Silicon

Silicon,-(symbol: Si, group IV A, atomic number 14) derived from the Latin word silex (Flint) was isolated for the first time in 1823 by the Swedish chemist Jons Jakob Berzelius. It is a tetravalent element, (same as Carbon), with an electronic configuration [Ne]s²3p²
Even if Silicon is the main component of the earth's crust (~ 28%), it is not found as a native element, but it is always combined (mainly with oxygen) as oxides (SiO₂) or silicates.

The main crystalline form of Silicon is the cubic one (c-Si). However, its oxide form, SiO₂, can occur in a wide variety of polymorphs, among which a-quartz (space group P₃₂₂₁, Number 154) represents the most stable one. Main uses of oxides are as glasses, ceramics, and in the production of pottery and cements.

From SiO_2,Silicon is obtained via a chemical process (carboreduction) that takes place at T > 1925 K (Si melting T)

SiO₂ + 2C—› Si + 2CO

Silicon so obtained is not pure and HCl is added to“wash” it; then, introducing H₂, a catalytic deposition is performed passing through a trichlorosilane intermediate. The physical process of Silicon purification is called zone melting or zone refining; this process is based on the fact that impurities contained in Silicon have a melting point temperature that is lower than Si, and in this way, it is easy to remove them.
The main feature of Silicon is its semiconductor behavior, i.e. its resistivity is between that of metals and dielectrics. Differently from metals, Si (and similarly the other semiconductors) has an energy bandgap between the highest occupied electronic level (also VB, Valence Band) and the lowest unoccupied one (CB, Conduction Band). The reported experimental value is Eg ~ 1.1 eV at 298 K.
Adding small amounts of different atoms can improve the conductive properties of Silicon. Indeed the presence of trivalent (B, Al, Ga) or pentavalent (P, As) atoms (p and n doping, respectively), formally corresponds to have an extra positive charge or an extra negative charge. The increased number of carriers thus improves the conductivity of Silicon.

The relatively low cost and these unique properties make Silicon the main component of modern technological devices, such as transistors, and integrated circuits, in particular, CMOS

Even primarily employed in electronics, Silicon plays a fundamental role as constituent of other classes of compounds:

Silicone (polymerized siloxanes with the common formula [R2SiO]n; R = CH3, C2H5 or C6H5) and Polysilsesquioxanes are both hybrids of organic/inorganic materials that have wide applications. The organic group is bound to Si via a Si-C bond, and the size and the properties of this organic group highly influence the overall properties of these polymeric materials in terms of porosity, thermal stability and other properties.

Silicone	Polysilsesquioxanes

More information on Silicon and its properties is available at the following web sites:

History
http://periodic.lanl.gov/elements/14.html
http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e01400.html

Crystal Lattice–Structures:
http://cst-www.nrl.navy.mil/lattice/
http://database.iem.ac.ru/mincryst/

ICs & Transistors
http://nobelprize.org/educational_games/physics/integrated_circuit/history/index.html
http://www.sciencedaily.com/articles/i/integrated_circuit.htm
http://www.answers.com/topic/integrated-circuit?cat=technology
http://nobelprize.org/nobel_prizes/physics/laureates/2000/illpres/kilby.html
http://www.sciencedaily.com/releases/2006/03/060318144306.htm

CMOS
http://www.research.ibm.com/journal/rd/443/isaac.html
http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=0ST287482183658
http://www.ti.com/research/docs/index.shtml
http://www.fairchildsemi.com/an/AN/AN-77.pdf
http://www.csee.umbc.edu/~plusquel/vlsi/slides/chap3_2.html
http://www.fujitsu.com/downloads/EDG/binary/pdf/products/foundry/65nm-cmos-process.pdf
http://www.canon.com/technology/canon_tech/explanation/coms.html

Zeolites
http://education.yahoo.com/reference/dictionary/entry/zeolite
http://mineral.galleries.com/minerals/silicate/zeolites.htm
http://www.uvm.edu/~ssolberg/Startside.html
http://www.unr.edu/chemengr/che101/zeolites.htm
http://palimpsest.stanford.edu/byorg/abbey/an/an20/an20-7/an20-702.html
http://en.wikipedia.org/wiki/Zeolite
http://www.nasaexplores.com/show2_912a.php?id=03-059&gl=912

This web page is prepared by Dr. Giacomo Giorgi from the University of Perugia, Italy