M.Sc. Physics 4th Semester
After awarding Andre and Kostya by 2010’s Nobel Prize, the weight of the topic “Graphene” became much heavier. Large number of researchers’ brain and money are being invested for its research why? Actually, what is Graphene? Why, this topic is so emerging? What miracle does it do ? It’s quite interesting to know.
Two dimensional hexagonal shape of single atomic layer of carbon is Graphene i.e. one atom thick layer of graphite. Graphene is basic structural element of other allotropes including graphite, charcoal, carbon nanotubes and fullerenes. Its supreme properties like mechanical strength, optical properties, thermal conductivity, electrical conductivity coercion to accept its nick-name as “Miracle Material”. Its optical and electrical properties make researcher crazy (about 97.3% transparent and known lowest resistivity at room temperature~10-6ohm.cm-1). Flexibility with good electrical conductivity and optical properties endorse the concept of flexible optoelectronic devices. Many characteristics (1. Room temperature electron mobility 2. Young modulus 3. Intrinsic strength 4. Thermal conductivity 5. Optical absorption 6. Complete impermeability to any gases 7. Ability to sustain extremely high electric current densities ~ 1,000,000 times higher than copper) measured in experiment have exceeded those obtained in any other material( reaching some theoretically predicted limits also). But some characteristics have been achieved only in mechanically exfolicated graphane.
Since, sheet resistance reaching 30 Ω/ cm-2 of 2D area in highly doped graphene sample; it meets electrical and optical requirement by giving excellent transmittance (~97.7% per layer) for Transparent Conductive Coating(TCC), widely used in electronic products like touch screen displays, e-paper (electronic paper) and organic light emitting diodes (OLEDs). Outstanding flexibility (fracture strain of graphene = 10 times of ITO) and chemical durability (better endurance than other available candidates ) of graphene can be used to make flexible electronic devices; in which ITO usually fails. Furthermore, for TCC, ITO deposition is expensive, so Graphene can replace the ITO and has a full capacity to secure good fraction of the market.
Many researchers believe that graphene transistors might have an opportunity to replace Silicon Technology only after 2020. New structures of graphene is needed to use it as a logic transistor. Grapheme’s supreme electrical and thermal conductivities and its excellent barrier properties might open door for this material towards being used as interconnects and for thermal dissipation in ICs.
Wavelength-independent absorption (π × α = 2.3%) takes place due to massless electron in graphene for normal incidence of light below~3eV. When optical energy < 2 × fermi energy for mono and bi-layer of graphene they become completely transparent. Such properties would push this material towards being used as controlled photonic devices. In photonics it can be used as Photodetector, Tunable fibre mode-locked laser, Solid-state mode-locked laser, Polarization controller, Optical modulator, Isolator etc., but for these purposes there are a few unsolved issues, which we need to address first. Photodetectors Graphene’s high operating bandwidth (in principle from ultraviolet to infrared) makes it suitable for high-speed data communications (presently bandwidth of photodetectors in Ga. As for optical communication and Ge for optical interconnection are limited to ~150 GHz and ~80 GHz respectively). But for its practical implementation it may require a new structure or doping control, and the modulator bandwidth must follow suit.
Tunable fibre mode-locked laser
Wide spectral range of Graphene brings the best possibility of making tunable fibre mode-locked laser.
High-quality graphene with low sheet resistance is needed to increase bandwidth to over 100 GHz this is the special challenge.
Solid State Mode-locked laser
Compact graphene is very easy to integrate with Si than bulky current polarization controlling devices. But first need to achieve full control on parameters of high-quality graphene. Composite materials, paints and coating Different outstanding properties along with its high aspect ratio are fruitful for its applications in composite materials. Many companies’ attraction is being shifted towards graphene. After some substantial developments and chemical modifications on graphene, however, the commercial position held by carbon fibres are so strong, it is believed that within few years carbon fibres might be replaced by graphene and its oxide. Graphenes conductive ink, electromagnetic interference shielding and gas barrier applications are the main areas where graphene based paint
can be used very interestingly. Because of its high chemical stability, it can act as a corrosion barrier against water and oxygen diffusion. Impermeable graphene membrane can be used as gas and moisture barrier, electromagnetic shielding is its next interesting application. It might increase the operating temperature level of composites, reduce moisture uptake, induce antistatic behaviour, give lightning strike protection and improve composite compressive strength.
Graphene for sensors and metrology
There is enough possibility for the uses of graphene as sensor, it is natural to consider using graphene from measurements of magnetic field to DNA sequencing and from the monitoring of the velocity of surrounding liquid to strain gauges (device used to measure strain on an object). Graphene crystal is stretchable, so it can enhance the working of such sensor significantly but it is most competitive application. Graphene can be used for the design of multidimensional devices (single device can work to measure strain, gas environment, pressure and magnetic field) so it can revolutionize the whole electronic world. It is more suitable for bio-sensing because functionalization for enhancing its selectivity for other sensors is expensive. Its unique band structure i.e., anomalously splitted large energy between zero and first landau levels makes it an ideal material to develop the universal resistance standard based on the quantum Hall effect. Graphene has beautiful uses in energy generation & storage devices and Bio-applications but there are also a few major issues need to address to obtain high performance. After addressing all issues the earth will be revolutionized. Paper computer & super capacitors are not so far.
1. Novoselov, K. S.; Colombo, L.; Gellert, P. R.; Schwab, M. G.; Kim, K. A roadmap for graphene. 11 October 2012 |vol.490|NATURE|199
2. Joseph Scott Bunch A Dissertation for Doctor of Philosophy Presented to the Faculty of the Graduate School of Cornell University|may 2008.