Thermodynamic Energy of Semi-Infinite Solids with a Two-Dimensional Hot Electron Gas near the Surface

Expressions for the thermodynamic energy of semi-infinite solids with a hot electron layer near the stress-free surface are derived for films and for large samples. Conditions are determined under which this energy is associated with the hot electron excitation energy, with the nonequilibrium Rayleigh waves energy, and with the equilibrium bulk phonon energy. The calculations use the Keldysh diagram technique.