First Principles Investigation on the Ultra-Incompressible and Hard TaN

The structural, electronic, and mechanical properties of TaN were investigated by use of the density functional theory (DFT). Eight structures were considered, i.e.. hexagonal WC TaN, NiAs, wurtzite, and CoSn structures. cubic NaCl. zinc-blende and CsCl structures. The results indicate that TaN in TaN-type structure is the most stable at ambient conditions among the considered structures. Above 5 GPa, TaN in WC-type structure becomes energetically the most stable phase. They are also stable both thermodynamically and mechanically. TaN in WC-type has the largest shear Modulus 243 GPa and large bulk modulus 337 GPa among the considered structures. The Volume compressibility is slightly larger than diamond, but smaller than c-BN at pressures from 0 to 100 GPa. The compressibility along the c axis is smaller than the linear compressibility of both diamond and c-BN.

Vacuum-deposited submonolayer thin films of a three-ring bent-core compound

Submonolayer thin films of a three-ring bent-core (that is, banana-shaped) compound, m-bis(4-n-octyloxystyryl)benzene (m-OSB), were prepared by the vacuum-deposition method, and their morphologies, structures, and phase behavior were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The films have island shapes ranging from compact elliptic or circular patterns at low temperatures (below 40 degreesC) to branched patterns at high temperatures (above 60 degreesC). This shape evolution is contrary to the prediction based on the traditional diffusion-limited aggregation (DLA) theory. AFM observations revealed that two different mechanisms governed the film growth, in which the compact islands were formed via a dewetting-like behavior, while the branched islands diffusion-mediated. It is suggested m-OSB forms a two-dimensional, liquid crystal at the low-temperature substrate that is responsible for the unusual formation of compact islands. All of the monolayer islands are unstable and apt to transform to slender bilayer crystals at room temperature. This phase transition results from the peculiar molecular shape and packing of the bent-core molecules and is interpreted as escaping from macroscopic net polarization by the formation of an antiferroelectric alignment.

Heterojunction ambipolar organic transistors fabricated by a two-step vacuum-deposition process

Ambipolar organic field-effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two-step vacuum-deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 degrees C) acts as the first (p-type component) layer, and hexadecafluorophthalocyaninatocopper (F16CuPc) deposited at room temperature (25 degrees C) acts as the second (n-type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10(-4) cm(2) V-1 s(-1) in air. Conductive channels are at the interface between the F16CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F16CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin-film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum-deposition process.

Characterization and thermodynamic study of ultra-fine particle of Ni-B amorphous alloy

Ultra-fine particle of Ni-B amorphous alloy was prepared by chemical reduction of Ni2+ with NaBH4 and characterized with TEM and XRD. The heat capacity and thermal stability were measured with a high-precision automatic adiabatic calorimeter and DTA. The upper limit of applied temperature of the substance was found to be 684 K for use as catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.

XRD and XPS studies on the ultra-uniform Raney-Ni catalyst prepared from the melt-quenching alloy

We present a novel method for preparing an ultra-uniform Raney-Ni catalyst, which includes melt-quenching, hydrogen treatment and leaching in an alkali solution. The resultant catalyst shows superior activity in the reaction of cyclohexanone hydrogenation. X-ray diffraction (XRD) and XPS have been employed to characterize the catalysts. As demonstrated, the pretreatment with hydrogen caused a distinct phase transfer of the Ni-Al alloys, forming more of the Ni2Al3 component. In the subsequent leaching process, the Ni2Al3 component shows high activity and the resultant catalyst exhibits high surface areas and small pores. Moreover, metallic Al in the hydrogen-pretreated alloy appeared to be leached more easily and thus the aluminium species remaining on the catalyst surface is aluminium oxide predominantly, which serves as a matrix to stabilize active Ni species on the surface. Copyright (C) 2001 John Wiley & Sons, Ltd.

Macro-Micro Modelling Analysis for High Density Packaged Flip Chips

A wide range of flip chip technologies with solder or adhesives have become dominant solutions for high density packaging applications due to the excellent electrical performance, high I/O density and good thermal performance. This paper discusses the use of modeling technique to predict the reliability of high density packaged flip chips in the humid environment. Reliability assessment is discussed for flip chip package at ultra-fine pitch with anisotropic conductive film (ACF). The purpose of this modeling work is to understand the role that moisture plays in the failure of ACF flip chips. A macro-micro 3D finite element modeling technique was used in order to make the multi-length-scale modeling of the ACF flip chip possible. Modeling results are consistent with the findings in the experimental work

Vacuum arc remelting time dependent modelling

Vacuum arc remelting (VAR) aims at production of high quality, segregation-free alloys. The quality of the produced ingots depends on the operating conditions which could be monitored and analyzed using numerical modelling. The remelting process uniformity is controlled by critical medium scale time variations of the order 1-100 s, which are physically initiated by the droplet detachment and the large scale arc motion at the top of liquid pool [1,2]. The newly developed numerical modelling tools are addressing the 3-dimensional magnetohydrodynamic and thermal behaviour in the liquid zone and the adjacent ingot, electrode and crucible.

Impulsive electric fields driven by high-intensity interactions

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing.

An experiment for two-color photoionization using high intensity extreme-UNT free electron and near-IR laser pulses

We describe an experimental system designed for single-shot photoelectron spectroscopy on free atoms and molecules at the Free Electron Laser in Hamburg (FLASH at DESY). The combination of the extreme ultra-violet (EUV) Free Electron Laser and a temporally synchronized optical fs laser (Ti:Sapphire) enables a variety of two-color pump-probe experiments. The spectral, temporal and spatial characteristics of both the EUV FEL and the optical laser pulses, the experimental procedure to control their overlap as well as the performance of an electron spectrometer used to obtain single-shot photoelectron spectra are discussed. As an illustration of the capabilities of this set-up, some results on two-photon two-color ionization of rare gases are presented. (c) 2007 Elsevier B.V. All rights reserved.

Wasp-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit

We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses, but 1.5-2 Jupiter radii, giving a density of 6%-14% that of Jupiter. WASP-17b is in a 3.7 day orbit around a sub-solar metallicity, V = 11.6, F6 star. Preliminary detection of the Rossiter-McLaughlin effect suggests that WASP-17b is in a retrograde orbit (? ˜ -150°), indicative of a violent history involving planet-planet or star-planet scattering. WASP-17b's bloated radius could be due to tidal heating resulting from recent or ongoing tidal circularization of an eccentric orbit, such as the highly eccentric orbits that typically result from scattering interactions. It will thus be important to determine more precisely the current orbital eccentricity by further high-precision radial velocity measurements or by timing the secondary eclipse, both to reduce the uncertainty on the planet's radius and to test tidal-heating models. Owing to its low surface gravity, WASP-17b's atmosphere has the largest scale height of any known planet, making it a good target for transmission spectroscopy.

Ultra-bright Optical Transients are Linked with Type Ic Supernovae

Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous optical transients. The initial discoveries of SN 2005ap by the Texas Supernova Search and SCP-06F6 in a deep Hubble pencil beam survey were followed by the Palomar Transient Factory confirmation of host redshifts for other similar transients. The transients share the common properties of high optical luminosities (peak magnitudes similar to -21 to -23), blue colors, and a lack of H or He spectral features. The physical mechanism that produces the luminosity is uncertain, with suggestions ranging from jet-driven explosion to pulsational pair instability. Here, we report the most detailed photometric and spectral coverage of an ultra-bright transient (SN 2010gx) detected in the Pan-STARRS 1 sky survey. In common with other transients in this family, early-time spectra show a blue continuum and prominent broad absorption lines of O II. However, about 25 days after discovery, the spectra developed type Ic supernova features, showing the characteristic broad Fe II and Si II absorption lines. Detailed, post-maximum follow-up may show that all SN 2005ap and SCP-06F6 type transients are linked to supernovae Ic. This poses problems in understanding the physics of the explosions: there is no indication from late-time photometry that the luminosity is powered by Ni-56, the broad light curves suggest very large ejected masses, and the slow spectral evolution is quite different from typical Ic timescales. The nature of the progenitor stars and the origin of the luminosity are intriguing and open questions.

How crucial is back gate misalignment/oversize in double gate MOSFETs for ultra-low-voltage analog/rf applications?

In the present work, by investigating the influence of source/drain (S/D) extension region engineering (also known as gate-underlap architecture) in planar Double Gate (DG) SOI MOSFETs, we offer new design insights to achieve high tolerance to gate misalignment/oversize in nanoscale devices for ultra-low-voltage (ULV) analog/rf applications. Our results show that (i) misaligned gate-underlap devices perform significantly better than DC devices with abrupt source/drain junctions with identical misalignment, (ii) misaligned gate underlap performance (with S/D optimization) exceeds perfectly aligned DG devices with abrupt S/D regions and (iii) 25% back gate misalignment can be tolerated without any significant degradation in cut-off frequency (f(T)) and intrinsic voltage gain (A(VO)). Gate-underlap DG devices designed with spacer-to-straggle ratio lying within the range 2.5 to 3.0 show best tolerance to misaligned/oversize back gate and indeed are better than self-aligned DG MOSFETs with non-underlap (abrupt) S/D regions. Impact of gate length and silicon film thickness scaling is also discussed. These results are very significant as the tolerable limit of misaligned/oversized back gate is considerably extended and the stringent process control requirements to achieve self-alignment can be relaxed for nanoscale planar ULV DG MOSFETs operating in weak-inversion region. The present work provides new opportunities for realizing future ULV analog/rf design with nanoscale gate-underlap DG MOSFETs. (C) 2008 Elsevier Ltd. All rights reserved.

MeV negative ion generation from ultra-intense laser interaction with a water spray

MeV negative oxygen ions are obtained from a water spray target irradiated by high intensity (5 x 10(19) W/cm(2)) and ultrashort (50 fs) laser pulses. Generation of negative ions is ascribed to electron-capture processes that the laser-accelerated high-energy positive ion experiences when it interacts with atoms in the spray. This mechanism implies the existence of a large number of MeV neutral oxygen atoms, which is consistent with indirect experimental evidence. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622664]

High contrast plasma mirror: spatial filtering and second harmonic generation at 10(19)Wcm(-2)

Recently, the use of plasma optics to improve temporal pulse contrast has had a remarkable impact on the field of high- power laser-solid density interaction physics. Opening an avenue to previously unachievable plasma density gradients in the high intensity focus, this advance has enabled researchers to investigate new regimes of harmonic generation and ion acceleration. Until now, however, plasma optics for fundamental laser reflection have been used in the sub-relativistic intensity regime (10(15) - 10(16)Wcm(-2)) showing high reflectivity (similar to 70%) and good focusability. Therefore, the question remains as to whether plasma optics can be used for such applications in the relativistic intensity regime (> 10(18)Wcm(-2)). Previous studies of plasma mirrors (PMs) indicate that, for 40 fs laser pulses, the reflectivity fluctuates by an order of magnitude and that focusability of the beam is lost as the intensity is increased above 5 x 10(16)Wcm(-2). However, these experiments were performed using laser pulses with a contrast ratio of similar to 10(7) to generate the reflecting surface. Here, we present results for PM operation using high contrast laser pulses resulting in a new regime of operation - the high contrast plasma mirror (HCPM). In this regime, pulses with contrast ratio > 10(10) are used to form the PM surface at > 10(19)Wcm(-2), displaying excellent spatial filtering, reflected near- field beam profile of the fundamental beam and reflectivities of 60 +/- 5%. Efficient second harmonic generation is also observed with exceptional beam quality suggesting that this may be a route to achieving the highest focusable harmonic intensities. Plasma optics therefore offer the opportunity to manipulate ultra-intense laser beams both spatially and temporally. They also allow for ultrafast frequency up-shifting without detrimental effects due to group velocity dispersion (GVD) or reduced focusability which frequently occur when nonlinear crystals are used for frequency conversion.