Fabrication of Highly Stable, Hybrid PbS Nanocomposites in PAMAM Dendrimer Matrix for Photodetection

A novel dendrimer-templating one step method for the in situ synthesis of hybrid nanocomposites of lead sulfide (PbS) quantum dots (QDs) of average diameter of 2.5–4.5 nm in poly­(amidoamine) dendrimer matrix (PAMAM) at ambient condition is reported here. The PbS QDs are developed in cubic crystallographic phase with a high degree of crystallinity. FTIR analysis confirm a direct evidence of PbS QDs linkage to the surface functional groups of dendrimer molecules, which provides a way to prevent the aggregation tendency of the PbS QDs retaining the original properties in 3D rigid dendrimer matrix. Additionally, the thermal stability of dendrimer molecule increases in the nanocomposite unit indicating strong interaction of inorganic phases with dendrimer. The as-prepared PbS nanocomposites could be stored for three months at 4 °C retaining original optical characteristics. The synthesis route provides a simplified colloidal route for producing monodisperse hybrid PbS nanocomposites with robust optical properties. Pure dendrimer is photo inactive, while upon white light irradiation, the PbS nanocomposites results in enhanced photocurrent compared to the dark measurement. Repetitive on–off device response upon white light illumination is found to be sharp and repeatable over successive on/off irradiation cycles. The photoresponse of PbS nanocomposites promises application in photoswitching and photosensitive detectors

Evolution of Long Range Bandgap Tunable Lead Sulfide Nanocrystals with Photovoltaic Properties

Monodispersed bandgap tunable lead sulfide nanocrystals ranging from 0.6 to 1.7 eV have been synthesized by adjusting the reaction temperature and growth time. An evolution from cuboctahedra to perfect cube takes place at higher reaction temperature with longer annealing time. The nanocrystals absorb light both in the visible and IR spectral range. Bandgap dependent photovoltaic studies reveal optimal device performance for a critical size nanocrystal with ∼1.2 eV bandgap revealing the role of optimum bandgap on the photovoltaic performance

Solution-Processed Free-Standing Ultrathin Two-Dimensional PbS Nanocrystals with Efficient and Highly Stable Dielectric Properties

Two-dimensional (2D) materials with downscaled thicknesses are the quest of the electronics industry because of their immense potential in modern microelectronics. Despite the discovery of several novel 2D materials, the flexible design of high-performance free-standing ultrathin 2D dielectric nanocrystals (NCs) with a large planar morphology remains the most challenging task. We develop a method for synthesizing high-quality free-standing ultrathin 2D NCs of PbS with a well-defined large rectangular morphology with a thickness of ∼2 nm. The lateral size can be tuned up to a few hundred nanometers by changing only the reaction annealing time. Microscopic and spectroscopic analyses at different stages of the reaction reveal formation of 2D NCs by a continuous growth mechanism. The 2D NCs exhibit a nearly temperature and frequency independent high dielectric constant (>13.4) with a small dielectric loss (0.0006 at 20 K and <0.06 at 350 K for 100 kHz) over broad temperature and frequency ranges. Low-frequency dispersion from 125 Hz to 1 MHz, frequency stability with a small dielectric loss (<0.03 at 100 kHz), and a stable temperature coefficient of the dielectric constant outline the merits of 2D NCs as a potential dielectric material. Complex impedance analyses demonstrate dominant intrinsic effects contributed by polarons in covalent NCs. Equal activation energies for the conduction and relaxation processes offer uniform energy barriers for the charges in NCs leading to high-performance dielectric behavior. This work opens up promising features of non-oxide binary semiconductors as dielectric alternatives for miniaturized electronics using flexible solution processing routes

Demonstration of Ultrarapid Interfacial Formation of 1D Fullerene Nanorods with Photovoltaic Properties

We demonstrate ultrarapid interfacial formation of one-dimensional (1D) single-crystalline fullerene C₆₀ nanorods at room temperature in 5 s. The nanorods of ∼11 μm in length and ∼215 nm in diameter are developed in a hexagonal close-pack crystal structure, contrary to the cubic crystal structure of pristine C₆₀. Vibrational and electronic spectroscopy provide strong evidence that the nanorods are a van der Waals solid, as evidenced from the preservation of the electronic structure of the C₆₀ molecules within the rods. Steady state optical spectroscopy reveals a dominance of charge transfer excitonic transitions in the nanorods. A significant enhancement of photogenerated charge carriers is observed in the nanorods in comparison to pristine C₆₀, revealing the effect of shape on the photovoltaic properties. Due to their ultrarapid, large-scale, room-temperature synthesis with single-crystalline structure and excellent optoelectronic properties, the nanorods are expected to be promising for photosensitive devices applications

Improved Mechanical Stability of Acetoxypropyl Cellulose upon Blending with Ultranarrow PbS Nanowires in Langmuir Monolayer Matrix

Cellulose and cellulose derivatives have long been used as membrane fabrication. Langmuir monolayer behavior, which naturally mimics membranes, of acetoxypropyl cellulose (APC) and lead sulfide (PbS) nanowire mixtures at different volume ratios is reported. Surface pressure (π)–area (<i>A</i>) isotherms of APC and PbS nanowires mixtures at different volume ratios show a gradual decrease in the monolayer area with increasing volume fraction of PbS nanowires. Change of surface potential with monolayer area at different volume ratios also reveals a gradual increase in the surface potential indicating incorporation of PbS nanowires within APC matrix. The compressibility and elastic constants measurements reveal an enhancement of the elasticity upon incorporation of PbS nanowires up to certain volume fractions. An enhancement in stability of the blend is observed upon PbS nanowire incorporation to the APC matrix. Rheological measurements also support the robustness of the mixture of APC and PbS nanowires in 3D bulk phase. Such robust ultrathin films of cellulose based-nanowire blend obtained by means of the Langmuir technique may lead to novel routes for designing cellulosic-based thin films and membranes

Two-Dimensional Hybrid Organohalide Perovskites from Ultrathin PbS Nanocrystals as Template

Direct conversion of preprocessed binary semiconductor NCs as template holds the key toward the shape control of hybrid perovskites. Here we report on an innovative route for realizing shape-controlled hybrid organohalide perovskite NCs from two-dimensional PbS NCs on solid substrates. Rectangular PbI₂ NCs are first synthesized by iodination of PbS NCs. Resultant PbI₂ NCs are subsequently transformed into the well-defined rectangular hybrid perovskite NCs upon controlled CH₃NH₃Br exposure. Structural analyses using X-ray absorption fine structure reveal transition of cubic lattice of PbS to hybrid perovskites with a mixture of cubic and tetragonal phases exhibiting a bimodal distribution of shorter Pb–Br and longer Pb–I bonds around an immediate neighboring lead absorber within the first coordination shell. This direct all anion exchange reaction route opens up new strategies for the fabrication of shape-controlled perovskite NCs on flexible substrates from suitable existing binary NCs as template for optoelectronic applications

Chemical Tailoring of Band Offsets at the Interface of ZnSe–CdS Heterostructures for Delocalized Photoexcited Charge Carriers

Monocomponent quantum dots (QDs) possess limited electron–hole delocalization capacity upon photoexcitation that suppresses the efficiency of photoenergy harvesting devices. Type II heterostructures offer band offsets at conduction and valence bands depending upon the band gaps of the constituent QDs which largely depend on their sizes. Hence, by keeping the size of one constituent QD fixed while varying the size of the other QD selectively, the band offsets at the interface can be engineered selectively. We report on the tuning of band offsets by synthesizing component size modulated heterostructures composed of a fixed sized ZnSe QD and size tuned CdS QDs with variable band gaps. The resultant heterostructures show spontaneous charge carrier separation across the interface upon photoexcitation depending on the extent of band offsets. Formation mechanism, epitaxial relationship, and the intrinsic nature of interface of the heterostructures are investigated. Experimental results are corroborated with <i>ab initio</i> electronic structure calculations based on density functional theory. Spontaneous charge carrier delocalization across the interface depends on the magnitude of band offsets, which facilitates fabrication of QD sensitized solar cells (QDSSCs). Improved device performances of QDSSCs in comparison to the limited photon-to-current conversion efficiencies of monocomponent QDs demonstrates the significance of band offsets for natural charge carrier separation

Colloidal Synthesis of Strongly Fluorescent CsPbBr₃ Nanowires with Width Tunable down to the Quantum Confinement Regime

Colloidal Synthesis of Strongly Fluorescent CsPbBr₃ Nanowires with Width Tunable down to the Quantum Confinement Regim

Acidic pH-Triggered Release of Doxorubicin from Ligand-Decorated Polymeric Micelles Potentiates Efficacy against Cancer Cells

Current chemotherapeutic strategies against various intractable cancers are futile due to inefficient delivery, poor bioavailability, and inadequate accumulation of anticancer drugs in the diseased site with toxicity caused to the healthy neighboring cells. Drug delivery systems aiming to deliver effective therapeutic concentrations to the site of action have emerged as a promising approach to address the above-mentioned issues. Thus, as several receptors have been identified as being overexpressed on cancer cells including folate receptor (FR), where up to 100–300 times higher overexpression is shown in cancer cells compared to healthy cells, approximately 1–10 million receptor copies per cancer cell can be targeted by a folic acid (FA) ligand. Herein, we developed FA-decorated and doxorubicin-conjugated polymeric micelles of 30 nm size. The hydrophilic block comprises poly(ethylene glycol) units, and the hydrophobic block contains aspartic acid. Decoration of FA on the micelle surface induces ligand–receptor interaction, resulting in enhanced internalization into the cancer cell and inside the endolysosomal compartment. Under acidic pH, the micelle structure is disrupted and the hydrazone bond is cleaved, which covalently binds the doxorubicin with the hydrophobic backbone of the polymer and release the drug. We observed that the cellular uptake and nuclear colocalization of the targeted micelle are 2–4 fold higher than the control micelle at various incubation times in FR-overexpressed various cancer cell lines (KB, HeLa, and C6). These results indicate significant prospects for anticancer therapy as an effective and translational treatment strategy