Large-Area and Uniform Surface-Enhanced Raman. Saturation

Transcription

1 Supporting Information Large-Area and Uniform Surface-Enhanced Raman Spectroscopy Substrate Optimized by Enhancement Saturation Daejong Yang 1, Hyunjun Cho 2, Sukmo Koo 1, Sagar R. Vaidyanathan 2, Kelly Woo 2, Youngzoon Yoon 3, and Hyuck Choo 1,2,* 1 Department of Medical Engineering, California Institute of Technology, Pasadena, CA 91125, United States 2 Department of Electrical Engineering, California Institute of Technology, Pasadena, CA 91125, United States 3 Device Lab, Device & System Research Center, Samsung Advanced Institute of Technology (SAIT), Suwon, 16678, Republic of Korea * Corresponding Author: Hyuck Choo (hchoo@caltech.edu) S-1

2 Figure S1. EDS data of 2DNP substrates (A) as a function of AuNP LPD repetition and (B) atomic % changes in Au and Si as a function of AuNP LPD repetition. S-2

3 Figure S2. EDS data measured from the top of 3DNP substrates (A) as a function of AuNP LPD repetition and (B) atomic % changes in Au, Si, and Zn as a function of AuNP LPD repetition. S-3

4 Figure S3. (A) Numerically simulated distributions of the electric field intensity ( E 2 ) inside the 3D stacks as a function of the layer depth with different gap sizes; (B) integrated E 4 enhancement vs. the layer depth for different gap sizes. Raman enhancement maximizes when the gap size is 15 nm standard deviation (7 nm). S-4

5 Figure S4. (A) Photograph of 3DNP-8 substrate synthesized on a 4-inch Si wafer; (B, D) 2D Raman mapping and (C, E) statistical distributions of Raman intensity at 999 cm -1 and 1022 cm -1, respectively, measured on a 4-inch wafer-sized 3DNP-8 substrate incubated in a 1-mM benzenethiol solution; (F) 2D Raman mapping and (G) statistical distribution of Raman intensity measured at 1072 cm -1 on a 4 4 3DNP-8 substrate incubated in 1-mM benzenethiol solution; (H) 2D Raman mapping and (I) statistical distribution of Raman intensity measured on a 2DNP-8 substrate incubated in 1-mM benzenethiol solution. S-5

6 Figure S5. Uniformity and mapping area comparison with previous large and uniform SERS substrates S-6

7 Table S1. SERS performance comparison with previous large and uniform SERS substrates Fabrication method Material Mapping Enhancement Relative Ref. area factor standard deviation This Hydrothermal synthesis and liquid Au % work phase deposition 6.8% 4 4 Previous works X-ray interference lithography and electron-beam vapor deposition Au % 1 Micro-contact printing Au % Laser interference lithography and electron-beam evaporation Au % 3 Laser interference lithography and electron-beam evaporation Ag % 4 Selective electrodeposition on PS bead and AAO template Ag % 5 Liquid phase deposition Au % 6 Liquid phase deposition Au 0.1 mm % 7 line Liquid phase deposition Au-Ag % S-7

8 Two-step solvothermal method Ag-TiO 2-rGO % Chemical vapor deposition and liquid phase deposition Ag-Ge % 10 Nanoimprint Pd 40.5Ni 40.5P % 11 Seed-mediated growth Au-Ag % Seed-mediated growth Au % Photocatalytic deposition Ag % Sputtering Au % 15 Nanoimprint and electron-beam vapor deposition Au % 16 S-8

9 Enhancement factor calculation. The enhancement factor (EF) was calculated using the following relation: EF = I SERS I bulk N bulk N ads where ISERS is the intensity of the SERS spectrum of benzenethiol (BT) obtained from AuNP cluster and IBulk is the intensity the Raman spectrum of BT solution measured in the cuvette. The intensities at 1072 cm -1 were used to calculate the EF value. Nbulk is the molecule number of the BT in the laser focal volume. The laser focal volume can be determined by the focal area and focal depth of the laser spot and is calculated to be 1314 µm 3. Thus the Nbulk of 1 mm BT solution in the focal spot is calculated to be Nads is the number of molecules adsorbed on the SERS substrate within the laser spot, defined as the following expression: N ads = N d A spot α where Nd is the packing density of BT ( cm -2 ), Aspot is the area of the focal spot of the laser (1.23 µm 2 ), and α is the ratio between the surface of nanoparticle cluster and a flat surface of the same horizontal dimensions. The nanoparticle cluster height is approx. 1 µm and the diameter of the AuNPs are about 20 nm, thus 50 layers of nanoparticles are theoretically stacked. Considering spherical shape of nanoparticles, connection area between nanoparticles, laser penetration depth and the porosity of nanoparticle cluster, α is calculated. Therefore, Nads is calculated to be about As shown in SEM image of 3D stacked AuNP cluster (Figure 3D) and simulation results (Figure S3a,b), intensity of electric field was exponentially decreased as laser light traveling toward the bottom layer and this screening effect was considered for EF calculation. The EF values of overall 3DNP substrate can be estimated to be The substrate is composition of connected nanoparticles and properly separated nanoparticles. High S-9

10 electromagnetic enhancement generates gaps between nanoparticles. The EF values at the gaps were calculated to be S-10

11 REFERENCES 1. Zhang, P.; Yang, S.; Wang, L.; Zhao, J.; Zhu, Z.; Liu, B.; Zhong, J.; Sun, X. Large-Scale Uniform Au Nanodisk Arrays Fabricated via X-Ray Interference Lithography for Reproducible and Sensitive SERS Substrate. Nanotechnology 2014, Zhang, L.; Guan, C. R.; Wang, Y.; Liao, J. H. Highly Effective and Uniform SERS Substrates Fabricated by Etching Multi-Layered gold Nanoparticle Arrays. Nanoscale 2016, 8, Kanipe, K. N.; Chidester, P. P. F.; Stucky, G. D.; Moskovits, M. Large Format Surface- Enhanced Raman Spectroscopy Substrate Optimized for Enhancement and Uniformity. ACS Nano 2016, 10, Xu, Z. D.; Jiang, J.; Wang, X. H.; Han, K.; Ameen, A.; Khan, I.; Chang, T. W.; Liu, G. L., Large-area, Uniform and Low-Cost Dual-Mode Plasmonic Naked-Eye Colorimetry and SERS Sensor with Handheld Raman Spectrometer. Nanoscale 2016, 8, Zhu, C. H.; Meng, G. W.; Zheng, P.; Huang, Q.; Li, Z. B.; Hu, X. Y.; Wang, X. J.; Huang, Z. L.; Li, F. D.; Wu, N. Q. A Hierarchically Ordered Array of Silver-Nanorod Bundles for Surface- Enhanced Raman Scattering Detection of Phenolic Pollutants. Adv. Mater. 2016, 28, Zhou, J. H.; Zhu, F.; Wang, Y.; Wang, T. One-Step Green Synthesis of High Uniform SERS Substrate Based on Au Nanoparticles Grown on Ge Wafer. Chem. Phys. Lett. 2015, 627, S-11

12 7. Wang, Y. W.; Kao, K. C.; Wang, J. K.; Mou, C. Y. Large-Scale Uniform Two-Dimensional Hexagonal Arrays of Gold Nanoparticles Templated from Mesoporous Silica Film for Surface- Enhanced Raman Spectroscopy. J. Phys. Chem. C 2016, 120, Chen, D. Z.; Song, Z. X.; Chen, F.; Huang, J.; Wei, J.; Zhao, Y. X. Simply Controllable Growth of Single Crystal Plasmonic Au-Ag Nano-Spines with Anisotropic Multiple Sites for Highly Sensitive and Uniform Surface-Enhanced Raman Scattering Sensing. RSC Adv. 2016, 6, Hsu, K. C.; Chen, D. H. Highly Sensitive, Uniform, and Reusable Surface-Enhanced Raman Scattering Substrate with TiO2 Interlayer between Ag Nanoparticles and Reduced Graphene Oxide. ACS Appl. Mater. Interfaces 2015, 7, Liu, J.; Meng, G. W.; Li, Z. B.; Huang, Z. L.; Li, X. D. Ag-NP@Ge-nanotaper/Si- Micropillar Ordered Arrays as Ultrasensitive and Uniform Surface Enhanced Raman Scattering Substrates. Nanoscale 2015, 7, Liu, X.; Shao, Y.; Tang, Y.; Yao, K. F. Highly Uniform and Reproducible Surface Enhanced Raman Scattering on Air-stable Metallic Glassy Nanowire Array. Sci. Rep. 2014, 4, Liu, Z.; Yang, Z. B.; Peng, B.; Cao, C.; Zhang, C.; You, H. J.; Xiong, Q. H.; Li, Z. Y.; Fang, J. X. Highly Sensitive, Uniform, and Reproducible Surface-Enhanced Raman Spectroscopy from Hollow Au-Ag Alloy Nanourchins. Adv. Mater. 2014, 26, S-12

13 13. Wang, X.; Li, M. H.; Meng, L. Y.; Lin, K. Q.; Feng, J. M.; Huang, T. X.; Yang, Z. L.; Ren, B. Probing the Location of Hot Spots by Surface-Enhanced Raman Spectroscopy: Toward Uniform Substrates. ACS Nano 2014, 8, Li, D. W.; Pan, L. J.; Li, S.; Liu, K.; Wu, S. F.; Peng, W. Controlled Preparation of Uniform TiO2-Catalyzed Silver Nanoparticle Films for Surface-Enhanced Raman Scattering. J. Phys. Chem. C 2013, 117, Chen, H. P. M.; Pang, L.; King, A.; Hwang, G. M.; Fainman, Y. Plasmonic Coupled Nanotorch Structures Leading to Uniform Surface Enhanced Raman Scattering Detection. Nanoscale 2012, 4, Li, W. D.; Ding, F.; Hu, J.; Chou, S. Y. Three-Dimensional Cavity Nanoantenna Coupled Plasmonic Nanodots for Ultrahigh and Uniform Surface-Enhanced Raman Scattering Over Large Area. Opt. Express 2011, 19, S-13