Supporting Information Highly Sensitive Color-Tunablility by Scalable Nanomorphology of Dielectric Layer in Liquid Permeable Metal-Insulator-Metal Structure Eui-Sang Yu,, Sin-Hyung Lee, Young-Gyu Bae, Jaebin Choi, Donggeun Lee,,ǁ Chulki Kim, Taikjin Lee, Seung-Yeol Lee, Sin-Doo Lee, *, and Yong-Sang Ryu, *, Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea Sensor System Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea School of Electronics Engineering, Kyungpook National University, Daegu 41566, Republic of Korea ǁ Department of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea Corresponding Author *E-mail: sidlee@plaza.snu.ac.kr (S.-D. Lee), ysryu82@kist.re.kr (Y.-S. Ryu) S-1
SUPPORTING FIGURES Figure S1. Self-assembly of Au nano-structures on hydrophobic CYTOP layer. (a) Water contact angle (110 º) on the CYTOP surface and its corresponding surface energy (17.1 mj/m 2 ), calculated using Young s equation combined with an equation of state for interfacial tensions. 1 SEM images of self-assembled Au nanostructures on the CYTOP surface in variation of the thermal deposition duration; (b) 333, (c) 667, and (d) 1000 s under vacuum level of 10-5 Torr and deposition rate of 0.3 Å/s. The self-assembled Au nanoparticles are grown and developed into the inter-connected semi-continuous amorphous layer with an increase of deposition duration. Figure S2. Optical simulations based on Bruggeman s EMT. (a) Schematic of the geometric model used for rigorously coupled wave analysis (RCWA) simulation; Bottom Au layer (100 nm), CYTOP insulator (168 nm, n = 1.34), amorphous top Au layer (30 nm), and environment (in the case of air, n = 1.00). The reflected spectrum in the visible range was calculated from the linearly x-polarized plane wave of normal incidence. The top Au layer is analyzed based on Bruggeman s EMT by adopting f Au, the fraction of the Au in the top area. 2-4 (b) Simulated reflectance spectra for different top layer conditions of f Au = 1.0, 0.9, 0.8, 0.7, and 0.6. (c) Evaluation of f Au in top layer by image processing and analysis; f Au = 0.75 ± 0.10. (d) Averaged reflectance spectrum of simulated reflection spectra based on the results in Figure S2c; from 0.65 to 0.85 every 0.01 steps. Note that we fixed parameters including layer thicknesses, light incidence, and f Au throughout the whole RCWA simulation processes. S-2
Figure S3. Maximum etching limit of RIE process. Photographs of etched samples (2 cm 2.5 cm) for different etching durations of 0, 20, 40, 60, and 70 s (from left to right). When the etching duration exceeds 60 s, the CYTOP nano-pillars in the insulator layer were completely etched away, leading to the collapse of the top layer. From this result, the etching durations of about 60 s is an experimental maximum etching limit which acts as a threshold of structure maintenance. Figure S4. Structure dependent optical characteristics under atmospheric environment. Simulated reflectance spectra as a function of continuous f CYTOP from 0 to 1, marked with the experimentally measured resonances (white circles; evaluated from Figure 3g); 662, 636, 596, and 556 nm for 0, 20, 40, and 60 s, respectively. S-3
Figure S5. Soft lithography patterning by PDMS stamp method. (a) The 60 s etched sample prior to the PDMS film attachment showing purple color over the entire surface. (b) Soft lithographic process for peeling off the background insulator and top Au layer leaving 6 units of 2-mmdiameter circular MIM structures. 5-7 For an enhancement of adhesive forces between the PDMS film with top Au layer, the PDMS film was pre-treated with O 2 plasma prior to the peeling-off procedure. (c) Another PDMS film with 4 mm-diameter circular holes was attached for liquid confinement and isolation. This system provides direct comparisons of multiple colorations under liquids with different RIs. Figure S6. Structure-dependent RI sensitivity. Simulated reflectance spectra as a function of continuous RI (from n =1.0 to 1.8) for different f CYTOP ; (a) 1.00, (b) 0.76, (c) 0.51, and (d) 0.18 yielding RI sensitivities of 7.1, 66.0, 203.2, and 347.2 nm/riu, respectively. Clearly, RIsensitivity is improved with a decrease of f CYTOP. That is, as the hollow voids in the insulator layer become larger, the amount of medium infiltration increase and enhances effective RI changes in the insulator layer. S-4
Figure S7. Selective light absorptions at FP resonances under different medium. Photographs showing colorations of the etched sample for 60 s (f CYTOP = 0.18) under different mediums; (a) n = 1.00 (air), (b) n = 1.34 (acetonitrile), and (c) n = 1.51 (anisole). (d) Corresponding experimental reflectance spectra and (e) simulated reflectance spectra marked with spectral positions of resonances; 573, 677, and 736 nm, for n = 1.00, 1.34, and 1.51, respectively. Simulation results of normalized E-field intensity distribution at resonances (573, 677, and 736 nm) under different mediums; (f) n = 1.00, (g) n = 1.34, and (h) n = 1.51. Clearly, the simulation results demonstrate the role of the liquid permeation on color changes. The E-field distribution under n = 1.00 shows the strongest absorption at 573 nm within the insulator area, whereas less absorptions were monitored at the 677 and 736 nm (Figure S7f). Same mechanism works for the cases of n = 1.34 and n = 1.51 showing the maximum absorptions at 677 and 736 nm, respectively (Figures S7g and S7h). S-5
Figure S8. Spatially selective surface modification by localized O 2 plasma treatment. (a) Hydrophobic nature of the device, inhibiting infiltration of deionized water into the hollow voids of the etched pattern. (b) The masked sample for spatially selective O 2 plasma treatment. The sample was covered with the shadow mask, and exposed to the O 2 plasma for 10 min. Figure S9. Repetitive immersion and removal of index-matching liquid. (a) The patterned sample under atmospheric environment. (b) Immersion of the sample under index-matching liquid (methanol; n = 1.34) and (c, d) removal by N 2 gas blow. A series of the processes were repetitively carried out within a few seconds without any damage, demonstrating instant responsibility, reproducibility and stability of the system (Movies 1 and 2). S-6
SUPPORTING MOVIES Movie 1. Dropping index-matching liquid (methanol; n = 1.34) on the sample with inscribed patterns. Movie 2. Removing index-matching liquid (methanol; n = 1.34) from the sample with inscribed patterns by N 2 gas blow. REFERENCES 1. Kwok, D. Y.; Neumann, A. W. Contact Angle Measurement and Contact Angle Interpretation. Adv. Colloid Interface Sci. 1999, 81, 167-249. 2. Bruggeman, D. A. G. The Calculation of Various Physical Constants of Heterogeneous Substances. I. The Dielectric Constants and Conductivities of Mixtures Composed of Isotropic Substances. Ann. Phys. 1935, 416, 636-791. 3. Choy, T. C. Effective Medium Theory: Principles and Applications; Oxford University Press: Oxford, UK, 2015. 4. Cai, W.; Shalaev, V. Optical Metamaterials: Fundamentals and Applications; Springer: New York, USA, 2009. 5. Qin, D.; Xia, Y.; Whitesides, G. M. Soft Lithography for Micro-and Nanoscale Patterning. Nat. Protoc. 2010, 5, 491. S-7
6. Park, H.-L.; Lee, B.-Y.; Kim, S.-U.; Suh, J.-H.; Kim, M.-H.; Lee, S.-D. Importance of Surface Modification of a Microcontact Stamp for Pattern Fidelity of Soluble Organic Semiconductors. J. Micro/Nanolith. MEMS MOEMS 2016, 15, 013501. 7. Ryu, Y. S.; Wittenberg, N. J.; Suh, J. H.; Lee, S. W.; Sohn, Y.; Oh, S. H.; Parikh, A. N.; Lee, S. D. Continuity of Monolayer-Bilayer Junctions for Localization of Lipid Raft Microdomains in Model Membranes. Sci. Rep. 2016, 6, 26823. S-8