Influence of interface mixing on the magnetic properties of Ni/Pt multilayers

Motivated by existing experimental data, we study here the influence of interface mixing on the magnetic behavior of Ni-6/Pt-5(111) multilayers. In the present ab initio calculations the mixing, restricted to the interface layers, was simulated by ordered two-dimensional Ni-Pt lattices. Two different degrees of mixing of the components at the interface were considered-namely, 25% and 50%. The perfect interface was also calculated and for some of the systems orbital moments were obtained. We find that interface mixing explains rather well the observed magnetic moment profile for Ni sites. But even with the inclusion of orbital contributions, the theoretical results tend to underestimate the induced moment at the Pt sites found experimentally.661

Carbon nanotube with square cross-section: An ab initio investigation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Recently, Lagos et al. [Nat. Nanotechnol. 4, 149 (2009)] reported the discovery of the smallest possible silver square cross-section nanotube. A natural question is whether similar carbon nanotubes can exist. In this work we report ab initio results for the structural, stability, and electronic properties for such hypothetical structures. Our results show that stable (or at least metastable) structures are possible with metallic properties. They also show that these structures can be obtained by a direct interconversion from SWNT (2,2). Large finite cubanelike oligomers, topologically related to these new tubes, were also investigated. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3483237]13312Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Self-consistent electronic structure of Mo(001) and W(001) surfaces

We report results for the surface band structures of molybdenum and tungsten (001) surfaces by employing the surface version of the first-principles, self-consistent real-space linear muffin-tin orbital method in the atomic sphere approximation. The surface state dispersions as well as the spectral density of states were obtained employing the transfer matrix scheme. The resulting surface band structures are compared with recent experimental measurements at temperatures above the transition temperature, as well as theoretical self-consistent calculations.6115104171042

Adsorption configuration effects on the surface diffusion of large organic molecules: The case of Violet Lander

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Violet Lander (C108H104) is a large organic molecule that when deposited on Cu(110) surface exhibits lock-and-key like behavior [Otero et al., Nature Mater. 3, 779 (2004)]. In this work, we report a detailed fully atomistic molecular mechanics and molecular dynamics study of this phenomenon. Our results show that it has its physical basis on the interplay of the molecular hydrogens and the Cu(110) atomic spacing, which is a direct consequence of the matching between molecule and surface dimensions. This information could be used to find new molecules capable of displaying lock-and-key behavior with new potential applications in nanotechnology. (C) 2010 American Institute of Physics. [doi:10.1063/1.3512623]13322Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Design and Analysis of Nanotube-Based Memory Cells

In this paper, we proposed a nanoelectromechanical design as memory cells. A simple design contains a double-walled nanotube-based oscillator. Atomistic materials are deposed on the outer nanotube as electrodes. Once the WRITE voltages are applied on electrodes, the induced electromagnetic force can overcome the interlayer friction between the inner and outer tubes so that the oscillator can provide stable oscillations. The READ voltages are employed to indicate logic 0/1 states based on the position of the inner tube. A new continuum modeling is developed in this paper to analyze large models of the proposed nanoelectromechanical design. Our simulations demonstrate the mechanisms of the proposed design as both static and dynamic random memory cells

Surface and interface states in the Cu/V(110) structure

We present ab initio calculations of the electronic structure of copper multilayers on V(110) surface. The calculations were based on density-functional theory and the real-space linear muffin-tin orbital method in the atomic-sphere approximation was used. Surface and interface states were investigated using the Green-function based transfer-matrix method. The results shown a variety of electronic states along the main symmetry lines of the two-dimensional Brillouin zone, and the presence of surface and interface states was verified. Also, the existence of a binding state about 1.8 eV below the Fermi level is in good agreement with recent photoemission experiments, such state can be interpreted as a quantum-well state.651

Chaotic signature in the motion of coupled carbon nanotube oscillators

The motion of coupled oscillators based on multiwalled carbon nanotubes is studied using rigid-body dynamics simulations. The results show the existence of chaotic and regular behaviours for a given total energy, indicating the manifestation of chaos in nanoscaled mechanical systems based on carbon nanotube oscillators. Different regular motions are observed for different total energies, and they can be obtained by appropriately choosing the initial conditions. This possibility can allow the construction of multi-functional nano-devices based on multiwalled carbon nanotube oscillators.16458358

Structure and dynamics of carbon nanoscrolls

Carbon nanotube scrolls (CNSs) provide an interesting form of carbon that ideally consists of a single sheet of graphite that is spiral wrapped to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical actuators.4588188

Ordered phases of encapsulated diamondoids into carbon nanotubes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Diamondoids are hydrogen-terminated nanosized diamond fragments that are present in petroleum crude oil at low concentrations. These fragments are found as oligomers of the smallest diamondoid, adamantane (C10H16). Due to their small size, diamondoids can be encapsulated into carbon nanotubes to form linear arrangements. We have investigated the encapsulation of diamondoids into single walled carbon nanotubes with diameters between 1.0 and 2.2 nm using fully atomistic simulations. We performed classical molecular dynamics and energy minimizations calculations to determine the most stable configurations. We observed molecular ordered phases (e. g. double, triple, 4- and 5-stranded helices) for the encapsulation of adamantane, diamantane, and dihydroxy diamantane. Our results also indicate that the functionalization of diamantane with hydroxyl groups can lead to an improvement on the molecular packing factor when compared to non-functionalized compounds. Comparisons to hard-sphere models revealed differences, especially when more asymmetrical diamondoids were considered. For larger diamondoids (i.e., adamantane tetramers), we have not observed long-range ordering but only a tendency to form incomplete helical structures. Our calculations predict that thermally stable (at least up to room temperature) complex ordered phases of diamondoids can be formed through encapsulation into carbon nanotubes.2231Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UEMFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq