Hi all,
Recently, I sputtered some gold on the surface of PTFE with a thickness of 1 nm and 3 nm (Please see the attached). The color was grey when it was done. However, after about one day, the color of gold turned to pink (Please see the attached).
I know when in solution, this change is attributed to the increase of Au particle size. But the gold in my situation is on the solid surface. So how could they combine with each other to form bigger particles or is this caused by other reasons?
Many thanks.
Very interesting effect, You should investigate the surface morphology more closely since there could be practical applications for this in nanofabrication.
I would say that you are indeed seeing the agglomeration of gold nanoparticles on the surface. PTFE isn't really a solid surface. Like most plastics, it's plastic properties are largely determined by the amount of crosslinking and entanglement between molecules that are somewhat free to move around. This movement is often at the nano scale and can mostly be ignored when considering the material as a bulk solid.
AFM on fresh vs. aged sample might make for a very interesting paper, especially if you can come up with a couple functional uses for an adhered monolayer of gold nanoparticles (of which there should be many).
There is one paper you should look at that anneals a thicker (~15 nm) layer of gold on PTFE and notes a morphological change, but they don't seem to come to the conclusion that your pictures may indicate. Article Annealing of gold nanostructures sputtered on polytetrafluoroethylene
I look forward to reading your paper. Best of luck!
Ron Reiserer Thank you very much. Really appreciate your answer and the recommended article. I will read it through and see if I can do some further investment although I haven't come up with any ideas where this can be applied for at the moment.
I think you are probably correct that PTFE is not really solid as I noticed this phenomenon only happens when the thickness of the Au is below 1 nm. Therefore, when the thickness increased, the new-sputtered Au will land on a layer of Au which is more solid than PTFE and thus largely reduced the transfer and agglomeration of Au nanoparticles.
Thanks a lot again for your help.
The size range will make a difference in the applications so you should first determine that. e.g. ~>1nm particles can act as a catalyst for converting CO to CO2 but the catalytic activity is reduced as size increases.
Some interesting experiments might include aging the films under inert atmosphere or at different temperatures to see if you can change the size range or catalytic activity of the nanoparticle film (if that's actually what you're getting).
It may also be interesting to do some experiments with different metals to see if this is a function of the PTFE surface or the gold thin film itself.
You may also want to check to see if you can use the film as a plasmon waveguide or other optical component. Because you see a color, there is clearly a wavelength dependent effect (which may extend outside the visible range so test UV and IR as well).
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