Nanostructure of thin silicon films by combining HRTEM, XRD and Raman spectroscopy measurements and the implication to the optical properties

A series of thin silicon films with different degrees of crystallinity were prepared by decomposition of silane gas highly diluted with hydrogen, in radiofrequency glow discharge. The crystallite size, shape, and the portion of crystalline phase were investigated by high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy (RS), and X-ray powder diffraction (XRD). The absorption coefficient (a) was calculated from the measurement of UV–vis-transmittance. By using RS, the volume fractions of the crystalline phase were estimated from the ratio of the integrated intensities of transversal optical (TO)-related crystalline and amorphous bands. These results were in excellent agreement with the mean crystallite sizes measured in HRTEM images and crystallite sizes refined from XRD measurements. The red shift of absorption, appearing as a result of the increase of the crystal fraction, depends on the size and distribution of nanocrystals

Tailoring anatase nanotubes for the photovoltaic device by the anodization process on behalf of microstructural features of titanium thin film

We prepared the anatase nanotubes (NT) and other nanostructured titania as electron accepting/transmitting layers in solar cells, using titanium anodization. Upon gaining control over the anodization, the parameters were held constant in order to observe the role of the deposited layers (by electron beam evaporation and magnetron sputtering) on the NT yield. The structural and microstructural parameters were investigated using FIB-FEGSEM, XRD, Raman and GIXRD. Differences in the titanium layers play a significant role on the type of titania nanostructures achieved. Only dense homogeneous titanium layer surface, uniform in thickness and without cracks at macroscale, with uniformly seized isotropic nanoparticles, will enable uniform electrochemical etching and thus favourable, reproducible formation of the titania NT, and upon thermal treatment the anatase NT. Transparent conductive oxide (TCO) layers, which are not in direct contact to the NT, can also exhibit influence on the morphology of the titania NT charge transfer layer. In order to reach large uniform areas of nanotubes, which is required for solar cell application, the preparation of titanium layer has to be tailored

ZnO@TiO₂ Core Shell Nanorod Arrays with Tailored Structural, Electrical, and Optical Properties for Photovoltaic Application

ZnO has prominent electron transport and optical properties, beneficial for photovoltaic application, but its surface is prone to the formation of defects. To overcome this problem, we deposited nanostructured TiO2 thin film on ZnO nanorods to form a stable shell. ZnO nanorods synthesized by wet-chemistry are single crystals. Three different procedures for deposition of TiO2 were applied. The influence of preparation methods and parameters on the structure, morphology, electrical and optical properties were studied. Nanostructured TiO2 shells show different morphologies dependent on deposition methods: (1) separated nanoparticles (by pulsed laser deposition (PLD) in Ar), (2) a layer with nonhomogeneous thickness (by PLD in vacuum or DC reactive magnetron sputtering), and (3) a homogenous thin layer along the nanorods (by chemical deposition). Based on the structural study, we chose the preparation parameters to obtain an anatase structure of the TiO2 shell. Impedance spectroscopy shows pure electron conductivity that was considerably better in all the ZnO@TiO2 than in bare ZnO nanorods or TiO2 layers. The best conductivity among the studied samples and the lowest activation energy was observed for the sample with a chemically deposited TiO2 shell. Higher transparency in the visible part of spectrum was achieved for the sample with a homogenousTiO2 layer along the nanorods, then in the samples with a layer of varying thickness