Remarkable electronic and optical anisotropy of layered 1T’-WTe2 2D materials

Qiankun Zhang,Xiaodong Hu,Rongjie Zhang,Wanfu Shen,Lianqing Zhu,Mingli Dong,Chunhua An,Jing Liu,Jiancui Chen

doi:10.3762/bjnano.10.170

Qiankun Zhang, Xiaodong Hu + Show 7 more

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https://doi.org/10.3762/bjnano.10.170

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Abstract

Anisotropic 2D materials exhibit novel optical, electrical and thermoelectric properties that open possibilities for a great variety of angle-dependent devices. Recently, quantitative research on 1T’-WTe2 has been reported, revealing its fascinating physical properties such as non-saturating magnetoresistance, highly anisotropic crystalline structure and anisotropic optical/electrical response. Especially for its anisotropic properties, surging research interest devoted solely to understanding its structural and optical properties has been undertaken. Here we report quantitative, comprehensive work on the highly anisotropic, optical, electrical and optoelectronic properties of few-layer 1T’-WTe2 by azimuth-dependent reflectance difference microscopy, DC conductance measurements, as well as polarization-resolved and wavelength-dependent optoelectrical measurements. The electrical conductance anisotropic ratio is found to ≈103 for a thin 1T’-WTe2 film, while the optoelectronic anisotropic ratio is around 300 for this material. The polarization dependence of the photo-response is ascribed to the unique anisotropic in-plane crystal structure, consistent with the optical absorption anisotropy results. In general, 1T’-WTe2, with its highly anisotropic electrical and photoresponsivity reported here, demonstrates a route to exploit the intrinsic anisotropy of 2D materials and the possibility to open up new ways for applications of 2D materials for light polarization detection.

Highlights

The first exfoliation of graphene [1] attracted extensive interest in 2D materials such as black phosphorus (BP) [2,3], hexagonal boron nitride (h-BN) [4,5] and transition metal dichalcogenides (TMDCs) with a common chemical formula MX2 [6,7,8,9,10]
Through a systematic characterization including Raman spectroscopy, X-ray photoelectron spectroscopy and azimuth-dependent reflectance difference microscopy (ADRDM), we firstly identified the 1T’-phase WTe2 to have an optical anisotropic crystal structure
The crystalline parameters of WTe2 were further studied through transmission electron microscopy (TEM), where a typical high-resolution TEM image displayed in Figure 1c shows the distorted 1T’ atomic phase, and the selected area electron diffraction (SEAD) pattern illustrated in Figure 1c, which demonstrates the rectangular symmetry of 1T’-WTe2 with space group Pmn21

Summary

Introduction

The first exfoliation of graphene [1] attracted extensive interest in 2D materials such as black phosphorus (BP) [2,3], hexagonal boron nitride (h-BN) [4,5] and transition metal dichalcogenides (TMDCs) with a common chemical formula MX2 [6,7,8,9,10]. All of the TMDCs have the same formula, the atomic structure of 1T’phase WTe2 is totally different from the other TMDCs. 1T’WTe2 exhibits a distorted structure relative to the 1T’ phase. Both Raman [23,24] and first-principles [25,26] calculations have been used to indicate that monolayer 1T’-WTe2 has a highly in-plane anisotropic crystal structure, in addition to anisotropic electrical, thermal and optical properties [23,24,25,26]. Most of the results are based on theoretical demonstrations of the anisotropic phenomenon, rather than further quantitative data for the characterization the natural anisotropy of 1T’-WTe2

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