Influences of Doping and Crystal Orientation on Surface Roughening upon Alcohol Grafting onto Silicon Hydride

Abstract

An alcohol bearing alkyne was thermally grafted to both p-type and n-type silicon (111) and (100) substrate of comparable doping levels and surface flatness. The surface topography as well as the surface chemistry was examined via atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. P-type silicon (111) was observed to experience roughening on the surface upon functionalization while n-type silicon (111) surfaces remained relatively unchanged. When the alcohol was grafted onto silicon (100) surface, the roughening effect was found to be even more profound for the p-type while the effects were marginal for the n-type surfaces. Both roughening effects were attributed to the differential weakening of the Si-Si backbond induced by majority carriers in p-and n-type silicon while (111) was observed to be able to resist the roughening effect better and this was explained by the notion of its denser adatom surface packing as well as the presence of surface defects.

Grafting Behavior for the Resonating Variants of Ethynylaniline on Hydrogenated Silicon (100) Surfaces under Thermal Hydrosilylation

“…From the onset, we noticed a huge reduction of the Si−O x for the 2‐ethynylaniline centering at 102.8 eV (see Figure a) when compared to the unmodified silicon oxide surface. Based on our previous studies, in a competitive fashion between a nucleophile and an unsaturated carbon end group, we expected to observe a preferential bonding to the Si−H surface via the nucleophilic NH 2 but this was not the case here. However, when the Si2p spectrum of the 3‐ethynylaniline was examined, a huge peak centering at 102.2 eV was observed and this is consistent with that of a Si−N bonding type .…”

XPS Analysis of 2- and 3-Aminothiophenol Grafted on Silicon (111) Hydride Surfaces

“…Under low temperature (130 °C), it was thought that there would be no homolysis of the silicon hydride bond and that the nucleophilic NH 2 and SH would react to the surface via direct nucleophilic addition mechanism. It is also important to note that hydrogen abstraction is a viable means of generating active radicals on the surface for reaction to the incoming aminothiophenol molecules [ 17 , 18 , 19 , 39 , 40 ]. However, considering that the Si2p analysis of 2-aminothiophenol did not display any appreciable Si–S linkage, this process was considered to be either relatively minimal or the nucleophilic addition reaction was the dominant process during the surface grafting.…”

“…Polar protic/aprotic solvents are not generally considered to be useful as the solvation effects may further enhance the nucleophilicity of the larger SH, and thus very little useful information would be obtained under such conditions. Furthermore, it is also highly possible that polar solvents would interfere with the reaction on the silicon hydride surfaces [ 19 , 39 , 41 ].…”

“…In a glass reactor setup that was similar to our previous reports [ 4 , 17 , 18 , 19 , 20 , 40 , 42 ], silicon wafers were sectioned via a diamond cutter at pieces measuring approximately 10 × 10 mm 2 in size. Prior to the reaction, the surfaces were cleaned for 30 min in hot Piranha solution (95 °C, 1 vol.…”

“…In reality, such direct nucleophilic addition to silicon-hydrogenated surfaces has already been examined with interest by various groups in the past [ 1 , 2 , 3 , 16 ]. In fact, many of our previous reports have suggested that under elevated thermal conditions, such nucleophilic groups possess a higher degree of preference compared to the nominal formation of Si–C linkage when introduced at equimolar concentrations [ 4 , 17 , 18 , 19 , 20 ]. In view of the potential charge-trapping on the surface from nucleophiles, such interaction with nucleophilic moieties during the self-assembly of organic monolayer has often been deemed detrimental for many electronic-based applications.…”