New method for making nanoparticles

An engineering researcher at the University of Arkansas and his colleagues at the University of Utah have discovered a new method of making nanoparticles and nanofilms that could be used in developing better electronic devices, biosensors and certain types of high-powered and highly specific microscopes used for scientific research.

The researchers’ nanoparticles, made of gold and deposited onto silicon substrates by a chemical process, are non-toxic and inexpensive to make and have good dimensions, densities and distribution when compared with other nanoparticles and conventional methods of producing nanoparticles.

The deposition has the further advantage of being able to rapidly coat fragile, three-dimensional and internal surfaces at the temperature and pressure of its surroundings without requiring conductive substrates or sophisticated equipment.

“Using successive thermal treatments, we characterised optical and structural features of an inexpensive, molecule-to-molecule, bottoms-up approach to create thermally stable, gold-nanoparticle ensembles on silica,” said Keith Roper, associate professor of chemical engineering at the University of Arkansas. “Images and analysis from scanning electron microscopy and atomic force microscopy revealed that particle densities are the highest reported to date. Our method also allows faster preparation than self-assembly or lithography and allows directed assembly of nanoparticle ensembles on 3D surfaces.”

The researchers’ approach improved on a method that involves depositing atoms from a solution onto a substrate with a tin-sensitised surface. The researchers used a novel continuous-deposition process and then heated these deposited atoms to transform “islands” of nanoparticle material into desired forms.

The resulting spherical nanoparticles had diameters between 5 and about 300 nm.

The microscopic images and spectroscopic data suggest that ultrathin films prepared by their new approach are smoother than conventional ‘sputtered’ or evaporated gold films and may exhibit better optical features, such as reduced surface-roughness scattering.

These features are desirable in devices such as photovoltaic cells in which narrow metal layers affect local electromagnetic fields. Smoother thin films also could improve the limits of detection, sensitivity and photocurrent in these devices.

The researchers’ recent studies in this area have been published in Langmuir and Journal of Physical Chemistry C, journals of the American Chemical Society.