bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 exhibiting colossal magnetoresistance
Authors: Rajeswari M. , Chen C. H. , Goyal A. , Kwon C. , Robson M. C. , Ramesh R. , Venkatesan T. , Lakeou S.
Published: July 2002

We report measurements of the low-frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 in the temperature range covering both the ferromagnetic metallic state and the paramagnetic insulating state. We observe a bolometric optical response in fully oxygenated films of the above composition as well as in oxygen deficient films. In both types of samples, the optical response is thermal in nature as indicated by its proportionality with the temperature derivative of the resistance dR/dT.
Laser-heated radiation dosimetry using transparent thermoluminescent glass
Authors: Justus Brian L. , Huston Alan L. , Johnson Tommy L.
Published: July 2002

Laser-stimulated thermoluminescence emission is reported from a novel transparent glass phosphor exposed to γ-ray or ultraviolet radiation. Laser-heated radiation dosimetry measurements, using this effect, are reported. A unique laser heating method permits the stimulation of the thermoluminescence without significantly raising the bulk temperature of the glass.
Diffusion and aggregation of size-selected silver clusters on a graphite surface
Authors: Goldby I. M. , Kuipers L. , von Issendorff B. , Palmer R. E.
Published: July 2002

We have investigated the early stages of film growth via deposition of size-selected silver clusters on graphite, as a function of incident cluster size. For all sizes from 50 to 250 atoms per cluster, the deposited clusters are mobile and coalesce into three-dimensional particles with a ‘‘universal’’ diameter of ≊14 nm, possibly a consequence of lattice strain between the silver and graphite. The 14 nm particles are found mainly in small aggregates, indicating that they themselves are to some degree mobile. We have also found evidence that the particle mobility is influenced by the cluster impact angle.
Structure of 3×2, 5×2, and 7×2 reconstructed 3C-SiC(001) surfaces obtained during epitaxial growth: Molecular dynamics simulations
Authors: Kitabatake Makoto , Greene J. E.
Published: July 2002

The stable Si-terminated 3C-SiC(001) surface exhibits a 2×1 reconstruction similar to Si(001)2×1, but with a longer dimer bond length, 2.49 vs 2.40 Å, due to a higher backbond strength. Molecular dynamics simulations show that deposition of Si adatoms on 3C-SiC(001)2×1 results in the formation of a series of missing-dimer-row type reconstructions of the type h×2 where h=...,7,5,3 with increasing ad-Si coverage. The basic building block for the h×2 surfaces is a two-ad-dimer unit. Si surface atoms below missing ad-Si dimers between neighboring ad-Si dimer pairs remain dimerized and 90° rotated. The most stable Si-terminated h×2 structure is 3C-SiC(001)3×2, which represents the closest-packed array of two-ad-dimer units, with a dangling bond density of 0.67 per 3C-SiC(001)1×1 unit cell.
Vacancy-type defects in molecular beam epitaxy low temperature grown GaAs, a positron beam lifetime study
Authors: Störmer J. , Triftshäuser W. , Hozhabri N. , Alavi K.
Published: July 2002

Positron beam lifetime spectroscopy has been utilized to study the depth distribution of vacancy-type defects in molecular beam epitaxy GaAs grown at low temperature. Lifetime spectra were measured as a function of positron energy. From the analysis of the positron lifetime in as-grown and annealed low temperature grown GaAs, the concentrations of Ga monovacancies and voids are estimated. Our results show that in an as-grown sample the Ga monovacancy concentration is >3×1018 cm−3. It is also known that vacancy-cluster concentration in an annealed sample exceeds 1018 cm−3 with a nonuniform spatial distribution.
Micromechanical detection of magnetic resonance by angular momentum absorption
Authors: Ascoli C. , Baschieri P. , Frediani C. , Lenci L. , Martinelli M. , Alzetta G. , Celli R. M. , Pardi L.
Published: July 2002

Observations of electron paramagnetic resonance by means of the angular momentum absorbed by a small sample are reported. The method is based on the detection of the torque induced in a microcantilever, like the ones employed in atomic force microscopy, integral with the sample. The results obtained with this experimental scheme are compared with the ones of the Sidles–Rugar method exploiting a force detection of the magnetic resonance in presence of strong magnetic field gradients. In particular, the signal drawn by angular momentum absorption shows opposite trends when the static magnetic field is swept in opposite directions, contrary to the case of experiments performed with force detection. The shape of the signal is characterized at different values of the static field and of radiation intensity.
Current capability of filaments depending on their position in (Bi,Pb)2Sr2Ca2Cu3O10+δ -multifilament tapes
Authors: Schuster Th. , Kuhn H. , Weißhardt A. , Kronmüller H. , Roas B. , Eibl O. , Leghissa M. , Neumüller H.-W.
Published: July 2002

The microstructures of single filaments of silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10+δ-multifilament tapes are investigated by polarized light and scanning electron microscopy. Large differences in the microstructure of filaments depending on their position in the cross section of the tape are found. The influence of this microstructure on the critical current density is investigated by magneto-optics. A drastic reduction of the critical current density by a factor of about 10 of the outer, compared to the filaments in the center of the tape is observed.
The effect of atomic hydrogen on the growth of gallium nitride by molecular beam epitaxy
Authors: Yu Zhonghai , Buczkowski S. L. , Giles N. C. , Myers T. H. , Richards-Babb M. R.
Published: July 2002

GaN was grown by molecular beam epitaxy using an rf plasma source. Growth under gallium-rich conditions at 730 °C was required to produce high quality layers as indicated by photoluminescence, Hall effect, atomic force microscopy, and x-ray diffraction measurements. Atomic hydrogen has a significant effect for Ga-rich growth, increasing growth rates by as much as a factor of 2.
Nanometer-scale characterization of SiO2/Si with a scanning capacitance microscope
Authors: Tomiye Hideto , Yao Takafumi , Kawami Hiroshi , Hayashi Tsukasa
Published: July 2002

A novel scanning capacitance microscope (SCaM) is developed using a tungsten stylus as a cantilever. The deflection of the cantilever is detected by projecting the cantilever onto a photodetector. A combined SCaM, atomic force microscope (AFM), and scanning tunneling microscope has been constructed. The spatial resolution for SCaM measurements is estimated to be less than 100 nm. Local electrical properties of a SiO2/Si system are investigated using the SCaM and AFM functions of the combined microscope. A lateral p-n junction is formed, by ion implantation of P into a lightly B-doped Si wafer, the structure is then annealed and thermally oxidized. It is demonstrated that (1) the p-n junction can be observed even through the oxide layer, (2) the local impurity concentration can be estimated from capacitance–voltage (C–V) characteristics, and (3) P diffuses into the B-doped region during the thermal processes.
Cubo-octahedral B12 clusters in silicon crystal
Authors: Okamoto Masakuni , Hashimoto Kazunobu , Takayanagi Kunio
Published: July 2002

We have calculated a new stable structure and the electronic structure of boron clusters in silicon crystal. According to our calculation, which was based on the first-principles local density functional approach for Si54B12H60 clusters, the cubo-octahedral B12 cluster was found to be more stable than the icosahedral one proposed previously. The total energy difference was about 4.6 eV. The analysis of the partial density of states showed that the cubo-octahedral B12 cluster should act as a double acceptor.
A combined nonlinear and linear magneto-optical microscopy
Authors: Kirilyuk V. , Kirilyuk A. , Rasing Th.
Published: July 2002

New possibilities for magnetic domain studies are demonstrated using a combination of nonlinear magneto-optical microscopy and a conventional linear polarizing microscope. The use of an optical response that is governed by a higher rank tensor offers sensitivity to additional combinations of magnetization directions and optical wave vector and polarization, which is demonstrated in magnetic garnet films of different crystallographic orientations. We observed a nontrivial modulated domain structure in a (210) film and a clear domain contrast for a (111) film, where the linear image only indicated simple up–down domains and no domain contrast for these two situations, respectively.
Explanation for the oxide thickness dependence of breakdown characteristics of metal-oxide-semiconductor structures
Authors: DiMaria D. J. , Stathis J. H.
Published: July 2002

Experimental evidence is presented showing that the thickness dependence observed for charge-to-breakdown measurements of very thin oxide layers in metal-oxide-semiconductor structures is correlated with that for the reduction in total generated microscopic defects necessary to induce destruction. These results are related to a percolation model for the formation of paths connecting some of these defects from the cathode to the anode at the time of breakdown.
Pixelless infrared imaging utilizing a p-type quantum well infrared photodetector integrated with a light emitting diode
Authors: Allard L. B. , Liu H. C. , Buchanan M. , Wasilewski Z. R.
Published: July 2002

We present experimental results which support a recently proposed scheme for infrared imaging through the combined use of a photon frequency up-conversion device with a charge coupled device (CCD) camera. The epitaxial device consists of a long wavelength p-type GaAs/AlGaAs quantum well infrared photodetector (QWIP) on top of which is grown a shorter wavelength InGaAs/GaAs light emitting diode (LED). Upon long wavelength infrared excitation of the QWIP, near infrared light is generated by the LED whose output is directed towards a commercial CCD array where the up-converted image of the long wavelength infrared source object is formed.
Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition
Authors: Tateno K. , Ohiso Y. , Amano C. , Wakatsuki A. , Kurokawa T.
Published: July 2002

Vertical-cavity surface-emitting laser (VCSEL) structures have been grown on GaAs (311)B substrates by metalorganic chemical vapor deposition. C-doped GaAs and AlAs layers with smooth surface morphology and a hole concentration of 1018 cm−3 were obtained by optimizing the growth conditions; these conditions contributed to high-quality p-type distributed Bragg reflectors (DBRs). The devices on the (311)B substrates exhibited a threshold current of 9.6 mA, voltage of 2.1 V, and maximum power of 4.1 mW at a 20 μm φ size; these characteristics are similar to those obtained on (100) substrates. The polarization was aligned to [2̄33̄].
Band offsets in Si/Si1−x−yGexCy heterojunctions measured by admittance spectroscopy
Authors: Stein B. L. , Yu E. T. , Croke E. T. , Hunter A. T. , Laursen T. , Bair A. E. , Mayer J. W. , Ahn C. C.
Published: July 2002

We have used admittance spectroscopy to measure conduction-band and valence-band offsets in Si/Si1−xGex and Si/Si1−x−yGexCy heterostructures grown by solid-source molecular-beam epitaxy. Valence-band offsets measured for Si/Si1−xGex heterojunctions were in excellent agreement with previously reported values. Incorporation of C into Si1−x−yGexCy lowers the valence- and conduction-band-edge energies compared to those in Si1−xGex with the same Ge concentration. Comparison of our measured band offsets with previously reported measurements of energy band gaps in Si1−x−yGexCy and Si1−yCy alloy layers indicate that the band alignment is Type I for the compositions we have studied and that our measured band offsets are in quantitative agreement with these previously reported results.
Fluorescence enhancement of Er3+-doped sol–gel glass by aluminum codoping
Authors: Zhou Y. , Lam Y. L. , Wang S. S. , Liu H. L. , Kam C. H. , Chan Y. C.
Published: July 2002

Erbium-doped silica glasses prepared by the sol–gel process are desirable for applications in high-power lasers and integrated optical devices. However, its fluorescence could be quenched due to the high hydroxyl (OH−) content. Although this OH− content can be greatly reduced through special gas treatment [Y. Zhou, S. S. Wang, H. L. Liu, Y. L. Lam, Y. C. Chan, and C. H. Kam, EEE J. 8, 109 (1996).], the fluorescence is still considered weak for practical applications. We have used sol–gel aluminum codoping to increase the solubility of the Er3+ ions in a silica glass host and, consequently, significantly enhanced the fluorescence intensity of Er3+-doped sol–gel glass to the extent suitable for practical usage.
Variations in vacuum gap location in a microsecond plasma opening switch
Authors: Lisitsyn I. V. , Kohno S. , Kawauchi T. , Akiyama H.
Published: July 2002

The process of vacuum gap formation in a microsecond plasma opening switch has been studied using a He–Ne laser interferometer. Time and spatially resolved density measurements are performed in the plasma opening switch, showing a density decrease during switch opening in almost the whole interelectrode gap. Despite fine triggering accuracy and generally good shot-to-shot reproducibility of voltage and current waveforms, measurements made with the same laser beam location indicated remarkable shot-to-shot variation. The unstable formation of the vacuum gap in the microsecond plasma opening switch may be a major limiting factor for efficient switch operation.
Band gap bowing and refractive index spectra of polycrystalline AlxIn1−xN films deposited by sputtering
Authors: Peng T. , Piprek J. , Qiu G. , Olowolafe J. O. , Unruh K. M. , Swann C. P. , Schubert E. F.
Published: July 2002

The AlGaInN semiconductor system is currently of high interest for applications in blue light emitting devices. AlInN is a prospective material for lattice matched confinement layers. We measure the refractive index as well as the band gap across the entire compositional range of high-quality polycrystalline AlInN samples. Strong band gap bowing is observed.
Local atomic environment of Cu ions in ion-exchanged silicate glass waveguides: An x-ray absorption spectroscopy study
Authors: D’Acapito F. , Colonna S. , Mobilio S. , Gonella F. , Cattaruzza E. , Mazzoldi P.
Published: July 2002

We present an x-ray absorption spectroscopy study at the Cu K edge on Cu-doped soda-lime and BK7 glass waveguides obtained by ion exchange under various preparation conditions. The total electron yield and x-ray fluorescence yield collection modes were used to evidence the chemical behavior of surfacial and deep Cu ions. In all the samples copper is found preferentially as Cu+ throughout the whole exchanged region. The first coordination shell is formed by two to three oxygen atoms at 1.86 Å, much shorter than the Na–O bond (2.3 Å) in soda-lime glasses.
A study of diamond field emission using micro-patterned monolithic diamond tips with different sp2 contents
Authors: Wisitsora-at A. , Kang W. P. , Davidson J. L. , Kerns D. V.
Published: July 2002

Electron field emission from an array of micro-patterned monolithic diamond tips with varying sp2 content has been systematically investigated. The experimental results show that the field emission characteristics can be improved and the turn-on electric field can be reduced more than 50% by increasing sp2 content. Two hypotheses are proposed as an explanation of the effect of sp2 content on the field emission characteristics of diamond tips: the lowering of the work function due to defect-induced band generated by sp2 content in the diamond lattice and an increase in the field enhancement factor due to embedded sp2–diamond–sp2 cascaded microstructures.
Ultralow-temperature atomic force microscopy for the investigation of mesoscopic systems
Authors: Pelekhov D. V. , Becker J. B. , Nunes G.
Published: July 2002

We have developed an atomic force microscope for the study of mesoscopic samples. The microscope operates at milliKelvin temperatures and in high magnetic fields. Sample images are presented showing atomic steps at 4.2 K and a mesoscopic ring at 30 mK in a 9 T field. Deflection of the force-sensing cantilever is detected via an optical fiber interferometer operating at very low power levels. The microscope is well suited to surface imaging simultaneous with transport measurements at ultralow temperatures, and to the in situ manipulation of sample properties.
Cross-sectional transmission electron microscopy analysis of {311} defects from Si implantation into silicon
Authors: Moller K. , Jones Kevin S. , Law Mark E.
Published: July 2002

Transient enhanced diffusion (TED) below the amorphization dose threshold is thought to be caused by the release of interstitials from {311} defects. The interstitials are annihilated by diffusion to and then recombination with the surface of the wafer. This would suggest that the layer of {311} defects formed from an implantation and anneal would dissolve from the surface down. Cross-section transmission electron microscopy (TEM) was used to investigate this hypothesis. It is shown that the {311} defects dissolve uniformly across the layer, and the width of the layer does not change until the {311} defects nearly completely dissolve. The total population was also measured using plan-view TEM, so that the dissolution and distribution functions could be plotted from the same annealing conditions. These data suggest that surface is not the limiting factor in the interstitial removal from {311} defects.
A microstructural study of annealed Ti/Co/Cu/Co/MnFe/Ti spin-valve films
Authors: Portier X. , Petford-Long A. K. , Bayle-Guillemaud P. , Anthony T. C. , Brug J. A.
Published: July 2002

Spin-valve properties are adversely affected by heat treatments and in order to study this effect, microstructural analyses of Ti/Co/Cu/Co/MnFe/Ti spin-valve films annealed at 225 and at 290 °C have been performed. Whereas the lower temperature tends to optimize the giant magnetoresistance (GMR) ratio, the higher temperature induces a significant decrease in the GMR ratio (from 7.5% to 5.2%). High resolution electron microscopy studies have explained this result as being due to the formation of a TiCo alloy at the Ti/Co interface and to a decrease in the thickness of the sense layer. No significant modification of either the Co/Cu or the Cu/Co interfaces has been observed.
Defect-induced Raman scattering in resonance with yellow luminescence transitions in hexagonal GaN on a sapphire substrate
Authors: Jiang De-Sheng , Ramsteiner M. , Ploog K. H. , Tews H. , Graber A. , Averbeck R. , Riechert H.
Published: July 2002

Strong defect-specific low-frequency peaks are detected in low-temperature Raman spectra of hexagonal GaN grown by molecular beam epitaxy on sapphire substrate. The intensity of these peaks is found to be enhanced by excitation in resonance with yellow luminescence transitions. The validity of the assignment to electronic Raman scattering (ERS), as proposed before for their counterparts in cubic GaN on GaAs [M. Ramsteiner, J. Menniger, O. Brandt, H. Yang, and K. H. Ploog, Appl. Phys. Lett. 69, 1276 (1996)], is confirmed. Our results imply that the observed ERS peaks are related to shallow donors which are not necessarily hydrogenic. One Raman peak at very low frequency (11.7 meV) is alternatively explained by a pseudo-localized vibrational mode.
Atomistic simulation of SiH interactions with silicon surfaces during deposition from silane containing plasmas
Authors: Ramalingam Shyam , Maroudas Dimitrios , Aydil Eray S.
Published: July 2002

A systematic atomic-scale analysis is presented of the interactions of SiH radicals from a silane plasma with amorphous hydrogenated silicon (a-Si:H) film surfaces based on molecular dynamics and Monte Carlo simulations. The coordination of the silicon surface atoms and the hydrogen surface concentration determine the mechanisms by which the SiH radical interacts with the surface and attaches itself to the film, as well as the “sticking” probability of the radical. On a-Si:H surfaces with low hydrogen concentration, SiH radicals remain on the surface and attach to silicon dangling bonds. In contrast, on a-Si:H surfaces with high hydrogen concentration and lower density of dangling bonds, radicals penetrate into the bulk film and attach to subsurface silicon atoms. An average reaction probability of 95% is predicted, which is in excellent agreement with recent experimental data.
All-optical inverter operating over a temperature range of 15–1400 K in erbium-doped lutetium aluminum garnet
Authors: Maeda Yoshinobu
Published: July 2002

An all-optical inverter, which operates over a range of 15–1400 K, was demonstrated in an erbium-doped lutetium aluminum garnet crystal with 787.3, 787.9 and 790 nm laser diodes. In the case of 787.3 nm, the reversed-phase wave forms were obtained in a temperature range of 15–1100 K. In the case of 787.9 and 790 nm, they were observed up to 1400 K. It has been confirmed that the negative nonlinear absorption effect can be explained by considering an enhanced absorption model for a five-level system of the Er3+ ion. The effect has a characteristic, which is almost independent of the ambient temperature because it is formed by optical transitions of the inner shell of the erbium atom.
Near-band-edge photoluminescence emission in AlxGa1−xN under high pressure
Authors: Shan W. , Ager J. W. , Walukiewicz W. , Haller E. E. , Little B. D. , Song J. J. , Schurman M. , Feng Z. C. , Stall R. A. , Goldenberg B.
Published: July 2002

We present results of pressure-dependent photoluminescence (PL) studies of single-crystal AlxGa1−xN epitaxial films grown on sapphire substrates by metalorganic chemical vapor deposition. PL measurements were performed under hydrostatic pressure using the diamond-anvil-cell technique. PL spectra taken from the AlxGa1−xN epitaxial films are dominated by strong near-band-edge luminescence emissions. The emission lines were found to shift linearly towards higher energy with increasing pressure. By examining the pressure dependence of the spectral features, the pressure coefficients for the PL emissions associated with the direct Γ band gap of AlxGa1−xN were determined. Our results yield a pressure coefficient of 4.0×10−3 eV/kbar for Al0.05Ga0.95N and 3.6×10−3 eV/kbar for Al0.35Ga0.65N.
Zinc and phosphorus co-implantation in indium phosphide
Authors: Yu Kin Man , Ridgway M. C.
Published: July 2002

Electrical activation and dopant diffusion in Zn-implanted InP after rapid thermal annealing have been investigated. For an as-implanted Zn concentration of ∼4×1019 cm−3, only ∼7% of the implanted Zn atoms formed electrically active shallow acceptors following a 950 °C/5 s annealing cycle. The low activation was the result of rapid Zn out-diffusion—only ∼14% of the implanted dopant was retained after annealing. A significant enhancement in electrical activation and a reduction in Zn loss were achieved in Zn+P co-implanted samples which yielded a net hole concentration of ⩽6×1018 cm−3 and >50% Zn retention. The saturation of the free hole concentration in Zn+P co-implanted samples was attributed to the formation of Zn interstitial donors and Group-V-related donor-type native defects. For comparison, Zn+Al and Zn+Al+P co-implanted samples were also examined to distinguish the relative influences of implantation-induced disorder and nonstoichiometry on electrical activation and dopant diffusion. For the given implant conditions, we found that nonstoichiometry was the dominant influence.
Vacancy defects in (Pb, La)(Zr, Ti)O3 capacitors observed by positron annihilation
Authors: Keeble D. J. , Nielsen B. , Krishnan A. , Lynn K. G. , Madhukar S. , Ramesh R. , Young C. F.
Published: July 2002

A study of vacancy-related defects in ferroelectric capacitors was performed using a variable energy positron beam (VEPB). Heterostructures of (Pb0.9La0.1)(Zr0.2Ti0.8)O3 (PLZT) ferroelectric with La0.5Sr0.5CoO3 (LSCO) electrodes were deposited by pulsed laser deposition and the effects of oxygen deficiency studied using structures grown with 760 and 1×10−5 Torr oxygen. The VEPB depth profile showed an increase in vacancy-related defects with increased oxygen nonstoichiometry. A study of LSCO and PLZT thin films was also performed. The formation of vacancy clusters in the LSCO top electrode, and VPb−VO defects in the PLZT layer, with increased oxygen deficiency is inferred.
Anisotropic misfit dislocation nucleation in two-dimensional grown InAs/GaAs(001) heterostructures
Authors: Trampert Achim , Ploog Klaus H. , Tournié Eric
Published: July 2002

We report on structural investigations of the plastic strain relief in the highly mismatched InAs/GaAs(001) system grown in the layer-by-layer growth mode. The misfit dislocation generation mechanism is observed to be anisotropic in the two perpendicular 〈110〉 directions. We explain this result by the interplay between the chemically inequivalent dislocation types present in compound semiconductors and the applied growth condition.
Analytical transmission electron microscopy of hydrogen-induced degradation in ferroelectric Pb(Zr, Ti)O3 on a Pt electrode
Authors: Ikarashi Nobuyuki
Published: July 2002

Changes in the crystal structure of Pb(Zr, Ti)O3 (PZT) on a Pt electrode caused by annealing in hydrogen-containing ambient have been studied using analytical transmission electron microscopy. A decrease in Pb composition and distortion in Ti–O coordination occur at the PZT/Pt interface. These findings indicate that preferential reduction of Pb and sequential diffusion of Pb from the PZT to the Pt electrode play an important role in the changes of the PZT crystal. Thus, changes in crystal structure due to annealing in a hydrogen-containing ambient can be avoided by using electrode materials that prevent Pb diffusion.
Neutron reflectometry, x-ray reflectometry, and spectroscopic ellipsometry characterization of thin SiO2 on Si
Authors: Dura J. A. , Richter C. A. , Majkrzak C. F. , Nguyen N. V.
Published: July 2002

We present here a comparison of neutron reflectometry, x-ray reflectometry, and spectroscopic ellipsometry on a thin oxide film. These three probes each independently determine the structure of the film as a function of depth. We find an excellent agreement between the three techniques for measurements of thicknesses and interfacial roughnesses for both the SiO2 and surface contamination layers found in the sample. Realistic models based on interface parameters measured herein indicate that as the SiO2 layers decrease to sizes projected for future generations of electronic devices, both spectroscopic ellipsometry and neutron reflectometry can easily measure SiO2 films to 2 nm thick or less.
Electrical properties of Ta2O5 thin films deposited on Ta
Authors: Ezhilvalavan S. , Tseng Tseung-Yuen
Published: July 2002

The electrical properties of reactively sputtered Ta2O5 thin films with Ta as the bottom electrodes were investigated. Ta films were deposited onto SiO2/n-Si substrates by sputtering in Ar and in situ annealed at 700 °C for 10 min in N2 at a chamber pressure of 20 mTorr. We compared the effectiveness of both as-deposited and annealed Ta bottom electrodes on the leakage characteristics of Ta2O5 thin films. We also envisaged the influence of the surface roughness and morphology of the Ta bottom electrode in modifying the resultant microstructure of the annealed Ta2O5 films. Present studies demonstrate the use of Ta as a potential bottom electrode material to replace the precious metal electrodes and to simplify the fabrication process of the Ta2O5 storage capacitor.
Time response of 1.54 μm emission from highly Er-doped nanocrystalline Si thin films prepared by laser ablation
Authors: Komuro Shuji , Katsumata Tooru , Morikawa Takitaro , Zhao Xinwei , Isshiki Hideo , Aoyagi Yoshinobu
Published: July 2002

Er-doped nanocrystalline Si thin films have been controllably prepared over the Er density of 1019–1021 cm−3 using a prescribed amount of Er in a bulk target by laser ablation. Intense photoluminescence at 1.54 μm originating from intra-4f shell transitions in Er3+ ions has been observed. The increase of Er density cannot immediately result in a linear increase in Er3+-emission intensity. The time response measurement indicated that the change in the rise time of the Er3+ emission directly shows that Er3+ ions are excited by the energy transfer associated with the recombination of electron–hole pairs generated optically in the Si host. We found that the decrease of the excitation efficiency of Er3+ ions was responsible for the suppression of the Er3+-emission intensity in highly Er-doped nanocrystalline Si thin films.
Microscopic observation of weak electric fields
Authors: Laı̈ W. , Degiovanni A. , Morin R.
Published: July 2002

Weak electric fields in vacuum around conductors like small metallic wires or tips are observed using a low-energy electron point projection microscope operating in interferential mode. Observations are made at room temperature with a sensitivity of a few hundred millivolts per micrometer and submicrometer spatial resolution.
Nanooxidation of silicon with an atomic force microscope: A pulsed voltage technique
Authors: Legrand B. , Stievenard D.
Published: July 2002

The use of an atomic force microscope (AFM) as an active tool to realize silicon nanolithography is now well known, using a continuous voltage applied between the AFM tip and the surface. The main drawback of this technique is the poor reliability of the tip due to the strong tip-surface interaction. An original way which both increases the reliability and improves the nanolithography resolution is the use of pulsed voltages instead of continuous polarization. In such a case, the interaction time of the tip with the surface under electric field decreases. The frequency oscillation (in noncontact mode) of the cantilever is taken as a reference, and pulsed voltages with variable phase and duty cycle are used. We show that the variation of the phase allows a 100% modulation of the oxide width. Finally, combining this lithography technique with wet etching, a 17.5 nm wide and 5.5 nm height nanowire has been obtained starting from a silicon-on-insulator substrate.
Low interface trap density in rapid thermally annealed Al/SiNx:H/InP metal–insulator–semiconductor devices
Authors: Redondo E. , Blanco N. , Mártil I. , Gonzalez-Díaz G.
Published: July 2002

A minimum interface trap density of 1012 eV−1 cm−2 was obtained on SiNx:H/InP metal–insulator–semiconductor structures without InP surface passivation. The SiNx:H gate insulator was obtained by the electron cyclotron resonance plasma method. This insulator was deposited in a single vacuum run and was composed of two layers with different nitrogen-to-silicon ratios. The first layer deposited onto the InP was grown with a nitrogen-to-silicon ratio of N/Si=1.55, whereas the second one was grown with a N/Si ratio of N/Si=1.43. After the insulator deposition, rapid thermal annealing of the devices was performed at a constant annealing time of 30 s. The interface trap density minimum value was obtained at an optimum annealing temperature of 500 °C. Higher annealing temperatures promote thermal degradation of the interface and a sharp increase in the trap density.
Temperature-dependent Hall scattering factor and drift mobility in remotely doped Si:B/SiGe/Si heterostructures
Authors: McGregor B. M. M. , Lander R. J. P. , Phillips P. J. , Parker E. H. C. , Whall T. E.
Published: July 2002

Hall-and-Strip measurements on modulation-doped SiGe heterostructures and combined Hall and capacitance–voltage measurements on metal-oxide-semiconductor (MOS)-gated enhancement mode structures have been used to deduce Hall scattering factors, rH, in the Si1−xGex two-dimensional hole gas. At 300 K, rH was found to be equal to 0.4 for x=0.2 and x=0.3. Knowing rH, it is possible to calculate the 300 K drift mobilities in the modulation-doped structures which are found to be 400 cm2 V−1 s−1 at a carrier density of 3.3×1011 cm−2 for x=0.2 and 300 cm2 V−1 s−1 at 6.3×1011 cm−2 for x=0.3, factors of between 1.5 and 2.0 greater than a Si pMOS control.
A memory cell with single-electron and metal-oxide-semiconductor transistor integration
Authors: Durrani Zahid A. K. , Irvine Andrew C. , Ahmed Haroon , Nakazato Kazuo
Published: July 2002

A single-electron transistor memory cell with metal-oxide-semiconductor field-effect transistor sensing has been fabricated in silicon-on-insulator material. The single-electron transistor, coupled to a memory node, is defined in the upper silicon layer. The memory node forms the gate of a metal-oxide-semiconductor field-effect transistor with its channel in the substrate silicon. At 4.2 K, there are two different states of the memory-node voltage, separated by the single-electron transistor Coulomb gap. These states are sensed at high-current output levels by the metal-oxide-semiconductor transistor. The metal-oxide-semiconductor transistor current also shows evidence of gate-dependent conductance oscillations in the coupled single-electron transistor.
Direct observation of orientation limit in a fast photorefractive polymer composite
Authors: Herlocker J. A. , Ferrio K. B. , Hendrickx E. , Guenther B. D. , Mery S. , Kippelen B. , Peyghambarian N.
Published: July 2002

We report on a photorefractive polymer with a 4-ms-response time in transient four-wave mixing experiments at 0.5 W/cm2 writing irradiance, 95 V/μm applied electric field, and a grating period of 3.1 μm. Complementary transient ellipsometry, however, reveals orientational birefringence response which leads the four-wave mixing response all the way to its saturation, despite complex dynamics in these processes. Orientation does not limit the dynamic formation of photorefractive gratings in this polymer, which suggests that even faster photorefractive responses are possible for polymer composites with improved charge generation and transport properties.
Two-step preparation of 6H–SiC(0001) surface for epitaxial growth of GaN thin film
Authors: Xue Qizhen , Xue Q. K. , Hasegawa Y. , Tsong I. S. T. , Sakurai T.
Published: July 2002

A scratch-free and atomically flat 6H–SiC(0001) surface has been successfully prepared by a two-step method which combines atmospheric hydrogen treatment and ultrahigh vacuum Si etching. On this surface, a high-quality GaN(0001) thin film is obtained by radio frequency nitrogen plasma assisted molecular beam epitaxy. Its surface exhibits a typical terrace-plus-step morphology, which enables us to study various GaN(0001) surface superstructures and hollow-core defects with atomic resolution by scanning tunneling microscopy.
Enhanced electron injection into light-emitting diodes via interfacial tunneling
Authors: Wolf U. , Bässler H.
Published: July 2002

A previous Monte Carlo simulation for hopping injection into a random organic dielectric has been extended to include the effect of tunneling through a thin inorganic insulator. The effect of the interface has been explained upon the fact that the attenuation length of an electron is much larger in a strongly bonded inorganic solid as compared to a van-der-Waals bonded organic. Depending upon the system parameters, significant improvement of injection is predicted.
Demonstration of high-performance 10.16 μm quantum cascade distributed feedback lasers fabricated without epitaxial regrowth
Authors: Hofstetter Daniel , Faist Jérôme , Beck Mattias , Müller Antoine , Oesterle Ursula
Published: July 2002

We present measurement results on high-power low threshold quantum cascade distributed feedback lasers emitting infrared radiation at 10.16 μm. A lateral current injection scheme allowed the use of a strongly coupled surface grating without metal coverage and epitaxial regrowth. Although this design resulted in a simplified processing, the fabrication of high performance devices was demonstrated. The laser emitted 230 mW of pulsed power at 85 K, and 80 mW at room temperature. Threshold current densities of 1.85 kA/cm2 at 85 K and 5.4 kA/cm2 at room temperature were observed. Since the spectrum showed single mode behavior for all temperatures and power levels of the operating range, this device will be ideal for optical sensor applications.
Freely migrating defects in ion-irradiated Cu3Au
Authors: Wei L. C. , Lang E. , Flynn C. P. , Averback R. S.
Published: July 2002

The efficiency of producing freely migrating vacancy defects in irradiated Cu3Au was examined using electrical resistivity measurements of radiation-induced ordering on highly perfect single-crystal films. Relative efficiencies for He, Ne, and Ar bombardments at different ion energy and specimen temperature were obtained. The ratio of the efficiencies of 0.6 MeV Ne to He increased with temperature from ∼0.25 at 340 K to a saturation value of ∼0.40 at 520 K. For Ar and He, the ratio increased from ∼0.11 at 360 K to ∼0.18 at 540 K. Estimates indicate that about half of all defects created in cascades are freely migrating.
Luminescence of ZnCdSe/ZnSe ridge quantum wires
Authors: Heiss W. , Prechtl G. , Stifter D. , Sitter H. , Springholz G. , Riemann T. , Bertram F. , Rudloff D. , Christen J. , Bley G. , Neukirch U. , Gutowski J. , Liu J.
Published: July 2002

Blue light-emitting quantum wire structures fabricated by molecular-beam epitaxial growth on submicrometer prepatterned GaAs substrates were investigated by spatially and time resolved luminescence experiments. The quantum wires are formed due to the different growth rates of ZnCdSe on the (111) and (100) surfaces of the grated substrate. With decreasing wire width, the exciton luminescence splits into two clearly distinguished lines. These lines can be assigned to the emission of the ridge quantum wire and the emission of ZnCdSe quantum wells at the bottom of the grooves. The two-dimensional quantum confinement in the ridge wire is confirmed by a maximum of the decay time at the energy of the ridge luminescence.
Near-field fluorescence imaging by localized field enhancement near a sharp probe tip
Authors: Hamann Hendrik F. , Gallagher Alan , Nesbitt David J.
Published: July 2002

This work describes near-field investigations of luminescent nanosamples based on monitoring fluorescence due to the enhanced field around a laser-illuminated probe tip. These fluorescence effects are investigated as a function of probe-sample separation, which identify a strong, spatially localized (≈7 nm) enhancement of the incident laser field in the vicinity of the probe tip. From a model fit to the fluorescence data, the localized enhancement of the electric field is estimated to be >tenfold, which predicts a significant increase in localized excitation intensity (>100-fold) for fluorescence imaging of molecular size samples.
Improved tip performance for scanning near-field optical microscopy by the attachment of a single gold nanoparticle
Authors: Sqalli O. , Bernal M.-P. , Hoffmann P. , Marquis-Weible F.
Published: July 2002

Nanometer-size optical probes are gaining increasing interest in near-field optical microscopy. Optimization of the probe shape is still a challenging research and development issue. Here, we propose to improve the optical properties of a fiber-based probe by attachment at the tip apex of one single gold particle of 60 nm diameter. This probe produces an enhancement of the light throughput, both in the near and the far fields, a homogenization of the diffracted light polarization, and a higher accuracy of the topographic sensitivity. In this letter, the chemical procedure for the fixation of one single gold particle on the apex of a standard tip for scanning near-field microscopy is described. Far-field as well as near-field measurements with this probe are performed, showing improvement of the light distribution in excellent agreement with the theory.
Predictive model for scanned probe oxidation kinetics
Authors: Dagata J. A. , Perez-Murano F. , Abadal G. , Morimoto K. , Inoue T. , Itoh J. , Yokoyama H.
Published: July 2002

Previous descriptions of scanned probe oxidation kinetics involved implicit assumptions that one-dimensional, steady-state models apply for arbitrary values of applied voltage and pulse duration. These assumptions have led to inconsistent interpretations regarding the fundamental processes that contribute to control of oxide growth rate. We propose a model that includes a temporal crossover of the system from transient to steady-state growth and a spatial crossover from predominantly vertical to coupled lateral growth. The model provides an excellent fit of available experimental data.
Surface electronic density of states of tetrahedral amorphous carbon investigated by scanning tunneling spectroscopy and ab initio calculations
Authors: Koivusaari K. Jarmo , Rantala Tapio T. , Levoska J. , Leppävuori S.
Published: July 2002

The surface electronic density of states of tetrahedral amorphous carbon has been measured by scanning tunneling microscopy and calculated by density functional theory. An analysis of these results and their comparison is presented here for a series of structures with different microscopic mass densities. The experimental structures were obtained by pulsed laser deposition with varying conditions resulting in diamond-like carbon thin films. The calculated carbon structures were generated by simulating a melting–cooling cycle with molecular dynamics using the density functional energetics within the local density approximation. The experimental and calculated densities of states show good agreement. Graphitic-like surface reconstruction is both observed at the sp3-rich tetrahedral amorphous carbon (ta-C) sample and found in the calculated ta-C slab structure.
Effects of thermal annealing on the luminescence and structural properties of high indium-content InGaN/GaN quantum wells
Authors: Chuo C.-C. , Lee C.-M. , Nee T.-E. , Chyi J.-I.
Published: July 2002

Postgrowth thermal annealing was applied to investigate the optical and structural properties of InxGa1−xN/GaN multiple quantum wells with high InN mole fraction. Thermal annealing at 900 °C results in a twentyfold increase of the integrated photoluminescence intensity. Photoluminescence emission is also improved from a broad band for the as-grown sample to two dominant peaks for the annealed sample. Cross-sectional transmission electron microscopy shows the existence of quantum dot-like islands in the wells for the as-grown sample but these islands are significantly reduced after thermal annealing at 900 °C.
Green II–VI light emitting diodes with long lifetime on InP substrate
Authors: Faschinger W. , Nürnberger J.
Published: July 2002

We demonstrate that the quaternary compound ZnMgSeTe can be grown by molecular beam epitaxy in reasonable quality. For layers with energy gaps as high as 3.1 eV, nitrogen doping leads to free hole concentrations around 1018 cm−3. In combination with n-ZnMgCdSe, this material allows the fabrication of II–VI diodes lattice matched to InP substrate. Light emitting diodes containing a tensile strained ZnCdSe quantum well in ZnMgCdSe emit green light when operated in forward direction. In contrast to diodes with a comparable density of extended defects grown on GaAs substrate, these diodes show no formation of dark line defects and a lifetime which is about three orders of magnitude longer.
Kinetic modeling of N incorporation in GaInNAs growth by plasma-assisted molecular-beam epitaxy
Authors: Pan Z. , Li L. H. , Zhang W. , Lin Y. W. , Wu R. H.
Published: July 2002

We have studied the growth of GaInNAs by a plasma-assisted molecular-beam epitaxy (MBE). It was found that the N-radicals were incorporated into the epitaxial layer like dopant atoms. In the range of 400–500 °C, the growth temperature (Tg) mainly affected the crystal quality of GaInNAs rather than the N concentration. The N concentration dropped rapidly when Tg exceeded 500 °C. Considering N desorption alone is insufficient to account for the strong falloff of the N concentration with Tg over 500 °C, the effect of thermally-activated N surface segregation must be taken into account. The N concentration was independent of the arsenic pressure and the In concentration in GaInNAs layers, but inversely proportional to the growth rate. Based on the experimental results, a kinetic model including N desorption and surface segregation was developed to analyze quantitatively the N incorporation in MBE growth.
Coherent structures in screened two-dimensional turbulence
Authors: Ganesh R. , Avinash K.
Published: July 2002

Using a collection of vortex patches as fundamental objects of interest, two-dimensional (2D) coherent structure solutions are constructed as extremum entropy states (long time states) for a system of interacting screened 2D vortices. For a typical initial condition considered, such as a thin film of generalized vorticity in a semi-periodic domain, the phase diagram is numerically obtained for a wide range of total energy values. The inverse cascade phenomenon (the formation of a large scale structure from small scales) is demonstrated by computing the entropies for various length scales at a fixed energy value. Finally, a Monte Carlo simulation of vortex patches is performed and it is found that except for very large energies, the simulation results agree well with the equilibrium calculations.
The relativistic scheme for eliminating small components Hamiltonian: Analysis of approximations
Authors: Barysz Maria
Published: July 2002

The derivation of the recently proposed one-component relativistic Hamiltonian, and the resulting relativistic scheme by eliminating small components (RESC) method of Nakajima and Hirao, are analyzed in terms of the Foldy–Wouthuysen transformation of the Dirac Hamiltonian. This approach reveals the meaning of different approximations used in the derivation of the RESC Hamiltonian and its close relation to approximate relativistic Hamiltonians resulting from the free-particle Foldy–Wouthuysen transformation. Moreover, the present derivation combined with what is called the classical approximation in Nakajima and Hirao’s approach shows that there is a whole family of the RESC-type Hamiltonians. Some of them, including the original RESC Hamiltonian, are analyzed numerically. It is documented that neither of the RESC-type Hamiltonians offers variational stability. As a consequence the RESC methods may suffer from the variational collapse for heavier systems. On the other hand the energy differences (e.g., ionization potentials) computed within the RESC approach turn out to be close to the values obtained in the Douglas–Kroll scheme.
Nonlinear kink modes in the presence of charged dust grains
Authors: Vranješ J. , Petrović D. , Shukla P. K.
Published: July 2002

A set of coupled nonlinear equations, which govern the dynamics of electromagnetic perturbations in the presence of a spatially nonuniform electron current in a magnetized dusty plasma, is derived. The linear stability of such a system is discussed. It is shown that in the presence of the dust an oscillatory, kink-type instability can develop with a threshold for the instability far exceeding the value for an ordinary electron–ion plasma. In the nonlinear regime, the possibility for several types of stationary, coherent solutions is demonstrated. For specific profiles of spatially dependent functions describing the basic state, traveling dipolar and tripolar vortices, and vortex chains are found.