Supplementary information for “Bottom-up & top-down manipulations for photonic crystallinity in a graphene-oxide colloid”
Tian-Zi Shen, Seung-Ho Hong, and Jang-Kun Song*
School of Electronics & Electrical Engineering, Sungkyunkwan University, Jangan-Gu, Suwon, Gyeonggi-do 440-746, Korea
* Corresponding Author E-mail:
Supplementary Figure S1. Characterisation of graphene oxide sample. a. Most of the GO particles were approximately 1-nm thick, indicative of a single-layer structure. b. The shape and size of the GO particles varied significantly, and the mean size was ~6.5 µm. c. X ray photoelectron spectroscopy (XPS) data revealed that the intensity of the oxidation peaks is significantly higher than that of the C-C/C=C bonding peak. This is indicative of the significant level of oxidation of the GO sample, as well as the high surface charge density of the aqueous dispersion.
Supplementary Figure S2. Difference between GO samples with and without structural colour reflection. Two bottles contain the same concentration GO (~ 1 wt%), but the left bottle displays clear blue colour reflection, and the right one does not. Well-prepared GO dispersion exhibits photonic crystallinity, but usual one does not.
Supplementary Figure S3. Fabrication of a cell with undulated surface morphology. a., A substrate with undulated surface morphology was fabricated by imprinting on sandpaper using PDMS. The SEM image reveals the bumpy surface of the substrate. Scale bar, 100 µm. b. The surface morphological profile was determined by using an alpha step profiler. The width and height of the bumps on the surface are ~30–70 µm and 15–25 µm, respectively. c. A cell was fabricated by using the uneven substrate and a flat substrate.
Supplementary Figure S4. Zeta potential for GO dispersion with ion addition and UV irradiation. a. The zeta potential of GO dispersions with NaCl addition were measured. The absolute value of zeta potential decreased with increasing ions, indicating increase in the electrostatic screening effect. b. GO dispersions were exposed to UV light (10 mW/cm2) for varying amounts of time, and the zeta potential of the GO samples were measured. The absolute value of zeta potential decreased with increasing UV irradiation time. This is due to the decrease in the surface charge density on GO particles (see Supplementary Fig. S4).
Supplementary Figure S5. Effect of UV illumination on the GO dispersion. a. GO dispersions were exposed to UV light (10 mW/cm2) for varying amounts of time, and the GO samples were analysed via XPS. The intensity of the oxidation peaks decreases, relative to that of the C-C peak, with increasing exposure time. b. The area ratio of C-O/C-C decreases with increasing UV exposure time. After UV exposure, the colour of the GO sample changed from brown to black. This indicates that GO particles undergo significant reduction during UV exposure.
Supplementary Figure S6. Multi-colour drawing obtained by dropping another GO dispersion. A colourful image was obtained when water was dropped in a beaker containing a high-concentration GO dispersion and stirred with a stick. The character was drawn when another GO dispersion, having a blue colour reflection along the ‘S’ line, was dropped into the beaker. The top blue colour replaced the bottom green colour, as shown in A. However, in region B, the bottom colour became partially mixed with the top colour, thereby resulting in the cyan colour observed. Region C, near the edge of the ‘S’ mark where the GO particles are aligned vertically owing to the flow effect, is black. In region D, a whitish colour was obtained owing to the mixing of various colours.