Lead-based piezoceramics are the dominant materials used in electronic devices, despite the known toxicity of lead. Developing safer piezoelectric materials has inspired the pursuit of lead-free piezoceramics, however some challenges remain in accessing these materials reproducibly. Here we demonstrate a simple and robust method for synthesis of the lead-free piezoceramic material, potassium sodium niobate (KxNa1-xNbO3, KNN) via an aqueous route. Stochiometric KNN (K0.5Na0.5NbO3) was prepared, by combining alkali-nitrate salts (NaNO3 and KNO3) with the hexaniobate ([HxNb6O19]8-x, Nb6) species in water, followed by heating at elevated temperatures for at least one hour. Ex situ heating of the amorphous alkali-Nb6 precursor reveals stoichiometric control and phase uniformity are possible in making KNN, versus a solid-state route. In situ heating in a transmission electron microscope (TEM), with selected area electron diffraction (SAED), facilitates monitoring the real-time transformation of the amorphous alkali-Nb6 precursor, to yield monoclinic KNN, in agreement with ex situ results. Therefore, an aqueous route via hexaniobate is an attractive alternative approach for developing lead-free piezoceramic materials.

Combining multiple III-V materials into axial nanowire heterostructures has enabled the fabrication of custom nanowire-based devices useful for a wide range of applications. However, our ability to form axial heterostructures between arbitrary combinations of III-V compounds is impeded by a lack of information on the dynamics of the heterojunction formation process, often resulting in suboptimal heterostructure morphologies, particularly for materials including Sb. In this work, we utilize environmental transmission electron microscopy to examine the formation of GaSb/GaAs heterojunctions in Au-seeded nanowires in situ. We demonstrate that the growth parameter window for successful GaSb/GaAs heterostructure formation is very narrow and requires the growth of a ternary GaSb x As1-x segment. Furthermore, we show that as the nanowire changes the composition from GaSb to GaAs, the nanoparticle and nanowire morphologies are highly dynamic. At the end of the transition, we observe that the nanoparticle volume is halved and the nanowire diameter is reduced from ≈40 to ≈30 nm at the liquid-solid interface. Moreover, the nanowire growth rate increases by a factor of 7, when GaAs composition is reached, at our optimized growth conditions. Additionally, we are able to observe that the change in the crystal phase from GaSb zincblende (ZB) to GaAs wurtzite (WZ) happens via a mixed ZB-4H-WZ regime and is dependent not only on the nanowire composition but also on the vapor-phase composition in the growth chamber. These results offer unique insight into the formation dynamics of axial nanowire heterostructures, elucidating the interplay between all phases and growth species.

Developing a reliable procedure for the growth of III-V nanowires (NW) on silicon (Si) substrates remains a significant challenge, as current methods rely on trial-and-error approaches with varying interpretations of critical process steps such as sample preparation, Au-Si alloy formation in the growth reactor, and NW alignment. Addressing these challenges is essential for enabling high-performance electronic and optoelectronic devices that combine the superior properties of III-V NW semiconductors with the well-established Si-based technology. Combining conventional scalable growth methods, such as metalorganic chemical vapor deposition (MOCVD) within situcharacterization using environmental transmission electron microscopy (ETEM-MOCVD) enables a deeper understanding of the growth dynamics, if that knowledge is transferable to the scalable processes. We report on successful epitaxial growth of Au-catalyzed GaAs NWs on Si(111) substrates using micro-electromechanical system chips with monocrystalline Si-cantilevers in both conventional MOCVD and ETEM-MOCVD systems. The conventional MOCVD provided a framework for initial parameter tuning, while ETEM-MOCVD offered valuable insights into early nucleation and catalyst-substrate interactions. Our findings show that nucleation is significantly influenced by the removal of native oxide layers and the initial formation of the Au-Si alloy. Ourin situstudies revealed different NW-substrate interfaces, essential for optimizing the epitaxial growth process. We identified three typical configurations of NW 'roots', each impacted by growth conditions and preparation steps, affecting the structural and potentially the optical properties of the NWs. Similarly, doping from the Si-substrate may affect both optical and electrical properties; however, compositional analysis revealed no traces of Si in NWs post-nucleation and a small amount in the catalytic droplet. Our research highlights the importance ofin situstudies for a comprehensive understanding of nucleation mechanisms, paving the way for optimizing III-V NW growth on Si substrates and developing high-performance III-V/Si devices.

We investigate experimentally the quantum coherence of an electronic two-level system in a double quantum dot under continuous charge detection. The charge state of the two-level system is monitored by a capacitively coupled single quantum dot detector that imposes a backaction effect on the system. The measured backaction is well described by an additional decoherence rate, approximately linearly proportional to the detector electron tunneling rate. We provide a model for the decoherence rate arising due to level detuning fluctuations induced by detector charge fluctuations. The theory predicts a factor of 2 lower decoherence rates than observed in the experiment, suggesting the need for a more elaborate theory accounting for additional sources of decoherence.

Epitaxially grown nanowires have shown promise for photovoltaic applications due to their nanophotonic properties. Moreover, the mechanical properties of nanowires can reduce crystallographic defect formation at interfaces to help enable new material combinations for photovoltaics. One material that stands to benefit from the nanowire morphology is zinc phosphide (Zn3P2), which, despite promising optoelectronic properties, has experienced limited applicability due to challenges achieving heteroepitaxy, stemming from its incompatible lattice parameter and coefficient of thermal expansion. Herein, we identify the requirements for successful epitaxy of Zn3P2 nanowires using metalorganic chemical vapor deposition and the impact on interface structure and defect formation. Furthermore, using high-throughput optical spectroscopy, we were able to demonstrate shifts in the photoluminescence intensity and energy by tuning the V/II ratio during growth, highlighting the compositional tunability of the optoelectronic properties of Zn3P2 nanowires.

Dissipative sensors typically use linear resonators with impedance matching to achieve maximal signal and fast operation. The impedance matching, however, sets an upper limit to the bandwidth of the readout. In this paper, we present a nonlinear resonator performing the readout of a double quantum dot charge state via a charge-sensing quantum dot. We show that by driving the resonator in the nonlinear regime, we achieve a near-unity signal for a dissipative sensor. This despite not satisfying the sensor impedance matching requirements necessary for such large signals in the linear regime. Our experiments, supported by numerical calculations, demonstrate that the signal increase stems from the sensor dissipation shifting the onset of the nonlinear resonator response. By lifting the matching requirement, we open up an avenue to ultrafast charge detectors as the resonator input-output coupling - setting the detector bandwidth - does not have to match to the typically much slower sensor dissipation rate.

Over the past decade, organic–inorganic hybrid perovskites have revolutionized next‐generation semiconductors, driving unprecedented advancements in cost‐effective optoelectronics. While lead‐based perovskite semiconductors exhibit exceptional optoelectronic properties, their inherent toxicity and vulnerability to environmental degradation remain significant barriers to widespread commercialization. Vacancy‐ordered layered double perovskites (LDPs) offer a viable alternative with direct bandgaps, reduced toxicity, superior stability, and tunable properties, while their divalent and trivalent cation integration enables precise control over electronic and photophysical characteristics for efficient optoelectronics. Herein, the M(III) cation site within the previously reported Cs4CoIn2Cl12 LDP system by substituting In3+ with Bi3+ and Sb3+ is systematically modified, achieving the first‐ever colloidal synthesis of Cs4CoBi2Cl12 and Cs4CoSb2Cl12 nanocrystals (NCs). A detailed investigation of their optoelectronic properties reveals significant structural distortions induced by different M(III) cations. Stability assessments demonstrate that Cs4CoSb2Cl12 exhibits exceptional air and compositional stability, maintaining its compositional integrity for over 100 days under ambient conditions. Furthermore, the photoelectrochemical (PEC) performance of these NCs in benzoquinone oxidation is explored, identifying Cs4CoBi2Cl12 as the most efficient candidate, with a stable photoresponse and enhanced photocurrent generation. Transient absorption studies further confirm that Cs4CoBi2Cl12 sustains the largest self‐trapped exciton population and longest half‐lifetime, highlighting its potential for sustainable, high‐performance PEC devices.

We present a superconducting cavity-coupled double quantum dot (DQD) photodiode that achieves a maximum photon-to-electron conversion efficiency of 25% in the microwave domain. With a higherquality-factor cavity and improved device design to prevent photon leakages through unwanted pathways, our device measures microwave signals down to the 100-aW power level and achieves sensitivity to probe microwave signals with one photon at a time in the cavity. We analyze the photodiode operation using the Jaynes-Cummings input-output theory, identifying the key improvements of stronger cavity-DQD coupling needed to achieve near-unity photodetection efficiency. The results presented in this work represent a crucial advancement toward near-unity microwave photodetection efficiency with single-cavity-photon sensitivity.

We demonstrate a microwave power-to-electrical energy conversion in a resonator-coupled double quantum dot. The system, operated as a photodiode, converts individual microwave photons to electrons tunneling through the double dot, resulting in an electrical current flowing against the applied voltage bias at input powers down to 1 femto-watt. The device attains a maximum power harvesting efficiency of 2%, with the photon-to-electron conversion efficiency reaching 12% in the single photon absorption regime. We find that the power conversion depends on thermal effects showing that thermodynamics plays a crucial role in the single photon energy conversion.

The files contain the raw and processed data used for the publication "Strong coupling between a microwave photon and a singlet-triplet qubit" in ascii format. See readme.txt for details.

AbstractVapor–solid–solid (VSS) growth of III‐V semiconductor nanowires (NWs) has long been considered an alternative for the vapor–liquid–solid (VLS) growth mode, with the potential to avoid the incorporation of deep‐level impurities into semiconductors and to form compositionally abrupt interfaces. Most research however indicates that VSS growth has a much lower growth rate than observed in the VLS growth regime, explained by the very slow mass transport at the solid seed particle‐NW interface. In this study, the direct observation of the VSS growth of GaP NWs under different mechanisms is reported, by using Ni as a seed material inside an environmental transmission electron microscope. These results reveal that when NWs are grown from seed particles exhibiting the NiGa and Ni2Ga3 phases, classic VSS growth occurs with slow NW growth and interface diffusion as the dominant mass transport pathway. In contrast, when NWs are grown by seed particles containing Ni2P phase, rapid NW growth is observed together with a continuous reshaping of the seed particle. A cation exchange reaction is proposed as the predominant growth mechanism. This research results demonstrate an entirely new variant of the VSS growth mode, opening up new degrees of freedom for tuning NW properties.

The growing interest in quantum information has enabled the manipulation and readout of microwave photon states with high fidelities. The presently available microwave photon counters, based on superconducting circuits, are limited to non-continuous pulsed mode operation, requiring additional steps for qubit state preparation before an actual measurement. Here, we present a continuous microwave photon counter based on superconducting cavity-coupled semiconductor quantum dots. The device utilizes photon-assisted tunneling in a double quantum dot with tunneling events being probed by a third dot. Our device detects both single and multiple-photon absorption events independently, thanks to the energy tunability of a two-level double-dot absorber. We show that the photon-assisted tunnel rates serve as the measure of the cavity photon state in line with the P(E) theory - a theoretical framework delineating the mediation of the cavity photon field via a two-level environment. We further describe the single photon detection using the Jaynes-Cummings input-output theory and show that it agrees with the P(E) theory predictions.

In nanoscale structures with rotational symmetry, such as quantum rings, the orbital motion of electrons combined with a spin-orbit interaction can produce a very strong and anisotropic Zeeman effect. Since symmetry is sensitive to electric fields, ring-like geometries provide an opportunity to manipulate magnetic properties over an exceptionally wide range. In this work, we show that it is possible to form rotationally symmetric confinement potentials inside a semiconductor quantum dot, resulting in electron orbitals with large orbital angular momentum and strong spin-orbit interactions. We find complete suppression of Zeeman spin splitting for magnetic fields applied in the quantum dot plane, similar to the expected behavior of an ideal quantum ring. Spin splitting reappears as orbital interactions are activated with symmetry-breaking electric fields. For two valence electrons, representing a common basis for spin-qubits, we find that modulating the rotational symmetry may offer new prospects for realizing tunable protection and interaction of spin-orbital states.