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Imaging and manipulation of single atoms and molecules: the science of the nanoscale world

Imaging and manipulation of single atoms and molecules: the science of the nanoscale world. Miquel Salmeron. Materials Science Division Lawrence Berkeley National Laboratory University of California, Berkeley, CA. USA. Content:. How does STM work ? Principles of atomic manipulation

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Imaging and manipulation of single atoms and molecules: the science of the nanoscale world

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  1. Imaging and manipulation of single atoms and molecules: the science of the nanoscale world Miquel Salmeron Materials Science Division Lawrence Berkeley National Laboratory University of California, Berkeley, CA. USA

  2. Content: How does STM work ? Principles of atomic manipulation STM as a writing tool Maps of atoms or maps of electronic states? Rotating molecules Making and breaking molecules Movies of molecular motion

  3. f tip f sample eV bias Z-resolution  0.1 pm - f A . z µ I V . N ( eV ).e e XY-resolution  100 pm Principle of operation of the Scanning Tunneling Microscope Z = 5-10 Å

  4. ((( ) ( ))) +/- +1 V -1 V Using the STM tip as a tool for atomic scale manipulation Repulsion (push) Attraction (pull) We need to unravel the mechanisms of interaction between our probe tip and single atoms /molecules Vibrational excitation + Electric field Transfer by voltage pulses

  5. Repulsive interaction manipulation: Plowing: Hammering:

  6. AFM as a writing tool Herman Hesse poem "Stages“ written in PMMA from The Glass Bead Game; image size: 1.6 µm x 1.6 µm, height scale: 26 nm). The storage capacity is much higher than for the CD shown in the background at the same magnification. Writen by Markus Heyde

  7. Building structures atom-by-atom Building of a quantum “corral” with Fe atoms on Cu Xe atoms on Ni(110) STM images courtesy of Don Eigler, IBM, San Jose

  8. H C C H TIP pz H + O porbital 1 cm (± 1 μm) Imaging: acetylene on Pd(111) at 28 K Molecular Image Tip cruising altitude ~700 pm Δz = 20 pm Why don’t we see the Pd atoms? Because the tip needs to be very close to image the Pd atoms and would knock the molecule away Surface atomic profile Tip cruising altitude ~500 pm Δz = 2 pm Calculated image (Philippe Sautet) If the tip was made as big as an airplane, it would be flying at 1 cm from the surface and waving up an down by 1 micrometer The STM image is a map of the pi-orbital of distorted acetylene

  9. Tip e- ((( ) ( ))) Excitation of frustrated rotational modes in acetylene molecules on Pd(111) at T = 30 K

  10. 32 -37mV 24 rotations per second 16 ((( ) ( ))) 8 0 0 50 100 150 200 250 300 350 400 450 V = 20 mV 200 1 current (pA) 150 100 50 2,3 0 100 1.72 seconds 253 pA 10 Log(Hops/s) 1 0.1 0 -50 -100 -150 -200 -250 -300 Tip Bias (mV) Measuring the excitation rate Pd Pd 3 2 2 x 1 Pd Pd Pd Pd Center of molecule Tip fixed at position 1: Current (pA)

  11. ((( ) ( ))) Excitation of translations of C2H2 molecules: Rotation by electron excitation: Tip R = 0.55 G  R = 150 M R = 94 M  z ~ -0.2 Å z ~ +0.8 Å z z ~ - 1 Å Translation by direct contact (orbital overlap): R = 10.5 M  Trajectories of molecule pushed by the tip

  12. 2 nm tip molecule atom ((( ) ( ))) Tip electrons 2.58 eV TIP tip O2 2O Tip-induced dissociation of O2 No dissociation using low tunnel current and low energy electrons High dissociation rate at high current and energy 2 nm Molecular oxygen at 30K Atomic oxygen Lifetime = 10-12 s 1 nA  10-10 s

  13. I = 11 nA O-pair separation hystogram 18 12 3 2 2 Ö7 1 Ö3 Equilibration of hot O atoms Images at 1 nA, 100 mV molecules pairs of atoms T = 43 K Distribution of O-atoms after dissociation of several molecules • Lifetime of O atoms in the excited state: • EOads ~ 4 eV; distance traveled ~ Ö3Pd lattices •   1 fs • de-excitation mechanism is by creation of e-h pairs in the Pd substrate Positions color-coded for distance

  14. Diffusion of water molecules on Pd(111) Atom-tracking Movies Trajectory of the tip following a water molecule water molecules Hopping rate, r = v·exp(-E/kT) Energy barrier, E = 126 ± 7 meV (2.9 kcal/mol) Attempt frequency, v = 1012.0 ± 0.6 s -1

  15. Why dimers move faster than monomers: Clustering and diffusion at 40 K 2 M Dimer • diffusion coefficients at 40 K: • monomer ~ 0.0023 Å2/s • dimer > 50 Å2/s • trimer,tetramer ~ 1.02 Å2/s b c a 5-H2O Trimer e f d The most stable cluster: hexagonal 6-H2O

  16. Collaborators: Jim Dunphy Claude Chapelier Stefan Behler Anne Borg Mark Rose Toshi Mitsui Evgueni Fomin Frank Ogletree Markus Heyde Funding by the US Department of Energy

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