Photoluminescence Induced by Substitutional Nitrogen in Single-Layer Tungsten Disulfide
Qingkai Qian, Wenjing Wu, Lintao Peng, Yuanxi Wang, Anne Marie Z. Tan, Liangbo Liang, Saban M. Hus, Ke Wang, Tanushree H. Choudhury, Joan M. Redwing, Alexander A. Puretzky, David B. Geohegan, Richard G. Hennig, Xuedan Ma, Shengxi Huang
Abstract
The electronic and optical properties of two-dimensional materials can be strongly influenced by defects, some of which can find significant implementations, such as controllable doping, prolonged valley lifetime, and single-photon emissions. In this work, we demonstrate that defects created by remote N2 plasma exposure in single-layer WS2 can induce a distinct low-energy photoluminescence (PL) peak at 1.59 eV, which is in sharp contrast to that caused by remote Ar plasma. This PL peak has a critical requirement on the N2 plasma exposure dose, which is strongest for WS2 with about 2.0% sulfur deficiencies (including substitutions and vacancies) and vanishes at 5.6% or higher sulfur deficiencies. Both experiments and first-principles calculations suggest that this 1.59 eV PL peak is caused by defects related to the sulfur substitutions by nitrogen, even though low-temperature PL measurements also reveal that not all the sulfur vacancies are remedied by the substitutional nitrogen. The distinct low-energy PL peak suggests that the substitutional nitrogen defect in single-layer WS2 can potentially serve as an isolated artificial atom for creating single-photon emitters, and its intensity can also be used to monitor the doping concentrations of substitutional nitrogen.