Showing papers by "Sven Stafström published in 2013"
TL;DR: It is shown that the halogen atoms can poison the surface, thus hindering long-range ordering of the self-assembled structures, and core-level shifts of the relevant carbon and halogens are presented, to provide reference data for reliably detecting self-assembly without the need for atomic-resolution scanning tunneling microscopy.
Abstract: We computationally study the reaction mechanisms of halogen-based covalent self-assembly, a major route for synthesizing molecular nanostructures and nanographenes on surfaces. Focusing on biphenyl as a small model system, we describe the dehalogenation, recombination, and diffusion processes. The kinetics of the different processes are also investigated, in particular how diffusion and coupling barriers affect recombination rates. Trends across the periodic table are derived from three commonly used close-packed (111) surfaces (Cu, Ag, and Au) and two halogens (Br and I). We show that the halogen atoms can poison the surface, thus hindering long-range ordering of the self-assembled structures. Finally, we present core-level shifts of the relevant carbon and halogen atoms, to provide reference data for reliably detecting self-assembly without the need for atomic-resolution scanning tunneling microscopy.
214 citations
TL;DR: A semiclassical model for studying charge transport in a two-dimensional molecular lattice is presented and applied to both a well ordered system and a system with disorder, finding that the parameter space for which the polaron is moving through the system is quite restricted.
Abstract: A semiclassical model for studying charge transport in a two-dimensional molecular lattice is presented and applied to both a well ordered system and a system with disorder. The model includes both intra- and inter-molecular electron-lattice interactions and the focus of the studies is to describe the dynamics of a charge carrier in the system. In particular, we study the dynamics of the system in which the polaron solution is dynamically stable. It is found that the parameter space for which the polaron is moving through the system is quite restricted and that the polaron is immobile for large electron-phonon coupling and weak intermolecular electron interactions and dynamically unstable and disassociates into a delocalized electronic state decoupled from the lattice for small electron-phonon coupling and strong intermolecular electron interactions. Disorder further limits the parameter space in which the polaron is mobile.
44 citations
TL;DR: In this paper, first-principles calculations were performed to investigate the stability of the (C2H5)3B:NH3 adduct formed by the initial precursor molecules triethylborane and ammonia NH3 in the metal-chemical-vapor-deposition (MOCVD) of hexagonal BN, and the energy barrier to the first ethane elimination through consistent unimolecular, ammonia-assisted and adduct-assisted reaction pathways.
36 citations
TL;DR: The simulations reveal important details of the charge separation process: the exciton in the donor polymer first dissociates into a "hot" charge transfer state, which is best described as a polaron pair, which favors exciton dissociation as well as the formation of free charge carriers.
Abstract: Exciton dissociation in a donor-accepter polymer heterojunction has been simulated using a nonadiabatic molecular dynamics approach, which allows for the coupled evolution of the nuclear degrees of freedom and the electronic degrees of freedom described by multiconfigurational electronic wavefunctions. The simulations reveal important details of the charge separation process: the exciton in the donor polymer first dissociates into a “hot” charge transfer state, which is best described as a polaron pair. The polaron pair can be separated into free polaron charge carriers if a sufficiently strong external electric field is applied. We have also studied the effects of inter-chain interaction, temperature, and the external electric field strength. Increasing inter-chain interactions makes it easier for the exciton to dissociate into a polaron pair state, but more difficult for the polaron pair to dissociate into free charge carriers. Higher temperature and higher electric field strength both favor exciton dissociation as well as the formation of free charge carriers.
33 citations