Projects per year
Abstract
This thesis is concerned with the interplay between electrical current and vibrational and plasmonic excitations. The development of nanoscale devices for electronics relies on the ability to identify individual atoms and molecules as well as their geometry and electronic structure. In this thesis we show how measuring the noise can give information about the quantum nature of the device and relate the high frequency noise to lightemission . A first principle method is presented for calculating the lightemission and is utilized to calculate the lightemission from two STM experiments: An adatom on a Ag(111)surface and a C_{60} molecule on a Cu(111) surface. The calculated photon yield is found to agree with experiments for photons with energies below the applied bias (hω < eV). Inelastic electron tunneling spectroscopy (IETS) serves as a powerful tool for nondestructive characterization. A new fast method for calculating the energy dependent IETS signal is presented, and applied to a onelevel model revealing how a symmetric system can give rise to peakdip features in the IETS. The new method is used to explain the IETS signal obtained for a 1,4benzenedithiol(BDT) molecule in a symmetric gold junction as a function of gate voltage. Gating molecules in 3D metal junctions is dicultdue to screening effects. On the other hand, graphene devices are routinely gated. Thus, we study the IETS signal from gated graphene nano ribbons (GNR). We study pristine GNRs with both zigzag and armchair chirality, and related the IETS signal to the phononic band structure. For the spinpolarized zigzag GNRs the role of the spinpolarization is investigated, revealing IETSas an indirect measurement of spinpolarization. Further, the role of impurities is explored, revealing the possibility of detecting defects in the hydrogen passivisation by IETS. Lastly a preliminary study of the heating due to the electrical current is described, investigating the effect of the deterministic currentinduced forces, treated within the framework of the semiclassical generalized Langevin equation(SGLE). For a pristine zigzag ribbon the deterministic currentinduced forces is seen to give rise to runaway modes. For an armchair ribbon with partly dehydrogenated edges the deterministic currentinduced forces is seen to break the symmetry and increase the excess heating
Original language  English 

Publisher  DTU Nanotech 

Number of pages  192 
Publication status  Published  2015 
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Projects
 1 Finished

Electronic transport and atomic dynamics in graphenebased nanostructures  theory and simulation
Christensen, R. B., Brandbyge, M., Jacobsen, K. W., Solomon, G. & Paulsson, M.
15/08/2011 → 07/05/2015
Project: PhD