bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of compositional pulling phenomenon in AlxGa1−xN (0.4<x<1.0) films grown on (0001) sapphire substrates
Authors: Tsai Yu-Li , Wang Cheng-Liang , Lin Po-Hung , Liao Wei-Tsai , Gong Jyh-Rong
Published: January 2003

High Al content AlxGa1−xN (0.4<x<1.0) films were grown at 1050 °C either on (0001) sapphire substrates or on AlN films by alternative supply of group III metalorganics (trimethylaluminum and trimethylgallium) and NH3 in an inductively heated quartz reactor operated at atmospheric pressure. θ–2θ x-ray diffraction data show a compositional separation in the AlxGa1−xN films grown on low-temperature (LT) aluminum nitride (AlN) buffer layer-coated (0001) sapphire substrates. Absorption spectroscopic measurements also reveal double cutoff edges in the AlxGa1−xN sample grown directly on a LT AlN-coated (0001) sapphire substrate while only one absorption edge having higher energy was observed in the AlxGa1−xN film grown on a 0.1-μm-thick high-temperature (HT) AlN intermediate layer, which was deposited on top of the (0001) sapphire substrate. Cross-sectional transmission electron microscopic observations show the bilayer nature of the AlxGa1−xN films grown directly on the LT AlN-coated sapphire substrate. Such a compositional pulling phenomenon in the AlxGa1−xN film without a HT AlN intermediate layer is attributed to the extensive biaxial strain caused by the large mismatch between the AlxGa1−xN film and the (0001) sapphire substrate.
GaN-free transparent ultraviolet light-emitting diodes
Authors: Nishida Toshio , Kobayashi Naoki , Ban Tomoyuki
Published: January 2003

By introducing a GaN-free layer structure, we have transparent light-emitting diodes (LEDs) at the ultraviolet emission wavelength of 348–351 nm, which is shorter than the GaN band gap wavelength of 363 nm. The buffer layer consists of an AlGaN alloy directly grown on an AlN template layer on a sapphire substrate, and a short period alloy superlattice is adopted as p-type cladding and p-type contact layers. The transparency of the epitaxially grown layer structure is confirmed from transmission spectra. The output powers of the device are 1 mW at injection currents of 20 and 7 mW at 220 mA under room temperature continuous wave operation. The highest external quantum efficiency is 1.4%. This value is superior to that of an ultraviolet LED grown on a high-quality bulk-GaN substrate, where the performance was significantly deteriorated by light absorption into the GaN substrate. The results here indicate the importance of a transparent device structure free of GaN to improve the performance of ultraviolet LEDs in wavelength ranges shorter than 363 nm.
“Nanoparticle route” for the synthesis of a stable and stoichiometric Cu2C2 phase—a semiconductor material
Authors: Balamurugan B. , Mehta B. R. , Shivaprasad S. M.
Published: January 2003

A stable and stoichiometric Cu2C2 phase in nanoparticle form has been synthesized using activated reactive evaporation technique. X-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy studies reveal the formation of a stoichiometric Cu2C2 nanophase having a tetragonal structure. Cu2C2 samples have a high absorption coefficient with a size-dependent optical absorption edge and n-type semiconducting nature. Due to its structural stability, chemical compatibility with other low-cost semiconductor materials, and suitable electrical and optical properties, the Cu2C2 phase has the potential of emerging as a semiconductor material.
Submicron manipulation tools driven by light in a liquid
Authors: Maruo Shoji , Ikuta Koji , Korogi Hayato
Published: January 2003

Optically driven micromanipulators with submicron probe tips are proposed and developed by using two-photon microstereolithography. The micromanipulators are worked by maneuvering their movable component with a focused laser beam, and an actual pair of microtweezers was opened and shut precisely. We also propose an effective method of controlling movable micromachines with great freedom of movement. In this method, a dot is attached to a movable component for trapping and driving it by a single laser beam. A microneedle was induced to perform several types of motion such as rotation and translation. The optically driven micromanipulators are useful for bionanotechnology applications that require work to be done in aqueous solutions.
Evidence of stress anisotropy and role of oxygen pressure in growth of pulsed-laser-deposited hexaferrite films
Authors: Lisfi A. , Lodder J. C. , Keim E. G. , Williams C. M.
Published: January 2003

BaFe 12 O 19 films have been grown by pulsed laser deposition (PLD) on (001) sapphire using two different conditions (with and without oxygen). Layers grown in O2 atmosphere exhibit an epitaxial structure (stressed at the interface) with a perpendicular easy axis whereas magnetic anisotropy is randomly oriented in those deposited without O2. The random structure is a consequence of the high energy of ions in the PLD plume which damage the smoothness of the substrate at an earlier stage of growth. Oxygen pressure can reduce the energy of arriving atoms and prevent deterioration of the interface sharpness, and lead to epitaxial growth. Stress induces in-plane anisotropy with the coercivity strongly dependent on the temperature (T0.75 law). An estimate of the stress confirms that it is too low to compete with magnetocrystalline anisotropy.
Temperature and field dependence of high-frequency magnetic noise in spin valve devices
Authors: Stutzke N. , Burkett S. L. , Russek S. E.
Published: January 2003

The high-frequency noise of micrometer-dimension spin valve devices has been measured as a function of applied field and temperature. The data are well fit with single-domain noise models that predict that the noise power is proportional to the imaginary part of the transverse magnetic susceptibility. The fits to the susceptibility yield the ferromagnetic resonance (FMR) frequency and the magnetic damping parameter. The resonant frequency increases, from 2.1 to 3.2 GHz, as the longitudinal field varies from −2 to 4 mT and increases from 2.2 to 3.3 GHz as the temperature decreases from 400 to 100 K. The shift in the FMR frequency with temperature is larger than that expected from the temperature dependence of the saturation magnetization, indicating that other temperature-dependent anisotropy energies are present, in addition to the dominant magnetostatic energies. The measured magnetic damping parameter α decreases from 0.016 to 0.006 as the temperature decreases from 400 to 100 K. The value of the damping parameter shows a peak as a function of longitudinal bias field, indicating that there is no strict correlation between the damping parameter and the resonant frequency.
Cutoff tailorability of heterojunction terahertz detectors
Authors: Matsik S. G. , Rinzan M. B. M. , Perera A. G. U. , Liu H. C. , Wasilewski Z. R. , Buchanan M.
Published: January 2003

Heterojunction interfacial work function internal photoemission (HEIWIP) detectors provide an interesting approach to the development of quantum detectors for the terahertz range. In this letter, the cutoff frequency/wavelength variation of HEIWIP detectors having different Al fractions in AlGaAs/GaAs structures is experimentally verified, and a model is presented for designing the structures. A key feature of HEIWIP responsivity is the ability to cover a broad frequency range in a single detector with cutoff tailorability by adjusting the Al fraction in the barrier regions. Extending the response to lower frequencies by the use of AlGaAs emitters and GaAs barriers is also discussed.
Submicron ferroelectric domain structures tailored by high-voltage scanning probe microscopy
Authors: Rosenman G. , Urenski P. , Agronin A. , Rosenwaks Y. , Molotskii M.
Published: January 2003

We have developed a high voltage atomic force microscope that allowed us to tailor submicrometer ferroelectric domains in bulk ferroelectrics. One- and two-dimensional domain configurations have been fabricated in LiNbO3, RbTiOPO4, and RbTiOAsO4 ferroelectric crystals. It is found that the application of superhigh electric fields (reaching 5×107 V/cm) by the atomic force microscope tip leads to a unique polarization reversal mechanism, and open the way to a technology for photonic and acoustic devices.
Selective enhancement of blue electroluminescence from GaN:Tm
Authors: Lee D. S. , Steckl A. J.
Published: January 2003

Selective enhancement of electroluminescent emission from high-energy transitions in Tm-doped GaN has been observed to be a strong function of GaN growth temperature. GaN:Tm thin films have been grown by molecular beam epitaxy at temperatures from 100 to 700 °C. At low growth temperatures (100–200 °C) the low energy (infrared-801 nm) transition dominates, while at higher growth temperatures (400–700 °C) the high energy (blue-477 nm) transition dominates. For films grown at low temperatures the main emission excitation mechanism is impact excitation, while for films grown at higher temperatures (⩾600 °C) the main excitation mechanism appears to be lattice impact ionization followed by energy transfer to Tm ions.
Direct evidence of a buried homojunction in Cu(In,Ga)Se2 solar cells
Authors: Jiang Chun-Sheng , Hasoon F. S. , Moutinho H. R. , Al-Thani H. A. , Romero M. J. , Al-Jassim M. M.
Published: January 2003

The built-in electrical potential of Cu(In,Ga)Se2 (CIGS) solar cells was measured quantitatively and resolved spatially using scanning Kelvin probe microscopy. Profiles of the electrical potential along cross sections of the device demonstrate that the p–n junction is a buried homojunction, and the p/n boundary is located 30–80 nm from the CIGS/CdS interface in the CIGS film. The built-in electric field terminates at the CIGS/CdS interface, indicating that the CdS and ZnO layers of the device structure are inactive for the collection of photoexcited carriers.
Internal friction study on low-temperature phase transitions in lead zirconate titanate ferroelectric ceramics
Authors: Dai Y. R. , Bao P. , Shen H. M. , Su D. , Zhu J. S. , Wang Y. N. , Zhu Y. P.
Published: January 2003

In this work, a bulk thermodynamics and microstructure study of lead zirconate titanate ferroelectric PbZr0.52Ti0.48O3 is performed through internal friction, Young’s modulus, differential scanning calorimetry (DSC), and electron diffraction measurements. Two internal friction peaks are observed near 261 and 225 K. The former correlates with an enthalpy change revealed by DSC data and is ascribable to a first-order tetragonal-to-monoclinic phase transition. The latter (225 K), however, showing asymmetric line shape together with a dramatic decrease in Young’s modulus, might correspond to a phase transition associated with the motion of domain walls. The emergence of new domains is evidenced from the superlattice reflections, and the direction of the superlattice is along the z-axis, as indicated by electron diffraction.
Diamond formation in cubic silicon carbide
Authors: Pécz B. , Weishart H. , Heera V. , Tóth L.
Published: January 2003

High-dose carbon implantation (3×1017 and 1×1018 ions/cm2) into cubic SiC on Si was carried out at elevated temperatures (600 to 1200 °C) and different dose rates (1×1013 to 1.5×1014 cm−2 s−1). Transmission electron microscopy revealed the formation of either graphite or diamond precipitates, depending on the implantation parameters. In all cases, the diamond grains were epitaxial to the SiC lattice, while the graphite was textured. The minimum temperature for diamond formation was 900 °C, while graphite formed at 600 °C. The synthesized phase depends as well on the dose rate; graphite was formed at 900 °C with a high dose rate. Obviously, a critical temperature for diamond formation exists and increases with increasing dose rate. This behavior is explained by the competition between the accumulation and dynamic annealing of radiation defects in the SiC lattice, which acts as a template for diamond nucleation. Diamond grains with diameters as large as 10 nm have been observed after implantation at 1200 °C.
Electrical control of the structure and lasing in chiral photonic band-gap liquid crystals
Authors: Furumi Seiichi , Yokoyama Shiyoshi , Otomo Akira , Mashiko Shinro
Published: January 2003

This letter describes the electrical control of structure and lasing in the photonic bandgaps of cholesteric liquid crystals (CLCs). Photoexcitation of dye-doped CLC cells with a linearly polarized laser gives rise to laser emission at the edge(s) of the chiral photonic band gap. Applying voltages to the optically pumped CLC cells enables reversible switching of the laser action as a result of the structural changes in the chiral photonic band gap.
Magnetic lithography using a flexible master: A method for instantaneous magnetic recording on media surfaces with flatness imperfections
Authors: Bandić Z. Z. , Xu H. , Albrecht T. R.
Published: January 2003

A method for instantaneous parallel recording on magnetic media using a flexible master has been developed. Magnetic lithography (qualitatively analogous to optical lithography) transfers information from a patterned magnetic mask (analog of optical photomask) to magnetic media (analog of photoresist). The mask consists of patterned soft magnetic material (FeNiCo, FeCo) on a flexible polyethylene tetraphthalate (PET) substrate. When uniformly magnetized media is brought into intimate contact with the magnetic mask, an externally applied magnetic field selectively changes the magnetic orientation in the areas not covered with the soft magnetic material. Imperfect flatness or the presence of particular contaminants can result in local loss of intimate contact between the master and media, resulting in loss of resolution of submicron features in the transferred magnetic pattern. A flexible master, held against the media via an applied pressure, offers superior compliance to imperfections, even at relatively small applied pressures. We fabricated samples of submicron patterned FeCo and FeNiCo magnetic masks, and successfully transferred patterns to hard disk CrPtCo-based magnetic media. The details of the method, including fabrication of the magnetic mask on flexible PET substrates, physics of the magnetic lithography pattern transfer, and magnetic force microscopy images of the magnetic transition patterns are reported.
Tuning the dynamic behavior of parametric resonance in a micromechanical oscillator
Authors: Zhang Wenhua , Baskaran Rajashree , Turner Kimberly
Published: January 2003

We describe how to significantly change the dynamic behavior of parametric resonance in a micromechanical oscillator. By varying the voltage amplitude of applied electrical signal, the frequency response of the first order parametric resonance changes dramatically. We attribute this variation to the tuning of effective cubic stiffness of the oscillator, which is a contribution of both structural and electrical cubic stiffness. This phenomenon is well explained by the first-order perturbation analysis of nonlinear Mathieu equation.
Magneto-optical studies of s,p–d exchange interactions in GaN:Mn with room-temperature ferromagnetism
Authors: Ando K.
Published: January 2003

Magnetic circular dichroism (MCD) spectra of a room-temperature ferromagnetic GaN:Mn film show that the film contains Ga1−xMnxN in which the band s,p-electrons interact with the d-electrons of the manganese ions. Both the magnetic field dependence and the temperature dependence of the MCD intensity show that Ga1−xMnxN is a paramagnetic diluted magnetic semiconductor (DMS). The ferromagnetism of the sample arises from an unidentified material that is not detected by the x-ray diffraction. This ferromagnetic material does not show the MCD signal, indicating that its electronic structure is different from that of Ga1−xMnxN. These results show that magneto-optical spectroscopy is indispensable to confirm the intrinsic ferromagnetism of DMS.
Effect of an indium-tin-oxide overlayer on transparent Ni/Au ohmic contact on p-type GaN
Authors: Kim Soo Young , Jang Ho Won , Lee Jong-Lam
Published: January 2003

We report a low-resistant, thermally stable, and transparent ohmic contact on p-type GaN using an indium-tin-oxide (ITO) overlayer on Ni/Au contact. Ni (20 Å)/Au (30 Å)/ITO (600 Å) contact with preannealing at 500 °C before ITO deposition showed lower contact resistivity by one order of magnitude than the contact without the preannealing. The preannealing produced NiO, acting in the role of diffusion barrier for outdiffusion of N and Ga atoms and indiffusion of In during the subsequent post-annealing. Thus, the formation of Au–In solid solution was effectively suppressed, resulting in the decrease of contact resistivity and enhancement in thermal stability.
Tunable electronic lens using a gradient polymer network liquid crystal
Authors: Ren Hongwen , Wu Shin-Tson
Published: January 2003

Tunable electronic lenses using gradient polymer network liquid crystal (PNLC) cells were demonstrated. By changing the photomask pattern, both positive and negative lenses were fabricated. The advantages of such a PNLC lens are low operation voltage, large aperture size, and simple electrode design. To overcome the polarization dependence, stacking two orthogonal homogeneous PNLC cells is considered.
Dielectric loss in a C60 film observed by coupling with the external electromagnetic field of a surface acoustic wave
Authors: Sun Yong , Yamasaki Yuichi , Kirimoto Kenta , Miyasato Tatsuro , Wigmore J. Keith , Moriyama Fuminori , Takase Tsuyoshi
Published: January 2003

The dielectric loss in C60 films was studied by a noncontacting technique utilizing the external electric fields associated with surface acoustic waves (SAW) on a piezoelectric crystal. A sharp increase in loss was observed at temperatures below 220 K together with other structure not found with standard SAW measurements. We believe that these features are due to induced current in C60, causing joule loss, and to the formation of localized dipole moments by charge transfer between adsorbed O2 and C60 molecules, giving rise to thermally activated relaxation.
Polarized neutron scattering from ordered magnetic domains on a mesoscopic permalloy antidot array
Authors: Lee D. R. , Srajer G. , Fitzsimmons M. R. , Metlushko V. , Sinha S. K.
Published: January 2003

Using polarized neutrons, we measured grazing-incidence scattering from a mesoscopic permalloy antidot array. A kinematical theory incorporating a highly anisotropic resolution function was developed to interpret the data. Calculations for a magnetic domain structure of the antidot array were obtained from a micromagnetic simulation and show good agreement with the experiment. In contrast, calculations based on a model of uniform magnetization between the antidots were not found to be consistent with the data.
Measurement of temperature distribution in multifinger AlGaN/GaN heterostructure field-effect transistors using micro-Raman spectroscopy
Authors: Kuball M. , Rajasingam S. , Sarua A. , Uren M. J. , Martin T. , Hughes B. T. , Hilton K. P. , Balmer R. S.
Published: January 2003

The temperature distribution in multifinger high-power AlGaN/GaN heterostructure field-effect transistors grown on SiC substrates was studied. Micro-Raman spectroscopy was used to measure channel temperature with 1 μm spatial resolution, not possible using infrared techniques. Thermal resistance values were determined for four different device layouts with varying number of fingers, finger width, and spacing. The experimental thermal resistance was in fair agreement to that predicted by three-dimensional finite difference heat dissipation simulations. Uncertainties in thermal properties of this device system made simulation less reliable than experiment.
Systematic design of antireflection coating for semi-infinite one-dimensional photonic crystals using Bloch wave expansion
Authors: Ushida Jun , Tokushima Masatoshi , Shirane Masayuki , Yamada Hirohito
Published: January 2003

We present a systematic method for designing a perfect antireflection coating (ARC) for a semi-infinite one-dimensional (1D) photonic crystal (PC) with an arbitrary unit cell. We use Bloch wave expansion and time reversal symmetry, which leads exactly to analytic formulas of structural parameters for the ARC and renormalized Fresnel coefficients of the PC. Surface immittance (admittance and impedance) matching plays an essential role in designing the ARCs of 1D PCs, which is shown together with a practical example.
Time of flight secondary ion mass spectrometry study of silicon nanoclusters embedded in thin silicon oxide layers
Authors: Perego M. , Ferrari S. , Spiga S. , Bonera E. , Fanciulli M. , Soncini V.
Published: January 2003

Si nanoclusters have been formed by 5 keV Si+ implantation at a fluence of 1×1016 atoms/cm2 into a 200 Å thin thermally grown SiO2 film on Si (100), followed by thermal treatment at 1000 °C with different annealing times. All the annealed samples show a broad photoluminescence spectrum with increasing intensity as function of annealing time. The use of a dual beam time of flight secondary ion mass spectrometry in negative mode with Cs+ ions at low energy for sputtering allows us to observe variations in Si− signal due to excess of silicon atoms introduced by implantation. With the high sensitivity achieved using this instrumental configuration it is possible to follow Sin− signals which give information about the chemical enviroment of the Si atoms. The possibility of studying the time evolution of the nucleation and growth of nanoclusters has been investigated.
Electronic transport studies of single-crystalline In2O3 nanowires
Authors: Zhang Daihua , Li Chao , Han Song , Liu Xiaolei , Tang Tao , Jin Wu , Zhou Chongwu
Published: January 2003

Single-crystalline In2O3 nanowires were synthesized and then utilized to construct field-effect transistors consisting of individual nanowires. These nanowire transistors exhibited nice n-type semiconductor characteristics with well-defined linear and saturation regimes, and on/off ratios as high as 104 were observed at room temperature. The temperature dependence of the conductance revealed thermal emission as the dominating transport mechanism. Oxygen molecules adsorbed on the nanowire surface were found to have profound effects, as manifested by a substantial improvement of the device performance in high vacuum. Our work paved the way for In2O3 nanowires to be used as nanoelectronic building blocks and nanosensors.
Intersubband absorption in n-doped InAs/AlSb multiple-quantum-well structures
Authors: Ohtani K. , Matsumoto N. , Sakuma H. , Ohno H.
Published: January 2003

Well-thickness dependence of intersubband absorption energies is investigated in n-doped InAs/AlSb multiple-quantum-well structures grown by molecular-beam epitaxy. Decreasing the InAs well thickness from 18 to 9 monolayers, the absorption peak shifts from 3.31 μm (375 meV) to 1.98 μm (627 meV). These absorption energies are found to be larger than those of the corresponding spatially indirect band gap between the electron ground state in the InAs well and the heavy-hole ground state in the AlSb barrier. Intersubband transition energies are calculated self-consistently using multiband k⋅p calculation combined with Poisson equation, and compared with the experimental results.
Reduction of stress at the initial stages of GaN growth on Si(111)
Authors: Dadgar A. , Poschenrieder M. , Reiher A. , Bläsing J. , Christen J. , Krtschil A. , Finger T. , Hempel T. , Diez A. , Krost A.
Published: January 2003

GaN growth on heterosubstrates usually leads to an initially high dislocation density at the substrate/seed layer interface. Due to the initial growth from small crystallites, tensile stress is generated at the coalescence boundaries during GaN growth. In addition, with tensile thermal stress this leads to cracking of GaN on Si and SiC substrates when cooling to room temperature. By partially masking the typically applied AlN seed layer on Si(111) with an in situ deposited SiN mask a reduction in tensile stress can be achieved for the subsequently grown GaN layer. Additionally, the 6 K GaN band edge photoluminescence is increased by about an order of magnitude and shifts by 21 meV, which can be attributed to a change in tensile stress of ∼0.8 GPa, in good agreement with x-ray diffractometry measurements. This improvement in material properties can be attributed to a reduction of grain boundaries by the growth of larger sized crystallites and lateral overgrowth of less defective GaN.
Strain relaxation during the layer by layer growth of cubic CdSe onto ZnSe
Authors: de Melo O. , Vargas-Hernández C. , Hernández-Calderón I.
Published: January 2003

A detailed reflection high-energy electron diffraction analysis shows relevant features of the lattice parameter relaxation of CdSe thin films grown in a layer-by-layer mode onto ZnSe. In situ investigations of different azimuths show a clear lattice parameter oscillation in the [110] azimuth. The lattice parameter has a minimum value (similar to that of ZnSe) during Se exposure steps, and a higher and increasing lattice parameter during Cd exposure steps. The behavior is ascribed to the formation of CdSe islands during Cd exposure steps. The cumulative effect in CdSe exposure steps is considered to be a consequence of a decrease in the island size with the number of cycles. Actual plastic deformation does occur after 5 ML.
Method for the measurement of the K22 nematic elastic constant
Authors: Raynes E. P. , Brown C. V. , Strömer J. F.
Published: January 2003

A technique has been developed for the measurement of the K22 twist elastic constant in nematic liquid crystal materials. This involves the measurement of the Freedericksz transition voltages in untwisted linear and π-twist regions in a wedge cell geometry. The method avoids the need for the accurate determination of the cell thickness and cholesteric pitch and is far more straightforward to implement than other methods in the literature. The validity of this method is demonstrated for the well-characterized material E7.
Hopping conduction in Mn-doped ZnO
Authors: Han Jiaping , Shen Mingrong , Cao Wenwu , Senos A. M. R. , Mantas P. Q.
Published: January 2003

The dc and ac conductivities of Mn-doped ZnO were investigated at temperatures from 10 to 100 K. The temperature dependence of the dc conductivity from 10 to 100 K shows an abrupt change at ∼18 K, manifesting a much lower activation energy for conduction below 18 K. From 10 to 18 K, the ac conductivity, σac(ω), varies as σac(ω)=Aωs in the frequency range from 102 to 106 Hz with s in the range of 0.6–1. The dc and ac conductivity observations suggest that the dominant conduction mechanism at temperatures between 10 to 18 K in these samples is a hopping conduction.
Nanoindentation of silicon nitride: A multimillion-atom molecular dynamics study
Authors: Walsh Phillip , Omeltchenko Andrey , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya , Saini Subhash
Published: January 2003

Nanoindentation of crystalline and amorphous silicon nitride films is studied using 10-million-atom molecular dynamics simulations. A rigid pyramid-shaped indenter tip is used. Load–displacement curves are computed and are used to derive hardness and elastic moduli of the simulated crystalline and amorphous films. Computer images of local pressure distributions and configuration snapshots show that plastic deformation in the film extends to regions far from the actual indent.
Distortions in Z-scan spectroscopy
Authors: Yang Qiguang , Seo JaeTae , Creekmore Santiel , Temple Doyle , Mott Andy , Min Namkung , Yoo KiPung , Kim Sun Young , Jung Sungsoo
Published: January 2003

The sample imperfection induced distortions in the closed Z-scan curve are analyzed. It is found that both the magnitudes of the peak and valley transmittances and the shape of the curve are distorted significantly by the inhomogeneous thickness, the nonuniform nonlinearity, and the curved surfaces of the sample. The results suggest that the I-scan method is a more practical choice for the measurement of the third-order nonlinear susceptibility of an inhomogeneous sample.
Surface structure and anchoring properties of modified self-assembled monolayers
Authors: Fonseca João G. , Hommet Jean , Galerne Yves
Published: January 2003

The surface structure of plasma-modified self-assembled monolayers is studied by x-ray photoelectron spectroscopy. The measurements show that the oxygen postplasma gas produces gradual chemical modifications in a pure polyethylene-type monolayer. Different oxygenated functions are observed and quantitatively, they are measured to be denser at shorter distances from the plasma source. Used as liquid crystal alignment layers, these surfaces present a fast transition between the homeotropic and planar anchorings. The average distance between the oxygen atoms on the organic layer is found to be ∼6–10 Å at the anchoring transition.
Shift multiplexing for holographic storage system using fiber bundle referencing
Authors: Zhang Jiasen , Yoshikado Shin , Aruga Tadashi
Published: January 2003

We propose a shift multiplexing method for volume holographic storage using fiber bundle referencing. The reference beam is guided by a fiber bundle and multiplexing can be implemented by shifting the recording medium for a small distance. No sidelobe or period has been found and the signal-to-noise ratio is high. Multiple images are stored in a crystal with a spatial separation of 3 μm between successive holograms.
Properties of optical phonons in cubic InxGa1−xN
Authors: Torii K. , Usukura N. , Nakamura A. , Sota T. , Chichibu S. F. , Kitamura T. , Okumura H.
Published: January 2003

Infrared reflectance spectroscopy was carried out to study the properties of zone center optical phonons in ternary cubic InxGa1−xN free from phase separation. Raman spectra were also measured as auxiliary measures. Optical phonon behavior was confirmed to be type I. It is demonstrated that the behavior arises from both the small mass ratio of Ga to In atoms and the rather strong ionicity of Ga–N and In–N bonds.
A general approach for the calculation of intermodulation distortion in cavities with superconducting endplates
Authors: Mateu J. , Collado C. , Menéndez O. , O’Callaghan J. M.
Published: January 2003

We report on a general procedure to calculate intermodulation distortion in cavities with superconducting endplates that is applicable to the dielectric-loaded cavities currently used for measurement of surface resistance in high-temperature superconductors. The procedure would enable the use such cavities for intermodulation characterization of unpatterned superconducting films, and would remove the uncertainty of measuring intermodulation on patterned devices, in which the effect of patterning damage might influence the outcome of the measurements. We have verified the calculation method by combining superconducting and copper endplates in a rutile-loaded cavity.
Analysis of metallic intermediate-band formation in photovoltaic materials
Authors: Tablero C. , Wahnón P.
Published: January 2003

The substitution of some transition atoms in III–V-type semiconductors may give rise to a type of high-efficiency photovoltaic material with an isolated intermediate narrow band in the middle of the band gap, capable of absorbing photons of low energies. We have carried out a comparative analysis of the nature and possibility of formation of the intermediate band in two compounds Ga4P3Ti and Ga3P4Ti in terms of density of states, electronic density, and atomic and orbital populations. We found that the intermediate band is formed only in one of these compounds.
High-Tm relaxor ferroelectrics: 0.3BiScO3–0.6PbTiO3–0.1Pb(Mn1/3Nb2/3)O3
Authors: Ryu Jungho , Priya Shashank , Uchino Kenji
Published: January 2003

High-Tm relaxor materials are being developed for high-temperature high-power density electrotransduction applications and high-temperature capacitors in automobile applications. A relaxor ferroelectric material of composition 0.3BiScO3–0.6PbTiO3–0.1Pb(Mn1/3Nb2/3)O3 having a very high dielectric maximum of ∼350 °C is reported. The relaxor behavior is confirmed by studying polarization relaxation and frequency and temperature dependent dielectric behavior. The dielectric constant in the low-temperature region of 10 °C<T<150 °C is found to be independent of the frequency with a temperature gradient of ∂ε/∂T=2.5/°C. The room-temperature magnitude of dielectric constant is ∼600.
The interface of epitaxial SrTiO3 on silicon: in situ and ex situ studies
Authors: Hu Xiaoming , Li H. , Liang Y. , Wei Y. , Yu Z. , Marshall D. , Edwards J. , Droopad R. , Zhang X. , Demkov A. A. , Moore K. , Kulik J.
Published: January 2003

The formation of interfacial layers between silicon and the overgrown epitaxial SrTiO3 as a function of the growth temperature has been studied in detail using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Models for the chemical compositions and atomic bonding states have been established. With a good understanding of the mechanisms of the interfacial layer formations, the molecular-beam epitaxy growth process can be well controlled to form high-quality, single-crystalline oxide films, as well as a desired interface between the grown oxide and silicon substrate. The epitaxial relationship has been found to be SrTiO3 (001)∥Si(001), and SrTiO3 〈100〉∥Si〈110〉.
A general relation between the ranges of stability of electrostatic actuators under charge or voltage control
Authors: Bochobza-Degani Ofir , Elata David , Nemirovsky Yael
Published: January 2003

Pull-in instability is a crucial effect in electrostatically-actuated microelectromechanical devices. This phenomenon was recently shown to occur under both voltage and charge control. So far, for all known cases, it has been shown that, under charge excitation, electrostatic actuators have a larger range of stability than under voltage excitation. No counter-examples are known, and whether this is a general rule for electrostatic actuators is an open question. In this work, a general proof is presented that shows this is indeed a fundamental rule for general electrostatic actuators.
Oxygen adsorption on graphite and nanotubes
Authors: Giannozzi P. , Car R. , Scoles G.
Published: January 2003

We study the binding of molecular oxygen to a graphene sheet and to a (8,0) single walled carbon nanotube, by means of spin-unrestricted density-functional calculations. We find that triplet oxygen retains its spin-polarized state when interacting with graphene or the nanotube. This leads to the formation of a weak bond with essentially no charge transfer between the molecule and the sheet or tube, as one would expect for a physisorptive bond. This result is independent on the approximation used for the exchange-correlation functional. The binding strength, however, depends strongly on the functional, reflecting the inability of current approximation functionals to deal correctly with dispersion forces. Gradient-corrected functionals yield very weak binding at distances around 4 Å, whereas local density functional results yield substantially stronger binding for both graphene and the nanotube at distances of less than 3 Å. The picture of oxygen physisorption is not substantially altered by the presence of topological defects such as 5–7 Stone–Wales pairs.
Understanding shunting behavior in hot-wire-deposited amorphous silicon solar cells
Authors: van Veen M. K. , Schropp R. E. I.
Published: January 2003

Amorphous silicon solar cells, in which the absorbing layer is deposited using the hot-wire chemical vapor deposition (CVD) technique, have potential advantages over solar cells made with the standard plasma enhanced CVD technique. Although it is possible to make high-quality solar cells, many cells occasionally show shunting behavior and better control over the variation in cell performance must be obtained. In this letter, we prove that this behavior is directly correlated with the filament age, and we present different methods for avoiding shunted cells and for improving the reproducibility of cell performance.
Ultraviolet-induced discharge currents and reduction of the piezoelectric coefficient in cellular polypropylene films
Authors: Mellinger Axel , Camacho González Francisco , Gerhard-Multhaupt Reimund
Published: January 2003

Photostimulated discharge spectroscopy of cellular polypropylene films between 200 and 400 nm showed the existence of at least three distinct trapping levels at 4.6, 5.6, and 6.3 eV. The effects of UV irradiation on the piezoelectric d33 coefficient was studied by monitoring thickness-extension resonances in the dielectric spectrum. Prolonged irradiation at wavelengths below 210 nm led to a reduction of the piezoelectric coefficient, caused by partial discharge of the polymer foam.
Modulation of steady‐state kinetics of digoxin by haplotypes of the P‐glycoprotein MDR1 gene
Authors: Johne Andreas , Köpke Karla , Gerloff Thomas , Mai Ingrid , Rietbrock Stephan , Meisel Christian , Hoffmeyer Sven , Kerb Reinhold , Fromm Martin F. , Brinkmann Ulrich , Eichelbaum Michel , Brockmöller Jürgen , Cascorbi Ingolf , Roots Ivar
Published: January 2003

Objective

We investigated the effect of polymorphisms in the P‐glycoprotein (P‐gp) MDR1 gene on steady‐state pharmacokinetics of digoxin in Caucasians. According to earlier data, homozygous TT of the exon 26 complementary deoxyribonucleic acid (cDNA) 3435C>T polymorphism was associated with low P‐gp expression in the human intestine.

Methods

Eight healthy male homozygous carriers of the wild‐type exon‐26 3435C>T (CC), 8 heterozygous subjects (CT), and 8 homozygous mutant (TT) subjects were selected. Seven further MDR1 polymorphisms were determined. Digoxin was administered orally twice daily on the first two study days; on days 3 to 5, 0.25 mg was given in the morning. On day 5, kinetic parameters were analyzed for genotype‐phenotype and haplotype‐phenotype relationships.

Results

The area under the plasma concentration‐time curve from time zero to 4 hours [AUC(0–4)] (P = .042) and Cmax (P = .043) values of digoxin were higher in subjects with the 3435TT genotype than in those with the 3435CC. No influence of other single nucleotide polymorphisms (SNPs) on digoxin parameters was detected. Comparison of genotypes deduced from SNPs 2677G>T (exon 21) and 3435C>T revealed significant differences for AUC(0–4) (P = .034) and Cmax (P = .039), which were substantiated by haplotype analysis. Haplotype 12 (2677G/3435T), which had a frequency of 13.3% in a randomly drawn Caucasian sample (n = 687), was associated (Mann‐Whitney test) with higher AUC(0–4) values (P = .009) than were found in noncarriers (mean ± SD, 5.7 ± 0.9 μg · h/L [n = 7] versus 4.8 ± 0.9 μg · h/L [n = 17]). Haplotype 11 (2677G/3435C) had lower AUC(0–4) values (P = .013) compared with those of noncarriers (mean ± SD, 4.7 ± 0.9 μg · h/L [n = 16] versus 5.6 ± 0.9 μg · h/L [n = 8]). Results of haplotype analysis match data of other MDR1 studies.

Conclusion

Haplotype 12 codes for high values of AUC(0–4) and Cmax of orally administered digoxin. Analysis of MDR1 haplotypes is superior to unphased SNP analysis to predict MDR1 phenotype.

Clinical Pharmacology & Therapeutics (2002) 72, 584–594; doi: 10.1067/mcp.2002.129196
Nitric oxide contributes to induction of innate immune responses to gram-negative bacteria inDrosophila
Authors: Foley Edan , O'Farrell Patrick H.
Published: January 2003

Studies in mammals uncovered important signaling roles of nitric oxide (NO), and contributions to innate immunity. Suggestions of conservation led us to explore the involvement of NO inDrosophilainnate immunity. Inhibition of nitric oxide synthase (NOS) increased larval sensitivity to gram-negative bacterial infection, and abrogated induction of the antimicrobial peptide Diptericin. NOS was up-regulated after infection. Antimicrobial peptide reporters revealed that NO triggered an immune response in uninfected larvae. NO induction of Diptericin reporters in the fat body requiredimmune deficiency(imd) anddomino. These findings show that NOS activity is required for a robust innate immune response to gram-negative bacteria, NOS is induced by infection, and NO is sufficient to trigger response in the absence of infection. We propose that NO mediates an early step of the signal transduction pathway, inducing the innate immune response upon natural infection with gram-negative bacteria.
Phosphorylation of histone H3 during transcriptional activation depends on promoter structure
Authors: Labrador Mariano , Corces Victor G.
Published: January 2003

Covalent modifications of histone N-terminal tails are required for the proper assembly and activation of the general transcription factors at promoters. Here, we analyze histone acetylation and phosphorylation inDrosophilatransgenes activated by the yeast Gal4 transcriptional activator in the context of different promoters. We show that, independent of the promoter, transcription does not correlate with acetylation of either H3-Lys 14 or H4-Lys 8. Histone H3 associated with the DNA of Gal4-induced transcribing transgenes driven by theDrosophila Hsp70promoter is hyperphosphorylated at Ser 10 during transcription. Surprisingly, histone H3 at Gal4-induced transgenes driven by the P element Transposase promoter is not hyperphosphorylated. The data suggest that transcription occurs without acetylated H4 and H3 in both transgenes inDrosophilapolytene chromosomes. Instead, phosphorylation of H3 is linked to transcription and can be modulated by the structure of the promoter.
Telomere-based crisis: functional differences between telomerase activation and ALT in tumor progression
Authors: Chang Sandy , Khoo Christine M. , Naylor Maria L. , Maser Richard S. , DePinho Ronald A.
Published: January 2003

Telomerase activation is a common feature of most advanced human cancers and is postulated to restore genomic stability to a level permissive for cell viability and tumor progression. Here, we used genetically defined transformed mouse embryonic fibroblast (MEF) cultures derived from late generationmTerc−/−Ink4a/Arf−/−mice to explore more directly how telomere-based crisis relates to the evolution of cancer cell genomes and to tumor biology. An exhaustive serial analysis of cytogenetic profiles over extensive passage in culture revealed that the emergence of chromosomal fusions (including dicentrics) coincided with onset of deletions and complex nonreciprocal translocations (NRTs), whereasmTerc-transduced cultures maintained intact chromosomes and stable genomes. Despite a high degree of telomere dysfunction and genomic instability, transformed late passagemTerc−/−Ink4a/Arf−/−cultures retained the capacity to form subcutaneous tumors in immunocompromised mice. However, even moderate levels of telomere dysfunction completely abrogated the capacity of these cells to form lung metastases after tail-vein injection, whereasmTercreconstitution alone conferred robust metastatic activity in these cells. Finally, serial subcutaneous tumor formation using late passage transformedmTerc−/−Ink4a/Arf−/−cultures revealed clear evidence of telomerase-independent alternative lengthening of telomeres (ALT). Significantly, despite a marked increase in telomere reserve, cells derived from the ALT+ subcutaneous tumors were unable to generate lung metastases, indicating in vivo functional differences in these principal mechanisms of telomere maintenance. Together, these results are consistent with the model that although telomere dysfunction provokes chromosomal aberrations that initiate carcinogenesis, telomerase-mediated telomere maintenance enables such initiated cells to efficiently achieve a fully malignant endpoint, including metastasis.
Pax5is required for recombination of transcribed, acetylated, 5′ IgH V gene segments
Authors: Hesslein David G.T. , Pflugh David L. , Chowdhury Dipanjan , Bothwell Alfred L. M. , Sen Ranjan , Schatz David G.
Published: January 2003

Pax5-deficient progenitor B (pro-B) cells are thought to be severely defective for recombination of all immunoglobulin heavy chain (IgH) V gene segments, but the mechanism by whichPax5regulates this process has not been defined. To address this issue, we have examined the assembly of the IgH locus inPax5-deficient pro-B cells and find, unexpectedly, that 3′ IgH V gene segments, which lie closest to the D-J-Cμ region, recombine efficiently, but progressively more distal V gene segments recombine progressively less efficiently. Histone acetylation and germ-line transcription correlate strongly with an open or an accessible chromatin structure thought to be permissive for V(D)J recombination, and defects in recombination are typically accompanied by deficits in these processes. We were therefore surprised to observe that distal VHgene segments in Pax5−/− pro-B cells exhibit no defect in these measures of accessibility. The finding of transcribed, histone acetylated gene segments that fail to recombine suggests that aPax5-dependent regulatory mechanism is required in addition to standard constraints of accessibility to control VHgene recombination.
The highly conserved Ndc80 complex is required for kinetochore assembly, chromosome congression, and spindle checkpoint activity
Authors: McCleland Mark L. , Gardner Richard D. , Kallio Marko J. , Daum John R. , Gorbsky Gary J. , Burke Daniel J. , Stukenberg P. Todd
Published: January 2003

We show that theXenopushomologs of Ndc80/Tid3/HEC1 (xNdc80) and Nuf2/MPP1/Him-10 (xNuf2) proteins physically interact in a 190-kD complex that associates with the outer kinetochore from prometaphase through anaphase. Injecting function-blocking antibodies to either xNdc80 or xNuf2 into XTC cells caused premature exit from mitosis without detectable chromosome congression or anaphase movements. Injected cells did not arrest in response to microtubule drugs, showing that the complex is required for the spindle checkpoint. Kinetochores assembled inXenopusextracts after immunodepletion of the complex did not contain xRod, xZw10, xP150 glued (Dynactin), xMad1, xMad2, xBub1, and xBub3, demonstrating that the xNdc80 complex is required for functional kinetochore assembly. In contrast, function-blocking antibodies did not affect the localization of other kinetochore proteins when added to extracts containing previously assembled kinetochores. These extracts with intact kinetochores were deficient in checkpoint signaling, suggesting that the Ndc80 complex participates in the spindle checkpoint. We also demonstrate that the spindle checkpoint can arrest budding yeast cells lacking Ndc80 or Nuf2, whereas yeast lacking both proteins fail to arrest in mitosis. Systematic deletion of yeast kinetochore genes suggests that the Ndc80 complex has a unique role in spindle checkpoint signaling. We propose that the Ndc80 complex has conserved roles in kinetochore assembly, chromosome congression, and spindle checkpoint signaling.
EGF-CFC proteins are essential coreceptors for the TGF-β signals Vg1 and GDF1
Authors: Cheng Simon K. , Olale Felix , Bennett James T. , Brivanlou Ali H. , Schier Alexander F.
Published: January 2003

The TGF-β signals Nodal, Activin, GDF1, and Vg1 have been implicated in mesoderm induction and left-right patterning. Nodal and Activin both activate Activin receptors, but only Nodal requires EGF-CFC coreceptors for signaling. We report that Vg1 and GDF1 signaling in zebrafish also depends on EGF-CFC proteins, but not on Nodal signals. Correspondingly, we find that inXenopusVg1 and GDF1 bind to and signal through Activin receptors only in the presence of EGF-CFC proteins. These results establish that multiple TGF-β signals converge on Activin receptor/EGF-CFC complexes and suggest a more widespread requirement for coreceptors in TGF-β signaling than anticipated previously.