Browsing by Author "Granberg, Fredric"

Copper has been used for thousands of years in various fields as a pure metal or in many copper alloys. Copper also plays a crucial role in modern society with its high electric and thermal conductivity. To be able to also use this versatile material in the nanoindustry, its properties must be investigated. It has been found that nanomaterials have different properties compared with the macroscopic materials. One of the most important properties is the thermal stability of nanowires. The thermal stability of copper nanowires has to be known to be able to use copper wires in nanosized electronics without problems. Due to complications with experiments on the nanowires, this study uses atomistic computer simulations to investigate the thermal stability of copper nanowires. In the first study, the dependence between the wire diameter and the melting point was investigated. Also different shapes of the wires were studied. Three different wire shapes and diameters between 1.5 nm and 20 nm were investigated with a simulation method called molecular dynamics. This simulation technique uses classical Newtonian mechanics to simulate how the material behaves. The results were compared with a semi-empirical model called the liquid-drop-model, and the results are in a good agreement with this model. In the investigation of wires with the diameter 1 nm, a reconstruction was found. This reconstruction could spontaneously appear due to thermal vibrations in the wire. This phenomenon was investigated both by observing the spontaneous growth and by stretching the wire. A spontaneous reconstruction could be seen over a wide temperature range and a reconstruction due to stretching could be seen at almost all temperatures, even over the predicted melting point. The stability of the reconstruction was also investigated with a quantum mechanical simulation technique called density functional theory. These results predict that the reconstruction is stable or metastable.