One step synthesis of ZnO nanoparticles in free organic medium: Structural and optical characterizations

Nano-sized ZnO particles are synthesized by the sol–gel method in aqueous medium without any annealing, ripening treatment or organic additive addition. The structure, morphology, and optical properties of these ZnO nanoparticles are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Ultraviolet–visible spectroscopy (UV–vis) respectively. The effect of the synthesis temperature on the morphological (shape and size) and optical properties of these nanoparticles have been examined for temperatures varying from 0 to 80 °C. XRD analysis shows that the as-prepared particles crystallize in the Würtzite hexagonal phase even at very low synthesis temperatures. Meanwhile, Transmission Electron Microscopy observations reveal that the particles present a significant change in shape and size as the temperature increases. They take a flower shape, at very low temperatures, a conical or ellipsoidal shape when the temperature is ranging from 20 °C to 50 °C and a rodlike shape with a hexagonal section at elevated temperatures (>50 °C). Moreover, it has been observed that the increasing of the synthesis temperature leads to a net increase in the average particle size. It affects especially the length in the minor axis direction while the length in the major direction (c-axis) remains nearly constant. Optical properties, carried out by spectrophotometric measurements, indicate that increasing the temperature results in lower band gap energy values.     

Synthesis of silver nanoparticles and the optical properties

Silver nanoparticles (NPs) of 5-15 nm are synthesized with the reduction of silver nitrate (AgNO3 ) by formaldehyde (HCHO) and using polyethylenemine (PEI) as a stabilizer. Transmission electron microscopy (TEM) analysis shows the size of the Ag NPs increases with the increase of HCHO contents. The absorption and emission peaks of the original colloids are red shifted with increasing the size of Ag NPs. The absorption and emission peaks are at 344 nm, 349 nm, 357 nm, 362 nm, 364 nm and 444 nm, 458 nm, 519 nm, 534 nm, 550 nm, respectively. The fluorescence intensities of the silver colloids increase with increasing the NPs size (or the contents of HCHO). With the diluted fold increasing, the fluorescence intensity of the diluted silver colloids increases firstly then decreases. Compared with that of the original silver colloids, the emission peaks are blue shifted. For the diluted silver colloids, when the fluorescence intensity is maximum, the emission peaks are all near 444 nm. The 16-fold diluted silver colloid gets to the maximum emission intensity when the mole ratio of AgNO3 and HCHO is 1:6.     

Stabilization of PbS Nanocrystals by Bovine Serum Albumin in its Native and Denatured States

PbS nanocrystals (NCs) are synthesized in aqueous phase within a temperature range of 40–80 °C in the presence of native and denatured states of bovine serum albumen (BSA) as the capping/stabilizing agent. The NCs are characterized with the help of field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray analysis. At 40 °C, large ball‐shaped NCs (145 ± 37 nm) with small surface protrusions are formed when 1 × 10^?4 g mL^?1 BSA is used. As the reaction temperature is increased towards 80 °C, the size of NCs decreases and they acquire somewhat cubic geometries (49.1 ± 7.0 nm) due to a change in the capping behavior of BSA between its native and denatured states. The native and denatured states of BSA are simultaneously studied by fluorescence spectroscopy using tryptophan emission, and pH measurements with respect to time and temperature. Gel electrophoresis is used to determine the polarity of the BSA capped NCs. Only the small sized NCs conjugated with relatively larger amounts of BSA show a displacement towards the positively charged electrode in comparison to larger NCs with lower amounts of BSA capping. It was concluded that the denatured state of BSA is more effective in controlling the crystal growth of PbS than its native state especially in the low concentration range.     

Amorphous and Crystalline GeTe Nanocrystals

A facile method for the synthesis of crystalline and amorphous GeTe nanoparticles (NPs) using bis((trimethylsilyl)amido)germanium(II), Ge[N(SiMe₃)₂]₂, and elemental tellurium dispersed in tri‐n‐octylphosphine (TOP) is reported. As synthesized, crystalline particles exhibit narrow dispersity at smaller sizes and tend to grow into anisotropic shapes with increasing reaction time (growth). Furthermore, crystalline GeTe NPs possess rhombohedral symmetry with absorption band energies in near IR region (0.76–0.86 eV). Amorphous GeTe particles prepared at low temperatures are nearly spherical in morphology and display amorphous‐to‐crystalline phase transition at 209–237 °C depending on their primary particle size. Detailed investigation of the local structure of the amorphous GeTe using pair distribution function (PDF) method reveals that it is closely related to that of the pressure‐ and temperature‐stabilized orthorhombic GeTe.     

Evolution of Light Absorption and Emission Characteristics of Organic Perylene Nanoparticles through Hydrothermal Process: Application to Solar Cells

The evolution of the structural and optical characteristics of polymorphic organic perylene nanoparticles (NPs) is demonstrated by controlling the π–π interactions using a hydrothermal process. The light‐emission colors of the perylene NPs vary gradually from yellow to green to light blue with increasing hydrothermal temperature from 110 to 160 °C. An enhanced crystallinity of the NPs from 110 °C to a critical temperature T_c of 140 °C and a transition to the amorphous phase above T_c are observed. The evolution of the photo‐luminescence (PL) and optical‐absorption characteristics in terms of variations in the crystallinity and physical dimensions (size and shape) of the perylene NPs resulting from the hydrothermal process are analyzed. These results are confirmed by nanoscale PL measurements for single NPs using laser confocal microscopy. The photovoltaic characteristics of organic solar cells (OSCs) are improved through the use of the perylene NPs. It is found that the performance of the OSCs is strongly correlated with the optical‐absorption properties of the perylene NPs.     

Silver Nanoparticle Paste for Low-Temperature Bonding of Copper

Silver nanoparticle (NP) paste was fabricated and used to bond copper wire to copper foil at low temperatures down to 160°C. The silver NP paste was developed by increasing the concentration of 50 nm silver NP sol from 0.001 vol.% to 0.1 vol.% by centrifugation. The 0.001 vol.% silver NP sol was fabricated in water by reducing silver nitrate (AgNO₃) using sodium citrate dihydrate (Na₃C₆H₅O₇·2H₂O). The bond was formed by solid-state sintering among the individual silver NPs and solid-state bonding of these silver NPs onto both copper wire and foil. Metallurgical bonds between silver NPs and copper were confirmed by transmission electron microscopy (TEM). The silver NPs were coated with an organic shell to prevent sintering at room temperature (RT). It was found that the organic shell decomposed at 160°C, the lowest temperature at which a bond could be formed. Shear tests showed that the joint strength increased as the bonding temperature increased, due to enhanced sintering of silver NPs at higher temperatures. Unlike low-temperature soldering techniques, bonds formed by our method have been proved to withstand temperatures above the bonding temperature.     

Phenylboronic Acid‐Decorated Chondroitin Sulfate A‐Based Theranostic Nanoparticles for Enhanced Tumor Targeting and Penetration

Phenylboronic acid‐functionalized chondroitin sulfate A (CSA)–deoxycholic‐acid (DOCA)‐based nanoparticles (NPs) are prepared for tumor targeting and penetration. (3‐Aminomethylphenyl)boronic acid (AMPB) is conjugated to CSA–DOCA conjugate via amide bond formation, and its successful synthesis is confirmed using proton nuclear magnetic resonance spectroscopy (¹H‐NMR). Doxorubicin (DOX)‐loaded CSA–DOCA–AMPB NPs with a mean diameter of ≈200 nm, a narrow size distribution, negative zeta potential, and spherical morphology are prepared. DOX release from NPs is enhanced at acidic pH compared to physiological pH. CSA–DOCA–AMPB NPs exhibit improved cellular uptake in A549 (human lung adenocarcinoma) cells and penetration into A549 multicellular spheroids compared to CSA–DOCA NPs as evidenced by confocal laser scanning microscopy and flow cytometry. In vivo tumor targeting and penetrating by CSA–DOCA–AMPB NPs, based on both CSA–CD44 receptor and boronic acid–sialic acid interactions, is revealed using near‐infrared fluorescence (NIRF) imaging. Penetration of NPs to the core of the tumor mass is observed in an A549 tumor xenografted mouse model and verified by three‐dimensional NIRF imaging. Multiple intravenous injections of DOX‐loaded CSA–DOCA–AMPB NPs efficiently inhibit the growth of A549 tumor in the xenografted mouse model and increase apoptosis. These boronic acid‐rich NPs are promising candidates for cancer therapy and imaging.     

Polymer-Protected Cu-Ag Mixed NPs for Low-Temperature Bonding Application

A simple method has been proposed to prepare polymer-protected Cu-Ag mixed nanoparticles (NPs), which are suitable for use as low-temperature bonding materials. The polymer coated on the Cu-Ag mixed NPs can protect them from oxidation effectively when heated in air at temperature lower than 280°C. The low-temperature bonding process utilizing Cu-Ag mixed NPs as the bonding material is investigated. The bonding experiments show that robust joints are formed using Cu-Ag mixed NPs at 160°C in air. The shear test shows that addition of copper to silver is helpful for improving joint strength. This novel sintering-bonding technology using Cu-Ag mixed NPs as an interconnection material has potential for application in the electronics packaging industry.     

Carboxylate-Passivated Silver Nanoparticles and Their Application to Sintered Interconnection: A Replacement for High Temperature Lead-Rich Solders

Lead-free silver nanoparticle pastes have been tested as a replacement for high temperature lead-rich solders used in electronic manufacturing. The pastes contain a small amount of solvent, and primarily consist of submicron-silver powder and passivated silver nanoparticles. The nanoparticles were synthesized from Ag₂CO₃ and a long-chain alcohol by a method that produced a passivating layer consisting almost exclusively of the carboxylate of the reactant alcohol. The pastes were used to connect a silicon diode chip to copper bases without applied pressure when sintered at 350°C under nitrogen. Diode packages made with sintered silver interconnects had electrical and thermal properties equal to those with lead-soldered interconnects, even after 3000 thermal cycles between −55°C and +150°C. The mechanical strength was half that of lead-rich solder joints, but still strong enough for practical use.     

Bio-fabrication of zinc oxide nanoparticles using leaf extract of curry leaf (Murraya koenigii) and its antimicrobial activities

The present study focused on the development of zinc oxide nanoparticles (ZnO NPs) from the leaf extract of Murraya koenigii where zinc nitrate acts as the precursor. The X-ray diffraction (XRD) analysis showed the crystalline structure, and atomic force microscopy (AFM) showed the morphology of the ZnO NPs to be spherical with an average size of 12 nm. Functional groups of the sample were identified by using Fourier transmission infrared (FT-IR) spectroscopy. Their shape, structure and composition were assessed by Field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The results depicted that synthesized ZnO NPs were moderately stable and hexagonal shape, spherical shape with maximum particle size less than 100 nm. The green-synthesized ZnO NPs had prominent activities against Staphylococcus aureus (14.0±0.50 mm) and followed by Bacillus subtilis (13.8±0.76 mm) at the concentration of 200 µg/mL.     

Study of Structural,Electrical and Optical Properties of (200)-Oriented CdTe Thin Films Depending on the Post-deposition Low Temperature

Cadmium telluride nanoparticles (CdTe NPs) have been synthesized by a sonochemical technique, deposited on glass and quartz glass at 100°C and 2.7?×?10^?6 kPa and then studied by analyzing the x-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), current–voltage test (I–V) and scanning electron microscopy (SEM). The XRD results indicated the formation of a strong preferential (200) orientation of CdTe with a cubic zinc-blende structure on both substrates. In order to show the effect of heating on the structure and optical properties of the prepared thin films, they were annealed at temperatures of 50°C, 70°C and 100°C for 1 h. It was found that the grain size in this orientation increases with the increase of the temperature. In addition, the obtained optical band gap energies by UV–Vis measurements were in the range of 1.46–1.53 eV. The electrical properties of the prepared films were observed to increase with annealing using I–V measurements. The thin films were also found to be uniform with a small particle size, as revealed by SEM.

     

Gold Core‐DNA‐Silver Shell Nanoparticles with Intense Plasmonic Chiroptical Activities

The strong plasmonic chiroptical activities of gold core‐DNA‐silver shell nanoparticles (NPs) are reported for the first time, using cytosine‐rich single‐stranded DNA as the template for the guidance of silver shell growth. The anisotropy factor of the optically active NPs at 420 nm reaches 1.93 × 10^?2. Their chiroptical properties are likely induced by the DNA–plasmon interaction and markedly amplified by the strong electromagnetic coupling between the gold core and silver shell.     

Impact of Morphology on Printed Contact Performance in Carbon Nanotube Thin‐Film Transistors

Silver nanoparticles (NPs) are the most widely used conductive material throughout the printed electronics space due to their high conductivity and low cost. However, when interfacing with other prominent printed materials, such as semiconducting carbon nanotubes (CNTs) in thin‐film transistors (TFTs), silver is suboptimal when compared to more expensive or less conductive materials. Consequently, there would be significant value to improving the interface of printed silver to CNT films. In this work, the impact of nanostructure morphology on the electrical properties of printed silver and nanotube junctions in CNT‐TFTs is investigated. Three distinct silver morphologies (NPs, nanoflakes – NFs, and nanowires – NWs) are explored with top‐ and bottom‐contact configurations for each. The NF morphology in a top‐contact configuration is found to yield the best electrical interface to CNTs, resulting in an average contact resistance of 1.2 MΩ ? µm. Beyond electrical performance, several trade‐offs in morphology selection are revealed, including print resolution and process temperature. While NF inks produce the best interfaces, NP inks produce the smallest features, and NW inks are compatible with low processing temperatures (<80 °C). These results outline the trade‐offs between silver contact morphologies in CNT‐TFTs and show that contact morphology selection can be tailored for specific applications.     

超细银粉的制备及其导电性研究

用化学还原法在醇水体系中制备出平均颗粒粒径为 0.8~1.2 μm、分散性好的超细球银。讨论了表面活性剂、还原剂的种类、温度、硝酸银含量及 pH 值对球银颗粒粒径和分散性的影响。将所得超细球银在水体系中高效率球磨得分散性好的光亮片状银粉,平均粒径<6 ìm,比表面积 0.7~1.3 m2/g。讨论了吸附在银粉表面的有机物的种类和比表面积对片银导电性能的影响,结果表明:比表面积越大,导电性越好。     

Facile Fabrication of Highly Dispersed Pd@Ag Core–Shell Nanoparticles Embedded in Spirulina platensis by Electroless Deposition and Their Catalytic Properties

Microorganisms are widely used as the biotemplates for producing micro/nanomaterials owing to their unique features, such as exquisite morphology, renewable, and environmentally friendly. However, mass intracellular synthesis of uniformly dispersed nanoparticles (NPs) inside microorganisms is still challenging, especially in a predictable and controllable manner. Here, a facile and efficiency strategy is proposed to controllably produce highly dispersed and surfactant‐free Pd@Ag core–shell NPs within the Spirulina platensis (Sp.) cells. In this approach, the Sp. cells' permeability is enhanced by the hydrochloric acid treatment first, which enables the Pd NPs penetrate the cell envelope and distribute uniformly inside the cells, and then they can work as the catalytic seeds for the following electroless silver deposition, resulting in the intracellular fabrication of Pd@Ag core–shell NPs with no agglomeration. The Pd@Ag NPs show excellent catalytic activity (turnover frequency is up to 2893 h^?1 for the 6.32 nm Pd@Ag NPs), good stability, and recyclability toward the 4‐nitrophenol reductions. The excellent properties are attributed to the asymmetrical core–shell structure, small size, and good dispersion of Pd@Ag NPs. Due to its facility, cost‐effectiveness, and versatility, this method can be expanded to other microorganisms, so it opens tremendous opportunities for various metallic nanoparticles intracellular synthesis as well as the practical application.     

Low temperature molten salt synthesis of YAG: Ce spherical powder and its thermally stable luminescent properties after post-annealing treatment

Spherical YAG: Ce particles were successfully synthesized at 350 °C by the molten-salt method. The effect of temperature and amount of salt on the crystallization and particle size of YAG: Ce were investigated thoroughly. The results demonstrated that the powders prepared at 350 °C in salt to reactant ratio 2:1 were pure YAG: Ce phase with 200–300 nm in particle size. The as-synthesized phosphors were later post annealed at 1200 °C in O₂, air and N₂, respectively. The results showed that the emission intensity of YAG: Ce sensitively depended on the post-treated atmosphere and the phosphor annealed in N₂ showed the highest emission intensities and a good thermal stability.     

Nanoplasmonic Enhanced ZnO/Si Heterojunction Metal–Semiconductor–Metal Photodetectors

This paper presents a nanoplasmonic enhanced ZnO/Si heterojunction metal–semiconductor–metal (MSM) photodetector (PD). By depositing different thicknesses of Ag thin film and annealing at a moderate temperature, well-defined silver (Ag) nanoparticles (NPs) with different diameters, densities, and size distributions were produced on the surface of ZnO/Si MSM photodetector devices. By tuning the characteristics of these NPs, a higher-performance ZnO/Si MSM photodetector has been realized. The photocurrent of the detector with NPs was increased by 160% to 680%, depending on the applied voltage. The spectral photocurrent enhancement by a factor of 7 to 18 was broadband from 350 nm to 850 nm.     

Temperature‐Sensitive Nanocapsules for Controlled Drug Release Caused by Magnetically Triggered Structural Disruption

Self‐assembled nanocapsules containing a hydrophilic core and a crosslinked yet thermosensitive shell are successfully prepared using poly(ethylene‐oxide)‐poly(propylene‐oxide)‐poly(ethylene‐oxide) block copolymers, 4‐nitrophenyl chloroformate, gelatin, and 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide. The core is further rendered magnetic by incorporating iron oxide nanoparticles via internal precipitation to enable externally controlled actuation under magnetic induction. The spherical nanocapsules exhibit a hydrophilic‐to‐hydrophobic transition at a characteristic but tunable temperature reaching 40 °C, triggering a size contraction and shrinkage of the core. The core content experiences very little leakage at 25 °C, has a half life about 5 h at 45 °C, but bursts out within a few minutes under magnetic heating due to iron oxide coarsening and core/shell disruption. Such burst‐like response may be utilized for controlled drug release as illustrated here using a model drug Vitamin B12.     

From Hybrid Microgels to Photonic Crystals

We have synthesized semiconductor and metal nanoparticles (NPs) in the constrained geometry of polymer microgels. We used electrostatically driven attraction between the ionic groups of the microgels and the precursor cations in the bulk liquid medium to introduce the cations in the interior of the microgel. In the second step, the cations in the microgel interior reacted with the anion (to obtain semiconductor NPs) or they were treated with a reducing agent (to obtain metal NPs). Good control over the size and the concentration of the NPs in the microgel particles was achieved by changing the composition of the corresponding microgel. The doped microgel spheres were heated at pH 4 above the volume‐transition temperature of the polymer to expel the water from the microsphere interior; then the polymer was encapsulated with a hydrophobic polymeric shell. Hybrid core–shell particles were used as the building blocks of the nanostructured material with properties of a photonic crystal.     

Stimuli‐Responsive Thin Coatings Using Elastin‐Like Polymers for Biomedical Applications

Smart thin coatings using a recombinant elastin‐like polymer (ELP) containing the cell attachment sequence arginine–glycine–(aspartic acid) (RGD) are fabricated for the first time through simple deposition of the ELP dissolved in aqueous‐based solutions. The biopolymer is produced and characterized using electrophoresis and mass spectroscopy. The temperature and pH responsiveness are assessed by aggregate size measurements and differential scanning calorimetry. The deposition of the studied ELP onto chitosan is followed in situ with a quartz‐crystal microbalance with dissipation monitoring (QCM‐D). Contact angle measurements are performed at room temperature and at 50 °C, showing reversible changes from a moderate hydrophobic behavior to an extremely wettable surface. AFM analysis performed at room temperature reveals a smooth surface and no organized structure. At 50 °C, the surface presents spherical nanometer‐sized structures of collapsed biopolymer chains. Such results suggest that the ELP chains, when collapsed, aggregate into micelle‐like structures at the surface of the substrate, increasing its water affinity. Cell adhesion tests on the developed coatings are conducted using a SaOS‐2 cell line. Enhanced cell adhesion could be observed in the H‐RGD6‐coated surfaces, as compared with the original chitosan monolayer. An intermediate behavior is found in chitosan coated with the corresponding ELP without the RGD sequence. Therefore, the developed films have great potential as biomimetic coatings of biomaterials for different biomedical applications, including tissue engineering and controlled delivery of bioactive agents. Their thermo‐responsive behavior can also be exploited for tunable cell adhesion and controlled protein adsorption.