## 3 Results
For \(p\)-type silicon, this could inherently result in the weakening of the silicon-silicon backbond that subsequently permits its breakage. Such weakening is, however, dependent upon the doping type, as the ease of the subsequent breakage of the silicon-silicon backbond depends on the concentration of valence band holes at the substratum surface. Figure 4: Roughness profile of silicon (111) after grafting for (**a**) \(p\)-type and (**b**) \(n\)-type while the profile for silicon (100) was also displayed for (**c**) \(p\)-type and (**d**) \(n\)-type. Figure 3: Atomic force microscopy (AFM) measurement of three conditions, (**a**,**d**,**g**,**j**) pristine silicon of various orientations and doping; (**b**,**e**,**h**,**k**) after a 30 s HF treatment and (**c**,**f**,**i**,**i**) after thermal reaction with alcohol. For \(p\)-type silicon (111), the large density of holes helps weaken the Si-Si bond at the surface, and this allows for nucleophilic attack according to the [PERSON]'s mechanism [29; 30]. This offers an explanation for the roughening of the semiconductor upon the formation of the Si-O-C on the surface, inducing a change in the surface dipole (Figure 4). However, it would be naive to perceive that alcohol would then proceed to etch the surface as in HF treatment. In the typical HF reaction to the surface, the Si-F bond energy is \(\sim\)160 kcal mol\({}^{-1}\) while the Si-O bond energy is 111 kcal mol\({}^{-1}\)[31]. The electron pull from the Si-F forming to the surface is strong enough to result in the breakage of the subsequent Si-Si backbond and this ultimately results in the liberation of a single SiF\({}_{4}\) from the silicon bulk material, hence creating the etching event. Instead, Si-O-C type linkage does not exert similar pull but only weakens the underlying Si-Si backbond, making it more susceptible to nucleophilic attack from the alcohol reactant. Since the reaction volume of the ethynylbenzyl alcohol was only 0.3 M in 5 mL of mesitylene and accounting for solute depletion and weaker Si-O linkage compared to Si-F, a gradual roughening of the surface initiated at surface defects is then well expected. This is in agreement with the observations reported by [PERSON] et al. [7] on \(p\)-type silicon substrate upon the formation of Si-O-C. The absence of surface roughening in (111) \(n\)-type silicon is similarly attributed to the lower density of holes (that are here minority carriers) when silicon is doped with phosphorus (arsenic in the case of the \(n\)-type silicon (100)). Typically, relevant hole densities can be generated only by applying an electrical bias, by photon absorption on the surface [32] or via hole injection from an oxidant [33]--but none of these effects were present in the current experimental conditions. Thus, the ethynylbenzyl alcohol reacted first to the surface via insertion to form a Si-O-C linkage but then it does not possess enough impetus to break the Si-Si backbond due to the electron compensation arising from the sea of electron-rich phosphorous dopant (Figure 5). This is consistent with the observation that on atomically flat \(n\)-type silicon, roughening of the surface upon formation of the Si-O-C linkage is localised along step edges while the terrace flat surface remains largely untouched (apart from defective sites) [8]. This is logical as step edge dangling bonds are the only ones that may be susceptible to Si-Si backbond weakening. Furthermore, the atomic flatness of the surface lattice does not permit any further attacks of Si-Si bonding [28], in good agreement with our observations. Figure 5: Schematic representation of the weakening of the Si-Si backbond on \(p\)-type and dopant compensation on the \(n\)-type silicon surface. On the other hand, these physical rationales and processes were relatively similar for the \(p\)-type silicon (100) surfaces with some notable differences: a HF acid treated (100) surface would exhibit inherent roughening as well as a mixed population of silicon monohydride, bihydride and trihydrides [34].