Journal articles from 2018

Anzahl der Treffer: 685
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Li, Feitao; Oliva Ramírez, Manuel; Wang, Dong; Schaaf, Peter
Formation and evolution of Au-SiOx heterostructures: from nanoflowers to nanosprouts. - In: Materials and design, ISSN 1873-4197, Bd. 209 (2021), 109956, insges. 11 S.

This work reports the formation of circular cavities and Au-SiOx nanoflowers after annealing of thin Au film deposited on SiO2/Si substrates, and the transformation of nanoflowers to nanosprouts with increasing the annealing time. Two reference experiments indicate that both H2 and Si are indispensable for the above structures. The formation of cavities can be attributed to the SiO2 layer decomposition and the product, volatile SiO, provides a Si source for the formation of nanoflowers at the early stage. A model is proposed to indicate that SiO gas produced at the Si/SiO2 interface can diffuse to the surface assisted by the defects in the SiO2 layer before the decomposed cavities are exposed. Then the exposing of those cavities introduces another volatile SiO from the active oxidation of Si substrate, provoking a change in the direction of the main Si source, which in turn makes the one nanoparticle of the nanoflower split in two and finally form the nanosprout. The model about the escape of SiO further details SiO2 decomposition process, and the transformation mechanism from nanoflowers to nanosprout sheds light on a feasible nanofabrication method to design tunable size and shape of nanoparticles.



https://doi.org/10.1016/j.matdes.2021.109956
Schaaf, Peter; Constantinescu, Catalin; Matei, Andreea
Preface on laser material interactions: from basic science to industrial applications (LaserMaterInter2020). - In: Applied surface science advances, ISSN 2666-5239, Bd. 6 (2021), 100133, insges. 1 S.

https://doi.org/10.1016/j.apsadv.2021.100133
Wang, Honglei; Cheng, Pengfei; Shi, Jun; Wang, Dong; Wang, Hongguang; Pezoldt, Jörg; Stich, Michael; Chen, Runfeng; Aken, Peter Antonie van; Huang, Wei; Schaaf, Peter
Efficient fabrication of MoS2 nanocomposites by water-assisted exfoliation for nonvolatile memories. - In: Green chemistry, ISSN 1463-9270, Bd. 23 (2021), 10, S. 3642-3648

Efficient and green exfoliation of bulk MoS2 into few-layered nanosheets in the semiconducting hexagonal phase (2H-phase) remains a great challenge. Here, we developed a new method, water-assisted exfoliation (WAE), for the scalable synthesis of carboxylated chitosan (CC)/2H-MoS2 nanocomposites. With facile hand grinding of the CC powder, bulk MoS2 and water followed by conventional liquid-phase exfoliation in water, this method can not only efficiently exfoliate the 2H-MoS2 nanosheets, but also produce two-dimensional (2D) CC/2H-MoS2 nanocomposites. Interestingly, the intercalated CC in MoS2 nanosheets increases the interlayer spacing of 2H-MoS2 to serve as good candidates for the semiconductor devices. 2D CC/2H-MoS2 nanocomposites show superior electronic rectification effects in nonvolatile write-once-read-many-times memory (WORM) behavior with an ON/OFF ratio over 103, which can be rationally controlled by the weight ratios of CC and MoS2. These findings by the WAE method would open tremendous potential opportunities to prepare commercially available semiconducting 2D nanocomposites for promising high-performance device applications.



https://doi.org/10.1039/D1GC00162K
Wang, Anni; Gallino, Isabella; Riegler, Sascha Sebastian; Lin, Yi-Ting; Isaac, Nishchay Angel; Sauni Camposano, Yesenia Haydee; Matthes, Sebastian; Flock, Dominik; Jacobs, Heiko O.; Yen, Hung-Wei; Schaaf, Peter
Ultrafast formation of single phase B2 AlCoCrFeNi high entropy alloy films by reactive Ni/Al multilayers as heat source. - In: Materials and design, ISSN 1873-4197, Bd. 206 (2021), 109790, insges. 12 S.

High entropy alloy films of AlCoCrFeNi B2-ordered structure are formed during an ultrafast heating process by reactive Ni/Al multilayers. The self-propagating high-temperature reaction occurring in reactive Ni/Al multilayers after ignition represents an ultrafast heat source which is used for the transformation of a thin films Al/CoFe/CrNi multilayer structure into a single-phase high entropy alloy film. The materials design of the combined multilayers thus determines the phase formation. Conventional rapid thermal annealing transforms the multilayer into a film with multiple equilibrium phases. Ultrafast combustion synthesis produces films with ultrafine-grained single-phase B2-ordered compound alloy. The heating rates during the combustion synthesis are in the order of one million K/s, much higher than those of the rapid thermal annealing, which is about 7 K/s. The results are compared with differential scanning calorimetry experiments with heating rates ranging from about 100 K/s up to 25000 K/s. It is shown that the heating rate clearly determines the phase formation in the multilayers. The rapid kinetics of the combustion prevents long-range diffusion and promotes the run-away transformation. Thus, multilayer combustion synthesis using reactive Ni/Al multilayers as heat source represents a new pathway for the fabrication of single phase high-entropy alloy films.



https://doi.org/10.1016/j.matdes.2021.109790
Hotovy, Ivan; Rehacek, Vlastimil; Kemeny, Martin; Ondrejka, Peter; Kostic, Ivan; Mikolasek, Miroslav; Spieß, Lothar
Preparation and gas-sensing properties of very thin sputtered NiO films. - In: Journal of electrical engineering, ISSN 1339-309X, Bd. 72 (2021), 1, S. 61-65

We present results on very thin NiO films which are able to detect 3 ppm of acetone, toluene and n-butyl acetate in synthetic air and to operate at 300˚C. NiO films with 25 and 50 nm thicknesses were prepared by dc reactive magnetron sputtering on alumina substrates previously coated by Pt layers as heater and as interdigitated electrodes. Annealed NiO films are indexed to the (fcc) crystalline structure of NiO and their calculated grain sizes are in the range from 22 to 27 nm. Surface morphology of the examined samples was influenced by a rough and compact granular structure of alumina substrate. Nanoporous NiO film is formed by an agglomeration of small grains with different shapes while they are created on every alumina grain.



https://doi.org/10.2478/jee-2021-0009
Dulanto, Jorge; Sevillano-Bendezú, Miguel Ángel; Grieseler, Rolf; Guerra, Jorge A.; Korte, Lars; Dittrich, Thomas; Töfflinger, Jan Amaru
Silicon interface passivation studied by modulated surface photovoltage spectroscopy. - In: Peruvian Workshop on Solar Energy 2020 (JOPES 2020), 25-26 June 2020, Lima, Peru, (2021), 012003, S. 1-7

We demonstrate that the modulated surface photovoltage spectroscopy (modulated SPS) technique can be applied to investigate interface states in the bandgap, i.e. interface passivation, of crystalline silicon coated with a downshift layer such as hydrogenated aluminum nitride with embedded terbium ions by suppressing straylight with a cut-off filter. Different hydrogen contents influence the surface photovoltage spectra at photon energies below the bandgap of crystalline silicon. Modulated SPS reveals that at higher hydrogen content there is a lower signal and, thus, a lower density of surface defect states. Our experiments show that modulated SPS can become a powerful tool for characterizing defect states at interfaces which cannot be easily studied by other methods.



https://doi.org/10.1088/1742-6596/1841/1/012003
Reiß, Stephanie; Hopfeld, Marcus; Romanus, Henry; Pfeifer, Kerstin; Krischok, Stefan; Rädlein, Edda
Chemical changes of float glass surfaces induced by different sand particles and mineralogical phases. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 566 (2021), 120868

Particles play an important role in the storage, transportation and natural weathering of glasses, but their influence on glass degradation is little studied. In this work, the influence of main sand components is investigated. Feldspar exhibits the strongest leaching rate for the network former Na, while quartz has the lowest. The leaching rate of natural sands is in between. Based on these findings, a model describing the leaching mechanism was developed: Hereby, hydroxyl groups adhering on sand grains adsorb network modifiers by substituting their hydrogen by network formers from the glass surface. The amount of available hydroxyl groups determines the leaching rate. This model is supported by loss on ignition performed for the sands, which might be a suitable method to roughly estimate their leaching rates. The adsorption of network modifiers suppresses carbonate formation, dendritic growth and Mg diffusion in the glass surface region. Pimple-like crystal growth is observed.



https://doi.org/10.1016/j.jnoncrysol.2021.120868
Cheng, Pengfei; Wang, Honglei; Wang, Hongguang; Aken, Peter Antonie van; Wang, Dong; Schaaf, Peter
High-efficiency photothermal water evaporation using broadband solar energy harvesting by ultrablack silicon structures. - In: Advanced energy & sustainability research, ISSN 2699-9412, Bd. 2 (2021), 4, 2000083, S. 1-9

Development of broadband absorption materials for solar energy harvesting is an important strategy to address global energy issues. Herein, it is demonstrated that an ultrablack silicon structure with abundant surface texturing can absorb about 98.7% solar light within the wavelength range of 300 to 2500 nm, i.e., a very large range and amount. Under 1 sun irradiation, the ultrablack silicon sample's surface temperature can increase from 21.2 to 51.2 ˚C in 15 min. During the photothermal water evaporation process, the ultrablack silicon sample's surface temperature can still reach a highest temperature of 43.2 ˚C. The average photothermal conversion efficiency (PTCE) can be as high as 72.96%. The excellent photothermal performance to the excellent light-trapping ability of the pyramidal surface nanostructures during solar illumination, which leads to extremely efficient absorption of light, is attributed. In addition, the large water contact area also enables fast vapor transport. The stability of the photothermal converter is also examined, presenting excellent structure and performance stabilities over 10 cycles. This indicates that the ultrablack Si absorber can be a promising photothermal conversion material for seawater desalination, water purification, photothermal therapy, and more.



https://doi.org/10.1002/aesr.202000083
Oliva Ramírez, Manuel; Schade, Philipp; Zobel, Christoph; Wang, Dong; Schaaf, Peter
Morphological and compositional mapping of supersaturated AuNi alloy nanoparticles fabricated by solid state dewetting. - In: Applied surface science advances, ISSN 2666-5239, Bd. 4 (2021), 100082, insges. 6 S.

The solid state dewetting (SSD) of metallic bilayers is a straightforward method for the fabrication of alloy nanoparticles. In particular, alloys that present a gap of miscibility offer a rich phenomenology regarding not only the particle formation but also the composition of their phases. In the present work, AuNi precursor bilayers have been annealed at different temperatures and times to produce AuNi alloy nanoparticles. The evolution of the shape, size, and interparticle distance as well as the composition of the different phases formed in the nanoparticles, allow to unravel the role of the annealing temperatures and times for the fabrication of AuNi supersaturated alloys. Furthermore, the results offer a morphological and compositional map for the fabrication of AuNi alloys nanoparticles of different shapes, sizes, and compositions. Therefore, this map is a useful tool for the tailored design of supersaturated or decomposed nanoparticles by SSD.



https://doi.org/10.1016/j.apsadv.2021.100082
Chen, Hong-Lei; Luo, Xue-Mei; Wang, Dong; Schaaf, Peter; Zhang, Guang-Ping
Achieving very high cycle fatigue performance of Au thin films for flexible electronic applications. - In: Journal of materials science & technology, ISSN 1941-1162, Bd. 89 (2021), S. 107-113

https://doi.org/10.1016/j.jmst.2021.02.025