PDMS coated grip. Au film. Delamination Zone

Transcription

1 P Delamination Zone a a PDMS coated grip t Au film Supplementary Figure S1. A schematic diagram of delamination zone at the interface between the Au thin film specimen under the tensile load, P, and the PDMS coated grip 1

2 a b (790, 457) (992, 457) Y Y-direction alignment Y-direction alignment X (488, 231) (1173, 231) Y X-direction alignment X-direction alignment X c (488, 231) Well-aligned Case Misaligned Case Grip (489, 917) Supplementary Figure S2. Details of in-plane alignment using CCD camera s images. a, Inplane alignment using the coordination of pixels in the image and XYZ positioning of microstages. b, Grip alignment using the images. c, The comparison of well-aligned and misaligned specimens. 2

3 a b c 0 μm height in each line 0 μm 7.5 μm 6.25 μm 15 μm 12.5 μm Gauge Length (3mm) Height Difference: 1.25 μm Height Difference: 2.5 μm d 22.5 μm μm e 30 μm 25 μm f 37.5 μm μm Height Difference: 3.75 μm Height Difference: 5 μm Height Difference: 6.25 μm Supplementary Figure S3. Brightness intensity differences due to out-of-plane misalignment. a-f, The brightness intensity differences with increasing height difference between each line. The out-of-plane alignment can be performed within the error of ~2 μm, because the brightness intensity difference between each line becomes noticeable from (c). 3

4 Tilting Angle, ( ) a b Out-of-plane Deformation (m) (applied load of 22mN) Aluminum grip Steel rod Bottom Area Tensile force Side View c Au Specimen θ Grip d nm thick film Film Thickness 400 nm 85 nm 55 nm Breaking Load (N) Tilting Angle, θ ( ) and 85 nm thick films Applied Load (N) Supplementary Figure S4. The analysis of possible out-of-plane misalignment from eccentric loading. a, A schematic of simulation model with applied tensile force on the bottom of grip. b, The result of the simulation representing the out-of-plane deformation. c, A schematic of tilted grip by bending moment exerted on the grip. Inset table shows the breaking load and the tilting angle of grip in each film thickness. d, The tilting angle of grip as a function of the applied load on the bottom of grip. 4

5 Stress (MPa) Stress (MPa) Stress (MPa) a Centric Loading Grip & rod Fixed Displacement Au specimen Simulation Result (Centric) c d nm Experimental data 100 Centric Eccentric (2.75mm) Strain nm b Fixed Eccentric Loading (2.75 mm) Grip & rod Displacement Au specimen e 200 Experimental data 100 Centric Eccentric (2.75mm) Strain nm 300 Simulation Result (Eccentric) 200 Experimental data 100 Centric Eccentric (2.75mm) Strain Supplementary Figure S5. The simulation analysis of the testing system for centric versus eccentric loading cases. a, The simulation model and result for the centric loading case. b, The simulation model and result for the eccentric loading case. c-e, The comparison of simulated and experimental stress-strain curves for 400, 85, and 55 nm thick specimens. 5

6 Normal Stress (MPa) Au Film Cross Section Top Middle Bottom nm 85 nm 55 nm Supplementary Figure S6. The tensile stresses at the top, middle and bottom positions on the middle cross section of the specimen under the eccentric loading (at σ middle = 300 MPa). 6

7 Load (N) a Well-aligned Misaligned b Well-aligned Misaligned (2.75mm) Weight mm 0.05 ~47.1mN for 4.81 g weight Load Cell Time (s) Supplementary Figure S7. Direct validation of possible misalignment effects exerted on the load cell. a, A constant load is applied to the load cell using weight in two different ways. Wellaligned and misaligned cases. b, The load data shows no difference between well-aligned and misaligned case. This result reveals that the bending moment exerted on the load cell due to the eccentric loading plane is almost negligible. 7

8 Viscosity (mpa s) 6 5 Benzyl alcohol 4 Isobutalol Supplementary Figure S8. Surface tension and viscosity of various liquids and solvents at room temperature. Ethanol Methanol Acetone Acetic acid Toluene High surface tension with low viscosity area Water Surface Tension (mn/m) Hydrogen peroxide 8

9 Supplementary Note 1: Validation of van der Waals adhesion of PDMS for the gripping technique The PDMS has been widely used in stamping transfer techniques 35,36 because it provides superior adhesion to the solid surfaces. Therefore, we have selected it as the gripping material. In order to verify the gripping technique for ultra-thin films, we have evaluated a delamination driving force, G, at the interface between the Au film and PDMS coating under the tensile load, 4, 37,38 P, using following equations ( σ ) ( ) ( σ ) ( ), (S1) (de d e ) σ. (S2) where U a is the reduction in potential energy of the system due to advance of the delamination, U2 a is the strain energy stored in the delaminated film, U1 a is the strain energy stored in the film before delamination, σ f is the applied stress on the film, E f is the Young s modulus of the Au film, B is the bonding width, t is the film thickness, and a is the delaminated crack length as shown in Supplementary Figure S1. When the delamination driving force, G, reaches the critical adhesion energy, G c, the Au film will be delaminated. The calculated maximum G of 74, 13 and 8 mj m^-2 for 400, 85 and 55 nm thick films are much lower than previously reported adhesion energy between PDMS to solid surfaces 39,40 around 100~2000 mj m^-2, resulting in no delamination during the tensile test. Therefore, van der Waals adhesion for gripping technique using PDMS provides superior adhesion without slippage or delamination during the tensile testing of ultra-thin films. 9

10 Supplementary Note 2: Specimen alignment For the in-plane alignment, we can align the specimen using the coordination of pixels in CCD camera s images and XYZ positioning of micro-stages (Supplementary Fig. S2a). Subsequently, a grip is aligned before attaching the grip on the specimen, and then it is attached to the specimen by lowering the grip using the micro-stages (Supplementary Fig. S2b). The well-aligned and misaligned specimens are shown in Supplementary Figure S2c. The out-of-plane alignment can be verified by the intensity of the brightness in the CCD camera s image. If the misalignment occurs in out-of-plane direction, the intensity of the brightness changes within the image due to the local height difference. We have manually changed the local height of specimen using micro-stages and observed the intensity of brightness (Supplementary Fig. S3). When the height difference of each line at the end of gauge length reaches to 2.5 μm, the brightness difference becomes noticeable (Fig. S3a-c). From the height difference over 2.5 μm, the brightness intensity differences of each line for all examples are easily detected (Fig. S3d-f). Therefore, we are able to perform the precise alignment using the images and the micro-stages within the error of ~2 μm, which is insignificant considering the specimen gauge length of ~2 mm. The insignificance of misalignment for the tensile test of thin films had also been reported in previous study

11 Supplementary Note 3: Analysis of possible bending moment effects from eccentric loading The simulation analysis was performed by using commercial finite element analysis codes to investigate the possible bending moment effects exerted on the specimen from the eccentric loading plane due to the shape of grip (Supplementary Fig. S4). When the tensile force is applied to the bottom of grip, the bending moment would be exerted on the grip (Fig. S4a). Subsequently, the grip will be tilted, and this would generate the out-of-plane misalignment of the specimen (Fig. S4b). However, if the grip is hardly tilted, the out-of-plane misalignment of the specimen and the error of tensile stress would be negligible. The tilting angle of grip was calculated from the simulation results, and it showed almost negligible values of 0.012, and , with respect to the applied load of 0.2, and N, respectively (Fig. S4c,d). Previously reported study 41 showed that the effects of out-ofplane misalignment for the thin film tensile test were insignificant in the degree range of 0~5. Therefore, the diminutive tilting of grip in our case would hardly generate the out-of-plane misalignment and bending moment exerted on the specimen. In addition, the bending stresses from the misalignment are insignificant for the thin film tensile test because the thin films are easily bent to eliminate the bending stresses 41. Therefore, considering the ratio of the specimen thickness to length around 3~ , and very small applied load, the bending moment exerted on the specimen and errors of tensile stress are negligible. We further confirmed that possible bending moment effects and consequent errors of tensile stress are negligible by performing the 3D simulation analysis of the testing system for centric loading (Supplementary Fig. S5a, and Movies 1, 2, 3 for 400, 85, 55 nm thick specimens, respectively) versus eccentric loading (Supplementary Fig. S5b, and Movies 4, 5, 6 for 400, 85, 55 nm thick specimens, respectively). The simulation was performed by increasing displacement up to the failure strains of 0.020, 0.011, and for the 400, 85, and 55 nm thick specimens, respectively (Supplementary Fig. S5c-e). It was demonstrated that the tensile stresses from experimental, centric, and eccentric cases are almost same as shown in Supplementary Figure 11

12 S5c, d, and e for the 400, 85, and 55 nm thick specimens. Therefore, it has been confirmed that the possible errors of tensile stress from eccentric loading are negligible in the present study. Furthermore, the tensile stresses at top, middle and bottom positions at middle cross section of the specimen were investigated to examine the possible bending moment exerted on the specimen from the eccentric loading. When the tensile stress at the middle position of the specimen was 300 MPa, the corresponding tensile stresses at the top and bottom positions were shown in Supplementary Figure S6. The results showed that the stresses are almost same, within only 1 KPa difference between top and bottom surfaces at the 400 nm thick specimen, which is the negligible error below ~ %. Therefore, it has been also confirmed that the eccentric loading has negligible bending moment effects on the thin film specimens in the present study. In the end, we have validated the possible error of load cell data from eccentric loading plane. To clarify this, we have directly examined the effects of bending moment exerted on the load cell as shown in Supplementary Figure S7. A constant load is applied to the load cell using a weight in different ways (Supplementary Fig. S7a). Assuming for both well-aligned and misaligned cases, the weight is placed along the loading plane and misaligned loading plane respectively (eccentric of 2.75 mm from loading plane). The results showed the same values in both cases; the load of 47.1 mn for 4.81 g weight as shown in Supplementary Figure S7b. Therefore, the error of load cell data due to the bending moment is also negligible. 12

13 Supplementary Note 4: Selection criteria for the supporting liquid The surface tension and viscosity of various liquids and solvents are shown in Supplementary Figure S8 42. The selection criteria that we used for the supporting liquid are high surface tension, low viscosity, and non-reactivity to the specimen. Only the water and the hydrogen peroxide have a higher surface tension of ~70 mn m^-1 with lower viscosity of ~1.0 mpa s compared to other liquids. Although both water and hydrogen peroxide offer ideal environments for floating the thin films with almost frictionless lateral movement, only the water is suitable for our method because it is clean, stable and non-reactive to most materials. 13

14 Supplementary References 35 Lim, K. S., Chang, W.-J., Koo, Y.-M. & Bashir, R. Reliable fabrication method of transferable micron scale metal pattern for poly (dimethylsiloxane) metallization. Lab on a Chip 6, (2006). 36 Meitl, M. A. et al. Transfer printing by kinetic control of adhesion to an elastomeric stamp. Nature Materials 5, (2005). 37 Anderson, T. L. Fracture mechanics: fundamentals and applications. (CRC PressI Llc, 2005). 38 Hutchinson, J. & Suo, Z. Mixed mode cracking in layered materials. Advances in applied mechanics 29, 191 (1992). 39 Deruelle, M., Tirrell, M., Marciano, Y., Hervet, H. & Léger, L. Adhesion energy between polymer networks and solid surfaces modified by polymer attachment. Faraday Discussions 98, (1994). 40 Sofla, A., Seker, E., Landers, J. P. & Begley, M. R. PDMS-glass interface adhesion energy determined via comprehensive solutions for thin film bulge/blister tests. Journal of applied mechanics 77 (2010). 41 Kang, D.-J., Park, J.-H., Shin, M.-S., Ha, J.-E. & Lee, H.-J. Specimen alignment in an axial tensile test of thin films using direct imaging and its influence on the mechanical properties of BeCu. Journal of Micromechanics and Microengineering 20, (2010). 42 ACCU DYNE TEST, Available at: Accessed Date: Aug 14,