Experimental Studies of Electron Affinity and Work Function from Aluminium on Oxidized Diamond (100) and (111) Surfaces

Three different procedures were used to deposit aluminium onto O-terminated (100) and (111) boron-doped diamond, with the aim of producing a thermally stable surface with low work function and negative electron affinity. The methods were: (i) deposition of a >20 nm film Al by high-vacuum evaporation, followed by HCl acid wash to remove excess metallic Al, (ii) deposition of <3 Å of Al by atomic layer deposition, and (iii) thin-film deposition of Al by electron-beam evaporation. The surface structure, work function and electron affinity were investigated after annealing at temperatures of 300°C, 600°C and 800°C. Except for loss of excess O upon first heating, the Al+O surfaces remained stable up to 800°C. The electron affinity values were generally between 0.0 and -1.0 eV, and the work functions were generally 4.5 ± 0.5 eV, depending upon the deposition method, coverage and annealing temperature. The values are in broad agreement with those predicted by computer simulations of Al+O (sub)monolayers on a diamond surface.