Plasticity amorphous silicon

Amorphous silicon can replace the expensive and more-efficient rigid monocrystalline and polycrystalline silicon sheets used in most common solar panels. Less efficient than crystalline silicon, it can be applied to a flexible plastic foil by Plasma Enhanced... 

Amorphous Silicon An alloy of silica and hydrogen, with a disordered, noncrystalline internal atomic arrangement, that can be deposited in thin layers (a few micrometers in thickness) by a number of deposition methods to produce thin-film photovoltaic cells on glass, metal or plastic substrates. 

Shingles can be made from a thin film of amorphous silicon on plastic. They can generate solar electricity for private homes or commercial buildings. Flexible roofing laminates can be designed to be bonded on 0.4 m (16-inch) wide, flat Galvalume pans. A 2.75 m (9 ft) PV roof pan is rated to generate a maximum of 64 watts. 

El4.21 Glasses are amorphous silicon-oxygen compounds. Starting from sand (which is mostly pure SiOi) and other oxide additives, a wide variety of glasses with different properties can be obtained, used and seen every day. Activated carbon (used as adsorbent), carbon fibres (used as additives in plastic to increase the strength), and carbon black (used as pigment) are three examples of amorphous and partially crystalline carbon. 

We follow the discussion of metallic glass alloys with a brief parallel consideration of the behavior of amorphous silicon that is based primarily on computer simulations that have not only introduced the corresponding behavior of space-network glasses but also permitted a much deeper mechanistic understanding both of structural relaxations, and, more importantly, of the nature of plastic shear relaxations by ubiquitous shear transformations in glassy solids of all types, particularly in glassy polymers. These are developed in detail later in Chapters 7 and 8. 

Argon, A. S. and Demkowicz, M. J. (2008) What can plasticity of amorphous silicon tell us about plasticity of metallic glasses , MetalL Mater. Trans., 39A, 1762-1778. 

Demkowicz, M. J. and Argon, A. S. (2005b) Autocatalytic avalanches of unit inelastic shearing events are the mechanism of plastic deformation in amorphous silicon, Phys. Rev.,B, 72, 245206 (1-17). 

In the sections that follow, we consider the kinematics and kinetics of plastic flow by repeated nucleation of STs, primarily in metallic glasses and amorphous silicon as key examples. Similar corresponding applications to glassy polymers are covered in Chapter 8. 

Fig. 7.21 The approach of plastic behavior to a unique flow state with increasing plastic strain yP for amorphous silicon for three values of initial (p with 9)5 = 0.45, 7r = 0.10,...

While amorphous silicon TFT sulfers from low electronic performance, it is very flexible in application and manufacturing. One important advantage is that amorphous Si can be deposited at temperatures as low as 75°C. This makes it possible for the device to be made not only on glass, but also on plastics. In addition, amorphous silicon can be deposited over very large areas by plasma-enhanced chemical vapor deposition (PECVD) with standard industrial equipments. Both features make mass-scale production of amorphous silicon TFT-based devices relatively easy and economic. The main application for amorphous silicon TFT is on liquid crystal displa (LCDs), in which each pixel is individually driven by a TFT transistor. 

The fabrication of a polycrystalline silicon film can be achieved through various CVD methods or crystallization of amorphous silicon. But these processes require high temperatures of at least 300°C, making the deposition only possible on glass but not plastic. A relatively new technique called laser recrystallization has been devised to crystallize a precursor amorphous silicon film by localized heating without damaging the plastic substrate. A transfer process has also been developed to fabricate poly-Si TFT circuits on plastic substrates [14]. 

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