Etching of thin crystals on a substrate leaves behind unreacted mono- and bilayer sheets

2D layers of transition metal dichalcogenides such as MoS₂ and WSe₂ have shown their potential use in applications such as flexible electronics, photodetectors, light harvesting and valleytronics. But despite rapid progress in this field, efficient and controlled synthesis of high quality 2D crystals remains a  challenge.

Last month, scientists from the National University of Singapore reported a promising new approach using a simple wet chemical method for thinning MoS₂ crystals.

In their study, published in the journal APL Materials, they show that concentrated nitric acid effectively etches thin MoS₂ crystals from their edges via formation of MoO₃. Moreover, etching of thin crystals on a substrate leaves behind unreacted mono- and bilayer sheets.

Figure 1: Schematic illustrating the etching of top layers of bulk MoS₂ down to its monolayer. In a typical experiment, the substrate was placed in contact with the top surface of the acid.

Figure 2: Optical image of a thick (>100 nm) MoS₂ flake (a) and (d) before and (b) and (e) after HNO₃ etching. (c) and (f) Fluorescence images of the etched flakes corresponding to the those shown in (b) and (e).

The researchers report that flakes obtained by chemical etching exhibit electronic qualities comparable to that of mechanically exfoliated counterparts, suggesting that self-limiting chemical etching is a promising top-down route to preparing atomically thin crystals from bulk layer compounds.

This is a brief summary of the paper 'Wet chemical thinning of molybdenum disulfide down to its monolayer' by Kiran Kumar Amara et al, APL Mat. 2, 092509 (2014)

AngelTech Live III: Join us on 12 April 2021!

AngelTech Live III will be broadcast on 12 April 2021, 10am BST, rebroadcast on 14 April (10am CTT) and 16 April (10am PST) and will feature online versions of the market-leading physical events: CS International and PIC International PLUS a brand new Silicon Semiconductor International Track!

Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

2021 is no different. Over the last few months interest in deep-UV LEDs has rocketed, due to its capability to disinfect and sanitise areas and combat Covid-19. We shall consider a roadmap for this device, along with technologies for boosting its output.

We shall also look at microLEDs, a display with many wonderful attributes, identifying processes for handling the mass transfer of tiny emitters that hold the key to commercialisation of this technology.

We shall also discuss electrification of transportation, underpinned by wide bandgap power electronics and supported by blue lasers that are ideal for processing copper.

Additional areas we will cover include the development of GaN ICs, to improve the reach of power electronics; the great strides that have been made with gallium oxide; and a look at new materials, such as cubic GaN and AlScN.

Having attracted 1500 delegates over the last 2 online summits, the 3rd event promises to be even bigger and better – with 3 interactive sessions over 1 day and will once again prove to be a key event across the semiconductor and photonic integrated circuits calendar.

So make sure you sign up today and discover the latest cutting edge developments across the compound semiconductor and integrated photonics value chain.

REGISTER FOR FREE

VIEW SESSIONS