Such behaviors were mainly attributed to the difference in the density of the dangling bonds as well as the backbonds on the silicon surface . As shown in Figure 7, the dangling bonds inhabit on the superficial layer of a given crystal plane, and the backbonds lie in the Lorlatinib subsurface of the plane as well as the in-plane bonds. The dangling bond is partly bonded to the silicon atom beneath and leads to a metastable surface matrix . Compared with Si-Si bonds in the subsurface, the dangling bond is speculated to be easily bended and rolled during scratching. Such instability provides an effective channel on the given silicon plane for the energy input, resulting in
the formation of more amorphous silicon and higher selleckchem hillock . Crystal plane with higher density of dangling bonds can cause much instability and can lead to higher hillock during scratching. Figure 7 Configuration of Si-Si covalent bonds on different planes of monocrystalline silicon. (a) Si(100); (b) Si(110) and (c) Si(111). The dangling bonds were indicated by dotted lines. GSK872 mw Some covalent bonds that inhibit on one atom are partly showed. With two dangling bonds on each silicon atom, the (100) plane has the highest density of
dangling bonds compared with the other crystal planes. Although only one dangling bond is attached to one silicon atom, the nonequilibrium in bonding state is further increased by the in-plane bonds on (110) plane . Even with the similar dangling bond number per atom as the (110) plane, the atom on the (111) plane is supported by three equivalent Si-Si backbonds, which enhance the mechanical
stability of the Si(111) surface ADAMTS5 [21, 24]. Therefore, under the same loading condition, the highest hillock was generated on Si(100), while the lowest hillock was formed on Si(111) either in air or in vacuum. However, the disturbance from the tip was reduced because of the protective effect of the adsorbed water, oxidation layer, and contamination in air. As a result, a little lower hillock was produced on silicon in air compared to that in vacuum. In summary, the friction-induced nanofabrication can be realized on different silicon crystal planes, with the contact pressure less than the hardness. At the same normal load, the silicon crystal plane with low elastic modulus or high density of dangling bonds can facilitate the formation of friction-induced hillock. Because of the configuration of Si-Si bonds, crystal silicon reveals different mechanical properties on various crystal planes, which eventually result in the variation of hillock formation in the present study. These findings may provide possibilities to control the hillock formation on monocrystalline silicon and help understand the subtle mechanism. Conclusions Nanofabrication tests were performed contrastively on Si(100), Si(110), and Si(111) surfaces using diamond tips.