I am trying to deposit a thin layer of TiO2, Could you please help me with your suggestions?
I need to tell that the precursor I use is Titanium Butoxide and the solvent is normal propanol.
But I wonder quite about the result of my experiments, In a series of experiments I have used a solution of 0.3 M precursor, soaking time 2 minutes and withdrawal speed of 0.5 mm/s, and the thickness of coated layer measured 180 nm.
In another series, the molarity was decreased to 0.2 M, with the same soaking time and withdrawal speed of 0.8 mm/s, however, the average thickness has increased to 250 nm.
Can anyone please let me know how it is possible as with decreasing the concentration of precursor it is expected to obtain a thinner layer.
Dear Mahsa Amiri,
Can you try to use much less concentration such as 0.01M, 0.05 M and 0.1M using the same speed for dip coating. The thickness of the films should be thinner.
Best luck
Xuhua
Your withdrawal speed is very low I would say. To obtain 30 nm layer, withdrawal at the speed in range of 2.5 cm/min should be used. Another important issue is the viscosity of your sol solution. The more viscous the sol is, the thicker the layers are. And be aware that viscosity depends not only on the concentration of precursor but also e.g. on the concentration of initiator (like acid or base) which enables chains formation in sol.
which solvent do you use for dispersion? concentration of precursors do matter. Nevertheless, change the immersion time.
Dear Mahsa Amiri
Dip coating, despite its apparent simplicity, is actually the result of a complex interaction among several factors: force of gravity, surface tension and its gradient along the film, viscous upward drag, etc.
So to get the film thickness you like, you should pay attention to the following
density and viscosity of the solution
immersion time
withdrawal speed
evaporation conditions
It depends on the Ti precursor you are using, for example try this 10 ml of D.I water in a pettri desh + 4 ul of TiCL4 diluted by Ethanol, keep the conductive samples FTO or ITO inside the pettri desh on 70C for 30 min, the concentration of diluted TiCL4 will determine the thickness. Or use 0.15 Tidiisopropoxide in IPA or Ethanol, same method, make sure the solution won’t evaporate, the samples after 70C 30 min not white.
So if you're using Titanium Butoxide, I've never dealt with, but if possible to try another solvent like IPA or Ethanol maybe the Viscosity less than propanol, again check the literature, Attached is a picture of compact layer of TiO2 using dip coating as I described above the source of Ti is TiCl4, thickness 60-80 nm on FTO.
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