Sol–gel tantalum pentoxide thin films with tunable refractive index for optical sensing applications

• Published in: Optical and quantum electronics Vol. 52; no. 10
• Main Authors: Georgiev, R., Georgieva, B., Lazarova, K., Vasileva, M., Babeva, T.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.10.2020; Springer Nature B.V
• Subjects: Acetone; Advanced Photonics Meets Machine Learning; Characterization and Evaluation of Materials; Computer Communication Networks; Copolymers; Curve fitting; Destructive testing; Effective medium theory; Electrical Engineering; Electron diffraction; Ethanol; Lasers; Nondestructive testing; Optical Devices; Optical properties; Optics; Photonics; Physics; Physics and Astronomy; Refractivity; Sol-gel processes; Spectrum analysis; Spin coating; Tantalum; Tantalum oxides; Thin films; VOCs; Volatile organic compounds; Optical vapor sensing; Sol–gel; Ta; Pluronic PE; Mesoporosity; O; thin films
• ISSN: 0306-8919; 1572-817X
• DOI: 10.1007/s11082-020-02540-0

Present study aims at development of thin films of sol–gel Ta 2 O 5 with tunable refractive index that could be used as an active medium for volatile organic compound (VOCs) optical detection. In order to tune the refractive index, mesoporosity is introduced through soft templating approach where series of co-polymers (Pluronics) are utilized as structure-directing agents. Thin films are prepared by spin-coating method using tantalum sol synthesized from TaCl 5 as a precursor and ethanol as a solvent. The temperature annealing at 320 °C finalizes the tantalum oxide lattice formation and decomposes the template being used. The morphology and elemental composition of the films are studied by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy in STEM, respectively, and the amorphous status of the films is confirmed by selected area electron diffraction. Non-linear curve fitting method and non-destructive UV–Vis reflectance measurements are used for determination of optical parameters of the films. The free volume fraction in the films is estimated through modeling of refractive index by Bruggeman effective medium approximation. The films are exposed to acetone vapors as a commonly studied VOC. The reaction of the film due to vapors’ exposure is recorded as a change in the reflection spectra of the film and the adsorbed acetone quantity is estimated. The influence of template composition on optical and sensing properties of Ta 2 O 5 films is revealed and discussed.