiOPO4 for visible light
Authors: Rottschalk M. , Ruske J.-P. , Unterschütz B. , Rasch A. , Gröber V.
Published: July 2002

Single mode integrated-optical wide-band channel waveguides (SOWCWs) have been defined as a novel type of channel waveguides. The wavelength ranges (bandwidths) of both single mode operation in the channel waveguide and efficient junction-splitting using the same channel waveguides, that is for constant combining or splitting of light in integrated-optical devices like Y junctions, can easily comprise the entire visible wavelength region. In this case, the SOWCW is a real single mode white light channel waveguide. The optical bandwidths of both Rb↔K ion-exchanged channel waveguides in KTiOPO4 (KTP) as an example of SOWCWs and Rb:KTP Y junctions in comparison with those of conventional titanium-indiffused channel waveguides and Y junctions in LiNbO3 have been theoretically calculated and experimentally verified. The channel waveguide attenuation, the coupling efficiency to single mode fibers, and the splitting ratio of Y junctions, especially, show no significant wavelength dependence in the Rb:KTP case. Use of SOWCWs could open up new directions of integrated optics. As an example, the basic three-color-mixing device is chosen from a variety of possible applications in the field of integrated-optical color image generation.
High-frequency behavior of waveguide integrated photodiodes monolithically integrated on InP using optical butt coupling
Authors: Umbach A. , Leone M. , Unterbörsch G.
Published: July 2002

p-i-n photodiodes with integrated optical waveguides were successfully fabricated in the GaInAsP/InP material system. This integration leads to optoelectronical integrated circuits of significantly increased functionality, and it also offers the possibility to build high-speed detectors with high quantum efficiency. Butt-joint coupling between waveguide and photodiode was used allowing smallest detector sizes. Selective embedded growth of the photodiode layer stack was accomplished by metal-organic vapor-phase epitaxy on partially masked substrates. This technique was proven to be suitable for device fabrication. To study the influence of the lateral growth interface between waveguide and the photoabsorbing GaInAs material, the spacing d between interface and p region of the photodiode was varied between 0 and 4 μm. The detector bandwidth is not limited by the electrical RC time constant up to frequencies of 50 GHz for devices with an active area of 10×11 μm2. Best values for the quantum efficiency and the electrical 3 dB cutoff frequency of 65% and 8 GHz are obtained. Both decrease strongly with increased spacing d due to an enhanced diffusion component and an increase of carriers trapping and recombination effects at the growth interface. This interpretation of the experimental data was well confirmed by a detailed analysis of the dynamic device behavior based on analytical calculations of the physical transport mechanisms. Consequently, for a redesigned photodiode the distance d has to be minimized as far as possible.
Quadratic power corrections to the dynamic magnetization using the transverse magnetostatic wave-optical interaction
Authors: Prabhakar A. , Stancil D. D.
Published: July 2002

A microstrip T-transducer excites forward volume magnetostatic waves (MSWs) in a [BiLu]3Fe5O12 film. An optical beam is edge coupled into the film and the transverse MSW–optical interaction is observed at high microwave power levels. Using the coupled mode equations, we demonstrate that a T-transducer causes the intensity of the diffracted beam to be a product of terms involving the magneto-optic coupling coefficient (κ) and the phase mismatch between the optical guided modes and the MSWs. Taylor series expansions for κ and the MSW wave number (β) are used to obtain an analytic expression for the MSW–optical interaction. The dependence on β causes a shift in the interaction spectrum with increasing power. After correcting for this shift, the residual dependence on power is attributed to a quadratic correction to the dynamic magnetization which in turn affects κ. We demonstrate how the quadratic dependence plays an important role in accurately determining an expansion for the MSW dispersion relation.
Digital-image-based models of two-dimensional microstructural evolution by surface diffusion and vapor transport
Authors: Bullard Jeffrey W.
Published: July 2002

A new and versatile model of capillary-driven microstructural evolution is described. The model operates on digital images of microstructures, and uses the local phase distribution to form an interpolated “equivalent sharp surface.’’ Local surface properties, like outward normal vectors and curvatures, are calculated and local driving forces for mass transport are determined using standard irreversible thermodynamic concepts. Mass transport kinetics are simulated using discretized rate laws for a specified path and rate-controlling step. Models of surface diffusion and of surface-attachment-limited kinetics are described and applied to several systems. Results for simple microstructures agree well with analytical predictions of transport rates and scaling laws, and useful quantitative information is extracted from simulations on more complex microstructures for which analytical predictions do not exist.
High power laser semiconductor interactions: A Monte Carlo study for silicon
Authors: Yeom K. , Jiang H. , Singh J.
Published: July 2002

In this article, we use Monte Carlo methods to study the interaction of high power laser pulses with electrons in the conduction band of semiconductors. The laser field is represented by a sinusoidal electric field which tends to cause an oscillatory motion in the electrons. The scattering of electrons from the lattice force the electrons to lose phase coherence with the field. The approach is applied to silicon. We use the approach to examine the carrier energy distribution and material breakdown due to the transfer of energy from the laser to the electrons followed by impact ionization. The impact ionization coefficient, α, and its dependence on the laser frequency and field strength is examined and compared to the values in a dc field. In general, the ac value is smaller than the dc value, but at low frequencies and high field strengths, the ac impact ionization coefficient approaches the dc value at the same rms field value. The importance of collisions in the energy transfer process is elucidated.
Analysis of optical properties of p-type GaAs/AlGaAs superlattices for multiwavelength normal incidence photodetectors
Authors: Kim B. W. , Mao E. , Majerfeld A.
Published: July 2002

A calculation on intersubband optical transitions including heavy and light hole bands to spin-split-off band in heavily doped p-type GaAs/AlGaAs multi-quantum well (MQW) structures is reported. The analysis is focused on elucidating the recent experimental observation of normal incidence absorption and photocurrent at photon wavelengths of 2–3 μm, in addition to the already-observed absorption at around 8 μm in heavily doped p-type GaAs/AlGaAs MQW structures. The calculation is an extension of our previous study which only includes transitions between heavy and light bands. The analysis, in which Hartree and exchange-correlation many-body interactions are taken into account within one-particle local density approximation, shows that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than the barrier height for p-type GaAs/AlGaAs superlattices with well doping of 2×1019 cm−3. One region has broad absorption peaks with coefficients of about 5000 cm−1 at around 8 μm, and the other has two rather sharp peaks at 2.7 and 3.4 μm with 1800 and 1300 cm−1, respectively. The result agrees reasonable well with the experimental observation in general absorption features. The existence of multiabsorption wavelengths in heavily doped GaAs/AlGaAs MQWs may allow the design of multicolor normal incidence photodetectors.
Simple method for the calculation of the deformation profiles in chiral nematic liquid crystal cells with asymmetric pretilt
Authors: Chen C.-J. , Lien A. , Nathan M. I.
Published: July 2002

We present a one-dimensional simulation methodology for determining the liquid crystal director distribution in a cell for arbitrary pretilt angles on two glass substrate surfaces. The method is illustrated for cases of an asymmetric twisted nematic cell, a hybrid alignment nematic cell, and a bend alignment nematic cell.
Magnetic properties of single domain ε-Fe3N synthesized by borohydride reduction route
Authors: Panda R. N. , Gajbhiye N. S.
Published: July 2002

Single domain ε-Fe3N nitride particles have been synthesized by chemical reduction followed by nitridation at 823 K. The ε-Fe3N phase crystallizes in hexagonal structure with unit cell parameters, a=2.70 Å and c=4.39 Å. There is a reduction of unpaired d electrons for intraband polarization as the nitrogen contributes to the density of states and thus results in lowering of magnetic moments. The reduction of intrinsic magnetizations and Curie temperatures with decreasing particle size is attributed to canted spin structure predominantly at the surface compared to the bulk of the particles. Chemisorption of oxygen results in the formation of oxynitride layer at the surface with a ferromagnetic coupling to the spins in the core of the particle. Mössbauer study of ε-Fe3N particles exhibits the coexistence of ferromagnetic and superparamagnetic particles and corroborates the observed magnetic properties.
Application of the second harmonic generation microscope to nondestructive observation of periodically poled ferroelectric domains in quasi-phase-matched wavelength converters
Authors: Kurimura Sunao , Uesu Yoshiaki
Published: July 2002

A technique for observation of 180° domains in ferroelectric crystals is demonstrated by the use of the second harmonic generation (SHG) microscope. The phase reversal of the SH wave accompanying inversion of spontaneous polarization is exploited to visualize domains. Interference between SH waves converts the phase information to the SH contrast. The domain mapping is achieved in LiNbO3 and LiTaO3 by nonlinear coefficients d33 and d22 under the microscope, which enables the characterization of a periodically poled structure in quasi-phase-matched wavelength converters in a nondestructive way. The validity of the technique is proved by another characterizing tool of destructive etching.
Optical characterization of InGaAs–GaAs multiple quantum wells using variable angle spectroscopic ellipsometry for designing tunable modulators
Authors: Cheung S. K. , Wang H. , Huang W. , Jain F.
Published: July 2002

Variable angle spectroscopic ellipsometry (VASE) technique is used to measure the optical constants of InGaAs/GaAs multiple quantum well (MQW) structures for the purpose of designing tunable optical modulators. The VASE measurements also include field-induced changes in index of refraction and absorption. These measured changes in MQWs are in agreement with theoretical computations. In addition, the design and simulated performance of an InGaAs/GaAs MQWs Fabry–Perot modulator using the VASE data is presented.
Steady state photocurrent and photoluminescence from single quantum wells as a function of temperature and bias
Authors: Barnes J. , Tsui E. S. M. , Barnham K. W. J. , McFarlane S. C. , Button C. , Roberts J. S.
Published: July 2002

We have studied the variation with applied bias and temperature of steady state photoluminescence (DCPL) and photoconductivity (DCPC) from a series of GaAs/AlGaAs single quantum well, p-i-n structures with different well widths. We present the DCPC and DCPL results, which when combined, allow us to assess how significant nonradiative recombination is in the samples and hence the quality of the material. We discuss the qualitative features in the light of a new theoretical approach presented here for the first time. This includes contributions from escape (of both electrons and holes) and makes it possible to extract from the experimental data two parameters, each reflecting the competition between escape and one of the recombination processes (radiative or nonradiative) in the absence of the other. We further comment qualitatively on the bias and temperature dependence of these different processes.
Extended states and dynamical localization in semiconductor superlattices
Authors: Domínguez-Adame F. , Sánchez Angel , Diez Enrique
Published: July 2002

We study the quantum dynamics of electronic wave packets in quantum-well based semiconductor superlattices subject to an applied electric field. Using a high-accuracy numerical method, we analyze the dynamical behavior of electronic wave packets in periodic, random and random dimer superlattices. The spatial extent of electronic states is characterized by means of the time-dependent inverse participation ratio. We show that the delocalized states recently found in random dimer superlattices become spatially localized under the action of the applied field (dynamical localization) but wavepackets are much less localized than in purely random superlattices at moderate field. We conclude that the resonant tunneling effects causing delocalization in dimer superlattices play an important role even in the presence of moderate electric field.
Electron migration in BaFCl:Eu2+ phosphors
Authors: Chen Wei , Song Qiaqing , Su Mianzeng
Published: July 2002

Here we report the electron migration by photo- or thermostimulation in BaFCl:Eu2+. Electrons released from F centers may be trapped by other defect sites to form F aggregates or another type of F center and vice versa. This migration reduces the photostimulated luminescence efficiency, lowers the imaging plate sensitivity, and causes the difference between the optical absorption and photostimulation spectra of color centers.
Quantum dot superlattices and their conductance
Authors: Xia Jian-Bai , Sheng Wei-Dong
Published: July 2002

The one-dimensional energy bands and corresponding conductivities of a T-shaped quantum-dot superlattice are studied in various cases: different periods, with potential barriers between dots, and in transverse electric fields. It is found that the conductivity of the superlattices has a similar energy relation to the conductance of a single quantum dot, but vanishes in the energy gap region. The energy band of a superlattice with periodically modulated conducting width in the perpendicular magnetic field is calculated for comparison with magneto-transport experiments. It is found that due to the edge state effect the electron has strong quantum transport features. The energy gaps change with the width of the channel, corresponding to the deep peaks in the conductance curve. This method of calculating the energy bands of quantum-dot superlattices is applicable to complex geometric structures without substantial difficulty.
Electronic transport and metastabilities in P-doped a-Si:H
Authors: Agarwal Pratima , Agarwal S. C.
Published: July 2002

Effect of thermal and light induced metastabilities on conductivity (σ) and thermopower (S) in phosphorus doped a-Si:H films has been studied. It has been found that although both conductivity and thermopower show a change upon fast quenching, the function Q=ln σ−eS/k does not change. This suggests that quenching results in a new frozen-in structure, in which the position of the Fermi level is changed, but there is no change in the potential fluctuations. No measurable effect of light soaking is observed in our films.
Doubly resonant second-harmonic generation in quantum wells with anisotropic and tilted valleys: Resonant screening effects
Authors: Załużny M. , Bondarenko V.
Published: July 2002

Second-harmonic generation due to intersubband transitions in near-doubly resonant systems with anisotropic and tilted valleys is discussed theoretically. Calculations are performed for the L-valley quantum well structures employing the perturbative density-matrix formulation within the self-consistent field approximation. The results obtained show that modification of the second-harmonic generation spectrum induced by the depolarization effect depends strongly on the polarization of the pumped and generated light.
Transient electrical field characteristics due to polarization of domains in bulk LiNbO3 during Czochralski growth
Authors: Bermúdez V. , Dutta P. S. , Serrano M. D. , Diéguez E.
Published: July 2002

The transient behavior of the electric field during simultaneous growth and in situ poling of LiNbO3 has been studied. The transient features have been correlated with the poling of the multidomain seed and crystal, and domain reversal in poled seed. A steady-state condition is obtained after the shoulder region of the crystal is terminated and the crystal reaches its final diameter. Finally, the critical values of field parameters necessary to obtain complete monodomain crystals without causing melt electrolysis at the solid–liquid interface have been analyzed.
CuInS
2
thin film growth monitoring by in situ electric conductivity measurements
Authors: Alt M. , Lewerenz H. J. , Scheer R.
Published: July 2002

The growth of CuInS2 thin films by coevaporation has been monitored by in situ electrical conductivity measurements. Films with different cation ratio In/(In+Cu) were investigated. During the controlled cool-down period we obtain conductivity versus temperature data which are completed ex situ in the low-temperature region. The formation of the semimetallic CuS phase in Cu-rich films is found during the cool-down period at a substrate temperature of about 450 K. For In-rich films the dominance of charged grain boundary states is discussed.
Scanning tunneling microscope of the “16×2’’ reconstructed Si(110) surface
Authors: Packard William E. , Dow John D.
Published: July 2002

The Si(110) surface, which is commonly employed for etching micro-machines, self-organizes into a “16×2’’ reconstruction or surface meso-crystal. A model of this surface crystal structure, based on scanning tunneling microscopy measurements, is proposed.
Observation of a long range surface mode with a polymer/silver/polymer multilayer
Authors: Sterkenburgh T. , Franke H.
Published: July 2002

The excitation of a long range surface mode in the visible region is reported. Using a vacuum evaporated silver film in a nearly symmetric embedding of two spincoated polymer films, a full spectrum of resonance lines in the angular reflectivity of the multilayer is recorded. In addition to the plasmon resonance of the Ag layer and the metal film enhanced leaky modes of the outer polymer film, the additional resonance is identified.
Control of light polarization in InGaAsP/InP lasers by injection of light pulses
Authors: Klehr A. , Müller R.
Published: July 2002

Light emission from a ridge waveguide 1.3 μm InGaAsP/InP semiconductor laser pumped both electrically and optically was analyzed by polarization- and time-resolved measurements. The electric and the optical excitation was realized with a dc-bias current and with 150 ps pulses from a Q-switched Nd-YAG laser at 1.064 μm wavelength, respectively. The pump light was introduced into the InGaAsP/InP laser through a window opened in the substrate gold contact. The steady-state P–I characteristics of the semiconductor laser exhibited a transition from TM- to TE-polarized light emission if the injection current surpasses a certain value that depends on the heatsink temperature. Depending on the dc-bias current and the optical pulse power, a variety of different emission characteristics of the semiconductor laser were observed: pure TE or TM pulsations, in combination with a background cw emission in some cases; simultaneous emission of TE and TM pulses and switching between TM and TE emission states with switching times as short as 30 ps.
Oxygen atomic flux O* enhancement by gas-pulsed electron cyclotron resonance plasma
Authors: Park Young Ju , O’Keeffe Patrick , Ozasa Kazunari , Mutoh Harunobu , Aoyagi Yoshinobu , Min Suk-Ki
Published: July 2002

We have investigated an oxygen gas-pulsed plasma in conjunction with the enhancement of atomic oxygen radical O* flux and its application. The measured mean O* flux of 5.9×1015 atoms/cm2 s from the gas-pulsed plasma with a duty cycle of 50% (periodically opened for 0.3 s and closed for 0.3 s) at 32 sccm is 1.6 times enhanced compared to that of a continuous wave plasma and is in good agreement with the increment obtained with the time averaged value of transient optical emission profiles of O* at 777.6 nm. The generation of a higher O* flux was interpreted by the mitigation of a recombinative reaction process through the interruption of gas flow injections in the gas pulsed plasma. As a preliminary application, an increase in critical temperature of superconducting YBa2Cu3O7−x thin films was achieved by the gas-pulsed plasma oxidation with a duty cycle of 50%.
Intrinsic carrier concentration and electron effective mass in Hg1−xZnxTe
Authors: Sha Yi-Gao , Su Ching-Hua , Lehoczky S. L.
Published: July 2002

The intrinsic carrier concentrations, Fermi energies, and the electron effective masses are calculated for Hg1−xZnxTe with 0<x⩽0.4 and 50 K⩽T⩽400 K. The numerical calculations are based on the Kane k⋅p model and no further analytical simplification or approximation is made for the energy band structure beyond those inherent in the Kane model. The results are compared to the previous calculations.
Hydrogen configurations and stability in amorphous sputtered silicon
Authors: Lusson L. , Lusson A. , Elkaim P. , Dixmier J. , Ballutaud D.
Published: July 2002

The effects of the deposition parameters on configurations and stability of hydrogen (deuterium) in amorphous sputtered silicon a-Si:H have been analyzed using Fourier transformed infrared absorption spectroscopy, deuterium effusion experiments, and x-ray diffractometry. The ratio of monohydride bonds Si–H was calculated from the infrared absorption stretching mode spectrum. This ratio was increased when the substrate temperature was increased. The effusion results in a-Si:D, when deposited with a simple cathode, have shown the presence of clustered deuterium weak bonds in microvoids (400 °C deuterium effusion peak), beside isolated Si–D bonds embedded in the more compact tissue (650 °C deuterium effusion peak). The deconvolutions of the stretching mode infrared absorption spectrum of the as-grown sample and after isothermal annealing at 510 °C have allowed one to conclude that it is not possible to identify the low temperature and high temperature effusion peaks, respectively, with the decomposition of Si–H2 and Si–H centers. The effusion of the less stable hydrogen improved the amorphous structural relaxation. The ratio of monohydride bonds was increased by introducing a magnetron cathode in the deposition chamber. At the same time, the deuterium effusion spectrum was modified, showing a continuous deuterium effusion from 350 °C, instead of two well-defined effusion peaks.
Josephson noise in quasiparticle mixers
Authors: Leridon Brigitte
Published: July 2002

The full quantum theory of mixing has been widely developed by Tucker. From theoretical analysis it allows one to predict the optimal performances of a quasiparticle superconducting insulator-superconducting junction mixer from knowing the junction current-voltage characteristics. This theory, however, considers only quasiparticle processes and neglects pair effects. At frequencies close to the superconductor energy gap, the Josephson currents become unavoidable and are reputed to be the cause of strong instabilities and noise. We present here a theoretical calculation of the Josephson noise and losses, which is consistent with experimental results. The width of the Josephson noise peaks is discussed.
Imaging of high harmonic radiation emitted during the interaction of a 20 TW laser with a solid target
Authors: Chambers D. M. , Preston S. G. , Zepf M. , Castro-Colin M. , Key M. H. , Wark J. S. , Dangor A. E. , Dyson A. , Neely D. , Norreys P. A.
Published: July 2002

We present images of the source of extreme ultraviolet (XUV) harmonic emission at a wavelength of 220 Å from the interaction of a 20 TW, 1.053 μm Nd:glass laser beam focused to intensities up to 4×1018 W cm−2 onto a solid target. From these measurements we determine an upper limit to the source size and brightness of the harmonic emission to show its efficacy as a novel source of short-pulse, coherent XUV radiation. We also demonstrate the empirical scaling of the harmonic generation efficiency with irradiance up to 1019 W μm2 cm−2, and extrapolate to estimate the possible source brightness at higher irradiances. These source brightnesses are compared to those available from an x-ray laser system.
Doppler spectroscopic measurements of sheath ion velocities in radio-frequency plasmas
Authors: Woodcock B. K. , Busby J. R. , Freegarde T. G. M. , Hancock G.
Published: July 2002

We have measured the distributions of N2+ ion velocity components parallel and perpendicular to the electrode in the sheath of a radio-frequency nitrogen reactive ion etching discharge, using pulsed laser-induced fluorescence. Parallel to the electrode, the ions have throughout a thermal distribution that is found to be consistent with the rotational temperature of 355 K. In the perpendicular direction, we see clearly the acceleration of the ions towards the electrode, and our results agree well with theoretical predictions although an unexpected peak of unaccelerated ions persists. We have also determined the absolute ion concentrations in the sheath, which we have calibrated by analyzing the decay in laser-induced fluorescence in the plasma bulk after discharge extinction. At 20 mTorr, the bulk concentration of 1.0×1010 cm−3 falls to around 2×108 cm−3 at 2 mm from the electrode.
Wavelets in the solution of the volume integral equation: Application to eddy current modeling
Authors: Wang Bing , Moulder John C. , Basart John P.
Published: July 2002

There is growing interest in the applications of wavelets as basis functions in solutions of integral equations, especially in the area of electromagnetic field problems. In this article we apply a wavelet expansion to the solution of the three-dimensional eddy current modeling problem based on the volume integral method. Although this method shows promise for eddy current modeling of three-dimensional flaws, it is restricted by the computing power required to solve a large linear system. In this article we show that applying a wavelet basis to the volume integral method can dramatically reduce the size of the linear system to be solved. In our approach, the unknown total field is expressed as a twofold summation of shifted and dilated forms of a properly chosen basis function that is often referred to as the mother wavelet. The wavelet expansion can adaptively fit itself to the total field distribution by distributing the localized functions near the flaw boundary, where the field change is large, and the more spatially diffused functions over the interior of the flaw where the total field tends to be smooth. The approach is thus best suited to modeling large three-dimensional flaws where the large number of elements used in the volume integral method requires extremely large memory space and computational capacity. The feasibility of the wavelet method is discussed in the context of the physical nature of eddy-current modeling problems. Numerical examples using both Haar wavelets and Daubechies compactly supported wavelets with periodic extension are given. The results of the wavelet method are also compared with experimental results from a cylindrical flat-bottom hole in an aluminum plate. These numerical examples and comparisons indicate that the wavelet method can greatly reduce the numerical complexity of the problem with negligible loss in accuracy.
Effect of metallic additives (M) on the exchange coupling of antiferromagnetic CrMnMx films to a ferromagnetic Ni81Fe19 film
Authors: Soeya Susumu , Hoshiya Hiroyuki , Arai Reiko , Fuyama Moriaki
Published: July 2002

Among metal additives M(M:Pt, Pd, Rh, Ir, and Cu) of antiferromagnetic CrMnMx films, Pd was the most suitable M for obtaining large exchange coupling. For the 50 nm CrMnPd5/40 nm Ni81Fe19 films, the exchange coupling field of ∼28 Oe and the blocking temperature of ∼380 °C could be obtained. The CrMn(Pt, Pd, or Rh)x films having the optimum content of ∼8, ∼5, or ∼11 at.% exhibited the same high blocking temperature. The high blocking temperature of the CrMnPt8, CrMnPd5, and CrMnRh11 films was attributed to the nearest neighbor Mn–Mn within the respective films being at the same distance as that at which the Mn–Mn exchange integral showed the maximum negative value.
Thermal relaxation effects observed in the giant magnetoresistance of NiFe/Ag degraded multilayers (abstract)
Authors: Wiggins J. , Gago-Sandoval P. A. , Watson M. L.
Published: July 2002

NiFe/Ag degraded multilayers have potential for use in sensors and data storage. The magnetoresistance (MR) observed in these materials, after thay have been optimized by postdeposition annealing, has been found to have a good field sensitivity. It is believed that the size and saturation field of the giant magnetoresistance (GMR) is a function of the size of magnetostatic interactions that occur between the magnetic layers in the system. In order to improve the field sensitivity of the GMR in these materials, the volume of the NiFe aligned antiparallel by magnetostatic coupling will have to be maximized. We have investigated time-dependent thermal relaxation effects in the GMR of these systems in an attempt to determine both the nature of the coupling and the distribution of blocking sizes. The multilayers were deposited onto glass substrates at the system ambient temperature, by dc sputtering in a sputtering pressure of 7.5 mTorr of Ar. Fifteen bilayer repeat multilayers were prepared by rotating the substrate over the NiFe and Ag targets, alternately. Both NiFe and Ta underlayers have been investigated. The postdeposition annealing strategy used was 315 °C for 10 min in a vacuum of better than 10−5 Torr. We have investigated the time dependence of the GMR using a linear four point probe and measurements have been made over a temperature range 10–450 K. The blocking temperature, and the particle/platelet size distribution, of the entities that cause the GMR can be determined from these measurements. In addition, we have found a number of interesting temperature-dependent MR effects, and it is seen that the blocking temperature is below 350 K in all cases (Fig. 1).
Thermoremanent relaxation in FeNiMn: An elementary decay model analysis
Authors: Li D. , Roshko R. M.
Published: July 2002

The relaxation of the thermoremanent magnetization of the reentrant ferromagnet (Fe0.65Ni0.35)0.882Mn0.118 has been measured as a function of temperature T and system age tw within the glass phase T<Tg≅65 K. The relaxation isotherms were fitted to functional forms predicted by the elementary decay model, which assumes that relaxation in disordered systems is a superposition of independently decaying thermal activations, with an age-dependent stochastic Poissonian distribution of energies. The behavior of the distributions is interpreted in the context of a picture of activated hopping among a set of metastable traps in configuration space.
Magnetic microscopy with small scale Hall probes (invited) (abstract)
Authors: Kent Andrew D. , Charalambous Melissa
Published: July 2002

The use of small scale Hall probes in the study of nanometer scale magnetic structures and high temperature superconductors is discussed. Micron sized Hall probes are a powerful means of studying local magnetic properties and are complementary to other local magnetometry methods such as those based on magnetic force microscopy and superconducting quantum interference device techniques. In addition to presenting an overview of our recent studies on nanofabricated magnetic samples1 and ring shaped superconductors,2 we discuss the factors that determine the spatial and field resolution of this technique. Among the important issues considered are the Hall response to inhomogeneous magnetic fields and the noise characteristics of sensor materials. A variety of materials have been studied including two-dimensional GaAs/GaAlAs heterostructures, three-dimensional InGaAs, and Bi semimetal thin films. Finally, our progress toward the realization of a variable temperatures scanning Hall probe microscope will be reported.
Magnetic field induced changes in the critical exponent β of the chiral triangular antiferromagnet CsMnBr3 in the presence of an electric field (abstract)
Authors: Visser D. , Monteith A. R. , Bargawi A. Y. , Zeiske Th.
Published: July 2002

The magnetic moments in the triangular antiferromagnetic CsMnBr3 order at TN=8.3 K with a frustration of the magnetic moments in a 120° type magnetic structure. The magnetic moments are either ordered in a clockwise or an anticlockwise direction resulting in a chirality ordering, which is characterized by the critical exponent of the magnetic sublattice magnetization β=0.25. It has been shown that an electric field applied along the [110] direction removes the chiral ordering and a linear Ising-like phase will be established; consequently, the value of β decreases. The subsequent application of a magnetic field of B=4 T along the [100] direction causes the critical exponent β to increase. The magnetic phase diagram of CsMnBr3 does not change due to the introduction of an electric field.
Antiferromagnetic phase breakdown of a randomly decorated Heisenberg model: Application to La2−xBaxCuO3 (abstract)
Authors: de Sousa J. Ricardo , Fittipaldi I. P.
Published: July 2002

The quenched decorated Ising model with competitive interactions recently introduced by Fittipaldi et al.1 is herein extended to the Heisenberg case. The model consists of planes in which the nodal spins interact antiferromagnetically (J<0) with their nearest neighbors, and ferromagnetically (K>0) with the spins that decorate the bonds, which are quenched randomly distributed over the lattice. The planes, which simulate the CuO2 layers in doped cuprates superconducting materials, interact antiferromagnetically (J′=λJ). By using the framework of an effective-field theory with correlations, we discuss the 3D antiferromagnetic-phase stability limit in the temperature-decorated bond concentration space (T−p), for various values of both interplane and intraplane exchange parameters λ and α=|J|/K, respectively. In particular, our numerical estimates of the vanishing temperature critical concentrations pc [i.e., pc at which TN(pc)=0] well compare with the experimental data of Kitaoka et al.2 for the La2−xBaxCuO4 in the nonsuperconducting phase.
Magnetic anomalies in EuO/nonmagnetic insulator multilayered films
Authors: Sohma M. , Kawaguchi K. , Oosawa Y.
Published: July 2002

Ferromagnetic EuO multilayered films (MLs) were fabricated with nonmagnetic oxides such as MgO, ZrO2, and Y2O3. The EuO MLs showed increased Curie temperature (Tc) and metal insulator transition temperature (Tmi) than the bulk values due to oxygen deficiency. However, Eu151 Mössbauer spectra did not exhibit such an anomaly in Tc. It suggests a field induced magnetic component in the MLs. Significant increase of coercive force (Hc) with decreasing EuO layer thickness was observed only in EuO/MgO MLs. It was suggested that this increase was originated from a kind of interface effect.
Measurement of fly height by scattered total internal reflection
Authors: Lo Jenny L. , Sides Paul J.
Published: July 2002

Scattered total internal reflection (SCATIR) is an optical phenomenon that allows measurement of the fly height of sliders. Good agreement between the measurements made with scattered total internal reflection (SCATIR) and the nominal fly heights (100, 65, and 25 nm) of three commercial sliders was obtained. Fluctuations in the flying height of a tri-pad slider as a function of load were observed. Applying a correction for the Gaussian profile of the incident laser revealed the crown of a 70% slider.