The residue of common photo‐ and electron‐beam resists, such as poly(methyl methacrylate) (PMMA), is often present on the surface of 2D crystals after device fabrication. The residue degrades device properties by decreasing carrier mobility and creating unwanted doping. Here, MoS2and WSe2field effect transistors (FETs) with residue are cleaned by contact mode atomic force microscopy (AFM) and the impact of the residue on: 1) the intrinsic electrical properties, and 2) the effectiveness of electric double layer (EDL) gating are measured. After cleaning, AFM measurements confirm that the surface roughness decreases to its intrinsic state (i.e., ≈0.23 nm for exfoliated MoS2and WSe2) and Raman spectroscopy shows that the characteristic peak intensities (E2gand A1g) increase. PMMA residue causes p‐type doping corresponding to a charge density of ≈7 × 1011cm−2on back‐gated MoS2and WSe2FETs. For FETs gated with polyethylene oxide (PEO)76:CsClO4, removing the residue increases the charge density by 4.5 × 1012cm−2, and the maximum drain current by 247% (statistically significant,
The oxidation mechanism of atomically thin molybdenum disulfide (MoS2) plays a critical role in its nanoelectronics, optoelectronics, and catalytic applications, where devices often operate in an elevated thermal environment. In this study, we systematically investigate the oxidation of mono- and few-layer MoS2flakes in the air at temperatures ranging from 23 °C to 525 °C and relative humidities of 10%–60% by using atomic force microscopy (AFM), Raman spectroscopy and x-ray photoelectron spectroscopy. Our study reveals the formation of a uniform nanometer-thick physical adsorption layer on the surface of MoS2, which is attributed to the adsorption of ambient moisture. This physical adsorption layer acts as a thermal shield of the underlying MoS2lattice to enhance its thermal stability and can be effectively removed by an AFM tip scanning in contact mode or annealing at 400 °C. Our study shows that high-temperature thermal annealing and AFM tip-based cleaning result in chemical adsorption on sulfur vacancies in MoS2, leading to p-type doping. Our study highlights the importance of humidity control in ensuring reliable and optimal performance for MoS2-based electronic and electrochemical devices and provides crucial insights into the surface engineering of MoS2, which are relevant to the study of other two-dimensional transition metal dichalcogenide materials and their applications.
more » « less- Award ID(s):
- 2006127
- NSF-PAR ID:
- 10487419
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Nanotechnology
- Volume:
- 34
- Issue:
- 40
- ISSN:
- 0957-4484
- Format(s):
- Medium: X Size: Article No. 405701
- Size(s):
- ["Article No. 405701"]
- Sponsoring Org:
- National Science Foundation
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