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Scanning Tunnelling
Microscopy Group
STM Research at the LCN
Research Application 1
Research Application 2
Silicon Nanotechnology
Acknowledgements
STM Group Members
Key Publications
Work funded by
Magnetic Nanostructures
• In addition to individual magnetic atoms, we also study
single molecule magnets (SMMs).
• SMMs can have a giant spin S and large magnetic
anisotropy D, which create an energy barrier U ≈ DS2
between the up and down spin orientations.
• Using STM-based spectroscopy, we can probe the spin
state and the anisotropy of an individual molecular spin. A three dimensional STM image of a Dy bis-Phthalocyanine
molecule on Cu (100)
Academic Staff
- Gabriel Aeppli, Department of Physics & Astronomy, UCL
- Neil Curson, Department of Electronic & Electrical Engineering, UCL
- Cyrus Hirjibehedin, Department of Physics & Astronomy and Department of Chemistry, UCL
- Steven Schofield, Department of Physics & Astronomy, UCL
Postdoctoral Staff
- Benjamin Bryant, UCL
- Reyes Calvo, UCL
- Fadi El Hallak, UCL
- Philipp Studer, UCL
PhD Students
- Jenny Oberg, Department of Physics & Astronomy, UCL
- Adam Rahnejat, Department of Physics & Astronomy, UCL
- Chris Rahnejat, Department of Physics & Astronomy, UCL
- Kitiphat Sinthiptharakoon, Department of Electronic &Electrical Engineering, UCL
- Ben Warner, Department of Physics & Astronomy, UCL
Dopants in Silicon
• Cross sectional STM, investigating the Si(211)-2x1 surface
• Individual Antimony and Bismuth dopants investigated
• Identified new, element dependent reconstructions
• Observed site dependant charge states
A three dimensional STM image of a Sb dopant in silicon
Key Publications
• Interplay between Kondo screening and the local environment for single and few atom spin structures [1,2]
• Exploring the process of oxygen migration in manganites [3]
• A model system for studying strain in silicon at the atomic scale [4]. This resulted in a patent disclosure [5]
• Organic semiconductors for flexible electronics and photovoltaic cells [6]
• Discovery of a charge density wave structure in a superconducting graphite intercalate [7]
• Structural and electronic properties of silicon and germanium surfaces [8,9]
• Interactions of organic molecules with the Si(001) surface [10,11]
1 Nature Physics 4, 847 (2008)
2 Phys. Rev. Lett. 103, 107203 (2009)
3 Nature Communications 2, 6 (2011)
4 Phys. Rev. B (2011)
5 Patent disclosure 1100248.2 (2011)
6 Appl. Phys. Lett. 98, 053302 (2011)
7 Nature Communications (2011)
8 J. Chem. Phys., 134 (2011) 064709
9 J. Chem. Phys., 133 (2010) 014703
10 Phys. Chem. Chem. Phys. 11 (2009) 2747,
11 J. Chem. Phys. 131 (2009) 104707
Ben Bryant
Research Application 2 Novel Materials
STM image of the surface of the stripe phase of CaC6.
• Graphitic systems have an electronic structure that can be
manipulated to yield a variety of electronic ground states.
• In superconducting CaC6, we have discovered a novel charge density
wave structure, which is linked to the onset of superconductivity in
other superconducting systems.
• This provides an exceptionally simple material – graphene – as a
starting point for understanding the relation between stripes and
superconductivity.
• Manganites are used extensively
as solid oxide fuel cell cathodes
• Oxygen adsorption and surface
exchange processes are critical
for catalytic action
• Scanning tunnelling microscope
images can show the dynamics of
oxygen adatoms at manganite
surfaces
Atomic resolution STM image of PrSr2Mn2O7 Oxygen adatoms and vacancies can be identified by STS
Cobalt Atoms on Cu2N Islands on a Cu(100) surface
Our group studies a broad range of
systems in a highly collaborative and
interdisciplinary environment, exploring
both basic science and applications
(1) Omicron Cryogenic STM
• Variable temperature (1.6K - 350K)
• Vector field (6T vertical, 1T in plane)
(2) Omicron LT/VT STM
• Variable temperature 3K - 900K
• Future upgrade to qPlus for STM/AFM
(3) Oxford STM
• Variable temperature (3K - 400K)
(2)
(3)
(1)
Organic Molecules on Silicon
Commercial low-temperature STM built by Omicron (Tmin ~ 4K)
It relies on the quantum mechanical
process of tunnelling. A potential difference
is applied between the sample and a very
sharp tip, and electrons are able to pass
between them to produce a small but
measurable current.
STM is a technique for probing the surface of a
solid with sufficient resolution (about 0.1 nm
laterally) to capture ‘ images ’ of individual
atoms.
• Magnetic nanostructures have interesting quantum properties
and play a central role in future data storage and computation
paradigms.
• We study the impact of the local environment on individual
magnetic spins at the atomic scale, including coupling to the
surface and interactions with nearby spins.
• Using the effects of the local environment, we can control and
engineer the quantum properties of spin systems.
1
2 3
4 5
2
3
4
5
1
Acetophenone (C8H8O) on a silicon (001) surface: STM image (left) and
calculated structural model (right). The bright protrusions in the image are
due to (1) pi-orbitals in the ring portion of the adsorbate, and (2-5) surface
dangling bonds that are enhanced by adsorption.
Controlled voltage ramps applied to individual
molecules by the STM tip can induce the adsorbate to
“stand up” (shown right). This occurs through
selective breakage of Si-C bonds and the dissociation
of H atoms to the surface. Such isolated and upright
molecules bring unique opportunities for single
molecule conductance measurements.
Silicon Nanotechnology Dopants in Silicon • Cross sectional STM, investigating the Si(111)-2x1 surface
• Individual Antimony and Bismuth dopants investigated
• Identified new, element dependent reconstructions
• Observed site dependant charge states
A three dimensional STM image of a Sb dopant in silicon
Organic Molecules on Silicon
Research Application 2
Ben Bryant
Research Application 2 Novel Materials
STM image of the surface of the stripe phase of CaC6.
• Graphitic systems have an electronic structure that can be
manipulated to yield a variety of electronic ground states.
• In superconducting CaC6, we have discovered a novel
charge density wave structure, which is linked to the onset
of superconductivity in other superconducting systems.
• This provides an exceptionally simple material – graphene –
as a starting point for understanding the relation between
stripes and superconductivity.
• Manganites are used extensively as solid
oxide fuel cell cathodes
• Oxygen adsorption and surface exchange
processes are critical for catalytic action
• Scanning tunnelling microscope images
can show the dynamics of oxygen adatoms
at manganite surfaces
Atomic resolution STM image of PrSr2Mn2O7
Oxygen adatoms and vacancies
can be identified by STS
Acknowledgements
Key Publications
• Single and few atom spin structures, which may be able to store one bit of information [1,2]
• Exploring the process of oxygen migration in manganites [3]
• A model system for studying strain in silicon at the atomic scale [4]. This has also resulted in a patent
disclosure [5]
• Organic semiconductors for flexible electronics and photovoltaic cells [6]
• Discovery of a charge density wave structure in a superconducting graphite intercalate [7]
• Structural and electronic properties of silicon and germanium surfaces [8,9]
• Interactions of organic molecules with the Si(001) surface [10,11]
1 Nature Physics 4, 847 (2008)
2 Phys. Rev. Lett. 103, 107203 (2009)
3 Nature Communications 2, 6 (2011)
4 Phys. Rev. B 84, 041306(R) (2011)
5 Patent disclosure 1100248.2 (2011)
6 Appl. Phys. Lett. 98, 053302 (2011)
7 Nature Communications (2011)
8 J. Chem. Phys. 134, 064709 (2011)
9 J. Chem. Phys. 133, 014703 (2010)
10 Phys. Chem. Chem. Phys. 11, 2747 (2009)
11 J. Chem. Phys. 131, 104707 (2009)
1
2
3
4
5
2
3
4
5
1
• Future electronic devices may use individual
molecules as functional components
• We use atomic-resolution imaging
and spectroscopy to study the
structural, chemical and electronic
properties of individual organic
molecules
• Controlled pulses to acetophenone
(left) cause it to ‘stand up’ (right)
