Focused electron beam irradiation has been used to create mono and divacancies in graphene within a defined area, which then act as trap sites for mobile Fe atoms initially resident on the graphene surface. Aberration-corrected transmission electron microscopy at 80 kV has been used to study the real time dynamics of Fe atoms filling the vacancy sites in graphene with atomic resolution. We find that the incorporation of a dopant atom results in pronounced displacements of the surrounding carbon atoms of up to 0.5 A, which is in good agreement with density functional theory calculations. Once incorporated into the graphene lattice, Fe atoms can transition to adjacent lattice positions and reversibly switch their bonding between four and three nearest neighbors. The C atoms adjacent to the Fe atoms are found to be more susceptible to Stone-Wales type bond rotations with these bond rotations associated with changes in the dopant bonding configuration. These results demonstrate the use of controlled electron ...

Dynamics of single Fe atoms in graphene vacancies.

Using first-principles calculations within density functional theory, we investigate the electronic and chemical properties of a single-layer MoS(2) adsorbed on Ir(111), Pd(111), or Ru(0001), three representative transition metal substrates having varying work functions but each with minimal lattice mismatch with the MoS(2) overlayer. We find that, for each of the metal substrates, the contact nature is of Schottky-barrier type, and the dependence of the barrier height on the work function exhibits a partial Fermi-level pinning picture. Using hydrogen adsorption as a testing example, we further demonstrate that the introduction of a metal substrate can substantially alter the chemical reactivity of the adsorbed MoS(2) layer. The enhanced binding of hydrogen, by as much as ~0.4 eV, is attributed in part to a stronger H-S coupling enabled by the transferred charge from the substrate to the MoS(2) overlayer, and in part to a stronger MoS(2)-metal interface by the hydrogen adsorption. These findings may prove to be instrumental in future design of MoS(2)-based electronics, as well as in exploring novel catalysts for hydrogen production and related chemical processes.

Tuning the Electronic and Chemical Properties of Monolayer MoS$_2$ Adsorbed on Transition Metal Substrates

We demonstrate enhanced light funneling through subwavelength features at optical frequencies using an epsilon near zero (ENZ) material layer. Transmission through a subwavelength slit filled with the epsilon near zero material is characterized.

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Funneling Light Through a Subwavelength Aperture Using Epsilon Near Zero Materials

Magnetic properties of a ferrimagnetic core/shell nanocube Ising model: A Monte Carlo simulation study

Hysteresis behaviors in a cylindrical Ising nanowire

The method of variational cumulant expansion (VCE) on the Ising model is applied to investigate phase transitions in magnetic alloy nano-particles, in which a random site distribution of component atoms is assumed. By introducing the effect exchange constant, it is shown numerically that nano-particles can be treated the same way as bulk materials. The Curie temperature and the Neel temperature of binary magnetic nano-particles with cubic lattices are calculated. It is found that both the Curie temperature and the Neel temperature decrease with decreasing size of the nano-particle. Phase diagrams of binary alloy nano-particles are investigated for variable doping concentration and the results are discussed. As the nano-particle size grows larger, the critical point approaches that of a bulk. On the other hand, the tri-critical point is independent of the nano-particle size and is always the same as that of the bulk.

Phase Diagram of Ising Nano-Particles with Cubic Structures

Theoretical investigations of magnetic properties of ferromagnetic single-walled nanotubes

Critical Point of Magnetic Nanostructures in the Ising Model

The adsorption of oxygen atoms on the Ti(0001) surface is investigated by the use of ab initio total-energy density-functional methods within the generalized gradient approximation. Two kinds of supercell model (a single-layer and a multiple-layer adsorption model) are designed to study the preference of occupation sites for oxygen atoms. In the single-layer adsorption model, the oxygen adatoms are restricted in the same adsorption layer. In the multiple-layer adsorption model, the adsorbed oxygen atoms occupy sites in different adsorption layers at the same time. Our calculated results show that the surface face-centred cubic (SFCC) sites are the most favourable sites for oxygen atoms to occupy when the oxygen coverage is 0.25 monolayer (ML); however, the system with one oxygen adatom occupying the SFCC sites and the other one occupying the octahedral sites between second and third Ti layers (Octa(2, 3)) is the most stable configuration when the oxygen coverage is 0.50 ML. As the oxygen coverage is increased to 1.0 ML, each of the oxygen atoms prefers occupying the SFCC and octahedral sites such as Octa(2, 3), Octa(4, 5) and Octa(6, 7) in the alternate layers, respectively. It can be found that there are strong repulsive interactions between the adsorbed oxygen atoms when they occupy adjacent interstitial sites. Our calculated results of the work functions and the total density of states with the multiple-layer adsorption model are in good agreement with experimental results of work function change and ultraviolet photoelectron spectroscopy. It should be noticed that the multiple-layer adsorption model must be taken into account for oxygen adsorption on the Ti(0001) surface.

https://iopscience.iop.org/article/10.1088/0953-8984/19/22/226004/pdf

Ab initio study of oxygen adsorption on the Ti(0001) surface

We calculate the lifetime distribution function of an assembly of polarized atoms in two-dimensional (2D) photonic crystals (PCs) at different polarization orientations of atomic dipole moments. We reveal a switching effect of atomic spontaneous emission (SE) and find a significant change of atomic lifetime, up to a factor of 33, by tuning the polarized orientation of the atoms. These observations suggest that the tuning of the polarized orientation of atoms provides a new way for the effective control of atomic SE processes in 2D PCs.

Yun-Song Zhou

Papers

Phase Diagram of Ising Nano-Particles with Cubic Structures

Theoretical investigations of magnetic properties of ferromagnetic single-walled nanotubes

Critical Point of Magnetic Nanostructures in the Ising Model

Ab initio study of oxygen adsorption on the Ti(0001) surface

Switching Control of Spontaneous Emission by Polarized Atoms in Two-Dimensional Photonic Crystals