Atomic Force Microscopy: Highlights

C60 Molecular Probes

This work shows that the precise orientation of a C₆₀ molecule which terminates the tip of a scanning probe microscope can be determined from submolecular contrast images of the fullerene cage. Noncontact atomic force microscopy resolves the atoms of the C₆₀ cage closest to the surface for a range of orientations. Measurements of the C₆₀ pair potential are in excellent agreement with theoretical predictions based on pairwise summation of the van der Waals interactions.

Image:

Atomic resolution imaging of a single molecule probe. The Si(111)-(7x7) unit cell is highlighted in green. In this case only two atoms of the fullerene cage are observed - the molecule is oriented such that a single or double bond is closest to the surface.

Relevant publication:

Phys. Rev. Lett. 108, 268302 (2012)

Simultaneous NC-AFM/STM

The Ag:Si(111)-(√3x√3)R30° surface structure has attracted considerable debate concerning interpretation of scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM) images. This work uses a combined NC-AFM/STM approach to conclusively show that the inequivalent trimer (IET) configuration best describes the surface ground state.

Image:

A composite of a topographic NC-AFM image (left) and a simultaneously-acquired tunnel current image (right), with the IET model configuration overlayed (bottom). Contrast in NC-AFM highlights Ag-Si bonds, whilst the tunnel current channel corresponds to Ag trimers.

Relevant publication:

Phys. Rev. B 87, 075310 (2013)