bluuebunny/crossref_metadata_2025 huggingface dataset:
Single sharp spot in fluorescence microscopy of two opposing lenses
Authors: Blanca C. M. , Bewersdorf J. , Hell S. W.
Published: July 2002

We demonstrate theoretically, experimentally, and in an imaging application the possibility to generate a single predominant sharp diffraction maximum in the effective point-spread function of a fluorescence microscope that coherently uses two opposing lenses. This is achieved through binary pupil filters that preclude the origination of the unfavorable strong interference side maxima that are otherwise present in these systems. Mathematical postprocessing, which has so far been a prerequisite to gain artifact-free images, is now optional or obsolete.
Ag(Ta, Nb)O
3
thin-film low-loss variable interdigital capacitors
Authors: Koh Jung-Hyuk , Grishin Alex
Published: July 2002

Epitaxial silver tantalate-niobate Ag(Ta, Nb)O3 (ATN) films have been grown on LaAlO3(001) MgO(001), and Al2O3(011_2) single crystals by pulsed ablation of stoichiometric AgTa0.38Nb0.62O3 ceramic target. Rutherford backscattering spectroscopy has revealed Ag0.9Ta0.42Nb0.58O3−δ composition of fabricated films. Micrometer size interdigital capacitor structures have been defined photolithographically on the top surface of ATN films. ATN/LaAlO3 thin-film capacitors exhibit superior overall performance: loss tangent as low as 0.0033 @1 MHz, dielectric permittivity 224 @1 kHz, weak frequency dispersion of 5.8% in 1 kHz to 1 MHz range, tunability as high as 16.8%, factor K=tunability/tan δ higher than 48, and leakage current as low as 230 nA/cm2 @100 kV/cm. ATN films on MgO show the lowest loss factor of 0.0025 @1 MHz and the weakest frequency dispersion of 2.5×10−8 Hz−1.
Factors controlling the a-axis orientation of strontium bismuth tantalate thin films fabricated by chemical solution deposition
Authors: Iijima Ryuta
Published: July 2002

The a-axis orientation of strontium bismuth tantalate (SBT) thin films on Pt/TiOx/SiO2/Si substrates was found to be controlled by the atomic composition of the precursor solution, heating rate for thermal annealing, and thickness of the single-annealed layer of chemical solution deposition. Under optimized conditions, an increase in the thickness of the total film caused the orientation to change from random to a-axis preferred. It was considered that anisotropic growth is available for preparing a-axis preferentially oriented films. The SBT thin film, whose relative intensity of the (200) peak [I(200)/I(115)] was 2.3, had a remanent polarization (2Pr) value of 30.4 μC/cm2.
Electron-beam-induced densification of Ge-doped flame hydrolysis silica for waveguide fabrication
Authors: Garcia Blanco S. , Glidle A. , Davies J. H. , Aitchison J. S. , Cooper J. M.
Published: July 2002

Experimentally we compare the densification induced by electron beam irradiation of Ge-doped silica, produced by flame hydrolysis deposition with the densification of thermally produced SiO2. By comparing these results to the predictions made by elasticity theory, we find good agreement for the thermal SiO2 by considering a single region of electron beam damage. For the Ge-doped flame-hydrolysis-deposited silica, we need to include in the model a second, shallow region, which densifies to a greater extent. X-ray photoelectron spectroscopy measurements suggest that the thickness of this additional region is comparable to a layer that was found to be depleted of Ge.
Electronic and optical properties of the (FeOs)Si2 ternaries
Authors: Migas D. B. , Miglio Leo
Published: July 2002

In this letter, we discuss the interesting changes in the band structure of two ternary (FeOs)Si2 configurations with respect to the isostructural binary β-FeSi2 and OsSi2 compounds. Our first-principle calculations also demonstrate that one of the ternaries is a direct-bandgap semiconductor with an appreciable value of the oscillator strength of the first direct transition at 0.78 eV.
Stress relaxation effect in porous 3C-SiC/Si heterostructure by micro-Raman spectroscopy
Authors: Lysenko V. , Barbier D. , Champagnon B.
Published: July 2002

Cubic (3C) SiC layers with initial biaxial stress value of about 0.4 GPa are observed by micro-Raman scattering measurements to be completely relaxed after formation of a porous network in the 3C-SiC/Si heterostructure. The porous heterostructure is obtained by an anodization procedure in HF acid solutions usually used for porous Si fabrication. The influence of some anodization parameters such as the anodization current density, HF concentration, and anodization depth on the stress relaxation effect is described. The relaxation is found to be mainly due to pore formation at the 3C-SiC/Si interface.
206 W continuous-wave TEM00 mode 1064 nm beam generation by a laser-diode-pumped Nd:YAG rod laser amplifier
Authors: Konno Susumu , Fujikawa Shuichi , Yasui Koji
Published: July 2002

We demonstrate a 206 W 1064 nm beam generation at a beam quality of M2=1.34 with a Nd:YAG laser amplifier system. We also report on an efficient 150 W TEM00 mode diode-pumped Nd:YAG rod laser.
Efficient technique for producing high-brightness, size-selected cluster beams
Authors: Denby P. M. , Eastham D. A.
Published: July 2002

An efficient technique for producing size-selected cluster beams from a magnetron cluster source is described. In this technique the clusters are ejected from a laminar gas expansion nozzle and the resulting size selection is achieved with a simple parallel-plate electrostatic separator. Using this method we have been able to select gold clusters in the size range from 250 to 16 000 atoms. The limiting size resolution is around 2% and because up to 40% of the clusters from the source are negatively charged the beam intensity is higher than many other sources. Furthermore, the angular divergence of the beam can be kept below 3° full width at half maximum for a 3-nm-diam exit nozzle so that it is possible to soft land size-selected clusters on surfaces by the simple expedient of applying a retarding voltage to the substrate.
Impurity-controlled dopant activation: Hydrogen-determined site selection of boron in silicon carbide
Authors: Aradi B. , Deák P. , Son N. T. , Janzén E. , Choyke W. J. , Devaty R. P.
Published: July 2002

The geometry and formation energy of substitutional B and Al dopants as well as their complexes with hydrogen have been calculated in 4H–SiC using first-principles methods. Our results show that boron selecting the silicon site and, therefore, getting activated as a shallow acceptor depends on the presence of hydrogen which is promoted into the crystal by boron itself. Without hydrogen, boron would mostly be incorporated at the carbon site. Aluminum does not show this behavior: it always selects the silicon site and is incorporated independently of hydrogen.
Field emission from aligned carbon nanotubes prepared by thermal chemical vapor deposition of Fe-phthalocyanine
Authors: Araki Hisashi , Katayama Tetsutaroh , Yoshino Katsumi
Published: July 2002

The field emission from aligned multiwalled carbon nanotubes prepared by thermal chemical vapor deposition of Fe-phthalocyanine is reported, with emphasis on the current–voltage characteristics and current fluctuation. By running of a pristine emitter at high current and/or voltage for a long time, the onset voltage is lowered from 400 to 125 V and the field-enhancement factor increases from 360 to 1110, demonstrating geometrical reconstruction of the nanotube apex. Deviation from the Fowler–Nordheim relation is caused at a constant local electric field of ∼4×103 V/μm and is related to high-field conditioning. Electron emission current under a high current density condition (>10 mA/cm2) is stable and noiseless. The reason for current noise in the lower current density is discussed.
Periodic composition modulations in InGaN epitaxial layers
Authors: Westmeyer A. N. , Mahajan S.
Published: July 2002

InGaN epitaxial layers grown by metalorganic chemical vapor deposition were investigated in order to understand the occurrence of composition modulations in the GaN–InN system. The In contents of the samples were determined to be x=0.21 and 0.31. Transmission electron microscopy was performed on [0001], [101̄0], and [112̄0] zone-axis specimens. Plan-view images display a domain structure, representing regions in which the directions of the modulations differ. Intersections between domains occur in 〈101̄0〉, and 〈112̄0〉, and other directions. Satellite spots appear in selected-area diffraction patterns. These observations can be explained by diffraction effects resulting from periodic composition modulations. An equation was derived relating the spacing between the satellites and the reflections to the wavelength of the modulations in the wurtzite structure. The sample with x=0.21 had a wavelength of λ=3.1±1.3 nm and the one with x=0.31 had λ=3.2±1.3 nm. Since Young’s modulus is isotropic in the (0001) plane, no particular direction is favored for the modulations based on strain energy considerations. This result is consistent with the observation of the variously oriented domains and satellites.
Self-consistent Ornstein–Zernike approximation compared with Monte Carlo results for two-dimensional lattice gases
Authors: Andresen N. U. , Borge A. , Ho/ye J. S.
Published: July 2002

The self-consistent Ornstein–Zernike approach (SCOZA) is solved numerically for a lattice gas or Ising model on the simple square lattice in two dimensions. Interactions of varying range are considered, and the results are compared with corresponding simulation ones. We focus especially upon the location of the critical temperature Tc which is identified with the maximum of the specific heat. The maximum remains finite for the finite-sized simulation sample and also for SCOZA, which treats infinite lattices in two dimensions as though they were finite samples. We also investigate the influence of the precise form of the interaction, first using an interaction that extends the nearest-neighbor case in a simple way and then considering the square-well interactions used in the simulations. We find that the shift in Tc away from its mean-field value is governed primarily by the range of interaction. Other specific features of the interaction leave a smaller influence but are relevant to a quantitative comparison with simulations. The SCOZA yields accurate results, and the influence of the precise form of the attractive interaction plays a significant role in SCOZA’s success.
Nanospark at the interface between organic solvents and tin-doped indium oxide
Authors: Uji-i Hiroshi , Hatanaka Koji , Hobley Jonathan , Fukumura Hiroshi
Published: July 2002

A nanometer-scale surface modification of tin-doped indium oxide (ITO) in organic solvent was performed using a scanning tunneling microscope (STM). The surface modification was attributed to localized field evaporation upon applying 10 V between the tunneling gap. White light sparking beneath the STM tip (nanospark) was observed during and after the surface modification. The addition of ionic species into the otherwise pure solvent also induced a nanospark even when applying lower voltages, but in this case, surface modification did not occur. Thus, it is proposed that a part of the ITO becomes dissolved in solution as ions, which results in electron avalanche in the presence of these induced ions.
Remarkable transmission of microwaves through a wall of long metallic bricks
Authors: Hibbins Alastair P. , Sambles J. Roy , Lawrence Chris R. , Robinson Donna M.
Published: July 2002

The transmitted intensity of a microwave beam through a thick continuous metal wall will be effectively zero due to the almost complete exclusion of the electric field from the metal. However, it is shown here that by removing less than 20% of the wall material to produce a regular array of bricks, up to 90% of the radiation is transmitted, despite the gaps between the bricks being less than 5% of the incident wavelength. This result is attributed to the excitation of a set of resonant waves along the cavity length through the coupling together of surface–plasmon modes across its width.
Micromagnetic structure images taken using platinum coated tips
Authors: Teschke O.
Published: July 2002

We report on magnetic force microscopy images of data tracks written in recording media taken using Pt-coated tips. The force acting on the tip when immersed in the magnetic field of the substrate was modeled assuming diamagnetic and paramagnetic interactions. The sample scanning using Pt-coated tips shows an improvement in the image delineation of the magnetic field distribution compared to the images taken using Co-coated hard magnetic tips and the display of at least a twice higher data track density.
High-Tc ramp-type Josephson junctions with a continually graded Y1−xPrxBa2Cu3Oy barrier
Authors: Gao J. , Sun J. L. , So S. M. , Tang W. H. , Li T. K.
Published: July 2002

High-Tc Josephson junctions with a graded barrier have been prepared by using a composite target. Such a barrier is synthesized by utilizing Y1−xPrxBa2Cu3Oy with a continually graded concentration of Pr, in which no lattice mismatch and other incompatible problems take place. The structural interfaces are absent in the weak link region and Josephson coupling occurs at the naturally formed superconducting/normal interfaces within the Y1−xPrxBa2Cu3Oy layer. Thus, it can significantly enhance the reproducibilty and performance of these junctions. The temperature dependences of the barrier thickness and Josephson were also studied.
Low temperature crystalline Ag–Ni alloy formation from silver and nickel nanoparticles entrapped in a fatty acid composite film
Authors: Kumar Ashavani , Damle Chinmay , Sastry Murali
Published: July 2002

Nanoparticles of silver and nickel were grown in thermally evaporated fatty acid (stearic acid) films by immersion of the film sequentially in solutions containing Ag+ ions and Ni2+ ions. Attractive electrostatic interaction between the metal cations and the carboxylate ions in the fatty acid film leads to entrapment of the cations in the film. Thereafter, the metal ions were reduced in situ to yield nanoparticles of Ag and Ni of ∼30 nm diameter within the fatty acid matrix. Thermal treatment of the stearic acid-(silver+nickel) nanocomposite films led to the formation of a Ni–Ag alloy at ∼100 °C. Prolonged heat treatment at this temperature resulted in the phase separation of the alloy and the reformation of individual Ag and Ni nanoparticles.
Annealing effect on the magnetoresistance in La0.75Ca0.25MnO3 thin films grown on Si (100) substrates
Authors: Lee Jong Cheol , You Dong Gyun , Ie Sang Yub , Sung Myeon Chang , Song Ho Shik , Park Hyun Soon , Kang Sei Kwon , Lee Sam Hyeon , Jeong Kwangho , Jin Kim Sam , Sung Kim Chul
Published: July 2002

Polycrystalline La0.75Ca0.25MnO3 thin films have been grown by rf magnetron sputtering on Si (100) substrates. The physical properties (lattice parameter, transition temperature, and activation energy) of the thin films were changed after annealing in oxygen. We obtained significantly improved magnetoresistance (MR) (Δρ/ρ0) values with the annealed films; 0.34, 0.29, and 0.27 at 1.5 T field for the films with deposition temperatures 700 °C, 750 °C and 800 °C, respectively. We investigated the effect of the out-of-plane lattice parameters on MR and transition temperature. Annealing effect on the change of the physical properties is discussed for the films. We suggest that oxygen refilling decreases the Mn–O–Mn bond angles as well as increases Mn4+/Mn3+ ratio. As a result, both out-of-plane lattice parameter and resistivity are reduced, while activation energy and the metal–insulator transition temperature are increased.
Electrical effects of a single stacking fault on fully depleted thin-film silicon-on-insulator P-channel metal–oxide–semiconductor field-effect transistors
Authors: Yang Jianan , Neudeck Gerold W. , Denton John P.
Published: July 2002

Electrical effects of a single stacking fault on fully depleted thin-film silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) were characterized. A simple method was demonstrated for the fabrication of fully depleted thin-film SOI MOSFETs with a single stacking fault in their channel region. SOI islands were created using selective epitaxial growth/epitaxial lateral overgrowth technology. The influence of a single stacking fault on device I–V characteristics was determined and compared to that of nearby identical devices without stacking faults. Off-state leakage currents, a threshold voltage shift, and drive current lowering were observed for devices with a single stacking fault in their channel region. Based on the location of the single stacking fault relative to the device channel region, various physical models were proposed to explain the phenomena observed.
The nature of arsenic incorporation in GaN
Authors: Bell A. , Ponce F. A. , Novikov S. V. , Foxon C. T. , Harrison I.
Published: July 2002

A systematic study of the nature of arsenic incorporation in GaN grown by molecular-beam epitaxy is presented. The samples were grown with concentrations of arsenic ranging from 3.4×1017 to 4.2×1018 cm−3. Secondary ion mass spectroscopy data show that increasing the As concentration has the effect of increasing the amount of As in the nitrogen site as compared to As in the gallium site. This trend is used to explain the reduction in carrier mobility with increasing As concentration.
Remanence enhancement and coercivity in two-phase CoPt bulk magnets
Authors: Xiao Q. F. , Brück E. , Zhang Z. D. , de Boer F. R. , Buschow K. H. J.
Published: July 2002

We have studied the effect of the atomic disorder–order transformation on remanence enhancement and coercivity in CoPt ingots by isothermal annealing at various temperatures well below the transformation point. The relative amount of the low-temperature hard-magnetic face-centered-tetragonal (fct) phase precipitated in the high-temperature magnetically soft face-centered-cubic (fcc) phase was determined by means of x-ray diffraction. As a function of annealing temperature, the mean grain size and the relative amount of the fct phase increase at the cost of the fcc phase. These changes were followed by means of magnetic measurements. We observed a continuous increase in coercivity with increasing annealing temperature, eventually reaching a maximum. The Kneller–Hawig model was used to explain the occurrence of remanence enhancement and the continuously changing degree of exchange coupling between the magnetically soft and hard phases.
Reduction of threading dislocation density in SiGe layers on Si (001) using a two-step strain–relaxation procedure
Authors: Sakai Akira , Sugimoto Ken , Yamamoto Takeo , Okada Masahisa , Ikeda Hiroya , Yasuda Yukio , Zaima Shigeaki
Published: July 2002

A method to obtain high-quality strain–relaxed SiGe buffer layers on Si(001) substrates is presented. In this method, the strain relaxation of the SiGe layer is performed using a two-step procedure. Firstly, a low-temperature-grown SiGe layer, whose surface is covered by a thin Si cap layer, is thermally annealed. At this stage, the strain is incompletely relaxed and an atomically flat surface can be realized. Then, a second SiGe layer is grown on the first layer to achieve further strain relaxation. Transmission electron microscopy has clearly revealed that dislocations are dispersively introduced into the first SiGe/Si substrate interface and thus no pile up of dislocations occurs. The formation of a periodic undulation on the growth surface of the second SiGe layer is the key to inducing a drastic reduction in the threading dislocation density.
Electrical characterization of magnesium implanted gallium nitride
Authors: Krtschil A. , Kielburg A. , Witte H. , Christen J. , Krost A. , Wenzel A. , Rauschenbach B.
Published: July 2002

Gallium nitride layers grown by molecular beam epitaxy on c axis oriented sapphire substrates were implanted with 180 keV magnesium ions with ion doses between 1×1014 and 1×1016 cm−2. The implantation induced defect states were investigated by temperature dependent conductivity (TDC) as well as by thermal and optical admittance spectroscopy (TAS, OAS) measurements. Dominant carrier emissions having thermal activation energies between 360 and 800 meV were found in TAS and TDC. These states are assigned to implantation induced electron traps since they do not appear in the nonimplanted reference sample. Defect states with similar transition energies were also observed in OAS resulting in an enhancement of defect-to-band transitions in the near band-gap region around 3.45 eV, in the blue band around 3.0 eV, as well as in the midgap range for photon energies between 2.5 and 1.80 eV, respectively. In addition, new transitions were found at 2.1 and 1.95 eV. Furthermore, transitions from implantation induced shallow states were observed, i.e., the magnesium acceptor as well as a new donor level at about 70 meV, tentatively discussed as nitrogen vacancy. The critical ion dose for amorphization was determined to be between 5×1015 and 1×1016 Mg+ cm−2 using x-ray diffraction.
Melting temperature effects on the size of ion-induced craters
Authors: Nordlund K. , Henriksson K. O. E. , Keinonen J.
Published: July 2002

Recent work on the sizes of craters produced by ion impacts of solids has shown that the size of the crater scales with the inverse square of the cohesive energy. This observation is in contrast to the size of craters produced in macroscopic impacts, which scale directly with the inverse of the cohesive energy. It has relied on the assumption that the melting temperature is proportional to the cohesive energy. Using computer simulations, we now show that the size scales in fact with the inverse of the product of the melting temperature and cohesive energy. This provides direct proof that the reason to the different behavior of macroscopic and ion-induced cratering is flow of the liquid produced by the ions.
Electromigration in multilevel interconnects with polymeric low-k interlevel dielectrics
Authors: Justison P. , Ogawa E. , Ho P. S. , Gall M. , Capasso C. , Jawarani D. , Wetzel J. , Kawasaki H.
Published: July 2002

The impact of low-k dielectrics on the reliability of advanced Cu interconnects is of growing importance. As a first step to understanding this impact, we have investigated the effect of two types of polymeric low-k materials on the electromigration (EM) behavior of multilevel Al(Cu) interconnects. The two polymers used as interlevel dielectrics in this work are a fluorinated polyimide and a poly(aryl) ether. Joule heating experiments and microstructural analysis were both conducted on Al(Cu) to ensure that there were no significant microstructural or thermal differences between the polymer samples and their oxide counterparts. The resulting EM behavior can then be directly attributed to differences in the mechanical properties of the low-k and oxide interlevel dielectrics. We have observed that the low-k samples had a higher steady-state drift rate and did not reach saturation, resulting in shorter EM lifetimes. These results indicate that the short length is greatly modified with the incorporation of mechanically weaker dielectrics and can potentially alter reliability design strategies as Cu/Low-k integration moves into the production stage.
Composite diamond-like carbon and silicon carbide tips grown on oblique-cut Si(111) substrates
Authors: Yeh W. Y. , Hwang J. , Lee A. P. , Kou C. S. , Chang H.
Published: July 2002

A diamond-like carbon (DLC) and silicon carbide (SiC) composite tip structure was successfully deposited on an oblique-cut Si(111) substrate of terrace width less than 21.1 Å. The DLC morphology depended on the Si(111) terrace width in the oblique-cut Si(111) surface. A continuous and dense DLC film started to form on the Si(111) substrate of terrace width higher than 27.8 Å. The density of the DLC/SiC composite tip also depended on the terrace width. The DLC films on the Si(111) with or without oblique cut had about the same Raman characteristics regardless of their different morphologies. The formation mechanism of the DLC/SiC tip structure was discussed.
Why are sputter deposited Nd1+xBa2−xCu3O7−δ thin films flatter than NdBa2Cu3O7−δ films?
Authors: Bals S. , Van Tendeloo G. , Salluzzo M. , Maggio-Aprile I.
Published: July 2002

High-resolution electron microscopy and scanning tunneling microscopy have been used to compare the microstructure of NdBa2Cu3O7−δ and Nd1+xBa2−xCu3O7−δ thin films. Both films contain comparable amounts of Nd2CuO4 inclusions. Antiphase boundaries are induced by unit cell high steps at the substrate or by a different interface stacking. In Nd1+xBa2−xCu3O7−δ the antiphase boundaries tend to annihilate by the insertion of extra Nd layers. Stacking faults, which can be characterized as local Nd2Ba2Cu4O9 inclusions, also absorb the excess Nd. A correlation is made between the excess Nd and the absence of growth spirals at the surface of the Nd-rich films.
Influence of oxygen precipitation on the measure of interstitial oxygen concentration in silicon from the 1207 cm−1 infrared absorption band
Authors: Sassella A. , Borghesi A. , Porrini M.
Published: July 2002

The possible use of the absorption band at 1207 cm−1 for the measurement of the concentration of interstitial oxygen (Oi) in silicon samples subjected to a precipitation thermal treatment is discussed. The results of low temperature infrared absorption measurements show that the conversion factor for such evaluation of the residual Oi after precipitation is strongly influenced by the presence of oxide precipitates; a limit value for the concentration of precipitated oxygen is identified, above which the measure becomes unreliable.
Probing the confined dynamics of a spherical colloid close to a surface by combined optical trapping and reflection interference contrast microscopy
Authors: Nadal François , Dazzi Alexandre , Argoul Françoise , Pouligny Bernard
Published: July 2002

A reflection interference contrast microscope and a two-beam optical trap have been combined to measure the interaction force between a colloidal particle (latex) and a solid wall (quartz plate). The particle-wall separation is measured with a nanometric resolution. The technique reveals the film drainage effect when the particle gets close to the wall and allows deducing the particle-wall equilibrium force profile, in the 0.1 to 10 pN range.
Observation of orientation dependence of electrorheology effect in ferroelectric liquid crystal using shear horizontal wave
Authors: Inoue M. , Yoshino K. , Moritake H. , Toda K.
Published: July 2002

The electrorheology (ER) effect of ferroelectric liquid crystals is observed under shear-horizontal (SH) wave propagation. The ER effect is strongly dependent on the orientation direction of the liquid-crystal molecule. The apparent viscosity is evaluated through the numerical analysis result on the propagation characteristics of a SH wave in a trilayer structure including a ferroelectric liquid-crystal (Chisso, CS1014) layer between two glass plates. The ER effect is examined by the relation between the orientation of smectic layers and the propagation direction of the SH wave.
Effect of pseudomorphic stress on structure and transport properties of ultrathin GdBa2Cu3O7 films on (001) SrTiO3 and NdGaO3
Authors: Cao L. X. , Zegenhagen J. , Cardona M. , Giannini C. , De Caro L. , Tapfer L.
Published: July 2002

We investigated the structure and transport properties of GdBa2Cu3O7 films on SrTiO3(001) and NdGaO3(001). We found that the films can be grown pseudomorphically up to at least 42 nm thickness on SrTiO3 whereas the critical thickness is less than 14 nm for films on NdGaO3. The carrier density of pseudomorphic films on SrTiO3 is tuned by the pseudomorphic stress field and films on SrTiO3 show higher T* and lower Tc compared to films of the same thickness on NdGaO3. For a 28 nm thick GdBa2Cu3O7 film on SrTiO3, the hole density per CuO2 plane is reduced to 0.12, compared to 0.16 for the optimally doped and stress-free RBa2Cu3O7. The measured temperature dependence of Jc can be understood and described by interface stress pinning.
Growth and characterization of p-type HgTe/Hg1−xCdxTe single quantum wells using nitrogen and arsenic
Authors: Ortner K. , Zhang X. C. , Oehling S. , Gerschütz J. , Pfeuffer-Jeschke A. , Hock V. , Becker C. R. , Landwehr G. , Molenkamp L. W.
Published: July 2002

p-type HgTe/Hg0.3Cd0.7Te(001) quantum wells (QWs) have been grown with molecular-beam epitaxy (MBE) on Cd0.96Zn0.04Te substrates using modulation doping techniques. Both plasma-excited nitrogen and evaporated cadmium arsenide have been utilized for in situ doping during MBE growth. A comparison of the electrical and structural properties of QWs fabricated by the two doping techniques has been made. Two-dimensional hole concentrations in nitrogen-doped QWs (up to 1.0×1012 cm−2) were significantly higher than in arsenic-doped QWs (below 0.5×1012 cm−2). However, by means of a gate-controlled Hall bar, hole densities up to 1.1×1012 cm−2 have been achieved in the latter system. Hall mobilities up to 1.0×105 cm2/(V s) have been measured. Whereas all samples exhibit pronounced although irregular Shubnikov–de Haas oscillations, quantum Hall plateaus in the arsenic-doped samples are broader and better defined.
Silicon self-diffusion under extrinsic conditions
Authors: Ural Ant , Griffin P. B. , Plummer J. D.
Published: July 2002

Self-diffusion in silicon is investigated under extrinsic carrier conditions by monitoring the diffusion of 30Si in isotopically enriched silicon layers with boron and phosphorus background doping. At 1000 °C, we find that the Si self-diffusion coefficient is slightly enhanced in both n- and p-type backgrounds. This is direct evidence of the existence of both negatively and positively charged native point defects in Si. We use a simple model involving three charge states to explain the data, which yield the relative contributions of these charge states to the overall self-diffusion coefficient and the locations of the deep levels they introduce in the band gap.
High single-mode power observed from a coupled-resonator vertical-cavity laser diode
Authors: Fischer A. J. , Choquette K. D. , Chow W. W. , Allerman A. A. , Serkland D. K. , Geib K. M.
Published: July 2002

We report a monolithic coupled-resonator vertical-cavity laser with an ion-implanted top cavity and a selectively oxidized bottom cavity which exhibits single fundamental-mode operation. The output powers are as high as 6.1 mW with side mode suppression ratios greater than 30 dB. The sizes of the implant and oxide current apertures are shown to be important for demonstrating the required selectivity for the fundamental lasing mode. With a fixed bias current on the implant cavity and increasing oxide cavity current, mode switching from single-mode operation to multimode operation and back to single-mode operation was observed. The intensities of the fundamental and first transverse modes were calculated by solving a set of multimode rate equations. The calculation indicates that the observed mode switching can be identified with changes in the optical length of the oxide cavity with increasing pump current. The observed mode dynamics are unique to coupled-resonator vertical-cavity lasers.
Quantum effects on bremsstrahlung spectrum from electron–positron plasmas
Authors: Jung Young-Dae
Published: July 2002

Quantum effects on the nonrelativistic electron–positron bremsstrahlung process in electron–positron plasmas are investigated using the corrected Kelbg potential taking into account the classical effect as well as the quantum-mechanical effect. The Born approximation is assumed for the initial and final states of the collision system. The results show that the electron–positron bremsstrahlung radiation cross section decreases with increasing thermal de Broglie wavelength (λ), i.e., decreasing plasma temperature (T). It is also found that the quantum effects on the bremsstrahlung radiation cross section increase with increasing radiation photon energy.
Generation of 1.2 ps electrical pulses through parallel gating in ultrathin silicon photoconductive switches
Authors: Holzman J. F. , Vermeulen F. E. , Elezzabi A. Y.
Published: July 2002

We report on a parallel-gating photoconductive switching technique which is capable of generating ultrashort electrical pulses. Carrier-lifetime-independent pulses as short as 1.2 ps are produced using a long-lifetime intrinsic float-zone (FZ) silicon substrate. The technique utilizes a thin FZ-silicon layer as the light-activated medium, where photoexcitation electrically contacts the switch output to both the bias line and the substrate ground plane. Model calculations based on transmission-line theory and lumped-element analysis accurately describe the experimental results.
Turn-off transients in current-modulated multitransverse-mode vertical-cavity surface-emitting lasers
Authors: Valle A. , Pesquera L.
Published: July 2002

Turn-off transients in current-modulated weakly index-guided vertical-cavity surface-emitting lasers (VCSELs) are analyzed by using a model that takes into account all the transverse modes supported by the waveguide. The turn-off transients strength is maximum for the current at which the VCSEL enters the multitransverse-mode regime. Their strength significatively decreases for the multimode regime and then operation in several modes is beneficial to avoiding turn-off transients when modulating the VCSEL well above threshold in order to achieve a required modulation rate or a sufficient optical output power.
Hexagonal GaN grown on GaAs{11n} substrates by metalorganic vapor-phase epitaxy using AlAs intermediate layers
Authors: Funato Mitsuru , Yamamoto Shuichiro , Kaisei Kiyohiro , Shimogami Koichiro , Fujita Shizuo , Fujita Shigeo
Published: July 2002

Hexagonal GaN (h-GaN) layers are grown by metalorganic vapor-phase epitaxy on GaAs{11n}A and B (n=8, 4, 3, 2, 1) substrates using AlAs intermediate layers. The best quality of h-GaN is obtained on (11̄4)B, where the crystallographic relationship is found from a pole figure to be h-GaN{0001}‖GaAs(33̄5)B and h-GaN{101̄2}‖GaAs(001). We propose a simple model that explains why such a crystallographic relationship is easily realized on {114} resulting in the superior structural and optical properties. Furthermore, from a comparison between the growth on the A and B substrates, it is pointed out that the polarity is a key factor in determining the crystallographic properties.
Metastable defects in 6H–SiC: experiments and modeling
Authors: Hemmingsson C. G. , Son N. T. , Kordina O. , Janzén E.
Published: July 2002

Using various junction space-charge techniques, annealing, and simulation, a metastable defect in 6H SiC have been characterized. We suggest a configuration coordinate diagram with three configurations, where two of them can only exist when the defect is occupied by one or more electrons. The thermal ionization energies for the different configurations were measured and the thermal barriers for two of the transitions have been determined. It is also shown that the transformation process is governed by electron capturing to the defect.
Structural deformation of single-walled carbon nanotubes and fullerene encapsulation due to magnetized-plasma ion irradiation
Authors: Jeong G.-H. , Hatakeyama R. , Hirata T. , Tohji K. , Motomiya K. , Sato N. , Kawazoe Y.
Published: July 2002

Positive and negative bias-voltages are applied to single-walled carbon nanotubes (SWNTs) in magnetized alkali–metal and alkali–fullerene plasmas. When accelerated ions are irradiated to the SWNTs through plasma sheaths, drastic structural deformations such as deflection and tube cutting of the SWNTs are observed to take place. Furthermore, this phenomenon is found to be accompanied by the fullerene encapsulation inside the SWNTs in the case of the positive-bias application in the alkali–fullerene plasma, giving the possibility that various kinds of atoms and molecules can effectively be intercalated by our plasma method.
Infrared tunable filter by the use of electrostatic force
Authors: Saito Mitsunori , Furukawa Hideki
Published: July 2002

An infrared Fabry–Pérot filter was fabricated by stacking two silicon plates with 7 μm spacing. As higher voltage was applied between the plates, the spacing decreased gradually due to the electrostatic force, and consequently, the interference peaks in the transmission spectrum shifted to a shorter wavelength; e.g., the peak at the 14.3 μm wavelength shifted to 9.5 μm by 88 V application. The transmittance of a 3.39 μm He–Ne laser was modulated between 5% and 60% by applying a 12 V modulation voltage together with 80 V bias voltage.
Evolution of self-assembled Ge/Si(211) islands
Authors: Floyd Margaret , Zhang Yangting , Drucker Jeff , Smith David J. , Tari S. , Sivananthan S.
Published: July 2002

Atomic force microscopy (AFM) and transmission electron microscopy have been used to investigate Ge islands, grown by molecular-beam epitaxy on Si(211) substrates with a nominal 15 Å Ge coverage at temperatures between 600 and 700 °C. The majority of islands grown at all three temperatures had irregular hexagonal footprints. Intermediate-sized islands grown at 650 and 700 °C became elongated laterally in the 〈111〉 direction parallel to the direction of substrate surface step edges. AFM cross-sectional analysis indicated that small coherent clusters were bound by {111} and {113} facets, whereas the largest dislocated clusters were primarily bound by {111} and {001} facets. The upper size bound for coherent clusters increased with increasing growth temperature.
Detection of THz radiation with semiconductor superlattices at polar-optic phonon frequencies
Authors: Ignatov Anatoly A. , Klappenberger F. , Schomburg E. , Renk K. F.
Published: July 2002

The nonlinear response of GaAs/AlAs superlattices to THz radiation has been analyzed over a wide frequency range (0.1 THz–15 THz), including the range of polar-optic phonon frequencies. Assuming that free electrons in a superlattice subjected to both a static and a THz field perform frequency-modulated damped Bloch oscillations, we have calculated a superlattice current responsivity, i.e., the ratio of the direct current change to the power of the incident radiation. The responsivity of superlattices has been measured in several recent experiments. An equivalent circuit taking into account the resonant properties associated with polar-optic phonons was used in a self-consistent treatment of the problem. It is shown that the responsivity is suppressed at frequencies of infrared-active, transverse polar-optic phonons due to dynamic screening of the THz field by the lattice. In contrast, the responsivity strongly increases at longitudinal polar-optic phonon frequencies due to a large enhancement of the THz field in the superlattice indicated by a longitudinal polar-optic phonon resonance, i.e., by an “anti- screening” effect. The described phenomenon can strongly influence the design and optimization of superlattice-based ultra-fast detectors for THz radiation.
Observation of enhanced spontaneous emission coupling factor in nitride-based vertical-cavity surface-emitting laser
Authors: Kako S. , Someya T. , Arakawa Y.
Published: July 2002

We demonstrate an enhancement of spontaneous emission coupling factor β in a nitride-based vertical-microcavity surface-emitting laser. The 2.5λ vertical microcavity, the quality factor of which reaches 740, is sandwiched between a nitride and an oxide distributed Bragg reflector. From input–output measurements and analyses of the rate equations, the β of the lasing mode at a wavelength of 396.1 nm is estimated to be 1.6×10−2. The estimated β can be well accounted for by a simple theoretical model.
Electrostatic drift modes in a closed field line configuration
Authors: Kesner J. , Hastie R. J.
Published: July 2002

The stability of electrostatic drift waves in a closed field line configuration in collisionality regimes ranging from collisional to collisionless is compared. The maximum sustainable pressure gradient is found to be dependent on the ratio of the temperature and density gradients (η≡d ln T/d ln n). The eigenmodes are seen to be flute-like. The stability boundary was found to be similar when both ions and electrons are collisional, when they are collisionless, and for collisional electrons and collisionless ions. The largest stable pressure gradients are obtained for η⩾2/3. As the collisionality is reduced one observes some reduction of the region of stability.
Power threshold and optical gain of a third order mode optically pumped AlGaAs laser
Authors: Semaltianos N. G.
Published: July 2002

We have characterized in detail the performance of an optically pumped semiconductor laser device which emits radiation on the third order laser mode. The sample was grown by molecular beam epitaxy and consists of an Al0.11Ga0.89As quantum well sandwiched between an Al0.50Ga0.50As/Al0.25Ga0.75As/AlAs double heterojunction. The structure was specially designed to emit laser radiation at 775 nm on the third order mode and used as a pump source towards generating twin photons at 1.55 μm on the fundamental mode via parametric fluorescence by utilizing the principle of modal phase matching between fundamental and third order laser modes in III–V semiconductors. The spectral and pumping power dependencies of the single pass optical gain of the structure were measured by varying the length of the excited region on the sample and recording the corresponding amplified spontaneous emissions. A maximum gain of 120 cm−1 was measured. The threshold for laser emission of barlike samples with surface waveguide ridges was measured systematically vs cavity length and sample temperature. The optimum cavity length for obtaining the lowest threshold was greater than 1.2 mm. Threshold equal to 42 kW/cm2 was measured at room temperature for a 1.44 mm long cavity, and the characteristic temperature which expresses the threshold in the exponential form was equal to 117 K. The transverse angular dependence of the third order mode laser radiation was measured for different pumping powers for processed as well as unprocessed samples.
Observation of large optical anisotropy and valence band splitting in AlInAs self-assembled lateral quantum wells
Authors: Francoeur S. , Hanna M. C. , Norman A. G. , Mascarenhas A.
Published: July 2002

Self-assembled lateral quantum wells in alloys of AlInAs, epitaxially deposited by metal–organic chemical vapor deposition on InP, are studied by transmission electron microscopy, modulation spectroscopy, and photoluminescence. Under particular growth conditions, the growth of a homogeneous layer results in the spontaneous self-assembly of a sequence of quantum wells with quantization axes oriented along the [110] direction. With respect to a homogeneous alloy of similar average composition, the band gap reduction observed is as large as 360 meV. A polarization anisotropy exceeding 90% is observed for the lowest energy transition and a large valence band splitting of 139 meV separates the heavy- and light-hole-like valence bands.
Color mapping by scanning tunneling microscopy: Chemical analysis of metal surfaces
Authors: Downes Andrew , Guaino Philippe , Dumas Philippe
Published: July 2002

We present true color maps of a metal surface imaged by scanning tunneling microscopy (STM). Light emission spectra were acquired at each imaging pixel, and converted into a real color map. A rough gold film was shown to exhibit minimal color changes across the sample, so spectra are dependent on material and not sample geometry, due to a small radius tip. A larger tip was still able to distinguish between Ag and Cu clusters with ∼10 nm resolution, despite the onset of geometric effects. We conclude that color mapping represents an ideal way of identifying metals in STM on the nanometer scale.
Properties of a Fe/GaAs(001) hybrid structure grown by molecular-beam epitaxy
Authors: Chye Y. , Huard V. , White M. E. , Petroff P. M.
Published: July 2002

We report on the epitaxy of Fe thin films on GaAs(001) using molecular-beam epitaxy with two different growth methods aimed at suppressing Fe and GaAs interdiffusion. These methods make use of low-temperature deposition at −150 °C and/or of an ultrathin Al interlayer, respectively. Good-quality single-crystal Fe films were obtained. The magnetic properties of the Fe films show square hysteresis loops and clear in-plane magnetic anisotropy with well-defined easy hard axes. The photoluminescence of an Al0.3Ga0.7As/GaAs quantum well in close proximity to the Fe film is measured in order to examine the quality of the Fe/GaAs interface.
Study on the effect of plasma treatment on TiN films in N2/H2 atmosphere using x-ray reflectivity and secondary ion mass spectroscopy
Authors: Banerjee S. , Gibaud A. , Chateigner D. , Ferrari S. , Wiemer C. , Dekadjevi D. T.
Published: July 2002

We report the effect of plasma treatment on TiN films in N2/H2 atmosphere grown by chemical vapor deposition. The physical parameters and chemical evolution of the film as a function of duration of plasma treatment was studied using grazing incidence x-ray reflectivity (GIXR). From the analysis of GIXR we obtained the electron density profile of the film as a function of its depth. The GIXR data were analyzed using matrix method and distorted wave Born approximation scheme. Comparison of both the analysis schemes gives proper interpretation of the parameters obtained. The results obtained from the analysis of x-ray reflectivity data are supported by time of flight secondary ion mass spectroscopy depth profiling.
Comment on “Stimulated scattering of a light wave in a dusty plasma” [Phys. Plasmas 8, 5053 (2001)]
Authors: Shukla P. K. , Stenflo L.
Published: July 2002

The theory of stimulated scattering of a light wave in a dusty plasma is re-examined, taking into account the dust charge fluctuations. It is shown that the latter somewhat modify the dust-acoustic waves which are involved in the scattering process. The present results significantly improve those of Lee [Phys. Plasmas 8, 5053 (2001)].
Comment on “Effect of flow profile on low frequency drift-type waves in a dusty plasma” [Phys. Plasmas 8, 3150 (2001)]
Authors: Vranješ J. , Pandey B. P. , Poedts S.
Published: July 2002

It is pointed out that a recently published study [Phys. Plasmas 8, 3150 (2001)] of the effects of magnetic shear and shear flow on dust-drift waves has already been studied earlier. Further, the results obtained in Phys. Plasmas 8, 3150 (2001) are erroneous as the shear flow effect has been included in an inappropriate manner.
Response to “Comment on ‘Effect of flow profile on low frequency drift-type waves in a dusty plasma’ ” [Phys. Plasmas 9, 1481 (2002)]
Authors: Chakraborty M. , Sarmah D. , Sen S.
Published: July 2002

The objections of Vranejes et al. are unfounded and are shown to be based on the complete misunderstanding of our manuscript by the authors.
Optical properties of inorganic (SiO2)1−x(Nd2O3)x alloy films for the color filter of plasma display panel
Authors: Lee D. K. , Seo S. M. , Lee S. G. , Sohn S. H. , Park S. H. , Kim H. M.
Published: July 2002

In order to improve the primary color purity of the plasma display panel (PDP), inorganic (SiO2)1−x(Nd2O3)x alloy films have been fabricated by the rf-magnetron sputtering method, and their optical properties have been investigated as functions of Nd2O3 contents in films and thickness of films. The study has revealed that absorption in (SiO2)1−x(Nd2O3)x films is due to intratransition within the 4f shell of the Nd3+ ion, and that it becomes larger with increasing Nd3+ ion concentrations in films and film thickness. In the PDP devices with our band rejection color filters, luminances from neon gas discharge itself and sidebands of phosphors are sufficiently reduced, resulting in wider color gamut and higher color purity.