Dynamic Structural Evolution and Dual Emission Behavior in Hybrid Organic Lead Bromide Perovskites.

The optoelectronic properties of organic lead halide perovskites (OLHPs) strongly depend on their underlying crystal symmetry and dynamics. Here, we exploit temperature-dependent synchrotron powder X-ray diffraction and temperature-dependent photoluminescence to investigate how the subtle structural changes happening in the pure and mixed A-site cation MA1-xFAxPbBr3 (x = 0, 0.5, and 1) systems influences their optoelectronic properties. Diffraction investigations reveal a cubic structure at high temperatures and tetragonal and orthorhombic structures with octahedral distortion at low temperatures. Steady state photoluminescence and time correlated single photon counting study reveals that the dual emission behavior of these OLHPs is due to the direct-indirect band formation. In the orthorhombic phase of MAPbBr3, the indirect band is dominated by self-trapped exciton (STE) emission due to the higher-order lattice distortions of PbBr6 octahedra. Our findings provide a comprehensive explanation of the dual emission behavior of OLHPs while also providing a rationale for previous experimental observations.

Titania Nanoparticle-Stimulated Ultralow Frequency Detection and High-Pass Filter Behavior of a Flexible Piezoelectric Nanogenerator: A Self-Sustaining Energy Harvester for Active Motion Tracking.

A significant driving force for the fabrication of IoT-compatible smart health gear integrated with multifunctional sensors is the growing trend in fitness and the overall wellness of the human body. In this work, we present an autonomous motion and activity-sensing device based on the efficacious nucleation of the polar ß-phase in an electroactive polymer. Representatively, we investigate the nucleating effect of TiO2 nanoparticles on weight-modulated PVDF-HFP films (PT-5, PT-10, and PT-15) and subsequently prototype a sensing device with the film that demonstrates superior ß-phase nucleation. The PT-10 film, with an optimal polar ß-phase, shows the highest remnant polarization (2Pr) and energy density of 0.36 µC/cm2 and 22.3 mJ/cm3, respectively, at 60 kV/cm. The films mimic a high pass filter at frequencies above 10 KHz with very low impedance and high ac conductivity values. The frequency-dependent impedance studies reveal an effective interfacial polarization between TiO2 nanoparticles and PVDF-HFP, explicitly observed in the low-frequency region. Consequently, the sensor fabricated with PT-10 as the sensing layer exhibits ultralow frequency detection (25 Hz) resulting from the blood flow muscle oxygenation. The device successfully senses voluntary joint movements of the human body and actively tracks a range of motions, from brisk walking to running. Additionally, through repetitive human finger-tapping motion, the nanogenerator lights up multiple light-emitting diodes in series and charges capacitors of varying magnitudes under 50 s. The real-time human motion sensing and movement tracking modalities of the sensor hold promise in the arena of smart wearables, sports biomechanics, and contact-based medical devices.

In Situ Pressure Controlled Growth of ZnO Nanoparticles: Tailoring Sizes, Defects, and Optical Properties.

ZnO, being an inexpensive, wide band gap semiconductor that possesses high mechanical, thermal, and chemical stabilities and suitable for a wide range of optical and electronic applications, is the preferred semiconductor of this era. In an effort to fully utilize its potential features, ZnO research is receiving increasing attention. This study investigates the influence of pressure on the crystallinity, defect density, size, and morphology of ZnO nanoparticles, synthesized using nonaqueous sol-gel method, and their respective impact on the optical properties. High-crystalline ZnO nanocrystals with a hexagonal wurtzite structure were synthesized at various pressures, including ambient pressure, 25, 37.5, 50, and 100 bars inside a high-pressure reactor. With the increase in pressure, a reduction in particle size was observed, reaching a minimum size (∼10 nm) at 50 bar pressure (ZnO-50). Further increase in pressure causes an enhancement in the particle size. This trend of size variation with pressure is attributed to a tradeoff between esterification and nucleation processes. Contrary to the expectation, smaller ZnO nanocrystals synthesized by the present method possess lesser number of defects, suggesting that high-pressure synthesis is a unique way that offers smaller ZnO nanocrystals of sub-10 nm sizes having high crystallinity and lesser defects in a shorter time span. Also, the optical transmittance of the systems could be greatly enhanced by carefully tuning the particle sizes, with ZnO-50 (∼10 nm particle size) having the highest transmittance (∼95% at 600 nm) among all samples. High crystallinity, uniform morphology, excellent visible transparency, wide band gap, and low defect density make these smaller ZnO nanocrystals a preferred choice for ultraviolet sensors and other optoelectronic devices.

Enhanced voltage response in TiO2nanoparticle-embedded piezoelectric nanogenerator.

Poly (vinylidene fluoride) (PVDF) and its copolymers have piqued a substantial amount of research interest for its use in modern flexible electronics. The piezoelectricß-phase of the polymers can be augmented with the addition of suitable fillers that promoteß-phase nucleation. In this work, we report an improved output voltage response of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with the incorporation of 10 wt.% Titanium (IV) oxide nanoparticles into the polymer matrix. The nano-filler was dispersed in the polymer matrix to form nanocomposite films via the solution casting technique. X-ray Diffraction and Scanning Electron Microscopy measurements were performed to verify the structure and morphology of the films. Fourier Transform Infrared Spectroscopy revealed enhancement in theß-phase nucleation from ∼15% to ∼36% with the addition of 10 wt.% titania nanoparticles. Thermogravimetric analysis and Differential Scanning Calorimetry results show improved thermal stability of the nanocomposite film, up to 345 °C, as compared to pristine PVDF-HFP. We also demonstrate a facile method for the fabrication of a piezoelectric nanogenerator withß-PVDF-HFP/TiO2nanocomposite as an active layer. The outputs from the fabricated nanogenerator reached up to 8.89 V through human finger tapping motions, paving way for its potential use in the field of sensors, actuators, and self-sustaining flexible devices.

Alteration of Wettability of Copper-Copper Oxide Nanocomposites through Cu-O Bond Breaking Swayed by Ultraviolet and Electron Irradiation.

Converting a nonwetting surface to a highly wetting one, aided by ultraviolet radiation, is well explored. Here, in this work, we show just the reverse behavior of a copper-copper oxide nanocomposite surface where ultraviolet radiation turned the superhydrophilic surface to a superhydrophobic one. This observation is explained both experimentally and theoretically using first-principles density functional theory-based calculations considering the metal-oxygen (Cu-O) bond breaking and related change in surface chemistry. This observation has further been corroborated with electron irradiation on the same nanocomposite material. To the best of our knowledge, for the first time, we show that the radiation-induced breaking of the copper-oxygen bond makes the nanostructure surface energetically unfavorable for water adsorption.

3D Porous Polymeric-Foam-Supported Pd Nanocrystal as a Highly Efficient and Recyclable Catalyst for Organic Transformations.

The efficient recovery of noble metal nanocrystals used in heterogeneous organic transformations has remained a significant challenge, hindering their use in industry. Herein, highly catalytic Pd nanoparticles (NPs) were first prepared having a yield of >98% by a novel hydrothermal method using PVP as the reducing cum stabilizing agent that exhibited excellent turnover frequencies of ∼38,000 h-1 for Suzuki-Miyaura cross-coupling and ∼1200 h-1 for catalytic reduction of nitroarene compounds in a benign aqueous reaction medium. The Pd NPs were more efficient for cross-coupling of aryl compounds with electron-donating substituents than with electron-donating ones. Further, to improve their recyclability, a strategy was developed to embed these Pd NPs on mechanically robust polyurethane foam (PUF) for the first time and a "dip-catalyst" (Pd-PUF) containing 3D interconnected 100-500 µm pores was constructed. The PUF was chosen as the support with an expectation to reduce the fabrication cost of the "dip-catalyst" as the production of PUF is already commercialized. Pd-PUF could be easily separated from the reaction aliquot and reused without any loss of activity because the leaching of Pd NPs was found to be negligible in the various reaction mixtures. We show that the Pd-PUF could be reused for over 50 catalytic cycles maintaining a similar activity. We further demonstrate a scale-up reaction with a single-reaction 1.5 g yield for the Suzuki-Miyaura cross-coupling reaction.

Adhesive hydrophobicity of Cu2O nano-columnar arrays induced by nitrogen ion irradiation.

Low energy nitrogen ions are used in this work to manipulate wetting properties of the surface of the array of Cu2O nano-columns, which yields remarkable results. The nano-columnar thin films were grown on a highly conductive silicon surface by a sputter deposition technique. The films were irradiated at two different fluences of 5 × 10(15) and 1 × 10(16) ions per cm(2), respectively. With increasing fluence the shape of column tip changes, columns are bent and porous channels between columns are clogged up. While the surface of the pristine sample is hydrophilic, the irradiated surface turns into hydrophobic but having adhesion properties. We have analysed the structural and chemical properties of the surface in detail to understand the initial and modified wetting properties. Furthermore, the temporal evolutions of different droplet parameters are investigated to realize the interactions between the water droplet, the sample surface and the atmosphere. We envisage that such modified surfaces can be beneficial for transport of a small volume of liquids with minimum loss and spectroscopic studies, where a small amount of water droplet is available for measurements.

Reversible Lithium Storage in Manganese 1,3,5-Benzenetricarboxylate Metal-Organic Framework with High Capacity and Rate Performance.

Metal organic frameworks (MOFs) with diverse structural chemistry are being projected as futuristic electrode materials for Li-ion batteries. In this work, we report synthesis of Mn-1,3,5-benzenetricarboxylate MOF by a simple solvothermal method and its application as an anode material for the first time. Scanning electron microscopy of the synthesized MOF shows a bar shaped morphology where these bars, about 1 µm wide and of varied lengths between 2 and 20 µm, are made of porous sheets containing mesoporous walls and macroporous channels. The MOF anode, when examined in the potential window of 0.01-2.0 V versus Li/Li(+), shows high specific capacities of 694 and 400 mAh g(-1) at current densities of 0.1 and 1.0 A g(-1) along with good cyclability, retention of capacity, and sustenance of the MOF network. Ex situ X-ray diffraction, Fourier transform infrared, and X-ray photoelectron spectroscopy studies on the electrode material at different states of charge suggest that the usual conversion reaction for Li storage might not be applicable in this case. Conjugated carboxylates being weakly electron withdrawing ligands with a stronger π-π interaction, a probable alternative Li storage mechanism has been proposed that involves the organic moiety. The present results show promise for applying Mn-1,3,5-benzenetricarboxylate MOF as high performance <2 V anode.

A simple, fast and cost-effective method of synthesis of cupric oxide nanoparticle with promising antibacterial potency: Unraveling the biological and chemical modes of action.

BACKGROUND: Gradual attainment of bacterial resistance to antibiotics led us to develop a robust method of synthesis of stable, colloidal cupric oxide nanoparticle of physiological pH with potential antibacterial action. METHODS: Cu(II) oxide NP was synthesized by reduction-oxidation of CuCl2, using polyvinyl alcohol as stabilizer. Characteristics and antibacterial activity of the particles were investigated by techniques like UV-Vis spectrophotometry, DLS, AFM, TEM, EDS, FTIR, AAS, agar plating, FACS, gel electrophoresis and XPS. RESULTS: The NPs were about 50 nm in size and cubic in shape with two surface plasmon peaks at 266 and 370 nm and had semi-conducting behavior with a band gap of 3.40 and 3.96 eV. About 80% of precursor CuCl2 was converted to NP. The minimum inhibitory and the minimum bactericidal concentrations of CuO-NP were respectively 120 and 160 µg/mL for Escherichia coli and 180 and 195 µg/mL for Staphylococcus aureus in Luria-Bertani medium. In growth media, the NPs got modified by media organics with displacement of the stabilizer PVA molecules. This modified NP (around 240 nm) killed cells by generating ROS, which finally caused membrane lipid per-oxidation and chromosomal DNA degradation in NP-treated cells. CONCLUSION: Reports indicate that we are among the few who had prepared CuO-NP in colloidal form. The antibacterial potency of our particle in growth media was much promising than other reports. Our findings demonstrated that 'particle-specific' effect, not 'ion-specific' one, was responsible for the NP action. GENERAL SIGNIFICANCE: The NP may be used as a sterilizing agent in various bioprocesses and as substituent of antibiotics, after thorough toxicological study.

Defects in chemically synthesized and thermally processed ZnO nanorods: implications for active layer properties in dye-sensitized solar cells.

We have carried out the effect of post annealing temperatures on the performance of solution-grown ZnO rods as photoanodes in dye-sensitized solar cells. Keeping our basic objective of exploring the effect of native defects on the performance of DSSC, we have synthesized ZnO rods having length in the range of 2-5 µm by a modified sonication-induced precipitation technique. We performed extensive characterization on the samples annealed at various temperatures and confirmed that annealing at 300 °C results in ZnO rods with minimum native defects that have been identified as doubly ionized oxygen vacancies. The electron paramagnetic resonance measurements on the samples, on the other hand, confirmed the presence of shallow donors in the low temperature annealed samples. We also carried out electrochemical impedance measurements to understand the transport properties at different interfaces in the solar cell assembly. We could conclude that solution-processed ZnO rods annealed at 300 °C are better suited for fabricating DSSC with improved efficiency (1.57%), current density (5.11 mA/cm(2)), and fill factor (45.29%). On the basis of our results, we were able to establish a close connection between the defects in the metal oxide electron transporting nano system and the DSSC performance.

Magnetic proximity effect as a pathway to spintronic applications of topological insulators.

Spin-based electronics in topological insulators (TIs) is favored by the long spin coherence(1,2) and consequently fault-tolerant information storage. Magnetically doped TIs are ferromagnetic up to 13 K,(3) well below any practical operating condition. Here we demonstrate that the long-range ferromagnetism at ambient temperature can be induced in Bi(2-x)Mn(x)Te(3) by the magnetic proximity effect through deposited Fe overlayer. This result opens a new path to interface-controlled ferromagnetism in TI-based spintronic devices.