扫描隧穿光谱法在CrBr3中显示出小的能隙,Physical Chemistry Chemical Physics

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扫描隧穿光谱法在CrBr3中显示出小的能隙
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2020-12-8 , DOI: 10.1039/d0cp05633b
Dinesh Baral _{1,

2,

3,

4} , Zhuangen Fu _{1,

2,

3,

4} , Andrei S. Zadorozhnyi _{1,

2,

3,

4} , Rabindra Dulal _{1,

2,

3,

4} , Aaron Wang _{1,

2,

3,

4} , Narendra Shrestha _{1,

2,

3,

4} , Uppalaiah Erugu _{1,

2,

3,

4} , Jinke Tang _{1,

2,

3,

4} , Yuri Dahnovsky _{1,

2,

3,

4} , Jifa Tian _{1,

2,

3,

4} , TeYu Chien _{1,

2,

3,

4}

Affiliation

CrBr ₃是一种分层的范德华材料，其磁序低至2D极限。几十年来，基于光学测量，据信CrBr ₃的能隙在1.68–2.1 eV的范围内。但是，有争议的结果表明，CrBr ₃的带隙可能小于该值。能隙的明确确定对于正确解释CrBr ₃的实验结果至关重要。在这里，我们介绍了CrBr ₃的扫描隧道显微镜和光谱（STM / S）结果薄而厚的薄片剥落在高度有序的热解石墨（HOPG）表面上，并通过密度泛函理论（DFT）计算得出较小的能隙（峰对峰能隙为0.57±0.04 eV；或起始信号能隙为从d I / d V光谱得到0.29±0.05 eV ）。原子分辨率的形貌图显示了无缺陷的晶体结构，并且d I / d V光谱显示了在77 K下测得的多个峰特征。在多峰d I / d V光谱中的导带-价带峰对非常吻合所有报告的光学跃迁。单层和双层CrBr _3的STM形貌图由于样品转移过程中空气暴露时间短（约15分钟），薄片显示出边缘降解。明确确定的小能隙解决了争议，并且是更好地了解CrBr ₃和类似材料的关键。

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Small energy gap revealed in CrBr3 by scanning tunneling spectroscopy

CrBr₃ is a layered van der Waals material with magnetic ordering down to the 2D limit. For decades, based on optical measurements, it is believed that the energy gap of CrBr₃ is in the range of 1.68–2.1 eV. However, controversial results have indicated that the band gap of CrBr₃ is possibly smaller than that. An unambiguous determination of the energy gap is critical to the correct interpretations of the experimental results of CrBr₃. Here, we present the scanning tunneling microscopy and spectroscopy (STM/S) results of CrBr₃ thin and thick flakes exfoliated onto highly ordered pyrolytic graphite (HOPG) surfaces and density functional theory (DFT) calculations to reveal the small energy gap (peak-to-peak energy gap to be 0.57 ± 0.04 eV; or the onset signal energy gap to be 0.29 ± 0.05 eV from dI/dV spectra). Atomic resolution topography images show the defect-free crystal structure and the dI/dV spectra exhibit multiple peak features measured at 77 K. The conduction band – valence band peak pairs in the multi-peak dI/dV spectrum agree very well with all reported optical transitions. STM topography images of mono- and bi-layer CrBr₃ flakes exhibit edge degradation due to short air exposure (∼15 min) during sample transfer. The unambiguously determined small energy gap settles the controversy and is the key in better understanding CrBr₃ and similar materials.

更新日期：2020-12-17

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