This graphene research update includes an investigation into the production of graphene from ethene on a rhodium substrate, and a novel speaker design that uses the expansion and contraction of graphene on heating and cooling to produce sound waves, removing the need for moving parts or heavy magnets.
Potential catalytic production of graphene from ethene
The current and most common fabrication methods for graphene synthesis include mechanical cleaving, or exfoliation, chemical exfoliation, chemical synthesis and chemical vapor deposition (CVD), as well as less commonly employed nanotube unzipping and microwave synthesis1.
Whether the “top down” or “bottom up” approach to graphene synthesis is applied, both types of processes involve the precise preparation of graphene structures be able to react with the particular surface chemistry of its substrate’s surface.
Recent investigational work has developed calculations to investigate the potential of ethylene, or ethene, to be catalytically hydrogenated to transient metal surfaces such as those present on cobalt, nickel, copper, silver, gold, and several others2.
As one of the most important manufactured chemicals, ethylene (C2H4) is a odorless and flammable hydrocarbon gas that is largely used as a production precursor to the widely used plastic material, polyethyelene3.
To further explore this postulated theory, a group of researchers in Germany and Scotland believe that the hydrogen atoms present on the ethene molecules can form and self-assemble into the honeycomb pattern of carbon atoms that characterizes graphene compounds.
To investigate this potential adhesion method, the researchers initially adsorbed ethene onto the rhodium, or Rh, (111) surface at a temperature of 300 K, thus resulting in the formation of ethylidyne. By further heating this newly formed ethylidyne/Rh (111) system to 370 K, the structure of the system exhibited a highly disordered arrangement that consisted of various carbon clusters consisting of C2, C4, and C6 species2.
The research team continued to increase the annealing temperature of the ethylidyne/Rh (111) system in a regulated and controlled manner in order to understand the dynamic restructuring processes that finally led to the condensation of graphene onto the material’s surface. Through their discovery, the researchers are hopeful that future work into developing catalytic substrate and adsborbate material combinations could enhance the way in which materials are produced.
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Magnet-free graphene speakers
The ability of graphene to revolutionize electronic devices is no novel concept, however, recent work conducted by researchers at the University of Exeter, located in Southwestern England, has found way to integrate this wonder material for speaker purposes.
Speakers are able to produce sound waves as a result of the interactions between an internal permanent magnet and electromagnet. While the permanent magnet remains in a fixed position, the electromagnet is a metal coil that creates a magnetic field following the application of an electric current that flows through this material. The flow of electrical pulses within the coil of the electromagnet will cause its magnetic field to change rapidly, which can either result in a constant attraction or repulsion between the electromagnet and the permanent magnetic, causing back and forth vibrations between the two magnets to generate sound waves4. Attached to the electromagnet is a cone, typically comprised of a flexible material such as paper or plastic, which will then amplify these vibrations.
To generate their graphene speaker, researchers from the University of Exeter looked to the Joule mechanism, which is a process that generates sound waves from heat. As an extremely thin and uniformly conducted material, the graphene material was rapidly heated and cooled following the application of an alternating current. The changes in this current caused the graphene to either expand or contract upon contact, thereby creating a reproducible method to produce sound waves5.
By eliminating the need to employ the various moving parts that are utilized in traditional speakers, graphene is able to produce sound waves that can be combined, amplified and equalized within a single, millimeter sized chip.
The inherently transparent nature of graphene offers the global audio and telecommunications industries an opportunity to develop new audiovisual technologies that are capable of transporting both images and sounds from the same material, such as a mobile phone screen.
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- “Synthesis of graphene” M.S.A. Bhuyan, M.N. Uddin, et. al. International Nano Letters. (2016). DOI: 10.1007/s40089-015-0176-1.
- “Structural and Energetic Trends of Ethylene Hydrogenation over Transition Metal Surfaces.” C. Heard, S. Siajrostami, et al. J. Phys. Chem. C. (2016). DOI: 10.1021/acs.jpcc.5b09735.
- “Propylene from Methanol” – Intratec
- “How do speakers work?” – physics.org
- “Multi-frequency sound production and mixing in graphene” M.S. Heath & D.W. Horsell. Scientific Reports. (2017). DOI: 10.1038/s41598-017-01467-z