Ivan Rungger

Possible doping strategies for MoS2 monolayers: An ab initio study

Density functional theory is used to systematically study the electronic and magnetic properties of doped MoS

Origin of the n-type and p-type conductivity of MoS2 monolayers on a SiO2 substrate

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Spin-Valve Effect in NiFe/MoS2/NiFe Junctions

monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS

Investigation of the conducting properties of a photoswitching dithienylethene molecule.

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Constrained-DFT method for accurate energy-level alignment of metal/molecule interfaces

conduction band, making the system n-type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n- and p-type conductivity, depending on the charge polarity of the adsorbed species.

Efficient spin injection and giant magnetoresistance in Fe/MoS2/Fe junctions

role, since the conduction band top and the valence band minimum of MoS2 are located approximately in the middle of the SiO2 band-gap. However, if Na impurities and O dangling bonds are introduced at the SiO2 surface, these lead to localized states, which modulate the conductivity of the MoS2 monolayer from n- to p-type. Our results show that the conductive properties of MoS2 deposited on SiO2 are mainly determined by the detailed structure of the MoS2/SiO2 interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS2-based devices. PACS numbers:

Finite-bias electronic transport of molecules in a water solution

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have been recently proposed as appealing candidate materials for spintronic applications owing to their distinctive atomic crystal structure and exotic physical properties arising from the large bonding anisotropy. Here we introduce the first MoS2-based spin-valves that employ monolayer MoS2 as the nonmagnetic spacer. In contrast with what is expected from the semiconducting band-structure of MoS2, the vertically sandwiched-MoS2 layers exhibit metallic behavior. This originates from their strong hybridization with the Ni and Fe atoms of the Permalloy (Py) electrode. The spin-valve effect is observed up to 240 K, with the highest magnetoresistance (MR) up to 0.73% at low temperatures. The experimental work is accompanied by the first principle electron transport calculations, which reveal an MR of ∼9% for an ideal Py/MoS2/Py junction. Our results clearly identify TMDs as a promising spacer compound in magnetic tunnel junctions and may open a new avenue for the TMDs-based spintronic applications.

Structural Origins of Conductance Fluctuations in Gold-Thiolate Molecular Transport Junctions.

Photoswitching molecules are attractive candidates as organic materials for optoelectronics applications because light impulses can switch them between states with different conducting characteristics. Here, we report a fully self-consistent density functional theory calculation of the electron transport properties of photoswitching dithienylethene attached to Au leads in both the open and closed conformations. The molecule is found to be a good conductor in both conformations, with the low-bias current for the closed one being about 20 times larger than that of the open. Importantly, the current-voltage characteristics away from the linear response are largely determined by molecular orbital rehybridization in an electric field, in close analogy to what happens for Mn(12) molecules. However, in the case of dithienylethene attached to Au, such a mechanism is effective also in conditions of strong electronic coupling to the electrodes. This makes the dithienylethene family an intriguing materials platform for constructing highly conducting organic optoelectronics switches.

Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions

We present a computational scheme for extracting the energy-level alignment of a metal/molecule interface, based on constrained density functional theory and local exchange and correlation functionals. The method, appliedheretobenzeneonLi(100),allowsustoevaluatecharge-transferenergies,aswellasthespatialdistribution of the image charge induced on the metal surface. We systematically study the energies for charge transfer from the molecule to the substrate as function of the molecule-substrate distance, and investigate the effects arising from image-charge confinement and local charge neutrality violation. For benzene on Li(100) we find that the image-charge plane is located at about 1.8 ˚ A above the Li surface, and that our calculated charge-transfer energies compare perfectly with those obtained with a classical electrostatic model having the image plane located at the same position. The methodology outlined here can be applied to study any metal/organic interface in the weak coupling limit at the computational cost of a total energy calculation. Most importantly, as the scheme is based on total energies and not on correcting the Kohn-Sham quasiparticle spectrum, accurate results can be obtained with local/semilocal exchange and correlation functionals. This enables a systematic approach to convergence.

Ab initio study of the magnetostructural properties of MnAs

We demonstrate giant magnetoresistance in