Atomically Resolved Defect-Engineering Scattering Potential in 2D Semiconductors

Abstract

Engineering atomic-scale defects has become an important strategy for the future application of transition metal dichalcogenide (TMD) materials in next-generation electronic technologies. Thus, providing an atomic understanding of the electron-defect interactions and supporting defect engineering development to improve carrier transport is crucial to future TMDs technologies. In this work, we utilize low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/S) to elicit how distinct types of defects bring forth scattering potential engineering based on intervalley quantum quasiparticle interference (QPI) in TMDs. Furthermore, quantifying the energy-dependent phase variation of the QPI standing wave reveals the detailed electron-defect interaction between the substitution-induced scattering potential and the carrier transport mechanism. By exploring the intrinsic electronic behavior of atomic-level defects to further understand how defects affect carrier transport in low-dimensional semiconductors, we offer potential technological applications that may contribute to the future expansion of TMDs.

Keywords: Atomic defect engineering; Intervalley quasiparticle interference; Phase shift; Scanning tunneling microscopy; Transition metal dichalcogenides.

Figure 1

STM topographic image and the spectroscopy of WS₂/HOPG. (a) The 15 × 15 nm² atomically resolved STM images of WS₂ at an energy level of 1.00 eV. (b) STS spectrum on the intrinsic defect-free WS₂ surface, revealing an energy gap of 2.62 ± 0.02 eV. (c) The dI/dV image corresponds to the scanning region on the topographic image in (a) and reveals the QPI patterns in real space. (The 1 × 1 atomic arrangement is removed by an FT filter.) (d) The 1.00 eV FT-STS map from (c) shows the reciprocal lattice G-point and the orange-dashed hexagon is the 1st Brillouin zone of WS₂. Obvious spots from the defect-induced QPI pattern are observed near the M-point.

Figure 2

STM image, dI/dV image, and spectroscopy of different types of atomic defects. (a) The local 2 × 2 nm² STM image of defects at an energy level of 1.00 eV, including O_s^(top), O_s^(bottom), Mo_w, and C_s^–. (b) The dI/dV spectra of O_s^(top), O_s^(bottom), Mo_w, and C_s^–. Only C_s^– presents the obvious in-gap states near the Fermi level (at sample bias V = 0). (c) The local 3 × 3 nm² STS maps at energy levels of 0.94, 1.04, and 1.14 eV, which correspond to STM images in (a) and directly reveal the energy-dependent QPI pattern variations in real space.

Figure 3

QPI enhanced dI/dV image, QPI standing wave evolution, and the fitting calculation. (a) The QPI pattern enhanced 4 × 4 nm² dI/dV image of C_s^– at an energy level of 0.94 and 1.04 eV. The blue and green half-figures on the corner indicate the wavefront of the QPI pattern distribution at 0.94 and 1.04 eV to show the energy-dependent QPI phase difference. (b) The energy-dependent landscape constructed by recording the continuous variation of the QPI standing waves nearby C_s^– in real space with the energy level 0.80 to 1.28 eV (per 0.02 eV interval). The blue and green lines directly indicate the phase difference (ϕ_diff) at 0.94 and 1.04 eV. (c) The fitting results (red-blue gradient color) and the experimental data of C_s^– (black curve), giving the calculated ϕ_shift = −13° ± 10.2° at energy level 0.94 eV.

Figure 4

Energy-dependent phase shift variation of the QPI standing wave and the defect scattering potential. (a) The energy-dependent phase shift diagram of O_s^(top), O_s^(bottom), Mo_w, and C_s^–. The C_s^– presents the negative degree tendency of the phase shift; in contrast, the other types of defects present the opposite behavior. (b) The schematic diagram of the defect scattering potential in the side view of WS₂ classifies O_s^(top), O_s^(bottom), Mo_w, and C_s^–. (c) The schematic diagram of the top view of WS₂ illustrates the electronic defect scattering event near O_s^(top), O_s^(bottom), Mo_w, and C_s^–.