Encontrados 27 documentos, a visualizar página 1 de 3
Strong light-matter interactions in heterostructures of atomically thin films
Britnell, Líam; Ribeiro, R. M.; Eckmann, A.; Jalil, R.; Belle, B. D.; Mishchenko, A.; Kim, Y.-J.; Gorbachev, R. V.; Georgiou, T.; Morozov, S. V.The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here we expand the range of such structures to photoactive ones by utilizing semico...
Band nesting and the optical response of two-dimensional semiconducting transit...
Carvalho, A.; Ribeiro, R. M.; Castro Neto, A. H.We have studied the optical conductivity of two-dimensional (2D) semiconducting transition metal dichalcogenides using ab initio density functional theory. We find that this class of materials presents large optical response due to the phenomenon of band nesting. The tendency towards band nesting is enhanced by the presence of van Hove singularities in the band structure of these materials. Given that 2D crysta...
Origin of indirect optical transitions in few-layer MoS2, WS2 and WSe2
Zhao, Weijie; Ribeiro, R. M.; Minglin, Toh; Carvalho, A.; Kloc, Christian; Castro Neto, A. H.; Eda, GokiIt has been well established that single layer MX2 (M=Mo,W and X=S,Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect gap multilayer counterparts. In few-layer MX2, there are two valleys along the Γ-K line with similar energy. There is little understanding on which of the two valleys forms the conduction band minimum (CBM) in this thickness regime. We inve...
Enhanced optical dichroism of graphene nanoribbons
Hipolito, Fábio; Chaves, A. J.; Ribeiro, R. M.; Vasilevskiy, Mikhail; Pereira, Vitor M.; Peres, N. M. R.The optical conductivity of graphene nanoribbons is analytical and exactly derived. It is shown that the absence of translational invariance along the transverse direction allows considerable intraband absorption in a narrow frequency window that varies with the ribbon width, and lies in the THz range domain for ribbons 10–100 nm wide. In this spectral region the absorption anisotropy can be as high as two orde...
Efficient graphene-based photodetector with two cavities
Ferreira, Aires; Peres, N. M. R.; Ribeiro, R. M.; Stauber, TobiasDocumento submetido para revisão pelos pares a publicar em Physical Review B. ; We present an efficient graphene-based photodetector with two Fabri-P\'erot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working ...
Pulsed DC reactive magnetron sputtering of vanadium dioxide thermochromic thin ...
Batista, C.; Teixeira, Vasco M. P.; Ribeiro, R. M.Vanadium oxides are an important class of materials with a large diversity of physical and chemical properties which derive from a range of single or mixed valences and a large variety of structures. They are already being used in many technological applications such as electrical and optical switching devices, light detectors, temperature sensors, etc. There has been a great interest in a particular phase, VO2...
Synthesis and characterization of VO2-based thermochromic thin films for energy...
Batista, C.; Ribeiro, R. M.; Teixeira, Vasco M. P.Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and in...
Stability of boron nitride bilayers : ground-state energies, interlayer distanc...
Ribeiro, R. M.; Peres, N. M. R.We have studied boron nitride monolayer and bilayer band structures. For bilayers, the ground-state energies of the different five stackings are computed using DFT in order to determine the most stable configuration. Also, the interlayer distance for the five different types of stacking in which boron-nitride bilayers can be found is determined. Using a minimal tight-binding model for the band structures of boron ...
Zigzag graphene nanoribbon edge reconstruction with stone-wales defects
Rodrigues, João N. B.; Gonçalves, P. A. D.; Rodrigues, N. F. G.; Ribeiro, R. M.; Santos, J. M. B. Lopes dos; Peres, N. M. R.In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge ...
The mesoscopic modelling of multilayered polymer diodes
Ribeiro, R. M.Poster apresentado no "European Materials Research Society Spring Meeting (E-MRS 2006 Spring Meeting)", Nice, France, Junho 2006. ; The performance of transparent devices based on semiconducting polymers depends on the component polymer molecules, on the device design, and on the polymer texture. The role of this texture and multilayers of different textures is the focus of this work. In this work, we build on...
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