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.
Anderson et al. (Sat,) studied this question.