Stability of Planar Slits in Multilayer Graphite Crystals

Using a two-dimensional coarse-grained chain model, planar slits in multilayer graphite crystals are simulated. It is shown that when covering a linear cavity on the flat surface of a graphite crystal with a multilayer graphene sheet, an open (unfilled slit) can form only if the cavity width does not exceed a critical value L_o (for width L>L_o, only a closed state of the slit is formed, with the cavity space filled by the covering sheet). The critical width of the open slit L_o increases monotonically with the number of layers K in the covering sheet. For a single-layer cavity, there is a finite critical value of its width L_o<3nm, while for two- and three-layer cavities, the maximum width of the open slit increases infinitely with increasing K as a power function K^\alpha with exponent 0<\alpha<1. Inside the crystal, two- and three-layer slits can have stable open states at any width. For a slit with width L>7.6nm, a stationary closed state is also possible, in which its lower and upper surfaces adhere to each other. Simulation of thermal oscillations showed that open states of two-layer slits with width L<15nm are always stable against thermal oscillations, while wider slits at T>400K transition from the open to the closed state. Open states of three-layer slits are always stable against thermal oscillations.