Applications for small photoelectron emission microscopes E.L. Montei 1 , V.W. Ballarotto, M.E. Little, M.E. Kordesch* Clippinger Research Laboratories, Department of Physics and Astronomy, Ohio University, Athens, OH 45701-2979, USA Received 15 July 1996; accepted 6 November 1996 Abstract Several applications of simple photoelectron emission microscopes for the observation of real time in situ surface processes are reviewed, including field emission, chemical vapor deposition, tribochemistry and liquids in ultra-high vacuum, and pulsed supersonic molecular beam film growth.  1997 Elsevier Science B.V. Keywords: Photoelectron emission microscopes; Diamond chemical vapor deposition; Surface diffusion; Tribology 1. Introduction The strength of ‘‘threshold’’ photoelectron emis- sion microscopy (PEEM), as practiced with laboratory light sources in the 5–10 eV illumination energy range, is the contrast that results from deposition, desorption or reaction of monoatomic surface layers. In our laboratory, we have used the surface sensitivity of PEEM in the study of several surface reactions, mostly related to the growth of potential electronic materials such as diamond [1–19]. Emission microscopes combined with surface analysis systems have a long tradition [20,21]; there are now two PEEMs available commercially [22,23]. New applications have arisen that can be studied with PEEM, where PEEM images may offer additional information on the spatial distribution of reactants or adsorbates that cannot easily be inferred from spectro- scopic data. As motivation for these studies, one might consider a comparison with typical low-energy electron dif- fraction (LEED) systems. LEED delivers ‘‘qualitative data’’ at the first instance, the diffraction pattern. It is reassuring to observe a fourfold symmetric diffraction pattern from a fourfold symmetric surface; however, interpretation of the pattern and some quantitative statement about the surface morphology is much more difficult to make based on a LEED pattern. Possibly, a calibration of surface coverage from LEED patterns is the most useful data available from simple LEED. These systems cost less than $30 000, and in spite of the limited number of ‘‘serious users’’ who do I–V curves or spot profile analysis, most surface scientists include LEED in their analysis systems. PEEM, in its simplest form, also delivers ‘‘qualita- tive’’ data, a map of the electron yield of a surface on a micrometer scale. Even with spectroscopic data from another source, correlation between ‘‘peaks’’ and features in a PEEM micrograph is difficult, and never unequivocal, because of possible effects due to the electric field and incident UV light. With con- siderably more effort, such as computerized image analysis [24] and synchrotron illumination for spectroscopy [11,25], quantitative data can also be Journal of Electron Spectroscopy and Related Phenomena 84 (1997) 129–136 0368-2048/97/$17.00  1997 Elsevier Science B.V. All rights reserved PII S0368-2048(97)00008-X * Corresponding author. Phone: +1 614 593 1718; fax: +1 614 593 0433. 1 American Chemical Society Petroleum Research Fund Post- doctoral Fellow.