High-entropy materials are an emerging pathway in the development of high-activity (electro)catalysts because of the inherent tunability and coexistence of multiple potential active sites, which may lead to earth-abundant catalyst materials for energy-efficient electrochemical energy storage. In this report, we identify how the multication composition in high-entropy perovskite oxides (HEO) contributes to high catalytic activity for the oxygen evolution reaction (OER), i.e., the key kinetically limiting half-reaction in several electrochemical energy conversion technologies, including green hydrogen generation. We compare the activity of the (001) facet of LaCr0.2Mn0.2Fe0.2Co0.2Ni0.2O3‑δ with the parent compounds (single B-site in the ABO3 perovskite). While the single B-site perovskites roughly follow the expected volcano-type activity trends, the HEO clearly outperforms all of its parent compounds with 17 to 680 times higher currents at a fixed overpotential. As all samples were grown as an epitaxial layer, our results indicate an intrinsic composition–function relationship, avoiding the effects of complex geometries or unknown surface composition. In-depth X-ray photoemission studies reveal a synergistic effect of simultaneous oxidation and reduction of different transition metal cations during the adsorption of reaction intermediates. The surprisingly high OER activity demonstrates that HEOs are a highly attractive, earth-abundant material class for high-activity OER electrocatalysts, possibly allowing the activity to be fine-tuned beyond the scaling limits of mono- or bimetallic oxides.

The current progress of system miniaturization relies extensively on the development of 3D machining techniques to increase the areal structure density. In this work, a wafer-scale out-of-plane 3D silicon (Si) shaping technology is reported, which combines a multistep plasma etching process with corner lithography. The multistep plasma etching procedure results in high aspect ratio structures with stacked semicircles etched deep into the sidewall and thereby introduces corners with a proper geometry for the subsequent corner lithography. Due to the geometrical contrast between the gaps and sidewall, residues are left only inside the gaps and form an inversion mask inside the semicircles. Using this mask, octahedra and donuts can be etched in a repeated manner into Si over the full wafer area, which demonstrates the potential of this technology for constructing high-density 3D structures with good dimensional control in the bulk of Si wafers.

High entropy materials are a new pathway in the development of high-activity (electro )catalysts because of the inherent tunability and coexistence of multiple potential active sites, which may lead to earth-abundant catalyst materials for energy-efficient electrochemical energy storage. In this report, we identify how the multi-cation composition in high entropy perovskite oxides (HEO) contributes to high catalytic activity for the oxygen evolution reaction (OER), i.e. the key kinetically limiting half-reactions in several electrochemical energy conversion technologies, including green hydrogen generation. We compare the activity of the (001) facet of LaCr0.2Mn0.2Fe0.2Co0.2Ni0.2O3-δ with the parent compounds (single B-site in the ABO3 perovskite). While the single B-site perovskites roughly follow the expected volcano-type activity trends, the HEO clearly outperforms all of its parent compounds with 2.8 to 100 times higher currents at fixed overpotential. As all samples were grown as an epitaxial layer, our results indicate an intrinsic composition–function relationships, avoiding the effects of complex geometries or unknown surface composition. In-depth X-ray photoemission studies reveal a synergistic effect of simultaneous oxidation and reduction of different transition metal cations during adsorption of reaction intermediates. The surprisingly high OER activity demonstrates that HEOs are a highly attractive, earth-abundant new material class for high-activity OER electrocatalysts, possibly allowing fine-tuning the activity beyond the scaling limits of mono- or bimetallic oxides.

strategy for conventional transparent conducting oxides (TCOs) is to resort to degenerately dope wide-bandgap semiconductors to achieve the two key properties: electrical conductivity and optical transparency. Wide bandgap semiconductors are selected as host materials, which have the interband transitions above the visible spectrum, whereas dopants increase carrier density and thus electrical conductivity. Tin-doped indium oxides (ITOs) have been widely used because of its best balance of high electrical conductivity and optical transparency in the visible spectrum. [3] However, the increasing use of ITO as TCOs has resulted in the increase in the cost of ITO due to the limited availability of indium ore. [4] Meanwhile, many other applications, such as solar blind detection, ultraviolet (UV) lithography, UV light-emitting diodes, and UV curing, require transparent conductors in the UV spectrum. [5][6][7][8] However, conventional TCOs with high conductivity present low transmittance on the UV side of the spectrum. [1] Recently, an alternative design strategy has been proposed to use correlated metals with the intrinsic high carrier density exhibiting strong electron correlations to achieve both high electrical conductivity, thus low resistivity, and optical transparency in the UV-visible spectral range, overcoming the limitations of conventional TCOs. [9][10][11][12][13][14][15][16][17][18][19] It has been shown that as correlated metal films on single crystal substrates get thin, they maintain low resistivity and thus low sheet resistance at room temperature (RT) whereas their optical transmittance is comparable to (or higher than) conventional TCOs in the visible (or UV) spectrum. [9,10,17] However, the epitaxy so far required expensive and size-limited single crystal substrates, which impedes the application of correlated metals as TCOs.Meanwhile, oxide nanosheets drew attention because they can be used as buffer layers to promote the growth of highquality and thus high-performance transition metal oxide films regardless the supporting substrates. [20][21][22][23][24][25][26] Almost full coverage of oxide nanosheets can be obtained on virtually any flat substrates without the limitation of the substrate size by using Langmuir-Blodgett method. [21,24,25] Boileau et al. showed that correlated CaVO 3 and SrVO 3 (SVO) films with a thickness of 40 nm on Ca 2 Nb 3 O 10 (CNO) nanosheets on glass had the RT Correlated metals with high carrier density and strongly correlated electron effects provide an alternative route to achieve transparent conducting materials, different from the conventional degenerately doped wide-bandgap transparent conducting oxides (TCO). The extremely low electrical resistivity and high optical transparency in the ultraviolet-visible spectral range shown in 4d correlated metals present an advantage over conventional TCOs. However, most of the 4d correlated metals are grown epitaxially on single crystal substrates. Here, it has been shown that Ca 2 Nb 3 O 10 nanosheets with different buffer laye...

The rapid advent of the piezoelectric microelectromechanical systems (PiezoMEMS) field has created a tremendous demand for low hysteretic piezoelectric thin films on Si. In this work, we present the integration of epitaxial Pb(Mg0.33Nb0.67)O3-PbTiO3 (PMN-PT) thin films with Si to enable device fabrication using state of the art methods. With optimized buffer layers and electronic contacts, high-quality low hysteretic PMN-PT thin films are integrated with Si, which is a significant stride towards employing PMN-PT thin film for PiezoMEMS devices. It is found that the processing of the necessary SrTiO3 buffer layer is crucial to achieve the growth of phase-pure perovskite PMN-PT layers on Si. Furthermore, we propose the engineering of the electronic contact for the PMN-PT-on-Si capacitors to obtain low hysteretic polarization and displacement responses.