Nanostructured silicon anodes

Teki R et al (2009) Nanostructured silicon anodes for lithium ion rechargeable batteries. 

Figure 2. Photovoltage transients for nanostructured silicon built-in the anodic alumina film (70 nm) at different temperatures. The shape of the laser pulse is presented for comparison.

Nanostructured silicon built-in an anodic alumina is evident to be a promising material for photovoltaic applications. In view of cheap materials and low cost equipment the investigated films could be used for solar cell fabrication on large area substrates. Thus the fabrication of new nanostructures based on silicon clusters built-in an anodic alumina opens new possibilities for nanotechnology in electronics and photonics. 

Another remarkable synthetic effort has been made by the preparation of colloidal Q-particles of the technically more relevant IV-IV materials (i.e., silicon and germanium) [20-25]. Silicon nanoparticles, especially, are currently drawing a lot of attention, since it was found by Canham [26] that nanostructured silicon formed under anodic etching of silicon wafers (called porous silicon ) exhibits bright red fluorescence. Due to the indirect nature of the band transition, bulk silicon shows, by contrast, almost no fluorescence and thus cannot be utilized for optoelectronic devices. 

Abel, P. R. Lin, Y.-M. CeUo, H. Heller, A. Mullins, C. B. Improving the stability of nanostructured silicon thin film lithium-ion battery anodes through their controlled oxidation, ACS Nano 2012, 6, 2506-2516. 

In addition to one-dimensional and two-dimensional silicon anodes, several forms of three-dimensional nanostructured silicon have been explored. For example, silicon nanotubes (Fig. 15.9) were investigated by Cho et al. [21] as an anode material for lithium-ion batteries. Both interior and exterior surfaces of the nanotubes are accessible to the electrolyte and lithium ions. Through carbon coating, a stable solid electrolyte interface (SEI) was generated on the inner and outer surfaces of the silicon nanotubes. These silicon/carbon assemblies showed a reversible capacity as high as 3,247 mAh/g (based on the weight of silicon) and good capacity retention. 

To further improve the mechanical and electrical stability of silicon-based anodes, a hierarchical bottom-up approach (Fig. 15.12) was successfully utilized to develop a three-dimensional nanostructured silicon/carbon porous composite [89]. The existence of pores in the composite granules provides sufficient space to accommodate silicon expansion during lithium insertion. CVD deposition of silicon clusters (Fig. 15.12b) avoids formation of SiO thus reducing the first cycle, irreversible capacity. A high specific capacity of 1,950 mAh/g (C/20 rate) based on the total weight of the silicon/carbon composite was reported. In addition, the composite anodes had negligible capacity fade after 100 cycles at 1C rate and excellent rate capability (870 mAh/g at 8C rate). 

Canham LT, Cullis AG, Pickering C, Dosser OD, Cox TI, Lyneh TP (1994) Lumineseent anodized silicon aerocrystal networks prepared by supercritical drying. Nature 368 133-135 Cao L, Price TP, Weiss M, Gao D (2008) Super water- and oil-repellent surfaces on intrinsically hydrophilic and oleophillic porous silicon films. Langmuir 24(5) 1640-1643 Chao Y (2011) Optical properties of nanostructured silicon. Compr NanoSci Technol 1 543-570 Chuang SF, Collins SD, Smith RL (1989) Porous silicon microstructure as studied by transmission electron microscopy. Appl Phys Lett 55 1540-1543 Costa J, Roura P, Morante JR, Bertran E (1998) Blackbody emission under laser excitation of silicon nanopowder produced by plasma-enhanced chemieal-vapour deposition. J Appl Phys 83(12) 7879-7885... 

Galiy PV, Lesiv TI, Monastyrskii LS, Nenchuk TM, Olenych IB (1998) Surface investigations of nanostructured porous silicon. Thin Solid Films 318 113-116 Gaponenko N (2001) Sol-gel derived Aims in meso-porous matrices porous silicon, anodic alumina and artificial opals. Synth Met 124 125-130... 

Szczech JR, Jin S (2011) Nanostructured silicon for high capacity lithium battery anodes. Energy Environ Sci 4 56-72. doi 10.1039/c0ee00281j... 

Usually the nanotube arrays have been made from a titanium thick film or foil, in which case the resulting nanotubes rest upon an underlying Ti substrate as separated by a barrier layer. The nanotube arrays have also been fabricated from a titanium thin film sputtered onto a variety of substrates, such as silicon and fluorine doped tin oxide (FTO) coated conductive glass. This extends the possibility for preparing technical catalysts by deposing a thin Ti layer over a substrate (a foam, for example) and then inducing the formation of the nanostructured titania film by anodic oxidation. ... 

Silicon oxide nanostruaures are prepared by local anodic oxidation on dodecyl-terminated silicon. Cationic dye molecules (Rhodamin 6G) bound electrostatically to the generated nanostructures are investigated by optical methods. Quenching of luminescence due to the interaction of the excited states with silicon can be found. The luminescence signal is attributed to monomeric Rh6G molecules with a slight blue shift of the emission due to the changed chemical environment... 

AC and DC responses are useful sources of information about Si-Me/Me"" nanostructured system during cathodic nucleation of metals on silicon and also their anodic oxidation. The impedance dependence on AC frequency is size-sensitive due to diffusion contribution to the interfacial impedance. This allows using potentiodynamic multi-frequency AC probing for fast qualitative characterization of the nanostructured interface at initial stages of metal deposition, when application of other techniques is hindered by nonstationar effects. 

Porous anodic alumina films were formed by a two-step anodic oxidation of aluminum foil (99.99% purity) (thickness 100 jum) or of thin aluminum film sputtered onto silicon substrate. First step was performed under lOmA/cm constant current density in 40 g/1 aqueous solution of (COOH)2 during 60 min. After first anodization the formed anodic oxide was removed in the aqueous solution of 0.35 M H3PO4 and 0.2 M CrOs at 90°C. The second anodization was performed in the same regimes as the first one. The formed oxide was removed from the specimen after the first anodization. Nanostructured aluminum samples were rinsed in deionized water and dried in an argon flow. 

Another interesting phenomenon is producing luminescence from electrochemical reactions. This can be achieved by doping crystalline metal oxides and related materials or anodic metal oxide layers (Meulenkamo et al., 1993) or depositing organic molecules onto nanostructured porous materials such silicon (Martin et al., 2006). 

Silicon nanostructures can be obtained in acidic fluoride-containing media or in alkaline solution at potentials negative from open circuit potential. The (photo) current-voltage characteristic of Si in fluoride-containing electrolytes reveals a series of phenomena which have attracted considerable attention in chemistry, physics, and solar energy conversion. Figure 2.39 provides an overview of these processes for both n- and p-type Si. The I-Vcurve is characterized by two maxima and periodic variations at higher applied anodic potential. These photocurrent... 

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