Methods for making large-area, free-standing metal oxide films
The present invention provides continuous, free-standing metal oxide films and methods for making said films. The methods are able to produce large-area, flexible, thin films having one or more continuous, single-crystalline metal oxide domains. The methods include the steps of forming a surfactant monolayer at the surface of an aqueous solution, wherein the headgroups of the surfactant molecules provide a metal oxide film growth template. When metal ions in the aqueous solution are exposed to the metal oxide film growth template in the presence of hydroxide ions under suitable conditions, a continuous, free-standing metal oxide film can be grown from the film growth template downward into the aqueous solution.
1. A method of making a metal oxide film, the method comprising:
(a) forming a surfactant monolayer at an air-aqueous solution interface at the surface of an aqueous solution, wherein the headgroups of the surfactant molecules provide a metal oxide film growth template; and
(b) exposing metal ions to the metal oxide film growth template in the presence of hydroxide ions under conditions that promote the growth of a metal oxide film from the metal oxide film growth template downward into the aqueous solution.
2. The method of claim 1 , wherein the metal ions are zinc ions.
3. The method of claim 2 , wherein the surfactant molecules are dodecyl sulfate molecules.
4. The method of claim 2 , wherein the metal oxide film comprises zinc oxide having a wurtzite structure.
5. The method of claim 4 , wherein the metal oxide film is a continuous, free-standing metal oxide film and comprises at least one continuous, single-crystalline zinc oxide domain that is characterized by a hexagonal lattice parameter.
6. The method of claim 2 , wherein the metal oxide film comprises zinc oxide having a Zn 0.75 O x structure.
7. The method of claim 6 , wherein the metal oxide film is a continuous, free-standing metal oxide film and comprises at least one continuous, single-crystalline zinc oxide domain that is characterized by a rectangular lattice parameter.
8. The method of claim 1 , wherein the metal oxide film is a continuous, free-standing metal oxide film and comprises at least one continuous, single-crystalline metal oxide domain having an area of at least 0.1 μm 2 .
9. The method of claim 1 , wherein the metal oxide film has a surface area of at least 1 cm 2 .
10. The method of claim 1 , wherein the metal ions comprise at least one of magnesium ions, copper ions, titanium ions, tin ions or barium ions.
11. The method of claim 1 , wherein the metal oxide film has a thickness of no greater than about 1000 nm.
12. The method of claim 1 , further comprising transferring the metal oxide film from the aqueous solution to a substrate.
13. The method of claim 12 , wherein the substrate is a flexible plastic substrate.
14. The method of claim 12 , further comprising lithographically patterning the metal oxide film.
15. The method of claim 12 , further comprising incorporating the metal oxide film into a thin film transistor, a solar cell, a light-emitting diode for the ultraviolet or a laser diode.