Authors: V. Ligatchev, E. Rusli, L-B Keng, L-F Khuen, Y. Rumin and J. Zhao
Affilation: Nanyang Technological University, Singapore
Pages: 381 - 384
Keywords: tantalum pentaoxide, nano-morphology, optical properties
Thin Ta2O5 layers (95 - 110 nm), deposited at room temperature using pulsed DC magnetron sputtering (PDCMS) in an argon-oxygen (Ar-O2) gas mixture, are investigated. The Ta2O5 samples were prepared at different Ar/O2 flow ratios (0.3 – 1.0), and then post-annealed in an oxygen ambient at 350, 600, and 900 0C. The XRD data clearly demonstrates the presence of a nanocrystalline phase in all the samples, including those that were as-deposited. The average size of the nano-crystals was estimated to range from 1.1 to 2.3 nm for the as-deposited samples and those annealed at 350 and 600 0C. For the films annealed at 900 0C, the average crystalline size varies from 10 to 16 nm. Nano-scaled morphology observed by AFM technique on the surfaces of all the Ta2O5 films studied. The samples annealed at 900 0C reveal nano-crystals with sizes of 5-15 nm, consistent with the results deduced from the XRD data. The Tauc bandgap, EG, varies across a relatively small range (4.30 – 4.53 eV) for the as-deposited samples and those annealed below 600 0C. However, it drops sharply to 3.6 eV for the films annealed at 900 0C. Such variation in EG are attributed to the quantum confinement effect.