Defect-induced tuning of the photoluminescence emission in WSe2 monolayers by energetic species bombardment

2018 E-MRS Spring Meeting and Exhibit will be held in the Convention Centre of Strasbourg (France), from June 18 to 22, 2018. --. https://www.european-mrs.com/meetings/2018-spring-meetingTwo-dimensional (2D) semiconductor transition-metal-dichalcogenides (TMDCs) show appealing and unique electrical and optical properties including indirect to direct band-gap transition in monolayer crystals with strong optical emission at room temperature, which makes them ideal candidates for optoelectronic and photonic applications (1). The recent discovery of single photon emission in 2D materials at low and room temperature has triggered an intensive research of new procedures for the deterministic fabrication of such emitters (2). In a previous work we showed that WSe2 monolayers can be encapsulated with a dielectric film by pulsed laser deposition (PLD) without inducing modification of their photoluminescence (PL) emission (3). Here we report on the generation of defects in WSe2 monolayer flakes in order to modify their PL. The defects are induced upon deposition of ultra-thin Al2O3 layers by PLD (¿ 10 nm). The PL of the encapsulated WSe2 monolayers has been assessed by micro-PL studies at RT and 10 K. Our findings show that as a result of the PLD deposition the characteristic PL emission of the WSe2 monolayers can be tuned by varying the deposition conditions. We discuss the influence of the nature and concentration of the induced defects on the PL, and how these defects can be modified by varying the kinetic energy of the ions during deposition. (1) Bhimanapati, G. R. et al. Recent Advances in Two-Dimensional Materials beyond Graphene. ACS Nano 9, 11509¿11539 (2015); (2) Grosso, G. et al. Tunable and high-purity room temperature single-photon emission from atomic defects in hexagonal boron nitride. Nat. Commun. 8, 705 (2017); (3) Martín-Sánchez, J. et al. Effects of dielectric stoichiometry on the photoluminescence properties of encapsulated WSe2 monolayers. Nano Res. 1, 1¿16 (2017)