Gabriele Schmidl

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.

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.

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.

Three-dimensional flexible solar fabrics based on hydrogenated amorphous silicon (a-Si:H) thin film solar cells were prepared and characterized. A glass fiber fabric with a polytetrafluoroethylene (PTFE) coating proved to be a suitable textile substrate. Interwoven metal wires enable an integrated electrical interconnection. An array of solar cells consisting of an a-Si:H layer stack with a highly p-type/intrinsic/highly n-type doping profile was deposited onto it. Silver was used as the back contact with indium tin oxide (ITO) as the front contact. The best solar cells show an efficiency of 3.9% with an open-circuit voltage of 876 mV and a short-circuit current density of 11.4 mA/cm². The high series resistance limits the fill factor to 39%. The potential of the textile solar cells is shown by the achieved pseudo fill factor of 79% when neglecting the series resistance, resulting in a pseudo efficiency of 7.6%. With four textile solar cells connected in a series, an open-circuit voltage of about 3 V is achieved.

The aim of this study was to investigate whether a textile electrode coated with an amorphous silicon thin film can be used as an actuator element in a lithium electrolysis process in comparison to a crysralline silicon wafer stripe. It is well known from battery research that a deformation of the silicon electrode occurs during lithiation. This reversible process is being studied as a mechanical switch to move lightweight textiles for potential applications such as ventilation, thermal management, privacy protection, etc. To identify a solution, silicon thin film coatings on textile substrates, electrolytes and the lithiation process have been examined under both inert laboratory and application conditions. Methods such as cyclic voltammetry, amperometry and impedance spectroscopy were used to analyze the electrolytic process, and secondary ion mass spectrometry and electrical analysis were used to obtain material information. It is shown that the charging and discharging of lithium ions is associated with bending for more than 5 cycles. During this process, repeated forward and backward movements of the textile electrode were observed at low voltages below −10 V. Bending forces in the range of 0.2–0.7 mN dependent on the charging time, and a current flow in the range of −0.01 to −440 µA dependent on the voltage, were measured. This is suitable for the scenario where low force is required.