Kinetics of alkanethiol monolayer desorption from gold in air

Abstract

Thermal desorption of an alkanethiol monolayer from a gold substrate into a gaseous medium under ambient pressure was investigated using XPS and it was found that there exist 2 consecutive 1st order kinetics mechanisms with activation energies of 29.9 and 32.7 kcal mol(-1), respectively, i.e. on average approximately 15% higher than reports for liquid media desorption.

X-ray Photoelectron Spectroscopy Analysis of Gold Surfaces after Removal of Thiolated DNA Oligomers by Ultraviolet/Ozone Treatment

“…Similarly the S 2p photoelectron is unusually intense. Indeed, the XPS spectrum of this sample show considerable signal at a BE of 168 eV, consistent with the presence of (water soluble) sulphates within the film [9,10,31].…”

“…Previously, the observation of S 2p photoelectron line has been used to identify the successful attachment and/or removal of alkanthiols [9,10] and DNA [31] onto gold substrates. Such studies report binding energies of ~ 162 eV for S 2p photo-electrons ejected from Au-bound S atoms (i.e., the -S-Au moiety), ~ 164 eV for unbound S and ~ 168 eV for sulphates and other S-O bond containing species.…”

“…Studies on Au-SAM cleaning procedures have generally been concerned with the removal of alkanethiols or other smaller contaminant molecules [9][10][11][13][14][15], but little is known about the efficacy of these methods for other types of contaminations. It is therefore of interest to find out if these present techniques can clean the gold substrates contaminated with more complex molecules.…”

“…Various cleaning methods have been studied and/or employed to remove impurities from gold surfaces prior to their use in SAM preparation. These have included standard cleaning agents such as piranha solutions [7], a novel mixture of NH 4 OH and H 2 O 2 [8], thermal desorption [9], plasma treatment [10], and most commonly, UV/ozonolysis (combined exposure to UV and ozone) [11][12][13][14][15]. Frequently, the effectiveness of such techniques has been demonstrated by removing an entire alkanethiol SAM from the gold, though this has been observed to decrease as the length of the adsorbed alkanthiol increases [16] (i.e., more time is required to remove greater mass).…”

“…Thermal desorption for removal of thiol molecules has been shown to be a successful method [9]. This technique was briefly examined in our laboratory.…”