Electron hopping rate measurements in ITO junctions: Charge diffusion in a layer-by-layer deposited ruthenium(II)-bis(benzimidazolyl)pyridine-phosphonate–TiO2 film

Focused ion beam (FIB) machining allowed a sub-micron trench to be cut through tin-doped indium oxide (ITO) film on glass to give a generator – collector junction electrode with narrow gap (ca. 600 nm). A layer-by-layer deposited film composed of a dinuclear ruthenium(II)-bis(benzimidazolyl)pyridine-phosphonate (as the negative component) and nanoparticulate TiO2 (ca. 6 nm diameter, as the positive component) was formed and investigated first on simple ITO electrodes and then on ITO junction electrodes. The charge transport within this film due to Ru(II/III) redox switching (electron hopping) was investigated and an apparent diffusion coefficient of ca. Dapp = 2 (± 1) × 10−15 m2 s−1 was observed with minimal contributions from intra-molecular Ru–Ru interactions. The benefits of FIB-cut ITO junctions as a tool in determining charge hopping rates are highlighted.

Graphical abstractProcesses in a layer-by-layer deposited film of TiO2 nanoparticles and a di-ruthenium(II) metal complex are investigated in a focused ion beam cut trench in an ITO electrode.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Focused ion beam cutting of ITO electrode. ► Electron hopping in nanostructured films. ► Apparent diffusion parameters are obtained.