bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of chloroplast translation: interactions of RNA elements, RNA-binding proteins and the plastid ribosome
Authors: Manuell A. , Beligni M.V. , Yamaguchi K. , Mayfield S.P.
Published: August 2004

Chloroplast gene expression is primarily controlled during the translation of plastid mRNAs into proteins, and genetic studies have identified cis-acting RNA elements and trans-acting protein factors required for chloroplast translation. Biochemical analysis has identified both general and specific mRNA-binding proteins as components of the regulation of chloroplast translation, and has revealed that chloroplast translation is related to bacterial translation but is more complex. Utilizing proteomic and bioinformatic analyses, we have identified the proteins that function in chloroplast translation, including a complete set of chloroplast ribosomal proteins, and homologues of the 70 S initiation, elongation and termination factors. These analyses show that the translational apparatus of chloroplasts is related to that of bacteria, but has adopted a number of eukaryotic mechanisms to facilitate and regulate chloroplast translation.
Translation inhibition during the induction of apoptosis: RNA or protein degradation?
Authors: Bushell M. , Stoneley M. , Sarnow P. , Willis A.E.
Published: August 2004

The induction of apoptosis leads to a substantial inhibition of protein synthesis. During this process changes to the translation-initiation factors, the ribosome and the cellular level of mRNA have been documented. However, it is by no means clear which of these events are necessary to achieve translational shutdown. In this article, we discuss modifications to the translational apparatus that occur during apoptosis and examine the potential contributions that they make to the inhibition of protein synthesis. Moreover, we present evidence that suggests that a global increase in the rate of mRNA degradation occurs before the caspase-dependent cleavage of initiation factors. Increased mRNA decay is temporally correlated with the shutdown of translation and therefore plays a major role in the inhibition of protein synthesis in apoptotic cells.
Mechanism of substrate recognition by Hsp70 chaperones
Authors: Erbse A. , Mayer M.P. , Bukau B.
Published: August 2004

The role of Hsp70 (heat-shock protein 70) chaperones in assisting protein-folding processes relies on their ability to associate with short peptide stretches of protein substrates in a transient and ATP-controlled manner. In the present study, we review the molecular details of the mechanism behind substrate recognition by Hsp70 proteins.
Heat-shock protein 70 and heat-shock protein 90 associate with Toll-like receptor 4 in response to bacterial lipopolysaccharide
Authors: Triantafilou M. , Triantafilou K.
Published: August 2004

Mammalian responses to bacterial LPS (lipopolysaccharide) from the outer membrane of Gram-negative bacteria can lead to an uncontrolled inflammatory response that can be deadly for the host. It has been shown that the innate immune system employs at least three cell surface receptors, CD14, TLR4 (Toll-like receptor 4) and MD-2, in order to recognize bacterial LPS. In our previous work we have found that Hsps (heat-shock proteins) are also involved in the innate recognition of bacterial products. Their presence on the cell surface, as well as their involvement in the innate recognition process, are poorly understood. In the present study we have investigated the association of TLR4 with Hsp70 and Hsp90 following LPS stimulation, both on the cell surface and intracellularly. Our results show that Hsp70 and Hsp90 form a cluster with TLR4 within lipid microdomains following LPS stimulation. In addition, Hsp70 and Hsp90 seem to be involved in TLR4/LPS trafficking and targeting to the Golgi apparatus, since upon LPS stimulation we found that both Hsps are targeted to the Golgi along with TLR4. The present study sheds new light into the involvement of Hsps in the innate immune response.
Role of AIP and its homologue the blindness-associated protein AIPL1 in regulating client protein nuclear translocation
Authors: Spuy J. van der , Cheetham M.E.
Published: August 2004

Mutations in the AIPL1 (aryl hydrocarbon receptor interacting protein-like 1) cause the blinding disease Leber's congenital amaurosis. AIPL1 is a homologue of the AIP. AIP functions as part of a chaperone heterocomplex to facilitate signalling by the AhR and plays an important role in regulating the nuclear translocation of the receptor. We review the evidence for the role of AIP in protein translocation and compare the potential functions of AIPL1 in the translocation of its interacting partner the NEDD8 ultimate buster protein 1.
Paradigm Wars: Ceasefire Announced who Will set up the New Administration?†
Authors: Mingers J
Published: August 2004

This paper presents a personal overview of the history of the IS discipline over the last 20 years. It highlights two particular strands of development over which there has been much controversy - the so-called paradigm wars which were an epistemological battle between positivism and interpretivism; and the related debate over a critical approach to information systems. It is argued that the battle has died down and a period of stability has emerged. But further development needs to occur, especially in the area of critical management, and the philosophy of critical realism can be a significant way forward.
Effects of anisotropic k·p interactions on energy bands and optical properties of type-II interband cascade lasers
Authors: Mu Yao-Ming , Pei S. S.
Published: August 2004

The validity of an eight-band k·p method with the axial approximation for modeling the band structures and optical properties of type-II interband cascade lasers is assessed by comparing its results with those from the standard eight-band k·p method. Explicit expressions for anisotropic k·p interaction terms, which are neglected by the axial approximation, are obtained. Then the band structures and optical properties of practical type-II interband cascade lasers are calculated using both eight-band k·p methods and the numerical results are discussed in detail. It is found that the axial approximation may be problematical for the simulation of type-II interband cascade lasers.
Electrical characterization of amorphous silicon nanoparticles
Authors: Shen Z. , Kortshagen U. , Campbell S. A.
Published: August 2004

Electrical contact to amorphous silicon nanoparticles was established with a method that self aligns the contacts to the particles. Charge transport characteristics were studied as a function of temperature and voltage. The conduction in these devices was not limited by the metal∕semiconductor barrier; rather it was limited by charge trapping in the particles themselves. The data are well fit to theory. It was shown that the space charge limited current (SCLC) model fits the medium voltage range (2–6V), while space charged limited current with Frenkel–Poole effect fits the relatively high voltage range (5–8V). Using a model for space charge limited current in the presence of an exponential distribution of traps, we estimate that the trap density is 2×1019cm−3. Based on SCLC enhanced with Frenkel–Poole effect, the activation energy measured at high voltage was determined to 0.44eV. This agrees well with the medium voltage activation energy, 0.41eV.
Time-dependent inelastic deformation of shocked soda-lime glass
Authors: Simha C. Hari Manoj , Gupta Y. M.
Published: August 2004

Plate impact experiments were carried out to understand inelastic deformation in soda-lime glass shocked between 3 and 10.8GPa. In-material, wave profile measurements were obtained using longitudinal and lateral stress gauges (4.6–10.8GPa), and electromagnetic particle velocity gauges (2.9–6GPa) at comparable sample thicknesses. The 4.6 and 6GPa experiments revealed time-dependent material inelastic response along with time-dependent loss of material strength. Because of the unsteady, two wave structure observed in the longitudinal wave profiles in conjunction with the time-dependent changes in the lateral stress data, previous interpretations of the shocked soda-lime glass response in terms of a propagating failure wave are not valid. At higher peak stresses (∼10GPa), the experimental results do not display time-dependent strength loss. The shock wave response of soda-lime glass over the 4–10GPa range is complex, and material strength and inelastic deformation features depend significantly on the peak stress. Using the experimental results, a phenomenological continuum model incorporating the various material phenomena was developed. Wave profile simulations using the continuum model show reasonable overall agreement with the experimental profiles at different stress levels. Because of the approximate nature of the continuum model, all of the experimental details were not reproduced in the wave propagation simulations. It is likely that around and above 10GPa, other material phenomena not included in our model may need to be considered.
Analysis of the calibration methods and error propagation for the sensitivity S and the cooling time constant τc of the gold metal foil bolometers
Authors: Murari A. , Cecconello M. , Marrelli L. , Mast K. F.
Published: August 2004

Bolometers are radiation sensors designed to have a spectral response as constant as possible in the region of interest. In high-temperature plasmas, the main radiation output is in the ultraviolet and SXR part of the spectrum and the metal foil bolometers are special detectors developed for this interval. For such sensors, as in general for all bolometers, the absolute calibration is a crucial issue. This problem becomes particularly severe when, like in nuclear fusion, the sensors are not easily accessible. In this article, a detailed description of the in situ calibration methods for the bolometer sensitivity S and the cooling time τc, the two essential parameters characterizing the behavior of the sensor, is provided and an estimate of the uncertainties for both constants is presented. The sensitivity S is determined via an electrical calibration, in which the effect of the cables connecting the bolometers to the powering circuitry is taken into account leading to an effective estimate for S. Experimental measurements confirming the quality of the adopted coaxial cable modelling are reported. The cooling time constant τc is calculated via an optical calibration, in which the bolometer is stimulated by a light-emitting diode. The behavior of τc in a broad pressure range is investigated, showing that it does not depend upon this quantity up until 10−2 mbar, well above the standard operating conditions of many applications. The described methods were tested on 36 bolometric channels of RFX tomography, providing a significant statistical basis for present applications and future developments of both the calibration procedures and the detectors.
Morphological instability of NiSi1−uGeu on single-crystal and polycrystalline Si1−xGex
Authors: Seger J. , Jarmar T. , Zhang Z.-B. , Radamson H. H. , Ericson F. , Smith U. , Zhang S.-L.
Published: August 2004

The morphological stability of NiSi1−uGeu ternary alloy films formed by reacting Ni with single-crystal (sc) and polycrystalline (poly) Si1−xGeu is studied (u can be different from x). The agglomeration of NiSi1−uGeu films on Si0.7Ge0.3 occurs at 550°C after rapid thermal processing for 30 s, independently of the crystallinity of the Si1−xGeu. This behavior distinctly different from NiSi: NiSi films on poly-Si display a poorer morphological stability and degrade at lower temperatures than NiSi on sc-Si. On strained Si1−xGex, the presence of Ge simultaneously gives rise to two effects of different origin: mechanical and thermodynamic. The main driving forces behind the agglomeration of NiSi1−uGeu on sc-Si1−xGex are found to be the stored strain energy in the Si1−xGex and the larger (absolute) free energy of formation of NiSi compared to NiGe. The latter constitutes the principal driving force behind the agglomeration of NiSi1−uGeu on poly-Si1−xGex and is not affected by the degree of crystallinity of Si1−xGex. The total free-energy change also includes terms corresponding to the entropy of mixing of Si and Ge in both Si1−xGex and NiSi1−uGeu. Calculations show that the strain energy and the total free-energy change can be 5–7 times (with 30at.% Ge) the surface/interface and grain-boundary energies in a NiSi film or the grain-boundary energy in an underlying poly-Si. These latter energies are responsible for the agglomeration of NiSi on sc- and poly-Si. The agglomeration takes place primarily via the interdiffusion of Si and Ge between Si1−xGex and NiSi1−uGeu. A structure likely to improve the stability of NiSi1−uGeu∕Si1−xGex is discussed.
Finite element analysis of valence band structures in quantum wires
Authors: Park Seoung-Hwan , Ahn Doyeol , Lee Yong-Tak
Published: August 2004

Valence band structures with spin-orbit (SO) coupling of quantum wires (QWRs), are investigated using the multiband effective-mass theory by a calculation procedure based on a finite-element method (FEM). The results are also compared to those obtained by finite difference method (FDM) and obtained by FEM without SO coupling. We expect FEM and FDM methods to give similar results, but the FDM has a limitation in dealing with various quantum wire shapes. In the case of QWR with small strains, the SO coupling effect does not greatly change subband energies and the trends of the subband dispersions. On the other hand, in the case of QWR with large strains, the subband energies of all states including the first state are considerably affected by the SO coupling. The amplitudes of the heavy-hole and light-hole wave functions have nonzero mixings even at the zone center (ky=0) in contrast to the case of quantum wells. It is found that the matrix elements for the TE polarization greatly increase due to the SO coupling effect.
Configuration and calibration of pickup coils for measurement of ac loss in long superconductors
Authors: Yang Y. , Martínez E. , Norris W. T.
Published: August 2004

Pickup coils are widely used for measurements of magnetic susceptibility and hysteretic losses in magnetic and superconducting materials. A general formulation for the calibration of such pickup coils with different geometries is presented. Although the procedure described here is general and can be applied to any coil and sample, special emphasis has been placed on the calibration of saddlelike coils usually used to measure ac losses of long superconductors under ac fields perpendicular to their long dimension. Numerical simulations and experimental measurements have been carried out in order to determine the geometrical limitations of the pickup coil/sample configurations. This is especially important when simple coils of small dimensions and number of turns are used and/or samples of high demagnetization factor are measured. Superconductors of different geometry, in particular, wires and tapes under parallel and perpendicular fields, have been analyzed.
Short channel effects in regioregular poly(thiophene) thin film transistors
Authors: Chabinyc Michael L. , Lu Jeng-Ping , Street Robert A. , Wu Yiliang , Liu Ping , Ong Beng S.
Published: August 2004

The effects of the physical channel length on the current-voltage characteristics of thin film transistors (TFTs) made with poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] were examined. Coplanar transistors with fully patterned electrodes on insulating substrates and with a common gate structure on thermal oxide were fabricated. The output characteristics of TFTs with channel lengths shorter than 10μm showed the presence of a parasitic contact resistance and the lack of current saturation. The origin of these nonidealities was examined by the application of models that included self-heating effects and breakdown of the channel region at high applied biases. The analysis suggests that carriers can break away from the channel at high bias voltages and flow through a bulk region of the semiconducting film leading to higher currents than otherwise expected.
The influence of cluster formation on the photodissociation of sulfur dioxide: Excitation to the E state
Authors: Knappenberger K. L. , Castleman A. W.
Published: August 2004

A femtosecond pump-probe technique was employed to study the dissociation dynamics of sulfur dioxide and sulfur dioxide clusters in real time. Dissociation is initiated by a multiphoton scheme that populates the E state. The SO2+ transient is fit to a biexponential decay comprising a fast and a slow component of 230 fs and 8 ps, respectively. The SO+ transient consists of a growth component of 225 fs as well as a subsequent decay of 373 fs. The pump-probe response obtained from the monomer clearly shows the predissociative cleavage of a S–O bond. Upon cluster formation, a sequential increase in the fast decay component is observed for increasing cluster size, extending to 435 fs for (SO2)4+. The transient response of cluster dissociation products SO(SO2)n+, where n=1–3, reflects no growth component indicating that formation proceeds through the ion state. Therefore, cluster formation results in a caging effect, which impedes the dissociation process. Further direct evidence for our proposed mechanism is obtained by a technique that employs a comparison of the amplitude coefficients of each respective component of the fit. This method makes possible the determination of branching ratios of competing relaxation processes and thereby the influence of cluster formation on each can be resolved. The caging effect is attributed to a steric hindrance placed on the SO2 chromophore, preventing it from attaining a linear geometry necessary for dissociation.
Fully printed integrated circuits from solution processable polymers
Authors: Knobloch A. , Manuelli A. , Bernds A. , Clemens W.
Published: August 2004

The discovery of (semi) conducting polymers opened a route to the fabrication of microelectronics by printing. We designed structural and electrical properties of printed polymeric thin films and multilayers to set up field-effect transistors. The polymeric transistors are fully logic capable as is proven by persistent operation of an integrated ring-oscillator circuit. Solution processing of the polymers in printing is completely done under ambient conditions resulting in stable operation of the printed transistors and microcircuits.
Hole mobility in organic single crystals measured by a “flip-crystal” field-effect technique
Authors: Goldmann C. , Haas S. , Krellner C. , Pernstich K. P. , Gundlach D. J. , Batlogg B.
Published: August 2004

We report on single crystal high mobility organic field-effect transistors prepared on prefabricated substrates using a “flip-crystal” approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the field-effect transistors' electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of 10.7, 1.3, and 1.4cm2∕Vs have been measured on rubrene, tetracene, and pentacene single crystals, respectively. Four-terminal measurements allow for the extraction of the “intrinsic” transistor channel resistance and the parasitic series contact resistances. The technique employed in this study shows potential as a general method for studying charge transport in field-accumulated carrier channels near the surface of organic single crystals.
Nonlinear anisotropic description for shocked single crystals: Thermoelastic response and pure mode wave propagation
Authors: Winey J. M. , Gupta Y. M.
Published: August 2004

An anisotropic continuum framework for describing the nonlinear thermoelastic response of shocked single crystals has been developed. Using this framework, the propagation of large amplitude stress waves along arbitrary directions in crystals of any symmetry can be examined. We developed an incremental approach, where the reference state for the dynamical variables and the material properties is updated throughout the calculation. Results from our incremental approach are in excellent agreement with the results from a finite strain formulation. Using a finite-difference wave propagation code, we performed numerical simulations of large amplitude elastic wave propagation in single crystals. Results of impact loading simulations for quartz and sapphire single crystals are presented. The framework developed was also useful for examining the propagation of pure mode nonlinear waves for various crystal symmetries. Our calculations showed that pure longitudinal waves resulted from impact loading along any rotational symmetry axis for all crystal symmetry classes. Differences between pure mode wave propagation for linear and nonlinear elastic deformation are discussed.
Dipole scattering in highly polar semiconductor alloys
Authors: Zhao Wei , Jena Debdeep
Published: August 2004

The wide gap polar semiconductors III-V nitrides, II-VI oxides, and ferroelectrics exhibit large spontaneous and piezoelectric polarization due to their nonsymmetric crystal structures. Electrical conductivity in alloys of such crystals is degraded by scattering from the varying polarization coupled to alloy disorder. We have modeled this effect by dipole scattering. We have calculated dipole scattering limited mobility in the relaxation time approximation of the Boltzmann equation. The results are applied to AlxGa1−xN layers coherently strained on GaN. For a typical carrier concentration of 1018(cm−3) in Al0.3Ga0.7N, dipole scattering limited mobilities are 2535 and 3420(cm2∕Vs) at 300 and 77K, respectively. Applying our results to ferroelectric alloys, we reach the interesting conclusion that dipole scattering in such alloys will lead to extremely low mobilities (1–10cm2∕Vs), since it degrades as the square of average dipole moment. This leads us to suggest that digital alloy growth might be necessary to achieve high conductivities in highly polar wide gap alloy semiconductors and ferroelectrics for device applications.
Anisotropic materials: A way to increase the efficiency of magnetic refrigeration
Authors: Lima A. L. , Gschneidner K. A. , Pecharsky V. K.
Published: August 2004

A breakthrough step in the development of magnetic refrigeration would be to find a way to increase the cooling capacity of the magnetic refrigerant material in order to make this technology even more energy efficient. In this paper, we present a theoretical study which shows how to increase the refrigerant capacity using anisotropic materials. We examine some of the well-known Laves phase compounds that can be described by a Hamiltonian which includes second order and spin reorientation effects. Our results indicate that in some cases it is theoretically possible to increase cooling capacity by up to ∼65%.
Structural and surface potential characterization of annealed HfO2 and (HfO2)x(SiO2)1-x films
Authors: Ludeke R. , Gusev E.
Published: August 2004

The evolution of the microscopic electrical properties of hafnium oxide and hafnium silicate films with high temperature anneals and their relationship to morphological changes is reported. The as-grown, amorphous 3nm thick HfO2 and 2.2nm thick Hf0.78Si0.22O2 layers were deposited ex situ on Si(100) by atomic layer deposition and metal organic vapor deposition, respectively, and annealed in situ in ultra high vacuum. A noncontact atomic force microscope operating in the electrostatic force mode was used to image the topography, contact potential difference (CPD), and differential capacitance. The as-grown and annealed films essentially retained their smoothness even after undergoing crystallization; rms roughness of ∼0.13nm for HfO2 and 0.077nm for the 900°C annealed Hf0.78Si0.22O2 layer were measured. These values compare favorably with state-of-the-art rapid thermal oxidation and nitrided SiO2 gate oxides. CPD or surface potential fluctuations of up to 0.3–0.4V were observed in images of area 200×200nm2; values that did not change appreciably with annealing. A lack of correlation between topographic and CPD image features for the as-grown amorphous samples changed dramatically once the films crystallized, with higher CPD values associated with grain boundaries for both oxide and silicate layers. CPD variations were about a factor of 2 larger than for SiO2 gate oxides. Differential capacitance images reflected mainly topographic surface features, as the high κ inhibits image contrast in the images for small to moderate changes in κ. Nevertheless, for the Hf0.78Si0.22O2 sample annealed at 900°C, which exhibited the lowest roughness, increase in differential capacitance could be attributed to microstructures of high-κ material, most likely HfO2, which phase separated during the anneal. Because of screening, the high κ dielectric also tends to suppress contributions of isolated charges to the CPD image. A spherical tip model is presented that supports these observations.
N
vacancy diffusion and trapping in Mg-doped wurtzite GaN
Authors: Wright A. F. , Mattsson T. R.
Published: August 2004

Density-functional theory has been used to investigate N vacancy (VN) diffusion in wurtzite GaN and VN complexes with a substitutional Mg acceptor (MgGaVN). Two VN diffusion paths were identified: a perpendicular path producing movement perpendicular to the c axis and a diagonal path producing movement both perpendicular and parallel to the c axis. The VN charge state was found to strongly influence the diffusion activation energies, which range from 2.49eV for VN+3 to 3.55eV for VN+1 along the perpendicular path and from 2.65eV for VN+3 to 3.96eV for VN+1 along the diagonal path. Two bound MgGaVN configurations were identified: a parallel configuration with VN located next to MgGa and along the c axis from it, and a perpendicular configuration with VN located next to MgGa and transverse to the c axis from it. The binding energies range from 0.29 to 0.58eV, depending on the MgGaVN configuration and charge state. The results were used to evaluate a recently proposed atomistic process [S. Hautakangas, J. Oila, M. Alatalo, and K. Saarinen, Phys. Rev. Lett. 90, 137402 (2003)], which involves MgGaVN dissociation and VN diffusion in wurtzite GaN.
Structure of star-burst dendrimers: A comparison between small angle x-ray scattering and computer simulation results
Authors: Rathgeber Silke , Pakula Tadeusz , Urban Volker
Published: August 2004

We investigated the generation dependent shape and internal structure of star-burst dendrimers under good solvent conditions using small angle x-ray scattering and molecular modeling. Measurements have been performed on poly(amidoamine) dendrimers with generations ranging from g=0 up to g=8 at low concentrations in methanol. We described the static form factor P(q) by a model taking into account the compact, globular shape as well as the loose, polymeric character of dendrimers. Monomer distributions within dendrimers are of special interest for potential applications and have been characterized by the pair correlation function γ(r), as well as by the monomer and end-group density profile, ρ(r) and ρe(r), respectively. Monomer density profiles and γ(r) can be derived from P(q) by modeling and via a model independent approach using the inverse Fourier transformation algorithm first introduced by Glatter. Experimental results are compared with computer simulations performed for single dendrimers of various generations using the cooperative motion algorithm. The simulation gives direct access to γ(r) and ρ(r), allows an independent determination of P(q), and yields in addition to the scattering experiment information about the distribution of the end groups. Excellent qualitative agreement between experiment and simulation has been found.
Determination of the thickness of pulsed laser deposited cylindrical Co films by their magnetoelastic effects
Authors: Favieres C. , Madurga V.
Published: August 2004

Soft magnetic Co films, with a grain size of 1–2nm and thickness between ≈1.3 and tens of nanometers were pulsed laser deposited on rotating metallic wire substrates, conferring them cylindrical geometry. These films showed a magnetostrictive property, making it possible to measure and study the magnetoelastic inverse Wiedemann effect, (IWE) of the longitudinal magnetic flux in the film as a function of the circular applied magnetic field, Φz−Hϕ. The IWE of these films was explained by the assumption of magnetic wall nucleation and magnetization rotation processes. This explanation allowed us to establish the relation of Φz with the spontaneous magnetization Ms and with the film's thickness. Then using the measured Φz and the known value of Ms: (1) we determine the thickness of the film by means of an inductive method; (2) we analyze the inaccuracy of the determined film thickness; (3) we achieve the limit of tfilm,min=1.3±0.3nm in thickness for measuring the films’ magnetic properties.
A two-dimensional model of the deformation of photoresist structures using elastoplastic polymer properties
Authors: Yoshimoto K. , Stoykovich M. P. , Cao H. B. , de Pablo J. J. , Nealey P. F. , Drugan W. J.
Published: August 2004

A model was developed for predicting the collapse behavior of photoresist structures due to the drying of rinse liquids during wet chemical processing. The magnitude of the capillary forces was estimated using the classical thermodynamics of surface tension, and the deformation of the structure was modeled using beam bending mechanics that accounts for both elastic and plastic modes of deformation. The two-dimensional model can predict the critical beam height of collapse as a function of the wetting behavior of the rinse liquid on the beam, the elastic and plastic mechanical properties of the polymeric photoresist, and the beam dimensions. Collapse behavior was predicted for polymer nanostructures with elastoplastic mechanical properties similar to those of bulk poly(methyl methacrylate). We have compared the collapse predictions from our model with the results of models that account only for elastic or plastic deformation behavior. Regimes in the elastic-plastic mechanical property space for which it is necessary to use the developed beam bending model have been highlighted. It is shown that in some cases the inclusion of both elastic and plastic mechanical properties is necessary for modeling the collapse behavior of polymer beams fabricated using the lithographic process.
Modeling the effect of hydrogen infiltration on the asymmetry in arsenic-enhanced solid phase epitaxy in silicon
Authors: Johnson B. C. , McCallum J. C.
Published: August 2004

The kinetics of solid phase epitaxy (SPE) in surface amorphous silicon layers doped with a single arsenic profile have been examined in relation to the generalized Fermi level shifting model of the SPE growth process. The model has been extended to include passivation by hydrogen of the defects responsible for SPE and∕or passivation of dopant atoms. A previous study has suggested that the asymmetry between the dopant-enhanced SPE rate and the arsenic concentration profile is due to the infiltration of hydrogen from the surface oxide. Theoretical calculations of the dopant-enhanced SPE rate compare well with experiment if it is assumed that the indiffusing hydrogen passivates some of the SPE defects and∕or some of the dopant atoms.
Magnetic and electrical properties of Cr- and Ni-doped β-FeSi2 single crystals
Authors: Arushanov E. , Nenkov K. , Eckert D. , Vinzelberg H. , Rößler U. K. , Behr G. , Müller K.-H. , Schumann J.
Published: August 2004

The magnetization, magnetic susceptibility, and resistivity for Cr-doped p type and Ni-doped n type FeSi2 single crystals have been investigated. The values of the paramagnetic Curie temperature as well as the activation energy of the donor levels are estimated. It is also shown that the magnetization behavior of Cr- and Ni-doped samples significantly depends on the cooling regime: cooling in zero external field and cooling with external field. This resembles the properties of spin glasses and indicates the presence of coupling between magnetic centers. The results of resistivity measurements are analyzed within the framework of different hopping conductivity models. Both the Mott and the Shklovskii-Efros regime of the variable-range hopping is observed. The values of the characteristic and transition temperatures and the width of the Coulomb quasigap are determined.
A three-dimensional quantum simulation of silicon nanowire transistors with the effective-mass approximation
Authors: Wang Jing , Polizzi Eric , Lundstrom Mark
Published: August 2004

The silicon nanowire transistor (SNWT) is a promising device structure for future integrated circuits, and simulations will be important for understanding its device physics and assessing its ultimate performance limits. In this work, we present a three-dimensional (3D) quantum mechanical simulation approach to treat various SNWTs within the effective-mass approximation. We begin by assuming ballistic transport, which gives the upper performance limit of the devices. The use of a mode space approach (either coupled or uncoupled) produces high computational efficiency that makes our 3D quantum simulator practical for extensive device simulation and design. Scattering in SNWTs is then treated by a simple model that uses so-called Büttiker probes, which was previously used in metal-oxide-semiconductor field effect transistor simulations. Using this simple approach, the effects of scattering on both internal device characteristics and terminal currents can be examined, which enables our simulator to be used for the exploration of realistic performance limits of SNWTs.
Intermode conversion in a near-field optical fiber probe
Authors: Bakunov M. I. , Bodrov S. B. , Hangyo M.
Published: August 2004

The propagation of light in metal-coated fiber probes used in scanning near-field optical microscopy is studied computationally by means of the cross-section method. In contrast to previous work focusing on the behavior of the HE11 mode in the vicinity of the end aperture of the probe, we trace the propagation of the incident fundamental mode of the optical fiber through the tapered probe. The transformation of the fiber mode into the probe modes, intermode conversion, and modes cutoff are consistently calculated. In particular, it is shown that in the conventional gradual tapered probe only a few percent of the input power are transformed into the HE11 mode which has the smallest cutoff radius. In addition, an easily manufacturable modification of the shape of the probe’s tip that can provide a tenfold enhancement in optical near-field intensity has been proposed.
Influence of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells
Authors: Zheng X. H. , Chen H. , Yan Z. B. , Li D. S. , Yu H. B. , Huang Q. , Zhou J. M.
Published: August 2004

We reported the effect of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells (MQWs) by photoluminescence (PL) and high-resolution x-ray diffraction techniques. The MQW samples on (0001)-plane sapphire substrates were prepared with a ramping method by metalorganic chemical deposition. It was found that the structural or interface quality of the MQW system improved as the deposition time of barrier layers increased from 10 to 14min, but lattice relaxation was still observed. The relaxation degree decreases from 33% to 6% as the deposition time increases. Temperature-dependent PL measurements from 12 to 300K indicated that the integrated PL intensities start to decay rapidly as temperature rises above 50K for the sample with the shorter deposition time, and above 100K for the sample with the longer deposition time. The luminescence thermal quenching of the two samples suggests the two nonradiative recombination centers based on a fit to Arrhenius plot of the normalized integrated PL intensity over the entire temperature range. The first centers at higher temperatures show less difference for the two samples. The second centers at lower temperatures can be attributed to the trapping of carriers at the rough interface for the sample with the shorter deposition time and to the thermal quenching of bound excitons for the sample with the longer deposition time, respectively.
Photoluminescence characteristics of Pb-doped, molecular-beam-epitaxy grown ZnSe crystal layers
Authors: Mita Yoh , Kuronuma Ryoichi , Inoue Masanori , Sasaki Shoichiro , Miyamoto Yoshinobu
Published: August 2004

The characteristic green photoluminescence emission and related phenomena in Pb-doped, molecular-beam-epitaxy (MBE)-grown ZnSe crystal layers were investigated to explore the nature of the center responsible for the green emission. The intensity of the green emission showed a distinct nonlinear dependence on excitation intensity. Pb-diffused polycrystalline ZnSe was similarly examined for comparison. The characteristic green emission has been observed only in MBE-grown ZnSe crystal layers with moderate Pb doping. The results of the investigations on the growth conditions, luminescence, and related properties of the ZnSe crystal layers suggest that the green emission is due to isolated Pb replacing Zn and surrounded with regular ZnSe lattice with a high perfection.
Hybrid techniques for electrostatic analysis of nanoelectromechanical systems
Authors: Li Gang , Aluru N. R.
Published: August 2004

In this paper, we propose an efficient approach, namely the hybrid BIE/Poisson/Schrödinger approach, for electrostatic analysis of nanoelectromechanical systems. In this approach, the interior and the exterior domain electrostatics are described by Poisson’s equation (or Poisson’s equation coupled with Schrödinger’s equation when quantum-mechanical effects are dominant) and the boundary integral formulation (BIE) of the potential equation, respectively. We employ a meshless finite cloud method and a boundary cloud method to solve the coupled BIE/Poisson/Schrödinger’s equations self-consistently. The proposed approach significantly reduces the computational cost and provides a higher accuracy of the solution.
Low temperature growth of ultrananocrystalline diamond
Authors: Xiao X. , Birrell J. , Gerbi J. E. , Auciello O. , Carlisle J. A.
Published: August 2004

Ultrananocrystalline diamond (UNCD) films were prepared by microwave plasma chemical vapor deposition using argon-rich Ar∕CH4 plasmas at substrate temperatures from ∼400 to 800°C. Different seeding processes were employed to enhance the initial nucleation density for UNCD growth to about 1011sites∕cm2. High-resolution transmission electron microscopy, near-edge x-ray absorption fine structure, visible and ultraviolet Raman spectroscopy, and scanning electron microscopy were used to study the bonding structure as a function of growth temperature. The results showed that the growth of UNCD films is much less dependent on substrate temperature than for hydrogen-based CH4∕H2 plasmas. UNCD with nearly the same nanoscale structure as those characteristic of high-temperature deposition can be grown at temperatures as low as 400°C with growth rates of about 0.2μm∕hr. The average grain size increased to about 8nm from 3 to 5nm that is characteristic of high-temperature growth, but the relative amounts of sp3 and sp2 bonding remained unchanged. These results suggest that the activation energy for UNCD growth is about 2–3Kcal∕mole compared with ∼28kcal∕mole for traditional growth chemistries, and that hydrogen plays an important role in the growth of UNCD films using hydrogen-poor plasmas.
How do nanoislands induced by ion suputtering evolve during the early stage of growth?
Authors: Xu M. , Teichert C.
Published: August 2004

The early evolution of GaSb nanoislands induced by ion sputtering was investigated by high-resolution atomic force microscopy. The growth of maximal nanoisland height varies logarithmically with the root-mean-square (rms) roughness in the short-time regime, beyond which it scales as the roughness, as expected from recent theoretical calculation. This is attributed to the gradual evolution of the nanoislands prior to their full formation. Furthermore, it was found that the rms roughness goes through a maximum of ∼8.6nm before decreasing slightly with further sputtering to reach a constant value of 5–6nm. The evolution of the island ordering is slower than the full formation of the nanoislands. These findings cannot be explained by the present Kuramoto-Sivashinsky (KS) equation and∕or corresponding numerical simulation. We suggest that the more complicated KS equation, i.e., including the variation of the erosion term and its effect on the nonlinear behavior, should be considered to describe the evolution of the nanoislands induced by ion sputtering.
A low-temperature high-sensitivity torsion balance magnetometer with in situ stator adjustment
Authors: Matthews A. J. , Usher A. , Williams C. D. H.
Published: August 2004

Torsion balance magnetometry can be used as a versatile probe of two-dimensional electron systems. We have developed a highly sensitive magnetometer, utilizing capacitive proximity detection of the rotor position, for use at temperatures below 10 mK. The instrument incorporates two piezo-electric linear motors to enable the stator positions to be adjusted in situ at base temperature. The magnetometer responsivity is inversely proportional to the square of the rotor–stator separation and the novel linear motor technique, accompanied by effective vibration isolation and optimized capacitance bridge electronics, achieves a resolution 6.5×10−12 N m Hz−1/2. This resolution, together with the low temperatures attainable, allows for experiments that probe the family of quantum fluid states responsible for the fractional quantum Hall effect, even at filling factors greater than one.
Characterization of aluminum oxyfluoride barrier in magnetic tunnel junctions
Authors: Kim D. S. , Yu Y. Y. , Char K.
Published: August 2004

The electrical characteristics and the interface structure of magnetic tunnel junctions with aluminum oxyfluoride barrier were studied. Compared to conventional junctions with aluminum oxide tunnel barrier, junctions with aluminum oxyfluoride barrier exhibit larger and nearly constant tunneling magnetoresistance (TMR) values over a wide range of junction resistance and show a smaller bias dependence of TMR, a smaller temperature dependence of junction resistance, and higher effective barrier height. The cross sectional TEM image demonstrates that the junction with oxyfluoride barrier has excellent barrier flatness and smooth interfaces. X-ray photoelectron spectroscopy indicates that the fluorine forms an aluminum oxyfluoride barrier together with oxygen and that the growth of fluorine-rich oxyfluoride layer near the top surface of the barrier plays an important role in the formation of the highly insulating barrier, resulting in nearly ideal barrier/electrode interfaces without a detrimental magnetically dead layer.
Coupled cluster calculations of optical rotatory dispersion of (S)-methyloxirane
Authors: Tam Mary C. , Russ Nicholas J. , Crawford T. Daniel
Published: August 2004

Coupled cluster (CC) and density-functional theory (DFT) calculations of optical rotation, [α]λ, have been carried out for the difficult case of (S)-methyloxirane for comparison to recently published gas-phase cavity ringdown polarimetry data. Both theoretical methods are exquisitely sensitive to the choice of one-electron basis set, and diffuse functions have a particularly large impact on the computed values of [α]λ. Furthermore, both methods show a surprising sensitivity to the choice of optimized geometry, with [α]355 values varying by as much as 15 deg dm−1 (g/mL)−1 among molecular structures that differ only negligibly. Although at first glance the DFT/B3LYP values of [α]355 appear to be superior to those from CC theory, the success of DFT in this case appears to stem from a significant underestimation of the lowest (Rydberg) excitation energy in methyloxirane, resulting in a shift of the first-order pole in [α]λ (the Cotton effect) towards the experimentally chosen incident radiation lines. This leads to a fortuitous positive shift in the value of [α]355 towards the experimental result. The coupled cluster singles and doubles model, on the other hand, correctly predicts the position of the absorption pole (to within 0.05 eV of the experimental result), but fails to describe correctly the shape/curvature of the ORD region λ=355, resulting in an incorrect prediction of both the magnitude and the sign of the optical rotation.
Macroporous silicon membranes as electron and x-ray transmissive windows
Authors: Schilling J. , Scherer A. , Gösele U. , Kolbe M.
Published: August 2004

Macroporous silicon membranes are fabricated whose pores are terminated with 60nm thin silicon dioxide shells. The transmission of electrons with energies of 5kV–25kV through these membranes was investigated reaching a maximum of 22% for 25kV. Furthermore, the transmission of electromagnetic radiation ranging from the far-infrared to the x-ray region was determined. The results suggest the application of the membrane as window material for electron optics and energy dispersive x-ray detectors.
Order parameters of the liquid crystal interface layer at a rubbed polymer surface
Authors: Xuan Li , Tohyama Takeshi , Miyashita Tetsuya , Uchida Tatsuo
Published: August 2004

In this paper, the liquid crystal (LC) order parameters of the interface layers at rubbed polymer surfaces were studied. The LC films in this study were made with either polyvinyl alcohol or polyimide and the test LCs were filled into wedge-shaped cells for various measurements. The real distribution of order parameters from LC bulk to the interface was obtained by measuring the anisotropic infrared absorbance of sample films. It was found that the order parameters start to decrease where the LC layer thickness is smaller than 10nm, and the order parameter of LC monolayer at the rubbed polymer surface is only 1∕3–1∕2 of that of the LC bulk even in a strong rubbing condition. When the temperature was increased to the transition point, the LC interface layer (excluding the adsorption monolayer) completed the phase transition while the bulk layer remained in LC phase. This was a further evidence that the order parameter of the interface layer is lower than that of the bulk.
Lateral correlation of SiGe Stranski-Krastanow islands on silicon as probed by high resolution x-ray diffraction
Authors: Hanke M. , Schmidbauer M. , Köhler R.
Published: August 2004

We describe a procedure to consider the impact of lateral positional correlation of SiGe nanoscale islands onto the diffuse scattering within a high resolution x-ray diffraction experiment. The samples have been grown by means of liquid phase epitaxy which provides monodisperse island ensembles containing up to 109 equivalent objects. It is shown that a proper numerical simulation of the x-ray diffuse scattering pattern requires careful consideration of the partial coherence of x rays. An appropriate numerical procedure consists of coherent summation over sample areas with lateral dimensions as given by the coherence properties of the radiation and subsequent incoherent summation over a large enough number of such areas. For the given case an effective lateral coherence length of ≈1μm has been used, which is derived taking into account also the detector resolution. The according simulation is in good agreement with the experimentally observed x-ray diffuse intensity pattern.
Micro-Raman Study of Orientation Effects of CuxSe-Crystallites on Cu-rich CuGaSe2 Thin Films
Authors: Xue C. , Papadimitriou D. , Raptis Y. S. , Richter W. , Esser N. , Siebentritt S. , Lux-Steiner M. Ch.
Published: August 2004

The structural properties of copper selenide (CuxSe), formed as a secondary phase on the surface of CuGaSe2 films grown under Cu-rich conditions on GaAs (100) substrates, were studied by micro-Raman spectroscopy. Raman bands at 45 and 263cm−1, observed on crystallites dispersed on the CuGaSe2 film, are in agreement with the Raman modes of CuSe and Cu2Se. Polarization- and angular-dependent micro-Raman measurements reveal that the CuxSe-crystallites are grown with a preferential orientation on the CuGaSe2 surface.