Supporting Information Topographically-Designed Triboelectric Nanogenerator via Block Copolymer Self- Assembly Chang Kyu Jeong,, Kwang Min Baek,, Simiao Niu, Tae Won Nam, Yoon Hyung Hur, Dae Yong Park, Geon-Tae Hwang, Myunghwan Byun, Zhong Lin Wang, Yeon Sik Jung,, * and Keon Jae Lee, * Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea E-mail: keonlee@kaist.ac.kr, ysjung@kaist.ac.kr School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332-0245, United States These authors contributed equally to this work. *E-mail: ysjung@kaist.ac.kr (Y.S.J); keonlee@kaist.ac.kr (K.J.L.) 1
Experimental Section Fabrication steps for an arch-shaped BCP-TENGs: Cr/Au (30 nm/200 nm) layers were deposited on a Kapton PI sheet (DuPont, 125 μm in thickness) with a size of 4 cm 3 cm as the bottom electrode of the TENG. On the other side of the Kapton sheet, SiOx (30 nm) was prepared by plasma-enhanced chemical vapor deposition (PECVD) as the adhesion layer for a thin glass film. Evaporable borosilicate glass thin film (Schott, 250 nm in thickness) was deposited on the SiOx adhesion layer using e-beam evaporation. Various elements were also detected by EDS from the borosilicate glass deposited on the bottom part (Figure S2). After cleaning the glass silica film surface, PS-b-PDMS BCP nanopatterning processes were employed to produce the various silica nanostructures on this bottom part of the BCP-TENGs. For a top part, a PTFE-based Teflon layer (DuPont, Teflon Amorphous Fluoropolymers (AF) 2400, 1 wt% dissolved in Fluoroinert solvent (3M)) was spin-cast (200 nm) on an ITO/PET flexible sheet (Sigma-Aldrich, 125 μm in thickness) with a size of 4.05 cm 3 cm. After drying and heating at 80 C for 30 min, the surface of the Teflon layer on the top part was faced to the nanopatterned silica surface of the bottom part. The control of adhesive wear property mainly determines the wear resistance. 1 Therefore, N2 and Ar plasma pre-treatment was applied before the deposition of silica/bcp and Teflon PTFE films, respectively, 2,3 achieving the excellent mechanical stability and durability of the TENG devices. For the assembling step, the edges of the two parts were anchored by PET tape (3M) along the length axis, making an arch-shaped TENG structure. The generated output of the TENGs were measured by a sourcemeter (Keithley 2612A) and a linear motor controller (Ecopia System). Various nanopatterns based on self-assembly of BCP microphase separation: (i) Morphologies of nanodots and nanogrates: The glass silica surface on the bottom part was functionalized by a hydroxylated PS homopolymer (PS-OH, Polymer Source, MW = 30 kg mol -1 ) for 2 h in a vacuum chamber. PS-b-PDMS BCPs (Polymer Source) with different 2
MWs of 56.1 kg mol -1 and 45.5 kg mol -1 were used for the morphologies of nanodots and nanogrates, respectively. BCP solutions of 0.8 wt% were made using a mixture of toluene, heptane, and propylene glycol monomethyl ether acetate (THP solution, volume fraction of 1:1:1, were all purchased from Sigma-Aldrich). After spin-casting the BCP solutions on the functionalized glass silica surface, the BCP thin films were treated by solvent vapor of toluene (40 ml) in a completely sealed chamber for 1 h. (ii) Morphology of HPL-based nanomeshes: The surface of glass silica was chemically modified by a PS-OH with MW of 150 kg mol -1. Another PS-b-PDMS BCP (MW = 36 kg mol -1 ) was dissolved as 0.7 wt% in the THP solution. The spin-casted BCP thin film on the glass silica surface was annealed at 45 C with solvent vapor of toluene (25 ml) in the isolated chamber for 5 min. (iii) Formation of silica nanopatterns: The self-assembled BCP thin films were treated under O2 plasma with CF4 gas using a reactive ion etching (RIE) system at 10 mtorr. During the plasma treatment, the PS domains of the BCP thin films were removed, and the fraction of PDMS nanopatterns were oxidized into silica. 3
Figure S1. EDS elemental mapping results of (a) C in the PTFE-based Teflon film, and (b) C and F merging with the SEM image of the Teflon film. Scale bar, 10 μm. 4
Figure S2. EDS elemental mapping data of the deposited borosilicate glass silica film of bottom part. (a) Si, (b) B, (c) O, (d) Al, (e) Na, and (f) Merging all elements with the SEM image. Scale bar, 100 μm. The evaporable glass silica is composed of amorphous SiO2-B2O3 doped with Al2O3 and Na2O. 4 5
Figure S3. Low-magnified SEM images of various BCP nanopatterns. Scale bar, 500 nm. 6
Figure S4. A cross-sectional SEM image of the nanodots pattern. Scale bar, 40 nm. 7
Figure S5. A cross-sectional SEM image of the fingerprint-like nanogrates pattern. Scale bar, 50 nm. 8
Figure S6. A cross-sectional SEM image of the nanomeshes pattern (HPL). Scale bar, 50 nm. 9
Figure S7. Expected and reported demerits of high aspect-ratio nanostructures in triboelectric nanogenerators. The case of (a) breakable and (b) deformable nanostructured materials, respectively. (c) In the case of mechanically robust nanostructures, the genuine contact area cannot be large since the pushed part is not able to protrude the deep nanostructures due to the limited solid ductility in spite of the large area of the high aspect-ratio nanostructures. 10
Figure S8. XPS data of Si2p in the silica surface (a) before and (b) after contact electrification (reciprocating contact cycles). 11
Figure S9. XPS survey analyses of Teflon surface (a) before and (b) after the contact electrification (reciprocating contact cycles). 12
Figure S10. (a) Topographic atomic force microscopy (AFM) image and (b) EFM images of nanopatterned silica surfaces (left) before and (right) after contact electrification. In the AFM image, there was no significant topological difference between electrified and non-electrified parts. On the contrary, the EFM image shows a clear difference between the two parts. In the magnified EFM images, moreover, the traces of nanopatterns are observed in the electrified region, whereas the traces are not shown in the non-electrified region. It is presumably because the surface ions ( O - and OH - ) of silica can be more easily transferred from the topographically pronounced surface (due to the existence of silica nanostructures) during contact electrification. 13
Figure S11. Friction coefficient versus various surface morphologies, showing the increase of static contact friction with the increase of nanoscale bumpy structures. The friction coefficients is measured by a customized equipment composed of a variable slope and a protractor, and calculated by tangent values. The counterpart surface is fixed as a PTFE-based Teflon/ITO/PET substrate (top part of our TENG). To prevent electrostatic charges as much as possible, all surfaces are treated by an anti-static gun. 14
Figure S12. An SEM image showing that the counterpart Teflon surface was not mechanically changed or imprinted by the silica nanopatterns converted from self-assembled BCPs. The cleavage of the layers in the image is due to sample cutting. 15
Figure S13. The forward/reverse signals of generated voltage and current from a BCP-TENG (nanomeshes) fabricated using a 75 μm-thick Kapton PI substrate as the bottom part. This result is almost same as that of original BCP-TENG with a 125 μm-thick Kapton PI substrate. It is presumably because the difference in dielectric effects of 75 μm- and 125 μm-thick PI substrates can be ignored, compared to the extremely high triboelectric potential in the air gap of TENG. 5 16
Calculation of energy conversion efficiency at device level The energy conversion efficiency (η %) is calculated as below definition: Generated electrical energy: As shown in Figure 4d, the maximum power density is achieved at the resistance of 100 MΩ, which corresponds to the highest Eelec. The electrical energy loaded by the fixed resistance is calculated according to the following equation, where I and R are current and resistance, respectively. The plot of I 2 R can be estimated by the I-t curve, and the integration of the curve in one cycle is calculated as Mechanical energy at device level: The compressive force applied to the arch-shaped top part of TENG for making a mechanical contact mainly works on straining the PET substrate of top part, because the thickness of ITO (~100 nm) and PTFE-Teflon (~200 nm) are much thinner than that of PET (~125 μm). Hence, the Emech can be calculated by the stored elastic energy (Eelas) of the PET substrate in a single deformation. 5 The stored elastic energy can be calculated by the following equation, where Y, ε, and V are Young s modulus, strain, and volume. The purposely-induced strain of PET substrate can be estimated as the strain of the outer surface, which is equal to 6 17
where r and h are the radius of curvature and thickness of the arch-shaped top part. According to the above equation, the maximum strain of top part is about 0.062 %. Using the Young s modulus of PET (~2.7 GPa) and the volume of PET substrate (~0.15 cm 3 ), we can calculate Therefore, the energy conversion efficiency can be estimated as, 18
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