Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-√3 × √3

Abstract

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-√3 × √3 surface and studied by scanning tunneling microscopy/spectroscopy and low energy electron diffraction (LEED). The growth mode was characterized as layer-by-layer growth with a single molecular unit cell in a short range order. The growth of the first two monolayers involves a molecule/substrate superstructure and a molecule/molecule superstructure. At higher coverages, the molecules in each layer were found to align so that unit cells are on top of each other. The experimentally obtained LEED pattern is described as a combination of patterns from the molecular unit cell and the molecule/substrate superstructure. The electronic structure was found to be strongly dependent on the film thickness for the first few layers: Several extra states are found at low coverages compared to higher coverages resulting in a very small pseudo gap of 0.9 eV for the first layer, which widens up to 4.0 eV for thicker films.

Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-23×23

“…In that system, at extremely low coverages (<0.02 ML), it is possible to find single molecules and 1D rows next to these nucleation sites, 7 but for coverages higher than this, the molecules grow well-ordered 2D islands in which the The Journal of Chemical Physics ARTICLE scitation.org/journal/jcp molecules arrange themselves in the canted structure. 7,14 The behavior is in stark contrast to what is found here for PTCDI on Sn-2 √ 3. On this substrate, the molecules do not move to defects or step edges but instead are found at specific sites on defect free and flat Sn-2 √ 3 areas.…”

“…This substitution is important because the N-H in the imide group of PTCDI blocks the type of hydrogen bondings between the bridging O and the side H atoms of the perylene core that 11,12 domino, 11 and canted phases. 7,[10][11][12][13][14] These all involve the aforementioned interactions. The Sn/Si(111)-2 √ 3 × 2 √ 3 reconstruction, henceforth called Sn-2 √ 3, is a metal-induced reconstruction formed at a Sn coverage above 1 monolayer (ML).…”

Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-3×3

“…The aforementioned shift for the main peak is the only change to the O 1s spectra, i. e. no large shifts or new components are found at low coverages. This is unexpected at first glance, considering the strong interaction between the substrate and the imide group which is revealed in the C 1s core levels, and the fact that an extra component in O 1s was found at submonolayer PTCDI coverages on the more weekly interacting substrate Ag-3 [20]. However, the intensity shift from C 1s component d to e at low coverages has previously been observed for PTCDI on both Ag(111) and Cu(111).…”

“…3 [20], henceforth Ag-3 , which would suggest that it could be due to an interaction between the perylene core of the molecules and the Sn-2 3 substrate.…”

“…The STM studies of PTCDI on Ag-3 and Sn-2 3 showed that the growth modes on the two surfaces are very different. On Ag-3 the growth mode is layer-by-layer while island growth after the first ML is found on Sn-2 3 [7,20]. A morphology with high islands with a fairly small top area will have a significant amount of molecules sitting on the edges of the islands.…”