Low‐Temperature Atomic Layer Deposition of MoS₂ Films

Abstract

Wetc hemical screening reveals the very high reactivity of Mo(NMe 2 ) 4 with H 2 Sf or the low-temperature synthesis of MoS 2 .This observation motivated an investigation of Mo(NMe 2 ) 4 as av olatile precursor for the atomic layer deposition (ALD) of MoS 2 thin films.H erein we report that Mo(NMe 2 ) 4 enables MoS 2 film growth at recordl ow temperatures-as lowas608 8C. The as-deposited films are amorphous but can be readily crystallized by annealing.I mportantly,t he low ALD growth temperature is compatible with photolithographic and lift-off patterning for the straightforwardfabrication of diverse device structures.Stimulated by the landmark discovery of two-dimensional (2D) monolayer graphene [1] and the vast body of subsequent work delineating the rich physical phenomena associated with the electronic structure of graphene, [2] interest has expanded to the exploration of inorganic graphene-analogous 2D materials. [3] Central to this family of materials are 2D layered transition metal dichalcogenides,MX 2 (M = Mo,W;X= S, Se, Te ), [4] themost notable of which is MoS 2 .Whereas graphene is az ero-band-gap-energy conductor,M oS 2 is al ayered semiconductor with athickness-dependent optical band gap in the range of 1.2-1.8 eV. [5] Mono-and few-layer MoS 2 have been demonstrated to possess properties [6] suitable for awide range of electronic [7] and optoelectronic [8] applications,a nd more recently for valleytronics [9] and spintronics. [10] Additionally, 2D MoS 2 has been utilized for battery, [11] gas, [12] and biosensor applications, [13] and extensively for catalytic hydrodesulfurization [14] and hydrogen evolution processes. [15,16] It is thus not surprising that MoS 2 has in recent years become one of the most intensely studied subjects in materials chemistry and materials science. [17] To date,awide range of synthetic approaches to monoand few-layer MoS 2 have been reported;t hese include hydrothermal [18] and electrochemical synthesis, [19] thermolysis of Mo-and S-containing species, [20] sulfurization of Mo-containing seed layers, [12,21] micromechanical [7b, 22] and liquid exfoliation of bulk MoS 2 , [23] as well as physical [24] and chemical vapor deposition [25] (PVD and CVD,r espectively). [26] The most commonly employed methods,e xfoliation and CVD, have,h owever, significant limitations.T op-down methods such as exfoliation can suffer from solvent contamination and ultimately yield collections of discrete flakes rather than continuous films.Bottom-up approaches such as CVD,while promising for MoS 2 film growth on solid supports,o ften require high volatilization/reaction temperatures which limit substrate scope and patterning techniques such as photolithography. [26] Thep recise,l arge-scale growth of mono-or few-layer MoS 2 on insulating substrates would enable the scalable fabrication of atomically thin high-performance transistors,p hotodetectors,a nd other desirable products on at echnologically relevant scale;t his currently represents asignificant challenge. [4,25c] Atomic layer d...

Synthesis of Thin‐Film Metal Pyrites by an Atomic Layer Deposition Approach

“…Very recently, motivated by many novel applications in low‐dimensional electronics and energy technologies, the ALD synthesis of metal sulfides has aroused significant attention, and many new ALD synthesis processes have been particularly developed for metal sulfides. Examples of the metal sulfides whose ALD synthesis approaches were only recently available include GaS x (2014), GeS (2014), MoS 2 (2014), Li 2 S (2014), Co 9 S 8 (2015), NiS (2016), MnS (2016), FeS (2017), VS 4 (2017), and ReS 2 (2018) . Despite the fast development as above, the ALD synthesis of the pyrite‐structured metal disulfides remained a significant challenge for quite a long period, and none of the metal pyrites had ever been synthesized by ALD before our recent work .…”

Armchair MoS2 nanoribbons turned into half metals through deposition of transition-metal and Si atomic chains

“…One-dimensional circuits, for example, can be made of tailored MoS 2 nanoribbons with specific types of edges and their associated band structures. Currently, synthesis of MoS 2 monolayers, nanosheets, or nanoribbons can be accomplished in various ways involving chemical 8 or mechanical exfoliation 9 , using chemical vapor deposition 10 , 11 , atomic layer deposition 12 , polymer-assisted deposition 13 , or a vapor–solid–solid mode 14 . MoS 2 nanoribbons encapsulated in carbon nanotubes 15 can have uniform widths as narrow as 1–4 nm and layer numbers down to 1–3.…”

Electronic structures of WS2 armchair nanoribbons doped with transition metals

“…Transition-metal dichalcogenides (TMDCs) 1 have layered crystalline structures and a variety of chemical compositions. The relatively weak van der Waals interactions between adjacent layers facilitate extraction and synthesis of TMDC monolayers [2][3][4][5][6][7][8][9][10] , which have direct band gaps and remarkable electrical and optical properties [11][12][13][14][15][16] . TMDC monolayers can be tailored to nanoribbons 9,10 that have atoms of either species at the two edges.…”