Unidirectional growth of epitaxial tantalum disulfide triangle crystals grown on sapphire by chemical vapour deposition with a separate-flow system

Abstract

Tantalum disulfide has been attracting considerable attention due to its rich phase diagram that includes polytypes and charge density waves, thus having potential for electrical device applications. However, epitaxial TaS₂ thin films grown by chemical vapour deposition are still limited due to few available precursors. Herein, an originally designed atmospheric chemical vapour deposition with a separate-flow system was proposed to accomplish the controlled synthesis of TaS₂ thin films. The sophisticated deposition sequence enables us to make unidirectional TaS₂ triangle domains on c-plane sapphire using a chloride precursor. The quality of the grown TaS₂ thin films was confirmed by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and observing a step-and-terrace structure without spiral defects. The growth mechanism was discussed and concluded as the Volmer–Weber mode from the surface morphologies and elemental analysis. Our strategy is expandable to the other transition metal dichalcogenides because all the chloride precursors show a considerable vapour pressure below 200 °C.