ABSTRACT
Dispersion-corrected density functional theory was used to investigate structures consisting of a stanene layer sandwiched between atomically-thin boron nitride and graphene. The parameters controlling the mirror symmetry, lattice rotation and stacking sequences were varied systematically to generate fifteen candidate trilayers. Two types of structural buckling occur in the heterostructures depending on whether the lattice vectors are co-aligned or non-collinear. The configurations with the honeycomb lattices rotated by π/6 with respect to the stanene generally have lower binding energy. In the majority of the trilayers, the electronic structures deviate strongly from the band structures of the isolated components. The boron nitride/stanene/boron nitride structure is identified as a special case where stanene has an electronic structure that is not perturbed by interlayer interactions and resembles the ideal monolayer form. For the other candidate structures, however, interlayer interactions drive significant modifications in the electronic structure thus indicating emergent features that go beyond the pure van der Waals description.
ABSTRACT
Epitaxial growth of stanene monolayers on graphene substrates is an attractive synthesis route for atomically-thin electronic components, however, it remains unclear how such composites will tolerate lattice strain and exposure to ambient atmosphere. Using density functional theory, we identified several epitaxial configurations for the stanene-graphene bilayer system and determined the effect of strain and water adsorption. In addition to previously reported co-aligned bilayers, we identify a second family of low energy structures involving rotation of one layer by thirty degrees. The band structures of the rotated configurations exhibit a fully metallic interface, whereas the co-aligned structures are poised at the transition between semimetallic and semiconductor characteristics. In general, the electronic states are directly correlated with differences in the buckling parameter of the tin layer assigned to the competition between sp2 and sp3 hybridization schemes. This can be controlled by strain to yield a metal-insulator transition in special circumstances. For the equilibrium structure, H2O preferentially adsorbs on the stanene layer, and the system remains metallic with a mixture of Dirac and parabolic bands at the Fermi surface.
ABSTRACT
Chemisorption of muonium onto the surface of gold nanoparticles has been observed. Muonium (µ+e-), a light hydrogen-like atom, reacts chemically with uncapped 7 nm gold nanoparticles embedded in mesoporous silica (SBA-15) with a strong temperature-dependent rate. The addition rate is fast enough to allow coherent spin transfer into a diamagnetic muon state on the nanoparticle surface. The muon is well established as a sensitive probe of static or slowly fluctuating magnetic fields in bulk matter. These results represent the first muon spin rotation signal on a nanoparticle surface or any metallic surface. Only weak magnetic effects are seen on the surface of these Au nanoparticles consistent with Pauli paramagnetism.
ABSTRACT
By measuring the prototypical antiferromagnet α-Fe_{2}O_{3}, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted ^{8}Li^{+} ions detected with ß-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α-Fe_{2}O_{3} occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T_{1} relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε=11±1 nm, closely matching the finite-size thresholds of hematite nanostructures.
