Number 167 (Story #3), March 3, 1994 by Phillip F. Schewe and Ben Stein DETERMINING THE NATURE OF CHEMICAL BONDS AT NEAR-ATOMIC RESOLUTION in the interfaces of inorganic solids is now possible using a combination of electron microscopy techniques. First, columns of atoms at an interface are imaged at sub-nm resolution using scanning transmission electron microscopy (STEM). Then information about the electronic states of atoms in the column are obtained through a technique known as electron energy-loss spectroscopy (EELS), in which a beam of electrons is sent down a specified column, after which the energy spectrum of the scattered electrons is measured. Philip Batson of IBM images layers of silicon atoms at a silicon-silicon dioxide interface and can deduce the chemical bonding states for silicon atoms from layer to layer. Meanwhile, David Muller at Cornell maps columns of carbon atoms between a diamond film and a silicon substrate. He finds that the carbon bonding states change between columns over a distance of less than 1 nm and that the diamond grows on an amorphous carbon layer, ruling out other proposed scenarios. This technique is likely to be a useful tool for studying and controlling properties of inorganic thin films as well as grain boundaries in metals and ceramics (Nature, 23/30 Dec. 1993). Furthermore, the combined use of STEM and EELS should result in the ability to map the presence of trace elements at a level of 10 parts per million in 10-nm-wide regions. (Science News, 26 Feb. 1994.)