bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen incorporation in thin oxides by constant current N2O plasma anodization of silicon and N2 plasma nitridation of silicon oxides
Authors: Kaluri Sita R. , Hess Dennis W.
Published: July 2002

A helical resonator plasma source was used to perform constant current N2O plasma anodization of silicon and N2 plasma nitridation of silicon oxides. The nitrogen bonding structure and distribution in the oxides were studied using angle resolved x-ray photoelectron spectroscopy. Nitrogen corresponding to a N–Si3 bonding structure was detected at the silicon side of the interface, the Si–SiO2 interfacial region, and the bulk oxide in a 4.5 nm N2O plasma grown oxide. The distribution profile of nitrogen in the oxide, determined from a normalized N 1s/Si 2p(ox) ratio, showed a continuous decrease from the silicon side of the interface towards the bulk oxide. Also, strong nitrogen peaks corresponding to either a N–Si3 or a N–Si2 bonding structure were detected throughout a 9.1 nm O2 plasma grown oxide after postanodization constant current N2 plasma nitridation.
Magnetic domain expansion readout for amplification of an ultra high density magneto-optical recording signal
Authors: Awano Hiroyuki , Ohnuki Satoru , Shirai Hiroshi , Ohta Norio , Yamaguchi Atushi , Sumi Satoshi , Torazawa Kenji
Published: July 2002

An amplified magneto-optical signal readout by using a dynamic domain expansion effect has been proposed and experimentally confirmed. Small domains of around 0.3 μm in diameter were expanded by a pulsed external field on the readout layer copied from the recording layer. An amplified readout signal up to three times larger than that of the original one has been achieved.
Magnetostatic effects in giant magnetoresistive spin-valve devices
Authors: Cross R. W. , Kim Young K. , Oti J. O. , Russek S. E.
Published: July 2002

We report on magnetotransport measurements of spin valve films that have been fabricated into rectangular stripes with Au current leads. The spin valve films consisted of two magnetic NiFe layers separated by a nonmagnetic Cu layer. The top NiFe layer was magnetically pinned by a FeMn layer with an effective pinning field of 12 kA/m (150 Oe). After device fabrication, the transport properties changed dramatically as the stripe-height of the device was decreased below 1 μm. Internal demagnetizing fields and magnetostatic interactions between the magnetic layers dominated the magnetic response. These interactions change the biasing point and the linearity, and cause a decrease in sensitivity to field changes. We have developed a simple single-domain rotation model that includes magnetostatic, anisotropy, and exchange interactions to describe the magnetic behavior, from which we calculate the transport response.
Self-biasing nonmagnetic giant magnetoresistance sensor
Authors: Solin S. A. , Thio Tineke , Bennett J. W. , Hines D. R. , Kawano M. , Oda N. , Sano M.
Published: July 2002

Room temperature giant magnetoresistance (GMR) has been measured in small band-gap thin-film Hg1−xCdxTe (x∼0.1) samples with Corbino disk electrode configurations. The GMR exhibits a zero-field offset of as much as 350 G at room temperature. The resultant asymmetry in the field dependence of the GMR constitutes a self-biasing effect. We show that this self-biasing results from spatial composition fluctuations in the sample and that the bias effect can be controlled by selective doping and/or deposition masking.
Effect of energetic particles on island formation in sputter deposition of Pt on Pt(111)
Authors: Kalff Matthias , Breeman Marinus , Morgenstern Markus , Michely Thomas , Comsa George
Published: July 2002

During ion beam sputter deposition besides the deposited atoms, which reach the substrate with kinetic energies in the 10 eV range, a certain amount of energetic particles also hit the substrate. These particles which have been reflected or sputtered at the target represent only a small fraction of the atoms reaching the substrate, but have energies of the order of the sputtering beam. The influence of these particles on the island formation of Pt films on a Pt(111) surface has been examined by variation of the deposition geometry, the primary ion energy, and the substrate temperature. It is demonstrated that the main effect is a dramatic increase in island density. The experimental results are in quantitative agreement with the results of a newly developed computer code.
Reflection anisotropy spectroscopy study of the near surface electric field in low-temperature grown GaAs (001)
Authors: Holden Todd , Pollak Fred H. , Freeouf J. L. , McInturff D. , Gray J. L. , Lundstrom M. , Woodall J. M.
Published: July 2002

We have evaluated an “effective depletion width” of ⩽45 Å and the sign (n-type/upward band bending) of the near surface electric field in low-temperature grown GaAs (001) using the optical method of reflection anisotropy spectroscopy in the vicinity of the spin-orbit split E1, E1+Δ1 optical features. Our results provide evidence that surface Fermi level pinning occurs for air exposed (001) surfaces of undoped low temperature grown GaAs.
Ultrafast carrier trapping in oxygen-doped metal-organic vapor phase epitaxy GaAs
Authors: Kang J. U. , Frankel M. Y. , Huang J.-W. , Kuech T. F.
Published: July 2002

We have experimentally investigated the ultrafast carrier dynamics in GaAs grown by metal-organic vapor phase epitaxy with an oxygen precursor. Using a time-resolved reflection ellipsometric technique, we measured the carrier-induced refractive and absorptive index changes as a function of oxygen and aluminum doping concentrations. The free carrier trapping time is inversely proportional to the aluminum-oxygen based complex concentration and can be as short as 300 fs. The material is also highly resistive and promises to be an excellent candidate for optoelectronic applications requiring short carrier lifetime and high dark isolation.
Room-temperature photoluminescence and electroluminescence from Er-doped silicon-rich silicon oxide
Authors: Tsybeskov L. , Duttagupta S. P. , Hirschman K. D. , Fauchet P. M. , Moore K. L. , Hall D. G.
Published: July 2002

Porous silicon was doped by Er ions using electroplating and was converted to silicon-rich silicon oxide (SRSO) by partial thermal oxidation at 900 °C. The room-temperature photoluminescence (PL) at ∼1.5 μm is intense and narrow (⩽15 meV) and decreases by less than 50% from 12 to 300 K. The PL spectrum reveals no luminescence bands related to Si-bandedge recombination, point defects, or dislocations and shows that the Er3+ centers are the most efficient radiative recombination centers. A light-emitting diode (LED) with an active layer made of Er-doped SRSO (SRSO:Er) was manufactured and room temperature electroluminescence at ∼1.5 μm was demonstrated.
Electronic structure at InP organic polymer layer interfaces
Authors: Kinrot N. , Shapira Yoram , Bica de Moraes M. A.
Published: July 2002

Organic polymer layer/p-InP(100) interfaces have been investigated using surface photovoltage spectroscopy (SPS) in conjunction with ultraviolet-visible absorption spectroscopy (AS), infrared transmission spectroscopy (IRTS), time-resolved photoluminescence (PL), and x-ray photoemission spectroscopy (XPS). Prior to deposition, the etched p-InP(100) surfaces exhibited two gap states, attributed to excess surface P and adsorbed O, respectively. Postdeposition measurements show that N-containing layers suppress the former state at the interface, while the latter state is suppressed if S and F are present in the organic polymer film. A mechanism of these interfacial phenomena is suggested.
Investigation of the electric-field distribution at the subwavelength aperture of a near-field scanning optical microscope
Authors: Decca R. S. , Drew H. D. , Empson K. L.
Published: July 2002

The reflectivity of a 9 nm AlAs layer embedded in a GaAs matrix was measured using a near-field scanning optical microscope. Results for freshly cleaved surfaced are understood considering the electrostatic nature of the electric field in the near field of a subwavelength aperture. The optical contrast arises from the different index of refraction of AlAs and GaAs, with topography associated effects playing no role. While keeping the wavelength of the incident radiation and the aperture dimensions fixed, |E| was mapped on planes perpendicular to the tip axis, as a function of the height of the tip above the sample. The results were compared with a finite element calculation for the scattered light. In the analysis, we model the sample with a position dependent dielectric constant. Good agreement between the model and the experimental data was found.
Electric-field-induced commensurate phase in ZrTiO4
Authors: Park Yung , Kim Ho-Gi
Published: July 2002

With the use of x-ray diffraction, the creation of a new commensurate phase with modulation wave-vector qo=26/50a* by the application of a dc electric field along the a axis in ZrTiO4 is demonstrated. The temperature range over which this induced phase exists (12 K at E=8 KV/cm), increases with the increasing dc electric field.
Growth of TiSi2 from codeposited TiSix layers and interfacial layers
Authors: Tung R. T. , Fujii K. , Kikuta K. , Chikaki S. , Kikkawa T.
Published: July 2002

The silicide formation characteristics from composition profiles created on Si by codepositions was investigated. It was shown that a thin interfacial amorphous TiSix layer, with x∼0.5–1, deposited between Si and the Ti film led to a significant reduction in the observed C49→C54 TiSi2 transformation temperature. The presence of the amorphous interfacial TiSix layer slowed down the initial silicidation rate, but promoted the nucleation of the final C54 TiSi2 phase. Predeposition and preannealing were also found to facilitate the growth of C54 TiSi2, as was growth from codeposited full TiSix layers with Ti-rich compositions. The efficacy of the (interfacial) TiSix layer was demonstrated for different temperature ramp rates and for a variety of substrates including undoped α-Si, preamorphized n+-Si, and preamorphized p+-Si. But this effect was found to be absent on single crystal Si. Possible mechanisms of the observed effects were discussed.
Epitaxial regrowth of Ge films on (001) GaAs by in situ thermal pulse annealing of evaporated amorphous germanium
Authors: Lui K. M. , Chik K. P. , Xu J. B.
Published: July 2002

Germanium thin films have been epitaxially regrown on (001) GaAs by in situ thermal pulse annealing of evaporated amorphous germanium under <102 Watt/cm2 broad-band irradiation in high vacuum. Epitaxial regrowth was found to occur only when the duration of the thermal pulse (te) was greater than a critical value tc (≃3.20 s). The crystal quality of the resultant film was examined by high resolution x-ray diffraction technique (HRXRD) and grazing-incidence x-ray diffraction technique (GIXRD). All rocking curves were found to have a full width at half-maximum of about 0.02°. Both HRXRD and GIXRD confirmed the Ge overlayer was grown epitaxially as well as pseudomorphically on the substrate. Scanning electron microscopy and atomic force microscopy revealed the very different surface morphologies resulting from different te. For te<tc, columnar germanium grains with a four-fold symmetry and a high uniformity in size were found, while for te⩾tc, epitaxial regrowth was observed. It is suggested that epitaxial regrowth takes place via a temporary formation of liquid phase Ge.
Electroluminescence of erbium-doped silicon films as grown by ion beam epitaxy
Authors: Matsuoka Morito , Tohno Shun-ichi
Published: July 2002

Sharp and well-split electroluminescence has been achieved from light-emitting diodes (LEDs) fabricated from as-grown erbium–oxygen codoped silicon films, where all elements were in situ incorporated during film growth. The LEDs were fabricated using ion beam epitaxy with an electric mirror sputtering-type metal ion source in an ultrahigh vacuum. Electroluminescence was observed from the LEDs under both forward and reverse biases. Each luminescence line corresponded well to the intra-4f transitions of Er+3 ions with almost single local coordination. The electroluminescence quenching factor with temperature under a forward bias was similar to that for photoluminescence. Sharp luminescence was, however, still observed even at room temperature under a forward bias. Under a reverse bias, strong electroluminescence was observed at room temperature without quenching.
Atomic-scale nature of the (3×3)-ordered GaAs(001):N surface prepared by plasma-assisted molecular-beam epitaxy
Authors: Gwo S. , Tokumoto H. , Miwa S.
Published: July 2002

In situ scanning tunneling microscopy and time-resolved reflection high-energy electron diffraction measurements were performed to study the nitridation process of the As-terminated GaAs(001)-(2×4) surface by using electron cyclotron resonance plasma-assisted molecular-beam epitaxy. We report the real-space atomic structure of the coherently strained (3×3)-ordered GaN monolayer on GaAs(001) after a limited-exposure nitridation process and the atomically smooth morphology of this nitrided surface. The unique (3×3) phase is found consisting of nitrogen dimers and a regular array of missing nitrogen rows in both [1̄10] and [110] directions.
The effect of the boron doping level on the thermal behavior of end-of-range defects in silicon
Authors: Bonafos C. , Claverie A. , Alquier D. , Bergaud C. , Martinez A. , Laânab L. , Mathiot D.
Published: July 2002

The effect of the doping level on the formation and growth of end-of-range (EOR) defects is studied. Transmission electron microscopy observations have been performed on boron doped Si wafers (from 1015 to 1020 atom3) preamorphized with germanium and subjected to rapid thermal annealing. When increasing the doping level up to a few 1018 atom3, a delay in the coarsening process encountered by the loops is observed while above this threshold the EOR defects quickly disappear. These results are interpreted by considering three possibly concomitant phenomena: the formation of boron/Si-interstitial clusters, the gettering of boron at the loop periphery, and a change from the intrinsic to the extrinsic regime for self-diffusion. Moreover, an estimate of the effective trapping efficiency of boron is reached and gives about 1±0.3 Si interstitial per boron atom, a value consistent with the one obtained from studies of B transient enhanced diffusion.
Lorentz transmission electron microscopy on NiFe/Cu/Co/NiFe/MnNi active spin valve elements
Authors: Portier X. , Petford-Long A. K. , Doole R. C. , Anthony T. C. , Brug J. A.
Published: July 2002

In situ magnetoresistance measurements on lithographically defined spin-valve elements were performed by means of Lorentz transmission electron microscopy. The observation of a magnetic domain structure and the simultaneous magnetoresistance measurement by applying controlled field and controlled current have led to a clear correlation between giant magnetoresistance and changes in the magnetic domain structure. A study of the spin-valve behavior with the increase of the applied current value is also shown.
Arrhenius-like behavior in plasma reactions
Authors: Spiliopoulos N. , Mataras D. , Rapakoulias D. E.
Published: July 2002

An Arrhenius-like behavior of the silane dissociation rate constant as a function of the power actually fed in a rf discharge system is reported. The rate constant is calculated using mass-spectrometric measurements of silane consumption for 50 and 75 mTorr discharges, while the power consumed in the discharge is determined by using detailed voltage and current measurements. The slope of the natural logarithm of the dissociation rate constant as a function of the inverse of the discharge power increases with pressure. This is attributed to a change in the shape and/or the mean energy of the electron energy distribution function, while the linearity indicates an analogous increase of the active electron concentration with increasing discharge power, excluding a significant change in the shape of the electron energy distribution function.
Microstructural evolution of {113} rodlike defects and {111} dislocation loops in silicon-implanted silicon
Authors: Pan G. Z. , Tu K. N. , Prussin S.
Published: July 2002

Recent study indicated that transient enhanced diffusion in implanted silicon is attributed to {113} rodlike defects. We have used plan-view and cross-sectional transmission electron microscopy to study the microstructural evolution of {113} rodlike defects as well as their transition to {111} dislocation loops in heat treatment of Si-amorphized silicon. We found that {113} rodlike defects undergo three stages of change during postimplantation anneals; accumulation of point defects to form homogeneous circular interstitial clusters, growth of these clusters along the 〈110〉 direction in a {113} habit plane, and dissolution into the matrix. We observed that the nucleation of {111} dislocation loops at the amorphous/crystalline interface lags behind that of the {113} defects and occurs while the latter grow and/or dissolve. This suggests that there is a period when {113} defects release interstitial point defects before the {111} dislocation loops nucleate from matrix. The {113} defects were found to disappear completely at 900 °C for 120 s, but the {111} dislocation loops disappear at 1100 °C for 60 s.
Retrieval of critical current distribution in small Josephson junctions
Authors: Nesher O. , Ribak E. N.
Published: July 2002

We have developed a method to retrieve or to estimate the spatial critical current distribution in a small Josephson junction from a critical current measurement in a magnetic field (the junction size is in reference to the Josephson length). The method is based on an iterative algorithm that uses fast Fourier transform and physical constraints to achieve the proper solution(s). We simulated some typical critical current distributions and the algorithm converged to a single solution. We applied the algorithm to measurements of the critical current of grain boundary junctions of an oxygen deficient YBa2Cu3O7−δ thin film. The convergence was always to one of a very few solutions very similar in nature.
Simulation of current transients through ultrathin gate oxides during plasma etching
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

Monte Carlo simulations of electron tunneling through a 3 nm gate oxide during etching of dense patterns of gate electrodes in uniform high-density plasmas reveal two current transients, which occur: (a) when the open area clears, and (b) when the polysilicon lines just become disconnected at the bottom of trenches. The first charging transient is fast (controlled by charging) and may be followed by a steady-state current which lasts until the lines get disconnected. The second charging transient lasts longer; the magnitude of the tunneling current generally decreases as the sloped polysilicon sidewalls become straighter. Most of the damage occurs at the edge gate when the open areas are covered by field oxide; however, the edge gate suffers no damage when the 3 nm oxide extends into the open areas.
Control of magnetic flux in a YBa2Cu3O7−δ thin film loop using femtosecond laser pulses
Authors: Tonouchi Masayoshi , Wada Noboru , Hangyo Masanori , Tani Masahiko , Sakai Kiyomi
Published: July 2002

A superconducting optical flux-trap memory with a femtosecond pulsed laser is proposed and then demonstrated. The magnetic flux is trapped in a simple YBa2Cu3O7−δ thin film loop with a polarity controlled by means of optical supercurrent modulation. After removing the external bias current, the trapped fluxes are detected by observing electromagnetic pulse radiation 60 cm away from the sample, which is excited by modulating a persistent current that circulates in the loop. The mechanism for the readin of the magnetic fluxes is discussed in relation to the current distribution in the memory.
Suppression of silicide formation in Ta/Si system by ion-beam-assisted deposition
Authors: Kwak Joon Seop , Baik Hong Koo , Kim Jong-Hoon , Lee Sung-Man
Published: July 2002

In order to increase the failure temperature of a Ta diffusion barrier for Cu, the suppression of silicide formation in a Ta/Si system by ion-beam-assisted deposition of Ta film was investigated. When the Ta layer was deposited without ion bombardment, the reaction between Ta and Si started at 600 °C. In the case where the Ta film was prepared with concurrent ion bombardment, however, the silicide formation was retarded up to 700 °C. The suppression of Ta silicide formation can be attributed to a densification of grain boundaries in the Ta film by ion bombardment, followed by a reduction of the chemical driving force for the initial stage of silicide formation. The Ta diffusion barrier deposited by ion-beam-assisted deposition effectively suppressed the reaction between Si and Cu layers up to 650 °C for 30 min.
Electroluminescence and photoluminescence of Ge+-implanted SiO2 films thermally grown on crystalline silicon
Authors: Zhang Jia-Yu , Wu Xing-Long , Bao Xi-Mao
Published: July 2002

Electroluminescent devices have been fabricated based on Ge+-implanted SiO2 films thermally grown on crystalline silicon. Both room-temperature electroluminescence and photoluminescence spectra are found to have three luminescent bands peaked at 3.1, 2.1, and 1.6 eV. The electroluminescent devices have onsets for emission under forward bias of 5 V and under reverse bias of −13 V. Its emission is stable and reproducible. Spectral analyses suggest that the electroluminescent excitation of the 3.1 eV band may be related to the impact ionization by hot electrons, whereas that of the 2.1 and 1.6 eV bands to the radiative recombination of hole-electron pairs.
Transverse energy spread of photoelectrons emitted from GaAs photocathodes with negative electron affinity
Authors: Pastuszka S. , Kratzmann D. , Schwalm D. , Wolf A. , Terekhov A. S.
Published: July 2002

The mean transverse energy (MTE) of electrons emitted from GaAs photocathodes was measured systematically using a new method based on adiabatic transverse expansion of an electron beam in a spatially decreasing magnetic field. Electrons with energies above the conduction band minimum are found to be thermalized with the lattice temperature of the cathode while electrons having suffered energy losses prior to their emission show enhanced transverse energies. For (Cs,O) and (Cs,F) activation layers on the same cathode the same MTE is found. By cooling the cathode with liquid nitrogen, the MTE of the high-energy electrons was reduced to ≈14 meV.
Scanning tunneling spectroscopy of Ag–As–Se ion-conducting glasses
Authors: Ohto M. , Tanaka K.
Published: July 2002

Electronic structures of Ag–As–Se glasses, which possess ion-hole mixed conduction, have been studied using a scanning tunneling microscope operating in tunneling-spectroscopy modes. The tunneling spectra show marked dependence on the scan speed of tip voltage. This scan-speed dependence appears to be caused by Ag+-ion migration which is induced by electric fields generated by tips.
Synthesis and magnetic properties of PrFe11V1−xTix and their nitrides
Authors: Tang S. L. , Wang B. W. , Zhang C. , Jin X. M. , Zhang S. Y. , Du Y. W.
Published: July 2002

We have succeeded in synthesizing PrFe11V1−xTix (x=0.2–1) compound and their nitrides with the ThMn12-type structure. The phase formation and magnetic properties have been investigated by x-ray diffraction, differential thermometric analysis, and magnetic measurement. The stable temperature range of the 1-12 phase for PrFe11V1−xTix alloys has been determined as a function of Ti content. PrFe11V compounds with the ThMn12-type structure do not exist and PrFe11Ti compounds with the TnMn12-type structure are obtained by annealing in a narrow temperature range between 1303 and 1383 K. Furthermore, 1-12 phase with the ThMn12-type structure can be obtained at lower temperature and wider temperature range with decreasing Ti content x (0.2⩽x⩽1). PrFe11V1−xTixNy with x=0.2–1 has a Tc of about 730–785 K, Ba larger than 8 T and Ms in the range 144–148 emu/g. These intrinsic magnetic properties are highly favorable for permanent magnet applications. As a preliminary, an intrinsic coercivity of 5.4 kOe is obtained for PrFe11V0.5Ti0.5Ny at room temperature by using mechanical alloying technique.
Direct writing of silicon gratings with highly coherent ultraviolet laser
Authors: Chao Chung-Yen , Chen Cheng-Yen , Liu Chee-Wee , Chang Yih , Yang C. C.
Published: July 2002

Silicon gratings with periods from 180 to 550 nm were fabricated with a laser ablation technique in which the interference fringe from an intense and coherent ultraviolet laser at 266 nm directly melted silicon surface. The scanning electron microscopy and atomic force microscopy pictures showed that the corrugations were in quite good quality with the depth as large as 70 nm. The measurement of grating period dependence on temperature showed that rapid thermal annealing could release the thermal strains, which were built during the melting and cooling process in laser ablation, and make the grating period variation more regular. Also, with an air gap between the sample and prism surfaces, the fabricated gratings had weaker thermal strains and more regular temperature dependencies. All the measurement results of temperature dependence were consistent with theoretical predictions.
Twin formation in As precipitates in low-temperature GaAs during high-temperature annealing
Authors: Ruvimov S. , Dicker Ch. , Washburn J. , Liliental-Weber Z.
Published: July 2002

High-resolution electron microscopy was employed to study the atomic structure of As precipitates formed in low-temperature GaAs during high-temperature annealing. Almost all the precipitates after annealing at 850 and 950 °C were found to be twinned with a {1̄104} crystallographic twin plane. Twinning is associated with the crystallization of amorphous or liquidlike As precipitates during cooling. Nucleation of rhombohedral As appears to be most favorable on the short facet that is parallel to the {111}B plane of GaAs. Twin formation usually initiates on the long facet bounded by the {111}A plane. The crystallization usually terminated with a void because of the shrinkage of the As volume during solidification.
Influence of barrier height on scanning tunneling spectroscopy experimental and theoretical aspects
Authors: Stiévenard D. , Grandidier B. , Nys J. P. , de la Broise X. , Delerue C. , Lannoo M.
Published: July 2002

Scanning tunneling spectroscopy allows the determination of the density of states of the involved electrodes as well as the associated barrier height. We have measured the barrier height between tungsten tip and the GaAs (110) surface with a scanning tunneling microscope (STM) in ultrahigh vacuum. When the tunneling junction exhibited a low barrier height, we observed and explained an apparent widening of the GaAs gap which can mislead the real doping concentration of the sample. A theoretical model based on the self-consistent Keldysh–Green functions formalism is used to calculate the STM current. It shows a possible lowering of the barrier height according to the adsorption of As or Ga atoms on the apex of the tungsten tip.
Transient photocurrents across organic–organic interfaces
Authors: Lin Liang-Bih , Young R. H. , Mason M. G. , Jenekhe S. A. , Borsenberger P. M.
Published: July 2002

Hole photocurrent transients in organic–organic bilayers are described. Transitions in the photocurrents for holes moving across the organic–organic interfaces are observed. The magnitude of the photocurrent increases (or decreases) when holes transfer from a lower (or higher) mobility material into a higher (or lower) one. These results demonstrate a novel technique for studying energetic barriers and hole injection dynamics at organic–organic interfaces.
Low temperature fabrication and properties of sol-gel derived (111) oriented Pb(Zr1−xTix)O3 thin films
Authors: Song Yoon J. , Zhu Yongfei , Desu Seshu B.
Published: July 2002

A novel processing method is developed for preparing sol-gel derived Pb(Zr1−xTix)O3 (x=0.47) thin films on Pt/Ti/SiO2/Si substrates. Using a modified precursor solution and a rapid heat treatment without pyrolysis, it was possible to obtain highly (111) oriented PZT thin films with high perovskite content at a low annealing temperature of 550 °C. The low temperature processing was assisted by taking advantage of the heterogeneous nucleation of the PZT films, which reduces the activation energy for perovskite phase formation. Using this method, the PZT thin films exhibited better dielectric and ferroelectric properties at 550 °C than those reported by other methods. For example, the PZT films annealed at 550 °C showed a well-saturated hysteresis loop at an applied voltage of 5 V with Pr and Ec of 12 μC/cm2 and 38 kV/cm, and their dielectric constant and dissipation factor at a frequency of 100 kHz were 410 and 0.021, respectively. The leakage current density was lower than 10−8 at an applied electric field of 150 kV/cm.
Femtosecond laser ablation of gallium arsenide investigated with time-of-flight mass spectroscopy
Authors: Cavalleri A. , Sokolowski-Tinten K. , Bialkowski J. , von der Linde D.
Published: July 2002

We have investigated femtosecond laser-induced ablation of gallium arsenide using time-of-flight mass spectroscopy. At the ablation threshold, we estimated surface temperatures on the order of 3500 K. We observed a clear thresholdlike effect in the number of detected particles and with increasing fluence free flight desorption transforms into a collisional expansion process. Above the ablation threshold, the behavior of gallium particles can be quantitatively described through Knudsen-layer theory.
Signs of nonlinear refraction in chloroaluminum phthalocyanine solution
Authors: Wei Tai-Huei , Huang Tzer-Hsiang , Lin Mu-Shih
Published: July 2002

Opposite signs of nonlinear refraction in chloroaluminum (ClAl) phthalocyanine (Pc) dissolved in methanol are observed using the Z-scan technique with two output modes of a frequency-doubled, Q-switched, mode-locked Nd:YAG laser operating at 10 Hz. Using the single picosecond (ps) pulses switched out of the pulse trains, positive nonlinear refraction is observed and attributed to population transitions among ClAlPc’s singlet states. Using the full nanosecond pulse trains, a sign change of nonlinear refraction relative to that of single ps-pulse excitation is observed, and is attributed to the heat-induced temperature rise and the population relaxing to ClAlPc’s triplet states.
Determination of the cubic to hexagonal fraction in GaN nucleation layers using grazing incidence x-ray scattering
Authors: Munkholm A. , Thompson C. , Foster C. M. , Eastman J. A. , Auciello O. , Stephenson G. B. , Fini P. , DenBaars S. P. , Speck J. S.
Published: July 2002

Recent electron diffraction and microscopy studies of GaN nucleation layers have shown that faults in the stacking of the close-packed planes result in the coexistence of cubic and hexagonal phases within the layers. Using grazing incidence x-ray scattering, we have quantified the proportion of the cubic and hexagonal phases throughout the nucleation layer. We compare the structure of a 20 nm nucleation layer grown on sapphire by atmospheric pressure metal-organic chemical vapor deposition at 525 °C to that of an identical layer heated to 1060 °C. The fractions of cubic and hexagonal phases in the layers are determined by a comparison of the scattering data with a Hendricks–Teller model. High temperature exposure results in a decrease of the cubic fraction from 0.56 to 0.17. The good agreement with the Hendricks–Teller model indicates that the positions of the stacking faults are uncorrelated.
Passivation of InGaAs surfaces and InGaAs/InP heterojunction bipolar transistors by sulfur treatment
Authors: Driad R. , Lu Z. H. , Charbonneau S. , McKinnon W. R. , Laframboise S. , Poole P. J. , McAlister S. P.
Published: July 2002

The surface properties of InGaAs(100) after ex situ treatment with (NH4)2S solution were investigated by photoluminescence (PL) and high-energy resolution x-ray photoelectron spectroscopy. The As 3d, Ga 2p3/2, and In 3d5/2 core level studies show that the surface is free of native oxides and is terminated by S after treatment. A dramatic increase (∼40 times) in the PL efficiency was observed on undoped InGaAs(100) surfaces after sulfur passivation. This S treatment has also been applied to the passivation of the extrinsic base of InGaAs/InP heterojunction bipolar transistors (HBTs). The effectiveness of the sulfur passivation treatment was confirmed by the resulting devices which exhibited dc current gain values of up to 200 at very low collector currents (nA). Further, the sulfur passivated HBTs do not show any dependence on the perimeter-to-area (P/A) ratio of the emitter junction which is of interest for high frequency characteristics while maintaining high current gain.
Swelling in organic–inorganic multilayer systems
Authors: Convertino A. , Valentini A. , De Vittorio M. , Cingolani R.
Published: July 2002

We have investigated the swelling of organic–inorganic structures based on fluorocarbon polymer (CF2) layers sandwiched by two layers of inorganic ionic (HfO2) and inorganic covalent (CdS) materials. The swelling of the CF2 layer produces cracks on the uppermost inorganic layer. The cracks form a network of hexagonal defects with random distribution. The extension of the pattern and the mean unit size have been measured for different solvents by using a purposely developed optical profilometer. We show that the swelling phenomenon strongly depends on the polar forces between the molecules of the solvent and those of the inorganic layers. The electric dipole moment of the solvents and the ionicity of the inorganic materials are thus the crucial parameters influencing the crack density and shape.
Evidence of Si presence in self-assembled Ge islands deposited on a Si(001) substrate
Authors: Magidson V. , Regelman D. V. , Beserman R. , Dettmer K.
Published: July 2002

Nominal Ge islands were grown by a molecular beam epitaxy technique on a Si(001) substrate. Island positions and shapes were measured by atomic force microscopy. Two types of islands with different sizes and shapes are present. The Si concentration distribution inside the islands was measured by Raman imaging technique with a 0.4 μm resolution, and was found to vary between 10% and 30% in large islands and be 10% in smaller islands.
Three-dimensional atom probe field-ion microscopy observation of Cu/Co multilayer film structures
Authors: Larson D. J. , Petford-Long A. K. , Cerezo A. , Smith G. D. W. , Foord D. T. , Anthony T. C.
Published: July 2002

Focused ion-beam milling has been used to fabricate field-ion specimens from a multilayer film structure containing 100 repetitions of a (Cu2 nm/Co2 nm) bilayer deposited directly onto a planar substrate. The as-deposited films showed a magnetoresistance ratio of ∼5% over a 250 Oe range at room temperature, and a coercivity of ∼60 Oe. The magnetic data suggest that the films are coupled ferromagnetically. Successful field-ion specimen preparation has allowed the observation of these layers by field-ion imaging and three-dimensional atom probe compositional analysis. Examination of the multilayer images reveals that, in some regions, the layers are nonparallel, but the interfaces are chemically quite sharp, with a diffuse interface region of ∼3 atomic layers. In addition, in some areas adjacent cobalt layers appear to be in contact. The fact that the layers are wavy suggests that the ferromagnetic coupling may be a result of Néel “orange peel” type magnetostatic coupling between adjacent cobalt layers. The relatively high coercivity may be a result of the poor layer planarity leading to a high number of domain wall pinning sites.
Temperature and stress polarity-dependent dielectric breakdown in ultrathin gate oxides
Authors: Eriguchi Koji , Niwa Masaaki
Published: July 2002

Temperature and stress polarity-dependent dielectric breakdown in thin silicon dioxides has been carefully investigated. The experimental data show that the time to breakdown under a constant-current injection has two kinks around 330 and 230 K for 4- and 10-nm-thick oxides under both stress polarities. It has been found that thinner oxides have a stronger temperature dependence (a larger activation energy) even if the field dependence of the activation energy is taken into consideration, and also that, from the gate voltage shift during the constant-current injection, the postbreakdown characteristics strongly depends on the stress polarity for thinner oxides.
Photothermal displacement measurement of transient melting and surface deformation during pulsed laser heating
Authors: Chen Shaochen , Grigoropoulos Costas P. , Park Hee K. , Kerstens Pieter , Tam Andrew C.
Published: July 2002

A photothermal displacement method has been developed to probe the pulsed laser-induced transient melting and surface deformation of Ni–P hard disk substrates. A probing He–Ne laser beam is aligned collinearly with the near-infrared nanosecond pulsed heating beam. The He–Ne beam spot is scanned on the microfeatures formed on the sample surface by the pulsed laser heating. The deflection signals show the variation of the feature shape resulting from different pulse energies of the heating laser beam. The transient deflection signal also reveals that the time scale of the surface motion is in the range of several hundred nanoseconds.
Structure and optical properties of amorphous diamond films prepared by ArF laser ablation as a function of carbon ion kinetic energy
Authors: Merkulov Vladimir I. , Lowndes Douglas H. , Jellison G. E. , Puretzky A. A. , Geohegan D. B.
Published: July 2002

Amorphous carbon films with variable sp3 content were produced by ArF (193 nm) pulsed laser deposition. Electron energy loss spectroscopy and spectroscopic ellipsometry were employed to systematically study changes in the bonding and optical properties of the carbon films as a function of the kinetic energy of ablated C ions, which was measured using an ion probe. The measurements reveal that the films with the most diamond-like properties are obtained at the C ion kinetic energy of ∼90 eV. In contrast to measurements made as a function of laser fluence, ion probe measurements of kinetic energy are a convenient as well as more accurate and fundamental method for monitoring deposition conditions, with the advantage of being readily transferable for interlaboratory comparisons.
Back action of a low noise dc SQUID
Authors: Falferi Paolo , Bonaldi Michele , Cerdonio Massimo , Vinante Andrea , Vitale Stefano
Published: July 2002

Measurements are presented of the back action of a low noise commercial dc superconducting quantum interference device (SQUID) on a strongly-coupled high-quality factor (Q≈106) electrical LC resonator operating at audio frequencies (≈1 kHz). The back-action effect, due to the voltage noise of the SQUID current amplifier, is in good agreement with the predictions. The value of the noise impedance of the SQUID coincides, within 5%, with its input coil inductance times the angular frequency.
A mechanically flexible tunneling contact operating at radio frequencies
Authors: Erbe A. , Blick R. H. , Tilke A. , Kriele A. , Kotthaus J. P.
Published: July 2002

We report on a nanomachined electromechanical resonator applied as a mechanically flexible tunneling contact. The resonator was machined out of a single-crystal silicon-on-insulator substrate and operates at room temperature with frequencies up to some 73 MHz, transferring electrons by mechanical motion.
Bulk and surface characterization of a dewetting thin film polymer bilayer
Authors: Ade H. , Winesett D. A. , Smith A. P. , Anders S. , Stammler T. , Heske C. , Slep D. , Rafailovich M. H. , Sokolov J. , Stöhr J.
Published: July 2002

We have monitored the progression of the dewetting of a partially brominated polystyrene (PBrS) thin film on top of a polystyrene (PS) thin film with scanning transmission x-ray microscopy (STXM) as well as photoemission electron microscopy (PEEM). We mapped the projected thickness of each constituent polymer species and the total thickness of the film with STXM, while we determined the surface composition with PEEM. Our data show that the PBrS top layer becomes encapsulated during the later stages of dewetting and that atomic force microscopy topographs cannot be utilized to determine the contact angle between PBrS and PS.
Far-infrared (λ=88 μm) electroluminescence in a quantum cascade structure
Authors: Rochat Michel , Faist Jérôme , Beck Mattias , Oesterle Ursula , Ilegems Marc
Published: July 2002

Intersubband electroluminescence has been investigated in a quantum cascade structure based on vertical transition designed for far-infrared (λ=88 μm) emission. A narrow luminescence peak with a full width at half maximum of 0.7 meV is measured at low excitation currents (30 A/cm2) and low temperature (T=5 K). The electroluminescence efficiency exhibits a strong temperature and current dependence, consistent with an interplay between electron–electron and optical phonon scattering.
Ultrafast optical switching by photoinduced electrochromism in cast films of polymeric 4,4′-bipyridinium salts with di-iodides
Authors: Inoue Hiroshi , Sakaguchi Hiroshi , Nagamura Toshihiko
Published: July 2002

Femtosecond dynamics of color changes due to photoinduced electron transfer and reverse reactions in polymeric 4,4′-bipyridinium di-iodides salts were studied with a fs laser pump–probe technique. The characteristic color change was shown to take place in less than 1 ps by fs-laser excitation of an ion-pair charge-transfer band, which may be applied to ultrafast THz all-optical switching devices using visible light.
Frequency-dependent interface capacitance of Al–Al2O3–Al tunnel junctions
Authors: McCarthy K. T. , Arnason S. B. , Hebard A. F.
Published: July 2002

Four-terminal ac impedance measurements have been used to characterize Al–Al2O3–Al tunnel-junction capacitors over the frequency range of 10 Hz–100 kHz. The insulating barriers are thin enough to assure that the response can be modeled by a frequency-dependent interface capacitance in parallel with a frequency-independent tunnel junction resistor R0. The data reveal no sign of loss peaks down to 10 Hz and the impedance curves for a single junction, annealed to give different tunnel-junction resistance, collapse onto a single curve when R0 is used as a scaling parameter. The loss mechanism is ascribed to interface traps and is found to give an unusual asymptotic phase angle response when the real and imaginary parts of the complex capacitance are plotted against each other.
Temperature-accelerated dielectric breakdown in ultrathin gate oxides
Authors: Chen C.-C. , Chang C.-Y. , Chien C.-H. , Huang T.-Y. , Lin H.-C. , Liang M.-S.
Published: July 2002

Temperature-accelerated effects on dielectric breakdown of ultrathin gate oxide with thickness ranging from 8.7 to 2.5 nm are investigated and analyzed. Although superior reliability for ultrathin gate oxide at room temperature has been reported in recent literatures, a strong temperature-accelerated degradation of oxide reliability is observed in this study. Experimental results show that both charge-to-breakdown (Qbd) and breakdown field (Ebd) characteristics are greatly aggravated for ultrathin oxide at elevated temperature. The Arrhenius plot also confirms that the activation energies of Qbd and Ebd increase significantly as oxide thickness decreases, explaining the higher sensitivity to temperature for thinner oxides.
Variable sample temperature scanning superconducting quantum interference device microscope
Authors: Kirtley J. R. , Tsuei C. C. , Moler K. A. , Kogan V. G. , Clem J. R. , Turberfield A. J.
Published: July 2002

We demonstrate a design for a scanning superconducting quantum interference device (SQUID) microscope in which the sample temperature can be varied over a large range. In this design, both sample and SQUID are in the same vacuum space, separated by a few microns. By firmly anchoring the SQUID to a low-temperature bath, the sample temperature can be changed while the SQUID remains superconducting. This allows magnetic imaging at varying sample temperatures with micron-scale spatial resolution and the sensitivity of a low-Tc SQUID. We demonstrate this approach by imaging the temperature dependence of Abrikosov vortices in thin films of the high-temperature superconductor YBa2Cu3O7−δ. We extract the in-plane penetration depth λab(T) in our samples from these measurements.
Study of wet treatment of polyimide by sum-frequency vibrational spectroscopy
Authors: Kim Doseok , Shen Y. R.
Published: July 2002

A polyimide surface treated with a strong NaOH solution for improvement of adhesion with metals was investigated using ultraviolet absorption and sum-frequency vibrational spectroscopy. Conversion of imide groups to amide groups at the polyimide surface was observed. This conversion and subsequent etching of the polyimide film by the solution seems to be more effective in the amorphous part of the film. Drying of the film converts the surface amides back to imides.
Exciton absorption in β-FeSi2 epitaxial films
Authors: Rebien M. , Henrion W. , Müller U. , Gramlich S.
Published: July 2002

Experimental evidence is given for excitonic transitions in semiconducting iron disilicide. Epitaxial films of β-FeSi2 on Si(100) were studied by optical transmission and reflection measurements at 10 K and at room temperature as well as room temperature spectral ellipsometry. Two sharp peaks were found in the low temperature spectra, which can be ascribed to the ground state and the first excited state of excitons. Assuming free Wannier–Mott excitons, a value of 16 meV is obtained for the binding energy. A value of 0.93 eV for the ionization energy results with this assumption. This coincides with the value of the direct energy gap determined at 10 K. Compared to room temperature the energy gap is blue shifted by 40 meV.
Low-temperature luminescence of exciton and defect states in heteroepitaxial GaN grown by hydride vapor phase epitaxy
Authors: Skromme B. J. , Jayapalan J. , Vaudo R. P. , Phanse V. M.
Published: July 2002

Low-temperature (1.7–20 K) photoluminescence and reflectance are used to investigate the free and bound exciton and shallow impurity states in GaN. A 300-μm-thick GaN layer grown by hydride vapor phase epitaxy on sapphire(0001), with an exceptionally low dislocation density (3×106 cm−2) is used to obtain very high quality spectra. Both free and bound n=2 excitons are identified, leading to a confirmation of the A free exciton binding energy as about 26.4 meV, independent of strain. Principal neutral donor-bound exciton (D0,X) peaks involving two to three different donors are resolved, as are two-electron satellites involving up to five different residual donors with binding energies ranging from 22 to 34.5 meV.
Oxide damage by ion implantation in silicon
Authors: Losavio A. , Crivelli B. , Cazzaniga F. , Martini M. , Spinolo G. , Vedda A.
Published: July 2002

A significant increase in the etching rate of 680 nm thermally grown silicon dioxide layers has been observed following high energy ion implantation. Phosphorous and boron implantations have been considered, and the dependence upon fluence (from 1012 to 1014 atom/cm2)and ion energy (from 700 to 3000 keV) has been investigated. The effect of ion implantation has also been analyzed by thermally stimulated luminescence measurements above room temperature, to obtain complementary information on the physical mechanisms involved in the damage process. Data related to thermal annealing of oxide damage are also presented, indicating that a monotonic recovery takes place at temperatures higher than 550 °C although residual damage is observed even after thermal treatment up to 1000 °C.
A self-assembled single-electron tunneling transistor
Authors: Magnus Persson S. H. , Olofsson Linda , Gunnarsson Linda
Published: July 2002

A single-electron tunneling transistor was made by capturing a chemically synthesized gold cluster between two gold electrodes. The transistor had a quasiperiodic modulation of the current–voltage characteristics as a function of a gate voltage applied to an oxidized aluminum electrode at 4.2 K. The Coulomb blockade voltage for this device was 50 mV observed at 4.2 K and room temperature. The maximum observed blockade voltage was 200 mV for devices without gate.