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Item type:Publication, Access status: with files , Which factor determines the optical losses in refractory tungsten thin films at high temperatures?(Elsevier, 2022-03-04); ; ; ; Refractory tungsten (W) plays an important role in high temperature photonic/plasmonic applications. Previously room temperature bulk single/poly-crystalline optical constants were extensively used to calculate the optical properties of W nanostructures at high temperatures. This might lead to a significant deviation between the predicted and measured optical properties due to the exclusion of electron–phonon interaction, as well as grain-boundary and surface-scattering. Herein, we show experimentally, how film thickness and temperature affects the optical losses in W. A drastic increase in the effective electron collision frequency is observed with decreasing the film thickness down to 5 nm, due to the grain-boundary and surface-scattering mechanisms. At sufficiently high temperatures (greater than 200 °C for W), the electron–phonon interaction eventually becomes the dominant mechanism, linearly increasing collision frequency with temperature, and it is independent of the geometry of the thin film structure. The impact of thickness and temperature-dependent optical properties of W is showcased with a hyperbolic 1D metamaterial structure acting as a thermophotovoltaic emitter. This work opens new directions in accurate prediction of the optical properties of nanostructures and design of efficient devices in various applications, such as aerospace, energy-efficient lighting, radiative cooling and energy harvesting, by incorporating thickness and temperature-dependent optical constants.Publicationtype: Journal ArticleScopus© Citations 6 89 445 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Alkaline induced indium gradient distribution in Znm In2 S3+m/In(OH)3 heterojunction for improved photocatalytic H2 generation(2020-11-15); ; ; ; Building a heterojunction composite which contains two or more semiconductors with matching energy band structures is an effective way to boost the photocatalytic performance. In this paper, a perfectly matching heterojunction constructed by semiconductors with a continuously changing energy band structure was demonstrated. It was found that migration of indium in layered ZnIn2S4 could be driven from the bulk to the surface under alkaline condition. Based on this, In(OH)3 was in situ grown on the surface of ZnIn2S4, and meanwhile, ZnIn2S4 was converted to ZnmIn2S3+m with m continuously variable. Due to the concentration gradient of indium, the conduction band (CB) of ZnmIn2S3+m/In(OH)3, which was formed by In5s5p orbitals mixed with Zn4s4p orbitals, displays a continuous change that can efficiently promote photogenerated charge separation and transfer.Publicationtype: Journal Article69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Laser-induced forward transfer of soft material nanolayers with millisecond pulses shows contact-based material deposition(2020-04-01); ; ; ; In this work, we present a qualitative and quantitative experimental analysis, as well as a numerical model, of a novel variant of the laser-induced forward transfer, which uses millisecond laser pulses. In this process, soft material nanolayer spots are transferred from a donor slide, which is coated with the soft material layer, to an acceptor slide via laser irradiation. This method offers a highly flexible material transfer to perform high-throughput combinatorial chemistry for the generation of biomolecule arrays. For the first time, we show visual evidence that the main transfer mechanism is contact-based, due to thermal surface expansion of the donor layer. Thus, the process is different from the many known variants of laser-induced forward transfer. We characterize the maximum axial surface expansion in relation to laser power and pulse duration. On this basis, we derive a numerical model that approximates the axial surface expansion within measurement tolerances. Finally, we analyze the topology of the transferred soft material nanolayer spots by fluorescence imaging and vertical scanning interferometry to determine width, height, and shape of the transferred material. Concluding from this experimental and numerical data, we can now predict the amount of transferred material in this process.Publicationtype: Journal Article9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Processing, growth mechanism and thermodynamic calculations of carbon foam with a hollow tetrapodal morphology – Aerographite(2019-03-15); ; ; ; B.V. Aerographite is a 3D interconnected carbon foam with a tetrapodal morphology. The synthesis of Aerographite is based on a two-step process: first the production of a zinc oxide (ZnO) template in a flame transport synthesis (FTS) followed by the replication into the carbon structure in a chemical vapour deposition process (CVD). This study presents a growth model of this 3D carbon foam via analyzing the newly formed carbon structure in an interrupted synthesis by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Moreover, the Gibbs free energy of the occurred replica CVD (rCVD) process, based on the reduction of ZnO and the formation of carbon layers, was calculated. During the CVD process the injected carbon deposits on the surfaces of the ZnO tetrapods, while simultaneously the replication into the carbon structure takes place, as a result of the reduction of ZnO into gaseous zinc and water vapour, which is due to the reaction of ZnO with the hydrogen (H 2 ) from the injected source. This replication of the ZnO template into a carbon structure is based on an epitaxial controlled process combined with a catalytic graphitization, whereby the morphology of the template structure is replicated by the carbon. Furthermore, the influence of the growth process on the arrangement of carbon in layers and formation of defects was explained.Publicationtype: Journal Article106 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigations into the structure of PEO-layers for understanding of layer formation(2018-06-15); ; ; ; Layer with a wide variety of structural and chemical properties influenced by the electrolytic system. This process enables the combined adjustment of various characteristics, i.e. the morphology and chemical composition. The procedure facilitates the possibility of generating an individual structure as well as forming a crystalline surface in a single step. A highly porous surface with a high crystalline content consisting of titanium dioxide phases is ensured through the process of plasma electrolytic oxidizing pure titanium. In the present study plasma electrolytic oxidized TiO 2 -layers were investigated regarding their crystallinity through the layer thickness. The layers were prepared with a high applied voltage of 280 V to obtain a PEO-layer with highly crystalline anatase and rutile amounts. Raman spectroscopy and electron backscatter diffraction (EBSD) were selected to clarify the structure of the oxide layer with regard to its crystallinity and phase composition. The composition of the TiO 2 -phases is more or less irregularly distributed as a result of the higher energy input on the uppermost side of the layer. Scanning transmission electron microscopy (STEM) provided a deeper understanding of the structure and the effects of plasma discharges on the layer. It was observed that the plasma discharges have a strong influence on crystallite formation on top of the oxide layer and also at the boundary layer to the titanium substrate. Therefore, small crystallites of TiO 2 could be detected in these regions. In addition, it was shown that amorphous TiO 2 phases are formed around the characteristic pore structures, which allows the conclusion to be drawn that a rapid cooling from the gas phase had to take place in these areas.Publicationtype: Journal Article85 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the mechanism of ion-induced bending of nanostructures(2018-02-06); ; ; This contribution concentrates on ion-induced bending phenomena which may serve as a versatile tool to manufacture nanostructured devices. In particular bending was studied in free standing Au cantilevers. The preparation and irradiation of the cantilevers were performed using a TESCAN LYRA dual beam system. Cantilevers with thicknesses ranging between 90 and 200 nm were irradiated with 30 keV Ga ions normal to the sample surface up to a maximum fluence of ∼3 × 10 20 Ga/m 2 . The bending of the cantilevers towards the incident beam is discussed in terms of local volume change due to accumulation of radiation-induced vacancies and substitutional Ga atoms in the Ga implantation layer, as well as due to accumulation of interstitial type clusters in the region beyond the Ga penetration range. A model is proposed to explain the observations, based on a set of rate equations for concentrations of point defects, i.e. vacancies, self-interstitials and implanted Ga atoms. The influence of preexisting defects is also discussed. The work shows that an in-depth understanding the ion-beam bending can play a predictive role in a quantitative control in for the micro- and nanofabrication of small-sized products.Publicationtype: Journal Article15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Development of a poly(dimethylacrylamide) based matrix material for solid phase high density peptide array synthesis employing a laser based material transfer(2016-12-15); ; ; ; von Bojnicic-Kninski, Clemens M.Poly(dimethylacrylamide) (PDMA) based matrix materials were developed for laser-based in situ solid phase peptide synthesis to produce high density arrays. In this specific array synthesis approach, amino acid derivatives are embedded into a matrix material, serving as a “solid” solvent material at room temperature. Then, a laser pulse transfers this mixture to the target position on a synthesis slide, where the peptide array is synthesized. Upon heating above the glass transition temperature of the matrix material, it softens, allowing diffusion of the amino acid derivatives to the synthesis surface and serving as a solvent for peptide bond formation. Here, we synthesized PDMA six-arm star polymers, offering the desired matrix material properties, using atom transfer radical polymerization. With the synthesized polymers as matrix material, we structured and synthesized arrays with combinatorial laser transfer. With densities of up to 20,000 peptide spots per cm <sup>2</sup> , the resolution could be increased compared to the commercially available standard matrix material. Time-of-Flight Secondary Ion Mass Spectrometry experiments revealed the penetration behavior of an amino acid derivative into the prepared acceptor synthesis surface and the effectiveness of the washing protocols.Publicationtype: Journal Article2 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Solid-material-based coupling efficiency analyzed with time-of-flight secondary ion mass spectrometry(2016)5 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effect of Al₂ Gd on microstructure and properties of laser clad Mg-Al-Gd coatings(2015-03-01); ; ; ; In order to investigate the effects of Gd addition on the microstructures and properties of magnesium coatings, the Mg-7.5Al-xGd (x = 0, 2.5, 5.0 and 7.5 wt.%) coatings on cast magnesium alloy were fabricated by laser cladding with wire feeding. The results indicated that the gadolinium (Gd) addition led to the formation of a cubic Al 2 Gd phase as well as suppressed the precipitation of eutectic Mg 17 Al 12 phase. The laser clad coating containing nominally 7.5 wt.% Gd presented the highest microhardness, ultimate tensile strength and yield strength at both room temperature and high temperatures. The enhancement of heat resistant capacities was chiefly attributed to the existence of thermally stable Al 2 Gd particles, which prevented tiny liquation of eutectic phases along the grain boundaries and made great contributions on maintaining high yield ratio during high-temperature deformation.Publicationtype: Journal Article47