bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-frequency photocurrent noise in semiconductors: Effect of nonlinear current–voltage characteristics
Authors: Carbone Anna , Mazzetti Piero , Rossi Fausto
Published: July 2002

A current noise model for planar metal–semiconductor–metal photodetectors is proposed, which allows one to account for the low-frequency excess-noise behavior measured in several semiconductor devices. According to the proposed model—based on a multiplicative noise mechanism—the photocurrent noise power can be directly related to the carrier density and to the photogeneration level. Moreover, in the absence of potential-barrier fluctuations, the standard 1/n behavior of the simple g–r noise model is recovered.
Cracking of GaN on sapphire from etch-process-induced nonuniformity in residual thermal stress
Authors: Lacroix Yves , Chung Sung-Hoon , Sakai Shiro
Published: July 2002

An experiment was performed to explain the appearance of cracks along mesa structures during the processing of GaN device layers grown on sapphire substrates. Micro-Raman spectroscopy was used to measure the position-dependent stress in the GaN layer. We show evidence that the stress at the interface with the substrate may be larger along the mesa structures than that of the as-grown layer, and that this increase in stress can be enough to induce cracks along mesa structures during processing. We report on the formation of cracks that propagate guided by the nonuniformity of the stress induced by the formation of mesa structures in the GaN layer, independent of crystal direction. The understanding of cracking mechanisms has implications in GaN-based device structures that require heteroepitaxial growth of layers with different lattice size and thermal expansion coefficients.
Electronic properties of α-Sn(100)2×1: Evidence for asymmetric dimer reconstruction
Authors: Cricenti A. , Perfetti P. , Barret N. , Guillot C. , Aristov V. Yu. , Le Lay G.
Published: July 2002

A well-ordered thick layer of α-Sn(100) has been grown on InSb(100). The low energy electron diffraction pattern showed a sharp 2×1 double domain reconstruction with very low background at room temperature. The electronic properties have been studied by core-level- and angle-resolved photoemission spectroscopy (ARPES). ARPES spectra showed the presence of a surface state at normal emission, 1.15 eV below the Fermi level. This state disperses downward 1.3 eV along the [010] direction. Core-level spectra are well fitted with three surface-shifted components at binding energies +0.22, −0.23, and −0.49 eV with respect to the bulk component. Such results are in agreement with theoretical calculations based on asymmetric dimers by [Z.-Y. Lu, G. Chiarotti, S. Scandolo, and E. Tosatti, Phys. Rev. B 58, 13698 (1998)], taking into account final state effects, and exclude the existence of symmetric dimers.
Voltage–current characteristics of high-current glow discharges
Authors: Takaki K. , Taguchi D. , Fujiwara T.
Published: July 2002

The voltage–current characteristics of glow discharges in gas mixture (N2:O2=8:2) at a pressure of 10 Torr were obtained with the discharge current up to 150 A. Parallel-plane electrodes with a diameter of 10.7 cm and a discharge chamber with co-axial geometry were used to produce glow discharge with high current. The glow discharge voltage was almost constant until the whole surface of the cathode was covered with glow, i.e., until the discharge current became 3.7 A in our experimental condition (a normal glow discharge mode). The voltage, however, increased with the current when the glow covered over the cathode (an abnormal glow discharge mode). The electron density in positive column of the high-current glow discharge was obtained to be 3×1011 cm−3 from Langmuir probe measurements.
Simple model to study soliton wave propagation in periodic-loaded nonlinear transmission lines
Authors: Martín F. , Oriols X.
Published: July 2002

A model to study soliton propagation characteristics in nonlinear transmission lines (NLTLs) periodically loaded with voltage dependent capacitances is presented. This is based on the LC ladder equivalent network of the NLTL, and can be applied to structures where the Korteweg–de Vries approach does not hold. Specifically, the model allows to numerically obtain soliton waveforms under arbitrary capacitance non linearity. To demonstrate its validity, it has been applied to structures loaded with symmetric capacitances, similar to those exhibited by actual heterostructure barrier varactors. The model can be of help to understand harmonic generation in monolithic NLTL-based frequency multipliers.
Electrical properties of low-arsenic-doped HgCdTe grown by molecular beam epitaxy
Authors: Aqariden F. , Shih H. D. , Kinch M. A. , Schaake H. F.
Published: July 2002

A study of the electrical properties of p-type, low-arsenic-doped Hg1−xCdxTe (x∼0.3, carrier concentration ∼1×10+15 cm−3) suitable for fabrication of high-operating-temperature photodetectors was carried out. The arsenic-doped HgCdTe samples were prepared by molecular beam epitaxy using an elemental arsenic source and were characterized by Hall measurements at 77 K after the samples were subjected to four different arsenic activation annealing schemes with annealing temperatures ranging from 300 to 450 °C. For comparison purpose, a sample doped to low-10+16 cm−3 was also prepared and subjected to the same annealing schemes. Although the four annealing schemes had little influence on the Hall data of the 10+16 cm−3 sample, they had significant impact on the Hall data of the 10+15 cm−3 sample. Furthermore, it was found that the Hall data could not be explained by any scattering mechanisms but could be satisfactorily modeled by a two-layer model in which an n-type skin layer is included.
Gain spectra of (GaIn)(NAs) laser diodes for the 1.3-μm-wavelength regime
Authors: Hofmann M. , Wagner A. , Ellmers C. , Schlichenmeier C. , Schäfer S. , Höhnsdorf F. , Koch J. , Stolz W. , Koch S. W. , Rühle W. W. , Hader J. , Moloney J. V. , O’Reilly E. P. , Borchert B. , Egorov A. Yu. , Riechert H.
Published: July 2002

Optical gain spectra of (GaIn)(NAs)/GaAs quantum-well lasers operating in the 1.3-μm-emission-wavelength regime are measured and compared to those of a commercial (GaIn)(AsP)/InP structure. Good agreement of the experimental results with computed spectra of a microscopic many-body theory is obtained. Due to the contributions of a second confined subband, a spectrally broad gain region is expected for (GaIn)(NAs)/GaAs at elevated carrier densities.
Enhanced band-gap blueshift due to group V intermixing in InGaAsP multiple quantum well laser structures induced by low temperature grown InP
Authors: Lee A. S. W. , MacKenzie M. , Thompson D. A. , Bursik J. , Robinson B. J. , Weatherly G. C.
Published: July 2002

Photoluminescence and cross-sectional transmission electron microscopy, combined with x-ray compositional analysis, have been used to study quantum well intermixing in an InGaAsP quantum well laser structure. Quantum well intermixing is induced by capping the samples with a layer of InP grown at low temperature (300 °C) and subjecting them to rapid thermal anneal treatments in the temperature range 600–800 °C. The presence of the low temperature InP layer, which contains an abundance of nonequilibrium point defects, significantly enhances the intermixing on annealing, producing a large band-gap blueshift. The microscopy results show good broadening with smeared interfaces, and the compositional analysis suggests this can be attributed to the intermixing of group V atoms.
Dewetting of resist/metal bilayers in resist stripping processes
Authors: Wu Yihong , Qiao Peiwen , Chong Towchong , Low Teck-Seng , Xie Hong , Luo Ping , Guo Zaibing , Qiu Jinjun
Published: July 2002

We report the observations of dewetting of resist/metal bilayers in a resist stripping process of nanofabrication in O2 plasma. The initiation of the dewetting process is tentatively associated with local heating caused by surface plasmon induced in metallic nanoparticles or nanowires. The surface patterns thus formed differ substantially from all the dewetting patterns reported so far, and they resemble trees at micrometer scale. The possible mechanism for the formation of this kind striking patterns is discussed and its implication to future nanoelectronics manufacturing is addressed.
Ultrasonic monitoring of laser damage in fused silica
Authors: Martin Louis P. , Norton Mary A. , Thomas Graham
Published: July 2002

The growth of a laser induced, surface damage site in a fused silica window was monitored by the ultrasonic pulse-echo technique. The laser damage was grown using 15 ns pulses of 1.053 μm wavelength light at a fluence of ∼25 J/cm2. The ultrasonic signal amplitude exhibited variations with the damage size which are attributable to the changing subsurface morphology of the damage site. The sensitivity to subsurface morphology makes the ultrasonic methodology a promising tool for monitoring laser damage in fused silica optics. This type of diagnostic capability may facilitate the safe deployment of large, high powered laser systems used in high energy and fusion research facilities.
Electrical transients in the ion-beam-induced nitridation of silicon
Authors: Petravic Mladen , Deenapanray Prakash N. K.
Published: July 2002

We have studied the dynamics of the initial stages of silicon nitride formation on silicon surfaces under nitrogen beam bombardment in the secondary ion mass spectrometry apparatus. We have shown that the secondary ion signal exhibits damped oscillations below the critical impact angle for nitride formation. We have described this oscillatory response by a second-order differential equation and argued that it is initiated by some fluctuations in film thickness followed by the fluctuations in surface charging.
Giant charge inversion of a macroion due to multivalent counterions and monovalent coions: Molecular dynamics study
Authors: Tanaka Motohiko , Grosberg A. Yu
Published: July 2002

We report molecular dynamics simulation of the (overall neutral) system consisting of an immobile macroion surrounded by the electrolyte of multivalent counterions and monovalent coions. In a short time (< a few nanoseconds), counterions adsorb on the macroion surface in the amount much exceeding neutralization requirement, thus effectively inverting the sign of the macroion charge. We find two conditions necessary for charge inversion, namely, counterions must be multivalently charged and Coulomb interactions must be strong enough compared to thermal energy. On the other hand, coion condensation on the multivalent counterions similar to Bjerrum pairing is the major factor restricting the amount of charge inversion. Depending on parameters, we observe inverted charge up to about 200% the original charge of the macroion in absolute value. The inverted charge scales as ∼ζ1/2 when ζ<1 and crosses over to ∼ζ for ζ>1, where ζ=(A0/rs)2, rs is the Debye screening length in the electrolyte and A0 is the distance between adsorbed counterions under neutralizing conditions. These findings are consistent with the theory of “giant charge inversion” [Phys. Rev. Lett. 85, 1568 (2000)].
Traveling-wave photodetector for 1.55 μm wavelength fabricated with unitraveling-carrier photodiodes
Authors: Hirota Y. , Hirono T. , Ishibashi T. , Ito H.
Published: July 2002

We report on a periodic traveling-wave photodetector (P-TW-PD) fabricated by unicarrier traveling photodiodes (UTC-PDs). It is comprised of three UTC-PDs periodically arranged along a coplanar waveguide transmission line. The photoresponse of the P-TW-UTC-PD is three times that of a single UTC-PD. A 3 dB bandwidth (f3dB) of 115 GHz at 1.55 μm was observed in a P-TW-UTC-PD with a terminal resistor located at the input end. This value of f3dB is almost the same as that observed in a single UTC-PD. In P-TW-UTC-PDs with no terminal resistor, the 3 dB bandwidth degrades to 56 GHz as a result of the reflection of backward-propagating microwaves at the input end. We conclude that our P-TW-UTC-PD provides velocity matching between electrical and optical waves.
Detection of two dangling bond centers with trigonal symmetry at and below a (100) Si/SiO2 interface
Authors: Langhanki B. , Greulich-Weber S. , Spaeth J.-M. , Michel J.
Published: July 2002

Using electrical detection of electron paramagnetic resonance (EDEPR), two defect centers located at the Si (100)/SiO2 interface and in regions several μm below the silicon surface have been observed at a low temperature. Improvements in the EDEPR measurement technique enabled the experimental detection of the g-factor anisotropy of two centers, labeled Pba and Pbb. Both appear with a [111]-oriented, trigonally symmetric g-tensor with g∥=2.0008/g⊥=2.0098 and g∥=1.9974/g⊥=2.0160, respectively (Δg=±0.0004). The data of the Pba center are very similar to those of the well known Pb0 center occurring on (100) oriented silicon. The location of the center which is significantly below the (100)Si/SiO2 interface is discussed.
Viscous nonlinear theory of Richtmyer–Meshkov instability
Authors: Carlès Pierre , Popinet Stéphane
Published: July 2002

We propose a quantitative prediction of the effect of viscosity on the weakly nonlinear impulsive Richtmyer–Meshkov instability between two fluids of arbitrary density and viscosity. This theory is based on an asymptotic analysis of the Navier–Stokes equations using singular perturbation techniques. The law obtained for interface deformation does not agree with former theoretical predictions of the effect of viscosity [K. O. Mikaelian, Phys. Rev. E 47, 375 (1993)], but compares very well with direct numerical simulations we performed using a front-tracking code developed in our laboratory. Application of this law to typical experimental parameters gives a formal demonstration of the relevance of inviscid models for the description of typical shock-tube experiments; at the same time, however, it shows that care should be taken with regard to viscosity in the case of impulsive experiments performed with liquids.
Quasielastic neutron scattering from trehalose aqueous solutions
Authors: Faraone A. , Magazà S. , Lechner R. E. , Longeville S. , Maisano G. , Majolino D. , Migliardo P. , Wanderlingh U.
Published: July 2002

The work reports quasielastic neutron scattering (QENS) results on aqueous solutions of trehalose, a biologically and biomedically important disaccharide. We collected data at the Berlin Neutron Scattering Center (BENSC) on α,α-trehalose deuterated (C12H14O11D8) samples in D2O and on α,α-trehalose hydrogenated (C12H22O11) samples in H2O at different water content. The employment of selectively deuterated samples allows the separation of the diffusive dynamics of water from that of trehalose. The aim of the work is to furnish new results on the molecular dynamics of trehalose and to investigate the effect of this disaccharide on the neighboring water. This study is part of a comprehensive research effort to understand the molecular processes underlying the bio-protectant effectiveness of the disaccharide using plenty of physical techniques [light scattering, nuclear magnetic resonance (NMR), neutron scattering, thermodynamic measurements]. The data analysis furnishes a microscopic whole-molecule diffusion coefficient in good agreement with NMR results. Furthermore it results that the dynamics of the neighboring water is strongly affected by the presence of trehalose.
Optical properties of gold and silver nanoclusters investigated by liquid chromatography
Authors: Wilcoxon J. P. , Martin J. E. , Provencio P.
Published: July 2002

We report high-pressure liquid chromatography (HPLC) and transmission electron microscopy studies of the size-dependent absorbance properties of Au and Ag nanoclusters dispersed in organic solvents. These nanosize metal clusters are synthesized by an inverse micelle synthetic technique at room temperature in inert oils and those investigated range in diameter from 1.3–8 nm. HPLC allows us to separate the clusters from all other chemicals and size select to a resolution of ±2 Å. We use an on-line photodiode array to study the size-dependent absorbance properties of these clusters. For both Au and Ag clusters in the size range d=8 to d=1.5 nm, the plasmon linewidth broadens following a 1/R linewidth size dependence whose slope is greatest for Au. The peak asymmetry in the plasmon band shape is greatest for Au and increases with decreasing size for both Au and Ag clusters. The plasmon peak energy blue shifts with decreasing size for Au clusters while in the case of Ag nanoclusters a red shift is observed.
Direct atomic scale characterization of interfaces and doping layers in field-effect transistors
Authors: Topuria T. , James E. M. , Browning N. D. , Ma Z.
Published: July 2002

Atomic-resolution Z-contrast imaging and electron energy loss spectroscopy combined with energy dispersive x-ray spectroscopy are used to investigate the structure-property relationships in an ideal metal–oxide–semiconductor device structure. Arsenic segregation with a very narrow profile occurring precisely at the silicide/Si interface was identified. Images show that the As is substitutional on the Si lattice sites, implying that it remains electrically active. These structural results imply desirable electronic properties for the device and are consistent with electrical measurements showing a decrease in contact resistance for these samples.
Spatial charge effects in retarding field analyzer ion measurements in a cathodic vacuum arc
Authors: Grondona D. , Kelly H. , Márquez A.
Published: July 2002

The ion energy distribution generated in a pulsed vacuum arc operated with a Ti cathode and N2 filling gas is reported. A retarding field analyzer system is employed, for which the usual derivation of the ion energy spectrum has been modified to take into account spatial charge effects in the grid-collector region of the analyzer. It allows one to interpret the decrease in the collector current at collector bias voltages unusually low (even negatives) observed in this experiment, as well as in others. It is found that spatial charge effects are more marked when the arc operates with gas filling because of the creation (by charge-exchange processes) of low energy gaseous ions which are easily stopped by the potential hump created by the positive charge in the grid-collector region of the analyzer.
Thermal evidence of stress-induced structural disorder of a Zr55Al10Ni5Cu30 glassy alloy in the non-Newtonian region
Authors: Chen H. S. , Kato H. , Inoue A. , Saida J. , Nishiyama N.
Published: July 2002

The evolution of specific heat near the glass transition temperature, Tg, of a Zr55Al10Ni5Cu30 glassy alloy subjected to different degrees of non-Newtonian flow conditions was investigated. At conditions in which non-Newtonian flow begins, a gradual exothermic relaxation near Tg was observed. This is attributed to the change in configuration of the long-range liquid structure of the alloy. At conditions in which a high degree of non-Newtonian flow is favored, the alloy exhibits both high-temperature and low-temperature relaxation due to a change in local short-range order. The enthalpy of relaxation is found to scale as the logarithm of the normalized viscosity and is interpreted in terms of the free volume model of viscous flow. The decrease in viscosity in the non-Newtonian flow region is associated with a highly disordered structure and induced free volume.
Evidence of isoelectronic traps in molecular beam epitaxy grown Zn1−xBexSe: Temperature- and pressure-dependent photoluminescence studies
Authors: Kim Bosang S. , Kuskovsky Igor L. , Tian C. , Herman Irving P. , Neumark G. F. , Guo S. P. , Tamargo M. C.
Published: July 2002

We have studied undoped Zn1−xBexSe alloys grown by molecular beam epitaxy by photoluminescence (PL) as a function of temperature and pressure. We suggest that there are isoelectronic excitonic traps in this material. The binding energy of the isoelectronic bound excitons is deep, between 40 and 50 meV. We have also shown that the temperature and pressure dependences of the Zn1−xBexSe PL are close to those of ZnSe. From this we conclude that the dominant excitonic recombination is of an “effective mass” type.
Control of charging in resonant tunneling through InAs nanocrystal quantum dots
Authors: Katz David , Millo Oded , Kan Shi-Hai , Banin Uri
Published: July 2002

Tunneling spectroscopy of InAs nanocrystals deposited on graphite was measured using scanning tunneling microscopy, in a double-barrier tunnel-junction configuration. The effect of the junction symmetry on the tunneling spectra is studied experimentally and modeled theoretically. When the tip is retracted, we observe resonant tunneling through the nanocrystal states without charging. Charging is regained upon reducing the tip–nanocrystal distance, making the junction more symmetric. The effect of voltage distribution between the junctions on the measured spectra is also discussed.
Solving the structural model for the Si(001)–In(4×3) surface
Authors: Schmidt T. M. , Castineira J. L. P. , Miwa R. H.
Published: July 2002

The atomic geometry, energetic, and scanning tunneling microscopy (STM) simulations of the In-induced Si(001)-(4×3) surface have been investigated using first-principles total energy calculations. We have studied three distinct (4×3) structural models, which have been proposed based on STM and x-ray diffraction experiments. The energetic stability calculations indicate that the (4×3) model formed by In–Si–In mixed trimer is the most stable structure. In addition, we have simulated the STM images (for occupied states) of these three models. Our STM image for the In–Si–In mixed trimer structure presents a good agreement with the experimentally observed single central protrusion localized on the top-layer Si atom. Also, the calculated equilibrium atomic geometry of the In–Si–In mixed trimer model presents a good agreement with the experimentally obtained x-ray diffraction results. The other two proposed models are energetically less favorable by as much as 0.2 eV/(1×1) compared to the mixed trimer model.
Photoelectron spectroscopy study of the electronic structures of Al/MgF2/tris-(8-hydroxyquinoline) aluminum interfaces
Authors: Park Y. , Lee J. , Lee S. K. , Kim D. Y.
Published: July 2002

We have studied the electronic structures of Al/MgF2/tris-(8-hydroxyquinoline)aluminum (Alq3) interface using UV and x-ray photoelectron spectroscopy [(UPS) and (XPS), respectively]. The UPS revealed that the valence peak shift occurred with MgF2 deposition before Al was deposited and was independent of the gap state formation. The XPS core level peaks indicated that the MgF2 strongly interacted with Al and O atoms in Alq3 even before Al was deposited, and the deposition of Al caused a slight change to the N 1s core level peak. These results indicate that the interaction mechanism in Al/MgF2/Alq3 is different from those found in Al/LiF/Alq3 and other metal/Alq3.
Zero-point oscillations in the vicinity of atoms
Authors: Shumovsky Alexander S.
Published: July 2002

It is shown that the vacuum fluctuations of an electromagnetic field are concentrated near atoms. This effect worsens the quantum limit of precision of the measurements in atomic systems.
Coherent nonlinear propagation of ultrafast electric field transients through intersubband resonances
Authors: Eickemeyer F. , Woerner M. , Weiner A. M. , Elsaesser T. , Hey R. , Ploog K. H.
Published: July 2002

Amplitude and phase-controlled midinfrared field transients at a wavelength of 12.5 μm induce resonant intersubband excitations in n-type modulation-doped GaAs/AlGaAs quantum wells. The transmitted electric field transients are directly measured by ultrafast electro-optic sampling. Coherent control of intersubband excitations is demonstrated by applying two phase-locked pulses with variable relative phase. A coherent nonlinear response corresponding to partial Rabi flops of up to 60° in the Bloch sphere is observed with excitation pulses of only 1 pJ energy.
Role of holes in the isotope effect and mechanisms for the metal–oxide–semiconductor device degradation
Authors: Chen Zhi , Garg Pradeep , Singh Vijay , Chetlur Sundar
Published: July 2002

An experiment that incorporates the deuterium isotope effect into the “hole trapping and electron filling” scenario in silicon metal–oxide–semiconductor (MOS) devices is presented. It is suggested that Lai’s physical model is only partially true in order to explain all of the observed MOS device degradation phenomena. The isotope effect is exclusively due to hot electrons, not hot holes. Holes might break the Si–O bonds to generate interface traps at VG near VT. The dominant degradation mechanism is the electron-stimulated Si–H bond breaking, although electron trapping also plays a role in degradation.
Quasi-one-dimensional transport characteristics of ridge-type InGaAs quantum-wire field-effect transistors
Authors: Sugaya Takeyoshi , Ogura Mutsuo , Sugiyama Yoshinobu , Shimizu Toshiyuki , Yonei Kenji , Jang Kee Youn , Bird Jonathan P. , Ferry David K.
Published: July 2002

Ridge-type InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. An analysis of the depopulation of one-dimensional subbands in these structures reveals little evidence for sidewall depletion, and yields an estimate for the carrier density in good agreement with that found in two-dimensional InGaAs/InAlAs heterojunctions. Subband splittings as large as 7.4 meV are obtained in the wires, indicating their excellent one-dimensional transport properties.
Atomic-scale observation of polarization switching in epitaxial ferroelectric thin films
Authors: Marasco D. L. , Kazimirov A. , Bedzyk M. J. , Lee T.-L. , Streiffer S. K. , Auciello O. , Bai G.-R.
Published: July 2002

The thin-film x-ray standing wave (XSW) technique is used for an atomic-scale study of polarization switching in ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT)/electrode heterostructures grown on SrTiO3(001). The XSW is selectively generated in the PZT by the interference between the incident x-ray wave and the weak (001) Bragg diffracted wave from the film. The XSW excites a fluorescence signal from the Pb ions in the PZT film, that is used to determine their subangström displacements after polarization switching has occurred. This experimental method yields unique information on the underlying atomic configurations for different polarization domain states.
Proof of a conjecture on the conductivity of checkerboards
Authors: Milton Graeme W.
Published: July 2002

In 1985 Mortola and Steffé conjectured a formula for the effective conductivity tensor of a checkerboard structure where the unit cell of periodicity is square and subdivided into four equal squares each having a different conductivity. In this article their conjecture is proven. The key idea is to superimpose suitably reflected potentials to obtain the solution to the dual problem. This is then related back to the original problem using a well known theorem of Keller, thereby proving the conjecture. The analysis also yields formulas relating the potentials in the four squares. Independently, Craster and Obnosov have obtained a completely different proof of the conjecture.
Direct observation of icosahedral cluster in Zr70Pd30 binary glassy alloy
Authors: Saida Junji , Matsushita Mitsuhide , Inoue Akihisa
Published: July 2002

The medium-range order in the Zr70Pd30 binary glassy alloy, where the nanoicosahedral phase precipitates as a primary phase, was examined using the high-resolution electron microscopic technique. The ordered region in the diameter of ∼2 nm was observed in the as-quenched glassy state. This region grows slightly to the diameter of 3–4 nm by annealing for 120 s at 690 K, where the amorphous structure remains. The nanobeam electron diffraction pattern taken from the medium-range order shows the fivefold symmetry, indicating that this region has the icosahedral structure. This result is recognized as a direct evidence for the existence of the icosahedral cluster in the alloy. For further annealing for 600 s at 690 K, the icosahedral quasicrystalline phase in the diameter of 5–8 nm precipitates by assimilating the icosahedral cluster. The formation of the nanoicosahedral phase originates from the existence of the quenched-in icosahedral clusters in the glassy state followed by their easy growth to the icosahedral particle without significant rearrangement of the constitutional elements.
Oxidative addition of Pd to C–H, C–C and C–Cl bonds: Importance of relativistic effects in DFT calculations
Authors: Diefenbach Axel , Bickelhaupt F. Matthias
Published: July 2002

To assess the importance of relativistic effects for the quantum chemical description of oxidative addition reactions of palladium to C–H, C–C and C–Cl bonds, we have carried out a systematic study of the corresponding reactions of CH4, C2H6 and CH3Cl with Pd-d10 using nonrelativistic (NR), quasirelativistic (QR), and zeroth-order regularly approximated (ZORA) relativistic density functional theory (DFT) at the BP86/TZ(2)P level. Relativistic effects are important according to both QR and ZORA, the former yielding similar but somewhat more pronounced effects than the latter, more reliable method: activation barriers are reduced by 6–14 kcal/mol and reaction enthalpies become 15–20 kcal/mol more exothermic if one goes from NR to ZORA. This yields, for example, 298 K activation enthalpies ΔH298≠ of −5.0 (C–H), 9.6 (C–C) and −6.0 kcal/mol (C–Cl) relative to the separate reactants at ZORA-BP86/TZ(2)P. In accordance with gas-phase experiments on reactions of Pd with alkanes, we find reaction profiles with pronounced potential wells for reactant complexes (collisionally stabilized and observed in experiments for alkanes larger than CH4) at −11.4 (CH4), −11.6 (C2H6) and −15.6 kcal/mol (CH3Cl) relative to separated reactants [ZORA-BP86/TZ(2)P]. Furthermore, we analyze the height of and the relativistic effects on the activation energies ΔE≠ in terms of the activation strain ΔEstrain≠ of and the transition-state interaction ΔEint≠ between the reactants in the activated complex, with ΔE≠=ΔEstrain≠+ΔEint≠.
Doping and intermixing in CdS/CdTe solar cells fabricated under different conditions
Authors: Jahn U. , Okamoto T. , Yamada A. , Konagai M.
Published: July 2002

Thin film CdS/CdTe solar cell structures have been investigated by spatially resolved cathodoluminescence (CL) spectroscopy. A postgrowth CdCl2 treatment of the CdTe layer was found to homogenize the distribution of acceptor-like defects or impurities leading to optimized p-type conversion of the polycrystalline CdTe. For values of the growth temperature (TG) of about 600 °C, the intermixed region between the CdS layer and CdTe grains is surprisingly thin. However, for TG as large as 630–650 °C, a gradual decrease of the CdTe band gap due to sulfur intermixing appears to be present up to 0.6 μm from the CdS/CdTe interface. The CL spectra of the CdS window layer exhibit two broad bands centered at 1.72 (red) and 2.04 eV (yellow). The yellow one is quenched by the CdCl2 treatment, indicating passivation or promoted outdiffusion of Cd interstitials.
Highly efficient mirrorless laser-like emission in an organic molecular salt
Authors: Bhowmik Achintya K. , Dharmadhikari Aditya , Thakur Mrinal
Published: July 2002

Unusually high conversion efficiency in laser-like emission has been observed in solutions of an organic molecular salt, styrylpyridinium cyanine dye, at a low threshold input pulse energy. Pumped with frequency-doubled 55 ps pulses from a Nd:YAG laser, a conversion efficiency as high as 40% was achieved without incorporating external mirrors. The spectrally narrowed output beam was observed to be polarized and having a low divergence. The exceptionally low threshold (<1 μJ with excitation area ∼5 mm2) and high conversion efficiency at a high molar concentration in spite of a very small photoluminescence quantum efficiency (<0.3%) can be attributed to the large dipole moments associated with the charge-transfer transitions of these molecules favoring strong cooperative emission.
Optical gain in Si/SiO2 lattice: Experimental evidence with nanosecond pulses
Authors: Khriachtchev Leonid , Räsänen Markku , Novikov Sergei , Sinkkonen Juha
Published: July 2002

Experimental evidence of population inversion and amplified spontaneous emission was found for Si nanocrystallites embedded in SiO2 surrounding under pumping with 5 ns light pulses at 380, 400, and 500 nm. As an important property, our experiments show a short lifetime of the population inversion allowing a generation of short (a few nanosecond) amplified light pulses in the Si/SiO2 lattice. The estimate for optical gain in the present samples is 6 cm−1 at 720 nm.
Moment analysis of hydrated electron cluster spectra: Surface or internal states?
Authors: Bartels David M.
Published: July 2002

Moment analysis is applied to the absorption spectra of size-selected water anion clusters measured by Ayotte and Johnson [J. Chem. Phys. 106, 811 (1997)], to extract the radius of gyration and the kinetic energy for the unpaired electron. Implications for the surface versus interior binding model controversy are discussed.
High-quality epitaxial iron nitride films grown by gas-assisted molecular-beam epitaxy
Authors: Borsa D. M. , Grachev S. , Boerma D. O. , Kerssemakers J. W. J.
Published: July 2002

Thin films of γ’-Fe4N were grown on polished (001) MgO substrates by molecular-beam epitaxy of iron in the presence of a gas flow from a rf atomic source. By means of x-ray diffraction, Mössbauer Spectroscopy, Rutherford backscattering/channeling, and scanning probe microscopy, it is shown that, with this method, single-phase, high-quality epitaxial thin films can be grown with a very smooth surface (root-mean-square roughness ∼0.4 nm). Magnetic measurements reveal square hysteresis loops, moderate coercivities (45 Oe for a 33 nm thick film) and complete in-plane orientation of the magnetization. These properties make the films interesting candidates for device applications.
Bulk diffusion of microwave plasma activated deuterium into undoped natural diamond
Authors: Laikhtman A. , Hoffman A. , Cytermann C.
Published: July 2002

In the present work undoped natural (100)-, (111)-, and (110)-oriented diamonds were exposed to microwave deuterium plasma. Secondary ion mass spectroscopy (SIMS) in static mode showed that surface deuterium concentration is the highest for (110) surface and the lowest one for (100)-oriented diamond. SIMS depth profile measurements unambiguously revealed the bulk diffusion of deuterium in the concentration of 1020–1021 atoms/cm3. Relative bulk concentrations of deuterium in the three differently oriented diamonds retained those on the surface. The measured diffusion length of deuterium is ∼0.6 μm. These results support previously performed theoretical calculations and enlighten the data obtained from absolute quantum photoyield measurements of hydrogenated natural diamond recently reported by us.
Microscale technique for in situ measurement of elastic parameters of materials under reactive atmosphere
Authors: Fabre Arnaud , Finot Eric , Demoment Jérôme , Contreras Serge , Goudonnet Jean Pierre
Published: July 2002

This article discusses a technique for measuring elastic bulk parameters of metallic samples of micrometric sizes (3–100 μm thick) under a controlled atmosphere. This method offers the benefit of being relatively easy to implement, relying on off-the-shelf instrumentation, while still providing an excellent sensitivity. Furthermore, this technique allows the analysis of the elastic behavior of thin film that is not possible with another approach. A small cell that holds microcantilever shaped metal has been designed to perform measurements from vacuum to several bars of reactive atmosphere such as hydrogen. Young’s modulus and internal friction of materials were measured by the flexural resonance response of the cantilever. We discuss the reliability of the continuum mechanics on a microscopic scale in order to understand the limit thickness of palladium microcantilever which was experimentally found to be 20 μm. Then, we demonstrate that the measurements of Young’s modulus of different materials (Al, Au, Cu, Fe, Pd) were accurate within 2%. This technique was found to be particularly suitable for investigating the change in elastic properties of thin materials during hydrogenation.
A mechanism for the multiple atomic configurations of inversion domain boundaries in GaN layers grown on Si(111)
Authors: Sanchez A. M. , Nouet G. , Ruterana P. , Pacheco F. J. , Molina S. I. , Garcia R.
Published: July 2002

Atomic structure investigation has been carried out on inversion domain boundaries in GaN layer grown on Si(111) by molecular-beam epitaxy. The comparison of the stacking sequences between simulated and experimental high resolution electron microscopy images shows the existence of two different atomic configurations for the inversion domain boundaries: the Holt model coexists with the V model inside the same layers. A mechanism allowing the switch from one model to the other by the interaction with the I1 stacking fault is proposed.
Giant magnetoimpedance of chemically thinned and polished magnetic amorphous ribbons
Authors: Amalou F. , Gijs M. A. M.
Published: July 2002

We have measured the giant magnetoimpedance (GMI) of microstructured Co-based Metglas® 2714a amorphous magnetic ribbons. Before micropatterning, the amorphous ribbons were chemically thinned or polished, to study the influence of sample thickness and surface state on the GMI effect. The magnetic domain structure of polished foils near saturation is observed using the bitter fluid technique. The well-defined geometry of the samples allows a quantitative comparison of the GMI effect with a simple skin depth model, from which we obtain the frequency-dependent permeability of the material. We have measured the GMI effect for magnetic fields parallel and transverse to the long axis of the sample. We compare the different measurement geometries and film preparation methods and, typically, find a room-temperature GMI ratio of about 35%–90% in fields of a few mT and at frequencies of 10–40 MHz.
Tailoring of self-assembled monolayer for polymer light-emitting diodes
Authors: Choi Beomrak , Rhee Jungsoo , Lee Hong H.
Published: July 2002

The choice of a self-assembled monolayer (SAM) is tailored to specifically remove water on an indium-tin oxide electrode and to reduce barrier height for long-term stability of polymer light-emitting diodes. Water, which is a major cause of long-term degradation, is shown to have entirely reversible effects on the power efficiency of the device. It is shown that the use of a SAM for the specific purposes results in a more than an order of magnitude increase in the half lifetime of the device based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene].
Orientation-controlled epitaxy of A2CuO3 (A: Sr, Ca) films with large optical nonlinearity
Authors: Manako T. , Okimoto Y. , Izumi M. , Shinomori S. , Kawasaki M. , Kishida H. , Okamoto H. , Fukumura T. , Ohtani M. , Tokura Y.
Published: July 2002

The one-dimensional Cu–O chains responsible for the large optical nonlinearity in Sr2CuO3 (SCO) and Ca2CuO3 (CCO) are aligned in one direction in films grown on LaSrAlO4 (LSAO) (1 0 0) substrates by using pulsed laser deposition. The CCO films deposited directly on lattice matched LSAO substrates have a single orientation with high crystallinity, while the SCO films include small portions of misoriented domains. Using a simple model of lattice mismatch, we developed a Sr2TiO4 buffer layer in order to grow orientation-controlled SCO films with both high crystallinity and a sharp optical absorption edge. This technique will be a key to fabricating ultrafast all-optical switches with a waveguide structure.
Matrix isolation study of the interaction of excited neon atoms with allene and propyne: Infrared spectra of H2CCCH2+ and H2CCCH−
Authors: Forney Daniel , Jacox Marilyn E. , Lugez Catherine L. , Thompson Warren E.
Published: July 2002

When a Ne:allene or a Ne:propyne sample was codeposited at approximately 5 K with a sample of pure neon that had been excited in a microwave discharge to provide a 16.6–16.85 eV energy source, prominent new infrared absorptions which can be assigned to the H2CCCH2+ cation appeared. Also present in the allene experiments were two absorptions which can be assigned to H2CCCH−. In the propyne experiments, an absorption is tentatively attributed to the strongest infrared fundamental of CH3CCH+. The structures and vibrational fundamentals obtained from density functional and ab initio calculations for various isotopomers of H2CCCH2+, CH3CCH+, cyc-C3H3+, H2CCCH+, and H2CCCH− are given. The infrared absorption pattern of the cation common to the allene and propyne experiments matches that of the predominant gas-phase product, cyc-C3H3+, reasonably well, except for the presence of extra peaks in the CH-stretching region. However, comparison of the results of experiments on isotopically substituted samples with the calculated spectra excludes that assignment and supports the identification of the neon-matrix product as H2CCCH2+. It is suggested that collisions with the excess of neon atoms in the sampling region rapidly remove excess energy from the initially formed allene and propyne cations, inhibiting the loss of an H atom from those two species.
Energetics and effects of planar defects in CdTe
Authors: Yan Yanfa , Al-Jassim M. M. , Demuth Thomas
Published: July 2002

The formation energies of planar defects such as lamellar twins and intrinsic and extrinsic stacking faults in CdTe are calculated using first-principles total-energy calculations. We find that the formation energies, 16 erg/cm2 for lamellar twins and 34 and 31 erg/cm2 for intrinsic and extrinsic stacking faults, are very small. This explains why high densities of planar defects are always present in the fast-grown CdTe thin films. The effects of the planar defects on the formations of important point defects in p-type CdTe are also investigated. We find that the planar defects have negligible effects on Cd vacancies and substitutional Cu, whereas they lower the formation energy of Te antisites by about 0.1 eV compared to the perfect regions.
Anisotropic resistivity correlated with atomic ordering in p-type GaAsSb
Authors: Fink V. , Chevalier E. , Pitts O. J. , Dvorak M. W. , Kavanagh K. L. , Bolognesi C. R. , Watkins S. P. , Hummel S. , Moll N.
Published: July 2002

We have detected three- and six-fold lateral ordering in undoped and carbon-doped GaAs1−xSbx films (0.4<x<0.6), using plan-view and cross-sectional transmission electron microscopy. The samples were grown by organometallic vapor phase epitaxy onto oriented InP (001) substrates, at temperatures ranging from 500 to 600 °C. Spontaneous lateral superlattices with modulation parallel to the [110] in-plane direction occur with two periodicities, 6 or 3 times the random alloy 〈110〉 lattice parameter. The degree of ordering or domain size increases with growth temperature, as seen by increasing definition of the superlattice fringes in the images, and by a change from streaks to superlattice spots in the selected area diffraction patterns. While the formation mechanism is likely a surface mediated process, no differences were detected for samples in compression or tension, or between those undoped or carbon doped. The ordering correlates with large anisotropies of up to 150% in [110]/[11_0] sheet resistance ratios.
Estimation of the dielectric properties of low-k materials using optical spectroscopy
Authors: Postava K. , Yamaguchi T. , Horie M.
Published: July 2002

The dielectric function spectra of low dielectric constant (low-k) materials have been determined using spectroscopic ellipsometry, near-normal incidence spectroscopic reflectometry, and Fourier transform infrared transmission spectrometry over a wide spectral range from 0.03 to 5.4 eV (230 nm to 40.5 μm wavelength region). The electronic and ionic contributions to the overall static dielectric constant were determined for representative materials used in the semiconductor industry for interlayer dielectrics: (1) FLARE—organic spin-on polymer, (2) HOSP—spin-on hybrid organic-siloxane polymer from the Honeywell Electronic Materials Company, and (3) SiLK—organic dielectric resin from the Dow Chemical Company. The main contributions to the static dielectric constant of the low-k materials studied were found to be the electronic and ionic absorptions.
Reactive recording with rare-earth transition metal
Authors: Kim Jooho , Kuwahara Masashi , Atoda Nobufumi , Tominaga Junji
Published: July 2002

Reactive recording was achieved with typical rare-earth transition metal (RE-TM) for magneto-optical recording. Almost the same carrier-to-noise ratio (CNR) and much higher modulation were obtained by the reactive recording, compared with conventional phase change (PC) recording. By applying this recording material to a super-resolution near-field structure for terabyte recording, CNR below 100-nm-mark length signal, readout durability, and power margin were greatly improved. To identify the recording mechanism, we examined the magnetic and thermo-optical properties, finding that the film properties of amorphous RE-TM are steeply changed at ∼773 K by crystallization and thermal-activated reaction with dielectric layers.
Propagation properties of light in AlGaN/GaN quantum-well waveguides
Authors: Oder T. N. , Lin J. Y. , Jiang H. X.
Published: July 2002

The dynamic properties of light propagation in AlGaN/GaN-based multiple-quantum-well waveguides have been investigated by time-resolved photoluminescence (PL) spectroscopy. The waveguides were patterned with a fixed width of 0.5 μm and length 500 μm using electron-beam lithography and inductively coupled plasma dry etching. Our results reveal a remarkable decrease in the PL intensity as well as an increase in time delay of the temporal response as the location of the laser excitation spot on the waveguide is varied. These results can be understood in terms of polariton propagation in the waveguides. From the time delay of the temporal response, it has been determined that the speed of generated polaritons, with energy corresponding to the well transitions in the waveguides, is approximately (1.26±0.16)×107 m/s. The implications of these results to waveguiding in optical devices based on the group III-nitride semiconductors are discussed.
Ab initio numerical simulation of left-handed metamaterials: Comparison of calculations and experiments
Authors: Weiland T. , Schuhmann R. , Greegor R. B. , Parazzoli C. G. , Vetter A. M. , Smith D. R. , Vier D. C. , Schultz S.
Published: July 2002

Using numerical simulation techniques, the transmission and reflection coefficients, or S parameters, for left-handed metamaterials are calculated. Metamaterials consist of a lattice of conducting, nonmagnetic elements that can be described by an effective magnetic permeability μeff and an effective electrical permittivity εeff, both of which can exhibit values not found in naturally occurring materials. Because the electromagnetic fields in conducting metamaterials can be localized to regions much smaller than the incident wavelength, it can be difficult to perform accurate numerical simulations. The metamaterials simulated here, for example, are based on arrays of split ring resonators (SRRs), which produce enhanced and highly localized electric fields within the gaps of the elements in response to applied time dependent fields. To obtain greater numerical accuracy we utilize the newly developed commercially available code MICROWAVE STUDIO, which is based on the finite integration technique with the perfect boundary approximation. The simulation results are in agreement with published experimental results for the frequencies and bandwidths of the propagation and stop bands associated with the various structures. We further analyze the properties of an individual SRR, and find the dependence of the resonant frequency on the SRR radius, ring thickness, inner/outer radial gap, azimuthal gap, electrical permittivity, and magnetic permeability of the components’ materials. Comparison with previously published analytical estimates shows only approximate agreement with the simulation results.