Morphology of Composite Nanoparticles of Immiscible Binary Systems Prepared by Gas-evaporation Technique and Subsequent Vapor Condensation

X–Y composite nanoparticles of four immiscible binary systems (Si–In, Ge–In, Al–In and Al–Pb) were prepared by the condensation of Y vapor onto X nanoparticles produced in advance by a gas-evaporation technique. The nanoparticles, which were observed by electron microscopy, were composed of two or more crystallites of the elements with different morphology. Their growth process is discussed with reference to the phase diagrams.     

From silver nanoparticles to nanostructures through matrix chemistry

Direct in situ reduction of silver ions by a biopolymer such as agar, without any other reducing nor capping agent is shown in this article to lead either to nanoparticles (typically 12(2) nm in an optimized case) or to more complex nanostructures depending on the reaction conditions used. This approach takes advantage of the porous polymer lattice acting as a template and leads to hybrid Ag–Agar materials with long-term synergic stability. Silver acts as an antibacterial agent for agar whereas the biopolymer prevents agglomeration of the inorganic nanoparticles leading to a stable nanocomposite formed by a thermoreversible biopolymer from which silver nanoparticles can eventually be recovered.     

Influence of the thickness of the tunnel layer on the charging characteristics of Si nanocrystals embedded in an ultra-thin SiO2 layer

In this paper, we have studied the effect of the thickness of the initial SiO₂ layer (5–7 nm) on the charge and discharge properties of a 2D array of Si nanoparticles embedded in these SiO₂ layers fabricated by ultra-low-energy ion implantation (ULE-II) and annealing. The structural characteristics of these nanocrystal-based memories (position of the nanocrystals with respect to the electrodes, size and surface density of the particles in the plane) were studied by transmission electron microscopy (TEM) and energy filtered TEM (EF-TEM). Electrical characterizations were performed at room temperature using a nano-MOS capacitor to be able to address only a few nanoparticles (nps). EFTEM gives the measurements of oxide thickness, injection, control and nps distances, size and density. I–V and I–t measurements exhibit current peaks and random telegraph signal fluctuations that can be interpreted as due to quantized charging of the nps and to some electrostatic interactions between the trapped charges and the tunnelling current. We have shown that these characteristics strongly vary with the initial oxide thickness, exhibiting several charging/discharging events for the 7-nm-thick layer while charging events prevail in the case of 5-nm-thick layer. These results indicate that the probability of discharging phenomena is reduced when the tunnel layer thickness decreases.     

Surface plasmon resonance in nano-gold antimony glass–ceramic dichroic nanocomposites: One-step synthesis and enhanced fluorescence application

A single-step melt-quench in situ thermochemical reduction technique has been used to synthesize a new series of Au° nanoparticles embedded antimony glass–ceramic (K₂O–B₂O₃–Sb₂O₃–ZnO) dichroic nanocomposites. X-ray and selected area electron diffractions manifest growth of Au° nanoparticles along (2 0 0) planes. The particle sizes obtained from X-ray diffraction patterns are found to vary in the range 4–21 nm. Dichroic behavior is attributed to the elliptical shape gold nanoparticles having aspect ratio 1.2, as observed from the transmission electron microscopy (TEM) images. The Au° nanoparticles exhibit surface plasmon resonance band (SPR) around 600 nm, which experiences red-shifts with increasing Au concentration. These nanocomposites when co-doped with Sm₂O₃ and excited at 949 nm, exhibit 2-fold intensification of 636 nm red emission transition (⁴G_5/2 → ⁶H_9/2) due to SPR induced local field enhancement of Au° nanoparticles and are promising materials for display applications.     

Dust ion-acoustic wave oscillations in single-walled carbon nanotubes

In this paper, a charged single-walled carbon nanotube that surrounded by charged nanoparticles is modeled as a cylindrical shell of electron–ion–dust plasma. By employing the fluid theory for electron–ion–dust plasma, the dispersion relation of the dust ion-acoustic wave oscillations in the composed system is studied. For negatively charged dust particles, with increasing dust charge density, the phase velocity of the dust ion-acoustic wave will increase in comparison to the pure ion-acoustic wave oscillations.     

Hybridization of surface-modified metal nanoparticles and a resin

Mercapto-terminated linear polymers, which were prepared by a reversible addition-fragmentation chain transfer (RAFT) technique, were used to modify metal nanoparticle surfaces. Au and Ag nanoparticles which are approximately 3–6 nm were used. This modification resulted in easy dispersion of the nanoparticles in polymer resins by simple mixing. The quality of the dispersion was confirmed by UV–Vis spectroscopy and transmission electron microscopy.     

Fabrication and electrical characterization of a MOS memory device containing self-assembled metallic nanoparticles

Floating gate devices with nanoparticles embedded in dielectrics have recently attracted much attention due to the fact that these devices operate as non-volatile memories with high speed, high density and low power consumption. In this paper, memory devices containing gold (Au) nanoparticles have been fabricated using e-gun evaporation. The Au nanoparticles are deposited on a very thin SiO₂ layer and are then fully covered by a HfO₂ layer. The HfO₂ is a high-k dielectric and gives good scalability to the fabricated devices. We studied the effect of the deposition parameters to the size and the shape of the Au nanoparticles using capacitance–voltage and conductance–voltage measurements, we demonstrated that the fabricated device can indeed operate as a low-voltage memory device.     

On surface plasmon damping in metallic nanoparticles

Two possible mechanisms of damping of surface plasmon (SP) oscillations in metallic nanoparticles (MNPs), not connected with the electron–phonon interaction, are investigated theoretically: (a) radiation damping of SPs and (b) resonant coupling of SP oscillations with electronic transitions in the matrix. For the mechanism (a) it is shown that the radiation damping rate is proportional to the number of electrons in a MNP and therefore this channel of energy outflow from the MNP becomes essential for relatively large particles. The strong frequency and size dependence of the radiation damping rate obtained allows us to separate the contributions of radiative processes and the electron–phonon interaction to the energy leakage. The investigation of the mechanism (b) shows that the rate of energy leakage of SP oscillations from a MNP does not depend on particle size and is fully determined by the optical characteristics of the matrix. It is demonstrated that for very small MNPs of -–3 5nm size, where the strong three-dimensional size quantization effect suppresses the electron–phonon interaction, the resonance coupling in certain cases provides an effective energy outflow. PACS 78.67.Bf     

Structure of MnO nanoparticles embedded into channel-type matrices

X-ray diffraction experiments were performed on MnO confined in mesoporous silica SBA-15 and MCM-41 matrices with different channel diameters. The measured patterns were analyzed by profile analysis and compared to numerical simulations of the diffraction from confined nanoparticles. From the lineshape and the specific shift of the diffraction reflections it was shown that the embedded objects form ribbon-like structures in the SBA-15 matrices with channels diameters of 47–87 Å, and nanowire-like structures in the MCM-41 matrices with channels diameters of 24–35 Å. In the latter case the confined nanoparticles appear to be narrower than the channel diameters. The physical reasons for the two different shapes of the confined nanoparticles are discussed.     

Structure and properties of PbS–polyacrylamide nanocomposites

A synthetic procedure for the incorporation of PbS nanoparticles in a polyacrylamide (PAM) matrix is introduced. The method is based on the simultaneous polymerization of the monomer and thermal decomposition of the dithiooxamide–lead complex. X-ray diffraction analysis revealed that the PbS nanoparticles have a sphalerite crystal structure (galena). A transmission electron micrograph showed spherical particles, with an average diameter of about 3 nm, well dispersed in the polymer matrix. Although a sharp edge was not observed, the optical absorption of the PAM–PbS nanocomposite is shifted towards lower wavelengths compared to the bulk PbS. It was also found that, despite a low concentration of the inorganic phase, the nanoparticles significantly affect the thermal properties of the matrix. PACS 82.35.Np; 81.07.-b     

Photo-induced CdS nanoparticles growth

A photochemical approach on the size control of CdS nanoparticles is presented. CdS nanoparticles were grown using the photo-induced reaction of sodium thiosulfate with Cadmium sulfate, in the absence of any surfactant. Particles of 5.5–11 nm were obtained by changing the illumination time. The dark growth of nanoparticles was negligible, however we found by optical scattering measurements that a ripening phenomenon occurs and the size of nanoparticles slightly increases with time.     

Gold nanoparticles having dipicolinic acid imprinted nanoshell for Bacillus cereus spores recognition

Taking into account the recognition element for sensors linked to molecular imprinted polymers (MIPs), a proliferation of interest has been witnessed by those who are interested in this subject. Indeed, MIP nanoparticles are theme which recently has come to light in the literature. In this study, we have proposed a novel thiol ligand-capping method with polymerizable methacryloylamidocysteine (MAC) attached to gold nanoparticles, reminiscent of a self-assembled monolayer. Furthermore, a surface shell by synthetic host polymers based on molecular imprinting method for recognition has been reconstructed. In this method, methacryloyl iminodiacetic acid-chrome (MAIDA–Cr(III)) has been used as a new metal-chelating monomer via metal coordination–chelation interactions and dipicolinic acid (DPA) which is the main participant of Bacillus cereus spores has been used as a template. Nanoshell sensors with templates produce a cavity that is selective for DPA. The DPA can simultaneously chelate to Cr(III) metal ion and fit into the shape-selective cavity. Thus, the interaction between Cr(III) ion and free coordination spheres has an effect on the binding ability of the gold nanoparticles nanosensor. The interactions between DPA and MIP particles were studied observing fluorescence measurements. DPA addition caused significant decreases in fluorescence intensity because they induced photoluminescence emission from Au nanoparticles through the specific binding to the recognition sites of the crosslinked nanoshell polymer matrix. The binding affinity of the DPA imprinted nanoparticles has been explored by using the Langmuir and Scatchard methods and the analysis of the quenching results has been performed in terms of the Stern–Volmer equation.     

Fabrication of polyaniline/ heterojunction structure using plasma enhanced polymerization technique

The work reports on the fabrication of a p–n heterojunction structure comprised of polyaniline (PANI) and TiO₂ nanoparticles. PANI was deposited by plasma enhanced polymerization on TiO₂ thin film substrates. The structural and the crystalline properties demonstrated the coherence and the substantive interaction of the plasma polymerized PANI molecules with the TiO₂ nanoparticle thin film. The UV–Vis studies of PANI/TiO₂ thin film supported the internalization of PANI with TiO₂ nanoparticles due to π–π^* transition of the phenyl rings with the lone pair electrons () of the nitrogen atom present in the PANI molecules. The I–V characteristics of the PANI/TiO₂ heterojunction structure were obtained in the forward and the reverse biased at applied voltage ranging from −1 V to +1 V with a scan rate of 2 mV/s. The proficient current in the PANI/TiO₂ heterojunction structure was attributed to the well penetration of PANI molecules into the pores of the TiO₂ nanoparticle thin film. The I–V characteristics ensured an efficient charge movement at the junction of PANI/TiO₂ interface and thus, behaved as a typical ohmic system.     

Bimodal Nanoparticle Size Distributions Produced by Laser Ablation of Microparticles in Aerosols

Silver nanoparticles were produced by laser ablation of a continuously flowing aerosol of microparticles in nitrogen at varying laser fluences. Transmission electron micrographs were analyzed to determine the effect of laser fluence on the nanoparticle size distribution. These distributions exhibited bimodality with a large number of particles in a mode at small sizes (3–6-nm) and a second, less populated mode at larger sizes (11–16-nm). Both modes shifted to larger sizes with increasing laser fluence, with the small size mode shifting by 35% and the larger size mode by 25% over a fluence range of 0.3–4.2-J/cm². Size histograms for each mode were found to be well represented by log-normal distributions. The distribution of mass displayed a striking shift from the large to the small size mode with increasing laser fluence. These results are discussed in terms of a model of nanoparticle formation from two distinct laser–solid interactions. Initially, laser vaporization of material from the surface leads to condensation of nanoparticles in the ambient gas. Material evaporation occurs until the plasma breakdown threshold of the microparticles is reached, generating a shock wave that propagates through the remaining material. Rapid condensation of the vapor in the low-pressure region occurs behind the traveling shock wave. Measurement of particle size distributions versus gas pressure in the ablation region, as well as, versus microparticle feedstock size confirmed the assignment of the larger size mode to surface-vaporization and the smaller size mode to shock-formed nanoparticles.     

Copper adsorption on magnetite-loaded chitosan microspheres: A kinetic and equilibrium study

A composite of Fe₃O₄ nanoparticles and the biopolymer chitosan, chemically crosslinked, was prepared as microspheres and used to adsorb copper ions, which were chosen as a model of contaminant metal in water.     

Bactericidal effects of Ag nanoparticles immobilized on surface of SiO2 thin film with high concentration

Bactericidal activity of high concentration Ag nanoparticles immobilized on surface of an aqueous sol–gel silica thin film was investigated against Escherichia coli and Staphylococcus aureus bacteria. Size of the surface nanoparticles was estimated in the range of 35–80 nm by using atomic force microscopy. Due to accumulation of the silver nanoparticles at near the surface (at depth of 6 nm and about 40 times greater than the silver concentration in the sol), the synthesized Ag–SiO₂ thin film (with area of 10 mm²) presented strong antibacterial activities against E. coli and S. aureus bacteria with relative rate of reduction of the viable bacteria of 1.05 and 0.73 h⁻¹ for initial concentration of about 10⁵ cfu/ml, respectively. In addition, the dominant mechanism of silver release in long times was determined based on water diffusion in surface pores of the silica film, unlike the usual diffusion of water on the surface of silver-based bulk materials. Therefore, the Ag nanoparticles embedded near the surface of the SiO₂ thin film can be utilized in various antibacterial applications with a strong and long life activity.     

Optical properties of Mg0.05Zn0.95O/SiO2 nanocomposite films prepared by sol–gel technique

Mg_0.05Zn_0.95O/SiO₂ nanocomposite films in the molar ratio 25:75 consisting of Mg_0.05Zn_0.95O nanoparticles embedded in a dielectric matrix were prepared by sol–gel technique (spin coating). Optical transmittance, Raman effect and photoluminescence measurements of the composites indicated effective capping of the Mg_0.05Zn_0.95O nanoparticles (radii 1. 61–1.68 nm) in the host showing practically no variation of particle size with the post deposition annealing treatments. The blue shift of the band gap (4.29–4.23 eV) from that of bulk Mg_0.05Zn_0.95O indicated strong carrier confinement for samples annealed at T ≤ 873 K. Highly intense UV emission ( ∼ 4.14 eV) compared to that of defect related emission (2.59 eV) at room temperature was obtained by incorporating 5% Mg in ZnO.     

Singular Diffusion as a Function of Nanoparticles Size in Antimony Film–Selenium Particles and Antimony Film–Tellurium Particles

A recently developed chemical synthesis method using the nanoparticle size as a parameter has been applied to Sb film–Se particle and Sb film–Te particle systems. In the Sb–Se system, the diffusion of Se atoms to the Sb film can be clearly seen for Se particle sizes less than 50 nm. Diffusion of Sb atoms predominantly took place in the case of the Sb–Te system. The uniqueness of the reaction consists in the diffusion direction of nanoparticles. Comparison with previous work (Kaito et al., 1998b) is made on the basis of the particle stability and electronegativity.     

Large two-photon absorbance of chitosan–ZnS quantum dots nanocomposite film

ZnS semiconductor nanoparticles with average size of 3.4 nm were prepared in situ in chitosan film. TEM, UV–vis spectra and PL spectra show the ZnS nanoparticles in chitosan template were monodispersed and well passivated. The two-photon absorption coefficient (β) of the chitosan–ZnS quantum dots (QDs) nanocomposite film was obtained to be 2.29×10² cm/Gw from a standard Z-scan setup with femtosecond laser pusles at 790 nm wavelength. Results show the novel biomacromolecule/QDs nanocomposite film has large third-order optical nonlinear absorption, the mechanism responsible for which was discussed.     

Hydroxyapatite Nanoparticles as a Novel Gene Carrier

Hydroxyapatite crystalline nanoparticles were created by a precipitation hydrothermal technique and the majority of crystal particles were in the size range of 40–60nm and exhibited a colloidal feature when suspended in water. The gastric cancer SGC-7901 cell line cells were cultivated in the presence of10–100 μg ml⁻¹ hydroxyapatite nanoparticle suspension and verified by MTT evaluation for their biocompatibility in vitro. The agarose gel electrophoresis analysis demonstrated that the HA nanoparticles potentially adsorb the green fluorescence protein EGFP-N1 plasmid DNA at pH 2 and 7, but not at pH 12. The DNA–nanoparticle complexes transfected EGFP-N1 pDNA into SGC-7901 cells in vitro with the efficiency about 80% as referenced with Lipofectmine TM 2000. In vivo animal experiment revealed no acute toxic adverse effect 2weeks after tail vein injection into mice, and TEM examination demonstrated their biodistribution and expression within the cytoplasm and also a little in the nuclei of the liver, kidney and brain tissue cells. These results suggest that the HA nanoparticle is a promising material that can be used as gene carrier, vectors.