Search

By performing first principles calculations, we investigate the edge reconstruction in free-standing 2D-Xene (X = Si, Ge, Sn) zigzag nanoribbons. Three different periodicities of edge reconstruction (2 a , 3 a , 4 a) are found, in which the reconstruction with 3 a periodicity has the lowest energy and shows non-magnetic ground state. The edge reconstruction can be understood by the reconfiguration of the dangling bond states and edge states at the zigzag edges. Due to the structural buckling, extra bonding states are formed between edge atoms and inner atoms, accompanied with charge transfer from the edge states to the dangling bond states. This results in one-third occupied dangling bond states and a Peierls-like structural reconstruction with 3 a periodicity at the edge which opens a small band gap. With a tight binding model, the reconstruction of the electronic structures at the edges are revealed by the hopping integrals between different edge X-p orbitals. • 2D Xene edge buckling leads to charge transfer from edge states to dangling bond states • 3a edge reconstruction originates from the 1/3 band filling of dangling bond states • Tight binding model reveals the charge transfer and bonding interactions at the edge [ABSTRACT FROM AUTHOR]

Abstract: Substantial potential steps ∼0.5eV are frequently observed in organic multilayers of donor and acceptor molecules. Often such potential steps depend on the order in which the individual layers are deposited, or on which substrate they are deposited. In this paper we outline a model for these potential steps, based upon integer charge transfer between donors and acceptors, charge equilibration across the multilayer, and simple electrostatics. Each donor, acceptor, or substrate material is characterized by a pinning level, and the potential profile can be deduced from the sequential order of the layers, and the differences between their pinning levels. For particular orderings we predict that intrinsic potential differences lead to electric fields across individual layers, which may falsely be interpreted as band bending. [Copyright &y& Elsevier]

Abstract: The Coulomb interaction between two holes on oligo-thiophene molecules is studied systematically as a function of the oligomer length using first principles density function calculations. The effect of molecular geometry relaxation upon this interaction is found to be small. In contrast, electronic polarization of the molecules that surround the charged oligomer in the crystal lattice reduces the bare Coulomb repulsion between the holes by approximately a factor of 2. In all cases, the effective hole–hole repulsion is much larger than the valence band width, which means that at high doping levels, strong correlation effects should become important. [Copyright &y& Elsevier]

Abstract: In this short review, we will give examples on how photoelectron spectroscopy (PES) assisted by models on interface energetics can be used to study properties important to bulk heterojunction type organic photovoltaic devices focusing on the well-known bulk heterojunction blend of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) and its model system P3HT:C60. We also will discuss some of the limitations of PES as applied to organic semiconductors (OS) and photovoltaic devices and finish with reviewing recent theoretical advances that now enable calculation of relevant parameters at (hybrid) interfaces measured by PES. [Copyright &y& Elsevier]