Preparation of Freestanding Porous Silicon Photonic Crystals
Nowadays, the photonic crystals are of great interest and are widely used in photonics, biosensing, optoelectronics and other fields of research. The one-dimensional photonic crystals manufactured on the basis of porous silicon were proved to be the most suitable for applications due to their high sorption ability, large surface area, easiness of fabrication, and possibility to precisely control porosity and refractive index during electrochemical etching. However, the sensitivity of various kinds of gas and biological sensors as well as the performance of solar cells and other devices on the basis of porous silicon structures may be significantly increased by detaching the structures from the substrate. Here, we have developed and investigated the fabrication procedure of freestanding one-dimensional photonic crystals on the basis of porous silicon with the use of electropolishing method followed stabilization of freestanding porous silicon photonic structures through their oxidation. We have demonstrated that the developed and applied lift-off procedure does not violate the morphology and the photonic properties of the samples.
Keywords: Porous silicon, photonic crystals, microcavity, thin films, freestanding photonic crystals.
 G. E. Kotkovskiy, Y. A. Kuzishchin, I. L. Martynov, A. A. Chistyakov, and I. Nabiev, “The photophysics of porous silicon: technological and biomedical implications,” Phys. Chem. Chem. Phys., vol. 14, pp. 13890–13902, 2012.
 G. Gaur, D. Koktysh, and S. M. Weiss, “Integrating Colloidal Quantum Dots with Porous Silicon for High Sensitivity Biosensing,” MRS Proc., vol. 1301, no. 9, pp. 241– 246, Jan. 2011.
 V. S. Lin, “A Porous Silicon-Based Optical Interferometric Biosensor,” Science (80-.)., vol. 278, no. 5339, pp. 840–843, Oct. 1997.
 M. B. de la Mora, M. Ocampo, R. Doti, J. E. Lugo, and J. Faubert, “Porous Silicon Biosensors,” in State of the Art in Biosensors - General Aspects, InTech, 2013, pp. 141–161.
 U. Resch-Genger, M. Grabolle, S. Cavaliere-Jaricot, R. Nitschke, and T. Nann, “Quantum dots versus organic dyes as fluorescent labels,” Nat. Methods, vol. 5, no. 9, pp. 763–775, Sep. 2008.
 I. Levitsky, “Porous Silicon Structures as Optical Gas Sensors,” Sensors, vol. 15, no. 8, pp. 19968–19991, Aug. 2015.
 C. S. Solanki, R. R. Bilyalov, J. Poortmans, G. Beaucarne, K. Van Nieuwenhuysen, J. Nijs, and R. Mertens, “Characterization of free-standing thin crystalline films on porous silicon for solar cells,” Thin Solid Films, vol. 451–452, pp. 649–654, Mar. 2004.
 S. Setzu, P. Ferrand, and R. Romestain, “Optical properties of multilayered porous silicon,” Mater. Sci. Eng. B, vol. 69–70, pp. 34–42, Jan. 2000.
 V. Kochergin and H. Foell, “Commercial applications of porous Si: optical filters and components,” Phys. status solidi, vol. 4, no. 6, pp. 1933–1940, May 2007.
 E. V Osipov, I. L. Martynov, D. S. Dovzhenko, P. S. Ananev, G. E. Kotkovskii, and A. A. Chistyakov, “Silicon Photonic Structures with Embedded Polymers for Novel Sensing Methods,” Opt. Spectrosc., vol. 122, no. 1, pp. 74–78, 2017.
 D. S. Dovzhenko, I. L. Martynov, P. S. Samokhvalov, I. S. Eremin, G. E. Kotkovskii, I. P. Sipailo, and A. A. Chistyakov, “Photoluminescence of CdSe/ZnS quantum dots in a porous silicon microcavity,” in Proceedings of SPIE - The International Society for Optical Engineering, 2014, vol. 9126, no. April, p. 91263O.
 R. L. Smith and S. D. Collins, “Porous silicon formation mechanisms,” J. Appl. Phys., vol. 71, no. 8, pp. R1–R22, Apr. 1992.
 Y. H. Xie, M. S. Hybertsen, and William L. Wilson, “Absorption and luminescence studies of free-standing porous silicon films,” Phys. Rev. B, vol. 49, no. 8, pp. 5386– 5397, 1994.
 J. von Behren, L. Tsybeskov, and P. M. Fauchet, “Preparation and characterization of ultrathin porous silicon films,” Appl. Phys. Lett., vol. 66, no. 13, pp. 1662–1664, Mar. 1995.
 M. J. Sailor, “Freestanding Porous Silicon Films and Particles,” in Porous Silicon in Practice, Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2012, pp. 119– 131.