INDEX porous structure

Block ID, Chan LL, Cunningham BT (2006) Photonic crystal optical biosensor incorporating structured low-index porous dielectric. Sensors Actuators B Chem 120 187-193... 

The porous structure of the gels has been characterized by N2-adsorption, scanning electron microscopy (SEM), atomic force microscopy (AFM), and emanation thermal analysis (ETA) [16, 20]. The porosity of films was evaluated by refractive index measurements. 

Porous silicon materials are described as a mixture of air, silicon, and, in some cases, silicon dioxide. The optical properties of a porous silicon layer are determined by the thickness, porosity, refractive index, and the shape and size of pores and are obtained from both experimental- and model-based approaches. Porous silicon is a very attractive material for refractive index fabrication because of the ease in changing its refractive index. Many studies have been made on one- and two-dimensional refractive index lattice structures. The refractive index is a complex function of wavelength, i.e., n(X) = n(X) — ik(k), where k is the extinction coefficient and determines how light waves propagate inside a material (Jackson 1975). The square of the refractive index is the dielectric function e(co) = n(co), which contributes to Maxwell s equations. 

Porous silicon can be specified as an effective medium, whose optical properties depend on the relative volumes of silicon and pore-filling medium. Full theoretical solutions can be provided by different effective medium approximation methods such as Maxwell-Gamett s, Looyenga s, or Bruggeman s (Arrand 1997). Effective medium theory describes the effective refractive index, fieff, of porous silicon as a function of the complex refractive index of silicon, fisi, and that of the porefilling material, flair = 1, for air. The porosity P and the topology of the porous structure will also affect fleff (Theiss et al. 1995). 

The pore size is determined by the distribution of spheres of different racUi in the porous structure, where the pore radius is equal to the radius of the sphere that in its inside is formed by the empty phase (Schulz et al, 2007). To avoid that large spaces are fractioned into smaller spaces, the spheres radii begin to be modified from a maximum limit to unity. The characterized spaces are identified by the following index function ... 

A variation of the water adsorption isotherm method was then developed (Yeatman, 1994 Dawnay, 1995) called Molecular Probe Ellipsometry (MPE). In this technique, refractive index readings are made in dry nitrogen, and then in nitrogen saturated with an adsorbate solvent vapor. The porous structure is modelled as an effective medium according to the Lorentz-Lorenz relation, giving a relation between the measured film index f and the indices of the material in the pores and of the solid skeleton, p and s, respectively ... 

Ifit is assumed that porous structure is extended in whole film, the calculated apparent porosity would be about 37%. The silicafilm heated at 500°C shows a lower refractive index of 1.23. Figure 32-9 shows magnified SEM image of this film. The bar length indicates 200 nm. There can be seen a lot of pores in this film. The calculated apparent porosity of this film should be about 50%. The marked decrease of the refractive index with increasing pore size indicates that pores are formed also in the inside of the films. 

The porous structure, the void volume and the surface roughness of a film can all be effectively studied using ellipsometry, as the refractive index is a function of the material s density, composition, and morphology. For the structure of a... 

Grayish-white porous mass cubic crystalline structure refractive index... 

Connectivity may be defined as the maximal number of particles (branches, cell walls, and so on) that may be cut without separating the structure. For several porous foods, such as foamed chocolate bar, honeycomb chocolate bar, chocolate muffin, marshmallow, and strawberry mousse, air cell connectivity was defined as a measure of the relative convexity or concavity of the total slid surface (Lim and Barigou, 2004). Concavity indicates connectivity, whereas convexity indicates isolated disconnected structures. Through the image analysis, authors compare the solid area and perimeter before and after an image dilation operation and calculate the index of connectivity as the following ... 

This paper reports an investigation of the effects of porous solid structures on their electrical behaviour at different frequencies (from 100 Hz to 100 kHz). For that, we study different parameters such as formation resistivity factor, cementation factor, chargeability, resistivity index and saturation exponent. Different porous solid structures are quantified from the petrographic image analysis and Hg-injection technique. Then, by using different models we obtain the permeability prediction from the electrical behaviour and structure parameters. 

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. 

Structure and optical parameters of the porous oxide films are listed in Table 1 for different Ti content. The size of the porous oxide cells is seen to change considerably in comparison with pure alumina films. Dielectric constant and refractive index can be changed gradually with varying of the Ti content in the alloy films. 

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