# Recent Progress on Irradiation-Induced Defect Engineering of Two-Dimensional 2H-MoS2 Few Layers
## 7 Conclusions and Outlook  
Semiconducting MoS\({}_{2}\) 2D layers have unique transport properties and have been applied in various devices. Their band-gap, doping, photonic, electric, electronic, magnetic, chemical, and bio-properties can be tuned effectively and simply by defect engineering. Various irradiation exposures, including swift-heavy ions, argon ions, alpha particles, protons, electrons, electromagnetic waves, can significantly induce defects in MoS\({}_{2}\) few-layers to manipulate various properties essentially. Various defects, mainly sulfur vacancies and molybdenum vacancies, have been generated/created in MoS\({}_{2}\) layers. MoS\({}_{2}\) layers can be significantly activated, functionalized, and modified. The irradiation-induced defects are beneficial for several applications including: solar cells [19; 19; 19; 194; 195; 196], batteries [54; 197; 198], supercapacitors [199], thin film transistors [15; 16; 80; 86; 110; 138; 200; 201; 202; 203; 204; 205], sensors [17; 55; 56; 106; 207; 208; 209; 210], hydrogen generators [8; 47; 50; 69; 134; 176; 177; 183; 211; 212], and applications in thermoelectrics [213; 214; 215; 216], piezotronics [63], valleytronics [65], and environments [45; 49]. MoS\({}_{2}\) 2D layers were damaged simultaneously under the irradiation and lost their unique properties. Therefore, it is critical to control the irradiation exposure to tune MoS\({}_{2}\) properties by the irradiation-induced defect engineering while avoid potential damages.  
Besides MoS\({}_{2}\) 2D layers, the irradiation techniques can be employed to tune physical properties of other disulfide 2D materials, such as NiS\({}_{2}\) urea-electrocatalysts [217], WS\({}_{2}\) hybrid catalysts [218], as well as selenide water-electrocatalysts [219], perovskite electrocatalytic nanoparticles [220], C\({}_{3}\)N\({}_{4}\) catalytic materials [221], hydroxide nanosheet battery-electrodes [222], oxide photocatalysts [223], low-dimensional thermoelectric materials [224; 225], graphene and carbon nanotubes [226; 227; 228], and even porous electrodes [229; 230].  
[PERSON] and [PERSON] conceived the idea, designed and went through with the manuscript. [PERSON] wrote the section of alpha-particle irradiation. [PERSON] and [PERSON] wrote the section of UV irradiation. [PERSON] and [PERSON] wrote the section of proton irradiation. [PERSON] was in charge of the section of magnetic properties. [PERSON] took charge of the theoretical analysis on irradiation. [PERSON] summarized background of MoS\({}_{2}\) materials. [PERSON]-[PERSON] was in charge of Raman scattering. [PERSON]-[PERSON] and [PERSON] wrote other sections. All authors provided constructive comments on the manuscript.  
Figure 35: (a) \(M\) vs \(H\) curve for a pristine without irradiation and an irradiated MoS\({}_{2}\) micron-thick flake at a fluence of \(5\times 10^{18}\) protons/cm\({}^{2}\) and (b) magnetization as a function of proton fluence from \(1\times 10^{17}\) protons/cm\({}^{2}\) to \(5\times 10^{18}\) protons/cm\({}^{2}\)[85]. Reprinted from Reference [85], with the permission of AIP Publishing.  
**Funding:** Y.L. is partially supported by the Army Research Laboratory under Cooperative Agreement Number W911 NF-12-2-0022. A.L. is thankful to the financial support from the National Science Foundation through research grant NSF DMR 1206380. C.W. thanks the financial support from the National Natural Science Foundation of China (grants 51502099), the National Key Research and Development Program of China (Grant No. 2017 YFE0120500), and the Hubei \"Chu-Tian Young Scholar\" program.  
**Acknowledgments:** The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U. S. Government. The U. S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.  
**Conflicts of Interest:** The authors declare no conflict of interest.