Browsing by Subject "Honeycomb structures"

Now showing 1 - 4 of 4

Open Access
Development of an innovative sandwich composite material for protection of lower limb against landmine explosion: mechanical leg test results
(SAGE Publications Ltd, 2017) Karahan, M.; Karahan, E. A.
This paper includes results of the blast tests which were performed with the aim of comparing the energy absorption and protection efficiency of protective boots with different sole configurations. Tests were performed on a mechanical leg model vestured with protective boots. Load and three axis acceleration values were measured during the blast tests to determine the protection efficiency of boot samples. Herewith, it was understood that merely a monolithic composite layer used in a sole does not provide protection, whereas compressible metallic honeycomb material-based sandwich composites demonstrate better energy absorption. With the innovative sandwich composite material developed in this study, energy absorption was increased by 209% in comparison to monolithic composites. © 2016, © The Author(s) 2016.
Open Access
Evolution of the Hofstadter butterfly in a tunable optical lattice
(American Physical Society, 2015) Yllmaz, F.; Ünal, F. N.; Oktel, M. O.
Recent advances in realizing artificial gauge fields on optical lattices promise experimental detection of topologically nontrivial energy spectra. Self-similar fractal energy structures generally known as Hofstadter butterflies depend sensitively on the geometry of the underlying lattice, as well as the applied magnetic field. The recent demonstration of an adjustable lattice geometry [L. Tarruell, D. Greif, T. Uehlinger, G. Jotzu, and T. Esslinger, Nature (London) 483, 302 (2012)NATUAS0028-083610.1038/nature10871] presents a unique opportunity to study this dependence. In this paper, we calculate the Hofstadter butterflies that can be obtained in such an adjustable lattice and find three qualitatively different regimes. We show that the existence of Dirac points at zero magnetic field does not imply the topological equivalence of spectra at finite field. As the real-space structure evolves from the checkerboard lattice to the honeycomb lattice, two square-lattice Hofstadter butterflies merge to form a honeycomb lattice butterfly. This merging is topologically nontrivial, as it is accomplished by sequential closings of gaps. Ensuing Chern number transfer between the bands can be probed with the adjustable lattice experiments. We also calculate the Chern numbers of the gaps for qualitatively different spectra and discuss the evolution of topological properties with underlying lattice geometry.
Open Access
Modulation of electronic properties in laterally and commensurately repeating graphene and boron nitride composite nanostructures
(American Chemical Society, 2015) Özçelik, V. O.; Durgun, Engin; Çıracı, Salim
Graphene and hexagonal boron nitride (h-BN) nanoribbons of diverse widths and edge geometries are laterally repeated to form commensurate, single-layer, hybrid honeycomb structures. The resulting composite materials appear as continuous, one atom thick stripes of graphene and BN having the average mechanical properties of constituent structures. However, depending on the widths of constituent stripes they can be metal or semiconductor with band gaps in the energy range of the visible light. These two-dimensional (2D) composite materials allow strong dimensionality in electrical conductivity and undergo transition from 2D to one-dimensional (1D) metal in a 2D medium, resulting in multichannel narrow conductors. As for the composite ribbons, such as one dielectric BN stripe placed between two graphene stripes with bare zigzag edges, charge separation of opposite polarity is possible under applied electric field and they exhibit resonant tunneling effects at nanoscale. Graphene/BN composite materials also form stable single-wall nanotubes with zigzag or armchair geometries.
Open Access
Two-and one-dimensional honeycomb structures of silicon and germanium
(American Physical Society, 2009) Cahangirov, S.; Topsakal, M.; Aktürk, E.; Şahin, H.; Çıracı, Salim
First-principles calculations of structure optimization, phonon modes, and finite temperature molecular dynamics predict that silicon and germanium can have stable, two-dimensional, low-buckled, honeycomb structures. Similar to graphene, these puckered structures are ambipolar and their charge carriers can behave like a massless Dirac fermion due to their π and π* bands which are crossed linearly at the Fermi level. In addition to these fundamental properties, bare and hydrogen passivated nanoribbons of Si and Ge show remarkable electronic and magnetic properties, which are size and orientation dependent. These properties offer interesting alternatives for the engineering of diverse nanodevices.