Supplementary Information for

Deflection Induced Cellular Focal Adhesion and Anisotropic Growth on Vertically Aligned Silicon Nanowires with Differing Elasticity

Yi-Seul Park†, Seo Young Yoon†, Jeong Su Park, and Jin Seok Lee*

Department of Chemistry, Sookmyung Women’s University, Seoul, 140-742, Korea

†These authors contributed equally to this work.

This Supprementary file includes:

Figures S1–S8

Calculation of the average elastic modulus of SiNWs

*Corresponding author

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Figure S1.Schematic diagram of the reaction used for the synthesis of vertically aligned SiNWs. C and D in the reaction diagram indicate the 10% H2 gas for carrier gas and dilution gas, respectively.

Figure S2.SEM images of AuNPs formed during the ramping process on a Si(111) substrate covered with a (a) 1-nm- or (b) 10-nm-thick Au film. Also shown are the diameter distributions of AuNPs formed on a Si(111) substrate covered with a (c) 1-nm- or (d) 10-nm-thick Au film. Mean diameters are (a, c) 13.18 nm ± 7.53 nm and (b, d) 243.14 ± 40.07 nm, respectively(N = 100 AuNPs).

Figure S3. The diameter distributions of SiNWs-01 and SiNWs-10 substrates (N = 100 SiNWs).

Figure S4. (a) Low-magnification TEM image of a SiNW-10. (b) High-resolution TEM image taken from the area designated in (a). The SiNW surface consists of a native oxide layer.

Figure S5. SEM images of HEK-293T cells cultured on (a) bare glass, (b) SiNWs-10 substrate, and (c) SiNWs-01 substrate after 48 h.

Figure S6. SEM images of HEK-293T cells cultured on (a) Au removed-SiNWs-10 substrate and (b) Au removed-SiNWs-01 substrate after 48 h (false-coloured red).

Figure S7. SEM images(20° tilt-view) of vertically aligned SiNWs after VLS growth on a Si(111) wafer covered with (a, b)10-nm- and (d, e) 1-nm-thick Au film at 860 °C. The average density of SiNWs-10 substrate is (a) 2.0 ± 0.3/μm2 and (b) 2.3 ± 0.4/μm2 (high density of SiNWs-10 substrate), whereas for SiNWs-01 substrate, these valuesare (d) 2.5 ± 0.3/μm2 and (e) 1.8 ± 0.2/μm2 (low density of SiNWs-01), respectively. SEM images of HEK-293T cells cultured on (c) high density of SiNWs-10 substrate and (f) low density of SiNWs-01 substrate after 48 h.

Figure S8. SEM images (20° tilt-view) of vertically aligned SiNWs after VLS growth on a Si(111) wafer covered with a 10-nm-thick Au film at 860°C for (a) 10 min, (b) 15 min, and (c) 30 min. The length of SiNWs is (a) 5.10 μm, (b) 9.50 μm, and (c) 12.79 μm, respectively.

Calculation of the average elastic modulus of SiNWs1

The elastic modulus (E) corresponding to the SiNWs is used as follows:

(1)

where K is the experimental parameter (K = f/x; where f is the maximum bending force, and x is the corresponding bending distance); L is the length of the SiNWs; and I is the momentum of inertia. If it is assumed that the SiNWs have a uniform circular cross-section along their length, I can be given as follows:

(2)

where d is the diameter of the SiNW.

Substituting equation (2) with I of equation (1), E can be determined as follows:

(3)

According to equation (3), the average elastic modulus is affected by the length and diameter of the SiNW. Because the lengths of two SiNWs used in our experiments (SiNWs-01 and SiNWs-10)are similar, it is their difference in diameter that significantly influences the average elastic modulus. The diameters of SiNWs-01 and SiNWs-10 are 72 nm and 218 nm, respectively, and this three-fold difference in diameter inducesan average elastic modulus of SiNWs-01 that is 81-times greater than that of SiNWs-10.

REFERENCES.

1 Li, Z.,Song, J.,Mantini, G.,Lu, M. –Y.,Fang, H.,Falconi, C.,Chen, L. –J.Wang, Z. L. Quantifying the traction force of a single eell by aligned silicon nanowire array. Nano Lett.9, 3575–3580 (2009).

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