Scanning probe energy loss spectroscopy (SPELS) of structured surfaces

• Main Author: Bauer, Karl
• Published: University of Birmingham 2015
• Subjects: 500; QC Physics
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659151

In scanning probe energy loss spectroscopy (SPELS) an STM tip is used as a localised source of field emitted electrons by applying a high voltage. Energy loss measurements of the backscattered electrons provide spectroscopic information from the sample. The energy resolution is ≈0.3eV. In principle, a raster scan provides a spatially resolved image of these excitations. In this work, a new generation instrument is employed and developed in which the electrons are captured by an electrostatic lens system and focussed onto a multichannel detector using a 127° cylindrical-sector analyser. Additionally, a compact retarding field analyser has been built, which can be placed within 20mm of the tip position. Both detectors have been positioned at an angle of 7° to the surface plane, as most of the backscattered electrons are expected to emerge near the surface plane due to the high electric field between tip and sample. Ag and Au nanostructures on graphite designed for the SPELS instrument covering a large sample area have been prepared by electron beam lithography. The characteristics of the instrument have been measured, with high spatial resolution (down to 25nm) images showing various contrast mechanisms. Spatially resolved silver surface plasmon maps are presented.