Jonathan Plentz

Light biases porphyrin COF stacking at soft interfaces, shifting registry from slipped AA′ toward AB during growth.

Transparent conductive graphene films are typically fabricated at processing temperatures above 500°C, making the applied processes unsuitable for flexible polymer substrates and limiting their integration into semiconductor device technologies. Here we demonstrate a method for fabricating such films at temperatures below 200°C. To this end, oxo‐graphene flakes are assembled into continuous films using the double self‐assembly technique. Subsequent hydroiodic acid (HI) vapor treatment at 40°C removes the oxygen‐containing groups and, combined with a mild 180°C annealing step on heat‐stable substrates, lowers the sheet resistance by more than a factor of five to about 3 kΩ/sq while preserving optical transparencies of up to 88% at 550 nm wavelength. The trade‐off between sheet resistance and transparency is set by the number of stacked layers, and on flexible polyethylene terephthalate (PET), where the annealing step is precluded, the films reach a sheet resistance of about 2.8 kΩ/sq after the HI step alone. These results demonstrate that the double self‐assembly of oxo‐functionalized graphene flakes, combined with mild HI‐vapor reduction and a 180°C annealing step, can deliver highly transparent and conductive graphene films while remaining compatible with semiconductor device technologies.

This study investigated indium tin oxide as an n-type thermoelectric material for textile-based energy harvesting. Comprehensive characterization revealed a strong influence of fabrication temperature on specific resistivity of the ITO films and on charge carrier mobility. The Seebeck coefficient (-20 to -30 µV/K) and thermal conductivity were also temperature dependent. X-ray diffraction confirmed crystalline ITO films with preferred (211) or (222) orientations. Optimized at 300 °C substrate temperature, the material exhibited power factors of 0.8–1.7 × 10⁻⁴ W/mK² and zT values ranging from 0.008 to 0.02 (at room temperature to 100 °C), respectively. This basic characterization enabled successful deposition of ITO onto textile fibers, maintaining comparable thermoelectric performance. A resulting textile-based thermo-electric generator demonstrated a five-fold power increase with a four-element stack, highlighting the benefits of series interconnection. Accurate temperature measurement, minimizing contact resistance and enhancing mechanical stability through encapsulation are identified as critical areas for future optimization to enhance device performance and durability.

Context . Modelling of spectral energy distributions of protoplanetary and debris disks relies on optical constants of the dust components. Iron(II) sulphides are a very likely component of the dust in these objects, and they could influence the dust opacity substantially due to their large optical constants at long wavelengths. The composition of these compounds ( Fe _1-x S, x = 0,..., 0.125) may considerably influence the optical constants. Aims . Complex refractive index data of iron(II) sulphides are scarce in the literature, especially for iron-deficient varieties, and not yet available over wide wavelength ranges. Our aim with this work is to enlarge the database by deriving optical constants from 210 nm to 2 mm wavelength for several varieties. We studied temperature dependencies from 300 K to 10 K to understand their influence for different astronomical environments. Methods . Polished samples of meteoritic troilite (stoichiometric FeS) and well-characterised terrestrial pyrrhotites were subjected to reflection ellipsometry from the ultraviolet-visible to the mid-infrared and to reflection spectroscopy from ultraviolet to sub-millimetre wavelengths. We derived the complex refractive index by minimisation of Drude and multiple Lorentz oscillator models. Phonon bands were investigated by polarised radiation in the infrared and at lower temperatures. Results . We discovered a binary spectroscopic behaviour between iron depleted and stoichiometric(-like) iron(II) sulphides. For the latter, we found that free charge carrier excitations only appear at sub-millimetre wavelengths, while for all pyrrhotites they are dominant from the mid-infrared to far-infrared. Troilite shows a strong temperature dependency for the lattice vibrations, whereas variations of the pyrrhotite spectra are within the instrumentation uncertainties. Conclusions . The optical constants of iron(II) sulphides depend strongly on the iron to sulphur ratio. Due to their metal-like spectroscopic properties, non-stoichiometric iron(II) sulphides can contribute to dust emission without being directly detectable by infrared bands.

This work demonstrates a method for producing well-ordered gold nanoparticle arrays using a pre-patterned silicon substrate. The study starts with an investigation of particle formation on flat silicon substrates. Surface coverage is presented as a function of different annealing temperatures (from unannealed to 1100 °C), and particle size distributions are characterized at 1100 °C to study first the annealing process. Silicon substrates pre-patterned with square features were also coated with gold layers ranging in thickness from 10 nm to 40 nm. The dewetting process was then induced by annealing in a furnace at 800 °C and 1100 °C. These varying temperatures and layer thicknesses revealed that a 20 nm initial gold layer deposited onto a square lattice and annealed at 1100 °C resulted in a well-defined nanoparticle array, in contrast to results obtained on flat substrates. Crystallite sizes, determined by X-ray diffraction were smaller than or equal to the smallest determined particle size. Optical absorbance spectroscopy measurements revealed shifts in spectra associated with the plasmonic properties of the nanoparticles.

Natural fibre-reinforced polypropylene (NFRP) composites are increasingly used as lightweight, bio-based structural materials in automotive and interior applications. To enable multifunctional components with integrated sensing, lighting or wiring, electrical conductor tracks need to be fabricated directly on NFRP surfaces. This is challenging, because NFRP exhibits pronounced surface roughness and porosity, while the polypropylene matrix imposes a restricted thermal budget that limits conventional high-temperature curing of conductive inks. In this work, we demonstrate the direct fabrication of silver conductor tracks on a hemp-fibre NFRP by combining a water-based starch filler layer with screen printing of a commercial thermoplastic polyurethane-based silver ink, followed by localized 808 nm laser sintering. The starch layer fills surface pores and smooths the NFRP surface while acting as an aqueous, bio-derived adhesive that can be dried at moderate temperatures, which is in line with the low-emission and moderate-temperature requirements of NFRP interior components and avoids the need for typical solvent-borne primers and higher curing temperatures that are less compatible with such substrates. We systematically compare track resistance and morphology on glass and on both sides of the NFRP and show that suitable pre-treatment of the NFRP surface, combined with laser sintering, enables low-resistance conductor tracks on the NFRP back side under process temperatures compatible with the polymer matrix. Localized near-infrared laser sintering further improves the conductivity without damaging the composite and enables continuous, low-resistance tracks to be realized on the NFRP substrate. To the best of our knowledge, this is the first study to demonstrate laser sintered, screen-printed silver conductors directly on an industrial natural fibre-reinforced polypropylene composite within its limited thermal budget using a water-based, starch-based filler layer. The results indicate a process- and environmentally compatible route towards multifunctional, lightweight NFRP components with integrated electrical functionalities.

High-harmonic generation (HHG) is used as a source for various imaging applications in the extreme ultraviolet spectral range. It offers spatially coherent radiation and unique elemental contrast with the potential for attosecond time resolution. The unfavorable efficiency scaling to higher photon energies prevented the imaging application in the soft X-ray range so far. In this work we demonstrate the feasibility of using harmonics for imaging in the water window spectral region (284 eV to 532 eV). We achieve nondestructive depth profile imaging in a heterostructure by utilizing a broadband and noise-resistant technique called soft X-ray Coherence Tomography (SXCT) at a high-flux lab-scale HHG source. SXCT is derived from Optical Coherence Tomography, a Fourier based technique that can use the full bandwidth of the source to reach an axial resolution of 12 nm in this demonstration. The employed source covers the entire water window, with a photon flux exceeding 10 ⁶ photons/eV/s at a photon energy of 500 eV. We show local cross sections of a sample consisting of Aluminium oxide and Platinum layers of varying thickness on a Zinc oxide substrate. We validate the findings with scanning and transmission electron microscopy after preparation with focused ion beam milling.

We aim to demonstrate the gold nanoparticle formation on silicon substrates by a time-consuming furnace process and a ns-short laser-induced process as methods that can be performed under ambient conditions. The properties of the particles are shown by means of electron microscopy and X-ray diffraction. We have found differences that suggest solid-state dewetting and liquid-state dewetting depending on the incorporated thermal energy. The short thermalization time of the laser process allows us to produce round-shaped polycrystalline nanoparticles. The nanoparticle formation by laser is dependent on the pulse energy and the pulse number. As a function of temperature from 300 to 1100 °C in a furnace, applied to thin gold films from 5 to 20 nm, the layers show complete dewetting of the substrate combined with the forming of nanoparticles with facette-like surfaces. Both methods show an improvement in the (111) texture with a small energy input up to the melting temperature of gold at 1060 °C compared to the original gold layer. However, with further increasing energy, the texture decreases again and falls below the level of the original layer. The particle size distributions, the crystallite sizes, and the intensity ratio of (111) and (002) reflexes are discussed.