Nanodots and nanorings have a number of potential applications, particularly in nanodevices such as light-emitting diodes and transistors. The realization of such devices necessitates the development of methods for producing large quantities of these nanostructures with well-defined thickness and size. Now, Guowen Meng and colleagues at the Chinese Academy of Sciences1 describe a method for synthesizing nanodots and nanorings based on simple sputtering and electrodeposition techniques. The thickness of their structures can be tuned, and the approach can be used to create rings and dots from a wide variety of materials.

Fig. 1: Sequential sputtering and electrodeposition of nanodots and nanorings using a porous AAO template.

In their approach, Meng and his colleagues used an anodic aluminum oxide (AAO) film with highly ordered, straight channels as a template for the fabrication of nanodots and nanorings (Fig. 1). They coated one side of the porous template with a gold layer by sputtering — a standard industrial technique by which atoms of the target material are ejected by excitation or bombardment to accumulate on the template surface. The extent of sputtering defined whether dots or rings were subsequently obtained. Nanodots resulted when the sputtering was continued until the pores of the template had become completely closed over, whereas rings were produced when sputtering was halted just before the pores had been closed, leaving a hole in the center.

In the second step, the researchers electrodeposited another material in the pores of the AAO using the sputtered gold layer as the electrode. They produced bismuth, nickel, copper, cadmium and cadmium-telluride structures — in fact the researcher stress that the method can be used with any material that can be electrodeposited. As the electrodeposited material nucleates and grows on the sputtered gold film at the bottom of the pores, dots or rings are created depending on the coverage of the gold film.

The thickness of the dots or rings could be tailored simply by varying the duration of electrodeposition, and the use of AAO templates with different pore sizes allows for structures with various diameters.

“We have developed generic procedures for synthesizing nanodots and nanorings with tunable geometrical sizes,” says Meng. “Our approach has the advantages of easy fabrication, low cost and potential for large-scale production.”

In addition, Meng explains that “heterostructured or layered nanodots and nanorings consisting of different materials with distinctive properties can be built via nanochannel-confined sequential sputtering and electrodeposition.”

Future plans include studying the properties of single-material and hybrid structures for potential applications such as high-density memory, superconducting devices and ultrasensitive biosensors.