arXiv subjects

Jana Zaumseil

Publications and source records attributed to Jana Zaumseil.

At least 19 recordsLinked to original sources

arXiv2026

Sulfur-rich Spirofluorene-Bridged N Heterotriangulene Redox-Active Polymers

Sulfur-rich spirofluorene-bridged N-heterotriangulene (FTN) polymers featuring covalently linked oligosulfide units and a terthiophene-based analogue were synthesized via nucleophilic aromatic substitution and Stille cross-coupling polymerization. The resulting materials are amorphous, insoluble solids with high thermal stability and sulfur contents up to 25 wt%. Structural and compositional analyses by combustion analysis, ToF-SIMS, FT-IR, XPS, and solid-state NMR confirm the efficient incorporation of short oligosulfide to disulfide linkages and well-defined terthiophene units in the respective polymers. Electrochemical characterization in lithium half-cells reveals a reversible, high-voltage oxidation of the FTN unit at 3.8-4.0 V (vs. Li/Li+), accompanied by low-voltage sulfur- or terthiophene-based redox processes between 1.5-2.5 V (vs. Li/Li+). Sulfur incorporation markedly increases the theoretical and initial discharge capacities (up to 129 mA h g-1), while the sulfide conversion processes exhibit rapid fading and poor reversibility due to sulfide dissolution. In contrast, the terthiophene-linked polymer shows only transient low-voltage activity while maintaining high Coulombic efficiencies (ca. 99.7%) governed by the persistent FTN backbone redox event. Our results highlight how different redox-active linkers influence the electrochemical behavior of FTN-based polymers and provide insights into the design of functional organic cathode materials featuring multi-redox processes.

cond-mat.mtrl-sci↗

arXiv2026

Resolving Scale-Dependent Diffusivity in the Brain Extracellular Space

Transport through the brain extracellular space has traditionally been summarized by effective diffusion coefficients measured over specific observation ranges. Whether local mobility remains predictive as the same molecule explores larger distances remains unresolved. Here, we track individual ultrashort carbon nanotubes in three dimensions within living hippocampal tissue, following their motion from nanometre to micrometre scales. Using freely diffusing nanotubes in water as an experimental reference, we resolve trajectory-specific crossover lengths beyond which instantaneous diffusivity decreases, with slice-level medians of 0.67 $μ$m in the pyramidal layer and 0.52 $μ$m in the radiatum. The pyramidal layer combines higher short-time diffusivity with an approximately twofold larger post-crossover restriction exponent than the radiatum ($\vartheta$ = 0.77 versus 0.38). This decoupling of local mobility from larger-scale exploration is incompatible with a scale-independent rescaling of transport, showing that effective extracellular diffusivity must be interpreted relative to the scale of exploration.

physics.bio-ph↗

arXiv2026

Photonic Waveguide Circuit Integrated with Carbon Nanotube Single-Photon Source Operating at Room Temperature

Photonic integrated circuits require robust room-temperature single-photon sources to enable scalable quantum technologies. Single-walled carbon nanotubes (CNTs), with their unique excitonic properties and chemical tunability, are attractive candidates, but their integration into photonic circuits remains challenging. In this work, we demonstrate the integration of functionalized CNTs as room-temperature single-photon emitters into photonic cavities and waveguide circuits. (6,5) CNTs with aryl sp$^3$ defects are either stochastically deposited via drop-casting or deterministically positioned on photonic cavities using an anthracene-assisted transfer method guided by real-time photoluminescence monitoring. Photoluminescence spectra reveal cavity-enhanced emission, while second-order autocorrelation measurements confirm single-photon propagation through the photonic integrated circuit, highlighting the potential of CNTs for scalable, room-temperature quantum photonic applications.

physics.optics↗

arXiv2025

Ultrashort Carbon Nanotubes with Luminescent Color Centers are Bright NIR-II Nano-Emitters

In the fields of bioimaging, photonics, and quantum science, it is equally crucial to combine high brightness with nanoscale size in short-wave infrared (SWIR) emitters. However, such nano-emitters are currently lacking. Here, we report that when functionalized with luminescent color centers, ultrashort carbon nanotubes with length much shorter than 100 nm, are surprisingly bright in the near-infrared second-biological window (NIR-II) of the SWIR domain. We discuss the origin of this exceptional brightness based on the uncontrollable presence of quenching defects in dispersed carbon nanotubes. We further investigate the nonlinear photoluminescence behavior of color centers functionalized carbon nanotubes in response to varying excitation conditions, spanning from ensemble measurements to single-nanotube experiments. We discuss how this behavior influences the determination of their photoluminescence quantum yields, which can reach values as high as 20% for ultrashort ones detected at the single nanotube level. Notably, the corresponding NIR-II brightness exceeds that of well-known visible emitters, including quantum dots. After rendering them biocompatible, we demonstrate point-spread function engineering and high-resolution, 3-dimensional single-particle tracking using these bright ultrashort carbon nanotubes allowing nanoscale imaging in the NIR-II window within thick brain tissue.

cond-mat.mtrl-sci↗

arXiv2025

Ion-Exchange Doping of Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWCNTs) are a promising thermoelectric material with high power factors after chemical p- or n-doping. Understanding the impact of dopant counterions on charge transport and thermoelectric properties of nanotube networks is essential to further optimize doping methods and to develop better dopants. Here, we utilize ion-exchange doping to systematically vary the size of counterions in thin films of small and large diameter, polymer-sorted semiconducting SWCNTs with AuCl3 as the initial p-dopant and investigate the impact of ion size on conductivity, Seebeck coefficients and power factors. Larger anions are found to correlate with higher electrical conductivities and improved doping stability, while no significant effect on the power factors is found. Importantly, the effect of counterion size on the thermoelectric properties of dense SWCNT networks is not obscured by morphological changes upon doping. The observed trends of carrier mobilities and Seebeck coefficients can be explained by a random resistor model for the nanotube network that accounts for overlapping Coulomb potentials leading to the formation of an impurity band whose depth depends on the carrier density and counterion size. These insights can be applied more broadly to understand the thermoelectric properties of doped percolating disordered systems, including semiconducting polymers.

cond-mat.mtrl-sci↗

arXiv2025

Bandgap-Dependent Doping of Semiconducting Carbon Nanotube Networks by Proton-Coupled Electron Transfer for Stable Thermoelectrics

Networks of semiconducting single-walled carbon nanotubes (SWNTs) are a promising material for thermoelectric energy harvesting due to their mechanical flexibility, solution processability, high Seebeck coefficients and high electrical conductivities after chemical p- or n-doping. Here, we demonstrate that proton-coupled electron transfer (PCET) with benzoquinone (BQ) as the oxidant and lithium bis(trifluoromethylsulfonyl)imide (Li[TFSI]) for electrolyte counterions is a promising method for p-doping of polymer-sorted semiconducting SWNT networks. The achieved doping levels, as determined from absorption bleaching, depend directly on both the pH of the aqueous doping solutions and the bandgap (i.e., diameter) of the nanotubes within the network. Fast screening of different nanotube networks under various doping conditions was enabled by a high-throughput setup for thermoelectric measurements of five samples in parallel. For small-bandgap SWNTs, PCET-doping is sufficient to reach the maximum thermoelectric power factors, which are equal to those obtained by conventional methods. In contrast to other doping methods, the electrical conductivity of PCET-doped SWNTs remains stable over at least 5 days in air. These results confirm PCET to be a suitable approach for more environmentally friendly and stable doping of semiconducting SWNTs as promising thermoelectric materials.

physics.app-ph↗

arXiv2024

How to Recognize Clustering of Luminescent Defects in Single-Wall Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (SWCNTs) are a promising material platform for near-infrared in-vivo imaging, optical sensing, and single-photon emission at telecommunication wavelengths. The functionalization of SWCNTs with luminescent defects can lead to significantly enhanced photoluminescence (PL) properties due to efficient trapping of highly mobile excitons and red-shifted emission from these trap states. Among the most studied luminescent defect types are oxygen and aryl defects that have largely similar optical properties. So far, no direct comparison between SWCNTs functionalized with oxygen and aryl defects under identical conditions has been performed. Here, we employ a combination of spectroscopic techniques to quantify the number of defects, their distribution along the nanotubes and thus their exciton trapping efficiencies. The different slopes of Raman D/G+ ratios versus calculated defect densities from PL quantum yield measurements indicate substantial dissimilarities between oxygen and aryl defects. Supported by statistical analysis of single-nanotube PL spectra at cryogenic temperatures it reveals clustering of oxygen defects. The clustering of 2-3 oxygen defects, which act as a single exciton trap, occurs irrespective of the functionalization method and thus enables the use of simple equations to determine the density of oxygen defects and oxygen defect clusters in SWCNTs based on standard Raman spectroscopy. The presented analytical approach is a versatile and sensitive tool to study defect distribution and clustering in SWCNTs and can be applied to any new functionalization method.

cond-mat.mtrl-sci↗

arXiv2024

Easy Access to Bright Oxygen Defects in Biocompatible Single-Walled Carbon Nanotubes via a Fenton-Like Reaction

The covalent functionalization of single-walled carbon nanotubes (SWNTs) with luminescent oxygen defects increases their brightness and enables their application as optical biosensors or fluorescent probes for in-vivo imaging in the second-biological window (NIR-II). However, obtaining luminescent defects with high brightness is challenging with the current functionalization methods due to a restricted window of reaction conditions or the necessity for controlled irradiation with ultraviolet light. Here we report a method for introducing luminescent oxygen defects via a Fenton-like reaction that uses benign and inexpensive chemicals without light irradiation. (6,5) SWNTs in aqueous dispersion functionalized with this method show bright $E_{11}$* emission (1105 nm) with 3.2-times higher peak intensities than the pristine $E_{11}$ emission and a reproducible photoluminescence quantum yield of 3%. The functionalization can be performed within a wide range of reaction parameters and even with unsorted nanotube raw material at high concentrations (100 mg/L), giving access to large amounts of brightly luminescent SWNTs. We further find that the introduced oxygen defects rearrange under light irradiation, which gives additional insights into the structure and dynamics of oxygen defects. Finally, the functionalization of ultra-short SWNTs with oxygen defects also enables high photoluminescence quantum yields and their excellent emission properties are retained after surfactant exchange with biocompatible pegylated phospholipids or single-stranded DNA to make them suitable for in-vivo NIR-II imaging and dopamine sensing.

cond-mat.mtrl-sci↗

arXiv2024

Dark excitons and hot electrons modulate exciton-photon strong coupling in metal-organic optical microcavities

Polaritons, formed as a result of strong hybridization of matter with light, are promising for important applications including organic solar cells, optical logic gates, and qubits. Owing to large binding energies of Frenkel excitons (matter), strong matter-light coupling phenomena are possible at room temperature, high exciton densities, and even with low-quality-factor microcavities. In such cases, due to polaritons' high degree of delocalization, simultaneous effects from dark excitons and hot electrons may affect performance of potential devices. Their understanding, therefore, is of paramount importance, but their disentanglement in optical spectroscopy, however, thus far remained unattainable. Here, we overcome this challenge by careful and systematic analysis of transient polaritonic spectra, supported by analytical models. In doing so, we conclude that dark excitons affect the strength of exciton-photon coupling and manifest themselves as Fano-like polaritonic gain-loss spectra. Free electrons add additional loss component to and imprint a two-temperature dynamics on the polaritonic response. The developed general methodology can be applied to a variety of other microcavity structures. Our findings are significant for distinguishing polaritons and other excitations in studies of polariton-electron and plasmon-electron coupling phenomena as well as photonic control over photophysical and photochemical processes.

physics.app-ph↗

arXiv2024

Photo-Activated, Solid-State Introduction of Luminescent Oxygen Defects into Semiconducting Single-Walled Carbon Nanotubes

Oxygen defects in semiconducting single-walled carbon nanotubes (SWCNTs) are localized disruptions in the carbon lattice caused by the formation of epoxy or ether groups, commonly through wet-chemical reactions. The associated modifications of the electronic structure can result in luminescent states with emission energies below those of pristine SWCNTs in the near-infrared range, which makes them promising candidates for applications in biosensing and as single-photon emitters. Here, we demonstrate the controlled introduction of luminescent oxygen defects into networks of monochiral (6,5) SWCNTs using a solid-state photocatalytic approach. UV irradiation of SWCNTs on the photoreactive surfaces of the transition metal oxides TiOx and ZnOx in the presence of trace amounts of water and oxygen results in the creation of reactive oxygen species that initiate radical reactions with the carbon lattice and the formation of oxygen defects. The created ether-d and epoxide-l defect configurations give rise to two distinct red-shifted emissive features. The chemical and dielectric properties of the photoactive oxides influence the final defect emission properties, with oxygen-functionalized SWCNTs on TiOx substrates being brighter than those on ZnOx or pristine SWCNTs on glass. The photoinduced functionalization of nanotubes is further employed to create lateral patterns of oxygen defects in (6,5) SWCNT networks with micrometer resolution and thus spatially controlled defect emission.

physics.app-ph↗

arXiv2024

Ratiometric fluorescent sensing of pyrophosphate with sp$^{3}$-functionalized single-walled carbon nanotubes

Inorganic pyrophosphate is a key molecule in many biological processes from DNA synthesis to cell metabolism. Here we introduce sp$^{3}$-functionalized (6,5) single-walled carbon nanotubes (SWNTs) with red-shifted defect emission as near-infrared luminescent probes for the optical detection and quantification of inorganic pyrophosphate. The sensing scheme is based on the immobilization of Cu$^{2+}$ ions on the SWNT surface promoted by coordination to covalently attached aryl alkyne groups and a triazole complex. The presence of Cu$^{2+}$ ions on the SWNT surface causes fluorescence quenching via photoinduced electron transfer, which is reversed by copper-complexing analytes such as pyrophosphate. The differences in the fluorescence response of sp$^{3}$-defect to pristine nanotube emission enables reproducible ratiometric measurements in a wide concentration window. Biocompatible, phospholipid-polyethylene glycol-coated SWNTs with such sp$^{3}$ defects are employed for the detection of pyrophosphate in cell lysate and for monitoring the progress of DNA synthesis in a polymerase chain reaction. This robust ratiometric and near-infrared luminescent probe for pyrophosphate may serve as a starting point for the rational design of nanotube-based biosensors.

physics.app-ph↗

arXiv2023

A Hands-On Guide to Shear Force Mixing of Single-Walled Carbon Nanotubes with Conjugated Polymers

This guide provides a detailed step-by-step procedure for the dispersion of (6,5) single-walled carbon nanotubes by shear force mixing with the conjugated polymer PFO-BPy in organic solvents. All processes presented here were developed in the Zaumseil group at Heidelberg University since 2015 and represent best practices to the best of our knowledge. In addition to the detailed instructions, we discuss potential pitfalls and problems, that we have encountered over eight years of operation and show how to solve them. This also includes a detailed description of how to maintain and service a shear force mixer to ensure long operation lifetime. Finally, we show how to expand our process to the dispersion other nanotube chiralities in electronic-grade quality and how to treat dispersions for subsequent processing (e.g., thin film deposition or functionalization).

physics.app-ph↗

arXiv2023

Unified Quantification of Quantum Defects in Small-Diameter Single-Walled Carbon Nanotubes by Raman Spectroscopy

The covalent functionalization of single-walled carbon nanotubes (SWCNTs) with luminescent quantum defects enables their application as near-infrared single-photon sources, as optical sensors, and for in-vivo tissue imaging. Tuning the emission wavelength and defect density are crucial for these applications. While the former can be controlled by different synthetic protocols and is easily measured, defect densities are still determined as relative rather than absolute values, limiting the comparability between different nanotube batches and chiralities. Here, we present an absolute and unified quantification metric for the defect density in SWCNT samples based on Raman spectroscopy. It is applicable to a range of small-diameter nanotubes and for arbitrary laser wavelengths. We observe a clear inverse correlation of the D/G$^{+}$ ratio increase with nanotube diameter, indicating that curvature effects contribute significantly to the defect-activation of Raman modes. Correlation of intermediate frequency modes with defect densities further corroborates their activation by defects and provides additional quantitative metrics for the characterization of functionalized SWCNTs.

cond-mat.mtrl-sci↗

arXiv2023

Tuning Electroluminescence from Functionalized SWCNT Networks further into the Near-Infrared

Near-infrared electroluminescence from carbon-based emitters, especially in the second biological window (NIR-II) or at telecommunication wavelengths, is difficult to achieve. Single-walled carbon nanotubes (SWCNTs) have been proposed as a possible solution due to their tunable and narrowband emission in the near-infrared and high charge carrier mobilities. Furthermore, the covalent functionalization of SWCNTs with a controlled number of luminescent sp$^{3}$ defects leads to even more red-shifted photoluminescence with enhanced quantum yields. Here, we demonstrate that by tailoring the binding configuration of the introduced sp$^{3}$ defects and hence tuning their optical trap depth we can generate emission from polymer-sorted (6,5) and (7,5) nanotubes that is mainly occurring in the telecommunication O-band (1260-1360 nm). Networks of these functionalized nanotubes are integrated in ambipolar, light-emitting field-effect transistors to yield the corresponding narrowband near-infrared electroluminescence. Further investigation of the current and carrier density-dependent electro- and photoluminescence spectra enable insights into the impact of different sp$^{3}$ defects on charge transport in networks of functionalized SWCNTs.

physics.app-ph↗

arXiv2023

Understanding the optical properties of doped and undoped 9-armchair graphene nanoribbons in dispersion

Graphene nanoribbons are one-dimensional stripes of graphene with width- and edge-structure-dependent electronic properties. They can be synthesized bottom-up in solution to obtain precise ribbon geometries. Here we investigate the optical properties of solution-synthesized 9-armchair graphene nanoribbons (9-aGNRs) that are stabilized as dispersions in organic solvents and further fractioned by liquid cascade centrifugation (LCC). Absorption and photoluminescence spectroscopy reveal two near-infrared absorption and emission peaks whose ratios depend on the LCC fraction. Low-temperature single-nanoribbon photoluminescence spectra suggest the presence of two different nanoribbon species. Based on density functional theory (DFT) and time-dependent DFT calculations, the lowest energy transition can be assigned to pristine 9-aGNRs, while 9-aGNRs with edge-defects, caused by incomplete graphitization, result in more blue-shifted transitions and higher Raman D/G-mode ratios. Hole doping of 9-aGNR dispersions with the electron acceptor F4TCNQ leads to concentration dependent bleaching and quenching of the main absorption and emission bands and the appearance of redshifted, charge-induced absorption features but no additional emission peaks, thus indicating the formation of polarons instead of the predicted trions (charged excitons) in doped 9-aGNRs.

cond-mat.mtrl-sci↗

arXiv2023

Near-Intrinsic Photo- and Electroluminescence from Single-Walled Carbon Nanotube Thin Films on BCB-Passivated Surfaces

Their outstanding electrical and optical properties make semiconducting single-walled carbon nanotubes (SWCNTs) highly suitable for charge transport and emissive layers in near-infrared optoelectronic devices. However, the luminescence spectra of SWCNT thin films on commonly used glass and Si/SiO2 substrates are often compromised by broadening of the main excitonic emission and unwanted low-energy sidebands. Surface passivation with a commercially available, low dielectric constant, cross-linked bis-benzocyclobutene-based polymer (BCB) enhances the emission properties of SWCNTs to the same level as hexagonal boron nitride (h-BN) flakes do. The presence of BCB suppresses sideband emission, especially from the Y1 band, which is attributed to defects introduced by the interaction of the nanotube lattice with oxygen-containing terminal groups of the substrate surface. The facile and reproducible deposition of homogeneous BCB films over large areas combined with their resistance against common solvents and chemicals employed during photolithography make them compatible with standard semiconductor device fabrication. Utilizing this approach, light-emitting (6,5) SWCNT network field-effect transistors are fabricated on BCB-treated glass substrates with excellent electrical characteristics and near-intrinsic electroluminescence. Hence, passivation with BCB is proposed as a standard treatment for substrates used for spectroscopic investigations of and optoelectronic devices with SWCNTs and other low-dimensional emitters.

physics.app-ph↗

arXiv2023

Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymer-sorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

cond-mat.mtrl-sci↗

arXiv2022

Trion emission from frozen p-n junctions in networks of electrolyte-gated (6,5) single-walled carbon nanotubes

We demonstrate exciton and charged exciton (trion) electroluminescence from frozen p-n junctions in networks of polymer-sorted, semiconducting (6,5) single-walled carbon nanotubes. Electrolyte-gating with an ionic liquid was employed to achieve injection and accumulation of high densities of holes and electrons in the nanotube network at low applied voltages. Static p-n junctions were formed by cooling the devices below the melting point of the ionic liquid while in the ambipolar regime. These frozen junctions showed diode-like rectification and enabled the investigation of electron-hole recombination and near-infrared electroluminescence under controlled conditions. The contributions of exciton and red-shifted trion emission to the electroluminescence spectra were influenced by the initial parameters of the p-n junction formation (balanced or unbalanced) and the applied lateral bias, but did not depend on temperature (30-200 K). The tilted potential profile along the fixed junction and consequently the number of excess carriers within the recombination zone were found to predominantly determine the emission intensity and observed trion to exciton ratio.

physics.app-ph↗