In the last 30 days

• Open/close Effects of chemical order and atomic relaxation on the electronic and magnetic properties of La_2/3Sr_1/3MnO₃

  B Zheng and N Binggeli  2009 J. Phys.: Condens. Matter 21 115602 Tag this article

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  We investigate the effects of Sr/La cation ordering/disordering and atomic relaxation on the electronic and magnetic properties of La _2/3Sr _1/3MnO ₃ (LSMO) by means of ab initio pseudopotential calculations. We consider a cation-ordered layered structure and a more homogeneously Sr-bulk-doped structure. Cation disordering and atomic relaxation both tend to push the LSMO system towards half-metallicity, increasing the minority-spin and spin-flip gaps. Lattice relaxation has a significant effect on the electronic density of states (DOS) of the layered LSMO and drastically reduces the initial differences found comparing the electronic properties of the perovskite structures with different dopant configurations. The trend with structural relaxation is understood in terms of an effective screening, due to the displacement of the O anions and La cations, of the local electric field produced by the ordered Sr dopants.

• Open/close The 12th International Workshop on Desorption Induced by Electronic Transitions (DIET XII) (Pine Mountain, Georgia, USA, 19–23 April 2009)

  Thomas M Orlando and Ulrike Diebold  2010 J. Phys.: Condens. Matter 22 080301 Tag this article

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  The 12th International Workshop on Desorption Induced by Electronic Transitions (DIET XII) took place from 19–23 April 2009 in Pine Mountain, Georgia, USA. This was the 12th conference in a strong and vibrant series, which dates back to the early 1980s. DIET XII continued the tradition of exceptional interdisciplinary science and focused on the study of desorption and dynamics induced by electronic excitations of surfaces and interfaces. The format involved invited lectures, contributed talks and a poster session on the most recent developments and advances in this area of surface physics.

  The Workshop International Steering Committee and attendees wish to dedicate DIET XII to the memory of the late Professor Theodore (Ted) Madey. Ted was one of the main pioneers of this field and was one of the primary individuals working to keep this area of science exciting and adventurous. His overall contributions to surface science were countless and his contributions to the DIET field and community were enormous. He is missed and remembered by many friends and colleagues throughout the world.

  The papers collected in this issue cover many of the highlights of DIET XII. Topics include ultrafast electron transfer at surfaces and interfaces, quantum and spatially resolved mapping of surface dynamics and desorption, photon-, electron- and ion-beam induced processes at complex interfaces, the role of non-thermal desorption in astrochemistry and astrophysics and laser-/ion-based methods of examining soft matter and biological media.

  Although the workshop attracted many scientists active in the general area of non-thermal surface processes, DIET XII also attracted many younger scientists (i.e., postdoctoral fellows, advanced graduate students, and a select number of advanced undergraduate students). This field has had an impact in a number of areas including nanoscience, device physics, astrophysics, and now biophysics. We believe that this special issue of Journal of Physics: Condensed Matter will help foster further progress in the study of DIET processes. Since the field remains vibrant and exciting, the workshop series will continue with DIET XIII. Professor Richard Palmer (University of Birmingham, UK) will chair DIET XIII in the UK in early summer 2012.

  We gratefully acknowledge financial support from SPECS, HIDEN Analytical, BRUKER, The United States National Science Foundation, Georgia Institute of Technology and The State University of New Jersey, Rutgers.

• Open/close QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

  Paolo Giannozzi et al  2009 J. Phys.: Condens. Matter 21 395502 Tag this article

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  QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

• Open/close Multiple atomic scale solid surface interconnects for atom circuits and molecule logic gates

  C Joachim et al  2010 J. Phys.: Condens. Matter 22 084025 Tag this article

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  The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes ( N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties of the targeted substrates, two types of machines are considered: on moderate surface band gap materials, scanning tunneling microscopy can be combined with scanning electron microscopy to provide an efficient navigation system, while on wide surface band gap materials, atomic force microscopy can be used in conjunction with optical microscopy. The size of the planar part of the circuit should be minimized on moderate band gap surfaces to avoid current leakage, while this requirement does not apply to wide band gap surfaces. These constraints impose different methods of connection, which are thoroughly discussed, in particular regarding the recent progress in single atom and molecule manipulations on a surface.

• Open/close The SIESTA method for ab initio order-N materials simulation

  José M Soler et al  2002 J. Phys.: Condens. Matter 14 2745 Tag this article

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  We have developed and implemented a selfconsistent density functional method using standard norm-conserving pseudopotentials and a flexible, numerical linear combination of atomic orbitals basis set, which includes multiple-zeta and polarization orbitals. Exchange and correlation are treated with the local spin density or generalized gradient approximations. The basis functions and the electron density are projected on a real-space grid, in order to calculate the Hartree and exchange-correlation potentials and matrix elements, with a number of operations that scales linearly with the size of the system. We use a modified energy functional, whose minimization produces orthogonal wavefunctions and the same energy and density as the Kohn-Sham energy functional, without the need for an explicit orthogonalization. Additionally, using localized Wannier-like electron wavefunctions allows the computation time and memory required to minimize the energy to also scale linearly with the size of the system. Forces and stresses are also calculated efficiently and accurately, thus allowing structural relaxation and molecular dynamics simulations.

• Open/close Magnetism of solids resulting from spin polarization of p orbitals

  O Volnianska and P Boguslawski  2010 J. Phys.: Condens. Matter 22 073202 Tag this article

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  Magnetism in systems that do not contain transition metal or rare earth ions was recently observed or predicted to exist in a wide variety of systems. We summarize both experimental and theoretical results obtained for ideal bulk II–V and II–IV compounds, molecular crystals containing O ₂ or N ₂ molecules as structural units, as well as for carbon-based materials such as graphite and graphene nanoribbons. Magnetism can be an intrinsic property of a perfect crystal, or it can be induced by non-magnetic dopants or defects. In the case of vacancies, spin polarization is local and results in their high spin states. The non-vanishing spin polarization is shown to originate in the strong spin polarization of the 2p shell of light atoms from the second row of the periodic table.

• Open/close Recent experimental studies of electron dephasing in metal and semiconductor mesoscopic structures

  J J Lin and J P Bird  2002 J. Phys.: Condens. Matter 14 R501 Tag this article

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  In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (τ ) in metal and semiconductor mesoscopic structures. A major focus of this review is on the use of weak localization, and other quantum-interference-related phenomena, to determine the value of τ in systems of different dimensionality and with different levels of disorder. Significant attention is devoted to a discussion of three-dimensional metal films, in which dephasing is found to predominantly arise from the influence of electron-phonon (e-ph) scattering. Both the temperature and electron mean free path dependences of τ that result from this scattering mechanism are found to be sensitive to the microscopic quality and degree of disorder in the sample. The results of these studies are compared with the predictions of recent theories for the e-ph interaction. We conclude that, in spite of progress in the theory for this scattering mechanism, our understanding of the e-ph interaction remains incomplete. We also discuss the origins of decoherence in low-diffusivity metal films, close to the metal-insulator transition, in which evidence for a crossover of the inelastic scattering, from e-ph to `critical' electron-electron (e-e) scattering, is observed. Electron-electron scattering is also found to be the dominant source of dephasing in experimental studies of semiconductor quantum wires, in which the effects of both large- and small-energy-transfer scattering must be taken into account. The latter, Nyquist, mechanism is the stronger effect at a few kelvins, and may be viewed as arising from fluctuations in the electromagnetic background, generated by the thermal motion of electrons. At higher temperatures, however, a crossover to inelastic e-e scattering typically occurs; and evidence for this large-energy-transfer process has been found at temperatures as high as 30 K. Electron-electron interactions are also thought to play an important role in dephasing in ballistic quantum dots, and the results of recent experiments in this area are reviewed. A common feature of experiments, in both dirty metals and ballistic and quasi-ballistic semiconductors, is found to be the observation of an unexpected `saturation' of the dephasing time at temperatures below a kelvin or so. The possible origins of this saturation are discussed, with an emphasis on recent experimental investigations of this effect.

• Open/close Atomic-scale structure of GeSe₂ glass revisited: a continuous or broken network of Ge–(Se_1/2)₄ tetrahedra?

  V Petkov and D Le Messurier  2010 J. Phys.: Condens. Matter 22 115402 Tag this article

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  The atomic-scale structure of germanium diselenide (GeSe ₂) glass has been revisited using a combination of high-energy x-ray diffraction and constrained reverse Monte Carlo simulations. The study shows that the glass structure may be very well described in terms of a continuous network of corner- and edge-sharing Ge–Se ₄ tetrahedra. The result is in contrast to other recent studies asserting that the chemical order and, hence, network integrity in GeSe ₂ glass are intrinsically broken. It is suggested that more elaborate studies are necessary to resolve the controversy.

• Open/close Zinc oxide nanostructures: growth, properties and applications

  Zhong Lin Wang  2004 J. Phys.: Condens. Matter 16 R829 Tag this article

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  Zinc oxide is a unique material that exhibits semiconducting and piezoelectric dual properties. Using a solid–vapour phase thermal sublimation technique, nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires and nanocages of ZnO have been synthesized under specific growth conditions. These unique nanostructures unambiguously demonstrate that ZnO probably has the richest family of nanostructures among all materials, both in structures and in properties. The nanostructures could have novel applications in optoelectronics, sensors, transducers and biomedical sciences. This article reviews the various nanostructures of ZnO grown by the solid–vapour phase technique and their corresponding growth mechanisms. The application of ZnO nanobelts as nanosensors, nanocantilevers, field effect transistors and nanoresonators is demonstrated.

• Open/close Chemical functionalization of graphene

  D W Boukhvalov and M I Katsnelson  2009 J. Phys.: Condens. Matter 21 344205 Tag this article

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  Experimental and theoretical results on chemical functionalization of graphene are reviewed. Using hydrogenated graphene as a model system, general principles of the chemical functionalization are formulated and discussed. It is shown that, as a rule, 100% coverage of graphene by complex functional groups (in contrast with hydrogen and fluorine) is unreachable. A possible destruction of graphene nanoribbons by fluorine is considered. The functionalization of infinite graphene and graphene nanoribbons by oxygen and by hydrofluoric acid is simulated step by step.