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

Abstract

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 CuSe 2 as annealing temperature is increased. Slow rates of temperature increase favor the formation of CuSe 2 over γ-CuSe and near 66% selenium only cubic CuSe 2 forms during an exothermic event between 100 °C and 110 °C. It is surprising that the metastable cubic CuSe 2 initially nucleates and grows rather than the thermodynamically stable orthorhombic CuSe 2 polymorph. Kissinger analysis yields an activation energy for nucleation of 1.6 eV for cubic CuSe 2. CuSe nucleates throughout the composition region investigated. Hexagonal α-CuSe reacts with selenium to form the thermodynamically stable orthorhombic polymorph of CuSe 2 as the temperature approaches the melting point of selenium.