Controlled growth and STM study of selenium nanostructures on Au(110) surface

Lakmal Ruwan Kumara^1*, Prakash Gautam¹, Liang-Wei Lan¹, Chien-Cheng Kuo¹

¹Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan

* Presenter:Lakmal Ruwan Kumara, email:ruwan07512@gmail.com

Trigonal selenium (t-Se) has gained much attention recently due to its observed and predicted intriguing electronic properties, such as current-induced spin polarization and spin Hall effect [1, 2, 3]. Further, previous theoretical studies have predicted that t-Se under strain can exhibit even more compelling phenomena, including a Weyl-semimetal state and a hedgehog-like radial spin texture [2]. While hydrostatic pressure can introduce strain in t-Se, its complexity and incompatibility limit the practical applications. Exploiting substrate-induced strain, in contrast, offers a straightforward approach to explore such properties in materials. However, Se, being a polymorphic material, occurs in several forms, necessitating the study of its growth mechanisms and structural transitions in order to comprehend the formation of strained t-Se. In ultra-high vacuum (UHV) deposition, a patterned substrate can guide adatom ordering through its preferential adsorption sites that reflect the underlying surface structure, thereby inducing strain in the deposited film.

Here, we chose Au(110) as the substrate to grow Se structures using UHV Se deposition, anticipating that the anisotropic Au(110) surface will introduce strain in as-grown Se structures. Further, we report epitaxial growth of distinct Se nanostructures by controlling Se coverage, substrate temperature, and post-annealing parameters. The as-grown structures probed with Low-Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM) revealed well-ordered structures, indicating a strong Se-Au interaction. Notably, one of the observed structures persisted up to about 400 ℃. This thermal stability suggests its potential to serve as a Se reservoir for growing Se-based compounds, eliminating the need for co-deposition, thereby minimizing the risk of Se contamination in UHV environments, experienced in traditional co-deposition methods.

References

[1] Ramírez-Montes, L., (2024). Physical Review Materials, 8 (6), 063601.
[2] Hirayama, M., (2015). Physical review letters, 114 (20), 206401.
[3] Roy, A., (2022). npj Computational Materials, 8 (1), 243.

Keywords: current-induced spin polarization, Weyl-semimetal, spin Hall effect