Double Core–Shell Semiconducting Molecular Chain Halogen-Bridged Metal Complexes with Ohmic Contact Heterojunctions

The fabrication of heterostructures from low-dimensional materials is very challenging, particularly the creation of low-dimensional heterojunctions that can be characterized at an atomic resolution. In a previous work, a two-dimensional (2D) heterostructure made from halogen-bridged metal complexes (MX-Chains), [Ni(chxn)₂Br]Br₂ (chxn = 1<i>R</i>,2<i>R</i>-diaminocyclohexane) and [Pd(chxn)₂Br]Br₂, has been synthesized, and the nature of the electronically 1D heterojunction at an atomic resolution was revealed. In the work reported here, we have successfully fabricated double core-shell crystals (Ni-Pd-Ni) from these MX-Chains, using a stepwise electrochemical epitaxial method. Upon cleavage of the heterostructure along the van der Waals layers, a double heterojunction surface is observed. The MX-Chains are aligned in the heterostructure and exhibit anisotropic optical properties based on their 1D electronic systems, as measured using UV-vis-NIR polarized reflectance microscopy. Current-voltage curves at different temperatures are recorded using three probes attached to different areas of the heterostructure and reveal the presence of ohmic conduction through the double 1D heterojunctions. The ohmic contact between the two types of MX-Chains arises from the atomic-scale connection of the MX-Chains at the heterojunction. This work represents the first example of a molecule-based heterostructure that has electronic conductivity and demonstrates electrical conduction through a 1D heterojunction.