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- ItemCurrent State-of-the-Art in the Interface/Surface Modification of Thermoelectric Materials(Weinheim : Wiley-VCH, 2021) He, Shiyang; Lehmann, Sebastian; Bahrami, Amin; Nielsch, KorneliusThermoelectric (TE) materials are prominent candidates for energy converting applications due to their excellent performance and reliability. Extensive efforts for improving their efficiency in single-/multi-phase composites comprising nano/micro-scale second phases are being made. The artificial decoration of second phases into the thermoelectric matrix in multi-phase composites, which is distinguished from the second-phase precipitation occurring during the thermally equilibrated synthesis of TE materials, can effectively enhance their performance. Theoretically, the interfacial manipulation of phase boundaries can be extended to a wide range of materials. High interface densities decrease thermal conductivity when nano/micro-scale grain boundaries are obtained and certain electronic structure modifications may increase the power factor of TE materials. Based on the distribution of second phases on the interface boundaries, the strategies can be divided into discontinuous and continuous interfacial modifications. The discontinuous interfacial modifications section in this review discusses five parts chosen according to their dispersion forms, including metals, oxides, semiconductors, carbonic compounds, and MXenes. Alternatively, gas- and solution-phase process techniques are adopted for realizing continuous surface changes, like the core–shell structure. This review offers a detailed analysis of the current state-of-the-art in the field, while identifying possibilities and obstacles for improving the performance of TE materials.
- ItemNanoscale Faceting and Ligand Shell Structure Dominate the Self-Assembly of Nonpolar Nanoparticles into Superlattices(Weinheim : Wiley-VCH, 2022) Bo, Arixin; Liu, Yawei; Kuttich, Björn; Kraus, Tobias; Widmer-Cooper, Asaph; de Jonge, NielsSelf-assembly of nanoscale structures at liquid–solid interfaces occurs in a broad range of industrial processes and is found in various phenomena in nature. Conventional theory assumes spherical particles and homogeneous surfaces, but that model is oversimplified, and nanoscale in situ observations are needed for a more complete understanding. Liquid-phase scanning transmission electron microscopy (LP-STEM) is used to examine the interactions that direct the self-assembly of superlattices formed by gold nanoparticles (AuNPs) in nonpolar liquids. Varying the molecular coating of the substrate modulates short-range attraction and leads to switching between a range of different geometric structures, including hexagonal close-packed (hcp), simple hexagonal (sh), dodecahedral quasi-crystal (dqc), and body-centered cubic (bcc) lattices, as well as random distributions. Langevin dynamics simulations explain the experimental results in terms of the interplay between nanoparticle faceting, ligand shell structure, and substrate–NP interactions.
- ItemSurface modification of the laser sintering standard powder polyamide 12 by plasma treatments(Weinheim : Wiley-VCH, 2018-6-7) Almansoori, Alaa; Masters, Robert; Abrams, Kerry; Schäfer, Jan; Gerling, Torsten; Majewski, Candice; Rodenburg, CorneliaPolyamide 12 (PA12) powder was exposed for up to 3 h to low pressure air plasma treatment (LP-PT) and several minutes by two different atmospheric pressure plasma jets (APPJ) i.e., kINPen (K-APPJ) and Hairline (H-APPJ). The chemical and physical changes resulting from LP-PT were observed by a combination of Scanning Electron Microscopy (SEM), Hot Stage Microscopy (HSM) and Fourier transform infrared spectroscopy (FTIR), which demonstrated significant changes between the plasma treated and untreated PA12 powders. PA12 exposed to LP-PT showed an increase in wettability, was relatively porous, and possessed a higher density, which resulted from the surface functionalization and materials removal during the plasma exposure. However, it showed poor melt behavior under heating conditions typical for Laser Sintering. In contrast, brief PJ treatments demonstrated similar changes in porosity, but crucially, retained the favorable melt characteristics of PA12 powder.