Supporting Information for. Standing Enokitake-Like Nanowire Films for Highly Stretchable Elastronics

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1 Supporting Information for Standing Enokitake-Like Nanowire Films for Highly Stretchable Elastronics Yan Wang, δ, Shu Gong, δ, Stephen. J. Wang,, Xinyi Yang, Yunzhi Ling, Lim Wei Yap, Dashen Dong, George. P. Simon,,,, Wenlong Cheng* Department of Chemical Engineering, Monash University, Clayton, Victoria 3800, Australia; The Melbourne Centre for Nanofabrication, Clayton, Victoria 3800, Australia; Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia. International Tangible Interaction Design Lab, Monash University, Clayton, Victoria 3800; Department of Innovation Design Engineering, School of Design, Royal College of Art, London, United Kingdom δ Both authors contributed equally to this manuscript *Correspondence author. W. L. Cheng Keywords: Standing enokitake-like nanowire, intrinsical stretchability, durable, elastronics, skin-like sensors

2 Figures: Figure S1. Schematic illustration of the fabrication standing enokitake nanowire-based gold films on elastomers. (a) First make a thin film of elastimeric substrate. (b) Coat with a layer of amino groups (positively charged) on the surface after plasma treatment. Then (c) attach small citrate-stabilized colloidal gold particles (negatively charged) and (d) finally put it in the nanowire growth solution to achieve uniform standing nanowires growth.

3 Figure S2. Universial growth and patternable property. (a) A photograph showing standing nanowires grown on polyurethane threads; (b-c) SEM images at different magnifications; (de) photograph (inset of d) and SEM images showing standing gold nanowires grown on fish lines; (f) A kangaroo pattern of gold nanowire-based gold films; (g) An optical micrograph of the standing nanowire-based gold films grown on a skin-textured Ecoflex replica.

4 Figure S3. Measured nanoparticle sizes and nanowire diameters with increased growth time.

5 Figure S4. Staircase growth. Left: Top view SEM image for mask-assisted staircase-like sanding nanowire based film. Scale bar: 5 µm. Right: A typical AFM image of a staircase-like standing gold nanowire film (top) and the corresponding line scan (bottom), scale bar is 5 µm.

6 Figure S5. Electrical responses of encapsulated standing enokitake nanowire-based films and no encapsulated standing enokitake nanowire-based films. Nanowire height: 1.5 µm.

7 Note S1: Previous works (ref 46-49) Yes Our standing AuNWs film Yes Appliying metal electroless depositon approach Active layer Cu, Ni, Ag, Au Au Metal layer configuration Continuous thin metal film 3D vertically aligned Au nanowires Intermediate layer polyelectrolyte nanoplatforms Amino groups materials Structure design Buckling/serpentine No Adhesion Passed scotch tape test Passed scotch tape test Maxium strain 300% 800% Table S1. Comparison of Janus gold film with previous works (ref 58-61), where both introduce an organic intermediate layer to enhance the overall performance of the stretchable conductive films.

8 Figure S6. A scheme illustrating possible structural changes of three different gold films during the stretching/releasing process: (a) Vacuum-evaporated bulk gold film, (b) lying-down mode percolation gold nanowire film and (c) Standing enokitake-like nanowire-based film.

9 Figure S7. In situ optical images (low and high resolutions) of three different locations (A, B, and C) of staning nanowire films under various strains (0%, 100%, 300%, 500%, 800% and back to 0%). Scale bar: 100 µm and 10 µm, respectively. Stretching strain is performed horizontally.

10 Figure S8. AFM featuring and height plots of standing nanowire films with different nanowire height. (a-b) 1.5 µm nanowire height standing enokitake nanowire-based film, (c-d) 7 µm nanowire height standing enokitake nanowire-based film under 200% strain, respectively.

11 Figure S9. Cross sectional SEM images of V-shaped standing nanowire/ecolflex film at 150% strain.

12 Figure S10. A schematic illustration showing the difference between V-shape crack (a) and U- shape crack (b).

13 Figure S11. Durability and stability performance of standing enokitake nanowire-based film. (a) 60,000 cycling test under 185% strain with a frequency of 1Hz. (b) Plots of resistance changes of 1-10 cycles and cycles. Nanowire height: 1.5 μm. SEM images of standing enokitake nanowire-based film (c, e) before and (d, f) after cycles of stretching and releasing under strain of 185 %, respectively, demonstrating full recovery of surface morphology. Nanowire height: 1.5 µm.

14 Figure S12. Long term stable electrical responses for standing enokitake nanowire-based films after storage at the temperature without encapsulation for 1, 7, 25 and 40 weeks, respectively. Nanowire height: 1.5 µm.

15 Figure S13. Stretch capacity and stress-strain of standing enokitake nanowire-based films with different nanowires height (1.5 µm, 3.5 µm, 5 µm, 7 µm and 14 µm).

16 Figure S14. Capacitive behavours of supercapacitors from standing enokitake nanowire-based janus conductors. (a) Cyclic voltammetry (CV) curves of the supercapacitors from standing enokitake nanowire-based janus films at different scan rate. (b) Galvanostatic chargingdischarging curves of the supercapacitors at a constant current of 0.1 ma, 0.2 ma and 0.5mA, respectively. (c) The calculated areal capacitances of the supercapacitor using CV curves. (d) The calculated areal capacitances of the supercapacitor using galvanostatic charge/discharge (GCD) curves. Nanowire height: 1.5 µm.

17 Figure S15. Stretchability of supercapacitors from standing enokitake nanowire-based janus conductors. (a) CV curves of the supercapacitor from standing enokitake nanowire-based janus film for applied strains up to 250% and a scan rate of 100 mv s-1. (b) Normalized surfacespecific capacitance of the supercapacitors as a function of tensile strains. (c) CV curves of the supercapacitor with different stretching cycles at a scan rate of 100 mv s-1. (d) Normalized surface-specific capacitance as a function of stretching cycles. Nanowire height: 1.5 µm.

18 Note S2: Comparison of Janus gold film with other aligned nanowires/nanotubes We acknowledge that both aligned nanowires or CNT has been used for elastic conductors in previous publication. Although our gold nanowires are also 1D building blocks, enokitake-like nanostructures (nanowire+nanoparticle) are essentially structures which are not present in any previous CNT-based films or any other active conductive films. This led to many more previously unknown properties, functions and mechanisms, which is entirely different from both vertically aligned and lying-down aligned CNT-based systems 1-4. The table below is a comparison between previously aligned 1D nanostructures and our vertically-aligned enokitake-like nanostructure in the context of soft electronic applications (Table. S2). Previous Aligned 1D Our standing AuNWs film film Conductive Yes Yes Stretchable Yes Yes Durability Good Good Interaction with elastomer Transfer printing Directly growth Max. stretchability without Up to 280% 800% additional structural design Adhesion N/A Passed scotch tape test Table S2. The comparison between aligned nanowire/nanotube and vertically-aligned enokitake-like nanostruct

19 References: 1. Shin, M. K.; Oh, J.; Lima, M.; Kozlov, M. E.; Kim, S. J.; Baughman, R. H. Elastomeric Conductive Composites Based on Carbon Nanotube Forests. Adv. Mater. 2010, 22, Li, L.; Yang, Z.; Gao, H.; Zhang, H.; Ren, J.; Sun, X.; Chen, T.; Kia, H. G.; Peng, H. Vertically Aligned and Penetrated Carbon Nanotube/Polymer Composite Film and Promising Electronic Applications. Adv. Mater. 2011, 23, Lee, D. H.; Kim, J. E.; Han, T. H.; Hwang, J. W.; Jeon, S.; Choi, S. Y.; Hong, S. H.; Lee, W. J.; Ruoff, R. S.; Kim, S. O. Versatile Carbon Hybrid Films Composed of Vertical Carbon Nanotubes Grown on Mechanically Compliant Graphene Films. Adv. Mater. 2010, 22, Yamada, T.; Hayamizu, Y.; Yamamoto, Y.; Yomogida, Y.; Izadi-Najafabadi, A.; Futaba, D. N.; Hata, K. A Stretchable Carbon Nanotube Strain Sensor for Human-Motion Detection. Nat. Nanotechnol. 2011, 6, 296.