Impurities and Electronic Property Variations of Natural MoS2 Crystal Surfaces

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• 作者：Rafik Addou ; Stephen McDonnell ; Diego Barrera ; Zaibing Guo ; Angelica Azcatl ; Jian Wang ; Hui Zhu ; Christopher L. Hinkle ; Manuel Quevedo-Lopez ; Husam N. Alshareef ; Luigi Colombo ; Julia W. P. Hsu ; Robert M. Wallace
• 刊名：ACS Nano
• 出版年：2015
• 出版时间：September 22, 2015
• 年：2015
• 卷：9
• 期：9
• 页码：9124-9133
• 全文大小：700K
• ISSN：1936-086X

文摘

Room temperature X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), high resolution Rutherford backscattering spectrometry (HR-RBS), Kelvin probe method, and scanning tunneling microscopy (STM) are employed to study the properties of a freshly exfoliated surface of geological MoS₂ crystals. Our findings reveal that the semiconductor 2H-MoS₂ exhibits both n- and p-type behavior, and the work function as measured by the Kelvin probe is found to vary from 4.4 to 5.3 eV. The presence of impurities in parts-per-million (ppm) and a surface defect density of up to 8% of the total area could explain the variation of the Fermi level position. High resolution RBS data also show a large variation in the MoS_x composition (1.8 < x < 2.05) at the surface. Thus, the variation in the conductivity, the work function, and stoichiometry across small areas of MoS₂ will have to be controlled during crystal growth in order to provide high quality uniform materials for future device fabrication.