Thermal Degradation of Monolayer MoS2 on SrTiO3 Supports
Thermal Degradation of Monolayer MoS2 on SrTiO3 Supports
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DOI：
10.1021/acs.jpcc.8b11298
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发表时间：
2019-02-14
影响因子：
3.7
通讯作者：
Castell, Martin R.
中科院分区：
文献类型：
--
作者：
Chen, Peiyu;Xu, Wenshuo;Castell, Martin R.
单层 MoS2 是一种宽带隙半导体，适用于高温电子产品。因此，了解其热稳定性非常重要。我们报告了超高真空 (UHV) 下 SrTiO3 基底上支撑的 MoS2 单层热降解的研究结果。我们的研究是在 SrTiO3 基底的 (111)、(110) 和 (001) 末端进行的，但发现 MoS2 在所有这些表面上都会以类似的方式降解。通过扫描隧道显微镜，我们发现MoS2单层晶体在特高压下高达700摄氏度时仍能保持其结构，此时沿着MoS2晶体的<2(11)overbar0>晶格方向（即硫封端的边缘方向）出现三角形蚀刻沟槽。这些沟槽是由于硫的优先损失造成的，使得钼被源自 SrTiO3 基底的氧氧化。在此温度下处理后，A 激子光致发光 (PL) 峰以及 E-2g(1) 和 A(1g) 拉曼信号的强度显着降低。晶体在超高真空中较高的退火温度下继续降解，直到在 900 摄氏度下转变为 MoOx (x = 2-3) 颗粒，并且 MoS2 的光学特性在 PL 和拉曼光谱中完全丧失。 X射线光电子能谱证实了最初的硫损失和MoOx的形成。 MoS2 晶体的宏观三角形形状得以保留，直到残余颗粒在 1000 摄氏度以上蒸发。700 和 800 摄氏度 UHV 退火样品的光学性能可以在硫退火后部分恢复。这项工作建立了 SrTiO3 负载的单层 MoS2 在真空中热降解的途径，从光滑的 MoS2 晶体到具有硫空位（蚀刻沟槽）的晶体，然后是 MoO2，最后是 MoO3 颗粒。我们还演示了如何使用硫退火来修复缺陷。
Monolayer MoS2 is a wide-bandgap semiconductor suitable for use in high-temperature electronics. It is therefore important to understand its thermal stability. We report the results of a study on thermal degradation of MoS2 monolayers supported on SrTiO3 substrates in ultrahigh vacuum (UHV). Our studies were carried out on the (111), (110), and (001) terminations of SrTiO3 substrates, but MoS2 was found to degrade on all of these surfaces in a similar way. By scanning tunneling microscopy, we show that MoS2 monolayer crystals maintain their structure up to 700 degrees C under UHV, at which point triangular etch trenches appear along the < 2 (11) over bar0 > lattice directions (i.e., sulfur-terminated edge directions) of the MoS2 crystals. The trenches are due to the preferential loss of sulfur, allowing molybdenum to be oxidized by oxygen originating from the SrTiO3 substrate. The intensity of the A-exciton photoluminescence (PL) peak and the E-2g(1) and A(1g) Raman signals reduced significantly following treatment at this temperature. The crystals continue to degrade at higher annealing temperatures in UHV until they transform into MoOx (x = 2-3) particles at 900 degrees C, and the optical properties characteristic of MoS2 are lost entirely in PL and Raman spectra. The initial sulfur loss and the formation of MoOx are confirmed by X-ray photoelectron spectroscopy. The macroscopic triangular shapes of the MoS2 crystals are retained until the residual particles evaporate at above 1000 degrees C. The optical properties of the 700 and 800 degrees C UHV-annealed samples can be partially recovered upon sulfur annealing. This work establishes a pathway of the thermal degradation of SrTiO3-supported monolayer MoS2 in vacuum from smooth MoS2 crystals to crystals with sulfur vacancies (etch trenches), followed by MoO2 and finally MoO3 particles. We also demonstrate how sulfur annealing can be used to heal the defects.