Ionization Energy and Energy Gap Structure of MoSI Molecular Wires: Kelvin Probe, Ultraviolet Photoelectron Spectroscopy, and Cyclic Voltammetry Measurements

Abstract

The work function W of Mo(6)S(3)I(6) molecular nanowires is determined by Kelvin probe (KP) measurements, UV photoelectron spectroscopy (UPS), and cyclic voltammetry (CV). The values obtained by all three methods agree well, giving W = 4.8 ± 0.1 eV. CV measurements also give a gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of E(g) = 1.2 ± 0.1 eV, in agreement with recent optical measurements, but in disagreement with theoretical calculations, which predict the material to be a metal. The electronic structure of Mo(6)S(3)I(6) suggests use of the material in applications such as bulk heterostructure photovoltaics and transparent electrodes and for molecular electronics devices.

The Role of Valence Electron Concentration in Tuning the Structure, Stability, and Electronic Properties of Mo6S9–xIx Nanowires

“…13 High-resolution transmission electron microscopy on these NWs 18 suggests the presence of Mo 6 octahedra, but the positions of I and S atoms are not clearly observed. Earlier theoretical studies 19,20 on the atomic structure and electronic properties of these NWs suggested them to be metallic, but it is not in agreement with experiments 20,21 according to which NWs such as Mo 6 S 3 I 6 are semiconducting with a band gap of about 1.2 eV. We have performed extensive ab initio calculations (refer to Table S1 of Supporting Information) and found new atomic structures of these NWs with unique decoration of S and I atoms that are lower in energy than the earlier models 15,19,20 and have semiconducting behavior as well as large Young's modulus in agreement with experiments.…”

“…The DOS of all the NWs except for x = 3 shows their semiconducting nature with an average energy band gap, E g , of 0.4 eV which is supported by the experimental results. 20,21 Note that the calculated gap is smaller due to the use of GGA. In contrast, the model proposed by the earlier theoretical studies with S on the bridge site shows the NWs to be metallic.…”

Lateral Photodetectors Based on Double-Cable Polymer/Two-Dimensional Perovskite Heterojunction

“…The UPS is measured as a film in high vacuum, and the nature of electronic states for UPS is different from that for CV, which is done in the solution. Besides, the surface conditions for UPS and the interface of electrode–electrolyte for CV would affect the results. , According to the UPS results, the offsets of the energy levels between the 2D-PPR and the polymer are beneficial for the charge transfer between the two films. For the polymer device, the GIWAXS image shown in Figure d indicates that it inclines to the “face-on” orientation more, which is not in favor of carrier transport in the lateral direction.…”

Unlocking the Functional Properties in One-Dimensional MoSI Cluster Polymers by Doping and Photoinduced Charge Transfer

“…31,35 Measurements on very thinly dispersed wires show the existence of an energy gap of 1.2 eV, much larger than predicted by any type of possible unit cell configuration, and that undoped nanowires already possess few occupied states near the Fermi level. 36 We reveal that the origin of these intragap states in MoSI bundles comes from doping by positively charged metal ions. MoSI nanowire bundles seem to already be intrinsically doped by excess molybdenum during synthesis; such doping we shall refer to as self-doping.…”

“…Control of the conductivity of MoSI wires by adsorption doping, which preserves their semiconducting character, can directly enhance the applicability of MoSI molecular wires in bulk heterostructure solar cells as electron-conducting highly dispersible wires with excellent percolation properties 36,53 and molecular-scale one-dimensional analogues of single-layer MoS 2 transistors. 54 The doping level in the presented experiments is very weak compared to CPs, where >0.5 charges/conjugate bond are needed for a substantial increase in conductivity, suggesting that much larger effect may be expected by stronger doping methods.…”