Surface Science 436 (1999) 131–140 www.elsevier.nl/locate/susc Angular and energy effects in sputtering of hexadecanethiol monolayers self-assembled on Ag(111) Sergei P. Chenakin 1, Bertram Heinz, Harald Morgner * Institut fu ¨r Experimentalphysik, Universita ¨ t Witten/Herdecke, Stockumer Str. 10, D-58448 Witten, Germany Received 27 January 1999; accepted for publication 28 April 1999 Abstract Sputtering of monolayers of hexadecanethiol (HDT ) molecules CH 3 (CH 2 ) 15 SH self-assembled on Ag(111) was studied with 1150 eV He+ bombardment under different angles of incidence ranging from 27° to 71° and with different He+ ion energies (800–1900 eV for 50° ). Sputtering kinetics in the dose range from 1×1014 to 1×1016 cm-2 was monitored with ion scattering spectroscopy ( ISS ), X-ray and ultraviolet photoelectron spectroscopies ( XPS, UPS) and metastable induced electron spectroscopy (MIES). A two-stage process in degradation of the layer under ion irradiation including high-rate fragmentation of standing hydrocarbon chains with formation of CC double bonds and ion desorption of the sulfur sublayer could be distinguished. The initial sputtering yield of fragments increases with incident angle as Y 0 =Y 0 (0° )/cos b. It lies in the range of 0.7–1.9 molecules/ion (11–30 CH 2 -groups/ion). On the basis of a model of sputtering of the HDT film, a cross-section of chain fragmentation was evaluated to be about 1.52±0.1 A ˚ 2. This cross-section, as well as Y 0 , decreases with increasing ion energy, exhibiting a linear correlation with the calculated ion energy loss in the HDT monolayer. The angular and energy dependencies of the sulfur desorption cross-section are compared with calculations based on Winters–Sigmund theory. © 1999 Elsevier Science B.V. All rights reserved. Keywords: ISS; MIES; Organic monolayer; Sputtering; UPS; XPS 1. Introduction sion cascade regime in amorphous solids. Ion bombardment of a surface with an adsorbed layer represents, however, a particular situation of sput- At a given energy of primary ions the angular tering. The ion induced desorption of a simple dependence of sputtering yield of solids, for not (monoatomic or diatomic) adsorbate from the too oblique incidence, can be described by the solid surface may involve three different processes inverse cosine law Y#1/cospb (where p is a func- and is mainly governed by binary collisions, with tion of the target-to-projectile atom mass ratio collision cascades having negligible contribution and b the angle of bombardment with respect to to the sputtering yield when using light projectiles the surface normal ) which is predicted by transport [2]. In this case a theory proposed by Winters and theory of sputtering of Sigmund [1] for the colli- Sigmund [2] predicts the inverse cosine angular dependence of the ion desorption cross-section and * Corresponding author. Fax: +49-2302-669-220. sputtering yield Y a #1/cos b. Good agreement of E-mail address: hmorgner@uni-wh.de ( H. Morgner) the experimental desorption cross-sections mea- 1 Present address: Institute of Metal Physics, Acad. Sci., Vernadsky Blvd. 36, 252142 Kiev, Ukraine. sured as a function of impact angle and ion energy 0039-6028/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0039-6028(99)00644-5