[Arctic-Nation]

Most of the time when I have procedural problems and find my colleagues or supervisors to be either not interested or too full of themselves (apart from those who are willing to help but have no experience in the matter at hand), I tend to rely on the literature to help me get along. In this case, however, literature tends to be contradictory (not the first time, of course ). My problem is with cleaning a gold surface (about 1x1 cm) to be used for contact angle measurements. This problem is a very profound one, as in my experience the values for the contact angles obtained rely heavily (and their reproducibility even more so) on the exact procedure followed in the preparation of the gold surfaces. The methods commonly used for the cleaning of gold (apart from the electrochemical ones, which are useless here) are piranha solutions and ozone chamber. Piranhas are good to oxidatively remove any adsorbed organic species, while ozone removes anything bound to the gold by oxidizing the gold itself.

Now, here's my problem: is it a good idea to reduce any gold oxides formed during ozone treatment by washing with ethanol before any modification (formation of a self-assembled monolayer), or not? The first procedure I used (as told by one of my colleagues) involved washing the gold with a quick jab of ethanol. However, this lead to less than satisfactory results. One of my supervisors then told me that, when she was doing contact angle years ago, no washing was done. Following this, my results became more reproducible, which was nice. However, I still noted the occasional (one third of the time, actually) result that was off, either by a bit or very, very much, which was very, very annoying. Now, I'm about to measure samples prepared by submerging the gold in ethanol for 30 minutes after the ozone treatment (giving very hydrophobic gold) to see what will happen.

Anyway, discuss. 

[Borek]

Any chances of airborne contamination changing between measurements are taken? This is a stab in the dark, but I guess it is all about cleanliness of the surface. If someone close by fries potatoes air is full of contaminants which can get on the surface when you transfer your gold. Now, for obvious reasons I don't think making fries is a source of the problem, but I can imagine that anything - parfumes, stink from the lab second door - can influence the result.

But I can be completely wrong.

Do you always use the same ethanol, from the same source?

[Arctic-Nation]

The airborne influence is something that I've experienced first-hand, unfortunately, as a few days back the construction workers who are renovating the building decided to burn wooden desks almost right below my lab. Apart from the smell, the measurements I made at that time were the worst I'd ever seen.

Ethanol comes from only one source, Poch, so no error (other than a systematic one) possible there.

[hirrpanii]

Hi Arctic-Nation,

I am curious have you published the results of your contact angle measurements with that 1x1 cm gold surface? I am working on a similar topic for my thesis. I need a rough idea about the surface energy of the gold. What was the purity of the gold you used?

Looking forward to hear from you.

Cheers