Multiple-Patterning Nanosphere Lithography for Fabricating Periodic Three-Dimensional Hierarchical Nanostructures

Transcription

1 Supporting Information Multiple-Patterning Nanosphere Lithography for Fabricating Periodic Three-Dimensional Hierarchical Nanostructures Xiaobin Xu, 1,2 Qing Yang, 1,2 Natcha Wattanatorn, 1,2 Chuanzhen Zhao, 1,2 Naihao Chiang, 1,2 Steven J. Jonas, 1,3,4,5 and Paul S. Weiss 1,2,6* 1 California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States 2 Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States 3 Department of Pediatrics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, United States 4 Eli & Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California, Los Angeles, Los Angeles, CA 90095, United States 5 Children s Discovery and Innovation Institute, University of California, Los Angeles, Los Angeles, CA 90095, United States 6 Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States * psw@cnsi.ucla.edu 1

2 Characterization of reflection spectra In the characterization of the reflection spectra of the plasmonic hierarchical nanostructures, we set the incident light and reflected light to be near normal to the substrate, as illustrated on the left. Note that we also used these settings for the finite-difference time-domain (FDTD) optical simulations. In order to obtain the reflection spectra across the wavelength range from 500 to 6000 nm, two spectrophotometers were used. One spectrophotometer measured the reflection spectra from 500 to 2500 nm and other measured the reflection spectra from 2500 to 6000 nm. An UV-3101PC UV-VIS-NIR Spectrophotometer (Shimadzu Co., Japan) with an integrating sphere attachment (ISR-3100) was used to collect the reflection spectra of the plasmonic hierarchical nanostructures within the wavelength range (500 to 2500 nm). The scan rate was set at 1 nm/s. A customized polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) instrument was used to collect the reflection spectra of the plasmonic hierarchical nanostructures in the range of 2500 to 6000 nm. The scan step size was set at 2 nm with medium scan rate. Due to the differences in sensitivities of the two spectrometers, for comparisons to the simulations, the two segments of the reflection spectra were stitched together as follows: Sample i) No changes were made to the reflection spectra from 500 to 2500 nm, and the intensity of reflection spectra from 2500 to 6000 nm was multiplied by 20 in order to combine the spectra. Sample ii) The overall intensity of the reflection spectra obtained from 500 to 2500 nm was increased by 20 (arbitrary units), while the intensity of the reflection spectra from 2500 to 6000 nm was multiplied by 20. See Figure S9A. 2

3 Figure S1: (A) A typical scanning electron microscope (SEM) image of close-packed 1 µm polystyrene spheres in micro-scale. (B) A photograph of Si wafers fully covered by close-packed 1 µm polystyrene spheres. The reflected colors indicate the well-ordered configuration of the polystyrene microspheres. (C) The corresponding fast Fourier transform (FFT) of the SEM image. 3

4 Figure S2. (A) A typical scanning electron microscope (SEM) image of a large area of the silicon nanotube arrays. (B) The corresponding fast Fourier transform (FFT) of the image. (C) A typical SEM image of large-area silicon nanotube arrays recorded at a tilt of 30. 4

5 Figure S3. A typical scanning electron microscope (SEM) image of a large area of silicon nanostructures recorded at a tilt of 30. 5

6 Figure S4. A typical scanning electron microscope image of polystyrene nanospheres with oblate ellipsoid shapes after oxygen plasma reactive ion etching. Figure S5. Enhancing the adhesion between the polystyrene nanospheres and the underlying silicon substrate before dry etching helps to prevent tilting of the etched polymer nanoparticles, which could lead to asymmetries in the final pillar/nanotube arrays without heating. 6

7 Figure S6. (A) A high-resolution scanning electron microscope (SEM) image of silicon nanopillars made via the Bosch process. The top surfaces of the silicon nanopillars are smooth. The average distance between valleys and peaks on the sidewall of a silicon nanopillar is ~25 nm. (B) A high-resolution SEM image of four-level silicon nanotowers shows the smooth surfaces on the four levels. 7

8 Figure S7. A scanning electron microscope (SEM) image of periodic silicon nanopillars with smooth sidewalls fabricated by single-step deep reactive ion etching. Figure S8. A high-resolution scanning electron microscope (SEM) image of 50 nm Au evaporated silicon nanostructures. 8

9 Figure S9. (A) The visible-infrared reflectance spectra of sample ii. Insets: simulation results of the electric-field distribution of sample ii under photoexcitation (cross section). (B-C) Simulation of charge distributions on the Au surfaces on different layers of the sample ii at the two major dips (1830 nm and 4500 nm), from which we can see the 1830 nm mode is a combination of different multipole modes from the three layers; while the 4500 nm mode corresponds to the quadrupole modes of all three layers. 9