bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of particle size on the giant magnetoresistance of La0.7Ca0.3MnO3
Authors: Mahesh R. , Mahendiran R. , Raychaudhuri A. K. , Rao C. N. R.
Published: July 2002

Effect of particle size on the electron transport and magnetic properties of La0.7Ca0.3MnO3 has been investigated. While the ferromagnetic Tc, low field magnetic susceptibility, and insulator-metal transition are markedly affected by the particle size, the maximum magnetoresistance exhibited by the samples near Tc is not sensitive to the particle size. However, the magnetoresistance at 4.2 K increases with decrease in particle size, suggesting a substantial contribution by the grain boundaries. Preliminary measurements on La0.7Sr0.3MnO3 samples of different particle sizes also corroborate the above conclusions.
All-optical switching by spatial walkoff compensation and solitary-wave locking
Authors: Torruellas William E. , Assanto Gaetano , Lawrence Brian L. , Fuerst Russell A. , Stegeman George I.
Published: July 2002

We demonstrate a novel approach to phase insensitive, all-optical steering and switching based on an intensity-induced change in the propagation direction of multidimensional spatial solitary waves in bulk, birefringent, quadratic nonlinear media. Our demonstration is based on second-harmonic generation in a KTP crystal. Compensation for the lateral displacements due to walkoff in SHG is observed.
Raman spectra of MoO3 implanted with protons
Authors: Hirata T. , Ishioka K. , Kitajima M.
Published: July 2002

The Raman spectra of MoO3 implanted with 1, 2, and 4×1016 H+/cm2 have been recorded at room temperature. It was found that most of the Raman modes of Ag and Bg symmetry, which are observed between 100 and 1100 cm−1, decrease in intensity by the electronic screening of phonons as a result of the electron transfer from hydrogen to Mo. In addition, both Raman modes of Ag symmetry at 998 and 811 cm−1 for MoO3 noticeably stiffened at 4×1016 H+/cm2, while the orthorhombic structure of MoO3 remains unchanged exhibiting no significant change in lattice parameters except for any possible distortion of the MoO6 octahedron. The present results are compared with previous studies, in reference to structural information of the hydrogen molybdenum bronzes as well as MoO3.
Deposition of hydrogen-free diamond-like carbon film by plasma enhanced chemical vapor deposition
Authors: Park Kyu Chang , Moon Jong Hyun , Jang Jin , Oh Myung Hwan
Published: July 2002

Hydrogen-free diamond-like carbon (DLC) films were deposited by the layer-by-layer technique using plasma enhanced chemical vapor deposition (PECVD), i.e., the alternative deposition of thin DLC layer and subsequent CF4 plasma exposure on its surface. The hydrogen-free DLC could be grown on the Si wafer by repeated deposition of the 5 nm DLC layer and subsequent 200 s CF4 plasma exposure on its surface. On the other hand, the conventional DLC deposited by PECVD contains 25 at. % hydrogen inside. The CF4 plasma exposure on the thin DLC layer appears to etch weak C–C bonds and break hydrogen bonds, resulting in a widening optical band gap and increasing conductivity activation energy.
Hydrogenated microcrystalline silicon germanium: A bottom cell material for amorphous silicon-based tandem solar cells
Authors: Ganguly G. , Ikeda T. , Nishimiya T. , Saitoh K. , Kondo M. , Matsuda A.
Published: July 2002

We have developed hydrogenated microcrystalline silicon germanium, which exhibits a red-shifted absorption spectrum relative to hydrogenated microcrystalline silicon, as a candidate material for the bottom cell of amorphous silicon-based tandem solar cells. Optical absorption, x-ray diffraction, and Raman scattering spectra are presented in addition to optoelectronic properties and light-induced changes.
Transition from self-organized InSb quantum-dots to quantum dashes
Authors: Utzmeier T. , Postigo P. A. , Tamayo J. , García R. , Briones F.
Published: July 2002

We have grown self-organized InSb quantum dots on semi-insulating InP (001) substrates by molecular beam epitaxy. We studied the size dependency of the uncapped InSb quantum dots on the nominal thickness of the deposited InSb by atomic force microscopy. The dot sizes have a pronounced minimum at about 2.2 monolayers of InSb. After a nominal thickness of 3.2 monolayers we observe a drastic change of the dot shape, from quantum dots to quantum dashes. From there on the dots grow in a quasicylindric shape aligned in the (110) direction.
Inhibitions of three dimensional island formation in InAs films grown on GaAs (111)A surface by molecular beam epitaxy
Authors: Yamaguchi H. , Fahy M. R. , Joyce B. A.
Published: July 2002

A comparison has been made of the surface morphology of thin InAs films grown on GaAs (001) and (111)A substrates by molecular beam epitaxy using in situ reflection high energy electron diffraction and ex situ atomic force microscopy. InAs growth on (001) surface proceeds via the Stranski-Krastanov mechanism, with three-dimensional island formation beginning between one and two monolayers, but on the (111)A surface there is a two-dimensional mode, independent of detailed growth conditions. This advantage accruing from the use of a novel index substrate provides the opportunity of fabricating a wide range of high quality heterostructures.
Electro-optic properties of the organic salt 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate
Authors: Pan F. , Knöpfle G. , Bosshard Ch. , Follonier S. , Spreiter R. , Wong M. S. , Günter P.
Published: July 2002

We show that the organic salt 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) is a very interesting material for electro-optic applications in the near infrared. The electro-optic coefficients, namely r111, r221, r331, r113, r223, and r333, were determined in the spectral range of 700 up to 1535 nm using optical samples cut from large high quality bulk crystals. DAST combines large electro-optic coefficients, e.g., r111=77±8 pm/V at λ=800 nm and r111=47±8 pm/V at λ=1535 nm, with low dielectric constants, e.g., ε1=5.2±0.4. This combination leads to large polarization-optical coefficients.
Layer splitting process in hydrogen-implanted Si, Ge, SiC, and diamond substrates
Authors: Tong Q.-Y. , Gutjahr K. , Hopfe S. , Gösele U. , Lee T.-H.
Published: July 2002

Si, Ge, SiC, and diamond samples were implanted with H2+ at 120–160 keV with 5.0×1016 ions/cm2 (corresponding to 1.0×1017 H+ ions/cm2) and annealed at various temperatures to introduce hydrogen filled microcracks. An effective activation energy was determined for the formation of optically detectable surface blisters from the time required to form such blisters at various temperatures. The measured effective activation energies are close to the respective bond energies in all four materials. The time required to completely split hydrogen implanted layers from bonded silicon substrates and to transfer them onto oxidized silicon wafers is a factor of about 10 longer. Both processes, blister formation and layer splitting, show the same activation energy.
In situ observation of combustion to form TiN during ball milling Ti in nitrogen
Authors: Chin Z.-H. , Perng T.-P.
Published: July 2002

Mechanical milling of Ti powder in nitrogen by a high-energy ball mill was performed. The pressure was monitored in situ. Initially, nitrogen was dissolved in Ti to form a solid solution. Under suitable conditions, when the nitrogen content had reached 32 at. %, the nitrogen pressure drastically dropped and instant formation of TiN took place. The TiN was formed by means of self-catalytic combustion, which was triggered by the high impact energy and the large clean surface of the fine Ti particles.
A stable Ti-based quasicrystal
Authors: Kelton K. F. , Kim W. J. , Stroud R. M.
Published: July 2002

The thermal stability of the icosahedral phase (i phase) in Ti45Zr38Ni17 alloys is demonstrated. As-cast alloys containing initially only the C14 hexagonal Laves and α-solid-solution phases transformed primarily to the icosahedral phase upon annealing in vacuum for 64 h at 570 °C. This confirms previous evidence for i-phase stability and firmly establishes this quasicrystal as the first nonaluminum stable icosahedral phase. Diffraction data show that this stable i phase is primitive; energy dispersive x-ray spectroscopy measurements place its composition near Ti41.5Zr41.5Ni17. These and other results suggest that the structure of this i phase is similar to that of i(AlLiCu).
Determination of the band-gap energy of Al1−xInxN grown by metal–organic chemical-vapor deposition
Authors: Kim K. S. , Saxler A. , Kung P. , Razeghi M. , Lim K. Y.
Published: July 2002

Ternary AlInN was grown by metal–organic chemical-vapor deposition in the high Al composition regime. The band-gap energy of AlInN ternary was measured by optical absorption spectroscopy at room temperature. The band-gap energy of Al0.92In0.08N is 5.26 eV. The potential application of AlInN as a barrier material for GaN is also discussed.
Anisotropy of electrical and optical properties in β-Ga2O3 single crystals
Authors: Ueda Naoyuki , Hosono Hideo , Waseda Ryuta , Kawazoe Hiroshi
Published: July 2002

Anisotropy of electrical and optical properties in β-Ga2O3 single crystals has been investigated at room temperature. The conductivity and mobility of the degenerate sample along the direction of b and c axes are 38 Ω−1 cm−1, 46 cm2 V−1 s−1, and 2.2 Ω−1 cm−1, 2.6 cm2 V−1 s−1, respectively. The absorption edges of the insulating sample for light polarized E//b and E//c were 4.79 and 4.52 eV, respectively. The rate of the band gap widening with increasing carrier concentration was much larger for E//b than E//c. The origin of these properties are discussed by considering the crystal and electronic structure of β-Ga2O3.
Observation and control of surface morphology of AlP grown by atomic layer epitaxy
Authors: Ishii Masashi , Iwai Sohachi , Ueki Tatzuo , Aoyagi Yoshinobu
Published: July 2002

The surface of the epitaxial layer of AlP grown by atomic layer epitaxy (ALE) was observed by atomic force microscopy. It was discovered that the atomic scale surface flatness was not always retained during ALE growth even though the self-limiting growth of 1 monolayer per 1 alternative source gas supply was maintained. A reaction process model that focused on the methyl adsorbate lifetime on the Al surface was proposed to explain the experimental results. Based on this model, AlP surface morphology was improved by gas feeding control, and a flat surface with atomic steps was obtained even after 250 cycles of the ALE sequence.
Epitaxial liftoff of thin oxide layers: Yttrium iron garnets onto GaAs
Authors: Levy M. , Osgood R. M. , Kumar A. , Bakhru H.
Published: July 2002

We report on the implementation of epitaxial liftoff in magnetic garnets. Deep-ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG epilayers grown on gadolinium gallium garnet. The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. 10-μm-thick films of excellent quality are lifted off and bonded to silicon and GaAs substrates. No noticeable degradation in magnetic coercivity due to domain pinning is observed. Stress-induced microfracturing in the thin oxide layers is also addressed.
Raman spectra of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5
Authors: Rincón C. , Wasim S. M. , Marı́n G. , Delgado J. M. , Huntzinger J. R. , Zwick A. , Galibert J.
Published: July 2002

The optical vibrational modes of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5 have been obtained by Raman spectra at various temperatures. The totally symmetric A1 mode appears around 155 and 167 cm−1 in CuIn3Se5 and CuGa3Se5, respectively. All the lines observed, except the B1 modes, present a reduction in their frequencies by about 10% as compared to the corresponding values in the CuInSe2 and CuGaSe2 chalcopyrites. This is due to the presence in these compounds of an array of vacancies occupying particular sites in the cation sublattice. These tend to relax the stretching forces thus reducing the vibrational frequencies.
Micro-Raman fingerprint of grain boundary in [100] oriented diamond films: Stress distribution and diamond phases
Authors: Rossi Maria Cristina
Published: July 2002

Local distribution of stress state and carbon bonding in diamond films are studied by micro-Raman spectroscopy. Large changes in intensity, line shape, and peak position of the diamond Raman line occur close to the grain boundary. The characteristic feature of such region is a 1326 cm−1 Raman peak, whose detection suggests that defect incorporation at the grain boundary may promote a diamond symmetry modification from a cubic to hexagonal one. Close to intergrain locations, large anisotropic stresses also induce frequency splitting of the Raman line. Suitable stress configurations consistent with the detection of an almost unshifted component and of a largely frequency-changing mode are analyzed.
Near-threshold gain mechanisms in GaN thin films in the temperature range of 20–700 K
Authors: Bidnyk S. , Schmidt T. J. , Little B. D. , Song J. J.
Published: July 2002

We report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers in the temperature range of 20–700 K. High-quality single-crystal GaN films grown on 6H–SiC and (0001) sapphire were used in this study. We show that the dominant near-threshold gain mechanism is inelastic exciton–exciton scattering for temperatures below ∼150 K, characterized by band-filling phenomena and a low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge-related emission indicates electron–hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. Based on our results, we discuss possibilities of reducing the room-temperature lasing threshold in laser diode structures with a GaN active medium.
Growth and electrostrictive properties of Pb(Mg1/3Nb2/3)O3 crystals
Authors: Lee Sang-Goo , Monteiro Ralph G. , Feigelson Robert S. , Lee Howard S. , Lee Myeongkyu , Park Seung-Eek
Published: July 2002

Transparent and stoichiometric lead-magnesium-niobate crystals were grown by the Bridgman method. Crystals of centimeter size were obtained without material loss by employing self-seeded and seeded techniques using sealed platinum crucibles. The fastest growth direction was found to be pseudocubic 〈111〉. As-grown crystals showed a broad absorption band centered near λ=600 nm and an OH absorption near λ=2830 nm. The electrostrictive coefficient Q11 was determined to be 1.15×10−2 m4 C−2 from the measured strain and polarization.
Nanoscale GaAs metal–semiconductor–metal photodetectors fabricated using nanoimprint lithography
Authors: Yu Zhaoning , Schablitsky Steven J. , Chou S. Y.
Published: July 2002

GaAs metal–semiconductor–metal photodetectors (MSM PDs) with a variety of nanoscale finger spacings and widths were fabricated using nanoimprint lithography (NIL). Compared with MSM-PDs fabricated using electron-beam lithography and photolithography, the MSM-PDs fabricated using NIL do not show observable degradation in the device characteristics if the imprinting pressures are kept at 600 psi or below, although they do degrade at higher pressures.
Transmission and photoluminescence images of three-dimensional memory in vitreous silica
Authors: Watanabe Mitsuru , Juodkazis Saulius , Sun Hong-Bo , Matsuo Shigeki , Misawa Hiroaki , Miwa Masafumi , Kaneko Reizo
Published: July 2002

We demonstrate separate readouts of three-dimensional memory by (i) transmission imaging using a conventional optical microscope and (ii) photoluminescence (PL) of the bits created by inducing optical damage within the vitreous silica. Recording was done by tightly focused (objective ×100, numerical aperture 1.3) single shot irradiation of 120 fs duration pulses at a 400 nm wavelength. For the readout, a broadband of PL at 470–600 nm was excited by 400 nm, 120 fs irradiation with pulse energy smaller by a factor of 106 compared with that for the recording. We found an erasing of the PL after 400 °C annealing, while the readability of the bits by the transmission was sustained. This shows the potential for two-bit information recording per single bit by means of separate readout procedures.
Ferroelectricity of YMnO3 thin films prepared via solution
Authors: Kitahata Hiroya , Tadanaga Kiyoharu , Minami Tsutomu , Fujimura Norifumi , Ito Taichiro
Published: July 2002

We have observed the ferroelectricity at room temperature in YMnO3 thin films prepared via solution. Precursor films of YMnO3 on Pt/sapphire or Y2O3/Si substrates were heat treated in vacuum or in air for controlling the crystallinity. X-ray diffraction measurements indicated that each film was a single phase of hexagonal YMnO3. While the film heat treated in air indicated an insufficient crystallinity, the film heat treated in vacuum showed a high crystallinity with a c-axis preferred orientation. The leakage current of the film heat treated in vacuum was at least three orders of magnitude lower than that heat treated in air. The ferroelectricity of the film heat treated in vacuum was confirmed in the capacitance–voltage measurement at room temperature due to its high crystallinity with the c-axis preferred orientation and the small leakage current.
Identification of the intrinsic self-trapped hole center in KD2PO4
Authors: Stevens K. T. , Garces N. Y. , Halliburton L. E. , Yan M. , Zaitseva N. P. , DeYoreo J. J. , Catella G. C. , Luken J. R.
Published: July 2002

The intrinsic “self-trapped” hole center in KD2PO4 crystals has been identified using electron paramagnetic resonance and electron-nuclear double resonance. These defects, labeled [D2PO4]o centers, can be formed at 77 K by irradiating with either 60 kV x rays or the fourth harmonic (266 nm) of a pulsed Nd:YAG laser. The hole is equally shared by two adjacent oxygen ions, and hyperfine interactions with one phosphorus and two equivalent deuterons are observed. The sample used in this investigation was approximately 80% deuterated, thus both [D2PO4]o and [HDPO4]o centers were detected, with the former being dominant. These intrinsic self-trapped hole centers are of interest because of their potential role in the transient optical absorption produced in KD2PO4 crystals at room temperature by intense 266 nm laser pulses.
Ultraviolet-blue emission and electron-hole states in ZnSe quantum dots
Authors: Smith C. A. , Lee H. W. H. , Leppert V. J. , Risbud S. H.
Published: July 2002

We observed the quantum-confined band edge emission from ZnSe quantum dots and the size dependence of the energy states, spin-orbit interaction, and Stokes shift. The band edge emission occurs in the ultraviolet blue. The energy gap=Eg+C/dn where d is the diameter and n is 1.19±0.13 and 1.21±0.13 for the first and second electron-hole transitions, respectively. The separation between these transitions approaches the bulk spin-orbit splitting, while the Stokes shift decreases with particle size. Effective mass theories cannot explain these results. Trap emission is observed in some samples in the green and red, resulting from Se-related traps.
Transparent conducting aluminum-doped zinc oxide thin films for organic light-emitting devices
Authors: Kim H. , Gilmore C. M. , Horwitz J. S. , Piqué A. , Murata H. , Kushto G. P. , Schlaf R. , Kafafi Z. H. , Chrisey D. B.
Published: July 2002

Aluminum-doped zinc oxide (AZO) thin films (∼3000 Å) with low electrical resistivity and high optical transparency have been grown by pulsed-laser deposition on glass substrates without a postdeposition anneal. Films were deposited at substrate temperatures ranging from room temperature to 400 °C in O2 partial pressures ranging from 0.1 to 50 mTorr. For 3000-Å-thick AZO films grown at room temperature in an oxygen pressure of 5 mTorr, the electrical resistivity was 8.7×10−4 Ω cm and the average optical transmittance was 86% in the visible range (400–700 nm). For 3000-Å-thick AZO films deposited at 200 °C in 5 mTorr of oxygen, the resistivity was 3.8×10−4 Ω cm and the average optical transmittance in the visible range was 91%. AZO films grown at 200 °C were used as an anode contact for organic light-emitting diodes. The external quantum efficiency measured from these devices was about 0.3% at a current density of 100 A/m2.
Direct observation of subpicosecond single-flux-quantum generation in pulse-driven Y–Ba–Cu–O Josephson junctions
Authors: Adam Roman , Currie Marc , Williams Carlo , Sobolewski Roman , Harnack Oliver , Darula Marian
Published: July 2002

We report our time-resolved measurements of switching dynamics of grain-boundary, 5-μm-wide Y–Ba–Cu–O (YBCO) Josephson junctions, excited by 2-ps-wide electrical pulses optically generated by a voltage-biased, 5-μm-wide, 10-μm-long YBCO microbridge. The time-resolved transients were recorded at 20 K using a subpicosecond cryogenic electro-optic sampling system. The intrinsic junction response was separated from the circuit-related feedthrough, and we observed both experimentally and in numerical simulations a 0.8-ps-wide, single-flux-quantum (SFQ) pulse, generated by the switching of the junction with the IcRn product equal to ∼2 mV. At the same time, the measured turn-on delay time was almost three times shorter than that obtained from simulations, questioning applicability of the resistively shunted tunnel junction model to nonhysteretic, high-temperature superconducting weak links. Our test structure's power consumption associated with the single SFQ pulse generation was ∼0.1 μW, leading to a (switching time)×(dissipated power) product equal to 0.08 aJ.
Lightwave propagation through a 120° sharply bent single-line-defect photonic crystal waveguide
Authors: Tokushima Masatoshi , Kosaka Hideo , Tomita Akihisa , Yamada Hirohito
Published: July 2002

We have demonstrated 1.55 μm wavelength lightwave propagation through a 120° sharply bent waveguide formed in a triangular-lattice two-dimensional photonic crystal (2D PC). Such propagation has not previously been experimentally confirmed. The photonic crystal was fabricated in a silicon-on-insulator (SOI) wafer with the top silicon layer of the wafer used as a core layer. A 877-μm-long single-line-defect waveguide was formed in the PC with a sharp 120° bend near the middle of the waveguide. A tapered-hemispherical-end fiber was coupled to the input end of the waveguide for the light input, and the output from the other end of the waveguide was directly observed by scanning its near-field profile with another tapered-hemispherical-end fiber.
Melt-spun precipitation-hardened Sm2(Co, Cu, Fe, Zr)17 magnets with abnormal temperature dependence of coercivity
Authors: Goll D. , Kleinschroth I. , Sigle W. , Kronmüller H.
Published: July 2002

Rapidly quenched Sm(CobalCu0.08Fe0.22Zr0.02)8.5 (Cu-/Fe-rich) and Sm(CobalCu0.05Fe0.10Zr0.03)8.5 (Cu-/Fe-poor) ribbons have been prepared by means of the melt-spinning technique. By applying an appropriate annealing procedure a microstructure similar to that of sintered magnets can be obtained. The energy dispersive x-ray microanalysis of the compositional dependence near the cell boundaries suggests a model for the profile of the crystal anisotropy constants responsible for the magnetic hardening. The Cu-/Fe-rich alloy shows a normal temperature dependence of coercivity with a negative temperature coefficient, but the Cu-/Fe-poor ribbons show a positive temperature coefficient in the temperature range from 400–700 K. The different temperature coefficients are discussed in terms of a pinning model.
Unusual disparity in electroluminescence and photoluminescence spectra of vacuum-evaporated films of 1,1-bis ((di-4-tolylamino) phenyl) cyclohexane
Authors: Kalinowski J. , Giro G. , Cocchi M. , Fattori V. , Di Marco P.
Published: July 2002

The electroluminescence (EL) and photoluminescence (PL) spectra of thin films of 1,1-bis((di-4-tolyloamino)phenyl) cyclohexane (TAPC) appear to be completely different. Whereas the broad PL spectra reveal major maxima at ≅370 and 450 nm, a strong regular band at 580 nm is characteristic of the EL spectra. It is shown that in contrast to PL, which is composed of molecular exciton (monomer) and excimer emission, EL can be explained by the direct cross recombination transition between electrons and holes trapped on tritolylamine (TTA) subunits of different TAPC molecules. Such a pair of trapped carriers, formed selectively under recombination of statistically independent (here injected at opposite electrodes) electrons and holes, is considered as a particular excited state (“electromer”) responsible also for the EL emission of some other compounds containing TTA or triphenylamine moieties, as for example an amino-substituted triphenylbenzene.
Three-dimensional microfabrication by use of single-photon-absorbed polymerization
Authors: Maruo Shoji , Ikuta Koji
Published: July 2002

We developed a promising method to fabricate three-dimensional microstructures by using single-photon-absorbed polymerization confined to the vicinity of a tightly focused spot. This localized polymerization is based on the nonlinear response of the photopolymerizable resin to optical intensity with sufficiently low exposure. The nonlinear response was verified by measuring polymerization exotherm at different light intensities. The proposed method enables us to make even movable microstructures without any of the supporting parts or sacrificial layers normally required with conventional micromachining. In the experiment reported here, we fabricated a microgear with an external diameter of 47 μm and an attached shaft.
Ultrafast interfacial charge separation processes from the singlet and triplet MLCT states of Ru(bpy)2(dcbpy) adsorbed on nanocrystalline SnO2 under negative applied bias
Authors: Iwai Shinichiro , Hara Kohjiro , Murata Shigeo , Katoh Ryuzi , Sugihara Hideki , Arakawa Hironori
Published: July 2002

We have observed the stimulated emission from the 1MLCT state of Ru(bpy)2(dcbpy) adsorbed on SnO2 nanocrystal by femtosecond pump–probe spectroscopy under applied bias (Vex) for the first time. The luminescence from the 3MLCT state has been also observed by picosecond time-resolved measurement. Observed lifetimes of the stimulated emission and the luminescence are 70 fs and 130 ps, respectively, at zero applied voltage. Both these lifetimes continuously increase with increasing negative bias and reach 320 fs (stimulated emission) and 6 ns (luminescence) at Vex=−0.7 V. The change in the lifetime of luminescence and of stimulated emission under negative applied bias is considered to be due to the change in the interfacial CS rate, although the possibility of the bias dependent desorption of the dye cannot be completely excluded. We analyzed the result by assuming that the changes in the lifetimes of the stimulated emission and the luminescence are due to the change in the interfacial CS rate constant. This analysis shows that interfacial CS occurs from both the 1MLCT and 3MLCT states. The competition between CS and intersystem crossing (ISC) from 1MLCT occurs in ∼100 fs time region. Assuming there is no nonradiative relaxation pathways from 1MLCT except for CS and for ISC, the rate constant of ISC was estimated to be 1/(320 fs). The ratio of the numbers of electrons injected from the 1MLCT and the 3MLCT states was 0.76:0.22. This means that unnegligible number of electrons are injected to SnO2 from the 1MLCT state.
Electrostatic charging and deflection of nonconventional droplet streams formed from capillary stream breakup
Authors: Orme Melissa , Courter Jon , Liu Qingbin , Huang Changzheng , Smith Robert
Published: July 2002

Droplet streams generated from capillary stream breakup and forced with amplitude-modulated (a-m) disturbances will undergo a systematic interdroplet merging process due to their relative velocities that result from the a-m disturbance. This paper concerns the electrostatic charging of droplets generated with a-m disturbances, and seeks an understanding between the competitive effects of the electrostatic repulsive force and the momentum associated with relative velocities that are due to the a-m disturbance. To this end, experimental results and numerical simulations that are in excellent agreement and predict the configuration of the charged droplet stream are presented. In this work, droplets are generated with the aforementioned technique and are electrostatically charged. It has been found that for droplets generated with a disturbance with a high degree of modulation, m, the momentum of the droplets dominates over the electrostatic force causing the droplet merging process to be similar to the uncharged case as attested by both experimental results and numerical simulations. Here, m is the ratio of modulation to original carrier amplitudes. For droplets with lower values of m, the electrostatic forces dominate and it is found that the relative positions of the droplets will oscillate along the direction of their flight path with maximum excursions not exceeding one wavelength of the carrier disturbance (i.e., the separation of the unmerged droplets).
Destruction of the superconductivity of an inhomogeneous film in the mixed state by the transport current
Authors: Bezuglyı̆ A. I.
Published: July 2002

The destruction of superconductivity by the transport current is investigated for the case of a wide film in a perpendicular magnetic field. The destruction of superconductivity occurs by two competing mechanisms: growth of a normal domain (ND), and instability of the viscous flow of the magnetic flux. Under conditions in which the first mechanism is dominant, analysis of the stationary domain states permits one to systematize all of the different types of current–voltage (IV) characteristics of a film with a local inhomogeneity and to find the dependence of the SN junction current from the values of the magnetic field B and the temperature T0 of the medium. It is shown that additional heating of a film with a ND on account of the dissipative motion of vortices in the S region can lead to vanishing of the hysteresis of the IV characteristic as B or T0 is increased. The known results on the current at which the magnetic flux flow becomes unstable are used to obtain the field dependence of the crossover temperature of these two mechanisms for the destruction of superconductivity. The main theoretical results are compared with experiment.
Structural and luminescence properties of nanostructured ZnS:Mn
Authors: Adachi Daisuke , Hasui Shigeki , Toyama Toshihiko , Okamoto Hiroaki
Published: July 2002

We have studied structural and luminescence properties of nanostructured (NS-) ZnS:Mn which has potential applications in thin-film electroluminescence (TFEL) devices. As a NS-ZnS:Mn system, a ZnS:Mn/Si3N4 multilayer having thicknesses of 2.5 nm for ZnS and 0.6 nm for Si3N4 was prepared by a conventional rf-magnetron sputtering method. Grazing incidence x-ray reflectometry and x-ray diffractometry show that ZnS:Mn nanocrystals were formed between the amorphous Si3N4 layers. Photoluminescence intensity associated with the Mn2+ transitions per total thickness of the ZnS:Mn layers is increased in NS-ZnS:Mn in comparison with that of the ZnS:Mn thin film, indicating the effects due to quantum confinement. The TFEL device with NS-ZnS:Mn as an emission layer exhibits a reddish-orange broad band emission with the maximum luminance of 2.8 cd/m2 under the 1-kHz sinusoidal wave operation at a voltage of 20.5 V0−p.
Characterization of coatings on magnetic metal using the swept-frequency eddy current method
Authors: Tai Cheng-Chi
Published: July 2002

A measurement technique using the swept-frequency eddy current (SFEC) method for determining the thickness, conductivity, and permeability of metallic coatings on metal substrates for the case when either coating, substrate, or both are magnetic was developed. This technique involved using the empirically determined permeability of the metals as input to the model calculation. This technique is demonstrated for nickel layers (25–200 μm) over copper substrates, copper layers (25–200 μm) over nickel substrates, and zinc layers (50–400 μm) over steel substrates. The electrical impedance was measured for air-core coils in the presence and absence of the layer using a 4194A Hewlett–Packard impedance analyzer. An analytic closed-form solution for calculating the impedance of a cylindrical air-core probe over a layered metallic half-space is presented. The determination of coating thickness and conductivity and permeability of the metals is based on the comparison of the data taken with air-core coils and theoretical calculation that using the closed-form solution developed. Most of the cases studied show experiment and theory agreeing fairly well, within 10%, with no adjustable parameters. The physical phenomena of eddy currents interaction with the coated magnetic metals are also discussed.
Magneto-optical mode conversion in Cd1−xMnxTe waveguide on GaAs substrate
Authors: Zaets W. , Ando K.
Published: July 2002

Magneto-optical mode conversion was achieved in a waveguide of diluted magnetic semiconductor Cd1−xMnxTe grown on GaAs substrate. Mode conversion ratio up to 34% under a magnetic field of 5.5 kG was obtained. Cd1−xMnxTe waveguide showed low optical loss, 4 dB/cm, and high magneto-optical figure-of-merit, 15 deg/dB/kG at λ=790 nm. This result shows the feasibility of monolithical integration of an optical isolator with semiconductor optoelectronic devices.
Temperature-dependent internal friction in silicon nanoelectromechanical systems
Authors: Evoy S. , Olkhovets A. , Sekaric L. , Parpia J. M. , Craighead H. G. , Carr D. W.
Published: July 2002

We report the temperature-dependent mechanical properties of nanofabricated silicon resonators operating in the megahertz range. Reduction of temperature leads to an increase of the resonant frequencies of up to 6.5%. Quality factors as high as 1000 and 2500 are observed at room temperature in metallized and nonmetallized devices, respectively. Although device metallization increases the overall level of dissipation, internal friction peaks are observed in all devices in the T=160–180 K range.
Approach to enhance deuterium incorporation for improved hot carrier reliability in metal-oxide-semiconductor devices
Authors: Cheng Kangguo , Lee Jinju , Lyding Joseph W.
Published: July 2002

The deuterium isotope effect has been widely demonstrated to improve hot-carrier reliability in metal-oxide-semiconductor transistors. Most of the interface traps, however, may have been passivated by hydrogen before the final deuterium anneal due to the ubiquitous presence of hydrogen in modern complementary metal-oxide-semiconductor processing technology. Therefore, effective deuteration requires both deuterium diffusion to the SiO2–Si interface and displacement of the previously bonded hydrogen. We have introduced a “prestress” process in which hydrogen is depassivated before deuterium annealing. We found that the prestressed transistors are more robust to hot-carrier stress than control transistors without the prestress. We have also found that the replacement of hydrogen with deuterium is the rate-limiting step for deuterium incorporation at the SiO2–Si interface. With the prestress, a lower deuterium annealing temperature can be applied without compromising the reliability improvement.
Diamond radiation detector made of an ultrahigh-purity type IIa diamond crystal grown by high-pressure and high-temperature synthesis
Authors: Tanaka Teruya , Kaneko Junichi , Takeuchi Daisuke , Sumiya Hitoshi , Katagiri Masaki , Nishitani Takeo , Takeuchi Hiroshi , Iida Toshiyuki , Ohkushi Hideyo
Published: July 2002

Synthetic diamond radiation detectors made of ultrahigh-purity type IIa diamond crystals were developed. The diamond crystals, which were grown by high-pressure and high-temperature synthesis, contained less nitrogen impurity than 0.1 ppm, i.e., 1/10 of conventional type IIa diamond crystals. Since the ultrahigh-purity type IIa diamond crystal was a p-type semiconductor due to a trace impurity of boron, a structure consisting of Schottky and ohmic contacts was adopted for the detectors to suppress an increase in leakage current. For the same purpose, a metal–insulator–semiconductor structure using a chemical vapor deposition diamond insulating layer was adopted for one of the detectors. Plural peaks were observed in the 5.486 MeV α energy spectra obtained by the detectors; motion of holes produced the main part of output pulses from the detectors on these measurements. One of the peaks in each spectrum was hardly influenced by light irradiation, even ultraviolet light of 370 nm (3.4 eV), compared with a peak obtained by the conventional type IIa diamond radiation detector. This experimental result indicated that there was a superior part in the crystal where deep energy levels did not exist so much. Although there was no direct evidence, influence of a distribution of the boron impurity in the crystal was expected. On the other hand, electron trapping severely occurred and resulted in loss in charge collection; an effect of the reduction in the nitrogen impurity was not confirmed on the behavior of electrons.
Behavior of laser-induced cavitation bubbles in liquid nitrogen
Authors: Tomita Y. , Tsubota M. , Nagane K. , An-naka N.
Published: July 2002

Initial behavior and the subsequent motion of a bubble in liquid nitrogen are investigated experimentally using high-speed photography. A bubble is generated by focusing a pulsed ruby laser into liquid nitrogen at 78.0 K, changing the ambient pressures up to 253.2 kPa which corresponds to the applied pressure (or overpressure), Δp, being 147.1 kPa. When the energy level of the laser beam at the focus exceeds an irradiance threshold, for instance 5.4×1011 W/cm2 for Δp=4.9 kPa, the optical breakdown occurs in the liquid nitrogen, followed by a series of high-speed phenomena such as plasma formation, shock wave emission, and vapor bubble generation. It is found that during a very short period after the plasma formation a bubble grows nonspherically reflecting from the plasma shape, but the bubble volume itself varies with time in the same way for all cases performed in the present experiment. The liquid inertia is a dominant factor affecting the bubble growth, while the thermal effect becomes remarkable during the bubble collapse, resulting in the retardation of the bubble motion. The characteristic behavior of a laser-induced cavitation bubble in liquid nitrogen is significantly influenced by the phase change of vapor at the bubble surface as well as by the vapor pressure inside the bubble. Immediately after the bubble rebound, instabilities are amplified over the bubble surface similar to those caused in the water case.
Thomas–Fermi–Dirac–von Weizsäcker models in finite systems
Authors: Chan Garnet Kin-Lic , Cohen Aron J. , Handy Nicholas C.
Published: July 2002

To gain an understanding of the variational behavior of kinetic energy functionals, we perform a numerical study of the Thomas–Fermi–Dirac–von Weizsäcker theory in finite systems. A general purpose Gaussian-based code is constructed to perform energy and geometry optimizations on polyatomic systems to high accuracy. We carry out benchmark studies on atomic and diatomic systems. Our results indicate that the Thomas–Fermi–Dirac–von Weizsäcker theory can give an approximate description of matter, with atomic energies, binding energies, and bond lengths of the correct order of magnitude, though not to the accuracy required of a qualitative chemical theory. We discuss the implications for the development of new kinetic functionals.
Mass and size dependence of single ion dynamics in molten monohalides
Authors: Alcaraz Olga , Trullàs Joaquim
Published: July 2002

This work is concerned with four molten monohalides with different ionic radii ratios (RbCl, NaI, AgCl, and CuCl) and ideal isotopic systems of these salts with different ionic mass ratios. The velocity autocorrelation functions of the two ionic species in each melt have been studied by both a theoretical approximation and molecular dynamics simulations. It is found that their main features may be qualitatively predicted by considering suitable combinations of the second and fourth frequency moments of their spectra. The analysis of these two parameters allows us to determine how the structure (strongly dependent on the ionic size difference) and the ionic masses contribute to the shape of the velocity autocorrelation functions. The results show that the averaged microscopic motion of the small ions is mainly determined by the first neighboring shell of unlike ions, whereas the nearest shell of like ions also affects the dynamics of the large ions. This effect is more pronounced as the size difference is greater. Furthermore, it is concluded that the size differences encourage the rattling motion of the large ions, whereas the mass difference encourages the backscattering and oscillations of the velocity autocorrelation function of the light ions. A simple rule is derived to determine the interplay between these two effects. Comparison between the mass and nearest distance ratios enables the prediction as to which species will experience a more pronounced backscattering motion. The size difference effects prevail in the hydrodynamics regime and the self-diffusion coefficient of the small ions is higher than that of the large ones. The difference between the self-diffusion coefficient increases as the size differences increases.
Photoacoustic analysis of the ferroelectric ceramics specific heat
Authors: Castañeda-Guzmán R. , Villagrán-Muniz M. , Saniger-Blesa J. M. , Pérez-Ruiz S. J. , Pérez-Martı́nez O.
Published: July 2002

Knowing the thermal expansion of a material and the correlation analysis of the photoacoustic signals, it is possible to obtain the phase transition temperature and a qualitative curve of the specific heat at constant pressure (Cp) for ceramic materials. This analysis was applied to a BaTiO3 ferroelectric ceramic and a good agreement with previously published Cp versus temperature curves was obtained. Additionally, the phase transition temperature and the Cp curve of a samarium-doped lead titanate ceramic (Pb0.88Sm0.08TiO3) are presented. The phase transition temperature of the Pb0.88Sm0.08TiO3 obtained with this technique was corroborated with classical differential thermal analysis and dielectric permittivity measurements.
The deviatoric response of polymethylmethacrylate to one-dimensional shock loading
Authors: Millett J. C. F. , Bourne N. K.
Published: July 2002

Samples of polymethylmethacrylate have been deformed by one-dimensional shock waves during plate impact. Manganin stress gauges have been introduced into the samples in such orientation that renders them sensitive to the lateral component of stress during shock loading. In combination with known Hugoniot data, these results have been used to determine the variation of shear strength with increasing impact stress. It has been observed that over the measured stress range, shear strength increases with increasing longitudinal stress. Comparison with the work of others shows close agreement. We also note that there is a small yet significant reduction in lateral stress, and hence an increase in shear strength behind the shock front. We believe this to be a manifestation of the viscoplastic response of this material. Finally, we observe no change in mechanical behavior at ∼2.0 GPa, where others have noticed large changes in thermal and electronic responses.
Crystal field, phonon coupling and emission shift of Mn2+ in ZnS:Mn nanoparticles
Authors: Chen Wei , Sammynaiken Ramaswami , Huang Yining , Malm Jan-Olle , Wallenberg Reine , Bovin Jan-Olov , Zwiller Valéry , Kotov Nicholas A.
Published: July 2002

The Mn2+ emission wavelengths are at 591, 588, 581 and 570 nm, respectively, for the ∼10, ∼4.5, ∼3.5 nm sized nanoparticles and the ZnS:Mn nanoparticles formed in an ultrastable zeolite-Y. To reveal the cause for the shift, the crystal field and phonon coupling were investigated. The results show that the predominant factor for the shift is the phonon coupling, whose strength is size dependent and is determined by both the size confinement and the surface modification of the nanoparticles. Although the crystal field strength decreases with the decreasing of the particle size, its change has little contribution to the emission shift of Mn2+ in ZnS:Mn nanoparticles.
Formation of quantum-dot quantum-well heteronanostructures with large lattice mismatch: ZnS/CdS/ZnS
Authors: Little Reginald B. , El-Sayed Mostafa A. , Bryant Garnett W. , Burke Susan
Published: July 2002

Two-dimensional heterostructures have been exploited extensively in the synthesis of optoelectronic devices. Structures with small lattice mismatch can be synthesized readily. Large lattice mismatch in II–VI film heterostructures makes synthesis of devices with these materials more difficult. However, these large mismatch heterostructures usually have useful optical properties. One such heterostructure is the ZnS/CdS system with a large exciton binding energy and a large band gap useful for blue–green emitting devices. In this work, small II–VI nanoparticles are studied. We show that II–VI heterostructures can be made in quantum dots, despite the large bulk lattice mismatch. Two well-known techniques are combined to synthesize first very small ZnS and CdS seed nanoparticles and then do nanoepitaxy on them to produce ZnS/CdS core/shell quantum-dot quantum-well heteronanostructures. These structures are characterized by UV visible absorbance. Measured spectra are compared with electronic level structures calculated for the fabricated heteronanostructures with a tight-binding model. The consistency of the observed spectra with the predicted transitions indicates that the desired core/shell and core/shell/clad structures were grown. The metastability of the ZnS/CdS/ZnS heteronanostructures is attributed to low-temperature construction and small crystal size (<3 nm). The small particle size should produce large surface forces and ZnS core contraction. Also, the small particle size should accommodate strain, as a result of the ZnS/CdS interfacial curvature, which is not possible for planar systems. Furthermore, this new structure is kinetically stabilized against alloying by the large size difference between the Cd2+ ion and Zn2+ ions. We suggest that all of these factors contribute to the formation of quantum-dot quantum-well ZnS/CdS/ZnS heteronanostructures.
Soft ellipsoid model for Gaussian polymer chains
Authors: Eurich Frank , Maass Philipp
Published: July 2002

A soft ellipsoid model for Gaussian polymer chains is studied, following an idea proposed by Murat and Kremer [J. Chem. Phys. 108, 4340 (1998)]. In this model chain molecules are mapped onto ellipsoids with certain shapes, and to each shape a monomer density is assigned. In the first part of the work, the probabilities for the shapes and the associated monomer densities are studied in detail for Gaussian chains. Both quantities are expressed in terms of simple approximate formulas. The free energy of a system composed of many ellipsoids is given by an intramolecular part accounting for the internal degrees of freedom and an intermolecular part following from pair interactions between the monomer densities. Structural and kinetic properties of both homogeneous systems and binary mixtures are subsequently studied by Monte Carlo simulations. It is shown that the model provides a powerful phenomenological approach for investigating polymeric systems on semimacroscopic time and length scales.