bluuebunny/crossref_metadata_2025 huggingface dataset:
Pd/Zn/Pd/Au and Pd/Zn/Au/LaB6/Au ohmic contacts to p-type In0.53Ga0.47As
Authors: Ressel P. , Leech P. W. , Reeves G. K. , Zhou W. , Kuphal E.
Published: July 2002

The resistivity and interfacial characteristics of Pd/Zn/Pd/Au and Pd/Zn/Au/LaB6/Au contacts to p-In0.53Ga0.47As have been investigated. Annealing of the contacts at 375–425 °C yielded a minimum in specific contact resistance, ρc, of 2×10−7 Ω cm2 for the Pd/Zn/Pd/Au contacts and 1×10−6 Ω cm2 for the Pd/Zn/Au/LaB6/Au configuration. The measurement of ρc for the Pd/Zn/Pd/Au system is the lowest reported for an ohmic contact to p-In0.53Ga0.47As doped to ≤1×1019 cm−3. In the Pd/Zn/Au/LaB6/Au scheme, the minimum in ρc was the same whether the Zn was incorporated as a structural layer or as Zn ions implanted into the interfacial Pd. At ≥375 °C, the LaB6 layer limited the indiffusion of Au and the degradation of the In0.53Ga0.47As substrate.
Low noise YBa2Cu3O7−x SQUID magnetometers operated with additional positive feedback
Authors: Drung D. , Dantsker E. , Ludwig F. , Koch H. , Kleiner R. , Clarke John , Krey S. , Reimer D. , David B. , Doessel O.
Published: July 2002

Three magnetometers based on dc superconducting quantum interference devices (SQUIDs) fabricated from YBa2Cu3O7−x have been operated in a magnetically shielded room using a flux-locked loop involving additional positive feedback with bias current reversal. Two of these devices, integrated multiloop dc SQUIDs with outer diameters of 7 mm, achieved white noise levels of 10 fT/√Hz for bicrystal junctions and 30 fT/√Hz for step-edge junctions. The third magnetometer involved a flux transformer with a 10×10 mm2 pickup coil connected to a 16-turn input coil which was inductively coupled to a bicrystal SQUID. This device achieved a white noise of 16.2 fT/√Hz. High quality magnetocardiograms were obtained without signal averaging.
Observation of negative differential resistance phenomenon in a two-step barrier diode
Authors: Wang S. J. , Lin J. C. , Liou W. R. , Luo Y. C. , Cheng C. Y.
Published: July 2002

In this work, the realization of AlxGa1−xAs/GaAs two-step barrier diode is presented. Experimental observation on the current–voltage characteristics of the two-step barrier diode is reported. At both room temperature and 77 K, it shows a strong negative differential resistance under forward bias while no similar phenomenon was observed under reverse bias. Such an asymmetric current–voltage characteristic would open the possibility of negative differential resistance in an ac field in the absence of a dc bias. Theoretical simulation and experimental current–voltage characteristics are compared and discussed.
Visualization of current filaments in n-GaAs by photoluminescence quenching
Authors: Eberle W. , Hirschinger J. , Margull U. , Prettl W. , Novák V. , Kostial H.
Published: July 2002

Hot electrons in semiconductors are known to quench radiative impurity and exciton recombination photoluminescence. This effect has been applied in a low invasive technique to determine the spatial form of current filaments generated by impurity breakdown in high purity n-GaAs epitaxial layers at low temperatures. Observations on samples with Corbino disc contacts clearly demonstrate symmetry breaking and self-organization by the current filamentation.
An infrared optical field effect transistor with high speed response
Authors: Chen F. Y. , Fang Y. K. , Sun M. J. , Chen Jiann-Ruey
Published: July 2002

An infrared optical field effect transistor has been developed using a thin film of lead titanate (PbTiO3) deposited on a n/p+ Si substrate by rf sputtering, in which the drain conductance changes in proportion to the infrared light power. A fast response with a rise time of 2.3 μs has been obtained that is about 150% faster than the other types of thermal infrared optical field effect transistor. The developed infrared sensor is a bulk channel field effect transistor structure, that possesses higher mobility. Thus, faster speed can be obtained. In addition, the sensor has been prepared on a Si substrate, which offers the potential to develop Si-based infrared optical-electric integrated circuits.
Applied-voltage induced fatigue of lithium niobate waveguide
Authors: Nagata Hirotoshi , Mitsugi Naoki , Sakamoto Toshihiro , Kiuchi Kazumasa , Ichikawa Junichiro
Published: July 2002

z-cut lithium niobate optical modulator devices were ac (Vp-p=20 V) operated at 130 °C with an accumulated dc bias voltage of 4 and 8 V. A consequent dc drift phenomenon was larger for the 8 V bias application. After the operation, inversed domains were found along the Mach–Zehnder waveguides, particularly on the waveguide placed under the hot electrode. The results suggested that the device operation at higher voltage and temperature led to an accelerated dc drift and a fatiguelike deterioration of the lithium niobate material.
Deep submicron pattern transfer using high density plasma etching and nanochannel glass replica technology
Authors: Eddy C. R. , Tonucci R. J. , Pearson D. H.
Published: July 2002

Nanochannel glass (NCG)-based lithography has been used in conjunction with electron cyclotron resonance microwave plasma reactive ion etching (ECR-RIE) to demonstrate deep submicron features in HgCdTe alloys and InAs/GaSb heterostructures. NCG-based lithography is attractive as a massively parallel, low cost technology for nanometer-scale patterning. Samples patterned using thin-film metal replicas of NCG and methyl-radical-based ECR-RIE demonstrate a high degree of uniformity and fidelity with individual features having nearly vertical sidewalls and aspect ratios of up to 2 to 1. Dot arrays with features as small as 250 nm (and with packing densities of ∼1010/cm2) and anti-dot arrays with features as small as 600 nm have been realized.
Electrically reversible depassivation/passivation mechanism in polycrystalline silicon
Authors: Suntharalingam Vyshnavi , Fonash Stephen J.
Published: July 2002

An electrically reversible depassivation/passivation phenomenon has been found for hydrogen passivated polysilicon. This reversible effect is seen in both ECR and rf hydrogen passivated n-channel thin films transistors (TFTs) but is not seen in the corresponding hydrogen passivated p-channel TFTs, nor is it seen in either n- or p-channel TFTs before hydrogenation. This phenomenon was observed while room temperature bias stressing n- and p-channel TFTs fabricated on the same solid phase crystallized polysilicon films on quartz substrates. A model involving hydrogen release or capture at defects and positively charged hydrogen motion in device electric field is proposed. This phenomenon has significant implications for polysilicon TFT design and operation.
Acceleration of electrons to >0.5 MeV during space–charge neutralization of a 20 keV transient electron beam
Authors: Frank K. , Christiansen J. , Redel T. , Stark R. , Setter M. , Gundersen M. A.
Published: July 2002

The effect of high fields produced during space–charge neutralization of an electron beam is demonstrated by production of relativistic electrons (≊0.6 MeV) from a simple, small hollow cathode source operated at 20 kV. Acceleration occurs during a well-characterized, repeatable, glow-type transient plasma phase. The accelerating electron beam is produced within the device, and the total number of ≳0.5 MeV electrons is estimated to be ≤1010. A model correlating time dependence of the transient plasma with energetic electron production is discussed.
Monolithic vacuum–solid-state photodetector
Authors: Jalonen Marko , Koskinen Mervi , Pessa Markus
Published: July 2002

We report on a monolithic microvacuum GaAs/AlGaAs photodetector which is suggested to form a basic building block for a novel large-area and low noise detector. The rudimentary structure consists of a Cs-coated p-GaAs photon absorption layer, a vacuum space, and a collector. Part of the photoelectrons generated in the absorption layer are emitted into vacuum inside the microstructure and accelerated across a 2-μm wide vacuum space by an applied electric field to be collected by a conductive GaAs substrate. The quantum efficiency of this detector was about 0.07% at the incident 676-nm light power of 0.28 mW. The detector exhibited a low dark current of 1 pA at the reverse bias of 10 V.
Local field in ferroelectrics: Direct measurements with an optical probe
Authors: Blinov L. M. , Verkhovskaya K. A. , Palto S. P. , Sorokin A. V.
Published: July 2002

A local electric field, which acts on an individual molecule incorporated in a ferroelectric matrix, has been measured. For this purpose, absorption spectra of electrochromic dyes with well-defined properties of the ground and excited states were measured in a ferroelectric copolymer matrix above and below the phase transition temperature. The local electric field, which is due to the spontaneous polarization, has been evaluated from a spectral shift of the absorption maximum at the transition from the paraelectric to the ferroelectric phase.
Droplet-target laser-plasma source for proximity x-ray lithography
Authors: Malmqvist L. , Rymell L. , Hertz H. M.
Published: July 2002

A compact, high-brightness and practically debris-free laser-plasma soft x-ray source for proximity x-ray lithography is described. The target of the source is small liquid fluorocarbon droplets injected into vacuum with a piezoelectrically vibrated nozzle. Emission from helium- and hydrogenlike fluorine in the 1.2–1.7 nm wavelength range was determined to ∼2×1012 photons/(sr-pulse), which corresponds to a conversion efficiency of ∼5% of the 70 mJ laser pulse. Exposure of a copolymer of PMMA–MAA confirms the measured photon flux. Debris production was approximately 70 pg/sr pulse. The applicability of the source for dedicated lithography systems is discussed.
Conductance–voltage characteristics of interfaces between YBa2Cu3O7 and metallic oxides
Authors: Antognazza L. , Char K. , Geballe T. H.
Published: July 2002

We present the conductance–voltage characteristics of interfaces between YBa2Cu3O7 and three conductive metallic oxides; CaRuO3, SrRuO3, and La0.5Sr0.5CoO3. In the case of all the YBa2Cu3O7/(Ca,Sr)RuO3 interfaces, we observe the zero bias conductance peaks with the increasing conductance background at high bias. The zero bias conductance peaks decrease with increasing temperature and disappear at temperatures between 30 and 40 K. However, we did not observe zero bias anomalies in the YBCO/La0.5Sr0.5CoO3 contacts, in spite of an interface resistance of similar magnitude. This work suggests that the origin of the zero bias conductance peak lies in the defects on the YBCO surface and the exact defect structure depends on the adjacent epitaxial material.
Aging effects of the microstructure and soft magnetic properties in an amorphous Fe–Si–B–Nb alloy
Authors: Naohara T.
Published: July 2002

The aging behavior of an amorphous Fe79Si6B10Nb5 alloy was investigated using differential scanning calorimetry, transmission electron microscopy, and soft magnetic measurements. The formation of a bcc-Fe phase with nanoscale grains was caused by aging for 3.6 ks at the first crystallization temperature; however, this alloy consisted of an amorphous phase after aging for 0.6 Ms below 623 K. A marked increase in the effective permeability was achieved upon such low-temperature aging, and these values reached 10 000 and 2700 at 1 kHz and 1 MHz, respectively. It was inferred that the origin of the improvement in the soft magnetic properties is closely related to the phase separation in the amorphous structure, which precedes the nanocrystallization.
Photoinduced molecular alignment relaxation in poled electro-optic polymer thin films
Authors: Shi Yongqiang , Olson David J. , Bechtel James H. , Kalluri Srinath , Steier William H. , Wang Wenshen , Chen Datong , Fetterman Harold R.
Published: July 2002

The photoinduced nonlinearity decay in poled nonlinear optical polymer, polyurethane/Disperse Red 19, films was studied at wavelengths from 543 to 1320 nm. Electro-optic gratings and waveguide modulators were used in measuring and monitoring material’s nonlinearity. No photoinduced nonlinearity decay was detected at near infrared wavelengths. However, the photoinduced relaxation rate increased approximately 5 orders of magnitude from 670 to 543 nm, as the excitation wavelength approaches π-π* transition of the chromophores. The photoinduced chromophore reorientation was identified as the dominant relaxation mechanism.
Crucial influences of K33/K11 ratio on viewing angle of display mode using a bend-alignment liquid-crystal cell with a compensator
Authors: Kuo Chen-Lung , Miyashita Tetsuya , Suzuki Makoto , Uchida Tatsuo
Published: July 2002

The critical splay-to-bend-alignment transition in a liquid-crystal cell treated by parallel rubbing (π cell) was investigated to improve the optical performance of the display mode using this cell with a compensator. By analyzing the free energy in liquid crystal cells, it was found that nematic media with a smaller K33/K11 ratio can reduce the transition voltage considerably, and therefore, also reduce the required optical anisotropy of the liquid-crystal cell. The significantly improved viewing angle for this mode, achieved by using these newly designed parameters, is also confirmed theoretically and experimentally.
n-type delta-doped quantum well lasers with extremely low transparency current density
Authors: Buchinsky O. , Blumin M. , Sarfaty R. , Fekete D. , Samid I. , Yust M.
Published: July 2002

It is demonstrated that placing an n-type Te δ doping aside a single strained quantum well (QW) is an efficient way to control the initial carrier concentration in the QW and thus to lower transparency current density, Jtr, while preserving low internal losses. This is in contrast with uniform doping of the active area. Jtr of 11.3 A/cm2 and threshold current density of 54.4 A/cm2, which are both the lowest values reported to date for strained InxGa1−xAs/GaAs semiconductor lasers, were obtained. A somewhat higher injection efficiency is obtained when the energy levels are adjusted so that the electrons tunnel from the delta well directly into the QW.
The effect of CO2 on the plasma remediation of NxOy
Authors: Gentile Ann C. , Kushner Mark J.
Published: July 2002

Plasma remediation is being investigated for the removal of oxides of nitrogen (NxOy) from atmospheric pressure gas streams. In previous works we have investigated the plasma remediation of NxOy from N2/O2/H2O mixtures using repetitively pulsed dielectric barrier discharges. As combustion effluents contain large percentages of CO2, in this paper we discuss the consequences of CO2 in the gas mixture on the efficiency of remediation and on the end products. We find that there is a small increase in the efficiency of total NxOy remediation (molecules/eV) with increasing CO2 fraction, however the efficiency of NO remediation alone generally decreases with increasing CO2. This differential is more pronounced at low energy deposition per pulse. More remediation occurs through the reduction channel with increasing CO2 while less NO2 and HNOx are produced through the oxidation channel. CO is produced by electron impact of CO2 though negligible amounts of cyanides are generated.
Dopant delineation on Si(100) using anodic oxidation and atomic force microscopy
Authors: Bardwell J. A. , Allegretto E. M. , Mason B. , Erickson L. E. , Champion H. G.
Published: July 2002

A procedure has been developed for delineation of lateral variations in the doping of Si(100). The procedure relies on the fact that the thickness of electrochemically grown oxide depends on the dopant density and type. By growing the oxide and then etching it off in cycles, the silicon is selectively removed according to the doping density. By using atomic force microscopy, the electrically effective n+, n, and p-type regions of the sample are delineated.
High pressure oxidation induced stress in submicron trench structures
Authors: Stengl R. , Timme H.-J. , Mandelman J. A. , Benedict J. , Acker B.
Published: July 2002

The maximum stress induced by high pressure oxidation (wet and dry) in the vertical bird’s beak of submicron trench structures has been investigated experimentally. The oxidation induced stress was measured via wafer bow on wafers that were patterned with a special trench mask featuring a pattern factor of 50%. For wet high pressure oxidations above 850 °C, the stress drops from 2×1010 dyne/cm2 at 850 °C to a value below 1×109 dyne/cm2 at 1000 °C. At oxidation temperatures between 700 and 900 °C, dry pressure oxidations show lower stress than wet oxidations.
Growth of nucleation sites on Pb-doped Bi2Sr2Ca1Cu2O8+δ
Authors: Finnemore D. K. , Xu Ming , Kouzoudis D. , Bloomer T. , Kramer M. J. , McKernan Stuart , Balachandran U. , Haldar Pradeep
Published: July 2002

In the growth of Bi2Sr2Ca2Cu3O10+δ from mixed powders of Pb-doped Bi2Sr2Ca1Cu2O8+δ and other oxides, it has been discovered that a dense array of hillocks or mesas grow at the interface between a Ag overlay and Pb-doped Bi2Sr2Ca1Cu2O8+δ grains during the ramp up to the reaction temperature. As viewed in an environmental scanning electron microscope, the Ag coated grains develop a texture that looks like ‘‘chicken pox’’ growing on the grains at about 700 °C. These hillocks are about 100 nm across and are spaced at about 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurements indicate that the hillocks are a recrystallization of (Bi,Pb)2Sr2Ca1Cu2O8+δ, and are definitely not a Pb rich phase.
Experimental study of dispersive effects in fiber ring lasers
Authors: Prasad D. , Fortenberry R. , Zanoni R.
Published: July 2002

The effects of dispersion on the pulsewidth of a mode-locked fiber ring laser are examined. We have identified two different modes of operation, one where the pulsewidth is determined by the path-integrated (global) dispersion of the cavity and another novel mode where pulsewidth is not limited by the global dispersion. Experimental results show that for some configurations, the local dispersion of the cavity plays an important role in determining the pulsewidth of the laser.
Ion implantation-induced strong photosensitivity in high-purity fused silica: Correlation of index changes with VUV color centers
Authors: Verhaegen M. , Brebner J. L. , Allard L. B. , Albert J.
Published: July 2002

We have studied optical changes induced by ArF (6.4 eV/193 nm) excimer laser light illumination of high purity SiO2 implanted with Si 2+ (5 MeV) at a fluence of 1015 ions/cm2. Optical absorption was measured from 3 eV (400 nm) to 8 eV (155 nm) and showed evidence of several well-defined absorption bands. A correlation in the bleaching behavior appears to exist between the so-called D band (located at 7.15 eV) and the well-known B2α band which is attributed to oxygen vacancies. Changes in the refractive index as a function of ArF illumination were measured and found to be in good quantitative agreement with a Kramers–Kronig analysis of the optical absorption data.
The director structure in smectic C-filled cells with strong surface anchoring
Authors: Ulrich D. C. , Elston S. J.
Published: July 2002

We determine the structures present in smectic C-filled liquid crystal cells under the assumption of strong surface anchoring conditions. This is more realistic than commonly used assumptions and allows the prediction of the near surface alignment structure in such cells. The director orientation structure as a function of surface pretilt is discussed and the energies of the states that exist presented.
Optical properties of glasses containing copper oxide particles
Authors: Araujo R. J. , Butty J. , Peyghambarian N.
Published: July 2002

Particles of cuprous oxide with 20 nm sizes have been precipitated from borosilicate glasses. The absorption spectra show distinct changes in glasses given different heat treatments. Only very weak nonlinear effects are observed.
Growth and x-ray characterization of strain compensated GaAs/AlAs distributed Bragg reflectors
Authors: Mazuelas A. , Nörenberg H. , Hey R. , Grahn H. T.
Published: July 2002

We have grown strain compensated GaAs/AlAs distributed Bragg reflectors by solid source molecular beam epitaxy using carbon doping densities up to about 2×1020 cm−3. The residual strain with respect to the GaAs substrate can be as low as 1×10−4. This results in a large increase of their critical thickness with regard to the undoped case. We demonstrate that simulations of the x-ray diffraction patterns are essential in order to determine the chemical profile as well as the structural parameters of the GaAs:C and AlAs:C layers with high accuracy. The effective incorporation of carbon on lattice sites is in AlAs:C twice as large as in GaAs:C using the same incident carbon flux.
Improved heterojunction bipolar transistor reliability with carbon-doped base
Authors: Wang Guan-Wu
Published: July 2002

AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with the carbon- or beryllium-doped base have been fabricated and characterized with respect to device reliability. Under high current stress at elevated temperature, the device characteristics of the HBT with the beryllium-doped base show severe degradation enhanced by ion implantation. In comparison, the HBT with the carbon-doped base is not affected by the ion implantation and exhibits negligible device degradation after the stress. These results indicate the advantage of carbon doping for better HBT reliability.
Characterization of diamond deposition from chloromethane reactants by laser reflective interferometry
Authors: Wu Jih-Jen , Yeh Shih-Hsien , Su Chin-Ta , Hong Franklin Chau-Nan
Published: July 2002

Laser reflective interferometry (LRI) was employed to compare the nucleation and film growth characteristics of diamond deposition between methane and chloromethane reactants. LRI has the capability of in situ monitoring of the film-forming stage and the film growth stage. During the film-forming stage deposition behavior involves the nucleation and subsequent growth of discrete diamond crystallites. During the film growth stage, it involves the growth of a continuous film. In comparison to methane reactant, chloromethane was observed to enhance slightly the growth rate during the film growth stage by 7%, 16%, and 39% at substrate temperatures of 850, 750, and 650 °C, respectively. However, chloromethane reduced the time required for film formation and increased the nucleation densities significantly, particularly at low growth temperatures. The reason that chloromethane enhances the total growth rates at low temperature is mainly due to its ability to stabilize diamond nucleus precursor and thus enhance diamond nucleation.
Effect of rapid thermal annealing on the electrical and physical properties of metalorganic chemical-vapor-deposited TiN
Authors: Sun S. C. , Tsai M. H.
Published: July 2002

This work reports on the effect of postdeposition thermal treatment using rapid thermal annealing on the physical and electrical properties of metalorganic chemical-vapor-deposited (MOCVD) titanium nitride (TiN) thin films. When ammonia is used as the annealing ambient, the resistivity decreases with increasing annealing temperature. The resistivity of MOCVD TiN was reduced from 6000 to 320 μΩ cm after 800 °C rapid thermal annealing in ammonia (RTN). Annealing in nitrogen ambient was found to be not nearly as effective as that in ammonia. The decrease in resistivity may be attributed to a reduction in the carbon and oxygen content, growth in grain size through polycrystalline recrystallization, as well as to an increase in film density.
The forward biased junction: a sensitive detector for far-infrared radiation
Authors: López Sáenz M. , Guerra Pérez J. M.
Published: July 2002

The strong bias dependence of the far-infrared laser-induced negative photoeffect is here attributed to an intrinsic bias dependent internal photoemission effect. Experimental results fit remarkably well with the carrier temperature and the transition potential predicted by our model. We demonstrate that any asymmetric heavily doped junction (P+/N, N+/P) which is properly forward biased is suitable to detect far infrared radiation. The sensitivity is reasonable (≊1 mV per kW at 300 K) for detection of pulsed radiation and the rise time is intrinsically fast (≤1 ns).
Visible electroluminescence from porous silicon/hydrogenated amorphous silicon pn-heterojunction devices
Authors: Sercel Peter C. , Kwon Daewon , Vilbrandt Teha , Yang Weidong , Hautala John , Cohen J. David , Lee Hao
Published: July 2002

We report the fabrication and characterization of a p-type porous silicon/ n-type hydrogenated amorphous silicon (a-Si:H) pn-heterojunction electroluminescent device structure. The devices exhibit electroluminescence in forward bias, demonstrating minority carrier injection from n-type a-Si:H into p-type porous silicon.
Conservation of photoluminescence splittings related to one-monolayer thickness variations in GaAs/AlGaAs quantum wells after SiO2 capping-induced intermixing
Authors: Pépin A. , Vieu C. , Schneider M. , Planel R. , Launois H. , Nissim Y.
Published: July 2002

Intermixing of GaAs/AlGaAs single quantum well heterostructures by SiO2 capping and subsequent annealing was investigated using low-temperature photoluminescence. In this letter we report the observation of the conservation of splittings related to one-monolayer thickness variations in the emission of quantum wells after an intermixing process. High photoluminescence intensities and narrow linewidths were also retained although very strong interdiffusion rates inducing energy blueshifts as large as 180 meV were achieved, thus revealing a very homogeneous and high quality intermixing technique.
Energy relations for space-charge waves in photorefractive materials
Authors: Kalinin V. A. , Solymar L.
Published: July 2002

An energy balance equation is derived with the aid of a partial differential equation describing the space-charge field in photorefractive materials. Expressions are found for power flux, losses, and the power absorbed from an external source both for the low- and high-frequency branches of space-charge waves. The efficiency of energy conversion from the external source into the space-charge wave is calculated and compared for two different mechanisms of optical excitation: (i) by a moving interference pattern and (ii) by a combination of a stationary interference pattern and an external ac field.
Structural study of nanocrystallized Cu83Co17 ribbons by scanning friction force microscopy
Authors: Correia A. , García N. , Massanell J. , Costa-Krämer J. L.
Published: July 2002

Nanocrystallized cobalt clusters embedded in a copper matrix exhibiting giant magnetoresistance have been revealed by scanning force and friction microscopy. The microscopic images reported here should be important to understand the magnetic properties of these novel systems.
Trace oxygen effects on copper nanoparticle size and morphology
Authors: Olynick D. L. , Gibson J. M. , Averback R. S.
Published: July 2002

Using an ultrahigh vacuum (UHV) magnetron sputtering system connected directly to a UHV transmission electron microscope (TEM), we study, in situ, the effect of trace levels of oxygen contamination on the early stages of sintering, coalescence, and morphology. Whereas, nanoparticles produced under clean conditions experience substantial sintering and grain growth upon contact, even at room temperature, particles deliberately exposed to trace amounts of oxygen remain distinct. It therefore appears difficult to form ultraclean nanophase materials, at least for copper, due to rapid sintering. These systematic studies of particle morphology as a function of oxygen exposure shed light on nanoparticle growth mechanisms in the gas phase and thus ways to approach the ideal nanophase material.
Long-lived excited state of C60 in C60/phthalocyanine heterojunction solar cell
Authors: Murata Kazuhiko , Ito Shoji , Takahashi Kohshin , Hoffman Brian M.
Published: July 2002

The photovoltaic properties of ITO (indium tin oxide)/C60/H2(pc), (pc=phthalocyanine)/Au sandwich solar cells are investigated. The cell prepared at a higher vacuum (1×10−6 Torr) shows an open-circuit photovoltage (VOC) of 0.18 V, a short-circuit photocurrent (JSC) of 89 μA cm−2, a fill factor (ff) of 0.25, and an energy conversion yield (η) of 0.03% when illuminated by white light with 12.5 mW  cm−2 intensity. The photocurrent action spectra of the cell reveal that photocurrent is generated at C60/H2(pc) interface with diffusion of C60 excitons because the excited state of C60 has a relatively long lifetime, while the cell prepared at a lower vacuum (3×10−5 Torr) shows a much smaller photocurrent (JSC=1.4 μA cm−2) because oxygen in C60 acts as carrier traps and increases the resistance of C60.
Beam induced deposition of an ultraviolet transparent silicon oxide film by focused gallium ion beam
Authors: Ogasawara M. , Kariya M. , Nakamura H. , Komano H. , Inoue S. , Sugihara K. , Hayasaka N. , Horioka K. , Takigawa T. , Okano H. , Mori I. , Yamazaki Y. , Miyoshi M. , Watanabe T. , Okumura K.
Published: July 2002

We have deposited a silicon oxide (SiOx) film with a high optical transmittance in the DUV region by a focused ion beam induced deposition technique using a gallium ion beam and a mixture of oxygen and TMCTS(1,3,5,7-tetramethylcyclotetrasiloxane) as a source gas. The optical transmittance of a 0.3 μm thick film is higher than 90% at the wavelength of 250 nm. The transmittance of the deposited SiOx film depends on both the source gas and ion beam irradiation conditions. A scaling to explain the transmittance along with the ion beam conditions is proposed.
Electrical characterization of the β-FeSi2/Si heterojunction after thermal oxidation
Authors: Erlesand U. , Östling M.
Published: July 2002

The influence of an oxidant ambient on the electrical transport properties of β-FeSi2/Si heterostructures has been investigated. Current-voltage and capacitance-voltage analyses on diodes formed on p-type silicon did not reveal any change in the dominant transport mechanism after oxidation, other than an increase of the 0 K hole barrier from 0.42 to 0.46 eV. The transport showed a thermally activated process and was interpreted as thermionic emission of holes from the silicon region to the silicide. However, on n-type silicon a change from a thermally activated process to a tunneling limited transport was observed after oxidation. A multistep recombination-tunneling mechanism was suggested with formed defects presumably situated close to the interface or inside the silicide film. It was also observed that dry oxidation was less detrimental to the heterojunction characteristics than oxidation in wet ambient.
Electro-optic beam scanner in KTiOPO4
Authors: Chiu Y. , Stancil D. D. , Schlesinger T. E. , Risk W. P.
Published: July 2002

We have fabricated and demonstrated both wafer and waveguide electro-optic beam scanners in KTiOPO4 using alternating domain-inverted triangular patterns in the substrate. This device is an extension of previous work in LiTaO3. The domain inversion was achieved by pulsed electric field poling. The deflection sensitivity was 2.1 mrad/kV, compared to the calculated value of 2.3 mrad/kV for this geometry. The bandwidth of the devices was measured to be at least 200 kHz, which was limited by the high voltage driver.
Asymmetric, reflection mode nonlinear Fabry–Perot modulator using bacteriorhodopsin
Authors: Zang De Yu , Millerd James E. , Smithey Daniel
Published: July 2002

We report on the design, fabrication, and testing of an asymmetric reflection mode Fabry–Perot modulator using bacteriorhodopsin as the nonlinear cavity material. The modulator was fabricated to be impedance matched, resulting in high quality modulator performance. A large contrast ratio of 61:1, a reflectivity of 94%, and a dynamic modulation range of 55.5 at a pump; intensity of 26 mW/cm2 were measured by this modulator.
Interface-state density at SiO2/GaAs assessed by direct measurement of surface band bending
Authors: Mochizuki Yasunori , Mizuta Masashi
Published: July 2002

Electroreflectance is applied to study the interface properties of metal/SiO2/GaAs structures. From a bias-voltage dependence of surface potential, which was evaluated from the measured surface field in i/n+-GaAs structures, energy distributions of interface-state density were determined based on the modulation spectroscopy technique. Upon biasing toward inversion, a strong pinning of surface Fermi level occurred at around 0.88 eV below the conduction-band minimum. This pinning, thus, is concluded to be due to a large number of interface states, and not due to an actual hole inversion. The method is free from numerical ambiguities encountered in capacitance-based techniques, in which the energy reference for surface Fermi level is model dependent, and thus, is a suitable tool for studying insulator/semiconductor interfaces, even having a large number of interface traps.
Theoretical model for an improved radiation pressure micromotor
Authors: Gauthier R. C.
Published: July 2002

A simple modification to an existing radiation pressure micromotor design is modeled. The results indicate that inclining the top surfaces of the micromotor increases the rotation inducing torque by a factor of 2. The direction of rotation can be selected by resizing the radiating light beam’s minimum waist.
Undriven periodic plasma oscillation in electron cyclotron resonance Ar plasma
Authors: Lee Pyung-Woo , Lee Sang-Won , Chang Hong-Young
Published: July 2002

We report experimental observation of periodic oscillation in a steady state electron cyclotron resonance argon plasma that is not driven by extra periodic forces. We interpret the oscillation according to the predator-prey model, which is a nonlinear plasma-neutral coupling in the plasma production region. The oscillation is observed in a narrow plasma parameter window and is evidence for neutral density depletion in a high density plasma system.
Spontaneous emission measurements for resolving damping mechanisms in direct modulation of quantum well lasers
Authors: Wu Ta-Chung , Vassilovski Dan , Cutrer David M. , Kan Sidney C. , Lau Kam Y.
Published: July 2002

We demonstrate a measurement technique for determining the contribution of carrier transport effect on the maximum modulation bandwidth in quantum well lasers. This technique independently measures the ratio of the effective carrier capture to escape times, as well as the contribution from intraband damping mechanisms, in an operating laser. Every single parameter in the present model for modulation dynamics of quantum well lasers can now be determined experimentally, which enables a consistency check on its validity.
Electro-optical characterization of poled-polymer films in transmission
Authors: Lundquist P. M. , Jurich M. , Wang J.-F. , Zhou H. , Marks T. J. , Wong G. K.
Published: July 2002

An improved version of the commonly employed C. C. Teng and H. I. Man (Appl. Phys. Lett. 56, 1734 [1990]) measurement technique is illustrated by the characterization of films of a new high glass transition temperature polyurea. Measurements taken in the transmission mode are shown to be free from non-negligible errors introduced by interference effects present in standard reflection geometry measurements.
A multiple-negative-differential-resistance switch with double InGaP barriers
Authors: Guo Der-Feng , Cheng Chin-Chuan , Lin Kun-Wei , Liu Wen-Chau , Lin Wei
Published: July 2002

A GaAs-InGaP switch has been fabricated and demonstrated. In this device, double i-InGaP layers are employed to provide the potential barriers for carrier tunneling and hole confinement. As sufficient external voltage is applied to this device, a double S-shaped negative-differential- resistance (NDR) characteristics is obtained resulting from the sequential avalanche multiplications in the high electric field regions. However, because of the poor confinement effect to holes, only a single S-shaped NDR phenomenon is observed at higher temperature. With device parameters appropriately adjusted, this device may show prominent potential for multiple-valued logic applications.
Photoluminescence study of InAsSb/InAsSbP heterostructures grown by low-pressure metalorganic chemical vapor deposition
Authors: Kim S. , Erdtmann M. , Wu D. , Kass E. , Yi H. , Diaz J. , Razeghi M.
Published: July 2002

Photoluminescence has been measured for double- and separate-confinement InAsSb/InAsSbP heterostructures grown by low-pressure metalorganic vapor deposition. A measurement of the integrated luminescence intensity at the temperature range of 77–300 K shows that over a wide range of excitation level (1–5×102 W/cm2) the radiative transitions are the dominant mechanism below T∼170 K. Auger recombination coefficient C=C0 exp(−Ea/kT) with C0≊5×10−27 cm6/s and Ea≊40 meV has been estimated.
Transient photoinduced absorption in (AlxGa1−x)0.5In0.5P fractal quantum well heterostructures
Authors: Sinclair M. B. , Gourley P. L. , Crawford M. Hagerott , Meissner K. E. , Schneider R. P.
Published: July 2002

Picosecond photoinduced absorption measurements have been performed on four different (AlxGa1−x)0.5In0.5P fractal quantum well heterostructures. The results of these measurements reveal that, at early times following pulsed excitation, the carriers remain near the surface layer in which they were photogenerated, and populate the higher lying branches of the V-shaped fractal structure. With increasing time, the carrier population relaxes toward the lowest energy, central wall. The rate at which the relaxation occurs is governed by the characteristic layer of widths of the fractal structure.
Structural properties of Pt/p -InP heterostructures
Authors: Kim T. W. , Yoon Y. S. , Lee J. Y.
Published: July 2002

Ion-beam-assisted deposition of Pt on p-InP at room temperature was performed in order to produce Pt epitaxial films with high quality and Pt/p-InP (100) heterostructures with sharp interfaces. From the x-ray diffraction analysis, the grown film was found to be a Pt heteroepitaxial film. Auger electron spectroscopy measurements showed that the composition of the as-grown film was Pt and that the interface quality between the Pt and the InP was relatively good. Transmission electron microscopy showed that the grown Pt was an epitaxial film. These results indicate that the Pt epitaxial films grown on p-InP (100) can be used for both stable contacts in optoelectronic devices and Pt/InP metal-semiconductor-field-effect transistors and that the Pt/InP heterostructures can give good motivation for the fabrication of Pt/InP superlattices.
Helium ion-induced stoichiometry modification in hydrogenated silicon oxide films
Authors: Godet C. , Etemadi R. , Clerc C.
Published: July 2002

The stoichiometry of amorphous hydrogenated silicon oxide films, grown in a dual-plasma system, has been investigated using elastic recoil detection (ERD), Rutherford backscattering, and infrared transmission. During ERD measurement of H profiles, using a 4He2+ beam of 3.0 MeV, ion-induced depletion of hydrogen atoms was observed, homogeneous over the 1 μm film thickness. Si-rich films (with H essentially bonded as Si–H) and nearly stoichiometric films (with H only bonded in Si–OH configurations) have been compared. The depletion is more pronounced in nearly stoichiometric oxides, whereas the apparent cross sections (≊1–2 nm2) are similar for both types of films. These observations are discussed in terms of an electron excitation process, with a subsequent chemical reconstruction via electron-hole recombination.
Enhancement of the acoustic phase conjugate reflectivity in nonlinear piezoelectric ceramics by applying static electric or static stress fields
Authors: Ohno M. , Takagi K.
Published: July 2002

A method to enhance the reflectivity of acoustic phase conjugate mirrors by nonlinear piezoelectricity is discussed. Static electric or static stress fields were applied together with the pump electric field. In highly nonlinear piezoelectric ceramics, the phase conjugate reflectivity was enhanced by the factor of 50 using this method. The maximum reflectivity reached 10−2.
Two-color midinfrared saturation spectroscopy of intersubband transitions in multiquantum wells
Authors: Vodopyanov K. L. , Chazapis V. , Phillips C. C.
Published: July 2002

A two-color pump–probe study of bound-to-bound and bound-to-quasibound intersubband transitions in InGaAs/AlGaAs and GaAs/AlGaAs multiquantum wells (MQW), with transition energies near 250 meV has been performed. Electrons were optically excited from the lowest to the upper subband using short midinfrared pulses of intensities up to 108 W/cm2 from a dual optical parametric generator. Differential transmission spectra, taken with the weaker probe pulses, evidence homogeneous line broadening behavior. From the width of the coherence peak, centered near the pump frequency, and arising from a dynamic population grating, the upper state lifetime (bound-to-bound transition) was found to be 0.6 ps, in good quantitative agreement with absorption saturation data.
Irradiation-induced improvement of crystalline quality of epitaxially grown Ag thin films on Si substrates
Authors: Takahiro K. , Nagata S. , Yamaguchi S.
Published: July 2002

We report the Rutherford backscattering spectroscopy/channeling studies of epitaxial grown Ag films on Si(100) substrates irradiated with fast ions (12C++, 19F++, 28Si++) in the energy range between 0.5 and 4 MeV at 200 and −150 °C. The quality of the Ag films is improved considerably by ion irradiation. Irradiation with 0.5 MeV 28Si ions to 2×1016/cm2 at 200 °C, for example, reduces the channeling minimum yield from 55% to 6% at the Ag surface. The improvement of crystalline quality is brought about by a decrease in mosaic spread in the Ag film. Also, it is found that the higher the crystallinity, the more radiation-induced defects are produced. The mechanism involved in the irradiation-induced improvement is discussed.
Effect of adlayer dimer orientation on the optical anisotropy of single domain Si(001)
Authors: Power J. R. , Farrell T. , Gerber P. , Chandola S. , Weightman P. , McGilp J. F.
Published: July 2002

The effect of adlayer dimer formation on the optical anisotropy of single domain Si(001) is reported. Reflection anisotropy spectroscopy (RAS) from Ga and Sb adsorbed on the Si(001) surface reveals complex behavior which depends strongly on the atomic species and the RAS signal cannot be simply related to dimer orientation. Dimer formation in the same direction on the surface by Si and Ga is shown to produce RAS signals, below the direct optical gap of Si, of the opposite sign. This contrasts with the simpler behavior observed for Ga and As adsorption on GaAs(001) surfaces.
Low temperature inorganic chemical vapor deposition of heteroepitaxial GaN
Authors: McMurran Jeffrey , Todd M. , Kouvetakis J. , Smith David J.
Published: July 2002

We have developed a highly efficient method of growing thin oriented films of GaN on basal plane sapphire and (100) Si substrates using an exclusively inorganic single-source precursor free of carbon and hydrogen. Cross sectional transmission electron microscopy of the highly conformal films revealed columnar material growth on Si and heteroepitaxial columnar growth of crystalline GaN on sapphire. Rutherford backscattering spectroscopy (RBS) of layers grown at 700 °C confirmed stoichiometric GaN. Auger and RBS oxygen and carbon resonance profiles indicated that the films were pure and highly homogeneous. With respect to current chemical vapor deposition processes for GaN growth, our approach offers a number of potentially important improvements. These include high growth rates of 5–350 nm/min, low deposition temperature of 650–700 °C, nearly ideal Ga–N stoichiometry, elimination of the highly inefficient use of toxic ammonia, and a carbon–hydrogen free growth environment that could prove to be beneficial to p-doping processes.
On surface plasmons in porous silicon: Measurements of the electron energy loss in etched silicon nanocrystals
Authors: Sassaki R. Massami , Galembeck F. , Teschke O.
Published: July 2002

Surface plasmons resulting from the interaction of the electron beam of a transmission electron microscope with porous silicon nanoparticles were measured. The inelastic scattering of fast electrons in H-covered silicon nanocylinders shows a peak at ∼5.5 eV. A gradual decrease of the first and second order plasma volumetric absorption simultaneous with a constant surface mode absorption amplitude was measured for decreasing silicon-slab thicknesses. Competitions between bulk and surface effects show, for the volume mode peak at 16.9 eV, a damping factor increase of ∼5 eV. The measured silicon particle diameter was ∼15 Å and a value of the dielectric constant is estimated from the surface plasmon data at 8.5, which is in agreement with recent theoretical work on the modified dielectric constant in quantum confined systems.
Studies of the temporal and spectral shape of terahertz pulses generated from photoconducting switches
Authors: Ludwig Christoph , Kuhl Jürgen
Published: July 2002

We present a systematic investigation of the operation conditions of photoconductive switches fabricated on LT-GaAs as sources of THz pulses. We find a pronounced dependence of the THz pulse intensities and spectra on bias voltage and excitation density, which can be explained in terms of carrier dynamics and screening of the electric bias field. This study provides guidelines for the selection of the optimal operation parameters to obtain short THz pulses with a given geometry of the photoconductive switch.
The deposition of a GaS epitaxial film on GaAs using an exchange reaction
Authors: Xin Q.-S. , Conrad S. , Zhu X.-Y.
Published: July 2002

A GaS thin film has been formed epitaxially on GaAs(100) using a photoassisted growth-etching reaction between H2S and the GaAs substrate. In the reaction, the growth of GaS is accomplished via the replacement of As in the GaAs lattice by the photochemically generated S atom, while As is etched from the substrate as arsenic sulfide. The surface of the resulting GaS thin film is characterized by a sharp (2×1) low energy electron diffraction pattern, indicating excellent crystalline quality.
Photorefractive two-wave mixing bistability in Fe: KNbO3 without external feedback: Increasing gain bistability
Authors: Jost Bradley M.
Published: July 2002

The observation of photorefractive two-wave mixing bistability without external feedback is reported. Hysteresis with an on/off contrast ratio of 30 was obtained through the interaction of two 514.5 nm laser beams within a Fe: KNbO3 crystal. A signal beam modulation rate less than 25 mHz was necessary to obtain the hysteresis when the total optical irradiance of the pump and signal beams was ∼1 mW/mm2. The data are shown to correspond well with a two-state increasing gain model.
Accuracy of the single-electron pump using an optimized step-like rf drive waveform
Authors: Fonseca L. R. C. , Korotkov A. N. , Likharev K. K.
Published: July 2002

We have performed an optimization of those parameters of a single-electron pump that may influence the accuracy of this device as a standard of dc current. Two types of rf drive were considered: the traditional triangular waveform and a step-like waveform. We have shown that, after optimization, the accuracy of the pump may be improved considerably in a wide range of drive frequencies, especially at low temperatures, using the step-like waveform. For example, the error of a five-junction pump with junction capacitances C=0.1 fF at 100 mK and 10 MHz may be as small as 10−13.
Nanostructuring on WSe2 with the atomic force microscope by a potential controlled electrochemical reaction
Authors: Böhmisch M. , Burmeister F. , Boneberg J. , Leiderer P.
Published: July 2002

We present a method for the controlled fabrication of stable nanostructures under ambient conditions. The surfaces under consideration, WSe2, are imaged by an atomic force microscope. By applying a voltage between the tip and the sample, we can control an etching process at the surface: different voltage thresholds for the creation and the growth of structures of one monolayer (Se–W–Se) depth are observed. Our measurements on p-doped WSe2 strongly support an electrochemical corrosion reaction in a physisorbed water film. This method allows the in situ preparation and characterization of individual nanometer-sized structures on WSe2 and other metal dichalcogenides.