Effects of pre-heating method on the optical, wetting, photo-catalytic and UV sensing properties of Al:ZnO thin films

Abstract

Aluminum doped zinc oxide thin films/ nanostructures have great importance in many technological applications such as transparent conducting oxides, photo-catalytic, electrochemical and opto-electronic devices. The pre-heating (drying) stage during sol–gel spin coating method is crucial for achieving better transparency level and smooth unstressed surface. In this research, effects of drying at fixed temperature (220 °C) and gradually rising temperature (rising rate 11 °C/min) under two different environments (i.e. temperature drying on i. hot plate ii. Oven) were explored. The SEM results showed that surface produced by fixed temperature drying on hot plate as well as in oven were cracked and rope stressed type, respectively. The texture obtained by gradually rising temperature was stressed granular on hot plate whereas uniformly distributed plane nano-granular in oven (on petri-dish). The XRD pattern revealed the polycrystalline nature and good crystal quality for sample with gradually rising temperature in oven. In case of gradually rising temperature in oven the maximum transmittance and band gap obtained were > 90% and 3.36 eV respectively. The refractive index and extinction coefficient were used to determine level of transparency in visible region by achieving values of 1.7 and 0.1 respectively. The super hydrophilic character achieved by contact angle 10° and better stain self-cleaning with degradation efficiency around 71% by photo-catalytic effect after UV irradiation. UV sensitivity was performed by using ardino microcontroller and max photo-response (voltage variation) was found 1.5 V. Moreover, response and recovery was around 14 s and 15 s respectively.