Surface Ohmic Conductivity on a Mott Insulator Based on a One‐dimensional Bromide‐bridged Nickel(III) Complex

Abstract

Ohmic contacts are of critical importance to improve the performance of semiconductor devices as well as those of low-dimensional materials. Halogen-bridged metal complexes (MX-Chains) are fascinating quasi-onedimensional (1D) electronic materials. However, reports on the electrical characteristics of MX-Chains remain elusive. Herein, we report the electrical characteristics of single crystals of [Ni(chxn) 2 Br]Br 2 (chxn: (1R,2R)-(À )-1,2-cyclohexanediamine), which is a 1D Mott insulator, using different probe arrangements. [Ni(chxn) 2 Br]Br 2 was shown for the first time to exhibit Ohmic characteristics on the crystal surface, albeit that the conductivity behavior of the interior of the crystal is nonlinear due to the Joule heating effect. The current flow on the surface is shallow (a few micrometers in depth) despite the millimeter-scale crystal size; this phenomenon is strongly connected to its structural anisotropy. The Ohmic contact revealed in this work should be valuable for the application of MX-Chains as electronic devices in the near future.

Orthogonal Grade-Separated Nanowiring of Molecular Single Chains

“…These hydrogen bonds support the 1D chains and cross-link them to form two-dimensional (2D) sheets. These hydrogen bond networks have been reported for various MX-Chains. − On the other hand, there are additional hydrogen bonds (Cl3 ax ···N1 // = 3.355 Å), represented as green dotted lines, in [Pt­(en) 2 Cl]­[Fe III Cl 5 ]. Two kinds of hydrogen bonds (green and red dotted lines, Figure b) cross-link orthogonal grade-separated chains three-dimensionally, which has never been reported for other MX-Chains.…”

“…In general, Ni-type MX-Chains are in a Mott–Hubbard (MH) state in an M­(III) averaged valence state because of a stronger electron correlation, whereas Pd- and Pt-type MX-Chains are in an M­(II)/M­(IV) mixed valent charge-density-wave (CDW) state due to strong Peierls instability . Optical, , magnetic, , and electrical properties − based on such 1D electronic systems, as well as ladder structures − and a 1D heterojunction, have been well studied so far. It should be noted that all reported MX-Chains adopt similar parallel arrangements.…”

Ni(III) Mott–Hubbard-like State Containing High-Spin Ni(II) in a Semiconductive Bromide-Bridged Ni-Chain Compound

“…The Arrhenius plot afforded an activation energy ( E a ) of 233 ± 4 meV. In comparison to the previously reported bromide-bridged MX-Chains, i.e., [Ni­(bn) 2 Br]­Br 2 , [Ni­(chxn) 2 Br]­Br 2 , and [Ni­(chxn) 2 Br]­(NO 3 ) 2 (Figure S7), 1 ·solvent had lower conductivity (Figure b). The log-scale conductivity shows a roughly negative correlation with the Ni···Ni distance of the chain; thus, one reason for the low conductivity for 1 ·solvent is its longer Ni···Ni distance.…”

“…In addition, the electrical conductivity for a single crystal of 1 ·solvent was measured using the two-point probe method (Figure a). The probes were attached at opposite sides of the chain direction using carbon paste . The conductivity of 1 ·solvent at 300 K (σ 300 K = 3.1 ± 2.1 × 10 –4 S cm –1 ) was estimated using the crystal size and the differential resistance at 0 V to avoid the Joule heating effect (Figure S6) and was measured using several single crystals.…”

“…The inset photograph shows a micro-photo-image of 1 ·solvent after the attachment of the probes using carbon paste in the side-attachment configuration. (b) Comparison of the electrical conductivity at 300 K for [Ni­(bn) 2 Br]­Br 2 , [Ni­(chxn) 2 Br]­Br 2 , , [Ni­(chxn) 2 Br]­(NO 3 ) 2 (Figure S7), and 1 ·solvent vs the Ni···Ni distances. The Ni···Ni distance for [Ni­(bn) 2 Br]­Br 2 was measured at 121 K, whereas the others were measured at 296 K.…”