We achieve tunneling spin injection from Co into single layer graphene (SLG) using TiO2 seeded MgO barriers. A non-local magnetoresistance ({\Delta}RNL) of 130 {\Omega} is observed at room temperature, which the largest value in any material. Investigating {\Delta}RNL vs. SLG conductivity transparent to contact regimes demonstrates contrasting behaviors predicted by drift-diffusion theory transport. Furthermore, tunnel barriers reduce contact-induced relaxation and are therefore important...

Abstract In bulk and quantum-confined semiconductors, magneto-optical studies have historically played an essential role in determining the fundamental parameters of excitons (size, binding energy, spin, dimensionality so on). Here we report low-temperature polarized reflection spectroscopy atomically thin WS 2 MoS high magnetic fields to 65 T. Both A B exhibit similar Zeeman splittings approximately −230 μeV T −1 ( g -factor ≃−4), thereby quantifying valley effect monolayer transition-metal...

Hydrogen adatoms are shown to generate magnetic moments inside single layer graphene. Spin transport measurements on graphene spin valves exhibit a dip in the nonlocal signal as function of applied field, which is due scattering (relaxation) pure currents by exchange coupling moments. Furthermore, Hanle precession indicate presence an field generated The entire experiment including performed ultrahigh vacuum chamber, and characteristic signatures moment formation appear only after hydrogen...

We investigate the effects of transition metals (TM) on electronic doping and scattering in graphene using molecular-beam epitaxy combined with situ transport measurements. The room-temperature deposition TM onto produces clusters that dope $n$ type for all investigated (Ti, Fe, Pt). also find by exhibits different behavior compared to $1/r$ Coulomb scattering. At high coverage, Pt films are able produce is either or weakly $p$ type, which provides experimental evidence a strong interfacial...

Van der Waals layered materials, such as transition metal dichalcogenides (TMDs), are an exciting class of materials with weak interlayer bonding, which enables one to create so-called van heterostructures (vdWH). One promising attribute vdWH is the ability rotate layers at arbitrary azimuthal angles relative another. Recent work has shown that control twist angle between can have a dramatic effect on TMD properties, but been treated solely through use rigid-lattice moiré patterns. No atomic...

An emerging class of semiconductor heterostructures involves stacking discrete monolayers such as transition metal dichalcogenides (TMDs) to form van der Waals heterostructures. In these structures, it is possible create interlayer excitons (ILEs), spatially indirect, bound electron–hole pairs with the electron in one TMD layer and hole an adjacent layer. We are able clearly resolve two distinct emission peaks separated by 24 meV from ILE a MoSe2/WSe2 heterostructure fabricated using...

The effects of surface chemical doping on spin transport in graphene are investigated by performing non-local measurements ultrahigh vacuum while depositing gold adsorbates. We demonstrate manipulation the gate-dependent signal as a function coverage. discover that charged impurity scattering is not dominant mechanism for relaxation graphene, despite its importance momentum scattering. Finally, unexpected enhancements lifetime illustrate complex nature graphene.

Heterostructures composed of multiple layers different atomically thin materials are interest due to their unique properties and potential for new device functionality. MoS 2 ‐graphene heterostructures have shown promise as photodetectors vertical tunnel transistors. However, progress is limited by the typically micrometer‐scale devices alignments required fabrication when utilizing mechanically exfoliated material. Here, synthesis large‐area, continuous, uniform monolayers directly on...

Two-dimensional (2D) materials exhibit many exciting phenomena that make them promising as for future electronic, optoelectronic, and mechanical devices. Because of their atomic thinness, interfaces play a dominant role in determining material behavior. In order to observe exploit the unique properties these materials, it is therefore vital obtain clean repeatable interfaces. However, conventional stacking atomically thin layers typically leads trapped contaminants spatially inhomogeneous...

Spin accumulation and spin precession in single-layer graphene are studied by non-local valve measurements at room temperature. The dependence of the magnetoresistance on electrode spacing is investigated results indicate a diffusion length ~1.6 microns injection/detection efficiency 0.013. Electrical detection confirms that signal originates from injection transport. Fitting Hanle data yields relaxation time ~84 ps ~1.5 microns, which consistent with value obtained through dependence.

We investigate the effect of gold (Au) atoms in form both point-like charged impurities and clusters on transport properties graphene. Cryogenic deposition (18 K) Au decreases mobility shifts Dirac point a manner that is consistent with scattering from impurities. Increasing temperature to room promotes formation clusters, which verified atomic force microscopy. find for fixed amount impurities, enhances causes shift back towards zero.

Strong Coulomb attraction in monolayer transition metal dichalcogenides gives rise to tightly bound excitons and many-body interactions that dominate their optoelectronic properties. However, this interaction can be screened through control of the surrounding dielectric environment as well applied voltage, which provides a potential means tuning bandgap, exciton binding energy, emission wavelength. Here, we directly show bandgap energy optically tuned by intensity incident light. Using...

Spin-dependent properties of single-layer graphene (SLG) have been studied by nonlocal spin valve measurements at room temperature. Gate voltage dependence shows that the magnetoresistance (MR) is proportional to conductivity SLG, which predicted behavior for transparent ferromagnetic-nonmagnetic contacts. While electron and hole bands in SLG are symmetric, gate bias MR reveal an electron-hole asymmetry roughly independent electrons, but varies significantly with holes.

The photoluminescence (PL) in monolayer transition metal dichalcogenides (TMDs) is dominated by recombination of electrons the conduction band with holes spin-orbit split valence bands, and there are two distinct emission features referred to as A-peak (ground state exciton) B-peak (higher state). intensity ratio these varies widely several contradictory interpretations have been reported. We analyze room temperature PL from MoS2, MoSe2, WS2, WSe2 monolayers show that variations arise...

Transition-metal dichalcogenides (TMDs) are an exciting class of 2D materials that exhibit many promising electronic and optoelectronic properties with potential for future device applications. The TMDs expected to be strongly influenced by a variety defects which result from growth procedures and/or fabrication. Despite the importance understanding defect-related phenomena, there remains need quantitative nanometer-scale characterization over large areas in order understand relationship...

Monolayer WS2 offers great promise for use in optical devices due to its direct bandgap and high photoluminescence intensity. While fundamental investigations can be performed on exfoliated material, large-area quality materials are essential implementation of technological applications. In this work, we synthesize monolayer under various controlled conditions characterize the films using photoluminescence, Raman x-ray photoelectron spectroscopies. We demonstrate that introduction hydrogen...

We report on preparation dependent properties observed in monolayer WS2 samples synthesized via chemical vapor deposition (CVD) a variety of common substrates (Si/SiO2, sapphire, fused silica) as well that were transferred from the growth substrate onto new substrate. The as-grown CVD materials (as-WS2) exhibit distinctly different optical than (x-WS2). In case Si/SiO2, following transfer to fresh Si/SiO2 there is ~50 meV shift ground state exciton higher emission energy both...

There is keen interest in monolayer transition metal dichalcogenide films for a variety of optoelectronic applications due to their direct band gap and fast carrier dynamics. However, the mechanisms dominating dynamics are poorly understood. By combining time-resolved terahertz (THz) spectroscopy transient absorption, we able shed light on properties large area CVD grown mono- multilayer MoS2 determine origins characteristic two-component excited state The photoinduced conductivity shows...

We present a paradigm for encoding strain into two-dimensional materials (2DMs) to create and deterministically place single-photon emitters (SPEs) in arbitrary locations with nanometer-scale precision. Our material platform consists of 2DM placed on top deformable polymer film. Upon application sufficient mechanical stress using an atomic force microscope tip, the 2DM/polymer composite deforms, resulting formation highly localized fields excellent control repeatability. show that SPEs are...

Reduced dimensionality and strong Coulombic interactions in monolayer semiconductors lead to enhanced many-body interactions. Here, we report Auger recombination, i.e., exciton-exciton annihilation, large-area chemical vapor deposition-grown WS2. Using ultrafast spectroscopy, experimentally determine the rate be 0.089 ± 0.001 cm2/s at room temperature, which is an order of magnitude greater than bulk value. This nonradiative recombination pathway dominates, regardless excitation energy, for...

Abstract Breaking the valley degeneracy in monolayer transition metal dichalcogenides through valley-selective optical Stark effect (OSE) can be exploited for classical and quantum valleytronic operations such as coherent manipulation of superposition states. The strong light-matter interactions responsible OSE have historically been described by a two-level dressed-atom model, which assumes noninteracting particles. Here we experimentally show that this works well semiconductors far from...

Monolayer transition metal dichalcogenides are promising materials for valleytronic operations. They exhibit two inequivalent valleys in the Brillouin zone, and valley populations can be directly controlled determined using circularly polarized optical excitation emission. The photoluminescence polarization reflects ratio of populations. A wide range values degree emission, Pcirc, has been reported monolayer WS2, although reasons disparity unclear. Here we optically populate one valley,...

Single layers of transition metal dichalcogenides (TMDs) are direct gap semiconductors with nondegenerate valley indices. An intriguing possibility for these materials is the use their index as an alternate state variable. Several limitations to such a utility include strong, phonon-enabled intervalley scattering, well multiparticle interactions leading multiple emission channels. We prepare single-layer WS$_{2}$ that photoluminescence from either neutral or charged exciton (trion). After...