Scanning Tunnelling Microscopy & Photoemission Studies on Nanostructures for Nanoelectronic Applications
A good understanding of the electronic behaviour of nanostructures is essential to fully exploit their unique properties, which will enable their integration into useful nanoelectronic devices. Photoemission spectroscopy and scanning tunnelling microscopy provide the appropriate tools for this task, as quantum confinement of electrons and the influence of surface effects play a major role in the way materials behave at the nanometre scale.
Photoelectron spectroscopy was developed to study the occupied electronic structure of materials and the Omicron Multiprobe system used for these studies is equipped with ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). XPS gives information on the elements present in the surface region and their chemical state, whereas UPS measures the electron distribution near the highest occupied energy levels enabling a direct measure of the work function and ionisation potential, which are of technological importance to devices. The Multiprobe system also contains a scanning tunnelling microscope (STM) which allows for atomic resolution imaging and probing the surface density of states in the vicinity of the Fermi Energy.
STM experiments on double-walled carbon nanotubes demonstrate that the contribution of inner layers is crucial, and this has serious implications when it particularly comes to fabricating electronic devices such as transistors and molecular interconnects.
The occupied electronic structure has been determined experimentally by means of UPS and changes in the work function and vacuum level shifts evidenced for various systems consisting of acene-nanocrystal heterojunctions. These findings are of relevance for the design and fabrication of future molecular optoelectronics devices.