Investigation of pressure-induced crystallization phenomenon under high pressure

• Grant number: 12/12380-0
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: October 01, 2012
• End date: May 31, 2013
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Antonio Ricardo Zanatta
• Grantee: Lucas Romano Muniz
• Host Institution: Instituto de Física de São Carlos (IFSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

The main goal of this project is to study the crystallization mechanisms induced by high hydrostatic pressures. The systems to be investigated are micro- or nano-structures embedded in amorphous inorganic semiconductors (a-Si and a-Ge), oxygen- (a-SiOx and a-GeOx) or nitrogen-containing (a-SiNx and a-GeNx) matrices. They will be prepared in the form of thin films under three different ways: doped (with varying concentrations of metal species), multi-layered (amorphous films intercalated with metal films), and patterned (lines or dots of metal surrounded by the amorphous film, for example). In all cases, the films (and/or structures) will be prepared by the radio frequency sputtering method under various experimental conditions: involving different metals (Al, Ni, Cr, Au, Ag, Zn, Cu, etc..), under different atomic concentrations (metal, oxygen, or nitrogen), and different thickness/geometry. Once prepared, the crystallization can take place "spontaneously " (from a specific concentration of metal) and/or be activated by thermal treatments or high hydrostatic pressures. Because of the presence of metallic species, the crystallization occurs at temperatures significantly lower than those observed in metal-free systems. Both crystallization processes originate from the presence of "crystal seeds" (micro- or nano-crystal) that develop as the thermal annealing advances. The films will be characterized by different experimental techniques such as: Raman scattering, optical spectroscopy (absorption and emission in the regions of UV-VIS-NIR), X-ray diffraction (XRD), electron microscopy (SEM and TEM), and Rutherford backscattering (RBS), for example. In addition to the preparation and systematic investigation of samples, the main differential of this project is the use of a pressure cell (DAC - diamond anvil cell) to study the crystallization mechanisms (PIC - pressure induced crystallization). According to this approach, we will investigate in detail the microscopic mechanisms involved in the crystallization process and the eventual formation of luminescent nano-structures from the combined action of metal species, temperature and pressure. Finally, and following a completely original methodology, we hope to get a microscopic (and realistic) view of the main phenomena that govern the formation of micro- or nano-structures embedded in amorphous semiconductors - due to the presence of metal species and/or by the application high pressures. Finally, we expect that the achievement of luminescent silicon/germanium nano-crystals (with light emission mainly in the visible region) may be substantially improved by the presence of metallic species, in which case the formation of crystallites will take place at temperatures lower than those usually reported in the literature.