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Chemical mapping of surfaces, high lateral resolution (50nm), STM imaging with atomic resolution.
About
The Solution A novel technique that combines the imaging capabilities of scanning tunnelling microscopy (STM) with the spectral information provided by electron energy loss spectroscopy (EELS) in reflection mode. Principle An STM tip operating in field emission mode is used as a local source of electrons. These electrons fall onto the surface of the sample and are consequently backscattered into a hemispherical electron energy analyser. The local energy loss spectra from solid surfaces with an expected spatial resolution of about 10nm and an energy resolution of 0.6 eV enable us to detect surface plasmons, interband transitions and molecular excitations. General Features Chemical Mapping of Surfaces, High Lateral Resolution ( 50nm), STM Imaging with Atomic Resolution. Unique Features Surface topography and high resolution chemical analysis can be obtained simultaneously, sample undamaged after analysis, due to the low energy of the incident electrons. The Technology The newest generation of the SPELS instrument utilises a room-temperature STM in combination with a cylindrical sector electron energy analyser. The energy analyser is fitted with a 128-channel (micro-channel plate) detector, which enables fast sampling of energy loss spectra. This means that spatially-resolved maps of surface topography and composition can be obtained. The spectral information obtained from the scattered electrons is used to infer the chemical nature of the surface. The chemical composition of the surface is mapped with a high lateral resolution by scanning the STM tip. SPELS analysis has recently been carried out also at 40V and a tip-sample distance of 50nm. SPELS can therefore be regarded as a powerful general analytical tool, which could find applications in various faculties, such as physics, chemistry, biology, engineering, medical science, material science etc. SPELS, in its current state can be used on bulk metallic and semi-metallic surfaces, inorganic thin films (e.g. superconducting thin films), and semiconductor films. With further development, including the micro-fabrication of co-axial tips to enhance count rates and introducing multi-channel detectors to increase detector efficiencies more delicate samples can be studied, such as, organic thin films, co-polymer thin films and biological samples.