Pham Thanh Huy

Novel silver nanoparticles: synthesis, properties and applications

In this paper, we present versatile and effective techniques to synthesise silver nanoparticles (Ag-NPs)-based compounds such as colloidal silver nanoparticles (CSNPs) and silver nanoparticles powders (SNPPs). The CSNPs stabilised by a surfactant oleic acid were produced for the first time through the reduction of [Ag(NH3)2]+(aq) complex by glucose with UV irradiation treatment, while the SNPPs were formed by thermal decomposition of silver-oleate complex at 330°C for 1 h. The CNPPs and CSNPs with average diameters (~9–10 nm) and highly stableaqueous dispersions were obtained. Noticeably, these synthesised Ag-NPs exhibited an excellent antibacterial activity against gram-negative Escherichia coli (ATCC 43888-O157:k-:H7) and methicillin-resistant gram-positive Staphylococcus aureus (ATCC 43300) bacteria. The electron microscopic technique provided deeper insights on the interaction and bactericidal mechanism of the Ag-NPs. Potential applications of the synthesised CSNPs and SNPPs for antibacterial – masterbatchs, acrylic emulsion paint as well as coating layer on cotton textiles were demonstrated.

Synthesis of Y2O3:Eu3+ micro- and nanophosphors by sol-gel process

In this paper, optical properties of Y2O3:Eu3+ micro- and nanophosphors synthesized by sol-gel process are reported. Citric acid and tartaric acid were employed as chelating agents. Different factors effecting structures and properties of the phosphors, such as concentration of Eu3+, sintered temperature and the ratio of metal ions to tartaric acid, were examined. Crystal structure of the particles was investigated by X-ray diffraction (XRD) technique. The results showed that the phosphor powders completely crystallized at 600°C. Morphology and particle size of the phosphors were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM). The particle size of the obtained phosphors varied from 1 to 6 μm (using citric acid as chelating agent) and from 20 to 30 nm (using tartaric acid as chelating agent). Photoluminescence measurements of the Y2O3:Eu3+ particles showed red emission peaks at 610 -612 nm (5D0→7F2). The optimal molar concentration to obtain the highest photoluminescent intensity for the phosphors was 7% of Eu3+.

Photochemical synthesis of highly bactericidal silver nanoparticles

In this work we describe an experimental technique that makes it possible to obtain highly bactericidal silver nanoparticles (NPs). Synthesis was carried out using nontoxic reagents, and the technique consisted of reducing silver by glucose via UV irradiation in the presence of oleic or myristic acids as stabilizers. The size of the NPs fell in the range of 4–18 nm, and the average diameter was about 7 ± 1 nm (oleic acid) and 4 ± 1 nm (myristic acid). Unlike previous reports, where the Tollens reaction was used only with the assistance of thermal activation, we conducted the UV reduction of a silver nitrate solution, glucose, and the stabilizer at room temperature for the first time. The minimum inhibition concentration of nanosized silver against a gram-negative Escherichia coli was 1 μg/ml. Thus, the activity of the NPs appeared to be considerably higher than that of nanosilver samples that are currently known.

Giant magnetoimpedance in layered composite micro-wires for high-sensitivity magnetic sensor applications

Currently, the design and development of novel magnetic materials with optimized properties is of relevance to study new phenomena and to use them for multifunctional applications of sensor technologies and magnetoelectronic devices. In this letter, we present a detailed investigation of giant magnetoimpedance (GMI) effect in layered magnetic microwires. A new family of layered microwire composite materials was fabricated by using rapidly quenching and coating techniques. The experimental measurements were performed using an impedance analyzer (HP 4191A) in the frequency range of 100 – 1000 MHz and a varying applied dc magnetic field within ± 300 Oe. Interestingly, the GMI ratio and magnetic-field sensitivity reached the largest values of 3200 and 2400%/Oe at a resonance frequency of 890.15 MHz for layered Co-rich microwire sample, respectively. These results are very ideal for the development of a new family of ultra-sensitive and high-frequency magnetic sensors. Finally, the layered composite magnetic micro-wire developed with enhanced sensitivity performance can be ideally used as sensing elements in magnetic sensor technologies.

Wet Chemical Preparation of Nanoparticles ZnO:Eu3

ZnO doped with Eu3+ and Tb3+ had been successfully prepared by wet chemical method with the assistance of microwave. The influence of reaction conditions such as temperature, time, content of Eu3+, Tb3+ ion, and annealing treatment on the structure and luminescent characteristics was studied. The analysis of energy dispersive spectroscopy (EDS) and photoluminescence spectra measurements indicated that Eu3+ and Tb3+ exist in host lattice and create the new emission region compared to ZnO crystalline host lattice. The field emission scanning electron microscope (FE-SEM) studies show the Eu3+, Tb3+ doped ZnO nanoparticles have a pseudohexagonal shape. The particle size was 30–50 nm for ZnO:Eu3+ and 40–60 nm for ZnO:Tb3+. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra at room temperature have been studied to recognize active centers for characteristic luminescence of ZnO:Eu3+ and ZnO:Tb3+. The characteristic luminescent lines of Eu3+ (5D0-7Fj) and Tb3+ (5D4-7Fj) were determined. It has been demonstrated that the wet chemical synthesis method with microwave assistance can strongly enhance the luminescent intensity of nanoparticles ZnO:Eu3+ in red and ZnO:Tb3+ in green.

Monte Carlo Study of Room-Temperature Ferromagnetism in C-Doped ZnO

The room-temperature ferromagnetism of diluted magnetic semiconductors (DMS) doped with light elements has been extensively studied for potential applications in spintronic devices. The existence and stability of ferromagnetism of DMS with low concentration regime is an interesting topic, followed by researches using both Monte Carlo (MC) simulation and first-principle calculations. Both continuous and discrete spin models were developed to describe the ferromagnetic phase but it is still unclear, which one produces a better outcome. To clarify the issue of a continuous spin model versus a discrete spin model, we have performed a large-scale MC simulation of C-doped ZnO system. We found that the discrete spin model exhibit magnetic phase transition at near room-temperature while the continuous spin model does not show phase transition in the investigated low temperature range.

Optical Properties of Silicon Nanoparticles Prepared by Laser Ablation Method in Various Media

Bright photoluminescent silicon nanoparticles were successfully fabricated from porous silicon target in air and n-hexane using 532 nm line of YAG:Nd pulsed laser. The whole procedure was carried out at room temperature, in atmosphere. The morphology and composition of as-synthesized nanoparticles were characterized by SEM and EDS measurements. Their optical properties were investigated. The PL peak position of the as-synthesized Si nanoparticle ablated in air is slightly blue-shifted in comparison with those ablated in n-hexane, while it was almost no change of peak position of Si nanoparticles fabricated from p-Si in hexane and original p-Si wafer target. In contrast to PL intensity quenching of original p-Si sample and particles produced in air, those produced in n-hexane solvent exhibited an enhancement. The presence of dangling bonds or energy transfer from excited Si particles to oxygen molecules on the surface can be the cause of the quenching effect.