Azusa Hattori and colleagues from Osaka University and Osaka Dental University in Japan have developed a technique for fabricating luminescent nanoscale boxes (Appl. Phys. Express 5, 125203; 2012). Their approach combines inclined pulsed laser deposition with a three-dimensional template prepared by nanoimprint lithography. The wall thickness of the boxes can be controlled over the range of 20–100 nm by varying the laser alignment. Additionally, the researchers hope that the boxes, with their luminescence peak at around 380 nm, may prove useful candidates for nanoscale device applications such as a luminescent light sources.

First, the researchers used reactive ion etching on a silicon substrate to obtain a pattern of cubic resist structures. Then they deposited ZnO onto the resist template pattern by inclined pulsed laser deposition using an ArF excimer laser (wavelength of 193 nm) with a ZnO ceramic target. Rotating the substrate in 90° steps ensured even ZnO deposition across the different surfaces of the cube. The researchers then used ion milling to etch the ZnO top surface of the cubes and remove unwanted ZnO from the silicon substrate. Finally, they employed acetone dipping to remove the remaining resist material inside the cubes, thus forming the boxes.

Credit: JSAP

Hattori explained to Nature Photonics that there is a balance between the size of the nanostructures and their shape and position in terms of functional nanodevice fabrication.

“Many nanofabrication approaches have been proposed previously but they are often applicable only to limited materials and have poor controllability,” Hattori told Nature Photonics. “Our three-dimensional nanotemplate pulsed laser deposition technique enables the construction of extremely small high-quality nanostructures of any type of material (metal, insulator or semiconductor) with well-defined shapes and locations. This approach allows for the production of extremely small ZnO nanostructures at arbitrary positions while controlling their size with nanometre resolution.”

In the future, the researchers would like to fabricate large arrays of structures of various shapes, including nanowires, nanopipes, triangular and polygonal nanoboxes, and core–shell nanostructures, for use in applications such as magnetically tunable photonic crystals, metamaterials, biosensors and light sources with angular momentum. Hattori explained that they have fabricated a ferromagnetic (Fe,Zn)3O4 semiconductor and a strongly correlated (La,Pr,Ca)MnO3 nanobox/nanowire structure, which are good candidates for applications in magnetically tunable photonic crystals.