Article
The rational design of inexpensive and durable oxygen reduction catalysts may lead to enhanced fuel cell performance. Here, the authors report a bio-inspired catalyst in which hybridization of iron 3d electrons with a carbon nanotube alters its electronic structure and improves catalytic performance.
Nature Communications doi: 10.1038/ncomms3076
Authors: Ruiguo Cao, Ranjit Thapa, Hyejung Kim, Xiaodong Xu, Min Gyu Kim, Qing Li, Noejung Park, Meilin Liu, Jaephil Cho
Magnetism in single-side hydrogenated (C$_2$H) and fluorinated (C$_2$F) graphene is analyzed in terms of the Heisenberg model with parameters determined from first principles. We predict a frustrated ground state for both systems, which means the instability of collinear spin structures and sheds light on the absence of a conventional magnetic ordering in defective graphene demonstrated in recent experiments. Moreover, our findings suggest a highly correlated magnetic behavior at low temperatures offering the possibility of a spin-liquid state.
Nature Chemistry 5, 577 (2013). doi:10.1038/nchem.1630
Authors: Joseph M. Zadrozny, Dianne J. Xiao, Mihail Atanasov, Gary J. Long, Fernande Grandjean, Frank Neese & Jeffrey R. Long
Mononuclear complexes of certain lanthanide ions are known to have large magnetization reversal barriers caused by strong spin–orbit coupling. Now, careful tuning of the ligand field of a transition metal complex has engendered a comparable spin-reversal barrier — and in turn magnetic blocking at 4.5 K.
Nature Chemistry 5, 556 (2013). doi:10.1038/nchem.1687
Author: Eckhard Bill
For more than a decade, single-molecule magnets have relied on multinuclear transition metal clusters and lanthanide compounds. Now, a mononuclear, two-coordinate iron(I) complex has shown that single transition metals can compete with the lanthanides when certain design principles from magnetochemistry are borne in mind.
Dr.jens.bredeSimmons: I really like their stuff.
Article
The spin of an electron bound to a single phosphorus atom in silicon is of interest for spin-based electronics such as quantum computing. Here, Büch et al . show these spin properties are retained even for clusters of a few phosphorus atoms, providing an additional means for quantum bit addressability.
Nature Communications doi: 10.1038/ncomms3017
Authors: H. Büch, S. Mahapatra, R. Rahman, A. Morello, M. Y. Simmons
In this work we study theoretically the coupling of single molecule magnets (SMMs) to a variety of quantum circuits, including microwave resonators with and without constrictions and flux qubits. The main results of this study is that it is possible to achieve strong and ultrastrong coupling regimes between SMM crystals and the superconducting circuit, with strong hints that such a coupling could also be reached for individual molecules close to constrictions. Building on the resulting coupling strengths and the typical coherence times of these molecules (of the order of microseconds), we conclude that SMMs can be used for coherent storage and manipulation of quantum information, either in the context of quantum computing or in quantum simulations. Throughout the work we also discuss in detail the family of molecules that are most suitable for such operations, based not only on the coupling strength, but also on the typical energy gaps and the simplicity with which they can be tuned and oriented. Finally, we also discuss practical advantages of SMMs, such as the possibility to fabricate the SMMs ensembles on the chip through the deposition of small droplets.
Using atomic resolved scanning tunneling microscopy, we present here the experimental evidence of a silicene sheet (graphene like structure) epitaxially grown on a close-packed silver surface (Ag(111)). This has been achieved via direct condensation of a silicon atomic flux onto the single-crystal substrate in ultra-high vacuum conditions. A highly ordered silicon structure, arranged within a honeycomb lattice is synthesized and presenting two silicon sub-lattices occupying positions at different heights (0.02 nm) indicating possible sp2-sp3 hybridizations.
Free electron like image potential states are observed in scanning tunneling spectroscopy on graphene quantum dots on Ir(111) acting as potential wells. The spectrum strongly depends on the size of the nanostructure as well as on the spatial position on top, indicating lateral confinement. Analysis of the substructure of the first state by spatial mapping of constant energy local density of states reveals characteristic patterns of confined states. The most pronounced state is not the ground state, but an excited state with a favorable combination of local density of states and parallel momentum transfer in the tunneling process. Chemical gating tunes the confining potential by changing the local workfunction. Our experimental determination of this workfunction allows to deduce the associated shift of the Dirac point.
“… There is no empirical proof that scientific systems with competitive funding have produced more knowledge, and especially more reliable knowledge than those that are not organized in this way …” Read more in the Editorial by Michael Hampe.
Author(s): Keigo Sato, Katsuyuki Shizu, Kazuaki Yoshimura, Atsushi Kawada, Hiroshi Miyazaki, and Chihaya Adachi
We demonstrate an organic molecule with an energy gap between its singlet and triplet excited states of almost zero (ΔEST∼0 eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and mea...
[Phys. Rev. Lett. 110, 247401] Published Mon Jun 10, 2013
Announcement: Nature papers enhanced
Nature 498, 7452 (2013). doi:10.1038/498006a
As the requirements for data presentation in research papers have grown, Nature’s space limitations have remained tight, so more and more essential displayed information has been relegated inappropriately to our Supplementary Information sections. Hard on the heels of our relaxation of constraints on our
Chemical mapping of a single molecule by plasmon-enhanced Raman scattering
Nature 498, 7452 (2013). doi:10.1038/nature12151
Authors: R. Zhang, Y. Zhang, Z. C. Dong, S. Jiang, C. Zhang, L. G. Chen, L. Zhang, Y. Liao, J. Aizpurua, Y. Luo, J. L. Yang & J. G. Hou
Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable ‘fingerprint’ for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3−15 nanometres, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.
Author(s): Weigang Wang (王魏刚), Ko Munakata, Michael Rozler, and Malcolm R. Beasley
Under mesoscopic conditions, the transport potential on a thin film carrying a current is theoretically expected to bear spatial variation due to quantum interference. Scanning tunneling potentiometry is the ideal tool to investigate such variation, by virtue of its high spatial resolution. We repor...
[Phys. Rev. Lett. 110, 236802] Published Tue Jun 04, 2013
Nature Nanotechnology 8, 381 (2013). doi:10.1038/nnano.2013.105
Author: Emanuel Lörtscher
Inexpensive, functional and atomically precise molecules could be the basis of future electronic devices, but integrating them into circuits will require the development of new ways to control the interface between molecules and electrodes.
Nature Nanotechnology 8, 385 (2013). doi:10.1038/nnano.2013.101
Leading researchers in molecular electronics discuss the motivation behind their work and what they consider to be the grand challenges for the field.
Nature Nanotechnology 8, 378 (2013). doi:10.1038/nnano.2013.110
Author: Mark Ratner
The field of molecular electronics has been around for more than 40 years, but only recently have some fundamental problems been overcome. It is now time for researchers to move beyond simple descriptions of charge transport and explore the numerous intrinsic features of molecules.
Cloning of Dirac fermions in graphene superlattices
Nature 497, 7451 (2013). doi:10.1038/nature12187
Authors: L. A. Ponomarenko, R. V. Gorbachev, G. L. Yu, D. C. Elias, R. Jalil, A. A. Patel, A. Mishchenko, A. S. Mayorov, C. R. Woods, J. R. Wallbank, M. Mucha-Kruczynski, B. A. Piot, M. Potemski, I. V. Grigorieva, K. S. Novoselov, F. Guinea, V. I. Fal’ko & A. K. Geim
Superlattices have attracted great interest because their use may make it possible to modify the spectra of two-dimensional electron systems and, ultimately, create materials with tailored electronic properties. In previous studies (see, for example, refs 1, 2, 3, 4, 5, 6, 7, 8), it proved difficult to realize superlattices with short periodicities and weak disorder, and most of their observed features could be explained in terms of cyclotron orbits commensurate with the superlattice. Evidence for the formation of superlattice minibands (forming a fractal spectrum known as Hofstadter’s butterfly) has been limited to the observation of new low-field oscillations and an internal structure within Landau levels. Here we report transport properties of graphene placed on a boron nitride substrate and accurately aligned along its crystallographic directions. The substrate’s moiré potential acts as a superlattice and leads to profound changes in the graphene’s electronic spectrum. Second-generation Dirac points appear as pronounced peaks in resistivity, accompanied by reversal of the Hall effect. The latter indicates that the effective sign of the charge carriers changes within graphene’s conduction and valence bands. Strong magnetic fields lead to Zak-type cloning of the third generation of Dirac points, which are observed as numerous neutrality points in fields where a unit fraction of the flux quantum pierces the superlattice unit cell. Graphene superlattices such as this one provide a way of studying the rich physics expected in incommensurable quantum systems and illustrate the possibility of controllably modifying the electronic spectra of two-dimensional atomic crystals by varying their crystallographic alignment within van der Waals heterostuctures.
