Remote Plasma Oxidation and Atomic Layer Etching of MoS₂

Abstract

Exfoliated molybdenum disulfide (MoS2) is shown to chemically oxidize in a layered manner upon exposure to a remote O2 plasma. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) are employed to characterize the surface chemistry, structure, and topography of the oxidation process and indicate that the oxidation mainly occurs on the topmost layer without altering the chemical composition of underlying layer. The formation of S-O bonds upon short, remote plasma exposure pins the surface Fermi level to the conduction band edge, while the MoOx formation at high temperature modulates the Fermi level toward the valence band through band alignment. A uniform coverage of monolayer amorphous MoO3 is obtained after 5 min or longer remote O2 plasma exposure at 200 °C, and the MoO3 can be completely removed by annealing at 500 °C, leaving a clean ordered MoS2 lattice structure as verified by XPS, LEED, AFM, and scanning tunneling microscopy. This work shows that a remote O2 plasma can be useful for both surface functionalization and a controlled thinning method for MoS2 device fabrication processes.

Rapid Wafer-Scale Growth of Polycrystalline 2H-MoS2 by Pulsed Metal–Organic Chemical Vapor Deposition

“…Film stoichiometry near the surface was determined to be S:Mo = 1.95±0.01 as calculated from the Mo 3d and S 2p core levels. A small degree of sulfur deficiency due to undercoordinated Mo edge sites has also been noted for other synthetic MoS 2 films and is likewise encountered in natural single crystals 64 .…”

Is Single Layer MoS2 Stable in the Air?

“…However, the local order at the oxidised edge is probably similar to the fully oxidised structure depicted in Figure . X‐ray photoemission spectroscopy experiments on oxidised MoS 2 revealed a shift of the Mo 3p and Mo 3d states towards higher binding energies, suggesting that the samples contained MoO 3 . To support this hypothesis, we used the Slater–Janak (half‐core hole) approach to calculate the core level shifts for Mo atoms in the fully oxidised nanostripe (Figure ).…”

“…Xray photoemission spectroscopy experimentso no xidised MoS 2 revealed as hift of the Mo 3p and Mo 3d states towards higher binding energies, suggestingt hat the samples contained MoO 3 . [37,36] To support this hypothesis, we used the Slater-Janak (half-core hole) approach to calculate the core level shifts for Mo atoms in the fully oxidised nanostripe (Figure 2). The binding energies of the 3p and 3d states of molybdenum atoms at the edge are 2eVh igher in energy than the corresponding states of Mo atoms in the middle of the nanostripe, whose local coordination environment is that of MoS 2 .T he experimental studies indicate as hift of % 3eVt owards higher binding energies, in good agreement with the calculated value.…”

Exploring the air stability of PdSe2 via electrical transport measurements and defect calculations

“…The discovery of atomically thin graphene in 2004 by Novoselov et al was the catalyst of the 2D materials revolution. 1 In layered materials, such as graphene, hexagonal boron nitride (BN), certain oxides and transition metal dichalcogenides (TMDs), weak Van der Waals forces uniquely keep layers bound together, 2 and thus preparation of atomically thin layers is relatively straightforward via exfoliation from bulk crystals [3][4][5] or thin film growth. 6,7 Due to its chemical structure, each TMD monolayer has an atomically pristine surface free of dangling bonds and interface traps, 8 which pose a significant issue for silicon and other semiconductor based materials.…”