First, we had the stone age. Then came the bronze age, followed by the iron age. And now, we’re in the information age. Or rather, from the ‘chemistry’ perspective, we could well say, we’re now in the silicon age.
Silicon defines the lifestyles of modern times. Today, silicon chips, those tiny electronic brains, are all over the place. From gadgets like television sets and microwave ovens in our homes to laptops, smartphones, stereos, cars, traffic signals, and solar panels, none of the sophisticated devices we use today could have been made without one common element – silicon. Meaning, silicon not only forms the backbone of the electronics industry, helped us replace bulky main-frame computers with sleek laptops and tablets, made high-speed communications possible, it has transformed our very life today in astonishing ways. Silicon plays such a key role in our world today, it has a whole high-tech region named after it – Silicon Valley!
History of silicon
Appearing just below carbon and above germanium in the periodic table, silicon is among the more common of Earth’s elements, being the second most abundant element after oxygen. Silicon dioxide (SiO2) or silica, silicon’s most common compound that is the principal constituent of soft white sands on our beaches, makes up around 75% of the Earth’s crust. It is a major component of other silicates too like quartzite and granite and is also found in quartz, rock crystal, amethyst, agate, flint, jasper, and opal.
Though silica may be the most abundant compound in the Earth’s crust, elemental silicon is hardly ever found in nature and people were not aware of its existence until the nineteenth century. However, humans have been using silicon compounds for millennia. For example, ancient civilizations used flint, a form of quartz, for making tools for hunting and everyday use. And when they built their clay huts or erected sandstone temples, they made use of silicon compounds.
In 1789, French chemist Antoine Lavoisier was the first to propose that a new chemical element that was very abundant could be present in quartz. Also, many scientists made attempts to isolate silicon from various materials. English scientist Sir Humphry Davy, who had developed a technique for separating elements from their compounds by melting these and passing an electric current through them, succeeded in separating elemental sodium, potassium, calcium, and some other elements for the first time. But he couldn’t separate silicon.
In 1824, Swedish chemist Jöns Jacob Berzelius, who also discovered cerium, selenium, and thorium, heated potassium chips with potassium fluorosilicate, thoroughly washed away the residual by-products and succeeded in separating a brown powder – the amorphous allotrope of silicon. He named the new element silicium, deriving it from the Latin word for flint – silex. Today, elemental silicon is produced on a large scale by heating silica with carbon.
Silicon was given its present name by Scottish chemist Thomas Thomson in 1831. Retaining a part of Berzelius’s name, he changed the ending to ‘on’ since the new element was more similar to the nonmetals boron and carbon than to metals such as calcium and magnesium. And since then the name of the newly discovered element came to be accepted as silicon.
In 1854, French chemist Henri Deville became the first to isolate crystalline silicon. He electrolyzed an impure melt of sodium aluminium chloride to produce aluminium silicide and then washed away the aluminium with water to obtain silicon crystals.
A fascinating chemistry
At first, scientists debated whether silicon could be classified as a metal or nonmetal. The concept of semiconductors being unknown at that time, they were unaware that silicon was an excellent example of one. While Berzelius believed it was a metal, Sir Humphry Davy thought it was a nonmetal. The main reason for this difference of opinion was that the new element was a better conductor of electricity than nonmetals, but not such a good conductor as metals.
As it was later discovered, silicon is neither a metal nor a nonmetal. It is a metalloid, an element that looks metallic but conducts electricity only under certain conditions. It is a semiconductor, meaning its electrical conductivity lies somewhere between that of metals and insulators. In the case of silicon, like other semiconductors, its conductivity gets better when its temperature is increased, but this can be further enhanced by the addition of minute amounts of elements such as arsenic, phosphorus, boron, gallium or germanium through a process known as doping. In fact, it is this characteristic of silicon, combined with its abundant availability that has been exploited to make it the element that ultimately ushered in the Information Age.
The rich chemistry of silicon continues to fascinate researchers, and new discoveries about this easily available element continue to surface. Single crystals of crystalline silicon can be grown through what is known as the Czochralski process. When doped with suitable elements like those mentioned earlier these crystals are then used in the manufacture of electronic devices, like microchips, transistors, and solar cells.
When ancient Egyptians used sand bed filters for purifying water, they were actually using sand grains as nanoparticles that had nano-sized spaces between them; the finer the sand, the better was the level of filtration. The amazing fact is that although the surface area of 1 g of sand particles may be extremely small, the area of their internal surface area could exceed 1,000 sq. metres! When such particles with ordered nanopores are synthesized in the presence of surfactant templates, this creates countless opportunities for the development of nanomaterials. For example, nanoporous silica-based particles are now being used for catalysis, separations, environmental purification, drug delivery, and nanotechnology.
Today, silicon chips that form the core of modern electronic devices and computing, are acknowledged to be some of the most complex devices ever manufactured, requiring high-tech manufacturing technology. According to a poll carried out in 2004 by CNN.com in which over one lakh people participated, the silicon chip was voted as the most revolutionary invention of the last 50 years. The World Wide Web and the Personal Computer were ranked second and third respectively – for both of which, silicon is the element we have to thank.
Nowadays, optical glass produced from silicon is used for manufacturing both optical fibres and liquid crystal displays. Silicon is also a vital element for the photovoltaic industries. Solar panels made from silicon produce electricity for domestic and industrial use besides powering remote telecommunications, weather, and irrigation infrastructure.
Silicones, that is, silicon-based polymers, are proving to be a smart alternative to environmentally harmful hydrocarbon-based products. In addition, though it is widely known that such polymers are used for making breast implants, we also unknowingly and routinely use them in everyday items ranging from lubricants and fabric softeners to haircare products and antiperspirants.
In 2006, scientists succeeded in creating a computer chip that melded silicon components with brain cells, making it possible for electrical signals from the brain cells to be transmitted to the silicon components of the chip, and vice versa. Their objective is to eventually create electronic devices for treating neurological disorders.
Despite silicon’s most important application today being in the manufacture of electronic equipment, the total quantity of silicon used for manufacturing such devices is relatively small. The bulk of silicon produced is used for making metal alloys that have numerous applications including in the automobile, glass, and construction industries.
Another interesting discovery is the large-scale formation of silica structures with nanoscale precision by different types of marine organisms. Studies of this naturally occurring ‘biosilification’ process could be the basis for the development of environmentally benign processes for making innovative silicon-based materials, ultimately leading to advances in the field now known as ‘silicon biotechnology’.
In other words, since its discovery around two centuries ago, silicon still continues to amaze us.
What next?
We are told that silicon microprocessors are beginning to show some worrying signs and that for all its flexibility and other beneficial qualities, silicon itself could be a part of the problem. The latest silicon chips are producing more heat than silicon can dissipate fast enough. As a result, microprocessors are unable to run at their full potential speed without melting.
So, are we moving towards a new age? Which material will replace silicon and define this next age? We may not have the answers yet, but experts are of the view that novel energy-efficient materials are necessary for supporting the future growth of micro-electronics. But till then, whether combined with other elements in numerous compounds, in ultrapure elemental form for electronic devices, or in newer forms, silicon will continue to be a vital part of our lives.
References
1. Mietek Jaroniec: Silicon beyond the valley – Nature Chemistry, 1 May 2009
2. Jefferson Lab: The element silicon – https://education.jlab.org/itselemental/ele014.html
3. Stephanie Pappas: Facts about silicon – Live Science, 16 September 2014
4. Chemicool.com: Silicon – 9 October 2012, https://www.chemicool.com/elements/silicon.html
5. CNN.com: Silicon chip ‘most important invention’ – 31 December 2004, http://edition.cnn.com/2004/TECH/12/27/explorers.silicon/index.html
6. Tessel Renzenbrink: Beyond the Silicon Age – Elektor Magazine, 19 September 2017
7. Los Alamos National Laboratory: Periodic table of elements – Silicon – http://periodic.lanl.gov/14.shtml
