bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy transfer from fluorescent thin films to metals in near-field optical microscopy: Comparison between time-resolved and intensity measurements
Authors: Pagnot Thierry , Barchiesi Dominique , Tribillon Gilbert
Published: July 2002

The fluorescence intensity, fluorescence decay time, and shear-force images of a thin film have been simultaneously investigated by reflection scanning near-field optical microscopy using an uncoated fiber tip. The sample is made of a europium chelate embedded in a 32-nm thick polymer layer that coats a periodic structure of gold and chromium. It is contended that the three images carry different and somewhat complementary information; the shear force supplying the sample profile while the intensity mainly depends on the local sample’s reflectance. Moreover, the decay time exhibits the local-energy-transfer process that takes place between the metallic substrate and the dye layer.
Co
59
nuclear magnetic resonance studies of magnetic excitations in ferromagnetic nanowires
Authors: Scarani Valerio , De Riedmatten Hugues , Ansermet Jean-Philippe
Published: July 2002

Magnetic excitations of cobalt-based nanowires are investigated by measuring the nuclear spin-lattice relaxation (SLR) of Co59 in zero and 1 T applied field. Co/Cu multilayers are shown to have a faster SLR than bulk Co. This relaxation is of magnetic origin and due to the layered structure. Oxidized wires have a temperature dependence of the SLR which provides direct evidence of the thermal fluctuation of the uncompensated spins of the CoO grains at the surface of the wires.
Magnetic study of texture in multifilamentary (Bi, Pb)2Sr2Ca2Cu3O10+x tapes: Evidence for anisotropic orientation
Authors: Cimberle M. R. , Ferdeghini C. , Grasso G. , Pallecchi I. , Putti M. , Siri A. S.
Published: July 2002

We present a simple method allowing the determination of the degree of texture of superconducting grains inside Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3O10+x tapes from a set of magnetic measurements. This procedure is based on the considerable anisotropy existing between the in-plane and out-of-plane critical current densities of individual crystallites in Bi-based superconducting compounds. By this method, we have monitored the evolution of the precursor Bi2Sr2CaCu2O8+y grain texturing in unreacted multifilamentary tapes in the course of the cold rolling deformation process. Evidence for anisotropic texturing, i.e., different longitudinal and transversal angle with respect to the rolling direction, has been observed. The accuracy of the method is discussed and the results compared with the current literature.
Vapor-grown atomic filaments of graphite
Authors: Okuyama F. , Hayashi T. , Kawasaki M. , Ibe K.
Published: July 2002

Field emission transmission electron microscopy has revealed the presence of atomic filaments extending from the open edge of a graphite cage formed in a glow-discharge plasma. The filaments are vapor grown, presenting complicated deformations such as curling, waving, and looping in the free space. The filaments correspond well to one carbon atom in diameter, strongly indicating that they are linear chains of carbon atoms, the presence of which was earlier suggested by Smalley et al. [Science 269, 1550 (1995)].
A wavelength multiplexer using cascaded three-dimensional vertical couplers
Authors: Liu Bin , Shakouri Ali , Abraham P. , Bowers John E.
Published: July 2002

A four-channel wavelength multiplexer/demultiplexer for sparse wavelength division multiplexing was demonstrated using cascaded three-dimensional (3D) vertical couplers. 17 nm channel spacing with crosstalk less than 15 dB was achieved. Strong coupled vertical couplers were fabricated using wafer bonding to invert a conventionally processed epitaxial layer and bond to a new host substrate. This technology makes the fabrication of 3D photonic integrated circuits and the realization of multilevel optical interconnects possible.
Metal-sulfur-based air-stable passivation of GaAs with very low surface-state densities
Authors: Ashby Carol I. H. , Zavadil Kevin R. , Baca Albert G. , Chang P.-C. , Hammons B. E. , Hafich M. J.
Published: July 2002

An air-stable electronic surface passivation for GaAs and other III–V compound semiconductors that employs sulfur and a suitable metal ion, e.g., Zn, and that is robust towards plasma dielectric deposition has been developed. Initial improvements in photoluminescence are twice that of S-only treatments and have been preserved for >11 months with SiOxNy dielectric encapsulation. Photoluminescence and x-ray photoelectron spectroscopies indicate that the passivation consists of two major components with one being stable for >2 years in air. This process improves heterojunction bipolar transistor current gain for both large and small area devices.
Stability of the single-mode output of a laser diode array with phase conjugate feedback
Authors: Jensen S. Juul , Løbel M. , Petersen P. M.
Published: July 2002

The stability of the output of a single-mode laser diode array with frequency selective phase conjugate feedback has been investigated experimentally. Both the long-term stability of the laser output and the sensitivity to feedback generated by external reflection of the output beam are examined. The output power and the center wavelength are found to be extremely stable in a 100 h stability measurement. External feedback of the output beam into the laser is seen to decrease both the spatial and the temporal coherence of the output significantly. We outline an approach to obtain a stable single-mode output when external feedback is present using spatial filtering in the path of the output beam.
1/f noise through the metal–nonmetal transition in percolating composites
Authors: Breeze A. J. , Carter S. A. , Alers G. B. , Heaney M. B.
Published: July 2002

We have measured the 1/f noise through the metal–nonmetal transition in carbon black/polymer composites as a function of temperature and doping. At the electronic transition, the resistivity power spectrum Sρ varies as Sρ∼ρQ, with Q=2.77, in agreement with classical three-dimensional percolation. At lower temperatures, a crossover to tunneling-dominated transport occurs with Sρ∼ln Sρ/ρ2. Our results show that 1/f noise can be a more sensitive technique than resistivity itself for probing transport behavior near a percolation-induced electronic transition.
Room-temperature silicidation using radiation-enhanced diffusion in hydrogenated amorphous silicon
Authors: Shannon J. M. , Chai M. K. , Sealy B. J.
Published: July 2002

Amorphous disilicides of the refractory metals chromium and molybdenum have been formed at room temperature in hydrogenated amorphous silicon. The silicides are produced by radiation-enhanced diffusion during bombardment through a thin metal film on the surface of the amorphous silicon. The properties of the layers are similar to those produced by thermal annealing at temperatures <300 °C.
Ultrafast two-dimensional electron gas detector and mixer for terahertz radiation
Authors: Yngvesson K. S.
Published: July 2002

A hot-electron bolometric detector and mixer (heterodyne detector), which uses the nonlinearities of the heated two-dimensional electron gas medium, is proposed and analyzed. The cooling process of the detector is through diffusion of the electrons into the contacts; a time constant of 1 ps and responsivity of 3000 V/W are calculated for a device which is 0.8 μm long. The predicted double-sideband receiver noise temperature for the mixer version is in the range 1000–2000 K at 1 THz, with a 100 GHz intermediate frequency bandwidth. The operating temperature would be 77 K and the local oscillator power 1 μW.
Accurate determination of quasi-Fermi-level separation of semiconductor lasers
Authors: Wu Linzhang
Published: July 2002

For characterization of semiconductor lasers, quasi-Fermi-level separation is a critical parameter due to its relationship with carrier density and gain. Its determination should be made with accuracy within ±10 meV. In this letter, we report a simple technique to accurately measure the quasi-Fermi-level separation, photon energy at gain peak, and intrinsic optical loss for a given current. Through theoretical calculation and experimental results, we believe that the quasi-Fermi-level separation measured by our technique is accurate to ±0.5 meV.
Adatom condensation and quantum dot sizes in InGaAs/GaAs (001)
Authors: Leon R. , Wellman J. , Liao X. Z. , Zou J. , Cockayne D. J. H.
Published: July 2002

The sizes and concentrations of capped and surface InGaAs/GaAs quantum dots (QDs) grown under the same conditions have been investigated. Comparisons obtained with transmission electron microscopy and scanning probe microscopy imaging show a significant enlargement in the sizes of surface QDs compared with capped QDs. This discrepancy in dot dimensions increases with decreasing island surface densities and can be partially explained by thermal adatom condensation during sample cooling. These findings suggest a technique to estimate adatom concentrations and their migration lengths in strained heteroepitaxy.
Conical diamond tips realized by a double-molding process for high-resolution profilometry and atomic force microscopy applications
Authors: Beuret C. , Akiyama T. , Staufer U. , de Rooij N. F. , Niedermann P. , Hänni W.
Published: July 2002

High aspect ratio diamond tips with a small radius of curvature were fabricated by means of a double-molding process and hot-filament chemical vapor deposition of diamond. The tips proved to perfectly reproduce the geometry of anisotropically etched silicon tips, which were used as first mold. The diamond tips were mounted on stubs for contact profilometry imaging as well as transferred to cantilevers for atomic force microscopy measurements. Both profilometry and atomic force microscopy investigations have demonstrated the high application potential of these tips.
Theoretical analysis of filamentation and fundamental-mode operation in InGaN quantum well lasers
Authors: Chow W. W. , Amano H. , Akasaki I.
Published: July 2002

Filamentation and, consequently, output beam quality in InGaN quantum-well lasers are found to be strong functions of quantum-well width because of the interplay of quantum-confined Stark effect and many-body interactions. For an In0.2Ga0.8N/GaN gain medium, the antiguiding factor in a thick 4 nm quantum well is considerably smaller than that for a narrow 2 nm one. As a result, lasers with the thicker quantum well maintain fundamental-mode operation with wider stripe widths and at significantly higher excitation levels.
Modification of GaN Schottky barrier interfaces probed by ballistic-electron-emission microscopy and spectroscopy
Authors: Bell L. D. , Smith R. P. , McDermott B. T. , Gertner E. R. , Pittman R. , Pierson R. L. , Sullivan G. J.
Published: July 2002

Ballistic-electron-emission microscopy (BEEM) and spectroscopy have been used to investigate the properties of Au/GaN interfaces. The effects of in situ and ex situ annealing on the starting GaN surface were examined, with the aim of increasing the surprisingly low value of interface electron transmission observed in previous BEEM measurements. BEEM imaging and spectroscopy have demonstrated that much higher, more uniform transmission across the Au/GaN interface can be achieved. However, while methods were identified that increase transmission by more than an order of magnitude, BEEM spectroscopy indicates that annealing can substantially alter the Schottky barrier height. These barrier height changes at moderate temperatures are attributed to vacancy diffusion.
Linewidth of a resistively shunted high-temperature-superconductor Josephson heterodyne oscillator
Authors: Macfarlane J. C. , Hao L. , Peden D. A. , Gallop J. C.
Published: July 2002

High-temperature-superconducting (HTS) resistively shunted superconducting quantum interference devices, consisting of two yttrium–barium–copper–oxide (YBCO) grain boundary junctions shunted by gold-film resistors of ∼20 μΩ, have been prepared and characterized at temperatures from 17 to 74 K. The small value and stability of the resistor allows narrow-band heterodyne oscillations to be generated between the Josephson oscillations in the individual junctions. The frequency can be precisely controlled in accordance with the ac Josephson effect by adjustment of an external current applied to the YBCO–Au–YBCO shunt resistor, and the linewidth is determined in principle only by Johnson noise in the resistor. Off-chip detection and spectral analysis of the heterodyne signal generated in this way has not been previously reported. Measurements of the signal power (∼nW), the tunability of the center frequency from 5 to 50 MHz, the frequency stability and the linewidth of the heterodyne Josephson oscillation are described. Although linewidth broadening due to nonthermal fluctuations is observed, the linewidth of ∼30 kHz at T=17 K, at a center frequency of 24 MHz, is believed to be the narrowest reported for Josephson oscillations in an HTS device of this type.
Resonant x-ray scattering at the Se edge in liquid crystal free-standing films and devices
Authors: Matkin L. S. , Gleeson H. F. , Mach P. , Huang C. C. , Pindak R. , Srajer G. , Pollmann J. , Goodby J. W. , Hird M. , Seed A.
Published: July 2002

Resonant x-ray diffraction was carried out at the Se K edge in thick free-standing films of a selenophene liquid crystalline material, revealing detail of the structure of the ferro-, ferri-, and antiferroelectric phases. The ferrielectric phase was shown to have a three-layer superlattice. Moreover, the structure of a lower temperature hexatic phase was established. For the antiferroelectric phase, investigations were also carried out in a planar device configuration. The device allowed resonant scattering experiments to be carried out with and without the application of an electric field and resonant data are compared with electro-optic measurements carried out on the same device.
In situ growth study of NiMnSb films on MgO(001) and Si(001)
Authors: Schlomka J.-P. , Tolan M. , Press W.
Published: July 2002

The sputter deposition of thin magnetic NiMnSb films on MgO(001) and Si(001) is investigated by in situ x-ray scattering. It is shown that the roughness of the layers as a function of the film thickness increases according to power laws with unusually large growth exponents. The optimum growth conditions are found on the substrate MgO(001) at temperatures of 250 °C during the deposition.
Experimental observation of anomalous absorption of bulk shear acoustic waves by a thin layer of viscous fluid
Authors: Lwin Mark J. , Gramotnev Dmitri K. , Mather Melissa L. , Bell John M. , Scott Will
Published: July 2002

This letter presents the results of an experimental observation and investigation of the recently predicted anomalous absorption of bulk shear acoustic waves polarized normally to the plane of incidence by an ultrathin layer of viscous fluid between two elastic media. Strong increase of the absorptivity of the incident wave by the fluid layer has been observed at layer thicknesses that are much smaller than the wavelength and wave penetration depth into the fluid. A good agreement between the experimental results and the theoretical predictions has been achieved.
Optical properties of InAs self-organized quantum dots in n–i–p–i GaAs superlattices
Authors: Wang J. Z. , Wang Z. M. , Wang Z. G. , Yang Z. , Feng S. L.
Published: July 2002

The optical properties of InAs quantum dots in n–i–p–i GaAs superlattices are investigated by photoluminescence (PL) characterization. We have observed an anomalously large blueshift of the PL peak and increase of the PL linewidth with increasing excitation intensity, much smaller PL intensity decrease, and faster PL peak redshift with increasing temperature as compared to conventional InAs quantum dots embedded in intrinsic GaAs barriers. The observed phenomena can all be attributed to the filling effects of the spatially separated photogenerated carriers.
Two-wave mixing in Stark geometry photorefractive quantum wells under a magnetic field
Authors: Zhang Y. F. , Sun J. M. , Zhang M. H. , Zhang Z. G. , Huang Q. , Zhou J. M.
Published: July 2002

Using a modified method for measuring photorefractive two-wave mixing gain, we presented the experimental demonstration of nonreciprocal energy transfer during two-wave mixing under an external magnetic field. The nonreciprocal energy transfer is observed with mixing gain approaching 164 cm−1 and showed the characteristics of nonlinearity and saturation. A simple model of resonant tunneling and ultrafast carrier lifetime was proposed to explain these results.
Thermally switched superconducting weak-link transistor with current gain
Authors: Lee S.-B. , Hasko D. G. , Ahmed H.
Published: July 2002

We report on a method of controling the critical current in a superconducting weak-link device. A superconducting weak-link transistor with an integrated, but electrically isolated, heater has been fabricated. The heater raises the temperature of the weak link above the bath temperature thus reducing the critical current required to give an output voltage. A maximum current gain (ratio of critical current change to applied heater current change) of 10.5 was achieved.
Electrically controllable azimuth optical rotator
Authors: Zhuang Zhizhong , Kim Young Jin , Patel J. S.
Published: July 2002

The transformation of the state of polarization (SOP) of light from one state to another can be graphically illustrated by a trajectory on the Poincaré sphere (PS). We use this method to illustrate the control of the azimuth SOP rotation on the PS. Traditionally, azimuth rotation is achieved by the use of a Faraday rotator or by the mechanical movements of birefringent wave plates. In this letter, an electrically controllable azimuth optical rotator is introduced theoretically and verified experimentally. It consists of two quarter-wave plates and one liquid-crystal variable wave plate and allows polarization rotation of an arbitrary polarized light by an angle determined by the magnitude of the applied field. This electrical approach avoids the errors and inconvenience associated with the magnetic field and the mechanical movements of other methods.
Features of hydrogenated amorphous silicon films developed under an unexplored region of parameter space of radio-frequency plasma-enhanced chemical vapor deposition
Authors: Hazra Sukti , Middya A. R. , Longeaud C. , Ray Swati
Published: July 2002

Searching to improve stability of electronic properties under intense light illumination, hydrogenated amorphous silicon (a-Si:H) films have been fabricated by radio-frequency plasma-enhanced chemical vapor deposition with helium dilution of silane. The deposition conditions which correspond to the transition between the α regime and the powder regime have not been explored properly yet. The resulting materials show many new features: hydrogen bonding mostly monohydride, lower bonded hydrogen content, compact structure, higher efficiency-mobility-lifetime product (ημτ) and density of states (DOS) above Fermi level lower than the reported values of the state-of-the-art a-Si:H films. The saturation time under light-soaking (AM 1) is fast (within 20 h) and the saturated value of ημτ and the DOS above the Fermi level is comparable to that of annealed state standard a-Si:H films.
Effect of plasma-induced damage on interfacial reactions of titanium thin films on silicon surfaces
Authors: Yamaguchi T. , Nikoh H. , Hama A. , Fujimura N. , Ito T.
Published: July 2002

Solid-state reactions of titanium thin films on Si surfaces damaged and amorphized by CHF3/O2 plasma treatment were investigated. The formation temperature of the C49–TiSi2 phase increased due to plasma-induced damage and contamination from decomposed gas elements. The presence of a plasma-induced damage layer suppressed the interdiffusion of Ti and Si. The Ti5Si3 phase was formed initially at an annealing temperature of 400 °C when a plasma-induced damage layer was present at the interface. The increase of the C49–TiSi2 formation temperature may be caused by the transformation of the Ti5Si3 phase into C49–TiSi2 rather than by the direct nucleation of the C49–TiSi2 phase with a clean interface.
Spatial instability of the nonlinear ferromagnetic resonance in uniaxial films
Authors: Popkov A. F. , Wöbbeking T. , Dötsch H. , Korneev V. I.
Published: July 2002

The spatial instability of the nonlinear magnetization precession in uniaxial films with low magnetization is analyzed analytically and numerically solving Landau–Lifshitz equations. The foldover effect is essential in this geometry. The formation of spatial soliton-like magnetization precessions is predicted for nonuniform driving inductions exceeding the threshold value. Time–space instability boundaries of the obtained soliton-like structures are calculated. The numerical simulations show that these structures are stabilized at the boundaries of the foldover region. This behavior is in qualitative agreement with a recent experiment where a spatial pattern formation by a nonuniformly driven ferromagnetic resonance in a garnet film has been observed.
High-Tc gradiometric superconducting quantum interference device and its incorporation into a single-layer gradiometer
Authors: Millar A. J. , Romans E. J. , Carr C. , Eulenburg A. , Donaldson G. B. , Maas P. , Pegrum C. M.
Published: July 2002

We describe a first-order gradiometric dc superconducting quantum interference device (SQUID) and its incorporation into a first-order directly coupled single-layer gradiometer. The gradiometric SQUIDs were fabricated from a single layer of YBa2Cu3O7, with a silicon dioxide insulating layer and a gold crossover structure. For several gradiometric SQUIDs, with estimated inductances of order 67 pH, we measured parasitic effective areas in the range 1–2 μm2, approximately two orders of magnitude lower than for conventional narrow linewidth SQUIDs of similar inductance. For a single-layer gradiometer incorporating a gradiometric SQUID, we measured a parasitic effective area of 95 μm2. We demonstrate that for this device, the SQUID itself makes a negligible contribution to the overall parasitic effective area. We show that the improved balance leads to better performance in an unshielded environment.
Interference-induced blockage of direct tunneling current in metal–insulator–semiconductor structure
Authors: Mohaidat J. M. , Ahmad-Bitar Riyad N.
Published: July 2002

Current density–field (J–E) characteristics of a metal–insulator–heavily doped semiconductor structure were computed numerically by solving the time-dependent Schrödinger equation for insulators (barriers) of different potentials and widths. It is shown that the (J–E) profile exhibits three regions of different J(E). The region of high E is found to consist of a slowly increasing part followed by a fast increasing one. The slow region part is attributed to quantum mechanical interference effects at the metal–insulator interface. The presence of this region in experimental results should be used as an evidence of tunneling-dominated conduction. The whole computed J–E curves are supported by experimental results published on thin films of semiconductor oxides and varistors. The effects of barrier width and height on the J–E characteristics are also discussed.
Temperature dependence of the iron donor level in silicon at device processing temperatures
Authors: Kohno H. , Hieslmair H. , Istratov A. A. , Weber E. R.
Published: July 2002

Iron depth profiles in a p-type silicon epitaxial layer on a p+-type silicon substrate have been examined by deep-level transient spectroscopy and computer simulations. By comparing the experimental results with the simulations, we revealed the position of the iron deep donor level to be 0.42±0.04 eV from the valence-band edge at 412–580 °C, which is in a device processing temperature range. The iron donor level was nearly temperature independent within error. Knowing the temperature dependence of the iron donor level at the device processing temperatures, we can design iron gettering in silicon more precisely.
GaNAs avalanche photodiode operating at 0.94 μm
Authors: Kinsey G. S. , Gotthold D. W. , Holmes A. L. , Streetman B. G. , Campbell J. C.
Published: July 2002

A p-i-n avalanche photodiode (APD) using GaNAs grown on GaAs has been demonstrated. Characterization of the excess noise in the material was used to determine that the ratio of ionization coefficients (k=β/α) is k=0.4. The quantum efficiency was above 25% at 0.94 μm for 0.75% nitrogen incorporation. The APDs exhibited low dark currents (<60 nA/mm2 at 90% of breakdown) and a gain-bandwidth product of 42 GHz. GaNAs therefore shows promise for extending the operation of GaAs-based APDs to longer wavelengths.
Desorption of organic species from the GaAs (100) surface at low temperatures using low energy electron irradiation in a hydrogen ambient
Authors: Chen Y. , Schmidt J. , Šiller L. , Barnard J. C. , Palmer R. E. , Burke T. M. , Smith M. P. , Brown S. J. , Ritchie D. A. , Pepper M.
Published: July 2002

We present a technique for the controlled removal of organic adsorbates from the GaAs (100) surface incorporating hydrogen dosing (atomic or molecular) combined with low-energy electron irradiation. High-resolution electron energy-loss and Auger electron spectroscopes verify a considerable desorption of carbon/hydrocarbons following electron irradiation at 50 eV under a hydrogen atom flux even at room temperature. At a sample temperature of 500 °C, static secondary ion mass spectroscopy data demonstrate selective area removal of carbon from the surface following 25 eV electron irradiation in a molecular hydrogen ambient, with a desorption rate controlled by the incident electron flux.
Surface relief gratings from electrostatically layered azo dye films
Authors: He Jin-An , Bian Shaoping , Li Lian , Kumar Jayant , Tripathy Sukant K. , Samuelson Lynne A.
Published: July 2002

Surface relief gratings (SRGs) were fabricated on composite films assembled by alternate electrostatic deposition of a polyelectrolyte, poly(dimethyldiallylammonium chloride), and an organic azo dye, congo red. The modulation of SRGs was found to increase with the thickness of the matrix films. Significant photochemical bleaching of the azo dye in the polymeric microenvironment as well as gradient-force-induced migration of the small azo dye contributes to the formation of the SRG structure. This finding demonstrates a facile method to fabricate SRGs for optical and information storage applications using commercially available azo dyes and polyelectrolytes.
Transient characteristics of self-phase modulation in liquid crystals
Authors: Ono Hiroshi , Kikuhara Junichi
Published: July 2002

Transient properties of nonlinear refractive index change originating in photothermal effects in guest-host liquid crystal (GHLC) have been characterized by use of heat-conduction analysis. By theoretical calculations using time-dependent heat-conduction analysis, we have a time constant of about 23 ms, in good agreement with the experimental observation (about 30 ms). The characterization technique described here is very useful for characterizing the quantitative properties of photothermal effects in GHLC.
Surface segregation determination by epitaxy temperature steps
Authors: Kasper E. , Oehme M.
Published: July 2002

A method for determination of surface segregation during molecular-beam epitaxy is proposed. At constant beam fluxes, the temperature is switched which causes a segregation-dependent doping profile. The segregation ratio is extracted from the integrated profile avoiding problems with limited depth resolution in the nanometer regime. The method was tested with boron segregation on (100) silicon (T=500–700 °C). A clear proof of the concentration dependence of the boron segregation is given. At 600 °C, the segregation ratio rs decreases from 55 to 12 nm when the doping level is increased from 3.5×1018 to 7.5×1019 cm−3.
Low pressure oxygen annealing at high temperature for high quality sputtered YBa2Cu3O7−δ films
Authors: Zhai H. Y. , Chu W. K.
Published: July 2002

We present an improvement in the procedure for fabricating YBa2Cu3O7−δ (YBCO) films by dc sputtering. An in situ anneal was used: (i) between as-deposition temperature Ts and 650 °C, 10 min annealing with oxygen pressure less than 20 Torr and (ii) cooling to room temperature in a pure argon atmosphere (oxygen free). This process has yielded stable, high-quality YBCO films with Tc of 92 K. Films were characterized using Rutherford backscattering spectrometry/channeling, elastic resonance reaction O16(α,α)16O and x-ray diffraction techniques. They were found to have ideal 1-2-3 stoichiometry and oxygen content in addition to good crystalline quality. This new procedure can improve the epitaxial quality of in situ multilayered structure and is more favorable for device formation than the standard procedure.
Nickel-platinum alloy monosilicidation-induced defects in n-type silicon
Authors: Chi D. Z. , Mangelinck D. , Dai J. Y. , Lahiri S. K. , Pey K. L. , Ho C. S.
Published: July 2002

Electrically active defects induced by the formation of nickel–platinum alloy monosilicide (formed at 600–800 °C) has been studied in n-type silicon using deep level transient spectroscopy and transmission electron microscopy measurements. A Ni-related electron trap level at Ec−0.42 eV is observed after silicidation at 600 °C or above and a Pt-related electron trap level at Ec−0.50 eV is detected after silicidation at 700 °C or above. Two hole trap levels at Ev+0.22 and Ev+0.28 eV are also detected, Ev+0.22 eV level for silicidation at 700 °C or above and Ev+0.28 eV level for 600 °C silicidation. For the sample silicided at 600 °C, an additional electron trap level (located at Ec − 0.16 eV) with a broad spectral peak is detected in the near-surface region (<0.65 μm) of the sample in which some {311} type defects of 50–100 Å long are also observed. Most of observed electrically active defects have been found to be present in near-surface regions (<2 μm). Lowest total defect concentration is observed in the sample silicided at 700 °C where lowest reverse saturation current is also observed, indicating that the Ni(Pt) monosilicidation-induced electrically active defects are effective recombination/generation centers.
Chemisorption pathways and Si 2p core-level shifts for the interaction of spherosiloxane clusters with Si(100): Implications for photoemission in Si/SiO2 systems
Authors: Raghavachari Krishnan , Pasquarello Alfredo , Eng Joseph , Hybertsen Mark S.
Published: July 2002

Using a first-principles density functional approach, we investigate the chemisorption mechanism for the interaction of spherosiloxane (H8Si8O12) clusters on Si(100). Our transition state studies reveal that the chemisorption pathway with the lowest activation barrier corresponds to attachment via Si–O bond cleavage across a surface dimer. Using the relaxed surface structure from this “cracked cluster” model, we calculate Si 2p core-level shifts, including core–hole relaxation effects, and show that the calculated values are in excellent agreement with the positions and intensities of all the experimentally observed core-level shifts.
Structural characterization of AlAs/AIP superlattices
Authors: Oishi Yuji , Nagano Masahiro , Ohnuma Toshiharu
Published: July 2002

( AlAs ) n /( AlP ) n  (n=1–3) short-period superlattices were grown by gas-source migration-enhanced epitaxy at a low growth temperature. Dynamical-theory simulations of x-ray diffraction patterns were conducted and showed good agreement with experimentally obtained patterns. In addition, cross-sectional transmission electron microscopy analysis was performed, which confirmed that high-quality short-period superlattices of AlAs/AlP were grown.
Self-field ac losses of a twisted multifilamentary (Bi, Pb)2Sr2Ca2Cu3O10/AgAu tape
Authors: Friend C. M. , Huang Y. B.
Published: July 2002

Self-field loss measurements at 77 K on a superconducting (Bi, Pb)2Sr2Ca2Cu3O10/AgAu tape with twisted filaments are presented. Using the first- and third-harmonic components of the electric field, the hysteretic losses are separated from the total loss. At peak transport currents less than half the critical current, the hysteretic losses are considerably reduced. However, sizable nonhysteretic losses are also observed. At higher currents, the hysteretic loss increases, dominating the total loss, and is similar to that for an untwisted tape.
Strain-induced optical anisotropy in self-organized quantum structures at the E1 transition
Authors: Prieto J. A. , Armelles G. , Priester C. , Garcı́a J. M. , González L. , Garcı́a R.
Published: July 2002

In-plane optical anisotropies of (001)-oriented InAs/InP self-assembled quantum wires and dots structures are studied by means of photoreflectance in the spectral region of the E1 transition of bulk InAs. The energy position of the transition observed in the quantum wires depends on the light polarization; quantum dots do not exhibit, in contrast, such an optical anisotropy. This anisotropy is attributed to the splitting of the four-fold degenerate E1 transition produced by the strong triaxial behavior of the strain that appears in wires and not in dots.
Critical size for localization of the L-like conduction states in InAs quantum dots grown on GaAs
Authors: Prieto J. A. , Armelles G. , Garcı́a J. M. , González L. , San Paulo A. , Garcı́a R.
Published: July 2002

The localization of the L-like conduction states is found to change from the islands to the substrate in InAs quantum dots grown on GaAs as the island-size decreases. This is due to a size-induced modification of the strain state of the islands. The critical size should correspond to dislocation formation. As a result, small InAs islands coherently strained to GaAs exhibit optical properties markedly different from those of bulk InAs.
Alignment control method for liquid crystalline molecules and its application for an all-optical device
Authors: Seomun San-Seong , Fukuda Takashi , Matsuda Hiro , Miyachi Hiroshi , Kato Masao
Published: July 2002

A nematic liquid crystalline monomer, containing photocrosslinkable divinyl and azobenzene moieties as functional groups was synthesized. Laser beam irradiation on a liquid crystalline cell of this material is capable of fabricating a very thin cross linked polymer layer on the alignment surface. The crosslinked polymer layer modifies the anchoring force between the alignment surface and liquid crystalline molecules. Meanwhile, the monomeric azobenzene moiety in the bulk interacts with incident light resulting in molecular reorientation through the trans-cis-trans-photoisomerization cycles. Combining the two characteristics mentioned above, a kind of optical device has been proposed. The driving mechanism of this device is the reversible phototriggered switching of the molecular orientation between the homogeneous and the homeotropic state.
Cd–Ne direct current glow discharge: An efficient source of ultraviolet radiation
Authors: Petrov G. M. , Petrova Ts. , Ogoyski A. , Blagoev A. B.
Published: July 2002

This investigation aims to present data of a potential light source based on Cd. Recent study of cadmium–neon direct current glow discharge at low and intermediate pressure showed that a significant fraction (∼80%) of the input power delivered to the plasma can be converted into resonance radiation, which leads us to conclusion that Cd can be an efficient light source, even more efficient than Hg. The conventional fluorescent lamps contain Hg, but environmental concerns urge for mercury-free light sources. The ultraviolet radiation from Cd(5p1P1) and Cd(5p3P1) resonance states has been investigated and the optimum discharge conditions of a potential light source are determined. At optimum discharge conditions 80%–87% of the input power is converted into resonance radiation.
Single titanium crystals encapsulated in carbon nanocages obtained by laser vaporization of sponge titanium in benzene vapor
Authors: Chen Hong , Huang Rong-bin , Tang Zi-chao , Zheng Lan-sun , Zhou Guang-wen , Zhang Ze
Published: July 2002

A technique, laser vaporization by ablating at a solid target in the vapor phase, is developed to produce encapsulated titanium nanocrystals. By vaporizing sponge titanium in benzene vapor, the single titanium crystals encapsulated in carbon nanocages have been synthesized in good yields. The sizes of the encapsulated crystals are around 5–15 nm and the numbers of the wrapped graphitic layers are on the order of 3–10 layers. Characteristic lattice spacings and angles observed by high-resolution transmission electron microscopy identify two phases of the nanocrystals inside the carbon onion cavities as α-Ti and β-Ti. The latter has never been stable below 850 °C until the experiment. The encapsulated titanium crystals adsorbed a large amount of hydrogen released in the synthesis.
Strong enhancement of second-order response coefficients in tellurium containing Ag–III–VI2 compounds
Authors: Rashkeev Sergey N. , Lambrecht Walter R. L.
Published: July 2002

First-principles calculations of the second-order optical response coefficients are reported for Ag–III–VI2 compounds with III=Ga, In and VI=S, Se, Te. While both the substitutions of In for Ga and Te for Se or S lower the band gap by similar amounts, the substitution of Se by Te is significantly more favorable for increasing χ(2). The enhancement of χ(2) by a factor 2 from AgGaSe2 to AgGaTe2 is surprising compared to the only modest enhancement obtained in II–VI compounds. The origin of these enhancements is analyzed in terms of the frequency-dependent response functions and the band structures.
Decay dynamics of visible luminescence in amorphous silicon nanoparticles
Authors: Kanemitsu Yoshihiko , Fukunishi Yunosuke , Kushida Takashi
Published: July 2002

We have studied the recombination dynamics of carriers in amorphous silicon (a-Si) nanoparticles prepared by electrochemical anodization of hydrogenated a-Si films. The photoluminescence (PL) lifetime of the fast-decay component in a-Si nanoparticles is shorter than that in crystalline silicon (c-Si) nanoparticles. The energy dependence of the PL lifetime in a-Si nanoparticles is different from that in c-Si nanoparticles. The PL decay dynamics of a-Si nanoparticles is determined by recombination processes of carriers localized in the band-tail state. The origin of the blueshift of the PL spectrum in a-Si nanoparticles will be discussed.
Vacancies in SiGe: Jahn–Teller distortion and spin effects
Authors: Lento J. , Pesola M. , Mozos J.-L. , Nieminen R. M.
Published: July 2002

The electronic structure of a vacancy in silicon-germanium is studied using ab initio total-energy minimization methods. The calculations are based on density-functional theory in the local-spin-density approximation. We report ionic relaxations, defect formation energies and ionization levels of Si and Ge vacancies in a zinc blende model structure (SiGe). The Ge vacancy in SiGe is characterized by symmetry-lowering Jahn–Teller (JT) distortions and a negative-effective-U effect, in those respects resembling the vacancy in elemental silicon. For Si vacancy, the exchange-coupling energy is found to overcome the JT energy, and symmetric high-spin ground states are predicted.
Temperature variation of nonradiative carrier recombination processes in high-quality CuGaSe2 thin films grown by molecular beam epitaxy
Authors: Yoshino Kenji , Maruoka Daisuke , Ikari Tetsuo , Fons Paul J. , Niki Shigeru , Yamada Akimasa
Published: July 2002

The piezoelectric photoacoustic (PPA) measurements for Cu-rich CuGaSe2(CGS)/GaAs(001) epitaxial layer were carried out between liquid helium and room temperatures. The band gap energies of CGS (A, B, and C bands) were measured to be 1.73, 1.83, and 2.04 eV at liquid nitrogen temperature, respectively. The A band was clearly obtained from 5 to 300 K, and the temperature dependence of the peak energy was fitted with the modified Manoogian–Woolley equation. PPA signals for CGS/GaAs (001) epitaxial layers were obtained between liquid helium and room temperature.
Structure variation of intersubband electron–acoustic phonon scattering rate in coupled quantum wells
Authors: Požela K. , Naran S. B. , Leburton J.-P. , Heyman J. N.
Published: July 2002

Intersubband electron–acoustic phonon scattering rates are calculated for asymmetric coupled AlGaAs/GaAs quantum wells (QW) at low temperature. Emphasis is placed on the dependence of the scattering rate on the thickness and position of the AlGaAs barrier in the QW. Strong variation of the scattering rate between the second and the first subbands is obtained for small barrier displacement from the center of the QW. These results show that intersubband scattering rates can be engineered to optimize the performances of far-infrared detectors, lasers, and photovoltaic devices. Moreover, this study shines new light on the discrepancy among recent experimental results for these structures.
Improved thermal stability of GaN{0001} surfaces by adsorbed C60 molecules
Authors: Nienhaus Hermann , Schepers Carsten , Grabowski Stefan P. , Mönch Winfried
Published: July 2002

Adsorption and desorption of C60 molecules on GaN{0001}-1×1 surfaces as well as the surface decomposition by heating were investigated with Auger electron spectroscopy. The first monolayer of C60 forms strong chemical bonds to the substrate atoms. A seven-step annealing procedure at temperatures up to 1275 K is presented which completely removes the adsorbed carbon without decomposing the surface. If the process is applied to clean, uncovered GaN{0001}-1×1 surfaces thermal etching with a significant Ga atom loss is observed. The results indicate that adsorbed C60 increases the thermal stability of the surfaces considerably and that thermal etching begins at defects or steps at the surface where the molecules are most strongly bound.
Superconducting quantum wells for the detection of submillimeter wave electromagnetic radiation
Authors: Rahman Faiz , Thornton Trevor
Published: July 2002

We propose the use of superconducting quantum well structures for use as detectors of submillimeter wave radiation. The energy levels formed due to quantum confinement by superconducting barriers provide a useful system for radiation sensing. The well width could be readily altered by varying the temperature or the strength of an applied magnetic field so that the levels can be shifted in energy. This provides a means of tuning the detector over a range of frequencies in the terahertz range, enabling both photometric and spectroscopic observations. Also, the structure of the device should permit use of cofabricated antennas allowing efficient radiation coupling into the active region of the device. The geometry also allows the possibility of implementing one- and two-dimensional arrays.
Two-dimensional delineation of ultrashallow junctions obtained by ion implantation and excimer laser annealing
Authors: Privitera Vittorio , Spinella Corrado , Fortunato Guglielmo , Mariucci Luigi
Published: July 2002

Junctions shallower than 100 nm, obtained by ion implantation and excimer laser annealing, have been characterized in two dimensions by transmission electron microscopy (TEM) on chemically treated samples. The chemical treatment selectively removes silicon as a function of the B concentration, making thinner the regions where B is present in the cross section of the sample, with respect to the n-type substrate. Both secondary ion mass spectrometry and spreading resistance profiling measurements have been performed, in order to quantify the contour line obtained by TEM in terms of B concentration. The results achieved by the two-dimensional technique show interesting features, related to the particular redistribution of B occurring when silicon is melted by excimer laser annealing irradiation. In particular, a rectangular shape of the doped region obtained by laser annealing could be evidenced, caused by the fast diffusion in the melted material, completely different from the typical half-moon-shaped, thermally annealed, two-dimensional B profile. The feasibility of ultrashallow junctions by laser annealing, with depths below 100 nm and high electrical activation, is demonstrated. However, a huge lateral diffusion in the melted silicon is also to be taken into account when considering excimer laser treatments as an alternative to standard rapid thermal annealing.
Quantum confinement energies in zinc-blende III–V and group IV semiconductors
Authors: Allan G. , Niquet Y. M. , Delerue C.
Published: July 2002

Blueshift of the band gap due to quantum confinement is calculated in a tight-binding model for a series of nine III–V zinc-blende AB (A=Al, Ga, or In, B=As, P, or Sb) and two diamond group-IV (Si and Ge) semiconductor clusters. Analytic expressions for the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are given as a function of the cluster size. Comparison is made to results obtained by the pseudopotential method and to experimental results.
Initial growth of heteroepitaxial 3C–SiC on Si using energetic species
Authors: Tsubouchi Nobuteru , Chayahara Akiyoshi , Kinomura Atsushi , Horino Yuji
Published: July 2002

Structural evolution of initial growth of heteroepitaxial 3C–SiC on Si(100) using mass-separated energetic (∼60 eV) ions of C+ and CH3+ has been investigated by in situ reflection high energy electron diffraction (RHEED). RHEED patterns indicated that carbonization reaction of Si occurred at as low as 590–690 °C by irradiation of C+ and CH3+ with 60 eV. The diffraction pattern of 3C–SiC using CH3+ ions exhibited sharp streak shapes in comparison with the use of C+ ions. The features of a carbonization process using energetic species is discussed.
Photoconductive properties of polysilane copolymers with pendant siloxane groups
Authors: Matsukawa Kimihiro , Tamai Toshiyuki , Inoue Hiroshi
Published: July 2002

The oxygen durability of poly(methylphenylsilane) (PMPS) in photoconduction has been improved by the use of copolysilanes with disiloxane-pendant groups. X-ray photoelectron spectroscopy analysis shows that disiloxane groups of the copolysilanes accumulate on their top-most surface at a much higher concentration than the bulk disiloxane concentration. The preferential coverage of disiloxane groups on the surface evidently leads to formation of a highly oxygen durable surface. The hole drift mobility of the charge carriers in copolysilanes with 5 mol % of disiloxane-pendant groups is over 10−4 cm2 V−1 s−1 at E>105 V cm−1, almost comparable to that of PMPS. It was noted that the practical Xerographic potential decay was stabilized by the copolysilanes, while PMPS deteriorated after oxygen exposure.
Segregation of Si in Ge overlayers grown on Si(100) with hydrogen surfactant
Authors: Kahng S.-J. , Ha Y. H. , Moon D. W. , Kuk Y.
Published: July 2002

Si surface segregation was studied quantitatively in Ge overlayers grown on Si(100)-(2×1) with medium energy ion scattering spectroscopy. The behavior of Si surface peak, as a function of Ge coverage, is explained with known growth structures in the Stranski–Krastanov Ge overlayers. We observed that the intermixing between Ge and Si is not significant in the presence of hydrogen surfactant. Possible microscopic models for the observed results are presented.
Field emission from boron-doped polycrystalline diamond film at the nanometer level within grains
Authors: Andrienko I. , Cimmino A. , Hoxley D. , Prawer S. , Kalish R.
Published: July 2002

Surface morphology, conductivity, and field emission properties of boron-doped polycrystalline diamond film have been studied using scanning tunneling microscopy, current imaging tunneling spectroscopy, and separation-voltage (S–V) spectroscopy focusing on the properties within a single grain. The emission properties show significant spatial variations within single grains at the nanometer level. S–V spectroscopy provided direct values of the field required for the emission from nanometer-sized structures at the surface. Strong correlation between surface conductivity and low-field emission has been found. The results suggest that the emission properties of the film on the nanometer level are determined by local hydrogen termination.