ABSTRACT
Sprayed transparent conductive oxides (TCOs) are an interesting alternative to sputtered TCOs for many applications due to the possible high throughput and a simple, atmospheric pressure process of spray deposition. In this work, the growth mechanism of sprayed ZnO:In was analyzed by transmission Kikuchi diffraction (TKD) analysis of the thin film's crystal orientation, which shows a preferred orientation of the growing grains and thus proves that the deposition occurs from the gas phase. It was observed that with increasing thickness of the layer, the average grain size increases and the measured resistivity significantly reduces to ≈5-6 × 10-3 Ω cm for layers of >500 nm thickness. Since many applications also require good electrical contact formation, the contact resistivity and the interface between sprayed IZO and n-type poly-Si and p-type GaAs, two materials that are commonly used in III-V/silicon tandem solar cells, were investigated by electrical measurements and high-resolution transmission electron microscopy (TEM) analyses. The interlayers observed in TEM were investigated by energy-dispersive X-ray spectroscopy (EDS) line scans. The results suggest that oxidic interlayers at the substrate/IZO interface are responsible for the observed higher contact resistivity compared to the contact resistivity of sputtered indium tin oxide (ITO) references. The results presented in this work lead to a better understanding of the deposition process occurring in spray pyrolysis and thus allow a more targeted optimization of process parameters depending on the future requirements of the application.
ABSTRACT
The lifetime of steam pipelines in long-term operation in coal-fired power plants are limited due to material damage that resulted from creep exposure. In the present study, the authors comparatively assess the damage of ex-service 12% Cr piping steel with varying degrees of exposure while using accelerated creep tests that employ digital image correlation (DIC) as well as microstructural investigation that is based on electron microscopy. The DIC technique, which allows multiple creep curves to be measured at temperatures ranging from 550-600 °C from a single specimen, revealed higher Zener-Hollomon parameters for a high damage material with a high void density when compared to a material with lower damage and lower void density. Both of the material states showed similar hardness values, subgrain sizes, and boundary character, despite the difference in void densities. Slightly higher inter-particle spacing of MX precipitates results in a lower threshold stress of 79 MPa for the high damage steel when compared to 97 MPa for the low damage material. Besides large Laves phase particles (>0.2 µm) that are found in the higher damaged materials that result in solid solution depletion, the most prominent microstructural damage indicator was a lower density of M23C6 precipitates. Therefore, the observations indicate that the Zener-Hollomon parameter and M23C6 particles are good damage assessment indicators between the most extreme damage states and they predict a lower damage level for a medium void density material.
