I have designed a SPR chip by using normal glass slide(Blue star No. 4slide)/Cu(5nm)/Ag(50nm). But it shows very less depth in the reflectance curve at resonance angle. What should be the reason ??
Dear Anil Kumar,
Theoretically, the substrate refractive index influences the surface plasmon resonance (SPR) wavelength in interesting ways. See Figure 8 and 9 from Mehdi Tavakoli et al.
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On another hand, the interface micromorphology among the dielectric substrate/adhesion layer/plasmonic material can also alter the SPR properties. As an example, defects in the crystal structure of the substrate can lead to scattering of the plasmon, preventing its propagation.
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Hello Anil,
The RI value of substrate and laser wavelength play important role to produce maximum SPR. Try manipulate these parameters. Based on my study, 50nm total thickesses of metal results the greatest SPR curve depth. Try to adjust total thickness of Ag + Cu, make it 50nm.
Good luck!
Dear Anil,
This message might be a little too late, but i thought i should add something to what the other mentioned. As Ali mentioned, there might be different reason to why you are notice a flattening (low depth) in the resonance curve. It could ofcourse be because of the refractive index of the glass slide, so you could try higher refractive index glasses like BK7. It could also be the due to damping effects, which can be because of multiple reason.
Firstly i always recommend to do an etch of the glass slide before metallization. It not only cleans the glass surface, but also flattens it, because it might not seem like it but these slides usually have highly irregular surfaces which effect the sensor response (specially positionally on your ROI). On top of that, during deposition of the metal, ultra high vacuums need to be maintained, specially when considering metals like Ag and Cu, any oxides forming can greatly reduce its adhesive properties and have significant damping effects. Moreover on the adhesive layer, i'm not sure why you might have opted for Cu, but i would have gone with metals like Cr/Ti . Because even though they have a lower plasmonic response they have much stronger adhesion, and at lower thickness (2nm) there effect on the resonance curve is almost negligible. However, Personally i did a Cr/Ag deposition and found that the response wasn't that great either, the adhesion between the layer wasn't better than Cr/Au. So i suggest you try some alternatives. The goal is to have an interdiffusion of between the layers which make the adhesion significantly stronger. Hopefully once you optimize your metallization recipe, you will be able to improve the sensor response significantly
Hope this helps and good luck
Thank you Jonathan Shilantha Weerakkody for sharing your expertise on the fabrication of SPR-based devices, especially regarding that pesky adhesion layer! A major challenge (i.e. hot topic for research) is to have a mechanically stable adhesion layer which does not deteriorate the plasmons at the interface.
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