Search Results (3 total)

We have studied a series of sharp photoluminescence emission lines between 1.65 and 1.80 eV in synthetic diamond films. The series of lines is decomposed into a set of parent lines plus vibrational sidebands spaced 24 meV apart. This energy does not correspond to any phonons with high density of states in the diamond crystal. The relative intensities of the main lines exhibit no temperature dependence (between 20 and 160 K), implying ground-state splitting. The narrow linewidth and temperature-independent emission energy imply only weak interaction with the diamond host. The temperature-dependence of the linewidth is well described by thermal broadening. We attribute the emission to optical centers as a consequence of tungsten incorporation into the diamond film. The tungsten originates from the electrode during deposition. © 1996 The American Physical Society.

We report cryogenic high-pressure measurements of a defect-related emission at 1.25 eV in silicon-doped GaAs. The pressure measurements prove that the 1.25-eV photon energy is relative to the conduction band, implying a deep defect level 0.30 eV above the valence band and an electron-capture process from the conduction band into the defect. The defect level moves up in the band gap at a rate of 23±3 meV/GPa. These results are consistent with a vacancy-related defect level, possibly stemming from a gallium-vacancy–silicon-at-gallium (second-nearest-neighbor) defect complex.

We have used Raman scattering to investigate the effects of intense laser pulses on the structure of resolidified graphite. Graphite was irradiated with 0.325–3.25-J/cm², 620-nm, 90-fs single-laser pulses causing it to melt and rapidly resolidify. Raman studies of the resolidified carbon in the crater show that the rapid annealing process (by pulses with energy fluences ≥0.82 J/cm²) causes a breakdown in the ordered layers of hexagonal carbon rings and disorder in the intraplanar spacing upon resolidification into a nanocrystalline material. The thickness of the nanocrystalline-graphite near-surface layer increases with increasing fluence. Residual planar structure of the resulting material is observed for the various pulse-energy values by comparing the narrow graphitic 1581-cm^-1 and the broad 1360-cm^-1 and 1600-cm^-1 vibrational bands. The interplanar structure of our nanocrystalline graphite is also studied quantitatively via the low-frequency shear mode at 42 cm^-1. The Raman spectrum of our glassy carbon is found to be well described by planar ordering approximately 2 to 3 layers in extent using a simple correlation function approach. Our results indicate a layered morphology is present in our nanocrystalline graphite, confirming a strong sp² bonding character.