David Kirkpatrick

July 12, 2010

Latest advance in nanoscience research

News like this is important because a lot of the science of nanotechnology is so new it’s essentially a high-wire act without a net. Working to set some baselines in nanoscience help to improve the entire field.

The release:

University of Toronto chemists make breakthrough in nanoscience research

TORONTO, ON – A team of scientists led by Eugenia Kumacheva of the Department of Chemistry at the University of Toronto has discovered a way to predict the organization of nanoparticles in larger forms by treating them much the same as ensembles of molecules formed from standard chemical reactions.

“Currently, no model exists describing the organization of nanoparticles,” says Kumacheva. “Our work paves the way for the prediction of the properties of nanoparticle ensembles and for the development of new design rules for such structures.”

The focus of nanoscience is gradually shifting from the synthesis of individual nanoparticles to their organization in larger structures. In order to use nanoparticle ensembles in functional devices such as memory storage devices or optical waveguides, it is important to achieve control of their structure.

According to the researchers’ observations, the self-organization of nanoparticles is an efficient strategy for producing nanostructures with complex, hierarchical architectures. “The past decade has witnessed great progress in nanoscience – particularly nanoparticle self-assembly – yet the quantitative prediction of the architecture of nanoparticle ensembles and of the kinetics of their formation remains a challenge,” she continues. “We report on the remarkable similarity between the self-assembly of metal nanoparticles and chemical reactions leading to the formation of polymer molecules. The nanoparticles act as multifunctional single units, which form reversible, noncovalent bonds at specific bond angles and organize themselves into a highly ordered polymer.”

“We developed a new approach that enables a quantitative prediction of the architecture of linear, branched, and cyclic self-assembled nanostructures, their aggregation numbers and size distribution, and the formation of structural isomers.”

Kumacheva was joined in the research by postdoctoral fellows Kun Liu, Nana Zhao and Wei Li, and former doctoral student Zhihong Nie, along with Professor Michael Rubinstein of the University of North Carolina. As polymer chemists, the team took an unconventional look at nanoparticle organization.

“We treated them as molecules, not particles, which in a process resembling a polymerization reaction, organize themselves into polymer-like assemblies,” says Kumacheva. “Using this analogy, we used the theory of polymerization and predicted the architecture of the so-called ‘molecules’ and also found other, unexpected features that can find interesting applications.”

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The findings were published in a report titled “Step-Growth Polymerization of Inorganic Nanoparticles” in the July 9 issue of Science. The research was funded with support from an NSERC Discovery Grant from the Natural Sciences and Engineering Research Council of Canada and Canada Research Chair funding.

January 16, 2009

The latest in organic solar cells

Another subject I haven’t had the opportunity to cover in a while. I really get the impression that basic research into advanced solar cell technology has passed a critical point where it’s when, and not how — and more importantly, the when part is now sooner than later.

The release:

U of T chemistry discovery brings organic solar cells a step closer

Inexpensive solar cells, vastly improved medical imaging techniques and lighter and more flexible television screens are among the potential applications envisioned for organic electronics.

Recent experiments conducted by Greg Scholes and Elisabetta Collini of University of Toronto’s Department of Chemistry may bring these within closer reach thanks to new insights into the way molecules absorb and move energy. Their findings will be published in the prestigious international journal Science on January 16.

The U of T team — whose work is devoted to investigating how light initiates physical processes at the molecular level and how humans might take better advantage of that fact — looked specifically at conjugated polymers which are believed to be one of the most promising candidates for building efficient organic solar cells.

Conjugated polymers are very long organic molecules that possess properties like those of semiconductors and so can be used to make transistors and LEDs. When these conductive polymers absorb light, the energy moves along and among the polymer chains before it is converted to electrical charges.

“One of the biggest obstacles to organic solar cells is that it is difficult to control what happens after light is absorbed: whether the desired property is transmitting energy, storing information or emitting light,” explains Collini. “Our experiment suggests it is possible to achieve control using quantum effects, even under relatively normal conditions.”

“We found that the ultrafast movement of energy through and between molecules happens by a quantum-mechanical mechanism rather than through random hopping, even at room temperature,” explains Scholes. “This is extraordinary and will greatly influence future work in the field because everyone thought that these kinds of quantum effects could only operate in complex systems at very low temperatures,” he says.

Scholes and Collini’s discovery opens the way to designing organic solar cells or sensors that capture light and transfer its energy much more effectively. It also has significant implications for quantum computing because it suggests that quantum information may survive significantly longer than previously believed.

In their experiment, the scientists used ultrashort laser pulses to put the conjugated polymer into a quantum-mechanical state, whereby it is simultaneously in the ground (normal) state and a state where light has been absorbed. This is called a superposition state or quantum coherence. Then they used a sophisticated method involving more ultrashort laser pulses to observe whether this quantum state can migrate along or between polymer chains. “It turns out that it only moves along polymer chains,” says Scholes. “The chemical framework that makes up the chain is a crucial ingredient for enabling quantum coherent energy transfer. In the absence of the chemical framework, energy is funneled by chance, rather than design.”

This means that a chemical property – structure — can be used to steer the ultrafast migration of energy using quantum coherence. The unique properties of conjugated polymers continue to surprise us,” he says.

 

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Greg Scholes and Elisabetta Collini are with the Department of Chemistry, the Institute for Optical Sciences and the Centre for Quantum Information and Quantum Control at the University of Toronto. The research was funded by the Natural Sciences and Engineering Research Council of Canada.