Flexible and Binder-Free Iron Phosphide Electrodes Using a Three-Dimensional Support for High Hydrogen Productivity

In this work, an inexpensive and reliable microstructured electrode for the hydrogen evolution reaction (HER) is developed. This cathode is made of Earth-abundant elements consisting of iron phosphide as an electrocatalyst and carbon felt (CF) as a flexible conductive scaffold. Its porous character and binder-free FeP coverage over the carbon fibers generate a high number of accessible active sites for the reaction, achieving a high value of the electrochemically active surface area. The electrode reaches 100 mA ⋅ cm by applying only −53 mV vs RHE at 50 °C in 0.5 M HSO, demonstrating excellent electrocatalytic activity for the HER and outstanding stability in acidic electrolyte. Furthermore, the feasibility of these electrodes for industrial application is evaluated using a PEM electrolyzer. The developed prototype with a cathodic area of 1.8 cm shows a very promising performance, reaching 14.9 mmol H ⋅ h ⋅ cm (corresponding to 800 mA ⋅ cm) at a voltage of only 2.1 V

Enhancement of proximity induced superconductivity in planar Germanium

Holes in planar Ge have high mobilities, strong spin-orbit interaction and electrically tunable g-factors, and are therefore emerging as a promising candidate for hybrid superconductorsemiconductor devices. This is further motivated by the observation of supercurrent transport in planar Ge Josephson Field effect transistors (JoFETs). A key challenge towards hybrid germanium quantum technology is the design of high quality interfaces and superconducting contacts that are robust against magnetic fields. By combining the assets of Al, which has a long superconducting coherence, and Nb, which has a significant superconducting gap, we form low-disordered JoFETs with large ICRN products that are capable of withstanding high magnetic fields. We furthermore demonstrate the ability of phase-biasing individual JoFETs opening up an avenue to explore topological superconductivity in planar Ge. The persistence of superconductivity in the reported hybrid devices beyond 1.8 T paves the way towards integrating spin qubits and proximity-induced superconductivity on the same chip

Reducing charge noise in quantum dots by using thin silicon quantum wells

Charge noise in the host semiconductor degrades the performance of spin-qubits and poses an obstacle to control large quantum processors. However, it is challenging to engineer the heterogeneous material stack of gate-defined quantum dots to improve charge noise systematically. Here, we address the semiconductor-dielectric interface and the buried quantum well of a 28 Si/SiGe heterostructure and show the connection between charge noise, measured locally in quantum dots, and global disorder in the host semiconductor, measured with macroscopic Hall bars. In 5 nm thick 28 Si quantum wells, we find that improvements in the scattering properties and uniformity of the two-dimensional electron gas over a 100 mm wafer correspond to a significant reduction in charge noise, with a minimum value of 0.29 ± 0.02 μeV/Hz ½ at 1 Hz averaged over several quantum dots. We extrapolate the measured charge noise to simulated dephasing times to -gate fidelities that improve nearly one order of magnitude. These results point to a clean and quiet crystalline environment for integrating long-lived and high-fidelity spin qubits into a larger system. Charge noise degrades the performance of spin qubits hindering scalability. Here the authors engineer the heterogeneous material stack in 28 Si/SiGe gate-defined quantum dots, to improve the scattering properties and to reduce charge noise

Author Correction : Reducing charge noise in quantum dots by using thin silicon quantum wells

The original version of this Article omitted fromthe author list the author Amir Sammakwho is from the 'QuTech and Netherlands Organisation for Applied Scientific Research (TNO), Delft, The Netherlands'. This has been corrected in both the PDF and HTML versions of the Article

A singlet triplet hole spin qubit in planar Ge

Spin qubits are considered to be among the most promising candidates for building a quantum processor. GroupIV hole spin qubits have moved into the focus of interest due to the ease of operation and compatibility with Si technology. In addition, Ge offers the option for monolithic superconductor-semiconductor integration. Here we demonstrate a hole spin qubit operating at fields below 10 mT, the critical field of Al, by exploiting the large out-of-plane hole g-factors in planar Ge and by encoding the qubit into the singlet-triplet states of a double quantum dot. We observe electrically controlled g-factor-difference-driven and exchange-driven rotations with tunable frequencies exceeding 100 MHz and dephasing times of 1 $\mu$s which we extend beyond 150 $\mu$s with echo techniques. These results demonstrate that Ge hole singlet-triplet qubits are competing with state-of-the art GaAs and Si singlet-triplet qubits. In addition, their rotation frequencies and coherence are on par with Ge single spin qubits, but they can be operated at much lower fields underlining their potential for on chip integration with superconducting technologies

Evaluating the local bandgap across InxGa1-xAs multiple quantum wells in a metamorphic laser via low-loss EELS

We investigate spatially resolved variations in the bandgap energy across multiple InxGa1-xAs quantum wells (QWs) on a GaAs substrate within a metamorphic laser structure. Using high resolution scanning transmission electron microscopy and low-loss electron energy loss spectroscopy, we present a detailed analysis of the local bandgap energy, indium concentration, and strain distribution within the QWs. Our findings reveal significant inhomogeneities, particularly near the interfaces, in both the strain and indium content, and a bandgap variability across QWs. These results are correlated with density functional theory simulations to further elucidate the interplay between strain, composition, and bandgap energy. This work underscores the importance of spatially resolved analysis in understanding, and optimising, the electronic and optical properties of semiconductor devices. The study suggests that the collective impact of individual QWs might affect the emission and performance of the final device, providing insights for the design of next-generation metamorphic lasers with multiple QWs as the active region

Low disorder and high valley splitting in silicon

The electrical characterisation of classical and quantum devices is a critical step in the development cycle of heterogeneous material stacks for semiconductor spin qubits. In the case of silicon, properties such as disorder and energy separation of conduction band valleys are commonly investigated individually upon modifications in selected parameters of the material stack. However, this reductionist approach fails to consider the interdependence between different structural and electronic properties at the danger of optimising one metric at the expense of the others. Here, we achieve a significant improvement in both disorder and valley splitting by taking a co-design approach to the material stack. We demonstrate isotopically-purified, strained quantum wells with high mobility of 3.14(8)$\times$10$^5$ cm$^2$/Vs and low percolation density of 6.9(1)$\times$10$^{10}$ cm$^{-2}$. These low disorder quantum wells support quantum dots with low charge noise of 0.9(3) $\mu$eV/Hz$^{1/2}$ and large mean valley splitting energy of 0.24(7) meV, measured in qubit devices. By striking the delicate balance between disorder, charge noise, and valley splitting, these findings provide a benchmark for silicon as a host semiconductor for quantum dot qubits. We foresee the application of these heterostructures in larger, high-performance quantum processors

Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth

Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10※000-25※000 cm V s consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of ∼8 μm at 50 mK in mesoscopic rings

Enhanced electrochemical hydrogenation of benzaldehyde to benzyl alcohol on Pd@Ni-MOF by modifying the adsorption configuration

Electrocatalytic hydrogenation (ECH) approaches under ambient temperature and pressure offer significant potential advantages over thermal hydrogenation processes but require highly active and efficient hydrogenation electrocatalysts. The performance of such hydrogenation electrocatalysts strongly depends not only on the active phase but also on the architecture and surface chemistry of the support material. Herein, Pd nanoparticles supported on a nickel metal-organic framework (MOF), Ni-MOF-74, are prepared, and their activity toward the ECH of benzaldehyde (BZH) in a 3 M acetate (pH 5.2) aqueous electrolyte is explored. An outstanding ECH rate up to 283 μmol cm-2 h-1 with a Faradaic efficiency (FE) of 76% is reached. Besides, higher FEs of up to 96% are achieved using a step-function voltage. Materials Studio and density functional theory calculations show these outstanding performances to be associated with the Ni-MOF support that promotes H-bond formation, facilitates water desorption, and induces favorable tilted BZH adsorption on the surface of the Pd nanoparticles. In this configuration, BZH is bonded to the Pd surface by the carbonyl group rather than through the aromatic ring, thus reducing the energy barriers of the elemental reaction steps and increasing the overall reaction efficiency.L.G. and C.Y.Z. thank the China Scholarship Council for the scholarship support. This work was financially supported by the SyDECat project from the Spanish MCIN/AEI/FEDER (PID2022-136883OB-C22). This work was supported by the Innovation Fund for Small and Medium-Sized Enterprises in Gansu Province (no. 22CX3JA006) and Lanzhou Talent Innovation and Entrepreneurship Project (no. 2022-2-81) and partially by the Fundamental Research Funds for the Central Universities (grant nos. lzujbky-2021-it33). The authors greatly acknowledge the support of the Supercomputing Center of Lanzhou University, China. J.L. is grateful for the project supported by the Natural Science Foundation of Sichuan Province (2022NSFSC1229). The authors also greatly thank for the generous help from Liming Deng and Professor Dr. Shengjie Peng (College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016, China). The project on which these results are based has received funding from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 801342 (Tecniospring INDUSTRY) and the Government of Catalonia’s Agency for Business Competitiveness (ACCIÓ). The authors acknowledge funding from Generalitat de Catalunya 2021SGR00457 and 2021SGR01581. ICN2 acknowledges funding from project PID2020-116093RB-C43, funded by MCIN/AEI/10.13039/501100011033/and by “ERDF A way of making Europe”, by the “European Union”. This study was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and Generalitat de Catalunya. ICN2 is supported by the Severo Ochoa program from Spanish MCIN/AEI (grant no. CEX2021-001214-S). ICN2 and IREC are funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autónoma de Barcelona Materials Science PhD program. M.B. acknowledges support from SUR Generalitat de Catalunya and the EU Social Fund; project ref 2020 FI 00103.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S).Peer reviewe