1. Amir A. Ahmad Zebari, Marek Kolmer and Jakub S. Prauzner-Bechcicki
STM tip-assisted engineering of molecular nanostructures: PTCDA islands on Ge(001):H surfaces
Beilstein Journal of Nanotechnology 2013, 4, 927–932
Abstract
Islands composed of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules are grown on a hydrogen passivated Ge(001):H surface. The islands are studied with room temperature scanning tunneling microscopy and spectroscopy. The spontaneous and tip-induced formation of the top-most layer of the island is presented. Assistance of the scanning probe seems to be one of the factors that facilitate and speed the process of formation of the top-most layer. PDF
2. Shigeki Kawai, Ali Sadeghi, Xu Feng, Peng Lifen, Re´my Pawlak, Thilo Glatzel, Alexander Willand, Akihiro Orita, Junzo Otera, Stefan Goedecker, Ernst Meyer
Obtaining Detailed Structural Information about Supramolecular Systems on Surfaces by CombiningHigh-Resolution Force Microscopy with ab Initio Calculations
ACS Nano, 2013, 7, 9098-9105
Abstract
State-of-the art experimental techniques such as scanning tunneling microscopy have great difficulties in extracting detailed structural information about molecules adsorbed on surfaces. By combining atomic force microscopy and Kelvin probe force microscopy with ab initio calculations, we demonstrate that we can obtain a wealth of detailed structural information about the molecule itself and its environment. Studying an FFPB molecule on a gold surface, we are able to determine its exact location on the surface, the nature of its bonding properties with neighboring molecules that lead to the growth of one-dimensional strips, and the internal torsions and bendings of the molecule. More
3. Amir A. Ahmad Zebari, Marek Kolmer, Jakub S. Prauzner-Bechcicki
Characterization of PTCDA nanocrystals on Ge(0 0 1):H-(2 × 1) surfaces
Applied Surface Science, 2015, 332, 403-408
Abstract
We analyze self-assembled nanocrystals of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) molecules on hydrogen passivated Ge(0 0 1) surfaces with use of scanning tunneling microscopy (STM) and spectroscopy (STS). At 0.7ML coverage, 2.1 nm high, elongated, hexagonal islands inclined at 37◦ with respect to the substrate row are mostly observed. By measuring the differential tunneling conductance, we observe an effect of electronic decoupling of the nanocrystals due to the introduced passivating layer. Finally, we shortly discuss the stability of the islands and their interaction with the scanning probe in the ultra-high vacuum environment. More
4. S. Godlewski, J. S. Prauzner-Bechcicki, T. Glatzel, E. Meyer. M. Szymoński
Transformations of PTCDA structures on rutile TiO2 induced by thermal annealing and intermolecular forces
Beilstein Journal of Nanotechnology 2015, 6, 1498–1507
Abstract
Transformations of molecular structures formed by perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules on a rutile TiO2 (110) surface are studied with low-temperature scanning tunnelling microscopy. We demonstrate that metastable molecular assemblies transform into differently ordered structures either due to additional energy provided by thermal annealing or when the influence of intermolecular forces is increased by the enlarged amount of deposited molecules. Proper adjustment of molecular coverage and substrate temperature during deposition allows for fabrication of desired assemblies. Differences between PTCDA/TiO2 (110) and PTCDA/TiO2 (011) systems obtained through identical experimental procedures are discussed.More
5. Res Jöhr, Antoine Hinaut, Rémy Pawlak, Ali Sadeghi, Santanu Saha, Stefan Goedecker, Bartosz Such, Marek Szymonski, Ernst Meyer, Thilo Glatzel
Characterization of individual molecular adsorption geometries by atomic force microscopy: Cu-TCPP on rutile TiO2 (110)
The Journal of Chemical Physics 143(9) (2015) 094202
Abstract
Functionalized materials consisting of inorganic substrates with organic adsorbates play an increasing role in emerging technologies like molecular electronics or hybrid photovoltaics. For such applications, the adsorption geometry of the molecules under operating conditions, e.g., ambient temperature, is crucial because it influences the electronic properties of the interface, which in turn determine the device performance. So far detailed experimental characterization of adsorbates at room temperature has mainly been done using a combination of complementary methods like photoelectron spectroscopy together with scanning tunneling microscopy. However, this approach is limited to ensembles of adsorbates. In this paper, we show that the characterization of individual molecules at room temperature, comprising the determination of the adsorption configuration and the electrostatic interaction with the surface, can be achieved experimentally by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate this by identifying two different adsorption configurations of isolated copper( ii) meso-tetra (4-carboxyphenyl) porphyrin (Cu-TCPP) on rutile TiO2 (110) in ultra-high vacuum. The local contact potential difference measured by KPFM indicates an interfacial dipole due to electron transfer from the Cu-TCPP to the TiO2. The experimental results are verified by state-of-the-art first principles calculations. We note that the improvement of the AFM resolution, achieved in this work, is crucial for such accurate calculations. Therefore, high resolution AFM at room temperature is promising for significantly promoting the understanding of molecular adsorption.
6. Rémy Pawlak, Laurent Marot, Ali Sadeghi, Shigeki Kawai, Thilo Glatzel, Peter Reimann, Stefan Goedecker, Hans-Joachim Güntherodt, Ernst Meyer
Chain-like structur elements in Ni 40 Ta 60 metallic glasses observed by scanning tunneling microscopy
Scientific Reports 5 (2015) 13143
Abstract
The structure of metallic glasses is a long-standing question because the lack of long-range order makes diffraction based techniques difficult to be applied. Here, we used scanning tunneling microscopy with large tunneling resistance of 6 GΩ at low temperature in order to minimize forces between probe and sample and reduce thermal fluctuations of metastable structures. Under these extremely gentle conditions, atomic structures of Ni40Ta60 metallic glasses are revealed with unprecedented lateral resolution. In agreement with previous models and experiments, icosahedral-like clusters are observed. The clusters show a high degree of mobility, which explains the need of low temperatures for stable imaging. In addition to icosahedrons, chain-like structures are resolved and comparative density functional theory (DFT) calculations confirm that these structures are meta-stable. The co-existence of icosahedral and chain-like structures might be an key ingredient for the understanding of the mechanical properties of metallic glasses.
7. Rémy Pawlak, Marcin Kisiel, Jelena Klinovaja, Tobias Meier, Shigeki Kawai, Thilo Glatzel, Daniel Loss, Ernst Meyer
Probing Atomic Structure and Majorana Wavefunctions in Mono-Atomic Fe-chains on Superconducting Pb-Surface
arXiv:1505.06078v2 [physics.atm-clus] 21 Aug 2015
Abstract
Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localization of MBSs is a key feature and crucial for their future implementation as qubits. Here, we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunneling microscopy (STM) and atomic force microscopy (AFM). We demonstrate that the Fe chains are mono-atomic, structured in a linear fashion, and exhibit zero-bias conductance peaks at their ends which we interprete as signature for a Majorana bound state. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localized at the chain ends (below 25 nm), with two localization lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum computing devices.
8, Piotr Olszowski, Łukasz Zając, Szymon Godlewski, Bartosz Such, Res Jöhr, Thilo Glatzel, Ernst Meyer, and Marek Szymonski
Role of a Carboxyl Group in the Adsorption of Zn Porphyrins on TiO2(011)-2×1 Surface
J. Phys. Chem. C, 2015, 119 (37), pp 21561–21566
Abstract
Adsorption of carboxylic-substituted Zn porphyrin molecules (COOH-ZnTPP) on the (011) surface of rutile TiO2 is examined by scanning tunneling microscopy at room temperature. The molecules are either flat, stabilized by the surface defects, or mobile with their movement limited to a reconstruction row of the substrate. Upon increasing the molecular coverage the molecules form 1D structures along the [1–10] direction, in which molecular boards are no longer parallel to the surface. This behavior is contrasted with the structures formed by Zn-TPP lacking the carboxylic group, which remain flat up to a monolayer coverage.
9. Res Jöhr, Lukasz Zajac, Gino Günzburger, Hubert Hug, Bartosz Such, Marek Szymonski, Ernst Meyer, Thilo Glatzel
Impact of Photocatalysis on Carotenoic Acid Dye-Sensitized Solar Cells
Hybrid Materials 2015; 2: 17–24
Abstract
Sensitized mesoporous titania is of increasing interest for catalysis and photovoltaic devices such as dye-sensitized solar cells (DSCs). For photovoltaic applications, the catalytic properties of TiO2 can cause degradation of the dyes during device fabrication. This is especially the case if natural sensitizers are used. We addressed this issue by fabrication of carotenoic acid sensitized solar cells under inert and ambient assembly conditions. The DSCs were investigated by currentvoltage and quantum efficiency measurements. Further characterization of the cells was made using impedance spectroscopy. The conversion efficiency of the DSCs prepared under inert conditions improved by at least 25% and the devices showed an enhanced reproducibility. The improvement of the DSCs correlated with the conversion efficiency of the sensitizers under inert conditions. We conclude that the photocatalytic bleaching depends on the electron injection efficiency of the sensitizer. Hence carotenoic acids support their own degradation. However, the photocatalytic decomposition of the sensitizers can be avoided by fabrication of the DSCs under inert conditions.
10. Łukasz Zając, Piotr Olszowski, Szymon Godlewski, Bartosz Such, Res Jöhr, Rémy Pawlak, Antoine Hinaut, Thilo Glatzel, Ernst Meyer, and Marek Szymonski
Ordered heteromolecular overlayers formed by metal phthalocyanines and porphyrins on rutile titanium dioxide surface studied at room temperature
The Journal of Chemical Physics 143, 224702 (2015)
Abstract
Molecular heterostructures are formed from meso-tetraphenyl porphyrins-Zn(ii) (ZnTPP) and Cu(ii)-phthalocyanines (CuPc) on the rutile TiO2(011) surface. We demonstrate that ZnTPP molecules form a quasi-ordered wetting layer with flat-lying molecules, which provides the support for growth of islands comprised of upright CuPc molecules. The incorporation of the ZnTPP layer and the growth of heterostructures increase the stability of the system and allow for room temperaturescanning tunneling microscopy(STM)measurements, which is contrasted with unstable STM probing of only CuPc species on TiO2. We demonstrate that within the CuPc layer the molecules arrange in two phases and we identify molecular dimers as basic building blocks of the dominant structural phase.
11. Lukasz Zajac, Piotr Olszowski, Szymon Godlewski, Lukasz Bodek, Bartosz Such, Res Jöhr, Remy Pawlak, Antoine Hinaut, Thilo Glatzel, Ernst Meyer, Marek Szymonski
Self-assembling of Zn porphyrins on a (110) face of rutile TiO2 – The anchoring role of carboxyl groups
Applied Surface Science 379 (2016) 277–281
Abstract
The ordering of zinc containing porphyrin molecules on surface of rutile TiO2(110)-(1×1) has been investigated using scanning tunneling microscopy (STM) in ultra-high vacuum at room temperature. It is demonstrated that a carboxylic group (COOH) has a profound impact on the immobilization of the molecules. At coverages below 0.1 monolayer only molecules equipped with the group COOH could be anchored to the surface and imaged with STM. At higher coverage both species, with and without the carboxyl substituent, assemble into ordered structures, forming complete monolayers. It is found, however, that the rhomboid unit cells of these structures exhibit differences in size.
Forthcoming publications
12. Bartosz Such, Thilo Glatzel, Shigeki Kawai, Sascha Koch, Remy Pawlak, Ernst Meyer, Jiří Míšek, Jana Vacek Chocholoušová, Jaroslav Vacek, Ivo Starý, Marek Szymonski, Irena G. Stará
“About the Role of Electrostatic Interactions in Self-Assembly of Enantiopure (Hetero)helicenes on the Ag(111) Surface”
To be submitted to: ACS Nano