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Manninen M.,Nanoscience Center | Viefers S.,University of Oslo | Reimann S.M.,Lund University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2012

The purpose of this overview paper, which can be viewed as a supplement to our previous review on quantum rings [S. Viefers et al., Physica E 21 (2004), 1-35], is to highlight the differences of boson and fermion systems in one-dimensional (1D) and quasi-one-dimensional (Q1D) quantum rings. In particular this involves comparing their many-body spectra and other properties, in various regimes and models, including spinless and spinful particles, finite versus infinite interaction, and continuum versus lattice models. Our aim is to present the topic in a comprehensive way, focusing on small systems where the many-body problem can be solved exactly. Mapping out the similarities and differences between the bosonic and fermionic cases is of renewed interest due to the experimental developments in recent years, allowing for more controlled fabrication of both fermionic and bosonic quantum rings. © 2012 Elsevier B.V. Source


Virtanen P.,Aalto University | Bergeret F.S.,Donostia International Physics Center | Bergeret F.S.,Carl von Ossietzky University | Heikkila T.T.,Aalto University | Heikkila T.T.,Nanoscience Center
Physical Review Letters | Year: 2014

We show that a huge thermoelectric effect can be observed by contacting a superconductor whose density of states is spin split by a Zeeman field with a ferromagnet with a nonzero polarization. The resulting thermopower exceeds kB/e by a large factor, and the thermoelectric figure of merit ZT can far exceed unity, leading to heat engine efficiencies close to the Carnot limit. We also show that spin-polarized currents can be generated in the superconductor by applying a temperature bias. © 2014 American Physical Society. Source


Zhou Y.,University of Cambridge | Robinson A.,University of Cambridge | Steiner U.,Nanoscience Center | Federle W.,University of Cambridge
Journal of the Royal Society Interface | Year: 2014

Insect climbing footpads are able to adhere to rough surfaces, but the details of this capability are still unclear. To overcome experimental limitations of randomly rough, opaque surfaces, we fabricated transparent test substrates containing square arrays of 1.4 μm diameter pillars, with variable height (0.5 and 1.4 μm) and spacing (from 3 to 22 μm). Smooth pads of cockroaches (Nauphoeta cinerea) made partial contact (limited to the tops of the structures) for the two densest arrays of tall pillars, but full contact (touching the substrate in between pillars) for larger spacings. The transition from partial to full contact was accompanied by a sharp increase in shear forces. Tests on hairy pads of dock beetles (Gastrophysa viridula) showed that setae adhered between pillars for larger spacings, but pads were equally unable to make full contact on the densest arrays. The beetles' shear forces similarly decreased for denser arrays, but also for short pillars and with a more gradual transition. These observations can be explained by simple contact models derived for soft uniform materials (smooth pads) or thin flat plates (hairy-pad spatulae). Our results show that microstructured substrates are powerful tools to reveal adaptations of natural adhesives for rough surfaces. © 2014 The Authors. Published by the Royal Society. Source


News Article
Site: http://phys.org/chemistry-news/

NREL's scientists took a different approach to the PEC process, which uses solar energy to split water into hydrogen and oxygen. The process requires special semiconductors, the PEC materials and catalysts to split the water. Previous work used precious metals such as platinum, ruthenium and iridium as catalysts attached to the semiconductors. A large-scale commercial effort using those precious metals wouldn't be cost-effective, however. The use of cheaper molecular catalysts instead of precious metals has been proposed, but these have encountered issues with stability, and were found to have a lifespan shorter than the metal-based catalysts. Instead, the NREL researchers decided to examine molecular catalysts outside of the liquid solution they are normally studied in to see if they could attach the catalyst directly onto the surface of the semiconductor. They were able to put a layer of titanium dioxide (TiO2) on the surface of the semiconductor and bond the molecular catalyst to the TiO2. Their work showed molecular catalysts can be as highly active as the precious metal-based catalysts. Their research, "Water Reduction by a p-GaInP2 Photoelectrode Stabilized by an Amorphous TiO2 Coating and a Molecular Cobalt Catalyst," has been published in Nature Materials. Jing Gu and Yong Yan are lead authors of the paper. Contributors James Young, Nathan Neale and John Turner are all with NREL's Chemistry and Nanoscience Center. Contributor K. Xerxes Steirer is with NREL's Materials Science Center. Turner points out that although the molecular catalysts aren't as stable as the metal-based catalysts, PEC systems are shut down each evening as the sun sets. That leaves time to regenerate a molecular catalyst. "Hopefully you would not have to do that every day, but it does point to the fact that low stability but highly active catalysts could be viable candidates as a long-term solution to the scalability issue for PEC water splitting systems," Turner said. Explore further: New nanomaterials will boost renewable energy More information: Jing Gu et al. Water reduction by a p-GaInP2 photoelectrode stabilized by an amorphous TiO2 coating and a molecular cobalt catalyst, Nature Materials (2015). DOI: 10.1038/nmat4511


Abstract: A wide international collaboration involving researchers from four countries - China, Australia, Germany and Finland - have managed to synthesize and characterize two previously unknown, record-large silver nanoclusters of 136 and 374 silver atoms. These diamond-shaped nanoclusters (see Figure), consisting of a silver core of 2 to 3 nanometers and a protecting layer of silver atoms and organic thiol molecules, are the largest ones whose structure is now known to atomic precision. The research (1) was published in Nature Communications on 9 September 2016. The nanoclusters where synthesized in Xiamen University in China and characterized by X-ray crystallography and electron microscopy in China, Australia and Germany. Their electronic structure and optical properties were studied computationally in the Nanoscience Center (NSC) of the University of Jyväskylä in Finland. Gold nanoclusters that are stabilized by a thiol molecular layer have been known for decades, but only during the latest years silver clusters have attracted more interest in the research community. Silver is a desirable material for nanocluster synthesis since it is a cheaper metal than gold and its optical properties are better controllable for applications. However, synthesis recipes that would produce silver clusters that are stable for prolonged times are not so widely known as for gold. "These largest atomically precise silver nanoclusters known thus far serve as excellent model systems to understand how silver nanoparticles grow," says Professor Nanfeng Zheng whose research group prepared the clusters in Xiamen University in China. "The internal structure of the metal core is a combination of little crystallites of silver that are joined together to form a five-fold symmetric diamond-shape structure." "From a theoretical point of view these new clusters are very interesting," says Academy Professor Hannu Häkkinen from the NSC in Jyväskylä. "These clusters are already big enough that they have properties similar to silver metal, such as strong absorption of light leading to collective oscillations of the electron cloud known as plasmons, yet small enough that we can study their electronic structure in detail. Much to our surprise, the calculations showed that electrons in the organic molecular layer take part actively in the collective oscillation of the silver electrons. It seems possible to then activate these clusters by light in order to do chemistry at the ligand surface." ### The other NSC researchers involved in the work were Xi Chen and Lauri Lehtovaara. The computational work was done at the CSC - the Finnish IT Centre for Science. The work at the University of Jyväskylä was supported by the Academy of Finland. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

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