Study of a brominated triphenylamine derivative on metal and semiconducting surfaces

Abstract

Room-temperature STM experiments were conducted for tribromotrioxoazatriangulene, (TBTANGO), on three surfaces: Si(111)-√3x√3-R30o-B, Ag(111), and Au(111) on mica. We found for the silicon samples there was a trade-off between attaining sufficient boron to passivate surface while remaining contamination free. STM imaging shows TBTANGO fragments were decomposed by surface dangling bonds. Of the procedures tested to prepare an atomically clean but passive surface, flashing near 1200oC, followed by annealing for 100 minutes at 930oC was the best. The (111) face of silver was explored at room-temperature and elevated-temperature as a molecular substrate. Both instances showed that TBTANGO forms two-dimensional organometallic structures. At room-temperature, short oligomers were formed. With the silver crystal at 240oC, large organometallic SAMNs were formed. The molecules formed a honeycomb organometallic network with trapped bromine atoms within many of the pores. The honeycomb cell of TBTANGO on hot silver is commensurate with the underlying substrate within error. The cell is s1 = 19.8 Å, s2 = 19.8 Å, θ = 60.3o. The pore-to-pore separation distance calculated by gas phase density functional theory was ~22.1 Å. The deposition of TBTANGO on hot silver also supported a close-packed phase believed to be an organometallic SA with 3 metal-carbon links. Thin films of Au(111) terminated facets supported the self-assembly of TBTANGO at a substrate temperature of 180oC. The unit cell was measured to be s1 = 10.5 Å, s2 = 10.5 Å, θ = 59.2o. Theoretical calculations for the self-assembled cell are s1 = 13.3 Å, s2 = 13.3 Å, θ = 60o. The discrepancy between the measured is attributed to STM drift.