Tribological properties of self-assembled monolayers covalently bonded to Si

The frictional properties of self-assembled monolayers (SAMs) covalently bonded to silicon (Si) substrates through Si–C or Si–O–C bonds were investigated using a pin-on-plate tribometer. Four kinds of molecules with different alkyl chain lengths and different head groups were used: 1-hexadecene, 1-hexadecanol, 1-dodecene and 1-dodecanol. The SAMs with longer alkyl chains exhibited lower friction coefficients than those with shorter alkyl chains. Of the SAMs with longer alkyl chains, the SAMs with the Si–C bond of the head group exhibited lower friction coefficients, higher wear resistance and higher durability than those with the Si–O–C bond. The head group and alkyl chain length of the molecules affected the frictional properties of the modified surfaces of the SAMs.