bluuebunny/crossref_metadata_2025 huggingface dataset:
Further characterization of pigment‐producing Malassezia strains
Authors: Mayser P. , Töws A. , Krämer H.‐J. , Weiß R.
Published: February 2004

Reference as well as field strains of Malassezia furfur (30), M. sympodialis (49), M. globosa (52), M. obtusa (one), M. restricta (one), M. slooffiae (seven), and M. pachydermatis (373) were investigated for their ability to produce pigment and fluorochromes when tryptophan (Trp) is offered as the main nitrogen source. Only the M. furfur strains produced pigment on a pigment‐inducing medium (p‐medium). Remarkably, the optical activity of Trp was not significant for pigment synthesis. Other nitrogen sources that are structurally similar to Trp (gramine, tryptamine, serotonin) did not induce pigment formation. All lipophilic non‐furfur species failed to grow and to form pigment on this agar. However, growth of all lipid‐dependent species was achieved on a modified Dixon agar in which peptone had been substituted by an equal amount of l‐Trp. Here, too, the M. furfur colonies were characterized by rapidly developing dark brown halos. Furthermore, about 11% of the M. pachydermatis strains tested produced pigment formation on the p‐medium, which was enhanced by addition of d‐glucose. In contrast to M. furfur, pigment formation occurred after a markedly longer incubation time (4 weeks unlike 3–5 days) with a lower yield and limited color spectrum (thin layer chromatography, TLC). The UV filter pityriacitrine recently described for M. furfur was also demonstrated for M. pachydermatis by extraction, high‐performance liquid chromatography (HPLC) analysis with co‐elution and mass spectroscopy. The phenotypic feature of pigment formation in some strains of M. pachydermatis may confirm recent molecular‐genetic findings suggesting a relationship between some strains of M. pachydermatis and M. furfur.
Secondary ion mass spectrometry for the identification of polymers with noncharacteristic secondary ions using multivariate statistical analysis
Authors: van Gennip W. J. H. , Thüne P. C. , Dijkstra J. B. , Niemantsverdriet J. W.
Published: February 2004

Eleven different, filler-free polymers were depth profiled until all secondary ion signals were stable. Discriminant function analysis and principal components analysis were performed on a dataset containing the intensities of noncharacteristic hydrocarbon secondary ions, measured in this steady state. Discriminant function analysis showed that these secondary ions were sufficient to correctly identify all polymers using leave-one-out correction. Even with principal components analysis, which uses no prior knowledge about the origin of a data point, identification was shown to be possible.
Application of tip-enhanced microscopy for nonlinear Raman spectroscopy
Authors: Ichimura Taro , Hayazawa Norihiko , Hashimoto Mamoru , Inouye Yasushi , Kawata Satoshi
Published: February 2004

A tip-enhanced electric field at a metallic probe tip of apertureless near-field scanning optical microscope was applied to a third-order nonlinear optical process, coherent anti-Stokes Raman spectroscopy. The combination of the enhanced field and third-order nonlinearity resolved molecular vibrations of adenine molecules embedded in deoxyribonucleic acid double-helix nanocrystals beyond the diffraction limit of light.
A monochromatic and high-power terahertz source tunable in the ranges of 2.7–38.4 and 58.2–3540 μm for variety of potential applications
Authors: Shi Wei , Ding Yujie J.
Published: February 2004

Based on phase-matched collinear difference-frequency generation in a single GaSe crystal, continuously tunable and coherent radiation in the extremely wide ranges of 2.7–38.4 and 58.2–3540 μm has been achieved. This unique source has the additional advantages of high coherence (narrow linewidth) and simple alignment. The peak output power for the terahertz radiation reaches 209 W at the wavelength of 196 μm (1.53 THz), which corresponds to a power conversion efficiency of 0.055%. Moreover, the terahertz transmission spectra on DNA macromolecules and protein were directly measured, demonstrating some potential and important applications of this terahertz source.
Fabrication of planar optical waveguides by electrical microcontact printing
Authors: Wolfe Daniel B. , Love J. Christopher , Gates Byron D. , Whitesides George M. , Conroy Richard S. , Prentiss Mara
Published: February 2004

This letter describes the fabrication by electrical microcontact printing (E-μCP) of planar, optical waveguides, and splitters made of poly(4-vinylphenol) doped with phloxine B. This soft-lithographic technique uses a poly(dimethylsiloxane) (PDMS) stamp coated with a thin gold film to pattern the flow of current through the film of doped polymer. The current bleaches the phloxine B, and thus creates regions of high (unbleached; waveguide core) and low (bleached; waveguide cladding) refractive index. The maximum exposure time to obtain Δn=0.025 was 90 s. This system is useful for guiding light having λ=600–1310 nm. These polymer waveguides preserve polarization, and are able to guide light around 90° corners with a minimum radius of curvature of 1.6 mm. E-μCP patterned a 1×4 optical power splitter in 10 s. This technique is potentially useful for rapid prototyping of planar and multilevel optical devices.
Improved blue light-emitting polymeric device by the tuning of drift mobility and charge balance
Authors: Chin Byung Doo , Suh Min Chul , Lee Seong Taek , Chung Ho Kyoon , Lee Chang Hee
Published: February 2004

We have prepared blue polymer-small molecule hybrid electroluminescence devices with improved efficiency and lower driving voltage by the statistical design method. Analysis of time-of-flight measurement shows that amorphous small molecule hole-transporter blended with a blue light-emitting polymer increases the field-dependent hole mobility, with transition from nondispersive to dispersive transport induced by the charge-trapping effect. Moreover, at the electroluminescent devices with different electron injection/transport layer (LiF/Al, LiF/Ca/Al, and Alq3/LiF/Al), efficiency was further increased. We have analyzed that carrier mobility of a multilayered device can also be controlled by the change of electron injection and transport layers. We find that structural design and matching overall charge balance is an essential factor to improve both the operating voltage and efficiency of existing blue polymer devices.
Multiple channeled phenomena in heterostructures with defects mode
Authors: Wang Zhanshan , Wang Li , Wu Yonggang , Chen Lingyan , Chen Xiaoshuang , Lu Wei
Published: February 2004

Transmission studies for multiple heterostructures inserted with defects are presented. The results show that the enlargement of the forbidden band and the realization of multiple channeled filtering can be reached simultaneously with these configurations. The frequency, frequency interval, and number of channels can be tuned by adjusting geometric and physical parameters of the defects. Sidebands of the forbidden band can be substantially restricted as compared with that of periodic structures. Experimental fabrication of the designed configurations is carried out with the heterostructures containing TiO2/SiO2 multilayer defects, and the results agree with the calculation very well.
Probing ion channel conformational dynamics using simultaneous single-molecule ultrafast spectroscopy and patch-clamp electric recording
Authors: Harms Greg , Orr Galya , Lu H. Peter
Published: February 2004

An approach to probing single-molecule ion channel kinetics and conformational dynamics, patch-clamp confocal fluorescence microscopy (PCCFM), uses simultaneous ultrafast fluorescence spectroscopy and single-channel electric current recording. PCCFM is applied to determine single-channel conformational dynamics by probing single-pair fluorescence resonant energy transfer, fluorescence self-quenching, and anisotropy of the dye-labeled gramicidin ion channel incorporated in an artificial lipid bilayer. Hidden conformational changes were observed, which strongly suggests that multiple intermediate conformation states are involved in gramicidin ion channel dynamics.
Reverse characteristics of pn diodes on 4H–SiC(000-1) C and (11-20) face
Authors: Tanaka Yasunori , Fukuda Kenji , Arai Kazuo , Kojima Kazutoshi , Suzuki Takaya , Yatsuo Tsutomu
Published: February 2004

We fabricated pn diodes on the 4H–SiC(000-1) C and (11-20) face. The epitaxial growth of the n-type drift layer was carried out in chemical vapor deposition (CVD) reactor under the optimized conditions for each substrate. The pn junction was formed by Al+ ion implantation with multiple energy implantation (30–200 kV) at 600 °C subsequent annealing at 1600 °C for 5 min in Ar ambient. In the case of the diode on the (000-1) C face, we observed an abrupt avalanche breakdown, which is very similar to the case of the (0001) Si face, at the theoretical breakdown voltage (1150 V) calculated from the doping concentration and the thickness of the drift layer. This result means that there is no difference in the quality of the epitaxial layer between the (0001) Si and the (000-1) C face. On the other hand, a lower breakdown voltage (1200 V) than the theoretical value (1900 V) was observed in the case of the diode on the (11-20) face, and moreover, serious reverse leakage current was also observed. On the basis of the observation of the light emission under the reverse bias, we presume that the crystal defects, parallel to the 〈11-20〉 direction, lead to such a high leakage current under the reverse bias.
Photoluminescence in quantum-confined SnO2 nanocrystals: Evidence of free exciton decay
Authors: Lee E. J. H. , Ribeiro C. , Giraldi T. R. , Longo E. , Leite E. R. , Varela J. A.
Published: February 2004

Nanocrystalline SnO2 quantum dots were synthesized at room temperature by hydrolysis reaction of SnCl2. The addition of tetrabutyl ammonium hydroxide and the use of hydrothermal treatment enabled one to obtain tin dioxide colloidal suspensions with mean particle radii ranging from 1.5 to 4.3 nm. The photoluminescent properties of the suspensions were studied. The particle size distribution was estimated by transmission electron microscopy. Assuming that the maximum intensity photon energy of the photoluminescence spectra is related to the band gap energy of the system, the size dependence of the band gap energies of the quantum-confined SnO2 particles was studied. This dependence was observed to agree very well with the weak confinement regime predicted by the effective mass model. This might be an indication that photoluminescence occurs as a result of a free exciton decay process.
Frequency dependent characterization of transport properties in carbon nanotube transistors
Authors: Appenzeller J. , Frank D. J.
Published: February 2004

We have experimentally verified that carbon nanotube field-effect transistors do not show any signal degradation when operated at frequencies up to 580 MHz, the limit of our current measurement setup. In order to characterize the high-frequency response of individual single wall carbon nanotubes in a three-terminal transistor configuration, a non-standard measurement approach was employed. By making use of the nonlinearity of nanotube transistor transfer characteristics, the response of a tube to a combined ac/dc signal was studied. This technique enables easy access to the high-frequency performance of nanoscale devices in general even for the rather low current levels typically observed for individual carbon nanotube field-effect transistors.
Reduction of positional errors in a four-point probe resistance measurement
Authors: Worledge D. C.
Published: February 2004

A method for reducing resistance errors due to inaccuracy in the positions of the probes in a collinear four-point probe resistance measurement of a thin film is presented. By using a linear combination of two measurements which differ by interchange of the I− and V− leads, positional errors can be eliminated to first order. Experimental data measured using microprobes show a substantial reduction in absolute error from 3.4% down to 0.01%–0.1%, and an improvement in precision by a factor of 2–4. The application of this technique to the current-in-plane tunneling method to measure electrical properties of unpatterned magnetic tunnel junction wafers is discussed.
Dielectric and electroactive strain properties of poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymers
Authors: Yu Zhi , Ang Chen , Cross L. E. , Petchsuk A. , Chung T. C.
Published: February 2004

The dielectric and electroactive strain properties of the poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymers with two different concentrations of chlorotrifluoroethylene (CTFE) have been studied down to cryogenic temperatures. The increase in the CTFE concentration shifts slightly the temperature where the dielectric constant maximum occurs to a lower temperature. High electroactive strain (∼1%) is obtained at room temperature for both compositions; however, the strain level decreases quickly with decreasing temperature. The dielectric relaxation process occurs for both compositions in the temperature range of 220 to 350 K, below which the dielectric constant decreases quickly to an “intrinsic” value (∼2.5). The similar variation tendency of the strain and the dielectric constant as a function of temperature indicates a close correlation between the dielectric behavior and strain activity.
On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials
Authors: George D. S. , Onischenko A. , Holmes A. S.
Published: February 2004

Focused laser ablation by single laser pulses at varying angles of incidence is studied in two materials of interest: a solgel (Ormocer 4) and a polymer (SU8). For a range of angles (up to 70° from normal), and for low-energy (<20 μJ), 40 ns pulses at 266 nm wavelength, the ablation depth along the direction of the incident laser beam is found to be independent of the angle of incidence. This allows the crater profiles at oblique incidence to be generated directly from the crater profiles at normal incidence by a simple coordinate transformation. This result is of use in the development of simulation tools for direct-write laser ablation. A simple model based on the moving ablation front approach is shown to be consistent with the observed behavior.
Temperature-insensitive Ge–B–SiO2 planar lightwave circuits by inductively coupled plasma-enhanced chemical vapor deposition
Authors: Zhang Q. Y. , Pita K. , Zuo L. P. , Takahashi S.
Published: February 2004

Low-propagation-loss Ge–B–SiO2 planar waveguides have been achieved by inductively coupled plasma-enhanced chemical vapor deposition. The significant effects due to annealing temperature, hydrogen loading, and KrF excimer ultraviolet laser irradiation on the optical properties of Ge–B–SiO2 films have been investigated. A temperature-insensitive Mach–Zehnder interferometer-like optical filter has been demonstrated by means of a double-core fabrication method using 10GeO2–90SiO2 (10G90S) and 8GeO2–5B2O3–87SiO2 (8G5B87S) as two different waveguide cores. We have achieved less than 0.5 pm/°C temperature dependence of the central wavelength of the filter at 1550 nm while varying the temperature from −20 to 80 °C.
Integrated microfluidic isolation platform for magnetic particle manipulation in biological systems
Authors: Mirowski Elizabeth , Moreland John , Russek Stephen E. , Donahue Michael J.
Published: February 2004

We have developed a micromachined fluid-cell platform that consists of patterned magnetic thin-film elements supported on a thin silicon–nitride membrane. In the presence of an external magnetic field, the field gradients near the magnetic elements are sufficiently large to trap magnetic particles that are separated from the patterned films by a 200 nm thick nitride membrane. The two main applications of this fluid-cell platform are to provide a means to control and position magnetic microparticles, which can be tethered to biological molecules, and also to sort superparamagnetic microparticles based on their size and magnetic susceptibility. We determine the characteristic trapping forces of each trap in the array by measuring the Brownian motion of the microparticle as a function of applied external field. Typical force constants and forces on the superparamagnetic particles are 4.8×10−4±0.7×10−4 N/m and 97±15 pN, respectively.
Controlling energy dissipation and stability of micromechanical silicon resonators with self-assembled monolayers
Authors: Henry Joshua A. , Wang Yu , Hines Melissa A.
Published: February 2004

Self-assembled alkyl monolayers that are directly tethered to the silicon surface with a Si–C bond suppress mechanical energy dissipation in megahertz-range micromechanical silicon oscillators as compared to the more common silicon oxide coating. Although not as low loss as freshly prepared H-terminated surfaces, Si–C tethered monolayers are more stable with time. Alkyl monolayers derived from chlorosilanes have much poorer mechanical performance. Both types of monolayers suppress adsorption.
Correlation of thermal stability with structural properties of ultrathin single-walled carbon nanotubes
Authors: Xiao Changyong , Chan Hardy Sze On , Xu Guo Qin , Lim Kwuan Tzee , Lin Jianyi
Published: February 2004

Based on quantum chemical calculations, we have established the relationship between the thermal stability and structural properties of ultrathin single-walled carbon nanotubes (SWCNTs). Our results on the heat of formation as a function of tube diameter predict a lower limit of 0.341 nm in diameter for experimentally observable SWCNTs. The absence of any distinctive minimum points on the heat of formation curve implies the experimental difficulties in obtaining uniform tubes. A detailed correlation between their curvature and chemical bonding properties was obtained for both the zigzag and armchair conformations.
Self-assembling fluidic machines
Authors: Grzybowski Bartosz A. , Radkowski Michal , Campbell Christopher J. , Lee Jessamine Ng , Whitesides George M.
Published: February 2004

This letter describes dynamic self-assembly of two-component rotors floating at the interface between liquid and air into simple, reconfigurable mechanical systems (“machines”). The rotors are powered by an external, rotating magnetic field, and their positions within the interface are controlled by: (i) repulsive hydrodynamic interactions between them and (ii) by localized magnetic fields produced by an array of small electromagnets located below the plane of the interface. The mechanical functions of the machines depend on the spatiotemporal sequence of activation of the electromagnets.
Threading dislocation generation in epitaxial (Ba,Sr) TiO3 films grown on (001) LaAlO3 by pulsed laser deposition
Authors: Misirlioglu I. B. , Vasiliev A. L. , Aindow M. , Alpay S. P. , Ramesh R.
Published: February 2004

Epitaxial Ba0.6Sr0.4TiO3 films were grown onto (001) LaAlO3 by pulsed-laser deposition, and the dislocation structures of the films were investigated using transmission electron microscopy. Misfit dislocations with a periodicity of about 7 nm and Burgers vectors b=a〈100〉 were observed at the interface. A high density of threading dislocations was present the films and these also had b=a〈100〉. The data indicate that the threading dislocations are not generated as the result of half-loop climb from the deposit surface as proposed previously, but are instead formed when misfit dislocations are forced away from the interface during island coalescence.
Two-photon lasing of dye-doped photonic crystal lasers
Authors: Shirota Koichiro , Sun Hong-Bo , Kawata Satoshi
Published: February 2004

We report two-photon pump lasing action of a photonic crystal laser, which comprises fluorescent dye-doped chiral nematic liquid crystals. The dye absorbs light peaking at 466 nm, while the pumping was conducted at 1000 nm wavelength. Due to redistribution of density of states by a stopping band, a strong single-mode stimulated emission was observed at the band edge wavelength of 608 nm with 1 nm detection-limited linewidth. A comparative study shows that under an identical pumping geometry, the two-photon lasing threshold is only 120 times larger than that for the single-photon excitation, a ratio lower than those generally reported for up-conversion lasing.
Recording of polarization holograms in photodarkened amorphous chalcogenide films
Authors: Asatryan K. E. , Frédérick S. , Galstian T. , Vallée R.
Published: February 2004

Polarization gratings were recorded in amorphous As2S3 chalcogenide thin films in three orthogonal recording configurations. The analysis of polarization discrimination properties of such vector gratings revealed a poor performance. It was shown that the main reason for this is the presence of nondesired scalar modulation of the same period. An exception is (s+p) recording configuration, where a pure polarization grating may be obtained even for relatively high photoexposures.
Thermal decomposition of a thin AgOx layer generating optical near-field
Authors: Kolobov A. V. , Rogalev A. , Wilhelm F. , Jaouen N. , Shima T. , Tominaga J.
Published: February 2004

Thermal decomposition of AgOx thin layers generating optical near field have been studied by Ag LIII edge x-ray absorption near-edge structure. We found that, different from previous assumptions, the starting layer is a mixture of AgO (∼40%) and Ag2O (∼60%). We further observed that thermal decomposition starts at a temperature as low as 50 °C. The decomposition process exhibits three stages and the oxide layer at intermediate stages consists of a mixture of AgO, Ag2O, and metallic Ag with different fractions of each phase. Activation energies of the decomposition of the thin oxide layer have been determined for different decomposition stages, the obtained values being different from that for powder oxides.
Effect of polymer-insulating nanolayers on electron injection in polymer light-emitting diodes
Authors: Park Jong Hyeok , Park O Ok , Yu Jae-Woong , Kim Jai Kyeong , Kim Young Chul
Published: February 2004

We report the effect of polymer-insulating nanolayers on electron injection in the polymer light-emitting diodes (PLEDs) in which a hole is the major charge carrier. Several different polymer nanolayers with varying dielectric constants were placed between the emitting layer and the aluminum cathode, and their influence on the device performance was investigated. The device with a nanolayer of lower dielectric constant demonstrated higher luminescence quantum efficiency. In particular, when a ∼10-nm-thick polystyrene layer was employed, the device gave approximately two orders of magnitude higher external quantum efficiency than that of the one without an insulating nanolayer.
Compressive shock wave response of a Zr-based bulk amorphous alloy
Authors: Turneaure Stefan J. , Winey J. M. , Gupta Y. M.
Published: February 2004

Plane shock wave experiments were performed at peak stresses up to 13 GPa on Zr-based bulk amorphous alloy (BAA) samples. A velocity interferometer was used to measure the particle velocity history either at the impact surface or at the rear surface of the BAA samples. From the measured particle velocity histories, the Hugoniot elastic limit (HEL) was determined to be 7.1±0.3 GPa, corresponding to an elastic strain of approximately 4%. For experiments in which the peak stress exceeded the HEL, a clear two-wave structure consisting of an elastic precursor followed by a plastic wave was observed. Measurements of the transmitted wave profiles, along with direct determination of the longitudinal stress and particle velocity at the impact surface, suggest that the shear strength of the Zr-based BAA is reduced as it is shocked above the elastic limit.
Tunable and white light-emitting diodes of monolayer fluorinated benzoxazole graft copolymers
Authors: Bai S. J. , Wu C. C. , Dang T. D. , Arnold F. E. , Sakaran B.
Published: February 2004

Coil-like graft copolymers of poly(Am-co-B(1−m)) containing identical heterocyclic aromatic benzoxazole with trifluoromethyl-ethyl as the backbone and pendants of monohydroxl (Am) and/or bidecyloxyl (B(1−m)) on their phenylene ring were studied for luminescence properties. The copolymers were synthesized with molar fraction m ranging from 0, 0.25, 0.5, 0.75, to 1, and then dissolved and spun onto a Spectrosil® quartz slide or an indium-tin-oxide (ITO) substrate. The fluorescence properties of copolymers were investigated by ultraviolet–visible absorption covering 185 nm to 800 nm and photoluminescence (PL) emission excited at 363 nm. The PL results exhibited an excellent chromatic tuning, ranging from green to white emission as m decreased. Aluminum electron injectors were evaporated onto the copolymer/ITO unit making it into monolayer light-emitting diodes for current–voltage and electroluminescence (EL) responses. An emission threshold voltage of 6 V was achieved for all the monolayer copolymer devices. The Commission Internationale de l’Eclairage coordinates of the EL emission were from (0.25, 0.53) to (0.24,0.31) covering a wide visible range including white light emission.
Critical current densities of powder-in-tube MgB2 tapes fabricated with nanometer-size Mg powder
Authors: Yamada H. , Hirakawa M. , Kumakura H. , Matsumoto A. , Kitaguchi H.
Published: February 2004

We fabricated powder-in-tube MgB2/Fe tapes using a powder mixture of nanometer-size Mg and commercial amorphous B and investigated the transport properties. High-purity nanometer-size Mg powder was fabricated by applying the thermal plasma method. 5–10 mol % SiC powder doping was tried to enhance the Jc properties. We found that the use of nanometer-size Mg powder was effective to increase the Jc values. The transport Jc values of the nondoped and 10 mol % SiC-doped tapes prepared with nanometer-size Mg powder reached 90 and 250 A/mm2 at 4.2 K and 10 T, respectively. These values were about five times higher than those of the tapes prepared with commercial Mg powder.
Tuning negative and positive magnetoresistances by variation of spin-polarized electron transfer into π-conjugated polymers
Authors: Luo Feng , Song Wei , Wang Zhe-Ming , Yan Chun-Hua
Published: February 2004

A series of polyparaphenyl derivatives with different conductivities have been synthesized to fabricate three kinds of polymer-embedded La0.7Ca0.3MnO3 (LCMO) composites by mixing different weight fractions of polymers and LCMO. X-ray diffraction and Fourier transform infrared spectra show the coexistence of the LCMO particles and polymers and no chemical reactions between each other. By adjusting the conductivity and π electron polarization of polymers, spin-polarized electron transfer from the surfaces of LCMO magnetic particles through the interfacial coupling into polymers can be tuned, leading to the tunable negative and positive magnetoresistances in these composites. This abnormal positive MR can be mainly attributed to the spin-polarized electron tunneling weakening and magnetic scattering enhancement on polarized π electrons through the LCMO/polymer interfaces.
Accurate formulas for interaction force and energy in frequency modulation force spectroscopy
Authors: Sader John E. , Jarvis Suzanne P.
Published: February 2004

Frequency modulation atomic force microscopy utilizes the change in resonant frequency of a cantilever to detect variations in the interaction force between cantilever tip and sample. While a simple relation exists enabling the frequency shift to be determined for a given force law, the required complementary inverse relation does not exist for arbitrary oscillation amplitudes of the cantilever. In this letter we address this problem and present simple yet accurate formulas that enable the interaction force and energy to be determined directly from the measured frequency shift. These formulas are valid for any oscillation amplitude and interaction force, and are therefore of widespread applicability in frequency modulation dynamic force spectroscopy.
Nanometer-sized antenna for enhancement of absorption of light by dye molecules
Authors: Zhdanov Vladimir P. , Kasemo Bengt
Published: February 2004

One of the ways to increase the absorbance of dye molecules is to optimize the property of their environment. In particular, a dye molecule can be surrounded by a few other molecules absorbing at lower frequencies. Our analysis indicates that the amplification factor of such nanometer-sized antennas may be up to about 200.
Electrostatic modulation of the electronic properties of Nb-doped SrTiO3 superconducting films
Authors: Takahashi K. S. , Matthey D. , Jaccard D. , Triscone J.-M. , Shibuya K. , Ohnishi T. , Lippmaa M.
Published: February 2004

We have performed ferroelectric field effect experiments using an epitaxial heterostructure composed of ferroelectric Pb(Zr0.2Ti0.8)O3 and superconducting Nb-doped SrTiO3. The films were prepared on (001) SrTiO3 substrates by off-axis radio-frequency magnetron sputtering and pulsed-laser deposition. By switching the polarization field of the 500-Å-thick Pb(Zr0.2Ti0.8)O3 layer, a large change of about 30% in resistivity and a 20% shift of Tc (ΔTc∼0.05 K) were induced in the 400-Å-thick epitaxial Nb-doped SrTiO3 layer. The relationship between Tc and the electrostatically modulated average carrier concentration can be mapped onto the phase diagram of chemically doped SrTiO3.
Single dye molecules in an oxygen-depleted environment as photostable organic triggered single-photon sources
Authors: Lill Y. , Hecht B.
Published: February 2004

We demonstrate, that under nitrogen atmosphere, 20% of single DiIC18(3) (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) molecules in poly(methylmethacrylate) show an extremely low photobleaching quantum yield of (4.66±0.07)×10−8 together with a reasonably short triplet lifetime. We exploit these properties to demonstrate that the system can be used to produce a triggered single-photon source based exclusively on organic materials.
Mechanism of bright selective imaging of single-walled carbon nanotubes on insulators by scanning electron microscopy
Authors: Homma Yoshikazu , Suzuki Satoru , Kobayashi Yoshihiro , Nagase Masao , Takagi Daisuke
Published: February 2004

Individual single-walled carbon nanotubes (SWNTs) produce highly bright images of the insulator surface around them when observed by scanning electron microscopy at low primary-electron voltage. We found that the insulator surface near SWNTs emits more secondary electrons due to electrons supplied through SWNTs connecting to the outside area of the primary-electron beam scanning. SWNTs are thus highlighted as bright lines corresponding to the electron-beam-induced current range around them. This technique provides a useful and effective way to investigate lateral growth morphology of SWNTs on the substrate.
Broadband tuning of external cavity bound-to-continuum quantum-cascade lasers
Authors: Maulini Richard , Beck Mattias , Faist Jérôme , Gini Emilio
Published: February 2004

A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over 150 cm−1 (1.45 μm), which is equal to 15% of the free running wavelength (λ≅10 μm), in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse.
Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering
Authors: Wang Y. P. , Zhou L. , Zhang M. F. , Chen X. Y. , Liu J.-M. , Liu Z. G.
Published: February 2004

Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.
Nonlinear optical properties of neodymium-doped bismuth titanate thin films using Z-scan technique
Authors: Wang Y. H. , Gu B. , Xu G. D. , Zhu Y. Y.
Published: February 2004

Bi 3.75 Nd 0.25 Ti 3 O 12  (BNT0.25) thin film with good surface morphology and layered perovskite structure was fabricated by a metalorganic solution deposition process. Their fundamental optical constants (the band gap, linear refractive index, and absorption coefficient) were obtained through optical transmittance measurements. The nonlinear optical properties of the film were investigated by using a top-hat Z-scan method. Large positive nonlinear refractive index n2 and two-photon absorption coefficient β were determined to be 4.52×10−7 esu and 5.24×10−7 m/W, respectively. All of the results show that the BNT0.25 thin film is promising for applications in nonlinear optical devices.
Application of strontium silicate yellow phosphor for white light-emitting diodes
Authors: Park Joung Kyu , Kim Chang Hae , Park Seung Hyok , Park Hee Dong , Choi Se Young
Published: February 2004

In order to develop a yellow phosphor that emits efficiently under the 450–470 nm excitation range, we have synthesized a Eu2+-activated Sr3SiO5 yellow phosphor and attempted to develop white light-emitting diodes (LEDs) by combining them with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Sr3SiO5:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based Sr3SiO5:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.
Properties of InN layers grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy
Authors: Ive Tommy , Brandt Oliver , Ramsteiner Manfred , Giehler Manfred , Kostial Helmar , Ploog Klaus H.
Published: February 2004

We study the impact of different buffer layers and growth conditions on the properties of InN layers grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy. Both GaN and AlN buffer layers result in a significant improvement of the structural quality compared to InN layers grown directly on the SiC substrate. However, to obtain layers exhibiting a high structural integrity, smooth surface morphology, high mobility and strong band-to-band photoluminescence, contradicting growth conditions are found to be required. Furthermore, since InN(0001) dissociates already at temperatures below the onset of In desorption, it is difficult to avoid In accumulation and inclusions of crystalline In in the layer under In-rich conditions.
Intense electron emission from graphite nanocraters and their application to time-resolved x-ray radiography
Authors: Matsumoto Takahiro , Mimura Hidenori
Published: February 2004

A high-density electron emission more than 20 mA/cm2 was achieved from a cold cathode fabricated by simple plasma etching nanocraters onto a graphite substrate. The magnitude of the field enhancement factor was about 30 000, which is similar to that for the highest reported performance for carbon nanotube. The performance of this cathode was demonstrated by obtaining high-intensity pulse x-ray generation. High-speed x-ray radiography images of dynamical processes of the order of 10 μs were successfully shown, thus offering a new technique for nondestructive inspections.
Extended phase matching of second-harmonic generation in periodically poled KTiOPO4 with zero group-velocity mismatch
Authors: König Friedrich , Wong Franco N. C.
Published: February 2004

Under extended phase-matching conditions, the first frequency derivative of the wave-vector mismatch is zero and the phase-matching bandwidth is greatly increased. We present extensive three-wave mixing measurements of the wave-vector mismatch and obtain improved Sellmeier equations for KTiOPO4. We observed a type-II extended phase-matching bandwidth of 100 nm for second-harmonic generation in periodically poled KTiOPO4, centered at the fundamental wavelength of 1584 nm. Applications in quantum entanglement and frequency metrology are discussed.
Lateral interband tunneling transistor in silicon-on-insulator
Authors: Aydin C. , Zaslavsky A. , Luryi S. , Cristoloveanu S. , Mariolle D. , Fraboulet D. , Deleonibus S.
Published: February 2004

We report on a lateral interband tunneling transistor, where the source and drain form a heavily doped lateral pn junction in a thin Si film on a silicon-on-insulator (SOI) substrate. The transistor action results from the control of the reverse-bias tunneling breakdown under drain bias VD by a gate voltage VG. We observe gate control over tunneling drain current ID at both polarities of VG with negligible gate leakage. Systematic ID(VG,VD) measurements, together with numerical device simulations, show that in first approximation ID depends on the maximum junction electric field Fmax(VG,VD). Excellent performance is hence predicted in devices with more abrupt junctions and thinner SOI films. The device does not have an inversion channel and is not subject to scaling rules of standard Si transistors.
Epitaxial growth of the diluted magnetic semiconductors CryGe1−y and CryMnxGe1−x−y
Authors: Kioseoglou G. , Hanbicki A. T. , Li C. H. , Erwin S. C. , Goswami R. , Jonker B. T.
Published: February 2004

We report the epitaxial growth of CryGe1−y and CryMnxGe1−x−y(001) thin films on GaAs(001), describe the structural and transport properties, and compare the measured magnetic properties with those predicted by theory. The samples are strongly p type, and hole densities increase with Cr concentration. The CryGe1−y system remains paramagnetic for the growth conditions and low Cr concentrations employed (y⩽0.04), consistent with density functional theory predictions. Addition of Cr into the ferromagnetic semiconductor MnxGe1−x host systematically reduces the Curie temperature and total magnetization.
Optically active erbium–oxygen complexes in GaAs
Authors: Coutinho J. , Jones R. , Shaw M. J. , Briddon P. R. , Öberg S.
Published: February 2004

Density functional modeling of Er and Er–O complexes in GaAs show that Er impurities at the Ga site are not efficient channels for exciton recombination, but decorative O atoms play crucial roles in inhibiting Er precipitation and in creating the necessary conditions for electron-hole capture. Among the defects studied, the ErGaOAs and ErGa(OAs)2 models have the symmetry and carrier trap location close to the defect responsible for the strong 1.54 μm photoluminescence band in Er, O codoped GaAs.
In situ control of the catalyst efficiency in chemical vapor deposition of vertically aligned carbon nanotubes on predeposited metal catalyst films
Authors: Eres Gyula , Puretzky A. A. , Geohegan D. B. , Cui H.
Published: February 2004

Premature termination of growth, presumably because of catalyst deactivation, is an undesirable side effect of chemical vapor deposition of vertically aligned carbon nanotubes on predeposited metal catalyst films. The addition of ferrocene, an effective precursor for in situ Fe formation, was found to enhance carbon nanotube growth rates and extend growth to 3.25 mm thick carbon nanotube films. Ferrocene was introduced into the gas stream by thermal evaporation concurrently with acetylene using a specially constructed source. The key factor facilitating the growth of thick carbon nanotube films was the independent and precise control of the ferrocene amount in the feedstock. The carbon nanotube films were characterized by scanning and transmission electron microscopy, and Raman spectroscopy. The temperature dependence of the carbon nanotube growth with ferrocene exhibits a steep drop at high substrate temperatures and a loss of vertical alignment at 900 °C. The negative temperature coefficient of the growth rate suggests that the reaction mechanism of vertically aligned carbon nanotube growth is governed by a heterogeneous intermediate step.
On the superlinear increase in conductivity with dopant concentration in excitonic semiconductors
Authors: Gregg Brian A. , Chen Si-Guang , Branz Howard M.
Published: February 2004

We show that the same factors that cause exciton formation in organic (excitonic) semiconductors, the low dielectric constant and the localized wave functions of the charge carriers, also control their doping processes. We compare doping in organic and inorganic semiconductors and show that the superlinear increase in conductivity with doping density should be a universal characteristic of excitonic semiconductors. The binding energy of the dopant electron to its conjugate cation in highly ordered perylene diimide films controls the free carrier density. The binding energy decreases with increasing dopant concentration because the neutral dopants increase the polarizability of the film.
Atmospheric pressure microplasmas for modifying sealed microfluidic devices
Authors: Evju Jon K. , Howell Peter B. , Locascio Laurie E. , Tarlov Michael J. , Hickman James J.
Published: February 2004

A dc microdischarge technique for the chemical modification of microchannel walls is reported. In this method, an atmospheric pressure plasma is ignited directly in the channels of assembled microfluidic devices. Our results show that strongly hydrophilic or hydrophobic properties are imparted to the walls of polystyrene microchannels by the appropriate selection of a plasma gas. This localized tuning of the surface and wetting properties is expected to be useful in the manufacture of microfluidic channels in a variety of substrates. Small area x-ray photoelectron spectroscopy was used to identify oxygen and fluorine on polystyrene surfaces resulting from the plasma treatments.
Correlation between photoelectric and optical absorption spectra of thermally evaporated pentacene films
Authors: Lee Jiyoul , Kim S. S. , Kim Kibum , Kim Jae Hoon , Im Seongil
Published: February 2004

We have measured the spectral photoresponse of Al/pentacene Schottky junction photodiodes and optical absorption spectra of pentacene films thermally evaporated on glass. The photoelectric response exhibited the genuine highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition at 1.97 eV and interband absorption peaks at 2.3 and 2.5 eV. These peaks are also identified in the optical absorption spectra, but they are dominated by additional strong exciton peaks at 1.82 and 2.1 eV. By comparing these complementary measurements, we determine the HOMO–LUMO gap energy of 1.97 eV and the fundamental exciton binding energy of 0.15 eV for thin solid pentacene.
Dynamic filamentation and beam quality of quantum-dot lasers
Authors: Gehrig E. , Hess O. , Ribbat C. , Sellin R. L. , Bimberg D.
Published: February 2004

We present a comparative study of numerical simulations and experiments on the spatiotemporal dynamics and emission characteristics of quantum-well and quantum-dot lasers of identical structure. They show that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude–phase coupling enable a significant improvement of beam quality compared to quantum-well lasers of identical geometry. Near-field profiles and beam quality (M2) parameters calculated on the basis of time-dependent effective Maxwell–Bloch equations into which the physical properties of the active media are included via space-dependent material parameters, effective time constants, and matrix elements are fully confirmed by experimental measurements. Together they indicate that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude–phase coupling enable a significant improvement of beam quality compared with quantum-well lasers of identical geometry.
Low-resistance Pt/Pd/Au ohmic contacts to p-type AlGaN
Authors: Kim Han-Ki , Seong Tae-Yeon , Adesida Ilesanmi , Tang Chak Wah , Lau Kei May
Published: February 2004

We report on a Pt/Pd/Au metallization scheme for producing low-resistance ohmic contacts to moderately doped p-AlGaN:Mg (1.5×1017 cm−3). Annealed Pt/Pd/Au contact exhibits linear current–voltage characteristics, showing that a high-quality ohmic contact is formed. The Pt/Pd/Au contact exhibits a specific contact resistivity of 3.1×10−4 Ω cm2 when annealed at 600 °C for 1 min in a flowing N2 atmosphere. Using Auger electron spectroscopy and x-ray photoelectron spectroscopy, a preliminary explanation for ohmic contact formation is described.
Effects of particle size, processing, and dry or liquid feeding on performance of piglets
Authors: Choct M. , Selby E. A. D. , Cadogan D. J. , Campbell R. G.
Published: February 2004

Currently, most feed grains are processed by either hammer mill or roller mill before the inclusion in pig diets. However, the effect of these two types of milling and particle size on the performance and feed utilisation has not been adequately examined. The effect of milling processing (hammer mill v. roller mill), particle size, and feeding method (liquid v. dry) was assessed in a factorial design with 120 weaner pigs over 21 days. These pigs had been weaned for 7 days when the experiment commenced. The results revealed that pigs fed on hammer-milled diets had a better performance than those on roller-milled diets. Particle size of hammer-milled diets did not affect the performance of pigs, but influenced the digestible energy content of the diets. However, the feed conversion ratio was poorer for pigs fed coarsely or medium roller-milled diets only at Day 7–14 after weaning. There was a marked advantage in terms of feed efficiency associated with liquid feeding. For pigs offered the hammer-milled diets between 0 and 14 days, simply adding the feed to water improved feed efficiency by some 22%. For the roller-milled diets the corresponding improvement in feed efficiency was 28%. Liquid feeding improved digestible energy (DE) value by 1.5 MJ/kg for medium particle size and depressed DE value by 0.8 MJ/kg for fine particle size for hammer mill. Liquid feeding improved DE values for both medium and fine particle treatments by 0.9 MJ/kg for roller-milled diets. It should be noted that the full advantages of liquid feeding could only be taken if feed wastage from this system can be minimised as much as possible.The study was conducted to investigate if processing method (roller v. hammer mill), particle size (coarse, medium, and fine), and feeding method (liquid v. dry) significantly improved the growth rate, feed intake, and feed conversion of the weaner pig.