The Role of Interdiffusion and Spatial Confinement in the Formation of Resonant Raman Spectra of Ge/Si(100) Heterostructures with Quantum-Dot Arrays

The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam epitaxy in an apparatus integrated with a chamber of the scanning tunneling microscope into a single high-vacuum system are investigated using Raman spectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes are considerably enhanced upon excitation of excitons between the valence band $\Lambda_3$ and the conduction band $\Lambda_1$ (the E1 and E1 + $\Delta_1$ transitions). This makes it possible to observe the Raman spectrum of very small amounts of germanium, such as one layer of quantum dots with a germanium layer thickness of 10 \r{A}. The enhancement of these modes suggests a strong electron-phonon interaction of the vibrational modes with the E1 and E1 + $\Delta_1$ excitons in the quantum dot. It is demonstrated that the frequency of the Ge-Ge mode decreases by 10 cm^-1 with a decrease in the thickness of the Ge layer from 10 to 6 \r{A} due to the spatial-confinement effect. The optimum thickness of the Ge layer, for which the size dispersion of quantum dots is minimum, is determined.Comment: 14 pages, 9 figure

Change of equivalent layer porosity of pellets along the length of burning conveyor machine

Difficulties in determining the flow resistance of layer of pellets in the burning conveyor type machines during the heat treatment, associated with significant changes in the layer structure due to its shrinkage during the drying process, the low strength of raw pellets, adjustment layer segregation, sintering and melting of pellets, were considered. As a result, flow resistance of pellets layer on conveyor machines greatly exceeds the resistance value which is obtained in laboratory tests of gas dynamics of pellet layer. According to the impact of many factors on the structure of a burnt pellets layer, which can be taken into account only in their cumulative effect, the authors have introduced the concept of an equivalent porosity. As a result of calculating the amount of equivalent porosity with the available literature data and the data obtained in working out the pellets burning technology in a high layer on Kachkanar conveyor machines, a pattern of its distribution along the length of the conveyor machine was revealed. It was established that most significantly the porosity of the layer reduce due to layer shrinkage in the drying zone and cracking of pellets at the outlet of it. The analysis of estimated expressions to determine the gas-dynamic characteristics of the pellets layer helped to get the dependencies that with a sufficient degree of accuracy can be used to calculate the gas-dynamic characteristics of the layer on the conveyor machines considering different porosity. The obtained results can be used in determining the gas dynamic and thermal conditions, providing work of burning conveyor machines with low specific fuel consumption and high quality of the calcined product. © 2017, National University of Science and Technology MISIS. All rights reserved