Abstract
A simple high-throughput approach is presented in this work to fabricate the Au nanoparticles (NPs)/nanogap/Au NPs structure for surface enhanced Raman scattering (SERS). This plasmonic nanostructure can be prepared feasibly by the combination of rapid thermal annealing (RTA), atomic layer deposition (ALD) and chemical etching process. The nanogap size between Au NPs can be easily and precisely tuned to nanometer scale by adjusting the thickness of sacrificial ALD Al2O3 layer. Finite-difference time-domain (FDTD) simulation data indicate that most of enhanced field locates at Au NPs nanogap area. Moreover, Au NPs/nanogap/Au NPs structure with smaller gap exhibits the larger electromagnetic field. Experimental results agree well with FDTD simulation data, the plasmonic structure with smaller nanogap size has a stronger Raman intensity. There is highly strong plasmonic coupling in the Au nanogap, so that a great SERS effect is obtained when detecting methylene blue (MB) molecules with an enhancement factor (EF) over 107. Furthermore, this plasmonic nanostructure can be designed on large area with high density and high intensity hot spots. This strategy of producing nanoscale metal gap on large area has significant implications for ultrasensitive Raman detection and practical SERS application.
Highlights
Numerous efforts have been made to design various forms of noble metallic nanostructures as surface enhanced Raman scattering (SERS) substrates, in which colloidal solution is widely employed to systhesis the metallic nanostructures, including nanoparticles, nanocubes and nanowires[3, 11, 12]
Au NPs arrays are formed by rapid thermal annealing (RTA) of Au nanofilm at 500 °C for 30 s
Repeat the step I and II, the second thin Au nanofilm is deposited on the Al2O3 coated Au NPs arrays, and subsequent second RTA process is again carried out to form the second Au NPs arrays on the original Au NPs arrays isolated by Al2O3 layer
Summary
Numerous efforts have been made to design various forms of noble metallic nanostructures as SERS substrates, in which colloidal solution is widely employed to systhesis the metallic nanostructures, including nanoparticles, nanocubes and nanowires[3, 11, 12]. We present a very simple but effective approach to fabricate the wafer-scale SERS structure of Au NPs/ nanogap/Au NPs. A sacrificial ultrathin Al2O3 isolation layer is introduced into the double-layer stacked Au NPs by ALD, forming Au NPs/Al2O3/Au NPs structure.
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