Detection of characteristic X-ray photons from a single atom

Several electron-microscopist groups have recently reported that a Si drift detector with a 60~100 mm² effective area can be used to detect characteristic X-rays from a single atom in nanomaterials such as silicon and platinum in monolayer and multilayer grapheme, as well as erbium in a C₈₂ fullerene cage supported in a single-walled carbon nanotube. They employed a tiny electron beam of 0.1 nm in the aberration-corrected scanning transmission electron microscope. As will be clear for readers of X-ray Spectroscopy journal, the discussion is a kind of major and/or minor component analysis of extremely small volume rather than so-called ultra trace element analysis. The signal intensity was apparently very weak, but was in the order of some counts/sec according to the reports. Such high sensitivity points to the significant potential of the energy dispersive detector system. On the other hand, further detailed analysis including the estimation of parasitic background will be necessary. For more information, see the papers, "Single atom identification by energy dispersive x-ray spectroscopy", T. C. Lovejoy et al., Appl. Phys. Lett., 100, 154101 (2012), and "Detection of photons emitted from single erbium atoms in energy-dispersive X-ray spectroscopy", K. Suenaga et al., Nature Photonics, advanced online publication doi:10.1038/nphoton.2012.148.