bluuebunny/crossref_metadata_2025 huggingface dataset:
Visualization of a gas flow instability in spin coating systems
Authors: Wahal Sanjay , Oztekin Alparslan , Bornside David E. , Brown Robert A. , Seidel Philip K. , Ackmann Paul W. , Geyling Franz T.
Published: July 2002

Flow visualization in the gas above the surface of a rotating wafer in an industrial spin coating apparatus demonstrates the presence of an Ekman-like flow instability that adversely affects the uniformity of the dried film. Experiments performed with a 6-in.-diam wafer and typical operating conditions show 6–8 spiral vortices around the wafer oriented with negative angle, as is indicative of the type II flow instability predicted by linear stability analysis. The critical Reynolds number for onset is in reasonable agreement with the theory.
Penetration depth λ(T) of YBa2Cu3O7−δ films determined from the kinetic inductance
Authors: Lee JuYoung , Lemberger Thomas R.
Published: July 2002

We examine the temperature dependence of the magnetic penetration depth λ(T) of YBa2Cu3O7−δ, determined from the kinetic inductance of a film patterned into a long meander line. This technique has sufficient sensitivity to study λ(T) to lower temperatures than have been examined previously. A numerical model which includes both the magnetic and kinetic inductances of the samples extracts λ(T) from the measured voltage. In reasonable agreement with other measurements, λ(0)≊2100 Å is deduced from fitting λ(0)2/λ(T)2 to the function 1−(T/Tc)2 for T/Tc≥0.4. We find λ(T)/λ(0)−1 is proportional to (T/Tc)2 for 0.06 ≤T/Tc≤0.4.
Liquid phase epitaxial regrowth on sulfide-passivated Ga1−xAlxAs
Authors: Berkovits V. L. , Lantratov V. M. , L’vova T. V. , Shakiashvili G. A. , Ulin V. P. , Paget D.
Published: July 2002

We demonstrate that Na2S passivation allows liquid phase epitaxial regrowth of Ga0.5Al0.5As upon Ga1−xAlxAs (0.3≤x≤0.8) after air exposure. Large aluminum concentrations require concentrated (2.4 M) sulfide solutions. We have also studied the Ga1−xAlxAs etching rate by Na2S. For large sulfide concentrations or small aluminum concentrations, the etching process stops after some time. These two phenomena are correlated because both of them require the presence on the surface of a stable protective layer. This can be understood by assuming the existence at the surface of two competing mechanisms: etching and passivation.
Spectral behavior of solar cells based on the ‘‘junction near local defect layer’’ design
Authors: Summonte C. , Biavati M. , Gabilli E. , Galloni R. , Guerri S. , Rizzoli R. , Zignani F.
Published: July 2002

The junction near local defect layer (JNLD) solar cell design [Li et al., Appl. Phys. Lett. 60, 2240 (1992)] was recently shown to greatly increase the short circuit current of silicon solar cells. The proposed mechanism is an enhancement of sub-band-gap light absorption through gap states, introduced by the presence of a defect layer situated in the junction region. Our measurements of JNLD solar cells evidence a change in the absorption spatial profile due to the defect layer. The result is a small enhancement in quantum efficiency in the visible red side of the spectrum that is in turn balanced by a recombination effect caused by the same defect layer, so that the final short circuit current does not increase. On the contrary, we detected a 20% decrease in the open circuit voltage that is attributed to the shorting effect of defect levels in the junction region. No sub-band-gap light absorption increase is detected.
Mode-beating spectroscopy in a few-mode optical guide
Authors: Eckhardt Ralf , Ulrich Reinhard
Published: July 2002

A mode-coupling modulator is scanned along an optical waveguide. At the output of the guide spatial beats are observed. From their spatial frequencies ‖βm−βn‖ a self-consistent set of propagation constants βm of the guided modes is derived in a manner similar to that used in atomic spectroscopy. The method is illustrated by magneto-optic modulation of the six lowest modes of an optical fiber. Assignment of the βm to modal fields yields the core ellipticity and internal stress of the fiber.
Absolute density determination of CH radicals in a methane plasma
Authors: Jacob W. , Engelhard M. , Möller W. , Koch A.
Published: July 2002

Laser-induced fluorescence was applied at the B–X transition of the CH radical to measure absolute densities of the CH radicals in an electron cyclotron resonance methane plasma. The absolute experimental uncertainty is only about 30% due to a new calibration procedure. The CH density correlates well with optical emission from the CH A–X and B–X transitions over a wide pressure range. Experimental results are in satisfactory agreement with predictions from a model based on rate equations for the electron-induced dissociation and ionization of the parent methane gas. This model also includes the interaction of the plasma species with the surrounding walls and the particle transport due to pumping.
Polarized luminescence study of ordered nonlinear optical material ZnGeP2
Authors: McCrae J. E. , Gregg M. R. , Hengehold R. L. , Yeo Y. K. , Ostdiek P. H. , Ohmer M. C. , Schunemann P. G. , Pollak T. M.
Published: July 2002

Polarized photoluminescence (PL) and cathodoluminescence studies have been made as a function of excitation laser wavelength or electron beam energy for the ordered nonlinear optical material ZnGeP2 grown by the Bridgman method. The luminescence signal is seen to be strongly polarized. Furthermore, several PL peaks appear on top of one large broad band, and the dominant peak shifts to a higher energy position as the excitation energy increases. This observation can be explained by the transitions from three conduction bands (Γ6, Γ7, Γ7) to acceptor level one triplet ground state levels which parody the top three valence subbands (Γ6, Γ7, Γ6). This explanation agrees well with the theoretical energy band diagram of this pseudodirect band-gap material.
Electrochemical Er doping of porous silicon and its room-temperature luminescence at ∼1.54 μm
Authors: Kimura T. , Yokoi A. , Horiguchi H. , Saito R. , Ikoma T. , Sato A.
Published: July 2002

We present a new electro-chemical method for incorporating high concentration Er ions deep into porous silicon layers and its intense photoluminescence at ∼1.54 μm at room temperature. Porous silicon layers prepared by anodic etching of p-type silicon substrates in HF/H2O are immersed in ErCl3/ethanol solution. Then the negative bias relative to a counter platinum electrode is applied to the samples. Er3+ ions are drawn into fine pores of the porous silicon layers by the electric field. After thermal annealing at ∼1300 °C in an O2/Ar atmosphere, the samples show sharp and intense Er3+-related photoluminescence at ∼1.54 μm at room temperature upon excitation with an Ar ion laser.
Small quantum-sized CdS particles assembled to form a regularly nanostructured porous film
Authors: Hoyer Patrick , Baba Nobuyoshi , Masuda Hideki
Published: July 2002

Submicroporous CdS films were fabricated by a two-step replication process, in which porous anodic alumina was used as a template. The films were grown on a porous gold support of the same structure, resulting in a free-standing CdS/Au membrane. The diameter of the holes of the regular porous structure is in the order of 100 nm. Moreover, the replicated CdS film consists of small-sized quantized crystalline particles, the size of which are in the range of 5 nm. Thus, the film is ordered in the 5 and 100 nm domain forming a superstructure.
Magnetostriction and giant magnetoresistance in annealed NiFe/Ag multilayers
Authors: Kim Y. K. , Sanders S. C.
Published: July 2002

Magnetostriction data are reported for NiFe/Ag multilayer thin films displaying giant magnetoresistance. Magnetostriction and magnetoresistance were measured as functions of annealing temperature for NiFe/Ag samples having different numbers of NiFe/Ag bilayers and Ag spacer thicknesses. They varied systematically with annealing temperature in a manner consistent with residual stress reduction and microstructural changes such as grain-boundary diffusion and grain growth. Zero magnetostriction concurrent with high magnetoresistance ratio (5%) and field sensitivity [7.5%/(kA/m) (0.6%/Oe)] was observed for an optimal multilayer configuration and annealing temperature. This combination of zero magnetostriction and high magnetoresistive response makes the NiFe/Ag multilayer system an attractive candidate for high-performance magnetic recording read-head sensors.
Techniques for determining thermal conductivity and heat capacity under hydrostatic pressure
Authors: Andersson S. , Bäckström G.
Published: July 2002

The paper describes a method for measuring the pressure dependence of the thermal conductivity and the heat capacity of hard materials and single crystals. Two parallel metal strips are evaporated onto a flat surface of the specimen, one being used as a heater, the other as a resistance thermometer. The appropriate theoretical expression for a specimen in a liquid medium is fitted to the temperature, sampled at constant time intervals. The thermophysical properties of the liquid high-pressure medium are taken from hot-wire experiments. The procedure has been thoroughly tested at atmospheric pressure using an MgO crystal and glass as specimens and liquids of different characteristics in lieu of high-pressure medium. The accuracy attainable was found to be 3% or better, the standard deviation of the measurements being about 0.3%. The potential of the system was demonstrated by measurements on single-crystal MgO under pressures up to 1 GPa.
Temperature variable long path cell for absorption measurements
Authors: Shetter R. E. , Davidson J. A. , Cantrell C. A. , Calvert J. G.
Published: July 2002

A long path cell has been designed and constructed for absorption measurements at temperatures ranging from 215 to 470 K and at pressures from vacuum to 10 atm. It enables us to measure temperature and pressure dependence of the spectra and reaction rates of gases of atmospheric interest.
Low energy electron-enhanced etching of Si(100) in hydrogen/helium direct-current plasma
Authors: Gillis H. P. , Choutov D. A. , Steiner P. A. , Piper J. D. , Crouch J. H. , Dove P. M. , Martin K. P.
Published: July 2002

Low energy electron-enhanced etching of Si(100) has been achieved by placing the sample on the anode of a dc discharge in hydrogen/helium mixtures. Over a broad range of gas composition, gas pressure, and discharge current, nonpatterned samples gave etch yields of 0.01–0.02 atoms/electron, and average etch rates of 2000–3000 Å/min. Postetch examination by atomic force microscopy revealed surface roughness of 2–3 nm. These results are related to incident flux of H atoms and electrons through a simple model of the anode sheath layer above the sample.
A sensitive cryogenic refractometer. Application to the refractive index determination of pure or mixed liquid methane, ethane, and nitrogen
Authors: Badoz J. , Liboux M. Le , Nahoum R. , Israel G. , Raulin F. , Torre J. P.
Published: July 2002

A cryogenic refractometer is described. It enables preparation of liquefied samples and measurement of their refractive index at low temperatures (down to 20 K). The liquid sample can be a pure liquefied gas or a mixture. The composition of the liquid mixture can be estimated from the volume and pressure of each gas measured during the liquefying process. The determination of absolute values of the refractive index necessitates a calibration, therefore the accuracy is limited to 10−3 index unit. Sensitivity and reproductibility are better (5× 10−4) and could be improved to 10−4. The refractive index of pure liquid methane was determined at several temperatures (91–106 K) and 670 nm. The results obtained agree with the published data. The refractive index of mixtures of liquid methane and ethane, with and without dissolved nitrogen, was also determined at 94 K and 1.5 bar total pressure, for which conditions no data were previously available.
Thermal lens spectroscopy using a diode laser and optical fibers
Authors: Rojas Dorys , Silva Robert J. , Russo Richard E.
Published: July 2002

A compact thermal lens spectrometer was developed using optical fibers and a diode laser for measurements of rare earth species in aqueous solutions. A cw GaAlAs diode laser coupled with a multimode step-index fiber was used as the excitation source. The thermal lens was probed with a He-Ne laser using a multimode 200 μm diameter core optical fiber as the aperture and to transmit the probe beam to the detector. The system was tested for the detection of Nd3+ in aqueous solutions at 794.6 nm. A sensitivity with detection limit of 79±4 M−1 and 8×10−5 M was obtained for an incident power of 10 mW and a power density of 11 W/cm2.
Photoluminescence study of the crossover from two-dimensional to three-dimensional growth for Ge on Si(100)
Authors: Schittenhelm P. , Gail M. , Brunner J. , Nützel J. F. , Abstreiter G.
Published: July 2002

Narrow Ge layers embedded in Si are investigated using photoluminescence (PL) spectroscopy. With increasing layer thickness a growth mode changeover from two-dimensional (2D) strained-layer growth to three dimensional Stranski–Krastanov growth is observed. Additional PL lines that are redshifted with respect to the PL signal of the 2D strained layers are attributed to islands formed by three-dimensional growth. The occurrence of these new lines is accompanied by a blueshift of the PL of the 2D layers, indicating a strong Ge diffusion from the 2D layers towards the islands.
Economical device for measuring thickness of a thin polymer film
Authors: Hirvi K. , Mäkelä T. , Pekola J. , Paalanen M.
Published: July 2002

An inexpensive device (about $2K) for thickness measurements of thin (<1 μm) polymer films has been constructed. The homogeneous film is placed on a bulk substrate and three semiconductor lasers of different wavelengths are used to measure the reflectances at normal incidence. The thickness can be deduced with typically 4–8 nm uncertainty.
Weissenberg camera for macromolecules with imaging plate data collection system at the Photon Factory: Present status and future plan (invited)
Authors: Sakabe N. , Ikemizu S. , Sakabe K. , Higashi T. , Nakagawa A. , Watanabe N. , Adachi S. , Sasaki K.
Published: July 2002

A Weissenberg camera for macromolecules with imaging plate data collection system at BL6A and BL18B stations in the Photon Factory is introduced and evaluated. The special feature of these systems is considered matching for both SR-x rays and protein crystallography. This system is user-friendly and can collect a large amount of data to higher resolution from the crystal with large unit cell dimensions. A newly developed camera can be used as a time-resolved Laue camera and a Weissenberg camera. A large image reader (IPR4080) that can scan 400×400 mm2 and 400×800 mm2 sizes of imaging plates has been developed and evaluated. The new data collection system combined with the new camera and IPR4080 will be installed at the BL18B station in October 1994.
Nanometer-scale imaging of potential profiles in optically excited n-i-p-i heterostructure using Kelvin probe force microscopy
Authors: Chavez-Pirson A. , Vatel O. , Tanimoto M. , Ando H. , Iwamura H. , Kanbe H.
Published: July 2002

We report on measurements of the potential profile of a GaAs/AlGaAs n-i-p-i multiple quantum well structure using a scanning Kelvin probe force microscope (KFM). Using this novel technique we directly measure with meV precision and sub-100 nm spatial resolution the potential difference between n-i-p-i layers with and without external optical excitation. The measured potential profiles, which have not been directly imaged previously, agree well with potential profiles calculated for optically excited n-i-p-i structures, but modified by band bending effects at the surface.
High-resolution electron time-of-flight apparatus for the soft x-ray region
Authors: Hemmers O. , Whitfield S. B. , Glans P. , Wang H. , Lindle D. W. , Wehlitz R. , Sellin I. A.
Published: July 2002

A gas-phase time-of-flight (TOF) apparatus, capable of supporting as many as six electron-TOF analyzers viewing the same interaction region, has been developed to measure energy- and angle-resolved electrons with kinetic energies up to 5 keV. Each analyzer includes a newly designed lens system that can retard electrons to about 2% of their initial kinetic energy without significant loss of transmission; the analyzers can thus achieve a resolving power (E/ΔE) greater than 104 over a wide kinetic-energy range. Such high resolving power is comparable to the photon energy resolution of state-of-the-art synchrotron–radiation beamlines in the soft x-ray range, opening the TOF technique to numerous high-resolution applications. In addition, the angular placement of the analyzers, by design, permits detailed studies of nondipolar angular distribution effects in gas-phase photoemission.
Absolute distance meter based on a frequency-modulated laser diode
Authors: Minoni U. , Rovati L. , Docchio F.
Published: July 2002

This article describes a distance measuring instrument based on a frequency-modulation continuous wave interferometer implemented in a compact setup suitable for industrial applications. The prototype uses a visible laser diode that is frequency-modulated with a triangular wave form. Measurements carried out with a cooperative target show a measuring range from 130 to 300 mm with a relative accuracy of 1.2×10−3.
Sample cell capable of 100% relative humidity suitable for x-ray diffraction of aligned lipid multibilayers
Authors: Katsaras J. , Watson M. J.
Published: July 2002

We describe a sample cell capable of attaining 100% relative humidity that is suitable for the study of aligned lipid multibilayers using x-ray diffraction. The basic principles of this cell are applicable to sample environments used in a variety of physical techniques (e.g., nuclear magnetic resonance, light scattering, infrared spectroscopies, etc.) thus enabling these techniques, for the first time, to study aligned samples having the same physical characteristics (i.e., repeat spacing, transition temperature, etc.) as their liposomal counterparts immersed in water.
Divergence effects in monochromatic x-ray microdiffraction using tapered capillary optics
Authors: Noyan I. C. , Wang P.-C. , Kaldor S. K. , Jordan-Sweet J. L. , Liniger E. G.
Published: July 2002

Tapered capillaries are frequently used as beam-concentrating optics in microbeam x-ray diffraction experiments. The beams exiting such devices are usually highly divergent and may possess nonuniform intensity distributions. In addition, their alignment poses some special challenges. In this article, the effects of these factors on the precision and accuracy of diffraction data are presented.
Raman spectra of polyparaphenylene-based carbon prepared at low heat-treatment temperatures
Authors: Matthews M. J. , Bi X. X. , Dresselhaus M. S. , Endo M. , Takahashi T.
Published: July 2002

Raman spectroscopy was used to characterize the structural development of polyparaphenylene (PPP) based carbon at various heat treatment temperatures (THT), with an emphasis on the low THT regime. Experimental data show that PPP-based carbons undergo a smooth transiiton from a mostly PPP polymer-type structure for heat treatments below ∼750 °C to a graphitized structure at a heat treatment temperature of 2700 °C. These results give insight into the unusually high specific capacities observed in lithium-PPP systems which are of particular interest for application to Li ion battery technology.
Effects of carbon implantation on generation lifetime in silicon
Authors: Ban Ibrahim , Öztürk Mehmet C. , Christensen Kim , Maher Dennis M.
Published: July 2002

In this study, we present characterization of metal–oxide–silicon (MOS) capacitors fabricated on carbon (C12) implanted Si substrates. Carbon was implanted at an energy of 50 keV with doses ranging from 1×1012 cm−2 to 4.1×1015 cm−2. Metal–oxide silicon capacitors were fabricated and used to determine the MOS capacitance–voltage (C–V) and capacitance–time (C–t) behavior. These measurements revealed a strong correlation between carrier lifetime and the C dose. Degradation in lifetime was observed for C dose levels as low as 4×1012 cm−2. At C doses equal to and above 6.4×1013 cm−2, extremely low generation lifetimes were obtained (∼10−7 s). On the other hand, for C dose levels higher than 2.7×1014 cm−2, a low accumulation capacitance was observed at high frequencies and attributed to hole traps. Below this dose, both flatband voltage and interface trap density of the C implanted samples were comparable to those of the monitors.
Raman spectroscopy of laser ablated BaTiO3/YBa2Cu3O7−x thin film bilayer structure
Authors: Cui Dafu , Li Chunling , Ma Kun , Zhou Yueliang , Liu Yanwei , Chen Zhenghao , Ma Jianwei , Li Lin
Published: July 2002

Raman scattering was used to characterize BaTiO3/YBa2Cu3O7−x thin film bilayer structure grown by pulsed laser ablation (PLA). The Raman spectra were compared with the x-ray diffraction (XRD) spectra. The Raman peaks due to the tetragonal phase of BaTiO3 (BTO) and to the 123 phase YBa2Cu3O7−x (YBCO) were observed at room temperature. XRD results showed that the BaTiO3 thin film has highly c-axis oriented tetragonal phase and is fully epitaxial. However, some impurity phases were observed from the Raman spectrum of the BaTiO3 thin film.
Ion implantation induced enhancement of magnetoresistance in La0.67Ca0.33MnO3
Authors: Chen C.-H. , Talyansky V. , Kwon C. , Rajeswari M. , Sharma R. P. , Ramesh R. , Venkatesan T. , Melngailis John , Zhang Z. , Chu W. K.
Published: July 2002

Thin films of colossal magnetoresistance (MR) material, La0.67Ca0.33MnO3, were implanted with different doses (1011–1015 ions/cm2) of 200 keV Ar+ ions. The implanted samples were examined by ion channeling and x-ray diffraction techniques. The channeling results clearly showed that the magnitude of the induced lattice disorder did not increase greatly for implantation doses up to 5×1013 ions/cm2. In this low dose implantation regime, the magnetoresistance {MR=[R(0)−R(H)]/R(0)} increased by 50%, the peak resistivity went up by two orders of magnitude, and the magnetoresistivity peak temperature decreased by 130 K compared to the original, unimplanted sample. For doses ≥5×1013 ions/cm2, the damage was significant and caused the sample to become semiconducting.
High power failure of superconducting microwave filters: Investigation by means of thermal imaging
Authors: Hampel G. , Kolodner P. , Gammel P. L. , Polakos P. A. , de Obaldia E. , Mankiewich P. M. , Anderson A. , Slattery R. , Zhang D. , Liang G. C. , Shih C. F.
Published: July 2002

We have investigated power handling of high-temperature superconducting microstrip filters employing highly sensitive thermal imaging. At low power, the images show small heating effects localized to areas with high current densities (ΔT<0.5 K), consistent with the known surface resistance and simulations of the current distribution. The breakdown at high-power levels, however, is always nucleated by a frequency independent local hot spot (T≳Tc). Scanning electron microscopy analysis of this area reveals a flaw in the superconducting material, presumably reducing the local critical current. The maximum power handling of these filters is, therefore, still open to improvement.
Improvement of the Young’s modulus of SiC film by low-pressure chemical vapor deposition with B2H6 gas
Authors: Murooka Ken-ichi , Higashikawa Iwao , Gomei Yoshio
Published: July 2002

SiC is one of the potential materials for use as an x-ray mask substrate. It is preferable for an x-ray mask substrate to have a large elastic modulus, so as to suppress any distortion of the extremely minute and precise patterns. The improvement of the Young’s modulus of polycrystalline SiC film using low-pressure chemical vapor deposition with the introduction of B 2H6 in the source gas was investigated. The Young’s modulus increased with the addition of B2H6, and a maximum value of 600 GPa, which was 25% higher than in the case without B2H6, was reached at a source gas ratio B/Si=0.02. Two models which would possibly explain this phenomenon are discussed, and the theory which takes into account the interaction between carrier and ion core is found to provide a more plausible explanation of the results.
Band lineup between CdS and ultra high vacuum-cleaved CuInS2 single crystals
Authors: Klein A. , Löher T. , Tomm Y. , Pettenkofer C. , Jaegermann W.
Published: July 2002

The interface formation between vacuum evaporated CdS and ultrahigh vacuum-cleaved CuInS2 single crystals has been studied by synchrotron excited photoelectron spectroscopy. The valence band discontinuity is determined directly from valence band difference spectra to be ΔEV=0.6 (±0.1) eV. This value is significantly smaller than for other preparation conditions given in the literature and evidently not suitable for solar cell applications. The similarity to observations at the CdS/CuInS2 interfaces suggests that neutrality levels play a dominant role in establishing the band lineup at interfaces containing chalcopyrite semiconductors.
Model near field calculations for optical data storage readout
Authors: Madrazo A. , Nieto-Vesperinas M.
Published: July 2002

We investigate the near field distribution of light diffracted from deep grooves of sub-wavelength lateral dimensions, carved on a flat metallic surface. It is shown that, in spite of multiple interaction, the reflected field presents, for s polarization, peaks very localized on the groove positions, and whose amplitude increases with the groove depth. For p polarization, however, the near field does not follow the surface profile. This permits us to establish for s polarization a threshold in order to distinguish signals produced on reflection from grooves having different profiles. This is of guidance in diffractive modeling of readout systems of high density optical disks.
Temperature-dependent electroluminescence from (Eu, Gd) coordination complexes
Authors: Zhang Xianmin , Sun Runguang , Zheng Qianbing , Kobayashi Takayoshi , Li Wenlian
Published: July 2002

Light emission from single-layered electroluminescent devices is described in which (Eu, Gd) coordination complexes, (Eu0.1Gd0.9)(TTA)3(TPPO)2, and electron transport material oxadiazole derivative, 2-(4-biphenyl)-5-(4-t-butylphenylyl)-1,3,4-oxadiazole, are dispersed in a hole-transporting host polymer poly(N-vinylcarbazole) film. The color of the emitted electroluminescence changes smoothly from green-white to red with temperature varying from 77 to 300 K. This phenomenon is discussed in terms of temperature dependent yields of phosphorescence from the triplet state of the Gd and Eu chelates and the intermolecular energy transfer from Gd-chelate to Eu-chelate cages.
Electrostatic force microscopy of silver nanocrystals with nanometer-scale resolution
Authors: Nyffenegger Ralph M. , Penner Reginald M. , Schierle Rainer
Published: July 2002

Silver nanoparticles on graphite basal plane surfaces were concurrently imaged using electrostatic force microscopy (EFM) and noncontact atomic force microscopy. EFM images were obtained having a lateral resolution of 4–5 nm, and a resolution perpendicular to the surface of ≈1 nm. The dependence of the contrast in the EFM data for the silver nanoparticles as a function of the applied tip bias was consistent with a positive charge for the silver nanocrystals on the graphite surface, qualitatively as expected by theory.
Practical SQUID instrument for nondestructive testing
Authors: Tralshawala N. , Claycomb J. R. , Miller J. H.
Published: July 2002

We report on the development of a scanning eddy-current imaging system designed to detect deep subsurface flaws in conducting materials. A high transition temperature (high-Tc) superconducting quantum interference device (SQUID) magnetometer is employed to provide the required sensitivity at low frequencies, while a combination of small cylindrical high-Tc superconducting and μ-metal shields enable the instrument to be scanned in a magnetically noisy environment, rather than the object under test. The shields are arranged to prevent unwanted excitation and ambient noise fields from reaching the SQUID, and to enhance spatial resolution and minimize undesirable edge effects. Thus far, the instrument has successfully detected cracks and pits through 10 layers of aluminum, with a combined thickness of 5 cm at room temperature.
Colossal magnetoresistance of spin-glass perovskite La0.67Ca0.33Mn0.9Fe0.1O3
Authors: Cai Jian-Wang , Wang Cong , Shen Bao-Gen , Zhao Jian-Gao , Zhan Wen-Shan
Published: July 2002

The magnetic and magnetotransport properties of the perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound. A metal-to-insulator transition and colossal magnetoresistance have been observed near its spin freezing temperature; besides, the insulator behavior has been found to reappear at lower temperature. The formation of ferromagnetic and antiferromagnetic clusters and the competition between them with the introduction of Fe3+ ions, which do not participate in the double-exchange process, have been suggested to explain the experimental results.
Fabrication of Ti/TiOx tunneling barriers by tapping mode atomic force microscopy induced local oxidation
Authors: Irmer B. , Kehrle M. , Lorenz H. , Kotthaus J. P.
Published: July 2002

We use an atomic force microscope operating in a dynamic modus, commonly called tapping mode, to completely oxidise through thin 5 nm titanium films using the very local electric field between the tip and the sample. Tapping mode local oxidation minimizes tip degradation and therefore enhances resolution and reliability. By working under a controllable environment and measuring the resistance in situ while oxidising we are able to fabricate well-defined isolating Ti–TiOx–Ti barriers as small as 15 nm. Their conductance shows an exponential dependence on the oxide width, thereby identifying tunneling as the dominant conduction mechanism. From the nonlinear current-voltage characteristic a tunneling barrier height of 178 meV is derived.
Observation of boron bound excitons in boron-implanted and annealed natural IIa diamonds
Authors: Sternschulte H. , Wahl S. , Thonke K. , Sauer R. , Dalmer M. , Ronning C. , Hofsäss H.
Published: July 2002

Cathodoluminescence at 77 K was used to study the optical properties of ion-implanted and annealed natural type IIa diamonds. The substrates were implanted at room temperature with C12+, B11+, P3+, and As75+ -ions with energies of up to 350 keV and doses of up to 13×1013cm−2. After annealing at 1200 °C, the cathodoluminescence spectra show a number of transitions which are induced by the radiation damage independent of the implanted ion species. Only in the BHe3implanted samples are there two transitions related to the implanted ion species: the 4.5 eV band and the boron bound exciton. The appearance of the bound exciton spectrum demonstrates the presence of isolated boron on substitutional lattice sites implying electrical acceptor activity. Our annealing studies indicate a minimum annealing temperature of 1000 ° for the activation of the implanted boron atoms onto the acceptor states.
Passivation and surface leakage in CdZnTe spectrometers
Authors: Ruzin A. , Nemirovsky Y.
Published: July 2002

The subject of surface leakage and passivation in spectrometers fabricated in high pressure Bridgman CdZnTe crystals with evaporated gold contacts has been examined. The surface leakage has been found to be the dominant mechanism of dark current leakage in metal–semiconductor–metal detectors with noninjecting contacts. Several passivation techniques have been examined with various degrees of success in terms of reducing the mean value and the power spectral density of dark noise characteristics. An insulating polymer was applied on the bare surface reducing the total leakage current by the factor of 6–7, while favorably affecting the dark noise spectral density by decreasing the corner frequency of the low frequency noise. However, a considerable surface leakage has been observed even in these apparently passivated spectrometers. A three terminal device with iso-potential high voltage contacts has been fabricated and tested, exhibiting a reduction of the total dark current leakage by approximately two orders of magnitude. With this three terminal design, the bulk resistivity of typical high pressure Bridgman crystals is correctly determined and found to be ∼2⋅1011 Ω⋅cm.
The dependence of particle permittivity on the shear stress of electrorheological fluids
Authors: Lan Yucheng , Men Shouqiang , Zhao Xiaopeng , Lu Kunquan
Published: July 2002

A ferroelectric TGS particle/silicone oil electrorheological (ER) fluid is introduced to investigate the dielectric dependence of the ER effect. The dielectric constant of ferroelectric changes violently with temperature at the Curie temperature (Tc). By measuring temperature dependence of shear stress across Tc, the effect of dielectric constant on shear stress can be directly obtained. All the results are more reliable due to the same conditions, such as size, shape, composition of particles, as well as the same chemical nature of particles and interface property between particles and liquid. The measurement was carried out under a high-frequency (1000 Hz) ac electric field where ER effect is dielectric constant dominated. For the first time, the dependence of the ER effect on dielectric mismatch has been quantitatively obtained experimentally. There is an obvious deviation of available theoretical calculations from our measured data. A more rigorous theoretical study should be developed to quantitatively interpret the relation of the shear stress and the permittivity mismatch factor.
Use of ionomer as an electron injecting and hole blocking material for polymer light-emitting diode
Authors: Lee Hyang-Mok , Choi Kang-Hoon , Hwang Do-Hoon , Do Lee-Mi , Zyung Taehyoung , Lee Jong-Woo , Park Jung-Ki
Published: July 2002

Light-emitting diodes of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEHPPV) are fabricated using sodium sulfonated polystyrene (SSPS) ionomer containing 10 mol % ionic groups as an electron injecting and hole blocking material. When an electric field stronger than 2.7×107 V/m is applied, SSPS in the indium–tin oxide ITO/MEH-PPV/SSPS/Al system causes a bridging effect between sodium ions and the Al cathode at the SSPS/Al interface, leading to excellent electron injection. Furthermore, the ionomer has a high band gap energy of ∼5 eV, resulting in hole blocking. The operating voltage for the ITO/MEH-PPV/SSPS/Al is reduced by ∼60% and the relative quantum efficiency is enhanced by three orders of magnitude compared with those of the corresponding single-layer MEH-PPV device.
Raman scattering investigation of KH2PO4 subsequent to high fluence laser irradiation
Authors: Demos S. G. , Yan M. , Staggs M. , De Yoreo J. J. , Radousky H. B.
Published: July 2002

The spectral characteristics of the internal (PO4 tetrahedron) modes of fast-grown KH2PO4 crystals under sub-damage threshold, 10 ns, 355 nm laser irradiation have been investigated. Pump-and-probe Raman spectroscopy indicates transient changes of the intensity of the 915 cm−1, –PO4 internal mode. This change is attributed to a transient increase of the absorption due to generation by the 355 nm pump pulse of electronic defects in the bulk of the crystal.
Ni and Ti Schottky barriers on n-AlGaN grown on SiC substrates
Authors: Yu L. S. , Qiao D. J. , Xing Q. J. , Lau S. S. , Boutros K. S. , Redwing J. M.
Published: July 2002

The electrical characteristics of Ni and Ti Schottky barriers on n-Al0.15Ga0.85N on SiC were investigated. We report that the barrier height for Ni on n-Al0.15Ga0.85N was about 1.26 eV and about 1 eV or less for Ti. These barrier heights are about 0.3–0.4 eV larger than those for Ni and Ti on n-GaN, which are in good agreement with Schottky model predictions.
Emission spectra and mode structure of InAs/GaAs self-organized quantum dot lasers
Authors: Harris L. , Mowbray D. J. , Skolnick M. S. , Hopkinson M. , Hill G.
Published: July 2002

A study of the emission spectra and mode structure of InAs/GaAs self-organized quantum dot lasers is presented. In contrast to conventional bulk or quantum well lasers, the number of lasing modes increases above threshold. This behavior is shown to be consistent with carriers localized in noninteracting dots and a resultant inhomogeneously broadened gain spectrum. The lasing spectra are found to have a complicated form with groups of longitudinal modes separated by nonlasing spectral regions and lasing occurring via a number of different lateral modes. These characteristics are discussed in terms of the spatially discrete nature of the quantum dots.
Intersublevel transitions in InAs/GaAs quantum dots infrared photodetectors
Authors: Maimon S. , Finkman E. , Bahir G. , Schacham S. E. , Garcia J. M. , Petroff P. M.
Published: July 2002

Thermal generation rate in quantum dots (QD) can be significantly smaller than in quantum wells, rendering a much improved signal to noise ratio. QDs infrared photodetectors were implemented, composed of ten layers of self-assembled InAs dots grown on GaAs substrate. Low temperature spectral response shows two peaks at low bias, and three at a high one, polarized differently. The electronic level structure is determined, based on polarization, bias, and temperature dependence of the transitions. Although absorbance was not observed, a photoconductive signal was recorded. This may be attributed to a large photoconductive gain due to a relatively long lifetime, which indicates, in turn, a reduced generation rate.
Fabrication and characterization of small tunnel junctions through a thin dielectric membrane
Authors: Aassime A. , Manninen A. J. , Pekola J. P.
Published: July 2002

We show that a small tapered hole through a thin silicon nitride membrane provides a mask for tunnel junction structures. Our experiments imply, unlike in the conventional planar electron beam lithography, that tunnel junctions are well voltage biased in this structure with vanishingly small on-chip impedance. Our technique allows fabrication of double junctions, and even multijunction linear arrays, with small metallic islands in between.
Ultrafast detection and autocorrelation of picosecond THz radiation pulses with a GaAs/AlAs superlattice
Authors: Winnerl S. , Seiwerth W. , Schomburg E. , Grenzer J. , Renk K. F. , Langerak C. J. G. M. , van der Meer A. F. G. , Pavel’ev D. G. , Koschurinov Yu. , Ignatov A. A. , Melzer B. , Ustinov V. , Ivanov S. , Kop’ev P. S.
Published: July 2002

We used a wide miniband GaAs/AlAs superlattice (at room temperature) for detection and autocorrelation of picosecond THz radiation pulses (frequency 4.3 THz) from a free-electron laser. The detection was based on a THz-field induced change in conductivity of the superlattice, and the correlation on the nonlinearity of the conductivity change at strong THz-pulse-power. The nonlinear conductivity change was due to two effects, which we attribute to dynamical localization of miniband electrons and to ionization of deep impurity centers.
Laplace-transform deep-level transient spectroscopy studies of the G4 gold–hydrogen complex in silicon
Authors: Deixler P. , Terry J. , Hawkins I. D. , Evans-Freeman J. H. , Peaker A. R. , Rubaldo L. , Maude D. K. , Portal J.-C. , Dobaczewski L. , Bonde Nielsen K. , Nylandsted Larsen A. , Mesli A.
Published: July 2002

We have studied n-type silicon containing gold and gold–hydrogen complexes using high-resolution “Laplace” deep-level transient spectroscopy. This technique has enabled two quite distinct electron emission rates to be observed at temperatures between 240 and 300 K. These are associated with the gold acceptor and the level referred to as G4, which is observed when hydrogen and gold are present in silicon. The gold acceptor has a measured activation energy for electron emission of 558±8 meV, and the G4 state of 542±8 meV. The directly measured electron capture cross section for G4 is determined to be 0.6±0.1 σn(gold acceptor) at 275 K from which it is inferred that the state is acceptor-like.
Hydrogen uptake in alumina thin films synthesized from an aluminum plasma stream in an oxygen ambient
Authors: Schneider Jochen M. , Anders André , Hjörvarsson Björgvin , Petrov Ivan , Macák Karol , Helmersson Ulf , Sundgren Jan-Eric
Published: July 2002

We describe the hydrogen uptake during the synthesis of alumina films from H2O present in the high vacuum gas background. The hydrogen concentration in the films was determined by the H1(N15,αγ)C12 nuclear resonance reaction. Furthermore, we show the presence of hydrogen ions in the plasma stream by time-of-flight mass spectrometry. The hydrogen content increased in both the film and the plasma stream, as the oxygen partial pressure was increased. On the basis of these measurements and thermodynamic considerations, we suggest that an aluminum oxide hydroxide compound is formed, both on the cathode surface as well as in the film. The large scatter in the data reported in the literature for refractive index and chemical stability of alumina thin films can be explained on the basis of the suggested aluminum oxide hydroxide formation.
Improvements in electrical properties of (Ba,Sr)TiO3 capacitor with chemical vapor deposited Pt top electrode using Pt hexafluoroacetylacetonate
Authors: Lee Jong Myeong , Kang Sang Yeol , Shin Ju Cheol , Kim Won Joon , Hwang Cheol Seong , Kim Hyeong Joon
Published: July 2002

Electrical properties of (Bs,Sr)TiO3 (BST) thin films are characterized with sputtered and metal organic chemical vapor deposited (MOCVD) Pt top electrodes. BST films with MOCVD Pt top electrodes, which were deposited using Pt(CF3COCHCOCF3)2 (Pt-HFA) as a precursor, showed less leakage current without bulged curves and a higher dielectric constant than those with sputtered Pt top electrodes. The improvement of electrical properties seems to result from the reduction of interface trap sites with the incorporation of fluorine atoms from HFA ligands.
Electron transport in starburst phenylquinoxalines
Authors: Redecker M. , Bradley D. D. C. , Jandke M. , Strohriegl P.
Published: July 2002

The electron transport properties of two soluble tris-phenylquinoxalines have been investigated by the time-of-flight technique. The electron mobilities for both compounds approach 10−4 cm2/V s at electric fields of 106 V/cm at room temperature. These are high values for isotropic electron transport materials suitable for use in organic light emitting diodes.
Structural and optical quality of GaN/metal/Si heterostructures fabricated by excimer laser lift-off
Authors: Wong W. S. , Cho Y. , Weber E. R. , Sands T. , Yu K. M. , Krüger J. , Wengrow A. B. , Cheung N. W.
Published: July 2002

Gallium nitride (GaN) thin films grown on sapphire substrates were successfully bonded and transferred onto Si substrates using a Pd–In metallic bond. After bonding, a single 600 mJ/cm2, 38 ns KrF (248 nm) excimer laser pulse was directed through the transparent sapphire followed by a low-temperature heat treatment to remove the substrate. Channeling-Rutherford backscattering measurements revealed the thickness of the defective interfacial region to be approximately 350 nm. The full width at half maximum, low-temperature (4 K), donor-bound exciton photoluminescence (PL) peak was larger by 25% on the exposed interfacial layer compared to the original GaN surface. Ion milling of the exposed interface to a depth of 400 nm was found to remove the interfacial layer and associated defects. The minimum channeling yield and PL linewidths from the exposed interface were found to be comparable to those obtained from the original GaN surface after ion milling.
In situ resistance measurements of strained carbon nanotubes
Authors: Paulson S. , Falvo M. R. , Snider N. , Helser A. , Hudson T. , Seeger A. , Taylor R. M. , Superfine R. , Washburn S.
Published: July 2002

We investigate the response of multiwalled carbon nanotubes to mechanical strain applied with an atomic force microscope probe. We find in some samples, changes in the contact resistance dominate the measured resistance change. In others, strain large enough to fracture the tube can be applied without a significant change in the contact resistance. In this case, we observe that enough force is applied to break the tube without any change in resistance until the tube fails. We have also manipulated the ends of the broken tube back in contact with each other, re-establishing a finite resistance. We observe that, in this broken configuration, the resistance of the sample is tunable to values 15–350 kΩ greater than prior to breaking.
Low-temperature near-field nonlinear absorption spectroscopy of InGaAs single quantum dots
Authors: Matsumoto Takuya , Ohtsu Motoichi , Matsuda Kazunari , Saiki Toshiharu , Saito Hideaki , Nishi Kenichi
Published: July 2002

Nonlinear absorption spectroscopy of InGaAs single quantum dots (QDs) was realized by means of a low-temperature near-field optical microscope. The spatial distribution of the nonlinear absorption change in single QDs was determined. The dependence of the nonlinear absorption change on the pump power density demonstrates that the nonlinearity originates from the state filling of the ground state. The nonlinear absorption spectrum showed a homogeneous broadening of the ground state of about 5 meV. Furthermore, the change in the absorption cross section of the single QD when the ground state is saturated with carriers is estimated to be 2.8±0.6 nm2, which agrees with the result predicted on the basis of theoretical consideration.
Influence of the liquid states on the crystallization process of nanocrystal-forming Zr–Cu–Pd–Al metallic glasses
Authors: Fan Cang , Inoue Akihisa
Published: July 2002

Rapidly solidified ribbons of nanocrystal-forming Zr–Cu–Pd–Al metallic glasses were prepared at various liquid temperatures (TL). Differential scanning calorimetry (DSC) traces show clearly the influence of the liquid states on the thermal properties and crystallization process. Namely, with increasing TL, the exothermal peaks of the DSC traces shift to higher temperatures, the super-cooled-liquid region ΔTx increases, and the decomposition of the metastable compound Zr2(Cu, Pd) becomes more difficult. These results suggest that the liquid state strongly controls the crystallization process of the nanocrystal-forming metallic glasses. This behavior may originate from the variation of the quenched-in nuclei, which highly depends on the short-range-order domains in liquid with different TL. We suggest that the stronger attractive interaction in Zr–Pd, which exhibits large negative mixing enthalpy, leads to the short-range order domains.
Blue InGaN-based laser diodes with an emission wavelength of 450 nm
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Matsushita Toshio , Mukai Takashi
Published: July 2002

Blue InGaN single-quantum-well-structure laser diodes (LDs) with an emission wavelength of 450 nm were grown on an epitaxially laterally overgrown GaN substrate by a metalorganic chemical vapor deposition method. The threshold current density and voltage were 4.6 kA cm−2 and 6.1 V, respectively. The estimated lifetime was approximately 200 h under room-temperature continuous-wave operation at an output power of 5 mW. When the number of InGaN well layers of the LDs with emission wavelengths longer than 435 nm varied from one to three, the lowest threshold current density was obtained when the number of well layers was one.
Synchrotron-radiation-induced, selective-area deposition of gold on polyimide from solution
Authors: Ma Qing , Moldovan Nicolaie , Mancini Derrick C. , Rosenberg Richard A.
Published: July 2002

Room-temperature photoinduced, selective-area deposition of gold films on polyimide from gold salt solution using synchrotron radiation x rays is described. A film growth rate as high as 40 nm/min is obtained. For thickness <50 nm, the films consist of nanograins with a grain size of about 200 nm. For thicker films, gold deposit forms a ramified morphology on top of the nanograin film. The change in morphology is discussed in terms of the change in the yield of the photoelectrons generated by x rays as a function of growth.