Porous silicon INDEX

Interferometry on porous silicon The average refractive index of the porous silicon layer is affected by analyte adsorption, resulting in a shift of the Fabry Perot fringes 6,18... 

The book starts with a brief introduction to nanomaterials followed by chapters dealing with the synthesis, structure and properties of various types of nanostructures. There are chapters devoted to oxomolybdates, porous silicon, polymers, electrochemistry, photochemistry, nanoporous solids and nanocatalysis. Nanomanipulation and lithography are covered in a separate chapter. In our attempt to make each contribution complete in itself, there is some unavoidable overlap amongst the chapters. Some chapters cover entire areas, while others expound on a single material or a technique. Our gratitude goes to S. Roy for his valuable support in preparing the index manuscript. 

Figure 2. Effective medium approximations relating porous silicon porosity to refractive index for a wavelength of 1.55 /am. The differences arise from different assumptions made about the porous silicon morphology.

Here we focus on the capabilities of a porous silicon waveguide biosensor for the detection of small molecules. The porous silicon waveguide, shown schematically in Figure 3a, consists of two porous silicon layers. Light is trapped in the top, high refractive index layer, based on total internal reflection at the interfaces with air and the bottom, low refractive index porous silicon... 

The very first studies of mesoporous silicon noted the different colors of anodized and so-called stain films (Uhlir 1956 Turner 1958 Archer 1960). Uhlir referred to his surfaces as having a matte black, brown or red deposif (Uhlir 1956). Turner commented that several orders of interference colors can be seen as the film thickens (Turner 1958). The first use of such colored silicon in the late 1950s was in p-n junction delineation (lies and Coppen 1958 Whoriskey 1958 Robbins 1962). Porous silicon, with its lower refractive index than solid silicon, induces optical interference effects as etched films on wafers. A colorimetric analysis for layer thicknesses below 500 nm, at quantified porosities, showed that interference color directly related to the optical thickness of anodized singlelayer structures (Lazarouk et al. 1997). Figure 1 shows examples for stain-etched p + wafers. The visual color of a given layer can be further changed by plasmonic effects of deposited metal nanoparticles (Lublow et al. 2012) or through controlled oxidation of the silicon skeleton. 

Properties of Porous Silicon, and Refractive Index of Porous Silicon ). Following the very first studies (Barla et al 1984 Drory et al. 1990), there have been continued but infrequent assessments (Da Fonesca et al 1995 Fang et al 2008 Rahmoun et al 2009 Aliev et al 2011 ). Nonetheless, there is a growing realization that robust porous silicon device and system performance will ultimately rely on achieving the appropriate mechanical properties, in conjunction with the novel functionality achieved through nanostructuring. 

Koyama H (2004) In-plane refractive-index anisotropy in porous silicon layers induced by polarized illumination during electrochemical etching. J Appl Phys 96(7) 3716-3720 Kiinzner N et al (2001) Giant birefringence in anisotropically nanostructured silicon. Opt Lett 26(16) 1265-1267... 

Muller F, Bimer A, Gosele U, Lehmann V, Ottow S, Foil H (2000) Structuring of macroporous silicon for applications as photonic crystals. J Porous Mater 7 201-204 Nassiopoulu AG, Kaltsas G (2000) Porous silicon as an effective material for thermal isolation on bulk crystalline silicon. Phys Stat Solidi (a) 182 307 Nava R, de la More MB, Taguena-Martinez J, del Rio JA (2009) Refractive index contrast in porous silicon multilayers. Phys Stat Solidi C6 1721-1724 Pettersson L, Hultman L, Arwin H (1998) Porosity depth profiling of thin porous silicon layers by variable angle spectroscopic ellipsometry a porosity graded layer model. Appl Optics 37(19) 4130 136... 

The first observation of visible photoluminescence in nanostructured porous silicon (PS) at room temperature opened the possibilities of a wide range photovoltaic and photonic applications due to tunable refractive index and band gap, large surface/volume ratio, simplicity of fabrication technology, etc. (Canham 1997). Today porous silicon has become a very interesting and versatile material... 

Porous silicon consists of silicon and air. The refl"aetive index of PS can be ehanged between refractive index of silicon (nsi = 3.84) and air (n = 1) depending on porosity. Reflectance of PS can be controlled by change of porosity during eleetroehemical fabrication by change of etching conditions (Perez 2007). For a dedicated review, see handbook chapter Refractive Index of Porous Silieon. It facilitates the application of PS layers on silicon as an ARC in solar cells. 

Three types of porous silicon layer as ARC are usually applied for silicon solar cell fabrication (1) single-layer PS of constant refractive index (of eonstant porosity), (2) single-layer PS of graded... 

Stress induced by high refractive index contrast has been reported to cause the rupturing of the structure (Pavesi and Turan 2010). The stresses are often capillary stresses caused by the evaporation of the electrolyte/rinsing solution. Hence, the quality of the multilayer can be improved by improving drying techniques (see handbook chapter Drying Techniques Applied to Porous Silicon ). 

Fig. 1 Schematics of porous silicon waveguides consisting of (a) one, (b) two, or (c) three porous silicon layers. Light is confined in a high refi active index (low porosity) porous silicon layer when surrounded by lower refi active index media, which can include a higher porosity porous silicon layer, air, or another low index solid, liquid, or gaseous substance...

High porosity porous silicon Low porosity porous silicon i Low refractive index polymer... 

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