Supporting Information. Direct Growth of Graphene Films on 3D Grating. Structural Quartz Substrates for High-performance. Pressure-Sensitive Sensor

Transcription

1 Supporting Information Direct Growth of Graphene Films on 3D Grating Structural Quartz Substrates for High-performance Pressure-Sensitive Sensor Xuefen Song, a,b Tai Sun b Jun Yang, b Leyong Yu, b Dacheng Wei, c Liang Fang a Bin Lu, b Chunlei Du b and Dapeng Wei b* a State Key Laboratory of Mechanical Transmission,& Key Laboratory of Biorheological Science and Technology (Ministry of Education), College of Physics, Chongqing University, Chongqing, , People s Republic of China b Chongqing Key Laboratory of Multi-scale Manufacturing Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing , People s Republic of China c State Key Laboratory of Molecular Engineering of Polymers &Department of Macromolecular Science, Fudan University, Shanghai , People s Republic of China Corresponding authors dpwei@cigit.ac.cn (D.W) S-1

2 1. EXPERIMENTAL METHOD 1.1. Preparation of Gr/GQ. A transparent quartz glass (thickness: 1mm; size: 2cm 2cm) with roughness of Ra~6.3 was used to as substrate. To fabricate the grating patterns, photoresist (AZ 1500) was homogenized on the surface of quartz for 30s at 3000 RPM and dried on 100 C for 10 min. Then, under the luminous intensity of 12mw/cm 2, the photoresist film on quartz was exposed for 2.5 s with grid patterns (with a period of 4µm) in the central area of 1cm 1cm by photolithography system (ABM/6/350/NUV). The exposed patterns were etched by ion beam etching (IBE) system (ME-3A) with mixed gases of NH 4 F:HF = 4:1 (v/v) and the power of 100W. After keeping for 60 min, the quartz substrates were successively washed by acetone and water, and finally were dried in air Synthesis of graphene. Graphene films were grown on the surface of 3D grating structural quartz substrates (with the size of 2cm 2cm, and the size of grating region is 1cm 1cm, named as Gr/GQ) using a chemical vapor deposition (CVD) system (with two-zone furnace). After cleaning, the substrate was placed into the downstream center of quartz tube and a copper wafer (25 µm thick in our experiment) was placed on the center of upstream temperature zone. The both zones of furnace were heated to 950 C. Under atmospheric pressure, mixture gases of methane (CH 4, purity: %), hydrogen (H 2, purity: %) and argon (Ar, S-2

3 purity: %) (with special ratio of CH 4 :H 2 :Ar=5:80:200 standard-state cubic centimeter per minute, sccm) were introduced into the chamber. The graphene growth maintained for minutes, and then the CH 4 as was turned off and the sample was cooled to room temperature Preparation of the pressure-sensitive sensor. The assembled graphene films were prepared on the flexible polymer polydimethylsiloxane (PDMS) through three major steps. First, we deposited graphene films on the surface of copper wafer (named graphene/cu). Then a 10:1 mixture of PDMS elastomer (SYLGARD 184, Dow Corning) with a cross-linker of silicone elastomer base was coated onto the surface of graphene/cu, and was dried on the hot plate at 80 C for at least 3 hours. A aqueous solution of ferric nitrate solution (Fe(NO 3 ) 3 ) was used to sufficiently dissolve copper without leaving any residue overnight at room temperature. After cleaning, the polymer hybrid composite structure of PDMS/Gr was obtained. Finally, the Gr/PDMS was cut into suitable shape and size, and then was attached to the upside of Gr/GQ. The silver paint was brushed on the one side of Gr/GQ and Gr/PDMS to fabricate multi-functional electrodes. S-3

4 2. SUPPORTING FIGURES Figure S1. a) low resolution SEM and b) high resolution SEM images of conformal graphene deposited on the surface of 3D grating micro-structured quartz substrates with the growth time of 120 min. After the growth for 120 min, graphene films were conformally deposited on the whole surface of GQ substrates. Figure S1 shows a typical scanning electron microscope (SEM) image of a Gr/GQ. On the low resolution SEM of Figure S1a, the respective regions of top, bottom and side were covered with the nearly uniform color, which declared that a continuous graphene film was prepared on the whole surface of dielectric 3D-substrate. Combining with high resolution SEM (Figure S1b), on the temperature of 950 C,we would conclude that the catalysis-free growth of CVD process was a proper method to prepare graphene films on dielectric substrates. S-4

5 Figure S2. a) The 3D image of grating quartz, measured by white light interferometer (New View 7100). b) Raman spectra of conformal graphene films with increasing layers, deposited on the surface of 3D grating micro-structured quartz substrates with different grown time of min. Figure S2a shows the 3D superficial morphology of grating quartz, measured by white light interferometer (New View 7100). This image reflects the uniform and integral 3D-morphology of grating micro-structured quartz. The perfect superficial patterns of quartz supply a precondition for the preparation of high-quality conformal graphene. Raman spectroscopy is a direct and effective tool to characterize the nature of graphene, including the defects, sizes of crystal grains, atomic layers, and so on. 1-2 In general, typical Raman spectra of the graphene have three peaks. 2 The G peak at ~1690cm-1indicatesa graphitized S-5

6 structure. 3 The D band at ~1350cm-1 is so-called defect band of graphene. 2 The 2D band at ~2700 cm-1is more useful. 4 Its shape and I2D/IG ratio are finger prints to identify the number of layers of graphene. 2, 5 With the increase of growth time, Raman spectra in Figure S4b show the decreasing intensity ratio of I2D/IG, reflecting the increase of stacked graphene layers. 5 In Figure S1b, low D peaks reveal small defects and edges, 2 resulting from growth mechanism of graphene on the non-catalytic substrates. 6-7 Figure S3. SEM images of top view of Gr/GQ a) before and b) after compression of PDMS elastomer. S-6

7 Figure S4. a) Raman spectra of Gr/GQ after the compression tests. b) Raman spectra of Gr/PDMS before and after the compression tests. After the pressure-response tests, Raman spectra of Gr/GQ and Gr/PDMS were characterized. The re-measured Raman spectra of Gr/GQ in Figure S4a are the similar to those of Gr/GQ before compression tests, which suggests that the compression of PDMS elastomer could not damaged graphene films on the surface of grating quartz. The consistent Raman spectra and weak defect peak in Figure S4b indicates that the graphene on the surface of the PDMS also could not be cracked during the compression of PDMS elastomer. The calculation of sheet resistance Figure S3. The sectional schematic of conformal Gr/GQ The size of superficial grating region is 1 1 cm 2, so we defined the length as l=1cm, width as w=1cm. During the preparation process of grating structures, the width (practical width W=w) had no change. But the practical length (defined as L) was elongated with the depth (defined S-7

8 as d) and the increasing period (defined as p) number of grating structures. Equation S1: L=2d (l/p)+l Equation S2: Sheet resistance: R=R* (W/L) Equation S3: w=l So, Equation S3: R= R* (W/L) = R* p/(2d+p) R is the real sheet resistance of conformal graphene; R* is the test value of the resistance, getting from the slope of I-V curve. References: 1. Song, X.; Wang, M.; Wei, D.; Liu, D.; Shi, H.; Hu, C.; Fang, L.; Zhang, W.; Du, C., Enhanced photoelectrochemical perporties of graphene nanowalls CdS composite materials. Journal of Alloys and Compounds 2015, 651, Ferrari, A. C., Raman spectroscopy of graphene and graphite: Disorder, electron phonon coupling, doping and nonadiabatic effects. Solid State Communications 2007, 143 (1-2), Song, X.; Liu, J.; Yu, L.; Yang, J.; Fang, L.; Shi, H.; Du, C.; Wei, D., Direct versatile PECVD growth of graphene nanowalls on multiple substrates. Materials Letters 2014, 137, Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S.; Geim, A. K., Raman Spectrum of Graphene and Graphene Layers. Physical Review Letters 2006, 97 (18). 5. Graf, D.; Molitor, F.; Ensslin, K.; Stampfer, C.; Jungen, A.; Hierold, C.; Wirtz, L., Spatially resolved raman spectroscopy of single- and few-layer graphene. Nano letters 2007, 7 (2), Camilli, L.; Sutter, E.; Sutter, P., Growth of two-dimensional materials on non-catalytic substrates: h-bn/au(111). 2D Materials 2014, 1 (2). 7. Lee, J.; Lee, N.; Lansac, Y.; Jang, Y. H., Charge inhomogeneity of graphene on SiO2: dispersion-corrected density functional theory study on the effect of reactive surface sites. Rsc Advances 2014, 4 (70), S-8