Rayleigh-Taylor Instability of an Ultrathin Foil Accelerated by the Radiation Pressure of an Intense Laser

We report experimental evidence for a Rayleigh-Taylor-like instability driven by radiation pressure of an ultraintense (1021W/cm2) laser pulse. The instability is witnessed by the highly modulated profile of the accelerated proton beam produced when the laser irradiates a 5 nm diamondlike carbon (90% C, 10% H) target. Clear anticorrelation between bubblelike modulations of the proton beam and transmitted laser profile further demonstrate the role of the radiation pressure in modulating the foil. Measurements of the modulation wavelength, and of the acceleration from Doppler-broadening of back-reflected light, agree quantitatively with particle-in-cell simulations performed for our experimental parameters and which confirm the existence of this instability. © 2012 American Physical Society.

Electronic, structural, and reactive properties of ultrathin aluminum oxide films on Pt(111)

Low-energy electron diffraction, X-ray photoelectron spectroscopy, high-resolution electron energy-loss spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction spectrometry results are reported for the structural and reactive behavior of alumina films grown on Pt(111) as a function of thickness and oxidation temperature. Submonolayer Al films undergo compete oxidation at 300 K, annealing at 1100 K resulting in formation of somewhat distorted crystalline gamma-alumina, Thicker deposits require 800 K oxidation to produce Al2O3, and these too undergo crystallization at 800 K, yielding islands of apparently undistorted gamma-alumina on the Pt(111) surface. Oxidation of a p(2 x 2) Pt3Al surface alloy occurs only at>800 K, resulting in Al extraction, These alumina films on Pt(lll) markedly increase the coverage of adsorbed SO4 resulting from SO2 chemisorption onto oxygen-precovered surfaces. This results in enhanced propane uptake and subsequent reactivity relative to SO4/Pt(111). A bifunctional mechanism is proposed to account for our observations, and the relevance of these to an understanding of the corresponding dispersed systems is discussed.

High temperature thermal stability studies of ultrathin Al2O3 layers deposited on native oxide and sulphur passivated InGaAs surfaces

High resolution synchrotron radiation core level photoemission measurements have been used to undertake a comparative study of the high temperature stability of ultrathin Al2O3 layers deposited by atomic layer deposition (ALD) on both sulphur passivated and native oxide covered InGaAs. The residual interfacial oxides between sulphur passivated InGaAs and the ultrathin Al2O3 layer can be substantially removed at high temperature (up to 700 °C) without impacting on the InGaAs stoichiometry while significant loss of indium was recorded at this temperature on the native oxide InGaAs surface.

Microplasma Processed Ultrathin Boron Nitride Nanosheets for Polymer Nanocomposites with Enhanced Thermal Transport Performance

This paper reports on the enhancement of the thermal transport properties of nanocomposite materials containing hexagonal boron nitride in poly (vinyl alcohol)through room-temperature atmospheric pressure direct-current microplasma processing. Results show that the microplasma treatment leads to exfoliation of the hexagonal boron nitride in isopropyl alcohol, reducing the number of stacks from >30to a few or single layers. The thermal diffusivity of the resulting nanocomposites reaches 8.5 mm2 s-1, 50 times greater than blank poly (vinyl alcohol) and twice that ofnanocomposites containing non-plasma treated boron nitride nanosheets. From TEM analysis, we observe much less aggregation of the nanosheets after plasma processing along with indications of an amorphous carbon interfacial layer which may contribute to stable dispersion of boron nitride nanosheets in the resulting plasma treated colloids.

Dynamic in situ optical and magneto-optical monitoring of the growth of Co-Pd multilayers

In situ ellipsometry and Kerr polarimetry have been used to follow the continuous evolution of the optical and magneto- optical properties of multiple layers of Co and Pd during their growth. Films were sputter deposited onto a Pd buffer layer on glass substrates up to a maximum of N = 10 bi-layer periods according to the scheme glass/Pd(10)Ar x (0.3Co/3Pd) (nm). Magnetic hysteresis measurements taken during the deposition consistently showed strong perpendicular anisotropy at all stages of film growth following the deposition of a single monolayer of Co. Magneto-optic signals associated with the normal-incidence polar Kerr effect indicated strong polarization of Pd atoms at both Co-Pd and Pd-Co interfaces and that the magnitude of the complex magneto-optic Voigt parameter and the magnetic moment of the Pd decrease exponentially with distance from the interface with a decay constant of 1.1 nm(- 1). Theoretical simulations have provided an understanding of the observations and allow the determination of the ultrathin- film values of the elements of the skew-symmetric permittivity tensor that describe the optical and magneto-optical properties for both CO and Pd. Detailed structure in the observed Kerr ellipticity shows distinct Pd-thickness-dependent oscillations with a spatial period of about 1.6 nm that are believed to be associated with quantum well levels in the growing Pd layer.

Ultra-thin tunable microwave absorber using liquid crystals

A dynamically adaptive radar absorber is described which is based on a periodic array of microstrip patches that are printed on a 500 mu m-thick liquid crystal substrate. The measured reflectivity of the structure is less than -38 dB with a 200 MHz -10 dB bandwidth at 10.19 GHz when a +4 DC bias is applied. It is shown that a 34 dB reduction in signal loss occurs when the bias voltage is increased to 20 V.

Coherent X-ray production via pulse reflection from laser-driven dense electron sheets

A scheme to obtain brilliant x-ray sources by coherent reflection of a counter-propagating pulse from laser-driven dense electron sheets is theoretically and numerically investigated in a self-consistent manner. A radiation pressure acceleration model for the dynamics of the electron sheets blown out from laser-irradiated ultrathin foils is developed and verified by PIC simulations. The first multidimensional and integral demonstration of the scheme by 2D PIC simulations is presented. It is found that the reflected pulse undergoes Doppler-upshift by a factor 4?z2, where ?z = (1- vz2/c2)-1/2 is the effective Lorentz factor of the electron sheet al ong its normal direction. Meanwhile the pulse electric field is intensified by a factor depending on the electron density of the sheet in its moving frame ne/?, where ? is the full Lorentz factor.

Endothelin-like immunoreactivity and receptor binding in the choroid and retina

This study has examined the localisation and receptor-binding of the endothelins in retina and choroid of human and rat origin. Immunoreactivity to anti-ET1 and anti-ET3 was investigated in trypsin digests, frozen sections and ultrathin sections using immunocytochemistry and immunogold labelling techniques. In addition, receptor binding of 125I-ET1 and 125I-ET3 was visualised and quantified using autoradiography and image analysis. Intense immunoreactivity to anti-ET1 and anti-ET3 was observed in the photoreceptor inner segments and in the outer plexiform layer (OPL) of human and rat retina. Ultrastructural localisation using immunogold labelling confirmed the presence of ET1 and ET3 in the photoreceptor cells. In retinal vascular digests, ET1 was visualised in the arteries, arterioles and at the pre-arteriolar sphincters, however, immunoreactivity to anti-ET3 was absent in the retinal vasculature. Both ETA and ETB-type receptor binding sites to 125I-ET1 and 125I-ET3 were detected in the vascular smooth muscle of choroidal and retinal vessels with the former being predominant. Extravascular binding sites of the ETB-type were found in the ganglion cell layer.

Enhanced Laser-Driven Ion Acceleration in the Relativistic Transparency Regime

We report on the acceleration of ion beams from ultrathin diamondlike carbon foils of thickness 50, 30, and 10 nm irradiated by ultrahigh contrast laser pulses at intensities of similar to 7 X 10(19) W/cm(2). An unprecedented maximum energy of 185 MeV (15 MeV/u) for fully ionized carbon atoms is observed at the optimum thickness of 30 nm. The enhanced acceleration is attributed to self-induced transparency, leading to strong volumetric heating of the classically overdense electron population in the bulk of the target. Our experimental results are supported by both particle-in-cell (PIC) simulations and an analytical model.