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Harvey T.B.,Center for Nano and Molecular Science and Technology | Harvey T.B.,Texas Materials Institute | Mori I.,University of Tokyo | Stolle C.J.,Center for Nano and Molecular Science and Technology | And 19 more authors.
ACS Applied Materials and Interfaces | Year: 2013

The power conversion efficiency of photovoltaic devices made with ink-deposited Cu(InxGa1-x)Se2 (CIGS) nanocrystal layers can be enhanced by sintering the nanocrystals with a high temperature selenization process. This process, however, can be challenging to control. Here, we report that ink deposition followed by annealing under inert gas and then selenization can provide better control over CIGS nanocrystal sintering and yield generally improved device efficiency. Annealing under argon at 525 C removes organic ligands and diffuses sodium from the underlying soda lime glass into the Mo back contact to improve the rate and quality of nanocrystal sintering during selenization at 500 C. Shorter selenization time alleviates excessive MoSe2 formation at the Mo back contact that leads to film delamination, which in turn enables multiple cycles of nanocrystal deposition and selenization to create thicker, more uniform absorber films. Devices with power conversion efficiency greater than 7% are fabricated using the multiple step nanocrystal deposition and sintering process. © 2013 American Chemical Society.


Mousavi S.H.,Center for Nano and Molecular Science and Technology | Kholmanov I.,University of Texas at Austin | Alici K.B.,Center for Nano and Molecular Science and Technology | Purtseladze D.,Center for Nano and Molecular Science and Technology | And 8 more authors.
Nano Letters | Year: 2013

Graphene is widely known for its anomalously strong broadband optical absorptivity of 2.3% that enables seeing its single-atom layer with the naked eye. However, in the mid-infrared part of the spectrum graphene represents a quintessential lossless zero-volume plasmonic material. We experimentally demonstrate that, when integrated with Fano-resonant plasmonic metasurfaces, single-layer graphene (SLG) can be used to tune their mid-infrared optical response. SLG's plasmonic response is shown to induce large blue shifts of the metasurface's resonance without reducing its spectral sharpness. This effect is explained by a generalized perturbation theory of SLG-metamaterial interaction that accounts for two unique properties of the SLG that set it apart from all other plasmonic materials: its anisotropic response and zero volume. These results pave the way to using gated SLG as a platform for dynamical spectral tuning of infrared metamaterials and metasurfaces. © 2013 American Chemical Society.


MacDonald A.H.,Stanford University | MacDonald A.H.,Center for Nano and Molecular Science and Technology | MacDonald A.H.,University of Texas at Austin | Tsoi M.,Stanford University | And 2 more authors.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

In this brief review, we explain the theoretical basis for the notion that spin-transfer torques (STTS) and giant-magnetoresistance effects can, in principle, occur in circuits containing only normal and antiferromagnetic (AFM) materials, and for the notion that antiferromagnets can play a role in STT phenomena in circuits containing both ferromagnetic and AFM elements. We review the experimental literature that provides partial evidence for these AFM spintronic effects but demonstrates that, like exchange-bias effects, they are sensitive to details of interface structure that are not always under experimental control. Finally, we speculate briefly on some strategies that might advance progress. © 2011 The Royal Society.


Pande S.,Center for Nano and Molecular Science and Technology | Pande S.,University of Texas at Austin | Weir M.G.,Center for Nano and Molecular Science and Technology | Weir M.G.,University of Texas at Austin | And 4 more authors.
New Journal of Chemistry | Year: 2011

In this report we present the synthesis and characterization of Pt and Pd dendrimer-encapsulated nanoparticles (DENs) using the method of galvanic exchange. Sixth-generation hydroxyl-terminated poly(amidoamine) dendrimers were used to prepare Cu DENs composed of 55 atoms. In the presence of either PtCl42- or PdCl42-, the less noble Cu DENs oxidize to Cu2+ leaving behind an equal-sized DEN of Pt or Pd, respectively. DENs prepared by direct reduction with BH4 -, which is the common synthetic route, and those prepared by galvanic exchange have the same composition, structure, and properties as judged by UV-vis spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and electrochemical methods. However, the galvanic exchange synthesis is much faster (3 h vs. 96 h), and the yield of reduced DENs is significantly higher (nearly 100% in the case of galvanic exchange). © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

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