Basel Universität

Oxides and Insulators

Anchoring of a dye precursor on NiO (001) studied by non-contact atomic
force microscopy.

Figure: a) Large scale RT ncAFM image of molecules on the NiO surface. b) Second pass frequency shift image on a single molecule. c) Suggested model for the molecule adsorption.

We performed high-resolution topographic measurements using bimodal nc-AFM at room temperature of the anchoring part of a larger dye molecule (DCPDMbpy) adsorbed on a NiO(001) crystal surface. First, the surface structure of NiO(001) is resolved with atomic resolution. Second, by using the multipass technique, we study the adsorption of molecule. For isolated molecule, small cluster and larger island we found that molecules are lying flat on the surface. Enantiomeric adsorption at room temperature is also evidenced.

For more information please see our publication in bjnano.

Atomic scale defects creation on alkali halides

Figure: Surface defects created on alkali halide surface with low temperature plasma exposure (LTP). a) Nanocluster after LTP of argon plasma treatment. b) Proposed model for the nanocluster shape. c) Single atomic vacancy created on the KBr(001) surface and stable at room temperature afterhelium LTP exposure.

We used a Low Temperature Plasma (LTP) source to create defects on the clean KBr(001) surface and characterized the surface at the atomic scale using our home made room temperature ncAFM system . Depending on the gas used to create the plasma we can obtain various nanostructuration of the surface. With Argon, we observed nanoclusters creation presenting edges alignment along unfavourable polar step edge. With Helium, we are able to create well distributed single atomic vacancies stable at room temperature.

For more information please see our publication in Phys. Chem. Chem. Phys.

C60 islands reshaping on BNL surface via ncAFM

Figure: Tip-Induced Shape Modi cation of a C60 Island. a-b) Topographic images recorded before and after the tip-induced shape modi cation process. c) Profiles of the C60 island acquired while modifying its shape from triangular to hexagonal. d-h) Sequence showing the shape modi cation process. The tip was continuously scanned over the island but the tip/sample distance was intentionally varied by changing frequency shift.

We used our home made RT AFM microscope , to study C60 molecules deposited on an organaic layered crystal (BNL). C60 molecules form islands at room temperature on the surface. We demonstrate the dynamical reshaping of those C60 nano-structures under the local action of the AFM tip at room temperature. The dissipated energy is about 75 meV and can be interpreted as the activation energy required for this migration process.

For more information please see our publication in ACSNano.

Electrospray Deposition of organic molecules on bulk insulators

Figure: a) Electrospray deposition. b) ncAFM topography image of the KBr(001) surface and molecular islands. c) Single molecule on KBr(001) and corresponding drawing.

We used a modified commercial electrospray deposition device , connected to the vacuum chamber of our microscope, to introduce large organic molecules in UHV and deposited them on bulk insulator surfaces. At large coverage, we measure a charging of the surface. Annealing is necessary to reduce the charging and observe molecular islands on the surface. At low coverage, no charging effect is measured and isolated single molecules are observed.

For more information please see our publication in the beilstein journal of nanotechnology.

Adsorption Geometries of Single Cu-TCPP Molecules on Rutile TiO2 (110)

Figure: a) High resolution AFM topography image and relaxed Cu-TCPP geometry from DFT calculations. b) and c) Topography image and corresponding slope corrected map of the local contact potential from KPFM.

We demonstrated the investigation of different Cu-TCPP binding geometries and adsorption sites on rutile TiO2(110) at room temperature using nc-AFM at the second flexural resonance of the cantilever and FM-KPFM. Topography images revealed two configurations that were differently oriented with respect to the TiO2 surface structure. KPFM indicated that there is a charge transfer to the surface upon adsorption leading to an interfacial dipole moment. The experimental results were verified and further investigated with DFT calculations.

See our publication in JCP

Atomic manipulation on bulk insulator at room temperature with ncAFM.

Vertical manipulation was successfully performed several times, perfectly aligning 20 Br- ions in the NaCl surface, forming a "Swiss cross" with a size of 5,64 x 5,64 nm. Note that this is the largest number of the atomic manipulations ever achieved at Room Temperature. The Br- ions are positioned at every other Cl- ion site on the surface, and the fabricated cross is stable for a relatively long time.

Atomically resolved bimodal DFM images of a KBr(001).

Figure: Atomically resolved bimodal DFM images of a KBr(001) surface obtained at a series of quasi-constant heights.
We present bimodal dynamic mode atomic force microscopy, in which two resonance modes are excited and detected. The combination of subangstrom amplitude at the second flexural resonance of a commercially available silicon cantilever with the commonly-used large amplitude oscillation at the fundamental resonance improves the spatial resolution while avoiding jump-to-contact instabilities.

See our publication in PRL.