Scanning Tunnelling Microscopy and Spectroscopy Investigation of C60 on Au(111) and HOPG Surfaces.

Grose, Megan (2022). Scanning Tunnelling Microscopy and Spectroscopy Investigation of C60 on Au(111) and HOPG Surfaces. University of Birmingham. Ph.D.

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Abstract

In this thesis the investigation of C60 on Au(111) and highly oriented pyrolitic graphite (HOPG) surfaces is performed using scanning tunneling microscope (STM) imaging and scanning tunneling spectroscopy (STS). For C60 on Au(111) the relative heights and orientations of bright and dim fullerene molecules are examined, for C60 on HOPG the relative heights of the dim molecules are discussed. It was found that the C60 orien- tation most commonly found for dim molecules on Au(111) was with the hexagon facet of the C60 molecule adhered to the substrate. This orientation was also the most fre- quently observed when analysing the orientation of individual molecules within islands of C60. The least commonly observed orientation was the pentagon facet of the fullerene adjacent to the substrate. The height analysis of C60 on HOPG found two groups of heights of 0.25nm and 1.4nm corresponding to the C60 monolayers being raised due to Au islands forming below the C60 monolayer and as a result of second layer C60 molecules. STS experiments on Au(111) and HOPG substrates at 77 K confirm results from prior studies; displaying that for HOPG the two unit cells have different local den- sity of states (LDOS), and for Au(111) varying packing structures on the surface display differing responses. The STS spectra for A and B HOPG atoms show at larger negative bias the B atom has a larger conductance but for low bias and large positive bias the A atom has larger conductance. For Au(111) spectra the face centered cubic (FCC) component displays a higher conductance around -0.2 V, hexagonal close packed (HCP) shows this peak shifted to -0.3V. Finally the STS investigation of C60 on Au(111) is detailed and the results presented. The Au/C60 spectra were not reproducible and no conclusions could be drawn from the data

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):