I want to produce surface hydroxyls on silicon particles surface. I've seen in litrature that piranha solution at different ratios (sulforic acid to hydrogen peroxide) and elevated temprature is working good. Do I need a pre-treatment with HF too?
HF etches residual/thermal oxide that is already on the particles, and creates a H passivation layer. I think it's a better idea to have an HF dip before you proceed.
Perhaps you can also use RIE (Reactive Ion Etching) with innert Gas (Ar) or Oxygen, it can remove organic materials (contamination). A clean surface under RIE, will be good start.
Piranha in combination with h2h2 and heating to 80 C work good in our hands.
the silanol goups formed by this treatment is not chemically similar to hydroxyl groups.
the surfade energy of the silanol surfade is very high, and unstable.
Thank you all for your responses.
To Prof. Elwing: Is there a way that I can keep the product stable after the treatment? I suppose that the high reactive surface silanols can easily make Si-O-Si bridges.
I Believe that low pH in water has a conserving effect on silanol groups due to the abundence of protons. Another way is to make the Surface hydrophobic with the use of silanes, eg dichloro di silane dissolved in Trichloro ethylene for example. Such treatment results in a fairly stable Surface modification (in air). What is the use of your surfaceses ?
The purpose is to attach a silane on the surface and then proceed with a polymerization of a monomer. I need the surface to have an efficient amount of silanols so as to have better coverage of the surface with the silane.
A frequently used method for this specific application (?() is to use APTS (alpha amino propyl tri ethoxy silane). Another way is to use mussel adhesive proteins (Mefp-1). Both coatings act as strong glues and are fairly stable in water. The basic problem with glass Surface (sio2 including silanols) is that the affinity to water is very high and that there are few chemical bondings that prevent water from "moving in" . Do you plan to add water on your Surface after your polymeris zation ?
the final product (Si-polymer) will be dispersed in a water solution in order to mix it with other materials and then will leave the solvent (water) to evaporate. In that step the wetting of surface is not very important since the polymer will be hydrophilic and cover the Si.