Discussion of the involvement of computer science students in a Computer Mediated Communucation c... more Discussion of the involvement of computer science students in a Computer Mediated Communucation created for distance learning. The different possibilities 'use of CMC to distance education and the reasons for doing so: Learning, Motivation, Socialist.' What 'more' important for students?
Two-dimensional (2D) metal-organic frameworks (MOFs) have been recently proposed as a flexible ma... more Two-dimensional (2D) metal-organic frameworks (MOFs) have been recently proposed as a flexible material platform for realizing exotic quantum phases including topological and anomalous quantum Hall insulators. Experimentally, direct synthesis of 2D MOFs has been essentially confined to metal substrates, where the strong interaction with the substrate masks the intrinsic electronic properties of the MOF. In addition to electronic decoupling from the underlying metal support, synthesis on weakly interacting substrates (e.g., graphene) would enable direct realization of heterostructures of 2D MOFs with inorganic 2D materials. Here, we demonstrate synthesis of 2D honeycomb MOFs on epitaxial graphene substrate. Using low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by density-functional theory (DFT) calculations, we show the formation of a 2D band structure in the MOF decoupled from the substrate. These results open the experimental path ...
Molecular self-assembly is a well-known technique to create highly functional nanostructures on s... more Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy (STM). The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials deposited on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly...
Field-emission resonances (FERs) can be used to map the work function of a conducting surface wit... more Field-emission resonances (FERs) can be used to map the work function of a conducting surface with a high spatial resolution. While FERs have been measured on different graphene systems, measurements on graphene transferred on insulating substrates have not been carried out previously. Here we have measured FERs on graphene transferred on hexagonal boron nitride (h-BN) and silicon dioxide (SiO2) substrates. We have also developed a simple 1D model that can be used to directly interpret the constant current spectroscopy experiments. On both surfaces, FERs can be used to map the local work function changes.
... 19. Saedi, A.; Berkelaar, RP; Kumar, A. Phys. Rev. B 2010, 82, 165306 [CrossRef]. 20. Berkela... more ... 19. Saedi, A.; Berkelaar, RP; Kumar, A. Phys. Rev. B 2010, 82, 165306 [CrossRef]. 20. Berkelaar, RP; S de, H.; Kumar, A. J. Phys. Chem. C 2011, 115, 2268 ...
Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are ... more Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are performed on heptathioether β-cyclodextrin (β-CD) self-assembled monolayers (SAMs) on Au. The β-CD molecules exhibit very rich dynamical behavior, which is not apparent in ensemble-averaged studies. The dynamics are reflected in the tunneling current-time traces, which are recorded with the STM feedback loop disabled. The dynamics are temperature independent, but increase with increasing tunneling current and sample bias, thus indicating that the conformational changes of the β-CD molecules are induced by electrons that tunnel inelastically. Even for sample biases as low as 10 mV, well-defined levels are observed in the tunneling current-time traces. These jumps are attributed to the excitations of the molecular vibration of the macrocyclic β-CD molecule. The results are of great importance for a proper understanding of transport measurements in SAMs.
The adsorption configurations of copper phthalocyanine (CuPc) molecules on platinum-modified Ge(0... more The adsorption configurations of copper phthalocyanine (CuPc) molecules on platinum-modified Ge(001) have been studied using scanning tunneling microscopy. After deposition at room temperature and cooling down to 77 K the CuPc molecules are still dynamic. However, after annealing ...
The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on ... more The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (β, δ, χ*, and φ) and one disordered phase (ε). We have determined the boundary free energies between the disordered and order phases by analyzing the thermally induced meandering of the domain boundaries. On the basis of these results, we are able to accurately predict the two-dimensional phase diagram of the decanethiolate/Au(111) system. The order-disorder phase transition of the χ* phase occurs at 295 K, followed by the order-disorder phase transition of the β phase at 325 K. Above temperatures of 325 K, only the densely packed φ and disordered ε phases remain. Our findings are in good agreement with the phase diagram of the decanethiolate/Au(111) system that was put forward by Poirier et al. [Langmuir 2001, 17 (4), 1176-1183].
Here, we show how a copper atom in a copperphthalocyanine (CuPc) molecule can be decoupled from i... more Here, we show how a copper atom in a copperphthalocyanine (CuPc) molecule can be decoupled from its environment. This is realized by trapping the CuPc molecule between two adjacent nanowires that are 1.6 nm apart. Using low-temperature scanning tunnelling microscopy and spectroscopy, the structural and electronic properties of CuPc in the stable "molecular bridge" configuration have been studied. Constant current and differential conductivity maps are recorded to reveal the spatial variation of the electronic structure of the cores and the lobes of CuPc molecules. The core of CuPc molecule is dim at low voltages, but suddenly becomes bright at a voltage of 5 V. Time-resolved scanning tunnelling microscopy measurements show that some of the CuPc lobes are very stable, while other lobes are very dynamic.
The POCKET project is building on the infrastructure provided by the Open University's OpenL... more The POCKET project is building on the infrastructure provided by the Open University's OpenLearn open educational repository. POCKET, the Project on Open Content for Knowledge Exposition and Teaching, is led by the University of Derby and partnered ...
Probing the electronic properties of an individual molecule is a far from trivial task. In order ... more Probing the electronic properties of an individual molecule is a far from trivial task. In order to measure, for instance, the conductance of a single molecule, the molecule must be contacted by two nanoscopic electrodes. Here we will give two examples of how a single molecule can be caught between two metallic electrodes. In the first example the conductance of a single octanethiol molecule is measured by trapping the molecule between an atomic Pt chain on a semiconductor surface and the apex of a scanning tunneling microscope tip. In the second example a Cu-phthalocyanine molecule is caught between two adjacent nanowires on a semiconductor surface. In this 'bridge' adsorption configuration the core of the CuPc molecule, i.e. the Cu atom, is fully decoupled from the underlying substrate. The electronic properties of the core of Cu-phthalocyanine molecule are probed with scanning tunneling spectroscopy.
ABSTRACT We report scanning tunneling microscopy (STM) and spectroscopy (STS) measurements on sin... more ABSTRACT We report scanning tunneling microscopy (STM) and spectroscopy (STS) measurements on single layer Ti0.87O2 nanosheets deposited on Pt(200 nm)/Si substrates. These nanosheets have a band gap of 3.8 eV and are virtually invisible in conventional STM images. However, an impressive contrast is observed in the di/dz map, which allows for a clear identification of the nanosheets. The di/dz signal is obtained by adding a high frequency, small amplitude modulation to the z-piezo using a lock-in amplifier.
Discussion of the involvement of computer science students in a Computer Mediated Communucation c... more Discussion of the involvement of computer science students in a Computer Mediated Communucation created for distance learning. The different possibilities 'use of CMC to distance education and the reasons for doing so: Learning, Motivation, Socialist.' What 'more' important for students?
Two-dimensional (2D) metal-organic frameworks (MOFs) have been recently proposed as a flexible ma... more Two-dimensional (2D) metal-organic frameworks (MOFs) have been recently proposed as a flexible material platform for realizing exotic quantum phases including topological and anomalous quantum Hall insulators. Experimentally, direct synthesis of 2D MOFs has been essentially confined to metal substrates, where the strong interaction with the substrate masks the intrinsic electronic properties of the MOF. In addition to electronic decoupling from the underlying metal support, synthesis on weakly interacting substrates (e.g., graphene) would enable direct realization of heterostructures of 2D MOFs with inorganic 2D materials. Here, we demonstrate synthesis of 2D honeycomb MOFs on epitaxial graphene substrate. Using low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by density-functional theory (DFT) calculations, we show the formation of a 2D band structure in the MOF decoupled from the substrate. These results open the experimental path ...
Molecular self-assembly is a well-known technique to create highly functional nanostructures on s... more Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy (STM). The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials deposited on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly...
Field-emission resonances (FERs) can be used to map the work function of a conducting surface wit... more Field-emission resonances (FERs) can be used to map the work function of a conducting surface with a high spatial resolution. While FERs have been measured on different graphene systems, measurements on graphene transferred on insulating substrates have not been carried out previously. Here we have measured FERs on graphene transferred on hexagonal boron nitride (h-BN) and silicon dioxide (SiO2) substrates. We have also developed a simple 1D model that can be used to directly interpret the constant current spectroscopy experiments. On both surfaces, FERs can be used to map the local work function changes.
... 19. Saedi, A.; Berkelaar, RP; Kumar, A. Phys. Rev. B 2010, 82, 165306 [CrossRef]. 20. Berkela... more ... 19. Saedi, A.; Berkelaar, RP; Kumar, A. Phys. Rev. B 2010, 82, 165306 [CrossRef]. 20. Berkelaar, RP; S de, H.; Kumar, A. J. Phys. Chem. C 2011, 115, 2268 ...
Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are ... more Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are performed on heptathioether β-cyclodextrin (β-CD) self-assembled monolayers (SAMs) on Au. The β-CD molecules exhibit very rich dynamical behavior, which is not apparent in ensemble-averaged studies. The dynamics are reflected in the tunneling current-time traces, which are recorded with the STM feedback loop disabled. The dynamics are temperature independent, but increase with increasing tunneling current and sample bias, thus indicating that the conformational changes of the β-CD molecules are induced by electrons that tunnel inelastically. Even for sample biases as low as 10 mV, well-defined levels are observed in the tunneling current-time traces. These jumps are attributed to the excitations of the molecular vibration of the macrocyclic β-CD molecule. The results are of great importance for a proper understanding of transport measurements in SAMs.
The adsorption configurations of copper phthalocyanine (CuPc) molecules on platinum-modified Ge(0... more The adsorption configurations of copper phthalocyanine (CuPc) molecules on platinum-modified Ge(001) have been studied using scanning tunneling microscopy. After deposition at room temperature and cooling down to 77 K the CuPc molecules are still dynamic. However, after annealing ...
The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on ... more The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (β, δ, χ*, and φ) and one disordered phase (ε). We have determined the boundary free energies between the disordered and order phases by analyzing the thermally induced meandering of the domain boundaries. On the basis of these results, we are able to accurately predict the two-dimensional phase diagram of the decanethiolate/Au(111) system. The order-disorder phase transition of the χ* phase occurs at 295 K, followed by the order-disorder phase transition of the β phase at 325 K. Above temperatures of 325 K, only the densely packed φ and disordered ε phases remain. Our findings are in good agreement with the phase diagram of the decanethiolate/Au(111) system that was put forward by Poirier et al. [Langmuir 2001, 17 (4), 1176-1183].
Here, we show how a copper atom in a copperphthalocyanine (CuPc) molecule can be decoupled from i... more Here, we show how a copper atom in a copperphthalocyanine (CuPc) molecule can be decoupled from its environment. This is realized by trapping the CuPc molecule between two adjacent nanowires that are 1.6 nm apart. Using low-temperature scanning tunnelling microscopy and spectroscopy, the structural and electronic properties of CuPc in the stable "molecular bridge" configuration have been studied. Constant current and differential conductivity maps are recorded to reveal the spatial variation of the electronic structure of the cores and the lobes of CuPc molecules. The core of CuPc molecule is dim at low voltages, but suddenly becomes bright at a voltage of 5 V. Time-resolved scanning tunnelling microscopy measurements show that some of the CuPc lobes are very stable, while other lobes are very dynamic.
The POCKET project is building on the infrastructure provided by the Open University's OpenL... more The POCKET project is building on the infrastructure provided by the Open University's OpenLearn open educational repository. POCKET, the Project on Open Content for Knowledge Exposition and Teaching, is led by the University of Derby and partnered ...
Probing the electronic properties of an individual molecule is a far from trivial task. In order ... more Probing the electronic properties of an individual molecule is a far from trivial task. In order to measure, for instance, the conductance of a single molecule, the molecule must be contacted by two nanoscopic electrodes. Here we will give two examples of how a single molecule can be caught between two metallic electrodes. In the first example the conductance of a single octanethiol molecule is measured by trapping the molecule between an atomic Pt chain on a semiconductor surface and the apex of a scanning tunneling microscope tip. In the second example a Cu-phthalocyanine molecule is caught between two adjacent nanowires on a semiconductor surface. In this 'bridge' adsorption configuration the core of the CuPc molecule, i.e. the Cu atom, is fully decoupled from the underlying substrate. The electronic properties of the core of Cu-phthalocyanine molecule are probed with scanning tunneling spectroscopy.
ABSTRACT We report scanning tunneling microscopy (STM) and spectroscopy (STS) measurements on sin... more ABSTRACT We report scanning tunneling microscopy (STM) and spectroscopy (STS) measurements on single layer Ti0.87O2 nanosheets deposited on Pt(200 nm)/Si substrates. These nanosheets have a band gap of 3.8 eV and are virtually invisible in conventional STM images. However, an impressive contrast is observed in the di/dz map, which allows for a clear identification of the nanosheets. The di/dz signal is obtained by adding a high frequency, small amplitude modulation to the z-piezo using a lock-in amplifier.
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