I never saw the use of APTES to coat ITO surfaces, but there are plenty of problems using APTES, the coverage is not very high, it depends, a lot ,in how dry is the solvent you are using, the presence of any trace of water or O2 may destroy your reaction. But I think that your bigger problem is because the glass surface is covered with ITO particles, so the functionalized surface will be very small. Sorry for not helping you, but I don't think that this experiment will not work.

I read some articles about APTES coating onto the ITO surface. It looks like it works. But i do not know why it is not working in my case.

How are you determining whether or not the APTES deposition is not working? Are you using XPS to determine surface nitrogen content, or are you using contact goniometery to look at contact angle before and after deposition? What methods are you using to determine if the reaction is working?

An additional note, a small amount of water in your reaction may be beneficial since this can effectively increase the amount of amino groups tethered to the surface by allowing some of the APTES to polymerize before deposition onto the surface.

Thanks for the suggestion. It is not working because aligned CNT should have covalent bonds with APTES under some condition. I follow the procedure in articles and i guess i do everything correctly. However aligned CNT does not attach to amine group on APTES.

What article are you using? How are you modifying the CNTs so they can covalently attach to the APTES covered surface? If you are modifying the CNTs have you characterized them appropriately so you are sure enough that they will react with the APTES surface?

Article is Ehnanced thermal transport at covalently functionalized carbon nanotube array interfaces (10.1038/ncomms4082). Here they do not use ITO and also use APS, similar to APTES. However, in another article they follow the similar procedure with APTES and ITO, also they get good result. I do plasma etching to modify CNT surface.

It's difficult to determine where your process is not working if the materials at each step are not characterized. I would start firstly with your APTES deposition. A quick and cheap way to determine whether the deposition worked properly is to look at the water contact angle before and after deposition. If there is a change in contact angle then you can be pretty sure the reaction was successful, however, a surface sensitive analysis would be more suitable.

Secondly, I'm assuming your plasma etch is with oxygen and that the CNT surface is oxygen rich after the process. The reason for this process is the carboxylic groups on the etched CNTs will firstly interact via an electrostatic interaction with the amino surface, then the 120 deg C treatment causes a condensation reaction to occur between the amine and acid groups resulting in an amide bond formation.

So, if your APTES deposition is successful I would look at the oxygen content and oxygen moiety types on your CNTs. Additionally, are you doing your heat treatment in an inert atmosphere (amino groups tend to oxidize readily at elevated temperatures)?

I did not do the heat treatment in the inert atmosphere. Actually i am not chemist so i did not know that amino groups can be oxidized easily. Thank you so much for the information. Maybe this is the reason for my failed experiment.