Scanning Helium Microscopy
The Centre for Organic Electronics at Newcastle, in collaboration with the University of Cambridge and with support through the Australian National Fabrication Facilities (ANFF) network, has been at the forefront of the development of a new instrument known as the Scanning Helium Microscope or SHeM. While existing microscopes utilising energetic beams of particles or light provide an excellent means of viewing structures down to the nanoscale, delicate materials are easily damaged under exposure to such beams. Furthermore, the charged nature of the probes presents difficulties when imaging with electric or magnetic fields, or for insulating materials where the addition of a conductive coating is not desirable. As a result, a wide range of samples including biological structures, adsorbate layers, explosives, or the polymers used in the creation of organic photovoltaics and thin film transistors have their experimental time severely restricted and the veracity of the resultant images called into question.
A beam of neutral helium can provide a probe particle with a wavelength of the order of Angstroms at a much lower energy - typically 20 - 100 meV (as opposed to around 10 keV for electrons). The neutral helium atoms backscatter from the outer electronic corrugation of the sample, thus giving the technique its absolute surface sensitivity and non-destructive qualities. Neutral helium atoms are then the ideal probe of delicate systems, a fact which has been exploited for many years in the diffraction-based technique of Helium Atom Scattering (HAS). SHeM seeks to spatially resolve HAS to allow the creation of detailed maps of surfaces.
As such, the SHeM provides the opportunity for a complementary imaging technique capable of examining delicate samples non-destructively, as well as offering a surface sensitive probe with a wavelength of the order of atomic dimensions. Perhaps even more exciting are a number of potential new contrast mechanisms open to the technique. In the future, these mechanisms will allow SHeM to chemically 'fingerprint' different materials, meaning that we can probe not only the shape of the surface, but also to examine composition and even dynamic surface processes.
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