Physical properties of interfaces (electronic, tribological, wetting, etc.) preferentially depend on the smoothness/roughness of surface and degree of ordering of adsorbed film. The thesis is devoted to the solving of an important and actual scientific problem – investigation of electrophysical and tribological properties of interfaces formed by metallic surfaces (including atomically flat), separated by thin lubrifiant film (in particular, monolayer).
Up to date the overwhelming majority of tribological studies were carried out with imperfect surfaces, with using of films with nondetermined component composition, structure and thickness. Significant shortcomings of previous tribological studies were: (i) the destructive regimes of measurements, (ii) the absence of nanoscale stability of the film during the measurements, (iii) the uncertainty of the surface morphology, (iiii) the uncertainty of the structure and component composition of the lubricating films. It made impossible to distinguish the interaction of interfaces in the general friction process.
This study differs from others, because the tribological measurements were performed with atomically flat surfaces covered by highly ordered monolayer films with a given component composition. For the first time a new non-destructive method, based on a magnetic levitation pendulum, has been proposed, constructed and tested for measuring of friction coefficients. The control of monolayer stability was carried out directly during the process of tribological measurements. To set up non-destructive regimes the simultaneous current-voltage spectra measurements were proposed and performed. Thus, it became possible to find out the influence of the structure and component composition of monolayer film on the tribological properties of friction interface.
Using non-destructive method the tribological properties of the interface n-alkane (n = 14, 16, 48, 50, 60) / gold(111) were investigated. The nonmonotonous dependence was obtained for friction coefficient μk0(L) on the length L of the n-alkane molecule. For alkanes with "magic length" (n multiple to 16) μk0 drastically decreases.
The influence of the components of the lubricant film on the friction coefficient was studied for the pairs of n-alkane/graphite. Using MLT-measurements it has been revealed the substantial lowering of friction coefficient μk0 for monolayers of C24H50+C48H98 (μk0 = 0.39) binary mixture in contrast to pure C24H50 (μk0 = 0.48) and C48H98 (μk0 = 0.81). The lowering of friction was explained in terms of incommensurability between alkyl chain (2.51Å) and graphite surface (2.46Å).
The polyol synthesis was realized to grow the nanoprisms of gold on atomically flat surfaces as objects for tribological studies. The optimal conditions of formation of gold nanostructures were established on the atomically flat surfaces of mica, MoS2, graphite. It was shown that in the growth solution the quantity of nanoprisms increases on the substrates during 48 hours in the order of mica, MoS2, graphite. This method has been adapted for obtaining of nanoparticles with clean (free of stabilizer) surface.
The method of measuring static friction (adhesion) on rotated substrates was proposed and implemented. It allows to estimate operatively the value of static friction of gold nanoparticles on the atomically flat surfaces. The boundary values of the friction coefficients were estimated using MLT, AFM methods and the method of rotated substrates for tribological pairs gold prism/PVP-stabilazer/mica. It was established that adsorption of the polymer-stabilizer on the prism surface increased adhesion of particles with the substrate.
