bluuebunny/crossref_metadata_2025 huggingface dataset:
The capacitance of Pt/Pb0.65La0.28Ti0.96O3/Pt structures
Authors: Shaw T. M. , Laibowitz R. B. , Beach D. , Duncombe P. R.
Published: July 2002

The capacitance/voltage characteristics of thin paraelectric lead lanthanum titanate films are measured using platinum electrodes. The films have a maximum capacitance when either a small positive or negative bias voltage is applied. This characteristic is consistent with the electrode interfaces acting as Schottky-like barriers. The voltage at which the capacitance maxima occur increases linearly with film thickness indicating that the film is highly resistive. On the basis of the high apparent film resistance it is proposed that the voltage dependence of the capacitance of the electrode interfaces arises from the ionization of deep level traps within the film and not from depletion layers associated with shallow donor or acceptor states. Application of voltages larger than about 2–3 V results in the disappearance of the capacitance maxima indicating that irreversible changes in the electrode interfaces occur at higher electric fields.
Persistent photoconductivity on ion irradiated carbon films prepared by plasma assisted chemical vapor deposition and determination of traps in the pseudo-gap region
Authors: Bhattacharyya Somnath , Koteswara Rao K. S. R. , Subramanyam S. V. , Kanjilal D.
Published: July 2002

The defects created by ion beam irradiation in disordered conducting carbon films have been studied by the photoconductivity technique. A very complex distribution of traps created mostly by random displacement of carbon atoms by energetic ion beam from its polymeric matrix showed a persistent photoconductivity at low temperature. The decay time constant estimated from the photocurrent is around 15 s at 10 K. From the time constant and the intensity of photocurrent the density of traps and the corresponding activation energies are calculated. This report shows how slow decay of photocurrent can be applied to probe distribution of traps in the amorphous carbon due to ion bombardment in the most general case.
Concentration of paramagnetic centers in boron doped polycrystalline diamond films
Authors: Colineau E. , Deneuville A. , Mambou J. , Gheeraert E.
Published: July 2002

Though no boron signal is identified, with respect to their boron content the narrow and broad components of the electron spin resonance signal in boron doped polycrystalline film decrease from 1018 to 1016 cm−3. This is ascribed to two different structural defects with concentration decreasing with the boron content, in agreement with theoretical predictions. Finally, we suggest a spatial location for these defects.
Steep magnetoresistance change with low saturation fields in Co/Ni multilayer thin films
Authors: Han De-Hua
Published: July 2002

Co/Ni multilayer thin films with a constant Co thickness of 2.2 nm, Ni thickness ranging from 0.5 to 5.0 nm, and a total of 20 bilayers were fabricated using dc magnetron sputtering. These multilayers show a steep magnetoresistance (MR) change with low saturation magnetic field, in-plane uniaxial anisotropic properties, and an especially large magnetoresistance change between magnetic field H applied parallel and perpendicular to the in-plane easy axis. For H parallel to the multilayer easy axis and H at 45° to the current I, a MR ratio of 15% with a FWHM of 13 Oe was obtained. While for H perpendicular to the easy axis and at 45° to I, a MR ratio of 19.1% with a FWHM of 34 Oe was obtained. The former implies a MR sensitivity of 1.15%/Oe, while the sensitivity of the latter is 0.56%/Oe. All the peaks of the MR curve appeared at the coercive field Hc of the multilayers. The most important characteristics of the MR change were a sharp increase in resistance followed by a very steep decrease with increasing H. These Co/Ni multilayers are promising candidates for magnetic storage and sensor technology.
Electronic structure of (GaAs)m/(Ge2)n (001) superlattices with 1⩽(m,n)⩽20
Authors: Rufinus Jeffrey , Crook G. E.
Published: July 2002

The semiempirical tight-binding method with second-nearest-neighbor interactions has been used to investigate the electronic structure of (GaAs)m/(Ge2)n (001) superlattices (SLs) with 1≤(m,n)≤20. We have found no correspondence between the calculated band structures of these (GaAs)/(Ge2) SLs and (GaAs)1−x(Ge2)x random alloys. The inclusion of second-nearest-neighbor interactions raised the predicted energies of the conduction band confined states while lowering that of the highest-lying interface state. For small values of m, the (GaAs)m/(Ge2)n SLs are predicted to have indirect band gaps regardless of the valence band offset used in the calculation. For larger values of m, however, the predicted SL band gaps become direct for large values of valence band offset.
Initial domain structure of hydride vapor phase epitaxy GaAs/Si(001) by using x-ray standing waves
Authors: Kawamura Tomoaki , Takenaka Hisataka , Hayashi Takayoshi , Tachikawa Masami , Mori Hidefumi
Published: July 2002

The initial domain structure of hydride vapor phase epitaxy grown GaAs films on Si(001) was investigated using x-ray standing waves. GaAs/Si(001) samples, 4 monolayers (ML) thick, grown on two different Si substrates were used: an epitaxial Si surface and a mechanochemically polished surface. X-ray standing-wave analysis revealed no single-domain structure in either sample. The ratio of the two domains was almost 1:1 on the mechanochemically polished surface and 6:4 on the epitaxial Si surface. The dominant GaAs domain on the epitaxial surface was the same as that obtained on thicker GaAs films on an epitaxial Si surface. This suggests a rapid decrease in the GaAs domain during the early stages of growth on an epitaxial Si surface.
Highly photosensitive CdSe coatings by screen printing and sintering technique
Authors: Gomez-Daza O. , García V. M. , Nair M. T. S. , Nair P. K.
Published: July 2002

CdSe powder precipitated from a chemical bath was screen printed on glass substrates using ZnCl2 as flux, with flux to powder ratio (FPR) varying in the range of 0.1 to 0.5 by weight, and propylene glycol as binder. After a subsequent sintering in air for 1 h at 450 °C, the screen printed coatings showed a photocurrent to darkcurrent ratio of ∼108 under tungsten halogen illumination of 2000 W m−2. X-ray diffraction studies showed that sintering causes the conversion of the ZnCl2 flux into hexagonal phase ZnO which would fill the void among the CdSe particles. The optimum FPR and the sintering temperature to achieve maximum photosensitivity in the coatings are presented. The coatings may be used in the development of highly photosensitive light dependent resistors.
New observation on the formation of PbS clusters in zeolite-Y
Authors: Chen Wei , Wang Zhanguo , Lin Zhaojun , Qian Jiajun , Lin Lanying
Published: July 2002

PbS clusters in zeolite-Y have been prepared with the reaction of Pb2+-ion-exchanged zeolite-Y with Na2S in solution at room temperature. Their absorption spectra show dramatic blue shifts from that of the bulk PbS. Obvious change of both the absorption edges and peak positions upon PbS concentrations have been observed. These phenomena provide evidences that PbS clusters have been formed within the zeolite. The absorption spectra show featureless structure and have no tails near the absorption edges. As the PbS loading density becomes higher, the absorption bands become stronger and sharpen. Order PbS clusters lattice with high quality might be formed in the supercages of zeolite-Y.
Cu segregation at the Al(Cu)/Al2O3 interface
Authors: Copel M. , Rodbell K. P. , Tromp R. M.
Published: July 2002

We have investigated the segregational properties of polycrystalline Al(Cu) alloys in the composition range of 0.04 to 0.5 at. % Cu using medium energy ion scattering. While Cu does not segregate to the bare surface, significant quantities of Cu are found at the interface between the Al(Cu) and aluminum oxide. By measuring the interfacial Cu concentration as a function of temperature, we have determined that the segregational energy is 0.21±0.03 eV.
Low field giant magnetoresistance in sputtered permalloy/Au multilayers
Authors: Parkin S. S. P. , Rabedeau T.
Published: July 2002

Polycrystalline permalloy/Au multilayers exhibit oscillatory variations in saturation magnetoresistance as a function of increasing Au layer thickness. The change in resistance is saturated in fields as low as a few Oe at room temperature leading to changes in resistance per unit field of more than 1%/Oe. These are the largest room temperature magnetic field sensitivities yet reported in simple magnetic multilayers.
Generation of a frequency agile modulated intense relativistic electron beam
Authors: Friedman M. , Pasour J. , Smithe D.
Published: July 2002

A new mechanism for self-modulation of an annular intense relativistic electron beam is being described. The frequency of modulation can be tuned 10% by magnetically compressing the diameter of the electron beam.
Growth and strain symmetrization of Si/Ge/C/Sn quaternary alloys by molecular beam epitaxy
Authors: Guarin F. J. , Iyer S. S. , Powell A. R. , Ek B. A.
Published: July 2002

We have synthesized, via molecular beam epitaxy alloys of SixSnyC1−x−y with symmetric strain. In this work we report the growth of systems with varying compositions/band gaps including the first silicon-based quaternary (Si/Ge/Sn/C) system, which offers an additional degree of freedom for strain and band gap engineering in Si-based alloys. We report the growth of Si.955Sn.03C.015 alloys up to 4500 Å in thickness and quaternaries of composition in the neighborhood of Si.835Ge.125Sn.03C.01. Infrared absorption spectroscopy and photoluminescence data have provided evidence of the potential for significant band gap modification in these alloys.
Spatially resolved analyses of epitaxial and electrical properties of YBa2Cu3O7 devices
Authors: Dieckmann N. , Bock A. , Merkt U.
Published: July 2002

We use scanning micro-Raman spectroscopy (SMRS) to characterize the epitaxial film quality as well as low-temperature scanning laser microscopy (LTSLM) to image electrical properties of YBa2Cu3O7 devices locally in both lateral dimensions. Investigations have been performed on crossovers as used in flux transformers of magnetometers, patterned in a multilayer process on SrTiO3 (100) substrates. We find a correlation between an inhomogeneous superconducting performance and a disturbance of epitaxy on locations where the crossovers pass edges of the underlying bridge. The distribution of the oxygen is not affected at these points.
Si and Si/P implants in In0.5Ga0.5P and In0.5Al0.5P
Authors: Zolper J. C. , Chui H. C.
Published: July 2002

Si and Si/P ion implantation doping of In0.5Ga0.5P and In0.5Al0.5P has been studied for several Si and P doses at energies of 90 and 100 keV, respectively. For single Si implants in InGaP a maximum Hall sheet electron concentration of 1.33×1013 cm−2 is achieved for a Si dose of 5×1013 cm−2. When an optimum dose (2.5×1013 cm−2) P coimplant is performed this electron concentration is increased by 65%. The same dose Si implants in InAlP show a maximum effective activation of 3.9% with no P coimplantation and 5.2% with a P-implant dose 1.5 times the silicon dose. The apparent donor ionization energies are estimated from variable temperature Hall measurements to be 2–5 meV for InGaP and ∼80 meV for InAlP. The deeper level in InAlP is attributed to the DX level found in the Al-containing material. The reduction in sheet resistance associated with the use of Si/P coimplantation in InGaP containing heterostructures should contribute to significant performance enhancements in HFETs and lasers.
Nonalloyed ohmic contacts to heavily Be-doped GaP and InxGa1−xP
Authors: Tagare M. V. , Chin T. P. , Woodall J. M.
Published: July 2002

Nonalloyed ohmic contacts, with contact resistances as low as 9 μΩ  cm2, are obtained to p++ GaP using Ni and Ti–Au. Very high p-type doping (5×1019 cm−3) is achieved in GaP using a growth temperature of 400 °C followed by an ex situ high-temperature rapid thermal anneal. The p-type dopant is beryllium and the films are grown by solid source molecular beam epitaxy equipped with a valved phosphorus cracker. A record high hole concentration (2×1019 cm−3) is reported in In0.49Ga0.51P by using a growth temperature of 350 °C.
Transport through an array of small ohmic contacts alloyed to the two-dimensional electron gas of a GaAs/AlGaAs heterostructure
Authors: Chabasseur-Molyneux V. , Frost J. E. F. , Simmons M. Y. , Ritchie D. A. , Pepper M.
Published: July 2002

We investigate transport through a two-dimensional electron gas (2DEG) underneath a submicron periodic array of small Ge-Ag alloyed ohmic contacts and compare the results with the resistance of the small contacts. We find that as the contacts form, the effective mobility of the 2DEG underneath the array decreases and that the carrier concentration between the small contacts is reduced. From the low-field magnetoresistance we are able to identify ballistic cyclotron orbits commensurate with the period of the array. We find that reducing the diameter of the ohmic metallization to 0.2 μm severely inhibits ohmic contact formation.
Pulsed supersonic jet epitaxy: A nonthermal approach to silicon growth
Authors: Malik Rajeev , Gulari Erdogan
Published: July 2002

In this letter, we demonstrate a unique approach for low temperature epitaxial growth of single crystal silicon films on Si(100). Pulsed supersonic jet epitaxy (PSJE), employs high kinetic energy jets of a disilane-hydrogen mixture incident on the surface leading to layer by layer growth. Precise control of film thickness and significantly higher sticking coefficients are demonstrated. Growth rate dependence of pulse frequency and its implications are discussed. We have been able to reproducibly deposit good quality single crystalline films at temperatures as low as 400 °C with this technique, without the use of any external activation.
Dynamics of barrier state electron self-localization in InGaAs/InGaAsP multiple quantum well lasers
Authors: Finzi D. , Tessler N. , Mikhaelashvili V. , Eisenstein G. , Dentai A. G. , Chandraskhar S. , Joyner C. H.
Published: July 2002

We report details of lasing transitions based on self-localized barrier state electrons in InGaAs/InGaAsP multiple quantum well lasers. We study the mechanisms responsible for the switching between conventional lasing transitions at 1460 nm and a self-induced transition at 1360 nm. Carrier effects and current heating contribute both on a time scale of a few ns with the current heating dominating. Carrier effects are separable from the thermal effects when 100 ps wide electrical drive pulses are used.
Reduction of relative intensity noise of the output field of semiconductor lasers due to propagation in dispersive optical fiber
Authors: Marshall W. K. , Paslaski J. , Yariv A.
Published: July 2002

The effect of dispersive, linear propagation (e.g., in single-mode optical fiber) on the intensity noise from semiconductor lasers is investigated. Relations between the frequency and amplitude noise variations of semiconductor lasers are obtained from the laser rate equations and used to calculate the change in the relative intensity noise (RIN) spectrum that occurs during dispersive propagation. Propagation in fiber with positive dispersion (D≳0) over moderate distances (several km for standard single-mode fiber at 1.55 μm) is found to reduce the RIN over a wide range of frequencies. Measurements with a 1.56 μm distributed feedback laser confirm the main theoretical results and demonstrate reductions in RIN of up to 11 dB with 4 km of standard fiber.
Magnetotransport in periodically modulated quantum wires
Authors: Bergmann R. , Schweizer H. , Härle V. , Scholz F.
Published: July 2002

Quantum wires with an artificially designed periodic potential have been fabricated by etching a chain of antidots along the central wire axis. The resistivity ρxx in the presence of a perpendicular magnetic field shows distinct peaks in the low magnetic field regime that can be explained by localized orbits around one antidot or between two neighboring antidots. By changing the lateral position of the antidot chain on the wire from the central axis to the wire side walls, a localized orbit in the region between four antidots has been detected.
Supercurrent distributions in YBa2Cu3O7–YBa2Co0.21Cu2.79O7–YBa2Cu3O7 edge Josephson junctions
Authors: Gausepohl S. C. , Lee Mark , Char K.
Published: July 2002

We report the measurement and analysis of critical current (Ic) modulations in magnetic field (H) for YBa2Cu3O7–YBa2Co0.21Cu2.97O7–YBa2Cu3O7 edge Josephson junctions operating at 77 K. The Ic(H) patterns are clean and reproducible enough to allow a quantitative, self-consistent Fourier transform analysis that reveals the major features of the spatial supercurrent density distribution. Use of YBa2Co0.21Cu2.97O7 as the weak link is seen to result in significantly more homogeneous characteristics than in most other high-Tc junctions reported to date.
On the origin of stacking faults at the GaAs/ZnSe heterointerface
Authors: Bourret-Courchesne Edith D.
Published: July 2002

A series of experiments was designed to assess the effects of the various stages of the nucleation process on the formation of stacking faults at the GaAs/ZnSe interface. Differential interference contrast microscopy was used to image stacking faults and misfit dislocations in 1000 Å thick ZnSe layers. We have demonstrated that an As-stabilized GaAs surface is needed to obtain a low density of stacking faults. However, an excess of As favors the formation of stacking faults. More importantly, the introduction of Zn drastically increases the stacking fault density.
Synthesis of nanometer-size silver coated polymerized diacetylene composite particles
Authors: Zhou H. S. , Wada T. , Sasabe H. , Komiyama H.
Published: July 2002

We report the synthesis of stable nanometer-size silver-coated polydiacetylene (PDA) particles. At first, an ethanol solution of diacetylene (DA) is dispersed into a Ag+ ion containing aqueous solution. Silver ions are attracted to –CCO− anions of DA, then monomer DA vesicles coated by silver ions are formed by a long-term ultrasonication treatment. The monomer DA vesicles are photopolymerized and the silver ions are photo-reduced simultaneously to form coated composite particles.
Highly efficient phase conjugation using spatially nondegenerate four-wave mixing in a broad-area laser diode
Authors: Kürz Peter , Nagar Ron , Mukai Takaaki
Published: July 2002

We report spatially nondegenerate four-wave mixing in a broad-area laser diode that acts as a fast phase conjugate mirror with nanosecond response times and high efficiencies. Phase conjugate reflectivities were found to depend strongly on the bias current of the broad-area laser diode. Operating the laser diode in an injection-locked regime above the lasing threshold gave phase conjugate reflectivities as high as 165%.
Formation and characterization of ultrasmall dimension GeSi wire structure by using pulsed laser-induced epitaxy
Authors: Deng C. , Sigmon T. W. , Wu J. C. , Wybourne M. N. , Rack J.
Published: July 2002

(100)Si substrates are patterned with arrays of Ge wires ∼60 nm in width and ∼6 nm in thickness. Ultrasmall dimension GeSi surface wire structures are then formed in Si in a pulsed laser-induced epitaxy process. The wire structures are analyzed by secondary electron microscopy, atomic force microscopy, Auger electron spectroscopy, and cross-sectional transmission electron microscopy. No defects are observed in the wires structures. However, significant side diffusion of Ge, much more than the vertical diffusion occurred during the ∼40 ns pulsed laser-induced epitaxy process, is observed in the Si substrate. Surface evolution is also observed. Possible explanations for the abnormal Ge side diffusion are discussed.
Very high efficiency four-wave mixing in a single semiconductor traveling-wave amplifier
Authors: D’ Ottavi A. , Martelli F. , Spano P. , Mecozzi A. , Scotti S. , Dall’ Ara R. , Eckner J. , Guekos G.
Published: July 2002

We report on high efficiency frequency-conversion obtained by four-wave mixing in a single traveling-wave semiconductor optical amplifier. Efficiency in excess of 0 dB is demonstrated for frequency conversion up to 2 THz. Measurements of the signal to the amplified spontaneous emission background ratio are also presented.
Magnetic field-mediated alignment of a nematic liquid crystal at a polymer surface exposed to ultraviolet light
Authors: Reznikov Yuriy , Petschek Rolfe G. , Rosenblatt Charles
Published: July 2002

A nematic liquid crystalline cell utilizing a substrate coated with polyvinylcinnamate was subjected to UV polarized light in the presence of a magnetic field. After removing the cell from the field it was found that the pretilt angle was large and both temporally and thermally robust. Irradiation in the absence of a field resulted in a rapid decay of the pretilt angle to zero, corresponding to planar alignment.
Epitaxial layer thickness measurement by cross-sectional atomic force microscopy
Authors: Howard A. J. , Blum O. , Chui H. , Baca A. G. , Crawford M. H.
Published: July 2002

An epitaxial layer thickness measurement technique has been developed using cross-sectional atomic force microscopy (XSAFM). Cleaved and etched epitaxial heterostructures of Al0.5Ga0.5As/GaAs have been analyzed using this technique. XSAFM analysis of a 20.5 period structure of 300-Å-thick Al0.5Ga0.5As/GaAs layers agreed to within 2% of x-ray diffraction data. XSAFM analysis of a structure consisting of GaAs wells ranging from ∼15 to 600 Å with 300 Å Al0.5Ga0.5As barriers was also performed. The XSAFM measured well thicknesses agreed quite well with photoluminescence (PL) measurements taken at 4 K. XSAFM can thus serve as a rapid alternative to conventional thickness measurement techniques such as SEM and TEM.
Dual-wavelength AlGaAs/GaAs laser by selective removal of a quantum well in an asymmetric dual quantum well structure
Authors: Beernink K. J. , Sun D. , Thornton R. L. , Treat D. W.
Published: July 2002

The longer-wavelength quantum well in an AlGaAs/GaAs asymmetric dual quantum well laser structure was selectively removed by localized intermixing. High Si doping on each side of the longer-wavelength well caused intermixing during an anneal under a SiNx cap, while leaving the other nearby well intact. During an anneal under an exposed GaAs surface layer, both quantum wells remained intact. By patterning the surface with alternating SiNx and exposed GaAs, the longer-wavelength quantum well was selectively intermixed. Integrated broad area lasers were fabricated with threshold current density and external quantum efficiency of 260 A/cm2 and 30%/facet at a wavelength of 751 nm in capped regions and 195 A/cm2, 32%/facet at 824 nm in the uncapped regions.
Optically induced birefringence in bacteriorhodopsin as an optical limiter
Authors: Dovgalenko George E. , Klotz Matthew , Salamo Gregory J. , Wood Gary L.
Published: July 2002

Experimental data are presented, which demonstrates an optical limiter based on a large birefringence which is optically induced in bacteriorhodopsin. The induced birefringence is observed to be a function of incident intensity, but saturates at a value of about 0.454 W/cm2. A measured value of Δn of 6.6×10−4 at a wavelength of 514 nm is reported. The observed birefringence is found to be in good agreement with a proposed model.
Narrow-band electroluminescence at 3.5 μm from impact excitation and ionization of Fe2+ ions in InP
Authors: Scamarcio Gaetano , Capasso Federico , Hutchinson Albert L. , Tanbun-Ek Tawee , Sivco Deborah , Cho Alfred Y.
Published: July 2002

Electroluminescence associated with impact excitation and ionization of deep metallic impurities, enhanced by the presence of high electric field domains in semiconductors, is reported. A large and abrupt increase of midinfrared (λ≊3.5 μm) electroluminescence is observed at cryogenic temperatures above the onset for the transferred-electron effect in n-type InP doped with Fe. Optical powers up to 40 nW have been measured. At 5 K the spectrum is dominated by a set of sharp lines corresponding to the symmetry allowed d-shell transitions of Fe2+ ions.
Scanning tunneling microscopy and tunneling luminescence of the surface of GaN films grown by vapor phase epitaxy
Authors: Garni B. , Ma Jian , Perkins N. , Liu Jutong , Kuech T. F. , Lagally M. G.
Published: July 2002

We report scanning tunneling microscopy (STM) images of surfaces of GaN films and the observation of luminescence from those films induced by highly spatially localized injection of electrons or holes using STM. This combination of scanning tunneling luminescence with STM for GaN surfaces and the ability to observe both morphology and luminescence in GaN is the first step to investigate possible correlations between surface morphology and optical properties.
Photoemission oscillation measurement of barrier thickness for InAs/AlSb resonant tunneling diodes
Authors: Zinck J. J. , Chow D. H. , Schulman J. N. , Dunlap H. L.
Published: July 2002

AlSb barrier thicknesses ranging from 5 to 12 monolayers have been measured during growth of InAs/AlSb resonant tunneling structures using the photoemission oscillation technique. A plot of peak current density as a function of both measured and estimated barrier thickness confirms that use of the photoemission oscillation technique reduces device performance variations with respect to the conventional time-based approach to layer thickness control. Our growth scheme involves a significant As background pressure during the AlSb growth which results in incorporation of As in the barrier layer. We have modeled the effect of the As incorporation on device properties and find that our measured peak current values are consistent with these calculations.
Self-limiting transformation of monodisperse Ga droplets into GaAs nanocrystals
Authors: Deppert Knut , Samuelson Lars
Published: July 2002

GaAs nanocrystals, of approximate diameter 10 nm, have been produced and deposited on various substrates. The fabrication route allows the production of nanocrystals with a very narrow size distribution. It utilizes the formation of ultrafine Ga particles and their self-limiting reaction with arsine at elevated temperatures. The kinetics of the reaction of Ga to produce GaAs depends on the temperature and the arsine flow. The temperature at which the reaction began was found to be as low as 200 °C. Our approach opens the possibility to produce size-selected nanocrystals of compound semiconductors in a simple, reliable, and efficient way.
Core level photoelectron spectroscopy on the lanthanide-induced hydrolysis of DNA
Authors: Shigekawa Hidemi , Ikawa Hiroyuki , Yoshizaki Ryozo , Iijima Yoshitoki , Sumaoka Jun , Komiyama Makoto
Published: July 2002

The electronic structures of the complexes of diphenyl phosphate (DPP), a model compound of DNA, with lanthanide ions have been investigated to shed light on the mechanism of the cerium (IV)-induced nonenzymatic hydrolysis of DNA. Binding energies of the P 2p core level of DPP were 134.2 eV for the complexes with La(III), Eu(III), and Lu(III), and was 134.4 eV for the Ce(IV) complex, when the metal/DPP molar ratio was 1:1. When the molar ratio was increased, only Ce(IV), the most active metal ion for DNA hydrolysis, showed a chemical shift of ∼0.5 eV toward the higher binding energy region. The chemical shift of ∼0.5 eV toward the higher binding energy region. The chemical shift was due to the systematic increase in the intensity of the higher binding energy component. The observed change in the electronic structure of the DPP-Ce(IV) complex may be related to the superb ability of Ce(IV) for the hydrolysis of DNA.
Electric field response of second order optical nonlinearity in dye doped poled polymer
Authors: Sugihara Takashi , Haga Hiroshi , Yamamoto Sadahiko
Published: July 2002

The optical nonlinearity induced by electrical poling decays gradually in poled polymers. This suggests that the molecular alignment can be reoriented in the polymer matrix at room temperature by the external electric field. We measured the frequency responses and the temperature characteristics of second-harmonic generation (SHG) in a dye doped polymer in order to clarify the electric field dependence of the nonlinearity. The experimental results show that there is a slow response of the SHG coefficient variation due to the reorientation of nonlinear molecules and another fast response. This characteristic can be applied to develop a new type of nonlinear optical devices by dynamically controlling the nonlinearity of the material by the external electric field.
Formation of deep thermal donors in heat-treated Czochralski silicon
Authors: Emtsev V. V. , Oganesyan G. A. , Schmalz K.
Published: July 2002

Formation of new donors in Czochralski silicon (Cz-Si) at temperatures T≥600 °C was studied. The contribution of deep donors was separated from those of other donor families with shallower states and in this way the formation kinetics of deep thermal donors was established. The results obtained make it possible to attribute these donor states at ≊EC−0.1 eV to ≊EC−0.25 eV to ribbonlike defects. Variations in the cross section of A-center formation under gamma irradiation of heat-treated Cz-Si were found to correlate with formation of deep thermal donors.
Molecular beam epitaxy growth of a layered cuprate having a multiple fluorite-type block for use in trilayer junctions
Authors: Ikegawa Sumio , Motoi Yuichi
Published: July 2002

(Pb2Cu)Sr2(Eu,Ce)nCu2Oy: n=3–8 (Pb-32n2 phase) has been synthesized by sequential deposition using the molecular beam epitaxy technique. This layered cuprate having a multiple-stacked fluorite-type block is thought to be suitable for use in trilayer Josephson junctions, from the viewpoints of atomic arrangement at the superconductor-insulator interface and the need for an atomically flat thin insulator. The thickness of the fluorite block, which will act as an intra-cell barrier, has been controlled up to 2.2 nm (n=8). Pb-3272/Pb-3212 epitaxial superlattices have also been prepared. The two-dimensional growth with the growth unit of a unit cell is observed by in situ reflection high-energy electron diffraction.
The intrinsic determinants of the critical current in SIS′ and SIS high-T
c Josephson junctions
Authors: Gonnelli R. S. , Puttero D. , Ummarino G. A.
Published: July 2002

We discuss the influence of a depressed order parameter at the surface of a high-Tc superconductor on the temperature dependence of the Josephson critical current in SIS′ and SIS junctions, where S denotes the high-Tc superconductor, S′ a conventional one, and I the insulating layer. The comparison with experimental data of planar YBCO-based SIS′ and SIS junctions shows that, when the quality of the junction interfaces is particularly good, the fit by using the depressed-gap models can accurately reproduce the experimental Ic(T) curves. As a consequence, the surface depression of the order parameter is the most plausible cause for the intrinsic deviations of the IcRN products from the ideal BCS values in this kind of junctions.
Dynamics of photoinduced Faraday rotation in semimagnetic semiconductors
Authors: Pankoke R. , Buss C. , Hugonnard-Bruyère S. , Leisching P. , Frey R. , Flytzanis C.
Published: July 2002

Time-resolved Faraday rotation measurements on a nanosecond time scale are performed for Cd1−xMnxTe samples grown by two different techniques. The dependence of the observed photoinduced dynamics on the purity, Mn++ concentration (x=0.03, 0.10, 0.15, 0.3), excitation density, and temperature (100–290 K) reveals several novel features. The relaxation for pure samples is monoexponential at 100 K and is slowing down with increasing temperature, in strong contrast to impure samples, where the opposite behavior is observed. All experimental observations can be well explained in a simple model based on rate equations for the free-carrier populations, provided that recombination centers and impurity traps are included in the model.
Direct measurements of spectral and temporal characteristics of dye lasing in ultralow-Q microcavities
Authors: Hung Nguyen Dai , Segawa Yusaburo , Myer Yves H.
Published: July 2002

The time and spectral characteristics of above-threshold lasing operation of different dye solutions in ultralow-Q microcavities are directly and simultaneously measured with a picosecond two-dimensional streak camera. A nonoscillatory spectrotemporal evolution with a very fast damping of the modes in the wings of the laser spectrum as a basic process of the multimode laser action is exposed. Application to single short-pulse production is shown. The characteristics of the single-mode laser operation are also reported.
In situ preparation of epitaxial TlBa2Ca2Cu3O9 high-T
c thin films
Authors: Reschauer N. , Spreitzer U. , Brozio W. , Piehler A. , Renk K. F. , Berger R. , Saemann-Ischenko G.
Published: July 2002

We report an in situ growth of epitaxial TlBa2Ca2Cu3O9 high-Tc thin films. The films (thickness 80–400 nm) were prepared on LaAlO3 (100) substrates by laser ablation from a thallium-free BaCaCuO target in the presence of Tl2O vapor. X-ray diffraction patterns of θ–2θ scans showed that the films consisted of highly oriented TlBa2Ca2Cu3O9 with the c axis perpendicular to the substrate surface, and φ scan measurements indicated epitaxial growth. Scanning electron microscope and atomic force microscope investigations showed smooth surfaces without platelike structures. The films had transition temperatures near 100 K.
On the mechanically driven rapid crystallization of amorphous Si3N4 ceramics
Authors: Fan G. J. , Quan M. X. , Hu Z. Q. , Li Y. L. , Liang Y.
Published: July 2002

The effect of high-energy ball milling on the structure of nanometer sized amorphous ceramics, a-Si3N4 and a-Si–N–C, respectively, has been investigated. At high milling intensity, a-Si3N4 may rapidly crystallize into a mixture of α-Si3N4 and β-Si3N4 after the initial 4 s of milling whereas no structural changes were observed at low milling intensity. For a-Si–N–C, mechanical milling does not cause structural changes at both low and high intensity. It was found that extension of mechanical milling of these hard ceramics can introduce large volume fractions of contamination fragments from the milling media. We conclude that the observed structural changes occurring in a-Si3N4 may be due to mechanical effect, rather than local heating and/or impurity effect.
Hydrogen passivation of visible p-i-n type thin-film light-emitting diodes
Authors: Lee Jong-Wook , Lim Koeng Su
Published: July 2002

The effects of hydrogen passivation on the performance of visible p-i-n thin-film light-emitting diodes (TFLEDs) have been investigated. The TFLEDs were fabricated using a photochemical vapor deposition method. The hydrogenation process was performed using an inductively coupled plasma system at a rf power of 800 W and a process pressure of 20 mTorr for 30 min. It was found that hydrogenation dramatically improved the performance of these TFLEDs. The threshold voltage was decreased by about 1 V, the electroluminescence (EL) peak shifted from 704.5 to 689 nm, the EL intensity increased by a factor of 3, and the brightness increased from 1 to 24 cd/m2 by 24 times.
Electron–phonon interactions in solid C60 studied by transient picosecond Raman spectroscopy
Authors: Tsen K. T. , Grann E. D. , Guha S. , Menendez J.
Published: July 2002

Electron–phonon interactions in solid C60 have been studied by transient Raman spectroscopy on a picosecond time scale. The electrons were photoinjected into the triply-degenerate states of solid C60 by an ultrashort laser pulse of photon energy ℏω=2.14 eV. These energetic electrons relax by emitting various phonons. By monitoring the phonon occupations at very low temperatures with anti-Stokes Raman scattering, direct information about the relative strength of the electron–phonon interactions in solid C60 was obtained. Our experimental results demonstrate that electrons interact much more strongly with the low-frequency radial Ag mode than the other phonon modes in solid C60.
Azimuthal rotation of diamond crystals epitaxially nucleated on silicon {001}
Authors: Tachibana T. , Hayashi K. , Kobashi K.
Published: July 2002

Highly oriented diamond films with {001} facets were grown on Si{001} using microwave plasma enhanced chemical vapor deposition. The tilt and rotation of the diamond crystals were measured by polar x-ray diffraction. The full widths at half-maximum of {004} and {220} diffraction peaks were 5° and 10°, respectively. It was found that the {220} diffraction poles split into two peaks by approximately 5°. This result indicated that there were two possible azimuthal rotations about the surface normal of the substrate for the epitaxially nucleated diamond grains.
Measurements of the spectral line shape function and frequency width of longitudinal mode in a multimode gas laser
Authors: Yin Jianping , Fang Jianxing , Zhu Shiqun , Gao Weijian , Wang Yuzhu
Published: July 2002

In terms of the quasiperiodicity of temporal coherence g(1)(τ) in a multimode gas laser, we present measurements of both spectral line shape function and frequency width of longitudinal mode in a multimode laser. The experimental result shows that the spectral line shape of longitudinal mode is Lorentzian line-shape function for a freely operated multimode gas laser with inhomogeneous broadening, it is not affected by the drift effect of longitudinal mode frequency. However, the frequency width of longitudinal mode is broadened greatly because of the influence of the drift effect of longitudinal mode frequency.
Bulk mismatch values of heterostructures as determined from convergent beam electron diffraction on thin cross sections
Authors: Balboni R. , Armigliato A. , Frabboni S.
Published: July 2002

High order Laue zone lines present in the central disk of convergent beam electron diffraction patterns have been used to determine the bulk mismatch in thinned, cross-sectioned heterostructures, where a relaxation occurs along the thinning direction. The position of these lines is sensitive to lattice parameters along different crystallographic directions, so that information on the residual strain along the growth and the thinning directions can be extracted from a single diffraction pattern. This information has been properly combined using the isotropic elasticity theory to give the bulk mismatch. The results are in good agreement with independently obtained bulk measurements.
Magnetic disaccommodation in single yttrium iron garnet crystal
Authors: Torres L. , Zazo M. , Iñiguez J. , de Francisco C. , Muñoz J. M. , Hernandez P.
Published: July 2002

Measurements of magnetic disaccommodation in single yttrium iron garnet (YIG) crystals are presented. Two peaks of 0.2%–0.3% are observed in the isochronal spectrum around 130 and 250 K. Comparison of our results with those on polycrystalline YIG samples and with similar data on illuminated and gamma ray irradiated single YIG crystal samples is provided.
New method of magnetic field and current generation outside laser plasma
Authors: Kabashin A. V. , Nikitin P. I.
Published: July 2002

A new mechanism of laser plasma generation of current along an irradiated conductive target, and a considerable (more than 1000 times) enhancement of magnetic field outside the plasma has been found. This mechanism is realized in experimental configurations with spatial asymmetries of target dimension scale. Such asymmetries with the largest possible scale was found to be the main factor that determines electromagnetic phenomena detected by external probes outside the laser plasma.
Plasma-deposited silylation resist for 193 nm lithography
Authors: Horn Mark W. , Rothschild Mordechai , Maxwell Brian E. , Goodman Russell B. , Kunz Roderick R. , Eriksen Lynn M.
Published: July 2002

Plasma-deposited carbon-based polymer films are examined for use as an all-dry positive-tone photoresist for 193 nm lithography. These films are designed to crosslink upon exposure to 193 nm radiation, enabling selective silicon uptake via reaction of silylamine gas with hydroxyl in the film. After oxygen plasma pattern transfer, features with resolution below 0.50 μm have been obtained with a 0.35 numerical aperture projection system.
Influence of ion bombardment on Si and SiGe films during molecular beam epitaxy growth
Authors: Ni W.-X. , Hansson G. V. , Buyanova I. A. , Henry A. , Chen W. M. , Momemar B.
Published: July 2002

Growth of Si and SiGe layers using molecular beam epitaxy was carried out with the substrate at a floating, positive or negative bias, in order to investigate effects of ion bombardment on the crystalline quality of grown materials. Although ion energies (100–1500 eV) and ion/atom flux ratios (∼0.005) used in the experiments were quite low, significant lattice distortion along the growth direction (Δa⊥/as up to ∼300 ppm) was observed by high resolution x-ray diffraction from the Si layers grown at 420 °C. At the same time, a broadband transition was observed in photoluminescence measurements from both Si and SiGe layers. Based on results of the annihilation behavior during postgrowth treatments using thermal annealing and hydrogenation, we attribute these effects to the ion bombardment induced formation and injection of different types of pointlike defects and defect clusters, which degrade the optical and electrical properties of grown layers.
Silicon interstitials: Injection during palladium silicide formation and trapping by ion implantation damage
Authors: Kringho/j Per
Published: July 2002

Injection of point defects into Si was examined by deep level transient spectroscopy. Preimplanted samples containing di-vacancies and O-vacancy pairs fabricated by low dose, high energy implantation of Ge (∼1×108, cm−2, 1.4 and 6.0 MeV) were used to monitor injection of point defects formed by low energy implants or Pd silicides. It was found that evaporation of Pd on preimplanted Si leads to a significant reduction of both the di-vacancy and O-vacancy signals, indicating injection of Si interstitials during the silicide formation. On the other hand low energy implants (52 keV Ge, 1×1013−5×1014 cm−2) resulted only in a small reduction of these signals probably due to self-trapping of the created interstitials, and furthermore prevented the reduction from the silicide formation, due to trapping of the injected interstitials in the damaged layer.
Observation of folded acoustic phonons in a porous silicon superlattice
Authors: Wu Xing-Long , Yan Feng , Pan Feng-Ming , Bao Xi-mao , Jiang Shu-Sheng , Zhang Ming-Sheng , Feng Duan
Published: July 2002

Porous silicon superlattice was fabricated and its Raman spectra were examined. The clear zone-folded doublets from longitudinal acoustic phonons were obtained up to fourth order. A similar phenomenon was not observed in ordinary porous silicon. Using the elastic continuum model, we calculated the frequencies of these folded doublets and the obtained results were in excellent agreement with the experimental ones.
In situ infrared spectroscopy as a real time diagnostic for plasma polymer film deposition
Authors: Pan Y. Vickie , Barrios Ernesto Z. , Denton Denice D.
Published: July 2002

In situ Fourier transform infrared spectroscopy (FTIR)/attenuated total reflection (ATR) was used to study the deposition of plasma polymerized methyl methacrylate (PPMMA) film. Real time absorption spectra of PPMMA films were obtained at a time resolution of 20–30 s which is mostly limited by the low optical throughput and low signal-to-noise ratio. Postplasma dynamics observed in the system demonstrate the need for an in situ and real time film diagnostic technique. This letter reports the use of this diagnostic on plasma deposited polymers.
SrTiO3 buffering effect on Pb1−xLaxTiO3 thin films prepared by pulsed laser deposition
Authors: Wang J. P. , Ling Y. C. , Yeh M. H. , Liu K. S. , Lin I. N.
Published: July 2002

Thin films of phase-pure perovskite PLT (Pb0.95La0.05Ti0.9875O3) were deposited in situ onto Si, Pt/Ti/SiO2/Si, and SrTiO3/Si substrates by pulsed laser deposition from stoichiometric targets. No Pb loss was observed in the near-surface region. The blocking of the interdiffusion between inner Si substrate and the outer PLT films by SrTiO3 buffer layer was evidenced using x-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS) analyses. The formation of TiO2 second phase in PLT/Pt/Ti/SiO2/Si films was indicated by XRD and SIMS spectra to be the outward diffusion of Ti atoms from the underlying Ti layer through the Pt layer, reacting with ambient O2 at the PLT-to-Pt interface.
Fishtail effect and small size normal core pinning in melt-textured-growth YBa2Cu3O7−δ bulks
Authors: Wen Hai-hu , Zhao Zhong-xian
Published: July 2002

By measuring the magnetization hysteresis loops and the remanent magnetization relaxation for a melt-textured-growth YBa2Cu3O7−δ bulk with two different oxygen concentrations, we found that the extra oxygen deficiencies enhance the flux pinning and the fishtail effect in low and intermediate temperature region. This strongly suggests that the fishtail effect is related to the elementary pinning centers. A model concerning the nonuniform distribution of upper critical field among the pinning sites is proposed to explain the fishtail effect. Finally, we present some evidence to support this model.
Effects of laser-ablation target damage on particulate production investigated by laser scattering with deposited thin film and target analysis
Authors: Spindler H. L. , Gilgenbach R. M. , Lash J. S.
Published: July 2002

Experiments have been carried out to correlate ablated particulate density and size to the number of KrF excimer laser (248 nm, 40 ns, <1.2 J) pulses incident on a single location of a pure solid aluminum target and to relate particulate production to target surface damage. An analysis of laser ablation deposited aluminum films on silicon substrates was used to determine the density of ablated particulate greater than 0.5 μm in diameter. For an undamaged target, the laser deposited particulate density was on the order of 8.6×105 cm−2 per 1000 shots. A damaged target (following 1000 laser pulses) produced a density on the order of 1.6×106 cm−2 per 1000 shots on the substrate. Dye laser optical scattering was also used to measure, in real time, the velocity of the particulate and the relative particulate density in the laser-ablation plume versus target damage. Results indicated a rapid rise in the production of particulate as target damage was increased up to 3000 laser pulses; after this number of shots the density of particulate in the laser ablation plume saturated. A peak in the scattered light for each stage of target damage occurred 40 μs after the initial KrF laser pulse, translating to a velocity of about 100 m/s for the smaller particulate (<1 μm diameter). The later scattered signal, around 160 μs, was apparently due to the larger particulate (5–15 μm), traveling at a velocity of approximately 25 m/s. Particulate production is related to the formation of laser ablation-induced cones on the damaged targets.
Observation of boron doping induced surface roughening in silicon molecular beam epitaxy
Authors: Lu Xuekun , Jiang Zuimin , Zhu Haijun , Zhang Xiangjiu , Wang Xun
Published: July 2002

Boron doping induced surface roughening was observed in conventional silicon molecular beam epitaxy. Reflection high energy electron diffraction and cross-sectional transmission electron microscopy revealed that as growth continued, the growth surface remained no longer planar but developed {113} facets. The facets evolved along with growth, and finally resulted in a severely roughened surface. The evolution of the roughening was found to remain the same in the boron doping concentration range of 1×1017–2×1020 cm−3 and the growth temperature range of 500–650 °C. This surface roughening effect is attributed to boron segregation behavior.