Abstract:The spin structure of the valence and conduction bands at the K and K' valleys of single-layer WS2 on Au(111) is determined by spin-and angle-resolved photoemission and inverse photoemission. The bands confining the direct band gap of 1.98 eV are out-of-plane spin polarized with spin-dependent energy splittings of 417 meV in the valence band and 16 meV in the conduction band. The sequence of the spin-split bands is the same in the valence and in the conduction bands and opposite at the K and the K' high-symmet… Show more
“…The interpretation of the band alignment in terms of a Schottky contact without Fermi level pinning relies on the quasi-freestanding nature of WS 2 on graphene 10,36 . It is consistent with the absence of hybridization between graphene and WS 2 bands in any of our spectra, as well as with the sharp VB features at , in contrast to the situation on metal substrates 9,11,24 .Fig. 5Interpretation of band alignments and luminescence features.…”
Section: Discussionsupporting
confidence: 90%
“…The construction of a two-dimensional (2D) electronic device, such as a pn -junction, can be envisioned using two strategies: The first is to smoothly join two 2D materials with different electronic properties, essentially following the established recipe for three-dimensional (3D) semiconductors. Alternatively, one can create junctions using a single uniform sheet of material placed over a suitably pre-patterned substrate 1–3 , exploiting the sensitivity of 2D materials to their environment via band alignment 4,5 , screening 6–9 , or hybridization 10–12 . This approach has several advantages, such as technical simplicity and the absence of a possibly defective interface 13,14 .…”
Control of atomic-scale interfaces between materials with distinct electronic structures is crucial for the design and fabrication of most electronic devices. In the case of two-dimensional materials, disparate electronic structures can be realized even within a single uniform sheet, merely by locally applying different vertical gate voltages. Here, we utilize the inherently nano-structured single layer and bilayer graphene on silicon carbide to investigate lateral electronic structure variations in an adjacent single layer of tungsten disulfide (WS
2
). The electronic band alignments are mapped in energy and momentum space using angle-resolved photoemission with a spatial resolution on the order of 500 nm (nanoARPES). We find that the WS
2
band offsets track the work function of the underlying single layer and bilayer graphene, and we relate such changes to observed lateral patterns of exciton and trion luminescence from WS
2
.
“…The interpretation of the band alignment in terms of a Schottky contact without Fermi level pinning relies on the quasi-freestanding nature of WS 2 on graphene 10,36 . It is consistent with the absence of hybridization between graphene and WS 2 bands in any of our spectra, as well as with the sharp VB features at , in contrast to the situation on metal substrates 9,11,24 .Fig. 5Interpretation of band alignments and luminescence features.…”
Section: Discussionsupporting
confidence: 90%
“…The construction of a two-dimensional (2D) electronic device, such as a pn -junction, can be envisioned using two strategies: The first is to smoothly join two 2D materials with different electronic properties, essentially following the established recipe for three-dimensional (3D) semiconductors. Alternatively, one can create junctions using a single uniform sheet of material placed over a suitably pre-patterned substrate 1–3 , exploiting the sensitivity of 2D materials to their environment via band alignment 4,5 , screening 6–9 , or hybridization 10–12 . This approach has several advantages, such as technical simplicity and the absence of a possibly defective interface 13,14 .…”
Control of atomic-scale interfaces between materials with distinct electronic structures is crucial for the design and fabrication of most electronic devices. In the case of two-dimensional materials, disparate electronic structures can be realized even within a single uniform sheet, merely by locally applying different vertical gate voltages. Here, we utilize the inherently nano-structured single layer and bilayer graphene on silicon carbide to investigate lateral electronic structure variations in an adjacent single layer of tungsten disulfide (WS
2
). The electronic band alignments are mapped in energy and momentum space using angle-resolved photoemission with a spatial resolution on the order of 500 nm (nanoARPES). We find that the WS
2
band offsets track the work function of the underlying single layer and bilayer graphene, and we relate such changes to observed lateral patterns of exciton and trion luminescence from WS
2
.
“…It has recently become possible to grow large area [10,11], single orientation epitaxial SL MoS 2 [12] and WS 2 [13] on Au(111). The very high quality of these samples offers the opportunity to study the spin texture [14] and electron-phonon coupling strength [15] near the valence band (VB) maximum at the K and K points experimentally and thus allowing access to parameters relevant for transport in hole-doped devices [16] or low-dimensional superconductivity [17]. Of particular interest is the spin-splitting near the VB top, as this entails the possibility to have a different electron-phonon coupling strengths for two states that mainly differ by their spin polarization.…”
The electron-phonon coupling strength in the spin-split valence band maximum of single-layer MoS 2 is studied using angle-resolved photoemission spectroscopy and density functional theorybased calculations. Values of the electron-phonon coupling parameter λ are obtained by measuring the linewidth of the spin-split bands as a function of temperature and fitting the data points using a Debye model. The experimental values of λ for the upper and lower spin-split bands at K are found to be 0.05 and 0.32, respectively, in excellent agreement with the calculated values for a free-standing single-layer MoS 2 . The results are discussed in the context of spin and phase-space restricted scattering channels, as reported earlier for single-layer WS 2 on Au(111). The fact that the absolute valence band maximum in single-layer MoS 2 at K is almost degenerate with the local valence band maximum at Γ can potentially be used to tune the strength of the electron-phonon interaction in this material.
“…Current SPIPES-dedicated sources either focus only on the surface component of the polarization or they tune the spin polarization perpendicular to the surface P ⊥ by rotating the sample around an axis at the surface. These setups allow to study a whole variety of systems 16,[18][19][20][21][22][23][24][25] .…”
A new spin-and angle-resolved inverse photoemission setup with a low-energy (5-100 eV) electron source is presented. The spin-polarized electron source, with a compact design, can decouple the spin polarization vector from the electron beam propagation vector, allowing to explore any spin orientation at any wavevector in angle-resolved inverse photoemission. The beam polarization can be tuned to any preferred direction with a shielded electron-optical system, preserving the parallel beam condition. We demonstrate the performances of the setup by measurements on Cu(001), Au(111) and ultrathin Co films. We estimate at room temperature the energy resolution of the overall system to be ∼ 170 meV from kT e f f of a Cu(001) Fermi level, allowing a direct comparison to photoemission. The spin-resolved operation of the setup has been demonstrated by measuring the Rashba splitting of the Au(111) Shockley surface state. The effective polarization of the electron beam is P = 30 ± 3 % and the wavevector resolution is ∆k F 0.06 Å −1 . Measurements on ultrathin Co films with out-of-plane magnetization and on Au(111) surface state demonstrate how the electron beam polarization direction can be tuned in the three spatial dimensions. In both systems the maximum of the spin asymmetry is reached when the electron beam polarization is aligned with the out-of-plane magnetization of the Co film or the in-plane spin-polarization of Au(111) surface state.
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