March 27, 2009

Berkeley Lab at the ACS in Salt Lake City

Contact: Lynn Yarris

Berkeley Lab Interim Director Paul Alivisatos led off the symposium on New Developments in Energy Conversion and Light-Harvesting, with a talk entitled: “Multicomponent nanocrystals for solar photovoltaics and photocatalysts.”

Paul Alivisatos.

In this talk he described how the ability to control the composition and spatial arrangements of interconnected nanocrystals has substantially improved in recent years.

“It is now possible to prepare multi-component nanoparticles with designed optical and electronic properties, and with defined topologies,” he said.

Alivisatos focused on two specific designs, one for a nanoparticle-based photovoltaic system, and one for a photocatalyst. The photovoltaic system consisted of a cadmium sulfide/copper sulfide segmented nanorod. The photocatalyst consisted of a cadmium sulfide tetrapod with particles of platinum deposited on the ends. In both cases, he said, the nanocrystals performed better than would have been expected based on conventional scientific wisdom which holds that granularity as a result of using nanocrystals in thin film solar cells leads to the trapping of electrical charges, which in turn degrades the film’s performance.

Alivisatos said that a review of the literature shows the research into potential photovoltaic materials that began in the 1960s collapsed into a very narrow focus in the aftermath of the 1970s oil crisis because people were looking for a quick fix to the energy problem. This time, he said, “Let’s be more patient and not rush to judgment until we have a better understanding of these materials.”

Berkeley Lab chemist and acclaimed nanoscientist Peidong Yang followed the Alivisatos talk with a discussion on semiconductor nanowires for solar energy harvesting.

Peidong Yang.

Semiconductor nanowires represent an important class of nanostructure building block for photovoltaics as well as for direct solar-to-fuel applications because of their high surface area, tunable bandgap and efficient charge transport and collection, Yang said. His lab has been testing semiconductor nanowires as both a means of harvesting solar energy in a solar cell and a means of  splitting water molecules - converting sunlight into hydrogen through water splitting is one of the most promising clean, sustainable and renewable alternatives to fossil fuels and is now considered to be the new Holy Grail of chemistry. The successes of the Yang group with nanowires fashioned from alloys, such as indium gallium nitride, bolster Alivisatos’ call for patience and suggest that such patience will be rewarded.

James De Yoreo of The Molecular Foundry, a national DOE nanoscience center located at Berkeley Lab, spoke at the symposium on Chemical Methods of Nanofabrication. His talk, titled “Using biomimetics as nanostructure templates,” described the use of proteins as scaffolds upon which the fabrication of inorganic nanostructures can be templated.

“At the Molecular Foundry efforts are underway to mimic nature’s strategy by creating nanometer-scale chemical templates, which direct the organization of engineered macromolecules and complexes, such as RNA, proteins and viruses, into micron-scale patterns,” De Yoreo said.

James De Yoreo.

De Yoreo illustrated his talk with videos embedded in  power points that often resembled wind-blown grains of sand sweeping across a desert surface but were actually molecular-scale resolution images showing inorganic crystal growth across a peptide surface. De Yoreo concluded his talk as he began it by reminding his audience that The Molecular Foundry is a national user facility and its unique capabilities are available to all qualified researchers.

In the blink of an eye, more attoseconds have expired than the age of Earth measured in – minutes. A lot more. To be  precise, an attosecond is one billionth of a billionth of a second. Hard as that may be to wrap your mind around, the attosecond time-scale is where you’ll find the electron action that is the starting point of all of chemistry. Not surprisingly, chemists are most eager to explore it. Berkeley Lab chemist and director of its Chemical Sciences Division Dan Neumark described a collaborative effort with Berkeley Lab’s Steve Leone to develop an attosecond beamline at Berkeley Lab’s Advanced Light Source.

“Our goal is to apply the new capabilities of this beamline  to the study of attosecond dynamics in molecules and clusters, thus building on the atomic experiments done in other laboratories,” Neumark said.

After describing how to achieve attosecond pulses of light and detailing some successful experiments with metal nanoparticles and small molecular systems, Neumark left his audience with this promise: “More experiments in the attosecond time-scale are on the way!”