arXiv subjects

Vanda Godinho

Publications and source records attributed to Vanda Godinho.

3 recordsLinked to original sources

arXiv2026

Engineering Chirality in Halide Perovskites

The ability to control chirality in halide perovskites offers new opportunities for circularly polarized photonics, spin-selective electronics, and quantum information technologies. Chirality in halide perovskites is commonly achieved through chiral molecular building blocks or externally imposed photonic architectures. Although both approaches can generate strong chiroptical responses, many spin-dependent functionalities require structural symmetry breaking embedded within the material itself. Here we show that chirality can emerge directly during crystal growth. By combining glancing angle deposition with controlled substrate rotation, we generate highly textured PbI2 nanostructures with growth-controlled crystallographic torsion. X-ray texture analysis reveals that substrate rotation progressively rotates the crystal orientation during growth while preserving the c-axis orientation, resulting in a twisted texture with giant and tuneable chiroptical responses, including ellipticities of 19{\deg} and absorption dissymmetry factors approaching 0.6. The chirality programmed during growth is transferred through vapour-phase conversion into multiple halide perovskite compositions, resulting in circularly polarized luminescence with glum values up to 0.23. These findings establish growth-controlled crystallographic torsion as a previously unexplored origin of chirality in halide perovskites.

cond-mat.mtrl-sci↗

arXiv2026

Polycrystalline ferroelectric croconic acid for multisource environmental energy harvesting

The development of organic ferroelectric materials through scalable and simplified fabrication routes remains a major challenge for next-generation energy-harvesting technologies. Here, polycrystalline croconic acid (CA) thin films are fabricated by vacuum sublimation onto Ar plasma-treated flexible substrates and stabilized by in situ encapsulation with an adamantane-based remote plasma polymer. This solvent-free strategy effectively suppresses surface degradation under ambient conditions, providing long-term stability. Piezoresponse force microscopy confirms robust ferroelectricity with an oblique polarization orientation, well-defined domains, and low nanoscale coercive fields. The films were integrated into multilayer piezoelectric and pyroelectric devices. The piezoelectric performance strongly depends on film thickness, while embedding the CA layer between dielectric polymeric films significantly improves the macroscopic response, reaching power densities of up to 37 microW m-2 for ca. 2 micrometer CA films. Despite the common assumption that high crystallinity is required to sustain ferro-, piezo-, and pyroelectricity, these polycrystalline CA films exhibit remarkable RT pyroelectricity, a property not previously demonstrated in CA-based devices. A pyroelectric coefficient of ca. 10 microC m-2 K-1 highlights a functional response comparable to that of well-established organic and inorganic pyroelectric materials, demonstrating the potential of CA thin films for thermal energy harvesting. Beyond their functional performance, the proposed low-T fabrication route combines deposition and encapsulation in a single in situ process, simplifying device fabrication. Its compatibility with scalable vacuum technologies, flexible substrates, and further process optimization makes this approach highly promising for developing low-cost, lead-free, multisource energy-harvesting systems.

cond-mat.mtrl-sci↗

arXiv2024

Triboelectric Pixels as building blocks for microscale and large area integration of drop energy harvesters

The ultimate step towards the exploitation of water as a clean and renewable energy source addresses the energies stored in the low frequencies of liquid flows, which demands flexible solutions to adapt to multiple scenarios, from raindrops to waves, including water moving in pipelines and microdevices. Thus, harvesting low-frequency flows is a young concept compared to solar and wind powers, where triboelectric nanogenerators have been revealed as the most promising relevant actors. However, despite widespread attempts by researchers, the drop energy harvesters' output power is still low, mainly because of the limitations in candidates endowed with ideal triboelectric and wetting properties and also the non-optimal and centimetre-scale device architecture that prevents the conversion of the complete kinetic energy of impinging drops. Herein, we disclose a microscale triboelectric nanogenerator that can harvest a high density of electrical power from drops through a single, submillisecond, long-lasting step. The mechanism relies on an instantaneous electrical capacitance variation owing to the high-speed contact of the drops with the electrodes' active area. We discuss the role of the precharged effect of the triboelectric surface in the time characteristic of the conversion event. The capacitive and microscale structure of the device is endowed with a small form factor that allows for the production of densely packed arrays. The proposed architecture can be adjusted to different liquids and scales and is compatible with a variety of triboelectric surfaces, including flexible, transparent, and thin-film approaches.

physics.app-ph↗