Controlling and Optimizing Photoinduced Charge Transfer across Ultrathin Silica Separation Membrane with Embedded Molecular Wires for Artificial Photosynthesis

Controlled electron transfer by molecular wires embedded in ultrathin insulating membranes for driving redox catalysis

Organic bilayers or amorphous silica films of a few nanometer thickness featuring embedded molecular wires offer opportunities for chemically separating while at the same time electronically connecting photo- or electrocatalytic components. Such ultrathin membranes enable the integration of components for which direct coupling is not sufficiently efficient or stable. Photoelectrocatalytic systems for the generation or utilization of renewable energy are among the most prominent ones for which ultrathin separation layers open up new approaches for component integration for improving efficiency. Recent advances in the assembly and spectroscopic, microscopic, and photoelectrochemical characterization have enabled the systematic optimization of the structure, energetics, and density of embedded molecular wires for maximum charge transfer efficiency. The progress enables interfacial designs for the nanoscale integration of the incompatible oxidation and reduction catalysis environments of artificial photosystems and of microbial (or biomolecular)-abiotic systems for renewable energy.

Multimodal Encapsulation to Selectively Permeate Hydrogen and Engineer Channel Conduction for p-Type SnOx Thin-Film Transistor Applications

It has been challenging to synthesize p-type SnO_x (1 < x < 2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band. Herein, we report on the multifunctional encapsulation of p-SnO_x to limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnO_x channel for thin-film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements identified that ultrathin SiO₂ as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnO_x and selectively diffused hydrogen across the entire thickness of the channel. Encapsulated p-SnO_x-based TFTs demonstrated much enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current (on/off ratio > 10³), field effect mobility of 3.41 cm²/(V s), and threshold voltages of ∼5-10 V. The fabricated devices show minimal deviations as small as ±6% in the TFT performance parameters, which demonstrates good reproducibility of the fabrication process. The relevance between the TFT performance and the effects of hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. Density functional theory calculations reveal that hydrogen-related impurity complexes are in charge of the enhanced channel conductance with gate biases, which further supports the selective permeation of hydrogen through a thin SiO₂ encapsulation.

Solution-Based Self-Assembly and Stability of Ruthenium(II) Tris-bipyridyl Monolayers on Gold

Ruthenium(II) polypyridyl complexes are commonly applied as photosensitizers in the fields of artificial photosynthesis and light harvesting. Their immobilization on gold surfaces is also of interest for sensing and biological applications. Here, we report the self-assembly of [Ru(dmbpy)₂(dcbpy)](PF₆)₂ complexes on gold substrates from solution (dmbpy: 4,4'-dimethyl-2,2'-bipyridine; dcbpy: 2,2'-bipyridine-4,4'-dicarboxylic acid). Applying X-ray photoelectron spectroscopy, we demonstrate the formation of self-assembled monolayers (SAMs) of the Ru(II) complexes upon loss of counterions with carboxylate groups oriented toward the gold surface. We investigate the stability of the formed SAMs toward the substitution in solvents with competing aliphatic and aromatic thiols such as 4'-nitro[1,1'-biphenyl]-4-thiol, [1,1'-biphenyl]-4-thiol, and 1-hexadecanethiol. We show that the exchange reactions may lead to both complete replacement of the Ru(II) complexes and controlled formation of mixed SAMs. Moreover, we demonstrate that thiol-based SAMs can also be replaced completely from gold via their immersion into solutions of [Ru(dmbpy)₂(dcbpy)](PF₆)₂, indicating a relatively high stability for the Ru(II) complex SAMs. Our findings open up a variety of opportunities for applications of carboxylate-based SAMs on gold in nanotechnology.