We have developed a Kramers–Kronig consistent analytical expression to fit the measured optical functions of hydrogenated amorphous silicon $\mathrm{(a-}\mathrm{Si:H})$ based alloys, i.e., the real and imaginary parts of the dielectric function ${\mathrm{(\epsilon }}_1{\mathrm{,\epsilon }}_2)$ (or the index of refraction n and absorption coefficient α) versus photon energy E for the alloys. The alloys of interest include amorphous silicon–germanium $\mathrm{(a-}{\mathrm{Si}}_{\text{1−x}}{\mathrm{Ge}}_x:\mathrm{H})$ and silicon–carbon $\mathrm{(a-}{\mathrm{Si}}_{\text{1−x}}{\mathrm{C}}_x:\mathrm{H}\mathrm{),}$ with band gaps ranging continuously from ∼1.30 to 1.95 eV. The analytical expression incorporates the minimum number of physically meaningful, E independent parameters required to fit ${\mathrm{(\epsilon }}_1{\mathrm{,\epsilon }}_2)$ versus E. The fit is performed simultaneously throughout the following three regions: (i) the below-band gap (or Urbach tail) region where α increases exponentially with E, (ii) the near-band gap region where transitions are assumed to occur between parabolic bands with constant dipole matrix element, and (iii) the above-band gap region where ${\mathrm{(\epsilon }}_1{\mathrm{,\epsilon }}_2)$ can be simulated assuming a single Lorentz oscillator. The expression developed here provides an improved description of ${\epsilon }_2$ (or α) in the below-band gap and near-band gap regions compared with previous approaches. Although the expression is more complicated analytically, it has numerous applications in the analysis and simulation of thin film $\mathrm{a-}\mathrm{Si:H}$ based $\mathrm{p-i-n}$ and $\mathrm{n-i-p}$ multilayer photovoltaic devices. First, we describe an approach whereby, from a single accessible measure of the optical band gap, the optical functions can be generated over the full solar spectrum for a sample set consisting of the highest quality intrinsic $\mathrm{a-}\mathrm{Si:H}$ based alloys prepared by plasma-enhanced chemical vapor deposition using the principle of maximal ${\mathrm{H}}_2$ dilution. Second, we describe quantitatively how such an approach can be modified for sample sets consisting of lower quality alloy materials. Finally, we demonstrate how the generated optical functions can be used in simulations of the absorption, reflection, and quantum efficiency spectra of $\mathrm{a-}\mathrm{Si:H}$ based single-junction and multijunction solar cells.

We present a detailed study on the growth process of cupric oxide (CuO) nanowires by thermal oxidation. The morphology of nanowires, obtained at different oxidation temperatures and times, was determined. The diameter of nanowires was found to depend linear on temperature whereas the time dependence of their length is modeled by a parabolic law. The results suggest that CuO nanowires are formed as a result of the competition between grain boundary and lattice diffusion of Cu atoms across a ${\text{Cu}}_2\text{O}$ layer. Electrical characterization of the nanowires was also performed. A field effect transistor was produced with an isolated nanowire showing $p$ -type characteristics. The resistivity, mobility, and density of carriers were calculated. Nanowire growth by thermal oxidation is very simple and has great potential to be used for large scale production; this opens possibilities for various kinds of application.

Real-time optical studies have been applied to develop phase diagrams that characterize plasma-enhanced chemical vapor deposition (PECVD) of silicon thin films at low temperature (200 °C). The deposition phase diagrams describe regimes over which predominantly amorphous and microcrystalline Si phases are obtained as a function of the accumulated thickness and the hydrogen-to-silane gas flow ratio $\mathrm{R=}{\mathrm{[H}}_{\mathrm{2}}{\mathrm{]/[SiH}}_{\mathrm{4}}\mathrm{]}$ in the PECVD process. The diagrams for different substrates provide insights into optimization of amorphous Si materials and solar cells.

The influence of chemical modification by acid treatment followed by triethylenetetramine (TETA) functionalization on the surface of multi-walled carbon nanotubes (MWCNT) was evaluated, both qualitative and quantitatively. Thermogravimetric analysis (TGA) showed that, in the case of amine-functionalized nanotubes, 29% of mass loss can be attributed to -C(=O)TETA and residual oxygen-containing functional groups. X-ray photoelectron spectroscopy (XPS) was used to observe the oxygenated and aminated functions covalently linked to the nanotube surface. Electric force microscopy (EFM) images indicated that the nanotubes with diverse surface chemistry showed distinct responses to the tip potential in the presence of air. Shifts in EFM phase images decreased when the nanotube surface was modified with oxygen and amine-containing functional groups. In dry and inert N2 atmosphere, however, the three different surfaces showed the same response to EFM. In addition, the hydrophilic character of the buckypapers increased in the order MWCNT < aminated-MWCNT < oxidized-MWCNT.