Video-STM, LEED and X-ray diffraction investigations of PTCDA on graphite

Abstract

Thin films of the organic molecule perylene-3,4,9,10-tetracarboxylic-dianhydride ("PTCDA") on graphite(0001) have been investigated from the mono-to the multilayer regime with low energy electron diffraction (LEED), X-ray-diffraction in Bragg-Brentano geometry, and high resolution scanning tunneling microscopy (STM). These different methods proved epitaxial growth in a coincident superstructure and yielded congruent results concerning details of the crystallographic structure of the epilayer. In addition it was possible to resolve submolecular structures in high resolution STM images; a comparison of the 10 resolved maxima of the tunneling current with the molecular structure leads us to question the conventional model description of tunneling.

STM investigations of PTCDA and PTCDI on graphite and MoS2. A systematic study of epitaxy and STM image contrast

“…As already described in a previous article PTCDA on graphite appears in high reslution STM images as a pattern of 10 bright spots [13]. Figure 10a-d show high resolution images of PTCDA and PTCDI on HOPG and MoS 2 all recorded under similar conditions.…”

“…With our Video-STM it is also possible to see individual molecules appearing and disappearing at the domain edges. Figure 3 shows a 300 A • 300 A image of PTCDA on M o S 2 with the typical herringbone structure of the overlayer as it is known from the bulk structure and from monolayers on graphite [13,14]. But unlike to graphite, where we observe a superstructure (Fig.…”

“…For P T C D A on both substrates the quadrupole moment leads to a closely packed herringbone structure with nearly rectangular unit cells [13]. Under these constraints there is only little room for structural variability.…”

“…Monolayers of PTCDA were studied by NEXAFS and ARUPS on Si(lll) and Ag(lll) and by X-ray diffraction and TEM on cleaved NaC1 and KC1 crystal surfaces [10][11][12]. On graphite the crystalline structure of PTCDA is known from the monolayer to the multilayer regime from STM, LEED and X-ray diffraction investigations [ 13].…”

STM investigations of C6Br6 on HOPG and MoS2

“…imaging of the underlying substrate after monolayer removal by slowly approaching the tip to the substrate, as described previously [12]. bate and substrate the overlayer shows a moire pattern.…”