Decomposition of triethylphosphine (TEP) and tertiarybutylphosphine (TBP) on a GaP(001)–(2×4) surface studied by HREELS

Abstract

Adsorption and decomposition of triethylphosphine (TEP) and t-butylphosphine (TBP) on a GaP(001)–(2×4) surface have been studied by using high-resolution electron energy loss spectroscopy (HREELS). For TEP, since the vibration modes corresponding to the ethyl group and the υ(PC) mode appear at 100 and 300 K, we conclude that TEP is adsorbed molecularly at those temperatures. All the modes are decreased in intensity upon annealing the sample above 300 K and have almost disappeared at 700 K. The υ(Ga–H) mode is not found at elevated temperatures, which is in sharp contrast to the previous result that the υ(Si–H) peak appears on a Si(001) surface for TEP. The absence of the υ(Ga-H) mode is explained as the decomposition of the ethyl group into ethylene and hydrogen through a β-hydride elimination which occurs at temperatures higher than the desorption temperature of hydrogen of Ga–H. Our HREELS data suggest that switching off the ethyl group to the surface and re-adsorption of ethylene on the surface do not occur. The latter process is important because it avoids carbon incorporation in the growth of films. For TBP, most of TBP is adsorbed molecularly at 100 K and is partially dissociated into (C 4H 9)PH (a) and H(a) at 300 K. All the modes corresponding to the t-butyl group are decreased in intensity above 300 K and almost disappear at 550 K. The increase in intensity of the υ(Ga–H) signal at elevated temperatures is not found; this can also be explained by the reason mentioned on TEP. It is also suggested that switching of tertiarybutyl group to the surface and re-adsorption of isobutene do not occur.