Fabrication and characterization of vacuum deposited fluorescein thin films

TL;DR

This study presents a simple vacuum evaporation method for depositing fluorescein thin films on various substrates, analyzing how substrate material and film thickness influence optical properties and electron transfer in nanoscale optoelectronic devices.

Contribution

Developed a compatible vacuum evaporation technique for dye thin films, enabling nanoscale optoelectronic device fabrication with substrate-dependent optical and electronic properties.

Findings

Surface topology varies with film thickness and substrate.

Absorption spectra depend on substrate material, with TiO2 causing red shift.

Emission spectra are substrate and thickness dependent, with quenching on TiO2.

Abstract

Simple vacuum evaporation technique for deposition of dyes on various solid surfaces has been developed. The method is compatible with conventional solvent-free nanofabrication processing enabling fabrication of nanoscale optoelectronic devices. Thin films of fluorescein were deposited on glass, fluorine-tin-oxide (FTO) coated glass with and without atomically layer deposited (ALD) nanocrystalline 20 nm thick anatase TiO2 coating. Surface topology, absorption and emission spectra of the films depends on their thickness and the material of supporting substrate. On a smooth glass surface the dye initially formes islands before merging into a uniform layer after 5 to 10 monolayers. On FTO covered glass the absorption spectra are similar to fluorescein solution in ethanol. Absorption spectra on ALD-TiO2 is red shifted compared to the film deposited on bare FTO. The corresponding emission spectra at {\lambda} = 458 nm excitation show various thickness and substrate dependent features, while the emission of films deposited on TiO2 is quenched due to the effective electron transfer to the semiconductor conduction band.