Mainly contamination, I consider the oxygen as contamination too

@ Mohammad Reza Zamani Kouhpanji but after checking with EDS, there is no foreign substance on the surface of the material. Only state Ti + Oxygen which is the main element that I use. So what is your suggestion to check whether the sample is contamination or not other than EDS?

Dear Syahirah

Do you test the phase stability of your sample with different oxygen flow rates? In some layers nonstochiometry of containing elements make them hydrophobic like TiO2, So I think the main problem is oxidization. I recommend AES analysis to determine O/Ti ratio.

Thank you Arezou Zarei. I already done the EDS which also has the ratio of the atomic percentage Ti and O for my sample. As the result, oxygen is higher than Ti. Most of my sample has similar result. But this is EDS result. Im not checking the AES yet, is it AES analysis is more accurate? Which one has better analysis between EDS and AES?

Syafa Syahirah Both of them are good with the same result. So you can reach stoichiometry again.

I doubt anything can become hydrophobic after being oxidized! Oxygen will make everything "less hydrophobic".

It is because it just dries out! I heard a lot of people have the same problem with TiO2 layers! Do you have your TiO2 layer on Si wafer? Try to keep your sample in moist (not directly in water) then look at it again!

Behzad Vaziri Hassas I have my TiO2 on FTO glass. I will try your suggestion. Thank you. Actually, I also thought that the oxygen will make the sample hydrophilic. But I already do the annealing treatment at 300 degrees for my sample as the result it become more hydrophilic. But after couple of days, it become hydrophobic back. My objective is to get the hydrophobic form, but I don't have any idea what the exact reasons for my samples change from hydrophilic to hydrophobic form after couple of month. Any suggestion for the faster way to get the hydrophobic form without changing the rutile structures?

Syafa Syahirah The Rutile itself is hydrophobic in nature, and if you heat it up to 200-300 C it will become hydrophobic again!

Try to keep your sample in desiccator after heating up, to see if the change happens or not. annealing may have effect I believe!

I would keep the sample in 70 C in vacuum. That will remain hydrophobic

Behzad Vaziri Hassas Actually, my experiment is to fabricate TiO2 nanostructured by using hydrothermal. After the hydrothermal process, I test the contact angle, the result shows hydrophilic, then I try to anneal (heat it up to 300 C) as I mention above and its still hydrophilic. However, after being keep for several month the result show hydrophobic. Therefore, I want to know the reasons why it become hydrophobic after several month. Is there other reason? and how can I prove it?

*By the way, I will try to keep the sample in desiccator. Thank you for your suggestion.

I also agree with behzad. Anything that has oxides bond or become oxidized, its hydrphilicity increases. As, it has more tendency to form hydrogen bond i. e. More hydrophilic in nature.

Abhyarthana Pattanaik do you means the hydrophilic characteristic is form when the material is being oxidized? what about if the hydrophobic is form after it being oxidized, what can we consider for that?

Carlos E Castano

I have investigated the some surface properties of ilmenite (FeTiO3) such as hydrophobicity, amount and distribution of surface ions and its effects on the flotation of ilmenite. the results showed that the conversion of Fe ions had a significant effect. It can be said that if your sample has some Fe substitution in the crystal structure of TiO2, the oxidation of Fe2+ ions to Fe3+ can be a reason for increasing the hydrophosbicity. You can investigate the amount of main ions on the surface of TIO2 via XPS analysis.

I hope you get some informations from this article.

I have also observed this effect on silicon wafer. After taking out a new silicon wafer and left it in air, its hydrophobicity increases gradually. I wonder does anyone know why?

The organic adsorbsion from the ambient air have been observe in several reports. The hydrophilic metal oxides could adsorb hydrophobic groups from the ambient air after a long time causing the surface to become hydrophobic. This phenomenon could be accelerated by using heat treatment. Besides, surface roughness is also an important factor affecting the wettability of the surface.

Ngoc Giang Tran Hi Dr.. Based on the wetting models, what is the roughness factor (r) definition? Is 'r' getting from the surface roughness profile or self-definition/calculation from the surface topographical profile?