17 research outputs found
Mechanical properties of Graphene Nanoribbons
Herein, we investigate the structural, electronic and mechanical properties
of zigzag graphene nanoribbons upon the presence of stress applying Density
Functional Theory within the GGA-PBE approximation. The uniaxial stress is
applied along the periodic direction, allowing a unitary deformation in the
range of +/- 0.02%. The mechanical properties show a linear-response within
that range while the non-linear dependence is found for higher strain. The most
relevant results indicate that Young's modulus is considerable higher than
those determined for graphene and carbon nanotubes. The geometrical
reconstruction of the C-C bonds at the edges hardness the nanostructure.
Electronic structure features are not sensitive to strain in this linear
elastic regime, being an additional promise for the using of carbon
nanostructures in nano-electronic devices in the near future.Comment: 30 pages. J. Phys.: Condens. Matter (accepted
Age and correlation of the Jurassic Tabanos Formation at Chacay Melehué and other localities of Neuquén and Mendoza
La sección jurásica aflorante en las inmediaciones del arroyo Chacay Melehué. en el extremo sur de la Cordillera del Viento, fue descripta someramente por primera vez por Keídel en 1910. Desde entonces, y especialmente en las tres últimas décadas, ha sido investigada por otros geólogos y paleontólogos, convirtiéndose en una de las localidades clásicas del Jurásico argentino. Pese a los numerosos estudios efectuados aún subsisten importantes diferencias de opinión en cuanto a la asignación formaclonal y ubicación cronológica de las unidades litoestratigráílcas comprendidas entre el Caloviano Inferior y el Tithoniano.Facultad de Ciencias Naturales y Muse
Ferromagnetism in graphene nanoribbons: split versus oxidative unzipped ribbons
Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons
(GNRs), and (b) oxidative unzipped and chemically converted graphene
nanoribbons (CCGNRs) were investigated for their magnetic properties using the
combination of static magnetization and electron spin resonance measurements.
The two types of ribbons possess remarkably different magnetic properties.
While the low temperature ferromagnet-like feature is observed in both types of
ribbons, such room temperature feature persists only in potassium-split
ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a
'positive exchange bias'. Electron spin resonance measurements infer that the
carbon related defects may responsible for the observed magnetic behaviour in
both types of ribbons. Furthermore, proton hyperfine coupling strength has been
obtained from hyperfine sublevel correlation experiments performed on the GNRs.
Electron spin resonance provides no indications for the presence of potassium
(cluster) related signals, emphasizing the intrinsic magnetic nature of the
ribbons. Our combined experimental results may infer the coexistence of
ferromagnetic clusters with anti-ferromagnetic regions leading to disordered
magnetic phase. We discuss the origin of the observed contrast in the magnetic
behaviours of these two types of ribbons
Crystal structure and absolute configuration of (3aS,4S,5R,7aR)-2,2,7-trimethyl-3a,4,5,7a-tetrahydro-1,3-benzodioxole-4,5-diol
The absolute configuration of the title compound, C10H16O4, determined as 3aS,4S,5R,7aR on the basis of the synthetic pathway, was confirmed by X-ray diffraction. The molecule contains a five- and a six-membered ring that adopt twisted and envelope conformations, respectively. The dihedral angle between the mean planes of the rings is 76.80 (11)° as a result of their cis-fusion. In the crystal, molecules are linked by two pairs of O—H...O hydrogen bonds, forming chains along [010]. These chains are further connected by weaker C—H...O interactions along [100], creating (001) sheets that interact only by weak van der Waals forces