The feasibility of using a high-resolution scanning transmission electron microscope to study the diffusion of heavy atoms on thin film substrates of low atomic number has been investigated. We have shown that it is possible to visualize the diffusion of individual uranium atoms adsorbed to thin carbon film substrates and that the observed motion of the atoms does not appear to be induced by the incident electron beam. Advances in high-resolution transmission electron microscopy during the past several years have made possible the observation of individual heavy atoms on thin substrates of low atomic number (e.g., refs. 1-5). Studies at atomic resolution of atoms adsorbed to light element substrates could be of value in acquiring an improved understanding of chemisorption, catalysis, and the earliest stages of thin film nucleation. It is the purpose of this paper to demonstrate that a scanning transmission electron microscope (STEM) capable of atomic resolution may be a useful instrument for surface science studies and, in particular, that it is capable of reliably observing the diffusion of individual atoms on thin film substrates.In the STEM, an atomic resolution image can be formed by scanning an electron beam less than 5 A in diameter across a specimen in a raster fashion while collecting the transmitted elastically scattered electrons with an annular detector located beneath the specimen (6) (see Fig.

Articles you may be interested inPerformances by the electron optical system of low energy electron beam proximity projection lithography tool with a large scanning field Electron optical image correction subsystem in electron beam projection lithography Electron beam direct-write lithography systems are capable of meeting the resolution requirements of all future ITRS nodes and have a significant cost of ownership advantage over masked technologies, but these systems typically have very poor throughput due to space charge limitations. Ion Diagnostics has developed a multicolumn, multibeam (MϫM™) direct-write system that circumvents the space charge limitations by spreading the electron current over the wafer. The resulting lithography system can achieve critical dimensions of less than 100 nm with production throughputs greater than 60 wafers per hour, independent of wafer size. In this article we describe the electron optical column used in this system. We have developed a novel, microfabricated electron gun that produces 32 parallel electron beams that are individually controlled and blanked and contain deflectors that allow the gun optics to act as a perfect lens. Each column is 2 cm ϫ2 cm and can align and scan the 32 beams in parallel on the wafer. The wafer voltage is typically held at 50-100 kV, and backscattered electrons are collected for imaging and alignment information. Theoretical results and some performance results for a prototype column are presented.

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