Transition metal dichalcogenides (TMDs) present a broad family of two-dimensional (2D) materials with properties ranging from insulators to superconductors. With the general formula of MX₂, the monolayer (1L) material consists of one plane of transition metal atoms M which is sandwiched between two planes of chalcogen atoms X. The most investigated TMD material is molybdenum disulfide – MoS₂. This semiconductor has a bandgap in the visible spectrum, making it a promising candidate for application in photovoltaics, solar cells, optoelectronics, field effect transistors [1-3]. Due to its 2D nature, MoS₂ is extremely susceptible to the environment: humidity, temperature, exposure to atmosphere [4]. For these reasons, the synthesis of high-quality monocrystals with non-deteriorating properties, is of great importance. Optimum synthesis conditions yield high-quality crystalline structure, which then in turn, leads to great properties – such as optical and electronic.

In the first part of my seminar I will discuss how different synthesis parameters influence the morphology and optical properties of MoS₂ samples [6]. In the second part, I will present the results of a detailed study on two different MoS₂ samples, synthesized under different growth temperatures, in order to understand the correlation between growth temperature and defects’ nature of the samples [6]. The influence of defects on optical and electronic properties is investigated with low-temperature photoluminescence measurements, room-temperature transient absorption microscopy, and Kelvin Probe Force Microscopy. In the final part of my talk, I will discuss how defects can be utilised in order to produce new properties in a host material via alloying and how apparently identical growth conditions can lead to different crystal structures.

REFERENCES

[1] J. S. Ross et al., Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p–n junctions, Nat Nanotechnol, vol. 9, no. 4, pp. 268–272, Apr. 2014.
[2] R. S. Sundaram et al., Electroluminescence in Single Layer MoS2, Nano Lett, vol. 13, no. 4, pp. 1416–1421, Apr. 2013.
[3] B. W. H. Baugher, H. O. H. Churchill, Y. Yang, and P. Jarillo-Herrero, Optoelectronic devices based on electrically tunable p–n diodes in a monolayer dichalcogenide, Nat Nanotechnol, vol. 9, no. 4, pp. 262–267, Apr. 2014.
[4] X. Wang et al., Defect Heterogeneity in Monolayer WS2 Unveiled by Work Function Variance, Chemistry of Materials, vol. 31, no. 19, pp. 7970–7978, Oct. 2019.
[5] A. Senkić, J. Bajo et al. Effects of CVD growth parameters on global and local optical properties of MoS2 monolayers, Materials Chemistry and Physics 296 (2023) 127185.
[6] A. Senkić et al. Microscopic Investigation of Intrinsic Defects in CVD Grown MoS2 Monolayers, IoP Nanotechnology, in review.

LOCATION:  Institute of Physics, 1st wing, big lecture hall + online

Seminar hosts: Neven Šantić and Damir Dominko