Surface physics has made great advances in the last twenty years, with the development of new surface-sensitive probes. Fundamental studies of surfaces have led to important developments in related areas of applied science, such as semiconductor microelectronics, thin films and corrosion science. In the last ten years, surface and interface optical techniques, epioptics, have advanced to the stage where unique information can be obtained about surfaces and interfaces. Epioptic techniques deliver the following:
- characterisation of all types of interface through transparent and semi-transparent media – solid-solid, solid-liquid, solid-gas, liquid-liquid, liquid-gas;
- atomic-scale resolution perpendicular to the surface or interface;
- sub-micron lateral resolution;
- femtosecond time resolution via pump-probe techniques;
- no significant material damage;
- no charging problems with insulating specimens.
Low dimensional nanostructures on planar silicon
Low dimensional electron systems are revealing new and interesting phenomena, such as spin–charge separation in a Luttinger liquid, charge density waves, the Peierls gap, mixed dimensionality and one-dimensional quantum well states, but much of the physics of these systems remains to be explored and understood. Low dimensional nanostructures have now been grown successfully, using self-assembly at aligned monatomic and diatomic steps onplanar silicon surfaces. Sub-nanometer conducting wires have been grown very recently by our group. This is technologically exciting, as it appears possible that nanoscale devices could be fabricated using techniques compatible with current semiconductor industry processes.The reduced symmetry of these low dimensional structures make themparticularly well-suited to characterisation by epioptic techniques, and this opens the possibility of controlled capping of the active structures in UHV, for protection from ambient conditions on removal from the growth chamber. Epioptic techniques will then, uniquely, allow characterisation of the active region through the protective layer. In the current project, different quasi-one-dimensional nanostructures are being grown by self-assembly in UHV on aligned-step, planar Si(111) surfaces, and are being characterised using optical SHG.
The technological drive to nanoscale devices also applies to magnetic structures, and SHG offers the additional advantage of being uniquely sensitive to surface and interface magnetism. In a second project, the approach described above is being extended by using magnetic SHG (MSHG) to probe the magnetic behaviour of nanoscale structures grown on planar silicon.
The application of an external magnetic field induces a magnetization in the magnetic material present on the vicinal surface.
The group, under the direction of Professor John McGilp, has extensive experience of international collaboration, including leading two large C.E.C. ESPRIT Basic Research Actions.
The group has been funded by the C.E.C., Science Foundation Ireland, Enterprise Ireland and the Programme for Research at Third Level Institutions of the Higher Education Authority.