iScience
Volume 24, Issue 9, 24 September 2021, 102990
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Article
Pressure dependent thermoreflectance spectroscopy induced by interband transitions in metallic nano-film

https://doi.org/10.1016/j.isci.2021.102990Get rights and content
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Highlights

  • Thermoreflectance (dR/dT) of Al films was measured under a pressure range of 0–25 GPa

  • A semi-quantum model well describes the pressure effect on optical properties

  • Pressure enlarges interband transition energy which makes dR/dT pressure-dependent

  • The resonant interband transitions let dR/dT change to negative at ∼6 GPa

Summary

Utilizing high-pressure to modulate optical properties, such as thermoreflectance (dR/dT), over a wide range has received much attention. Nevertheless, how the pressure exerts on the complex dielectric constant and finally on dR/dT remains elusive. Here, we perform a thoroughly experimental and theoretical investigation on dR/dT of Al nano-film from 0 to 25 GPa. The dR/dT values exhibit a sine-like pressure-dependence, with the zero-crossing appearing at around 6 GPa. These special phenomena are well explained from electron transition viewpoints. The first-principles calculations show that the energy difference of parallel bands is enlarged from 1.45 to 2 eV, thereby increasing the threshold for electron transitions. The lifted threshold changes the optical absorption rates of Al and the density of states of the electrons involving interband transitions; finally, the resulting dR/dT exhibits such a pressure-dependent behavior. Our findings provide a deep insight on pressure-induced electronic transitions and photon-electron interactions in metals.

Subject areas

Condensed matter physics
Nanotechnology
Materials synthesis

Data and code availability

  • Data reported in this paper will be shared by the lead contact upon request.

  • This paper does not report original codes. Computational algorithms are written in the STAR Methods.

  • Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

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