Simply make a scratch by using a blade before taking the SEM. Then the nanotube arrays will be peeled off from the surface. This will help you to measure the length.

As Aijo says simply scratch your sample or bend it also it should work.

Thank you all for your replies.

And I think I will try your method, and I will make a scratch on the surface, and I hope I could succeed.

Dr. Waleed in Assiut university we do not have FE-SEM, How you get your very clear morphology?

All researchers in this field say that you have to use FE-SEM to get clear images.

With SEM you do get information on diameter, wall thickness etc. I believe that is what you mean by cross section. Scratching of gives chunks of TiO2 nanotubes that you can see with good cross-sectional view. If images are needed for publication I would suggest getting it imaged at a third party facility which has FE-SEM. Should give you very good images with minimal effort.

Thank you Dr. Harikrishnan for your interest, 

I meant by cross-section the side view of the array of nanotubes

See Fig. 4 in attached work. You can see side-view obtained using scratching of pieces and imaged using Hitachi S-4800.

Article Anodized titania nanotube array microfluidic device for phot...

AFM

Dear Yasser,

Cross sectional SEM image will give the cross e\sectional view. even if you don't scratch, using anodized sample on studs which is suitable for taking cross sectional image will help you to get cross sectional view and can directly measure the length of the nanotubes.

By scratching the TiO2 nanotube prepared foil followed by SEM/FESEM will solve your problem easily