Improved stability and sensitivity of plasmonics metal layers with MPTS adhesion layer and CVD grown graphene transfer in water

Introduction:  To date, the use of metallic adhesion layer such as Cr and Ti severely deteriorates the plasmonics features of thin metal film by damping the plasmon mode due to intermetallic diffusion and dissipative... [ view full abstract ]

Introduction: 

To date, the use of metallic adhesion layer such as Cr and Ti severely deteriorates the plasmonics features of thin metal film by damping the plasmon mode due to intermetallic diffusion and dissipative dielectric functions and thus depleted the active plasmonics properties of thin metal film for practical applications. Here we successfully demonstrated the use of a low absorption molecular adhesion layer and graphene protected metallic thin film with the aim to enhance the plasmonics properties and temporal stability of gold and silver thin film deposited on SF4 substrates functionalized with (3-mercaptopropyl) trimethoxysilane (MPTS). Graphene has been proposed as a promising material for sensitivity enhancement and for the detection of toxic mercury (Hg⁺²) ions due to its high surface to volume ratio and exceptional optical and chemical properties. 

Methods:

The schematic representation of our proposed structure is shown in figure 1.  

Results:

The instability of the SPR signal for different configuration was monitored in term of shift in resonance angle (Δθ_SPR) and change in FWHM over 24 hours in DI water as shown in the figure 2. The major result that we detected for the first time is the significant decrease in ΔFWHM% of about 5% up to 5 hours in the case of MPTS/Au/H₂O, which is attributed to the rearrangement of evaporated Au atoms on top of S-atoms of MPTS due to hydartion of siloxane (Si-O-Si) bond and revert to silanol (Si-OH) groups and leave the surface smooth confirm by our AFM results. The graphene based SPR sensors show a higher bulk refractive index sensitivity as compared to conventional metal thin sensors as shown in figure 3(a). The SPR resonance angle shows a rapid response of about 0.06⁰ upto a concentration of 0.005ppm, which reveals a greater affinity of graphene SPR sensors to Hg⁺² ions as shown in figure 3(b).  

Conclusion

We have demonstrated the temporal stability and sensitivity of SPR sensor consists of Cr and MPTS as adhesion layer and graphene as protecting layer. Our results validated the outstanding performance of Graphene SPR sensor, suggesting that its application as a heavy metal detector in environmental monitoring.