Thermodynamics and kinetics study of growth behaviour of sono-electrodeposited thin films

Abstract

Thin films have wide spread applications like in electronics, optical and magnetic devices and systems because of their improved properties (electrical, magnetic, optical, mechanical) and size reduction as compared to the bulk materials. These films when applied in real applications fail to provide the required properties, if their reliability is affected. Growth of the film is one of the factors which affect their reliability. So the growth behavior in thin films needs concern. In this work we have explored the grain growth phenomena in sono-electrodeposited copper samples.

The samples have been prepared by the above mentioned technique at various (5, 10, 15, 20, 25°C) temperatures. A potential of -300mV was selected for the deposition. Sono- electrodeposition is the modified form of electrodeposition technique. The ultrasound affects the microstructure as well as the adherence of deposit. The phenomenon of cavitation in the presence of ultrasonic field i.e. repeated creation and collapse of the microbubbles at the electrode surface, induces secondary nucleation by crystal fragmentation. Very bright and adherent deposits have been observed after deposition. The investigation of growth behavior in the copper deposits starts by the non-isothermal treatment by Differential Scanning Calorimetry (DSC). The DSC scan is performed from 25-400°C at a temperature ramp of 5, 10, 20°/min. The films are characterized before and after thermal treatment for phase, microstructural and compositional analysis by XRD, SEM, AFM. The surface energies before and after treatment are found by the contact angle measuring instrument. The exothermic peak is observed around 300°C which indicates the occurrence of grain growth. At different heating rates the position of upward peaks shift to higher temperatures indicating growth phenomena is kinetic in nature. To verify the kinetic nature a set of activation energy values have been calculated using Kissinger model. The values varies from 0.8-2.9 eV indicating grain boundary self diffusion growth mechanism. There is variation in surface energy values in treated samples as compared to untreated one, indicates the transition of abnormal grain growth behavior to normal grain growth behavior. The microstructural analysis also reveals the growth phenomena due to variation of grain sizes between treated and as-deposited samples.