Nanotribological Properties of Octadecyltrichlorosilane Self-Assembled Ultrathin Films Studied by Atomic Force Microscopy:  Contact and Tapping Modes

Abstract

Atomic force microscopy, working in contact and tapping modes, has been used to probe the mechanical response of octadecyltrichlorosilane, CH3−(CH2)17−SiCl3 (OTS), self-assembled ultrathin films grafted on silicon-treated surfaces. To assess the adhesion hysteresis and the elasticity of the films, we have performed loading and unloading experiments in contact mode. The effect of compression is observed while the load is being applied to the film. Once the load is fully removed, the film remains compressed showing a clear deviation from perfect elasticity, with relaxation times in the range of 0.1 s. In the tapping mode, the loading/unloading experiments show again the deviation from perfect elastic recovery of the films. Upon loading, three different regions are encountered. These can be associated with an initial disorder of the chains produced by the indenting tip, followed by a smooth compression and a final hardening effect due to repulsive forces between the compressed chains. The tapping mode is also used to provide strong evidence of a “cushioning” effect. The tribological properties of our OTS layers seem to be influenced by molecular disorder of the alkyl chains.

Detachment of Particles from Surfaces: An AFM Study

“…Most data were fitted to DVLO theory with constant and dissimilar surface potential boundary conditions (20) and nonretarded van der Waals interaction (26). However, for hydrophobic interactions an additional acid-base (AB) attractive term was added (27), and the final expression for force normalized with the particle radius (F/R) in N/m is [8] where ε 0 is the permittivity of free space (C 2 /J m), κ is the reciprocal Debye length (m Interactions in deionized water. Results for experiments conducted in deionized water (pH ∼ 6) are presented graphically in Fig.…”

“…Garcia-Parajo et al (8) assessed the adhesion hysteresis and the elasticity of thin films of octadecyltrichlorosilane (OTS) grafted on silicon-treated surfaces. They performed loading and unloading experiments and verified that the film exhibited viscoelasticity, with relaxation times in the range of 0.1 s. Feldman et al (9) measured pull-off forces between a series of polymer films and spherical probes (glass and polystyrene).…”

Challenges and developments of self-assembled monolayers and polymer brushes as a green lubrication solution for tribological applications

“…70 However, the authors found the OTS SAMs instantly breakdown and failed under a higher load of 1 N. Garcia-Parajo et al studied OTS SAMs on silicon with force distance curves and compressive forces, and proposed that rearrangement of OTS under compression and the subsequent reformation aer load was removed contributes to the lubricity of OTS SAMs. 165 Flater et al demonstrated that OTS SAMs can reduce adhesion of silicon wafers through pull off measurements using AFM, and also noticed that friction is reduced further when OTS SAMs are created on both the cantilever and substrate. 164 Inuence of chain length and head group.…”

Effects of Self-Assembled Monolayer and PFPE Lubricant on Wear Characteristics of Flat Silicon Tips

“…It has been reported that SAM could be damaged at a pressure of \1 GPa at the nano-scale [46,47]. However, the critical pressure at which SAM is destroyed is difficult to assess since it varies according to the contact area and also because SAM layer includes defects or disorders that are hard to characterize [48][49][50]. When the contact area increases, the number of defects or disorders involved in the force interaction is likely to increase as well.…”