Graphene Frontiers’ innovative roll-to-roll production method is bringing graphene technology to consumers.
Graphene, the world’s first free-standing two-dimensional material and subject of the 2010 Nobel Prize in Physics, consists of a single atomic layer of carbon. Graphene’s novel properties—strength, flexibility, optical transparency, conductivity and impermeability—have attracted the attention of researchers around the globe. However, the commercialization of graphene applications has been hindered by the lack of a cost-effective method for manufacturing large-area graphene sheets. Graphene Frontiers, an advanced materials and nanotechnology company based in Philadelphia, aims to change that.
The Discovery of Graphene
Graphite, a carbon allotrope used in pencil leads, consists of millions of stacked graphene sheets. Although graphene sheets found in graphite or intercalated in other materials are naturally occurring, free-standing two-dimensional materials were long thought impossible. Researchers theorized that the high temperatures required for the formation of 2-D materials would disrupt the stability of their structure.
In 2004, Dr. Andre Geim and Konstantin Novoselov, then a post-doctoral student at the University of Manchester, isolated graphene using mechanical cleavage, or the “scotch tape technique”. The researchers applied adhesive tape to a large chunk of graphite, peeling off a thin layer. By repeatedly folding and unfolding the tape upon itself, they eventually isolated a few tiny flakes, or nanoplatelets, of single atomic layer graphene, some as large as a few millimeters in length.
Geim and Novoselov received the 2010 Nobel Prize in Physics for the discovery that graphene can be produced artificially, even though energy constraints prevent two-dimensional materials from forming spontaneously.
Growing Research Interest
Few scientific discoveries have developed as quickly as graphene technology. The number of graphene papers published has doubled every year since its 2004 discovery, and bibliometric predictions show the trend continuing over the next few years. This flurry of interest is enabled by the ease of graphene platelet production.
Despite its tedium, Geim and Novoselov’s scotch tape technique is reproducible and cost-effective, making it the leading technique for researchers performing proof-of-concept and low-volume experiments. For industrial applications, however, several new production methods have been developed to facilitate graphene commercialization.
Ultrasonic cleavage is an automated version of mechanical cleavage, where ultrasonic waves are used to cleave the graphite in solution. This process can be aided by chemical processes to loosen graphene layers within the graphite before sonication.
Another method for producing graphene platelets is the chemical reduction of graphene oxide. First, graphite is exposed to a strong oxidizing agent, such as sulfuric acid, to loosen the graphene layers. Once the reaction is complete, the graphite oxide is dispersed in solution, completely separating the layers to create graphene oxide. The graphene oxide is reduced to graphene by treating the flakes with hydrazine and exposing it to a high-energy light. This method is capable of producing industrial-scale quantities of graphene flakes.
Graphene Applications
Enabled by huge funding initiatives, such as the European Union’s €1 billion Graphene Flagship fund, the popularity of graphene research has given rise to an explosion of new graphene applications.
Some of the earliest applications to be commercialized will include conductive inks, drilling fluids and graphene-polymer composites. In these applications, tiny platelets of graphene are integrated into a liquid polymer.
Originally, graphene nanoplatelets were produced via mechanical cleavage, the labor-intensive scotch tape technique used in Geim and Novoselov’s Nobel-winning paper. Although mechanical cleavage cannot produce graphene flakes in sufficient amounts for commercialization, the chemical reduction of graphene oxide can produce graphene nanoplatelets at industrial scale. This method is currently preferred for producing graphene additives for conductive inks and extra-strong graphene-polymer composites, where product performance does not depend on the connectivity from platelet to platelet.
Many of the most exciting graphene applications require continuous graphene. These applications include desalination membranes, flexible solar panels and flexible electronic displays, where a large-area graphene sheet would serve as an impermeable, conductive barrier.
Large-Area Production
Compared to conductive inks and composites, the development of graphene membranes and displays has been slow. There is no effective way to connect nanoplatelets into a continuous sheet. Instead, graphene researchers have developed a new graphene production method based on established chemical vapor deposition technology.
Chemical vapor deposition enables fast and easy graphene production. The process begins with a metal substrate, most often copper. The copper substrate is annealed in a vacuum furnace at roughly 1000 oC. Next, a carbon feedstock gas is pumped into the chamber. The copper acts as a catalyst for graphene deposition. Tiny nucleation sites form, growing into larger crystals that connect into a continuous sheet, in the same way that ice forms on a pond in winter.
Graphene sheets produced via chemical vapor deposition are much higher quality than graphene flakes produced via chemical reduction of graphene oxide. Not only are there no toxic chemicals introduced, but the low-pressure atmosphere limits concerns of particulate contamination. The process is fast, requiring only a few minutes to deposit, and cost-effective. Many labs have the capacity to produce graphene sheets as large as 60 in2.
Although it is fast and inexpensive to produce high-quality graphene via chemical vapor deposition, graphene membranes and displays are not yet commercially available. Significant drawbacks to chemical vapor deposition have limited the commercialization of large-area graphene applications.
Image 1: Roll to roll production method schematic (Graphene Frontiers).
First, chemical vapor deposition is a batch process. It can take over two hours to produce a single 60 in2 graphene sheet due to heating and cooling time. Second, the maximum graphene area is limited by furnace size, so the graphene sheets produced rarely exceed 5” wide. Most significantly, the graphene must be transferred from the copper substrate to a polymer or silicon substrate for use in most membrane and electronics applications. The only way to separate the graphene from the substrate is to slowly etch away the copper using harsh chemicals. In order to limit etch time, and thus limiting potential damage to the graphene, the copper substrate must be a very thin foil. This can make handling difficult, resulting in damaged graphene. The etch process is slow, toxic and destructive of the copper substrate.
The Future of Graphene Commercialization
Graphene Frontiers, an advanced materials and nanotechnology device company based in Philadelphia, aims to solve the problems of chemical vapor deposition to enable exciting new graphene membrane and graphene display applications. In September 2013, Graphene Frontiers was awarded a $745,000 Phase II Small Business Innovation Research grant from the National Science Foundation to develop the company’s scale-up technology.
Graphene Frontiers uses atmospheric chemical vapor deposition to produce graphene. This eliminates the need for a closed furnace, enabling continuous production of graphene. Air contamination is limited using a system of filters and purge gases, similar to established semiconductor fabrication methods. Atmospheric pressure chemical vapor deposition enables Graphene Frontiers to make much larger areas of graphene at a much faster rate than is possible using established low pressure methods.
Furthermore, Graphene Frontiers has developed a gentle, etch-free separation method, enabling the reuse of the copper substrate and paving the way for roll-to-roll production.
Graphene Frontiers’ roll-to-roll graphene production method is fast, inexpensive and non-toxic. Graphene Frontiers plans to license the technology to large electronics manufacturers, where the roll-to-roll graphene system can be easily integrated into existing production lines.
Graphene Frontiers was founded at the University of Pennsylvania by University of Pennsylvania professor A.T. Charlie Johnson and Hong Kong University of Science and Technology professor Zhengtang Luo, then a post-doctoral student in Johnson’s lab. CEO Mike Patterson, a serial entrepreneur and Wharton MBA, learned of the team through Penn’s Center for Technology Transfer. Graphene Frontiers was selected for the NSF’s inaugural Innovation Corps class.
With innovative technology that will enable the continuous production of uniform, meter-length single atomic layer graphene films, Graphene Frontiers is dedicated to providing custom graphene solutions at a commercial scale—and an affordable cost. Graphene Frontiers will soon offer customized production design services for companies that have a graphene application and specific requirements.
AUTHOR: Paige Boehmcke, Senior Product Manager at Graphene Frontiers, (267)225-5003 or paige@graphenefrontiers.com. All graphene images courtesy of Graphene Frontiers.
