PME Special Seminar - Prof. Saw Wai Hla, PhD

X-Raying Just One Atom

Since the discovery of X-rays by Roentgen in 1895, their utility has been ubiquitous, from medical and environmental applications to materials sciences. X-ray characterization of materials has been revolutionized after the invention of synchrotron X-rays in the mid-20th century. The capabilities of synchrotron light sources have been continuously upgraded leading to detection of attogram amount of sample by X-rays. However, it is still in the range of ≥104 atoms or more and further reducing the material quantity is a long-standing goal. This talk will present our recent groundbreaking results of X-ray spectroscopy and microscopy of just one atom. Using synchrotron X-rays, and a specialized detector tip positioned directly above a single atom in extreme proximity, X-ray excited current in quantum tunneling regime can be recorded [1]. Using this method, a variety of X-ray spectroscopies such as X-ray absorption spectroscopy (XAS), near-edge X-ray absorption fine structure (NEXAFS), and X-ray magnetic circular dichroism (XMCD) can be performed on just one atom. Thus, we can now simultaneously determine an atom's elemental, chemical, and magnetic properties on a one-atom-at-a-time basis. Moreover, we can now directly image individual atoms with chemical sensitivity using X-ray microscopy. These achievements open a new avenue of materials characterization, which will greatly impact many research areas from environmental, and biological to quantum information sciences. 

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