Joost W M Frenken
University of Amsterdam, Physics, Faculty Member
- Joost Frenken is the Director of the Advanced Research Center for Nanolithography (ARCNL) in Amsterdam, the Netherlan... moreJoost Frenken is the Director of the Advanced Research Center for Nanolithography (ARCNL) in Amsterdam, the Netherlands, and a professor of Physics at both universities in Amsterdam (UvA and VU). His scientific expertise is in the structure, diffusion, chemical reactions, phase transitions and friction phenomena at surfaces and interfaces, investigated with advanced instruments, developed under his supervision. His achievements have been recognized in several research awards and a membership of the KNAW, The Netherlands Royal Academy of Sciences. Frenken has (co)-initiated two companies, Leiden Probe Microscopy BV and Applied Nanolayers BV.edit
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The increase of chemical reactivity in curved graphene explains the reduction in friction for monolayer graphene over oxidized/unoxidized copper substrates.
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Friction between two surfaces is due to nanoand micro-asperities at the interface that establish true contact and are responsible for the energy dissipation. To understand the friction mechanism, often single-asperity model experiments... more
Friction between two surfaces is due to nanoand micro-asperities at the interface that establish true contact and are responsible for the energy dissipation. To understand the friction mechanism, often single-asperity model experiments are conducted in atomic-force microscopes. Here, we show that the conventional interpretation of the typical results of such experiments, based on a simple mass-spring model, hides a fundamental contradiction. Via an estimate of the order of magnitude of the dissipative forces required to produce atomic-scale patterns in the stick-slip motion of a frictional nano-contact, we find that the energy dissipation must be dominated by a very small, highly dynamic mass at the very end of the asperity. Our conclusion casts new light on the behavior of sliding surfaces and invites us to speculate about new ways to control friction by manipulation of the contact geometry.
The effect of a sequential oxidation and resulfidation treatment on γ-Al2O3 supported (Ni/Co)MoS2 catalyst nanoparticles was investigated using (HR)TEM, XPS, and thiophene HDS catalytic performance experiments. Analysis of the HRTEM... more
The effect of a sequential oxidation and resulfidation treatment on γ-Al2O3 supported (Ni/Co)MoS2 catalyst nanoparticles was investigated using (HR)TEM, XPS, and thiophene HDS catalytic performance experiments. Analysis of the HRTEM images revealed that, after initial sulfidation and oxidation, the resulfidation treatment restored the original slab length or increased it. The chemical composition of the samples, as determined by XPS, also slightly changed: the concentration of oxidic species increased, especially for the Ni promoter atoms. Comparing the catalytic HDS activity of the samples before and after the oxidation-resulfidation treatment showed that the catalysts were more than 20% more active after resulfidation. This increase in HDS activity is ascribed to a redistribution of the (Ni/Co)MoS2 slabs during the second sulfidation treatment, indicating a size effect.
Scanning Tunneling Microscopy is an excellent technique to image the surfaces of materials with extreme spatial resolution. However, it is difficult to maintain its imaging quality, when applying the technique under the conditions of many... more
Scanning Tunneling Microscopy is an excellent technique to image the surfaces of materials with extreme spatial resolution. However, it is difficult to maintain its imaging quality, when applying the technique under the conditions of many practical processes, such as chemical vapor deposition and catalysis. In this review article, we describe two special classes of STM instruments that are capable of maintaining good imaging quality under ‘difficult’ conditions, namely one for high and variable temperatures and the other for the combination of high temperatures and high gas pressures. In both cases, we discuss the special design features that make these instruments robust with respect to the challenging imaging conditions and provide examples to illustrate how they are applied.
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An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image... more
An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image model catalysts such as those consisting of metal nanoparticles on flat oxide supports in a gas atmosphere up to 6 bar and at a temperature up to 600 K, while the catalytic activity can be measured using mass spectrometry. The high-pressure reactor is placed inside an Ultrahigh Vacuum (UHV) system to supplement it with standard UHV sample preparation and characterization techniques. To demonstrate that this instrument successfully bridges both the pressure gap and the materials gap, images have been recorded of supported palladium nanoparticles catalyzing the oxidation of carbon monoxide under high-pressure, high-temperature conditions.
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We are grateful to Dr. B.N.J. Persson for his prompt attention to our work (Hu et al. in Tribol Lett, 10.1007/s11249-019-1247-7, 2020). In his Comment, he remarks (i) that near-critical damping of motion in/on solids, one of our main... more
We are grateful to Dr. B.N.J. Persson for his prompt attention to our work (Hu et al. in Tribol Lett, 10.1007/s11249-019-1247-7, 2020). In his Comment, he remarks (i) that near-critical damping of motion in/on solids, one of our main results, is well known for atoms and molecules at surfaces and (ii) that this result may be invalid for real practical cases (Persson in Tribol Lett, this issue). We fully agree with both statements. However, some discussion is justified.
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The origin of the friction between sliding bodies establishes an outstanding scientific problem. In this article, we demonstrate that the energy loss in each microscopic slip event between the bodies readily follows from the dephasing of... more
The origin of the friction between sliding bodies establishes an outstanding scientific problem. In this article, we demonstrate that the energy loss in each microscopic slip event between the bodies readily follows from the dephasing of phonons that are generated in the slip process. The dephasing mechanism directly links the typical timescales of the lattice vibrations with those of the experienced energy ‘dissipation’ and manifests itself as if the slip-induced motion were close to critically damped. Graphical abstract
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While continuum descriptions of oxide film growth are well established, the local structural dynamics during oxide growth are largely unexplored. Here, we investigate this using scanning tunneling microscopy (STM) and X-ray photoelectron... more
While continuum descriptions of oxide film growth are well established, the local structural dynamics during oxide growth are largely unexplored. Here, we investigate this using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) for the example of alumina film growth on NiAl(110) following NO2 exposure. To maintain a well-defined system, we have adopted a cyclic growth approach of NO2 adsorption and annealing. NO2 adsorption at 693 K results in the formation of a vacancy island pattern in the NiAl(110) substrate, which is filled with AlOx by diffusion of O through the alumina film. The patches of AlOx coalesce to form smooth terraces upon annealing to 1200 K. By repeated cycling, we have grown films of up to 0.9 nm thick. While peak shifts in the XPS spectra indicate that the film maintains its insulating character upon thickening, our STM data show that there is a finite density of states within the band gap. The thickening of the alumina film is accompa...
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Application of surface-science techniques, such as XPS, SXRD, STM, and IR spectroscopy under catalytic reactions conditions yield new structural and chemical information. Recent experiments focusing on CO oxidation over Pt and Pd model... more
Application of surface-science techniques, such as XPS, SXRD, STM, and IR spectroscopy under catalytic reactions conditions yield new structural and chemical information. Recent experiments focusing on CO oxidation over Pt and Pd model catalysts were reviewed.
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We have developed a new instrument combining a scanning probe microscope (SPM) and an X-ray scattering platform for ambient-pressure catalysis studies. The two instruments are integrated with a flow reactor and an ultra-high vacuum system... more
We have developed a new instrument combining a scanning probe microscope (SPM) and an X-ray scattering platform for ambient-pressure catalysis studies. The two instruments are integrated with a flow reactor and an ultra-high vacuum system that can be mounted easily on the diffractometer at a synchrotron end station. This makes it possible to perform SPM and X-ray scattering experiments in the same instrument under identical conditions that are relevant for catalysis.
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Using a MEMS nanoreactor in combination with a specially designed in situ Transmission Electron Microscope (TEM) holder and gas supply system, we imaged the formation of multiple layers of graphene encapsulating a cobalt nanoparticle, at... more
Using a MEMS nanoreactor in combination with a specially designed in situ Transmission Electron Microscope (TEM) holder and gas supply system, we imaged the formation of multiple layers of graphene encapsulating a cobalt nanoparticle, at 1 bar CO : N2 (1 : 1) and 500 °C. The cobalt nanoparticle was imaged live in a TEM during the Boudouard reaction. The in situ/operando TEM studies give insight into the behaviour of the catalyst at the nanometer-scale, under industrially relevant conditions. When switching from Fischer–Tropsch syngas conditions (CO : H2 : N2 1 : 2 : 3 at 1 bar) to CO-rich conditions (CO : N2 1 : 1 at 1 bar), we observed the formation of multi-layered graphene on Co nanoparticles at 500 °C. Due to the high temperature, the surface of the Co nanoparticles facilitated the Boudouard reaction, causing CO dissociation and the formation of layers of graphene. After the formation of the first patches of graphene at the surface of the nanoparticle, more and more layers grew ...
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Fischer-Tropsch synthesis is a heterogeneous catalytic reaction that creates approximately 2% of the world's fuel. It involves the synthesis of linear hydrocarbon molecules from a gaseous mixture of carbon monoxide and... more
Fischer-Tropsch synthesis is a heterogeneous catalytic reaction that creates approximately 2% of the world's fuel. It involves the synthesis of linear hydrocarbon molecules from a gaseous mixture of carbon monoxide and hydrogen at high pressures (from a few to tens of bars) and high temperatures (200-350 °C). To gain further insight into the fundamental mechanisms of this industrial process, we have used a purpose-built scanning tunnelling microscope to monitor a cobalt model catalyst under reaction conditions. We show that, after 30 minutes of reaction, the terraces of the cobalt catalyst are covered by parallel arrays of stripes. We propose that the stripes are formed by the self-assembly of linear hydrocarbon product molecules. Surprisingly, the width of the stripes corresponds to molecules that are 14 or 15 carbon atoms long. We introduce a simple model that explains the accumulation of such long molecules by describing their monomer-by-monomer synthesis and explicitly accounting for their thermal desorption.
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These two issues of Surface Review and Letters comprise papers presented at the Seventh In-ternational Conference on the Structure of Surfaces, which was held in Newcastle, New South Wales, Australia during the period 21–26 July 2002. This conference series brings together a broad range of surfac...more
ABSTRACT We report several direct observations of manifestations of capillary condensation in atomic-scale friction experiments. We have used a dedicated high-resolution friction force microscope to investigate the forces between a... more
ABSTRACT We report several direct observations of manifestations of capillary condensation in atomic-scale friction experiments. We have used a dedicated high-resolution friction force microscope to investigate the forces between a tungsten tip and a graphite surface under ambient conditions at a range of relative humidities. The velocity dependence of the friction shows a variety of new effects. We observe high friction and pronounced stick-slip instabilities with periods differing from those on graphite at very low scan velocities and moderate humidities. On the other hand, we see smooth sliding with strongly velocity dependent friction at higher humidities. We show that all aspects of the observed behavior can be interpreted in terms of capillary condensation of water, melting-freezing transitions and visco-elastic effects.