Unique lack of chemical reactivity for 2,3-dimethyl-2-butene on a Si(100)-2X1 surface

Adsorption of 2,3-dimethyl-2-butene on Si(100)-2X1 has been studied by a combination of multiple internal reflection Fourier transform infrared spectroscopy and computational investigations implementing density functional theory (DFT). Since the previously studied olefins have been shown to form a di-sigma product on this surface following [2+2] cycloaddition, it was also initially expected for 2,3-dimethyl-2-butene. Infrared spectra taken at 100 K show that 2,3-dimethyl-2-butene adsorbs on the surface molecularly at this temperature. Heating the surface to room temperature left no indication of a chemisorbed product. Large doses at room temperature did not produce any observable absorption bands in the infrared spectrum, indicating that [2+2] cycloaddition of 2,3-dimethyl-2-butene does not occur. This assessment was verified by the Auger electron spectroscopy studies confirming that neither room temperature exposure nor annealing to 800 K produced any carbon remaining on this surface. These experimental observations of the absence of a chemical reaction between an olefin and a very reactive silicon surface were substantiated by DFT investigation of the adsorption kinetics. The formation of two possible pi-bonded precursors was considered, and the energies required to form the di-sigma-bonded product from either one of these precursors were predicted to be substantially higher than the desorption barrier. Thus, 2,3-dimethyl-2-butene is a unique olefin that is very inert with respect to the Si(100)-2X1 surface, making it a desirable carrier gas or a ligand in the precursor molecules in a number of deposition processes involving silicon substrates. (c) 2008 American Vacuum Society.