Why Did the Electron Cross the Road? A Scanning Tunneling Microscopy (STM) Study of Molecular Conductance for the Physical Chemistry Lab
- Ewers, Bradley W.; Schuckman, Amanda E.; Batteas, James D.
A series of experiments employing scanning tunneling
microscopy (STM) have been developed for the physical chemistry laboratory.
These experiments are designed to engage students in cutting edge research
techniques while introducing and reinforcing topics in physical chemistry,
quantum mechanics, solid-state chemistry, and the electronic structure of
molecules and materials. In the ?rst of three experiments, students are
introduced to the basics of STM operation while imaging and conducting
spectroscopy on the highly oriented pyrolytic graphite (HOPG) surface.
Images of the surface are used to determine the crystal structure of the
material, and scanning tunneling spectroscopy is used to determine the
electronic properties of the material and study the tunneling phenomenon....
The Scanning Theremin Microscope: A Model Scanning Probe Instrument for Hands-On Activities
- Quardokus, Rebecca C.; Wasio, Natalie A.; Kandel, S. Alex
A model scanning probe microscope, designed using similar principles of operation to research instruments, is
described. Proximity sensing is done using a capacitance probe, and a mechanical linkage is used to scan this probe across
surfaces. The signal is transduced as an audio tone using a heterodyne detection circuit analogous to that used in the theremin
(one of the ?rst electronic musical instruments, invented in the early 20th century). The instrument is useful for demonstrations
and hands-on activities that introduce fundamentals of scanning probe microscopy and, by extension, nanoscience and
nanotechnology. The details of instrument construction are provided, along with instructions for assembly and troubleshooting
Tailoring structural and electronic properties of RuO2 nanotubes: a many-body approach and electronic transport
- Martínez, J. L.; Abad, Enrique; Calle, Fernando; Alonso, J. A.
The electrical conduction properties of ruthenium oxide nanocables are of high interest. These cables can be built as thin shells of RuO2 surrounding an inner solid nanowire of a dielectric insulating silica material. With this motivation we have investigated the structural, electronic and transport properties of RuO2 nanotubes using the density functional formalism, and applying many-body corrections to the electronic band structure. The structures obtained for the thinnest nanotubes are of the rutile type. The structures of nanotubes with larger diameters deviate from the rutile structure and have in common the formation of dimerized Ru-Ru rows along the axial direction....
Synthesis and characterization of R2MnTiO7 (R = Y and Er) pyrochlores oxides
- Martínez-Coronado, R.; Alonso, J. A.; Fernández-Díaz, M. T.
New pyrochlore-like phases of composition R2MnTiO7 (R = Er and Y) have been synthesized by a soft-chemistry procedure involving citrates of the different metal ions followed by thermal treatments at moderate temperatures (850 C for 12 h in air). A characterization by X-ray diffraction and neutron powder diffraction (NPD) has been carried out in order to determine the crystal structure features: these phyrochlores are cubic, space group Fd-3m, defining an intrinsically frustrated three-dimensional system. The Rietveld-refinement from NPD data at room temperature evidences an antisite cation disorder (distribution of Mn between A and B positions) that is accompanied by an...
Surprising resistivity decrease in manganites with constant electronic density
- Cortés-Gil, R.; Ruíz-González, M. L.; Alonso, J. M.; Martínez, J. L.; Hernando, Antonio; Vallet-Regí, M.; González-Calbet, José M.
A decrease of eight orders of magnitude in the resistance of (La 0.5Ca0.5)zMnO3 has been detected when the electronic density is kept constant while the calcium content is modified by introducing cationic vacancies. This effect is related to the disappearance of the charge ordering state and the emergence of an antiferromagnetic-ferromagnetic transition. Moreover, high values of the colossal magnetoresistance above room temperature are attained. © 2013 IOP Publishing Ltd.
Stoichiometric magnetite grown by infrared nanosecond pulsed laser deposition
- Sanz, Mikel; Oujja, M.; Rebollar, E.; Marco, J. F.; Figuera, Juan de la; Monti, Matteo; Bollero, A.; Camarero, J.; Pedrosa, Francisco J.; García-Hernández, M.; Castillejo, Marta
Pulsed laser deposition (PLD) is a versatile technique for the fabrication of nanostructures due to the possibilities it offers to control size and shape of nanostructured deposits by varying the laser parameters. Magnetite nanostructures are currently promising materials to be used in computing, electronic devices and spintronic applications. For all these uses the fabrication of uniform nanostructured pure magnetite thin films is highly advantageous. In PLD of magnetite, the laser irradiation wavelength and substrate temperature crucially affect the composition, crystallinity, surface structure and the magnetic properties of the grown samples. This work shows that the use of nanosecond IR laser...
Nanostructured oxide ceramic/N-W material, method for preparing and uses thereof
- Moya, J. S.; Pecharromán, C.; López Esteban, Sonia; Rodríguez Suárez, Teresa; Díaz Rodríguez, Luis Antonio; Torrecillas, Ramón
The subject matter of the present invention is an nanostructured ceramic oxide/n-w composite material of nanometric size, 1 to 20 nm, with a tungsten content between 0.05 vol.% and 30 vol.%. Also described is the method for preparing the ceramic oxide/n-W material of the invention. This novel material can be useful in the manufacture of electronic components, catalysers, structural technical ceramics and pigments, dyes and coatings on metal substrates.
Method for modulating the electrical properties of sodium-niobate-derived oxides with a perovskite-type structure through the creation of cation vacancies
- Tottes Pardo, Almudena; García González, Esther; Jiménez Riobóo, R. J.; González-Calbet, José M.
[EN] The invention relates to a method for the controlled modification of the electrical properties of NaNb03 oxide
through the creation of cation vacancies in subnetwork A of the perovskite-type structure. The gradual introduction of vacancies into subnetwork A by means of doping with an alkaline-earth ion, e.g. Sr2+, or with a rare-eaxth ion, e.g. La3+, enables the stabilisation of a ferroelectric material and continuous conversion from ferroelectric to ferroelectric relaxor behaviour characteristic of lead-ftee perovskite-type solid solutions. The invention relates to a method for obtaining oxides which, depending on the properties thereof, can be used in electronic devices and as...
Anharmonic effects on the structural and vibrational properties of the ethyl radical: A path integral Monte Carlo study
- López Ciudad, Telesforo; Ramírez, Rafael; Schulte, J.; Böhm, Michael C.
The structural and vibrational properties of the ethyl radical have been investigated by a series of finite temperature simulations that treat the nuclei as quantum particles. The potential energy surface of the electronic ground state has been described by a nonorthogonal tight-binding Hamiltonian that provides results in reasonable agreement with ab initio methods. The quantum nature of the nuclei has been described by path integral Monte Carlo simulations at temperatures between 25 and 1000 K. Special interest deserves the determination of anharmonic and tunneling effects in the zero-point vibrational structure. In particular, we have studied the influence of anharmonic effects...
Rampas tecnológicas en actividades de Educación Física: desarrollo de un Localizador Sónico para niños con discapacidad visual
- Mártire, Lucas; Mele, Ayelén Magalí; Massarutti, Jorge
Los niños y jóvenes con discapacidad visual pueden ser beneficiados con herramientas innovadoras específicas para poder desenvolverse y facilitar su inclusión en el medio. Debe destacarse que la falta de visión hace que el desarrollo de los niños con esta discapacidad se vea retrasado particularmente en movilidad, locomoción, orientación, en el control y manipulación de objetos y otras habilidades, haciendo que su participación en los juegos se vea notablemente restringida.
En el Área de Desarrollo Tecnológico del UNITEC LATE (Laboratorio de Asistencia Técnica a Establecimientos de Educación Especial) de la UID UNITEC se desarrollan adaptaciones e innovaciones electrónicas de hardware y...
Thermoelectric performance of multiphase XNiSn (X = Ti, Zr, Hf) half-Heusler alloys
- Downie, R.A.; MacLaren, D.A.; Bos, J.-W.G.
Quantitative X-ray powder diffraction analysis demonstrates that mixing Ti, Zr and Hf on the ionic site in the half-Heusler structure, which is a common strategy to lower the lattice thermal conductivity in this important class of thermoelectric materials, leads to multiphase behaviour. For example, nominal Ti0.5Zr0.5NiSn has a distribution of Ti1−xZrxNiSn compositions between 0.24 ≤ x ≤ 0.70. Similar variations are observed for Zr0.50Hf0.5NiSn and Ti0.5Hf0.5NiSn. Electron microscopy and elemental mapping demonstrate that the main compositional variations occur over micrometre length scales. The thermoelectric power factors of the mixed phase samples are improved compared to the single phase end-members (e.g....
An evaluation of RTP circuit breaker performance on LTE networks
- Sarker, Zaheduzzaman; Singh, Varun; Perkins, Colin
Real-time multimedia comprises a large, and growing, fraction of mobile data traffic. An important subset of such flows are from interactive conferencing applications using RTP on UDP/IP to reduce latency. UDP has no congestion control, and while the IETF is developing RTP-level congestion control algorithms as part of the WebRTC standards, these will take time to finalise and deploy. In the interim, we proposed an RTP circuit breaker to the IETF. This can detect and stop RTP flows that cause excessive network congestion, acting as an envelope within which a congestion control algorithm can operate. We briefly review the design...
Documentation of delirium in the VA electronic health record
- Hope, Carol; Estrada, Nicollete; Weir, Charlene; Teng, Chia-Chen; Damal, Kavitha; Sauer, Brian C
ISO 2146 : Information and documentation -- Registry services for libraries and related organizations
- Organización Internacional de Normalización
La ISO 2146:2010 establece las normas para los registros que operan en un entorno de red para proporcionar la información sobre colecciones, partes, actividades y servicios que necesitan las bibliotecas y organizaciones relacionadas para gestionar sus colecciones y ofrecer servicios de información y documentación a través de un rango de aplicaciones y dominios.
La ISO 2146:2010 presenta un directorio de datos que puede ser utilizado como un marco para la recogida de los datos apropiados y compartirlo con otros servicios de registro, proporcionando acceso a los datos del registro a través de protocolos estándar siempre que sea necesario como parte de...
Defining a network management architecture
- Jiménez Agudelo, Yury Andrea; Cervelló Pastor, Cristina; García García, Aurelio Javier
This work proposes an algorithm called k-CriticalNode to solve the controller placement problem in SoftwareDefined Networks. K-Critical finds the minimum number ofcontrollers to satisfy a target communication delay betweencontroller and nodes, Dreq. In addition, the controller selectedcreate a management architecture that improves the subjacentnetwork performance. In this work we focus on the controllersselection procedure, and show the desired management architecturecharacteristics that optimize the control and managementof the network. The results show that our managementtrees balance the load among them and reduce the data loss.
The nature of radiative transitions in TiO2-based nanosheets
- Palummo, Maurizia; Chiodo, Letizia; Rubio Secades, Ángel
Because of rapid progress in the synthesis methods, TiO2-based nanomaterials are nowadays the object of strong research interest for their promising performances in photocatalysis and photovoltaics applications. In particular, large quantities of two-dimensional (2D) nanosheets (NSs) can be produced and used for further assembling of new nanostructured materials with different morphologies and functionalities. Investigating the microscopic nature of their opto-electronic properties is a fundamental prerequisite for rationalizing experimental data and improving devices performances. By means of first-principles excited-state simulations, we reveal here the excitonic nature of radiative transitions (in the vis–UV spectral range) of TiO2-based NSs. Furthermore these calculations on...
Structural and optoelectronic properties of unsaturated ZnO and ZnS nanoclusters
- Malloci, Giuliano; Chiodo, Letizia; Rubio Secades, Ángel; Mattoni, Alessandro
We report a systematic computational study of the structural and optoelectronic properties of unsaturated ZnO and ZnS nanoclusters with hexagonal prism structure, as a function of length and diameter. We computed the fundamental gap using density functional theory (DFT) in the framework of the ?SCF scheme and the optical gap by means of time-dependent DFT (TDDFT). We found that all ZnO nanostructures transform from wurtzite to graphitic phase. On the contrary, ZnS nanocrystals with diameters above ∼1 nm are found to transform to a zeolite BCT phase. These different structural properties reflect in a very different size dependence of the...
Substitution effects on the absorption spectra of nitrophenolate isomers
- Wanko, Marius; Brøndsted Nielsen, Mogens; Brøndsted Nielsen, Steen; Rubio Secades, Ángel
Charge-transfer excitations highly depend on the electronic coupling between the donor and acceptor groups. Nitrophenolates are simple examples of charge-transfer systems where the degree of coupling differs between ortho, meta and para isomers. Here we report the absorption spectra of the isolated anions in vacuo to avoid the complications of solvent effects. Gas-phase action spectroscopy was done with two different setups, an electrostatic ion storage ring and an accelerator mass spectrometer. The results are interpreted on the basis of CC2 quantum chemical calculations. We identified absorption maxima at 393, 532, and 399 nm for the para, meta, and ortho isomer,...
Role of nonlocal exchange in the electronic structure of correlated oxides
- Iori, Federico; Gatti, Matteo; Rubio Secades, Ángel
We present a systematic study of the electronic structure of several prototypical correlated transition-metal oxides: VO2, V2O3, Ti2O3, LaTiO3, and YTiO3. In all these materials, in the low-temperature insulating phases the local and semilocal density approximations (LDA and GGA, respectively) of density-functional theory yield a metallic Kohn-Sham band structure. Here we show that, without invoking strong-correlation effects, the role of nonlocal exchange is essential to cure the LDA/GGA delocalization error and provide a band-structure description of the electronic properties in qualitative agreement with the experimental photoemission results. To this end, we make use of hybrid functionals that mix a portion...
Challenges in truncating the hierarchy of time-dependent reduced density matrices equations
- Akbari, A.; Hashemi, M. J.; Rubio Secades, Ángel; Nieminen, R. M.; Leeuwen, R. van
In this work, we analyze the Born, Bogoliubov, Green, Kirkwood, and Yvon (BBGKY) hierarchy of equations for describing the full time evolution of a many-body fermionic system in terms of its reduced density matrices (at all orders). We provide an exhaustive study of the challenges and open problems linked to the truncation of such a hierarchy of equations to make them practically applicable. We restrict our analysis to the coupled evolution of the one- and two-body reduced density matrices, where higher-order correlation effects are embodied into the approximation used to close the equations. We prove that within this approach, the...