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Thyrotoxicose à déclenchement tardif après arrêt de l’amiodarone : à propos d’un cas. MÉDECINE NUCLÉAIRE 2023. [DOI: 10.1016/j.mednuc.2023.01.087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
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Optimisation des temps d’acquisition avec un TEP-TDM haute sensibilité de dernière génération. MÉDECINE NUCLÉAIRE 2023. [DOI: 10.1016/j.mednuc.2023.01.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
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Apport de la TEMP/TDM osseuse dans le diagnostic d’un syndrome SAPHO au stade précoce : à propos d’un cas. MÉDECINE NUCLÉAIRE 2023. [DOI: 10.1016/j.mednuc.2023.01.084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
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4
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Exploring the enhancement of the thermoelectric properties of bilayer graphyne nanoribbons. Phys Chem Chem Phys 2022; 24:9324-9332. [PMID: 35383347 DOI: 10.1039/d1cp05491k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Carbon materials are vital for sustainable energy applications based on abundant and non-toxic raw materials. In this scenario, carbon nanoribbons have superior thermoelectric properties in comparison with their 2D material counterparts, owing to their particular electronic and transport properties. Therefore, we explore the electronic and thermoelectric properties of bilayer α-graphyne nanoribbons (α-BGyNRs) by means of density functional theory, tight-binding, and the non-equilibrium Green's functions (NEGF) method. Our calculations indicate that Ab stacking is the most stable configuration regardless of the edge type. The band structure presents finite band gaps with different features for armchair and zigzag nanoribbons. Concerning the thermoelectric quantities, the Seebeck coefficient is highly sensitive to the width and edge type, while its room-temperature values can achieve a measurable mV K-1 scale. The electric conductance is found to increase due to layering, thus enhancing the power factor for α-BGyNRs compared with single nanoribbons. These findings therefore indicate the possibility of engineering such systems for thermal nanodevices.
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Thermoelectric properties of nanostructured systems based on narrow armchair graphene nanoribbons. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:125303. [PMID: 30654349 DOI: 10.1088/1361-648x/aaffb6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Thermoelectric properties of hybrid systems composed of graphene nanoribbons (GNRs) coupled to rectangular rings or functionalized with aromatic carbon molecules are theoretically addressed here. Graphene-based nanostructures are designed with the purpose of enhancing thermopower responses compared to the thermal performance of pristine GNRs. The electronic transport is calculated using standard tight binding models and the Landauer transport formalism. We found that both semiconducting and metallic armchair nanoribbons coupled to rings exhibit a pronounced enhancement of the thermoelectric responses with comparable intensities, due to Fano antiresonance and Breit-Wigner-like resonances in the electronic transport. As expected, details of the ring geometry and ribbons are important in determining the precise chemical potential values for optimal performance. Different configurations of attached aromatic molecules (single and double molecules) at the graphene nanoribbon edges are addressed. Our findings show that the presence of a molecule induces a gap formation in the metallic pristine GNRs, and a pronounced peak of the Seebeck coefficient is revealed for low chemical potential values, independent of the molecule length. Other features on the Seebeck spectra are found to depend on the electronic nature of the GNRs and on the molecule length and distribution. We have shown that by playing with them, it is possible to design better thermoelectric devices based on GNRs.
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Optical properties of graphene nanocones under electric and magnetic fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:455304. [PMID: 29049035 DOI: 10.1088/1361-648x/aa8dca] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Here we present a theoretical study of the optical properties of graphene nanocones tuned by external electric and magnetic fields. We investigate the effects of the size and topology of the carbon nanostructures on the density of states and on the electro- and magneto-absorption of linearly polarized electromagnetic radiation in different nanocone geometries. We find that the electric field induces changes in the electric charge distribution mainly at the cone edges. In the infrared range the absorption coefficient shows a peculiar dependence on the electric field (magnitude and direction) and on the photon polarization for all investigated structures. Our results suggest that the electric field may be used to control the electric charge at the apex and for a selective light absorption. The presence of an axial magnetic field induces new features in the nanocone density of states due to the induced localization effects. For high fields the density of states exhibits a sequence of peaks resembling the graphene Landau spectra. The magneto-absorption spectra present a series of resonances strongly sensitive to the photon polarization opening routes for manipulation of the optical responses.
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Fano resonances in hexagonal zigzag graphene rings under external magnetic flux. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:175301. [PMID: 25836340 DOI: 10.1088/0953-8984/27/17/175301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We study transport properties of hexagonal zigzag graphene quantum rings connected to semi-infinite nanoribbons. Open two-fold symmetric structures support localized states that can be traced back to those existing in the isolated six-fold symmetric rings. Using a tight-binding Hamiltonian within the Green's function formalism, we show that an external magnetic field promotes these localized states to Fano resonances with robust signatures in transport. Local density of states and current distributions of the resonant states are calculated as a function of the magnetic flux intensity. For structures on corrugated substrates we analyze the effect of strain by including an out-of-plane centro-symmetric deformation in the model. We show that small strains shift the resonance positions without further modifications, while high strains introduce new ones.
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Magnetic response of zigzag nanoribbons under electric fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:216002. [PMID: 24806106 DOI: 10.1088/0953-8984/26/21/216002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Spin excitations in zigzag graphene nanoribbons are studied when the system is subjected to an electric field in the transversal direction. The magnetic properties and the lifetime of the spin excitations are systematically investigated and compared using a tight-binding electron-electron model treated by a mean-field Hubbard model. The effects of electron-hole asymmetry introduced by next-nearest neighbor hopping are also investigated. We show that by increasing the electric field, the antiferromagnetic correlations between the edges of the nanoribbons are decreased due to a reduction of the magnetic moments. The results show that the spin wave lifetime may be controlled by the intensity of the transversal electric field, indicating that zigzag nanoribbons may be considered great candidates for future spintronic applications.
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Helicoidal fields and spin polarized currents in carbon nanotube-DNA hybrids. PHYSICAL REVIEW LETTERS 2012; 108:126601. [PMID: 22540607 DOI: 10.1103/physrevlett.108.126601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Indexed: 05/31/2023]
Abstract
We report on theoretical studies of electronic transport in the archetypical molecular hybrid formed by DNA wrapped around single-walled carbon nanotubes (CNTs). Using a Green's function formalism in a π-orbital tight-binding representation, we investigate the role that spin-orbit interactions play on the CNT in the case of the helicoidal electric field induced by the polar nature of the adsorbed DNA molecule. We find that spin polarization of the current can take place in the absence of magnetic fields, depending strongly on the direction of the wrapping and length of the helicoidal field. These findings open new routes for using CNTs in spintronic devices.
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Carbon nanotube bundles under electric field perturbations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:095301. [PMID: 22316531 DOI: 10.1088/0953-8984/24/9/095301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Here we address the important role played by electric fields applied in carbon nanotube bundles in providing convenient scenarios for their use in electronic devices. We show that a gap modulation may be derived depending on the bundle configuration and the details of the applied field configuration. The system is described by a tight binding Hamiltonian and the Green function formalism is used to calculate the local density of states. Small bundles were used to validate our model on the basis of ab initio calculations. Further analysis shows that the number of tubes, geometrical configuration details and field intensities may be controlled to tune the electronic structure close to the Fermi energy, envisaging atomic-scale devices.
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Probing optical spectra of carbon nanotubes with external fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:065301. [PMID: 21406922 DOI: 10.1088/0953-8984/23/6/065301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Here we present a theoretical study of the interplay between electronic and optical properties of carbon nanotubes. External perturbations such as electric and magnetic fields are applied on the systems which are probed by parallel and perpendicularly polarized light sources. We demonstrate that the optical transitions can be fully controlled by the fields. Likewise, extra optical excitations can be induced in different energy ranges of the absorption spectra due to degeneracy splitting of the states. In most of the theoretical works developed in this realm, a remarkable discrepancy between the results obtained via the tight binding approximation and first principle calculations is found. The disagreement can be enhanced when external perturbation fields act on the tubes forcing the realization of demanding charge self-consistent calculations. In this sense, we profit from novel parametrization schemes for the tight binding approach to describe the optical response of nanotubes of any diameter size and with similar accuracy to density functional theory.
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Abstract
The transport properties of graphene nanoribbons with linear benzene-based molecules pinned at the ribbon edges are studied. The systems are described by a single pi-band tight-binding Hamiltonian and by using the Green functions formalism based on real-space renormalization techniques. Different configurations have been considered, such as two and three attached molecules separated by a variable distance d, and the case of a finite array of molecules attached to the ribbon in different geometries (one-side and alternated sequence). In the latter case the conductance behavior is compared with the case of a molecular superlattice-like structure. In these hybrid systems of ribbons with a large number of regular attached foreign structures, we have shown the formation of well-defined energy gaps for which the conductance is completely suppressed. These gaps can be tuned by varying the number, relative distance, and length of the attached molecules. An analysis is performed to understand the nature of the conductance gap and its relation with the foreign molecular structures, providing a mechanism to delineate novel molecular sensors.
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Transport properties of graphene nanoribbons with side-attached organic molecules. NANOTECHNOLOGY 2008; 19:065402. [PMID: 21730698 DOI: 10.1088/0957-4484/19/6/065402] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this work we address the effects on the conductance of graphene nanoribbons (GNRs) of organic molecules adsorbed at the ribbon edge. We studied the case of armchair and zigzag GNRs with quasi-one-dimensional side-attached molecules, such as linear poly-aromatic hydrocarbons and poly(para-phenylene). These nanostructures are described using a single-band tight-binding Hamiltonian and their electronic conductance and density of states are calculated within the Green's function formalism based on real-space renormalization techniques. We found that the conductance exhibits an even-odd parity effect as a function of the length of the attached molecules. Furthermore, the corresponding energy spectrum of the molecules can be obtained as a series of Fano antiresonances in the conductance of the system. The latter result suggests that GNRs can be used as a spectrograph sensor device.
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Electric field effects on the energy spectrum of carbon nanotubes. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2005; 17:5839-5847. [PMID: 32397053 DOI: 10.1088/0953-8984/17/37/019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Electronic properties of straight carbon nanotubes under an external electric are investigated, following a single-π-orbital tight binding approximation. Metal-insulator transitions in metallic tubes and energy gap modulations in semiconducting ones were found due to the action of the electric field. Reductions in the tube symmetry operations induced by the field are manifested in the energy spectrum as a function of the angle determined by the field direction and equivalent in-plane atomic positions along the circumferential direction. We find that particular energies in the spectra exhibit a periodic oscillation with this dephasing angle. The range and position of those energies, as well the amplitude of the oscillation, can be properly manipulated by changing the strength and direction of the applied electric field.
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Intradonor absorption spectra under external fields in quantum wells. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 53:10160-10166. [PMID: 9982583 DOI: 10.1103/physrevb.53.10160] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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1s-2p+/- infrared-absorption spectra of donor-doped quantum wells under electric and magnetic fields. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 51:13344-13348. [PMID: 9978138 DOI: 10.1103/physrevb.51.13344] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Donor 1s-2p+/- transitions in doped GaAs-Ga1-xAlxAs quantum wells: Effects of electric and magnetic fields. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 51:2259-2263. [PMID: 9978975 DOI: 10.1103/physrevb.51.2259] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Current fluctuations in strongly electron-correlated one-dimensional double-barrier heterostructures. PHYSICAL REVIEW. B, CONDENSED MATTER 1994; 50:8559-8563. [PMID: 9974873 DOI: 10.1103/physrevb.50.8559] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Impurities in a quantum dot: A comparative study. PHYSICAL REVIEW. B, CONDENSED MATTER 1994; 50:4913-4916. [PMID: 9976810 DOI: 10.1103/physrevb.50.4913] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Donor-excited states and infrared-transition strengths in cylindrical GaAs-(Ga,Al)As quantum-well wires. PHYSICAL REVIEW. B, CONDENSED MATTER 1994; 49:10450-10455. [PMID: 10009869 DOI: 10.1103/physrevb.49.10450] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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23
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Acceptor-related photoluminescence spectra of GaAs quantum-wire microcrystals: A model calculation. PHYSICAL REVIEW. B, CONDENSED MATTER 1993; 47:13864-13867. [PMID: 10005710 DOI: 10.1103/physrevb.47.13864] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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24
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Collective electron excitations on a two-dimensional lattice. PHYSICAL REVIEW. B, CONDENSED MATTER 1993; 47:4798-4801. [PMID: 10006634 DOI: 10.1103/physrevb.47.4798] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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25
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Infrared transitions between hydrogenic states in cylindrical GaAs-(Ga,Al)As quantum-well wires. PHYSICAL REVIEW. B, CONDENSED MATTER 1992; 45:9420-9423. [PMID: 10000810 DOI: 10.1103/physrevb.45.9420] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Photoluminescence study of shallow acceptors in GaAs-Ga1-xAlxAs cylindrical quantum-well wires. PHYSICAL REVIEW. B, CONDENSED MATTER 1992; 45:6742-6746. [PMID: 10000436 DOI: 10.1103/physrevb.45.6742] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Oxygen-disorder and correlation effects on the hole concentration and metal-nonmetal transition in YBa2Cu3O6+x. PHYSICAL REVIEW. B, CONDENSED MATTER 1990; 42:4288-4297. [PMID: 9995955 DOI: 10.1103/physrevb.42.4288] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Effects of correlation and disorder on the phase diagram of YBa2Cu3O6+x. PHYSICAL REVIEW. B, CONDENSED MATTER 1990; 42:2543-2546. [PMID: 9995707 DOI: 10.1103/physrevb.42.2543] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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