Formation of 3D Ge quantum dots array for advanced photovolatics in layer-cake technique
Placement of quantum dots (QDs) and insight into QD's basic internal structure and optical properties lay nature cornerstones for advanced photonic devices. We report a manageable growth method for placing dense three-dimensional Ge QD arrays in a uniform or a grading size distribution, using thermal oxidation of poly-SiGe in layer-cake techniques. The QD size and spatial density in each stack could be well modulated by Ge content in poly-Si1−xGex, oxidation and underlay buffer layer conditions. Size-dependent internal structure, strain, and photoluminesce properties of Ge QDs are systematically investigated. Optimization of processing conditions was carried out for producing dense Ge QD arrays for maximizing photovoltaic efficiency.
Miniband formulation in Ge/Si quantum dot array
In this work, we estimate the coupling effect of miniband structure and density of states (DoS) resulting from different qunatum-dot physical parameters in a well-aligned Ge/Si quantum dot (QD) array fabricated by neutral beam etching technology. The density of QDs dominates the coupling effect and miniband’s bandwidth, the radius of QDs affects the magnitude of energy levels and miniband bandwidth, and the thickness of QDs has a great impact on the magnitude of energy levels. Among the different shapes of Ge/Si QDs, discoid QDs exhibit the most band crossing and broadest bandwith under the same physical parameters.
Review of Literature on Probability of Detection for Magnetic Particle Nondestructive Testing
Abstract : A critical review of the available literature concerning the minimum reliably detectable defect size aNDI for magnetic particle testing (MPT) in aerospace applications is presented. Four probability of detection (POD) studies relevant to detection of fatigue cracks in aircraft components were found over the period 1968 to 2011. As the statistical methods used in these four previous studies were either outdated or otherwise deficient, the original data were reanalysed using currently accepted techniques. A meta-analysis of the results is presented, with emphasis on statistical inferences for the defect size expected to be detected with 90% POD. It is shown that the minimum reliably detectable defect size aNDI = 2.0 mm currently specified by the Royal Australian Air Force for wet fluorescent magnetic particle inspection using the continuous method is consistent with estimates of the average performance of MPT derived from the reanalysis of the literature.