Hydrogenated TiO2 nanoparticles loaded with Au nanoclusters demonstrating largely enhanced performance for electrochemical reduction of nitrogen to ammonia. - In: Energy technology, ISSN 2194-4296, Bd. 10 (2022), 7, 2200085, S. 1-9
Pristine TiO2/Au (P-TiO2/Au) is modified by hydrogen plasma (H-TiO2/Au) or hydrogen and oxygen plasma (H-O-TiO2/Au) treatment, and then used as electrochemical catalysts for nitrogen reduction reaction (NRR). H-TiO2/Au shows enhanced performance for the NRR process compared with both P-TiO2/Au and H-O-TiO2/Au. After hydrogenation treatment, some disordered regions on the surface of TiO2 nanoparticles are formed, and a large number of oxygen vacancies are incorporated into the TiO2 crystalline structures. When the samples are used as catalysts for electrochemical NRR, the yield of NH3 of H-TiO2/Au is about ten times compared to that of P-TiO2/Au and about three times that of H-O-TiO2/Au, while the highest Faradaic efficiency of 2.7% is also obtained at the potential of -0.1 V for the H-TiO2/Au catalyst. The density functional theory (DFT) calculation results confirm that H-TiO2/Au with oxygen vacancies and the disordered surface layer is much preferred energetically for the NRR process. It proves that enhanced adsorption of N2 molecules on the catalyst and reduced reaction barriers due to the presence of defects play an important role in improving catalysts’ performances. The results show that the plasma hydrogenation technique can be used as an efficient method to modify catalysts for electrochemical NRR processes.
https://doi.org/10.1002/ente.202200085
Anisotropy of the ΔE effect in Ni-based magnetoelectric cantilevers: a finite element method analysis. - In: Sensors, ISSN 1424-8220, Bd. 22 (2022), 13, 4958, S. 1-16
In recent investigations of magnetoelectric sensors based on microelectromechanical cantilevers made of TiN/AlN/Ni, a complex eigenfrequency behavior arising from the anisotropic ΔE effect was demonstrated. Within this work, a FEM simulation model based on this material system is presented to allow an investigation of the vibrational properties of cantilever-based sensors derived from magnetocrystalline anisotropy while avoiding other anisotropic contributions. Using the magnetocrystalline ΔE effect, a magnetic hardening of Nickel is demonstrated for the (110) as well as the (111) orientation. The sensitivity is extracted from the field-dependent eigenfrequency curves. It is found, that the transitions of the individual magnetic domain states in the magnetization process are the dominant influencing factor on the sensitivity for all crystal orientations. It is shown, that Nickel layers in the sensor aligned along the medium or hard axis yield a higher sensitivity than layers along the easy axis. The peak sensitivity was determined to 41.3 T−1 for (110) in-plane-oriented Nickel at a magnetic bias flux of 1.78 mT. The results achieved by FEM simulations are compared to the results calculated by the Euler-Bernoulli theory.
https://doi.org/10.3390/s22134958
Perturbed angular correlation technique at ISOLDE/CERN applied for studies of hydrogenated titanium dioxide (TiO2): observation of Cd-H Pairs. - In: Crystals, ISSN 2073-4352, Bd. 12 (2022), 6, 756, S. 1-10
Profound understanding of the local electronic and defect structure in semiconductors always plays a vital role in the further developing of applications of such materials. In the present work an investigation of the electronic structure in hydrogenated TiO2 (rutile) thin films is conducted by virtue of Time-Differential γ-γ Perturbed Angular Correlation spectroscopy (TDPAC or PAC) with 111mCd/Cd isotope, produced and implanted at ISOLDE/CERN. The measurements were performed at 581 K as a function of the temperature of the samples during hydrogenation. Despite the fact, that rutile single crystals usually show the presence of two local environments, when are studies with Cd/In isotopes, the current pristine thin films sample had a single electric field gradient. Upon various degrees of hydrogenation, Cd probe atoms showed underwent alterations, resulting in up to 3 different local surroundings, generally with high electric field gradients. Broad EFG distributions are likely due to randomly distributed point defects in the neighbourhood of Cd acceptors. Observed results suggest that hydrogenations performed at RT and 423 K are not able to promote unique defect configurations, while in the range of 473-573 K the formation of such configurations is observed. Therefore, one may assume that the formation of Cd-defect complexes (Cd-H pairs) is temperature enhanced. At higher levels of hydrogenation (663 K), the samples become partly amorphous that further hinders any atomistic studies with strong damped PAC spectra. Cd-H complexes seem to be stable up to annealing up to 581 K annealing. The obtained results give a deep insight into complex hydrogen defects, their interactions and bond formations with Cd acceptor.
https://doi.org/10.3390/cryst12060756
Controllable Si oxidation mediated by annealing temperature and atmosphere. - In: Journal of materials science, ISSN 1573-4803, Bd. 57 (2022), 24, S. 10943-10952
The morphology evolution by thermal annealing induced dewetting of gold (Au) thin films on silicon (Si) substrates with a native oxide layer and its dependences on annealing temperature and atmosphere are investigated. Both dewetting degree of thin film and Au/Si interdiffusion extent are enhanced with the annealing temperature. Au/Si interdiffusion can be observed beyond 800 ˚C and Au-Si droplets form in both argon and oxygen (Ar + O2) and argon and hydrogen (Ar + H2) environments. In Ar + O2 case, the passive oxidation (Si + O2 &flech; SiO2) of diffused Si happens and thick silicon oxide (SiOx) covering layers are formed. A high temperature of 1050 ˚C can even activate the outward growth of free-standing SiOx nanowires from droplets. Similarly, annealing at 800 ˚C under Ar + H2 situation also enables the slight Si passive oxidation, resulting in the formation of stripe-like SiOx areas. However, higher temperatures of 950-1050 ˚C in Ar + H2 environment initiate both the SiOx decomposition and the Si active oxidation (2Si + O2 &flech; 2SiO(g)), and the formation of solid SiOx is absent, leading to the only formation of isolated Au-Si droplets at elevated temperatures and droplets evolve to particles presenting two contrasts due to the Au/Si phase separation upon cooling.
https://doi.org/10.1007/s10853-022-07354-x
Influence of contact pressure on the specific electrical contact resistance of copper. - In: IEEE transactions on components, packaging and manufacturing technology, ISSN 2156-3985, Bd. 12 (2022), 6, S. 973-980
The specific electrical contact resistance (SECR) [ Ωm2 ] of Cu-ETP (CW004A) contacts is characterized in dependence of contact pressure up to high pressures close to the tensile strength of the base material. Two different material states are considered, R200 (soft) and R300. Static four-wire measurements are carried out on a special experimental setup, which favors homogeneous contact states during mechanical loading. A finite-element simulation is utilized for interpretation and evaluation of the measurements, including the deformation of the samples during the test. The results show that the SECR of the harder material state R300 is higher than that of the softer material R200. The developed data show a decrease of SECR with increasing contact pressure. For contact pressures up to 0.5 of the tensile strength σt of the base material, the SECR decreases according to a power law. For contact pressures above 0.6 σt , the decrease shifts toward a linear behavior. In addition, the measurements show that the SECR vanishes at contact pressures in region of the tensile strength of the base material.
https://doi.org/10.1109/TCPMT.2022.3176740
Tuning of high-temperature dielectric properties in the system (Bi0.5Na0.5)TiO3-BaTiO3-CaZrO3. - In: Ceramics international, ISSN 1873-3956, Bd. 48 (2022), 15, S. 22228-22236
Solid solutions of the (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xCaZrO3 system are regarded as promising dielectrics for high-temperature capacitors as they exhibit a remarkable flat trend of the permittivity over a large temperature range coupled with comparable low dielectric losses. In this work, the composition 0.8(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.2CaZrO3 was chosen in an attempt to optimize especially the high-temperature dielectric properties above 200 ˚C. In particular, the influence of excess bismuth to account for element losses caused by evaporation, and the effect of manganese as acceptor dopant are reported. Conventional solid-state reaction route was used to synthesize selected compositions. X-ray diffraction was used to confirm a pseudo-cubic perovskite main phase in all examined compositions, although small traces of a zirconia secondary phase were also detected. All samples exhibit an expected flat trend of the relative permittivity with a maximum deviation of the permittivity lower than 15% between -80 ˚C and 300 ˚C. The unmodified base composition shows small dielectric loss (<2%) between -55 ˚C and 265 ˚C. By using small quantities of manganese doping, the small-loss temperature range was extended (-70 ˚C and 300 ˚C). Excess bismuth also affects the temperature-dependent dielectric losses, resulting in a narrowed temperature range, eventually limiting the application possibilities.
https://doi.org/10.1016/j.ceramint.2022.04.220
Silicon carbide formation in reactive silicon-carbon multilayers. - In: Materials science forum, ISSN 1662-9752, Bd. 1062 (2022), S. 44-48
An alternative low thermal budget silicon carbide syntheses route is presented. The method is based on self-propagating high-temperature synthesis of binary silicon-carbon-based reactive multilayers. With this technique, it is possible to obtain cubic polycrystalline silicon carbide at relatively low annealing temperatures by a solid state reaction. The reaction starts above 600 ˚C. The transformation process proceeds in a four-step process. The reaction enthalpy was determined to be (-70 ± 4) kJ/mol.
https://doi.org/10.4028/p-7u1v90
Photo-thermoelectric conversion and photo-induced thermal imaging using 2D/3D ReS2carbon framework with enhanced photon harvesting. - In: The chemical engineering journal, ISSN 1873-3212, Bd. 446 (2022), 137084
Solar energy is a promising renewable energy with the potential for the sustainable development of the world. Efficient photo-thermal conversion is essential for harvesting and conversion of solar energy, therefore, the main challenge is the development of efficient and low-cost photothermal conversion materials. Carbon framework can be considered as a candidate but somehow its application potential can be still constrained due to the limited absorption of near-infrared (NIR) light. Herein, we propose a general strategy for preparing two-dimensional (2D) transition metal dichalcogenides nanosheets and three-dimensional (3D) carbon framework composites (2D/3D ReS2C) as a photothermal material, which has an excellent broadband light absorption performance (in the wavelength range from 200 to 2500 nm). A small thermoelectric (TE) module with an area of 4 × 4 cm2 is integrated with annealed ReS2@C as a light absorber for the investigation of photo-thermoelectric conversion. The open-circuit voltage of the assembled device increases clearly under solar illumination and reaches the maximum value of 136.3 mV, which is ∼ five times larger than that without the absorber. In addition, 20 TE modules coated with ReS2@C absorber layers are connected in series, which can produce a maximum open-circuit voltage of 2.12 V (∼66.25 V/m2) to light up a red light-emitting diode (LED) under natural sunlight. Moreover, the annealed ReS2@C powder demonstrates a rapid and strong photothermal response under NIR light (wavelength ＞800 nm), which indicates a great application potential in photothermal imaging and photothermal cancer therapy.
https://doi.org/10.1016/j.cej.2022.137084
Black silver: three-dimensional Ag hybrid plasmonic nanostructures with strong photon coupling for scalable photothermoelectric power generation. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 14 (2022), 14, S. 16894-16900
The conversion of solar energy into electric power has been extensively studied, for example, by photovoltaics. However, photo-thermoelectric (P-TE) conversion as an effective solar-to-electricity conversion process is less studied. Here, we present an efficient full-solar-spectrum plasmonic absorber for scalable P-TE conversion based on a simple integration of light absorber and commercial thermoelectric modules. Our developed light absorber of silica-silver hybrid structures achieves an average absorption of 99.4% in the wavelength range from 200 to 2500 nm, which covers over 98% solar energy in this range. It thus appears fully matte black and is named black silver. The light absorber includes a hierarchical structure with Ag nanoparticles attached on three-dimensional SiO2 nanostructures, resulting in ultrahigh absorption. Strong localized surface plasmon resonance hybridization together with multiple scattering causes the perfect light absorption. Using the black silver as a light absorber for P-TE power generation, it can achieve a peak voltage density as high as 82.5 V m-2 under a solar intensity of 100 mW cm-2, which is large enough to power numerous electronic devices. By assembling 20 thermoelectric modules in series, we test their possibility of practical application, and they can also achieve an average voltage density of 70.66 V m-2. Our work opens up a promising technology that facilitates high-efficiency and scalable solar energy conversion via the P-TE effect.
https://doi.org/10.1021/acsami.2c01181
Thin film nanostructuring at oblique angles by substrate patterning. - In: Surface and coatings technology, ISSN 1879-3347, Bd. 436 (2022), 128293, insges. 12 S.
It is demonstrated that, besides classical nanocolumnar arrays, the oblique angle geometry induces the growth of singular structures in the nanoscale when using wisely designed patterned substrates. Well-ordered array of crosses, cylindrical nanorods or hole structures arranged in square or hexagonal regular geometries are reported as examples, among others. The fundamental framework connecting substrate topography and film growth at oblique angles is presented, allowing the use of substrate patterning as a feasible thin film nanostructuring technique. A systematic analysis of the growth of TiO2 thin films on 4 different lithographic patterned substrates in 4 different scale lengths is also presented. A first conclusion is the existence of a height-based selective growth in the initial stages of the deposition, by which the film preferentially develops on top of the tallest substrate features. This behavior is maintained until the film reaches a critical thickness, the so-called Oblivion Thickness, above which the film topography becomes gradually independent of the substrate features. A general formula relating the spatial features of the pattern, the coarsening exponent and the Oblivion Thickness has been deduced.
https://doi.org/10.1016/j.surfcoat.2022.128293