Formation and tribology study of amide-containing stratified self-assembled monolayers: Influences of the underlayer structure

Three kinds of amide-containing stratified self-assembled films are grafted onto silicon surfaces by a two-step method. (3-Aminopropyl)triethoxylsilane (APS), N-[3-(trimethoxylsilyl)propyl]ethylenediamine (DA), and N-[3-(trimethoxylsilyl)propyl]diethylenetriamine (TA) are separately self-assembled on silicon surfaces to form the first layer followed by derivatization with lauroyl chloride to form the second layer via surface coupling reaction. The formation and structure of these films are characterized by means of contact angle measurement, ellipsometry, and attenuated total reflectance Fourier transform infrared spectroscopy. It is shown that DA and TA form more densely packed films than APS and the density of the amino-terminated films largely affects the density of the subsequent lauroyl layer. A microtribological study of these films is carried out with an atomic force microscope, and the macrotribological property is tested with a ball-on-plate tribometer. The results indicate that the packing density of the films is greatly influenced by the underlayers of them, and therefore, their tribological performances are varied. The DAC12 film formed is more densely packed and possesses a lower frictional coefficient than the other two.