Dear Mr.Xiaojing,
H2O2 and HF or HNO3 and HF mixtures are generally used for Ti etching. May be
one of them can be tried if their use is not a problem in you case
Bhat
Quoting Xiaojing Zou :

> Hi:
>
>     Is there anybody having experience with wet etching single crystal TiO2
> substrate??? I want to etch the surface for half micron deep.  I tried H2SO4
> and HF, but it does not do the job. But as far as I know, acid will attach
> TiO2.
>
>    I do not quite understand why it is so hard to etch single crystal
> materials??