STM tip-assisted engineering of molecular nanostructures: PTCDA islands on Ge(001):H surfaces

Abstract

SummaryIslands composed of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules are grown on a hydrogen passivated Ge(001):H surface. The islands are studied with room temperature scanning tunneling microscopy and spectroscopy. The spontaneous and tip-induced formation of the top-most layer of the island is presented. Assistance of the scanning probe seems to be one of the factors that facilitate and speed the process of formation of the top-most layer.

Characterization of PTCDA nanocrystals on Ge(001):H-(2×1) surfaces

“…The island edges, height and general morphology all are preserved. However, we have found that there is a possibility to interact with such a stable nanocrystal through the change in scanning conditions [20]. Indeed, by applying voltage pulses in the vicinity or on the top of the island a dynamic process leading to formation on new on-top molecular layer is initiated.…”

“…Actually, if there is no STM tip development of the new layer may be even one order of magnitude slower [20]. It must be stated clearly; once the process of growth is started by the pulse it may proceed without the assistance of scanning probe.…”

“…For example, in case of metal surfaces such a scenario is realized by means of few monolayers of insulator, like NaCl [5][6][7][8][9][10][11][12][13], for semiconductor surfaces it might be either few monolayers of insulator, like KBr on InSb [14,15], or a single layer of atomic hydrogen, e.g. Si:H and Ge:H surfaces [16][17][18][19][20]. The buffer layer dramatically enhances mobility of adsorbed molecular species and eventually may ease their selfassembly and formation of molecular nanocrystals [9][10][11]20,21].…”

“…the long-term stability under UHV conditions and the stability under typical STM scanning conditions. The last point is important with respect to our latest report on feasibility of reshaping of these islands with use of STM tip [20].…”

“…Si:H and Ge:H surfaces [16][17][18][19][20]. The buffer layer dramatically enhances mobility of adsorbed molecular species and eventually may ease their selfassembly and formation of molecular nanocrystals [9][10][11]20,21].…”