Chemical Reduction at Solid-Liquid Interface: Growth and Electrical Conductance of Thin Films of Cu/Ag-TCNQ and Cu-Hexacyanoferrate

Abstract

An interface is a boundary between two spatial regions either occupied by different matters or by matters in different physical states, for examples, solid-solid, solid-liquid and liquid-liquid interfaces. Notable interfacial phenomena are two-dimensional electron-gas, spinterface, and heterogeneous catalysis. Various chemical reactions involving oxidation and reduction processes at interfaces may vary from those in conventional liquid (solid)-phase reactions and could thus influence the overall outcome.

The present work primarily focuses on studying metal-ligand coordination at solid-liquid interface. Remarkably, spontaneous reduction of Cu(II) to Cu(I) at a solid-liquid interface – without the need of any extraneous reducing agent was observed – unlike in liquid-phase reaction whereby no reduction of Cu(II) to Cu(I) took place. As a consequence of the interfacial reduction reaction (IRR), thin films of Cu-TCNQ and Cu-Hexacyanoferrate (Cu-HCF) were deposited onto a thiol-functionalized Au substrate via layer-by-layer (LbL) method. Also, a sacrificial LbL method was developed to grow thin film of Ag-TCNQ on functionalized Au substrate. Prototypical thin film device of Cu-TCNQ was fabricated by employing electron-beam lithography technique. Electrical conductance in these thin films were thoroughly studied including the influence of chemical as well as physical stimuli. IRR is anticipated to be very useful in generating new materials which are otherwise difficult to achieve via conventional liquid-phase reactions.