Nucleation and growth kinetics of co-deposited copper and selenium precursors to form metastable copper selenides

The nucleation and growth kinetics of binary copper–selenium compounds from co-deposited copper and selenium films as a function of annealing temperature and time was investigated. The thermally driven evolution of crystalline phases was followed using differential scanning calorimetry and X-ray diffraction. Below 60% selenium, hexagonal α-CuSe formed during the deposition and a reversible endothermic transition at ∼130 °C was observed for the phase transition into hexagonal γ-CuSe. Above 60% selenium the samples are amorphous as deposited and there is competition between the formation of γ-CuSe and cubic CuSe2 as annealing temperature is increased. Slow rates of temperature increase favor the formation of CuSe2 over γ-CuSe and near 66% selenium only cubic CuSe2 forms during an exothermic event between 100 °C and 110 °C. It is surprising that the metastable cubic CuSe2 initially nucleates and grows rather than the thermodynamically stable orthorhombic CuSe2 polymorph. Kissinger analysis yields an activation energy for nucleation of 1.6 eV for cubic CuSe2. CuSe nucleates throughout the composition region investigated. Hexagonal α-CuSe reacts with selenium to form the thermodynamically stable orthorhombic polymorph of CuSe2 as the temperature approaches the melting point of selenium.

► Nucleation and growth of compounds from co-deposited Cu and Se films investigated.
► α-CuSe forms on deposit of films with less than 60% Se.
► Metastable cubic CuSe2 nucleates for Se rich films.
► Slow heating rates favor nucleation of metastable cubic CuSe2 over γ-CuSe.