Received: January 17, 2007

In Final Form: July 19, 2007

Abstract:

The thermal stability and electronic structure of deuterated C₆₀ films were studied by temperature-resolved mass spectroscopy and ultraviolet photoionization/photoelectron spectroscopy, UPS. The films were prepared by exposing C₆₀ layers predeposited onto HOPG to a flux of thermal energy atomic deuterium. The initial stage of on-top deuteration at room temperature is associated with the formation of a capping layer that exhibits a higher thermal stability than pristine C₆₀ films. The sublimation heat of the capping layer increases with the deuterium dose applied and levels off at a value of 2.15 ± 0.05 eV/cage at deuterium exposures in the range of 10¹⁶ D/cm^-2. Capping layers appear to kinetically hinder further deuteration of subsurface C₆₀. This hindrance can be reduced by performing the initial (and subsequent) deuteration at elevated sample temperatures. Further deuterium exposure leads to the formation of higher deuterofullerenes (e.g., C₆₀D₃₆). These exhibit sublimation enthalpies of 1.39 ± 0.1 eV/cage, considerably lower than the capping layers but comparable to pristine C₆₀ films. Capping layers are air-resistant and amenable to the fabrication of stable multilayered [C₆₀/C₆₀D_x]_m structures.

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