Morphology control and transferability of ordered through-pore arrays based on electrodeposition and colloidal monolayers

Ordered porous films have received considerable attention in recent years([1-5]) due to their unique properties and potential applications in catalysis,([1]) photonic crystals,([2]) optoelectronic devices,([3]) etc. They are also excellent substrates for surface-enhanced Raman spectroscopy (SERS)([5]) and cell cultures.([6]) There are many techniques available for the formation of porous films, such as electron-beam lithography,([7]) micro-contact printing,([8]) electrochemical etching,([9]) self-assembly,([10,11]) and particle-array template methods, ([12]) some of which can be used to control the morphology of the films to a certain degree, which is obviously important for the applications and the properties of the films. A recently reported technique-the colloidal-crystal template approach-is very promising for the fabrication of ordered porous materials with controlled morphologies, as has been shown by the synthesis of three-dimensional (3D) photonic crystals([13]) and some surface nanostructures.([14]) The templates used in this method are mainly 3D colloidal crystals. Two-dimensional (2D) colloidal crystals, especially colloidal monolayers, have generally been used as masks for the fabrication of periodical particle arrays, which have been studied extensively.([15-17]) In addition, they could also be excellent templates for the synthesis of ordered pore arrays (films) with one-pore thickness.([18]) Several groups have synthesized TiO(2) and poly(divinylbenzene) porous films by combining the spray-pyrolysis technique([1]) and the sol-gel technique, respectively,([6]) and a selective dissolution procedure.([19]) However, the challenge of producing ordered porous films with controlled morphologies and one-pore thickness still remains. To obtain such structures, it is necessary that the film grows from the bottom. As is well known, electrodeposition is an effective method to make a material grow from the bottom and has been used to synthesize 3D ordered porous materials based on 3D colloidal crystal templates.([20-22]) Recently, noble metal (Au, Ag, and Pt) ordered porous films have also been reported using a colloidal monolayer as a template.([23]) The pores possess a bowl-like shape and the diameters of the openings at the film surface can be tuned by the electrodeposition time to some degree. In this communication we introduce a strategy-heated template-directed electrodeposition-for the synthesis of morphology-controlled ordered through-pore arrays with one pore thickness. The film morphology can be controlled by heating the colloidal-monolayer-coated substrate, and electrodeposition. We have synthesized a series of metal, oxide, and semiconductor through-pore arrays with controlled morphologies. More interestingly, the deposited film can be transferred onto any desired substrate, especially onto an insulating substrate or curved surface, neither of which can normally be used for electrodeposition. As far as we know there are no other methods to transfer a pure film to another surface easily. We chose gold as a good example to demonstrate the morphology-controlled fabrication of 2D ordered pore-arrays based on electrodeposition and a colloidal monolayer because, as a noble metal, it has found many applications in areas such as catalysis,([24]) sensors,([25]) molecular electronics,([26]) and optics([27]) (all associated with different morphologies).