Large area chemical vapor deposition growth of monolayer MoSe 2 and its controlled sulfurization to MoS 2
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Layered transition metal dichalcogenides which are part of the two dimensional materials family are experiencing rapidly growing interest owing to their diverse physical and optoelectronic properties. Large area controllable synthesis of these materials is required for transition from lab scale research to practical applications. In this work, we present a single step chemical vapor deposition process for large area monolayer growth of molybdenum selenide (MoSe2). We also demonstrate controllable thermal conversion from molybdenum selenide to molybdenum sulfide.
I. INTRODUCTION
Since the isolation of graphene in 2004 (Ref. 1) there has been an incredible amount of research in the field of two-dimensional (2D) materials. Although, graphene boasts of many remarkable properties, the lack of a band gap makes it unsuitable for digital electronics. Transition metal dichalcogenide (TMDs) is a family of materials with the general chemical formula MX2, where the M stands for a transition metal and X stands for a chalcogen. Nearly 40 different TMDs have layered structures and among these members the properties vary from metallic to semimetallic to semiconducting.2 Even among the semiconducting members there exist a large variation of band gaps and this opens up a route for designer optoelectronic devices. It also opens up the possibility of tuning material properties by controlling the TMD chemical composition. Of the different TMDs, so far MoS2 has been at the forefront.3 Since the initial demonstration of single layer MoS2 transistors4 using mechanically exfoliated samples, significant effort has been invested to not only improve device performance5–9 but also demonstrate device capabilities of synthesized materials.10,11 Of the different synthesis processes used for MoS2, the vapor transport process using solid precursors (MoO3 and S) has shown the best electrical performance. Due to the success of this process similar synthesis efforts have been successfully used to produce other TMDs such as WS2, WSe2, and MoSe2. However, this growth process inherently includes a variety of meso-scale imperfections12 that might affect nano-scale devices. This growth process is initiated by isolated domains that merge together to form Contributing Editor: Andrey Voevodin a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.7
pseudocontinuous regions. Performances of devices built across these grain boundaries suffer due to charge scattering. For TMDs to move to commercial applications it is essential to synthesize atomically flat and defect free regions over large areas. To truly explore the versatility of different TMDs, the synthesis processes should either be interchangeable between different TMDs or simple post-growth processes need to be explored for this interchangeability. In this work, we demonstrate a single step process to obtain monolayer MoSe2, continuous over a large area (.1 cm 3 cm) with sub-nanometer surface roughness. In addition, we discovered that this large area film can be co
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