Presentation on theme: "Graphene conductivity A lot of effort has been devoted to the question of transport in pure graphene due to the remarkable fact that the dc conductivity."— Presentation transcript:
Graphene conductivity A lot of effort has been devoted to the question of transport in pure graphene due to the remarkable fact that the dc conductivity is finite without any dissipation process present.
M. Lewkowicz and B. Rosenstein, PRL 102, (2009) Dynamics of Particle-Hole Pair Creation in Graphene find: They support this value of the dc conductivity of pure graphene Other authors find
Measurement of conductivity
8 Fullerenes Sir Harold W. Kroto, University od Sussex,Nobel Prize for Chemistry in 1996 Discovery September 4,1985 Fullerenes consist of 20 hexagonal and 12 pentagonal rings as the basis of an icosohedral symmetry closed cage structure. Was known initially as soccerene
9 Il fullerene non è molto reattivo data la stabilità dei legami simili a quelli della grafite ed è inoltre ragionevolmenteinsolubile nella maggioranza dei solventi. I ricercatori hanno potuto aumentare la reattività fissando dei gruppi attivi alla superficie del fullerene.reattivografiteinsolubilesolventi In theory, an infinite number of fullerenes can exist, their structure based on pentagonal and hexagonal rings, constructed according to rules for making icosahedra.
10 per produrre i fullereni: arco elettrico, a circa 5300°K, con una corrente elevata e bassa tensione, utilizzando elettrodi in grafite in atmosfera inerte (argon) a bassa pressione.argon
11 Endohedral compounds They are fullerene cages with La or other metal atoms inside. Some have been crystallized and found to superconduct
12 The art of hitting the goal with every shot We have observed de Broglie wave interference of the buckminsterfullerene C 60 with a wavelength of about 3 pm through diffraction at a SiN x absorption grating with 100 nm period. This molecule is the by far most complex object revealing wave behaviour so far. The buckyball is the most stable fullerene with a mass of 720 atomic units, composed of 60 tightly bound carbon atoms.
13 Carbon Nanotubes Fascinating electronic and mechanical Properties: 1.Depending on their chiralities, nanotubes can be metallic, semimetallic or semiconducting 2. Remarkably high Youngs moduli and tensile strength Imagine the possibilities: materials with ten times the strength of steel and only a small fraction of the weight! Former resident Bill Clinton
15 S. Iijima. "Helical microtubules of graphitic carbon." Nature (1991) Multi-Walled NanoTube (MWNT)
17 Carbon Nanotubes S. Iijima, Nature 354, 56 (1991)
18 From Wikipedia Carbon Nanotubes: Lattice Structure
19 Carbon Nanotubes: Lattice Structure Graphene sheetNanotube S. Iijima, Nature 354, 56 (1991) L1 m dnmdnm
20 This is a possible choice of the basis which is often used: Then, (n,0) nanotubes are called zigzag nanotubes, and (n,n) nanotubes are called armchair nanotubes. Otherwise, they are called chiral.
21 axis of CNT path towards the tip path around the belt: 2n atoms (n,0) alias Zigzag CNT
22 path along the y axis All armchair nanotubes are metallic, as suggested by paths along axis armchair CNT CNT axis = y axis
23 Chiral geometry all the rest Armchair geometry (n,m) with m=n, always metallic Zig-zag geometry (n,m) with m=0 e.g. (5,0),(6,4),(9,1) are semiconducting
24 The alternative basis which we used for the band structure of Graphene is also in use for CNT Since both conventions are used we must be ready to handle both of them. path around the belt: 2n atoms Zigzag CNT
25 Zigzag CNT using alternative basis CNT axis = x axis
26 p z Electronic bands of (n,-n) zigzag CNT-tight-binding approximation
27 Carbon Nanotubes as quasi 1D systems: one component of k quantized NT: Compact transverse dimension Discretization of k Band Structure of graphene Subbands correspond to different values of k k || is a continuous variable k ||
29 Note: the (4,-4) zigzag CNT has 8 atoms around the belt. Generally, (n,-n) zigzag 2n atoms in belt 2n bands
31 From Mahans nutshell book : band structure of a (5,0) zigzag nanotube. Labels indicate angular momentum values
32 From Mahans nutshell book : band structure of a (6,0) zigzag nanotube. Labels indicate angular momentum values. If m-n is a multiple of 3 the nanotube is metallic.
33 path along the axis All armchair nanotubes are metallic, as suggested by paths along axis armchair CNT CNT axis = y axis
34 Recall Primitive vectors
35 Armchairs are (n,n) using basis CNT axis = y axis
37 From Mahans nutshell book : band structure of a (5,5) armchair nanotube. Labels indicate angular momentum values. All armchair nanotubes are metallic.