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

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 Content:

Principle of operation of the Scanning Tunneling Microscope IVNeVe Az  .().e.  Z-resolution  0.1 pm XY-resolution  100 pm Z = 5-10 Å

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

Repulsive interaction manipulation: Plowing: Hammering:

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. AFM as a writing tool Writen by Markus Heyde

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

C C H H Calculated image (Philippe Sautet)   orbital pzpz TIP H O + Imaging: acetylene on Pd(111) at 28 K Molecular Image Tip cruising altitude ~700 pm Δz = 20 pm Surface atomic profile Tip cruising altitude ~500 pm Δz = 2 pm 1 cm (± 1 μm) The STM image is a map of the pi-orbital of distorted acetylene 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 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

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

-37mV current (pA) rotations per second 1.72 seconds V = 20 mV ,3 Pd Measuring the excitation rate Tip fixed at position 1: Current (pA) ((( ) ( ))) x Center of molecule

Excitation of translations of C 2 H 2 molecules: R = 150 M  R = 94 M  R = 0.55 G  Rotation by electron excitation: R = 10.5 M  Translation by direct contact (orbital overlap):  z ~ +0.8 Å  z ~ -0.2 Å  z ~ - 1 Å Tip zz ((( ) ( ))) Trajectories of molecule pushed by the tip

Molecular oxygen at 30K 2 nm No dissociation using low tunnel current and low energy electrons molecule tip 2 nm Atomic oxygen High dissociation rate at high current and energy atom tip TIP O2O2 2O 2.58 eV Tip-induced dissociation of O 2 Tip electrons Lifetime = s 1 nA  s ((( ) ( )))

I = 11 nA T = 43 K Images at 1 nA, 100 mV Equilibration of hot O atoms molecules pairs of atoms   O-pair separation hystogram Lifetime of O atoms in the excited state: E Oads ~ 4 eV; distance traveled ~  Pd lattices    1 fs  de-excitation mechanism is by creation of e-h pairs in the Pd substrate Distribution of O-atoms after dissociation of several molecules Positions color-coded for distance

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

a bc d e f 2 M Dimer Trimer 5-H 2 O Clustering and diffusion at 40 K diffusion coefficients at 40 K: monomer ~ Å 2 /s monomer ~ Å 2 /s dimer > 50 Å 2 /s dimer > 50 Å 2 /s trimer, tetramer ~ 1.02 Å 2 /s trimer, tetramer ~ 1.02 Å 2 /s The most stable cluster: hexagonal 6-H 2 O Why dimers move faster than monomers:

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