Dear colleague Gopi Krishnan Dendukuru ,

Have a nice time and good day.

To get a uniform thickness please check the next:

1- Check the equilibrium of the spin coater. and consequently the substrate

2- Put the drop carefully on the center of the substrate. 

I wish this is useful and help you.

Yours

A. El-Denglawey

Thanks a lot A. El-Denglawey for the suggestions. I'll go through the suggestions to rectify the defect. The other scenario that I must ensure is the solubility of Titanium diisopropoxide, as the islands were found uniformly throughout the substrate.

I bet your most severe issue is the cleanliness of the substrate - it must be perfectly wettable otherwise the spin-coated layer will always break up in droplets and you get "island" patterns

Roman kubrin thanks for the response, I followed a cleaning process from beginning. Cleaning in deionized water(Helmanex added ), followed by sonication in isopropanol and rinsing in deionized water (60C)  again. This gave good results for most of the films that we prepared. Can you let me know about how the substrate wettability has to be improved. 

If you dip your freshly cleaned substrate in ethanol and pull it out vertically, does the  solvent stay a continuous film or it produces separate droplets on the surface? What is the material of the substrate?

I think problem is from TiO2 particle dispersion or problem with ethanol, disperse the particle using  tip sonicator, it may help.

Hello Karwan ,hope you are fine.

Try to adjust the substrate temperature and the speed of spinning. Can you use the Si (100) as substrate? However, there are other techniques for preparation the Titanium oxide such as MOCVD Method in addition to Sol-Gel based process, you can try that.