The many forms of carbon Carbon is not only the basis of life, it also provides an enormous variety of structures for nanotechnology. This versatility is connected to the ability of carbon to form two stable bonding configurations (sp 2, sp 3 ) with different bond geometry (planar, tetrahedral). sp 2 sp 3 + pzpz  -bonds  -bonds

Fullerene 0D Graphite, Graphene (= single sheet) 2D sp 2 Diamond 3D sp 3 Nanotube 1D

Diamondoids are small nanocrystals of diamond with the surface passivated by hydrogen atoms. Diamondoids: The smallest possible diamonds

C 60 solution in toluene Buckminsterfullerene C 60 has the same hexagon + pentagon pattern as a soccer ball. The pentagons (highlighted) provide the curvature. Fullerenes Buckminster Fuller, father of the geodesic dome

Fullerenes with increasing size Fewer pentagons produce less curvature. Symmetry

Mass spectrum showing the different fullerenes generated. Plasma generation of fullerenes in a Krätschmer-Huffman apparatus. Production of fullerenes

Formation of fullerenes during cooling of the plasma. Carbon clusters smaller than C 60 are often short chains.

Molecular orbitals of C 60 The high symmetry of C 60 leads to highly degenerate levels. i.e., many distinct wave functions have the same energy. Up to 6 electrons can be placed into the LUMO of a single C 60 (see next). The LUMO (lowest unoccupied molecular orbital) is located at the five-fold rings:

Empty orbitals of C 60 from X-ray absorption spectroscopy (XAS) LUMO, located at the strained five-fold rings The continuous of  * and  * bands of graphite (top) become quantized into discrete levels (bottom). Terminello et al., Chem. Phys. Lett. 182, 491 (1991). core level

C 60 can be charged with up to 6 electrons The ability to take up that much charge makes C 60 a popular electron acceptor for molecular electronics, for example in organic solar cells.

Endo-fullerenes An endofullerene is a fullerene with an atom (or molecule) inside. Terminology: C 60

Lefebvre et al., PRL 90, (2003) Carbon nanotubes grown free-standing between pillars Controlling the location of nanowires is a difficult task, but critical for the wiring of nano-devices. These nanotubes start at catalytic metal clusters (Ni, Co, Fe,…).

Atomic force microscopy image of an isolated carbon nanotube deposited onto seven Pt electrodes by spin-coating from dichloroethane solution. An auxiliary electrode is used as electrostatic gate (upper right). Carbon nanotube electronics

Chen et al., Science 311, 1735 (2006) Device containing several transistors on a single nanotube Transistors with a nanotube channel work better than silicon, but are difficult to mass-produce.

Geim and McDonald, Physics Today, August 2007, p. 35 Artist’s view of a futuristic transistor made of graphene, a single sheet of graphite Electrons Standard silicon transistor: A positive gate voltage draws electrons into the channel. These electrons carry a current between source and drain. The switch is on. sourcedrain gate channel

A.Longitudinal acoustic mode B.Transverse acoustic mode C.Twisting (acoustic) mode D.E 2g(2) mode E.A 1g mode (radial breathing mode) Calculated sound velocities are given for the acoustic modes. D,E are Raman active (see next). Vibrations of a single wall nanotube (SWNT)

Raman spectrum of acid purified nanotube material. The Raman active E 2g(2) and A 1g modes (G-band and D-band) are observed. Observing vibrations of nanotubes by Raman spectroscopy Intense laser light excites vibrations in a nanotube. The photon energy h photon is reduced by the energy h photon of a vibrational mode.

TEM image of a multi wall nanotube (MWNT) filled with Sm 2 O 3. The horizontal lines are the concentric nanotubes, viewed edge-on. The Sm 2 O 3 crystal can be seen at the center. Filling of nanotubes

Nano-peapods: Nanotubes filled with fullerenes

Graphene: A single sheet of graphite