Atomistic Frictional Properties of the C(100)2x1-H Surface
Figure 2
(a) Electron density difference map through the C–H bonds in the dimer parallel to the -axis of the C(100)2x1 slab, black = (−10%) to (−5%), dark gray = (−5%) to (0%) density loss, light gray = (0%) to (5%), and white = (5%) to (10%) density gain, inset is the same map with −100% to +100% in four equal steps from density loss to gain as in part (a) and shows little density build up; however, some +25% ±25% density difference light gray areas are slightly visible between the carbon atoms in the dimer. (b) Electron density map through the C–H bonds on the upper and lower slabs dimers when at a separation with a net cohesive stabilization, electron density difference color scheme is the same as part (a); inset is map through the lower slab dimer C–H with color scheme as in inset to part (a), showing more electron density build up between the C–C atoms in the dimer than (a). (c) Electron density map through the C–H bonds on the upper and lower slab dimers at a separation having a net repulsive interaction, electron density difference color scheme is the same as part (a) black patches between opposing dimer hydrogen atoms, has negative electron density difference, and is assigned to Pauli repulsion at this separation; inset is map through the lower slab dimer C–H with color scheme as in inset to part (a), showing no electron density build up between the C–C atoms in the dimer. (d) Map of the highest occupied orbital centered on the dimer on the C(100)2x1-H surface through the C–H bonds and parallel to the -axis, darker colors are negative phase and lighter colors the positive; steps plotted are from −0.02 to −0.01, −0.01 to 0, 0 to 0.01, and 0.01 to 0.02 electron/Å3; orbital is dominantly due to the σ C–C bond with highest values between the carbon atoms. (e) Map of the highest occupied orbital centered on the C–H on the C(100)2x1-H surface through the C–H bonds, color scheme is the same as in part (d); orbital is dominantly due to the σ C–H bond with some overlap between neighboring hydrogen atoms on different dimers. (f) Similar map of the highest occupied orbital centered on the dimers on the C(100)2x1-H surface-to-surface interaction at a separation having a net cohesive stabilization, orbital is dominantly due to the σ C–C bond that has changed little from part (d). (g) Similar map of the highest occupied orbital centered on the C–H when slabs have net cohesive stabilization; orbital is dominantly due to the σ C–H bond with no overlap between neighboring hydrogen atoms on different dimers. (h) Similar map of the highest occupied orbital centered on the dimer when the slabs are experiencing a repulsive interaction; orbital is dominantly due to the σ C–C bond now having high orbital values moved from between the carbon atoms to beneath and outside of the C–C bond. (i) Similar map of the highest occupied orbital centered on the C–H when the interacting slabs experience a net repulsion; orbital is dominantly due to the σ C–H bond now with some overlap between neighboring hydrogen atoms on different dimers.
