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Physical Review B 12/2012; 86:195416. · 3.69 Impact Factor
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ABSTRACT: This work investigates the scaled height distribution, ρ(q), of irregular profiles that are grown based on two sets of local rules: those of the restricted solid on solid (RSOS) and ballistic deposition (BD) models. At each time step, these rules are respectively chosen with probability p and r=1-p. Large-scale Monte Carlo simulations indicate that the system behaves differently in three succeeding intervals of values of p: I_{B}≈[0,0.75),I_{T}≈(0.75,0.9), and I_{R}≈(0.9,1.0]. In I_{B}, the ballistic character prevails: the growth velocity υ_{∞} decreases with p in a linear way, and similar behavior is found for Γ_{∞}(p), the amplitude of the t^{1/3}-fluctuations, which is measured from the second-order height cumulant. The distribution of scaled height fluctuations follows the Gaussian orthogonal ensemble (GOE) Tracy-Widom (TW) distribution with resolution roughly close to 10^{-4}. The skewness and kurtosis of the computed distribution coincide with those for TW distribution. Similar results are observed in the interval I_{R}, with prevalent RSOS features. In this case, the skewness become negative. In the transition interval I_{T}, the system goes smoothly from one regime to the other: the height distribution becomes apparently Gaussian, which motivates us to identify this phenomenon as a transition from Kardar-Parisi-Zhang (KPZ) behavior to Edwards-Wilkinson (EW) behavior back to KPZ behavior.
Physical Review E 11/2012; 86(5-1):051607. · 2.26 Impact Factor
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ABSTRACT: In this work, ab initio density functional theory calculations were performed in order to study the structural and electronic properties of halogens (X = fluorine, chlorine, bromine or iodine) that were deposited on both sides of graphene single layers (X-graphene). The adsorption of these atoms on only one side of the layer with hydrogen atoms adsorbed on the other was also considered (H,X-graphene). The results indicate that the F-C bond in the F-graphene system causes an sp(2) to sp(3) transition of the carbon orbitals, and similar effects seem to occur in the H,X-graphene systems. For the other cases, two configurations are found: bonded (B) and non-bonded (NB). For the B configuration, the structural arrangement of the atoms was similar to F-graphene and H-graphene (graphane), although the electronic structures present some differences. In the NB configuration, the interaction between the adsorbed atoms and the graphene layer seems to be essentially of the van der Waals type. In these cases, the original shape of the graphene layer presents only small deviations from the pristine form and the adsorbed atoms reach equilibrium far from the sheet. The F-graphene structure has a direct bandgap of approximately 3.16 eV at the Γ point, which is a value that is close to the value of 3.50 eV that was found for graphane. The Cl-graphene (B configuration), H,F-graphene and H,Cl-graphene systems have smaller bandgap values. All of the other systems present metallic behaviours. Energy calculations indicate the possible stability of these X-graphene layers, although some considerations about the possibility of spontaneous formation have to be taken into account.
Nanotechnology 12/2010; 21(48):485701. · 3.98 Impact Factor
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ABSTRACT: This work investigates, using first-principles calculations, electronic and structural properties of hydrogen, lithium, sodium, potassium and rubidium that are adsorbed, in a regular pattern, on a graphene surface. The results for H-graphene (graphane) and Li-graphene were compared with previous calculations. The present results do not support previous claims that the Li-C bond in such a layer would result in an sp(2) to an sp(3) transition of carbon orbitals, being more compatible with some ionic character for the covalent bond and with lithium acting as an electron acceptor in a bridging environment. Calculations were also performed for the Na, K, and Rb-graphene systems, resulting in a similar electronic behaviour but with a more pronounced ionic character than for Li-graphene. Energy calculations indicate the possible stability of such ad-graphene layers, with only the Li-graphene being possible to be spontaneously obtained.
Nanotechnology 02/2010; 21(11):115701. · 3.98 Impact Factor
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ABSTRACT: We probe the linear optical properties of the neat liquid acetonitrile (CH(3)CN) at ambient conditions using ab initio density functional theory. Uncorrelated structures extracted from Monte Carlo simulation are employed to efficiently calculate average electronic properties. It becomes evident that condensation leads to a conduction band with a large degree of dispersion, which is consistent with the description of dipolar liquids. This allows an interpretation of the dielectric spectrum based on the electronic structure of liquid CH(3)CN, and clearly shows the influence of intermolecular interactions in the absorption features. We find that the lowest-lying excitation of the condensed phase occurs at 7.8 eV, which is reasonable as compared to the 8-9.5 eV absorption region measured in the gas phase.
The Journal of Physical Chemistry B 07/2009; 113(28):9489-92. · 3.70 Impact Factor
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ABSTRACT: We investigate, using first-principles calculations, the electronic
structure of substitutional and vacancy defects in a boron nitride
monolayer. We found that the incorporation of a substitutional carbon atom
induces appreciable modification on the electronic properties, when compared
to a non-defective boron nitride sheet. The incorporation of substitutional
carbon impurity also induces a significant reduction of the work function.
In addition, we found that defects introduce electronic states in the
energy-gap region, with strong impact on the optical properties of the
material. The calculation results indicate that spin polarization is
obtained when substitutional impurities or vacancy defects are introduced in
the structure
Physics of Condensed Matter 01/2009; 67(4):507-512. · 1.53 Impact Factor
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ABSTRACT: We investigate the impact of hydroxyl groups on the properties of C(60)(OH)(n) systems, with n = 1, 2, 3, 4, 8, 10, 16, 18, 24, 32 and 36 by means of first-principles density functional theory calculations. A detailed analysis from the local density of states has shown that adsorbed OH groups can induce dangling bonds in specific carbon atoms around the adsorption site. This increases the tendency to form polyhydroxylated fullerenes (fullerenols). The structural stability is analyzed in terms of the calculated formation enthalpy of each species. Also, a careful examination of the electron density of states for different fullerenols shows the possibility of synthesizing single molecules with tunable optical properties.
Nanotechnology 09/2008; 19(36):365703. · 3.98 Impact Factor
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ABSTRACT: We have investigated, using first-principles calculations, the energetic stability and structural properties of antisites, vacancies and substitutional carbon defects in a boron nitride monolayer. We have found that the incorporation of a carbon atom substituting for one boron atom, in an N-rich growth condition, or a nitrogen atom, in a B-rich medium, lowers the formation energy, as compared to antisites and vacancy defects. We also verify that defects, inducing an excess of nitrogen or boron, such as N(B) and B(N), are more stable in its reverse atmosphere, i.e. N(B) is more stable in a B-rich growth medium, while B(N) is more stable in a N-rich condition. In addition we have found that the formation energy of a C(N), in a N-rich medium, and C(B) in a B-rich medium, present formation energies comparable to those of the vacancies, V(N) and V(B), respectively.
Nanotechnology 12/2007; 18(49):495707. · 3.98 Impact Factor
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ABSTRACT: We examine the electronic properties of the hydrated C60 fullerene under ambient conditions using a sequential Monte Carlo/density functional theory scheme. In this procedure, the average electronic properties of the first hydration shell of C60 equilibrate for ca. 40 uncorrelated configurations of the fullerene aqueous solution. We obtain a systematic red-shift of 0.8 eV in the band gap of the hydrated system, which is mainly attributed to the thermal fluctuations of the aqueous environment.
Nano Letters 07/2007; 7(6):1526-31. · 13.20 Impact Factor
