Fabrication and tribological properties of self-assembled monolayer of n-alkyltrimethoxysilane on silicon: Effect of SAM alkyl chain length

• Published in: Applied surface science Vol. 396; pp. 865 - 869
• Main Authors: Huo, Lixia, Du, Pengcheng, Zhou, Hui, Zhang, Kaifeng, Liu, Peng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 28.02.2017
• Subjects: Alkyl chain length; n-alkyltrimethoxysilane; Self-assembled monolayer (SAM); Silicon wafer; Tribological behavior; Self-assembled monolayer (SAM); Alkyl chain length; Tribological behavior; Silicon wafer; n-alkyltrimethoxysilane
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2016.11.049

[Display omitted] •n-Alkyltrimethoxysilanes with various chain lengths were self-assembled on silicon.•Effect of alkyl chain lengths (C6, C12, or C18) on the SAMs was investigated.•Surface roughness of the SAMs decreased with increasing the alkyl chain lengths.•The C12-SAM possessed superior friction reduction and wear resistance. It is well known that the self-assembled organic molecules on a solid surface exhibit the friction-reducing performance. However, the effect of the molecular size of the self-assembled organic molecules has not been established. In the present work, self-assembled monolayers (SAMs) of n-alkyltrimethoxysilanes with different alkyl chain lengths (C6, C12, or C18) were fabricated on silicon substrate. The water contact angles of the SAMs increased from 26.8° of the hydroxylated silicon substrate to near 60° after self-assembly. The atomic force microscopy (AFM) analysis results showed that the mean roughness (Ra) of the SAMs decreased with increasing the alkyl chain length. The tribological properties of the SAMs sliding against Al2O3 ball were evaluated on an UMT-2 tribometer, and the worn surfaces of the samples were analyzed by means of Nano Scratch Tester and surface profilometry. It was found that lowest friction coefficient and smallest width of wear were achieved with the SAMs of C12 alkyl chain (C12-SAM). The superior friction reduction and wear resistance of the SAMs in comparison with the bare silicon substrate are attributed to good adhesion of the self-assembled films to the substrate, especially the C12-SAM with desirable alkyl chain length.