Publications by authors named "van Der Molen SJ"
Article Synopsis
- In 2015, the Dutch research council implemented changes to address gender bias in their Talent Programme, which offers grants for researchers at different career stages.
- The study investigates whether these measures successfully eliminated gender disparities in grant funding by analyzing data from over 16,000 applications submitted since 2012.
- Findings reveal that female applicants now have a higher likelihood of receiving the initial Veni grant, indicating a shift in gender effects, although significant disparities persist in the later Vidi and Vici tiers.
Article Synopsis
- Single fluorescent molecules in host crystals are effective probes for studying dynamics at the nanoscale, particularly due to their fine optical linewidth at low temperatures.
- However, these linewidths significantly increase when molecules are near surfaces, with no 0-0 zero-phonon line (ZPL) observed on surfaces until now.
- This study successfully detects the 0-0 ZPL of terrylene molecules on hexagonal boron-nitride surfaces, showing improved spectral stability in molecules on annealed flakes compared to non-annealed ones.
Article Synopsis
- Connectomics, a method that utilizes large-volume serial electron microscopy, is an essential tool for understanding neural circuits.
- Current imaging techniques like transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have limitations in achieving synaptic resolution.
- The introduction of photoemission electron microscopy (PEEM) offers a new approach that combines fast imaging with high resolution, allowing for efficient circuit mapping in neuroscience.
The recent observation of correlated phases in transition metal dichalcogenide moiré systems at integer and fractional filling promises new insight into metal-insulator transitions and the unusual states of matter that can emerge near such transitions. Here, we combine real- and momentum-space mapping techniques to study moiré superlattice effects in 57.4° twisted WSe_{2} (tWSe_{2}).
View Article and Find Full Text PDFA new, complementary technique based on Photo Emission Electron Microscopy (PEEM) is demonstrated. In contrast to PEEM, the sample is placed on a transparent substrate and is illuminated from the back side while electrons are collected from the other (front) side. In this paper, the working principle of this technique, coined back-illuminated PEEM (BIPEEM), is described.
View Article and Find Full Text PDFArticle Synopsis
- The paper discusses a new cryogenic sample chamber designed for low energy electron microscopy (LEEM) and shares initial experimental findings.
- Modifications were made to the LEEM instrument to enable cooling mechanisms and minimize heat load, achieving sample temperatures as low as 15 K using liquid nitrogen and helium.
- Initial low-temperature LEEM experiments on a three-monolayer pentacene film revealed a significant decrease in electron beam damage at lower temperatures and changes in the LEEM-IV spectra, with explanations provided for these observations.
Article Synopsis
- The LEEM-IV spectra of few-layer graphene reveal specific energy minima that vary with the number of layers, while low-energy TEM spectra show transmission maxima at those corresponding energy levels.
- The observed patterns in both LEEM and TEM can be explained through electron wave function interference in an elastic scattering model.
- A new model is proposed that incorporates both elastic and inelastic scattering effects, allowing for a self-consistent extraction of Mean Free Path (MFP) values and a comparison with existing research.
Article Synopsis
- In 'magic angle' twisted bilayer graphene, a flat band leads to correlated insulating behavior and superconductivity, but the variable moiré structure affects device conductance.
- By employing aberration-corrected Low Energy Electron Microscopy, researchers found smaller spatial variations in the moiré pattern than earlier studies and observed thermal fluctuations of collective atomic displacements.
- The study determined that thermal annealing can reduce local disorder without any untwisting detected at temperatures up to 600°C, and identified edge dislocations that may reveal unique electronic properties.
Low-Energy Electron Irradiation Damage in Few-Monolayer Pentacene Films.
J Phys Chem C Nanomater Interfaces
December 2021
Crystalline films of pentacene molecules, two to four monolayers in thickness, are grown via in situ sublimation on silicon substrates in the ultrahigh vacuum chamber of a low-energy electron microscope. It is observed that the diffraction pattern of the pentacene layers fades upon irradiation with low-energy electrons. The damage cross section is found to increase by more than an order of magnitude for electron energies from 0 to 10 eV and by another order of magnitude from 10 to 40 eV.
View Article and Find Full Text PDFArticle Synopsis
- Transmission electron microscopy at very low energy reduces damage to sensitive biological samples by using a modified setup with an additional electron source for imaging in the 0-30 eV range.
- The technique, demonstrated with materials like free-standing graphene, achieves imaging and spectroscopy in both transmission and reflection modes at nanometer resolution.
- Notable results include detailed images of gold nanoparticles and DNA origami rectangles, showing the potential of eV-TEM for safe, high-resolution imaging of biological samples.
For many complex materials systems, low-energy electron microscopy (LEEM) offers detailed insights into morphology and crystallography by naturally combining real-space and reciprocal-space information. Its unique strength, however, is that all measurements can easily be performed energy-dependently. Consequently, one should treat LEEM measurements as multi-dimensional, spectroscopic datasets rather than as images to fully harvest this potential.
View Article and Find Full Text PDFArticle Synopsis
- Extreme ultraviolet (EUV) lithography is a cutting-edge technology enabling the creation of tiny electronic circuits under 20 nm in size, with low-energy electrons (LEEs) playing a key role in this process.
- Researchers used advanced techniques like LEE microscopy, electron energy loss spectroscopy, and atomic force microscopy to examine how electrons in the range of 0-40 eV affect a specific EUV resist material, revealing that even very low-energy electrons can trigger significant chemical reactions.
- A proposed reaction model suggests that a small quantity of electrons (about 10 per molecule) is sufficient to render the resist material insoluble, aligning with the observed sensitivity of tin-oxo cage materials in EUV lithography.
In contrast to the in-plane transport electron mean-free path in graphene, the transverse mean-free path has received little attention and is often assumed to follow the "universal" mean-free path (MFP) curve broadly adopted in surface and interface science. Here we directly measure transverse electron scattering through graphene from 0 to 25 eV above the vacuum level both in reflection using low energy electron microscopy and in transmission using electronvolt transmission electron microscopy. From these data, we obtain quantitative MFPs for both elastic and inelastic scattering.
View Article and Find Full Text PDFArticle Synopsis
- Low-energy electron microscopy (LEEM) is used to measure the local work function of surfaces with high lateral resolution but can produce artifacts due to surface electrostatic fields.
- These artifacts occur near areas of work function discontinuities, extending hundreds of nanometers, and can lead to an overestimation of the true work function difference by 1.6 times when using standard analysis methods.
- Comparing LEEM data with ray-tracing simulations provides a more accurate estimate of work function differences, as demonstrated on a mixed-terminated strontium titanate surface.
The effects of exposure to ionizing radiation are central in many areas of science and technology, including medicine and biology. Absorption of UV and soft-x-ray photons releases photoelectrons, followed by a cascade of lower energy secondary electrons with energies down to 0 eV. While these low energy electrons give rise to most chemical and physical changes, their interactions with soft materials are not well studied or understood.
View Article and Find Full Text PDFArticle Synopsis
- Recent advancements have shown that molecular rectifiers can achieve high rectification ratios (RR), exceeding previous limits by utilizing unique top contacts and probing methods.
- A new device was developed that allows for a switchable RR, changing significantly (by over three orders of magnitude) in response to varying humidity levels, altering its current-voltage characteristics from symmetric to diode-like.
- This functionality relies on the interaction between two localized molecular orbitals that shift alignment due to humidity-induced displacement of counter ions, demonstrating humidity-controlled electronic behavior.
Article Synopsis
- Charge transport in many systems is influenced more by local features than by a single resistance measure, making understanding local electronic potential crucial for device analysis.
- A new low-energy electron microscopy (LEEM) potentiometry method has been developed that is fast, non-invasive, and allows for easy zooming and a large field of view.
- This method utilizes a mirror mode transition sensitive to local electrostatic surface potentials, enabling broader application across materials, and has been successfully demonstrated on Si(111) surfaces and metal-semiconductor junctions.
Article Synopsis
- Charge transport in systems often depends on local features rather than a single global resistance value, highlighting the need for techniques that map local electronic potentials.
- A new potentiometry method using low-energy electron microscopy (LEEM) has been developed, which is fast, has a large field of view, and is non-invasive, but is limited by the availability of characteristic reflectivity features in some materials.
- The paper introduces an alternative low-energy electron potentiometry (LEEP) method based on a universal mirror mode transition, which is effective for a wider range of materials, and demonstrates its application in analyzing electrostatic surface potential variations and the Schottky effect in metal-semiconductor junctions.
Article Synopsis
- High electron mobility is a crucial property of graphene, especially in its heterostructures with hexagonal boron nitride, widely used in research and applications.
- Despite the common assumption that the electronic states in these layered systems do not couple significantly, this study reveals that graphene and boron nitride bands show no interaction across a broad energy range.
- The angle-resolved reflected-electron spectroscopy method we utilized can be applied to investigate interactions in other van der Waals layered materials, enhancing our understanding of how electronic coupling contributes to the creation of novel materials.
By combining low-energy electron microscopy with in situ pulsed laser deposition we have developed a new technique for film growth analysis, making use of both diffraction and real-space information. Working at the growth temperature, we can use: the intensity and profile variations of the specular beam to follow the coverage in a layer-by-layer fashion; real-space microscopy to follow e.g.
View Article and Find Full Text PDFArticle Synopsis
- The electronic band structure of materials determines their properties by defining the allowed energy states for electrons.
- Measuring occupied bands is easy, but characterizing unoccupied bands (those above the Fermi level) has been challenging until now.
- The authors present a new technique using low-energy electron microscopy that can directly measure these unoccupied bands in graphene layers with high spatial resolution and potential application to various nanomaterials.
Charge transport measurements form an essential tool in condensed matter physics. The usual approach is to contact a sample by two or four probes, measure the resistance and derive the resistivity, assuming homogeneity within the sample. A more thorough understanding, however, requires knowledge of local resistivity variations.
View Article and Find Full Text PDFArticle Synopsis
- We are developing eV-TEM, a transmission electron microscope that operates at low electron energies (0-40 eV) to improve the study of thin samples.
- At these low energies, fewer energy loss pathways mean electrons can travel further without losing energy, enhancing the ability to observe interactions.
- The use of aberration correction techniques aims for spatial resolution at the nanoscale, making it ideal for studying delicate biological samples like proteins and cell membranes while reducing radiation damage.
Article Synopsis
- This study explores whether spin crossover molecules maintain their functionality when integrated into a device, specifically gold nanoparticle arrays featuring a specific room-temperature spin crossover molecule, Fe(S-BPP)2.
- Three experimental techniques—temperature-dependent Raman, magnetization measurements, and charge transport assessments—are employed to analyze the molecular-nanoparticle structures and confirm that spin transitions occur within the arrays.
- Results show a unique resistance minimum in temperature-resistance curves for the Fe(S-BPP)2 device, suggesting that this behavior is linked to spin transitions and differs from passive molecule networks, with theoretical backing indicating higher resistance in the high spin state compared to the low spin state.
Article Synopsis
- The paper discusses the electronic and optoelectronic properties of ordered nanoparticle arrays connected by molecular linkers, highlighting how these structures can enhance performance in various applications.
- It emphasizes the importance of molecular linkers in affecting the arrangement and interactions between nanoparticles, which can impact their overall functionality.
- The correction addresses potential errors or clarifications needed regarding the original findings, ensuring that the scientific community has accurate information for future research.