Imaging perylene derivatives on rutileTiO2(110)by noncontact atomic force microscopy

Abstract

The adsorption of 3,4,9,10-perylene tetracarboxylic diimide derivative molecules on the rutile TiO 2 ͑110͒ surface was investigated by noncontact atomic force microscopy and density-functional theory ͑DFT͒ calculations. After submonolayer deposition, individual molecules are observed to adsorb with their main axis aligned along the ͓001͔ direction and centered on top of the bridging oxygen rows. Depending on the tip termination, two distinctly different molecular contrasts are achieved. In the first mode, the molecules are imaged as bright elongated features, while in another mode the molecules appear with a bright rim and a dark bow-shaped center. Comparison with the defect density on the bare TiO 2 ͑110͒ surface suggests that the molecules preferentially anchor to surface defects. Our DFT calculations reveal details of the molecular adsorption position, confirming the experimentally observed adsorption on top of the bridging oxygen rows. The DFT results indicate that diffusion along the rows should be quite easily possible, while diffusion perpendicular to the rows seems to be hindered by a significant energy barrier.

Single-molecule switching with non-contact atomic force microscopy

“…• towards the Ti troughs (see figure 2(c)) [27]. This tilted adsorption position is explaining the previously mentioned bent imaging of the molecules.…”

“…Note that all switching events were exclusively observed when the tip was scanned over the molecule, in other words, we did not observe spontaneous switching events. From the calculations carried out to elucidate the detailed adsorption position of PTCDI on the rutile (110) surface [27] we are also able to obtain an estimate for the energy barrier, which must be overcome to push the molecule from one side of the bridging oxygen row to the other side. To reduce the needed calculation time, two simplifications are made: first, bare PTCDI without the alkyl chain side groups are considered for the calculations.…”

“…In previous investigations we have observed two different imaging modes for the molecules [27], which are shown in figure 2. In mode I (figure 2(a)) the molecules were imaged as bright and unstructured features, while in mode II (figure 2(b)) the molecules were imaged as features with a dark center and a bright rim.…”

“…The chemical structure of this molecule, referred to as PTCDI S-13, is shown in figure 1(a). After a cleaning procedure (heating for 12 h at 400 K) the molecules were sublimated in situ at a temperature of 455 K. For more details on the preparation, adsorption and imaging characteristics see [27]. PTCDI S-13 was studied on the (110) surface of rutile titanium dioxide, which is shown in figure 1(b).…”

Calculating the Entropy Loss on Adsorption of Organic Molecules at Insulating Surfaces

“…[16][17][18][19][20][21][22][23][24] Adsorption geometries in particular can be investigated using scanning probe methods such as non-contact atomic force microscopy (NC-AFM). [25][26][27] However, achieving high resolution in NC-AFM images at room temperature is still a challenge 28 and often the interpretation of images down to an atomistic level requires a detailed understanding of the tip-sample interactions.…”