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From an Atom to a Solid

3d. 4s. Energy below the Vacuum level (eV). From an Atom to a Solid.

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From an Atom to a Solid

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  1. 3d 4s Energy below the Vacuum level (eV) From an Atom to a Solid Photoemission spectra of negative copper clusters versus number of atoms in the cluster. The highest energy peak corres-ponds to the lowest unoccupied energy level of neutral Cu.Typically, there are two regimes:1) For <102 atoms per cluster, the energy levels change rapidly when adding a single atom (e. g. due to spin pairing).2) For >102 atoms per cluster, the energy levels change continuously (e. g. due to the electric charging energy (next slide).

  2. Energy Levels of Cu Clusters vs. Cluster Radius R Solid Atom ΔE=(E-ER)1/R (charged sphere)

  3. The Band Gap of Silicon Nanoclusters GaAs Bulk Silicon 3 nm : Gap begins to change

  4. The Band Gap of Silicon Nanoclusters 3 nm : Gap begins to change

  5. Increase of the Band Gap in Small Nanoclusters by Quantum Confinement Conduction Band Gap k2 k1 Valence Band

  6. Size Dependent Band Gap in CdSe Nanocrystals

  7. Photon Energy vs. Wavelength: h(eV) = 1240/(nm) The Band Gap of CdSe Nanocrystals Size: 

  8. Beating the size distribution of quantum dots Quantum dots formed by thin spots in GaAs layers

  9. Termination of nanocrystals Critical for their electronic behavior H-terminated Si nanocrystal: Electrons stay inside, passivation, long lifetime Oxyen atom at the surface: Electrons drawn to the oxygen Fluorine at the surface: Complex behavior From Giulia Galli’s group

  10. e- e- dot electrons Single Electron Transistor A single electron e- tunnels in two steps from source to drain through the dot. The dot replaces the channel of a normal transistor (below).

  11. Designs for Single Electron Transistors Large (≈m) for operation at liquid He temperature Small (10nm) for operation around room temperature Nanoparticle attracted electrostatically to the gap between source and drain electrodes. The gate is underneath.

  12. * * The elements of this Periodic Table are named after team members from NTT and Delft. Quantum Dots as Artificial Atoms in Two Dimensions Filling electron shells in 2D

  13. Magnetic Clusters “Ferric Wheel”

  14. Magnetic Nanoclusters in Biology

  15. The Holy Grail of Catalysis: Reactions at a Specific Nanoparticle Want this image chemically resolved. Have chemical resolution in micro-spectroscopy via X-ray absorption but insufficient spatial resolution. Fischer-Tropsch process converts coal to fuel using an iron catalyst. Di and Schlögl De Smit et al., Nature (2008)

  16. The Oxygen Evolving Complex 4 Mn + 1 Ca Instead of rare metals with 5d or 4d electrons, such as Pt, Rh, Ru,one finds plentiful 3d transition metals in bio-catalysts: Mn, Fe.Nature does it by necessity. Can we do that in artificial photosynthesis ?

  17. Biocatalysts = Enzymes Most biocatalysts consist of a protein with a small metal cluster at the active site. The activeFe6Mocenter of nitrogenase, Nature’s efficient way of fixing nitrogen.

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