Comparison of optical properties of periodic photonic–plasmonic and randomly textured back reflectors for nc-Si solar cells

Light trapping is essential to harvest long-wavelength red and near-infrared photons in thin film silicon solar cells. Light trapping in p-i-n thin film cells is commonly achieved with back-reflectors, and in n-i-p cells with textured front transparent conductors. We systematically compare the optical properties and performance of randomly roughened back reflectors with periodic plasmonic-photonic back-reflectors in p-i-n solar cells. The randomly textured back reflectors were prepared to have very high diffuse reflectance comparable to the state of the art. The periodic back reflectors of tapered nano-pillars/bumps show enhanced quantum efficiency and optical absorption over randomly structured back reflectors using the same solar cell architecture in nc-Si solar cells. The strong diffraction and light concentration in periodic back reflectors may be more beneficial than the light scattering offered by randomly textured back reflectors.     

Influence of oxygen on defect densities in nanocrystalline Si

A differential capacitance vs. frequency technique for determining trap densities as a function of energy in amorphous and nanocrystalline Si devices is presented. Through differential capacitance measurements, trap states can be accurately measured and profiled within the bandgap as a function of energy. Defects for amorphous silicon were shown to be Gaussian approximately 0.7 eV below the conduction band, on the order of 10¹⁵–10¹⁶ cm^? 3 depending on deposition. This agrees with both external a-Si measurements and C–V defect measurements. Defects in nano-crystalline silicon were studied as a function of oxygen present in the material. Five different depositions were carried out with varying amounts of oxygen. The defect densities of each device were then measured. A large increase in defect densities corresponding to an increase in oxygen content is observed.     

Particles dispersion on fluid-liquid interfaces

This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. In this paper we show that motion of particles normal to the interface is inertia domin...     

Spin decoherence in an iron-based magnetic cluster

Continuous wave (cw) and pulsed high frequency electron paramagnetic resonance (HF-EPR) measurements were performed on an Fe-based magnetic cluster: Fe₇O₄(O₂CPh)₁₁(dmem)₂, abbreviated Fe₇. The cw EPR results show that two different molecular species exist in the crystal, with slightly different zero-field-splitting parameters. The spin decoherence time, T₂, was measured at high magnetic fields and low temperatures, which makes it possible to obtain high spin polarization and to significantly reduce decoherence due to electron spin flip-flop processes. Theoretical fitting of T₂ versus temperature shows that, for crystalline samples of this molecule, spin flip-flop fluctuations represent the main source of spin decoherence at low temperatures, as reported also for the Fe₈ single-molecule magnet [Phys. Rev. Lett. 102 (2009) 087603]. Moreover, it is found that T₂ is position dependent within the EPR line, a model for which is given. We also note that this is the third example of an Fe-based cluster that exhibits a measurable decoherence time, and only the second involving a crystal.     

Luminescent Features of Ternary Europium Complexes: Photophysical and Optoelectronic Evaluation

Journal of Fluorescence - Trivalent europium complexes exhibit good luminescent characteristics. A series of octacoordinated ternary europium complexes with fluorinated diketone and heteroaromatic...     

Nanostructures in Physical Materials Chemistry: An Exploratory Laboratory

The blend of nanotechnology and material science is often beyond the scope of undergraduate laboratories. Through undergraduate research, graphite-intercalated compounds have been incorporated in the production of carbon-based nanostructures. Based on this work a series of exploratory exercises were designed for the undergraduate physical chemistry laboratory emphasizing nanostructure material science. This rapidly expanding area of science and technology can be introduced at an undergraduate level using a high temperature oven to produce nanostructure samples that are analyzed by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy at research university laboratories, infrared spectroscopy, and a bomb calorimeter. In these experiments we use samples of pure graphite, fluorinated graphite, and lanthanum oxide to induce the formation of nanostructures. An overview of fullerenes, nanotubes, boron nitride and Si nanostructures, other carbon forms, graphite-intercalated compounds, and the storage of hydrogen in nanotubes are provided in an appendix. Several extensions of the laboratory are proposed.     

A transformation‐free HOC scheme for steady convection–diffusion on non‐uniform grids

A higher order compact (HOC) finite difference solution procedure has been proposed for the steady two‐dimensional (2D) convection–diffusion equation on non‐uniform orthogonal Cartesian grids involving no transformation from the physical space to the computational space. Effectiveness of the method is seen from the fact that for the first time, an HOC algorithm on non‐uniform grid has been extended to the Navier–Stokes (N–S) equations. Apart from avoiding usual computational complexities associated with conventional transformation techniques, the method produces very accurate solutions for difficult test cases. Besides including the good features of ordinary HOC schemes, the method has the advantage of better scale resolution with smaller number of grid points, with resultant saving of memory and CPU time. Gain in time however may not be proportional to the decrease in the number of grid points as grid non‐uniformity imparts asymmetry to some of the associated matrices which otherwise would have been symmetric. The solution procedure is also highly robust as it computes complex flows such as that in the lid‐driven square cavity at high Reynolds numbers (Re), for which no HOC results have so far been seen. Copyright © 2004 John Wiley & Sons, Ltd.