Well, let me know what kind of the organic molecules, is it macromolecule, polymer molecule, polar or non-polar molecules, etc. It is because surface morphology of any material is tightly influenced by typical interactions occur between the molecules and its substrate. In your case, SiO2 substrate is polar in properties so you should use hydrophilic organic molecule-based materials with various concentration and volume to obtain a good 2D surface morphology. rather than varying temperature.

Dear Pratama Juju

Thanks for the response. The organic molecules i am using is derivatives of Diarylethene photochromic Molecules. You mean i have to do surfacetreatment like PMMA or HMDS first and then deposit the organic material. 

Thats a pretty wide range of compounds you describe there. Do you have to vapor deposit them? 

But I guess what wibawa means is that the surface energies of your sio2 and your compounds have to match in order for the molecules to "wet" the sio2. So if your molecules are hydrofobic you need a hydrofobic coating on you sio2. 

Cheers 

Dear  Soren Thanks for your use full answer.

i using thermal deposition at high vacuum to deposit the molecules. 

Which are beast hydrophobic Coating available. can i use PMMA or HMDS

Again, you might not need the most hydrofobic  coating to get the best result. The coating which is most similar to your molecules should be the best. 

Cheers 

Hi Alam,

Diarylethene molecule itself is not polar molecule so that it is hydrophobic in properties. However if its derivative is polar it will be hydrophilic so that it can be dissolved in water medium. If so, you should remove any oily matters from your substrate (SiO2) with strong oxidizing solution such as piranha solution on 80oC for about 25 minutes first, subsequently you can use it to deposit your sample. In addition, you can try to use gently drop coating method to deposit your sample instead of either PVD or CVD method. Dropping method can be performed on room temperature and atmospheric pressure.