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
STM as a writing tool
Maps of atoms or maps of electronic states?
Rotating molecules
Making and breaking molecules
Movies of molecular motion
Principle of operation of the
Scanning Tunneling Microscope
f tip
eVbias
fsample
Z = 5-10 Å
-A

I V. N(eV).ee
f .z
Z-resolution  0.1 pm
XY-resolution  100 pm
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
+/+1 V
-1 V
Transfer by
voltage pulses
Repulsive interaction manipulation:
Plowing:
Hammering:
AFM as a writing tool
Writen by Markus Heyde
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.
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
Imaging: acetylene on Pd(111) at 28 K
Molecular Image
Tip cruising altitude ~700 pm
Δz = 20 pm
H
C
C
H
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
TIP
pz
H
+
O
p orbital
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
1 cm
(± 1 μm)
Excitation of frustrated rotational modes in
acetylene molecules on Pd(111) at T = 30 K
Tip
e-
((( ) (
)))
Measuring the excitation rate
Pd
3
2
x
1
Pd
Pd
Pd
((( ) (
2
Pd
Center of molecule
Tip fixed at position 1:
V = 20 mV
-37mV
24
16
8
0
100
100
2,3
1.72 seconds
100 150 200 250 300 350 400 450
current (pA)
253 pA
10
1
0.1
0
50
1
150
50
32
)))
0
Log(Hops/s)
Current (pA)
200
rotations per second
Pd
0
-50
-100
-150
-200
Tip Bias (mV)
-250
-300
Excitation of translations of C2H2 molecules:
Rotation by electron excitation:
((( ) (
Tip
R = 94 M 
R = 150 M
z
z ~ -0.2 Å
R = 0.55 G 
z ~ +0.8 Å
z ~ - 1 Å
Translation by direct contact (orbital overlap):
R = 10.5 M 
Trajectories of molecule pushed by the tip
)))
Tip-induced dissociation of O2
No dissociation using low tunnel
current and low energy electrons
High dissociation rate at
high current and energy
tip
2 nm
2 nm
molecule
tip
Molecular oxygen at 30K
atom
TIP
Atomic oxygen
Tip electrons
2.58 eV
((( ) (
10-12
O2
2O
Lifetime =
s
-10
1 nA  10 s
)))
Equilibration of hot O atoms
Images at 1 nA, 100 mV
molecules
pairs of atoms
T = 43 K
I = 11 nA
Distribution of O-atoms after dissociation of several molecules
O-pair separation hystogram
18
12
3
2
1

2

Lifetime of O atoms in the excited state:
EOads ~ 4 eV; distance traveled ~  Pd lattices
   1 fs
 de-excitation mechanism is by creation of
e-h pairs in the Pd substrate
Positions color-coded for distance
Diffusion of water molecules on Pd(111)
a)
Atom-tracking
Movies
b)
Trajectory of the
tip following a
water molecule
water molecules
100
Hop rate(1/sec)
Atom -tracking
Hopping rate,
Movies
1
Energy barrier,
r = v·exp(-E/kT)
E = 126 ± 7 meV
(2.9 kcal/mol)
0.01
Attempt frequency, v = 1012.0 ± 0.6 s
0.0001
0.018
0.02
0.022
1/T(1/K)
0.024
0.026
-1
Clustering and diffusion at 40 K
2M
a
Dimer
b
diffusion coefficients at 40 K:
c
• monomer
• dimer
~ 0.0023 Å2/s
> 50 Å2/s
• trimer, tetramer ~ 1.02 Å2/s
5-H2O
Trimer
f
The most stable cluster: hexagonal
6-H2O
e
d
Why dimers move faster than monomers:
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