Spintronics holds the promise for future information technologies. Devices based on manipulation of spin are most likely to replace the current silicon complementary metal‐oxide semiconductor devices that are based on manipulation of charge. The challenge is to identify or design materials that can be used to generate, detect, and manipulate spin. Since the successful isolation of graphene and other two‐dimensional (2D) materials, there has been a strong focus on spintronics based on 2D materials due to their attractive properties, and much progress has been made, both theoretically and experimentally. Here, we summarize recent developments in spintronics based on 2D materials. We focus mainly on materials of truly 2D nature, that is, atomic crystal layers such as graphene, phosphorene, monolayer transition metal dichalcogenides, and others, but also highlight current research foci in heterostructures or interfaces. In particular, we emphasize roles played by computation based on first‐principles methods which has contributed significantly in the designs of spintronic materials and devices. We also highlight challenges and suggest possible directions for further studies. WIREs Comput Mol Sci 2017, 7:e1313. doi: 10.1002/wcms.1313 This article is categorized under: Structure and Mechanism > Computational Materials Science Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory

Coarsening (i.e., ripening) of single-atom-high, metal homoepitaxial islands provides a useful window on the mechanism and kinetics of mass transport at metal surfaces. This article focuses on this type of coarsening on the surfaces of coinage metals (Cu, Ag, Au), both clean and with an adsorbed chalcogen (O, S) present. For the clean surfaces, three aspects are summarized: (1) the balance between the two major mechanisms-Ostwald ripening (the most commonly anticipated mechanism) and Smoluchowski ripening-and how that balance depends on island size; (2) the nature of the mass transport agents, which are metal adatoms in almost all known cases; and (3) the dependence of the ripening kinetics on surface crystallography. Ripening rates are in the order (110)>(111)>(100), a feature that can be rationalized in terms of the energetics of key processes. This discussion of behavior on the clean surfaces establishes a background for understanding why coarsening can be accelerated by adsorbates. Evidence that O and S accelerate mass transport on Ag, Cu, and Au surfaces is then reviewed. The most detailed information is available for two specific systems, S/Ag (111) and S/Cu(111). Here, metal-chalcogen clusters are clearly responsible for accelerated coarsening. This conclusion rests partly on deductive reasoning, partly on calculations of key energetic quantities for the clusters (compared with quantities for the clean surfaces), and partly on direct experimental observations. In these two systems, it appears that the adsorbate, S, must first decorate-and, in fact, saturate-the edges of metal islands and steps, and then build up at least slightly in coverage on the terraces before acceleration begins. Acceleration can occur at coverages as low as a few thousandths to a few hundredths of a monolayer. Despite the significant recent advances in our understanding of these systems, many open questions remain. Among them is the identification of the agents of mass transport on crystallographically different surfaces e.g., 111, 110, and 100. Articles you may be interested in Transition metal atoms pathways on rutile TiO2 (110) surface: Distribution of Ti3+ states and evidence of enhanced peripheral charge accumulation Vibrational lifetimes of cyanide and carbon monoxide on noble and transition metal surfaces Coarsening i.e., ripening of single-atom-high, metal homoepitaxial islands provides a useful window on the mechanism and kinetics of mass transport at metal surfaces. This article focuses on this type of coarsening on the surfaces of coinage metals Cu, Ag, Au, both clean and with an adsorbed chalcogen O, S present. For the clean surfaces, three aspects are summarized: 1 the balance between the two major mechanisms-Ostwald ripening the most commonly anticipated mechanism and Smoluchowski ripening-and how that balance depends on island size; 2 the nature of the mass transport agents, which are metal adatoms in almost all known cases; and 3 the dependence of the ripening kinetics on surface crystallography. Ripening rates are i...

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While direct bandgap monolayer 2D transition metal dichalcogenides (TMDs) have emerged as an important optoelectronic material due to strong light−matter interactions, their multilayer counterparts exhibit an indirect bandgap resulting in poor photon emission quantum yield. We report strong direct bandgap-like photoluminescence at ∼1.9 eV from multilayer MoS 2 grown on SrTiO 3 , whose intensity is significantly higher than that observed in multilayer MoS 2 / SiO 2 . Using high-resolution electron microscopy we observe interlayer twist and >8% increase in the van der Waals gap, which leads to weaker interlayer coupling. This affects the evolution of the band structure in multilayer MoS 2 as probed by transient absorption spectroscopy, causing higher photo carrier recombination at the direct gap. Our results provide a platform that could enable multilayer TMDs for robust optical device applications.

Using first-principles calculations, we have systematically investigated the magnetic properties of Mg-doped AlN (1 0 1 0) and (0 0 0 1) surfaces. Both the polar and non-polar surfaces are found to be magnetic and the magnetic moments are mainly due to spin polarized 2p orbitals of surface N atoms surrounding Mg. The splitting of energy levels in both cases favours charge hopping between the minority spin states of N 2p orbitals, which leads to a stable ferromagnetic ground state. However, the range of magnetic coupling and the stability of the ferromagnetic state differ between the polar and non-polar surfaces and are dependent on the nature of localization of the defect states. The ferromagnetic state in a Mg-doped reconstructed (0 0 0 1) surface is more stable than in a Mg-doped AlN (1 0 1 0) surface.

A thorough investigation of the structural parameters of micromechanically exfoliated multilayer WSe2 flakes was undertaken between 400 K to 110 K. Crystal structure of WSe2 remains in the trigonal prismatic structure in this temperature range, however, with a clear difference in the temperature dependence of the in-plane a, and the out-of-plane c, lattice parameters. The linear coefficients of thermal expansion of a and c are 5.132 × 10−6/K and 8.105 × 10−6/K, respectively. The temperature dependence of the unit-cell volume is analyzed using zero-pressure equation-of-state which yielded the Debye temperature of the WSe2 to be 160 K. Following the temperature dependence of the W-Se and W-W bond distances, a nonlinear behavior is observed in the former in contrast to a rather regular behavior of the later. This significant difference in the temperature dependence of the a and c lattice parameters can have consequences in the macroscopic physical properties of the system. A good correlation between the temperature dependence of the W-Se bond distance and Raman E2g1 mode has been observed.

The surface magnetism of Mg-doped AlN is investigated by the first-principles method. All studied surfaces, whether they are non-polar, polar or semi-polar, favor a ferromagnetic ground state, which is stabilized by the virtual charge hopping between partially filled states of MgN clusters. However, the stability of ferromagnetism varies from surface to surface owing to the interplay among the localization of magnetic moments, energy level splitting, and sp–p interaction between MgN clusters. Among the various surfaces being studied, the Mg-doped AlN surface is expected to be ferromagnetic at room temperature as a result of its strong localization of defect states.

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