Vortex flow induced self-assembly in CsPbI3 rods leads to an improved electrical response towards external analytes.

We present a facile and versatile strategy for enabling CsPbI3 rods to self-assemble at an air-water interface. The CsPbI3 rods, which float at the air-water interface, align under the influence of the rotational flow field due to the vortex motion of a water subphase. The aligned CsPbI3 rods could be transferred onto various substrates without involving any sophisticated instrumentation. The temperature of the subphase, the concentration of the CsPbI3 aliquot, the rotational speed inducing vortex motion, and the lift-off position and angle of the substrate were optimized to achieve high coverage of the self-assembled rods of CsPbI3 on glass. The Rietveld refinement of the XRD profile confirms that the aligned CsPbI3 is in the pure orthorhombic phase ascribed to the Pnma space group. The hydrophilic carboxylic group of the oleic acid attaches to the Pb atoms of the halide perovskite rods, while their hydrophobic tails encapsulate the rods within their shell, creating a shielding barrier between the water and the perovskite surface like a reverse micelle. The aligned CsPbI3 rods exhibit a nearly 47-fold increment in current upon exposure to ammonia gas (amounting to 5.6 times higher sensitivity in ammonia sensing) compared to the non-aligned CsPbI3 rods.

Halide Tunablility Leads to Enhanced Biomechanical Energy Harvesting in Lead-Free Cs2SnX6-PVDF Composites.

The main challenges impeding the widespread use of organic-inorganic lead halide perovskites in modern-day technological devices are their long-term instability and lead contamination. Among other environmentally convivial and sustainable alternatives, Cs2SnX6 (X = Cl, Br, and I) compounds have shown promise as ambient-stable, lead-free materials for energy harvesting, and optoelectronic applications. Additionally, they have demonstrated tremendous potential for the fabrication of self-powered nanogenerators in conjunction with piezoelectric polymers like polyvinylidene-fluoride (PVDF). We report on the fabrication of composites constituting solvothermally synthesized Cs2SnX6 nanostructures and PVDF. The electroactive phases in PVDF were boosted by the incorporation of Cs2SnX6, leading to enhanced piezoelectricity in the composites. First-principles density functional theory (DFT) studies were carried out to understand the interfacial interaction between the Cs2SnX6 and PVDF, which unravels the mechanism of physisorption between the perovskite and PVDF, leading to enhanced piezoresponse. The halide ions in the inorganic Cs2SnX6 perovskites were varied systematically, and the piezoelectric behaviors of the respective piezoelectric nanogenerators (PENGs) were investigated. Further, the dielectric properties of these halide perovskite-based hybrids are quantified, and their piezoresponse amplitude, piezoelectric output signals, and charging capacity are also evaluated. Out of the several films fabricated, the optimized Cs2SnI6_PVDF film shows a piezoelectric coefficient (d33) value of ∼200 pm V-1 and a remanent polarization of ∼0.74 µC cm-2 estimated from piezoresponse force microscopy and polarization hysteresis loop measurement, respectively. The optimized Cs2SnI6_PVDF-based device produced an instantaneous output voltage of ∼167 V, a current of ∼5.0 µA, and a power of ∼835 µW across a 5 MΩ resistor when subjected to periodic vertical compression. The output voltage of this device is used to charge a capacitor with a 10 µF capacitance up to 2.2 V, which is then used to power some commercial LEDs. In addition to being used as a pressure sensor, the device is employed to monitor human physiological activities. The device demonstrates excellent operational durability over a span of several months in an ambient environment vouching for its exceptional potential in application to mechanical energy harvesting and pressure sensing applications.

Preferential perovskite surface-termination induced high piezoresponse in lead-free in situ fabricated Cs3Bi2Br9-PVDF nanocomposites promotes biomechanical energy harvesting.

Lead-free halide perovskites have gained immense popularity in photovoltaic and energy harvesting applications because of their excellent optical and electrical attributes with minimal toxicity. We synthesized composite films of lead-free Cs3Bi2Br9 perovskite embedded in the polyvinylidene fluoride (PVDF) matrix and have investigated their piezoelectric energy harvesting. Five PVDF@Cs3Bi2Br9 composite films were fabricated with varying wt% of the perovskite in the PVDF. The composite with a 4 wt% of the perovskite shows 85% activation of the electroactive ß-phase of PVDF. Additionally, this composite exhibits a maximum polarisation of ∼0.1 µC cm-2 and the best energy storage density of ∼0.8 mJ cm-3 at an applied field of ∼16 kV cm-1 among all the synthesized composites. A nanogenerator fabricated using 4 wt% loading in the composite film produced an instantaneous output voltage of ∼40 V, an instantaneous current of ∼4.1 µA, and a power density of ∼17.8 µW cm-2 across 10 MΩ resistance when repeatedly hammered by the human hand. The nanogenerator is further employed to light up several LEDs and to charge capacitors with a small active area demonstrating significant promise for prospective wearables and portable devices and paving the way for high-performance nanogenerators using lead-free halide perovskites. Density functional theory calculations were performed to understand the interaction of the electroactive phase of the PVDF with different perovskite surface terminations to unravel the various interaction mechanisms and their ensuing charge transfer properties.

Shape dependent multiferroic behavior in Bi2Fe4O9nanoparticles.

Ferroelectric and magnetic properties are investigated for Bi2Fe4O9nanoparticles with different shapes (cuboid and sphere-like) synthesized by hydrothermal and sol-gel method. The magnetic study reveals that coercivity, Neel temperature and remanent magnetization strongly depend on shape of the particle. The nanoparticle with sphere-like shape exhibits magnetization curve of antiferromagnetic (AFM) ordering with ferromagnetic (FM) component. As the particle shape changes from sphere-like to cuboid, the AFM component is dominating over the ferromagnetic component. A small exchange bias is also observed at low temperature in both the sphere-like and cuboid nanoparticle. The coercivity, remanent magnetization and Neel temperature of sphere-like nanoparticle is greater than cuboid nanoparticle. Ferroelectric measurement shows the remanent polarization of cuboid is greater than sphere-like nanoparticle but the coercivity is almost same. This Bi2Fe4O9nanoparticle shows a small change in polarization under magnetic field. The polarization value decreases with magnetic field increases. The magnetoelectric coupling-measured by change of remanent polarization under magnetic field are found to be greater in Bi2Fe4O9sphere-like nanoparticles. These shape dependent magnetic and ferroelectric properties are coming because of shape anisotropy.

Solution-processed light-induced multilevel non-volatile wearable memory device based on CsPb2Br5 perovskite.

Despite the recent advancements in memory devices, the quest for building materials with low power consumption is still on, with the ultimate focus on the durability of the system and reliability and reproducibility of its performance. Halide perovskites (HPs), which have several intriguing photoelectrical traits, have recently been utilized for memory applications; one of the highlights of these materials is the ionic-motion-based fast switching in their crystal structure. In this work, a CsPb2Br5 film is applied as a switching layer to implement memory devices with a flexible Al/CsPb2Br5/ITO-PET structure. The device exhibits a pronounced bipolar resistive switching (RS) characteristic at low operating voltage. The as-fabricated flexible device presented RS features with no initial forming process, concentrated distributions of high and low resistance states (HRS and LRS), uniform switching, endurance over 100 cycles, and a long retention time of 103 s with a high on/off ratio of around 102. Multilevel data-storage capability was also observed via subtle control of the compliance current (CC). Considering the current demand for smart, wearable, and flexible electronic gadgets, the current-voltage (I-V) characteristics of the as-fabricated all-inorganic halide-perovskite-based memory device were further explored under different bending conditions to determine its electrical reliability and mechanical stability. This flexible device exhibited no discernible difference in device performance under flat or bent conditions, and the performance remained nearly the same even after 500 bending cycles. In addition to control of the RS effect of the device using an electrical field, the performance of the device under light was also explored. Blue light modulates the resistive states by regulating the condition of photo-generated electron-hole pairs, and the SET and RESET voltages are changed from 2.34 to 2.14 V and from -2.04 to -1.90 V, respectively. The observed RS behavior is explained on the basis of the creation and partial annihilation of conductive multifilaments, which is dominated by the migration of bromine ions and their associated vacancies in the HP layer. We believe that this work will offer a new context to understand the intrinsic characteristics of HPs for RS applications at low voltage and validate their potential in the design of next-generation stable and nonvolatile memory devices for future flexible electronic systems.

Temperature-dependent dielectric properties of CsPb2Br5: a 2D inorganic halide perovskite.

Two dimensional (2D) CsPb2Br5have been successfully synthesized via the chemical precipitation method. Detailed structural, morphological, optical, and dielectric studies of these materials have been performed. These 2D CsPb2Br5plates (of thickness around 200-300 nm) are ascribed to a tetragonal lattice system withI4/mcmspace group. The dielectric attributes such as dielectric constant, electrical modulus, loss factor, and the DC, and AC conductivities, are observed to be varying appreciably with temperature over an extensive frequency window of 10 Hz-50 MHz. The Nyquist plots are investigated using the Maxwell-Wagner equivalent circuit model, which shows the impact of grains and grain boundaries on the overall impedance. Both the free charge conductivity and space charge increase with an increment in temperature, as revealed from the modified Cole-Cole plot. The relaxation time and relaxation mechanism of 2D CsPb2Br5are estimated using the Kohlrausch-Williams-Watts equation. Variation in DC conductivity and relaxation time, as a function of temperature, closely resembles Arrhenius' behavior. Value of activation energy calculated from the DC conductivity corroborates with the same derived from relaxation time. The observation of high dielectric constant and nominal dielectric loss for CsPb2Br5perovskite offers enormous potential in energy harvesting and storage devices.

Secondary Structure-Dependent Physicochemical Interaction of Oligonucleotides with Gold Nanorod and Photothermal Effect for Future Applications: A New Insight.

We investigate the physicochemical interactions of gold nanorod (GNR) with single-stranded, double-stranded, and hairpin DNA structures to improve the biological compatibility as well as the therapeutic potential, including the photothermal effect of the conjugates. Studies have demonstrated that different DNA secondary structures, containing thiol group, have different patterns of physicochemical interaction. Conjugation efficiency of paired oligonucleotides are significantly higher than that of oligonucleotides with naked bases. Furthermore, hairpin-shaped DNA structures are most efficient in terms of conjugation and increased dispersion, with least interference on GNR near-infrared absorbance and photothermal effect. Our conjugation method can successfully exchange the overall coating of the GNR, attaching the maximum number of DNA molecules, thus far reported. Chemical mapping depicted uniform attachment of thiolated DNA molecules without any topological preference on the GNR surface. Hairpin DNA-coated GNR are suitable for intracellular uptake and remain dispersed in the cellular environment. Finally, we conjugated GNR with 5-fluoro-2'-deoxyuridine-containing DNA hairpin and the conjugate demonstrated significant cytotoxic activity against human cervical cancer cell line (KB). Thus, hairpin DNA structures could be utilized for optimal dispersion and photothermal effect of GNR, along with the delivery of cytotoxic nucleotides, developing the concept of multimodality approach.