Schottky barrier lowering due to interface states in 2D heterophase devices

The Schottky barrier of a metal-semiconductor junction is one of the key quantities affecting the charge transport in a transistor. The Schottky barrier height depends on several factors, such as work function difference, local atomic configuration in the interface, and impurity doping. We show that also the presence of interface states at 2D metal-semiconductor junctions can give rise to a large renormalization of the effective Schottky barrier determined from the temperature dependence of the current. We investigate the charge transport in n- and p-doped monolayer MoTe$_2$ 1T'-1H junctions using ab-initio quantum transport calculations. The Schottky barriers are extracted both from the projected density of states and the transmission spectrum, and by simulating the IT-characteristic and applying the thermionic emission model. We find interface states originating from the metallic 1T' phase rather than the semiconducting 1H phase in contrast to the phenomenon of Fermi level pinning. Furthermore, we find that these interface states mediate large tunneling currents which dominates the charge transport and can lower the effective barrier to a value of only 55 meV.Comment: 6 figure

The surface chemistry of metal-oxygen interactions: a first-principles study of O:Rh(110)

We report on a computational study of the clean and oxygen-covered Rh(110) surface, based on density-functional theory within the local-density approximation. We have used plane-wave basis sets and Vanderbilt ultra-soft pseudopotentials. For the clean surface, we present results for the equilibrium structure, surface energy, and surface stress of the unreconstructed and $(1\times 2)$ reconstructed structures. For the oxygen-covered surface we have performed a geometry optimization at $1\over 2$, 1, and 2 monolayer oxygen coverages, and we present results for the equilibrium configurations, workfunctions and oxygen chemisorption energies. At half monolayer coverage, we find that oxygen induces a $(1\times 2)$ reconstruction of the surface, while at one monolayer coverage the chemisorption energy is highest for the unreconstructed surface. Our results are rationalized by a simple tight-binding description of the interaction between the O$-2p$ orbitals and the metal valence states. The resulting bonds are stronger when established with low coordinated metal atoms, and give rise to an effective adsorbate-adsorbate interaction when two oxygen atoms are bound to the same metal orbital.Comment: 23 pages, REVTEX, 8 figure

Spontaneous breaking of time-reversal symmetry at the edges of 1T' monolayer transition metal dichalcogenides

Using density functional theory calculations and the Greens's function formalism, we report the existence of magnetic edge states with a non-collinear spin texture present on different edges of the 1T' phase of the three monolayer transition metal dichalcogenides (TMDs): MoS$_2$, MoTe$_2$ and WTe$_2$. The magnetic states are gapless and accompanied by a spontaneous breaking of the time-reversal symmetry. This may have an impact on the prospects of utilizing WTe$_2$ as a quantum spin Hall insulator. It has previously been suggested that the topologically protected edge states of the 1T' TMDs could be switched off by applying a perpendicular electric field. We confirm with fully self-consistent DFT calculations, that the topological edge states can be switched off. The investigated magnetic edge states are seen to be robust and remains gapless when applying a field.Comment: 7 pages, 7 figure

Simple model of stacking-fault energies

A simple model for the energetics of stacking faults in fcc metals is constructed. The model contains third-nearest-neighbor pairwise interactions and a term involving the fourth moment of the electronic density of states. The model is in excellent agreement with recently published local-density calculations of stacking-fault energies, and gives a simple way of understanding the calculated energy contributions from the different atomic layers in the stacking-fault region. The two parameters in the model describe the relative energy contributions of the s and d electrons in the noble and transition metals, and thereby explain the pronounced differences in energetics in these two classes of metals. The model is discussed in the framework of the effective-medium theory where it is possible to find a functional form for the pair potential and relate the contribution associated with the fourth moment of the density of states with the so-called electron correction energy

Chemical composition of aquatic dissolved organic matter in five boreal forest catchments sampled in spring and fall seasons

The chemical composition and carbon isotope signature of aquatic dissolved organic matter (DOM) in five boreal forest catchments in Scandinavia were investigated. The DOM was isolated during spring and fall seasons using a reverse osmosis technique. The DOM samples were analyzed by elemental analysis, FT-IR, solid-state CP-MAS 13C-NMR, and C-1s NEXAFS spectroscopy. In addition, the relative abundance of carbon isotopes (12C, 13C, 14C) in the samples was measured. There were no significant differences in the chemical composition or carbon isotope signature of the DOM sampled in spring and fall seasons. Also, differences in DOM composition between the five catchments were minor. Compared to reference peat fulvic and humic acids, all DOM samples were richer in O-alkyl carbon and contained less aromatic and phenolic carbon, as shown by FT-IR, 13C-NMR, and C-1s NEXAFS spectroscopy. The DOM was clearly enriched in 14C relative to the NBS oxalic acid standard of 1950, indicating that the aquatic DOM contained considerable amounts of organic carbon younger than about 50years. The weight-based C:N ratios of 31 ± 6 and the $$\delta^{13}\hbox{C}$$ values of -29\pm2\permille indicate that the isolated DOM is of terrestrial rather than aquatic origin. We conclude that young, hydrophilic carbon compounds of terrestrial origin are predominant in the samples investigated, and that the composition of the aquatic DOM in the studied boreal forest catchments is rather stable during low to intermediate flow condition

Ablation of the Locus Coeruleus Increases Oxidative Stress in Tg-2576 Transgenic but Not Wild-Type Mice

Mice transgenic for production of excessive or mutant forms of beta-amyloid differ from patients with Alzheimer's disease in the degree of inflammation, oxidative damage, and alteration of intermediary metabolism, as well as the paucity or absence of neuronal atrophy and cognitive impairment. Previous observers have suggested that differences in inflammatory response reflect a discrepancy in the state of the locus coeruleus (LC), loss of which is an early change in Alzheimer's disease but which is preserved in the transgenic mice. In this paper, we extend these observations by examining the effects of the LC on markers of oxidative stress and intermediary metabolism. We compare four groups: wild-type or Tg2576 Aβ transgenic mice injected with DSP4 or vehicle. Of greatest interest were metabolites different between ablated and intact transgenics, but not between ablated and intact wild-type animals. The Tg2576_DSP4 mice were distinguished from the other three groups by oxidative stress and altered energy metabolism. These observations provide further support for the hypothesis that Tg2576 Aβ transgenic mice with this ablation may be a more congruent model of Alzheimer's disease than are transgenics with an intact LC