1. No category

International workshop
High-resolution AFM/STM imaging
23rd-24th February 2015, Prague, Czech Republic
Institute of Physics of the Czech Academy of Science
Location
Vila Lanna
V sadech 1/1
Prague 6 -Bubeneč
CZ-160 00
Local organizers
Pavel Jelínek
Martin Švec
Prokop Hapala
Sponsors
[email protected]
[email protected]
[email protected]
Scope of the workshop
The aim of the workshop is to bring together scientists to critically discuss experimental and
theoretical aspects of high-resolution images with functionalized probes. Following topics will
be addressed during the workshop:
1. Chemical resolution
(chairs: I. Swart, P. Liljeroth, P. Moriarty, N. Moll)
- Recognition of true bonds and their character (bond order; triple bonds)
- Recognition of chemical species
- Determination of chemically active sites on molecules
- Covalent vs. ionic bonds; what can HR imaging do for us? Are we able to resolve
ionicity of bonds?
2. Beyond the high-resolution imaging
(chairs: L. Gross, J. Repp, F. Giessibl, T. Glatzel, A. Schwarz)
- What can we learn from image distortions?
- Role of charge distribution on imaging (electrostatic forces); relation to KPFM; bias
dependent imaging
- Pauli repulsion and charge distribution
- Difference between Xe and CO-tip functionalization (charged tips); other
perspective tip-functionalization, stiff tip functionalization
- Subatomic resolution
- Towards fitting of semi-empirical potentials from 3D mapping
- Imaging unknown true 3D structures (bio-molecules)
- Towards high resolution imaging on "true" insulators (without the possibility to use
constant height mode)
3. Cross-correlation AFM with other channels STM, IETS-STM
(chairs: S. Tautz, R. Temirov, I. Pascual, A. Shluger, P. Grutter)
- Transducing information between different channels
- Commons and differences of AFM/STM/IETS-STM imaging
- What is about other vibration modes in IETS? Role of CO stiffness, current(bias) on
resolution;
- What can we learn from simultaneous AFM/STM? Application to new
systems/phenomena
- Dissipation signal: real physical meaning or artifacts of electronics?
- Technical aspects of high-resolution imaging & high-resolution imaging in 'extreme'
conditions (beyond LT, Si-cantilevers)
- Detection of lateral forces
- How can we quantify and exclude regulatory artifacts, coming from various
interacting feed-back loops [amplitude never exactly constant, input impedance of
current amplifier (esp. at high currents and high frequency)]
Program
The time schedule of the workshop is only tentative. Remember, the aim of the workshop
is to provide a platform for deep and stimulating discussions. Thus we encourage speakers to
prepare talk in way of addressing open questions, challenging the status or propose new
concepts related to high-resolution images. We suggest to keep the program only tentative
and make it really discussion forum instead or a series of regular talks. To fit to the
proposed format, we suggest following rules:
1/ encourage speakers to prepare talks in more informal way, addressing problems,
challenges and controversies instead of presenting regular results; keeping presentations
short as much as possible but still providing sufficient information to stimulate discussion;
2/ encourage audience to make questions during presentations as much as possible
3/ chairs of each topic will moderate/promote the discussion; first designated speaker of each
topic will try to make an introduction to given section
4/ the schedule might be adjusted during breaks according to necessity
Oral presentations
Computers dedicated for the presentations will
provide full compatibility with Microsoft Office (up to
2007), Adobe PDF (up to 2009) and standard
multimedia. It is a responsibility of every speaker to
check in advance that her/his presentation will be
displayed correctly by the conference projector; it
will be possible to do so before and after the end of
the sessions, during the breaks, etc. Optionally, it
will be also possible to connect own computers to
the projectors. However, it is the responsibility of the
speaker to ensure that the connection with a
personal computer is working properly before the
start of a given session.
Posters
• Dimensions of the poster boards 120 cm (height) x
100 cm (width)
• Fixing material (pins) will be available on site.
Wi-Fi connection
There will be Wi-Fi connection available during the
workshop.
SSID: lanna_AV
Password: Lanna123
Encryption: WPA
1
ORAL CONTRIBUTIONS
Probing the Polar Nature of Bonds by
means of Atomic Force Microscopy
Investigation of the surface termination of
BiTeI by combined STM/AFM
Florian Albrecht
Julian Berwanger
Kelvin probe force spectroscopy was used to characterize
the charge distribution of individual molecules with polar
bonds. Whereas this technique represents the charge distribution with moderate resolution for large tip-molecule
separations, it fails for short distances. Here we introduce
a novel local force spectroscopy technique, which allows one
to better disentangle electrostatic from other contributions
in the force signal. It enables obtaining charge maps at
even closer tip-sample distances where the lateral resolution is further enhanced. This enhanced resolution allows
one to even resolve the polar nature of individual bonds.
Cleaved BiTeI surfaces consist of domains which are either
terminated by Te or I. The size of these domains depends
on the bulk crystallinity of the sample and ranges from 100
µm to 100 nm. We observe smaller domains and find two
different step heights. The larger step height corresponds
to the height of a -Bi-Te-I- stack. The smaller step height
was also suggested to be a structural step caused by a stacking fault. In contrast, the atomically resolved STM/AFM
data of the smaller “step” suggests that this is indeed an
atomically flat layer. The observed step height in STM
is a purely electronic effect due to the different density of
states at the Fermi-level of Te- and I-terminated surfaces.
Thus we demonstrate that combined STM/AFM can help
to identify artifacts that mimic structural steps by density
of states effects.
High-Resolution Multichannel Scanning
Probe Microscopy: 3D Force Field
Spectroscopy, Tip Apex Identification, and
Cross-Talk
Atomic connectivities in graphene
nanostructure junctions
Mehmet Z Baykara
The controlled nano-structuring of graphene sheets will
be a key technology towards the application of graphenebased materials in future electronic devices. Only recently,
the synthesis of atomically precise graphene nanoribbons
(GNR) by surface-catalyzed reactions of suitably designed
precursor molecules was achieved [1, 2]. In this context
scanning probe microscopy plays an important role in the
investigation of the involved on-surface reactions and the
characterization of their products. Here, we report on the
structural and electronic characterization of junctions between atomically well-defined armchair GNRs, characterized by an armchair structure along the edge and 7 rows
of carbon atom pairs across the ribbon width (7-AGNR).
Once the produced GNRs come into close proximity to
each other, they can undergo cross-dehydrogenative coupling reactions and from more complex structures [3, 4].
We use low-temperature non-contact scanning probe microscopy with CO-functionalized tips and simultaneously
acquire the tunneling current in conjunction with tightbinding simulations to unravel the atomic connectivity at
the junction.
Thomas Dienel
High-resolution atomic force microscopy with complementary recording of the tunneling current offers the promise
of simultaneous characterization of the chemical reactivity and the electronic structure of surfaces on the atomic
scale. Using surface-oxidized copper (100) as a representative sample surface, we demonstrate in this talk that a comparative evaluation of the force and the tunneling current
channels in three spatial dimensions leads to the detection
of surface defects and the resulting modulation in chemical
interaction forces exhibited by individual atoms. While ab
initio calculations allow the structural and chemical identification of the tip apex and the defects, a large data set
of STM images obtained at various experimental settings
is utilized to uncover the details of complex STM contrast
formation mechanisms on metal oxides. Finally, the effect
of topography-feedback-induced cross-talk on multichannel
scanning probe microscopy experiments is analyzed.
1. L. Grill et al., Nature Nanotech. 2, 687-691 (2007).
2. J. Cai et al., Nature 466, 470 (2010).
3. M. Ijaes et al., Phys. Rev. B 88, 075429 (2013).
1
4. J. van der Lit et al., Nat. Commun. 4, 2023 (2013).
Metal Apex NCAFM High Resolution
Imaging of G/Pt(111)
Force Microscopy with Sub-Atomic
Resolution Reveals Internal Structure and
Adsorption Geometry of Small Iron
Clusters
Michael Ellner
A test of the capabilities of the AFM to obtain high resolution images are weakly coupled 2D systems such as
Graphene (G) on weakly interacting metals such as G/Pt
in which the G flake corrugates less than 2 pm [1]. In this
work we present long amplitudes ( 20 ˚
A) - cantilever based
LT-NCAFM measurements of G/Pt(111) which not only
yield atomic contrast on the G, but also the modulation of
the moir´
e patterns. Through DFT calculations, and a simple continuous model we rationalize the moir´
e contrast as
sensing small variations of the effective local stiffness of the
G arising from subtle differences in the G/Pt interaction,
possible due to the use of a metal tip which in the repulsive
regime is stiff enough as to deform the G, and in the attractive, reactive enough as to adhere to the G sheet. Our
results point out a new route to explore the local mechanical properties of low-dimensional weakly coupled systems.
Franz Giessibl
Clusters built from individual Fe atoms are investigated by
atomic force microscopy (AFM) with subatomic resolution,
revealing their internal structure as well as their bonding
and adsorption configuration. In the past, STM has been
considered to be the microscopy technique that provides the
greatest spatial resolution of atoms on surfaces. In STM,
small atom clusters appear as roughly Gaussian peaks with
an apparent height h determined by the number of atoms
N with h = 0.1 nm for a one atom Fe cluster, 0.15 nm
for two, 0.2 nm for three etc.. Here, we introduce AFM
with subatomic spatial resolution, where single Cu and Fe
adatoms appear as toroidal structures and multi-atom clusters appear as connected structures, showing each individual atom as a torus. For single adatoms, we find that the
toroidal shape of the AFM image reflects the bonding symmetry of the adatom to the underlying structure, showing
a torus with two bumps for Cu/Cu(110) and three bumps
for Fe/Cu(111).
1. M. M. Ugeda, et al. Phys Rev Lett. 107, 116803
(2011)
Manipulating single-molecule vibrational
spectroscopy using functionalized STM
tips
Challenges of Molecular Structure
Elucidation by AFM
Leo Gross
Aran Garcia-Lekue
AFM can assist in molecular structure elucidation [1-3].
Selecting suited molecules as model systems also bond
order, adsorption height, and charge distribution within
molecules were mapped on the atomic scale. However, the
AFM contrast relates to all these properties and for most
molecules the separation of the contributions is challenging. Moreover, element specific contrast – demonstrated
by AFM on semiconductor surfaces [4] – is highly desirable on molecules. To disentangle the different contributions of AFM contrast and to obtain chemical contrast on
molecules, improvements in experiment, theory, and simulations are needed. Approaches and challenges towards
these goals will be discussed.
The recent developments in high-resolution STM and AFM
imaging with functionalized tips calls for a detailed theoretical understanding of the role of the tip. Within this scenario, our earlier work on the effect of the STM tip on IETS
measurements acquires a renewed significance. In particular, we performed first-principle simulations of vibrational
spectra of a single CO molecule on Cu(111) using different
chemically modified tips, and we compared our results with
our previous simulations for a bare metallic Cu tip [2]. Our
results indicate that functionalized tips can increase the resolving power of IETS and can yield inelastic signals not
observed with a bare metallic tip. Such effects are originated by changes in the symmetry of the orbitals involved
in the inelastic scattering, and reveal that single molecule
IETS can be modulated by modifying the tip orbital symmetry.
1. L. Gross et al. Nature Chem. 2, 821 (2010)
2. K. O. Hanssen, et al. Angew. Chem. Int. Ed. 51,
12238 (2012)
1. A. Garcia-Lekue et al., PRB83, 155417(2011).
3. D. G. de Oteyza et al. Science 340, 1434 (2013)
2. L. Vitali et al., Nano Letters 10, 657(2010).
4. Y. Sugimoto et al. Nature 446, 64 (2007)
2
AFM with atomically defined tips
Open questions in the mechanical model of
High-resolution AFM
Peter Grutter
Prokop Hapala
AFM can experimentally image the structure of surfaces
with very high spatial resolution. Determination of structural information from this data needs theoretical modeling to compare to experimentally observed contrast. This
is challenging, in particular if other properties such as electrical conductivity should be determined simultaneously,
thus enabling powerful, quantitative structure-function relationships to be extracted from AFM experiments. On a
fundamental level the major reason why this is challenging
is because theoretical models need to make assumptions
and experiments typically don’t know enough atomic scale
details of the AFM tip, leaving substantial room for approximations. I will discuss the experimental challenges
in combining AFM/STM with field ion microscopy (FIM).
FIM allows the atomic scale characterization and manipulation of tips. I will discuss the particular challenges of
keeping a tip atomically well defined as it approaches and
interacts with the sample.
Many experimental high-resolution SPM images can be
reproduced with a numerical model based on pairwise
Lennard-Jones potential [1] combined with electrostatic
force field [2] if relaxation of probe particle is taken into
account. However, there are several observations, which
this model is unable to reproduce [3,4]. In this talk we will
discuss, which ingredients and aspects of the model need to
be improved in order to correct for the discrepancies. Can
the problem be solved by incorporation of Pauli repulsion,
which is dependent on actual electronic density as proposed
by Moll et al. [5]?
1. Hapala, P. et al. Phys. Rev. B 90, 085421 (2014).
2. Hapala, P. et al. Phys. Rev. Lett. 113, 226101
(2014).
3. Moll, N. et al. Nano Lett. (2014).
4. Guo, C. et al. J. Phys. Chem. C 141229184529007
(2014).
5. Moll, N. et al. New J. Phys. 14, 083023 (2012).
Intermolecular contrast in AFM images
without intermolecular bonds
Force field analysis of STM/AFM tips for
atomic manipulation
Sampsa H¨
am¨
al¨
ainen
Ferdinand Huber
Intermolecular features in recent atomic force microscopy
(AFM) images of organic molecules have been ascribed to
intermolecular hydrogen bonds. The experiments typically
use molecule modified AFM tips, where a single molecule
is picked up on the metallic AFM tip. We show that the
intermolecular features in the AFM images can also be explained by the flexibility of molecule-terminated tips. We
probe this effect by carrying out atomic force microscopy
experiments on a model system that contains regions where
intermolecular bonds should and should not exist between
close-by molecules. Intermolecular features are observed in
both regions, demonstrating that intermolecular contrast
cannot be directly interpreted as intermolecular bonds.
We study the physics of atomic manipulation of CO on a
Cu(111) surface by combined STM and AFM at liquid helium temperatures. In atomic manipulation, an adsorbed
atom or molecule is arranged on the surface using the interaction of the adsorbate with substrate and tip. While
previous experiments are consistent with a linear superposition model of tip and substrate forces, we find that the
force threshold depends on the force field of the tip. Here,
we use carbon monoxide front atom identification (COFI)
to characterize the tip’s force field. Tips that show COFI
profiles with an attractive center can manipulate CO in
any direction while tips with a repulsive center can only
manipulate in certain directions. The force thresholds are
independent of bias voltage in a range from 1 to 10 mV and
independent of temperature in a range of 4.5 to 7.5 K.
3
Intermolecular artefacts observed in 2D
C60 assemblies
Role of orbital structure in
High-resolution STM of molecules
Samuel Jarvis
Ondˇrej Krejˇc´ı
The question surrounding the origin of intermolecular features in scanning probe microscopy (SPM) has been under
debate since the first high-resolution images were revealed
using the STHM technique. More recently, intermolecular
features have also been observed with non-contact atomic
force microscopy (NC-AFM) with a number of reports examining the origins for apparent intermolecular features focussing on the role of tip flexibility. In this work we examine
hexagonally close-packed islands of highly non-planar C60
molecules adsorbed across a range of surface materials with
NC-AFM. At very small tip-sample distances, similar intermolecular resolution as previously reported is observed,
resulting in the appearance of distinct apparent intermolecular bonds. We discuss the origins of the intermolecular
contrast using a simple Lennard-Jones force-field model to
examine the relative contributions from tip-sample convolution and tip relaxation.
Recently, we demonstrated that most features visible in
high-resolution STM and AFM images can be explained
by simple mechanical model considering relaxation of an
atomistic particle attached to the tip. The simple model
for STM simulations considers only inter-atomic hoppings
between relaxed atomistic particle and molecule [1]. The
model is able to reproduce the main characteristics of highresolution STM maps in close distance regime where the relaxation effects prevail. But it fails at far distances, since it
neglects an electronic structure of the sample. In this work,
we implemented an efficient method for simulation of the
high resolution STM images considering the molecular electronic structure and the atomistic particle relaxation. The
method is able to reproduce observed contrast in both the
close and the far distance regimes. It gives solid theoretical background for better understanding of high resolution
STM experiments. [1]P. Hapala et al., Phys. Rev. B 90,
085421 (2014).
Chemical structures of organometallic
intermediate and carbon-carbon link in
on-surface chemical reaction
Probing single donor-acceptor molecules
on thin insulating films
Tobias Meier
Shigeki Kawai
The intramolecular charge transfer in fused DonorAcceptor molecules which strongly determines the device
performance of opto-electronics for example organic solar
cells is still poorly understood at the single molecular scale.
In this work we used the TTF-dppz, a planar and and piconjugated Donor-Acceptor molecule, adsorbed on thin layers of NaCl on Cu(111). By combining STM and AFM, we
spatially characterized the separation of the HOMO and
LUMO with respect to the chemical structure of the TTFdppz molecule observed by AFM. We further investigated
with force and current based spectroscopic techniques [1,2]
the electronic properties of the molecule and its charge redistribution. To gain more insights into the optical excitation of a single molecule, we are currently performing
spectroscopic measurements under illumination.
On-surface chemical reaction is a unique technique to synthesize polymers by linking carbon and carbon on solid
surfaces. However, the irreversible reaction usually leads
a low production yield. Thus, observing the intermediate
products is beneficial to control and understand the reaction. Here, we use a CO functionalized tip of atomic
force microscopy to study the Ullmann-type coupling, in
which the dehalogenation of iodine in precursor molecules
on Ag(111) induces the reaction. We found that the thermally sublimated molecules attack surface Ag atoms even
at below 150 K and consequently a short-lived C-Ag-I bond
forms. When two molecules meet each other, the dissociation of I induces the C-Ag-C organometallic bond. Further,
the Ag atom can desorb by annealing at 350 K, and hence
a C-C link establishes. We found that the Ag atom affects to bending and tilt angle and adsorption height of the
molecule.
1. R. Pawlak et al., Nano Lett. (2013).
2. S. Kawai et al., ACS Nano (2013).
4
Lateral forces determined by tuning fork
force microscopy?
Mapping Force-Fields for Molecular
Assemblies: Do We Really See Bonds?
Ernst Meyer
Philip Moriarty
Though the frequency shift of tuning fork force microscopy
is primarily related to normal force gradients, there are
some examples of experiments, which provide valuable information about lateral forces or energy barriers in the lateral direction. Either 2d- or 3d-frequency data are acquired
and transferred into force or energy fields by integration,
where instabilities limit the applicability of this method.
Alternatively, models are used, where the essential parameters are included to simulate the frequency shift data.
An example is given by the pulling of polymeric chains
on Au(111), where the detachment of the chain leads to
oscillations of the normal and lateral forces. The comparison with the model allows to determine the adhesive
energy per subunit of the molecular chain. Lateral manipulation gives insight about the movement of one dimensional chains on surfaces, which is close to the ideal of the
Frenkel-Kontorova model.
As Hapala et al. [1] and H¨
am¨
al¨
ainen and co-workers [2]
have both convincingly demonstrated, tip dynamics and
probe convolution can generate features in dynamic force
microscopy images which mimic ’expected’ intermolecular
structure. In this context, I shall discuss our experimental data and theoretical calculations (based on both density
functional theory and analytical approaches similar to Refs.
[1,2]) for two very different molecular systems: assemblies
of the planar NTCDI [3], and the spherical C60 molecule.
We focus on a quantitative analysis of the force-field and
potential energy surface associated with each system.
Image Distortions of Molecules in Atomic
Force Microscopy with Carbon Monoxide
Terminated Tips
Electrostatic properties of Xe and CO
terminated tips
1. P Hapala, et al, Phys. Rev. B 90, 085421 (2014)
2. Sampsa K. H¨
am¨
al¨
ainen, et al.t, Phys. Rev. Lett.
113 186102 (2014)
3. A. Sweetman et al., Nature Comm. 5 3931 (2014)
Martin Ondr´aˇcek
Nikolaj Moll
Atomic force microscopy and scanning tunneling microscopy with functionalized tips allow imaging of organic
molecules with sub-molecular resolution. Simple examples
of suitable tip terminations are a CO molecule or Xe atom
[G. Kichin et al., PRB 87, 081408(R); F. Mohn et al., Appl.
Phys. Lett. 102, 073109]. Proper interpretation of such experiments requires understanding of what forces act on the
tip and how the tip termination reacts to them [P. Hapala
et al., PRB 90, 085421]. Apart from attractive dispersion
forces and Pauli repulsion, electrostatic forces can also substantially contribute to the force field felt by the tip termination in the vicinity of the sample [P. Hapala et al., PRB
113, 226101]. I will present ab initio calculations which
strive to elucidate the main differences between the CO
and Xe terminations in terms of their electrostatic properties, such as charge distribution and electric polarizability.
Using functionalized tips, the atomic resolution of a single organic molecule can be achieved by atomic force microscopy (AFM) operating in the regime of short-ranged
repulsive Pauli forces while the van-der-Waals and electrostatic interactions only add a diffuse attractive background.
The underlying mechanisms of image distortions in AFM
with CO-terminated tips are identified and studied in detail. Parts of a molecule appear different in size, which
primarily originates from the charge density. Further, tilting of the CO at the tip, induced by van der Waals forces,
enlarges the apparent size of parts of the molecule by up
to 50
5
What is the orientation of the tip in a
scanning tunneling microscope?
STM/AFM study of Majorana bound
state in mono-atomic Fe chains on lead
Krisztian Palotas
R´emy Pawlak
We introduce a statistical correlation analysis method to
obtain information on the local geometry and orientation
of the tip used in scanning tunneling microscopy (STM)
experiments. The key quantity is the relative brightness
correlation of constant-current topographs between experimental and simulated data. This correlation can be analyzed statistically for a large number of tip geometries and
orientations in particular. Assuming a stable tip during
STM scans and based on the correlation distribution, it
is possible to determine the tip orientations that are most
likely present in an STM experiment, and exclude other
orientations. We illustrate the applicability of the method
considering the HOPG(0001) surface in combination with
tungsten tip models of different apex geometries in close to
20,000 orientations. We find that a blunt tip model provides better correlation with the experiment for a wider
range of tip orientations and bias voltages than a sharp tip
model.
Majorana fermions (MF) are fermionic particles which are
their own anti-particles. After more than 80 years search,
this elusive particle has been recently observed by STM at
the end of Fe chains deposited on lead [1]. In this contribution, the structure and electronic properties of such chains
on Pb(110) are compared by means of STM, AFM and
conductance mapping at low temperature. The conductance maps confirm the MF presence at the wire ends which
are also used to determine the decay length of its wavefunction. Interestingly, AFM imaging reveals the atomic
structure along the chain with an additional force signature at the MF location, that might result from its intrinsic
topological protection.
Force Spectroscopy at the Molecular Scale
Attempts to test an alternative
electrodynamic theory of superconductors
1. S. Nadj-Perge et al. Science 346, 602 (2014).
Nacho Pascual
Angelo Peronio
Force spectroscopy has extended our toolset for resolving electrostatic and mechanical properties of individual
molecules with sub-molecular resolution. This particularly
remarkable when combined with tunneling electron spectroscopy, because it allows us to identify charge distributions and conformational states and associated to a new
way of imaging surfaces and adsorbates. In this presentation, I will show several results comparing tunnel and
force spectroscopy of molecular system with a notable redistribution of their charge. First, the positioning a CO
molecule close to a C2H2 adsorbate leads to a redistribution of their charges, and dipolar contribution to their van
der Waals interaction. Second, we show that the charge
redistribution in a charge.-transfer salt – TCNQ/Na – is
detectable through KPFM. Third, KPFM is also sensitive
to the electric field induced transitions of a molecular adsorbate between two charge states.
An alternative form of London’s electrodynamic description
of superconductors has been hypothesized, which allows for
the presence of electric fields in their interior [1]. In this
theory, an applied electric field penetrates a superconductor up to the London penetration depth ( 50 nm), much
larger than the Thomas-Fermi screening length of a normal
metal ( 0.1 nm). We present an ongoing attempt to test
this theory by means of an AFM experiment [2].
1. J.E. Hirsch, Phys. Rev. B 69, 214515 (2004)
http://dx.doi.org/10.1103/PhysRevB.69.214515
2. J.E. Hirsch,
Physica C 508,
21 (2015)
http://dx.doi.org/10.1016/j.physc.2014.10.018
6
Chemical structure determination of
reactants, intermediates and products in
single-molecule reactions
Advantages of using metallic tips in AFM
imaging
Alexander Shluger
Alexander Riss
Recently we have demonstrated that using metallic tips for
noncontact atomic force microscopy (NC-AFM) imaging
at relatively large (¿0.5 nm) tip-surface separations provides a reliable method for studying molecules on insulating
surfaces with chemical resolution and greatly reduces the
complexity of interpreting experimental data. The experimental NC-AFM imaging and theoretical simulations were
carried out for the NiO(001) surface as well as adsorbed CO
and Co-Salen molecules using Cr-coated Si tips. By analyzing the experimental scanlines we could directly determine
the dipole moment of the Cr-coated tip and show that it
can be approximated by a point dipole. We will discuss
methods for characterizing the structure of common Si tips
and the application of these tips to imaging large adsorbed
molecules on insulating surfaces (e.g. CDB on KCl). Although the point dipole model still works, controlling such
tips is much more difficult than metallic tips.
The identification of the chemical structure of intermediates and products of chemical reactions is of huge importance in chemical synthesis. Complex reaction schemes
in organic chemistry, which often exhibit many competitive pathways, impede the use of ensemble-averaging spectroscopic techniques. In our studies we used non-contact
atomic force microscopy (nc-AFM) to track the bond rearrangements associated with surface-supported cyclization
reactions of single enediyne molecules. Determination of
the precise chemical structure of reactants, intermediates
and products, as well as their change in abundance allows
us to establish a fundamental understanding of the reaction mechanisms. Supported by theoretical simulations,
we show that the reaction kinetics are governed not only
by the potential energy landscape, but also by selective
energy dissipation to the substrate and entropic effects.
Contrast Formation on Adsorbed CO:
Pauli-Repulsion vs. Dipole-Dipole
Interaction
Boron-Doped Graphene Nanoribbons with
STM, AFM, DFT and MD
Peter Spijker
Alexander Schwarz
Boron (B) is a unique element in terms of electron deficiency, yet having a comparable size to carbon. Incorporation of B-atoms into an aromatic carbon framework like
graphene offers a wide variety of functionality. However,
the intrinsic instability of organoboron compounds has hindered the development of B-doped nanocarbon chemistry.
Controlling the coordination environment of the B-sites in
graphitic carbons is difficult, in contrast to the preparation of N-doped nanocarbons. Here we report the surfaceassisted bottom-up preparation of the B-doped graphene
nanoribbons (B-GNR) having uniform BC3 sites in periodic
structures. The use of an organoboron precursor enables
the programmed incorporation of the B-sites. Furthermore,
the B-GNRs are thermally fused at the armchair edges on
an gold surface, affording broader B-GNRs with 2D textures of the doping sites. The chemical and electronic structures are characterised by a combination of STM and AFM,
DFT and empirical calculations.
Single CO molecules have been used as tip termination to
achieve intramolecular resolution. They also have been
studied adsorbed on various flat surfaces, where they often exhibit a ring-like contrast, i.e., a repulsive interaction
in the center surrounded by an attractive interaction. Two
different interpretations have been proposed to explain the
repulsive interaction in the center: (i) Pauli-Repulsion between tip apex and CO molecule at small separations and
(ii) electrostatic repulsion due to the presence of localized
dipoles at the tip apex and the CO molecule, which point
with their positive pole towards each other. Here I will discuss both interpretations and argue that the electrostatic
dipole-dipole repulsion is probably more relevant in most
experimental situation and thus should be considered first.
Furthermore, one need to consider that non-pyramidal tip
apices can generate complex contrast patterns of electrostatic origin, leading to tip artifacts.
7
Imaging three-dimensional surface objects
with submolecular resolution by atomic
force microscopy
Scanning tunnelling microscopy with
single molecule force sensors
Stefan Tautz
Oleksandr Stetsovych
If the tunnelling junction of a scanning tunnelling microscope (STM) is functionalized with a nanoscale particle,
such as a hydrogen or carbon monoxide molecule or a xenon
atom, this particle effectively acts as a nanoscale force sensor. It senses forces stemming from the sample and transduces them into a measurable conductance signal. With
this hybrid AFM/STM method images can be obtained
that reveal the geometric structure of the substrate, very
similar to highest resolution non-contact dynamic AFM.
This contribution provides a survey of experimental results,
explains the mechanism, and discusses the prospects of this
novel scanning probe method.
Submolecular imaging by atomic force microscopy (AFM)
has recently been established as a stunning technique to reveal the chemical structure of unknown molecules, to characterise intramolecular charge distributions and bond ordering, as well as to study chemical transformations and
intermolecular interactions. So far, most of these feats
were achieved on planar molecular systems because highresolution imaging of three-dimensional (3D) surface structures with AFM remains challenging. Here we present a
method for high-resolution imaging of non-planar molecules
and 3D surface systems using AFM with silicon cantilevers
as force sensors. We demonstrate this method by resolving
the step-edges of the (101) anatase surface at the atomic
scale, by simultaneously visualising the structure of a pentacene molecule together with the atomic positions of the
substrate, and by resolving the contour and probe-surface
force field on a C60 molecule with intramolecular resolution.
Comparison of experimental 3D data
volumes with theory: extracting the
effective tip charge values
Chemical identification of atoms in an
organic molecule using high-resolution
AFM
ˇ
Martin Svec
Nadine van der Heijden
In this contribution, we will show an approach to compare
3D df data taken on the PTCDA/Ag(111) system, obtained
with a Xe-functionalized Ag tip. Two 3D experimental
data blocks are aligned and recalibrated by subtracting the
long-range contribution. Afterward, this data is registered
onto the theoretical datasets, generated using varying tip
charges and realistic experimental parameters. By finding
the best-matching pairs of the experiment and theory, we
are able to estimate the effective charge of the functionalized tip.
Scanning probe techniques, such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), can
provide detailed information about the geometric and electronic structure of surfaces and molecules with atomic spatial resolution. However, current methods lack one important capability essential to realize the full potential of these
techniques in molecular electronics and chemistry: sensitivity towards element, valence and functional group. Here,
we show that AFM combined with force-distance spectroscopy (FDS) and theoretical calculations can be used
to achieve this goal. The central idea is that the force versus distance spectra depend on the chemical nature of the
atom atop of which the spectrum is acquired. By acquiring
a 3D force grid over a model molecule, we demonstrate that
chemical sensitivity can indeed be obtained.
8
Determining power-law interactions with
LFM
Jay Weymouth
Many interactions between particles can be described by a
power law. Determining the power, however, is complicated
by two factors: a measure of absolute distance and isolation
of the short-range components. Lateral force microscopy
(LFM) is only sensitive to short-range interactions, and
can be used to determine absolute distances. We demonstrate this analysis on a CO molecule on Cu(111). The tip
was verified to be a single-atom metal tip with an STMbased COFI method, as proposed by Welker and Giessibl.
The interaction energy is shown to have a 1/r dependance.
Given the metal tip is known to end in a positive charge,
this implies that the CO molecule has a negative charge at
its apex.
9
2
POSTERS
Single Iron-Phthalocyanine molecules on
Fe/W(001): A non-contact atomic force
microscopy study at low temperature in
UHV
Intramolecular Dipole of Merocyanine
Probed by Local Contact Potential
Difference Measurements
Christian Lotze
Josef Grenz
While magnetic exchange force microscopy has been
achieved on various substrates, the detection of a magnetic
signal stemming from a single molecule employing atomic
force microscopy (AFM) has not been observed. Recent
work on Cobalt-Phthalocyanine on Fe/W(110) utilizing
spin-polarized STM revealed a strong hybridization of the
molecular orbitals and substrate 3d states depending on the
molecular adsorption, which affects their magnetic character. In this study we deposit single in gas phase paramagnetic Iron-Phthalocyanine molecules on Fe/W(001) and
find 7 different adsorption geometries using nc-AFM. Particularly, we were able to identify the adsorption sites of the
central Fe ion for the different geometries on the antiferromagnetic Fe monolayer on W(001), which will influence the
magnetic properties of the molecule in its adsorbed state.
In gas phase and solution 1,3,3-Trimethylindolino-6’nitrobenzopyrylospiran can be switched reversibly by light
and temperature to its merocyanine form. This form has
been shown to exhibit an intramolecular dipole [1]. When
adsorbed on a metal surface the switching back to the
spiropyran form is inhibited [2]. Charge redistribution and
screening may considerably alter the expected dipole behavior of the merocyanine form. Utilizing combined lowtemperature scanning tunneling microscopy and dynamic
atomic force microscopy, we characterize the adsorption of
merocyanine on Au(111). The intramolecular charge distribution is measured by the local contact potential difference
(LCPD) [3]. The vertical and lateral distribution of the
LCPD hints at the persistence of an intramolecular dipole.
1. Lapienis-Grochowska et al., JCS, Far.Trans. 2 1979,
75, 312
2. Marten Piantek et al., J. Am. Chem. Soc. 2009, 131,
12729
3. Mohn et al., Nature Nanotechnology 2012, 7, 227-231
In-situ homo-coupling and structural
identification of porphine dimers by AFM
STM and NC-AFM investigations of
Graphene on Ir(111)
Yuanqin He
Violeta Simic-Milosevic
An on-surface homo-coupling protocol between unsubstituted free-base porphine units yielding dimers, trimers, and
larger oligomers directly on a Ag(111) support has been recently reported [1]. The oligomers have been characterized
by a multitechnique approach combining scanning tunneling microscopy, near-edge X-ray absorption fine structure
and photoelectron spectroscopy complemented by theoretical modeling, however an atomically resolved study of the
resulting nanostructures is lacking. Thanks to the development of the frequency-modulated AFM, nanostructures
down to benzene rings can now be directly resolved. Here
we use a combined STM/AFM with a qPlus sensor to identify the resulting binding motifs. The results confirm the
models that were proposed on the basis of STM data, and
are a benchmark for our recently installed commercial ncAFM system.
We present the systematic investigations of the geometry, electronic structure and their effects on the observed
imaging contrast during STM and AFM experiments on
graphene/Ir(111). Microscopy experiments were performed
in constant current / constant frequency shift (CC/CFS)
and constant height (CH) modes, exploiting a combination
of the STM and NC-AFM capabilities of the SPM Aarhus
150 system. We found that in STM imaging the electronic
contribution is prevailing compared to the topographic one
and the inversion of the contrast can be assigned to the
particular features in the electronic structure of graphene
on Ir(111). Contrast changes observed in constant height
AFM measurements are analyzed on the basis of the energy,
force, and frequency shift curves, obtained in DFT calculations, reflecting the interaction of the W-tip with the surface and are attributed to the difference in the height and
the different interaction strength for high-symmetry cites
within the moir`
e unit cell
1. A. Wiengarten et al. J. Am. Chem. Soc., 136, 9346
(2014).
10
Direct Imaging of the Induced-Fit Effect
in Molecular Self-Assembly
Zechao Yang
We investigated the self-assembly of dicyanovinylhexathiophenes (DCV6T), a prototype molecule for highly
efficient organic solar cells, on Au(111) by using low
temperature scanning tunneling microscopy (STM) and
atomic force microscopy (AFM). DCV6T forms organic
islands and chains simultaneously on the surface, stabilized
by hydrogen bonding (and probably also electrostatic
interaction). In islands, the molecule adopts the most stable configuration in energy. While, the atomicly-resolved
AFM imaging reveals that the molecule is deformed
to an energetically unfavorable geometry by the linear
intermolecular hydrogen bonds upon self-assembly into
chains. On the other hand, the density functional theory
(DFT) calculations demonstrate that the deformation
of individual molecules optimizes the bonding structure,
therefore, contributes additional binding energy to the
whole system, which can be interpreted by the “Induced
Fit Effect”.
11
3
LIST OF PARTICIPANTS
Florian Albrecht
Mehmet Z Baykara
Julian Berwanger
[email protected]
[email protected]
[email protected]
Jana V. Chocholousova
[email protected]
J¨
urgen Chrost
Thomas Dienel
[email protected]
[email protected]
Janette Dunn
Michael Ellner
Shadi Fatayer
Giuseppe Foti
Thomas Frederiksen
Aran Garcia-Lekue
[email protected]
[email protected]
[email protected]
[email protected]
thomas [email protected]
[email protected]
Manuela Garnica Alonso
Franz Giessibl
Thilo Glatzel
Josef Grenz
[email protected]
[email protected]
[email protected]
[email protected]
Leo Gross
Peter Grutter
Sampsa H¨
am¨
al¨
ainen
Prokop Hapala
Ferdinand Huber
Yuanqin He
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Samuel Jarvis
Pavel Jelinek
Shigeki Kawai
Juergen Koeble
Krzysztof Ko´smider
Nils Krane
Ondˇrej Krejˇc´ı
Michael Krzyzowski
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Jeremy Leaf
Ioannis Lekkas
Peter Liljeroth
Jes´
us Rub´en L´
opez Redondo
Christian Lotze
Zsolt Majzik
Tobias Meier
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Ernst Meyer
Morten Moeller
[email protected]
[email protected]
Nikolaj Moll
[email protected]
12
University of Regensburg
Bilkent University
Institut f¨
ur Experimentelle und
Angewandte Physik, Universit¨
at
Regensburg
Institute of Organic Chemistry
and Biochemistry ASCR
Omicron Nanotechnology GmbH
Swiss Federal Laboratories for
Materials Science and Technology, Switzerland
University of Nottingham, UK
UAM
IBM Research - Zurich
Institute of Physics ASCR
DIPC, San Sebastian
DIPC (Donostia International
Physics Center)
Technische Universit¨at M¨
unchen
University of Regensburg
University of Basel, Switzerland
Institute of Applied Physics,
University of Hamburg
IBM Research - Zurich
McGill University
Aalto University
Institute of Physics ASCR
University of Regensburg
Physik Department E20, Technische Universit¨at M¨
unchen,
Germany
University of Nottingham
Institute of Physics ASCR
University of Basel, Switzerland
Omicron Nanotechnology GmbH
Institute of Physics ASCR
FU Berlin
Institute of Physics ASCR
CryoVac - Low Temperature
Technology GmbH and Co KG
University of Nottingham
University of Nottingham
Aalto University
Institute of Physics ASCR
FU Berlin
CIC NanoGune
Department of Physics, University of Basel
University of Basel, Switzerland
Group of Philip Moriarty, University of Nottingham
IBM Research - Zurich
Philip Moriarty
Pingo Mutombo
Martin Ondr´
aˇcek
Jo Onoda
Krisztian Palotas
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Nacho Pascual
R´emy Pawlak
Angelo Peronio
[email protected]
[email protected]
[email protected]
Pablo Pou
[email protected]
Andrea Raccanelli
[email protected]
Philipp Rahe
Jascha Repp
[email protected]
[email protected]
Alexander Riss
[email protected]
Pascal Ruffieux
Fabian Schulz
[email protected]
[email protected]
Alexander Schwarz
[email protected]
Alexander Shluger
Violeta Simic-Milosevic
[email protected]
[email protected]
Peter Spijker
[email protected]
Irena G. Stara
[email protected]
Ivo Stary
[email protected]
Oleksandr Stetsovych
Bartosz Such
[email protected]
[email protected]
ˇ
Martin Svec
Ingmar Swart
Stefan Tautz
[email protected]
[email protected]
[email protected]
Mykola Telychko
Ruslan Temirov
Markus Ternes
Jaroslav Vacek
[email protected]
[email protected]
[email protected]
[email protected]
Nadine van der Heijden
Jay Weymouth
Zechao Yang
[email protected]
[email protected]
[email protected]
13
University of Nottingham
Institute of Physics ASCR
Institute of Physics ASCR
Osaka University
Budapest University of Technology and Economics
CIC nanogune
Universit¨at Basel
Institut f¨
ur Experimentelle und
Angewandte Physik, Universit¨
at
Regensburg
Universidad
Autonoma
de
Madrid
CryoVac - Low Temperature
Technology GmbH and Co KG
University of Nottingham
University Regensburg, Germany
Institute of Applied Physics, Vienna University of Technology,
Austria
Empa
Aalto University School of Science, Espoo, Finland
Institute of Applied Physics,
University of Hamburg
University College London
SPECS Surface Nano Analysis
GmbH
Aalto University, Helsinki, Finland
Institute of Organic Chemistry
and Biochemistry ASCR
Institute of Organic Chemistry
and Biochemistry ASCR
Institute of Physics ASCR
Jagiellonian University, Krakow,
Poland
Institute of Physics ASCR
Utrecht University
Peter Gr¨
unberg Institut (PGI-3),
Forschungszentrum J¨
ulich 52425
J¨
ulich, Germany
Institute of Physics ASCR
Forschungszentrum J¨
ulich
MPI Stuttgart
Institute of Organic Chemistry
and Biochemistry ASCR
Utrecht University
University of Regensburg
Physical Department of Universit¨at Erlangen-N¨
urnberg (Results got at Freie Universit¨
at
Berlin)
Vladimir Zobac
[email protected]
Institute of Physics ASCR
14