ELSEVIER Surface Science 357-358 (1996) 820-824 surface science PEEM and REM studies of surface dynamics: electromigration and C1 adsorption and desorption Y. Shidahara, K. Aoki *, Y. Tanishiro, H. Minoda, K. Yagi Physics Department, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152, Japan Received 15 August 1995; accepted for publication 23 September 1995 Abstract We have developed a UHV electron microscope which can image surfaces in photoemission electron microscope (PEEM) and reflection electron microscope (REM) modes. One application of it was to observe surface electromigration of Ag on Si(111) surfaces. In PEEM mode, step bands were imaged and anisotropic migration depending on the direction and sense of the step bands was noted. The migration was faster along the upper sides of the step bands than along the lower sides. The other application of the microscope was to observe adsorption and desorption of C1 on Si(111) surfaces in two modes for comparative studies. An effect of electron beam irradiation on Cl-adsorbed Si(lll) and Si(ll 1)~-X V~--Ag surfaces was noted and clearly observed in PEEM mode. Keywords: Adsorption; Chlorine; Photoemission electron microscopy (PEEM); Reflection electron microscopy (REM); Silicon 1. Introduction Reflection electron microscopy (REM) is sensi- tive to changes of ordered crystallographic structures of surfaces and has been used as a useful technique for the investigation of surface structures and surface dynamics [1]. However, REM is not sensitive to disordered structures since the image contrast in REM is a diffraction contrast. On the contrary, pho- toemission electron microscopy (PEEM) is sensitive to changes of electronic structures not only for or- dered states but also for disordered states, since its contrast is due to a change of surface work function [2]. PEEM is nondestructive since its probe is ultra- violet light, while REM is destructive for surfaces with weakly adsorbed atoms and molecules since the * Corresponding author. Fax: + 81 3 5734 2079. probe of REM is a high energy, high density electron beam. We have developed an ultra-high vacuum (UHV) REM-PEEM method [3] and found that steps and step bands on Si(111) can be recorded without fore- shortening by PEEM [4]. In the present paper, the REM-PEEM method was applied to two dynamic systems: electromigration on Si surfaces [5,6] and C1 adsorption and desorption on Si surfaces. The Cl-ad- sorbed Si surface is known as an interesting photore- active system [7] and as a reactive etching surface. 2. Experimental Two microscopes were used in the present study. Preliminary observations of Cl-adsorbed Si surfaces were carried out with a modified JEM-100B UHV electron microscope [5,6]. A few ~-cm resistivity Si(111) specimens (1 X 7 X 0.3 mm 3) were used. 0039-6028/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved PII S0039-6028(96)00172-0