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Two‐Dimensional Palladium Diselenide with Strong In‐Plane Optical Anisotropy and High Mobility Grown by Chemical Vapor De...

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Advanced Materials
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Two‐dimensional (2D) palladium diselenide (PdSe2) has strong interlayer coupling and a puckered pentagonal structure, leading to remarkable layer‐dependent electronic structures and highly anisotropic in‐plane optical and electronic properties. However, the lack of high‐quality, 2D PdSe2 crystals grown by bottom‐up approaches limits the study of their exotic properties and practical applications. In this work, chemical vapor deposition growth of highly crystalline few‐layer (≥2 layers) PdSe2 crystals on various substrates is reported. The high quality of the PdSe2 crystals is confirmed by low‐frequency Raman spectroscopy, scanning transmission electron microscopy, and electrical characterization. In addition, strong in‐plane optical anisotropy is demonstrated via polarized Raman spectroscopy and second‐harmonic generation maps of the PdSe2 flakes. A theoretical model based on kinetic Wulff construction theory and density functional theory calculations is developed and described the observed evolution of “square‐like” shaped PdSe2 crystals into rhombus due to the higher nucleation barriers for stable attachment on the (1,1) and (1,−1) edges, which results in their slower growth rates. Few‐layer PdSe2 field‐effect transistors reveal tunable ambipolar charge carrier conduction with an electron mobility up to ≈294 cm2 V−1 s−1, which is comparable to that of exfoliated PdSe2, indicating the promise of this anisotropic 2D material for electronics.