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Drs. Iskandar Kholmanov and Rodney S. Ruoff in the lab. Knolmanov is holding a sample of the new anti-bacterial, flexible conductive transparent film alloy they have made of graphene oxide, silver and gold.

Drs. Iskandar Kholmanov and Rodney S. Ruoff in the lab. Knolmanov is holding a sample of the new anti-bacterial, flexible conductive transparent film alloy they have made of graphene oxide, silver and gold.

 

Iskandar Kholmanov and Rodney S. Ruoff, as well as Meryl Stoller, Jonathan Edgeworth, Wi Hyoung Lee, Huifeng Li, Jongho Lee, Craig Barnhart, Jeffrey Potts, Richard Piner, Deji Akinwande, and Jeffrey E. Barrick, recently proposed a new transparent conductive film (TCF) "alloy." This work has been done in Professor Rodney Ruoff's research group, Nanoscience and Technology Lab, in the Department of Mechanical Engineering at The University of Texas at Austin, in collaboration with Professors Deji Akinwande and Jeffrey Barrick from the Department of Electrical Engineering and Institute for Cellular and Molecular Biology at The University of Texas at Austin, respectively.

Kholmanov is a post-doc in Rodney Ruoff's research group, and first author on the paper which has been selected to be highlighted by the journal ACS Nano. The team has produced a new transparent conductive film as described in their paper. Currently, transparent conductive films are used in many of today's digital electronic products, and one that is relatively inexpensive to produce, flexible and anti-bacterial could receive widespread use in a large number of applications. The team is in the beginning stage of fundamental research on gold, silver and graphene oxide based films that might eventually have an impact in this market niche.

What are Transparent Conductive Films?

A copy of Kholmanov et al.'s research paper viewed through a transparent conductive film.

A copy of Kholmanov et al.'s research paper viewed through a transparent conductive film.

Transparent conductive films, or TCFs, are used to coat everything from plasma TVs and the liquid crystal display (LCD) monitors to solar cells and electronic ink devices like e-book readers. They also can protect electronics from static electricity and electromagnetic interference, shield cars from heat by reflecting infrared rays, and serve as antireflective coatings for eyeglasses and computer screens. They are used in digital cameras, touch screens, and strain gauges for gas turbines and jet engines.

So what makes TCFs so special?

As the name suggests, transparent conductive films are extremely thin sheets of material that are both electrically conductive and optically transparent. Very few materials possess both of these qualities; typical electrical conductors such as metals are not transparent at necessary thicknesses while most transparent materials like glass and plastic are not electrically conductive. Aside from some other unique properties, these two qualities found together in TCFs give them numerous applications in modern technology - and the applications are expanding rapidly.

Indium tin oxide, the current industry choice, has limitations

Indium tin oxide (ITO) is currently the most common material used in TCF applications. It possesses good electrical conductivity while transmitting 80-90% of visible light, both very desirable and necessary qualities to have in a TCF. However, ITO has several other properties that make it unfavorable. For one, ITO is notoriously brittle. Flat, flexible electronics such as keyboards, touch screens and even cell phones that can be bent and rolled up are one proposed use for TCFs that would require the materials to withstand being bent or rolled. Furthermore, the price of the indium is already high and steadily increasing.

Other transparent conductive film options

Although other TCFs exist, they each have certain disadvantages that make them less desirable than ITO. Conductive polymers degrade under ultraviolet light and humidity, carbon nanotubes and metal nanowires contain discontinuities that reduce uniformity, and graphene lacks an efficient process of manufacturing at this time. Reduced graphene oxide is cheap and can bind to many surfaces, but is a relatively poor electrical conductor.

Alloys of metals are very useful because they combine desirable properties from each component to achieve the desired effect. In a similar way, Kholmanov and Ruoff have proposed using a combination of several types of nano-material to produce a comparable, or maybe even better, TCF than the current leading material, ITO.

By combining gold nanoparticles (NPs), silver nanowires (NWs), and reduced graphene oxide (RG-O) nanoplatelets, Kholmanov and Ruoff have produced a TCF "alloy" that utilizes all the benefits of its constituent materials: RG-O's low costs and flexibility and the high, uniform conductivity provided by the gold and silver nano-structures. Using the chemical symbols for gold (Au) and silver (Ag), they abbreviate these TCF-hybrid sheets as "RG-O/Au NP/Ag NW films."

Aside from the potential benefits of providing a cheap and effective new way of producing TCFs, the hybrid TCF developed by Kholmanov and Ruoff has the interesting ability of killing E. coli and other microorganisms. This opens up a new set of possible healthcare applications for hybrid TCFs, both traditional and novel. Antimicrobial TCFs might be used for the same touch screens, computer displays and cell phones that utilize them now in sterile medical environments, and also to provide health benefits for everyday consumers, but the discovery also opens an entirely new frontier for research into the possible biomedical applications of antimicrobial TCFs.


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