School of Materials Science and Engineering, Georgia Institute of Technology , 771 Ferst Drive, Atlanta, Georgia 30332, United States.
Materials Characterization Facility, Institute for Electronics and Nanotechnology, Georgia Institute of Technology , 345 Ferst Drive, Atlanta, Georgia 30332, United States.
ACS Appl Mater Interfaces. 2017 Sep 20;9(37):32394-32404. doi: 10.1021/acsami.7b10230. Epub 2017 Sep 5.
Nanoscale transition-metal dichalcogenide (TMDC) materials, such as MoS, exhibit promising behavior in next-generation electronics and energy-storage devices. TMDCs have a highly anisotropic crystal structure, with edge sites and basal planes exhibiting different structural, chemical, and electronic properties. In virtually all applications, two-dimensional or bulk TMDCs must be interfaced with other materials (such as electrical contacts in a transistor). The presence of edge sites vs basal planes (i.e., the crystallographic orientation of the TMDC) could influence the chemical and electronic properties of these solid-state interfaces, but such effects are not well understood. Here, we use in situ X-ray photoelectron spectroscopy (XPS) to investigate how the crystallography and structure of MoS influence chemical transformations at solid-state interfaces with various other materials. MoS materials with controllably aligned crystal structures (horizontal vs vertical orientation of basal planes) were fabricated, and in situ XPS was carried out by sputter-depositing three different materials (Li, Ge, and Ag) onto MoS within an XPS instrument while periodically collecting photoelectron spectra; these deposited materials are of interest due to their application in electronic devices or energy storage. The results showed that Li reacts readily with both crystallographic orientations of MoS to form metallic Mo and LiS, while Ag showed very little chemical or electronic interaction with either type of MoS. In contrast, Ge showed significant chemical interactions with MoS basal planes, but only minor chemical changes were observed when Ge contacted MoS edge sites. These findings have implications for electronic transport and band alignment at these interfaces, which is of significant interest for a variety of applications.
纳米级过渡金属二卤族化合物（TMDC）材料，如 MoS，在下一代电子和储能设备中表现出有前景的性能。TMDC 具有各向异性的晶体结构，边缘位和基面表现出不同的结构、化学和电子特性。在几乎所有应用中，二维或块状 TMDC 必须与其他材料（如晶体管中的电接触）接口。边缘位与基面（即 TMDC 的晶体取向）的存在可能会影响这些固态界面的化学和电子特性，但这些影响尚未得到很好的理解。在这里，我们使用原位 X 射线光电子能谱（XPS）来研究 MoS 的晶体学和结构如何影响与各种其他材料的固态界面的化学转化。制备了具有可控排列晶体结构的 MoS 材料（基面的水平和垂直取向），并在 XPS 仪器中通过溅射沉积三种不同的材料（Li、Ge 和 Ag）到 MoS 上来进行原位 XPS，同时定期收集光电子能谱；这些沉积材料由于它们在电子器件或储能中的应用而具有重要意义。结果表明，Li 很容易与 MoS 的两种晶体取向反应，形成金属 Mo 和 LiS，而 Ag 与任何一种 MoS 的化学或电子相互作用都非常小。相比之下，Ge 与 MoS 基面表现出显著的化学相互作用，但当 Ge 接触 MoS 边缘位时，仅观察到微小的化学变化。这些发现对这些界面的电子输运和能带排列具有重要意义，这对各种应用都具有重要意义。
