Department of Electrical Engineering, Indian Institute of Technology, Bombay 400076, India.
School of Nano Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
ACS Sens. 2021 Sep 24;6(9):3398-3408. doi: 10.1021/acssensors.1c01258. Epub 2021 Sep 8.
Two-dimensional layered materials (like MoS and WS) those are being used as sensing layers in chemoresistive gas sensors suffer from poor sensitivity and selectivity. Mere surface functionalization (decorating of material surface) with metal nanoparticles (NPs) might not improve the sensor performance significantly. In this respect, doping of the layered material can play a significant role. Here, we report a simple yet effective substitutional doping technique to dope MoS with noble metals. Through various material characterization techniques like X-ray diffraction, scanning tunneling spectroscopy images, and selected area electron diffraction pattern, we were able to put forward the difference between surface decoration and substitutional doping by Au at S-vacancy sites of MoS. Lattice strain was found to exist in the Au-doped MoS samples, while being absent in the Au NP-decorated samples. Surface chemistry studies performed using X-ray photoelectron spectroscopy showed a shift of Mo 3d peaks to lower binding energies, thus realizing -type doping due to Au. The blue shift of the peaks as observed in Raman spectroscopy further confirmed the -type doping. We found that gold-doped MoS was more sensitive and selective toward ammonia (with a response of 150% for 500 ppm of ammonia at 90 °C) as compared to gold NP-decorated MoS. The advantages of substitutional doping and the gas-sensing mechanism were also explained by the density functional theory study. From the first principles study, it was found that the adsorption of Au atoms on the S-vacancy site of a monolayer of the MoS sheet was thermodynamically favorable with the adsorption energy of 2.39 eV. We also successfully doped MoS with Pt using the same technique. It was found that Pt-doped MoS gives huge response toward humidity (60,000% at 80% relative humidity). Thus, various noble metal doping of MoS selectively improved the sensing response toward specific analytes. From this work, we believe that this method could also be useful to dope other layered nanomaterials to design gas sensors with improved selectivity.
二维层状材料（如 MoS 和 WS）被用作化学电阻式气体传感器中的传感层，其灵敏度和选择性较差。仅仅通过金属纳米粒子（NPs）对材料表面进行功能化（材料表面的修饰）可能不会显著提高传感器的性能。在这方面，层状材料的掺杂可以发挥重要作用。在这里，我们报告了一种简单而有效的替代掺杂技术，即用贵金属对 MoS 进行掺杂。通过各种材料特性表征技术，如 X 射线衍射、扫描隧道显微镜图像和选区电子衍射图案，我们能够提出在 MoS 的 S 空位处用 Au 进行表面装饰和替代掺杂之间的区别。发现晶格应变存在于 Au 掺杂的 MoS 样品中，而在 Au NP 修饰的样品中则不存在。使用 X 射线光电子能谱进行的表面化学研究表明，Mo 3d 峰向较低的结合能移动，从而由于 Au 实现了 n 型掺杂。拉曼光谱中观察到的峰的蓝移进一步证实了 n 型掺杂。我们发现，与 Au NP 修饰的 MoS 相比，金掺杂的 MoS 对氨气更敏感和选择性（在 90°C 时，对 500 ppm 的氨气的响应为 150%）。还通过密度泛函理论研究解释了替代掺杂的优势和气体传感机制。从第一性原理研究中发现，Au 原子在 MoS 单层的 S 空位上的吸附在热力学上是有利的，吸附能为 2.39 eV。我们还使用相同的技术成功地对 MoS 进行了 Pt 掺杂。发现 Pt 掺杂的 MoS 对湿度具有巨大的响应（在 80%相对湿度下为 60,000%）。因此，各种贵金属对 MoS 的掺杂选择性地提高了对特定分析物的传感响应。从这项工作中，我们相信这种方法也可用于掺杂其他层状纳米材料，以设计具有改进选择性的气体传感器。
