Electronic Structure and Stacking Arrangement of Tungsten Disulfide at the Gold Contact

Abstract

There is an intensive effort to control the nature of attractive interactions between ultrathin semiconductors and metals and to understand its impact on the electronic properties at the junction. Here, we present a photoelectron spectroscopy study on the interface between WS2 films and gold, with a focus on the occupied electronic states near the Brillouin zone center (i.e., the Γ point). To delineate the spectra of WS2 supported on crystalline Au from the suspended WS2, we employ a microscopy approach and a tailored sample structure, in which the WS2/Au junction forms a semi-epitaxial relationship and is adjacent to suspended WS2 regions. The photoelectron spectra, as a function of WS2 thickness, display the expected splitting of the highest occupied states at the Γ point. In multilayer WS2, we discovered variations in the electronic states that spatially align with the crystalline grains of underlying Au. Corroborated by density functional theory calculations, we attribute the electronic structure variations to stacking variations within the WS2 films. We propose that strong interactions exerted by Au grains cause slippage of the interfacing WS2 layer with respect to the rest of the WS2 film. Our findings illustrate that the electronic properties of transition metal dichalcogenides, and more generally 2D layered materials, are physically altered by the interactions with the interfacing materials, in addition to the electron screening and defects that have been widely considered.

Structure modulation of two-dimensional transition metal chalcogenides: recent advances in methodology, mechanism and applications

“…The bandgaps of few-layer semiconducting twisted H-phase TMDs vary due to the band valleys located in different symmetric sites of their Brillouin zones. [226][227][228] Fig. 21(a) shows the band structures of monolayer and bilayer MoS 2 with different twist angles as an example.…”

Challenges of Wafer‐Scale Integration of 2D Semiconductors for High‐Performance Transistor Circuits

“…The main contact metal candidates for N-channel metalsemiconductor (NMOS) MX 2 devices are: Ti, Ni, Au, and semimetals such as Bi and Sb. [3,14,23,[52][53][54][55][56] Considering the fact that Au processing is typically banned in a Si-based fab, the introduction of Au would be accompanied by a very strict contamination protocol like is the case for Pd or Pd. The best contact results for NMOS so far were obtained with Bi and Sb contacts.…”

Engineering of Nanoscale Heterogeneous Transition Metal Dichalcogenide–Au Interfaces

“…33 Monolayer (1L), bilayer (2L), and trilayer (3L) WS 2 and WSe 2 crystals were identified after exfoliation using optical contrast (Figure S1), Raman spectroscopy, photoluminescence, and atomic force microscopy. 11,20,34 Exfoliation of TMDs directly onto these substrates generates regions of 1L, 2L, and 3L Au-supported crystals with comparable yields and cleanliness suitable for surface science investigations.…”

“…Throughout this work we discuss TMD–Au interfaces fabricated through mechanical exfoliation on three different types of electron beam evaporated Au substrates: (i) Au films that received no additional processing between deposition and TMD exfoliation (termed “as-deposited”); (ii) Au films treated with an O 2 plasma before TMD exfoliation (termed “plasma-treated”); and (iii) Au films deposited without an adhesion layer (e.g., Ti or Cr) and sequentially annealed in a H 2 /Ar gas after TMD exfoliation (termed “OPEN”, meaning “oriented porous metallic network”), which is reported elsewhere and described in the Supporting Information . Monolayer (1L), bilayer (2L), and trilayer (3L) WS 2 and WSe 2 crystals were identified after exfoliation using optical contrast (Figure S1), Raman spectroscopy, photoluminescence, and atomic force microscopy. ,, Exfoliation of TMDs directly onto these substrates generates regions of 1L, 2L, and 3L Au-supported crystals with comparable yields and cleanliness suitable for surface science investigations.…”