Facile Patterning of Periodic Arrays of Metal Oxides

Abstract

Highly ordered arrays of periodic nanostructures [1] show interesting characteristics for applications in photonics, [2] electronics, [3] optoelectronics, [4] sensing, [5] biochips, [6] and catalysis. [7] The array properties are determined by the choice of material and can be tuned further by varying the geometry, chemical composition, periodicity, and the size of the nanostructures. [4,8] Such controlled and elaborate arrays are commonly fabricated by X-ray or electron-beam lithography. However, there are limitations to patterning over large areas using these lithographical techniques due to long processing times, which result in higher costs. Relatively simple and costeffective nanopatterning processes have been developed to address these inherent limitations, including interference lithography, [9] nanosphere lithography, [10] and soft lithography. [11] In order to pattern metals or metal oxides, however, the non-conventional methods still require multistep processing as does conventional photoresist lithography. In this paper, we demonstrate a novel but simple methodology for the fabrication of periodic structures comprising metal oxides at the sub-100 nm scale using polymeric templates, colloids, and common laboratory equipment. Thus, this nanopatterning technique does not require high-vacuum deposition, etching, or photoresists, which are common in other processes. The patterns produced with this method were periodic and composed of 1D or 2D arrays of nanostructures over large areas. Fabrication of these metal oxide nanostructures required only a few hours once the nanometer-sized colloid of the metal oxide and polymeric templates were available. The structural resolution of the resulting pattern was determined by the amount of colloidal deposition onto the grooves (or grating) of the templates used. Although this process utilized microstructured templates, it is possible to fabricate features of metal oxide at the 100 nm scale. The geometry and periodicity of the structure can be well defined and controlled through selection from a wide variety of polymeric templates fabricated by numerous techniques. This unique strategy to achieve controlled nanopatterning can utilize a wide variety of inorganic colloids and/or intricate templates (or masks) available from various established lithographic methods. Microstructured polymeric templates have been prepared using a single-step holographic patterning process by exposing films of azobenzene-functionalized polymers (AFPs) on substrates to an argon-ion laser (488 nm) interference pattern. [12] The interference pattern produced photoinduced mass transfer in the polymer film giving rise to a surface-relief structure without additional processing.[13] Such surface modulation leads to 1D or 2D periodic arrays of surface-relief-grating (SRG) structures on the polymeric films. A variety of holographic surface structures can be designed and fabricated with good control over the modulation and periodicity of the patterns. In this work, SRG structures from thin films of ...

Efficient Polymer Solar Cells with Surface Relief Gratings Fabricated by Simple Soft Lithography

“…Compared to the conventional photolithographic method, the use of azo polymers as a master can provide significant advantages as follows: it is a one-step process; duplication of the method is feasible; it allows control of the grating profiles; it has the capability of superimposing multiple patterns; and, azo polymers are easily prepared. [25][26][27][28] Preparation of the PDMS molds with SRGs was successfully confirmed by AFM, as shown in Figure 2. The 1D (period ¼ 500 nm, height %20 nm) and 2D (period ¼ 500 nm, height %20 nm) SRGs on the PDMS molds are shown in Figure 2a and b, respectively.…”

Azopolymer‐based micro‐ and nanopatterning for photonic applications

“…Transmissive phase gratings can be obtained by holographically inscribing an SRG onto an azopolymer film. Reflective gratings can in turn be created by coating an already patterned polymer film with a reflective material, such as metal; note that other coating materials have also been used for improvement of optical properties, quality, and stability of the gratings …”

“…Reflective gratings can in turn be created by coating an already patterned polymer film with a reflective material, such as metal; [105][106][107][108] note that other coating materials have also been used for improvement of optical properties, quality, and stability of the gratings. [109][110][111] The overall diffraction efficiency of an azopolymer SRG is always a sum of multiple effects. For instance, bulk reorientation of the azobenzene molecules upon illumination gives rise to a birefringence grating that in principle is always present, but whose contribution to the overall diffraction efficiency of thin films of amorphous azopolymers is small.…”

“…We emphasize, however, that microfabrication techniques in which azopolymer SRGs can be used as templates may significantly differ from the techniques described above (see, e.g., refs. [193][194][195]). In ref.…”

Fabrication of TiO2 nanotubes by using electrodeposited ZnO nanorod template and their application to hybrid solar cells

“…To fabricate TiO 2 -covered ZnO nanostructures, the Ti-precursor solution was dropped on the ITO substrates with freestanding ZnO nanorods and then spun at room temperature, followed by heat treatment at 450 • C for 30 min in a furnace to form the TiO 2 crystalline structures. Here, the ratio of each component was optimized to control the rate of hydrolysis of Ti isopropoxide and prevent the unnecessary wet-etch of ZnO nanorods during the spin coating process, resulting in well-defined and vertically aligned TiO 2 -covered ZnO nanorod arrays [28,[40][41].…”