The structures of interstitial hydrogen centers in VO2 in the dilute limit from their vibrational properties and theory.

The introduction of a large concentration of H into VO2 is known to suppress the insulating phase of the metal-insulator transition that occurs upon cooling below 340 K. We have used infrared spectroscopy and complementary theory to study the properties of interstitial H and D in VO2 in the dilute limit to determine the vibrational frequencies, thermal stabilities, and equilibrium positions of isolated interstitial H and D centers. The vibrational lines of several OH and OD centers were observed to have thermal stabilities similar to that of the hydrogen that suppresses the insulating phase. Theory associates two of the four possible OH configurations for Hi in the insulating VO2 monoclinic phase with OH lines seen by experiment. Furthermore, theory predicts the energies and vibrational frequencies for configurations with Hi trapped near a substitutional impurity and suggests such defects as candidates for additional OH centers that have been observed.

Key to understanding interstitial H2 in Si.

A new IR absorption line at 3191.1 cm(-1) has been discovered for the interstitial HD molecule in Si. This new line appears for sample temperatures above approximately 20 K and lies 73.9 cm(-1) below the 3265.0 cm(-1) line previously observed for HD. We attribute the 73.9 cm(-1) energy difference to the rotation of the interstitial HD molecule. The selection rules associated with these two lines are consistent with the puzzling absence of an ortho-para splitting in the IR absorption spectra of H2 and D2 in Si.