Crystallinities and Light Emitting Properties of Nanostructured SiGe Alloy Prepared by Pulsed Laser Ablation in Inert Background Gases

For studying the material properties of nanostructured group IV materials, we have developed a pulsed laser ablation method into inert background gases. SiGe alloy nanocrystallites have the possibility of novel band structure engineering by controlling not only compositions but also particle sizes. An ArF excimer laser was focused onto the surface of the powder-sintered SixGe1-x target. During the laser ablation, He gas was introduced into a vacuum chamber and was maintained at a constant pressure. Size distribution of the SixGe1-x ultrafine particles decreases with decreasing composition x under fixed conditions of deposition such as background gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks ascribed to mixed crystalline SiGe after annealing, and the linewidths of these peaks broaden due to the reduced size of the crystallites. The frequencies and intensities of the peaks depend on the composition x. Visible PL spectra have broad peaks from 2.25 eV to 2.10 eV, at room temperature. The peak positions show blue shifts with increasing x. Electroluminescent diodes with the Si(.8)Ge(.2) nanocrystallite active region were fabricated, and emit visible light peaked at around 1.8 eV, at room temperature.Engineering and Applied Science

A novel absorptive/reflective solar concentrator for heat and electricity generation: an optical and thermal analysis.

The crossed compound parabolic concentrator (CCPC) is one of the most efficient non-imaging solar concentrators used as a stationary solar concentrator or as a second stage solar concentrator. In this study, the CCPC is modified to demonstrate for the first time a new generation of solar concentrators working simultaneously as an electricity generator and thermal collector. The CCPC is designed to have two complementary surfaces, one reflective and one absorptive, and is named as an absorptive/reflective CCPC (AR-CCPC). Usually, the height of the CCPC is truncated with a minor sacrifice of the geometric concentration. These truncated surfaces rather than being eliminated are instead replaced with absorbent surfaces to collect heat from solar radiation. The optical efficiency including absorptive/reflective part of the AR-CCPC was simulated and compared for different geometric concentration ratios varying from 3.6× to 4×. It was found that the combined optical efficiency of the AR-CCPC 3.6×/4× remained constant and high all day long and that it had the highest total optical efficiency compared to other concentrators. In addition, the temperature distributions of AR-CCPC surfaces and the assembled solar cell were simulated based on those heat flux boundary conditions. It was shown that the addition of a thermal absorbent surface can increase the wall temperature. The maximum value reached 321.5 K at the front wall under 50° incidence. The experimental verification was also adopted to show the benefits of using absorbent surfaces. The initial results are very promising and significant for the enhancement of solar concentrator systems with lower concentrations

Coupled simulation of performance of a crossed compound parabolic concentrator with solar cell

An optimal installation of a compound parabolic concentrator (CCPC) into a scalable solar thermoelectrics and photovoltaics system is desirable by applying analytical tools to improve the optical and thermal performance of a CCPC with a solar cell. In this paper, the optical and thermal performances of an isolated CCPC with solar cell are investigated by employing commercial software ‘ANSYS CFX 15.0’ with a coupled optical grey and multiphysics model. Numerical results are validated against the experimental data at various incidence angles, especially for the optical concentration ratio and optical efficiency. Results confirm that ‘ANSYS CFX’ is an effective numerical tool for determining correctly both the optical and thermal behaviour of CCPC. The very important finding is a highest temperature core in the silicon layer of solar cell which may be responsible for a solar cell to work properly. The limitation of the work is that the electric performance of the solar cell is not involved and the simulations are steady

Intracellular integration of synthetic nanostructures with viable cells for controlled biochemical manipulation

Abstract We demonstrate the integration of vertically aligned carbon nanofibe