The present thesis addresses the characterization of Si high-pressure phases by transmission electron microscopy in order to elucidate the mechanisms leading to their formation in different Si-based materials. The specific fabrication of the high-pressure phases Si-III, Si-IV, Si-XII and Si-XIII by means of indentation and scratching, respectively, served as model system for spectroscopic characterizations. Calculations of the s,d-like pDOS of these phases via density functional theory are presented for the first time together with experimental EEL-spectra of their L2,3-edges. A distinct alteration of the near-edge fine structure becomes evident compared to reference spectra of Si-I and a-Si. The second part of the thesis presents examples of applications in materials science, e.g. the discussion of the mechanisms leading to the generation of Si high-pressure phases inside ripples after the repeated interaction of fs-laser pulses with Si surfaces.