Atomic layer deposition on 2D transition metal chalcogenides: layer dependent reactivity and seeding with organic ad-layers

Abstract

This commmunication presents a study of atomic layer deposition of Al 2 O 3 on transition metal dichalcogenide (TMD) two-dimensional films which is crucial for use of these promising materials for electronic applications. Deposition of Al 2 O 3 on pristine chemical vapour deposited MoS 2 and WS 2 crystals is demonstrated. This deposition is dependent on the number of TMD layers as there is no deposition on pristine monolayers. In addition, we show that it is possible to reliably seed the deposition, even on the monolayer, using non-covalent functionalisation with perylene derivatives as anchor unit.The integration of transition metal dichalcogenides (TMDs) into existing semiconductor technology is of major interest. 1,2 The synthesis of these materials has been vastly improved over the last few years and many possible devices have been proposed and realised. [3][4][5][6] But to finally achieve their large-scale integration and production, it is necessary to make TMDs fully CMOS processable. One prerequisite for this is the deposition of subsequent layers on top of the TMD for gating and passivation as the performance and stability of TMD based devices hugely depends on their dielectric environment. This task is nontrivial as any impact on the surface of the TMD will result in the destruction of its electronic properties. It has been shown that encapsulation of the 2D material by mechanical deposition of hexagonal boron nitride results in the best preservation of its electronic properties but this approach is not scalable. 7 Other frequently used deposition methods for oxides such as sputtering or plasma-enhanced chemical vapour deposition (PECVD) are not suitable as their application will cause damage to the monolayer.Atomic layer deposition (ALD) is a mild and highly precise technique for thin film deposition, mainly used for depositing gate oxides in integrated circuits. 8 The most common ALD process is the deposition of Al 2 O 3 from alternating exposures of trimethylaluminium (TMA, Al(CH 3 ) 3 ) and water according to the reaction: 9 2Al(CH 3 ) 3 + 3H 2 O -Al 2 O 3 + 6CH 4 DH = À376 kcal This reaction is thermodynamically highly favourable and works over a large range of temperatures with temperatures between 33 1C and 500 1C demonstrated, making it very reliable and common in the silicon and III-V semiconductor industries. 10,11 However, in the initial step the TMA needs a surface hydroxyl group with which it reacts and the lack of such groups on the TMD's basal plane makes starting the deposition non-trivial; a challenge also encountered with graphene. [12][13][14][15] Using ozone instead of water may prove harmful to the oxidation-sensitive TMD layers, though there have been some recent successes. 16 An initial, purely adsorptionbased deposition can be achieved but tends to be dependent on temperature and other factors like underlying electronic structure and is therefore often not entirely reproducible; it has been shown several times that studies may not reproduce results under apparently similar condit...

Noncovalent Functionalization and Charge Transfer in Antimonene

“…Specifically, we carried out the functionalization process by drop‐casting a THF solution (1E −5 m ) of a tailormade EDTA‐PDI (EDTA=ethylenediaminetetraacetic acid) derivative on the exfoliated flakes, followed by a thorough washing process after the functionalization (see the Supporting Information for details). This family of compounds exhibits high performance in the functionalization of several nanomaterials such as carbon nanotubes, graphene, molybdenum disulfide (MoS 2 ), and BP . The Raman characterization of very thin antimonene flakes, obtained by microexfoliation, is challenging because of the very low non‐resonant Raman intensities, as recently reported by our group .…”

Noncovalent Functionalization of Black Phosphorus

“…Indeed, our group has used these molecules for the noncovalent functionalization of carbon nanotubes, graphene, and MoS 2 . They exhibit a strong absorption due to their large aromatic core, which can become attached to the 2D layers through van der Waals interactions . The structure of the selected molecule is depicted in Scheme ; we used a protected EDTA–PDI molecule to avoid any preferential interaction of the carboxylic moieties (see Figure S7 for synthetic details) .…”

Noncovalent Functionalization and Charge Transfer in Antimonene

“…This family of compounds exhibits high performance in the functionalization of several nanomaterials such as carbon nanotubes,g raphene,m olybdenum disulfide (MoS 2 ), and BP. [27,[29][30][31] TheR aman characterization of very thin antimonene flakes,o btained by microexfoliation, is challenging because of the very low non-resonant Raman intensities,asrecently reported by our group. [12,13] Therefore, fast detection of the exfoliated flakes is precluded by Raman spectroscopy,s ow eh ave recently optimized optical microscopy conditions to facilitate the identification of few-layer antimonene flakes.…”