Integration of 2D PtSe₂ nanolayers in device applications

We report the synthesis details of 2D PtSe2 layers on soda lime (glass) substrates by selenization of pre-deposited Pt films using thermally assisted conversion (TAC) method at 430°C and atmospheric pressure. PtSe2 layers with different thicknesses were prepared by varying the Pt deposition time (Pt 3s, Pt 8s and Pt 10s), afterwards estimated by ellipsometric measurements to correspond to 7nm, 9 nm and 12nm, respectively. The X-Ray diffraction patterns showed the diffraction peaks characteristic with improving crystallinity when increasing the Pt deposition time. The Raman spectra revealed typical PtSe2 modes, while a decrease of Se/Pt ratio and a transition from p-doped to n-doped PtSe2 for longer Pt deposition times was found by X-ray photoelectron spectroscopy analysis. Formation of reactive oxygen species (ROS), mainly hydroxyl radicals (OH) on the PtSe2 surface under light irradiation was demonstrated by EPR analysis.
PtSe2 coatings demonstrate antibacterial activity against Escherichia coli in dark and under light irradiation owing to their 2D layered morphology, crystalline structure and optical properties. The antibacterial activity was tested applying ISO standard procedure: (i) in dark, the antibacterial activity increased with the increase of Pt deposition time and the viability of the bacteria was reduced to 30% (Pt 3s) and 15% (Pt 10s) after treatment for 6 h. The effect was attributed to the increasing film thickness, roughness and surface coverage which facilitate the mechanical destruction of the bacteria cell; (ii) under light irradiation, the activity of PtSe2 (Pt 3s) was similar to that in dark showing low sensitivity to light. On the contrary, the PtSe2 (Pt 8s) and (Pt 10s) appeared very effective under light, with the bacteria viability after 6 h being only 7.3% and 1.2%, respectively. The observed photo-induced antibacterial activity is related to the synergy of several parameters, i.e. high crystallinity, semiconductor behavior and chemical composition.
In addition, integration of PtSe2 as transparent, conductive layers in Polymer Dispersed Liquid Crystal (PDLC) structures operating as near infrared light shutters is demonstrated. The proposed simple and inexpensive synthesis approach opens new directions towards PtSe2 potential technological applications, including ITO-free optoelectronics.
Acknowledgement: We acknowledge the support of Bulgarian Science Fund under the project number FNI KP-06-H58/12. Financial support from the Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science is also acknowledged. V.M. and N.M. acknowledge the financial support by the European Regional Development Fund within the Operational Programme“Science and Education for Smart Growth 2014−2020” under the Project CoE ‘National Center of Mechatronics and Clean Technologies’ BG05M2OP001-1.001-0008-C01.