Abstract
We study the enhanced dewetting of ultrathin Polystyrene (PS)/Poly (methyl methacrylate) (PMMA) blend films in a mixed solution, and reveal the dewetting can act as a simple and effective method to fabricate large-area surface-enhanced Raman scattering (SERS) substrate. A bilayer structure consisting of under PMMA layer and upper PS layer forms due to vertical phase separation of immiscible PS/PMMA during the spin-coating process. The thicker layer of the bilayer structure dominates the dewetting structures of PS/PMMA blend films. The diameter and diameter distribution of droplets, and the average separation spacing between the droplets can be precisely controlled via the change of blend ratio and film thickness. The dewetting structure of 8 nm PS/PMMA (1:1 wt%) blend film is proved to successfully fabricate large-area (3.5 cm × 3.5 cm) universal SERS substrate via deposited a silver layer on the dewetting structure. The SERS substrate shows good SERS-signal reproducibility (RSD < 7.2%) and high enhancement factor (2.5 × 107). The enhanced dewetting of polymer blend films broadens the application of dewetting of polymer films, especially in the nanotechnology, and may open a new approach for the fabrication of large-area SERS substrate to promote the application of SERS substrate in the rapid sensitive detection of trace molecules.
Highlights
The simple dewetting of thin polymer films has the promising potential for application in the fabrication of the large-area surface-enhanced Raman scattering (SERS) substrate
In the case of S50/M50 film, both thicknesses of the PS-rich layer and the PMMA-rich layer are close to half of the blend film thickness so that the thickness dominating diameter of droplets (Dd) and droplet separation spacing (Ds) reaches minimum
We investigate the dewetting of ultrathin PS/PMMA blend films under mixed solution of methyl ethyl ketone (MEK), acetone and water, and fabricate the larger-scale SERS substrate by using the dewetting structure of PS/PMMA blend film
Summary
The simple dewetting of thin polymer films has the promising potential for application in the fabrication of the large-area SERS substrate. The unusual dewetting method successfully reduces the instability length scale to nanometer size. Another limitation for application in nanotechnology of the simple dewetting method is that it produces droplets with relative big diameter, wide diameter distribution and relative larger mean separation spacing between the droplets. The dewetting structure of thin polymer blend films in the mixed solution is demonstrated to be successful in being the building block of SERS substrate. Once a thin silver film is deposited on the dewetting structures of 8 nm PS/ PMMA (1:1 wt%) blend films, we can fabricate large-area (3.5 cm × 3.5 cm), high efficient (enhancement factor EF > 2.5 × 107) and good SERS-signal reproducibility (RSD < 7.2%) SERS substrate, which is very convenience in fabrication and manipulation
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