Soliton Resonances in Helium Films

The phenomenon of two-soliton resonances of the Kadomtsev-Petviashvilli equation for the superfluid surface density fluctuation in He films is studied. The velocity of the resonant soliton is obtained.

Two Dimensional Large Amplitude Quasi Solitons in Thin Helium Films

Large amplitude local density fluctuations in a thin superfluid He film is considered. It is shown that these large amplitude fluctuations travel and behave like "quasi-solitons" under collision, even when the full nonlinearity arising from the Van der Waals potential is taken into account.

Giant photoinduced optical bleaching at room and liquid helium temperatures in Sb/As(2)S(3) multilayered films

We report the observation of giant photo induced optical bleaching in Sb/As(2)S(3) multilayered film at room and liquid He temperatures, when irradiated with 532 nm laser at moderate intensities. The experimental results show a dramatic increase in transmittance near the band gap regime at both the temperatures; however the rates at which transmission change occurs are rather slow at low temperature. The huge change in transmission is due to the photo induced intermixing of As(2)S(3) layer with Sb. Our XPS measurements show that photo induced intermixing occurs through the wrong homopolar bonds, which under actinic light illumination are converted into energetically favored hetropolar bonds. (C) 2011 Elsevier B.V. All rights reserved.

Effect of helium implantation on the properties of plasma polymer films

Polymer films, deposited from acetylene and argon plasma mixtures, were bombarded with 150 keV He+ ions, varying the fluence, Phi, from 10(18) to 10(21) ions/m(2). Molecular structure and optical gap of the samples were investigated by infrared and ultraviolet-visible spectroscopies, respectively. Two-point probe was employed to determine the electrical resistivity while hardness was measured by nanoindentation technique. It was verified modification of the molecular structure and composition of the films. There was loss of H and increment in the concentration of unsaturated carbon bonds with Phi. Optical gap and electrical resistivity decreased while hardness increased with Phi. Interpretation of these results is proposed in terms of chain crosslinking and unsaturation. (C) 2002 Elsevier B.V. B.V. All rights reserved.

XPS investigation of plasma-deposited polysiloxane films irradiated with helium ions

This work describes an XPS investigation of plasma-deposited polysiloxane films irradiated with 170 keV He+ ions at fluences, Phi, ranging from 1 x 10(14) to 1 x 10(16) cm(-2). Modifications in the atomic concentrations of the surface atoms with (D were revealed by changes in the [O]/[Si], [O]/[C] and [C]/[Si] atomic ratios. Surface chemical structure modifications were evidenced by the increasing C1s peak width and asymmetry as Phi was increased, due to the formation of ether and carboxyl functionalities. Moreover, structural transformations were indicated by the positive binding energy shift of the Si2p peaks, due to the increasing Si oxidation. Correlations of the XPS data with other results from previous work on polysiloxanes illustrate the role of ion beam-induced bond breaking on the structural modifications.

Helium ion irradiation of polymer films deposited from TMS-Ar plasmas

Polymer films synthesized from plasmas of a tetramethylsilane - Ar mixture were modified by irradiation with 170 keV He ions at fluences ranging from 1 x 10(14) to 1 x 10(16) cm(-2). As revealed by infrared spectroscopy, the ion beam produced intense bond rearrangements, such as the depletion of bonding groups (C-H and Si-H), and induced the formation of new ones, such as O-H and Si-O. From the nanoindentation measurements, a remarkable increase in the surface hardness of the films was observed as the ion fluence was increased. The increases in hardness were accompanied by an increase in the film compaction as shown by using a combination of RBS and film thickness measurements. From both hardness and infrared measurements A was concluded that, under the He ion bombardment, the polymer structure is transformed into a silicon oxycarbide network.

Effects of nitrogen ion irradiation on plasma polymerized films produced from titanium tetraiso pro poxide-oxygen-helium mixtures

In this work films were produced by the plasma enhanced chemical vapor deposition (PECVD) of titanium tetraisopropoxide-oxygen-helium mixtures and irradiated with 150 keV singly-charged nitrogen ions (N(+)) at fluences, phi, between 10(14) and 10(16) cm(-2). Irradiation resulted in compaction, which reached about 40% (measured via the film thickness) at the highest fluence. Infrared reflection-absorption spectroscopy (IRRAS) revealed the presence of Ti-O bonds in all films. Both O-H and C-H groups were present in the as-deposited films, but the density of each of these decreased with increasing phi and was absent at high phi, indicating a loss of hydrogen. X-ray photoelectron spectroscopy (XPS) analyses revealed an increase in the C to Ti atomic ratio as phi increased, while the O to Ti ratio hardly altered, remaining at around 2.8. The optical gap of the films, derived from data obtained by ultraviolet-visible spectroscopy (UVS), remained at about 3.6 eV for all fluences except the highest, for which an abrupt fall to around 1.0 eV was observed. For the irradiated films, the electrical conductivity, measured using the two-point method, showed a systematic increase with increasing phi. (c) 2008 Elsevier B.V. All rights reserved.

Role of rigidity and temperature in the kinetics of photodarkening in Ge(x)As((45-x))Se(55) thin films

We present insightful results on the kinetics of photodarkening (PD) in Ge(x)As(45-x)Se(55) glasses at the ambient and liquid helium temperatures when the network rigidity is increased by varying x from 0 to 16. We observe a many fold change in PD and its kinetics with decreasing network flexibility and temperature. Moreover, temporal evolution of PD shows a dramatic change with increasing x. (C)2011 Optical Society of America

Low-temperature (≤600 °C) semi-insulating oxygen-doped silicon films by the PECVD technique for large-area power applications

This work describes the deposition, annealing and characterisation of semi-insulating oxygen-doped silicon films at temperatures compatible with polysilicon circuitry on glass. The semi-insulating layers are deposited by the plasma enhanced chemical vapour deposition technique from silane (SiH4), nitrous oxide (N2O) and helium (He) gas mixtures at a temperature of 350 °C. The as-deposited films are then furnace annealed at 600 °C which is the maximum process temperature. Raman analysis shows the as-deposited and annealed films to be completely amorphous. The most important deposition variable is the N2O SiH4 gas ratio. By varying the N2O SiH4 ratio the conductivity of the annealed films can be accurately controlled, for the first time, down to a minimum of ≈10-7Ω-1cm-1 where they exhibit a T -1 4 temperature dependence indicative of a hopping conduction mechanism. Helium dilution of the reactant gases is shown to improve both film uniformity and reproducibility. A model for the microstructure of these semi-insulating amorphous oxygen-doped silicon films is proposed to explain the observed physical and electrical properties. © 1995.

Low temperature (≤ 600°C) semi-insulating oxygen-doped silicon films by the PECVD technique for large area power applications

This work describes the annealing and characterisation of semi-insulating oxygen-doped silicon films deposited by the Plasma Enhanced Chemical Vapour Deposition (PECVD) technique from silane (SiH4), nitrous oxide (N2O) and helium (He) gas mixtures. The maximum process temperature is chosen to be compatible with large area polycrystalline silicon (poly-Si) circuitry on glass. The most important deposition variable is shown to be the N2O SiH4 gas ratio. Helium dilution results in improved film uniformity and reproducibility. Raman analysis shows the 'as-deposited' and annealed films to be completely amorphous. A model for the microstructure of these Semi-Insulating Amorphous Oxygen-doped Silicon (SIAOS) films is proposed to explain the observed physical and electrical properties. © 1995.

On the photoluminescence of a-C:H films

a-C:H films deposited from methane and helium mixture in a capacitively coupled rf plasma were found to show photoluminescence (PL) with peak intensities at energies far above the Taue gap of these films. Apart from the PL the films were investigated with respect to their IR and UV/VIS absorption properties as well as their Raman spectra were examined. The ultraviolet (UV) and blue luminescence from hard a-C:H thin films are explained by incorporation of polycyclic hydrocarbons from gas-phase reactions in the methane helium plasma into the film.

Single ionization of helium by antiproton impact

We study the ionization of helium (fie) in collision with antiprotons (p) in the energy range from 10 keV to 1000 keV. We adopt a semiclassical single center close coupling approach in which the wave function for the electron is expanded in a B-spline basis centered on the nucleus of the He atom, The calculations are performed using two different models: the independent particle (IP) model and the one-electron (OE) approximation. The interaction between the active electron and the rest of the atom, i.e. passive electron and nucleus, is represented by a model potential. The results obtained are compared with experimental data as well as with existing theoretical calculations. (c) 2005 Published by Elsevier B.V.

Photoconductivity studies on some semiconducting thin films for photovoltaic applications

Photoconductivity (PC) processes may be the most suitable technique for obtaining information about the states in the gap. It finds applications in photovoItaics, photo detection and radiation measurements. The main task in the area of photovoltaics, is to increase the efficiency of the device and also to develop new materials with good optoelectronic properties useful for energy conversion, keeping the idea of cost effectiveness. Photoconduction includes generation and recombination of carriers and their transport to the electrodes. So thermal relaxation process, charge carrier statistics, effects of electrodes and several mechanisms of recombination are involved in photoconductivity.A major effect of trapping is to make the experimentally observed decay time of photocurrent, longer than carrier lifetime. If no trapping centers are present, then observed photocurrent will decay in the same way as the density of free carriers and the observed decay time will be equal to carrier lifetime. If the density of free carriers is much less than density of trapped carriers, the entire decay of photocurrent is effectively dominated by the rate of trap emptying rather than by the rate of recombination.In the present study, the decay time of carriers was measured using photoconductive decay (PCD) technique. For the measurements, the film was loaded in a liquid Helium cryostat and the temperature was controlled using Lakshore Auto tuning temperature controller (Model 321). White light was used to illuminate the required area of the sample. Heat radiation from the light source was avoided by passing the light beam through a water filter. The decay current. after switching off the illumination. was measured using a Kiethely 2000 multi meter. Sets of PCD measurements were taken varying sample temperature, sample preparation temperature, thickness of the film, partial pressure of Oxygen and concentration of a particular element in a compound. Decay times were calculated using the rate window technique, which is a decay sampling technique particularly suited to computerized analysis. For PCD curves with two well-defined regions, two windows were chosen, one at the fast decay region and the other at the slow decay region. The curves in a particular window were exponentially fitted using Microsoft Excel 2000 programme. These decay times were plotted against sample temperature and sample preparation temperature to study the effect of various defects in the film. These studies were done in order to optimize conditions of preparation technique so as to get good photosensitive samples. useful for photovoltaic applications.Materials selected for the study were CdS, In2Se3, CuIn2Se3 and CuInS2• Photoconductivity studies done on these samples are organised in six chapters including introduction and conclusion.