Using ab initio density functional theory calculations, we characterize changes in the electronic structure of MoS monolayers introduced by missing or additional adsorbed sulfur atoms. We furthermore identify the chemical and electronic function of substances that have been reported to reduce the adverse effect of sulfur vacancies in quenching photoluminescence and reducing electronic conductance. We find that thiol-group-containing molecules adsorbed at vacancy sites may reinsert missing sulfur atoms. In the presence of additional adsorbed sulfur atoms, thiols may form disulfides on the MoS surface to mitigate the adverse effect of defects.

Surface dipoles are a powerful tool in interfacial modification for improving device output via energy level matching. Fluorinated alkanethiols show a strong promise for these applications as they can generate large and tunable dipoles based on fluorine location and chain length. Furthermore, these chains can be designed to possess fluorocarbons solely along the backbone, enabling an "embedded" configuration that generates a significant dipole effect from the fluorines while maintaining surface chemistry to prevent deleterious side effects from altered surface interactions. However, fluorine substitution can modify other molecular electronic properties, and it is important to consider the transport properties of these interfacial modifiers so that knowledge can be used to tailor the optimal device performance. In this paper, we report the transport properties of selfassembled monolayers derived from a series of fluorinated alkanethiols, both with and without the embedded dipole structure. Photoelectron spectroscopy and Kelvin probe force microscopy show significant work function modification from all fluorinecontaining molecules compared to purely hydrocarbon thiols. However, although embedded fluorocarbons generate a smaller electrostatic effect than terminal fluorocarbons, they yield higher tunneling currents across Au/monolayer/eutectic gallium− indium junctions compared to both terminal fluorocarbon and purely hydrocarbon alkanethiols. Computational studies show that the location of the fluorine constituents modifies not only dipoles and energy levels but also molecular orbitals, enabling the presence of delocalized lowest unoccupied molecular orbital levels within the alkanethiol backbone and, thereby, the appearance of larger tunneling currents compared to other alkanethiols. Ultimately, we show that fluorinated alkanethiols and the embedded dipole architecture are both powerful tools, but they must be thoroughly analyzed for proper utilization in a device setting.

Recent experimental and theoretical studies indicate that thiols (R-SH) can be used to repair sulfur vacancy defects in MoS monolayers (MLs). This density functional theory study investigates how the thiol repair mechanism process can be used to dope MoS MLs. Fluorinated thiols as well as amine-containing ones are used to p- and n-dope the MoS ML, respectively. It is shown that functional groups are only physisorbed on the repaired MoS surface. This explains the reversible doping with fluorinated thiols.

The influence of an electric field on different properties of the donor−acceptor polymer diketo-pyrrolopyrrole bithiophene thienothiophene (DPPT-TT) that are essential for the charge transport process is studied. The main focus is on whether the transport in DPPT-TT-based organic transistors can be tuned by electric fields in the gate direction. The considered electric fields are in the range 10 8 −10 10 V m −1 . We show that strong electric fields (∼10 9 V m −1 ) which are parallel to the polymer backbone can influence the reorganization energy in a Markus-type approach. Weaker electric fields parallel to the polymer backbone result in minimal changes to the reorganization energy. The coupling element of DPPT-TT shows a pronounced affinity to be influenced by electric fields in the charge transport direction independent of the field strength.