Session 3-1

Abstract

Since the discovery of X-rays by Roentgen in 1895, their applications have been ubiquitous, ranging from medical and environmental uses to materials science. 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, enabling the detection of an atto-gram amount of a sample using X-rays. However, it is still in the range of ≥104 atoms or more. Further reducing the material quantity is a long-standing goal, and this talk will present the groundbreaking X-ray spectroscopy and microscopy results 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 a quantum tunneling regime can be recorded at ~30 K substrate temperature [1]. Indeed, this method can also be applied to detect single-atom signals at room temperature [2]. Using this method, a variety of X-ray spectroscopies, such as X-ray absorption spectroscopies (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 the elemental, chemical, and magnetic properties of one atom inside a molecule. Moreover, we can now directly image individual atoms with chemical sensitivity using X-ray microscopy. These achievements open a new avenue for material characterization, which will significantly impact various research areas, ranging from environmental and biological sciences to nano and quantum sciences.