CC BY
24LP-I-3
Direct laser synthesis of two-dimensional transition metal dichalcogenides in ambient conditions
S. Mailis1, O. Abbas2, A.H. Lewis2, N. Aspiotis2, C.C. Huang2,1. Zeimpekis2, D. Hewak2, P. Sazio2 1Skolkovo Institute of Science and Technology, Photonics and Quantum Materials, Moscow, Russian Federation
2University of Southampton, Optoelectronics Research Centre, Southampton, United Kingdom
The emergence of nanomaterials with their often superior mechanical, electronic, magnetic and optical properties compared with bulk, demands a mature and robust technology that can synthesize, modify and pattern both scalably and cost effectively. This can be fulfilled via laser processing protocols which produce such materials with both high precision and excellent spatial controllability [1]. Direct laser synthesis of nanomaterials such as graphene and nano-structured metal oxides have been explored thoroughly for a wide range of applications [2,3]. However, to date, there are only a few reports associated with the laser processing of two-dimensional transition metal dichalcogenides (2D-TMDCs) [4]. These mainly utilize laser radiation for thinning thick TMDC films through sublimation down to a single molecular layer [1]. However, this top-down approach is not practical for large-area and scalable production. In addition, further processing steps such as micro-patterning are then required for discrete device fabrication.
Here we present a novel method for the local synthesis and patterning of MoS2 and WS2 2D layers. The synthesis of these materials is achieved by spatially selective, visible laser irradiation of suitable precursors, which are deposited, on the surface of planar substrates under ambient, room temperature conditions. The non-exposed precursor regions are then completely removed in a single step, revealing the synthesised 2D material. This method can produce micro-patterned films with lateral dimensions that can be as narrow as the diffraction limit of the focussed laser beam permits. An example of such laser synthesised MoS2 tracks can be seen in the optical microscopy image of Figure 1(a). Using this method we have achieved local synthesis of of MoS2 and WS2 with thickness down to three layers for MoS2 and monolayer WS2 on various glass and crystalline substrates. The quality and thickness of the resulting films can be tuned by modifying the precursor chemistry and laser parameters. Different microprobe and spectroscopic techniques, such as optical microscopy, stylus profilometry, Raman spectroscopy, photoluminescence spectroscopy (PL) and X-ray photoelectron spectroscopy (XPS) have been used to assess the quality and thickness of the deposited MoS2 and WS2 structures. Finally, we have demonstrated the electronic functionality of our films by fabricating a thin film transistor (TFT). The transfer characteristics of such a TFT (source-drain current vs gate voltage) using a laser-synthesised MoS2 channel is shown in Figure 1(b).
Fig. 1. (a) optical microscopy image of MoS2 tracks deposited by direct laser synthesis on SiO2/Si substrte. (b) transfer characteristics (source-drain current vs gate voltage) of a back-gate thin film transistor (TFT) using a laser
synthsised MoS2 channel.
References
[1] S. Hong, H. Lee, J. Yeo, and S. H. Ko, "Digital selective laser methods for nanomaterials: From synthesis to processing," Nano Today. 11, 547-564 (2016).
[2] M. F. El-Kady and R. B. Kaner, "Direct Laser Writing of Graphene Electronics," ACS Nano. 8, 87258729 (2014).
[3] H. Palneedi, J. H. Park, D. Maurya, M. Peddigari, G. T. Hwang, V. Annapureddy, J. W. Kim, J. J. Choi, B. D. Hahn, S. Priya, K. J. Lee, and J. Ryu, "Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances," Adv. Mater. 30, 1705148 (2018).
[4] M. Samadi, N. Sarikhani, M. Zirak, H. Zhang, H. L. Zhang, and A. Z. Moshfegh, "Group 6 transition metal dichalcogenides nanomaterials: Synthesis, applications and future perspectives," Nanoscale Horiz. 3, 90-204 (2018).
