Innovative Technique for Building Multifunctional Nanoscale Structures

The naturally occurring nanoscale geometry of these new materials is really exciting. Because a thin layer of aluminum oxide separates the two materials, we can independently tune their properties to suit our needs in future applications.

Researchers at the Rice University have used individual nanoscale nuggets of aluminum, copper, gold, silver and similar metals—with the ability to tap energy of light and use it for various applications—and have found an innovative technique for developing multifunctional nanoscale structures.

Apart from including an aluminum core, the novel structures are even dotted with smaller metallic islands. The materials have the ability to withstand localized surface plasmon resonances, that is, collective electron oscillations activated inside the nanostructure upon irradiating the particle by light.

Such nanoscale oscillations of electrons have the ability to activate chemical reactions and even stimulate reaction-promoting catalysts.

The method formulated in the labs of Emilie Ringe and Naomi Halas, Rice materials scientists, uses aluminum nanocrystals as a core for size-tunable transition metal islands that activate localized surface plasmon resonances. An earlier work performed by the teams of Halas and Ringe has shown that aluminum is known to be an effective plasmonic material, and the addition of smaller catalytic particles from three periodic table columns improves the ability of the structure to stimulate chemical reactions activated by the energy light.

According to the Scientists, the method paves the way for customizable surface chemistry as well as reactivity in a single material. It can be handy in the processes of surface-enhanced spectroscopy, photocatalysis and quantum plasmonics (i.e. the investigation of light’s quantum properties and the manner in which they interact with nanoparticles).

The study had been reported in the ACS Nano journal published by the American Chemical Society.

The Scientists stated that the general polyol method developed by them can be applied to blend a number of materials by using an uncomplicated and controllable procedure.

Dayne Swearer—Lead Author of the study and a Graduate Student at Rice—and his collaborators adopted a two-step synthetic technique, the first step of which is to reduce an aluminum precursor to synthesize purified aluminum particles with a width of 50-150 nm. Next, the purified aluminum particles are suspended in ethylene glycol, a metal salt precursor is added, and the solution is boiled to reduce the salts which ultimately nucleate and grow into nano-islands that adorned the surface of the original aluminum nanocrystals.

By means of an electron microscope, the Scientists discovered that a native aluminum oxide layer with a width of 2-4 nm divided the aluminum nanocrystal from the catalytic nano-islands. Moreover, the team worked in cooperation with Cambridge University Material Scientists Rowan Leary and Paul Midgley to adopt electron tomography to determine the location and size of over 500 individual ruthenium nano-islands formed on a single aluminum nanocrystal.

The naturally occurring nanoscale geometry of these new materials is really exciting. Because a thin layer of aluminum oxide separates the two materials, we can independently tune their properties to suit our needs in future applications.