Oxygen vacancies （OVs） play a critical role in the physical properties and applications of titanium dioxide nanos- tructures, which are widely used in electrochemistry and photo catalysis nowadays. In this work, OVs were artificially introduced in the surface of a pure TiO2 single crystal by pulsed laser irradiation. Raman spectra showed that the intensity of Eg mode was enhanced. Theoretical calculations disclose that this was caused by the strong coupling effect between the phonon vibration and plasmon induced by the OVs-related surface deformation, and good agreement was achieved between the experiments and theory.
High pressure has a significant influence onβ-FeSi_2 band gaps and optical absorption tuning.In this work,using density functional theory,we investigate the effect of high pressure on the optical absorption behavior of aβ-FeSi_2（100）/Si（001） interface with some Si vacancies.As the pressure increases,the optical absorption peak down-shifts firstly,reach minimum values,and then un-shifts slowly.The electronic orbital analysis indicates that the electronic transition between the highest occupied states and the lowest unoccupied states mainly originate from Fe atoms at the interface regions.Structural analysis discloses that the Si（001） slab partially offsets the pressure exerted on theβ-FeSi_2（100） interface,but this effect will become weaker with further increasing pressure,and this physical mechanism plays an important role in its optical absorption behavior.
Increases in Si content and the calculated Raman spectra acquired from the Si_xGe_（1-x） alloys reveal that the frequencies of the Ge-Si and Si-Si modes are up-shifted obviously,meanwhile that of the Ge-Ge optical mode is down-shifted,which is strongly dependent on their microstructural changes.The linear decrease and increase caused by their force constant（bond lengths and bond angles） changes,which can be used as a fingerprint to identify the average Si content.The complex microstructural changes induced by increasing Si content can be clearly displayed by Raman spectra transformation.
