Crystalline silicon anode

Figure 15.2 shows the typical cycling performance of a pure crystalline silicon anode [13]. This sample has a discharge capacity of 3,260 mAh/g, and a charge capacity of 1,170 mAh/g, which gives an irreversible loss of 64%. Such a large irreversible capacity loss in the first cycle is commonly observed for silicon-based anodes when discharged to near-zero potential. The coexistence of an amorphous... 

A spatial distribution of Pb centres (g = 2.0029, g — 2.0086) has been revealed in porous silicon formed by anodic etching of crystalline silicon in hydrofluoric acid.144 Oxygen ions were also implanted using accelerator at 2 MeV and compared with photoluminescence. 

The wafers containing the etched trenches are anodically bonded to Pyrex glass to form closed channels. The bond strength thus formed is strong enough to withstand pressures up to 250 bar. At that point a breakdown even takes place in the mono crystalline silicon and not at the bonded interface. Clearly, the indicated structures are useful for HPLC applications. 

Positronium formation was also found in porous Si obtained by anodization of crystalline silicon in HF acid solutions. Itoh, Murakmi and Kinoshita [11] found a long-lived (>10 ns) component in the positron lifetime spectrum measured by conventional PALS. The authors investigated Ps behavior in porous Si at various temperatures by means of PALS with a monoenergetic pulsed positron beam [12],[13]. 

The density of PS can be expressed as absolute density in units of grams per cubic centimeter or relative density (versus single-crystalline silicon) in units of percent. It can also be expressed as porosity which measures the amount of the open space with PS. Thus, the relative density plus porosity equals 1. In many studies the density of PS is determined by a simple gravimetric method of measuring the weight difference before and after anodization and the actual volume of ps 32,36,48,50 determined... 

The mechanism of electrochemical etching to produce porous silicon has been studied by a number of researchers [11-13]. Although it is certain that several different reactions are occurring simultaneously, anodic etching of crystalline silicon ultimately leads to oxidation and dissolution of the surface to silicon hexafluoride (Scheme 16.1). Under these conditions, Si-Si bonds are electrochemically activated and react with fluoride ions to form soluble, molecular perfluoro species solvation of these silicon fluorides by the etching medium yields a physically irregular, high area porous silicon matrix. Visual indicators for the anodization are the appearance... 

Except for one experimental artifact shown later in Figure 2.18, where two components present in the La characteristic spectrum of W (filament material contaminating Cu anode of a relatively old x-ray tube) are clearly recognizable in the diffraction pattern collected from the oriented single crystalline silicon wafer. 

OLEDs are normally fabricated on a transparent substrate and therefore on top of a transparent anode. However, several potential applications, such as micro-displays integrated on a crystalline silicon chip or a totally transparent OLED array for a heads-up display, require a transparent top electrode. There has been some work published describing the development of transparent cathodes. The most obvious approach is to use a very thin metal layer, such as Mg Ag, overcoated with a transparent conductor, such a.s ITO [94]. This is not so trivial as it appears, since the cathode metal must survive the reactive sputtering process employed to deposit the ITO. Another approach uses no metal but rather a CuPc layer between the electron-transporting Alqs and the ITO [95]. It is suggested dial the oxidative environment during ITO deposition results in heavy n-type doping near the CuPc interface. 

Porous silicon (PS) is one of the nanoscale modifications of silicon. There are various approaches to PS producing that are now in use. The technique most generally employed today is known as wet anodization of a crystalline silicon. With this technique, yield parameters of porous material (porosity, pore size and shape, interpore distance) may be readily varied by anodization regimes. However, it is well known the problem of the PS stability influencing the physical properties of the PS layers. P S instability is c onditioned b y very large specific surface area of the porous material. 

A simple nondestructive capacitance method is proposed (Adamyan et al, 2006) for the determination of basic PSi parameters such as layer thickness, porosity and dielectric permittivity. The method is based on two comparative measurements of the capacitance of the metal/PSi/single crystalline silicon/metal structure one measurement is taken when there are air-filled pores, while the other measurement involves pores filled by an organic compound with a high value of dielectric permittivity. Comparison of results obtained in Adamyan et al. (2006) by the ball lap and the gravimetric techniques before and after anodization, with the data of capacitance measurements carried out with the same samples prior to their destruction, shows sufficiently good agreement. 

Amorphous silicon demonstrates different features than those of crystalline silicon when subjected to lithiation at room temperature. 8tudies on an amorphous silicon thin-film anode prepared by magnetron sputtering and an amorphous silicon anode obtained through chemical delithiation of Lii2Si7 phase show two distinctive. 

Because of isotropic expansion of the particles/grains, amorphous thin-hlm silicon anodes typically perform better than crystalline thin hlms. Maranchi et al. [12, 72] demonstrated that 250-nm-thick amorphous silicon thin hlms deposited by radio-frequency magnetron sputtering on copper substrates achieved near theoretical capacity for a limited number of cycles. The authors stated that growth of... 

Other examples are enzymes immobilized on beads which are trapped in a microreactor by etched weirs [88], enzymes encapsulated in hydrogel patches or sol-gel silica [89] and enzymes attached on the surface of (porous) microstructures (for example, on porous silicon manufactured by anodization of single-crystalline silicon see Figure 1.10 [91]), of mesoporous silica or polymer monoliths or directly... 

Foil H, Hartz H, Ossei-Wusu E, Carstensen J, Riemenschneider O (2010) Si nanowire arrays as anodes in Li ion batteries. Phys Status Solidi RRL 4 4-6 Foil H, Grabmaier J, Lehmann V (1983) Process for producing crystalline silicon bodies having a structure which increases the surface area, and use of said bodies as substrates for solar cells and catalysts. German Patent DE 3324232... 

Porous silicon layers have also been made using electroless techniques. The technique is used with thin films of microcrystalline silicon produced by PECVD and leads to PL intensities (efficiency 1-10 %) comparable with that obtained from anodized crystalline silicon (Solomon et al. 2008). 

One alternative solution to obtain very thick porous silicon layers without any damaging stress of the wafer is to perform the electrical isolation with localized macroporous silicon. Unfortunately, the surface of such material is inappropriate for successive layer deposition processes. So, Li et al. (2007) propose a silicon anodization process of the sample backside and the realization of an RF device on the remaining crystalline silicon. This layer must be as thinner as possible, i.e., less than 10 pm, to be efficient. Capelle et al. proposed also a mesoporous/macroporous bilayer to achieve RF inductors on high thickness pSi (Capelle et al. 2011). 

In essence, a DSSC device is composed of a transparent photoactive anode and a photo-inert counter electrode (cathode) sandwiching an electrolyte-containing redox mediator (Figure 6.1(a)). Conceptually, the device is based on the superposition of active layers whose thicknesses are 10- to 20-fold less than that of crystalline silicon wafers. Moreover, the requested purity of materials is 10-100 times less than for a silicon device. 

The formation of etch pits and tunnels on n-Si during anodization in HF solutions was reported in the early 1970 s. It was found that the solid surface layer is the remaining substrate silicon left after anodic dissolution. The large current observed on n-Si at an anodic potential was postulated to be due to barrier breakdown.5,6 By early 80 s7"11 it was established that the brown films formed by anodization on silicon substrate of all types are a porous material with the same single crystalline structure as the substrate. 

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