Semana 5: “12 de diciembre hasta el 18 de diciembre de 2019”

Toward our future goal of demonstrating tunable metamaterials, we performed electro filling of holes etched using MacEtch with silver. In our first set of experiments, we used an array of circular disks of catalyst metal with a diameter of ~300 nm and pitch of ~5 µm, and etched the samples to achieve an etch depth of ~260 nm. These samples were subjected to electrodeposition of silver to fill the holes with the metal. The SEM images in Figure 7.3 show the metal overflowing from the holes after the electrodeposition process. We are currently working on repeating the electrofilled process in high aspect ratio structures as our end goal in this dissertation is to demonstrate metallic nanostructures with controlled chirality having a non-linear structure with very high aspect ratios.

Figure 7.3 (a-c) Top-view SEM images of MacEtched samples electrofilled with silver under different magnifications.

99 APPENDIX A

SUMMARY OF DOPING CONDITIONS USED FOR POST-DOPING OF SILICON NANOWIRE ARRAYS

Table A.1 Summary of doping conditions used for p-type and n-type silicon nanowire arrays with different sidewall roughness.

Type Sidewall roughness in nm (roughening process time shown inside parentheses) Drive-in

conditions Diameter (nm) Measured 2PP resistivity (milliOhm- cm) Calculated resistivity without contact contribution (milliOhm-cm) P+ 0 nm (smooth) 950 °C, 5 min 82-191 5-13 0.63-1.80 0 nm (smooth) 950 °C, 10 min 84-113 8-16 0.22-0.66 2 nm (14 sec) 950 °C, 10 min 86-107 43-55 1.37-1.57 2.25 nm (17 sec) 950 °C, 10 min 68-150 48-80 1.11-4.27 N+ 0 nm (smooth) 900 °C, 10 min 84-128 30-69 0.74-1.63 0 nm (smooth) 950 °C, 10 min 47-130 2-23 0.21-1.09

100 APPENDIX B

HALF-CELL REACTIONS RESPONSIBLE FOR MACETCH OF GALLIUM ARSENIDE

In MacEtch, the metal catalyst acts as the cathode and the semiconductor acts as the anode. Table B.1 lists relevant half reactions involving chemical species used for etching in this dissertation, as well as possible products and participating reactants in the overall reaction. Table B.1 Half-cell electrochemical potentials.

Cathode Reaction (metal) Eo_/V

MnO4- + 8H+ + 5e-  Mn2+ + 4H2O 1.507 MnO4- + 4H+ + 3e-  MnO2 + 2H2O 1.679 H2O2 + 2H+ + 2e-  2H2O 1.776 Anode Reaction Eo_/V Ga  Ga3+ + 3e- 0.549 2As + 3H2O  As2O3 + 6H+ + 6e- -0.234 As + 2H2O  HAsO2 + 3H+ + 3e- -0.248 HAsO2 + 2H2O  H3AsO4 + 2H+ + 2e- -0.560 Overall Reaction GaAs + MnO4- + H+  Ga3+ + As3+ + Mn2+ + H2O

Overall reaction with possible forms of the products (balanced) GaAs + 2KMnO4 + H2O+ 5HF  HAsO2 + GaF3•3H2O + 2MnO2 + 2KF

3GaAs + 8KMnO4 + 17HF + 5H2O 3H3AsO4 + 3(GaF3•3H2O) + 8MnO2 + 8KF

10GaAs + 12KMnO4 + 33H2SO4  10HAsO2 + 12MnSO4 + 6K2SO4 + 5Ga2(SO4)3 + 28H2O

101 APPENDIX C

THEORETICAL CALCULATION OF SIZE OF HYDROGEN GAS BUBBLES RELEASED DURING MACETCH

We have performed a theoretical calculation of the size of the Hydrogen gas bubbles that are released during the etch process and compared the number to the diameter of the gold catalyst. From the MacEtch mechanism discussed in Section 2.2, let us consider the chemical reactions involved in the process once again.

At Cathode: H2O2 + 2H+  2H2O + 2h+ (Local reduction)

2H+ _{ H}

2 + 2h+ (Hydrogen gas formation)

At Anode: Si + 6HF + 4h+  H2SiF6 + 4H+ (Dissolution of silicon)

Net reaction: Si + 6HF + H2O2  H2SiF6 + 2H2O + H2

As we can see from the chemical equations above, for every one mole of Si atoms reacting with one mole of Hydrogen peroxide, one mole of Hydrogen gas gets liberated. In the case under study, we used an array of dot patterns with a diameter of 125 nm and pitch of 200 nm. Also, there were 1800 rows and 250 columns of dots in our layout for e-beam writing. Since the surface areal density of Si atoms for a (100) Si wafer is 6.78*1014 _cm-2_{, the number of Si atoms that are under}

the Au catalyst disk, denoted by A, is given by,

A = 6.78*1014*1800*250*3.14*(125*10-7)2/4 A = 3.74*109 Si atoms

Therefore, the number of moles of Si undergoing oxidation, denoted as N, is given by, N = 3.74*109_{/ (6.023*10}23_{) = 6.21*10}-14

By looking at the net reaction of MacEtch process, we can state that for every N moles of Si atoms, we must liberate N moles of Hydrogen gas bubbles. But this is only possible when we have at least N moles of Hydrogen peroxide reducing into water at the cathode. In our case, we are

102

limiting the number of Si atoms undergoing oxidation to a small percentage, denoted as Y, and is given by,

Y = (9.79*10-6*x*N)

where x is the volume in microliters of 30% Hydrogen peroxide used for the trial. Knowing the number of Si atoms that can be oxidized during MacEtch, we can estimate the volume of Hydrogen gas bubbles that can be generated during the etch process from the available amount of Si atoms using the ideal gas equation (PV = nRT) where the pressure (P) is 1 atm and temperature (T) is 300 K.

Table C.1 Summary of dimension of gas bubbles liberated under different etch conditions. Volume of H2O2 (x in µL) Number of moles of Si atoms oxidized (Y) Total volume of Hydrogen gas generated (in µL) Radius of gas bubble (nm) 1 6.08*10-19 1.5*10-11 153 5 3.04*10-18 7.5*10-11 262 20 1.21*10-17 3*10-10 415

In Table C.1, we have listed the values of the volume of Hydrogen gas bubble that could be generated, and the corresponding radius of the bubble for the three different cases studied in our experiments. It should be noted that, for the case with 1 µL of H2O2, the radius of the gas

bubble is smaller than the pitch (200 nm) used in our study. This is the only case where we see a stable sinking of the catalyst disk during the MacEtch process. As a future work, it would be worth exploring MacEtch at higher pressures to verify our hypothesis on the lack of catalyst stability during MacEtch using the volume of gas bubbles liberated.

103 APPENDIX D

CALCULATION OF MAGNETIC PRESSURE APPLIED ON IRON FILM

For all the mesh patterns considered in our experiments, we use a length and width of 2 mm each. Knowing the width and pitch of the square-shaped openings in the mesh pattern, we can calculate the total surface area of the iron film used in our study. Table D.1 summarizes the magnetic pressure (in lbs/mm2) applied on the iron film at different values of magnetic pull forces. Table D.1 Summary of magnetic pressure applied on iron film.

Design D (µm) P (µm) Area of Fe (mm2) P_m (F_z=494 lbs) P_m (F_z=1555 lbs) P_m (F_z=2333 lbs) D1 10 30 3.742 132.015 415.553 623.463 D2 20 60 3.735 132.2624 416.332 624.632 D3 30 90 3.727 132.5463 417.226 625.973 D4 50 150 3.711 133.1178 419.024 628.671

104 APPENDIX E

RECIPE FOR DRYING OF HIGH ASPECT RATIO SILICON NANOPILLARS

In order to dry the samples with high aspect ratio silicon nanopillars made using MacEtch, we recommend not to rinse the samples in deionized water due to its relatively high surface tension causing cluttering of pillars. Instead, we recommend the following sequence of rinsing steps: (1)15-20 seconds in methanol, (2)15-20 seconds in IPA, and (3) drying the sample on a hot plate kept at above 100 °C. In addition, the use of a Nitrogen gun for blow drying should also be avoided to minimize the cluttering of pillars during our processing.

105 REFERENCES

[1] Z. Huang, N. Geyer, P. Werner, J. de Boor, and U. Gösele, “Metal-assisted chemical etching of silicon: A review,” Adv. Mater., vol. 23, pp. 285–308, Sep. 2011.

[2] X. Li and P. W. Bohn, “Metal-assisted chemical etching in HF/H2O2 produces porous

silicon,” Appl. Phys. Lett., vol. 77, no. 16, pp. 2572–2574, 2000.

[3] C. Chartier, S. Bastide, and C. Lévy-Clément, “Metal-assisted chemical etching of silicon in HF–H2O2,” Electrochim. Acta, vol. 53, no. 17, pp. 5509–5516, Jul. 2008.

[4] X. Li, “Metal-assisted chemical etching for high aspect ratio nanostructures: A review of characteristics and applications in photovoltaics,” Curr. Opin. Solid State Mater. Sci., vol. 16, pp. 1045–1047, Dec. 2012.

[5] O. J. Hildreth, W. Lin, and C. P. Wong, “Effect of catalyst shape and etchant composition on etching direction in metal-assisted chemical etching of silicon to fabricate 3D

nanostructures,” ACS Nano, vol. 3, no. 12, pp. 4033–42, Dec. 2009.

[6] P. Lianto, S. Yu, J. Wu, C. V. Thompson, and W. K. Choi, “Vertical etching with isolated catalysts in metal-assisted chemical etching of silicon,” Nanoscale, no. 4, pp. 7532–7539, 2012.

[7] J. C. Shin, D. Chanda, W. Chern, K. J. Yu, and J. A. Rogers, “Experimental study of design parameters in silicon micropillar array solar cells produced by soft lithography and metal-assisted chemical etching,” IEEE J. Photovoltaics, 2012.

[8] K. Balasundaram, J. S. Sadhu, J. C. Shin, B. Azeredo, D. Chanda, M. Malik, K. Hsu, J. A. Rogers, P. Ferreira, S. Sinha, and X. Li, “Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires,” Nanotechnology, vol. 23, no. 30, p. 305304, Aug. 2012.

[9] H. Hu, P. K. Mohseni, L. Pan, X. Li, S. Somnath, J. R. Felts, M. A. Shannon, and W. P. King, “Fabrication of arbitrarily shaped silicon and silicon oxide nanostructures using tip- based nanofabrication,” J. Vac. Sci. Technol. B Microelectron. Nanom. Struct., vol. 31, no. 6, p. 06FJ01, 2013.

[10] B. Mikhael, B. Elise, M. Xavier, S. Sebastian, M. Johann, and P. Laetitia, “New silicon architectures by gold-assisted chemical etching,” ACS Appl. Mater. Interfaces, vol. 3, no. 10, pp. 3866–73, Oct. 2011.

[11] K. Peng, Y. Yan, S. Gao, and J. Zhu, “Dendrite-assisted growth of silicon nanowires in electroless metal deposition,” Adv. Funct. Mater., vol. 13, no. 2, pp. 127–132, Feb. 2003.

106

[12] Z. Huang, T. Shimizu, S. Senz, Z. Zhang, X. Zhang, W. Lee, N. Geyer, and U. Go, “Ordered arrays of vertically aligned [ 110 ] silicon nanowires by suppressing the crystallographically preferred <100> etching directions,” Nano Lett., vol. 9, no. 7, pp. 2519–2525, 2009.

[13] Z. Huang, X. Zhang, M. Reiche, L. Liu, W. Lee, T. Shimizu, S. Senz, and U. Gösele, “Extended arrays of vertically aligned sub-10 nm diameter [100] Si nanowires by metal- assisted chemical etching,” Nano Lett., vol. 8, no. 9, pp. 3046–51, Sep. 2008.

[14] X. Wang, K. L. Pey, W. K. Choi, C. K. F. Ho, E. Fitzgerald, and D. Antoniadis, “Arrayed Si∕SiGe nanowire and heterostructure formations via Au-assisted wet chemical etching method,” Electrochem. Solid-State Lett., vol. 12, no. 5, p. K37, 2009.

[15] H.-J. Choi, S. Baek, H. S. Jang, S. B. Kim, B.-Y. Oh, and J. H. Kim, “Optimization of metal-assisted chemical etching process in fabrication of p-type silicon wire arrays,” Curr. Appl. Phys., vol. 11, no. 1, pp. S25–S29, Jan. 2011.

[16] J. A. Rogers and R. G. Nuzzo, “Recent progress in soft lithography,” Methods, no. 1 Feb., pp. 50–56, 2005.

[17] Z. P. Huang, N. Geyer, L. F. Liu, M. Y. Li, and P. Zhong, “Metal-assisted electrochemical etching of silicon,” Nanotechnology, vol. 21, no. 46, p. 465301, Nov. 2010.

[18] Y. Cheng, Z. Gang, L. Dae-Young, L. Hua-Min, L. Young-Dae, Y. W. Jong, P. Young- Jun, and K. Jong-Min, “Self-assembled wire arrays and ITO contacts for silicon nanowire solar cell applications,” Chinese Phys. Lett., vol. 28, no. 3, p. 035202, Mar. 2011.

[19] S. Cruz, A. Hönig-d’Orville, and J. Müller, “Fabrication and optimization of porous silicon substrates for diffusion membrane applications,” J. Electrochem. Soc., vol. 152, no. 6, p. C418, 2005.

[20] P. K. Mohseni, S. Hyun Kim, X. Zhao, K. Balasundaram, J. Dong Kim, L. Pan, J. A. Rogers, J. J. Coleman, and X. Li, “GaAs pillar array-based light emitting diodes fabricated by metal-assisted chemical etching,” J. Appl. Phys., vol. 114, no. 6, p. 064909, Aug. 2013. [21] W. Chern, K. J. Yu, D. Chanda, J. C. Shin, J. A. Rogers, and X. Li, “Ordered silicon

nanowire array based solar cells produced by metal-assisted chemical etching,” in 23rd Annual Meeting of the IEEE Photonics Society, 2010, pp. 718–719.

[22] S. H. Kim, P. K. Mohseni, Y. Song, T. Ishihara, and X. Li, “Inverse metal-assisted chemical etching produces smooth high aspect ratio InP nanostructures,” Nano Lett., vol. 15, no. 1, pp. 641–648, 2015.

[23] A. Sidorenko, T. Krupenkin, A. Taylor, P. Fratzl, and J. Aizenberg, “Reversible switching of hydrogel-actuated nanostructures into complex micropatterns,” Science, vol. 315, no. 5811, pp. 487–90, Jan. 2007.

107

[24] B. Zhang, H. Wang, L. Lu, K. Ai, G. Zhang, and X. Cheng, “Large-area silver-coated silicon nanowire arrays for molecular sensing using surface-enhanced Raman

spectroscopy,” Adv. Funct. Mater., vol. 18, no. 16, pp. 2348–2355, Aug. 2008. [25] Y. Tanaka, K. Sato, T. Shimizu, M. Yamato, T. Okano, I. Manabe, R. Nagai, and T.

Kitamori, “Demonstration of a bio-microactuator powered by vascular smooth muscle cells coupled to polymer micropillars,” Lab Chip, vol. 8, no. 1, pp. 58–61, Jan. 2008. [26] C. R. Field, H. J. In, N. J. Begue, and P. E. Pehrsson, “Vapor detection performance of

vertically aligned, ordered arrays of silicon nanowires with a porous electrode,” Anal. Chem., vol. 83, no. 12, pp. 4724–8, Jun. 2011.

[27] H. J. In, C. R. Field, and P. E. Pehrsson, “Periodically porous top electrodes on vertical nanowire arrays for highly sensitive gas detection,” Nanotechnology, vol. 22, no. 35, p. 355501, Sep. 2011.

[28] B. S. Kim, S. Shin, S. J. Shin, K. M. Kim, and H. H. Cho, “Micro-nano hybrid structures with manipulated wettability using a two-step silicon etching on a large area,” Nanoscale Res. Lett., vol. 6, no. 1, p. 333, Jan. 2011.

[29] H. Han, J. Kim, H. S. Shin, J. Y. Song, and W. Lee, “Air-bridged ohmic contact on vertically aligned Si nanowire arrays: Application to molecule sensors,” Adv. Mater., pp. 2284–2288, Apr. 2012.

[30] S. Wu, T. Zhang, R. Zheng, and G. Cheng, “Photoelectrochemical responses of silicon nanowire arrays for light detection,” Chem. Phys. Lett., vol. 538, pp. 102–107, Jun. 2012. [31] B.-R. Huang, Y.-K. Yang, T.-C. Lin, and W.-L. Yang, “A simple and low-cost technique for silicon nanowire arrays based solar cells,” Sol. Energy Mater. Sol. Cells, vol. 98, no. 2012, pp. 357–362, 2012.

[32] X. Li, “Metal-assisted chemical etching for high aspect ratio nanostructures: A review of characteristics and applications in photovoltaics,” Curr. Opin. Solid State Mater. Sci., vol. 16, no. 2, pp. 71–81, Apr. 2012.

[33] S. W. Chang, J. Oh, S. T. Boles, and C. V. Thompson, “Fabrication of silicon nanopillar- based nanocapacitor arrays,” Appl. Phys. Lett., vol. 96, no. 15, pp. 15–18, 2010.

[34] A. I. Hochbaum, R. Chen, R. D. Delgado, W. Liang, E. C. Garnett, M. Najarian, A. Majumdar, and P. Yang, “Enhanced thermoelectric performance of rough silicon nanowires,” Nature, vol. 451, no. 7175, pp. 163–7, Jan. 2008.

[35] K. Balasundaram, J. S. Sadhu, J. C. Shin, B. Azeredo, D. Chanda, M. Malik, K. Hsu, J. A. Rogers, P. Ferreira, S. Sinha, and X. Li, “Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowire,” Nanotechnology, vol. 23, no. 30, p. 305304, Aug. 2012.

108

[36] C. Chiappini, X. Liu, J. R. Fakhoury, and M. Ferrari, “Biodegradable porous silicon barcode nanowires with defined geometry,” Adv. Funct. Mater., vol. 20, no. 14, pp. 2231– 2239, Jul. 2010.

[37] H. Chen, H. Wang, X.-H. Zhang, C.-S. Lee, and S.-T. Lee, “Wafer-scale synthesis of single-crystal zigzag silicon nanowire arrays with controlled turning angles,” Nano Lett., vol. 10, no. 3, pp. 864–8, Mar. 2010.

[38] J. Kim, Y. H. Kim, S.-H. Choi, and W. Lee, “Curved silicon nanowires with ribbon-like cross sections by metal-assisted chemical etching,” ACS Nano, vol. 5, no. 6, pp. 5242–8, Jun. 2011.

[39] M. Zaremba-Tymieniecki and Z. A. K. Durrani, “Schottky-barrier lowering in silicon nanowire field-effect transistors prepared by metal-assisted chemical etching,” Appl. Phys. Lett., vol. 98, no. 10, p. 102113, 2011.

[40] B. Zhu, L. J. Li, Q. Q. Sun, H. L. Lu, S. J. Ding, and W. Zhang, “Formation of cylindrical nanoholes in heavily doped p-type Si(100) substrate via Pt nanoparticles-assisted chemical etching,” Adv. Mater. Res., vol. 535–537, pp. 362–367, Jun. 2012.

[41] K. Tsujino and M. Matsumura, “Helical nanoholes bored in silicon by wet chemical etching using platinum nanoparticles as catalyst,” Electrochem. Solid-State Lett., vol. 8, no. 12, p. C193, 2005.

[42] X.-M. Zhang and N. Fukata, “Fabrication of holey silicon structures with inner radial p–n junction for solar cells,” Solid State Commun., vol. 156, pp. 76–79, Nov. 2013.

[43] Y. Oh, C. Choi, D. Hong, S. D. Kong, and S. Jin, “Magnetically guided nano-micro shaping and slicing of silicon,” Nano Lett., vol. 12, pp. 2045–50, Mar. 2012.

[44] H. Yang, D. Zhao, S. Chuwongin, J. Seo, W. Yang, Y. Shuai, J. Berggren, M. Hammar, Z. Ma, and W. Zhou, “Transfer-printed stacked nanomembrane lasers on silicon,” Nat. Photonics, vol. 6, pp. 615–620, Sep. 2012.

[45] Y. Shuai, D. Zhao, G. Medhi, R. Peale, Z. Ma, W. Buchwald, R. Soref, and W. Zhou, “Fano-resonance photonic crystal membrane reflectors at mid- and far-Infrared,” IEEE Photonics J., vol. 5, no. 1, pp. 4700206–4700206, Feb. 2013.

[46] C. M. Soukoulis and M. Wegener, “Optical metamaterials-more bulky and less lossy,” Science, vol. 330, pp. 1633–1634, 2010.

[47] P. K. Mohseni, S. Hyun Kim, X. Zhao, K. Balasundaram, J. Dong Kim, L. Pan, J. A. Rogers, J. J. Coleman, and X. Li, “GaAs pillar array-based light emitting diodes fabricated by metal-assisted chemical etching,” J. Appl. Phys., vol. 114, no. 6, p. 064909, 2013.

109

[48] C. Q. Lai, H. Cheng, W. K. Choi, and C. V. Thompson, “Mechanics of catalyst motion during metal-assisted chemical etching of silicon,” J. Phys. Chem. C, vol. 117, pp. 20802– 20809, Sep. 2013.

[49] M. A. Meitl, Z.-T. Zhu, V. Kumar, K. J. Lee, X. Feng, Y. Y. Huang, I. Adesida, R. G. Nuzzo, and J. A. Rogers, “Transfer printing by kinetic control of adhesion to an elastomeric stamp,” Nat. Mater., vol. 5, no. 1, pp. 33–38, Dec. 2005.

[50] H. Yang, D. Zhao, J. Seo, S. Chuwongin, S. Kim, J. A. Rogers, Z. Ma, W. Zhou, and S. Member, “Broadband membrane reflectors on glass,” IEEE Photonics Technol. Lett., vol. 24, no. 6, pp. 476–478, 2012.

[51] O. J. Hildreth, C. Honrao, V. Sundaram, and C. P. Wong, “Combining electroless filling with metal-assisted chemical etching to fabricate 3D metallic structures with nanoscale resolutions,” ECS Solid State Lett., vol. 2, no. 5, pp. 39-41, Feb. 2013.

[52] http://www.magnet4less.com/product_info.php?products_id=347. [53] http://www.magnet4less.com/product_info.php?products_id=1105. [54] https://www.kjmagnetics.com/proddetail.asp?prod=BY0Y0X0-N52. [55] https://www.kjmagnetics.com.