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Near-Perfect Graphene
May 7, 2015   
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A team of researchers led by Prof. Piotr Kula from the Lodz University of Technology has developed a method for producing large sheets of graphene with mechanical and electrical properties similar to those of single-crystal graphene.

Graphene is an allotropic form of carbon with a two-dimensional structure. Thanks to its unique physical and chemical properties, this material may revolutionize many technologies in the near future. The main features of graphene are its high thermal and electrical conductivity, which is likely to revolutionize electronics. The material’s high relative strength can also help produce a breakthrough in all industries that require lightweight structural materials, for example in aviation. And the unique sorption and filtration capabilities of graphene (selective permeability of molecules) could lead to new solutions for storing energy and cleaning liquids and gases. With these attributes, graphene could also contribute to the development of highly sensitive sensors.

The 2010 Nobel Prize in Physics went to researchers who separated a layer of graphene from graphite and examined its properties. Since then, intensive work has been in progress on the practical application of graphene. The greatest barrier at the moment to the widespread use of this material is the difficult industrial production of large graphene sheets with properties close to those obtained in laboratory conditions. Single-crystal layers free from crystalline-structure defects exhibit such properties.

At present there are many methods of producing graphene larger than one square meter in size, but this material is far from perfect. Structural defects form during the synthesis of graphene and largely depend on the method of fabrication.

The method developed by Prof. Kula and his team involves the synthesis of graphene from the gas phase on a liquid metal substrate. During this high-temperature process, carbon is supplied to the composite substrate from a mixture of hydrocarbons and hydrogen in precisely specified proportions. As a result of thermal decomposition, a crystalline layer of carbon consisting of only single carbons—in other words graphene—forms on the surface of the liquid metallic phase. This process has a huge advantage over methods of obtaining graphene based on solid substrates because it yields defect-free structures forming on a perfectly smooth liquid surface. During the process of forming graphene on solid substrates, a defect-free surface cannot emerge because the substrate is uneven and defective. The formation of large sheets of graphene on a liquid-phase surface has the additional advantage of enabling the self-organization of graphene grains formed. This results from the possibility of rotating graphene sheets on the liquid phase prior to the formation of a continuous layer. Therefore the resulting structure has a structure similar to that of single-crystal (ideal) graphene.

Research conducted at the Lodz University of Technology has shown that graphene sheets produced with this method have much better mechanical properties than polycrystalline graphene produced with other methods, and therefore this type of graphene is known in international nomenclature as High Strength Metallurgical Graphene (HSMG). In addition to its superior mechanical properties, this type of graphene has physical and chemical properties similar to those of single-crystal graphene.

The Lodz University of Technology, in collaboration with the Seco Warwick company, has designed and created a special generator for the synthesis of large-sized graphene on a liquid metallic-phase substrate. This device enables industrial-scale production of graphene sized 120 x 240 mm. Ultimately, the generator will make it possible to continuously produce graphene on bimetallic composite tapes with a width of 1,500 mm.

KonradDybowski
Institute of Materials Science and Engineering
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