Chamlagain Bhim, Khondaker Saiful I
NanoScience Technology Center and Department of Physics, University of Central Florida, Orlando, Florida 32826, United States.
School of Electrical Engineering and Computer Science, University of Central Florida, Orlando, Florida 32826, United States.
ACS Omega. 2021 Sep 9;6(37):24075-24081. doi: 10.1021/acsomega.1c03522. eCollection 2021 Sep 21.
The MoS thin film has attracted a lot of attention due to its potential applications in flexible electronics, sensors, catalysis, and heterostructures. Understanding the effect of long-term ambient exposure on the electrical properties of the thin film is important for achieving many overreaching goals of this material. Here, we report for the first time a systematic study of electrical property variation and stability of MoS thin films under ambient exposure of up to a year. The MoS thin films were grown via the sulfurization of 6 nm thick molybdenum films. We found that the resistance of the samples increases by 114% just in 4 weeks and 430% in 4 months and they become fully insulated in a year of ambient exposure. The dual-sweep current-voltage (-) characteristic shows hysteretic behavior for a 4-month-old sample which further exhibits pronounced nonlinear - curves and hysteretic behavior after 8 months. The X-ray photoelectron spectroscopy measurements show that the MoS thin film gradually oxidizes and 13.1% of MoO and 11.8% oxide of sulfur were formed in 4 months, which further increased to 23.1 and 12.7% in a year, respectively. The oxide of the sulfur peak was not reported in any previous stability studies of exfoliated and chemical vapor deposition-grown MoS, suggesting that the origin of this peak is related to the distinct crystallinity of the MoS thin film due to its smaller grain sizes, abundant grain boundaries, and exposed edges. Raman studies show the broadening of E and A peaks with increasing exposure time, suggesting an increase in the disorder in MoS. It is also found that coating the MoS thin film with polymethylmethacrylate can effectively prevent the electrical property degradation, showing only a 6% increase in resistance in 4 months and 40% over a year of ambient exposure.
由于其在柔性电子、传感器、催化和异质结构等方面的潜在应用，二硫化钼（MoS）薄膜引起了广泛关注。了解长期环境暴露对薄膜电学性能的影响对于实现该材料的诸多长远目标至关重要。在此，我们首次报告了对MoS薄膜在长达一年的环境暴露下电学性能变化及稳定性的系统研究。MoS薄膜通过对6纳米厚的钼膜进行硫化生长而成。我们发现，样品的电阻在4周内仅增加114%，4个月内增加430%，并且在一年的环境暴露后完全绝缘。双扫描电流-电压（I-V）特性显示，对于一个4个月龄的样品呈现出滞后行为，在8个月后进一步表现出明显的非线性I-V曲线和滞后行为。X射线光电子能谱测量表明，MoS薄膜逐渐氧化，在4个月内形成了13.1%的MoO和11.8%的硫氧化物，在一年后分别进一步增加到23.1%和12.7%。在以往对剥离和化学气相沉积生长的MoS的任何稳定性研究中都未报道过硫氧化物峰，这表明该峰的起源与MoS薄膜由于其较小的晶粒尺寸、丰富的晶界和暴露的边缘而具有的独特结晶度有关。拉曼研究表明，随着暴露时间的增加，E和A峰变宽，表明MoS中的无序度增加。还发现，用聚甲基丙烯酸甲酯涂覆MoS薄膜可以有效防止电学性能退化，在4个月内电阻仅增加6%，在一年的环境暴露后增加40%。
