Size-dependent thermo-optical properties of embedded Bi nanostructures

Area of Science:

• Materials Science
• Nanotechnology
• Optical Physics

Background:

• Bismuth (Bi) nanostructures embedded in amorphous aluminum oxide (Al(2)O(3)) thin films exhibit thermally induced optical transmission changes.
• Understanding size-dependent phase transitions in nanostructures is crucial for advanced material applications.

Purpose of the Study:

• Investigate the impact of characteristic nanostructure sizes (7-35 nm) on the optical transmission changes during melting and solidification of Bi.
• Analyze the relationship between nanostructure size and the melting/solidification temperatures and optical contrast.

Main Methods:

• Studied thermally induced optical transmission changes in Bi nanostructures within Al(2)O(3) thin films.
• Varied the characteristic sizes of Bi nanostructures to observe size-dependent effects.
• Analyzed the optical transmission-temperature hysteresis loops to determine melting and solidification points.

Main Results:

• Observed repeatable optical transmission-temperature hysteresis loops with sharp transitions at melting and solidification points.
• Melting and solidification temperatures decreased linearly with decreasing nanostructure size, deviating from bulk Bi.
• Melting temperatures were consistently higher than bulk Bi, attributed to Bi contraction and matrix effects.
• Optical contrast increased with nanostructure size, reaching up to 16%.

Conclusions:

• The size of Bi nanostructures significantly influences their melting and solidification temperatures and optical properties.
• The observed higher melting points are linked to contraction upon melting and surface energy balances with the Al(2)O(3) matrix.
• Solidification behavior showed a weaker size dependence, suggesting a volume-controlled process.
• Controlling Bi nanostructure dimensions allows tuning their operability as thermally driven optical switches over a 73 K range.