Nanotechnology with gold 

Gold is the material of choice in many electronic applications, especially in telecommunications, information technology and other high performance and safety critical applications. Twenty first century belongs to electronics and gold is used in the manufacture of approximately 50 million computers each year, as well as millions of televisions, DVDs, VCRs, video cameras, mobile phones and home appliances like washing machines, dishwashers and even the humble pocket calculator. The most significant uses of gold in electronics include:

* Gold based finishes on contacts and connectors

* Gold bonding wires in semiconductor devices

* Thick and thin film gold paste applications

* Sputtered gold metallization

* Gold based solder alloys

* Solder able gold based coatings for printed circuit boards

Even with the miniaturization of electronic equipment, the overall gold use has not been reduced due to the growing scale of the modern electronics industry as gold plated contacts and connectors are an essential part of modern electronics. The more sophisticated the equipment and the greater the degree of reliability required, the more gold plating is used in connectors. Gold-plated contacts are used in everything from washing to computers to telecommunications. The ordinary touch-tone telephone contains thirty-three gold contact points. Gold-plated connectors are an integral part of plugs and sockets for cable terminations, integrated circuit sockets, computer back plates and printed circuit boards. Gold's other main electronic use is in fine wire or strip to bond or connect parts of semi-conductors such as transistors and integrated circuits to ensure reliable connections between components. This means that in telecommunications, especially satellites, computers and, above all, in defence systems, gold is indispensable.

Research and development is continuing to study the optimum use of gold in the electronic sector, including the development of high strength connecting wires and improved wetting solder alloys. Innovations required for information technology in the future will be highly integrated electronic devices, designed and fabricated on the nanometre scale (one billionth of a metre). Gold will be an indispensable element for nanoscale electronic devices because it is resistant to oxidation and mechanically robust at the incredibly small dimensions defined by nanotechnology. As a result of the growth of these sectors, long term annual consumption of gold in electronics is increasing.

Microelectronics industry will soon have to deal with the finite nature of matter found at the nanoscale. The imminent problem (known by the semiconductor industry as "the red brick wall") provides a major motivation for a better understanding of electronic behavior at the nanoscale, for reliable nanofabrication processes, and the development of novel computational architectures. While purely top-down silicon processing can likely continue improving at a steady rate for 5-10 years, nanoelectronics is expected to bring about a new paradigm in computing, and is a very hot application for nanotechnology. Even with nano-scaling of modern electronics industry overall gold use has not been reduced. The more sophisticated the equipment and the greater the degree of reliability required, the more gold plating is used in connectors. This means that in telecommunications, especially satellites, computers and, above all, in defence systems, gold is indispensable. Gold's other main electronic use is in fine wire or strip to bond or connect parts of semi-conductors such as transistors and integrated circuits to ensure reliable connections between components. A third use is 'thick' and 'thin' film used in microcircuitry, in which the circuit is printed on a ceramic base using an ink-like paste containing gold.

A review of publications on nanotechnology related research and applications reveal the widespread use of gold in nanotechnology. The nobility of gold and its resistance to surface oxidation (which would hinder the operation of nano-scale technologies and devices based on other metals) is one important material characteristic. The optical properties of gold at the nanoscale are also exciting, because gold nanoparticles have a colour varying from red to purple depending on particle size, a property that can be successfully exploited in a range of applications. Additionally, gold nanoparticles are now known to be catalytically active for a range of commercially important reactions and they also have a surface chemistry particularly suited to the attachment of sulphur-containing molecules, such as thiols, which permits the 'bottom-up' assembly of interesting and useful structures.Based on these unique properties, exciting new nanotechnology applications using gold are being developed. These include:

* Low resistance printable gold nanoparticulate inks for flexible electronics

* Gold nanowires for interconnections in future electronic devices

* Nanoparticulate gold colloid for rapid tests and biomedical assays

* Goldsilica nanoshells for targeted destruction of cancer cells

* Improved decorative coatings using thiol stabilised gold nanoparticles

* Thermosetting gold nanoparticle containing paints exhibiting novel aesthetic effects

* Nanoparticulate gold catalysts for pollution control and chemical synthesis

* Fuel cell electrocatalysts based on carbon supported nanoparticulate gold

The report states that nanoparticles of precious metals platinum and palladium are already used in significant quantities in automotive emission control catalysts. The precious metals used in this application exist in the form of tiny nanoparticles within the catalyst (for both cost and technical reasons), yet total platinum and palladium demand generated through this application is still over 200 tonnes a year. The report goes on to list water purification, air pollution control applications and new medical technologies will make use of gold nanoparticles. It states that these new nanotechnology based applications will provide the foundations for industrial gold demand in the longer term and which could have very significant positive environmental benefits and the potential to substantially enhance quality of life.

Dr SS Verma, Dept of Physics, SLIET, Longowal