The contact angle on any surface can vary over time (usually increasing) as
organics and other molecules adsorb to the surface.

I have measured the following for evaporated gold (on Cr on a Si wafer).
These are averages of three measurements, with outliers discarded (if a
particle is near or under the water drop, it affects the measurement).
After deposition, then a year in a PP wafer box: 71.2 deg.
Freshly cleaned, rinsed, and spin-dried  in PRS-3000 (a commercial
photoresist stripper), withing an hours: 81.2 deg.
After cleaning, then after 3 days in a PP wafer box: 70.8 deg.

I have a book (Butt, Graf, and Kappel; Physics and Chemistry of Interfaces)
that says that gold has a wetting angle of 0 deg when perfectly clean.

    --Kirt Williams

----- Original Message -----
From: "Steven Yang" 
To: "mems-talk" 
Sent: Thursday, September 13, 2007 8:17 AM
Subject: [mems-talk] Wettability of EB evaporated Au surface


> Hi, all
> Does anyone know what is the wettability of EB evaporated Au Surface?
> Always treat it as hydrophobic, which means water contact anlge large
> than 90degree. However, recently read a paper giving the data of
> around 60 degree on smooth surface and 80 degree on rough surface.
> Kind of confusing. So, it wil be appreciated if you have any
> experiment data to share on water contact angle on EB evaporated gold
> surface.