Modifications to a scanning tunnelling microscope : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physics at Massey University, Palmerston North, New Zealand
A scanning tunnelling microscope (STM), previously constructed as part of a PhD project, has been modified to improve its reliability and accessibility. Initially the aim was to obtain atomic resolution (~ 0.1 nm) on a routine basis but for an unknown reason this has not been obtained and thus far we are limited to a resolution of about 1 nm. Improvements to the device that converts the tunnelling current into a voltage were made resulting in a 1 pA resolution with a 17nA range. This resolution is an order of magnitude better than previously obtained, while the bandwidth (5 kHz) is essentially unchanged. A major aspect of this work was the fabrication of the sharp tungsten tips used as the STM probe. Careful control of the chemical etching process resulted in reproducibly shaped tips, with a radius of curvature of less than 20 nm in some cases.