Structural Studies of Strained and Nanostructured Rare Earth Silicides and Germanides Using MEIS and STM.

As the silicon transistor, which is the digital switch at the heart of the microprocessor, gets smaller and smaller in order to increase switching speeds there are many challenges facing the semiconductor industry which are both technological and fundamental. One area of electronic devices which is increasingly important as devices shrink in size is the junction or interface between metals and semiconductor material. There is a need not only to understand the properties of this metal-semiconductor interface, but to develop new and novel interfaces which will aid this understanding and be of potential benefit in the challenges ahead. New interfaces include those between magnetic materials and semiconductors, which offer a route to controlling the spin of the electron. This is a very active area of research which has the potential for a wide range of new devices, including sensors. The research here is at the fundamental end which underpins these technological developments, it is to determine the structure of a range of metal-semiconductor interfaces and to investigate ways of modifying the structure by exploiting the subtle differences in the spacings between different rare earth silicides (compounds of silicon and lanthanide metals) to generate differing amounts of strain in the growth of materials on the silicide. Other approaches will be to use buffer layers, different growth temperatures (including cooling below room temperature), and different semiconductor substrates with the aim of preventing certain silicide formations or modifying the interface structure. These structural studies will be carried out using the techniques of medium-energy ion scattering (MEIS) at the UK national MEIS facility at Daresbury and Scanning Tunnelling Microscopy (STM) at York. MEIS uses a beam of ions (usually hydrogen ions) which scatter off the atoms within the material, their scattered energy depends on the mass of the atom that the ions have hit and the number leaving the material in specific directions depends on whether their outgoing path is blocked by atoms in the material. This technique has two key advantages: it can achieve sub-nanometre depth resolution in materials and is sensitive to the atomic species in the material. It is therefore well suited to the study of metals on semiconductors where there is good mass difference between the metal and semiconductor atoms, and where the metal atoms are incorporated into the interface such as in the case of silicide formation.