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Piezoelectric optomechanical platforms provide a promising avenue for efficient signal transduction between microwave and optical domains. Lead zirconate titanate (PZT) thin film stands out as a compelling choice for building such a platform given its high piezoelectricity and optical transparency, enabling strong electro-optomechanical transduction. This work explores the application of such transduction to induce Fano resonance in a silicon photonics integrated circuit (PIC). Our methodology involves integrating a PZT thin film onto a silicon PIC and subsequently removing the SiO2 layer to suspend the silicon waveguide, allowing controlled mechanical vibrations. Fano resonances, characterized by their distinctive asymmetric line shape, were observed at frequencies up to 6.7 GHz with an extinction ratio of 21 dB. A high extinction ratio of 41 dB was achieved at the lower resonance frequency of 223 MHz. Our results demonstrate the potential of piezoelectric thin film integration for the generation of Fano resonances on passive photonic platforms such as Si, paving the way for highly sensitive, compact, and power-efficient devices relevant to a wide range of applications. [ABSTRACT FROM AUTHOR]

The in-plane dielectric and ferroelectric properties of preferentially oriented lead zirconate titanate (PZT) thin films are characterized using interdigitated transducers (IDTs). By combining finite element method simulations and capacitance measurements, values of the dielectric constant of films with thicknesses between 150 nm and 800 nm are obtained. A modified Sawyer–Tower circuit is used to investigate the polarization loops measured in-plane using IDT electrodes. A well-defined hysteresis loop is obtained demonstrating the switching of the polarization of the ferroelectric domains. Leakage current measurements reveal high resistivity and are an indication of the high quality of the PZT film. The obtained characteristics are used to determine the total impedance of the IDT-PZT structure. Here, the structure is represented by an equivalent ladder circuit using the inductance and resistance of the IDT electrodes and the capacitance and conductance of the PZT film. The obtained total impedance matches low frequency measurements. [ABSTRACT FROM AUTHOR]

In contrast to the widely studied electrical properties of Pb(Zr,Ti)O 3 thin films, which have led to their applicability in various application areas such as thin film capacitors, microelectronics, and ferroelectric memories, the electro-optic (EO) properties are far less studied, which hinders the applicability of Pb(Zr,Ti)O 3 films for EO applications such as heterogeneously integrated phase modulators in silicon (Si) photonics. Therefore, the EO properties of Pb(Zr,Ti)O 3 films need to be further investigated to pave the way for the applicability of Pb(Zr,Ti)O 3 films in EO applications. As the EO properties of ferroelectric thin films strongly depend on their crystal phase and texture, which in turn are influenced by the method of film fabrication. Therefore, in this work, we investigate the EO properties of a promising solution process using a La 2 O 2 CO 3 template film. We successively characterize the precursor ink, microstructure and EO properties of the solution-processed Pb(Zr,Ti)O 3 film. The Pb(Zr,Ti)O 3 film exhibits a fiber texture and has a large maximum and remnant Pockels coefficient ( r eff ) of 69 pm V -1 and 66 pm V -1 , respectively. The integration into a ring resonator-based modulator shows a V π L of 2.019 V cm. The determination of these promising EO properties could further pave the way for the applicability of Pb(Zr,Ti)O 3 thin films in Si photonics.

The most efficient upconversion (UC) materials reported to date are based on fluoride hosts with low phonon energies, which reduce the amount of nonradiative transitions. In particular, NaYF 4 doped with Yb 3+ and Er 3+ at appropriate ratios is known as one of the most efficient UC phosphors. However, its low thermal stability limits its use for certain applications. On the other hand, oxide hosts exhibit better thermal stability, yet they have higher phonon energies and are thus prone to lower UC efficiencies. As a result, developing host nanomaterials that combine the robustness of oxides with the high upconversion efficiencies of fluorides remains an intriguing prospect. Herein, we demonstrate the formation of ytrrium doped oxyfluoride (YOF:Yb 3+ ,Er 3+ ) particles, which are prepared by growing a NaYF 4 :Yb 3+ ,Er 3+ layer around SiO 2 spherical particles and consecutively applying a high-temperature annealing step followed by the removal of SiO 2 template. Our interest lies in employing these materials as Boltzmann type physiological range luminescence thermometers, but their weak green emission is a drawback. To overcome this issue, and engineer materials suitable for Boltzmann type thermometry, we have studied the effect of introducing different metal ion co-dopants (Gd 3+ , Li + or Mn 2+ ) into the YOF:Yb 3+ ,Er 3+ particles, focusing on the overall emission intensity, as well as the green to red ratio, upon 975 nm laser excitation. These materials are explored for their use as ratiometric thermometers, and further also as drug carriers, including their simultaneous use for these two applications. The investigation also includes examining their level of toxicity towards specific human cells - normal human dermal fibroblasts (NHDFs) - to evaluate their potential use for biological applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We report the evolution of the superconducting properties of a commercial coated conductor during deoxygenation and reoxygenation processes. By analyzing the changes on the critical temperature, T c , and critical current density, J c , at 4 and 77 K, we have identified the conditions that cause a complete deoxygenation of the coated conductor and, also, the reoxygenation conditions that allow a recovery of the superconducting properties. A complete suppression of superconductivity happens at ~ 500-550 °C under a pure argon flow. After a complete deoxygenation, we observed that a reoxygenation process at ~ 400-450 °C in pure oxygen flow allows, not only a full recovery, but even an improvement in J c , both at 4 and 77 K. Such an increase of J c is kept or even enhanced, especially at 77 K, in the presence of magnetic fields up to ~ 6 T. A microstructural analysis by transmission electron microscopy did not give evidence of major differences in the densities of Y 2 O 3 nanoparticles and stacking faults between the pristine and reoxygenated samples, suggesting that these defects should not be the cause of the observed enhancement of J c . Therefore, the combined action of other types of defects, which could appear as a consequence of our reoxygenation process, and of a new level of oxygen doping should be responsible of the J c enhancement. The higher J c that can be achieved by using our simple reoxygenation process opens new parameter space for CCs optimization, which means choosing a proper pO 2 -temperature-time trajectory for optimizing J c ., (© 2023. Springer Nature Limited.)

In this study, we report hybrid crystalline lanthanide-containing 3D covalent organic framework (Ln@3D COF) materials that are suitable for temperature sensing applications. Different routes to obtain these hybrid materials were tested and compared for material quality and thermometric properties. In the first approach, a bipyridine-containing 3D COF (Bipy COF) was grafted with a range of visible emitting lanthanide (Eu 3+ , Tb 3+ , Dy 3+ , and Eu 3+ /Tb 3+ ) β-diketonate complexes. In the second approach, a novel nanocomposite material was prepared by embedding NaYF 4 :Er,Yb nanoparticles on the surface of a nonfunctionalized 3D COF (COF-300). To the best of our knowledge, the luminescent materials developed here are the first 3D COFs to be tested as ratiometric temperature sensors. In fact, for the Bipy COF, two different types of thermometers were tested (the Eu 3+ /Tb 3+ system and a rare Dy 3+ system), with both showing excellent temperature sensing properties. The reported NaYF 4 :Er,Yb/COF-300 nanocomposite material combines upconverting nanoparticles with 3D COFs, similar to previously reported metal organic framework (MOF) nanocomposite materials; however, this type of hybrid material has not yet been explored for COFs. As such, our findings open a new pathway toward potential multifunctional materials that can combine thermometry with other modalities, such as catalysis or drug delivery, in just one nanocomposite material.

Covalent organic frameworks (COFs) are emerging as a new class of photoactive organic semiconductors, which possess crystalline ordered structures and high surface areas. COFs can be tailor-made toward specific (photocatalytic) applications, and the size and position of their band gaps can be tuned by the choice of building blocks and linkages. However, many types of building blocks are still unexplored as photocatalytic moieties and the scope of reactions photocatalyzed by COFs remains quite limited. In this work, we report the synthesis and application of two bipyridine- or phenylpyridine-based COFs: TpBpyCOF and TpPpyCOF . Due to their good photocatalytic properties, both materials were applied as metal-free photocatalysts for the tandem aerobic oxidation/Povarov cyclization and α-oxidation of N -aryl glycine derivatives, with the bipyridine-based TpBpyCOF exhibiting the highest activity. By expanding the range of reactions that can be photocatalyzed by COFs, this work paves the way toward the more widespread application of COFs as metal-free heterogeneous photocatalysts as a convenient alternative for commonly used homogeneous (metal-based) photocatalysts.

Employing luminescence thermometry in the biomedical field is undeniably appealing as many health conditions are accompanied by temperature changes. In this work, we show our ongoing efforts and results at designing novel vehicles for dual-mode thermometry and pH-dependent drug release based on hollow spheres. Hereby for that purpose, we exploit the hollow Y 2 O 3 and Y 2 O 2 SO 4 host materials. These two inorganic hollow phosphors were investigated and showed to have excellent upconversion Er 3+ -Yb 3+ luminescence properties and could be effectively used as optical temperature sensors in the physiological temperature range when induced by near-infrared CW light (975 nm). Further, doxorubicin was exploited as a model anti-cancer drug to monitor the pH-dependent drug release of these materials showing that they can be used for simultaneous thermometry and drug delivery applications., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Lanthanide-based luminescent nanoparticles that are thermally responsive can be used to probe temperature changes at a nanoscale regime. However, materials that can work as both a nanothermometer and a catalyst are limited. Herein, we show that covalent organic frameworks (COFs), which is an emerging class of porous crystalline materials, can be grown around lanthanide nanoparticles to create unique core-shell nanostructures. In this way, the COF (shell) supports copper metal ions as catalytic sites and simultaneously lanthanide nanoparticles (β-NaLuF 4 :Gd,Er,Yb-core) locally measure the temperature during the catalytic reaction. Moreover, β-NaLuF 4 :Gd,Er,Yb nanoparticles are upconverting materials and hence can be excited at longer wavelengths (975 nm), which do not affect the catalysis substrates or the COF. As a proof-of-principle, a three-component addition reaction of benzaldehyde, indole, and malononitrile was studied. The local temperature was probed using luminescence nanothermometry during the catalytic reaction.

Through a series of post synthetic modification methods applied to the 100% trans ethenylene-bridged Periodic Mesoporous Organosilica (ePMO), the lanthanide-functionalized hybrid nanomaterial ePMO@Eu_PA (PA = picolinic acid) has been prepared. The pristine and lanthanide-grafted ePMO materials were characterized by powder X-ray diffraction, DRIFTs, TGA, N 2 sorption, SEM and TEM. The selected PA ligand could effectively sensitize the Eu 3+ ion, leading to the characteristic luminescence of Eu 3+ in ePMO@Eu_PA. The luminescence properties of the ePMO@Eu_PA were studied in detail in the solid state and after dispersing in water. The material was investigated for the use as ion sensor and showed a selective monitoring of Fe 3+ , Co 2 + and Cu 2+ ions with luminescence quenching. In addition, the material showed a linear relationship between the luminescence intensity and the pH value in the pH range from 7.7 to 10.2. These findings demonstrate that ePMO@Eu_PA possesses potential practical applications in ion sensing as well as in pH sensing.

A nanograined YBCO target, where a great number of grain boundaries, pores etc. exist, is shown to hold an alternative approach to future pulsed laser deposition based high-temperature superconductor thin film and coated conductor technologies. Although the nanograined material is introduced earlier, in this work, we comprehensively demonstrate the modified ablation process, together with unconventional nucleation and growth mechanisms that produces dramatically enhanced flux pinning properties. The results can be generalized to other complex magnetic oxides, where an increased number of defects are needed for modifying their magnetic and electrical properties, thus improving their usability in the future technological challenges.

A low-cost chemical solution deposition technique was employed to prepare YBa 2 Cu 3 O 7-δ (YBCO) nanocomposite films starting from a colloidal solution containing preformed ZrO 2 nanocrystals. As previous publications revealed, an increase in the amount of nanocrystals results in a progressive deterioration of the film properties. The parameters that control this process and their interplay are still unknown in detail. Using definitive screening design (DSD), a design-of-experiments approach, allowed determining which of the multiple growth parameters play a key role for improving the superconducting properties of YBCO nanocomposite films even with a large concentration of nanocrystals. In order to show the potential of DSD, it has been applied for the optimization of two different properties: the critical temperature T c and the full width at half-maximum of the (005) YBCO reflection. This work shows that DSD is a powerful and efficient method that allows optimizing certain processes with a minimal number of experiments.

Covalent Organic Frameworks (COFs), an emerging class of crystalline porous materials, are a new type of support for grafting lanthanide ions (Ln 3+ ), which can be employed as ratiometric luminescent thermometers. In this work we have shown that COFs co-grafted with lanthanide ions (Eu 3+ , Tb 3+ ) and Cu 2+ (or potentially other d-metals) can synchronously be employed both as a nanothermometer and catalyst during a chemical reaction. The performance of the thermometer could be tuned by changing the grafted d-metal and solvent environment. As a proof of principle, the Glaser coupling reaction was investigated. We show that temperature can be precisely measured during the course of the catalytic reaction using luminescence thermometry. This concept could be potentially easily extended to other catalytic reactions by grafting other d-metal ions on the Ln@COF platform., (© 2020 Wiley-VCH GmbH.)

Here, the excellent thermal sensing capability of Ho3+, Yb3+ doped β-NaGdF4 nanoparticles, where the system is excited into the 5F5 ← 5I8 transition of Ho3+ (640 nm), is reported. The ratio of the 2F5/2 → 2F7/2 transition peak of Yb3+ and the 5I6 → 5I8 transition peak of Ho3+ was employed for thermometry applications, resulting in a novel thermometer, which could potentially operate in BW-I and BW-II (BW - biological window). Additionally, interesting findings were made about the influence of the reaction time on the particle morphology and the presence of intermediate morphology forms.

Due to the beneficial properties of silver, it is anticipated that the number of commercially available applications will keep growing during the next decade. In this study, 14 different commercial products that claim to contain solid silver were characterized by visual analysis, UV-VIS spectroscopy, inductive coupled plasma optical emission spectrometry (ICP-OES), scanning transmission electron microscopy with energy dispersive x-ray spectroscopy (STEM-EDX), and dynamic light scattering (DLS). Moreover the variation between production batches-which has never been researched before-was investigated. All four techniques corroborated that some products were highly concentrated and contained spherically-shaped silver nanoparticles (AgNPs), while in others, no (solid) silver was detected or only irregularly-shaped silver particles with a high size polydispersity were present. For almost all products, a significant difference between the claimed and measured silver concentration was detected and a high variability between different production batches of the same product was observed. Our results show the need for a more rigorous approach regarding the manufacturing, labeling, and use of silver-containing products.

In order to understand how the doping with self-assembled nanorods of different sizes and concentrations as well as applied magnetic fields affect the critical current anisotropy in YBa 2 Cu 3 O 7-x (YBCO) thin films close to YBCO c-axis, we present an extensive and systematic computational study done by molecular dynamics simulation. The simulations are also used to understand experimentally measured J c (θ) curves for BaHfO 3 , BaZrO 3 and BaSnO 3 doped YBCO thin films with the help of nanorod parameters obtained from transmission electron microscopy measurements. Our simulations reveal that the relation between applied and matching field plays a crucial role in the formation of J c (θ)-peak around YBCO c-axis (c-peak) due to vortex-vortex interactions. We also find how different concentrations of different size nanorods effect the shape of the c-peak and explain how different features, such as double c-peak structures, arise. In addition to this, we have quantitatively explained that, even in an ideal superconductor, the overdoping of nanorods results in decrease of the critical current. Our results can be widely used to understand and predict the critical current anisotropy of YBCO thin films to improve and develop new pinscapes for various transport applications.

Chemical solution deposition (CSD) was used to grow Y 1-x Gd x Ba 2 Cu 3 O 7-δ -BaHfO 3 (YGBCO-BHO) nanocomposite films containing 12 mol% BHO nanoparticles and various amounts of Gd, x , on two kinds of buffered metallic tapes: Ni5W and IBAD. The influence of the rare-earth stoichiometry on structure, morphology and superconducting properties of these films was studied. The growth process was carefully studied in order to find the most appropriate growth conditions for each composition and substrate. This led to a clear improvement in film quality, probably due to the reduction of BaCeO 3 formation. In general, the superconducting properties of the films on Ni5W are significantly better. For x > 0.5, epitaxial ~270 nm thick YGBCO-BHO films with T c > 93 K and self-field J c at 77 K ~2 MA/cm² were obtained on Ni5W. These results highlight the potential of this approach for the fabrication of high-quality coated conductors., Competing Interests: The authors declare no conflict of interest.

Striving to improve the critical current density Jc of superconducting YBa 2 Cu 3 O 6+x (YBCO) thin films via enhanced vortex pinning, the interplay between film growth mechanisms and the formation of nanosized defects, both natural and artificial, is systematically studied in undoped and BaZrO 3 (BZO)-doped YBCO thin films. The films were grown via pulsed laser deposition (PLD), varying the crystal grain size of the targets in addition to the dopant content. The microstructure of the PLD target has been observed to have a great impact on that of the deposited thin films, including the formation of vortex pinning centers, which has direct implications on the superconducting performance, especially on the isotropy of flux pinning properties. Based on experimentally measured angular dependencies of Jc, coupled with a molecular dynamics (MD) simulation of flux pinning in the YBCO films, we present a quantitative model of how the splay and fragmentation of BZO nanorods artifically introduced into the YBCO film matrix explain the majority of the observed critical current anisotropy.

The thickness characterization of transparent protective coatings on functional, transparent materials is often problematic. In this paper, a toolbox to determine the thicknesses of a transparent coating on functional window films is presented. The toolbox consists of a combination of secondary ion mass spectrometry and profilometry and can be transferred to other transparent polymeric materials. A coating was deposited on designed model samples, which were characterized with cross-sectional views in transmission and in scanning/transmission electron microscopy and ellipsometry. The toolbox was then used to assess the thicknesses of the protective coatings on the pilot-scale window films. This coating was synthesized using straightforward sol-gel alkoxide chemistry. The kinetics of the condensation are studied in order to obtain a precursor that allows fast drying and complete condensation after simple heat treatment. The shelf life of this precursor solution was investigated in order to verify its accordance to industrial requirements. Deposition was performed successfully at low temperatures below 100 °C, which makes deposition on polymeric foils possible. By using roll-to-roll coating, the findings of this paper are easily transferrable to industrial scale. The coating was tested for scratch resistance and adhesion. Values for the emissivity (ε) of the films were recorded to justify the use of the films obtained as infrared reflective window films. In this work, it is shown that the toolbox measures similar thicknesses to those measured by electron microscopy and can be used to set a required thickness for protective coatings.

The formation of superconducting nanocomposites from preformed nanocrystals is still not well understood. Here, we examine the case of ZrO₂ nanocrystals in a YBa₂Cu₃O 7−x matrix. First we analyzed the preformed ZrO₂ nanocrystals via atomic pair distribution function analysis and found that the nanocrystals have a distorted tetragonal crystal structure. Second, we investigated the influence of various surface ligands attached to the ZrO₂ nanocrystals on the distribution of metal ions in the pyrolyzed matrix via secondary ion mass spectroscopy technique. The choice of stabilizing ligand is crucial in order to obtain good superconducting nanocomposite films with vortex pinning. Short, carboxylate based ligands lead to poor superconducting properties due to the inhomogeneity of metal content in the pyrolyzed matrix. Counter-intuitively, a phosphonate ligand with long chains does not disturb the growth of YBa₂Cu₃O 7−x . Even more surprisingly, bisphosphonate polymeric ligands provide good colloidal stability in solution but do not prevent coagulation in the final film, resulting in poor pinning. These results thus shed light on the various stages of the superconducting nanocomposite formation.

The flux pinning properties of the high temperature superconductor YBa 2 Cu 3 O 7-δ (YBCO) have been conventionally improved by creating both columnar and dot-like pinning centres into the YBCO matrix. To study the effects of differently doped multilayer structures on pinning, several samples consisting of a multiple number of individually BaZrO 3 (BZO) and BaCeO 3 (BCO) doped YBCO layers were fabricated. In the YBCO matrix, BZO forms columnar and BCO dot-like defects. The multilayer structure improves pinning capability throughout the whole angular range, giving rise to a high critical current density, J c . However, the BZO doped monolayer reference still has the most isotropic J c . Even though BZO forms nanorods, in this work the samples with multiple thin layers do not exhibit a c axis peak in the angular dependence of J c . The angular dependencies and the approximately correct magnitude of J c were also verified using a molecular dynamics simulation.

Ligand exchange is a crucial step between nanocrystal synthesis and nanocrystal application. Although colloidal stability and ligand exchange in nonpolar media are readily established, the exchange of native, hydrophobic ligands with polar ligands is less systematic. In this paper, we present a versatile ligand exchange strategy for the phase transfer of carboxylic acid capped HfO2 and ZrO2 nanocrystals to various polar solvents, based on small amino acids as the incoming ligand. To gain insight in the fundamental mechanism of the exchange, we study this system with a combination of FTIR, zeta potential measurements, and solution (1)H NMR techniques. The detection of surface-associated, small ligands with solution NMR proves challenging in this respect. Tightly bound amino acids are undetectable, but their existence can be proven through displacement with other ligands in titration experiments. Alternatively, we find that methyl moieties belonging to bound species can circumvent these limitations because of their more favorable relaxation properties as a result of internal mobility. As such, our results are not limited to amino acids but to any short-chained ligand and will therefore facilitate the rigorous investigation and understanding of various ligand exchange processes.