Publications by authors named "Alexander Croy"

15 Publications

  • Page 1 of 1

A nanographene disk rotating a single molecule gear on a Cu(111) surface.

Nanotechnology 2022 Jan 13. Epub 2022 Jan 13.

Institute for Materials Science, Technische Universität Dresden, Hallwachsstr. 3, Dresden, Sachsen, 01062, GERMANY.

We perform molecular dynamics simulations to study the collective rotation of a graphene nanodisk functionalized on its circumference by tert-butylphenyl chemical groups in interaction with a molecule-gear hexa-tert-butylphenylbenzene supported by a Cu(111) surface. The rotational motion can be categorized underdriving, driving and overdriving regimes calculating the locking coefficient of this machinery as a function of external torque applied. Moreover, the rotational friction with the surface of both the phononic and electronic contributions is investigated. It shows that for small size graphene nanodisks the phononic friction is the main contribution, whereas the electronic one dominates for the larger disks putting constrains on the experimental way of achieving the transfer of rotation from a graphene nanodisk to single molecule-gear.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6528/ac4b4bDOI Listing
January 2022

Multiscale Modeling Strategy of 2D Covalent Organic Frameworks Confined at an Air-Water Interface.

ACS Appl Mater Interfaces 2021 Jun 26;13(22):26411-26420. Epub 2021 May 26.

Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, 01062 Dresden, Germany.

Two-dimensional covalent organic frameworks (2D COFs) have attracted attention as versatile active materials in many applications. Recent advances have demonstrated the synthesis of monolayer 2D COF via an air-water interface. However, the interfacial 2D polymerization mechanism has been elusive. In this work, we have used a multiscale modeling strategy to study dimethylmethylene-bridged triphenylamine building blocks confined at the air-water interface to form a 2D COF via Schiff-base reaction. A synergy between the computational investigations and experiments allowed the synthesis of a 2D-COF with one of the linkers considered. Our simulations complement the experimental characterization and show the preference of the building blocks to be at the interface with a favorable orientation for the polymerization. The air-water interface is shown to be a key factor to stabilize a flat conformation when a dimer molecule is considered. The structural and electronic properties of the monolayer COFs based on the two monomers are calculated and show a semiconducting nature with direct bandgaps. Our strategy provides a first step toward the polymerization of 2D COFs at air-water interfaces capturing the initial steps of the synthesis up to the prediction of electronic properties of the 2D material.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.1c05967DOI Listing
June 2021

Olfactory Perception in Relation to the Physicochemical Odor Space.

Brain Sci 2021 Apr 28;11(5). Epub 2021 Apr 28.

Institute for Materials Science, Technische Universität Dresden, 01062 Dresden, Germany.

A growing body of research aims at solving what is often referred to as the in olfactory perception. Although computational efforts have made it possible to predict perceptual impressions from the physicochemical space of odors, studies with large psychophysical datasets from non-experts remain scarce. Following previous approaches, we developed a physicochemical odor space using 4094 molecular descriptors of 1389 odor molecules. For 20 of these odors, we examined associations with perceived pleasantness, intensity, odor quality and detection threshold, obtained from a dataset of 2000 naïve participants. Our results show significant differences in perceptual ratings, and we were able to replicate previous findings on the association between perceptual ratings and the first dimensions of the physicochemical odor space. However, the present analyses also revealed striking interindividual variations in perceived pleasantness and intensity. Additionally, interactions between pleasantness, intensity, and olfactory and trigeminal qualitative dimensions were found. To conclude, our results support previous findings on the relation between structure and perception on the group level in our sample of non-expert raters. In the challenging task to relate olfactory stimulus and percept, the physicochemical odor space can serve as a reliable and helpful tool to structure the high-dimensional space of olfactory stimuli. Nevertheless, human olfactory perception in the individual is not an analytic process of molecule detection alone, but is part of a holistic integration of multisensory inputs, context and experience.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/brainsci11050563DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8146962PMC
April 2021

Predicting the bulk modulus of single-layer covalent organic frameworks with square-lattice topology from molecular building-block properties.

Nanoscale 2021 Jan;13(2):1077-1085

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany. and Dresden Center for Computational Materials Science (DCMS), TU Dresden, 01062 Dresden, Germany.

Two-dimensional Covalent Organic Frameworks (2D COFs) have attracted a lot of interest because of their potential for a broad range of applications. Different combinations of their molecular building blocks can lead to new materials with different physical and chemical properties. In this study, the elasticity of different single-layer tetrabenzoporphyrin (H2-TBPor) and phthalocyanine (H2-Pc) based 2D COFs is numerically investigated using a density-functional based tight-binding approach. Specifically, we calculate the 2D bulk modulus and the equivalent spring constants of the respective molecular building-blocks. Using a spring network model we are able to predict the 2D bulk modulus based on the properties of the isolated molecules. This provides a path to optimize elastic properties of 2D COFs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0nr07666jDOI Listing
January 2021

Stabilization of aqueous graphene dispersions utilizing a biocompatible dispersant: a molecular dynamics study.

Phys Chem Chem Phys 2019 Nov 24;21(43):24007-24016. Epub 2019 Oct 24.

Institute for Materials Science and Max Bergmann Center for Biomaterials, Technische Universität Dresden, 01062 Dresden, Germany.

Flavin mononucleotide sodium (FMNS) was recently reported as a highly efficient dispersant for the exfoliation of defect-free, few-layer, stabilized aqueous graphene dispersions. Most importantly, FMNS is innocuous and eco-friendly and can facilitate biomedical applications of graphene. Complementing those experimental studies, the influence of FMNS molecules on the aggregation behavior of graphene flakes in solution is investigated via all-atom molecular dynamics simulations. The stabilizing role of FMNS is demonstrated by the potential of mean force calculations for pairs of graphene flakes covered by FMNS molecules. These results indicate that the optimal amount ratio between FMNS molecules and carbon atoms in monolayer graphene is about 0.026 leading to a surface coverage of 0.34 FMNS molecules per nm on the graphene flakes. Overall the simulations support the high efficiency of FMNS as a surfactant compared to other surfactants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9cp04742eDOI Listing
November 2019

Influence of Mesityl and Thiophene Peripheral Substituents on Surface Attachment, Redox Chemistry, and ORR Activity of Molecular Iron Porphyrin Catalysts on Electrodes.

Inorg Chem 2019 Aug 6;58(16):10637-10647. Epub 2019 Aug 6.

Faculty of Chemistry and Food Chemistry , Dresden University of Technology , 01062 Dresden , Germany.

Two iron porphyrin complexes with either mesityl (FeTMP) or thiophene (FeT3ThP) peripheral substituents were attached to basal pyrolytic graphite and Ag electrodes via different immobilization methods. By combining cyclic voltammetry and in-operando surface-enhanced Raman spectroscopy along with MD simulations and DFT calculations, their respective surface attachment, redox chemistry and activity toward electrocatalytic oxygen reduction was investigated. For both porphyrin complexes, it could be shown that catalytic activity is restricted to the first (few) molecular layer(s), although electrodes covered with thiophene-substituted complexes showed a better capability to consume the oxygen at a given overpotential even in thicker films. The spectroscopic data and simulations suggest that both porphyrin complexes attach to a Ag electrode surface in a way that maximum planarity and minimum distance between the catalytic iron site and the electrode is achieved. However, due to the distinctive design of the FeT3ThP complex, the thiophene rings are capable of occupying a conformation, via rotation around the bonding axis to the porphyrin, in which all four sulfur atoms can coordinate to the Ag surface. This effect creates a dense and planar surface coverage of the porphyrin on the electrode facilitating a fast (multi) electron transfer via several covalent Ag-S bonds. In contrast, bulky mesityl groups as peripheral substituents, which have been initially introduced to prevent aggregation and improve catalytic behavior , exert a negative effect on the overall electrocatalytic performance in the state as a less dense coverage and less stable interactions with the surface are formed. Our results underline the importance of rationally designed heterogenized molecular catalysts to achieve optimal turnover, which not only strictly applies to the here discussed oxygen reduction reaction but eventually holds also true for other energy conversion reactions such as carbon dioxide reduction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.inorgchem.9b00043DOI Listing
August 2019

Quantum Phonon Transport in Nanomaterials: Combining Atomistic with Non-Equilibrium Green's Function Techniques.

Entropy (Basel) 2019 Jul 27;21(8). Epub 2019 Jul 27.

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.

A crucial goal for increasing thermal energy harvesting will be to progress towards atomistic design strategies for smart nanodevices and nanomaterials. This requires the combination of computationally efficient atomistic methodologies with quantum transport based approaches. Here, we review our recent work on this problem, by presenting selected applications of the PHONON tool to the description of phonon transport in nanostructured materials. The PHONON tool is a module developed as part of the Density-Functional Tight-Binding (DFTB) software platform. We discuss the anisotropic phonon band structure of selected puckered two-dimensional materials, helical and horizontal doping effects in the phonon thermal conductivity of boron nitride-carbon heteronanotubes, phonon filtering in molecular junctions, and a novel computational methodology to investigate time-dependent phonon transport at the atomistic level. These examples illustrate the versatility of our implementation of phonon transport in combination with density functional-based methods to address specific nanoscale functionalities, thus potentially allowing for designing novel thermal devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/e21080735DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515264PMC
July 2019

Multi-scale approach for strain-engineering of phosphorene.

J Phys Condens Matter 2017 May 15;29(18):185702. Epub 2017 Mar 15.

Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.

A multi-scale approach for the theoretical description of deformed phosphorene is presented. This approach combines a valence-force model to relate macroscopic strain to microscopic displacements of atoms and a tight-binding model with distance-dependent hopping parameters to obtain electronic properties. The resulting self-consistent electromechanical model is suitable for large-scale modeling of phosphorene devices. We demonstrate this for the case of inhomogeneously deformed phosphorene drum, which may be used as an exciton funnel.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-648X/aa66d4DOI Listing
May 2017

Valence-force model and nanomechanics of single-layer phosphorene.

Phys Chem Chem Phys 2016 Aug;18(33):23312-9

Max-Planck-Institute for the Physics of Complex Systems, Dresden, Germany.

In order to understand the relation of strain and material properties, both a microscopic model connecting a given strain to the displacement of atoms, and a macroscopic model relating applied stress to induced strain, are required. Starting from a valence-force model for black phosphorous [Kaneta et al., Solid State Communications, 1982, 44, 613] we use recent experimental and computational results to obtain an improved set of valence-force parameters for phosphorene. From the model we calculate the phonon dispersion and the elastic properties of single-layer phosphorene. Finally, we use these results to derive a complete continuum model, including the bending rigidities, valid for long-wavelength deformations of phosphorene. This continuum model is then used to study the properties of pressurized suspended phosphorene sheets.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6cp04361eDOI Listing
August 2016

Comment on 'Parametrization of Stillinger-Weber potential based on a valence force field model: application to single-layer MoS2 and black phosphorus'.

Nanotechnology 2016 Jun 28;27(23):238001. Epub 2016 Apr 28.

Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, D-01187 Dresden, Germany.

We compare the simplified valence-force model for single-layer black phosphorus with the original model and recent ab initio results. Using an analytic approach and numerical calculations we find that the simplified model yields Young's moduli that are smaller compared to the original model and are almost a factor of two smaller than ab initio results. Moreover, the Poisson ratios are an order of magnitude smaller than values found in the literature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/27/23/238001DOI Listing
June 2016

Strain-tuning of vacancy-induced magnetism in graphene nanoribbons.

J Phys Condens Matter 2016 Feb 8;28(4):045302. Epub 2016 Jan 8.

Max-Planck-Institut für Physik komplexer Systeme, 01187 Dresden, Germany.

Vacancies in graphene lead to the appearance of localized electronic states with non-vanishing spin moments. Using a mean-field Hubbard model and an effective double-quantum dot description we investigate the influence of strain on localization and magnetic properties of the vacancy-induced states in semiconducting armchair nanoribbons. We find that the exchange splitting of a single vacancy and the singlet-triplet splitting for two vacancies can be widely tuned by applying uniaxial strain, which is crucial for spintronic applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0953-8984/28/4/045302DOI Listing
February 2016

Nonlinear phononics using atomically thin membranes.

Nat Commun 2014 Sep 10;5:4838. Epub 2014 Sep 10.

Department of Applied Physics, Chalmers University of Technology, S-41296 Göteborg, Sweden.

Phononic crystals and acoustic metamaterials are used to tailor phonon and sound propagation properties by utilizing artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein condensates in optical lattices. However, creating nonlinear phononic crystals or nonlinear acoustic metamaterials remains challenging and only few examples have been demonstrated. Here, we show that atomically thin and periodically pinned membranes support coupled localized modes with nonlinear dynamics. The proposed system provides a platform for investigating nonlinear phononics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms5838DOI Listing
September 2014

Fermi-Pasta-Ulam physics with nanomechanical graphene resonators: intrinsic relaxation and thermalization from flexural mode coupling.

Phys Rev Lett 2014 Apr 10;112(14):145503. Epub 2014 Apr 10.

Department of Mechanical Engineering, Boston University, Boston, Massachsetts 02215, USA.

Thermalization in nonlinear systems is a central concept in statistical mechanics and has been extensively studied theoretically since the seminal work of Fermi, Pasta, and Ulam. Using molecular dynamics and continuum modeling of a ring-down setup, we show that thermalization due to nonlinear mode coupling intrinsically limits the quality factor of nanomechanical graphene drums and turns them into potential test beds for Fermi-Pasta-Ulam physics. We find the thermalization rate Γ to be independent of radius and scaling as Γ∼T*/εpre2, where T* and εpre are effective resonator temperature and prestrain.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevLett.112.145503DOI Listing
April 2014

Suppression of photoionization by a static field.

Phys Rev Lett 2008 Oct 17;101(16):163002. Epub 2008 Oct 17.

Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa, Israel.

The dc field Stark effect is studied theoretically for atoms in high intensity laser fields. We prove that the first-order perturbation corrections for the energy and photoionization rate vanish when the dc field strength serves as a perturbational strength parameter. Our calculations show that by applying a dc field in the same direction as the polarization direction of the ac field, the photoinduced ionization rate is almost entirely suppressed. This suppression is attributed to changes in the phase shift of the continuum atomic wave functions which can be controlled by the dc field.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevLett.101.163002DOI Listing
October 2008
-->