Angular and energy effects in sputtering of hexadecanethiol monolayers self-assembled on Ag(111)
1999; Elsevier BV; Volume: 436; Issue: 1-3 Linguagem: Inglês
10.1016/s0039-6028(99)00644-5
ISSN1879-2758
AutoresSergei P. Chenakin, Bertram Heinz, Harald Morgner,
Tópico(s)Graphene research and applications
ResumoSputtering of monolayers of hexadecanethiol (HDT) molecules CH3(CH2)15SH 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 CC double bonds and ion desorption of the sulfur sublayer could be distinguished. The initial sputtering yield of fragments increases with incident angle as Y0=Y0(0°)/cos β. It lies in the range of 0.7–1.9 molecules/ion (11–30 CH2-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 Å2. This cross-section, as well as Y0, 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.
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