Investigation into machining and etching capabilities for the manufacture of x-ray interferometers.

Wage: £17,000 (circa)
Location: Cranfield University
Closing Date: Ongoing

The project will identify and review machining methods of silicon with the aim of establishing a UK capability for the production of new designs of x-ray interferometers. The project will begin with specifying the machining requirements for x-ray interferometers followed by identification and investigation of machining methods for interferometer production. Some experimental work will also be undertaken. In addition, it is necessary to etch the silicon to obtain a smooth surface finish. Previously this was done chemically, however, in recent years plasma etching has emerged as a promising alternative. Work will also be undertaken to identify the optimum method for plasma etching of silicon.

The x-ray interferometer can be regarded as a ruler or translation stage for nanometrology. The ruler graduations or steps of the stage are based on the lattice parameter of silicon which has been traceably measured to 1 few parts in 108. An example of an x-ray interferometer is shown in figure 1. It is made from a single crystal of defect free silicon. There are three thin parallel equally spaced lamella approximately 0.5 mm thick machined out of a silicon block and a flexure stage is machined around the third lamella. The angular errors associated with the translation stage are at the sub arc second level and the stage is actuated with a piezo electric transducer. X-rays are diffracted from the lamella and the fringes produced have a period of 192 pm. Displacement measurement is realised by counting x-ray fringes.

The project will provide the opportunity to learn about state of the art dimensional nanometrology, ultra-precision machining of silicon machining and plasma etching techniques and mechanical design of precision flexure systems.

The project will be undertaken in collaboration with the National Physical Laboratory, the UK’s national metrology institute, where x-ray interferometry is successfully used for nanometrology.