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.
Strained ZnSe nanostructures investigated by x-ray diffraction, atomic force microscopy, transmission electron microscopy and optical absorption and luminescence spectroscopy
Nanostructured ZnSe (Q-ZnSe) films synthesized by a wet chemical route have been studied. The evolution of particle size dependent strain, morphology and luminescence properties have been investigated, using x-ray diffraction, atomic force microscopy, transmission electron microscopy and optical absorption and luminescence spectroscopy. It is shown that the degree of structural orientation, self-organization and the nature of strain are dependent on particle size. Self-organized Q-ZnSe films with narrow particle size distribution have been successfully synthesized. Systematic particle size dependent blue shifts in the optical absorption edge and PL maxima have also been reported.
Achievements and contradictions of the Peruvian agrarian reform
Different paths of transition to capitalist agriculture, as well as different types of agrarian reform, can be distinguished. The Peruvian agrarian reform is analysed within this context and evaluated in terms of its contribution to rural development. The Peruvian case underlines the importance of understanding the rationality of the pre‐existent agrarian system for a successful restructuring of the agrarian economy and society. The contradictions which arose between the State's model and the peasants’ model of agrarian reform, as well as those between different types of peasants, are discussed. Peru's experience is also a reminder that a land reform is not a sufficient condition for rural development unless accompanied by proper price, marketing, credit and investment policies.