bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of deterministic fractal polymer networks: Hydrodynamic interactions and the absence of scaling
Authors: Jurjiu A. , Koslowski Th. , Blumen A.
Published: January 2003

We numerically analyze the scaling behavior of experimentally accessible dynamical relaxation forms for networks modeled through finite Sierpinski-type lattices. Previous work has established unequivocally for such lattices that in the Rouse picture both the mechanical and the dielectric relaxation forms scale in frequency and in time. As we show here, in the Zimm model, based on the preaveraged Oseen tensor, the picture changes drastically; the introduction of the hydrodynamic interactions leads to relaxation patterns which do not scale. Our results show that the relaxation forms are very sensitive to the number of monomers in the network and to the strength of the hydrodynamic interaction parameter.
Chain orientation and slow dynamics in elastomers by mixed magic-Hahn echo decays
Authors: Fechete R. , Demco D. E. , Blümich B.
Published: January 2003

The decays of the mixed H1 echo represented by a combination of the magic and the Hahn echoes was measured in a series of cross-linked elastomers. The mixed echo refocuses the homogeneous and inhomogeneous spin interactions. It allows the investigation of the fluctuation of the dipolar interaction of polymer chains in the slow motion regime. The method accounts for multispin dipolar interactions and eliminates the interference of linear spin interactions due to chemical shielding, magnetic field inhomogeneities, local susceptibility variations, and heteronuclear dipolar interactions. The multispin dipolar correlation functions characterizing the mixed echo decay are derived in the approximation of a single correlation time and for a distribution of correlation times. Based on these dipolar correlation functions the H1 residual second van Vleck moment, correlation times, and parameters of the correlation time distribution are determined for a series of natural rubber samples with different cross-link densities. The segmental order measured by the residual second van Vleck moment was shown to scale with a polynomial dependence on cross-link density or shear modulus. This can be interpreted by considering high-order corrections to a Gaussian distribution of the end-to-end vectors. By assuming a log-Gaussian distribution function for the correlation times and the validity of the Williams–Landel–Ferry equation, the center of gravity and the logarithmic width of the distribution function of the correlation times describing the slow motion of the network chains scale with the degree of topological constraints and the chemical cross-link density by a power-law with exponents 2.85±0.65 and 3.09±0.23, respectively.
A new concise expression for the free energy of a reaction coordinate
Authors: Schlitter Jürgen , Klähn Marco
Published: January 2003

For processes that can be parametrized by a reaction coordinate, the calculation of the free energy against this coordinate is the first step towards equilibrium constants and transition rates. We present a new concise expression for the free energy that is computed from data sampled at a fixed (constrained) reaction coordinate. It is consistent with previous theories and satisfies a more general criterion for free energy profiles.
Determination of the conditional association constants from the sound velocity data in binary liquid mixtures
Authors: Gliński Jacek
Published: January 2003

Two models of calculating the association constants in mixtures of two weakly interacting liquids are proposed and analyzed: one of them assumes additivity of acoustic impedance with the molar fractions of components, and the other assumes additivity of the time of transmission of the acoustic signal with the volume fractions. The models were tested for different systems, showing that the latter yields results much more reliable and closer to expectations. The presented attempt seems to be an interesting alternative way in interpreting the experimental results of sound velocity measurements in liquid mixtures.
Orientational relaxation and vibrational excitation transfer in methanol–carbon tetrachloride solutions
Authors: Gaffney K. J. , Piletic I. R. , Fayer M. D.
Published: January 2003

Time and polarization resolved ultrafast infrared vibrational spectroscopy of the hydroxyl stretch of methanol dissolved in carbon tetrachloride has been utilized to investigate orientational relaxation and vibrational excitation transfer. The anisotropy decay of the deuterated hydroxyl stretch of methanol-d was measured in two solutions: Isotopically mixed 0.8 mol % methanol-d 23 mol % methanol-h in CCl4 and isotopically pure methanol-d at 26 mol % in CCl4. The anisotropy decay in the isotopically mixed methanol solution is a biexponential characterized by 1.7±0.7 ps and 17±3 ps time constants, with 40±10% of the decay occurring with the slower time constant. The biexponential anisotropy decay has been analyzed with a restricted orientational diffusion model that involves fast orientational diffusion within a cone of semi-angle θc, followed by slower, full orientational relaxation. The fast orientational relaxation occurs within a cone semi-angle of θc=45°±5°, with a diffusion coefficient of Dc−1=13±5 ps. The slower anisotropy decay results from the full orientational diffusion and occurs with a diffusion coefficient of Dθ−1=100±20 ps. The anisotropy decay for isotopically pure methanol-d in CCl4 is much faster because of vibrational excitation transfer in addition to the orientational relaxation. The excitation transfer has been successfully analyzed as transition dipole–transition dipole mediated transfer using a theory developed for randomly distributed chromophores.
Martensitic transformation and shape memory effect in ferromagnetic Heusler alloy Ni2FeGa
Authors: Liu Z. H. , Zhang M. , Cui Y. T. , Zhou Y. Q. , Wang W. H. , Wu G. H. , Zhang X. X. , Xiao Gang
Published: January 2003

We have synthesized ferromagnetic Heusler alloy Ni2FeGa using the melt-spinning technique. The Ni2FeGa ribbon, having a high chemical ordering L21 structure, exhibits a thermoelastic martensitic transformation from cubic to orthorhombic structure at 142 K and a premartensitic transformation. The alloy has a relatively high Curie temperature of 430 K, a magnetization of 73 Am2/kg, and a low saturated field of 0.6 T. The textured samples with preferentially oriented grains show a completely recoverable two-way shape memory effect with a strain of 0.3% upon the thermoelastic martensitic transformation.
Control of growth orientation for carbon nanotubes
Authors: Lee Ki-Hong , Cho Jeong-Min , Sigmund Wolfgang
Published: January 2003

Laterally aligned carbon nanotubes were synthesized on substrates over iron nanoparticles using chemical vapor deposition. In addition, aligned carbon nanotubes grown vertically and with tilt angle to the substrates were produced, which means that it is possible to grow aligned carbon nanotubes at any angle relative to the substrate. The growth direction of the carbon nanotubes was controlled by a magnetic field that is applied in the process of adhering catalyst particles on silicon oxide substrates from dispersion. The ferromagnetic property of the iron nanoparticles fixes them in a defined orientation under magnetic field, which results in aligned growth of the carbon nanotubes. These results indicate that carbon nanotubes preferentially grow from certain facets of the catalyst particles, suggesting a crucial clue in investigating the growth mechanism of carbon nanotubes. The laterally aligned carbon nanotubes could make it possible to integrate them in nanoelectronic devices, such as a channel for field-effect transistors.
Mechanical gating of coupled nanoelectromechanical resonators operating at radio frequency
Authors: Pescini Laura , Lorenz Heribert , Blick Robert H.
Published: January 2003

We report measurements on hybrid gold/silicon suspended nanostructures operating as electromechanical resonators in the rf regime. The device consists of two nanoresonators operating as mechanical gating elements. We demonstrate this gating mechanism by tuning the mechanical modes of the device. Detailed numerical calculations are performed to model the device.
Tunable liquid microlens
Authors: Krupenkin T. , Yang S. , Mach P.
Published: January 2003

A tunable liquid microlens capable of adjusting its focal length and lateral position is demonstrated. The microlens consists of a droplet of a transparent conductive liquid placed on a dielectric substrate with a low surface energy coating. By varying the voltage applied to a set of electrodes positioned underneath of the dielectric substrate, both the position and curvature of the microlens can be reversibly changed. The dependence of the microlens behavior on the properties of the materials involved is experimentally investigated and supported by theoretical calculations. Potential limitations of the microlens performance associated with the contact angle hysteresis and stick–slip phenomena are outlined and possible ways to alleviate them are proposed. Possible extensions of the proposed approach are also discussed.
Thermally stable Ir Schottky contact on AlGaN/GaN heterostructure
Authors: Jeon Chang Min , Jang Ho Won , Lee Jong-Lam
Published: January 2003

We report thermally stable Ir Schottky contacts on AlGaN/GaN heterostructure. The Schottky barrier height was increased from 0.68 to 1.07 eV, and the reverse leakage current dramatically decreased after annealing at 500 °C under O2 ambient. No degradation in Schottky barrier height was observed after annealing at 500 °C for 24 h. The oxidation annealing caused predominant Ga outdiffusion to the surface, leading to the shift of surface Fermi level to the energy level of Ga vacancy. This played a role in forming the Schottky contact with large barrier height and excellent thermal stability.
Enhanced dynamic annealing in Ga+ ion-implanted GaN nanowires
Authors: Dhara S. , Datta A. , Wu C. T. , Lan Z. H. , Chen K. H. , Wang Y. L. , Chen L. C. , Hsu C. W. , Lin H. M. , Chen C. C.
Published: January 2003

Ga + ion implantation of chemical-vapor-deposited GaN nanowires (NWs) is studied using a 50-keV Ga+ focused ion beam. The role of dynamic annealing (defect-annihilation) is discussed with an emphasis on the fluence-dependent defect structure. Unlike heavy-ion-irradiated epitaxial GaN film, large-scale amorphization is suppressed until a very high fluence of 2×1016 ions cm−2. In contrast to extended-defects as reported for heavy-ion-irradiated epitaxial GaN film, point-defect clusters are identified as major component in irradiated NWs. Enhanced dynamic annealing induced by high diffusivity of mobile point-defects in the confined geometry of NWs is identified as the probable reason for observed differences.
Ultrarapid nanostructuring of poly(methylmethacrylate) films using Ga+ focused ion beams
Authors: Liu Y. , Longo D. M. , Hull R.
Published: January 2003

Topographical patterns were fabricated with speeds >103 features per second into poly(methylmethacrylate) (PMMA) films with a Ga+ focused ion beam. This material removal rate is orders of magnitude greater than expected in conventional sputtering. The relevant ion-beam sputtering parameters have been investigated to explore the mechanism of the extraordinary materials removal rate. It is speculated that structural changes during ion bombardment, specifically a beam-enhanced unzipping reaction of the PMMA chains, play an important role for the high material removal rate. These high throughput PMMA topographic patterns can be used as masters for high-resolution elastomer molding and microcontact printing.
Ge island formation on stripe-patterned Si(001) substrates
Authors: Zhong Zhenyang , Halilovic A. , Mühlberger M. , Schäffler F. , Bauer G.
Published: January 2003

Self-assembled Ge islands were grown by solid-source molecular-beam epitaxy on the submicron stripe-patterned Si(001) substrates at 650 °C. Atomic-force microscopy shows that the Ge islands grow preferentially at the sidewall of the Si stripes, oriented along the [−110] direction. The migration of the Ge adatoms from the top terrace down to the sidewall accounts for the island formation at the sidewall of the stripes. However, most of the Ge islands are formed on the top terraces when the patterned stripes are covered by a strained GeSi multilayer buffer prior to Ge island growth. Apparently, the strained buffer layer acts as a stressor and contributes to the preferential growth of islands on the top terrace.
Realization of high-efficiency/high-luminance small-molecule organic light-emitting diodes: synergistic effects of siloxane anode functionalization/hole-injection layers, and hole/exciton-blocking/electron-transport layers
Authors: Huang Qinglan , Cui Ji , Veinot Jonathan G. C. , Yan He , Marks Tobin J.
Published: January 2003

High-efficiency/high-luminance small-molecule organic light-emitting diodes (OLEDs) are fabricated by combining thin, covalently-bound triarylamine hole injection/adhesion interlayers with hole- and exciton-blocking/electron transport interlayers in tris(8-hydroxyquinolato)aluminum (III) (Alq)-based OLEDs. Power and forward external quantum efficiencies as high as 15.2 lm/W and 4.4±0.5%, respectively, and turn-on voltages ∼4.5 V are achieved in devices of the structure ITO/TPDSi2/NPB/Alq:DIQA/BCP/Li/MgAg [NPB=(N,N′-di(1-napthl)-N,N′-diphenyl benzidine)] TPDSi2 interlayers are straightforwardly fabricated by spin-casting N,N′-diphenyl-N,N′- bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine TPDSi2 onto the ITO surface, while 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) interlayers are introduced by thermal evaporation. High quantum efficiencies are attributed to the synergistic enhanced hole/electron injection and exciton confinement effects of the TPDSi2 and BCP interlayers, respectively.
Microelectromechanical displacement sensing using InAs/AlGaSb heterostructures
Authors: Yamaguchi Hiroshi , Miyashita Sen , Hirayama Yoshiro
Published: January 2003

We fabricated self-sensing microelectromechanical displacement sensors from InAs/AlGaSb heterostructures. The sensitivity increased with reduced InAs thickness showing that the piezoresistivity was strongly enhanced when the quantum level approached to the pinning position of surface Fermi level. The high-sensitivity allowed us to detect a subangstrom displacement induced by thermal vibration of cantilevers.
Exciton relaxation processes in colloidal core/shell ZnSe/ZnS nanocrystals
Authors: Lomascolo Mauro , Cretı̀ Arianna , Leo Gabriella , Vasanelli Lorenzo , Manna Liberato
Published: January 2003

Colloidal ZnSe nanocrystals are coated with a ZnS shell and are investigated by means of time-resolved photoluminescence spectroscopy. These nanocrystals are stable against photooxidation and have photoluminescence quantum efficiencies around 15% even months after the synthesis. Recombination processes are investigated as a function of the excitation intensity and the emission energy. Nonlinear processes such as Auger recombination dominate in the early times after the photogeneration of electron-hole pairs. The lifetime of single exciton states is shorter in smaller ZnSe dots than in larger ones, in accordance with theoretical predictions and as previously observed on similar systems.
Charge carrier mobility in an organic-inorganic hybrid nanocomposite
Authors: Choudhury Kaushik Roy , Winiarz Jeffrey G. , Samoc Marek , Prasad Paras N.
Published: January 2003

Organic-inorganic hybrid materials are media for electronic and optoelectronic applications. We present a study of the electronic transport in such a model nanoparticle-sensitized hybrid organic-inorganic photorefractive host system, consisting of poly(N-vinylcarbazole) doped with quantum dots of cadmium sulfide, using standard time-of-flight techniques. The photocurrent transients exhibit features typical of dispersive transport in an amorphous semiconductor. The hole mobility depends strongly on the electric field and temperature indicating Poole–Frenkel-like activated hopping transport; a thickness dependence of the mobility is observed. The presence of nanoparticles does not lead to increased trapping of holes. Conversely, a surprising result is observed: the mobility actually increases with the increase of nanoparticle concentration even though it is well below the percolation limit.
Temperature dependence of free-exciton luminescence in cubic CdS films
Authors: Kanemitsu Yoshihiko , Nagai Takehiko , Yamada Yoichi , Taguchi Tsunemasa
Published: January 2003

Free-exciton photoluminescence (PL) properties of cubic CdS films on GaAs substrates have been studied by means of picosecond time-resolved PL spectrum measurements. A PL band appears at the light-hole exciton energy in strained CdS films. The linewidth of the free-exciton PL is determined by the inhomogeneous strains and the exciton–phonon interactions. At high temperatures above 80 K, the linewidth of the exciton luminescence drastically increases and the exciton-optical-phonon interaction is the dominant scattering process. The temperature dependence of free-exciton luminescence has been determined for cubic CdS films.
Ge hut cluster luminescence below bulk Ge band gap
Authors: Denker U. , Stoffel M. , Schmidt O. G. , Sigg H.
Published: January 2003

We report on the photoluminescence (PL) properties of Ge hut cluster islands on Si(001) that were overgrown at temperatures as low as 250 °C. We find that the island-related photoluminescence systematically redshifts as the overgrowth temperature is reduced from 500 to 360 °C, which is attributed to a reduced Ge segregation. For even lower overgrowth temperatures, the emission energy saturates at 0.63 eV or 1.96 μm, more than 110 meV smaller than the band gap of unstrained bulk Ge. We report a PL peak centered at 2.01 μm at low excitation power, in good agreement with the estimated transition energy for a spatially indirect transition between holes confined in the strained Ge island and electrons confined in the surrounding Si matrix. PL is observed up to a temperature of 185 K and an activation energy of 40 meV is deduced from fitting the temperature-dependent peak intensity. Annealing experiments reveal a systematic blueshift of the hut cluster-related PL, thus verifying unambiguously, that the PL signal originates from the hut clusters and not from defects.
Semiconductor absorption in photonic crystals
Authors: Eichmann R. , Pasenow B. , Meier T. , Stroucken T. , Thomas P. , Koch S. W.
Published: January 2003

Absorption spectra of semiconductor structures in photonic crystal environments are investigated numerically. It is shown that the periodic dielectric structuring changes the local optical and Coulomb interaction properties of semiconductor electron–hole excitations. The structurally induced modifications offer the possibility to design important aspects of the optoelectronic semiconductor properties.
Amorphous metallic foam
Authors: Schroers Jan , Veazey Chris , Johnson William L.
Published: January 2003

The bulk glass forming alloy Pd43Ni10Cu27P20 is processed into a low-density amorphous metallic foam. Pd43Ni10Cu27P20 is mixed with hydrated B2O3, which releases gas at elevated temperature and/or low pressure. Very homogeneous foams are achieved due to the high viscosity of the alloy even at its liquidus temperature. By processing at the liquidus temperature and decreasing the pressure to 10−2 mbar, well-distributed bubbles expand to foam the material. Foam densities as low as 1.4×103 kg/m3 were obtained, corresponding to a bubble volume fraction of 84%. The bubble diameter ranges between 2×10−4 and 1×10−3 m. Thermal analysis by differential scanning calorimetry confirms the amorphous nature of the foam. Furthermore, it reveals that the foam’s thermal stability is comparable to the bulk material.
Light emission and microstructure of Mg-doped AlGaN grown on patterned sapphire
Authors: Bell A. , Liu R. , Ponce F. A. , Amano H. , Akasaki I. , Cherns D.
Published: January 2003

Distinct crystalline and optical properties have been observed in Mg-doped Al0.03Ga0.97N grown on a patterned sapphire substrate; the pattern consisting of etched trenches along the sapphire 〈112̄0〉 direction. The epilayer has two distinct regions: one grown directly onto the sapphire mesa and the other an epitaxial lateral overgrowth (ELO) region that overhangs the trench. Transmission electron microscopy shows the presence of pyramidal defects as well as large dislocation densities in the region grown directly on sapphire. In contrast, the ELO region is defect free and contains no Mg-related pyramidal defects. Cathodoluminescence measurements show superior near-band-edge emission in the ELO region, suggesting that the emission is susceptible to nonradiative centers caused by the high defect density in the rest of the sample. The Mg-related donor–acceptor-pair emission is fairly uniform throughout the film, indicating that it is not affected by the nonradiative centers. These optical and structural properties of AlGaN are closely related to the direction of the growth front.
Direct molding of nanopatterned polymeric films: Resolution and errors
Authors: Azzaroni O. , Schilardi P. L. , Salvarezza R. C. , Gago R. , Vázquez L.
Published: January 2003

The capability of the direct polymer molding method to transfer ordered nanopatterns from a surface-modified silicon template to polymeric materials, such as polystyrene (PS) and high-impact polystyrene (HIPS) is investigated by tapping mode atomic force microscopy (AFM). The lateral resolution of the method for both materials is 54±1 nm while the vertical resolution is 5±1 nm and 3±1 nm, for PS and HIPS, respectively. This difference is explained by considering the different nanomechanical properties of the polymers. In contrast, HIPS surfaces are more resistant to the wear induced by the repetitive “reading” of the surface structure with the AFM tip.
Anomalous hard x-ray emission mode in a plasma focus discharge with hydrogen-argon mixtures
Authors: Heo Hoon , Park Duck Kyu
Published: January 2003

We observed an anomalous discharge mode causing explosive surface evaporation and emission of hard x rays of 10–40 keV in the regime of the lower hydrogen partial pressures of hydrogen–argon mixture in a Mather type plasma focus device of 1.5 kJ. At the anomalous mode, the x rays were emitted from only the surface of the anode without emissions from a plasma column or hot spots, accompanying with explosive evaporations of the anode surface.
Chemical structure of the interface between MgO films and Fe(001)
Authors: Oh H. , Lee S. B. , Seo Jikeun , Min H. G. , Kim J.-S.
Published: January 2003

The chemical structure of the interface formed during MgO growth on Fe(001) is studied by vibration spectroscopy employing a high resolution electron energy loss spectrometer. We find direct, spectroscopic evidence for the formation of FeO layer at the interface that is triggered by the dissociation of oxygen molecule by deposited Mg. Even though the growth conditions of MgO are widely varied, FeO cannot be eradicated at the interface. Hence, we propose that the phase where FeO and MgO coexist at the interface, is an entropically stabilized one in regards to the very small difference between the bond dissociation energy of FeO and that of MgO.
Lasing from InGaAs quantum dots in an injection microdisk
Authors: Zhang Lidong , Hu E.
Published: January 2003

An injection microdisk laser structure is realized using self-assembled InGaAs quantum dots (QDs) as the active layer. Single-mode continuous-wave lasing at ∼5 K from double layer (∼2.5×1010 cm−2 per layer) QDs in ∼4 μm diameter microdisks is reported. The threshold current of this device was as low as 69 μA. The estimated spontaneous emission factor is >0.05.
Superconducting bolometer for far-infrared Fourier transform spectroscopy
Authors: Skidmore J. T. , Gildemeister J. , Lee A. T. , Myers M. J. , Richards P. L.
Published: January 2003

A voltage-biased superconducting bolometer with a heat sink temperature of 4.2 K has been developed for Fourier transform spectroscopy in the far infrared. This device is based on a Nb transition edge sensor with Tc=8.1 K. It will operate for absorbed infrared power up to 3×10−6 W and has an absorber area of 7 mm2. The response is inherently linear and the noise equivalent power (NEP)=1.2×10−13 W Hz−1/2 is dominated by thermal fluctuation noise. This NEP is at least a factor 10 better than that expected for a conventional 4.2 K semiconductor bolometer which is optimized for 1% saturation at the same infrared power. The optical response time τ=1.2 ms is dominated by the internal thermalization time. A smaller version of this bolometer could be useful for diffraction-limited spectroscopy of small samples throughout the infrared. Estimates suggest that values of detectivity D*>1011 cm Hz+1/2 W−1 and time constants approaching 270 μs could be achieved.
Transpolyacetylene chains in hydrogenated amorphous carbon films free of nanocrystalline diamond
Authors: Piazza F. , Golanski A. , Schulze S. , Relihan G.
Published: January 2003

The microstructure of distributed electron cyclotron resonance plasma-deposited hydrogenated amorphous carbon films (a-C:H) was investigated using electron diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Experimental evidence of the existence of transpolyacetylene (TPA) chains in a-C:H films free of nanocrystalline diamond is presented. The values of the mean bond angles and lengths and first neighbor numbers are consistent with the TPA data. The Raman spectra were fitted using the G and D bands and the bands centered at 1140, 1233, and 1475 cm−1 assigned to TPA chains modes. The relative intensity of the latter decreases while hydrogen content decreases. A significant sp2-CH olefinic mode contribution to the infrared stretching band is observed for the low-density films (∼1.2 g/cm3). TPA chains growth is enhanced when ion current density and energy decrease.
Mode locking of semiconductor laser with curved waveguide and passive mode expander
Authors: Williamson C. A. , Adams M. J. , Ellis A. D. , Borghesani A.
Published: January 2003

Active mode locking is reported for a 1.55 μm semiconductor laser with a curved waveguide and passive mode expander, placed in a wavelength tunable external cavity. One facet with a very low reflectivity of 8×10−6 is achieved through a curved active region that tapers into an underlying passive waveguide, thus expanding the mode to give reduced divergence. 10 GHz pulses of 3.1 ps duration have been generated, with a linewidth of 0.81 nm.
Electrical field effect of H-implantation induced defect states in GaN
Authors: Krtschil A. , Kielburg A. , Witte H. , Krost A. , Christen J. , Wenzel A. , Rauschenbach B.
Published: January 2003

Gallium nitride layers grown by metalorganic vapor phase epitaxy on sapphire substrates were implanted with 20 keV hydrogen ions with fluences between 2×1014 and 2×1015 ions per cm2. The resulting deep level spectrum was analyzed by deep level transient as well as by admittance spectroscopy. Beside several electron traps of probably intrinsic nature already known from other implantation experiments, a group of defects exclusively appeared after hydrogen implantation showing a strong electrical field effect in the corresponding emission characteristics. These peculiar states were characterized in detail and compared with defects showing a similar field effect already observed by other groups, suggesting the interpretation as hydrogen-decorated dislocations.
Optical waveguiding in magnetron-sputtered Na0.5K0.5NbO3 thin films on sapphire substrates
Authors: Blomqvist Mats , Khartsev Sergey , Grishin Alex , Petraru Adrian , Buchal Christoph
Published: January 2003

Preferentially oriented perovskite-structured Na0.5K0.5NbO3 (NKN) thin films have been deposited on hexagonal Al2O3(011_2) substrates using rf magnetron sputtering of a stoichiometric, high-density, ceramic target. Structural and film surface properties were measured using x-ray diffraction and atomic force microscopy, respectively. Optical and waveguiding properties were characterized using a prism-coupling technique. We observed sharp and distinguishable TM and TE propagation modes and measured the refractive index of NKN thin films of different thicknesses. The ordinary and extraordinary refractive indices were calculated to be no=2.247±0.002 and ne=2.216±0.002 for a 2.0-μm-thick film at 632.8 nm. This implies a birefringence Δn=ne−no=−0.031±0.002 in the film. These first results show the potential use of rf-sputtered NKN films as an electro-optical active material.
Radio-frequency microdischarge arrays for large-area cold atmospheric plasma generation
Authors: Guo Yoou-Bin , Hong Franklin Chau-Nan
Published: January 2003

By flowing gases through arrays of microhollow cathode holes, large area (12 mm in diameter) uniform and stable discharges could be generated by a rf power supply. Both the rf power and the gas flow through the cathode holes played key roles in maintaining uniform and stable discharges. The discharges could be stable for a period longer than one hour in pure helium (He) and in He containing 1% hexamethyldisiloxane (HMDSO). By using a third steel electrode biased with a pulse power supply (100 kHz, 50% duty cycle), the plasma from arrays of cathode holes could be extended to 20 mm in length. Amorphous carbon films deposited by the extended atmospheric plasma using 1% HMDSO/He reactants exhibited the same structure as those by low pressure plasma chemical vapor deposition.
Growth of large periodic arrays of carbon nanotubes
Authors: Huang Z. P. , Carnahan D. L. , Rybczynski J. , Giersig M. , Sennett M. , Wang D. Z. , Wen J. G. , Kempa K. , Ren Z. F.
Published: January 2003

Large periodic arrays of carbon nanotubes have been grown by plasma-enhanced hot filament chemical vapor deposition on periodic arrays of nickel dots that were prepared by polystyrene nanosphere lithography. A single layer of self-assembled polystyrene spheres was first uniformly deposited on a silicon wafer as a mask, and then electron beam vaporization was used to deposit a nickel layer through the mask. The size of and spacing between the nickel dots are tunable by varying the diameter of the polystyrene spheres, which consequently determines the diameter and site density of carbon nanotubes. The technique can be scaled up at much lower cost than electron beam lithography.
Polarization dependent focusing lens by use of quantized Pancharatnam–Berry phase diffractive optics
Authors: Hasman Erez , Kleiner Vladimir , Biener Gabriel , Niv Avi
Published: January 2003

Quantized Pancharatnam–Berry phase diffractive optics using computer-generated space-variant subwavelength dielectric grating is presented. The formation of the geometrical phase is done by discrete orientation of the local subwavelength grating. We discuss a theoretical analysis and experimentally demonstrate a quantized geometrical blazed phase of polarization diffraction grating, as well as polarization dependent focusing lens for infrared radiation at wavelength 10.6 μm.
One-dimensional continuum and exciton states in quantum wires
Authors: Akiyama Hidefumi , Yoshita Masahiro , Pfeiffer Loren N. , West Ken W. , Pinczuk Aron
Published: January 2003

High-quality T-shaped quantum wires are fabricated by cleaved-edge overgrowth with molecular-beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Characterization by micro-photoluminescence (PL) and PL excitation (PLE) spectroscopy at 5 K reveals high uniformity, a sharp spectral width, and a small Stokes shift of one-dimensional (1D) excitons. The PLE spectrum for 1D states shows a large peak of ground-state excitons and a small absorption band ascribed to 1D continuum states with an onset at 11 meV above the exciton peak.
Mobility enhancement in strained Si modulation-doped structures by chemical mechanical polishing
Authors: Sawano K. , Koh S. , Shiraki Y. , Hirose Y. , Hattori T. , Nakagawa K.
Published: January 2003

The strained Si modulation-doped (MOD) structure formed on the strain-relaxed SiGe buffer layer planarized by chemical mechanical polishing (CMP) was found to show significant mobility enhancement. The enhancement reaches a factor of 6 at low temperatures. The backgate dependence as well as temperature dependence of the transport properties of the MOD structure were investigated, and it was suggested that CMP drastically reduced the roughness scattering and increased the mobility of two-dimensional electron gas in the strained Si.
Magnetoresistance and switching of electrochemically etched Ni wires
Authors: Abdi A. Nait , Bucher J. P.
Published: January 2003

Nickel wires, a few 100 nm in diameter, with a resistance up to 20 Ω, have been prepared by controlled electrochemical etching of macroscopic wires. Although the wires are polycrystalline and the presence of domain walls can be inferred directly from the magnetoresistance curves, the switching field, HSW, for complete reversal is insensitive to details of the wire diameters provided their aspect ratio is larger than 100. Order of magnitude arguments show evidence for spin accumulation at domain walls, while the angular dependence HSW(ϑ) with respect to the wire axis is well described by the analytical form of the curling model, indicating a wider range of applicability of this model than previously thought.
Optical transitions in GaInNAs/GaAs multi-quantum wells with varying N content investigated by photoluminescence excitation spectroscopy
Authors: Sun H. D. , Dawson M. D. , Othman M. , Yong J. C. L. , Rorison J. M. , Gilet P. , Grenouillet L. , Million A.
Published: January 2003

We report on the nitrogen-concentration dependence of optical transitions between quantized states of electrons and holes in GaInNAs/GaAs multi-quantum wells. Using low-temperature photoluminescence excitation spectroscopy, systematic studies have been performed on a series of samples with nitrogen concentrations in the range 0%–1.14%. The observed data were compared with theoretical fitting based on the band anticrossing model in which the localized N states interact with the extended states in the conduction band, taking strain effects into account. Our results are consistent with the band anticrossing model, but with differing coupling strength between different quantum states of electrons in the quantum wells.
Enhanced stimulated Raman scattering in optical parametric oscillators from periodically poled KTiOPO4
Authors: Pasiskevicius V. , Fragemann A. , Laurell F. , Butkus R. , Smilgevicius V. , Piskarskas A.
Published: January 2003

Enhanced Raman scattering and concurrent Raman oscillation have been observed in nanosecond optical parametric oscillators in the near-infrared spectral region for certain periodicities of periodically poled KTiOPO4. The increased Raman activity is associated with direct excitation of the phonon overtone band by the idler wave. The decrease in efficiency of stimulated Raman scattering at crystal temperature above 80 °C is explained by higher dephasing rate of coherently driven lattice polarization due to interaction with thermally generated phonons.
Local structure of crystallized GeTe films
Authors: Kolobov A. V. , Tominaga J. , Fons P. , Uruga T.
Published: January 2003

The structure of crystallized GeTe films has been studied by x-ray absorption fine structure spectroscopy. We find that in addition to Ge–Te bonds (2.20 and 3.13 Å) ∼10% of Ge–Ge bonds are present. Our results indicate that the crystallized GeTe film consists of GeTe crystallites with 10% Ge vacancies, separated by a quasiamorphous-Ge phase.
Ferroelectric properties of Bi3.25La0.75Ti3O12 thin films grown on the highly oriented LaNiO3 buffered Pt/Ti/SiO2/Si substrates
Authors: Zhai Jiwei , Chen Haydn
Published: January 2003

Bi 3.25 La 0.75 Ti 3 O 12 (BLT) thin films were grown on Pt/Ti/SiO2/Si and on LaNiO3 (LNO) buffered Pt/Ti/SiO2/Si substrates using sol-gel processing. Scanning electron micrographs showed the BLT films are composed of peg-like or platelet-like grains depending upon annealing temperature and the substrate type. Large platelet grains were found in BLT films deposited on the LNO/Pt/Ti/SiO2/Si substrates; those thin films showed better polarization–voltage, capacitance–voltage, and current–voltage characteristics. More importantly, they did not show any significant fatigue up to 2×1010 switching cycles at a frequency of 1 MHz and electric field 85 kV/cm.
Controlling molecular ground-state dissociation by optimizing vibrational ladder climbing
Authors: Witte T. , Hornung T. , Windhorn L. , Proch D. , de Vivie-Riedle R. , Motzkus M. , Kompa K. L.
Published: January 2003

To achieve large population transfer to high vibrational levels in a selected ground-state mode of a polyatomic molecule [Cr(CO)6], we apply chirped femtosecond mid-infrared laser pulses at 2000 cm−1 to optimize vibrational ladder climbing as an energy deposition mechanism, which in turn controls the outcome of a unimolecular dissociation process. Its dependence on excitation parameters (frequency, intensity, chirp) is investigated and found to be in excellent agreement with a theoretical calculation. In particular, it is shown that optimizing vibrational ladder climbing allows for coherently controlled excitation even in a polyatomic molecule.
SVIP Is a Novel VCP/p97-interacting Protein Whose Expression Causes Cell Vacuolation
Authors: Nagahama Masami , Suzuki Mie , Hamada Yuko , Hatsuzawa Kiyotaka , Tani Katsuko , Yamamoto Akitsugu , Tagaya Mitsuo
Published: January 2003

VCP/p97 is involved in a variety of cellular processes, including membrane fusion and ubiquitin-dependent protein degradation. It has been suggested that adaptor proteins such as p47 and Ufd1p confer functional versatility to VCP/p97. To identify novel adaptors, we searched for proteins that interact specifically with VCP/p97 by using the yeast two-hybrid system, and discovered a novel VCP/p97-interacting protein named smallVCP/p97-interactingprotein (SVIP). Rat SVIP is a 76-amino acid protein that contains two putative coiled-coil regions, and potential myristoylation and palmitoylation sites at the N terminus. Binding experiments revealed that the N-terminal coiled-coil region of SVIP, and the N-terminal and subsequent ATP-binding regions (ND1 domain) of VCP/p97, interact with each other. SVIP and previously identified adaptors p47 and ufd1p interact with VCP/p97 in a mutually exclusive manner. Overexpression of full-length SVIP or a truncated mutant did not markedly affect the structure of the Golgi apparatus, but caused extensive cell vacuolation reminiscent of that seen upon the expression of VCP/p97 mutants or polyglutamine proteins in neuronal cells. The vacuoles seemed to be derived from endoplasmic reticulum membranes. These results together suggest that SVIP is a novelVCP/p97 adaptor whose function is related to the integrity of the endoplasmic reticulum.
Long-Term Potentiation of Exocytosis and Cell Membrane Repair in Fibroblasts
Authors: Togo Tatsuru , Alderton Janet M. , Steinhardt Richard A.
Published: January 2003

We previously found that a microdisruption of the plasma membrane evokes Ca2+-regulated exocytosis near the wound site, which is essential for membrane resealing. We demonstrate herein that repeated membrane disruption reveals long-term potentiation of Ca2+-regulated exocytosis in 3T3 fibroblasts, which is closely correlated with faster membrane resealing rates. This potentiation of exocytosis is cAMP-dependent protein kinase A dependent in the early stages (minutes), in the intermediate term (hours) requires protein synthesis, and for long term (24 h) depends on the activation of cAMP response element-binding protein (CREB). We were able to demonstrate that wounding cells activated CREB within 3.5 h. In all three phases, the increase in the amount of exocytosis was correlated with an increase in the rate of membrane resealing. However, a brief treatment with forskolin, which is effective for short-term potentiation and which could also activate CREB, was not sufficient to induce long-term potentiation of resealing. These results imply that long-term potentiation by CREB required activation by another, cAMP-independent pathway.
A New Identity for MLK3 as an NIMA-related, Cell Cycle–regulated Kinase That Is Localized near Centrosomes and Influences Microtubule Organization
Authors: Swenson Katherine I. , Winkler Katharine E. , Means Anthony R.
Published: January 2003

Although conserved counterparts for most proteins involved in the G2/M transition of the cell cycle have been found in all eukaryotes, a notable exception is the essential but functionally enigmatic fungal kinase NIMA. While a number of vertebrate kinases have been identified with catalytic domain homology to NIMA, none of these resemble NIMA within its extensive noncatalytic region, a region critical for NIMA function in Aspergillus nidulans. We used a bioinformatics approach to search for proteins with homology to the noncatalytic region of NIMA and identified mixed lineage kinase 3 (MLK3). MLK3 has been proposed to serve as a component in MAP kinase cascades, particularly those resulting in the activation of the c-Jun N-terminal kinase (JNK). Here we describe the first in-depth study of endogenous MLK3 and report that, like NIMA, MLK3 phosphorylation and activity are enhanced during G2/M, whereas JNK remains inactive. Coincident with the G2/M transition, a period marked by dramatic reorganization of the cytoplasmic microtubule network, endogenous MLK3 transiently disperses away from the centrosome and centrosomal-proximal sites where it is localized during interphase. Furthermore, when overexpressed, MLK3, like NIMA, localizes to the centrosomal region, induces profound disruption of cytoplasmic microtubules and a nuclear distortion phenotype that differs from mitotic chromosome condensation. Cellular depletion of MLK3 protein using siRNA technology results in an increased sensitivity to the microtubule-stabilizing agent taxol. Our studies suggest a new role for MLK3, separable from its function in the JNK pathway, that may contribute to promoting microtubule instability, a hallmark of M phase entry.
Localization, Dynamics, and Function of Survivin Revealed by Expression of Functional SurvivinDsRed Fusion Proteins in the Living Cell
Authors: Temme Achim , Rieger Michael , Reber Friedemann , Lindemann Dirk , Weigle Bernd , Diestelkoetter-Bachert Petra , Ehninger Gerhard , Tatsuka Masaaki , Terada Yasuhiko , Rieber Ernst Peter
Published: January 2003

Survivin, a member of the inhibitor of apoptosis protein family, has attracted growing attention due to its expression in various tumors and its potential application in tumor therapy. However, its subcellular localization and function have remained controversial: Recent studies revealed that survivin is localized at the mitotic spindle, binds caspases, and could thus protect cells from apoptosis. The cell cycle-dependent expression of survivin and its antiapoptotic function led to the hypothesis that survivin connects the cell cycle with apoptosis, thus providing a death switch for the termination of defective mitosis. In other studies, survivin was detected at kinetochores, cleavage furrow, and midbody, localizations being characteristic for chromosomal passenger proteins. These proteins are involved in cytokinesis as inferred from the observation that RNA interference and expression of mutant proteins led to cytokinesis defects without an increase in apoptosis. To remedy these discrepancies, we analyzed the localizations of a survivinDsRed fusion protein in HeLa cells by using confocal laser scanning microscopy and time-lapse video imaging. SurvivinDsRed was excluded from the interphase nucleus and was detected in centrosomes and at kinetochores. It dissociated from chromosomes at the anaphase/telophase transition and accumulated at the ends of polar microtubuli where it was immediately condensed to the midbody. Overexpression of both survivinDsRed and of a phosphorylation-defective mutant conferred resistance against apoptosis-inducing reagents, but only the overexpressed mutant protein caused an aberrant cytokinesis. These data characterize in detail the dynamics of survivin in vertebrate cells and confirm that survivin represents a chromosomal passenger protein.
The Protein Tyrosine Phosphatase PTP-BL Associates with the Midbody and Is Involved in the Regulation of Cytokinesis
Authors: Herrmann Lutz , Dittmar Thomas , Erdmann Kai S.
Published: January 2003

PTP-BL is a highly modular protein tyrosine phosphatase of unknown function. It consists of an N-terminal FERM domain, five PDZ domains, and a C-terminally located tyrosine phosphatase domain. Here we show that PTP-BL is involved in the regulation of cytokinesis. We demonstrate localization of endogenous PTP-BL at the centrosomes during inter- and metaphase and at the spindle midzone during anaphase. Finally PTP-BL is concentrated at the midbody in cytokinesis. We show that PTP-BL is targeted to the midbody and centrosome by a specific splicing variant of the N-terminus characterized by an insertion of 182 amino acids. Moreover, we demonstrate that the FERM domain of PTP-BL is associated with the contractile ring and can be cosedimented with filamentous actin, whereas the N-terminus can be cosedimented with microtubules. We demonstrate that elevating the expression level of wild-type PTP-BL or expression of PTP-BL with an inactive tyrosine phosphatase domain leads to defects in cytokinesis and to the generation of multinucleate cells. We suggest that PTP-BL plays a role in the regulation of cytokinesis.
Yeast Glycogen Synthase Kinase-3 Activates Msn2p-dependent Transcription of Stress Responsive Genes
Authors: Hirata Yuzoh , Andoh Tomoko , Asahara Toshimasa , Kikuchi Akira
Published: January 2003

The yeast Saccharomyces cerevisiae has four genes,MCK1, MDS1 (RIM11),MRK1, and YOL128c, that encode homologues of mammalian glycogen synthase kinase 3 (GSK-3). A gsk-3null mutant in which these four genes are disrupted showed growth defects on galactose medium. We isolated several multicopy suppressors of this growth defect. Two of them encoded Msn2p and phosphoglucomutase (PGM). Msn2p is a transcription factor that binds to the stress-response element (STRE). PGM is an enzyme that interconverts glucose-1 phosphate and glucose-6 phosphate and is regulated by Msn2p at the transcriptional level. Expression of the mRNAs ofPGM2 and DDR2, whose promoter regions possess STRE sequences, on induction by heat shock or salt stress was reduced not only in an msn2 msn4 (msn2homologue) double mutant but also in the gsk-3 null mutant. STRE-dependent transcription was greatly inhibited in thegsk-3 null mutant or mck1 mds1 double mutant, and this phenotype was suppressed by the expression of Mck1p but not of a kinase-inactive form of Mck1p. Although Msn2p accumulated in the nucleus of the gsk-3 null mutant as well as in the wild-type strain under various stress conditions, its STRE-binding activity was reduced in extracts prepared from the gsk-3null mutant or mck1 mds1 double mutant. These results suggest that yeast GSK-3 promotes formation of a complex between Msn2p and DNA, which is required for the proper response to different forms of stress. Because neither Msn2p–GSK-3 complex formation nor GSK-3–dependent phosphorylation of Msn2p could be detected, the regulation of Msn2p by GSK-3 may be indirect.