Is vacuum annealing converts p-type single wall carbon nanotube field effect transistor (in air) to n-type (in vacuum) is universially true (?)

Our study on nickel silicide and gold contacted single-wall-carbon-nanotube field effect transistors (SWCN-FETs) is in sharp contrast to earlier published reports of type conversion in SWCN-FETs (from p- to n-) when cycled between air and vacuum, and indicates that (1) band gap of SWCN (2) the extent to which Fermi level of the metal contact gets shifted due to adsorption/desorption of oxygen and (3) relative position of the Fermi level of the metal contact with respect to the top of the valance band of SWCN (in an oxygen-free environment) are some of the important factors that governs such phenomena.