16 November 2010
A technique known as sequential infiltration synthesis (SIS) that creates molecular “stencils” has been developed by researchers at the US Department of Energy’s Argonne National Laboratory and may pave the way to new materials that could potentially find their way into future generations of solar cells.
For the technique, a film composed of large molecules called block copolymers acts as a template that can be used to create of a highly-tunable patterned material. It is an extension of atomic layer deposition (ALD), a popular technique for materials synthesis that is routinely used by Argonne scientists. Instead of just layering two-dimensional films of different nanomaterials on top of one another, however, SIS allows scientists to construct materials with much more complex geometries.
“This new technique allows us to create materials that just weren’t possible with ALD or block copolymers alone,” said Seth Darling, an Argonne nanoscientist with the Center for Nanoscale Materials and Energy Systems Division. “Having the ability to control the geometry of the material we’re making as well as its chemical composition opens the door to a whole universe of new materials.”
The technique, which Darling along with Argonne chemist Jeff Elam helped develop, relies on the unique chemistry of block copolymers. Each block copolymer has two chemically distinct subunits. One subunit might have an affinity for water while the other might repel water. In such a case, like would seek out like, creating a heterogeneous matrix of interspersed homogenous regions.
This film of block copolymers shows the material's characteristic tendency to separate into distinct regions. Courtesy of Argonne National Laboratory.
Depending on the initial substrate, the block copolymers, and the processing that materials scientists use, regions can form that have many different shapes, from spherical to cylindrical to planar. While there are many types of block copolymers, typically they cannot serve as many purposes as inorganic materials. The challenge, according to Darling, is to bring the self-assembly of block copolymers together with the functionality of inorganic materials.
The physical and chemical properties of a material generated using SIS depend on how block copolymer chemistry and morphology interact with the chemistry of ALD techniques. “We can tailor our materials synthesis efforts in a much more precise way than we ever could before,” Darling said.
Darling and Elam have spent most of their careers at Argonne focused on the development of new types of materials, including the development of solar cells that combine organic and inorganic components. They believe that the types of materials that SIS can generate will drive fundamental solar energy technologies to greater efficiencies and lower cost.
“Our solar energy future does not have a one-size-fits-all solution,” Elam said. “We need to investigate the problem from many different angles with many different materials, and SIS will give researchers like us many new routes of attack.”
The Center for Nanoscale Materials is supported by the US Department of Energy's Office of Basic Energy Sciences (BES). This work was supported in part by the Argonne-Northwestern Solar Energy Research Center, an Energy Frontier Research Center also supported by BES.
Written by Nancy Lamontagne, Contributing Editor - US