Use this URL to cite or link to this record in EThOS:
Title: Chemical vapour deposition of atomically thin tungsten disulphide
Author: Reale, Francesco
ISNI:       0000 0004 6496 9523
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
Availability of Full Text:
Access from EThOS:
Access from Institution:
Transition metal dichalcogenides (TMDs) are van der Waals layered materials that have been known and studied for decades in their bulk form for applications such as solid-state lubricants and catalysts. However, TMDs were largely unexplored in their two-dimensional, atomically thin form. Their unique optical and electrical properties due to their reduced dimensionality started to emerge only in the last decade. In particular, group VI-TMDs (i.e., MoS2, WS2, MoSe2, WSe2) have been recently attracting tremendous attention as emerging post-graphene materials owing to their direct band-gap in the visible range which opens many prospects for diverse optoelectronic devices. Among them, atomically thin tungsten disulphide (WS2) has emerged as unique candidate for future nanotechnologies due to its superior optical, electrical and thermal properties. Any envisioned application of WS2 requires high-quality and large-area material obtainable via a scalable synthesis method. The chemical vapour deposition (CVD) of group VI-TMDs holds promise for the synthesis of high quality monolayered material extended over wafer-size areas. Nevertheless, the CVD growth of high-quality atomically thin WS2 layers requires further development since film continuity and thickness uniformity are normally limited to a few tens of micron-sized areas. The most extensively used CVD method to synthesize WS2 entails co-evaporation of tungsten oxide (WO3) and sulphur (S) powders. This choice of precursors is mainly dictated by their low toxicity compared to halides/organic precursors and effective replacement of O by S. However, due to the high sublimation temperature of WO3, the growth has to be carried out at high temperatures in between 950-1070°C and low pressures. In this work we demonstrate a novel facilitated CVD growth of high-quality atomically thin WS2 by using a novel molecular precursor approach. This strategy involves reagents which are carbon free, volatile and easily decomposable at low temperatures, allowing for the growth of mono- and bi-layered WS2 crystals with lateral sizes of 300µm at temperatures as low as 750°C, and with superior optical and electrical properties than those of naturally occurring materials. The charge carrier mobilities that we report are also higher compared to the ones obtained using innovative synthesis procedures, such as CVD growth on reusable gold substrates or metalorganic CVD on different oxides. Further we demonstrate tunability of the optical and electrical properties of WS2, inducing atomic doping with Indium.
Supervisor: Mattevi, Cecilia ; Saiz Gutierrez, Eduardo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral