Nov 20, 2008
In brief: research round-up
Thin film grows into lens array
Depositing silicon dioxide (SiO2) over a square-patterned substrate could turn out to be an attractive route to making arrays of micro and nanosized lenses. "There's no need for substrate etching and [the process] results in a high fill factor," commented the researchers in their paper. Rather than conforming to the shape of the individual squares, the deposited SiO2 layer adopts an almost spherical profile that is ideal for optical applications. The scientists from the University of Illinois at Chicago, US, used e-beam lithography to pattern their sample, but point out that nanoimprint techniques could also be used to prepare the substrate.
Device maker formulates copper nanoink
Engineers at Samsung, Korea, have synthesized copper nanoparticles for use in inkjet-printed electronics. According to the results reported in Nanotechnology, the formulation suits low-temperature sintering, which is significant as it opens the door to the use of inexpensive plastic substrates. Inkjet printing is a versatile approach to patterning electronic circuits with additional benefits such as the ability to perform corrective overprinting. Silver inks have been shown to be effective, but are relatively expensive. Copper is a cheaper alternative, but has proved much harder to formulate for inkjet printing applications.
Cobalt nanoparticles damage cancer cells
Graphitic carbon-coated ferromagnetic cobalt nanoparticles are a promising candidate for the thermal ablation of tumours in vivo, according to the results of a recent study published in Nanotechnology. The cobalt-rich particles measure around 7 nm in diameter and are covered with 2–4 layers of grahitic carbon, which provides a protective barrier between the metallic core and the liquid biological environment.
When excited by low radio frequency radiation, the structures heat up and induce localized damage in the surrounding cells. In tests, the team found that 75.2–90.1% of the cells were destroyed when magnetic cobalt nanoparticles were used as the thermal agent compared with only 3.1–6.6% when the experiment was repeated with carbon nanotubes.
Lithography prepares CNT for electrical test
Making reliable electrical connections to nanowires and nanotubes can be problematic, but researchers based at the National University of Singapore think that they have found a solution. The scientists have devised a self-aligning technique that places a top layer of metal on electrodes at either end of the nanostructure. Nanowires are guided into position using dielectrophoresis and then the sample is flipped over and exposed from the substrate side using the same light source that was used earlier for the front-side lithography of the primary electrodes. For full details of the self-masking process, see Nanotechnology 19 455305.
About the author
James Tyrrell is editor of nanotechweb.org.