Free-standing electronic character of monolayerMoS2in van der Waals epitaxy

Abstract

We have evaluated as-grown MoS 2 crystals, epitaxially grown on a monocrystalline sapphire by chemical vapor deposition (CVD), with direct electronic band-structure measurements by energy-filtered k-space photoelectron emission microscopy performed with a conventional laboratory vacuum ultraviolet He I light source under off-normal illumination. The valence states of the epitaxial MoS 2 were mapped in momentum space down to 7 eV below the Fermi level. Despite the high nucleation density within the imaged area, the CVD MoS 2 possesses an electronic structure similar to the free-standing monolayer MoS 2 single crystal, and it exhibits hole effective masses of 2.41 ± 0.05 m 0 , and 0.81 ± 0.05 m 0 , respectively, at and K high-symmetry points that are consistent with the van der Waals epitaxial growth mechanism. This demonstrates the excellent ability of the MoS 2 CVD on sapphire to yield a highly aligned growth of well-stitched grains through epitaxial registry with a strongly preferred crystallographic orientation.

Electronic Properties of Transferable Atomically Thin MoSe2/h-BN Heterostructures Grown on Rh(111)

“…The close examination of the experimental and theoretical band structures reveals the presence of a small band compression, often associated with the presence of a substrate. 34,35,38 Similarly, the band dispersions along Γ to M are also plotted, and the band structures are in line with the theoretical calculations, with the exception of an energy upshift near the M point (Supporting Information section 7). Although the differences are small in our case, this is possibly due to screening by the substrate and charge redistribution at the interface caused by the metallic Rh substrate below the BN monolayer as well as the unintentional n-doping of MoSe 2 .…”

“…Unlike conventional angle-resolved photoelectron spectroscopy, which requires a predefined high-symmetry direction and is usually time-consuming due to the sequential acquisition of the k -space photoemission signal by sample rotation, k PEEM uses parallel angular detection at a given photoelectron energy in the valence band by spectroscopic imaging of the back focal plane of the PEEM. Therefore, the entire reciprocal space is sampled, which makes k PEEM an ideal tool for directly assessing the electronic properties of 2D materials. , The three-dimensional imaging not only provides the band structures along high symmetry points but also gives insights into the film quality and band distortion due to interaction with the substrate. , Here, k PEEM was performed with off -normal vacuum ultraviolet excitation (He I, h ν = 21.2 eV), providing an enhanced transition probability at the Γ point, , thereby facilitating the determination of the valence band maximum (VBM)…”

“…33,34 The three-dimensional imaging not only provides the band structures along high symmetry points but also gives insights into the film quality and band distortion due to interaction with the substrate. 34,35 Here, kPEEM was performed with offnormal vacuum ultraviolet excitation (He I, hν = 21.2 eV), providing an enhanced transition probability at the Γ point, 33,34 thereby facilitating the determination of the valence band maximum (VBM). 36 Representative images of the kPEEM spectroscopic image series of the heterostructure are shown in Figure 3.…”

NaCl-assisted substrate dependent 2D planar nucleated growth of MoS2

“…7c], 3d5/2 and 3d3/2 are centered at 230.0 and 233.1 eV, respectively with FWHM of 1.7 eV which are consistent with the previous reports 36 . The Mo 4+ 3d5/2 has low intense absorption shoulder positioned at 227.3 eV belongs to oxidation of sulfur with -2, and lowintensity peak at 236.0 eV belongs to Mo 6+ oxidation state, possibly created from the oxidation of sample near the grain boundary and/or other defects 37 . S 2p spectrum exhibits spin-orbit doublets (Fig.…”

A Perspective on the Application of Spatially Resolved ARPES for 2D Materials

“…An example of this is the micro-ARPES study on suspended MoS 2 compared to the more prevalent use of SiO x which confirms the extreme sensitivity of 2D layers to the underlying substrate [ 109 ]. Examples of spatially-localized ARPES on CVD grown TMDCs has been reported for WS 2 , WSe 2 and MoS 2 , where the band structure has been studied by micro-ARPES [ 78 , 81 , 110 , 111 , 112 , 113 ]. An interesting study of artificially built bi-layers of CVD-grown MoS 2 has been carried out by micro-ARPES; the band structure changes as a function of the angle between the layers and a remarkable dependence of the angle with the electron effective mass and of the position of the bands has been found [ 112 ].…”