High Temperature Surface Metallization of Ge(111) Detected by Electron Energy Loss Spectroscopy

Using electron energy loss spectroscopy (EELS) we show that the Ge(111) surface is metallic for $T>600$ K. The surface conductivity increases almost linearly with temperature for 600 $<T<1040$ K but exhibits a steplike increase at T=Tc≈1040 K after which it stays constant up to the bulk melting temperature Tₘ=1210 K. The data support a picture where at T≈1040 K incomplete surface melting takes place. The surface free carrier concentration deduced from the EELS intensity is consistent with the assumption that only the top surface bilayer has melted, in agreement with recent theoretical work.