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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 (sp2, sp3) with different bond geometry (planar, tetrahedral). sp2 sp3 -bonds + pz -bonds
Diamond3D sp3 Graphite,Graphene (= single sheet)2D sp2 Fullerene0D Nanotube1D
Diamondoids: The smallest possible diamonds Diamondoids are small nanocrystals of diamond with the surface passivated by hydrogen atoms.
Fullerenes Buckminster Fuller, father of the geodesic dome Buckminsterfullerene C60 has the same hexagon+pentagon pattern as a soccer ball. The pentagons (highlighted) provide the curvature. C60 solution in toluene
Symmetry Fullerenes with increasing sizeFewer pentagons produce less curvature.
Production of fullerenes Plasma generation of fullerenes in a Krätschmer-Huffman apparatus. Mass spectrum showing the different fullerenes generated.
Formation of fullerenes during cooling of the plasma. Carbon clusters smaller than C60 are often short chains.
Molecular orbitals of C60 The LUMO (lowest unoccupied molecular orbital) is located at the five-fold rings: The high symmetry of C60 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 C60 (see next).
core level LUMO, located at the strained five-fold rings Empty orbitals of C60 from X-ray absorption spectroscopy (XAS) The continuous of * and * bands of graphite (top) become quantized into discrete levels (bottom). Terminello et al., Chem. Phys. Lett. 182, 491 (1991).
C60 can be charged with up to 6 electrons The ability to take up that much charge makes C60 a popular electron acceptor for molecular electronics, for example in organic solar cells.
Endo-fullerenesAn endofullerene is a fullerene with an atom (or molecule) inside.Terminology: Ti@C60
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,…). Lefebvre et al., PRL 90, 217401 (2003)
Carbon nanotube electronics 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).
Device containing several transistors on a single nanotube Transistors with a nanotube channel work better than silicon, but are difficult to mass-produce. Chen et al., Science 311, 1735 (2006)
Artist’s view of a futuristic transistor made of graphene, a single sheet of graphite gate channel source drain Electrons Geim and McDonald, Physics Today, August 2007, p. 35 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.
Vibrations of a single wall nanotube (SWNT) • Longitudinal acoustic mode • Transverse acoustic mode • Twisting (acoustic) mode • E2g(2) mode • A1g mode (radial breathing mode) • Calculated sound velocities are given for the acoustic modes. • D,E are Raman active (see next).
Observing vibrations of nanotubes by Raman spectroscopy Intense laser light excites vibrations in a nanotube. The photon energy hphoton is reduced by the energy hphoton of a vibrational mode. Raman spectrum of acid purified nanotube material. The Raman active E2g(2) and A1gmodes (G-band and D-band) are observed.
Filling of nanotubes TEM image of a multi wall nanotube (MWNT) filled with Sm2O3. The horizontal lines are the concentric nanotubes, viewed edge-on. The Sm2O3 crystal can be seen at the center.
