Bond Confinement-Dependent Peierls Distortion in Epitaxially Grown Bismuth Films

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Bismuth (Bi) is a semimetal with unique electronic properties.
• Thin films exhibit size-dependent phenomena crucial for electronic applications.
• Metavalent bonding presents a distinct bonding paradigm influencing material properties.

Purpose of the Study:

• To systematically investigate the influence of film thickness on the physical properties of bismuth films.
• To understand the underlying mechanisms responsible for thickness-dependent property variations.
• To explore the potential for tailoring bismuth film properties via thickness control.

Main Methods:

• Epitaxial growth of high-quality bismuth films on Si(111) substrates with varying thicknesses (1.9–29.9 nm).
• Broadband optical spectroscopy to analyze optical dielectric constant and absorption spectra.
• Raman and pump-probe spectroscopy to study phonon mode frequencies.
• X-ray diffraction to assess structural changes like Peierls distortion.
• Quantum chemical bonding analysis and density functional theory (DFT) calculations.

Main Results:

• Decreasing film thickness led to a reduced optical dielectric constant and absorption peak height.
• Absorption maxima shifted to higher photon energies with decreasing thickness.
• Phonon mode frequencies increased with reduced thickness, showing a 10% rise in in-plane mode frequency.
• X-ray diffraction indicated an increasing Peierls distortion in thinner films.
• DFT calculations revealed an interplay between electron localization and delocalization influencing properties.

Conclusions:

• Film thickness is a critical parameter for tuning the properties of bismuth films.
• Observed changes are attributed to increased Peierls distortion and metavalent bonding characteristics.
• Thickness reduction offers a viable route to engineer material properties without altering stoichiometry.