Pressure Dependence of Shear Strengths of Thin Films on Metal Surfaces Measured in Ultrahigh Vacuum

Abstract

The friction coefficient is measured for systems consisting of a thin potassium chloride film deposited onto a variety of clean, flat metal substrates, namely Pb, Sn, Au, Ag, Cu, Pd, Fe, Ta, and two types of steel, which are rubbed by a tungsten carbide pin in an ultrahigh vacuum. The friction coefficients are plotted versus 1/H S , the inverse of the substrate hardness, where two regimes are found. In the first regime, where deformation at the asperity tips is suggested to be plastic, the observed variation in friction coefficient with substrate hardness is rationalized by assuming that the shear strength S for sliding on a KCl film varies with contact pressure P as S = S 0 + aP, yielding values for a of 0.14 ± 0.02 and S 0 of *60-70 MPa. In the second regime, it is proposed that the softer, film-covered Pb and Sn substrates are closer to being in conformal contact with the rough tribopin. These values of S 0 and a, along with the measured surface asperity height distribution of the tribopin and the value of the friction coefficient for a KCl monolayer on the metal, are used to rationalize the observed increase in friction coefficient with increasing film thickness.

On the Pressure Dependence of Shear Strengths in Sliding, Boundary-Layer Friction

“…The experimental shear strength has been measured for KCl evaporated onto metal substrates in ultrahigh vacuum to obtain and maintain clean, wellcharacterized films [24]. The experiment values are S 0 = 65 ± 5 MPa and a = 0.14 ± 0.02 [24]. Thus the experimental and theoretical values of S 0 are in good agreement.…”

“…The resulting potentials were used to calculate the values of S 0 and yielded a value of 79.8 MPa for sliding along the h10i and 70.3 MPa along the h11i directions [23]. The experimental shear strength has been measured for KCl evaporated onto metal substrates in ultrahigh vacuum to obtain and maintain clean, wellcharacterized films [24]. The experiment values are S 0 = 65 ± 5 MPa and a = 0.14 ± 0.02 [24].…”

Thermodynamic Properties of Free Standing Thin Metal films Investigated Using Statistical Moment Method: Temperature and Pressure Dependence

“…(4), (6), and (8) we obtain equation of state for surface layers of the metal thin film with face-centered cubic structure at zero temperature …”

“…The dependence on pressure of the thermodynamic properties of thin film is of great interest not only from a fundamental point of view but also for technological applications [3][4][5][6][7][8][9][10]. In general, investigating for dependence on pressure of thin film almost at low-pressure and in deposition process of thin film on substrate [5,7,8].…”

“…In general, investigating for dependence on pressure of thin film almost at low-pressure and in deposition process of thin film on substrate [5,7,8]. Most of researches of thin films are mainly experimental work [3][4][5][6][7][8][9][10] but very few studies are theoretical ones. The influence of oxygen pressure on the growth of (Ba 0:02 Sr 0:98 ATiO 3 thin film on MgO substrate by pulsed laser deposition techniques have been investigated in the oxygen pressure range from 40 to 10 3 Pa [7].…”