bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-edge x-ray absorption of carbon materials for determining bond hybridization in mixed sp2/sp3 bonded materials
Authors: Coffman F. L. , Cao R. , Pianetta P. A. , Kapoor S. , Kelly M. , Terminello L. J.
Published: July 2002

Near-edge x-ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type. Diamond, chemical vapor deposited (CVD) diamond films of varying quality. Diamond-like carbon (DLC) films, and graphite were examined with this technique and these measurements were compared with Raman spectroscopy results and scanning electron microscopy images of carbon film morphology. For the mixed sp2 and sp3 bonded DLC materials, NEXAFS does not suffer from the large Raman cross-section difference between sp2 and sp3 type bonds, thus allowing unambiguous characterization of carbon thin films with a broader range of sp2/sp3 bonding ratios than possible with Raman spectroscopy alone. This capability was used to determine the transition point where the sequential-CVD carbon film growth technique produces predominately sp3 or sp2 bonded material.
Determination of slant angle of p–n interface by multiwavelength near-field photocurrent measurement
Authors: Saiki T. , Saito N. , Kusano J. , Ohtsu M.
Published: July 2002

Near-field photocurrent measurements with multiwavelength excitation sources are applied to the investigation of a lateral p–n junction grown on patterned GaAs (111)A substrate. In order to probe the internal properties of this device, propagation modes into the sample are utilized retaining high resolution with the contribution of a penetration depth smaller than the aperture diameter. By systematically varying the penetration depth over a wide range up to 900 nm, photocurrent signals due to internal optical response clearly appear. The capability of ‘‘tomographic’’ diagnostics is demonstrated and the slant angle of the p–n interface is determined to be 30±8°.
Antenna-coupled high-T
c bolometers for visible and near-infrared detection using organic dyes as light-harvesting layers
Authors: Jurbergs David C. , Zhao Jianai , McDevitt John T.
Published: July 2002

Antenna-coupled high-Tc bolometers fabricated from YBa2Cu3O7−δ thin films have been prepared using molecular organic dyes. Light-harvesting layers derived from these visible and near-infrared absorbers have been utilized to produce detectors which exhibit wavelength-selective response characteristics in the visible and near-infrared spectral regions. Using such hybrid structures, initial studies documenting efficient energy transfer between molecular dye layers and superconductor surfaces have been completed.
Reliable operation of strain-compensated 1.06 μm InGaAs/InGaAsP/GaAs single quantum well lasers
Authors: Fukunaga Toshiaki , Wada Mitsugu , Hayakawa Toshiro
Published: July 2002

We report the reliable operation of strain-compensated InGaAs/InGaAsP/GaAs 1.06 μm separate confinement heterostructure single-quantum-well laser diodes with tensile-strained InGaAsP barriers grown on GaAs substrate. High band-gap strain-compensation barriers are used to suppress the carrier leakage from a quantum well. This device has a high characteristic temperature of 268 K and low threshold current density of 200 A/cm2 with 0.75 mm cavity length. It was found that the characteristics of lasers without strain-compensation are worse than those of strain-compensated lasers at 1.06 μm wavelength. No catastrophic failure in strain-compensated lasers is observed during 1000 h aging test at 25 °C under an automatic power control of 250 mW while all 1.06 μm lasers without strain-compensation show catastrophic failure within 1000 h. It suggests that the crystal quality of laser with strain compensation is much better than that without strain compensation. The formation of defects caused by the presence of the well with highly compressive strain more than 2% is significantly suppressed using strain-compensated layer with moderate tensile strain of 0.7%.
Photoluminescence study of Si1−yCy/Si quantum well structures grown by molecular beam epitaxy
Authors: Brunner K. , Eberl K. , Winter W. , Jin-Phillipp N. Y.
Published: July 2002

Low-temperature photoluminescence (PL) spectroscopy is applied to investigate pseudomorphic Si1−yCy/Si quantum well structures grown by solid-source molecular beam epitaxy on Si substrates. The influence of substrate temperature during growth, growth rate, C content, and layer width on PL spectra is studied. Distinct band-edge related no-phonon and Si-like TO phonon replica PL lines are observed from samples grown at substrate temperatures of about Ts=500–600 °C. The band gap in strained Si1−yCy alloy layers on Si decreases strongly with increasing C content. Even a single Si0.988C0.012 layer of 60 Å thickness shows clear PL of confined excitons. Si1−yCy layers of 11 Å width reveal band-edge PL for a C content up to about y=6.4%. A high layer quality is observed in transmission electron microscopy. The intrinsic and extrinsic Si1−yCy alloy properties, quantum confinement, and layer quality are discussed on the basis of the PL results.
Excited-state dynamics of thiophene thin films studied by time-resolved degenerate four-wave mixing
Authors: Harris David , Dorsinville Roger , Mukai Takeo
Published: July 2002

The resonant nonlinear optical response and singlet excited-state dynamics in the thin film of polydithieno (3,2-b; 2′, 3′-d) thiophene are studied by time-resolved degenerate four-wave mixing. Our experimental results, using <1 ps excitation at 635 nm, show that bimolecular decay via exciton–exciton annihilation dominates the temporal response at high intensities, thus decreasing the singlet lifetime. The measured rate constant of the singlet annihilation is k2=7.5×10−9 cm3/s. Estimates of the singlet-singlet annihilation, exciton diffusion coefficient, and hopping rate are obtained from the measurements.
Stability of fixed holograms in LiNbO3
Authors: Arizmendi L. , Méndez A. , Álvarez-Bravo J. V.
Published: July 2002

The stability of fixed volume phase holograms in lithium niobate is studied. The new measurement method is able to distinguish between electronic compensation and true erasure. It is found that at temperatures in the range of 70–120 °C both electronic thermal detrapping and ionic movement are active effects. The actual lifetime of fixed holograms is determined in this temperature range. From these measurements, we extrapolate a lifetime for the fixed hologram refractive index change of 3.7 years at room temperature.
Determination of intervalley scattering times in GaAs from electroluminescence spectroscopy of single barrier tunneling devices
Authors: Cockburn J. W. , Finley J. J. , Skolnick M. S. , Wisniewski P. , Grey R. , Hill G. , Pate M. A.
Published: July 2002

We report the results of hot electron electroluminescence (EL) experiments carried out on p-i-n GaAs/AlGaAs single barrier tunneling structures. The EL spectra show peaks arising from recombination of both ballistic and intervalley-scattered electrons with neutral acceptors in the p-type collector region. From the relative intensities of these EL features we have obtained direct spectroscopic measurements of the Γ-L and Γ-X intervalley scattering times for high energy ballistic electrons in GaAs.
Boltzmann machine neuron circuit using single-electron tunneling
Authors: Akazawa Masamichi , Amemiya Yoshihito
Published: July 2002

The inherent stochastic character of single-electron tunneling can be effectively utilized for creating novel electronic circuits having high-level functions. As a sample application, we present a stochastic-response circuit for implementing Boltzmann machine neurons. The circuit consists of a single-electron circuit operating under unstable conditions. It can produce an output of a random 1–0 bit stream with the probability for an output of 1 controlled by an input signal—a task that is difficult for conventional circuits using ordinary electronic devices.
Characterization of multilayer HgCdTe heterostructures by differential absorption spectroscopy
Authors: Ariel V. , Garber V. , Bahir G. , Raizman A. , Sher A.
Published: July 2002

In this work, we apply differential absorption spectroscopy to characterization of multilayer epitaxial HgCdTe samples. Transmission of the sample is measured at room temperature and data filtering is applied to remove noise and interference fringes. We use the spectrum of the interference fringes to estimate the thickness of individual HgCdTe layers. The absorption coefficient is extracted from transmission and differentiated twice with respect to the photon energy, which allows us to determine the band gap of each of the layers. The accuracy of the differential absorption procedure applied to multilayer structures appears to be lower than for single-layer samples. Nevertheless, differential absorption spectroscopy is simple, nondestructive, and applicable at room temperature; consequently, it seems suitable for routine characterization of multilayer HgCdTe wafers.
Rigid-cage effects on the optical properties of the dye 3,3′-diethyloxadicarbocyanine incorporated in silica-gel glasses
Authors: Casalboni M. , Senesi R. , Prosposito P. , De Matteis F. , Pizzoferrato R.
Published: July 2002

We investigated the optical properties of the saturable absorber 3,3′-diethyloxadicarbocyanine iodide incorporated in a matrix of silica-gel glass by the sol-gel technique. Absorption, emission, and fluorescence lifetime were studied as functions of the densification procedures. With respect to the liquid solutions, we observed a strong quenching of the P-isomer luminescence and an increase of the N-isomer fluorescence lifetime. These effects are ascribed to a restriction on the molecular photoisomerization rearrangement caused by the rigidity of the silica cage. Moreover, entrapping reduces intermolecular concentration effects. Finally, different from other glass-embedded dyes, both the absorption and the emission are blue-shifted by about 20 nm.
Paramagnetic resonance in GaN-based single quantum wells
Authors: Carlos W. E. , Nakamura Shuji
Published: July 2002

We report electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AlGaN single-quantum-well light emitting diodes. The dominant feature detected by either technique is a broad resonance (ΔB≈13 mT) at g≈2.01 due to a deep defect. Depending on bias, this defect results in either an increase or a decrease in electroluminescence at resonance while the EDMR gives a current enhancement at resonance. Based on a comparison of signal intensities for the two measurements, we conclude that this defect is present in at least two locations: (1) a nonradiative recombination path, in parallel with the radiative recombination path, and (2) a recombination channel in the depletion region of one of the contacts. A second resonance with g≈1.99 and ΔB≈7 mT is very similar to the deep donor trap, previously observed in double heterostructure diodes, and produces a decrease in both the current and electroluminescence at resonance.
Photoluminescence and electroluminescence of ZnS:Cu nanocrystals in polymeric networks
Authors: Huang Jinman , Yang Yi , Xue Shanhua , Yang Bai , Liu Shiyong , Shen Jiacong
Published: July 2002

ZnS:Cu nanocrystals were synthesized in polymeric networks. X-ray photoemission spectroscopy and atomic absorption data show that the Zn and Cu ion mass contents were about 8.2% and 0.12%, respectively. The particle size of ZnS:Cu nanocrystals was about 3.0 nm, measured by UV-vis spectrum. Due to the quantum size effects, the band gap energy of ZnS nanocrystals was about 4.2 eV. Compared with the photoluminescence of ZnS which peaks at 390 nm, the photoemission of ZnS:Cu/polymer thin films was peaking at 415 nm because of Cu acting as luminescent centers. The ZnS:Cu/polymer was also used to fabricate light-emitting diode (LED), as the emitting layer of LED, the blue light of electroluminescence was observed at room temperature, and its turn-on voltage was less than 4 V.
An efficient supersonic chemical oxygen–iodine laser operating without buffer gas and with simple nozzle geometry
Authors: Furman D. , Barmashenko B. D. , Rosenwaks S.
Published: July 2002

We report on an efficient supersonic chemical oxygen-iodine laser, energized by a jet-type singlet oxygen generator, operating without primary buffer gas and applying simple nozzle geometry and transonic mixing of iodine and oxygen. Output power of 177 W with chemical efficiency of 17% was obtained in a 5 cm gain length for Cl2 flow rate of 11 mmol/s. The power is almost unaffected by water vapor in the medium.
Phonon properties and microstructure of annealed LiTaO3:Nd
Authors: Wu X. L. , Bao X. M. , Jiang S. S. , Feng D. , Tong S.
Published: July 2002

Phonon properties and microstructure of annealed Nd-doped LiTaO3 (LT:Nd) were examined by means of Raman scattering and infrared spectra. Raman spectra show the splitting of A1(TO) mode at 204 cm−1 and the appearance of an additional shoulder peak at ∼208 cm−1, indicating that the homogeneous distribution of Nd ions leads to the structural recovery of partial oxygen octahedra centered with Li and Ta ions, but the microstructural deviation from original LT trigonal system still exists. The enhancement of E(TO) mode intensities and the reduction of A1(TO) mode intensities in the A1+E symmetry spectrum are mainly attributed to the microstructural deviation of LT:Nd and the changed photorefractive effect due to annealing. Infrared spectra in the OH stretching region suggest that the changed photorefractive effect arises from the displacements of positive ions along the optical z axis.
Micro-electroreflectance and photoreflectance characterization of the bias dependence of the quantum confined Stark effect in a fabricated 0.98 μm InGaAs/GaAs/InGaP laser
Authors: Aigouy Lionel , Pollak Fred H. , Gumbs Godfrey
Published: July 2002

Using electro- and photoreflectance with a spatial resolution of ≈10 μm we have evaluated the energy of the fundamental conduction to heavy-hole (1C–1HH) quantum transition of a fabricated 0.98 μm InGaAs/GaAs/InGaP p-i-n quantum well laser structure as a function of bias and position on the laser stripe. From a comparison of the measured forward/reverse bias dependence of the 1C–1HH energy with a theoretical calculation of the quantum confined Stark effect, we have been able to evaluate the built-in electric field and width of the insulating region.
Chemical vapor deposition of titanium–silicon–nitride films
Authors: Smith Paul Martin , Custer J. S.
Published: July 2002

Titanium–silicon–nitride films were grown by metal-organic chemical vapor deposition. At temperatures between 300 and 450 °C, tetrakis(diethylamido)titanium, ammonia, and silane react to form films with average compositions near the TiN–Si3N4 tie line and low impurity contents (C<1.5 at. %, H between 5 and 15 at. %, with no other impurities present). The film resistivity is a strong function of Si content in the films, ranging continuously from 400 μΩ cm for pure TiN up to 1 Ω cm for films with 25 at. % Si. Step coverages of approximately 75% on 0.35 μm, 3:1 aspect ratio trenches, and 35%–40% on 0.1 μm/10:1 trenches are found for films with resistivities below 1000 μΩ cm. These films are promising candidates for diffusion barriers in microelectronic applications.
Ballistic electron luminescence studies of superlattice minibands
Authors: Petrov M. V. , Lyon S. A.
Published: July 2002

Short-period superlattice minibands have been studied by ballistic electron luminescence spectroscopy. Using a combination of optical and electrical measurements in a single device, electron transport through an AlGaAs/GaAs superlattice was observed. The optical measurement provided a precise energy scale for calibration of voltages obtained in the electrical experiment. A three terminal n-p-p device was used, where the electrons were injected through an emitter-base tunnel barrier into a p-type base, which was separated from the p-doped collector by a superlattice. Luminescence emitted by ballistic electrons recombining in the base was used to measure their kinetic energy. Oscillations in the transistor gain were detected and are due to transport through the superlattice miniband.
Ideal anodization of silicon
Authors: Yamani Zain , Thompson W. Howard , AbuHassan Laila , Nayfeh Munir H.
Published: July 2002

Silicon has been anodized such that the porous layer is passivated with a homogeneous stretching phase by incorporating H2O2 in the anodization mixture. Fourier transform infrared spectroscopy measurements show that the Si–H stretching mode oriented perpendicular to the surface at ∼2100 cm−1 dominates the spectrum with negligible contribution from the bending modes in the 600–900 cm−1 region. Material analysis using Auger electron spectroscopy shows that the samples have very little impurities, and that the luminescent layer is very thin (5–10 nm). Scanning electron microscopy shows that the surface is smoother with features smaller than those of conventional samples.
Thermal conductivity of isotopically enriched Si
Authors: Capinski W. S. , Maris H. J. , Bauser E. , Silier I. , Asen-Palmer M. , Ruf T. , Cardona M. , Gmelin E.
Published: July 2002

We have used an optical pump-and-probe technique to measure the temperature dependence of the thermal conductivity, κ(T), of isotopically pure Si. The sample was made from 99.7% Si28 by liquid phase epitaxy. Measurements were performed over the temperature range of 100–375 K. We found an increase in the thermal conductivity of isotopically pure Si, as compared to Si of natural isotopic abundance, throughout the entire temperature range. The results were theoretically reproduced by appropriately scaling the parameters used recently to fit the thermal conductivity of Ge samples with different isotopic compositions. A maximum in κ(T) of ∼4×104 W m−1 K−1 is predicted for Si28 at T≃33 K.
A time resolved double pump–probe experimental technique to characterize excited-state parameters of organic dyes
Authors: Swatton Stewart N. R. , Welford Kevin R. , Hollins Richard C. , Sambles J. Roy
Published: July 2002

We report a novel time resolved double pump–probe experimental technique that may be used to characterize the excited-state parameters of organic dyes. We show that by monitoring the time evolution of the transmittance of a dye after excitation with two pump pulses, the excited singlet and triplet absorption cross sections, the lifetime of the excited singlet state, and the triplet quantum yield may all be measured. This technique has been demonstrated for silicon 2,3-naphthalocyanine bis(trihexylsiloxide).
Evaluation of effective mass transport coefficients through comparison of solidification on the ground and on board a satellite
Authors: Liu R. P. , Sun L. L. , Zhao J. H. , Zhang X. Y. , He D. W. , Qin Z. C. , Xu Y. F. , Wang W. K.
Published: July 2002

Mass transport caused by buoyancy convection in front of the solid–liquid interface was evaluated in terms of measurements of primary dendritic spacing combining with separation of the effective (or integral) mass transport coefficient DL. It was shown that DL in normal gravity (1g) condition was 1.64 times as high as that in microgravity (μg) condition at the cooling rate (v) of 0.056 K/s for Pd40Ni40P20 alloy. The higher DL value is due to the contribution of buoyancy convection on the ground.
Magnetic dissipation force microscopy
Authors: Grütter P. , Liu Y. , LeBlanc P. , Dürig U.
Published: July 2002

A method of measuring magnetic dissipation on a sub-100 nm scale is presented. This technique relies on measuring changes in the damping of the oscillating tip in a magnetic force microscope (MFM). Damping contrast is strongly correlated with micromagnetic structure and in the case of NiFe, is in quantitative agreement with magnetoelastic losses in the sample. On recording tracks, large damping signals are observed. This has direct consequences on the interpretation of traditional MFM images acquired with detectors that convolute frequency and damping information.
Thermal stability of Ir/polycrystalline-Si structure for bottom electrode of integrated ferroelectric capacitors
Authors: Jeon Yoo-Chan , Seon Jeong-Min , Joo Jae-Hyun , Oh Ki-Young , Roh Jae-Sung , Kim Jae-Jeong , Kim Dae-Sik
Published: July 2002

Ir films deposited on polycrystalline silicon (poly-Si), with and without barrier layer, were annealed and the thermal stability was investigated to check the feasibility of the structure for bottom electrode of integrated ferroelectric capacitors. Ir did not form silicide up to 700 °C and did not get oxidized up to 550 °C. It was found that Ir prevented diffusion of oxygen through it when annealed at 700 °C. Ir/poly-Si is believed to be most promising for bottom electrode structure from the results.
Evidence of nonuniform carrier distribution in multiple quantum well lasers
Authors: Yamazaki Hiroyuki , Tomita Akihisa , Yamaguchi Masayuki , Sasaki Yoshihiro
Published: July 2002

Carrier distribution in multiple quantum well (MQW) lasers is studied by measuring laser wavelength. The MQW is designed to contain wells with different thicknesses. The MQW laser wavelength agreed with the transition wavelength of the wells near the p-clad layer at room temperature. At low temperatures, however, the laser wavelength corresponded to the thicker wells. The results imply that hole localization takes place at room temperature but disappears at low temperatures. This shows the invalidity of the conventional capture/escape model. The importance of the mean free path of unbound carriers is pointed out.
Ultrafast-laser driven micro-explosions in transparent materials
Authors: Glezer E. N. , Mazur E.
Published: July 2002

We initiate micro-explosions inside fused silica, quartz, sapphire, and other transparent materials using tightly focused 100 fs laser pulses. In the micro-explosions, material is ejected from the center, forming a cavity surrounded by a region of compacted material. We examine the resulting structures with optical microscopy, diffraction, and atomic force microscopy of internal cross sections. We find the structures have a diameter of only 200–250 nm, which we attribute to strong self-focusing of the laser pulse. These experiments probe a unique regime of light propagation inside materials at intensities approaching 1021 W/m2, the electron ionization that accompanies it, and the material response to extreme pressure and temperature conditions. The micro-explosions also provide a novel technique for internal microstructuring of transparent materials.
Contradirectional two-wave mixing in Rh-doped BaTiO3 crystal
Authors: Mu Xiaodong , Xu Xinguang , Shao Zongshu , Jiang Minhua , Luo Haosu , Zhong Weizhuo
Published: July 2002

Contradirectional two-wave mixing (CTWM) in Rh-doped BaTiO3 crystal is investigated. The experimental results show that the energy transfer of CTWM has some distinctive characteristics different from forward two-wave mixing. Theoretical analysis of CTWM is presented in good agreement with the experimental observations. Both the experimental and theoretical studies show that the energy transfer direction of CTWM depends not only on the orientation of the crystal c axis and the sign of the light-induced carriers, but also on the electro-optic coefficients.
Heterostructure integrated thermionic coolers
Authors: Shakouri Ali , Bowers John E.
Published: July 2002

Thermionic emission in heterostructures is proposed for integrated cooling of high power electronic and optoelectronic devices. This evaporative cooling is achieved by selective emission of hot electrons over a barrier layer from the cathode to the anode. It is shown that with available high electron mobility and low thermal conductivity materials, and with optimized conduction band offsets in heterostructures, single-stage room temperature cooling of up to 20°–40° over thicknesses of the order of microns is possible.
Shrinkage-corrected volume holograms based on photopolymeric phase media for surface-normal optical interconnects
Authors: Zhao Chunhe , Liu Jian , Fu Zhenhai , Chen Ray T.
Published: July 2002

The film shrinkage effect of photopolymeric phase media failed to provide the desired volume holograms for point-to-point optical interconnects. In this letter, we report a compensation method to physically correct the shrinkage effect that resulted from the holographic recording and the postbaking. Dupont photopolymer HRF-600X001 is studied. The correction of the Bragg diffraction angle shift of 1°21′, which is induced by a 5.25% film shrinkage, is successfully demonstrated with the surface-normal configuration. A shrinkage-corrected volume hologram with 80% diffraction efficiency is experimentally confirmed. The methodology reported herein is applicable to other phase media when the associated film shrinkage data are experimentally determined.
Mechanical relaxation of strained semiconducting stripes: Influence on optoelectronic properties
Authors: Fierling G. , Buchheit M. , Letartre X. , Gendry M. , Viktorovitch P. , Sidoroff F. , Lainé J. P.
Published: July 2002

The mechanical relaxation of strained semiconducting stripes is studied. The deformation tensor is calculated using a classical approach of elasticity problem with predeformations; the electronic band structure is then simulated using an 8 band kp model including strain. To confirm the models developed, compressively and tensely strained stripes were fabricated and characterized by photoluminescence measurements. Theoretical and experimental results are in very good agreement and show the importance of mechanical anisotropic relaxation phenomena in optoelectronic devices like waveguide structures, modulators, or lasers.
Avalanche breakdown-related electroluminescence in single crystal Si:Er:O
Authors: Sobolev N. A. , Emel’yanov A. M. , Shtel’makh K. F.
Published: July 2002

Er 3+ -related electroluminescence (EL) at ∼1.54 μm from single-crystal silicon light-emitting diodes fabricated by erbium and oxygen co-implantation and subsequent annealing has been observed in the avalanche breakdown regime in the 80–300 K temperature range. The EL intensity decreased by a factor of 2 with a temperature increase from 80 to 300 K. The room-temperature yield under the reverse bias was over one order of magnitude higher than that under the forward bias.
Energy-gap narrowing in a current injected InGaN/AlGaN surface light emitting diode
Authors: Zhao G. Y. , Yu G. , Egawa T. , Watanabe J. , Jimbo T. , Umeno M.
Published: July 2002

The emission spectrum of a current injected InGaN/AlGaN surface emitting diode has been investigated. A clear redshift of the low energy edge with increasing injected current has been observed, and is attributed to the many body effects. The carrier density and band gap narrowing are obtained by fitting the line shape of the emission spectrum, using Landsberg model which includes many body effects. A redshift of around 92 meV of the low energy edge is obtained as injected current increases from 400 to 4000 mA. The band gap change can be described well in proportion to the 1/3 power of the carrier density, which is just suggested by the exchange energy of electron–electron, and hole–hole interactions.
Effect of electronic corrections on the thickness dependence of thin oxide reliability
Authors: Alers G. B. , Oates A. S. , Monroe D. , Krisch K. S. , Weir B. E.
Published: July 2002

The thickness dependence of constant voltage lifetime tests are compared for ultrathin oxides in the range of 50–125 Å. An apparent factor of 100 enhancement in the lifetime of 50 Å oxides relative to the 125 Å oxides is observed at a fixed electric field when the field in the oxide is calculated using the physical thickness of the oxide as determined by ellipsometry. When corrections are made for the distribution of electrons at the silicon interface including depletion in the silicon and quantum-mechanical screening effects then this apparent enhancement is reduced and all oxides have similar lifetimes at a fixed field. Such a rescaling of oxide reliability demonstrates the importance of accurate determination of electric field and oxide voltage in thin oxides and that oxide reliability is not significantly affected by thickness down to 50 Å, depending only on field. We compare different techniques for determining the effective thickness using current-voltage or capacitance-voltage (C-V) curves. We show that accurate estimates of the electric field can be obtained from integration of the C-V relation of the capacitor. When electric fields are calculated using C-V curves, a consistent set of extrapolation parameters can be obtained for all thicknesses.
Coherent phonons in alkali metal-doped C60
Authors: Fleischer S. B. , Pevzner B. , Dougherty D. J. , Zeiger H. J. , Dresselhaus G. , Dresselhaus M. S. , Ippen E. P. , Hebard A. F.
Published: July 2002

We report the femtosecond impulsive excitation of coherent phonons in alkali metal-doped fullerenes. These excitations appear as small oscillations of the reflectivity (ΔR/R∼10−7) produced by the pump in an optical pump-probe experiment. The observed phonons include previously unobserved highly damped modes near 150 cm−1 as well as long-lived Ag(1) modes near 490 cm−1.
Nondegenerate four-wave mixing in a semiconductor microcavity
Authors: Tsuchiya M. , Shah J. , Damen T. C. , Cunningham J. E.
Published: July 2002

We report the observation of highly nondegenerate four-wave mixing from a semiconductor microcavity. The phase mismatch originating from the unique relationship between a beam incidence angle and its cavity resonance frequency was minimized by using a new method where both of pump and probe beams are obliquely incident. External efficiency of 1.6% was measured at 10 K for 1.5 THz frequency conversion of probe pulses by using 1 ps pump pulses of 55 pJ incident pulse energy.
Bound-free vacuum uv emissions of (XeCs)+ and (KrCs)+ ionic excimers by relativistic electron beam excitation
Authors: Xing Da , Wang Qi , Tan Shi-ci , Ueda Ken-ichi
Published: July 2002

Bound-free vacuum uv emissions from rare-gas alkali ionic excimers were observed by relativistic electron beam pumping of gas mixtures of Xe or Kr with hot cesium vapor. The observed two diffuse emission bands centered at 159 and 131 nm are assigned to be the 2 1Σ+→1 1Σ+ transition of (XeCs)+ and (KrCs)+ ionic excimers, respectively.
Photoluminescence of Nd-doped LiNbO3 films prepared by pulsed laser deposition
Authors: Alfonso J. E. , Martı́n M. J. , Zaldo C.
Published: July 2002

Nd-doped LiNbO3 films have been prepared on (012) sapphire substrates by pulsed laser deposition. LiNbO3 phase is formed using Li rich targets, a 1.5×10−2 mbar oxygen pressure atmosphere, and heating the substrate to 520 °C. The crystallinity of 1-μm-thick films has been enhanced by postdeposition thermal treatments at 600 °C. The [Nd]/[Nb] concentration ratio in the film is equal to its value in the target; however, a limit for the Nd incorporation to the LiNbO3 phase has been found due to the preferential nucleation of Li deficient phases for [Nd]/[Nb]>0.1. The Nd photoluminescence of the films have been studied at 77 K exciting the F43/2 multiplet. The photoluminescence of congruent LiNbO3 single crystals is well reproduced in films prepared from targets with a [Li]/[Nb]=1.6 composition. Films prepared from targets with a [Li]/[Nb]=3 composition, additionally show an emission, with a main maximum at 1064 nm, the splitting of the F43/2 multiplet being 80 cm−1. The possible origin of the latter photoluminescence is discussed.
Spatially selective disordering of InGaAs/GaAs quantum wells using an AlAs native oxide and thermal annealing technique
Authors: Lin Chao-Kun , Zhang Xingang , Dapkus P. Daniel , Rich Daniel H.
Published: July 2002

An InGaAs/GaAs quantum well (QW) disordering technique using AlAs native oxide and thermal annealing is presented. Unlike dielectric cap disordering, the AlAs native oxide can be placed close to quantum wells allowing for a spatially selective disordering deep within multilayer structures. The QW energy shifts and spatial control of the disordering were studied with photoluminescence and cathodoluminescence. The QW energy shift of thermally disordered regions containing buried oxide layer is ∼45 meV greater than that of regions not containing buried oxide layers. The disordering transition width is estimated to be ∼1 μm.
Luminescent intrazeolitic Si nanoclusters: Size study by Si K and L2,3 x-ray absorption near-edge structure, x-ray photoelectron and photoluminescence spectroscopies
Authors: He Jiliang , Klug Dennis D. , Tse John S. , Ratcliffe Chris I. , Preston Keith F.
Published: July 2002

A series of intrazeolitic silicon nanoclusters prepared from different Si loadings are investigated by Si K and L2,3 x-ray absorption near-edge structure, x-ray photoelectron and photoluminescence spectroscopies. They exhibit strong room-temperature photoluminescence in the yellow-orange region. It is found that the growth of Si clusters within the pores of zeolite Y is limited to an average size of about 75 Si atoms per unit cell.
Mechanism for flux pinning in NdBa2Cu3O7−δ melt-textured in low oxygen partial pressure
Authors: Wu H. , Kramer M. J. , Dennis K. W. , McCallum R. W.
Published: July 2002

When NdBa2Cu3O7−δ (Nd123) is melt-textured in low oxygen partial pressure (Po2) and subsequently annealed in oxygen to produce the superconducting phase, there is a considerable enhancement of flux pinning compared to Y123. This enhancement is accompanied by a precipitation mechanism due to a change of the solubility limits of Nd1+xBa2−xCu3O7−δ between the high temperature low Po2 conditions used in melt-textured growth and the low temperature oxygen annealing. Transmission electron microscopy reveals a coherent intermediate precipitate structure with a composition of BaCuO2 and a high density of dislocations. We believe these defects are responsible for the strong flux pinning in this material.
Influence of atomic force microscope tip–sample interaction on the study of scaling behavior
Authors: Aué J. , De Hosson J. Th. M.
Published: July 2002

Images acquired with atomic force microscopy are based on tip–sample interaction. It is shown that using scanning probe techniques for determining scaling parameters of a surface leads to an underestimate of the actual scaling dimension, due to the dilation of tip and surface. How much we underestimate the scaling exponent depends on the shape and aspect ratio of the tip, the actual fractal dimension of the surface, and its lateral–vertical ratio.
Sensitization of the minority carrier lifetime in hydrogenated amorphous silicon
Authors: Rapaport R. , Lubianiker Y. , Balberg I. , Fonseca L.
Published: July 2002

While sensitization of the photoconductivity, i.e., the increase of the majority carrier lifetime by the addition of recombination centers, is known for many years, there was no evidence or suggestion for the corresponding sensitization of the minority carrier lifetime. In this letter, we present experimental evidence for the existence of such an effect in device quality undoped hydrogenated amorphous silicon films. We propose possible scenarios that can yield the observed effect and mention the possible benefits of the minority carrier sensitization for the improvement of bipolar optoelectronic devices made of this material.
Aluminum mediated low temperature growth of crystalline silicon by plasma-enhanced chemical vapor and sputter deposition
Authors: Drüsedau Tilo P. , Bläsing Jürgen , Gnaser Hubert
Published: July 2002

The growth of nanocrystalline silicon on an aluminum underlayer of 4–32 nm thickness on silica substrates by plasma-enhanced chemical vapor deposition (PECVD) or sputter deposition is observed at standard conditions for the preparation of device quality hydrogenated amorphous silicon (substrate temperature of 500 K, deposition rate of 0.5 μm/h). The crystallite size determined by wide angle x-ray scattering ranges from 10 to 30 nm, and the crystallite fraction reaches 25%. The efficiency of aluminum mediated crystallization is about one order of magnitude higher for PECVD films than for sputtered films. Variations of the incident angle of the x rays show that the formation of silicon crystallites takes place at the Al/Si interface. Diffusion of Al into the silicon is enhanced for the PECVD films, whereas it plays a comparatively minor role for sputter deposition. The effect of the aluminum mediated crystallite growth is related to the existence of a metastable aluminum silicide and diffusion processes.
Improving the Al-bearing native-oxide/GaAs interface formed by wet oxidation with a thin GaP barrier layer
Authors: Chou L. J. , Hsieh K. C. , Moy A. , Wohlert D. E. , Pickrell G. , Cheng K. Y.
Published: July 2002

A method of improving the Al-bearing compound/GaAs interface against water vapor oxidation has been demonstrated. Amorphous native oxide formed by wet oxidation of an amorphous (Ga, As)/(Al, As) heterostructure on GaAs has exhibited an improved oxide/semiconductor interface with the incorporation of a thin GaP barrier layer of about two monolayers on the GaAs substrate. High resolution transmission electron microscopy shows an interfacial roughness on the order of 15 Å, and an enhancement of photoluminescence of three order of magnitude as compared to the as-grown counterpart without a GaP barrier indicates a great reduction in interface electronic traps. Having an improved interfacial roughness, a reduced interface trap density and an amorphous native oxide, this technique has a potential use in GaAs-based metal-oxide-semiconductor field-effect transistors.
Photon emission from Ag and Au clusters in the scanning tunneling microscope
Authors: Downes A. , Welland M. E.
Published: July 2002

In principle, chemical information is obtainable from metal surfaces by means of photon emission from the scanning tunneling microscope (STM). However, the photon emission varies significantly with topography and choice of tip. We address the important issue of geometry by studying the emission characteristics of Ag and Au spheres. First, photon maps of Ag clusters, consisting in some cases of just a few atoms, demonstrate that they can be uniquely identified from other nonmetallic particles. Then, the bias at which there is an onset of photon emission for 1 nm Ag and Au clusters is measured and found to be ≈3.3 and ≈2.1 V, respectively. This allows for the demonstration of the ability of the STM to distinguish different metal particles by their photon emission. The value of the onset bias for each metal can be made almost invariant to sample topography by an appropriate choice of tip; only then is the photon emission related purely to the optical properties of the surface. We envisage a form of chemical microscopy, whereby the bias of emission onset is mapped.
The kinetic glass transition of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass former-supercooled liquids on a long time scale
Authors: Busch R. , Johnson W. L.
Published: July 2002

Viscosity and enthalpy relaxation from the amorphous state into the supercooled liquid state was investigated in the bulk metallic glass forming Zr46.75Ti8.25Cu7.5Ni10Be27.5 alloy below the calorimetric glass transition. At different temperatures, the viscosities relax into states that obey the same Vogel–Fulcher–Tammann relation as the data obtained at higher temperatures in the supercooled liquid. Enthalpy recovery experiments after relaxation in the same temperature range show that the enthalpy of the material reaches values that also corresponds to the supercooled liquid state. The glass relaxes into a metastable supercooled liquid state, if it is observed on a long time scale. Equilibration is possible far below the calorimetric glass transition and very likely even below the isentropic temperature.
Highly stable surfaces of Nd1Ba2Cu3Oy single crystals
Authors: Ting Wu , Koshizuka N. , Tanaka S.
Published: July 2002

Single crystals of Nd1Ba2Cu3Oy (Nd123) high-temperature superconductors have been studied using an ultrahigh vacuum scanning tunneling microscope/spectroscopy system at room temperature. A square lattice with average lattice spacings of 4×4 Å2 has been observed on the surfaces of the single crystals without any surface protections or treatments. The as-prepared surfaces are found to be terminated by the CuO chain layer. Several surface defect structures presumably caused by the oxygen depletion are revealed. Among them, an one dimensional structural modulation with period of 1.5 nm along b axis is seen, which is suggested to be created by the ordering of the oxygen vacancies. The surfaces of Nd123 single crystals are proved to be highly clean and stable in air. Our results indicate that Nd123 single crystals are good materials for surface sensitive scientific researches and device applications.
Phase noise of a resonant-tunneling relaxation oscillator
Authors: Verghese S. , Parker C. D. , Brown E. R.
Published: July 2002

Experimental results are presented for the phase noise of a relaxation oscillator consisting of a resonant-tunneling diode in series connection with a transmission line, one end of which is shorted. Unlike constant-wave negative-resistance oscillators, the resonant-tunneling relaxation oscillator (RTRO) emits a sequence of sharp current pulses that are mode locked to the fundamental mode of the cavity formed by the short-circuited transmission line. The phase noise in the RTRO was investigated with and without injection locking by a weak sinusoidal source. Injection-locking gain of 51 dB was measured for fundamental injection locking. Subharmonic injection locking was demonstrated out to the 12th subharmonic. Also, timing jitter as low as 200 fs was measured for an RTRO that emitted ∼ 30 ps pulses at a repetition rate of 1.1 GHz.
Scanning thermal microscopy using batch fabricated thermocouple probes
Authors: Mills G. , Zhou H. , Midha A. , Donaldson L. , Weaver J. M. R.
Published: July 2002

We have developed scanning thermal microscopy probes for high resolution analysis of thermal properties in an atomic force microscope (AFM). Electron beam lithography and silicon micromachining have been used to batch fabricate Au/Pd thermocouples situated at the end of Si3N4 cantilevers. The cantilevers are patterned on the side of traditional style pyramidal AFM tips, giving a new shape of probe which is favorable for access to specimens containing significant topographic variation. Tip radius is approximately 50 nm and the probe has a macroscopic opening angle of 70°. The probes were scanned in the repulsive mode using a conventional AFM. Force feedback was optically employed to give topographic and thermal maps simultaneously by maintaining a constant force of approximately 5 nN. During initial scans using a photothermal test specimen, 80 nm period metal gratings were thermally resolved.
Field-free core, current distribution, and alternating current losses in self fields for rectangular superconductor tapes
Authors: Fukunaga T. , Inada R. , Oota A.
Published: July 2002

A method is proposed to calculate the shape of field-free core, the current distribution, and accordingly the alternating current (ac) losses in self fields as a parameter of current amplitude I0 for straight superconductor tapes with the arbitrary sectional geometry. The validity for this is justified by showing that magnetic fields inside the field-free core are negligibly small and by checking that calculation results of ac losses for elliptic tapes agree with the prediction by the theory of Norris. The ac losses for rectangular tapes behave as a thin strip superconductor in high I0 values near critical current, while showing a gradual deviation from this behavior as I0 is lowered. A decrease in the aspect ratio of width to thickness in the rectangular tape makes the deviation more remarkable.
1.5 μm asymmetric Fabry–Perot modulators with two distinct modulation and chirp characteristics
Authors: Yoo S. J. B. , Koza M. A. , Bhat Raj , Caneau Catherine
Published: July 2002

This letter discusses the design and the realization of asymmetric Fabry–Perot modulators with InP/InGaAsP distributed Bragg reflectors and 80 AlInGaAs quantum wells. We demonstrate two types of modulators utilizing two different top reflectors: an InP to air interface and a Si/SiO2/Si coating. The first modulator showed a monotonic reduction in the reflectivity as the bias voltage increased, and achieved a 2.2 dB insertion loss and a 15 dB contrast ratio at the resonant wavelength. The second modulator showed an initial reduction and then an increase in the reflectivity as the bias changed from 0 to −10 V. The chirp calculation based on the measured data reveals that the second modulator exhibits two distinct positive and negative chirp characteristics.
Dispersion correction of surface-normal optical interconnection using two compensated holograms
Authors: Zhou Charles C. , Fu Zhenhai , Chen Ray T. , Davies Brian M.
Published: July 2002

Performance of optical interconnects using volume holographic gratings and substrate-guided waves is subject to source wavelength detuning which originates from laser chirping and operating temperature changes. In this letter, we characterize and measure the dispersion of commonly used surface-normal volume holographic gratings. Dispersion characteristics of a 20 μm thick photopolymer volume holographic grating are evaluated. A dispersion correction method is demonstrated to provide a dispersion-free surface-normal optical interconnect using two dispersion-compensated volume holographic gratings and substrate-guided waves which automatically compensate the dispersion that results from detuning over a 5.7 nm bandwidth.
Edge detection readout signal and cross talk in phase-change optical data storage
Authors: Peng Chubing , Mansuripur M. , Nagata K.
Published: July 2002

Readout signal, noise, and cross-track cross talk were investigated for edge detection in a phase-change optical data storage system. Both theoretical and experimental results indicate that edge detection has a performance superior to the conventional detection of reflectance variations, especially when the amorphous marks are shorter than the size of the focused spot. More than 50 dB of carrier to noise ratio for marks of 0.36 μm in length is obtained using light at a wavelength of 690 nm and an objective lens of 0.6 numerical aperture. Diffraction analysis on the cross talk has shown that, in the scheme of land-groove recording, there is no optimum groove depth which can cancel the cross talk from adjacent tracks.
A method for Fermi energy measurements
Authors: Tsukernik A. , Slutzky M. , Palevski A. , Luryi S. , Shtrikman H.
Published: July 2002

We describe a method of Fermi energy measurement, based on the analysis of thermionic emission and diffusion over a barrier with a built-in charge. The method can be applied to a variety of semiconductors and has been successfully tested by measuring the Fermi energy in GaAs.
Excess noise caused by transverse inhomogeneity of conductive channels
Authors: Bulashenko O. M. , Rubı́ J. M. , Kochelap V. A.
Published: July 2002

A type of excess noise which emerges in transversely inhomogeneous conductive channels is described. Its origin is traced back to the diffusion of the electric-field and carrier-density fluctuations across the channel. By making use of a WKB analysis, explicit analytical formulas for the current-noise spectrum are obtained. It is argued, that this type of noise should be manifested in a variety of currently used semiconductor devices.
Direct assessment of tunable Schottky barriers by internal photoemission spectroscopy
Authors: Gigli G. , Lomascolo M. , De Vittorio M. , Cingolani R. , Cola A. , Quaranta F. , Sorba L. , Mueller B. , Franciosi A.
Published: July 2002

Al/GaAs(001) junctions in which the Schottky barrier was tuned through fabrication of a pseudomorphic Si interface layer were characterized by internal photoemission spectroscopy. Well-defined photoabsorption onsets corresponding to Schottky barrier heights ranging from 0.3 to 1.1 eV were observed in different devices. Our results point to the possible exploitation of tunable Schottky barriers in metal/semiconductor and metal/semiconductor/metal photon detectors.