The influence of stress during ion beam mixing

It is well established that thermodynamic forces influence ion mixing. Systems with a negative enthalpy of formation experience enhanced ion mixing while systems with a positive enthalpy of formation experience no mixing or even “de-mixing”. Recent experimental results have suggested that intrinsic stresses should be considered when evaluating the thermodynamic driving forces that influence ion mixing. We have studied the effects of thermal annealing and Ar ion irradiation on the structure and stability of multilayered DC sputtered thin films of TiN/B–C–N. These samples are in a state of bi-axial compression in their as-deposited form. Following thermal annealing, to temperatures as high as 1000°C for 1 h, it is observed that the intrinsic stresses are rapidly relieved and no interdiffusion or break down of the layered structure takes place. However, when samples are ion irradiated, we do observe intermixing and at the highest dose (5×1016 ions cm−2) the multilayered structure partly disappears. The rate of intermixing is well correlated with the magnitude of compressive stress as a function of irradiation dose. We believe that the observed ion mixing, in this otherwise immiscible system, is being controlled by stress derived thermodynamic forces.