Image Credit: Soonthorn Wongsaita/Shutterstock.com
Thin films are an emergent area of study, research, and development with many applications. Coating other materials (substrates) with certain thin films can produce synthetic materials with unique and useful features. A thin film material can be any material that is applied in such a way, and the applications of thin film technology are varied.
Optical coatings are some of the oldest applications of thin film technology. Large-area materials coated in a thin film of silver to create a highly reflective surface – mirrors – have been available since the 19th century. Meanwhile, refractive coatings on various sensors have enabled modern photography and cinematography.
Advanced optical thin film coatings are used in nearly everybody’s pocket globally – in smartphone cameras – and optical coatings now provide anti-reflection properties for eyeglasses and solar panels.
An even older use of thin films is in decorative coatings. Gold leaf was in use since at least the third millennium before the Common Era in ancient India. Today, titanium dioxide is applied as a thin film coating to glass to produce a rainbow-colored effect.
A thin film coating can also be applied to protect the substrate material. A common example of this is found in plastic drink bottles. Here, the out-diffusion of carbon dioxide is prevented by the bottle’s coating of thin layers of anti-diffusion materials. Diamond-like carbon (DLC) is also applied in a protective thin film coating in the automotive industry, to avoid abrasion of the engine parts caused by their mechanical movement.
Another kind of protective thin film coating is related to a cutting-edge thin film technology application. Thin titanium nitride films are applied to microelectronic chips to prevent aluminum-oxide forming between electrically conductive aluminum lines and the insulating silicon-oxide they are embedded inside.
Various applications for the electronic properties of certain materials applied in a thin film are being used in the latest technological advances. Printed circuit boards in computers utilize the high-conductivity of materials like copper, aluminum, gold, and silver in a thin film application. Coaxial cables used in modern information technology to carry high-frequency transmission with low loss levels frequently include thin film electrically operating coatings as well.
Even batteries are now able to be printed onto various substrate materials. The solid-state energy storage capabilities of materials like lithium polymers can be applied in a thin film to a substrate material to create uniquely adaptable, flexible, or robust batteries for specialist applications. Thin film batteries can also be directly applied to computer chips of any size.
This latest application of thin film batteries will promote the widely anticipated Internet-of-Things (IoT) where all kinds of devices, materials, and processes will become “smart”. The ability to connect to almost anything will eventually create significant efficiency and automation gains in the industry. For example, in energy generation, distribution and consumption, data acquisition, and a plethora of aspects of modern life.
Finally (but by no means exclusively), thin film technology is being applied to significantly reduce the cost of producing photovoltaic cells for solar panels. Printed photovoltaic materials minimize the requirement for materials, as well as reducing energy costs, handling costs, and the capital investment needed to manufacture photovoltaics. Experimental techniques include organic thin film photovoltaics, nanocrystals, and polymer solar cells.
How Fat Can a Thin Film Be?
In all of these applications, the size of thin films varies. The term is generally used whenever a material is applied to a substrate to create a new synthetic material with unique or useful properties. The thickness of these layers varies, but a commonly accepted definition is between a few micrometers (millionths of a meter) at the fatter end and mere fractions of a nanometer (billionths of a meter) at the atom-thin end.