Density functional theory- (DFT-) based ab initio calculations were used to investigate the surface-to-surface interaction and frictional behavior of two hydrogenated C(100) dimer surfaces. A monolayer of hydrogen atoms was applied to the fully relaxed C(100)2x1 surface having rows of C=C dimers with a bond length of 1.39？？. The obtained C(100)2x1-H surfaces (C–H bond length 1.15？？) were placed in a large vacuum space and translated toward each other. A cohesive state at a surface separation of 4.32？？ that is stabilized by approximately 0.42？eV was observed. An increase in the charge separation in the surface dimer was calculated at this separation having a 0.04？e transfer from the hydrogen atom to the carbon atom. The Mayer bond orders were calculated for the C–C and C–H bonds and were found to be 0.962 and 0.947, respectively. σ C–H bonds did not change substantially from the fully separated state. A significant decrease in the electron density difference between the hydrogen atoms on opposite surfaces was seen and assigned to the effects of Pauli repulsion. The surfaces were translated relative to each other in the (100) plane, and the friction force was obtained as a function of slab spacing, which yielded a 0.157 coefficient of friction. 1. Introduction Carbon-based surface films are now ubiquitous as frictional barriers that lower the wear rates of interacting bodies. They have found extensive use within the information storage industry as films for protecting both the hard disk surface and the sensitive read-write transducers from damage due friction during incremental and in some instances purposeful head-to-disk contact [1, 2]. Because of this industrial importance, a rich and extensive literature exists of both theoretical and experimental studies probing the fundamental properties of these complicated and diverse surface films [3, 4]. Within the range of these studies single crystal diamond surfaces have been extensively employed as models of the more important larger-scale industrial surfaces. Insight gained from these studies has helped the community understand surface energetic processes, including the recent manifestation of super lubricity of hydrogen-covered surfaces [5, 6]. Carbon films deposited under energetic conditions assume complicated amorphous structures, which depend on the exact conditions of deposition. Specifically, the extent of surface wear protection has been attributed to film properties that can be tailored through the manipulation of deposition parameters, precursor materials, and postdeposition processing, the
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