bluuebunny/crossref_metadata_2025 huggingface dataset:
Precipitation of superconducting, single phase EuBa2Cu4O8 from molten hydroxide at 475 °C
Authors: Sandford David , Marquez Linda N. , Stacy Angelica M.
Published: July 2002

A solution route involving reactive precipitation from molten hydroxide melts is presented for the synthesis of EuBa2Cu4O8. The melt consisted of a mixture of NaOH, KOH, and Ba(OH)2, and was heated at 475 °C for ∼2 h prior to reactant addition. Eu2O3 and CuO were then added, and in several hours crystallites of EuBa2Cu4O8 were obtained. The product was a single phase as determined by powder x-ray diffraction and the onset of superconductivity was observed at 78 K by dc magnetic susceptibility.
Effects of an electric field on the static friction of a metal on a ferroelectric material
Authors: Seto Takatoshi
Published: July 2002

We investigated the static friction of a metal placed on ferroelectrics when an alternating current (ac) electric field was applied. Specifically, we studied the angle at which a stainless-steel disc placed on a lead zirconate titanate (PZT) plate begins to slide, namely, the friction angle. It was found that under a constant voltage the friction angle increased as the frequency of the applied voltage was increased. A time dependency of the static friction coefficient on electrostatic force was discussed.
Dual microchannel plate module for a gated monochromatic x-ray imager
Authors: Oertel J. A. , Archuleta T. , Peterson C. G. , Marshall F. J.
Published: July 2002

Development and testing of a dual microchannel plate (MCP) module to be used in the national inertial confinement fusion (ICF) program has recently been completed. The MCP module is a key component of a new monochromatic x-ray imaging diagnostic which is designed around a four channel Kirkpatrick–Baez microscope and diffraction crystals and is located at the University of Rochester’s Omega laser system. The MCP module has two separate MCP regions with centers spaced 53 mm apart. Each region contains a 25 mm MCP proximity focused to a P-11 phosphor coated fiberoptic faceplate. The two L/D=40, MCPs have a 10.2 mm wide, 8 ohm stripline constructed of 500 nm copper overcoated with 100 nm gold. A 4 kV, 150 ps electrical pulse provides an optical gatewidth of 80 ps and spatial resolution has been measured at 20 lp/mm.
Design and performance of an integrated fluorescence, polarized fluorescence, and Brewster angle microscope/Langmuir trough assembly for the study of lung surfactant monolayers
Authors: Lipp Michael M. , Lee Ka Yee C. , Zasadzinski Joseph A. , Waring Alan J.
Published: July 2002

We describe an integrated fluorescence, polarized fluorescence, and Brewster angle microscope/Langmuir trough assembly. This apparatus was specifically designed for the study of lung surfactant (LS) monolayers, and is well suited for the study of other lipid/protein monolayer systems. The apparatus can be operated simultaneously in both the fluorescence and Brewster angle modes under a wide range of conditions, including physiological subphases and temperatures. The combination of information obtained from these microscopy techniques facilitates the identification of the composition of coexisting phases, allows us to systematically study the effects of specific proteins on lipid monolayers, and eliminates possible artifacts inherent to fluorescence. To demonstrate this system we present images of mixed monolayers of the anionic and unsaturated lipid components of LS and show that synergistic interactions between certain LS proteins and these lipids hold the key to the proper functioning of LS monolayers.
Aqueous sample holders for high-frequency electron spin resonance
Authors: Barnes Jeff P. , Freed Jack H.
Published: July 2002

A quasioptical approach is utilized to design a resonator and sample holder for aqueous samples for high-frequency (250 GHz) electron spin resonance (ESR) spectroscopy. A disk shaped sample geometry was chosen to match the field contours of the fundamental mode in a Fabry–Perot resonator. A transmission-line analysis is used to determine the optimum sample geometry while taking into account diffractive effects of the sample and the sample holder on the far infrared (FIR) radiation field. FIR-ESR spectra of several aqueous solutions of nitroxide spin labels, including membrane vesicles and a labeled protein, are shown to demonstrate the success of the technique.
Phase comparison technique for measuring liquid–liquid phase equilibrium
Authors: Lu Z. , Daridon J. L. , Lagourette B. , Ye S.
Published: July 2002

In this article, a new method is demonstrated to measure the liquid–liquid phase equilibrium for binary systems. A phase comparison technique was employed to real-time display the phase–time curve in a “wave form (time) object” of Hewlett–Packard visual engineering environment. It was found that the phase–time curve showed a distorted wave form when liquid–liquid phase transition took place. The abnormal curve can therefore be used to detect liquid–liquid phase transitions. Measurements were performed in several binary systems such as nitromethane+1-hexanol, nitromethane+butanol, and nitroethane+n-hexane. The experimental results are in good agreement with those in the literature.
A new simple compact refractometer applied to measurements of air density fluctuations
Authors: Fang H. , Juncar P.
Published: July 2002

We describe a new simple, compact refractometer for air refractive index measurements. It consists of a double plane–plane Fabry Perot interferometer. Both interferometers consisting of Zerodur spacers of thickness of 1 and 100 mm are illuminated independently by the same single mode laser diode. The shorter cavity allows unambiguous identification of the transmission peak of the longer one to which the laser frequency is servo-locked. The refractive index of air is obtained via a heterodyne comparison with a second laser locked to a hyperfine component of the rubidium D2 line. We obtain a resolution of order 10−10 and accuracy of a few times 10−8. The metrological characteristics of the interferometer in vacuum are presented. Initial results for refractive index measurements agree with values calculated using the revised Edlen formulas. We also describe how this refractometer is used to measure variations of the density of air and their correlation with changes of refractive index of air. The density of air is used to make buoyancy corrections when comparing mass standards of different volume. Our preliminary results indicate that the values of air density determined by refractometry agree with those calculated using the Comité International des Poids et Mesures formula, which is based on measurements of temperature, pressure, moisture content, and CO2 concentration.
Variable temperature fluid stage for atomic force microscopy
Authors: Workman R. K. , Manne S.
Published: July 2002

The design of a simple, variable temperature fluid cell for an atomic force microscope is presented. The stage is based on a thermoelectric heating/cooling element, which allows control of sample and fluid temperature from −5 to 130 °C. The stage is stable enough to image at molecular resolution almost throughout the range of accessible temperature and can be used for imaging in either gas or liquids. This allows the molecular scale investigation of surface phase transitions and chemical kinetics at solid/liquid interfaces by varying the temperature. As an example, we present results of temperature-induced phase transitions in self-assembled surfactant aggregates at solid/liquid interfaces.
CdF2:In: A novel material for optically written storage of information
Authors: Ryskin A. I. , Shcheulin A. S. , Koziarska B. , Langer J. M. , Suchocki A. , Buczinskaya I. I. , Fedorov P. P. , Sobolev B. P.
Published: July 2002

We demonstrate that semiconducting CdF2 crystals doped with indium is an efficient medium for optical storage of information in static and dynamic regimes. A metastable phototransformation of 1018 cm−3 In centers from a localized deep state to a hydrogenlike shallow state leads to a change of the refractive index Δn of about 10−4 for the probe beam at the wavelength of 500 nm. The diffraction efficiency is temperature dependent due to spontaneous decay of the grating caused by thermal recovery of the In impurity from the metastable hydrogenic state to the localized ground state.
Microcontact printing and pattern transfer using trichlorosilanes on oxide substrates
Authors: St. John Pamela M. , Craighead H. G.
Published: July 2002

Microcontact printing was used to pattern silicon, aluminum, and titanium substrates using octadecyltrichlorosilane as the ink and an elastomer as the stamp. Patterns were transferred into the substrates using both dry and wet etching. The Al and Ti were etched using an electron cyclotron resonance (ECR) plasma source at low ion energies and low pressure. Silicon was etched in HF to remove the native oxide, followed by KOH. Microcontact printing using OTS ink is a convenient and easy way to pattern both semiconductor and metal surfaces without the extended use of photolithography.
Oscillatory magnetic interlayer exchange coupling in Fe–N/TiN multilayers
Authors: Wang Zhen-Jun , Wen L. S. , Chang Xiang-Rong , Gu Y. S. , Tian Zhong-Zhuo , Xiao J. M.
Published: July 2002

The discovery of oscillatory interlayer exchange coupling in a new type of ceramic superlattice system Fe–N/TiN, is reported. The magnitude of the exchange coupling was found to oscillate with the thickness of the TiN spacer layer and Fe–N ferromagnetic layer with periods about 0.8 and 0.6 nm, respectively.
Growth of epitaxial a-axis and c-axis oriented Sr2RuO4 films
Authors: Madhavan S. , Schlom D. G. , Dabkowski A. , Dabkowska H. A. , Liu Ying
Published: July 2002

Epitaxial films of Sr2RuO4 have been grown in situ by pulsed laser deposition on (100) LaAlO3 and (100) LaSrGaO4 substrates. X-ray diffraction results show that the films are single domain and grow c-axis oriented on (100) LaAlO3 and a-axis oriented on (100) LaSrGaO4 substrates. X-ray φ scans indicate epitaxial alignment of the film and substrate in-plane axes in both cases. Resistivity versus temperature measurements reveal that the as-grown c-axis oriented films are semiconducting and the a-axis oriented films are metallic.
Organic insulating films of nanometer thicknesses
Authors: Vuillaume D. , Boulas C. , Collet J. , Davidovits J. V. , Rondelez F.
Published: July 2002

It is demonstrated that monolayers of organic molecules (long chain hydrocarbons) as thin as 1.9 nm, deposited by the self-assembly technique on silicon, form high performance electrically insulating barriers. Their properties are compared with those of silicon dioxide. Leakage current densities through the organic monolayers of the order of 10−8–10−7A/cm2 have been obtained. These values are 4–5 decades lower than those for silicon dioxide of equivalent thickness. Larger tunneling barriers for organic monolayers than for silicon dioxide explain these results.
Paramagnetic susceptibility of semiconducting CdF2:In crystals: Direct evidence of the negative-U nature of the DX-like center
Authors: Kazanskii S. A. , Ryskin A. I. , Romanov V. V.
Published: July 2002

Paramagnetic susceptibility κpara of CdF2 crystals with bistable In centers is measured in the temperature range T=4–300 K. For crystals cooled in the dark down to liquid helium temperature, κpara is determined by the trace Mn2+ impurity. Illumination of the sample by the ultraviolet-visible light results in the appearance of the photoinduced δκpara signal due to formation of centers with the magnetic moment J=1/2. This gives a clear evidence of an absence of paramagnetism in the deep state of the bistable In center and its presence in the shallow state, i.e., proves the negative-U nature of the deep state.
Colossal magnetoresistance in epitaxial La(1−x−y)NayMnO3 thin film
Authors: Sahana M. , Singh R. N. , Shivakumara C. , Vasanthacharya N. Y. , Hegde M. S. , Subramanian S. , Prasad V. , Subramanyam S. V.
Published: July 2002

We have synthesized La0.83Na0.11MnO2.93 by heating La2O3 and MnCO3 in NaCl melt at 900 °C. The exact composition was arrived by analyzing each ion by an independent chemical method. The compound crystallized in a rhombohedral structure and showed an insulator-to-metal transition at 290 K. Epitaxial thin films were fabricated on LaAlO3 (100) using a pulsed laser deposition technique. The film also showed an insulator-to-metal transition at 290 K. Magnetoresistance [ΔR/R0=(RH−R0)/R0] was −71% near the insulator-to-metal transition temperature of 290 K at 6 T magnetic field.
Ultrafast all-optical gate switch based on frequency shift accompanied by semiconductor band-filling effect
Authors: Nakamura Shigeru , Tajima Kazuhito
Published: July 2002

We propose a novel all-optical gate switch based on a frequency shift accompanied by the semiconductor band-filling effect. This all-optical switch is very simple in structure, yet is capable of ultra-high-speed and high-efficiency switching. The switching characteristics are numerically investigated with a rate equation model for nonlinear phase shift. Then, the principle of operation is experimentally verified by measuring the spectral and time-domain properties of the switch. Its switching time is nearly the same as the duration (600 fs in the present experiment) of a control pulse.
Experimental study of integrated-optics microcavity resonators: Toward an all-optical switching device
Authors: Blom F. C. , van Dijk D. R. , Hoekstra H. J. W. M. , Driessen A. , Popma Th. J. A.
Published: July 2002

An integrated all-optical switch based on a high-Q nonlinear cylindrical microcavity resonator is proposed. The switch consists of single mode planar waveguides that allow coupling light in and out to a microresonator, exhibiting whispering gallery modes. Due to the high Q factor and the small dimensions, fast switching at low power is feasible for devices based on presently available nonlinear polymers as the active material. In this approach, the transmission of an integrated optical waveguide close to a microcavity has been measured and related to the resonances of the cylindrical microcavity.
Picosecond responses of low-dosage arsenic-ion-implanted GaAs photoconductors
Authors: Lin Gong-Ru , Pan Ci-Ling
Published: July 2002

Ultrafast optoelectronic characteristics of GaAs implanted with 200 keV arsenic ions at dosage as low as 1013 ions/cm2 are reported. Ultrashort photoexcited carrier lifetimes of 0.23±0.02, 0.87±0.02, and 3±0.2 ps were determined for as-implanted, rapid thermal annealing (RTA) (600 °C for 30 s) and furnace-annealed (600 °C for 30 min) arsenic-ion-implanted GaAs or GaAs:As+, respectively. The switching response of photoconductive switches (PCSs) fabricated on the latter two materials were ∼3 and 8 ps, respectively. The leakage current of the PCS fabricated on furnace-annealed sample was as low as 30 nA. The breakdown fields exceeded 150 (instrument-limited) and 90 kV/cm for furnace- and RTA-annealed samples, respectively. The optical responsivity of low-dosage arsenic-implanted GaAs photoconductive switch can be as high as 0.01 A/W. This also compared favorably with the same device made on state-of-the-art photoconductor such as molecular-beam epitaxy grown GaAs at low temperatures.
Effects of proton irradiation on the high-temperature superconducting system Y1−xPrxBa2Cu3O7−δ
Authors: Paulius L. M. , Shamu R. E. , Ferguson S. , de Andrade M. C. , Maple M. B.
Published: July 2002

Magnetic measurements have been performed on polycrystalline samples of Y1−xPrxBa2Cu3O7−δ (x=0, 0.1, 0.2, and 0.3) before and after irradiation with 12 MeV protons. While magnetic hysteresis measurements reveal that the critical current density Jc increases for all the samples after irradiation, magnetic relaxation measurements show that the effective pinning energy Ueff increases only for the samples with x⩽0.1 and actually decreases for the samples with x⩾0.2.
A reflection high-energy electron diffraction and atomic force microscopy study of the chemical beam epitaxial growth of InAs and InP islands on (001) GaP
Authors: Junno B. , Junno T. , Miller M. S. , Samuelson L.
Published: July 2002

We have studied the formation of strained InAs and InP island structures on GaP surfaces grown by chemical beam epitaxy. InP grows pseudomorphically for 3 ML before island crystallization is observed by reflection high-energy electron diffraction, following a typical Stranski–Krastanov growth mode. For the growth of InAs on GaP, three-dimensional diffraction peaks are observed after 0.9 ML of InAs have been deposited, indicating a Volmer–Weber growth mode. Atomic force microscopy studies of these structures are presented and the optical properties are discussed.
Coupling of GaN- and AlN-like longitudinal optic phonons in Ga1−xAlxN solid solutions
Authors: Demangeot F. , Groenen J. , Frandon J. , Renucci M. A. , Briot O. , Clur S. , Aulombard R. L.
Published: July 2002

Long-wavelength optical phonons of Ga1−xAlxN solid solutions have been identified in a wide compositional range by Raman spectroscopy. The A1 and E1 polar phonon frequencies evolve continuously with x from one-member crystal to the other. The same behavior seems to hold true for the silent B1 mode, which manifests itself by an interference with an unidentified continuum. Coupling of the longitudinal-optic (LO) modes associated with the two types of bonds, via the macroscopic electric field, is treated by a generalization of the dielectric model [D. T. Hon and W. L. Faust, J. Appl. Phys. 1, 241 (1973)]. This approach accounts for the observed frequencies and supports the apparent one-mode behavior of the polar LO phonons.
Molecular dynamics simulation of enhanced oxygen ion diffusion in strained yttria-stabilized zirconia
Authors: Suzuki Ken , Kubo Momoji , Oumi Yasunori , Miura Ryuji , Takaba Hiromitsu , Fahmi Adil , Chatterjee Abhijit , Teraishi Kazuo , Miyamoto Akira
Published: July 2002

The application of strain to yttria-stabilized zirconia (YSZ), which can be realized by sandwiching a thin YSZ film epitaxially between layers of a material with larger lattice constants, is proposed as a means to enhance oxygen ion mobility. The possible mechanism of such an enhancement was investigated by molecular dynamics using a CeO2–YSZ superlattice. The calculated diffusion coefficient of oxygen ions in the superlattice is some 1.7 times higher than in YSZ alone due to a decreased activation barrier from the strain of the YSZ structure.
Optical band gap in Ga1−xInxN (0<x<0.2) on GaN by photoreflection spectroscopy
Authors: Wetzel C. , Takeuchi T. , Yamaguchi S. , Katoh H. , Amano H. , Akasaki I.
Published: July 2002

The optical band gap in 40 nm Ga1−xInxN/GaN single heterostructures is investigated in the composition range 0<x<0.2 by photoreflection spectroscopy (PR) at room temperature and compared with photoluminescence (PL) data. Clear PR oscillations at the GaInN band gap are observed as originating in the large piezoelectric field. Effective band gap bowing parameters b are derived for pseudomorphically stressed GaInN on GaN: b=2.6 eV (PR) and b=3.2 eV (PL in localized states). Using experimental deformation potentials of GaN, b=3.8 eV is extrapolated for the optical band gap in relaxed GaInN material. Previously reported smaller values are discussed.
Enhanced electro-optic response of layered composite materials
Authors: Nelson Robert L. , Boyd Robert W.
Published: July 2002

We have constructed a multilayered composite material consisting of alternating layers of rf-sputtered barium titanate and spin-coated polycarbonate containing a third-order nonlinear optical organic dopant. The effective nonlinear susceptibility of the composite describing the quadratic electro-optic effect was measured to have the value χ(3)=(3.2+0.2i)×10−21±25% (m/V)2. The real part of this value is a factor of 3.2±50% times larger than that of the doped polycarbonate, which is the dominant electro-optic component of the composite. We have modeled the experiment by using both effective medium theory and by solving the wave equation for our multilayered system, and we find that these approaches give consistent predictions which are in good agreement to the experimental results.
Leakage current behaviors of acceptor- and donor-doped (Ba0.5Sr0.5)TiO3 thin films
Authors: Kim Sang Sub , Park Chanro
Published: July 2002

We have investigated the effects of acceptor and donor doping on the leakage current behavior of Pt/(Ba0.5Sr0.5)TiO3/Pt film capacitors prepared by a pulsed-laser deposition method. We selected Mn/Al and Nb as acceptor and donor dopants, respectively. The leakage current behavior depends strongly on the type of dopants. Al doping decreases the leakage current level, and Mn doping decreases it further. Nb doping greatly increases it. The decrease in leakage current associated with acceptor doping seems to partly result from a decrease in tunneling current due to expansion of the depletion layer width. The converse appears to apply with donor doping.
Influence of annealing on carrier dynamics in As ion-implanted epitaxially lifted-off GaAs layers
Authors: Marcinkevičius S. , Jagadish C. , Tan H. H. , Kaminska M. , Korona K. , Adomavičius R. , Krotkus A.
Published: July 2002

Electrical and dynamical optical characterization of As-ion implanted and annealed GaAs has been performed. Changes of physical properties induced by annealing have been studied in detail by using layers annealed in small steps in the temperature range 500–700 °C. The carrier trapping rate increases exponentially with increase of inverse annealing temperature indicating that in ion-implanted GaAs ultrafast carrier capture occurs to the same trapping centers as in low-temperature-grown GaAs. Relatively large resistivity and electron mobility in As-implanted GaAs have been observed after annealing, which shows that this material possesses properties required for a variety of ultrafast optoelectronic applications.
Silicon nanowires grown on iron-patterned silicon substrates
Authors: Gu Qian , Dang Haiyan , Cao Jien , Zhao Jianhong , Fan Shoushan
Published: July 2002

This letter reports the synthesis of silicon nanowires on iron-patterned silicon substrates in a controlled fashion using a method involving thermal evaporation of pure silicon powder. The positions of these silicon nanowires were controlled by depositing iron in desired areas on the substrates. Transmission electron microscopy, high-resolution transmission electron microscopy, and scanning electron microscopy images indicate that the products are straight crystalline silicon nanowires with diameters of 10–60 nm. The formation mechanism of the nanowires is discussed.
The structure and spectroscopy of monolayers of water on MgO: An ab initio study
Authors: Delle Site L. , Alavi A. , Lynden-Bell R. M.
Published: July 2002

The structure and energetics of a monolayer of water on a perfect MgO substrate is investigated by ab initio calculations. Several minima in the potential energy surface were found including both physisorbed and chemisorbed states in which one third of the water molecules were dissociated. In the more stable of the physisorbed states, the water molecules were not all parallel to the surface, but some showed hydrogen bonding with surface oxygen ions. Even in the physisorbed state, the geometry of these surface H-bonded water molecules were distorted relative to the bulk. One of the stable chemisorbed states was the same as that found in earlier work by Giordano et al. [Phys. Rev. Lett. 81, 1271 (1998)]. Two more stable chemisorbed structures were found in which strong hydrogen bonds to the hydroxide ions in the water layer were formed. The existence of different minima appears to be the result of a subtle interplay between hydrogen bonding between adsorbed species and with the surface oxide ions. Harmonic vibrational frequencies were determined for both a chemisorbed and a physisorbed states and spectroscopic features which should discriminate between chemisorbed and physisorbed states are identified.
The structure of liquid and supercritical deuterium fluoride from neutron scattering using high-pressure techniques
Authors: Pfleiderer Till , Waldner Isabella , Bertagnolli Helmut , Tödheide Klaus , Fischer Henry E.
Published: July 2002

We present neutron diffraction data for deuterium fluoride at two liquid and four supercritical states in the temperature range of 300–473 K and for pressures up to 320 bar, spanning a factor of 4 in sample density. The intra- and intermolecular parts of the measured structure factors were separated and conclusions about the temperature and density dependence of the intra- and intermolecular structure are deduced. © 2000 American Institute of Physics.
Shot-noise suppression in Schottky barrier diodes
Authors: Gomila G. , Reggiani L. , Rubı́ J. M.
Published: July 2002

We give a theoretical interpretation of the noise properties of Schottky barrier diodes based on the role played by the long range Coulomb interaction. We show that at low bias Schottky diodes display shot noise because the presence of the depletion layer makes the effects of the Coulomb interaction negligible on the current fluctuations. When the device passes from barrier to flat band conditions, the Coulomb interaction becomes active, thus introducing correlation between different current fluctuations. Therefore, the crossover between shot and thermal noise represents the suppression due to long range Coulomb interaction of the otherwise full shot noise. Similar ideas can be used to interpret the noise properties of other semiconductor devices.
Molecular Ornstein–Zernike approach to the solvent effects on solute electronic structures in solution
Authors: Yoshida Norio , Kato Shigeki
Published: July 2002

A new approach to ab initio electronic structure calculations of solute molecules in solution is presented. Combined with the molecular Ornstein–Zernike (MOZ) integral equation theory for polyatomic liquids, solute electronic wave function and solvent distribution around a solute are determined in a self-consistent manner. The hypernetted chain approximation is employed for solving the MOZ equation. In order to describe the short-range solute–solvent interactions, the effective potential operating solute electron is placed on a solute molecule, which is determined by a least-squares fitting to ab initio exchange repulsion/charge transfer energies. The present method, referred to as the MOZ self-consistent-field (SCF) method, is applied to a solute H2O molecule in water solvent. The solvent shift for the vertical excitation to the nπ* state of H2CO in aqueous solution is also examined. The results obtained by the MOZ-SCF calculations are compared with those by the reference interaction site model-SCF theory and the polarizable continuum model.
Thermoelectric properties of chemically substituted skutterudites YbyCo4SnxSb12−x
Authors: Dilley N. R. , Bauer E. D. , Maple M. B. , Sales B. C.
Published: July 2002

We report the results of a study of thermoelectric properties of chemically substituted quasiternary materials related to the recently discovered filled skutterudite compound YbFe4Sb12. The study explored partial filling at the Yb site as well as chemical doping with Sn at the Sb site in an attempt to optimize the thermoelectric figure of merit ZT in the system YbyCo4SnxSb12−x. Our measurements of these physical quantities from room temperature down to T=10 K indicate that, in our study, only the alloy Yb0.44Co4Sb12 possessed thermoelectric properties that are improved over the parent compound YbFe4Sb12, attaining a value of ZT=0.1 at T=300 K.
Observation and first-principles calculation of buried wurtzite phases in zinc-blende CdTe thin films
Authors: Yan Y. , Al-Jassim M. M. , Jones K. M. , Wei S.-H. , Zhang S. B.
Published: July 2002

We report direct observation of the existence of buried thin wurtzite CdTe layers in nominally pure zinc-blende CdTe thin films using high-resolution transmission electron microscopy. The formation of the buried wurtzite layers is a result of the formation of high density of planar defects in the zinc-blende films—the wurtzite layers are formed by closely spaced lamellar twins. First-principles calculations reveal that the presence of the buried wurtzite layers may be responsible for the poor electrical properties of the polycrystalline zinc-blende CdTe films.
Diffusional behavior of polypeptides in the thermotropic liquid crystalline state as studied by the pulse field-gradient spin-echo H1 nuclear magnetic resonance method
Authors: Yin Yige , Zhao Chenhua , Kuroki Shigeki , Ando Isao
Published: July 2002

The self-diffusion coefficients (D) and H1 spin–spin relaxation times (T2) of poly(γ-oleyl L-glutamate)(POLLG) with long oleyl side chains and poly(γ-n-octadecyl L-glutamate)(POLG) with n-alkyl side chains have been measured by the pulse field-gradient spin-echo H1 nuclear magnetic resonance (NMR) method and the Carr–Purcell/Meiboom–Gill (CPMG) H1 NMR method, respectively, over a wide range of temperatures from 30 to 80 °C, in order to elucidate the dynamic behavior of polypeptides in the thermotropic liquid crystalline state, which take the α-helical conformation. From these experiments, it was found that the diffusion coefficients of POLLG and POLG chains in the thermotropic liquid crystalline state at 60 °C are 9.97×10−7 and 3.53×10−7 cm2/s, respectively, and the former diffuses faster than the latter. The diffusion coefficients of POLG in the directions parallel (D∥) and perpendicular (D⊥) to the α-helical chain axis were determined over a wide range of temperatures, and the D∥ value was found to be much larger than the D⊥ value. Further, from the H1 T2 experiments, it was suggested that the mobility of the side chains relates closely to the diffusion process.
Picosecond time-resolved resonance Raman observation of the iso-CH2I–I photoproduct from the “photoisomerization” reaction of diiodomethane in the solution phase
Authors: Kwok Wai Ming , Ma Chensheng , Parker Anthony W. , Phillips David , Towrie Michael , Matousek Pavel , Phillips David Lee
Published: July 2002

We report a preliminary picosecond Stokes and anti-Stokes time-resolved resonance Raman (267 nm pump and 400 nm probe excitation wavelengths) investigation of the initial formation and vibrational cooling of the iso-CH2I–I photoproduct species produced after ultraviolet excitation of diiodomethane in room temperature solutions. A comparison of the picosecond resonance Raman spectra with previously reported nanosecond transient resonance Raman spectra and density functional theory computations shows that the iso-CH2I–I photoproduct species is predominantly responsible for the ∼385 nm transient absorption band observed from several picoseconds to nanoseconds after ultraviolet excitation of diiodomethane in the solution phase. Similar results were obtained in both nonpolar solution (cyclohexane solvent) and polar solution (acetonitrile) solvent. The picosecond resonance Raman spectra confirm that the iso-CH2I–I photoproduct species is formed vibrationally hot within several picoseconds and then subsequently undergoes vibrational cooling on the 4–50 ps time scale. This is consistent with the absorption bands changes occurring over similar times in a recent femtosecond transient absorption study. We discuss a possible qualitative scenario for the formation of the iso-CH2I–I species that is in agreement with the available gas phase experimental results for the ultraviolet photodissociation reaction of diiodomethane and gas phase collisional deactivation studies of the CH2I radical. The proposed hypothesis is consistent with the lack of distinct resonance Raman bands in the first few picoseconds of our solution phase spectra of the iso-CH2I–I photoproduct as well as previously reported femtosecond transient absorption bands that are broad and weak in the 300–500 nm region over the 0.3–3 ps time scale.
Mechanical mixing in nonlinear nanomechanical resonators
Authors: Erbe A. , Krömmer H. , Kraus A. , Blick R. H. , Corso G. , Richter K.
Published: July 2002

The physics of nonlinear dynamics has been studied in detail in macroscopic mechanical systems like the driven classical pendulum. By now, it is possible to build mechanical devices on the nanometer scale with eigenfrequencies on the order of several 100 MHz. In this work, we want to present how to machine such nanomechanical resonators out of silicon-on-insulator wafers and how to operate them in the nonlinear regime in order to investigate higher-order mechanical mixing at radio frequencies. The nonlinear response then is compared in detail to nth-order perturbation theory and nonperturbative numerical calculations.
Interdiffusion of CdS/CdTe thin films: Modeling x-ray diffraction line profiles
Authors: McCandless Brian E. , Engelmann Michael G. , Birkmire Robert W.
Published: July 2002

A method for analyzing the diffusion process for CdS into CdTe thin films using x-ray diffraction is presented, allowing both bulk and grain boundary diffusion coefficients to be estimated. The equilibrium phase diagram for the CdTe1−xSx and CdS1−yTey alloy system was determined for temperatures from 625 °C to 415 °C. Measured diffraction line profiles for time-progressive diffusion of CdS into CdTe films resulting from thermal treatment at 440° were modeled using bulk and grain boundary diffusion coefficients of 1.25×10−13 cm2/s and 1.5×10−8 cm2/s, respectively. Modeling diffraction line profiles of samples treated at temperatures from 380 °C to 480 °C yielded Arrhenius activation energies for bulk and grain boundary diffusion processes of 2.8 eV and 2.0 eV, respectively. The bulk diffusion coefficients obtained from thin film structures were comparable to those obtained by Auger depth profiles for CdS/CdTe couples using CdTe single crystals.
Temperature dependence of inclusion-dissociation behavior between molecular nanotubes and linear polymers
Authors: Saito Makoto , Shimomura Takeshi , Okumura Yasushi , Ito Kohzo , Hayakawa Reinosuke
Published: July 2002

We have investigated the inclusion-dissociation behavior between molecular nanotubes and linear polymers in solutions by measuring the induced circular dichroism of the mixture of the molecular nanotubes, which are composed of α-cyclodextrins linked by three cross-linking bridges, and poly(ethylene glycol) modified with azobenzene. It was found that the inclusion complex between the nanotubes and the linear polymers was formed at room temperature, and that the polymers were dissociated from the nanotubes with increasing temperature, as expected theoretically.
Structural and magnetoresistance properties of La2/3Ca1/3MnO3 thin films on buffered silicon substrates
Authors: Kumar D. , Chattopadhyay S. , Gilmore Walter M. , Lee C. B. , Sankar J. , Kvit A. , Sharma A. K. , Narayan J. , Pietambaram S. V. , Singh Rajiv K.
Published: July 2002

We report an epitaxial growth of LCMO (La2/3Ca1/3MnO3) film on Si by using a highly conducting diffusion barrier layer of TiN. In order to achieve epitaxial growth of LCMO films, MgO, and SrTiO3 films were used as intermediate layers between LCMO and TiN layers. The results have indicated that the properties of LCMO films on Si substrates, deposited under an optimized condition, are on par with the properties of LCMO films on conventional oxide substrates such as LaAlO3 and SrTiO3 in terms of paramagnetic to ferromagnetic transition temperature, insulator to metal transition temperature, and magnetoresistance ratio.
Anomalous transport on polymeric porous film electrodes in the dopant-induced insulator-to-conductor transition analyzed by electrochemical impedance
Authors: Garcia-Belmonte Germà , Bisquert Juan , Pereira Ernesto C. , Fabregat-Santiago Francisco
Published: July 2002

In the present letter, we have identified anomalous transport patterns on conducting polymer thin-film electrodes [poly(thiophene-3-acetic acid)] by means of electrochemical impedance measurements. This type of electrical behavior yields conductance responses exhibiting frequency dispersion at frequencies in excess of the ac onset ωc. The study of impedance spectra under variation of the applied potential allows to determine the threshold potential at which a dopant-induced insulator-to-conductor transition takes place. Moreover, since the charge carrier concentration in the polymer matrix is directly modulated by the insertion of anions via the applied potential, some relevant aspects of the doping process, such as the dimensionality of the ion insertion, can be properly investigated.
Effect of scattering at lateral edges on the current-perpendicular-to plane giant magnetoresistance of submicronic pillars
Authors: Dieny B. , Li M. , Liao S. , Ju K.
Published: July 2002

From a phenomenological point of view, we have investigated the effect of scattering at lateral edges on the current-perpendicular-to-plane (CPP) transport properties of submicronic magnetic multilayer pillars. This scattering can be considered as a current-in-plane contribution in the CPP geometry. As a first attempt to calculate the CPP resistance and GMR in this situation, we have combined the serial resistance network model of CPP transport with an exponential variation of the local conductivity as a function of the distance from the edges of the pillars assuming that the scattering is perfectly diffusive at the edges of the pillars. As the lateral size of the pillars decreases below 100 nm, it is shown that this scattering leads to a strong increase in the CPP resistivity as well as a decrease in both ΔR/R and ΔR* area. Furthermore, due to the difference in mean-free paths from layer to layer, the current lines are no longer uniform in the pillar even if the latter is the shape of an infinite cylinder.
Training effect of exchange biased iron–oxide/ferromagnet systems
Authors: Zhang K. , Zhao T. , Fujiwara H.
Published: July 2002

Substantial training effect in hysteresis loops was observed in ferromagnet (F)–antiferromagnet (AF) exchange coupled systems of the structure, Si(100)/iron–oxide(tAF)/F layer (5 nm)/Ta(10 nm), prepared by magnetron sputtering. The exchange bias field and the coercivity decrease with increasing number of loop cycles. The initially asymmetric hysteresis loop becomes more symmetric as the number of loop cycles increases. The effect is more prominent in the descending curve starting from the saturation in the positive (parallel to the pinned direction) direction than in the ascending curve of the hysteresis loop. The value of the ascending curve switching field |Hsw+| is rather unchanged while the switching field |Hsw−| in the descending curve decreases drastically with repeated hysteresis loop cycling as was observed in some CoO/Co and NiO/NiFe systems. Those phenomena can be interpreted by a modification of the extended model of Fulcomer and Charap’s: the essential modification being the introduction of positive and negative exchange coupling between AF grains.
Picosecond time-resolved resonance Raman observation of the iso-CH2Cl–I and iso-CH2I–Cl photoproducts from the “photoisomerization” reactions of CH2ICl in the solution phase
Authors: Kwok Wai Ming , Ma Chensheng , Parker Anthony W. , Phillips David , Towrie Michael , Matousek Pavel , Zheng Xuming , Phillips David Lee
Published: July 2002

We report a preliminary picosecond Stokes time-resolved resonance Raman investigation of the initial formation and subsequent decay of the photoproduct produced following 267 nm excitation of CH2ClI in acetonitrile solution. Density-functional theory computations were done for several probable photoproduct species. Comparison of these computational results and results from a recent femtosecond transient absorption study to our present picosecond resonance Raman spectra indicate that the iso-CH2Cl–I species is mainly produced and associated with the ∼460 nm transient absorption band. The iso-CH2Cl–I species appears to decay and form appreciable amounts of the more stable iso-CH2I–Cl species that is associated with a ∼370 nm transient absorption band after a few hundred ps.
Correlation between the x-ray induced and the electron-induced electron emission yields of insulators
Authors: Cazaux Jacques
Published: July 2002

Similarly to the constant loss model used for expressing the electron-induced secondary electron yield from solids, δ, a simple model is used for expressing the x-ray-induced electron emission yield, δX, from uncharged insulators. The two yields involve common mechanisms for the transport and the escape of the secondary electrons and are sensitive to the crystalline state, to the temperature and to the surface composition of the investigated insulator. For practical purposes, it is thus possible to estimate δX of the insulator of interest from the knowledge of δ and vice versa. In particular, these two yields may be related to each other by an expression of the form: δX/δ=μR hν/E0 (with μ linear absorption coefficient of the material of interest for incident photons of energy hν) when the range, R, of incident electrons (of energy E0) is far larger than the escape depth, s, of the secondary electrons. Deduced from some published δ(E0) curves, the illustrations concern the evolution in the photon energy range 0.5–10 keV for diamond and of CsI. Similar results on the temperature dependence of δX (between 77 K and 593 K) are also reported for NaCl. Conversely, the evolution of δ(E0) in the 0.5–5 keV energy range for CsI and for solid Xe is deduced from the data of photo electron emission δX experiments. The trends of δ in the 5-20 keV range are also established for various alkali halides while the application of the method to other materials such as metallic oxides, polymers or glasses is also suggested.
Electrostatic fluctuations in a direct current magnetron sputtering plasma
Authors: Martines E. , Cavazzana R. , Serianni G. , Spolaore M. , Tramontin L. , Zuin M. , Antoni V.
Published: July 2002

Electrostatic fluctuations (up to 500 kHz) have been studied in a planar dc magnetron device using Langmuir probes measuring the floating potential and the ion saturation current. Fluctuation levels as high as 30% have been found inside the magnetic trap. A two-point spectral analysis has shown that the fluctuations are due to coherent modes with a low azimuthal mode number. The modes are present only when the discharge power and the neutral gas pressure are above a threshold. Their frequency spacing decreases when the neutral gas pressure is raised, so that increasing the pressure leads to a more turbulent state. The modes have been interpreted as unstable E×B/density gradient modes.
Waves in two component electron-dust plasma
Authors: Khrapak S. A. , Morfill G.
Published: July 2002

A self-consistent model of linear waves propagating in a two component dusty plasma whose constituents are positively charged dust grains and electrons is presented. Ionization and recombination processes on the dust particle surface, elastic Coulomb collisions of electrons with dust, electron-neutral collisions, dust-electron and dust-neutral collisions, as well as dust charge variations are taken into account. The relationships between the characteristic frequencies of these processes are studied. A linear dispersion relation is obtained and some limiting cases are analyzed. It is shown that Langmuir waves are damped due to electron collisions. It is also found that low frequency waves are always stable in such a system, and there exist two dust-acoustic modes: (1) the usual dust acoustic mode, similar to the ion acoustic wave in electron-ion plasmas; and (2) an acoustic mode with reduced phase velocity, associated with dust particle charge variations. The static response of electron-dust plasmas is examined and the screening length of the system is determined.
Transient photoluminescence of defect transitions in freestanding GaN
Authors: Reshchikov M. A. , Morkoç H. , Park S. S. , Lee K. Y.
Published: July 2002

Deep level defects responsible for the 2.4 eV photoluminescence (PL) band in a freestanding GaN template were studied by transient photoluminescence. A nonexponential decay of PL intensity observed at low temperature is attributed to a donor–acceptor pair recombination involving a shallow donor and a deep acceptor. At room temperature, a single-exponential PL decay with a lifetime of 30 μs was observed at the high-energy side of the band, whereas the second component with a lifetime of about 750 μs was detected at the low-energy side of the band. The PL decay and transformation of the PL spectrum at room temperature can be explained by transitions from the conduction band to two deep acceptors. Electron-capture cross section has been estimated as 4×10−21 and 10−19 cm2 for the yellow and green bands, respectively, contributing to the broad 2.4 eV band.
On the detectivity of quantum-dot infrared photodetectors
Authors: Ryzhii V. , Khmyrova I. , Mitin V. , Stroscio M. , Willander M.
Published: July 2002

We report on the analysis of thermally-limited operation of quantum-dot infrared photodetectors (QDIPs). A device model is developed and used to calculate the QDIP detectivity as a function of the structural parameters, temperature, and applied voltage, as well as to determine the conditions for the detectivity maximum. The QDIP detectivity is compared with that of quantum-well infrared photodetectors (QWIPs). This work clarifies why the existing QDIPs are still inferior to QWIPs and shows that a significant improvement in the QDIP performance can be accomplished by the utilization of dense QD arrays with small QDs.
Polarization imprint and size effects in mesoscopic ferroelectric structures
Authors: Alexe M. , Harnagea C. , Hesse D. , Gösele U.
Published: July 2002

Piezoresponse scanning force microscopy measurements performed on lead zirconate titanate mesoscopic structures revealed a negative shift of the initial piezoelectric hysteresis loop. The shift is dependent on the size of the structure and is most probably due to the pinning of ferroelectric domains at the free lateral surface and ferroelectric–electrode interface. Considering a simple model, the thickness of the pinned domain layers is found to be about 15 and 70 nm at the ferroelectric–electrode interface and lateral free surface, respectively.
Epitaxial nanocrystalline tin dioxide thin films grown on (0001) sapphire by femtosecond pulsed laser deposition
Authors: Dominguez J. E. , Fu L. , Pan X. Q.
Published: July 2002

Nanocrystalline tin dioxide (SnO2) thin films of different thicknesses were fabricated on the (0001) surface of α-Al2O3 (sapphire) using femtosecond pulsed laser deposition. X-ray diffraction and transmission electron microscopy (TEM) analysis revealed that the microstructure of the films strongly depends on the film thickness. The films with a small thickness (<30 nm) are composed of nanosized columnar (100) oriented grains (3–5 nm in diameter) which grow epitaxially on the substrate with three different in-plane grain orientations. The (101) oriented grains (25 nm in diameter) appear when the film thickness becomes larger than a critical value (about 60 nm). The volume fraction of the (101) grains increases with film thickness. Cross-section TEM studies indicated that the (101) oriented grains nucleate on the top of the (100) oriented nanosized grains and show abnormal grain growth driven by surface energy minimization. As a result, the electrical transport properties are strongly dependent on the film thickness.
Hole carrier in MgB2 characterized by Hall measurements
Authors: Kang W. N. , Jung C. U. , Kim Kijoon H. P. , Park Min-Seok , Lee S. Y. , Kim Hyeong-Jin , Choi Eun-Mi , Kim Kyung Hee , Kim Mun-Seog , Lee Sung-Ik
Published: July 2002

The longitudinal resistivity (ρxx) and Hall coefficient (RH) were measured for MgB2 sintered under high pressure. We found that RH is positive like cuprate high-Tc superconductors, and decreases as the temperature increases for 40 K <T<300 K. The cotangent of the Hall angle was found to follow a+bT2 behavior from Tc to 300 K. At T=100 K, RH=4.1×10−11 m3/C from which the hole carrier density was determined to be 1.5×1023/cm3. This carrier density is 1–2 orders of magnitude larger than those of Nb3Sn and optimally doped YBa2Cu3Oy superconductors.