I coated polymerized PDMS with a 50 nm layer of Al in an evaporator and got a satisfactory thin layer coverage, but then when using a 532 nm layer on it, it seems to make holes on it (powers between 22 mW and 0.2 mW), and when water is present it overheats it even at very low laser powers. Any idea of why?
Dear Julia,
I have no experience with Laser Ablation, so cant answer that part of the question. But I am doing experiments related to your work. I am using SYLGARD 184 and evaporating Ag on it, my PDMS surface is structure with grating. I can share more information with you but first I would like to ask you: Are you using the same PDMS ?
Best,
Imran
Hi. By the look of the damage circle I would suspect this is a thrmal damage rather than ablation. Do you use CW laser? or very short pulses? If CW, then most likely it is thermal damage. You can use wider spot size on target or reducd power. I guess the former is better for faster results. Short pulses "drill" flat holes without "crater" side ramps... whicj I think you have in this image.
Hi Khan,
I am using SYLGARD 184 with 10% crosslinker. It would be very useful to know how are evaporating the metal in your lab, I have been reading that the adhesion of Au for instance is quite poor without using Ti or Cr.
Hi Yariv,
what we are using is a CW laser, and I wasn't intending to create a hole (I would rather want the surface to be quite stable even when using a laser on it). It is indeed probably thermal, because when water was present it does evaporate very quickly, but this doesn't happen when using the same laser powers in the same PDMS device but without the metal. Could some reaction of the Al be taking place?
Hey Julia, without knowig the specific details of your test, metal has much lower heat capacity Vs. Water. therefore, if it absorbs the photon energy, even partially, it can heat up quickly. it can also concvect heat out, but the specific thermal management strongly depends on details:materials, contacts, structure and ambients. So, it is no surprise that this metallic face damaged. If you need it to endure the laser you should either reduce the intensity (larger spot) or enable better cooling; contact to cool heat sing / fan from any side, direct cooling water on it...
Hey Julia, PDMS (SYLGARD 184) is soft, porous. Once you put it inside the vacuum chamber to deposit an Al layer on it, something bad is happening during evacuating the vacuum chamber and venting back (becuse of the soft, porous, sponge nature of the PDMS). For example, see the attached picture, this was my nicely structured (gratings with very good periodicity) PDMS surface, and after depositing an Ag layer with evaporation process, how bad it looks now. So I will suggest, use Hard PDMS, for example SYLGARD 186, I hope that will help.
Hi Khan,
Yes, I am experiencing some cracks on the metal layers that I have tried, it makes sense seeing how soft the PDMS is. Have SYLGARD 186 helped you with your Ag deposition on PDMS?
Hi Julia, does your layer look reflective or scattering (white)? Thanks.
Hi Elena. It does look grey-ish. When using Bright field it does look mostly opaque.
Hi Julia, I agree with Yariv. With a layer of Al on PDMS, the laser photons are collected and turned into heat. As your Al layer is thin, the thermal effect gets accumulated rather than dissipated, so at some point a crater is formed due to melting or most likely evaporation. What is the size of the laser spot on your sample? Without Al, PDMS is transparent to 532 nm laser light, photons pass through the PDMS without heating.
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