spin coating liquid metal on quartz

Baylor Triplett baylortriplett at earthlink.net
Mon Oct 3 12:31:12 PDT 2005

      What you want to do sounds very difficult indeed. Ga, like 
mercury, has high surface tension and does not wet a hydrophillic 
surface such as quartz. By contrast, it can wet metallic surfaces as 
long as their is not serious interference from the formation of alloys. 
So, like mercury, Ga will tend to form little balls (generally much 
bigger than 1 micron) on the quartz and not tend to wet it.
        I have used Ga and Ga-In alloys to make metallic contact to the 
back of pure Ge detectors...typically by scratching the Ge oxide off the 
surface so the Ga will wet the metallic Ge in spots. Even here you 
cannot get a smooth flat surface like a true supercooled liquid.
         In trying to approach Ga on quartz, you might try to get a very 
thin metallic layer on the quartz, this can be achieved by something 
like Cr-gold. That is depositing 50 A of Cr to bond to the oxide in the 
quartz and then 100 A of Au to bond to the metallic character of the Cr 
top surface. This uses the Cr as an adhesion layer to switch from one 
type of bonding to the other. Alternatively, you could a chemical 
adhesion promoting layer to try to do the same thing (but these can be 
harder to make work in all situations. ) Once a Cr-Au layer (or maybe 
Cr-Pt might be better) is deposited , you might be able to spin a 
wetting layer of Ga on the surface of the Au or Pt.
         I do not know enough about why you want to do this to comment 
further at this point. In my case, the purpose of the contact was to 
form a liquid metal metallic contact that would not harden and damage 
the sensitive detectors as they were cooled to liquid He temperatures.
                                            Regards,         Baylor Triplett

Junxian Fu wrote:

> Hi, all,
> Is there anybody having experience on spin coating liquid metal 
> (gallium, for example) on quartz? The goal is to make a relatively 
> uniform layer (less than 1um) at temperature a little bit higher than 
> room-temperature. How about the edge-beads and hump behavior? 
> Relationship between spin speed and layer thickness?
> Thanks a lot,
> Junxian

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