Showing 1–16 of 16 results for author: Hansen, N

Velocity-tunable exciton-photon hybridization in cathodoluminescence

Authors: Sven Ebel, Martin Nørgaard, Christian Nicolaisen Hansen, N. Asger Mortensen, Sergii Morozov

Abstract: Exciton-photon hybridization is typically realised in geometrically defined optical cavities, where tunability is achieved by modifying either the cavity or the excitonic medium. Here we investigate transition-radiation interferences in suspended subwavelength films resembling a free-electron-defined resonance and explore their interaction with excitons in transition metal dichalcogenides. We demo… ▽ More Exciton-photon hybridization is typically realised in geometrically defined optical cavities, where tunability is achieved by modifying either the cavity or the excitonic medium. Here we investigate transition-radiation interferences in suspended subwavelength films resembling a free-electron-defined resonance and explore their interaction with excitons in transition metal dichalcogenides. We demonstrate that these resonances hybridize with excitonic transitions and can be tuned continuously by varying the electron energy. The resulting detuning depends on both film thickness and electron velocity, establishing the latter as an external and continuous knob for exciton-photon coupling. This approach enables tunable hybridization without structural modification and provides a free-electron-driven nanoscale platform for studying exciton-light interactions. △ Less

Submitted 16 March, 2026; originally announced March 2026.

Journal ref: Advanced Functional Materials 36, e76737 (2026)

Theoretical investigation of patterned two-dimensional semiconductors for tailored light--matter interactions

Authors: Christian Nicolaisen Hansen, Line Jelver, Christos Tserkezis

Abstract: We introduce theoretical methods for describing the optical response of two-dimensional (2D) materials patterned at the nanoscale into both arrays of ribbons along a planar surface and spherical particles. Fourier-Floquet decompositions of the electromagnetic fields are used in order to obtain the reflectance, transmittance and absorbance of the nanoribbon array. The spherical particles consist of… ▽ More We introduce theoretical methods for describing the optical response of two-dimensional (2D) materials patterned at the nanoscale into both arrays of ribbons along a planar surface and spherical particles. Fourier-Floquet decompositions of the electromagnetic fields are used in order to obtain the reflectance, transmittance and absorbance of the nanoribbon array. The spherical particles consist of a vacuum or dielectric core, coated by single 2D material layers. A Mie theory, with boundary conditions modified to accommodate a 2D material at the interface, is applied to theoretically examine these spherical particles. As examples of 2D materials, we consider the excitonic response of hexagonal boron nitride in the ultraviolet, and of the transition-metal dichalcogenide WS2 in the visible. The most important steps and equations for implementing the various methods are provided as a means to an easy introduction to the theory of patterned 2D materials. This renders the article a toolset for investigating the patterning of any 2D material with the intention to tune their optical response and/or introduce hybridization schemes with their excitons. The methods are not restricted to exciton polaritons in 2D semiconductors, but can be applied, by simple replacement of the optical conductivity, to 2D materials exhibiting any polaritonic response. △ Less

Submitted 15 December, 2025; originally announced December 2025.

An experimentally validated end-to-end framework for operando modeling of intrinsically complex metallosilicates

Authors: Jong Hyun Jung, Tom Schächtel, Yongliang Ou, Selina Itzigehl, Marc Högler, Niels Hansen, Johanna R. Bruckner, Blazej Grabowski

Abstract: Structurally and chemically complex materials such as amorphous metallosilicates underpin major catalytic and separation technologies, yet their intrinsic complexity challenges reliable atomistic modeling under realistic conditions. Consequently, simulations that connect composition to material properties remain largely inaccessible for these materials. Here, we enable quantitative operando atomis… ▽ More Structurally and chemically complex materials such as amorphous metallosilicates underpin major catalytic and separation technologies, yet their intrinsic complexity challenges reliable atomistic modeling under realistic conditions. Consequently, simulations that connect composition to material properties remain largely inaccessible for these materials. Here, we enable quantitative operando atomistic modeling of intrinsically complex materials through an experimentally validated end-to-end computational framework. The approach combines separation of simulation domains, lightweight machine-learning potentials trained on high-fidelity data, and large-scale de novo in silico synthesis that mimics experimental procedures. We apply the framework to realistic mesoporous SiO$_2$(Al$_2$O$_3$)$_{x/2}$ (0 $\leq x \leq$ 0.4) and validate the results experimentally. Simulations quantitatively reproduce multiple experimental observables, including bulk densities, pair distribution functions, infrared spectra, and hydroxyl densities. Beyond prediction, the framework enables analysis of acid sites and vibrations for catalytic and adsorption processes. By integrating simulation and experiment within a unified workflow, we advance the realism and reliability of atomistic modeling for intrinsically complex materials. △ Less

Submitted 13 April, 2026; v1 submitted 1 December, 2025; originally announced December 2025.

Comments: 20 pages, 8 figures, supplementary 34 pages

High-Yield Assembly of Plasmon-Coupled Nanodiamonds via DNA Origami for Tailored Emission

Authors: Niklas Hansen, Jakub Copak, Marek Kindermann, David Roesel, Federica Scollo, Ilko Bald, Petr Cigler, Vladimira Petrakova

Abstract: Controlling the spatial arrangement of optically active elements is crucial for the advancement of engineered photonic systems. Color centers in nanodiamond offer unique advantages for quantum sensing and information processing; however, their integration into complex optical architectures is limited by challenges in precise and reproducible positioning, as well as efficient coupling. DNA origami… ▽ More Controlling the spatial arrangement of optically active elements is crucial for the advancement of engineered photonic systems. Color centers in nanodiamond offer unique advantages for quantum sensing and information processing; however, their integration into complex optical architectures is limited by challenges in precise and reproducible positioning, as well as efficient coupling. DNA origami provides an elegant solution, as demonstrated by recent studies showcasing nanoscale positioning of fluorescent nanodiamonds and plasmonic gold nanoparticles. Here, we present a scalable and robust method for covalently functionalizing nanodiamonds with DNA, enabling high-yield, spatially controlled assembly of diamond and gold nanoparticles onto DNA origami. By precisely controlling the interparticle spacing, we reveal distance-dependent modulation of NV center photoluminescence with a 10-fold increase in the fastest decay pathway at short interparticle distances. Our findings indicate selective plasmon-driven effects and interplay between radiative and non-radiative processes. This work overcomes key limitations in current nanodiamond assembly strategies and provides insights into engineering NV photoluminescence by plasmonic coupling that advance toward quantum photonic and sensing applications. △ Less

Submitted 14 April, 2025; v1 submitted 2 April, 2025; originally announced April 2025.

Microstructural and Micromechanical Evolution of Olivine Aggregates During Transient Creep

Authors: Harison S. Wiesman, Thomas Breithaupt, David Wallis, Lars N. Hansen

Abstract: To examine the microstructural evolution that occurs during transient creep, we deformed olivine aggregates to different strains that spanned the initial transient deformation. Two sets of samples with different initial grain sizes of 5 $μ$m and 20 $μ$m were deformed in torsion at T = 1523 K, P = 300 MPa, and a constant shear strain rate of 1.5 $\times$ 10$^{-4}$ s$^{-1}$. Both sets of samples exp… ▽ More To examine the microstructural evolution that occurs during transient creep, we deformed olivine aggregates to different strains that spanned the initial transient deformation. Two sets of samples with different initial grain sizes of 5 $μ$m and 20 $μ$m were deformed in torsion at T = 1523 K, P = 300 MPa, and a constant shear strain rate of 1.5 $\times$ 10$^{-4}$ s$^{-1}$. Both sets of samples experienced strain hardening during deformation. We characterized the microstructures at the end of each experiment using high-angular resolution electron backscatter diffraction (HR-EBSD) and dislocation decoration. In the coarse-grained samples, dislocation density increased from 1.5 $\times$ 10$^{11}$ m$^{-2}$ to 3.6 $\times$ 10$^{12}$ m$^{-2}$ with strain. Although the same final dislocation density was reached in the fine-grained samples, it did not vary significantly at small strains, potentially due to concurrent grain growth during deformation. In both sets of samples, HR-EBSD analysis revealed that intragranular stress heterogeneity increased in magnitude with strain and that elevated stresses are associated with regions of high geometrically necessary dislocation density. Further analysis of the stresses and their probability distributions indicate that the stresses are imparted by long-range elastic interactions among dislocations. These characteristics indicate that dislocation interactions were the primary cause of strain hardening during transient creep. A comparison of the results to predictions from three recent models reveals that the models do not correctly predict the evolution in stress and dislocation density with strain for our experiments due to a lack of previous such data in their calibrations. △ Less

Submitted 6 July, 2024; originally announced July 2024.

Quantum-informed plasmonics for strong coupling: the role of electron spill-out

Authors: Ida Juliane Bundgaard, Christian Nicolaisen Hansen, P. Elli Stamatopoulou, Christos Tserkezis

Abstract: The effect of nonlocality on the optical response of metals lies at the forefront of research in nanoscale physics and, in particular, quantum plasmonics. In alkali metals, nonlocality manifests predominantly as electron density spill-out at the metal boundary, and as surface-enabled Landau damping. For an accurate description of plasmonic modes, these effects need be taken into account in the the… ▽ More The effect of nonlocality on the optical response of metals lies at the forefront of research in nanoscale physics and, in particular, quantum plasmonics. In alkali metals, nonlocality manifests predominantly as electron density spill-out at the metal boundary, and as surface-enabled Landau damping. For an accurate description of plasmonic modes, these effects need be taken into account in the theoretical modelling of the material. The resulting modal frequency shifts and broadening become particularly relevant when dealing with the strong interaction between plasmons and excitons, where hybrid modes emerge and the way they are affected can reflect modifications of the coupling strength. Both nonlocal phenomena can be incorporated in the classical local theory by applying a surface-response formalism embodied by the Feibelman parameters. Here, we implement surface-response corrections in Mie theory to study the optical response of spherical plasmonic--excitonic composites in core--shell configurations. We investigate sodium, a jellium metal dominated by spill-out, for which it has been anticipated that nonlocal corrections should lead to an observable change in the coupling strength, appearing as a modification of the width of the mode splitting. We show that, contrary to expectations, the influence of nonlocality on the anticrossing is minimal, thus validating the accuracy of the local response approximation in strong-coupling photonics. △ Less

Submitted 10 November, 2023; originally announced November 2023.

Journal ref: J. Opt. Soc. Am. B 41, 1144 (2024)

High speed microcircuit and synthetic biosignal widefield imaging using nitrogen vacancies in diamond

Authors: James L. Webb, Luca Troise, Nikolaj W. Hansen, Louise F. Frellsen, Christian Osterkamp, Fedor Jelezko, Steffen Jankuhn, Jan Meijer, Kirstine Berg-Sørensen, Jean-François Perrier, Alexander Huck, Ulrik Lund Andersen

Abstract: The ability to measure the passage of electrical current with high spatial and temporal resolution is vital for applications ranging from inspection of microscopic electronic circuits to biosensing. Being able to image such signals passively and remotely at the same time is of high importance, to measure without invasive disruption of the system under study or the signal itself. A new approach to… ▽ More The ability to measure the passage of electrical current with high spatial and temporal resolution is vital for applications ranging from inspection of microscopic electronic circuits to biosensing. Being able to image such signals passively and remotely at the same time is of high importance, to measure without invasive disruption of the system under study or the signal itself. A new approach to achieve this utilises point defects in solid state materials, in particular nitrogen vacancy (NV) centres in diamond. Acting as a high density array of independent sensors, addressable opto-electronically and highly sensitive to factors including temperature and magnetic field, these are ideally suited to microscopic widefield imaging. In this work we demonstrate such imaging of signals from a microscopic lithographically patterned circuit at the micrometer scale. Using a new type of lock-in amplifier camera, we demonstrate sub-millisecond (up to 3500 frames-per-second) spatially resolved recovery of AC and pulsed electrical current signals, without aliasing or undersampling. Finally, we demonstrate as a proof of principle the recovery of synthetic signals replicating the exact form of signals in a biological neural network: the hippocampus of a mouse. △ Less

Submitted 29 July, 2021; originally announced July 2021.

Adsorption of Light Gases in Covalent Organic Frameworks: Comparison of Classical Density Functional Theory and Grand Canonical Monte Carlo Simulations

Authors: Christopher Kessler, Johannes Eller, Joachim Gross, Niels Hansen

Abstract: A classical density functional theory (cDFT) based on the PC-SAFT equation of state is proposed for the calculation of adsorption equilibria of pure substances and their mixtures in covalent organic frameworks (COFs). Adsorption isotherms of methane, ethane, n-butane and nitrogen in the COFs TpPa-1 and 2,3-DhaTph are calculated and compared to results from grand canonical Monte Carlo (GCMC) simula… ▽ More A classical density functional theory (cDFT) based on the PC-SAFT equation of state is proposed for the calculation of adsorption equilibria of pure substances and their mixtures in covalent organic frameworks (COFs). Adsorption isotherms of methane, ethane, n-butane and nitrogen in the COFs TpPa-1 and 2,3-DhaTph are calculated and compared to results from grand canonical Monte Carlo (GCMC) simulations. Mixture adsorption is investigated for the methane/ethane and methane/n-butane binary systems. Excellent agreement between PC-SAFT DFT and GCMC is obtained for all adsorption isotherms up to pressures of 50 bar. The cDFT formalism accurately predicts the selective accumulation of longer hydrocarbons for binary mixtures in the considered COFs. This application shows substantial predictive power of PC-SAFT DFT solved in three-dimensional geometries and the results suggest the method can in the future also be applied for efficient optimization of force field parameters or of structural properties of the porous material based on an analytical theory as opposed to a stochastic simulation. △ Less

Submitted 23 March, 2021; originally announced March 2021.

The role of grain-environment heterogeneity in normal grain growth: a stochastic approach

Authors: Thomas Breithaupt, Lars N. Hansen, Srikanth Toppaladoddi, Richard F. Katz

Abstract: The size distribution of grains is a fundamental characteristic of polycrystalline solids. In the absence of deformation, the grain-size distribution is controlled by normal grain growth. The canonical model of normal grain growth, developed by Hillert, predicts a grain-size distribution that bears a systematic discrepancy with observed distributions. To address this, we propose a change to the Hi… ▽ More The size distribution of grains is a fundamental characteristic of polycrystalline solids. In the absence of deformation, the grain-size distribution is controlled by normal grain growth. The canonical model of normal grain growth, developed by Hillert, predicts a grain-size distribution that bears a systematic discrepancy with observed distributions. To address this, we propose a change to the Hillert model that accounts for the influence of heterogeneity in the local environment of grains. In our model, each grain evolves in response to its own local environment of neighbouring grains, rather than to the global population of grains. The local environment of each grain evolves according to an Ornstein-Uhlenbeck stochastic process. Our results are consistent with accepted grain-growth kinetics. Crucially, our model indicates that the size of relatively large grains evolves as a random walk due to the inherent variability in their local environments. This leads to a broader grain-size distribution than the Hillert model and indicates that heterogeneity has a critical influence on the evolution of microstructure. △ Less

Submitted 2 February, 2021; originally announced February 2021.

Comments: 24 pages, 8 figures, to be published in Acta Materialia

Biominerals with Texture Gradients are Functionally Graded Bioceramics Toughened by Stress Delocalization

Authors: David Wallis, Joe Harris, Corinna F. Böhm, Di Wang, Pablo Zavattieri, Patrick Feldner, Benoit Merle, Vitaliy Pipich, Katrin Hurle, Simon Leupold, Lars N. Hansen, Frédéric Marin, Stephan E. Wolf

Abstract: Biomineralizing organisms are widely noted and extensively studied due to their ability to generate structures exhibiting exceptional crystallographic control. Primarily, it is the organisms, such as sea-urchins or bivalves, that generate nearly single-crystalline biocrystals that have attracted attention. In contrast, biomineralizing organisms with seemingly disordered polycrystalline bio-armor h… ▽ More Biomineralizing organisms are widely noted and extensively studied due to their ability to generate structures exhibiting exceptional crystallographic control. Primarily, it is the organisms, such as sea-urchins or bivalves, that generate nearly single-crystalline biocrystals that have attracted attention. In contrast, biomineralizing organisms with seemingly disordered polycrystalline bio-armor have been left relatively unstudied. However, the crystalline ordering in the black-lipped pearl oyster, Pinctada margaritifera, reveals that biominerals with varying crystal textures are an unrecognized class of functionally graded materials. Changing crystal textures inevitably cause a variation in Young modulus due to the orientation-dependent mechanical properties of crystals. The case of Pinctada margaritifera demonstrates that bioceramics with such crystallographical gradients are toughened by stress delocalization and reduced stress intensity factors, outperforming non-graded counterparts. These findings suggest that a multitude of biominerals, which are perceived as poorly ordered because of their polycrystallinity and changing crystal textures, may be considered as graded materials with hitherto unidentified emergent mechanical properties. The underlying design principle is remarkably simple and applicable to a wide range of crystalline material classes and may thus serve as a blueprint for future bioinspired functional materials. △ Less

Submitted 13 August, 2020; originally announced August 2020.

Journal ref: Material Advances, 2022

Dislocation interactions in olivine control postseismic creep of the upper mantle

Authors: David Wallis, Lars N. Hansen, Angus J. Wilkinson, Ricardo A. Lebensohn

Abstract: Changes in stress applied to mantle rocks, such as those imposed by earthquakes, induce a period of evolution in viscosity and microstructure. This transient creep is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the intragranular accumulation of stresses among dislocations is the dominant cause of strain ha… ▽ More Changes in stress applied to mantle rocks, such as those imposed by earthquakes, induce a period of evolution in viscosity and microstructure. This transient creep is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the intragranular accumulation of stresses among dislocations is the dominant cause of strain hardening in olivine at low temperatures, raising the question of whether the same process contributes to transient creep at higher temperatures. Here, we demonstrate that olivine samples deformed at 25°C or 1150 to 1250°C both contain stress heterogeneities of ~1 GPa that are imparted by dislocations and have correlation lengths of ~1 micrometre. The similar stress distributions formed in both temperature regimes indicate that accumulation of stresses among dislocations also provides a contribution to transient creep at high temperatures. The results motivate a new generation of models that capture these intragranular processes and may refine predictions of evolving mantle viscosity over the earthquake cycle. △ Less

Submitted 9 June, 2020; originally announced June 2020.

Comments: 17 pages, 5 figures, 2 tables

Dislocation interactions during low-temperature plasticity of olivine strengthen the lithospheric mantle

Authors: David Wallis, Lars. N. Hansen, Kathryn M. Kumamoto, Christopher A. Thom, Oliver Plümper, Markus Ohl, William B. Durham, David L. Goldsby, David E. J. Armstrong, Cameron D. Meyers, Rellie Goddard, Jessica M. Warren, Thomas Breithaupt, Martyn R. Drury, Angus J. Wilkinson

Abstract: The strength of the lithosphere is typically modelled based on constitutive equations for steady-state flow. However, models of lithospheric flexure reveal differences in lithospheric strength that are difficult to reconcile based on such flow laws. Recent rheological data from low-temperature deformation experiments on olivine suggest that this discrepancy may be largely explained by strain harde… ▽ More The strength of the lithosphere is typically modelled based on constitutive equations for steady-state flow. However, models of lithospheric flexure reveal differences in lithospheric strength that are difficult to reconcile based on such flow laws. Recent rheological data from low-temperature deformation experiments on olivine suggest that this discrepancy may be largely explained by strain hardening. Details of the mechanical data, specifically the effects of temperature-independent back stresses stored in the samples, indicate that strain hardening in olivine occurs primarily due to long-range elastic interactions between dislocations. These interpretations provided the basis for a new flow law that incorporates hardening by development of back stress. Here, we test this hypothesis by examining the microstructures of olivine samples deformed plastically at room temperature either in a deformation-DIA apparatus at differential stresses of < 4.3 GPa or in a nanoindenter at applied contact stresses of > 10.2 GPa. High-angular resolution electron backscatter diffraction maps reveal the presence of geometrically necessary dislocations with densities commonly above 10$^{14}$ m$^{-2}$ and intragranular heterogeneities in residual stress on the order of 1 GPa in both sets of samples. Scanning transmission electron micrographs reveal straight dislocations aligned along slip bands and interacting with dislocations of other types that act as obstacles. The stress heterogeneities and accumulations of dislocations along their slip planes are consistent with strain hardening resulting from long-range back-stresses acting between dislocations. These results corroborate the mechanical data in supporting the form of the new flow law for low-temperature plasticity and provide new microstructural criteria for identifying the operation of this deformation mechanism in natural samples. △ Less

Submitted 18 September, 2019; originally announced September 2019.

Insight into the microphysics of antigorite deformation from spherical nanoindentation

Authors: Lars N. Hansen, Emmanuel C. David, Nicolas Brantut, David Wallis

Abstract: The mechanical behavior of antigorite strongly influences the strength and deformation of the subduction interface. Although there is microstructural evidence elucidating the nature of brittle deformation at low pressures, there is often conflicting evidence regarding the potential for plastic deformation in the ductile regime at higher pressures. Here, we present a series of spherical nanoindenta… ▽ More The mechanical behavior of antigorite strongly influences the strength and deformation of the subduction interface. Although there is microstructural evidence elucidating the nature of brittle deformation at low pressures, there is often conflicting evidence regarding the potential for plastic deformation in the ductile regime at higher pressures. Here, we present a series of spherical nanoindentation experiments on aggregates of natural antigorite. These experiments effectively investigate the single-crystal mechanical behavior because the volume of deformed material is significantly smaller than the grain size. Individual indents reveal elastic loading followed by yield and strain hardening. The magnitude of the yield stress is a function of crystal orientation, with lower values associated with indents parallel to the basal plane. Unloading paths reveal more strain recovery than expected for purely elastic unloading. The magnitude of inelastic strain recovery is highest for indents parallel to the basal plane. We also imposed indents with cyclical loading paths, and observed strain energy dissipation during unloading-loading cycles conducted up to a fixed maximum indentation load and depth. The magnitude of this dissipated strain energy was highest for indents parallel to the basal plane. Subsequent scanning electron microscopy revealed surface impressions accommodated by shear cracks and a general lack of lattice misorientation around indents, indicating the absence of dislocations. Based on these observations, we suggest that antigorite deformation at high pressures is dominated by sliding on shear cracks. We develop a microphysical model that is able to quantitatively explain the Young's modulus and dissipated strain energy data during cyclic loading experiments, based on either frictional or cohesive sliding of an array of cracks contained in the basal plane. △ Less

Submitted 1 November, 2019; v1 submitted 20 May, 2019; originally announced May 2019.

High-angular resolution electron backscatter diffraction as a new tool for mapping lattice distortion in geological minerals

Authors: David Wallis, Lars N. Hansen, T. Ben Britton, Angus J. Wilkinson

Abstract: Analysis of distortions of the crystal lattice within individual mineral grains is central to the investigation of microscale processes that control and record tectonic events. These distortions are generally combinations of lattice rotations and elastic strains, but a lack of suitable observational techniques has prevented these components being mapped simultaneously and routinely in earth scienc… ▽ More Analysis of distortions of the crystal lattice within individual mineral grains is central to the investigation of microscale processes that control and record tectonic events. These distortions are generally combinations of lattice rotations and elastic strains, but a lack of suitable observational techniques has prevented these components being mapped simultaneously and routinely in earth science laboratories. However, the technique of high-angular resolution electron backscatter diffraction (HR-EBSD) provides the opportunity to simultaneously map lattice rotations and elastic strains with exceptional precision, on the order of 0.01 degree for rotations and 10-4 in strain, using a scanning electron microscope. Importantly, these rotations and lattice strains relate to densities of geometrically necessary dislocations and residual stresses. Recent works have begun to apply and adapt HR-EBSD to geological minerals, highlighting the potential of the technique to provide new insights into the microphysics of rock deformation. Therefore, the purpose of this overview is to provide a summary of the technique, to identify caveats and targets for further development, and to suggest areas where it offers potential for major advances. In particular, HREBSD is well suited to characterising the roles of different dislocation types during crystal plastic deformation and to mapping heterogeneous internal stress fields associated with specific deformation mechanisms/microstructures or changes in temperature, confining pressure, or applied deviatoric stress. These capabilities make HR-EBSD a particularly powerful new technique for analysing the microstructures of deformed geological materials. △ Less

Submitted 31 May, 2019; v1 submitted 17 April, 2019; originally announced April 2019.

Comments: resubmitted article

Anisotropic electron mobility studies on Cl2-NDI single crystals and the role of static and dynamic lattice deformations upon temperature variation

Authors: Nis Hauke Hansen, Falk May, Daniel Kälblein, Teresa Schmeiler, Christian Lennartz, Roel Sanchez-Carrera, Alexander Steeger, Christian Burschka, Matthias Stolte, Frank Würthner, Jochen Brill, Jens Pflaum

Abstract: The anisotropic electron transport in the (001) plane of sublimation-grown Cl$_{2}$-NDI (naphthalene diimide) single crystals is analysed over a temperature range between 175 K and 300 K. Upon cooling from room temperature to 175 K the electron mobility along the direction of preferred transport monotonously increases from 1.5 cm$^{2}$/Vs to 2.8 cm$^{2}$/Vs according to a distinct temperature rela… ▽ More The anisotropic electron transport in the (001) plane of sublimation-grown Cl$_{2}$-NDI (naphthalene diimide) single crystals is analysed over a temperature range between 175 K and 300 K. Upon cooling from room temperature to 175 K the electron mobility along the direction of preferred transport monotonously increases from 1.5 cm$^{2}$/Vs to 2.8 cm$^{2}$/Vs according to a distinct temperature relation of $~T^{-1.3}$. At first glance, these characteristics allude to a coherent, i.e. band-like charge carrier transport predominantly governed by inelastic scattering with accoustic phonons. However, as we will demonstrate, the experimental mobility data can be consistently described within the framework of incoherent, hopping-type transport modeled by Levich-Jortner rates, explicitly accounting for the inner and outer relaxation energies related to thermally induced lattice effects and enhanced electron-phonon interaction at elevated temperatures. Complementary band-structure calculations yielding temperature dependent effective mass tensors deviate stronger from experimentally observed spatially anisotropic transport behavior. Thus, these results hint at the fact that by the particular interplay of the transport energies the mobility of a given organic semiconducting material might appear to be band-like in a certain temperature regime even though the underlying charge carrier transport can be of incoherent, hopping-type nature. Building on this description, we further explore the role of the intermolecular electronic coupling and develop a procedure to distinguish between its dependence on static and dynamic lattice deformation upon temperature variation. △ Less

Submitted 9 June, 2016; v1 submitted 8 January, 2015; originally announced January 2015.

Probing exciton interaction with a spatially defined charge accumulation layer in the organic semiconductor Diindenoperylene

Authors: N. H. Hansen, C. Wunderlich, A. K. Topczak, J. Pflaum

Abstract: We present an investigation of the microscopic interplay between excitons and charge carriers by means of combined photoluminescence (PL) and charge carrier transport measurements on organic thin film transistors (OTFT). For this purpose, the prototypical organic semiconductor Diindenoperylene (DIP) was utilized as active material. The OTFT accumulation layer provides a spatially defined interacti… ▽ More We present an investigation of the microscopic interplay between excitons and charge carriers by means of combined photoluminescence (PL) and charge carrier transport measurements on organic thin film transistors (OTFT). For this purpose, the prototypical organic semiconductor Diindenoperylene (DIP) was utilized as active material. The OTFT accumulation layer provides a spatially defined interaction zone for charges and photo-generated excitons leading to a PL intensity reduction of up to 4.5%. This effect correlates with the accumulated hole carrier density and provides a lower estimate of about 1.3E-10 cm3/s for the cross-section of non-radiative exciton-hole processes. It is rationalized that these processes are preferentially mediated by trapped holes. △ Less

Submitted 16 March, 2013; originally announced March 2013.