Scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and theoretical studies of trimethylphosphine (TMP) on a Si(111)-(7×7) surface

Abstract Adsorption of trimethylphosphine (TMP) on a Si(111)-(7×7) surface was studied using scanning tunneling microscopy (STM), high-resolution electron energy loss spectroscopy (HREELS), and theoretical calculations. It was found from STM and HREELS that most of the TMP molecules are adsorbed molecularly on center adatom sites at room temperature. A semi-empirical calculation (AM1 method) verified that this is energetically favorable. It is also found that one of the protrusions (unoccupied state images) on the center adatom site moves to the rest atom site and three protrusions (occupied state images) appear on the corner and center adatom sites in the second scan (interval of a few minutes). The results of a theoretical calculation indicate that adsorption of the three CH 3 groups and the P atom on the adatom and rest atom sites, respectively, is energetically favorable. This explains the STM images well. The HREELS result suggests that the CH 3 group is split off and dissociated into CH 2 (or CH) and H upon heating the sample. The result of the theoretical calculation shows that the dissociation of CH 3 into CH 2 and H is energetically preferable when CH 2 is bridged between an Si adatom and an Si atom in the second layer and H is on the rest atom site.