Surface modification of XSe (X = Cu and Ag) monolayers by grope 1 elements: A metal to semiconductor transition by a first-principles perspective.

Two-dimensional (2D) materials can be effectively functionalized by chemically modified using doping. Very recently, a flat AgSe monolayer was successfully prepared through direct selenization of the Ag(111) surface. Besides, the results indicate that the AgSe monolayer like CuSe, has a honeycomb lattice. Motivated by the experimental outcomes, in this work, employing first-principles calculations, we systematically investigate the electronic and optical properties of AgSe and CuSe monolayers, as well as the impact of alkali metals (Li, Na and K). Without functionalization, both the CuSe and AgSe monolayers exhibit metallic characteristics. The Li (Na)-CuSe and Na (K)-AgSe systems are dynamically stable while, the K- and Li-CuSe and Li-AgSe are dynamically unstable. Interestingly, the functionalized CuSe system with Li and Na atom as well as AgSe with K and Na atom, can open the band gaps, leading to the actualization of metal to semiconductor transitions. Our results show that, the electronic characteristics of the Na-CuSe/AgSe system can be modulated by adjusting the adsorption heights, which gives rise to the change in the electronic properties and the band gap may be controlled. Furthermore, from the optical properties we can find that the K-AgSe system is the best candidate monolayer to absorb infrared radiation and visible light. Consequently, our findings shed light on the functionalization of 2D materials based CuSe and AgSe monolayers and can potentially enhance and motivate studies in producing these monolayers for current nanodevices and future applications.