Multiscale Modelling of a Nanoelectromechanical Shuttle

Licentiatavhandling, 2005

Nanoelectromechanical systems couple mechanical and electronic degrees of freedom creating a new type of electrical components. The nanoelectromechanical shuttle consists of a double junction with a movable central island. Under the right circumstances, electrons can be shuttled between the leads by the central island, greatly enhancing the current through the junction. We have examined from first-principles, the effects on the island dynamics of a non-continuous distribution of the energy levels on the central island. We have also developed a model for the grain-electrode interactions for our system. The system consists of a single copper atom moving between two semi-infinite jellium electrodes 15 Å apart. The model is divided into a microscopic and a macroscopic part. The core of the former part is density functional theory calculations for the wave functions and eigenvalues of the island. Transition rates are then computed from the atomic wave functions with the transfer Hamiltonian method. The forces are calculated including interactions with induced charge, repulsion, polarisation effects and a bias voltage of 3 V. The second part uses the forces and transition rates as parameters in a classical picture of the motion. Dynamic Monte Carlo is used to determine the transition events. We show that the system shuttles with a current of 0.19 μA. We also show that the system is very sensitive to surface forces. Additionally, the shaping of the non-trivial energy levelling is paramount for the possibility of the circuit to enter the shuttling regime.