64 research outputs found
Uso do prato ascendente e da altura do pasto para estimativa da biomassa disponível em sistema ILP.
Resumo.Fernando Flores Cardoso, Daniel Portella Montardo, José Carlos Ferrugem Moraes, Marcos Flávio Silva Borba, Sandro da Silva Camargo, editores técnicos
Uso de sensor multiespectral em aeronave remotamente pilotada para avaliação da infestação de pastagem nativa por Eragrostis plana (Ness).
Resumo.Fernando Flores Cardoso, Daniel Portella Montardo, José Carlos Ferrugem Moraes, Marcos Flávio Silva Borba, Sandro da Silva Camargo, editores técnicos
Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions
We investigate the optical properties of edge-functionalized graphene
nanosystems, focusing on the formation of junctions and charge transfer
excitons. We consider a class of graphene structures which combine the main
electronic features of graphene with the wide tunability of large polycyclic
aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we
show that, upon convenient choice of functional groups, low energy excitations
with remarkable charge transfer character and large oscillator strength are
obtained. These properties can be further modulated through an appropriate
width variation, thus spanning a wide range in the low-energy region of the
UV-Vis spectra. Our results are relevant in view of designing all-graphene
optoelectronic nanodevices, which take advantage of the versatility of
molecular functionalization, together with the stability and the electronic
properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres
Change of Structural Behaviors of Organo-Silane Exposed Graphene Nanoflakes
[[abstract]]The electronic structures of graphene nanoflakes (GNFs) exposed to an organo-silane precursor [tetramethylsilane, TMS, Si(CH3)4] were studied using electron field emission (EFE), Raman spectroscopy, X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and first-principles calculation. The results of XANES, XPS, and Raman spectroscopy indicate that the silyl radical strong covalent bonds were formed in GNFs, which induced local structural relaxations and enhanced sp3 hybridization. Comparison of calculated electronic structure, XANES, and XES spectra of Sitreated GNFs suggests that the Si atom substitutes one 3-fold coordinated C atom in a given graphene layer and relaxes outward to form sp3 bonding with another C atom in the adjacent graphene layer. The EFE measurements show an increase in the turn-on electric field with the increase of the Si content, which suggests an enhancement of the nonmetallic sp3 bonding[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]US
Density functional theory calculations of the carbon ELNES of small diameter armchair and zigzag nanotubes: core-hole, curvature and momentum transfer orientation effects
We perform density functional theory calculations on a series of armchair and
zigzag nanotubes of diameters less than 1nm using the all-electron
Full-Potential(-Linearised)-Augmented-Plane-Wave (FPLAPW) method. Emphasis is
laid on the effects of curvature, the electron beam orientation and the
inclusion of the core-hole on the carbon electron energy loss K-edge. The
electron energy loss near-edge spectra of all the studied tubes show strong
curvature effects compared to that of flat graphene. The curvature induced
hybridisation is shown to have a more drastic effect on the
electronic properties of zigzag tubes than on those of armchair tubes. We show
that the core-hole effect must be accounted for in order to correctly reproduce
electron energy loss measurements. We also find that, the energy loss near edge
spectra of these carbon systems are dominantly dipole selected and that they
can be expressed simply as a proportionality with the local momentum projected
density of states, thus portraying the weak energy dependence of the transition
matrix elements. Compared to graphite, the ELNES of carbon nanotubes show a
reduced anisotropy.Comment: 25 pages, 15 figures, revtex4 submitted for publication to Phys. Rev.
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