期刊
JOURNAL OF PHYSICS-CONDENSED MATTER
卷 24, 期 8, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0953-8984/24/8/084005
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资金
- Swiss National Science Foundation (SNF)
- ESF EUROCORE
- Swiss National Center of Competence in Research on 'Nanoscale Science' (NCCR-NANO)
Recent advances in non-contact atomic force microscopy (nc-AFM) have led to the possibility of achieving unprecedented resolution within molecular structures, accomplished by probing short-range repulsive interaction forces. Here we investigate C-60 molecules adsorbed on KBr(111) and Cu(111) by tuning-fork-based nc-AFM. First, measurements of C-60 deposited on KBr(001) were conducted in cryogenic conditions revealing highly resolved nc-AFM images of the self-assembly. Using constant-frequency shift mode as well as three-dimensional spectroscopic measurements, we observe that the relatively weak molecule-substrate interaction generally leads to the disruption of molecular assembled structures when the tip is probing the short-range force regime. This particular issue hindered us in resolving the chemical structure of this molecule on the KBr surface. To obtain a better anchoring of C-60 molecules, nc-AFM measurements were performed on Cu(111). Sub-molecular resolutions within the molecules was achieved which allowed a direct and unambiguous visualization of their orientations on the supporting substrate. Furthermore, three-dimensional spectroscopic measurements of simultaneous force and current have been performed above the single molecules giving information of the C-60 molecular orientation as well as its local conductivity. We further discuss the different imaging modes in nc-AFM such as constant-frequency shift nc-AFM, constant-height nc-AFM and constant-current nc-AFM as well as three-dimensional spectroscopic measurement (3D-DFS) employed to achieve such resolution at the sub-molecular scale.
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