Thomas Lippert

Last Name

Lippert

First Name

Thomas

ORCID

0000-0001-8559-1900

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01509 - Lehre Chemie u. Ang. Biowiss.

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Publications1 - 10 of 66

In situ stress observation in oxide films and how tensile stress influences oxygen ion conduction
Fluri, Aline; Pergolesi, Daniele; Roddatis, Vladimir; et al. (2016)
Nature Communications
Many properties of materials can be changed by varying the interatomic distances in the crystal lattice by applying stress. Ideal model systems for investigations are heteroepitaxial thin films where lattice distortions can be induced by the crystallographic mismatch with the substrate. Here we describe an in situ simultaneous diagnostic of growth mode and stress during pulsed laser deposition of oxide thin films. The stress state and evolution up to the relaxation onset are monitored during the growth of oxygen ion conducting Ce0.85Sm0.15O2-δ thin films via optical wafer curvature measurements. Increasing tensile stress lowers the activation energy for charge transport and a thorough characterization of stress and morphology allows quantifying this effect using samples with the conductive properties of single crystals. The combined in situ application of optical deflectometry and electron diffraction provides an invaluable tool for strain engineering in Materials Science to fabricate novel devices with intriguing functionalities.
Ultra-high energy storage density and efficiency at low electric fields/voltages in dielectric thin film capacitors through synergistic effects
Belhadi, Jamal; Hanani, Zouhair; Shepelin, Nick A.; et al. (2025)
Journal of Materiomics
Ensuring reliable and safe operation of high-power electronic devices necessitates the development of high-quality dielectric nano-capacitors with high recoverable energy density (URec) and efficiency (η) at low applied electric fields (E)/voltages. In this work, we demonstrate ultra-high URec and η at low E < 500 kV/cm in as-grown epitaxial relaxor ferroelectric (RFE) PMN-33PT films, rivaling those typically achieved in state-of-the-art RFE and antiferroelectric (AFE) materials. The high energy storage properties were achieved using a synergistic strategy involving large polarization, a giant built-in potential/imprint (five times higher than the coercive field), and AFE like behavior. The structural, chemical, and electrical investigations revealed that these achievements mainly arise from the effects of strain, dipole defects, and chemical composition. For instance, at low E, the capacitors exhibit under 160 kV/cm (i.e., 8 V) and 400 kV/cm (i.e., 20 V), respectively, an ultra-high ΔP (45 μC/cm2 and 60 μC/cm2), UE= URec/E (21 J⸱MV/cm2 and 17 J⸱MV/cm2), and UF=URec/(1–η) (20 J/cm3 and 47 J/cm3) with a robust charge-discharge fatigue endurance and outstanding frequency and thermal stability. Additionally, the designed films exhibit outstanding energy storage performance at higher E up to 2 MV/cm (ΔP ≈ 78 μC/cm2, UE ≈ 17.3 J⸱MV/cm2 and UF ≈ 288 J/cm3) due to their low leakage current density.
Enabling high-temperature processing of thin film Li-ion batteries using a LISICON based solid-state electrolyte
Montazerian, Mohammadhossein; Stephens, Kyle J.; Roddatis, Vladimir; et al. (2026)
Journal of Materials Chemistry A
Lithium-ion batteries employing solid-state electrolytes (SSEs) are emerging as a safer and more compact alternative to conventional batteries using liquid electrolytes, especially for miniaturized energy storage systems. However, the industry-standard SSE, LiPON, imposes limitations due to its incompatibility with high-temperature processing. In this study, we investigate Li4-xGe1-xPxO4 (LGPO), a LISICON-type oxide, as a promising alternative thin-film SSE. LGPO thin films are fabricated using pulsed laser deposition under four distinct deposition conditions, with in situ impedance spectroscopy enabling precise conductivity measurements without ambient exposure. We systematically correlate deposition temperature, background pressure, chemical composition, crystallinity, and morphology with ionic transport properties. Polycrystalline LGPO films grown at high temperature (535 degrees C) and low oxygen pressure (0.01 mbar) exhibited the highest room-temperature ionic conductivity (similar to 10⁻⁵ S cm⁻¹), exceeding that of LiPON by an order of magnitude, with an activation energy of 0.47 eV. In contrast, amorphous films show significantly lower conductivity (similar to 5.2 x 10⁻⁸ S cm⁻¹) and higher activation energy (0.72 eV). The results reveal that crystallinity, chemical composition, and grain boundary density critically affect ion transport, highlighting the importance of microstructural control. This work establishes LGPO as a viable, high-performance oxide SSE compatible with high-temperature processing for next-generation microbattery architectures.
High-Sensitivity Ammonia Sensors with Carbon Nanowall Active Material via Laser-Induced Transfer
Palla-Papavlu, Alexandra; Vizireanu, Sorin; Filipescu, Mihaela; et al. (2022)
Nanomaterials
Ammonia sensors with high sensitivity, reproducible response, and low cost are of paramount importance for medicine, i.e., being a biomarker to diagnose lung and renal conditions, and agriculture, given that fertilizer application and livestock manure account for more than 80% of NH3 emissions. Thus, in this work, we report the fabrication of ultra-sensitive ammonia sensors by a rapid, efficient, and solvent-free laser-based procedure, i.e., laser-induced forward transfer (LIFT). LIFT has been used to transfer carbon nanowalls (CNWs) onto flexible polyimide substrates pre-patterned with metallic electrodes. The feasibility of LIFT is validated by the excellent performance of the laser-printed CNW-based sensors in detecting different concentrations of NH3 in the air, at room temperature. The sensors prepared by LIFT show reversible responses to ammonia when exposed to 20 ppm, whilst at higher NH3 concentrations, the responses are quasi-dosimetric. Furthermore, the laser-printed CNW-based sensors have a detection limit as low as 89 ppb and a response time below 10 min for a 20 ppm exposure. In addition, the laser-printed CNW-based sensors are very robust and can withstand more than 200 bending cycles without loss of performance. This work paves the way for the application and integration of laser-based techniques in device fabrication, overcoming the challenges associated with solvent-assisted chemical functionalization.
Highly selective surface acoustic wave e-nose implemented by laser direct writing
Benetti, Massimiliano; Cannatà, Domenico; Verona, Enrico; et al. (2019)
Sensors and Actuators B: Chemical
Oxygen Isotope Fingerprints of Electron-Phonon Coupling in SrVO₃ Films
Singh, Gyanendra; Huang, Xiaochun; Mirjolet, Mathieu; et al. (2026)
Physical Review Letters
Transition metals exemplify correlated electronic systems, where electron-electron (e-e) scattering often results in a quadratic temperature dependence of the electrical resistivity, ρ(T)∝T². In SrVO₃ (SVO), a material with a V-3d¹ electronic configuration that ensures metallicity through narrow 3d-t_2g bands, a ρ(T)∝T² dependence has been reported. While traditionally attributed to e-e scattering, recent studies suggest that electron-phonon (e-ph) interactions may play a significant role. To unravel the influence of phonon interactions on carrier transport in SVO, we present a comparative study of the transport and optical properties of SVO films with partial substitution of ¹⁶O ions by their heavier isotope, ¹⁸O. Our findings reveal that ¹⁸O substitution induces a change in the slope of dρ(T)/dT at nominal fixed carrier density, highlighting the dominant contribution of e-ph coupling over e-e scattering in determining ρ(T). Furthermore, it is found that the ¹⁸O substitution softens the phonon lattice and promotes a reduction in plasma frequency and an increase in the carrier effective mass. These results indicate that the e-ph coupling strength increases upon ¹⁸O substitution. Our findings suggest that e-ph interactions may surpass e-e scattering in governing the resistivity of metallic ionic lattices.
Laser fragmentation of a high-entropy oxide for enhanced photocatalytic carbon dioxide (CO2) conversion and hydrogen (H2) production
Tehrani, Zahra Pourmand; Fromme, Theo; Reichenberger, Sven; et al. (2024)
Advanced Powder Technology
High entropy oxides (HEOs) have recently emerged as potential candidates for photocatalytic CO₂ conversion and H₂ production driven by their high structural stability and diversified elemental compositions. However, their practical use in photocatalysis is still limited particularly due to their comparatively small light absorbance and low active surface area. In this study, CO₂ conversion and H₂ production of an HEO TiZrHfNbTaO11 photocatalysts, originally synthesized by high-pressure torsion (HPT), were enhanced by employing pulsed laser processing in water to effectively fragment micropowders to nanopowders. The process led to a 30 times larger active surface area and accordingly to enhanced light absorbance and higher photoelectrochemical performance for CO₂ and H₂O conversion. The generation of the large active surface area together with the formation of laser-induced crystal lattice defects not only enhanced the photocatalytic efficiency by at least one order of magnitude but also yielded CO, H₂ and CH₄ production even without requiring any additional co-catalyst. This study represents a notable step forward in developing active high-entropy photocatalysts by using new strategies such as laser fragmentation.
Characterization of Stable NiOₓ/SrTaOₓNᵧ Bilayers Boosting the Oxygen Evolution Reaction for Solar Water Splitting
Pourmand Tehrani, Zahra; Stephens, Kyle Joseph; Roddatis, Vladimir; et al. (2026)
Small Science
SrTaO_xN_y (STON) is a well-known visible light-responsive semiconductor with ideally located band edges that allow the operability of overall water splitting. Like many oxynitrides, STON shows evidence of detrimental physicochemical changes under oxygen evolution reaction (OER) conditions involving strong caustic electrolytes. We investigate the development of STON instability with detailed electron microscopy and neutron reflectometry (NR) techniques using epitaxial thin films. Different crystallographic orientations are compared with ex situ analysis before and after OER in photoelectrochemical testing. A remarkable difference in stability of the STON surface is observed depending on the crystalline facets, with the [011] lattice planes being the more favorable orientation as compared to [001]. In addition, we show that the electrochemical stability of the photoelectrode surface can be dramatically improved by a homogeneous coating of NiO_x, which significantly improves OER kinetics and surface stability in the alkaline environment. NR is realized in this work as a novel route to monitor this photoelectrochemical environment, and it lies in agreement with its microscopy counterpart to monitor the physicochemical changes. This demonstrates potential of NR as an alternative and complementary tool that also has the feasibility for future in situ experimental design.
Growth of LixLaySrzMnO3 thin films by pulsed laser deposition: complex relation between thin film composition and deposition parameters
Bimashofer, Gesara; Smetaczek, Stefan; Gilardi, Elisa; et al. (2021)
Applied Physics A
LixLaySrzMnO3 thin films of various compositions (x,y,z) have been grown using pulsed laser deposition. The compositions of the films have been studied as a function of deposition temperature, target-to-substrate distance and deposition pressure with respect to different cation ratios of the targets by inductively coupled plasma mass spectrometry. When growing multi-elemental oxide thin films containing lithium (with its large mass difference to other elements), lithium loss is most probably inevitable. But the desired thin film composition can be achieved by selecting specific growth conditions and different target compositions. The experiments also elucidate some of the mechanisms behind the incongruent lithium transfer from the targets to thin films.
Anionic Disorder and Its Impact on the Surface Electronic Structure of Oxynitride Photoactive Semiconductors
Hartl, Anna; Minár, Ján; Constantinou, Procopios; et al. (2024)
Chemistry of Materials
The conversion of solar energy into chemical energy, stored in the form of hydrogen, bears enormous potential as a sustainable fuel for powering emerging technologies. Photoactive oxynitrides are promising materials for splitting water into molecular oxygen and hydrogen. However, one of the issues limiting widespread commercial use of oxynitrides is degradation during operation. While recent studies have shown the loss of nitrogen, its relation to reduced efficiency has not been directly and systematically addressed with experiments. In this study, we demonstrate the impact of the anionic stoichiometry of BaTaO x N y on its electronic structure and functional properties. Through experimental ion scattering, electron microscopy, and photoelectron spectroscopy investigations, we determine the anionic composition ranging from the bulk toward the surface of BaTaO x N y thin films. This further serves as input for band structure computations modeling the substitutional disorder of the anion sites. Combining our experimental and computational approaches, we reveal the depth-dependent elemental composition of oxynitride films, resulting in downward band bending and the loss of semiconducting character toward the surface. Extending beyond idealized systems, we demonstrate the relation between the electronic properties of real oxynitride photoanodes and their performance, providing guidelines for engineering highly efficient photoelectrodes and photocatalysts for clean hydrogen production.

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Thomas Lippert

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