Metal nanoparticles are things of particular interest because of their ability to maintain surface plasmon resonances. This is simply the resonating of the conduction band electrons when they are driven by electromagnetic radiation. Of course just because something is small it doesn’t have to be spherical. Nanorods are equally valid constructions that can be used to control the resonance simply by changing the ratio of height to diameter of the cylinder. There are multiple ways of producing nanorods with the most common method being colloidal synthesis, where the solutions are heated to high temperatures, the precursor material breaks down and then nucleates into the required nanorods. The rods produced this way are suspended in the solution and so it is challenging to get them to all align once they are produced.
Alignment is not required for all nanorod uses but it is required for some and so another production method is often applied when it is necessary. It is possible to grow and elongate nanoparticles suspended in a matrix by irradiating them with fast moving heavy ions. The maximum size is more limited in this method and the same control over the length to diameter ratio and volume cannot be achieved. However there is absolutely no deviation in the direction the rods point as the nanoparticles may only grow parallel to the incoming radiation.
Work has been done showing this process working for cobalt, gold, platinum, silver, zinc and nickel nanoparticles. Even if it is known to be effective the physics behind the elongation of spheres into rods is not really understood. In order to understand the process more, researchers have aimed to gather information about the deformation during the midway points between sphere and rod. Silver (Ag) nanoparticles were used in a supporting matrix which was then bombarded with 40 MeV bromine (Br) ions. Both transmission electron microscopy and optical absorption spectroscopy were used to analyse the nanoparticles during their transformation. Four well defined evolution regions were found along with the elongation kinetics of the particles. Hopefully the experimental data will go on to assist in a theoretical model being created to describe this process.