M. Goryl

Surface structure of metal-organic framework grown on self-assembled monolayers revealed by high-resolution atomic force microscopy.

The surface structure of an individual metal-organic framework (MOF) microcrystal grown on a functionalized surface has been successfully investigated for the first time in air and vacuum using high-resolution atomic force microscopy. Moreover, this detailed surface analysis has been utilized to optimize the MOF formation procedure to obtain a defect-free surface structure. Comparison of obtained data with recent microscopic studies performed on the same MOF crystal but grown by a conventional procedure clearly shows a much higher quality of crystals produced by surface oriented growth. Importantly, this method of preparing crystals suitable for microscopic analysis is also much faster (3 days compared to 2 years) and, in contrast to the conventional method, produces material suitable for in situ study. These results thus demonstrate for the first time the possibility of nanoscale investigation/modification of MOF surface structure.

Copper phthalocyanine molecules on an InSb(001) c(8 × 2) surface studied by ultra-high-vacuum STM and non-contact AFM

The surface ordering of copper phthalocyanine (CuPc) molecules deposited onto an InSb(001) c(8 × 2) reconstructed surface has been studied using scanning tunneling microscopy (STM), non-contact atomic force microscopy (nc-AFM) and low-energy electron diffraction (LEED). It was found that at room temperature the CuPc molecules are only weakly bound to the InSb surface and the adjacent molecules and consequently they are relatively mobile at submonolayer coverage. STM images show that at the initial stages of growth molecules are assembled in ordered molecular chains parallel to the surface reconstruction rows, i.e. along the [110] crystallographic direction. Furthermore, adsorption of the molecules at step edges is observed. At coverages below 1 ML molecules diffuse at the surface and form two-dimensional islands, which leads to an additional characteristic (n × 3) LEED pattern indicating one-dimensional ordering within the molecular chains. High-resolution STM imaging at negative sample bias reveals a unique structure of the molecular contrast which may be related to the highest occupied molecular orbital (HOMO) of the individual CuPc molecules. For CuPc monolayer coverage submolecular resolution is also obtained for nc-AFM imaging. Finally, examples of single molecule manipulation by the STM tip are given.

PTCDA molecules on an InSb(001) surface studied with atomic force microscopy.

PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) molecular structures assembled on an InSb(001) c(8 × 2) reconstructed surface have been studied using frequency modulated atomic force microscopy. The high-resolution imaging of the structures is possible through repulsive interactions, using the constant height scanning mode. During initial stages of growth the [110] diffusion channel dominates as indicated by formation of long PTCDA molecular chains parallel to the [110] crystallographic direction on the InSb surface. For a single monolayer coverage a wetting layer of PTCDA is formed. Finally it is shown that the PTCDA/InSb is a promising system for building molecular nanostructures by manipulation of single molecules with the AFM tip.