Inorganic Capping Research Articles

Femtosecond laser direct nanolithography of perovskite hydration for temporally programmable holograms

Modern nanofabrication technologies have propelled significant advancement of high-resolution and optically thin holograms. However, it remains a long-standing challenge to tune the complex hologram patterns at the nanoscale for temporal light field control. Here, we report femtosecond laser direct lithography of perovskites with nanoscale feature size and pixel-level temporal dynamics control for temporally programmable holograms. Specifically, under tightly focused laser irradiation, the organic molecules of layered perovskites (PEA)2PbI4 can be exfoliated with nanometric thickness precision and subwavelength lateral size. This creates inorganic lead halide capping nanostructures that retard perovskite hydration, enabling tunable hydration time constant. Leveraging advanced inverse design methods, temporal holograms in which multiple independent images are multiplexed with low cross talk are demonstrated. Furthermore, cascaded holograms are constructed to form temporally holographic neural networks with programmable optical inference functionality. Our work opens up new opportunities for tunable photonic devices with broad impacts on holography display and storage, high-dimensional optical encryption and artificial intelligence.

Inorganic Capping Layers in RDL Technologies: Process Advantages and Reliability

Inorganic Capping Layers in RDL Technologies: Process Advantages and Reliability

Vapor deposited thin organic–inorganic capping layers preventing copper line oxidation in polymer-based RDL technologies

Hybrid organic–inorganic and inorganic multilayer films were deposited using a combination of CVD and ALD processes to develop an ultra-thin barrier to prevent copper oxidation in a polymer-based RDL technology. ALD layers are known to be effective permeation barriers due to their uniformity and pinhole-free morphology. However, the low deposition temperature, required by the presence of polymers in the final product, increases their susceptibility to degradation by water. In this study, polymer-embedded copper lines protected by ultra-thin vapor deposited cappings, processed at temperatures below or equal to 100 °C, were exposed to oxidation and corrosion stress tests for more than 1000 h. Above an inorganic layer critical thickness of 5 nm, copper oxidation is fully blocked. In addition, it is demonstrated that some of these ultra-thin layers can withstand a corrosion stress test paving the road for their integration in polymer-based RDL technologies.

Photoluminescence Enhancement of NIR‐II Emissive Ag2S Quantum Dots via Chloride‐Mediated Growth and Passivation

AbstractAg2S quantum dots (QDs) with high photoluminescence quantum yield (PLQY) in the second near‐infrared (NIR‐II, 1000–1700 nm) window are urgently pursued. Halide atoms (especially chloride) have been studied as inorganic capping ligands on improving the PLQY of Cd‐, Pb‐based chalcogenide QDs; however, it remains a challenge to well replace the organic ligand with chloride ligand from silver chalcogenide QDs. Herein, a novel strategy to prepare Ag2S QDs with significant photoluminescence (PL) enhancement via chloride‐mediated growth and passivation is demonstrated. The oleylamine and oleate ligands on the surface of silver‐rich Ag2S QDs are readily replaced by chloride ligands due to the smaller size and higher binding affinity with Ag+. Upon partial ligand exchange and chloride passivation, the surface trap states in Ag2S QDs are reduced through a decrease of unsaturated surface Ag atoms. Therefore, Ag2S QDs with approximately 300‐fold enhancement of PL intensity, and a PLQY of 47.6% at 1220 nm emission, and a lifetime of 256 ns are obtained because the nonradiative recombination is inhibited. This work reveals that the passivation of Ag2S QDs with chloride ligands is fully feasible, providing new insights into improving the PLQY of silver chalcogenide QDs.

Nano-Antibacterials Using Medicinal Plant Components: An Overview.

Gradual emergence of new bacterial strains, resistant to one or more antibiotics, necessitates development of new antibacterials to prevent us from newly evolved disease-causing, drug-resistant, pathogenic bacteria. Different inorganic and organic compounds have been synthesized as antibacterials, but with the problem of toxicity. Other alternatives of using green products, i.e., the medicinal plant extracts with biocompatible and potent antibacterial characteristics, also had limitation because of their low aqueous solubility and therefore less bioavailability. Use of nanotechnological strategy appears to be a savior, where phytochemicals are nanonized through encapsulation or entrapment within inorganic or organic hydrophilic capping agents. Nanonization of such products not only makes them water soluble but also helps to attain high surface to volume ratio and therefore high reaction area of the nanonized products with better therapeutic potential, over that of the equivalent amount of raw bulk products. Medicinal plant extracts, whose prime components are flavonoids, alkaloids, terpenoids, polyphenolic compounds, and essential oils, are in one hand nanonized (capped and stabilized) by polymers, lipids, or clay materials for developing nanodrugs; on the other hand, high antioxidant activity of those plant extracts is also used to reduce various metal salts to produce metallic nanoparticles. In this review, five medicinal plants, viz., tulsi (Ocimum sanctum), turmeric (Curcuma longa), aloe vera (Aloe vera), oregano (Oregano vulgare), and eucalyptus (Eucalyptus globulus), with promising antibacterial potential and the nanoformulations associated with the plants’ crude extracts and their respective major components (eugenol, curcumin, anthraquinone, carvacrol, eucalyptus oil) have been discussed with respect to their antibacterial potency.

Comparative Study of the New Type Capping Layer for Hf0.5Zr0.5O2 Ferroelectric Film

The capping layers have great influences on the ferroelectricity of the Hf0.5Zr05O2 (HZO) film during annealing process. In this paper we compared the properties of the HZO film with two inorganic nonmetallic capping layers and no capping layer. The remnant (2Pr) of HZO films are 23.5 uC/cm2, 27.3 uC/cm2 and 20.3 uC/cm2 for no capping layer, Si3N4 capping layer and SiO2 capping layer, respectively. The capping layer can change the direction of the coercive filed shift even though the capacitors have the same metal electrodes.

A sandwich-type cluster containing Ge@Pd3 planar fragment flanked by aromatic nonagermanide caps

Sandwich-type clusters with the planar fragment containing a heterometallic sheet have remained elusive. In this work, we introduce the [K(2,2,2-crypt)]4{(Ge9)2[η6-Ge(PdPPh3)3]} complex that contains a heterometallic sandwich fragment. The title compound is structurally characterized by means of single-crystal X-ray diffraction, which reveals the presence of an unusual heteroatomic metal planar fragment Ge@Pd3. The planar fragment contains a rare formal zerovalent germanium core and a peculiar bonding mode of sp2-Ge@(PdPPh3)3 trigonal planar structure, whereas the nonagermanide fragments act as capping ligands. The chemical bonding pattern of the planar fragment consists of three 2c-2e Pd-Ge σ-bonds attaching Pd atoms to the core Ge atom, while the binding between the planar fragment and the aromatic Ge9 ligands is provided by six 2c-2e Pd-Ge σ-bonds and two delocalized 4c-2e σ-bonds. The synthesized cluster represents a rare example of a sandwich compound with the heteroatomic metal planar fragment and inorganic aromatic capping ligands.

Synthesis and characterization of novel calcium phosphate glass-derived cements for vital pulp therapy.

Evaluation of the physicochemical behavior and setting reactions of a novel inorganic pulp capping cement which makes use of the unique corrosion properties of sodium metasilicate (NaSi) glass. NaSi and calcium phosphate (CaP) glass powders were synthesized through a melt-quench method. Cements were created by mixing various amounts of the glasses with deionized water at a powder-to-liquid ratio of 2.5 g mL-1. Working and setting times were measured using the indentation standard ISO 9917-1. Sealing ability was tested by placing set samples of each composition in methylene blue dye solution for 24 h. Set samples were also submerged in phosphate buffered saline and incubated at 37 °C for one week. X-ray diffraction was used to identify mature crystalline phases after incubation. Infrared spectroscopy and scanning electron microscopy were used to characterize cements before and after setting and after incubation. Working and setting times measured in the ranges of 2-5 and 10-25 min, respectively. Working and setting time generally decrease with increased NaSi concentration. Cements with compositions of 25 and 33 wt% NaSi were found to resist the infiltration of dye and maintain their shape. Compositions outside this range absorbed dye and collapsed. Infrared spectroscopy provided insight into the setting mechanism of these cements. After one week in vitro, cements were found to contain crystalline phases matching chemically stable, bioactive phases. The combination of NaSi and CaP glasses has favorable setting behavior, sealing ability, and mature phases for pulp capping while relying on a relatively simple, inorganic composition.

A simple approach to synthetize folic acid decorated magnetite@SiO2 nanostructures for hyperthermia applications.

Superparamagnetic magnetite nanoparticles were synthetized and capped by a SiO2 shell in order to avoid oxidation and aggregation of the iron oxide nanostructures. The inorganic capping was then further decorated by folic acid molecules, by using a very simple procedure exploiting supramolecular interactions among the organic moieties and the inorganic nanoparticles. The supramolecular nanoadduct thanks to folic acid molecules could act as a "Trojan horse" for the cancer cells and due to its superparamagnetic properties could induce local heat generation upon an appropriate magnetic field application. In fact, temperature was increased up to 42 °C when a 18 mT magnetic field was applied to the nanoparticles and the hybrid nanostructures were verified to be selectively internalized by HeLa cells, a human cervical cancer line known to overexpress the folic acid receptor.

Improved photoluminescence quantum yield and stability of CdSe-TOP, CdSe-ODA-TOPO, CdSe/CdS and CdSe/EP nanocomposites

Size-controllable monodisperse CdSe nanocrystals with different organic capping were prepared based on the hot-injection method. The effective separation of nucleation and growth was achieved by rapidly mixing two highly reactive precursors. As a contrast, we prepared CdSe/CdS nanocrystals (NCs) successfully based on the selective ion layer adsorption and reaction (SILAR) technique. This inorganic capping obtained higher photoluminescence quantum yield (PLQY) of 59.3% compared with organic capping of 40.8%. Furthermore, the CdSe-epoxy resin (EP) composites were prepared by adopting a flexible ex situ method, and showed excellent stability in the ambient environment for one year. So the composites with both high PLQY of nanocrystals and excellent stability are very promising to device application.

Host-guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals.

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host–guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 1011 Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs.

SnS4(4-), SbS4(3-), and AsS3(3-) Metal Chalcogenide Surface Ligands: Couplings to Quantum Dots, Electron Transfers, and All-Inorganic Multilayered Quantum Dot Sensitized Solar Cells.

Three inorganic capping ligands (ICLs) for quantum dots (QDs), SnS4(4-), SbS4(3-) and AsS3(3-), were synthesized and the energy levels determined. Proximity between the ICL LUMO and QD conduction level governed the electronic couplings such as absorption shift upon ligand exchange, and electron transfer rate to TiO2. QD-sensitized solar cells were fabricated, using the ICL-QDs and also using QD multilayers layer-by-layer assembled by bridging coordinations, and studied as a function of the ICL ligand and the number of QD layers.

Structure of Colloidal Quantum Dots from Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy.

Understanding the chemistry of colloidal quantum dots (QDs) is primarily hampered by the lack of analytical methods to selectively and discriminately probe the QD core, QD surface and capping ligands. Here, we present a general concept for studying a broad range of QDs such as CdSe, CdTe, InP, PbSe, PbTe, CsPbBr3, etc., capped with both organic and inorganic surface capping ligands, through dynamic nuclear polarization (DNP) surface enhanced NMR spectroscopy. DNP can enhance NMR signals by factors of 10-100, thereby reducing the measurement times by 2-4 orders of magnitude. 1D DNP enhanced spectra acquired in this way are shown to clearly distinguish QD surface atoms from those of the QD core, and environmental effects such as oxidation. Furthermore, 2D NMR correlation experiments, which were previously inconceivable for QD surfaces, are demonstrated to be readily performed with DNP and provide the bonding motifs between the QD surfaces and the capping ligands.

Optical, structural and morphological studies of ZnS nanoparticles synthesized using inorganic capping agent

Metal chalcogenide ZnS nanoparticles have been synthesized using simple capped precipitation method using Potassium pyrosulfate as capping agent. The synthesized nano powder was characterized by X-ray diffraction (XRD), UV–Vis absorption, transmission electron microscopy, infrared spectroscopy, thermogravimetric analysis and fluorescence emission spectroscopy. The XRD pattern exhibits three major peaks at d-values 3.12, 1.904, 1.626 A belonging to 2θ = 28.60°, 47.76° and 56.60° respectively showing Wurtzite crystal phase of ZnS. UV–Vis spectrum exhibits quantum confinement effect by a very sharp peak around 290 nm remarkably blue shifted compared to its bulk counterpart. The room temperature photoluminescence spectrum of the nanoparticles showed two strong emission bands at 421 and 447 nm. This first blue emission peak at 421 nm is due to sulphur vacancy and other peak at 447 nm belongs to native defect states.

An inorganic capping strategy for the seeded growth of versatile bimetallic nanostructures.

Metal nanostructures have attracted great attention in various fields due to their tunable properties through precisely tailored sizes, compositions and structures. Using mesoporous silica (mSiO2) as the inorganic capping agent and encapsulated Pt nanoparticles as the seeds, we developed a robust seeded growth method to prepare uniform bimetallic nanoparticles encapsulated in mesoporous silica shells (PtM@mSiO2, M = Pd, Rh, Ni and Cu). Unexpectedly, we found that the inorganic silica shell is able to accommodate an eight-fold volume increase in the metallic core by reducing its thickness. The bimetallic nanoparticles encapsulated in mesoporous silica shells showed enhanced catalytic properties and thermal stabilities compared with those prepared with organic capping agents. This inorganic capping strategy could find a broad application in the synthesis of versatile bimetallic nanostructures with exceptional structural control and enhanced catalytic properties.

Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals.

Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MXn, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV–VI, II–VI, and III–V semiconductor nanocrystals. In particular, we show that the Lewis acid–base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20–30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50–65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.

Thermal Stability of Colloidal InP Nanocrystals: Small Inorganic Ligands Boost High-Temperature Photoluminescence

We examine the stability of excitons in quantum-confined InP nanocrystals as a function of temperature elevation up to 800 K. Through the use of static and time-resolved spectroscopy, we find that small inorganic capping ligands substantially improve the temperature dependent photoluminescence quantum yield relative to native organic ligands and perform similarly to a wide band gap inorganic shell. For this composition, we identify the primary exciton loss mechanism as electron trapping through a combination of transient absorption and transient photoluminescence measurements. Density functional theory indicates little impact of studied inorganic ligands on InP core states, suggesting that reduced thermal degradation relative to organic ligands yields improved stability; this is further supported by a lack of size dependence in photoluminescence quenching, pointing to the dominance of surface processes, and by relative thermal stabilities of the surface passivating media. Thus, small inorganic ligands, which benefit device applications due to improved carrier access, also improve the electronic integrity of the material during elevated temperature operation and subsequent to high temperature material processing.

Multifunctional Nanostructured Materials for Oxidation of Methanol

Herein, we report on our investigation on the use of the aqueous solution of the phosphotungstate heteropolyblue as a reducing agent and stabilizer for the synthesis of gold nanoparticles deposited on multiwalled carbon nanotubes and functionalized with CO-type surface groups. Chemical reduction method allowed producing multi-walled carbon nanotube-supported gold (Au/MWCNTs) catalysts with high dispersion and loading of Au up to 5 wt%. The average diameter of Au nanoparticles on MWCNTs was 2.0-4.5 nm. The resulting gold nanoparticles were subsequently cleaned from their inorganic capping agents (PW12O40 3-) by converting to alkaline medium (NaOHaq). The high dispersion of gold nanoparticles at MWCNTs (pretreated with HCl, HNO3 and H3PMo12O40) was attributed to the presence of a high density of active sites for nucleation created during the functionalization procedure. The nanocomposite system based on multi-walled carbon nanotubes decorated with gold nanoparticles was probed towards electrocatalytic oxidation of methanol in alkaline medium under voltammetric conditions. The existence of mesopores created at the surfaces of multi-walled carbon nanotubes originated from an easy accessibility of the OH- groups and methanol molecules at the electrocatalytic interface. The chemical functionalization of the open ends and the side walls of MWCNTs played a vital role in tailoring their electrochemical properties. Electrochemical studies demonstrated the promotional effect of quick pseudofaradaic reactions of surface polar groups created on carbon nanotubes during the methanol electrooxidation process.

Controlling the optical efficiency of the transparent organic light-emitting diode using capping layers

The performance of transparent organic light-emitting diodes (TOLEDs) that use a combination of organic and inorganic capping layers (CLs) is reported. The first organic layer on top of the transparent cathode was used to increase the light output of the normally directed emission toward the top direction. The second layer, which had high-refractive-index inorganic materials on top of the first organic layer, was used as a reflector to enhance the efficiency of the bottom direction by taking advantage of the discrepancy in the refractive index against the air. By incorporating these CLs, control of the optical properties of the TOLEDs was achieved to allow the application of the transparent lighting-source.

Monodisperse and Inorganically Capped Sn and Sn/SnO2 Nanocrystals for High-Performance Li-Ion Battery Anodes

We report a facile synthesis of highly monodisperse colloidal Sn and Sn/SnO2 nanocrystals with mean sizes tunable over the range 9-23 nm and size distributions below 10%. For testing the utility of Sn/SnO2 nanocrystals as an active anode material in Li-ion batteries, a simple ligand-exchange procedure using inorganic capping ligands was applied to facilitate electronic connectivity within the components of the nanocrystalline electrode. Electrochemical measurements demonstrated that 10 nm Sn/SnO2 nanocrystals enable high Li insertion/removal cycling stability, in striking contrast to commercial 100-150 nm powders of Sn and SnO2. In particular, reversible Li-storage capacities above 700 mA h g(-1) were obtained after 100 cycles of deep charging (0.005-2 V) at a relatively high current of 1000 mA h g(-1).