arXiv subjects

Henning Lebius

Publications and source records attributed to Henning Lebius.

8 recordsLinked to original sources

arXiv2026

Phenomenological Growth Regimes in Liquid-Precursor CVD of MoS$_2$ on Functional Substrates

The integration of two-dimensional transition-metal dichalcogenides (TMDCs) onto functional substrates remains constrained by stochastic vapor-phase growth dynamics. Here, we show that liquid-phase precursor chemical vapor deposition (CVD) of MoS$_2$ introduces growth conditions that are consistent with a substrate-influenced reaction-diffusion process. By utilizing pre-growth spin-coated MoO$_3$ intermediates across a diverse crystalline library (sapphire, SrTiO$_3$, rutile TiO$_2$, MgO, and 6H-SiC), we find that substrate-dependent variations in precursor wetting, surface chemistry, and inferred mass-transport constraints correlate with distinct growth morphologies. These substrate-dependent growth regimes are interpreted in terms of reduced effective lateral growth length on SrTiO$_3$, possible precursor anchoring on TiO$_2$, likely chemical surface restructuring on MgO, and possible step-edge growth on SiC. Raman and photoluminescence spectroscopy reveal substrate-dependent variations in vibrational and optical response that correlate with differences in strain, charge environment, and dielectric screening. Ultimately, this work highlights a substrate-dependent reaction-diffusion framework as a potentially useful route for tuning the structural and optical properties of large-area 2D materials.

cond-mat.mtrl-sci↗

arXiv2022

Mass transport via in-plane nanopores in graphene oxide membranes

Angstrom confined solvents in two-dimensional laminates travel through interlayer spacings, gaps between adjacent sheets, and via in plane pores. Among these, experimental access to investigate the mass transport through in plane pores is lacking. Here, we create these nanopores in graphene oxide membranes via ion irradiation with precise control over functional groups, pore size and pore density. Low ion induced pore densities result in mild reduction and increased water permeation for the membranes. Higher pore densities lead to pronounced reduction and complete blockage of pure water however allows permeation of ethanol water mixture due to weakening of hydrogen network. We confirm with simulations, that the attraction of the solvents towards the pores with functional groups and disruption of the angstrom confined hydrogen network is crucial to allow in plane pore transport.

cond-mat.mtrl-sci↗

arXiv2020

Graphene Effusion-based Gas Sensor

Porous, atomically thin graphene membranes have interesting properties for filtration and sieving applications because they can accommodate small pore sizes, while maintaining high permeability. These membranes are therefore receiving much attention for novel gas and water purification applications. Here we show that the atomic thickness and high resonance frequency of porous graphene membranes enables an effusion based gas sensing method that distinguishes gases based on their molecular mass. Graphene membranes are used to pump gases through nanopores using optothermal forces. By monitoring the time delay between the actuation force and the membrane mechanical motion, the permeation time-constants of various gases are shown to be significantly different. The measured linear relation between the effusion time constant and the square root of the molecular mass provides a method for sensing gases based on their molecular mass. The presented microscopic effusion based gas sensor can provide a small, low-power alternative for large, high-power, mass-spectrometry and optical spectrometry based gas sensing methods.

physics.app-ph↗

arXiv2015

SHIPS: A new setup for the investigation of swift heavy ion induced particle emission and surface modifications

The irradiation with fast ions with kinetic energies of > 10 MeV leads to the deposition of a high amount of energy along their trajectory (up to several ten keV/nm). The energy is mainly transferred to the electronic subsystem and induces different secondary processes of excitations which result in significant material modifications. A new setup to study these ion induced effects on surfaces will be described in this paper. The setup combines a variable irradiation chamber with different techniques of surface characterizations like scanning probe microscopy, time-of-flight secondary ion and neutral mass spectrometry, as well as low energy electron diffraction under ultra high vacuum conditions, and is mounted at a beamline of the universal linear accelerator (UNILAC) of the GSI facility in Darmstadt, Germany. Here, samples can be irradiated with high-energy ions with a total kinetic energy up to several GeVs under different angles of incidence. Our setup enables the preparation and in-situ analysis of different types of sample systems ranging from metals to insulators. Time-of-flight secondary ion mass spectrometry enables us to study the chemical composition of the surface, while scanning probe microscopy allows a detailed view into the local electrical and morphological conditions of the sample surface down to atomic scales. With the new setup particle emission during irradiation as well as persistent modifications of the surface after irradiation can thus be studied. We present first data obtained with the new setup, including a novel measuring protocol for time-of-flight mass spectrometry with the GSI UNILAC accelerator.

physics.ins-det↗

arXiv2009

Energy threshold for nanodot creation by swift heavy ions

We present theoretical and experimental data on the threshold behaviour of nanodot creation with swift heavy ions. A model calculation based on a two-temperature model taking the spatially resolved electron density into account gives a threshold of 12 keV/nm below which the energy density at the end of the track is no longer high enough to melt the material. In the corresponding experiments we irradiated SrTiO$_3$ surfaces under grazing incidence with swift heavy ions. The resulting chains of nanodots were analyzed by atomic force microscopy. In addition, samples irradiated under normal incidence were analyzed by transmission electron microscopy. Both experiments show two thresholds, connected to the appearance of tracks and to the creation of fully developed tracks, respectively. The threshold values are similar for surface and bulk tracks, suggesting that the same processes occur at glancing and normal incidence. The experimental threshold for the formation of fully developed tracks compares well to the value obtained by the theoretical description.

cond-mat.mtrl-sci↗

arXiv2008

Conductive nanodots on the surface of irradiated CaF2

CaF2(111) single crystal surfaces have been irradiated with swift heavy ions under oblique angles resulting in chains of nanosized hillocks. In order to characterize these nanodots with respect to their conductivity we have applied non-contact atomic force microscopy using a magnetic tip. Measurements in UHV as well as under ambient conditions reveal a clearly enhanced electromagnetic interaction between the magnetic tip and the nanodots. The dissipated energy per cycle is comparable to the value found for metals, indicating that the interaction of the ion with the target material leads to the creation of metallic Ca nanodots on the surface.

physics.atom-ph↗

arXiv2008

Swift heavy ion irradiation of SrTiO$_3$ under grazing incidence

The irradiation of SrTiO$_3$ single crystals with swift heavy ions leads to modifications of the surface. The details of the morphology of these modifications depends strongly on the angle of incidence and can be characterized by atomic force microscopy. At glancing angles, discontinuous chains of nanosized hillocks appear on the surface. The latent track radius can be determined from the variation of the length of the chains with the angle of incidence. This radius is material specific and allows the calculation of the electron-phonon-coupling constant for SrTiO$_3$. We show that a theoretical description of the nanodot creation is possible within a two-temperature model if the spatial electron density is taken into account. The appearance of discontinuous features can be explained easily within this model, but it turns out that the electronic excitation dissipates on a femtosecond time scale and thus too rapidly to feed sufficient energy into the phonon system in order to induce a thermal melting process. We demonstrate that this can be solved if the temperature dependent diffusion coefficient is introduced into the model.

cond-mat.mtrl-sci↗

arXiv2007

Creation of multiple nanodots by single ions

In the challenging search for tools that are able to modify surfaces on the nanometer scale, heavy ions with energies of several 10 MeV are becoming more and more attractive. In contrast to slow ions where nuclear stopping is important and the energy is dissipated into a large volume in the crystal, in the high energy regime the stopping is due to electronic excitations only. Because of the extremely local (< 1 nm) energy deposition with densities of up to 10E19 W/cm^2, nanoscaled hillocks can be created under normal incidence. Usually, each nanodot is due to the impact of a single ion and the dots are randomly distributed. We demonstrate that multiple periodically spaced dots separated by a few 10 nanometers can be created by a single ion if the sample is irradiated under grazing angles of incidence. By varying this angle the number of dots can be controlled.

cond-mat.mtrl-sci↗