Thermal conductance of graphene nanoribbons (GNRs) with the width varying
from 0.5 to 35 nm is systematically investigated using nonequilibrium Green's
function method. Anisotropic thermal conductance is observed with the room
temperature thermal conductance of zigzag GNRs up to ~ 30% larger than that of
armchair GNRs. At room temperature, the anisotropy is found to disappear until
the width is larger than 100 nm. This intrinsic anisotropy originate from
different boundary condition at ribbon edges, and can be used to tune thermal
conductance, which have important implications for the applications of GNRs in
nanoelectronics and thermoelectricity.Comment: 4 pages, 3 figure
Here we present a shape recovery phenomenon of Pt-Ni bimetallic nanocrystals that is unequivocally attributed to the defect effects. High-resolution electron microscopy revealed the overall process of conversion from concave octahedral Pt3Ni to regular octahedral Pt3Ni@Ni upon Ni deposition. Further experiments and theoretical investigations indicated that the intrinsic defect-dominated growth mechanism allows the site-selective nucleation of a third metal around the defects to achieve the sophisticated design of trimetallic Pt3Ni@M core-shell structures (M = Au, Ag, Cu, Rh). Consideration of geometrical and electronic effects indicated that trimetallic atomic steps in Pt3Ni@M could serve as reactive sites to significantly improve the catalytic performance, and this was corroborated by several model reactions. The synthesis strategy based on our work paves the way for the atomic-level design of trimetallic catalysts.
Spin caloritronics refers to generating spin current by thermal gradient. Here we report a theoretical study demonstrating giant spin caloritronic effects in a new class of materials, called spin semiconductors, which are characterized with a 'spin gap', the energy gap between spin-up and -down channels. Generally, spin Seebeck coefficient (Ss) is shown to increase linearly with the spin gap. Specifically, unprecedented large Ss ∼ 3.4 mV/K and spin figure of merit, ZsT ∼ 119 were found in spin-semiconducting graphene nanoribbons (GNRs) with sawtooth (ST) zigzag edges, based on first-principles calculations. Such giant spin caloritronic effects are shown to originate from a large spin gap of ST GNRs, in addition to two other spin-independent features of large band gap and narrow band width which are commonly known for good thermoelectric materials. Our studies suggest that spin-semiconducting nanostructures, such as ST GNRs, are promising candidates for room-temperature spin caloritronics with high efficiency.
We report theoretical analysis of thermal-spin and thermoelectric properties of noncollinear spin-valves driven by a high frequency AC voltage bias. The spin-valve consists of two ferromagnetic contacts sandwiching a single-level or multi-level quantum dot (QD). A general formulation for the time-averaged thermal-spin and thermoelectric properties of spin-valves is derived within the nonequilibrium Green's function theory, which provides a starting point for further numerical calculations of these properties. Numerical results of a spinvalve having a spin-degenerate single-level QD are given as an example. The AC bias induces various photonassisted transmission peaks which can greatly enhance the Seebeck coefficients and the figures of merit, and offer a new possibility to tune both the spin-dependent and normal thermoelectric properties of the spin-valve. Details of these properties and how they depend on the non-collinearity of the spin-valve, magnetic polarization, temperature, AC bias, and other control parameters are reported. A particularly interesting result is the opposite dependency of the thermoelectric properties on the magnetic polarization and non-collinearity for contacts with or without spin accumulation.2
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.