Nov 27, 2013
Patterning gold nanorods on substrates: non-agglomerated deposition and alignment
Gold nanoparticles are usually synthesized in solution, but for many applications they need to be deposited on a substrate. This is usually done by drop casting, but the liquid evaporation processes involved here bring capillary forces into play, leading to agglomeration of the nanoparticles. Moreover, anisotropic nanoparticles randomly orient during such a procedure – something that greatly affects their final optical properties. Researchers at Leiden University, The Netherlands, COMSATS Institute of Information Technology in Pakistan and the University of Twente, also in The Netherlands, have now overcome these problems by using hydrophilic-hydrophobic contrast stripe patterned substrates to selectively pattern gold nanorods on substrates with controlled orientation and interparticle spacing.
The technique involves placing a droplet of a nanorod suspension on the patterned substrate for a short while and then removing it. Thanks to the fact that water recedes much more slowly from the hydrophilic strip as compared with the hydrophobic stripe, the act of removing the droplet leaves a stripe of liquid film in the hydrophilic region. The liquid film evaporates very fast because of the large surface area of the liquid. This prevents the nanorods from agglomerating because they do not have enough time to collide and come together under the influence of capillary forces that are only at play for a brief period.
The researchers further showed that when longer-length nanorods were used, they aligned themselves along the stripe length and were orientated over long distances. They found that they could manage the assembly mode and degree of alignment of the nanorods by controlling the concentration of the rods in solution, and also by varying the ratio of a nanorod’s length and hydrophilic stripe width.
We believe that being able to control interparticle distance and orientation in this way will be very useful for future optical applications of gold nanorods and the method might even be extended to other nanoparticle materials, says the team.
More information about the research can be found in the journal Nanotechnology (in press).
About the author
Dr Waqqar Ahmed is an assistant professor at COMSATS Institute of Information Technology in Islamabad, Pakistan. He was a postdoctoral researcher in the Atomic and Molecular Conductors (AMC) group at Leiden University, The Netherlands. Prof. Jan van Ruitenbeek is the head of the AMC group at Leiden and Christian Glass is a PhD student in the same group. Dr E Stefan Kooij is an associate professor at University of Twente, The Netherlands.