Atom Eyes: Scanning HElium atom Microscopy

Microscopy is an indispensable tool for the investigation of materials and surfaces. It has often been said that the whole field of Nanotechnology and Nanoscience began with the invention of Scanning Tunneling Microscopy (STM) and Scanning Force Microscopy (SFM). Recent years have also seen an immense development in particle probe microscopes, allowing atomic resolution in Transmission Electron Microscopy (TEM). State of the art microscopy and imaging techniques are very powerful, in particular with respect to their high resolution, but there are some inherent challenging issues. Charged particle probe techniques like electron or ion microscopes as well as STM normally require the sample to be electrically conducting, whilst scanning probe techniques in general are rather slow and can only be used on quite flat samples and for small areas. Recent years have shown big achievements in the field of scanning helium atom microscopy (SHeM) [1-5] enabling the development of a new type of matter wave microscopes which utilize neutral atoms as a probe beam. The major advantage of the SHeM technique is that the neutral helium probe has a much lower beam-energy than other particle probe microscopes: less than 100meV for a de Broglie wavelength of less than 0.1nm. This energy is simply too low to cause any surface damage or penetration into solid material. At the same time the helium atoms are uncharged (neutral) and chemically inert. Thus, SHeM offers a completely non-destructive imaging technique that is equally suited to insulators, semiconductors, metals and delicate samples such as organic materials. The few current existing SHeM microscopes are either based on a pinhole camera approach [2, 3] or use a focused helium beam concept [1,4,5]. Here I present the concept and advantages of the SHeM technique as well as the design of our focused NEutral helium beam MIcroscope NEMI, which we developed in Bergen. As one of the few existing instruments in the novel field of scanning helium microscopy, NEMI offers promising possibilities in its unique way of imaging with a focused neutral helium beam.