What is unit element, amorphous silicon and artificial corundum?

unit elements define the concept that zero and one or two numbers are abstracted into unit elements. Zero is the unit element of addition and one is the unit element of multiplication. For an arbitrary binary operation *, the unit element e must satisfy two conditions: a*e=a and e * a = a. It is a+=a and +a=a in addition, and a×1=a and 1×a=a in multiplication. However, if positive natural numbers are added, there is no unit element. Amorphous silicon (a-Si), also known as amorphous silicon, is an allotrope of silicon. Crystalline silicon is usually arranged in a regular tetrahedron, and each silicon atom is located at the vertex of the regular tetrahedron and closely combined with the other four silicon atoms by valence bonds. This kind of structure can be extended very large, thus forming a stable lattice structure. However, there is no such extended lattice structure in amorphous silicon, and the lattice network between atoms is disordered. In other words, not all atoms are arranged in strict accordance with regular tetrahedron with other atoms. Because of this instability, some atoms in amorphous silicon contain dangling bond. These dangling bonds have a great negative effect on the properties of silicon as a conductor. However, these dangling bonds can be filled with hydrogen, and after hydrogenation, the density of dangling bonds in amorphous silicon will be significantly reduced, which is enough to meet the standards of semiconductor materials. Unfortunately, under the irradiation of light, the conductivity of hydrogenated amorphous silicon will obviously decline, which is called the SWE effect. American scientist Stanford R. Ovshinsky has many patents on amorphous silicon, including semiconductors and solar cells. Their cost is much lower than that of the corresponding crystalline silicon products. In addition, amorphous silicon can be used as a microbolometer in a Thermal Camera. The naturally occurring α -alumina crystal is called corundum, which often shows different colors because of different impurities. Generally, corundum is bluish or yellowish gray with glass or diamond luster, with a density of 3.9-4.1g/cm3 and a hardness of 8.8, which is second only to diamond and silicon carbide, and can withstand high temperature. The corundum sand containing iron oxide is called emery, which is dark gray and dark black, and is often used as a grinding material for making various grinding papers and silicon carbide.