NIHERST: Tsunamis

In 2004, a Manchester-based researcher and his group made a ground-breaking discovery at the University of Manchester, England. For the first reported time in history Andre Geim and his co-workers were able to successfully isolate a single sheet of carbon, one cell thick using a simple yet clever approach of mechanical cleavage with graphite and Scotch tape. Without the use of any sophisticated machinery, these scientists alternated a piece of graphite between two pieces of Scotch tape with their hands, a process which resulted in what is known today as graphene.¹³

FIG 1: Graphical representation of a finite graphene fragment¹⁵

Graphene has been added to the list of 2-dimensional materials, a term used to describe the collection of materials that have in common a thickness of one atom and that have recently sparked much interest in the science world. Moreover, long before graphene was actually isolated it was considered simply a theoretical material because scientists rendered impossible the existence of a single, free sheet of graphene on the grounds that it was not thermodynamically feasible and therefore the sheet would fold up and buckle on itself to give a structure that would be three-dimensional. Yet the notion of a single sheet of carbon continued to excite researchers because of the physical and material properties that were predicted for graphene.

Finally, when experimental work was conducted on the graphene sample, most of the nanoscale properties of graphene that were predicted were in fact confirmed. Since then, its discovery has opened up countless prospects in a number of different applications such as nanoelectronics, biosensors and pharmaceuticals, chemical sensors, and ultra-capacitance devices among other applications. Of particular significance is the potential of graphene to totally transform the face of electronics and the larger scope of nanotechnology. In the field of electronics, graphene has already opened up new prospects in extending the existing limitations of microchips and made tangible the possibility of the first zero-resistance ballistic transistor. These possibilities arise particularly because graphene displays a unique energy band structure that gives rise to special and tuneable electronic properties.

Where materials development is concerned, Professor Geim and others have reported the synthesis of graphane which describes the product of the reaction of pristine graphene with molecular hydrogen.13 This new material displays insulation properties that allow for the control of the electronic behaviour of graphene and therefore allow for the production of high performance transistors.2 It has been predicted that the use of graphene as the core basis for electronic applications in the future provides greater simplification in producing applications like semiconductors while it also offers the most cost-effective approach envisioned thus far. Presently, the semiconductor industry makes use of a range of elements yet with the possibilities of fine-tuning and controlling the properties of graphene with the use of far fewer elements, makes this approach significantly competitive and favourable. Therefore graphene is forecasted as that material that will be able to cover the entire spectrum needed for electronic applications.

Another burgeoning area of experimentation and research in materials development is the production of composite materials using graphene-based formulations. For instance, electronics-based companies are considering exploiting the use of highly conductive graphene dispersions in conductive coatings and compounds. Additionally, the inclusion of graphene-based nanoparticles in the bulk matrix of materials like polymers strongly influences the mechanical properties of these materials such as the stiffness and the elasticity. The structure of traditional polymers has been reinforced by the addition of nanoparticles to the polymers that result in light weight material that can be used to replace metals in construction for instance.6 Geim and his co-workers imagine that the route they took in creating graphane will lead to the synthesis of new graphane-based materials and advanced composites via simple chemical modifications. In turn, they are hopeful that this will open up the flood gates for new applications that offer benefits such as increased stability and greater functionality.¹

FIG 2: Schematic of a Graphene Transistor ¹⁴

The application of nanotechnology to the broad field of pharmaceutical and biomedical research takes particular advantage of the ability to add functionality to nanomaterials by allowing them to interact with biological materials and structures. The fact that most nanomaterials are of the same scale as biological materials makes it possible to create interaction both through in vitro or in vivo approaches and research based on such interactions has led to the development of applications such as drug delivery systems, analytical tools and diagnostic devices among others. ¹¹

FIG 3: Schematic of a graphene-based polymer composite¹⁶
showing functionalized graphene sheet- polystyrene (FGS-PS) composite

With drug delivery systems, nanotechnology makes it possible for pharmaceutical drugs to be transported to specific cells within the body, a reality which is significantly advantageous for a number of reasons. Firstly, if the necessary cells can be targeted, this eradicates the need to consume more than the required amount of medication thus reducing the occurrence of side effects. If lower dosages are required, this in turn reduces the cost of medication and medical care. A particular application of this highly selective approach involves research based on the use of electrochemical systems that allow the active release of drugs based on chemical indicators in the organism. Cancer treatment using this method requires the use of iron or gold nanoparticles. The tuneable electronic properties of graphene and its inertness in body tissue make it a viable option in constructing implantable delivery systems. For instance, Sun and others at Stanford University have studied the use of a graphene derivative, nano-graphene oxide (NGO) for use in drug delivery.

The exploitation of nanotechnology in the area of electronics is particularly geared towards the creation of devices and systems that reduce energy consumption and are more environmentally friendly. Currently, the most involved nanotechnology projects that are energy related focus on areas such as device storage and memory, efficiency of energy conversion and overall manufacturing processes that pertain to reduced process rates, reduced energy consumption and reduced raw materials. Where memory storage is concerned, the research and development of ultra-high memory densities is forefront, the basis of which is the use of cross-bar switch based electronics as opposed to the traditional use of transistors. The company Nantero has recently developed a carbon based cross-bar memory which uses reconfigurable interconnections between vertical and horizontal wiring arrays to achieve the high memory density. Research regarding the use of graphene in such devices is currently underway, with predictions that graphene-based devices will replace carbon nanotube devices. Wang and others at Hefei National Labs in China, report work on a graphene switch, similar to the cross-bar switch technology.¹²

FIG 4: Schematic showing layered graphene as is required in graphene-based electronics¹⁷

The data storage density of hard disk drives and the consequent reliance on the gigabyte range have significantly increased due to the amplified dependence of the resistance of nanomaterials on an external magnetic field. This amplified effect can now be used to create non-volatile main memory for computers such as the magnetic random access memory (MRAM), so called since the dependence of the resistance of materials on an external magnetic field is called magnetoresistance. Modern communication technology based on nanoelectronics is increasingly exploiting the use of optics and optoelectronic devices which offer large bandwidth and capacity. Such devices include photonic crystals and quantum dots. Photonic crystals have selectable, nano-sized band gaps that can be used to propagate specific wavelengths and thus produce certain signals. Quantum dots are nanoscale particles that are used in creation of lasers that are cheaper and that offer a higher quality beam than traditional lasers.

It can be seen that the use of graphene in several areas of nanotechnology and nanoscale applications holds great promise and new prospects are emerging at a rapid pace. As researchers continue to investigate the possibilities that can be reached by taking advantage of the quantum properties of graphene, engineers and scientists elsewhere put the finishing touches on graphene based applications that have already been synthesized.

References

REFERENCES
1. Nagpal S. Grapehne confirmed to be one of the Strongest Materials known to Man
http://www.topnews.in/graphene-confirmed-be-one-strongest-materials-known-science-253472 accessed 09 May 2008

2. Future Electronics Science Daily 9 February 2009. 2 January 2010
http://www.sciencedaily.com /releases/2009/02/090205103502.htm

3. University of Waterloo Nanotechnology in Targeted Cancer Therapy http://www.youtube.com/watch?v=RBjWwlnq3cA 15 January 2010

4. Press Release: American Elements Announces P-Mite Line of Platinum Nanoparticles for Catalyst Applications October 3, 2007

5. Nanotechweb.org Platinum nanoparticles bring spontaneous ignition, April 25, 2005

6. Esteban P. et al. Electrocatalytic Oxidation of Methanol on Platinum dispersed in Polyaniline Conducting Polymers

7. Hillie, Thembela and Mbhuti Nanotechnology and the Challenge of clean water. Nature.com/naturenanotechonolgy. November 2007: Volume 2.

8. Hillie, Thembela; Hlophe, Mbhuti (2007). "Nanotechnology and the Challenge of Clean Water". Nature Nanotechnology 2: 663–664. doi:10.1038/nnano.2007.350.

9. Waldner, Jean-Baptiste (2007). Nanocomputers and Swarm Intelligence. London: ISTE. p. 26. ISBN 1847040020.

10. Suresh Neethirajan, Digvir Jayas. 2009. Nanotechnology for food and bioprocessing industries. 5th CIGR International Technical Symposium on Food Processing, Monitoring Technology in Bioprocesses and Food Quality Management, Postdam, Germany. 8 p.

11. Sun, X. et al Nano-graphene oxide for cellular imaging and drug delivery. Nano Research v.1. 3

12. Wang Z. et al. Emerging nanodevice paradigm: Graphene-based Electronics for Nanoscale Computing ACM JETC v 5.3 2009

13. A.K. Geim, K.S. Novoselov, "The rise of graphene," Nature Materials, 6(3): 183-91, 2007.

Meet Graphene - one of the newest super-materials!

References