Porous silicon pore array

Porous silicon was discovered over 35 years ago by Uhlir.28 The porous material is created by electrochemical dissolution in HF-based electrolytes. Hydrofluoric acid, on its own, etches single-crystal Si extremely slowly, at a rate of only nanometers per hour. However, passing an electric current between the acid electrolyte and the Si sample speeds up the process considerably, leaving an array of deep narrow pores that generally run perpendicular to the Si surface. Pores measuring only nanometers across, but micrometers deep, have been achieved under specific etching conditions. 

Based on these characteristics, porous silicon may be described as a random array of channel-like pores or etch tunnels growing in <100) directions. For the case of n-type silicon these channels are isolated from each other and, for etching in the dark, the pore spacing is approximately equal to the depletion layer width at a planar surface [83-86]. For the case of p-type silicon the channels are interconnected. The... 

Nb thin films have been deposited on porous silicon (PS) substrates. The PS templates consists of a short-range order matrix of pores with mean diameter of 10 nm and mean interpore distance of 40 nm, which act as an array of artificial pinning centers. Commensurability effects between the Abrikosov vortex lattice and the artificial one were investigated by transport measurements. 

Granitzer P, Rumpf K, Polt P, Simic S, Krenn H (2008b) Three-dimensional quasi-regular arrays of Ni nanostructures grown within the pores of a porous silicon layer - magnetic characteristics. 

Fig. 4 Pore density versus silicon electrode doping density for porous silicon layers of different geometries. Notice that macropores are essentially obtained on low to moderately doped substrates. The dashed line shows the pore density of a triangular pore pattern with a pore pitch equal to two times the SCR width for a 3 V applied bias. Note that only macropores on n-type substrates may show a pore spacing significantly exceeding this limit. The regime of stable macropore array formation on n-Si is indicated by a dot pattern. Doping type and etching current density (in mA/cm ) are indicated in the legend (After Lehmann 1993)...

Lehmann V (1995) The physies of macroporous silicon formation. Thin Solid Films 255 1-4 Lehmann V (2002) Chapter 9, Macroporous silicon. In Electrochemistry of silieon. Wiley-VCH Lehmann V (2005) Eleetroehemieal pore array fabrieation on n-type silicon electrodes. In Wehrspohn RB (ed) Ordered porous nanostmctures and appheations. Chapter I. Springer, New... 

Methods for electrochemical, catalytic (metal assisted), and deep reactive ion etching (DRIE) of silicon have been developed, which enable fabrication of arrays of deep cylindrical or modulated pores, walls, tubes, combinations of these, and other forms with vertical walls (Wu et al. 2010). As a rule, the regular arrays produced by electrochemical etching are characterized by constant porosity and pore depths (up to 500 pm) and form a planar front propagating into the substrate. Various devices and functional elements for micromechanics, photonics, chemical power sources, microfluidics, photovoltaics, etc. (see Porous Silicon Application Survey chapter), are commonly fabricated on the basis of these arrays by post-anodization treatment intended to modify the structure and properties of macroporous silicon to raise or reduce its porosity, change the shape of pores, transform the pore array into a column array, change the properties of the inner surface of pores, coat it with the film of a metal or insulator, open up pores, fill pores with various fillers, dope the silicon walls, etc. Some procedures can be performed locally, which requires formation of a pattern and subsequent structuring. 

If the sputtered metallic species, on the other hand, exclusively interacts with one of the blocks of the copolymer, then it is also possible to use this method for producing arrays of nanorods. This was shown in the case of sputtering of titanium in the porous PS-Z -PVP(HABA) SMA templates in the presence of oxygen. The titanium dioxide so generated went exclusively to the cylindrical pores of the SMA templates. The thermal degradation of the polymer template then produced arrays of Ti02 nanorods on a silicon substrate. 

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