Graphene a material for the future

Transcription

1 Graphene a material for the future by Olav Thorsen

2 What is graphene?

3 What is graphene? Simply put, it is a thin layer of pure carbon

4 What is graphene? Simply put, it is a thin layer of pure carbon It has a hexagonal atomic arrangement

5 What is graphene? It is a 2 dimensional crystalline allotrope of carbon All the C C bonds are sp2 oriented It is the basic building block for other compounds like graphite, charcoal, carbon nanotubes and fullerenes It has many great qualities: little weight, high strength, great electric and thermal conductivity, 2 dimensionality

6 Discovery of graphene The graphite structure were figured out in 1916 Graphene were theoretic development by P.R.Wallace in 1947 for understanding electric properties of 3 dimensional graphite In 1948 the first TEM pictures of thin layers of graphite were published

7 Simple development of graphene In the 1970s graphene were grown on top of other materials, but this epitaxial graphene got a lot of charge from its host In 2004 graphene got extracted from bulk graphite by micromechanical clevage and deposited on a thin layer of silicon, a process that gives almost charge neutral graphene due to backtrack through the layer of silicon Oshima, C. and Nagashima, A. (1997). "Ultra thin epitaxial films of graphite and hexagonal boron nitride on solid surfaces". J. Phys.: Condens. Matter 9: 1.

8 Physical attributes Self repairing in contact with carbon It is only one atom thick, this gives 1 square meter the weight of 0.77 milligrams, roughly 1/1000th of a paper With a tensile strength measured to about 130 gigapascals it is the strongest known compound today, times stronger than steel It has also great elastic properties, though this requires a very pure and perfect material to be really considerate

9 Chemical attributes It is the most chemical active form of carbon due to all atoms being placed on two surfaces in flat sp2 bonds It reacts with oxygen at about 260 degree Celcius, it burns at 350 degrees Its good reactivity makes it easy to modify the compound using oxygen and nitrogen groups Denis, P. A.; Iribarne F. (2013). "Comparative Study of Defect Reactivity in Graphene". Journal of Physical Chemistry C 117 (37)

10 Electrical attributes It is a zero overlap semimetal, 2 holes and 2 electrons can be charge carriers It has 4 outer electrons, but are bonded to 3 other carbon atoms in 2 dimensions. This gives 1 free pielectron pr atom that moves freely above and along the surface. By either p or n type doping graphene easily conducts better than copper at room temperature Its electron mobility is in the range of cm 2 V 1 s 1. Typical mobility for silicon is 1400 cm 2 V 1 s 1

11 Optical attributes Graphene has unique optical abilities A single layer absorbs 2.3 % of white light, this is cumulative with number of layers It also readily reaches saturable adsorption This speciality makes it very usable with mode locking fibre lasers and with other types of ultrafast photonics. Its optical response can be tuned electrically

12 Thermal attributes Its thermal conductivity is better than both diamond and graphite It is phonon dominated Graphene has 3 different acoustic phonon modes that gives a linear dispersion relation along the plane and quadratic dispersion relation out of the plane, that means that thermal conductivity is dominated out of the plane at low temperatures but vica versa at high Mingo N., Broido, D.A. (2005). "Carbon Nanotube Ballistic Thermal Conductance and Its Limits". Physical Review Letters 95 (9):

13 Other attributes Massive electrons Spin transport Anomalous quantum Hall effect

14 Areas of interest and use Field Effect Transistors Biodevices Potential supercapacitor Piezoelectric controller Transparent conducting electrodes (touchscreens, organic photovoltaics, liquid crystal display etc..) Solar cells!! Increased PCR DNA production Quantum dots Thermal interface Ultrafiltration Composite materials

15 Production today Mechanical exfoliation, splitting of graphite Epitaxial growth, mainly on SiC Reduction of graphite oxide Metal carbon melting Sonication (f.ex. Interface trapping)

16 THE END