Solid-vapor equilibrium phase diagram of hydrogen-adsorbed carbon

We studied the phase equilibrium of carbon which holds the hydrogen-adsorbe d surface at low pressure. All of the molecules in a chamber of a finite vo lume are assumed to be fully decomposed so that the system is considered to be a mixture of atomic hydrogen and carbon vapor with a crystalline carbon . The equilibrium conditions are characterized by the same chemical potenti als for both phases of each ingredient. The phase boundary of a two-dimensi onal solid with a smaller bond strength is separable from that of a three-d imensional solid with a larger bond strength. The covering ratio of hydroge n atoms on the surface was also calculated and turns out to be larger for a two-dimensional solid.