10.1021/nn5047844.s001 Peida Zhao Peida Zhao Daisuke Kiriya Daisuke Kiriya Angelica Azcatl Angelica Azcatl Chenxi Zhang Chenxi Zhang Mahmut Tosun Mahmut Tosun Yi-Sheng Liu Yi-Sheng Liu Mark Hettick Mark Hettick Jeong Seuk Kang Jeong Seuk Kang Stephen McDonnell Stephen McDonnell Santosh KC Santosh KC Jinghua Guo Jinghua Guo Kyeongjae Cho Kyeongjae Cho Robert M. Wallace Robert M. Wallace Ali Javey Ali Javey Air Stable p‑Doping of WSe<sub>2</sub> by Covalent Functionalization American Chemical Society 2014 transition metal dichalcogenides XAS XPS hole concentration WSe 2 Se vacancy sites TMDC spectroscopy Covalent FunctionalizationCovalent functionalization Ab initio simulations WSe 2 thickness 2014-10-28 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Air_Stable_p_Doping_of_WSe_sub_2_sub_by_Covalent_Functionalization/2241469 Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-stable chemical doping. Specifically, p-doping of WSe<sub>2</sub> <i>via</i> NO<sub><i>x</i></sub> chemisorption at 150 °C is explored, with the hole concentration tuned by reaction time. Synchrotron based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) depict the formation of various WSe<sub>2–<i>x</i>–<i>y</i></sub>O<sub><i>x</i></sub>N<sub><i>y</i></sub> species both on the surface and interface between layers upon chemisorption reaction. <i>Ab initio</i> simulations corroborate our spectroscopy results in identifying the energetically favorable complexes, and predicting WSe<sub>2</sub>:NO at the Se vacancy sites as the predominant dopant species. A maximum hole concentration of ∼10<sup>19</sup> cm<sup>–3</sup> is obtained from XPS and electrical measurements, which is found to be independent of WSe<sub>2</sub> thickness. This degenerate doping level facilitates 5 orders of magnitude reduction in contact resistance between Pd, a common p-type contact metal, and WSe<sub>2</sub>. More generally, the work presents a platform for manipulating the electrical properties and band structure of TMDCs using covalent functionalization.