Controlled Plasma Thinning of Bulk MoS₂ Flakes for Photodetector Fabrication

Abstract

The electronic properties of layered materials are directly determined based on their thicknesses. Remarkable progress has been carried out on synthesis of wafer-scale atomically molybdenum disulfide (MoS2) layers as a two-dimensional material in the past few years in order to transform them into commercial products. Although chemical/mechanical exfoliation techniques are used to obtain a high-quality monolayer of MoS2, the lack of suitable control in the thickness and the lateral size of the flakes restrict their benefits. As a result, a straightforward, effective, and reliable approach is widely demanded to achieve a large-area MoS2 flake with control in its thickness for optoelectronic applications. In this study, thick MoS2 flakes are obtained by a short-time bath sonication in dimethylformamide solvent, which are thinned with the aid of a sequential plasma etching process using H2, O2, and SF6 plasma. A comprehensive study has been carried out on MoS2 flakes based on scanning electron microscopy, atomic force microscopy, Raman, transmission electron microscopy, and X-ray photoelectron microscopy measurements, which ultimately leads to a two-cycle plasma thinning method. In this approach, H2 is used in the passivation step in the first subcycle, and O2/SF6 plasma acts as an etching step for removing the MoS2 layers in the second subcycle. Finally, we show that this technique can be enthusiastically used to fabricate MoS2-based photodetectors with a considerable photoresponsivity of 1.39 A/W and a response time of 0.45 s under laser excitation of 532 nm.

Plasma-assisted three-dimensional lightscribe graphene as high-performance supercapacitors

“…In fact, in this work, the combination of oxygen + fluorine plasma has been used for two purposes. Fluorine alone etches a large proportion of rGo, which drastically reduces the electrical conductivity while adding oxygen slows down the etch process because the product of its reaction with fluorine gas is highly volatile SOF 4 that reduces the density of fluorine radicals 37 . In addition, XPS results show that fluoride ions remain within rGO even after the lightscribe step to some extent, which promotes the electrochemical properties of the rGO 38 .…”

Vertically aligned carbon nanotubes, MoS2–rGo based optoelectronic hybrids for NO2 gas sensing

“…Figure 5c shows the photocurrent measurements under 405 nm laser illumination at 2 V biasing voltage for different power intensities. Based on it, an increase in the incident power results in more electron/hole pairs generation and subsequently leads to the photocurrent enhancement 30 www.nature.com/scientificreports/ where I ph , P, A d , and A l are the photocurrent, optical power, active area of the device and illumination area of the laser source, respectively. In all measurements, a higher photoresponsivity is measured for the VACNTs contact, because of the lower SBH at the junctions, which facilitated the extraction/injection of electron-hole carrier pairs within the channel.…”

“…The R values decrease with increasing incident powers. This behavior can be justified as follows: increasing the optical power generates more electron-hole pairs, which increases the probability of carrier being captured in traps and hence decreases the R 30 . For Au contacted device, a lower photoresponsivity value is measured than the VACNTs contacted device, indicating the importance of the SBH.…”

“…The photoresponsivities of 11.67 A/W and 3.47 A/W are obtained for the VACNTs and Au junctions at a 0.17 µW incident power of 405 nm radiation, respectively. The photoresponsivity can be fitted as a function of optical power by a power law, R ∝ P β−1 where β is a dimensionless parameter relating to the recombination kinetics of the photoexcited carriers 21,30 . In the absence of trap states, β takes 1 value and it gets close to 0 in the presence of trap states 31 .…”

Plasma Treatment of Ultrathin Layered Semiconductors for Electronic Device Applications

“…The gaseous product is typically removed by the reaction chamber vacuum pump, leaving a chemically modified site where the chalcogen atom was ejected. Under certain circumstances, the metal oxide itself can be volatile in ultrahigh-vacuum (UHV) environments, which may also lead to unexpected electronic properties in the remaining functionalized flake. − We remark here that mixed products, e.g., MX 2– z O z , oxysulfides, and/or lower valence metal oxides are also possible and are often observed with spectroscopic methods such as X-ray photoemission spectroscopy (XPS). ,, It is worth noting that commonly used noble gas species are in a class of their own, as they cannot react chemically to form new compounds with TMDs. This limits their ability to functionalize the surface of materials such as MoS 2 , and places them closer to low-energy inert ion beam irradiation.…”