Long-Term Stability and Electrical Performance of Organic Monolayers on Hydrogen-Terminated Silicon

The long-term stability (gradual oxidation) of two structurally different organic monolayers, C 6 H 5 (CH 2 ) 3 −Si≡ ( C3Ph −Si≡) and CH 3 (CH 2 ) 11 −Si≡ ( C12 −Si≡), covalently bonded to n-type silicon(111) was studied and correlated to the electrical performance of the thus formed mercury | monolayer | n-Si junctions. High-resolution XPS analysis of the O 1s region on freshly prepared samples identified physically adsorbed oxygen (O ad ) and oxygen-containing species (SiO x ) bound to silicon at 532.2 and 533.5 eV, respectively. When left under ambient conditions, both bands increased in intensity as time progressed, while no change in the carbon content (C 1s peak) was observed. More importantly, upon aging, there was a noticeable increase in the electrical current flow of both <Hg| C12 −Si≡> and <Hg| C3Ph −Si≡> junctions; a considerably larger increase occurred in the former sample, which has less oxygen content than that of the latter junction (based on the O 1s(O−Si)/Si 2p peak area ratios). These results suggest that the slow oxidation of molecularly modified silicon may, in fact, dictate the electrical performance of the thus formed molecular diode junctions.