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New Nano Architecture for SERS                  ApplicationsGayatri Kumari and Chandrabhas Narayana*        Chemistry and ...
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JPCL 10.1021/jz3001344 Kumari Presentation

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  1. 1. New Nano Architecture for SERS ApplicationsGayatri Kumari and Chandrabhas Narayana* Chemistry and Physics of Materials Unit,Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P. O., Bangalore 560064, India J. Phys. Chem. Lett. 2012, 3, 1130-1135 1
  2. 2. Schematic to show path of light through Ag@SiO2@Au sandwich nanoparticles resulting in multiple reflections. Incident light can be reflected or transmitted. Transmitted light can undergo total internal reflection before coming emerging out where it again meets incident light and can interfere constructively resulting in high field intensity at its surface.Scheme of formation of sandwich nanoparticles Ag np Ag@SiO2 Ag@SiO2@Au Ag@SiO2@Au seed Proprietary and Confidential 2 American Chemical Society
  3. 3. (a) Normalized extinction spectra of silver (purple) and silver core silica shell (green) nanoparticles,(b) Silver silica gold seed (blue), the sandwich nanoparticles (red) and silica core gold island nanoparticles (dark gray). Figure 3: TEM images for different steps of synthesis of silver silica gold sandwich nanstructures. (a) Silver nanoparticles, (b) silver core silica shell, (c) gold seeds on silver core silica shell nanoparticles, (d) silver silica gold sandwich nanoparticles. The arrow in Figure (c) points to core where complete oxidation of silver has occurred. Scale bar 100 nm (a,d) and 50 nm (b,c).Proprietary and Confidential 3 American Chemical Society
  4. 4. BET curve for Ag@SiO2 nanoparticles FESEM of Ag@SiO2@Au sandwich nanoparticlesXRD pattern of Ag@SiO2@Au nanoparticles Proprietary and Confidential 4 American Chemical Society
  5. 5. SERS spectra of thiophenol with Ag@SiO2@Au sandwich nanoparticles and SiO2@Au core shell particles SERS spectra of thiophenol on Ag@SiO2@Au sandwich nanoparticles. (b) SERS spectra of 10-5 M thiophenol (c) SERS spectra of 10-7 M thiophenol. Laser wavelength used was 632.8 nm and power was 8 mW at the sample.Enhancement factor = 106EFAg@SiO2@Au = 6X EFSiO2@AuDetection limit of Ag@SiO2@Au is 100 times more than SiO2@Au nanoparticles Proprietary and Confidential 5 American Chemical Society
  6. 6. Ag@SiO2 nanoparticles with different silica shell thicknessTEM images of Ag@SiO2 with 40 nm (a), 50 nm (b), 60 nm (c) silica shell. Scale bar 50 nm (a,b) and 100 nm (c). Extinction spectra of silver core silica shell nanoparticles with different silica shell thickness (60 nm, 50 nm, 40 nm, 25 nm). Proprietary and Confidential 6 American Chemical Society
  7. 7. Ag@SiO2@Au particles with varying silica shell thickness TEM image showing Ag@SiO2@Au with different silica shell thickness. (a) 25 nm, (b) 40 nm, (c) 60 nm. Scale bar 20 nm (a, b) and 50 nm (c). Ag@SiO2@Au particles with different densities of gold island TEM image of sandwich particles with different densities of gold island Proprietary and Confidential 7 American Chemical Society
  8. 8. SERS spectra of thiophenol with different types of sandwich nanoparticlesSERS spectra of thiophenol. 10-4 M concentration was used SERS spectra of 10-3 M thiophenol on SN1, SN2 andfor 40 nm and 60 nm silica shell and 1mM was used for 25 nm SN3 sandwich nanoparticles. Gold coverage on silicasilica shell sandwich nanoparticles. shell is SN1 < SN2 < SN3. SERS EF decreased when the dielectric shell thickness was changed OR Gold island densities were increased or decreased Proprietary and Confidential 8 American Chemical Society
  9. 9. Conclusions •We have demonstrated a facile method to synthesize Ag@SiO2@Au sandwich nanoparticles. •SERS EF of Ag@SiO2@Au was found to be 106 which was 6 times higher than SiO2@Au nanoparticles under similar experimental conditions. Gayatri Kumari •SERS EF was found to decrease when silica layer thickness was varied from 40 nm or density of gold islands were changed beyond an optimum value. Acknowledgments The authors acknowledge Swedish Research Links and JNCASR for providing the financial support. We are thankful to Dr. Usha Tumkurkar for doing the TEM Chandrabhas Narayana measurements and Dr. Karthik Bala for the FESEM measurements.Proprietary and Confidential 9 American Chemical Society

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