Hi, I have a couple of thoughts and observations. Whilst you are using high purity materials I would want to see an improved vacuum level, towards 2E-6 mbar. Another area is the substrate temperature, this is a good idea, but at the current vacuum level you might be baking contaminants onto your substrate, and what is your vacuum pumping system? One question, how thick are your films, thinner films will exhibit less stress and should be continuous by 50/60nm. Wet chemical cleaning might also be used to remove organic and mineral deposits before coating.

Good luck,

Martin

Hi, I think that the coatings are thicker, so adhesion decreases. If the temperature is reduced and glow discharge time is reduced, the adhesion may enhance.

One common technique in such cases is to use some form of intermediate coating to help bonding between the glass (?) and coating, such as a deposit of an oxide first. Though this is mostly only practical with a sputter system.

I would also try not to deposit at elevated temperature, as your substrate will contract when it cools down and this could increase any stress effects between the substrate and coating. Heating your substrate initially will however help to remove any traces of organics or cleaning solvent, and so reduce the likelihood of pinholes in the film.

You might also see if using a low & controlled deposition rate helps, as this allows the growing film more time to relax as it forms.

From your comment it is not clear if the streaks(?) while cleaning are seen on the top surface or as a result of coating over streaks on the substrate. "Drying marks" can be very difficult to prevent when cleaning, you may have some success blowing the samples dry with clean nitrogen. We have found that by far the best method for cleaning is to "reflux" the samples by using a large "soxhlet extractor" (after sonication in acetone, then isopropanol). This ensures only distilled (particle free) solvent is in contact with the substrate material, and that the substrate dries slowly in a vapour rich environment which gives the solvent plenty of time to run off. (It is similar to "vapour degreasing" technique).

I agree with Martin's opinion that the vacuum level far too low. You need at least 2×10-6 mbar to be able to get good coating. According to your description about the substrate, it looks like your substrate didn't have throughly cleaned. As all of them suggested, to keep the film on the substrate strongly or with higher strength, thinner films are suggested such as 50 to 60nm. It depends what you want to do with chromium layer. If you want to use the chromium layer as adhesion layer for other metal coating such as gold. The chromium layer has normally with 10nm or so.