Energy Focus
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Energy Focus Study on energy transfer in CdSe/CdS nanocrystals uncovers role of particle morphology
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emiconductor heterostructures that have large absorption cross sections, high stability, and quantum yields as well as size-tunable electronic structures are good candidates for light-harvesting and energy conversion applications. Nanoscale CdSe/CdS heterostructures have been reported to exhibit either Type I behavior, in which a photogenerated electron–hole pair remains in one of the materials, or Type II behavior in which the electron and hole separate between the materials. This distinction in carrier migration behavior determines for which applications a structure may be used, light emission (Type I) versus photovoltaics (Type II) for example. A detailed understanding of the origin of the electronic structure of such heterojunctions is not only crucial for engineering particles
generated by the sulfonic acid groups. The H2 uptake and surface areas were measured for TEG and functionalized TEG with a custombuilt, high-precision system at NREL. The H2 uptake (measured as a weight-percent per 500 m2/g at 77 K and 2 bar) for the functionalized TEG samples were higher Functionalization and cross-linking of thermally exfoliated graphene than the H2 uptake (TEG) sheets were performed in chlorosulfonic acid and in oleum. The degree of functionalization in chlorosulfonic acid is higher for TEG by 60%, than in oleum. Reproduced with permission from Chem. Mater. 40%, 40%, and 10% 23 (4)(2011) DOI: 10.1021/cm1025188; p. 923. © 2011 American Chemical Society. for 1a, 1b, 2a, and 2b, respectively (see Scheme). The redemonstrates a possible route to further searchers said that they expect the H2 uptake by the functionalized TEGs to be increase the hydrogen storage capacity substantially higher at higher pressures, of graphene materials.” and that the “hydrogen uptake enhanceSteven Trohalaki ment of TEG by organic cross-linking
for the desired application, but can also lead to the ability to fine-tune the material for optimal performance. N.J. Borys and M.J. Walter from the University of Utah, J. Huang and D.V. Talapin from the University of Chicago, and J.M. Lupton from the University of Utah and the Universität Regensburg, Germany, report on the morphological effects of CdSe/ CdS nanocrystals on interfacial energy transfer properties as published in the December 3, 2010 issue of Science (DOI: 10.1126/science.1198070; p. 1371). The researchers used single-particle light-harvesting action spectroscopy on a range of CdSe/CdS heterostructures to probe the electronic structure of the heterojunctions. Specifically they measured photoluminescence excitation (PLE) of absorbing CdS through emission from CdSe. The single-particle approach enables the detection of properties that might be obscured in ensemble measurements. Typically nanoscale CdS exhibits a peak in its PLE spectrum due to the quantum-confined exiton state.
Intriguingly, results from single-particle spectroscopy showed this peak only occurred in some fraction of the
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