Structural and electronic manipulation of fullerenes for use in molecular electronics

Abstract

The work in this thesis focuses on how the properties of Buckminster Fullerene, C₆₀, and the related endohedral fullerene, Li@C₆₀, can be manipulated to alter their properties using Scanning Tunnelling Microscopy. The end goal of this is, eventually, for such molecules to be used to form functional electronic components.

Using lateral manipulation of isolated C₆₀ molecules on a Cu(111) surfaces, the distance dependence of superatom molecular orbital (SAMO) hybridisation between two fullerenes is demonstrated. The possibility of using the SAMOs to form artificial nearly-free electron (NFE) structures is then investigated. The electron transport properties of SAMOs are then investigated through tunnelling current induced molecular decomposition. When tunnelling through the SAMOs it is found that the molecules can withstand much greater currents than when electron transport occurs primarily through the lowest unoccupied molecular orbitals (LUMOs). Using this decomposition method the possibility of selectively patterning fullerene monolayers (and thus the delocalised SAMO states) is explored through the creation of an “artificial graphene” structure.

The endohedral fullerene, Li@C₆₀, and C₆₀ are investigated for use as molecular switches. A possible switching mechanism involving static Jahn-Teller (JT) distortions of the C₆₀ cage is proposed and the observed switched states assigned JT distortions with the aid of Hückel Molecular Orbital (HMO) theory simulated STM images. The thermally induced loss of lithium from Li@C₆₀ is investigated, in which Li@C₆₀ is converted to C₆₀ at high temperatures. This process is demonstrated to only occur in molecules at the perimeter of molecular islands with the rate of Li loss plateauing after several hours at high temperature.