Hybrid Nanoparticle Film Material

A new hybrid material consisting of a nanoparticle film on a flexible, porous substrate is formed. The hybrid nanoparticle films are non-redispersable in solvents, yet remain porous and flexible. Visually, the hybrid films are highly reflective and metallic gold in appearance. However, the electronic properties of the films are characteristic for materials made from separate, non-sintered nanoparticles. Films of large area (several tens of cm²) and several microns in thickness can be formed. The method of formation is based on cross-linking gold nanoparticles using alkane-dithiols followed by filtration onto nanoporous supports. The films were characterized by transmission electron microscopy, atomic force microscopy and resistance measurements. The effect of the ratio of alkane-dithiol cross-linker to gold nanoparticles on the resistance of the nanoparticle films was also studied.     

First-principles study on the Ni@Pt12 Ih core-shell nanoparticles: A good catalyst for oxygen reduction reaction

The adsorption, diffusion and dissociation properties of O₂ on the icosahedron (Ih) Ni@Pt12 core-shell nanoparticle were investigated using the ab initio density functional theory calculations. It is found that, compared with the Pt(111) surface, the Ih Ni@Pt12 core-shell nanoparticle can enhance the adsorption, diffusion and dissociation of O₂, as well as the adsorption and diffusion of the atomic O (the dissociation product of O₂), and therefore serve as a good catalyst for oxygen reduction reaction. Our study gives a reasonable theoretical explanation to the high catalytic activity of the Ni@Pt core-shell nanoparticles for the oxygen reduction reaction.     

Fabrication and optical study of Ag@SnO<Subscript>2</Subscript> core-shell structure nanoparticle thin films

Ag@SnO₂ core-shell nanoparticles dispersed in poly-(vinyl) alcohol films were fabricated on glass substrate by employing a dip-coating technique. Synthesis of Ag@SnO₂ nanoparticles with core-shell morphology is carried out by a soft-chemical technique in aqueous phase at 60°C. Formation of core-shell structure is monitored by the red-shift of the surface plasmon band of Ag nanoparticles (from 390 to 410 nm) in the UV-visible spectrum. These nanoparticles are deposited on the glass substrate. The structure and morphology of these films were investigated by X-ray diffraction technique and field-emission transmission electron microscopy, respectively. Optical properties of these pseudo-solids were studied by UV-visible spectroscopy. Surface plasmon spectrum of the core-shell nanoparticles film remained unaltered with increase in the number of layers. However, silver nanoparticles films have shown peak broadening and development of additional peaks with increase in the number of layers. Our investigations showed that the surface plasmon band of the silver nanoparticles could be preserved by controlled deposition of the tin dioxide shell.     

Self-assembled silver nanoparticle films at an air-liquid interface and their applications in SERS and electrochemistry

In this paper, we present a novel technique to prepare silver nanoparticle films by controlling the self-assembly of nanoparticles at an air-liquid interface. In an ethanol-water phase, silver nanoparticles were prepared by reduction of AgNO₃ aqueous solution with NaBH₄ in the presence of cinnamic acid. It was found that the silver nanoparticles in this process could be trapped at the air-liquid interface to form 2-dimensional nanoparticle films. The morphology of nanoparticle films could be controlled by systematic variation of the experimental parameters. It is worth noting that the nanoparticle films could serve as the active substrates for surface-enhanced Raman scattering (SERS). 4-Aminothiophenol (4-ATP) molecule was used as a test probe to investigate the SERS sensitivity of different nanoparticle films. The results indicated that the nanoparticle films showed excellent Raman enhancement effect. Furthermore, the nanoparticle films prepared by our strategy were found to be efficient electrocatalysts for anodic oxidation of formaldehyde in alkaline medium.     

Towards Nanoscale Biomedical Devices in Medicine: Biofunctional and Spectroscopic Characterization of Superparamagnetic Nanoparticles

Medical interest in nanotechnology originates from a belief that nanoscale therapeutic devices can be constructed and directed towards its target inside the human body. Such nanodevices can be engineered by coupling superparamagnetic nanoparticle to biomedically active proteins. We hereby report the immobilization of a PhEst, a S-formylglutathione hydrolase from the psychrophilic P. haloplanktis TAC125 onto the gold coated surface of modified superparamagnetic core-shell nanoparticles (Fe₃O₄@Au). The synthesis of the nanoparticles is also reported. S-formylglutathione hydrolases constitute a family of ubiquitous enzymes which play a key role in formaldehyde detoxification both in prokaryotes and eukaryotes. PhEst was originally annotated as a putative feruloyl esterase, an enzyme that releases ferulic acid (an antioxidant reactive towards free radicals such as reactive oxygen species) from polysaccharides esters. Dynamic light scattering, scanning electron microscopy with energy dispersive X-ray spectroscopy, UV–visible absorption spectroscopy, fluorescence spectroscopy, magnetic separation technique and enzyme catalytic assay confirmed the chemical composition of the gold covered superparamagnetic nanoparticles, the binding and activity of the enzyme onto the nanoparticles. Activity data in U/ml confirmed that the immobilized enzyme is approximately 2 times more active than the free enzyme in solution. Such particles can be directed with external magnetic fields for bio-separation and focused towards a medical target for therapeutical as well as bio-sensor applications.     

Nanostructures of gold coated iron core-shell nanoparticles and the nanobands assembled under magnetic field

Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with a stable noble metal, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties, which possess the potential application in high density memory device by forming self-assembling nanoarrays. Gold-coated iron core-shell structure nanoparticles (Fe/Au) synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 1∼2 nm shell. Since the gold shell is not epitaxial growth related to the iron core, the morié pattern can be seen from the overlapping of iron core and gold shell. However, the gold shell lattice can be seen by changing the defocus of TEM. An energy dispersive X-ray spectrum (EDS) also shows the nanoparticles are air-stable. The magnetic measurement of the nanoparticles also proved successful synthesis of gold coated iron core-shell structure. The nanoparticles were then assembled under 0.5 T magnetic field and formed parallel nanobands with about 10 μm long. Assembling two dimensional ordered nanoarrays are still under going. Received 29 November 2000     

Gas sensing behavior of SnO1.8:Ag films composed of size-selected nanoparticles

Size-selected SnO_1.8:Ag mixed nanoparticle films have been prepared using a gas phase condensation method. Transmission electron microscopy showed that the applied size-selection technique yields well-defined, monodisperse and spherical SnO_1.8 and Ag nanoparticles, both with a fixed diameter of 20 nm. The technique allows an independent variation of the particle size of both materials as well as the concentration of Ag. It allows to assess the influence of these parameters on the gas-sensing properties of the films, here for ethanol vapor in synthetic air. SnO_1.8:Ag nanoparticle films show optimal values of the sensor signal and response time at a Ag nanoparticle concentration of 5%. Due to the fact that the Ag nanoparticles are clearly distinct from the SnO_1.8 nanoparticles in the film, the most probable mechanism leading to improved sensor properties is chemical sensitization via a spill-over effect.     

Formation of gold nanoparticles in heat-treated reactive co-sputtered Au-SiO2 thin films

In this work, formation of gold nanoparticles in radio frequency (RF) reactive magnetron co-sputtered Au-SiO₂ thin films post annealed at different temperatures in Ar + H₂ atmosphere has been investigated. Optical, surface topography, chemical state and crystalline properties of the prepared films were analyzed by using UV-visible spectrophotometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD) techniques, respectively. Optical absorption spectrum of the Au-SiO₂ thin films annealed at 800 °C showed one surface plasmon resonance (SPR) absorption peak located at 520 nm relating to gold nanoparticles. According to XPS analysis, it was found that the gold nanoparticles had a tendency to accumulate on surface of the heat-treated films in the metallic state. AFM images showed that the nanoparticles were uniformly distributed on the film surface with grain size of about 30 nm. Using XRD analysis average crystalline size of the Au particles was estimated to about 20 nm.     

Structure and frictional properties of Langmuir-Blodgett films of Cu nanoparticles modified by dialkyldithiophosphate

Langmuir-Blodgett (LB) films of dialkyldithiophosphate (DDP) modified Cu nanoparticles were prepared. The structure, microfrictional behaviors and adhesion of the LB films were investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic/friction force microscopy (AFM/FFM). Our results showed that the modified Cu nanoparticles have a typical core-shell structure and fine film-forming ability. The images of AFM/FFM showed that LB films of modified Cu nanoparticles were composed of many nanoparticles arranged closely and orderly and the nanoparticles had favorable behaviors of lower friction. The friction loop of the films indicated that the friction force was affected prominently by the surface slope of the Cu nanoparticles and the microfrictional behaviors showed obvious “ratchet effect”. The adhesion experiment showed that the modified Cu nanoparticle had a very small adhesive force.     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

Sonochemically synthesized core-shell structured Au–Pd nanoparticles supported on γ-Fe2O3 particles

A sample of Au–Pd bimetallic nanoparticles supported on γ-Fe₂O₃ was synthesized in a sonochemically one-pot process. The structural analyses of the synthesized sample were performed by the techniques of X-ray Absorption Fine Structure (XAFS), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and UV–vis spectrometry. Results indicated that the synthesized sample formed a core-shell structure in which a gold core was surrounded by a thin palladium shell. The reaction rate constant for the hydrogenation of cyclohexene of the present sample showed higher value than that of Pd nanoparticles supported on γ-Fe₂O₃ and core-shell structured Au–Pd nanoparticles supported on SiO₂. The present sample is a promising catalyst material which has a high catalytic activity.     

Room-temperature synthesis of gold nanoparticles and nanoplates using Shewanella algae cell extract

Biosynthesis of spherical gold nanoparticles and gold nanoplates was achieved at room temperature and pH 2.8 when cell extract from the metal-reducing bacterium Shewanella algae was used as both a reducing and shape-controlling agent. Cell extract, prepared by sonicating a suspension of S. algae cells, was capable of reducing 1 mol/m³ aqueous AuCl₄ ⁻ ions into elemental gold within 10 min when H₂ gas was provided as an electron donor. The time interval lapsed since the beginning of the bioreductive reaction was found to be an important factor in controlling the morphology of biogenic gold nanoparticles. After 1 h, there was a large population of well-dispersed, spherical gold nanoparticles with a mean size of 9.6 nm. Gold nanoplates with an edge length of 100 nm appeared after 6 h, and 60% of the total nanoparticle population was due to gold nanoplates with an edge length of 100–200 nm after 24 h. The yield of gold nanoplates prepared with S. algae extract was four times higher than that prepared with resting cells of S. algae. The resulting biogenic gold nanoparticle suspensions showed a large variation in color, ranging from pale pink to purple due to changes in nanoparticle morphology.     

Inhibition effect of self-assembled films formed by gold nanoparticles on iron surface

The self-assembled (SA) films formed by gold nanoparticles on iron surface had been proved to have inhibition effect for the substrate in 0.5 M H₂SO₄ solutions. The inhibition action was investigated using electrochemical impedance spectroscopy (EIS). The SA films formed by gold nanoparticles protected with sodium oleate had better corrosion protection to the iron substrate than only by sodium oleate. Scanning electron microscopy (SEM) was used to observe the imagines of the SA films. In addition, it was found that the gold nanoparticles could influence the nickel electroless plating films on the iron substrate. The structure and composition of the plating films were test by electron probe microanalyzer (EPMA). The mechanisms of the formation of the SA films and the nickel electroless plating reaction were also discussed.     

Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles

CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO₃⁻ or NH₂⁺ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfaces.     

不同生长环境下砷化镓纳米颗粒的应变场模拟

对于埋嵌在薄膜材料中的纳米颗粒,在其生长过程中总是不可避免地伴随着应变场的产生,而这种应变场的分布能反映纳米颗粒的结构变化,纳米颗粒结构与它的物理性能有重要的关系.研究埋嵌在不同薄膜材料中的纳米颗粒生长过程中的应变场分布对于调控纳米颗粒的物理性能有着重要的意义.本文利用有限元算法分别计算了埋嵌在非晶氧化铝薄膜和非晶二氧化硅薄膜材料中的砷化镓纳米颗粒生长过程中的应变场分布.砷化镓纳米颗粒在以上两薄膜材料生长过程中都受到非均匀偏应变作用.对于埋嵌在氧化铝薄膜中的砷化镓纳米颗粒,其生长过程中,纳米颗粒内部受到的应变大于纳米颗粒表面受到的应变;而对于埋嵌在二氧化硅薄膜中的砷化镓纳米颗粒,纳米颗粒内部受到的应变小于纳米颗粒表面受到的应变.选择砷化镓纳米颗粒生长的薄膜材料可以调控纳米颗粒生长过程中的应变场分布,从而进一步调控纳米颗粒的晶格结构和形貌及其物理性能.     

Model for UV induced formation of gold nanoparticles in solid polymeric matrices

UV irradiation of polymeric PMMA films containing HAuCl₄ followed by annealing at 60-80 °C forms gold nanoparticles directly within the bulk material. The kinetics of nanoparticle formation was traced by extinction spectra of nanocomposite film changes vs annealing time. We propose that UV irradiation causes HAuCl₄ dissociation and thus provides a polymeric matrix with atomic gold. The presence of an oversaturated solid solution of atomic gold in the polymeric matrix leads to Au nanoparticle formation during annealing. This process can be understood as a phase transition of the first order. In this paper we apply several common kinetic models of the phase transition for describing Au nanoparticle formation inside the solid polymer matrix. We compare predictions of these models with the experimental data and show that these models cannot describe the process. We propose that the stabilization effect of the matrix on the growing gold nanoparticles is important. The simplest model introducing some probability for the transition from growing nanoparticle to the non-growing, stabilized form is suggested. It is shown that this model satisfactorily describes the experimentally observed evolution of the extinction spectrum of Au nanoparticles forming in a polymer matrix.     

Photocatalytic degradation of methyl orange by gold silver nano-core/silica nano-shell

The silica nanoparticles (SiO₂ NPs), silver (Ag) NPs and gold (Au) NPs coated with SiO₂ NPs (core-shell) were prepared. The sizes and morphology of the particles were indicated. The three prepared NPs were used for photocatalytic degradation of methyl orange (MO) dye by xenon lamp. Rate of photocatalytic degradation reaction constant and lifetime were calculated for each catalyst. Moreover, the mechanism of the photocatalytic reaction was studied.     

Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Synthesis and characterisations of Au-nanoparticle-doped TiO2 and CdO thin films

In the present study, pure and gold nanoparticle (Au NP)-doped titanium dioxide (TiO₂) and cadmium oxide (CdO) thin film were prepared by the sol–gel method, and the effect of Au NP doping on the optical, structural and morphological properties of these thin films was investigated. The prepared thin films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible–near infrared (UV–Vis–NIR) spectra. While the optical band increases from 3.62 to 3.73 for TiO₂ thin films, it decreases from 2.20 to 1.55 for CdO thin films with increasing Au doping concentration. Analysis of XRD indicates that the intensities of peaks of the crystalline phase have increased with the increasing Au NP concentrations in all thin films. SEM images demonstrate that the surface morphologies of the samples were affected by the incorporation of Au NPs. Consequently, the most significant results of the present study are that the Au NPs can be used to modify the optical, structural and morphological properties of TiO₂ and CdO thin films.     

Influence of lithium potassium zirconate nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) films

We investigated the influence of lithium potassium zirconate (LiKZrO₃) nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) (PVA) films. PVA/LiKZrO₃ nanocomposite films were prepared by casting of aqueous solutions with varying LiKZrO₃ content (0.5, 1.0, and 2.0 wt.%). The dielectric constant (ε′), dielectric loss (ε″), AC conductivity (σ_ac), dielectric loss tangent (tan δ), and electric modulus (M′ and M″) of the nanocomposite films were measured over a range of frequencies at ambient temperature. The results show increases in σ_ac and M′ with frequency, whereas ε′, ε″, and tan δ decreased with increasing frequency. The films were also characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. DSC and XRD revealed the nature of LiKZrO₃ nanoparticle interaction with the PVA matrix. TGA analysis revealed an increase in thermal stability of the nanocomposites with increasing nanoparticle concentration. Scanning electron microscopy confirmed uniform dispersion of LiKZrO₃ nanoparticles in the PVA matrix.