Volume 91, Issue 2, 15 January 2002
Index of content:
- INTERDISCIPLINARY AND GENERAL PHYSICS (PACS 1-41, 43-47, 79, 81-84, 89-99)
Effects of visible light illumination during plasma enhanced chemical vapor deposition growth on the film properties of hydrogenated amorphous silicon91(2002); http://dx.doi.org/10.1063/1.1421242View Description Hide Description
Experimental studies have revealed that defect related properties in hydrogenated amorphous silicon can be modified by visible-light illumination during plasma enhanced chemical vapor depositiongrowth; light-induced degradation after growth and initial defect density has been reduced in the samples prepared under illumination with and without a shield mesh separating the plasma region and a substrate in the deposition chamber, respectively. These properties are metastable below the deposition temperature and are a result of the counterbalance between illumination and the thermal effects during growth. The reduction of the light-induced changes in the present samples does not relate to changes in hydrogen bonding. The defect annihilation reaction during growth has been enhanced and the reaction barrier has been lowered from 0.57 to 0.34 eV under illumination. It has also been found that the defect density depends exponentially on the intensity of incident visible light.
Low-temperature scanning near-field optical microscope for rapid measurement of thousands of absorption spectra91(2002); http://dx.doi.org/10.1063/1.1423390View Description Hide Description
The design and performance of a developed scanning near-field optical microscope suited to the rapid measurement of absorption spectra at many pixels to obtain absorption images at low temperatures are described. An optical system composed of a tungsten–halogen lamp and a charge-coupled devicecamera as a broadband white light source and a multichannel detector, respectively, is employed to reduce acquisition time for a single-pixel spectrum down to 100 ms. Moreover, this microscope can be operated in both illumination and collection modes. The latter mode can provide polarization dependence of absorption spectra. The experiments with molecular J aggregates dispersed in a thin polymer film demonstrate the capability of this instrument to measure near-field absorption spectra at scanned positions within 5 min and to obtain absorption images at different wavelengths. They offer useful information about the spatial distributions of the absorbing materials on the sample surface.
91(2002); http://dx.doi.org/10.1063/1.1423394View Description Hide Description
The interaction of free electrons with intense laser beams in vacuum is studied using a three-dimensional test particle simulation model that solves the relativistic Newton–Lorentz equations of motion in analytically specified laser fields. Recently, a group of solutions was found for very intense laser fields that show interesting and unusual characteristics. In particular, it was found that an electron can be captured within the high-intensity laser region, rather than expelled from it, and the captured electron can be accelerated to GeV energies with acceleration gradients on the order of tens of GeV/cm. This phenomenon is termed the capture and acceleration scenario (CAS) and is studied in detail in this article. The accelerated GeV electron bunch is a macropulse, with duration equal to or less than that of the laser pulse, which is composed of many micropulses that are periodic at the laser frequency. The energy spectrum of the CAS electron bunch is presented. The dependence of the energy exchange in the CAS on various parameters, e.g., (laser intensity), (laser radius at focus), (laser pulse duration), (the impact parameter), and (the injection angle with respect to the laser propagation direction), are explored in detail. A comparison with diverse theoreticalmodels is also presented, including a classical model based on phase velocities and a quantum model based on nonlinear Compton scattering.
Growth and bonding structure of hard hydrogenated amorphous carbon thin films deposited from an electron cyclotron resonance plasma91(2002); http://dx.doi.org/10.1063/1.1423786View Description Hide Description
Analysis of hard hydrogenated amorphous carbonfilmsdeposited from an electron cyclotron resonance radio frequency discharge of methane–argon (5%) mixture at low pressure is reported. The properties of films were determined in their as deposited state using elastic recoil detection analysis, infrared absorption,Raman spectroscopy, transmission spectroscopy,photothermal deflexion spectroscopy, and residual stress measurements. The microstructural changes (i.e., hydrogen content and ratio) have been explained qualitatively in terms of a balance between implantation and relaxation processes. A good correlation is observed between the variation of Raman features and the optical gap as a function of the self-bias substrate. The residual stress versus bias plot shows behavior similar to that already obtained for tetrahedral amorphous carbonfilms and the optimum energy, which corresponds to films of maximum is similar to those obtained in the literature.
91(2002); http://dx.doi.org/10.1063/1.1426238View Description Hide Description
A promising approach to obtain epitaxialfilms of oxide semiconductors was demonstrated, namely helicon-wave-excited-plasma sputteringepitaxy. Due to the surface-damage-free nature, completely a-axis-locked c(0001)-orientation ZnO epilayers were successfully grown on sapphire (0001) substrates having ultrasmooth surfaces with atomic steps. The ZnO epilayer exhibited a dominant near-band-edge photoluminescence(PL) peak at 300 K. Since the PL was considered to be due to the recombination of excitons bound to an impurity or a defect and certain tilting and twisting of the films were observed when were used as sputtering gases, purification and optimization of the overall process are necessary to obtain improved epilayer qualities.