Electrical and optoelectronic anisotropy and surface electron accumulation in ReS2 nanostructures

Hemanth Kumar Bangolla; Muhammad Yusuf Fakhri; Ching-Hsuan Lin; Cheng-Maw Cheng; Yi-Hung Lu; Tsu-Yi Fu; Pushpa Selvarasu; Rajesh Kumar Ulaganathan; Raman Sankar; Ruei-San Chen

doi:10.1039/d3nr04830f

Electrical and optoelectronic anisotropy and surface electron accumulation in ReS₂ nanostructures

Nanoscale. 2023 Dec 14;15(48):19735-19745. doi: 10.1039/d3nr04830f.

Authors

Affiliations

¹ Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 10607, Taiwan. rsc@mail.ntust.edu.tw.
² National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
³ Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.
⁴ Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan.
⁵ Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council, Taipei 10601, Taiwan.
⁶ Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan.
⁷ Institute of Physics, Academia Sinica, Taipei 115201, Taiwan.

PMID: 38047470
DOI: 10.1039/d3nr04830f

Abstract

Two interesting electronic transport properties including in-plane anisotropy and nonhomogeneous carrier distribution were observed in ReS₂ nanoflakes. The electrical conductivity defined by the current parallel to the b-axis (‖b) is 32 times higher than that perpendicular to the b-axis (⊥b). Similar anisotropy was also observed in optoelectronic properties in which the ratio of responsivity ‖b to ⊥b reaches 20. In addition, conductivity and thermal activation energy with substantial thickness dependence were observed, which indicates a surface-dominant 2D transport in ReS₂ nanoflakes. The presence of surface electron accumulation (SEA) in ReS₂ has been confirmed by angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy. The electron concentration (∼10¹⁹ cm^-3) at the surface is over three orders of magnitude higher than that of the bulks. Sulfur vacancies which are sensitive to air molecules are suggested to be the major factor resulting in SEA and high conductivity in ReS₂ nanostructures.