Abstract
Friction force microscopy experiments at the nanometer scale are applied to study low friction of hydrogenated fullerene-like carbon films. The measured friction coefficients indicate that lower hydrogen concentration during preparation is beneficial to enter the low friction regime, especially in combination with only methane as precursor. Furthermore, two regions are found with distinct friction coefficients and surface roughnesses related to different surface structures. One is rich in amorphous carbon and the other is rich in fullerene-like carbon, dispersed on the same surface. Transmission electron microscopy and Raman spectroscopy images verify this observation of the two separated structures, especially with the extracted fullerene-like structures in the wear debris from macro friction experiments. It is speculated that hydrogen may tend to impair the growth of fullerene-like carbon and is therefore detrimental for lubricity.
Highlights
Carbon-based layers with different structures have excellent protective function for efficient control of the heat transfer rate at the solid-liquid interface and better viability of the living matters [1].Considering high hardness, low friction coefficients and chemical inertness, these materials are applied for the design and manufacture of nanoelectromechanical systems (NEMS) [2]
In the low humidity regime the friction coefficient is known to depend on the precursor used to make the amorphous hydrogenated carbon films (a-C):H films [27]
The fullerene-like hydrogenated carbon (FL-C):H films are prepared by plasma enhanced chemical vapor deposition (PECVD), where tribological properties at the nanoscale are investigated by Friction force microscopy (FFM) in dry nitrogen atmosphere and under ambient conditions
Summary
Carbon-based layers with different structures have excellent protective function for efficient control of the heat transfer rate at the solid-liquid interface and better viability of the living matters [1].Considering high hardness, low friction coefficients and chemical inertness, these materials are applied for the design and manufacture of nanoelectromechanical systems (NEMS) [2]. The main cause for low friction in dry atmosphere are the dangling C−H bonds of the hydrogenated DLC films, which lead to a complete passivation and can prevent charge accumulation at the interface [7]. Apart from DLC films, disordered solid interfaces in fullerene-like nanoparticles (such as MoS2 and WS2 ) have shown a great potential to obtain low friction in recent years [11,12]. During the friction, these particles will be modified by the contact pressure and broken into individual sheets under stress [13,14].
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