Bottom-Up Fabrication of Bicontinuous Bulk Nanocomposites for Optical and Electronic Applications

Fabrication of bulk nanocomposite solids with macroscopic form factor and nanoscopic structural control is a central challenge in nanomaterials engineering. This work introduces an approach to this challenge wherein precise nanostructural control is provided by ultrahigh-aspect-ratio atomic layer deposition and complete densification with nanostructure preservation is enabled by environmentally controlled pressure-assisted sintering. To demonstrate the capability to tune functional properties via nanocomposite design, this approach is used to produce millimeter-scale, fully dense, bicontinuous SiO2/ZnO:Al nanocomposites: atomic layer deposition is used to infiltrate SiO2 nanoparticle compacts with conductive ZnO:Al, and then environmentally controlled pressure-assisted sintering is used to remove the residual porosity. The nanocomposites’ optical and electrical properties are dictated by the ZnO:Al channel width and volume fraction, which are precisely controllable via the number of atomic layer deposition cycles. Increasing the ZnO:Al channel width from ∼6.5 to ∼13 nm (increasing the volume fraction from 16% to 27%) intensifies visible reflectance (producing a bright blue color) and increases the electrical conductivity by nearly an order of magnitude (from 0.69 to 6.5 Ω–1 cm–1). Temperature-dependent conductivity measurements indicate Efros-Shklovskii variable range hopping while also suggesting proximity to a metal–insulator transition. Due to their tunable optical and electronic properties and robust mechanical properties, these SiO2/ZnO:Al nanocomposites are promising candidates for conductive window applications; more broadly, the fabrication strategy demonstrated here is amenable to a wide range of material combinations, and it enables nanoscale architectures with tailorable properties for application areas including photonics, sensing, energy generation and storage, thermal management, and structural materials.