Background: Silicon is a major component in semiconductors due to its good electrical properties reasonable cost and manufacturability. Zinc oxide is promising as a semiconductive material because it has a large bandgap (providing high power) and high exciton binding energy (a relatively large amount of energy is needed to free electrons from electron-hole pairs for potential high temperature luminescence). Zinc oxide also is a direct bandgap material (for potential light-emitting devices) and is abundant and inexpensive as compared to silicon. Unfortunately the techniques used for silicon thin film manufacturing cannot be applied to metal oxide films. Many metal oxide single-crystalline films including zinc oxide films can be grown on a solid substrate but no known chemical etchants are able to selectively remove the substrate and allow for transferring the film. Films of polycrystalline metal oxides may be formed using processes such as sputter deposition and chemical vapor deposition but the resulting polycrystalline films lack the desirable semiconducting properties of single-crystalline metal oxide films. A need exists for a method of generating single-crystalline zinc oxide thin films that are transferrable. Technology Description: UW-Madison researchers have developed a continuous free-standing metal oxide film and a method of making such films. The method produces zinc oxide nanomembranes with large areas through film synthesis on a water surface. A wetting agent forms a planar template on the water surface and attracts zinc cations contained in the water to the surface. The template expands over the water surface during formation and results in growth of a large zinc oxide membrane. The membrane floats on the water surface and can be transferred easily onto a variety of substrates allowing for use in a variety of applications. The single-crystalline structure of the continuous metal oxide film aligns either in a hexagonal or rectangular pattern depending on temperature and growth time. The single-crystalline structure provides the desirable semiconducting properties unavailable in current polycrystalline metal oxide films. Applications: 1) Transparent electrodes 2) Light-emitting diodes 3) Flexible high-frequency electronics 4) Solar panels
1) Provides only technology capable of producing single-crystalline zinc oxide thin films 2) Enables easy roll-to-roll manufacturing of large area membranes