Mose2 lattice constant9/1/2023 ![]() These as-grown TMDs were then detached from sapphire substrates and transferred onto Si wafers with native oxides to form the HJ stacks (see the Methods section). In addition, the first-principles calculations are performed to elucidate the interlayer interaction.įor μ-XPS measurements, the single-crystalline monolayer TMDs were synthesized using chemical vapour deposition on sapphire substrates 18, 19, 20. The special combination of μ-XPS and STM/S measurements allow us to deduce the precise band offset values including both the VBO and conduction band offset (CBO). Moreover, by using scanning tunnelling microscopy/spectroscopy (STM/S) to measure individual TMDs we determine the quasi-particle gaps and the fine structures involved, such as the energy difference between the VBM at Γ and K. In the following, by using microbeam X-ray photoelectron spectroscopy (μ-XPS) where the photon spot can be focused down to sub-microns (spot size ∼100 nm), we are able to measure the core-level alignment across the TMD HJs at the local scale. In single-layer (SL) TMDs, the DOS near VBM has a complicated line shape due to the different characteristics of the states near Γ and K. This allows for a precise determination of the VBM through curve fitting. In conventional semiconductors, the valence bands primarily comprise of sp orbitals, with a smooth density of states (DOS). The second challenge is the determination of the VBM position. It is thus necessary to locate such locally formed HJs and measure the core-level alignment across the junction. First, the HJ is formed only locally with a lateral lengthscale of only a few microns, owing to the limited lateral size of available TMD monolayer samples. The application of this technique to TMD HJs, however, faces two technical challenges. Then with additional information on the core-level position relative to the valence band maximum (VBM) measured separately for individual semiconductors, the VBM alignment across the HJ can be determined. ![]() This method relies on finding the core-level alignment of two constituent semiconductors across the HJ. In conventional semiconductor heterojunctions (HJs), one commonly used technique to determine the valence band offset (VBO) is XPS 14, 15, 16, 17. Heterojunction band offset is the key parameter for designing HJ-based electronic/photonic devices and accurate determination of this parameter is of critically important. Many proposed novel devices are based on heterostructures formed between dissimilar TMDs 6, 7, 8, 9, 10, 11, 12, 13. Transition metal dichalcogenides (TMDs) have emerged as a new platform for atomic layer electronics 1 and optoelectronics 2, 3, 4, 5. ![]()
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