Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

Samarium nickelate (SmNiO₃) thin films were successfully synthesized on LaAlO₃ and SrTiO₃ substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO₃ samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing.

Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications

In this work, we demonstrate a full process for fabricating high aspect ratio diffraction optics for extreme ultraviolet lithography. The transmissive optics consists in nanometer scale tungsten patterns standing on flat, ultrathin (100 nm) and highly transparent (>85% at 13.5 nm) silicon membranes (diameter of 1 mm). These tungsten patterns were achieved using an innovative pseudo-Bosch etching process based on an inductively coupled plasma ignited in a mixture of SF6 and C4F8. Circular ultra-thin Si membranes were fabricated through a state-of-the-art method using direct-bonding with thermal difference. The silicon membranes were sputter-coated with a few hundred nanometers (100-300 nm) of stress-controlled tungsten and a very thin layer of chromium. Nanoscale features were written in a thin resist layer by electron beam lithography and transferred onto tungsten by plasma etching of both the chromium hard mask and the tungsten layer. This etching process results in highly anisotropic tungsten features at room temperature. The homogeneity and the aspect ratio of the advanced pattern transfer on the membranes were characterized with scanning electron microscopy after focus ion beam milling. An aspect ratio of about 6 for 35 nm size pattern is successfully obtained on a 1 mm diameter 100 nm thick Si membrane. The whole fabrication process is fully compatible with standard industrial semiconductor technology.

Nonlocal effect of plasma resonances on the electron energy-distribution function in microwave plasma columns

Spatially resolved trace rare gases optical emission spectroscopy was used to analyze the electron energy-distribution function (EEDF) in low-pressure argon plasma columns sustained by surface waves. At frequencies >1 GHz, in the microwave-sustained region, the EEDF departs from a Maxwellian, characterized by a depletion of low-energy electrons and a high-energy tail, whereas in the field-free zone, the EEDF is Maxwellian. Abnormal behavior of the EEDF results from the acceleration of low-energy electrons due to the conversion of surface waves into volume plasmons at the resonance point where the plasma frequency equals the wave frequency and their absorption by either collisional or Landau damping.

Large Longitude Libration of Mercury Reveals a Molten Core

Observations of radar speckle patterns tied to the rotation of Mercury establish that the planet occupies a Cassini state with obliquity of 2.11 +/- 0.1 arc minutes. The measurements show that the planet exhibits librations in longitude that are forced at the 88-day orbital period, as predicted by theory. The large amplitude of the oscillations, 35.8 +/- 2 arc seconds, together with the Mariner 10 determination of the gravitational harmonic coefficient C22, indicates that the mantle of Mercury is decoupled from a core that is at least partially molten.

Influence of the laser pulse duration on spectrochemical analysis of solids by laser-induced plasma spectroscopy

Quantitative analysis of aluminum and copper alloys by means of laser-induced plasma spectroscopy (LIPS) has been investigated for three representative laser pulse durations (80 fs, 2 ps, and 270 ps). The experiments were carried out in air at atmospheric pressure with a constant energy density of 20 J/cm2. Because the decay rate of the spectral emission depends on the laser pulse duration, the optimum detection requires an optimization of the temporal gating acquisition parameters. LIPS calibration (sensitivity and nonlinearity) and the limit of detection (LOD) are discussed in detail. While the LOD of minor elements embedded in alloy samples obtained by sub-picosecond or sub-nanosecond laser pulses are both time and element dependent, provided an appropriate temporal window is chosen, the optimum LODs (several parts per million (ppm)) prove to be independent of the laser pulse duration. Finally, it is found that for elements such as those detected here, gated LIPS spectra using picosecond or sub-picosecond laser pulses provide much better LOD values than non-gated spectra.

A low-density M-type asteroid in the main belt

The orbital parameters of a satellite revolving around 22 Kalliope indicate that the bulk density of this main-belt asteroid is 2.37 +/- 0.4 grams per cubic centimeter. M-type asteroids such as Kalliope are thought to be the disrupted metallic cores of differentiated bodies. The low-density indicates that Kalliope cannot be predominantly composed of metal and may be composed of chondritic material with approximately 30% porosity. The satellite orbit is circular, suggesting that Kalliope and its satellite have different internal structures and tidal dissipation rates. The satellite may be an aggregate of impact ejecta from an earlier collision with Kalliope.

Fluid modeling of the laser ablation depth as a function of the pulse duration for conductors

Laser ablation of an aluminum target as a function of the pulse duration, for fluences up to 30 J/cm(2) and a wavelength of 0.8 microm, is investigated by means of a fluid code. For a given fluence, the ablation depth shows a minimum for a pulse duration of approximately 10 ps between a maximum obtained for pulses shorter than approximately 1 ps and a lower maximum obtained for pulses in the nanosecond range, in qualitative agreement with published experimental results. The decrease in ablation depth with increase in pulse duration observed between 1 and 10 ps results from the reduced temperature rise near the surface due to increased inward heat transport. The increase in the ablation depth above approximately 10 ps is due to the increase in electron density gradient length while the laser pulse intensity is close to maximum, which thus enables the plasma to absorb more of the laser pulse energy for increased ablation.

Binary asteroids in the near-Earth object population

Radar images of near-Earth asteroid 2000 DP107 show that it is composed of an approximately 800-meter-diameter primary and an approximately 300-meter-diameter secondary revolving around their common center of mass. The orbital period of 1.755 +/- 0.007 days and semimajor axis of 2620 +/- 160 meters constrain the total mass of the system to 4.6 +/- 0.5 x 10(11) kilograms and the bulk density of the primary to 1.7 +/- 1.1 grams per cubic centimeter. This system and other binary near-Earth asteroids have spheroidal primaries spinning near the breakup point for strengthless bodies, suggesting that the binaries formed by spin-up and fission, probably as a result of tidal disruption during close planetary encounters. About 16% of near-Earth asteroids larger than 200 meters in diameter may be binary systems.

Asteroid 1950 DA's encounter with Earth in 2880: physical limits of collision probability prediction

Integration of the orbit of asteroid (29075) 1950 DA, which is based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a nonnegligible probability of the 1-kilometer object colliding with Earth. Trajectory knowledge remains accurate until then because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. The approach distance uncertainty in 2880 is determined primarily by uncertainty in the accelerations arising from thermal re-radiation of solar energy absorbed by the asteroid. Those accelerations depend on the spin axis, composition, and surface properties of the asteroid, so that refining the collision probability may require direct inspection by a spacecraft.

Critical-point phase separation in laser ablation of conductors

Laser ablation due to an ultrashort laser pulse on a massive aluminum target was investigated by means of a one-dimensional fluid code. Clear separation between the ablated matter and the unablated target is seen to occur through spinodal decomposition involving thermodynamic instabilities near the critical point of aluminum. The code also shows that the end of the ablation process is preceded by the ejection of droplets, which form about 15% of the total ejected mass.

Radar observations of asteroid 216 kleopatra

Radar observations of the main-belt, M-class asteroid 216 Kleopatra reveal a dumbbell-shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers (+/-25%). The asteroid's surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of lunar soil. Kleopatra's shape is probably the outcome of an exotic sequence of collisional events, and much of its interior may have an unconsolidated rubble-pile structure.

Topography of the lunar poles from radar interferometry: a survey of cold trap locations

Detailed topographic maps of the lunar poles have been obtained by Earth-based radar interferometry with the 3.5-centimeter wavelength Goldstone Solar System Radar. The interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150-meter spatial resolution and 50-meter height resolution. Using ray tracing, these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits. Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles, respectively.

Cell-density (cycle) dependent silencer of the rat insulin-like growth factor binding protein-2 (IGFBP-2) gene

An element which has a negative effect on transcription has been identified in the 5'-flanking region of the rat insulin-like growth factor binding protein-2 (IGFBP-2) gene. This element was confirmed to be a silencer by truncation or by linking it to a heterologous promoter. The silencer activity disappeared in the growth-arrested BRL-3A cells at the G1/S border by high cell density where the IGFBP-2 production is highly elevated. This observation may represent a novel mechanism through which gene expression is controlled by modulation of a silencer. Taken together, these results suggest a regulatory link between cell growth and IGFBP-2 expression regulated by its silencer.

Atomic spectroscopy with surface wave plasmas

The use of microwave induced plasmas, particularly of surface wave plasmas, as detectors in atomic emission spectrometry for elemental analysis is reviewed. Surface wave plasmas have been produced at low HF power and used as gas chromatographic detectors. The analytical performances for the detection of non-metals with a Fourier transform spectrometer and a two-channel filter unit are reported. The excitation behavior of non-metals in helium-based mixed gas-plasmas has also be studied. In particular, the effect of power and of nitrogen concentration on the bromine emission has been systematically investigated. A nine-fold improvement of the detection limits for bromine can be obtained in a high power (900 W) helium-nitrogen (0.1-0.2%) plasma.