Results in our study indicate that hydrogen atoms segregate to form metastable, highly hydrogenated domains on as-dosed C(1 1 1)-(1 x 1) surface with a significant temperature dependence of domain growth. Heating of the partially hydrogenated C(1 1 1) surface causes shrinking of the (2 x 1) domains as well as the relaxation of the hydrogenated domains. In this work, low energy electron diffraction in conjunction with gated heating techniques have been applied to observe the thermal effect on the structural instability of the diamond C(1 1 1) surface.