Photoinduced Topotaxial Exchange Reactions in Cadmium Sulphide Thin Films

A CO2 laser, operating at 10.6μm, has been used to promote the growth of topotaxial layers of the chalcocite phase of cuprous sulphide in cadmium sulphide thin films immersed in an organic solution of a cuprous salt at ambient temperature. Cuprous sulphide growth is initiated by the laser beam which passes through the liquid and raises the surface temperature of the CdS allowing ion exchange to take place without changing the surface topography. An investigation into different combinations of organic solvents and cuprous/cupric salts has revealed that cuprous iodide in acetonitrile or propionitrile yields the fastest growth rates. The results are compared with those obtained from junctions fabricated using lasers operating in the visible frequency range.