Abstract
While the sonochemical grafting of molecules on silicon hydride surface to form stable Si–C bond via hydrosilylation has been previously described, the susceptibility towards nucleophilic functional groups during the sonochemical reaction process remains unclear. In this work, a competitive study between a well-established thermal reaction and sonochemical reaction of nucleophilic molecules (cyclopropylamine and 3-Butyn-1-ol) was performed on p-type silicon hydride (111) surfaces. The nature of surface grafting from these reactions was examined through contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Cyclopropylamine, being a sensitive radical clock, did not experience any ring-opening events. This suggested that either the Si–H may not have undergone homolysis as reported previously under sonochemical reaction or that the interaction to the surface hydride via a lone-pair electron coordination bond was reversible during the process. On the other hand, silicon back-bond breakage and subsequent surface roughening were observed for 3-Butyn-1-ol at high-temperature grafting (≈150 °C). Interestingly, the sonochemical reaction did not produce appreciable topographical changes to surfaces at the nano scale and the further XPS analysis may suggest Si–C formation. This indicated that while a sonochemical reaction may be indifferent towards nucleophilic groups, the surface was more reactive towards unsaturated carbons. To the best of the author’s knowledge, this is the first attempt at elucidating the underlying reactivity mechanisms of nucleophilic groups and unsaturated carbon bonds during sonochemical reaction of silicon hydride surfaces.
Highlights
Silicon is an important industrial element for modern transistors [1,2] as well as being of significant importance to the scientific community in the areas of biotechnology applications [3,4] and in biosensing [5,6,7]
A long reaction time as well as the use of high temperature during thermal reaction increase the chance of unnecessary oxidation [18,25], while both thermal and ultraviolet strategies can be highly susceptible to surface adventitious carbon contamination [26,27]
The notion that a sonochemical-based reaction is merely a mechanistic rather than a chemical operation was discussed by Kegelaers et al [77] who, after repeating the same series of experiments as described by Ando et al [75], came to the different conclusion that sonochemical reaction served as a mechanistic approach akin to those from extensive stirring that shortens the reaction time [78] but by itself did not induce a chemical change
Summary
Silicon is an important industrial element for modern transistors [1,2] as well as being of significant importance to the scientific community in the areas of biotechnology applications [3,4] and in biosensing [5,6,7]. The formation of stable Si–C linkages on silicon surfaces results in highly resilient surfaces that can withstand harsh conditions [8,9]. These surfaces are deemed important in various fields such as in electronics [10,11,12], semiconductors [13,14], and biosensors [15,16]. The literature is rich with various hydrosilylation methodologies ranging from transition metal catalysis [17] to thermal [18,19], ultraviolet initiation [20,21], microwaves activation [22,23] and sonochemical reaction [24], to achieve the formation of stable monolayers on silicon surfaces. A long reaction time as well as the use of high temperature during thermal reaction increase the chance of unnecessary oxidation [18,25], while both thermal and ultraviolet strategies can be highly susceptible to surface adventitious carbon contamination [26,27]
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