Templated growth of 3,4,9,10-perylenetetracarboxylic dianhydride molecules on a nanostructured insulator

Abstract

Nanometre-scale 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) crystallites were produced by trapping the molecules inside monolayer-deep rectangular pits on an alkali halide surface. Noncontact atomic force microscopy was used to measure the crystallite dimensions and lattice structure with molecular resolution. The molecule-substrate lattice mismatch and island heights, typically three to four PTCDA layers, indicate a stress in the first two layers. One-and two-layer crystallites were only observed in pits with side lengths smaller than 10 nm.

Role of van der Waals forces in the adsorption and diffusion of organic molecules on an insulating surface

“…In experimental AFM images, we observe that PTCDA molecules preferentially trap in the pits of irradiated alkali halide surfaces forming regularly arrayed islands, either completely or partially filling pits, or even overfilling them. 8 Islands are not formed on the atomically flat terraces of the surface, and isolated molecules are never observed on the terraces or at straight step edges. However, we have occasionally observed them at the edge of pits at kink sites.…”

“…[2][3][4] Among candidate molecules, 3,4,9,10-perylenetetracarboxylic-dianhydride ͑PTCDA͒ is a prototype organic semiconductor that has been increasingly studied on insulating surfaces to provide the electrical isolation of the molecule from the substrate essential for device performance. [5][6][7][8][9][10][11] In general, characterization of molecular ordering on the surface requires high-resolution imaging and is only possible on insulating surfaces with noncontact atomic force microscopy ͑NC-AFM͒. 12 Earlier studies have shown that PTCDA islands with a well-defined herringbone arrangement form preferentially at the bottom of step edges.…”

“…6 Moreover, atomic depth rectangular pits can be used as a means of trapping the molecules, resulting in islands which have the dimensions of the templating pits. 7,8,13 To date, there is little known about the pit trapping mechanism, nor the nature of the bonding between organic molecules such as PTCDA and insulating surfaces in general-a topic that has proved controversial for PTCDA on metal surfaces. [14][15][16][17][18][19][20][21] In order to investigate the nucleation and the trapping of PTCDA molecules, we used irradiation to controllably produce monolayer ͑ML͒ depth pits to act as trapping sites and used NC-AFM to study PTCDA in the submonolayer regime.…”

Ehrlich-Schwoebel effect for organic molecules: Direct calculation of the step-edge barrier using empirical potentials

“…The strength of the step edge barrier controls the amount of mass transport between different crystalline layers, and hence determines the temperature dependence of the kinetic growth mode (two-dimensional layer-by-layer or threedimensional mound growth) in situations where energetic driving forces shaping the surface morphology can be neglected. 4 There is considerable indirect evidence that points to the presence of a step edge barrier for prototypical organic semiconductor molecules like 3,4,9,10-perylenetetracaboxylic-dianhydride (PTCDA) 5,6,7,8,9 and pentacene, 10,11,12 and the ES effect has been invoked in several simulation studies of organic film growth 9,10,13 . Very recently a quantitative estimate for the step edge barrier on pentacene has been obtained from an analysis of experimental layer coverages 14 .…”

“…This is, e.g., described in ref. 8 ; the authors explain this behavior with mobile molecules that are diffusing on the topmost layer.…”