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Viewing upcoming talks containing the keyword: 8
Cond Mat Seminars
Speaker: Behnam Tonekaboni Faghihnasiri (University of Queensland)
Heat engines are the heart of the thermodynamics. Different quantum heat engines have been proposed and built since 1980â€™s (For examples looking at [1, 2]). All of these engines use time-dependent, periodic Hamiltonian. Alternatively, we are interested in an autonomous quantum heat engine. Our proposed engine is a single-electron shuttle oscillating between two leads. This system was studied in  where it behaves as a mesoscopic electric motor driven by an external electrical bias. In contrast, our heat engine is a single-electron shuttle between two Fermi seas with the same chemical potentials but a temperature difference. Electrons can move from the high-temperature lead (source) to the low-temperature (drain) via the shuttle. The shuttle feels a force, when it carries an electron, due to the Johnson noise of the finite temperature lead. Since the average of the Johnson noise is zero; we need a rectifier to direct the force toward the drain. The rectification can be achieved by letting the shuttle oscillate in a half-harmonic potential.
Moreover, we propose a quantum ratchet battery which can be charged by absorbing the phonons from the engine. Then we define the power output of the engine as the rate of the absorption by the battery.
 Â R. Kosloff, The Journal of chemical physics 80, 1625 (1984).Â
 Â J. RoÃŸnagel, S. T. Dawkins, K. N. Tolazzi, O. Abah, E. Lutz, F. Schmidt-Kaler, and K. Singer, Science 352, 325 (2016).Â
 Â D. W. Utami, H.-S. Goan, C. Holmes, and G. Milburn, Physical Review B 74, 014303 (2006).
On: March 23, 2017 From: 12h00 To: 13h00View talk
Cond Mat Seminars
Speaker: Helena Knowles (Cambridge)
A system consisting of a bright spin coherently coupled to a dark spin cluster has been at the heart of many exciting proposals in recent years, from implementations of spin chains to environment-assisted schemes that enhance the performance of a single-spin magnetic field sensor1,2. Realised in a nanodiamond crystal such a cluster could transform the performance of a unique sensing device that enables temperature and magnetic field measurements inside living cells. Experimental progress on this front has been promising, albeit hindered by the limited ability to polarise, control and readout dark spins.â€¨
In this talk I will show how we use the nitrogen-vacancy centre in diamond (NV) to polarise and probe individual spins of a cluster formed of three nitrogen (N) electron spins surrounding the NV. We locate the N spins to within a few lattice sites and report the first observation of coherent spin exchange between NV and N electron spins3, essential for any exploitation of such multi-spin systems. Key to the success of these experiments is the use of a nanodiamond particle, which provides a contained spin ensemble, leading to reduced spin polarisation diffusion4.â€¨
I will also show our ability to address and coherently control nuclear spins close to the NV centre. The long coherence times provided by nuclear spins allow for enhanced sensitivity of such a hybrid system, which is of particular interest for NV centres in diamond nanocrystals as they typically have short coherence times (~Î¼s) compared with their bulk counterparts (~ms). We observe a coherence time enhancement of two orders of magnitude for the NV-nuclear spin coupled system in diamond nanocrystals and perform nuclear spin-assisted readout enhancing the NV readout signal by over two orders of magnitude.
 G. Goldstein et al. PRL 106 140502 (2011),  N. Yao et al. Nat. Commun. 3 800 (2012),  H. Knowles et al. PRL 117 100802 (2016),  H. Knowles et al. Nat. Mater. 13 21-25 (2014)
On: March 29, 2017 From: 12h00 To: 13h00View talk
Speaker: Nicola Armaroli (ISOF, Bologna)
The research of our group is focus ed on luminescence and photoinduced energy and electron transfer processes in organic molecules, metal complexes, supramolecular arrays and nanomaterials. In particular we investigate (i) light harvesting and charge separation in model solar energy conversion s ystems, (ii) luminescent materials for electroluminescent devices, (iii) photoredox catalysts for organic synthesis. A survey of our work in these areas will be made, with focus on multichromophoric systems for solar energy conversion, photoactive Ir(III) and Cu(I) complexes as luminescent and photoredox materials, hybrids made of Eu(III) -based luminophores and carbon nanonotubes, fully organic triplet emitters. Emphasis will be put on strategies to tune and optimize excited state properties for enhanced ph otochemical, photoluminescence and photoredox performance.
References 1. A. Gualandi, E. Matteucci, F. Monti, A. Baschieri, N. Armaroli, L. Sambri, P. G. Cozzi, Photoredox Radical Conjugate Addition of Dithiane -2-Carboxylate Promoted by an Iridium(III) P henyl -Tetrazole Complex: A Formal Radical Methylation of Michael Acceptors, Chem. Sci. 2017 , 8, DOI: . 2. T. Miletic, E. Pavoni, V. Trifiletti, A. Rizzo, A. Listorti, S. Colella, N. Armaroli, D. Bonifazi, Covalently Functionalized Swcnts as Tailored P -Type Dopants for Perovskite Solar Cells, ACS Appl. Mater. Inter. 2016 , 8, 27966 -27973. 3. N. Armaroli, V. Balz ani, Solar Electricity and Solar Fuels: Status and Perspectives in the Context of the Energy Transition, Chem. - Eur. J. 2016 , 22, 32 -57. 4. F. Monti, A. Baschieri, E. Matteucci, A. Mazzanti, L. Sambri, A. Barbieri, N. Armaroli, A Chelating Diisocyanide Liga nd for Cyclometalated Ir(III) Complexes with Strong and Tunable Luminescence, Faraday Discuss. 2015 , 185 , 233 -248. 5. A. Kremer, C. Aurisicchio, F. De Leo, B. Ventura, J. Wouters, N. Armaroli, A. Barbieri, D. Bonifazi, Walking Down the Chalcog enic Group of the Periodic Table: From Singlet to Triplet Organic Emitters, Chem. -Eur. J. 2015 , 21, 15377 -15387. 6. K. Yoosaf, J. Iehl, I. Nierengarten, M. Hmadeh, A. M. Albrecht -Gary, J. F. Nierengarten, N. Armaroli, A Supramolecular Photosynthetic Model Made of a Mul tiporphyrinic Array Constructed around a C 60 Core and a C 60-Imidazole Derivative, Chem. - Eur. J. 2014 , 20, 223 -231. 7. M. Mohankumar, F. Monti, M. Holler, F. Niess, B. Delavaux -Nicot, N. Armaroli, J. P. Sauvage, J. F. Nierengarten, Combining Topological and Steric Constraints for the Preparation of Heteroleptic Copper(I) Complexes, Chem. -Eur. J. 2014 , 20, 12083 - 12090. 8. J. Mohanraj, N. Armaroli, Luminophores and Carbon Nanotubes: An Odd Combination?, J. Phys. Chem. Lett. 2013 , 4, 767 -778. Download PDF
On: April 19, 2017 From: 15h30 To: 16h30View talk
Physics and Astronomy Colloquia
Speaker: Dr Silvia Vignolini (University of Cambridge)
Natureâ€™s most vivid colours rely on the ability to produce complex and hierarchical photonic structures with lattice constants on the order of the wavelength of visible radiation .Â A recurring strategy design that is found both in the animal and plant kingdoms for producing such effects is the helicoidal multilayers [2,3]. In such structures, a series of individual nano-fibers (made of natural polymers as cellulose and chitin) are arranged parallel to each other in stacked planes. When distance between such planes is comparable to the wavelength of light, a strong polarised, colour selective response can be obtained . These helicoidal multilayers are generally structured on the micro-scale and macroscopic scale giving rise to complex hierarchical structures.
Biomimetic with cellulose-based architectures enables us to fabricate novel photonic structures using low cost materials in ambient conditions [5-7]. Importantly, it also allows us to understand the biological processes at work during the growth of these structures in plants. In this talk the route for the fabrication of complex bio-mimetic cellulose-based photonic structures will be presented and the optical properties of artificial structures will be analyzed and compared with the natural ones. Kinoshita, S. et al. (2008). Physics of structural colors. Rep. Prog. Phys. 71(7), 076401.
 Vignolini, S. et al. (2012). Pointillist structural color in Pollia fruit PNAS 109, 15712-15716.
 Wilts, B. D, et al. (2014). Natural Helicoidal Structures: Morphology, Self-assembly and Optical Properties. Materials Today: Proceedings, 1, 177â€“185.
 de Vries, H. (1951). Rotatory power and other optical properties of certain liquid crystals. Acta Cryst., 4(3), 219â€“226.
 Dumanli, A. G., et al. (2014). Controlled, Bio-inspired Self-Assembly of Cellulose-Based Chiral Reflectors. Adv. Opt Mat., 2(7), 646â€“650.
 Parker R. et al. (2016). Hierarchical Self-Assembly of Cellulose Nanocrystals in a Confined Geometry ACS Nano, 2016, 10 (9), 8443â€“8449
 Kamita G. et al. (2016). Biocompatible and Sustainable Optical Strain Sensors for Large-Area Applications Adv. Opt. Mat. DOI: 10.1002/adom.201600451
On: April 21, 2017 From: 10h00 To: 11h00View talk
Cond Mat Seminars
Speaker: Lin Jiao (MPI Dresden)
In the past few years, the concept of topological insulators has attracted great research interest. Particularly, SmB6 has been proposed as a topological Kondo insulator, which possesses topologically protected nontrivial surface states inside the bulk hybridization gap. Experimentally, the observation of many basic properties is still controversial. In this talk, I will shortly introduce the controversial observations and its possible reasons. Then, I will present the results of our scanning tunneling microscopy and spectroscopy measurements, which enable us to perform local measurements on well identiï¬ed non-reconstructed (001) surfaces . Above ~7 K and up to 80 K, the electronic states in SmB6 are governed by the Kondo effect of the bulk . Down to 0.35 K, we observed several well-resolved states within the hybridization gap (Â±20 meV) of SmB6 for the first time . These states possess sharp peak-like features with a strong temperature dependence below 7 K, i.e. at a temperature similar to the one at which the well-known plateau in the resistance of SmB6 sets in. This provides evidence for an additional energy scale at the surface of SmB6, in addition to the bulk Kondo temperature scale, in line with a suppression of the Kondo effect at the materialâ€™s surface. At the last part, I will briefly introduce our recent work on magnetic and non-magnetic atoms doped SmB6, which provides further insight into the topological nature of the surface states. These high resolution data offer the opportunity to directly compare our spectroscopy with band structure calculations, and analyze their surface or bulk origin, which may help reconciling many contradicting assertions in this material.Reference: S. RÃ¶ÃŸler et al., Surface and electronic structure of SmB6 through Scanning Tunneling Microscopy, Phil. Mag. 96, 3262 (2016). S. RÃ¶ÃŸler et al., Hybridization gap and Fano resonance in SmB6, Proc. Natl. Acad. Sci. USA 111, 4798 (2014). L. Jiao et al., Additional energy scale in SmB6 at low temperature, Nat. Commun. 7, 13762 (2016)
On: May 16, 2017 From: 12h00 To: 13h00View talk
Speaker: Makoto Fujita (Tokyo)
Coordination Self -Assembly: From the Origins to the Latest Advances Makoto Fujita
Department of Applied Chemistry, The University of Tokyo firstname.lastname@example.org -tokyo.ac.jp
Molecular self -assembly based on coordination chemistry has made an explosive development in recent years. Over the last >25years, we have been showing that the simple combination of transition -metal’s square planer geometry (a 90 degree coordination angle) with pyridine -based bridging ligands gives rise to the quantitative self -as sembly of nano -sized, discrete organic frameworks. Representative examples include square molecules (1990), 1 linked -ring molecules (1994), 2 cages (1995), 3 capsules (1999), 4 and tubes (2004) 5 that are self -assembled from simple and small components. Origin ated from these earlier works, current interests in our group focus on i) molecular confinement effects in coordination cages, 6 ii) solution chemistry in crystalline porous complexes (as applied to “crystalline sponge method”), 7 and iii) and giant self -ass emblies (Figure 1), 8 as disclosed in this lecture.
Figure 1. The latest giant self - assembly from 144 small components. 8b The network topology is described as a “tetravalent Goldberg polyhedron” that has never been discussed to describe real 3D objects.
1. M. Fujita, J. Yazaki, and K. Ogura, J. Am. Chem. Soc. 1990 , 112 , 5645 -5647 2. M. Fujita, F. Ibukuro, H. Hagihara, K. Ogura, Nature 1994 , 367 , 720. 3. M. Fujita, D. Oguro, M. Miyazawa, H. Oka, K. Yamaguchi, K. Ogura, Nature 1995 , 378 , 469 -471 4. M. Fujita, N. Fujita, K. Ogura, and K. Yamaguchi Nature 1999 , 400 , 52 -55. 5. T. Yamaguchi, S. Tashiro, M. Tominaga, M. Kawano, T. Ozeki, and M. Fujita, J. Am. Chem. Soc. 2004 , 126 , 10818 - 10819. 6. (a) M. Yoshizawa, J. K. Klosterman, and M. Fujit a, Angew. Chem. Int . Ed. 2009 , 48 , 3418 -3438 (review). (b) M. Yoshizawa, M. Tamura, and M. Fujita, Science 2006 , 312 , 251 -254. 7. (a) Y. Inokuma, S. Yoshioka, J. Ariyoshi, T. Arai, Y. Hitora, K. Takada, S. Matsunaga, K. Rissanen, M. Fujita Nature 2013 , 495 , 461 -466. (b) M. Hoshino, A. Khutia, H. Xing, Y. Inokuma, M. Fujita, IUCrJ , 2016 , 3, 139 -151 . 8. (a) D. Fujita, Y. Ueda, S. Sato, H. Yokoyama, N. Mizuno, T. Kumasaka, M. Fujita, Chem 2016 , 1, 91 -101. (b) D. Fujita, Y. Ueda, S. Sato, N. Mizuno, T. Kumasaka, M. Fujita, Nature 2016, 540 , 563 –566 . Download PDF
On: May 19, 2017 From: 15h30 To: 16h30View talk