Oxidized porous silicon

In this section the properties of chemically and thermally oxidized and nitridized PS will be discussed. Wet anodic oxidation of PS is commonly accompanied by luminescence and is therefore discussed in Section 7.4. 

Microporous and mesoporous silicon can be partly oxidized by chemical or electrochemical methods, while thermal oxidation is needed for a complete conversion of the porous layer to oxide. This complete conversion was the aim of the first studies in this field. 

The stress of oxidized PS layers is always compressive. For porous oxides, values below 108 N nT2 are reported [Ba5], which is nearly one order of magnitude smaller than values of intrinsic stress generated by low-temperature thermal oxidation of bulk silicon. The compressive stress in OPS has successfully been used to lift up released mesoporous films and thereby fabricate 3D microstructures [La9], 

Annealing of porous oxides at temperatures above 1000 °C leads to a densifica-tion. If the porosity of the initial PS was optimized to 56% the densification does not affect the layer thickness, while otherwise the layer thickness increases (for 

The doping dependence of the PS formation process and the possibility of transforming PS to oxide at relatively low temperatures has been used to form dielectrically isolated silicon islands, as shown in Fig. 10.23. 

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NHE OCP ONO OPS PCD PDS PL PLE PMMA PP PP PS PSG PSL PTFE PVC PVDF normal hydrogen electrode (= SHE) open circuit potential oxide-nitride-oxide dielectric oxidized porous silicon photoconductive decay photothermal displacement spectroscopy photoluminescence photoluminescence excitation spectroscopy polymethyl methacrylate passivation potential polypropylene porous silicon phosphosilicate glass porous silicon layer polytetrafluoroethylene polyvinyl chloride polyvinylidene fluoride... 

Starkov V.V., Micro-Fabrication using Oxidized Porous Silicon. Nano- and Microsystems Engineering. N°2, 2005, pp. 24-28. 

K. Barla, R. Herino, and G. Bomchil, Stress in oxidized porous silicon layers, J. Appl. Phys. 59,439, 1986. 

R. P. Holmstrom and J. Y. Chi, Complete dielectric isolation by highly selective and self-stopping formation of oxidized porous silicon, Appl. Phys. Lett. 42, 386, 1983. 

S. Zangooie, R. Bjorklund, and H. Arwin, Water interaction with thermal oxidation porous silicon layers, J. Electrochem. Soc. 144, 4027, 1997. 

PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY OF ERBIUM INCORPORATED WITH IRON IN OXIDIZED POROUS SILICON... 

Photoluminescence excitation (PLE) spectroscopy was carried out at 77K on oxidized porous silicon containing iron/erbium oxide clusters. The novel PLE spectrum of the 1535 nm Er PL band comprises a broad band extending from 350 to 570 nm and very week bands located at 640, 840, and 895 nm. The excitation at wavelengths of 400 - 560 nm was shown to be the most effective. No resonant PLE peaks related to the direct optical excitation of Er by absorption of pump photons were observed. The lack of the direct optical excitation indicates conclusively that Er is in the bound state and may be excited by the energy transfer within the clusters. 

Optical properties of dielectrics can be modified by incorporating nanosize clusters of foreign materials. Recently Si nanoclusters were shown to excite rare-earth element Er in the silica glass host [1,2]. The favorable effect of Si nanoclusters on the photoluminescence of Er in oxidized porous silicon (OPS) was also demonstrated [3], In silica hosts doped with Si nanoclusters it was shown that the excitation energy can be transferred from nanoclusters to Er ions located in a silicalike environment near the clusters. Nowadays, there is a principal interest to incorporate Er ions inside clusters due to influence on the excitation process. 

Recently, Wolkin et al. observed an upper limit of the PL emission energy of 2.1 eV in oxidized porous silicon even if the nanocrystal size became smaller than 2 nm. This behavior, which seems to contradict quantum confinement, was explained in terms of the formation of stabilized electronic states on Si=0 bonds at the surface. For nanocrystals with diameters smaller than 2.8 nm, the widening of the band gap due to quantum confinement makes them appear as inner band gap states. Including the results of Wolkin et al. in our model calculations, we obtained nice agreement with the experimental data. " ... 

Thin palladium membrane microreactors with oxidized porous silicon support and their application, J. Micromech. Microeng. 

Oton, C. J. Navarro-Urrios, D. Capuj, N. E. Ghulinyan, M. Pavesi, L. Gonzalez-Perez, S. Lahoz, F. Martin, I. R. Optical gain in dye-impregnated oxidized porous silicon waveguides. Appl. Phys. Lett. 2006, 89, 011107/1-011107/3. 

With the aim of developing a drug delivery vehicle, hydrosilylated and thermally oxidized porous silicon microparticles were injected into the vitreous of rabbit eyes (Cheng et al. 2008). It was noted that the particles settled into the inferior vitreous cavity over a few days. Degradation of the hydrosilylated particles took considerable time (>4 months) in comparison to untreated particles which degraded within a period of 3 weeks. No adverse effects were observed in ocular tissues including the retina and the lens. Furthermore, normal ocular pressure was maintained. 

Fig. 2 Difference in the morphology of cells cultured on various surface-modified porous silicon. Top panel PC12 cells cultured on (A) freshly etched porous silicon, (B) oxidized porous silicon, and (C) amino-silanized surface (Low et al. 2006). Bottom panel CHO cells cultured on (a) oxidized porous silicon, (b) fluoro-silanized surface, and (c) amino-silanized surface (Yang et al. 2010)...

Chinese hamster ovary cell fine (CHO) The study used plasma-oxidized porous silicon and porous silicon silanized to present amine or fluorine groups and plasma-oxidized porous silicon. CHO cells attached to the amine and oxidized smfaces but not the surface containing fluorine groups. Cells displayed rounded morphology on the oxidized and fluorinated surface, but spread and adhered well on the amine surface Yang etal. (2010)... 

Table 2 Absorption bands appearing in oxidized porous silicon (except SiHx relating vibrations) ...

Bondarenko V, Kazuchits N, Volchek S (2003) Fine structure of photoluminescence spectra Irom erbium incorporated with iron in oxidized porous silicon. Phys Status Sohdi (A) 197 441—445 Boukherroub R, Wayner DDM, Lockwood DJ, Canham LT (2001) Passivated luminescent porous silicon. J Electrochem Soc 148 H91-H97... 

Zangooie S, Bjorklund R, Arwin H (1998) Protein adsorption in thermally oxidized porous silicon layers. Thin Solid Films 313-314 825-830... 

Cullis AG, Canham LT, Williams GM, Smith PW, Dosser OD (1994) Correlation of the structural and optical properties of luminescent, highly oxidized porous silicon. J Appl Phys 75(1) 493... 

Table 4 EL charaeteristics of most devices based on partially oxidized porous silicon. D and L mean that anodization ...

Takeda E, Nakamura T, Fujii M, Miura S, Hayashi S (2006) Surface plasmon polariton mediated photoluminescence from excitons in silicon nanocrystals. Appl Phys Lett 89(10) 101907 Tsybeskov L, Duttagupta SP, Fauchet PM (1995) Photoluminescence and electroluminescence in partially oxidized porous silicon. Solid State Commun 95(7) 429-433 Tsybeskov L, Duttagupta SP, Hirschman KD, Fauchet PM (1996) Stable and efficient electroluminescence from a porous silicon-based bipolar device. Appl Phys Lett 68(15) 2058-2060 Valenta J, Lalic N, Linnros J (2004) Electroluminescence of single silicon nanocrystals. Appl Phys Lett 84(9) 1459-1461... 

Fang Z, Hu M, Zhang W, Zhang X, Yang H (2008) Thermal conductivity and nanoindentation hardness of as-prepared and oxidized porous silicon layers. J Mater Sci Mater Electron 19 1128-1134... 

Bsiesy A, Vial JC, Gaspard F et al (1991) Photoluminescence of high porosity and of electrochem-ically oxidized porous silicon layers. Surf Sci 254 195-200 Canham L (ed) (1997) Properties of porous silicon. INSPEC - The Institution of Electrical... 

Golovan LA et al (2006) Form birefringence of oxidized porous silicon. Appl Phys Lett 88(24) 241113-3... 

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