AVS 50th International Symposium
    Applied Surface Science Wednesday Sessions
       Session AS-WeP

Paper AS-WeP11
Investigation of Secondary Cluster Ion Emission from Self-Assembled Monolayers of Alkanethiols on Gold with TOF-SIMS

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: H.F. Arlinghaus, Westfälische Wilhelms-Universität, Germany
Authors: S. Sohn, Westfälische Wilhelms-Universität, Germany
M. Schröder, Westfälische Wilhelms-Universität, Germany
H.F. Arlinghaus, Westfälische Wilhelms-Universität, Germany
Correspondent: Click to Email
Self-assembled monolayers (SAMs) of alkanethiols on gold are ideal model systems for studying the emission processes of secondary ions from thin organic layers on metal substrates under keV ion bombardment. In this experimental study, we focus on the emission processes of gold-alkanethiolate cluster ions, which are not well understood yet. For this purpose we carried out time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements on SAMs of different alkanethiols CH@sub 3@(CH@sub 2@)@sub n@SH with various alkyl chain lengths (1 @<=@ n @<=@ 17) on gold substrates. The gold-alkanethiolate cluster ions Au@sub x@M@sub y@@super -@ with M = CH@sub 3@(CH@sub 2@)@sub n@S, 1 @<=@ x @<=@ 7 and x-3 @<=@ y @<=@ x+1 show intense peaks in negative mass spectra of all investigated alkanethiol SAMs under 10 keV Ar@super +@ bombardment. Around the corresponding peaks, a characteristic peak pattern of additional ions is observed. We analysed the contribution of different cluster ions formed by an attachment or a loss of up to five hydrogen atoms and their isotopy to the individual peaks of the peak pattern. We found two different types of gold-alkanethiolate cluster ions. The first type has only one parent ion, which has no hydrogen atom attached. The second type has two parent ions, one with no attachment of additional hydrogen atoms and another with one additional hydrogen atom. Moreover, we found a universally valid sum formula, which predicts the most intense peak in the peak pattern of gold-alkanethiolate cluster ions of all investigated alkanethiol SAMs.