Apr 11, 2003
Nanoflowers blossom in place of nanotubes
Scientists at the National Institute for Materials Science in Japan have made nanoflowers of molybdenum sulphide (MoS2). The flowers contained tens to hundreds of petals several nanometres thick and were excellent field emitters.
"Preparing MoS2 nanoflowers was not our original aim," researcher Yubao Li told nanotechweb.org. "We tried to develop a simple technique for the growth of aligned MoS2 nanotubes. To our surprise, we found elegant black nanoflowers formed."
The scientists made the nanoflowers while heating an MoO2 thin film on a 10 mm square piece of molybdenum foil in an atmosphere of sulphur vapour. The nanoflowers, which were up to 2 µm across, grew over the foil at a density of 1.5-2.0 x 105/mm2. Each hexagonal petal was 100-300 nm wide and several nanometres thick. Near the edges of the flower the number of layers of petals decreased, giving very thin edges - typically less than 3 nm thick.
To produce a current of 10 µA/cm2, the nanoflowers required a "turn-on" field of 4.5-5.5 V/µm, while the threshold field needed to give a current of 10 mA/cm2 was 7.6-8.6 V/µm. This threshold field is close to that for open-ended carbon nanotubes (~ 5 V/µm) and indicates that the nanoflowers are excellent field emitters.
"Our preliminary results show the nanoflowers would have a promising application as field emitters thanks to their thin open edges," added Li. "In addition, we hope they will have uses in future nanoelectronic devices."
Now the team is trying to control the density and dimensions of the nanoflowers, and looking for other interesting applications. The researchers published their work in Applied Physics Letters.
About the author
Liz Kalaugher is editor of nanotechweb.org.