Optical and structural characteristics of silicon nanoparticles thin film prepared by laser ablation

In this paper thin film of silicon nanoparticles on glass substrates have been prepared by dip-coating method using colloidal silicon nanoparticles generated by nanosecond laser ablation of silicon wafer in ethanol. The resulting nanoparticles and structural properties and morphology of thin film were characterized by UV-Visible absorption spectrometry, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction pattern and atomic force microscopy image. Nanoparticles with diameters ~ 9 nm were observed to be formed in the colloidal solution. The atomic force microscopy image of Si nanoparticles thin film shows that the overall average width is about 80 nm.     

Magnetic properties of encapsulated nanoparticles in nitrogen-doped multiwalled cabon nanotubes embedded in SiOx matrices

We report the production, characterization, thermal transformations (400-1000 degrees C), and magnetic properties of nanoparticles encapsulated in nitrogen-doped multiwall carbon nanotubes (CNx-MWNT), which were embedded in silicon oxide (SiOx) matrices via sol-gel techniques. The vapor chemical deposition (CVD) method with ferrocene-benzelamine mixtures was used to synthesize Fe and Fe3C nanoparticles inside CNx-MWNTs. Composites consisting of CNx-MWNTs (filler) and SiOx (matrix) were fabricated and thermally treated to different temperatures and exposure times (t). All samples were characterized using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), thermogravimetic analysis (TGA), and magnetometry (vibrating sample). We found that upon thermal treatment, the ferromagnetic nanoparticles modify their morphology, composition and aspect ratio, thus resulting in drastic changes in the magnetic and structural properties. In particular, as produced encapsulated nanoparticles mainly consisting of Fe and Fe3C phases were thermally modified into magnetite (Fe3O4). We have also observed that the hysteresis loops are very sensitive to the thermal treatment of the sample. Thus we can control the magnetic properties of the samples using thermal treatments.     

Atomic-resolution scanning transmission electron microscopy through 50-nm-thick silicon nitride membranes

Silicon nitride membranes can be used for windows of environmental chambers for in situ electron microscopy. We report that aberration corrected scanning transmission electron microscopy (STEM) achieved atomic resolution on gold nanoparticles placed on both sides of a 50-nm-thick silicon nitride membrane at 200 keV electron beam energy. Spatial frequencies of 1∕1.2 ? were visible for a beam semi-angle of 26.5 mrad. Imaging though a 100-nm-thick membrane was also tested. The achieved imaging contrast was evaluated using Monte Carlo simulations of the STEM imaging of a sample of with a representative geometry and composition.     

成核剂调控的具有不同泡孔结构聚乙烯泡沫的尺寸稳定性

研究了几种纳米颗粒调控的聚乙烯(PE)泡沫的尺寸稳定性,通过差示扫描量热仪、扫描电镜考察了几种纳米颗粒对PE结晶行为和发泡形貌的影响。结果表明,纳米颗粒作为结晶成核剂可以提高PE的结晶温度,同时作为发泡成核剂还可以使PE泡沫的泡孔密度增大,且其形状和表面化学性质会影响成核效果,进而影响最终的发泡形貌。进一步研究还发现,不同泡孔结构的PE泡沫的尺寸稳定性存在差异,未添加成核剂的PE泡沫收缩最严重,而添加成核剂后PE泡沫的泡孔尺寸减小,尺寸稳定性得到提高。通过建立立方体泡孔结构模型模拟计算了泡孔孔径对尺寸稳定性的影响,计算结果与实验数据较为吻合,结果表明,泡孔尺寸越小,PE泡沫的尺寸稳定性越好。     

GaP纳米晶对溶剂热合成氮化硼的物相和微观形貌的影响

研究了溶剂热方法合成氮化硼纳米晶过程中异种晶粒对氮化硼微现形貌和物相的影响,结果表明：在不改变反应原料种类的情况下,当体系内加入GaP纳米颗粒时．制备的氮化硼纳米晶呈现“树枝”状形貌．且样品中立方氮化硼为主要物相。文中对这种微观形貌的成因进行了简单讨论。     

Writing Silica Structures in Liquid with Scanning Transmission Electron Microscopy

Silica nanoparticles are imaged in solution with scanning transmission electron microscopy (STEM) using a liquid cell with silicon nitride (SiN) membrane windows. The STEM images reveal that silica structures are deposited in well‐defined patches on the upper SiN membranes upon electron beam irradiation. The thickness of the deposits is linear with the applied electron dose. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrate that the deposited patches are a result of the merging of the original 20 nm‐diameter nanoparticles, and that the related surface roughness depends on the electron dose rate used. Using this approach, sub‐micrometer scale structures are written on the SiN in liquid by controlling the electron exposure as function of the lateral position.     

Effects of surfactants on the particle morphology and self-organization of Co nanocrystals

A synthesis method based in the principles of the so-called polyol process has been developed to prepare Co nanocrystals of 5, 8 and 20 nm average diameter. The influence of stabilizers, as oleic and lauric acids, on the morphology and the self-assembled aggregates of the final Co nanocrystals has been analysed, as well as on their magnetic properties. Rather spherical Co nanoparticles were obtained using oleic and lauric acid, respectively, with 8 and 5 nm in diameter and narrow particle size distribution. The lauric acid, having a shorter chain length, seems to be more effective in coating the particles.     

Preparation of cobalt-zinc ferrite (Co0.8Zn0.2Fe2O4) nanopowder via combustion method and investigation of its magnetic properties

Cobalt-zinc ferrite (Co_0.8Zn_0.2Fe₂O₄) was prepared by combustion method, using cobalt, zinc and iron nitrates. The crystallinity of the as-burnt powder was developed by annealing at 700 °C. Crystalline phase was investigated by XRD. Using Williamson-Hall method, the average crystallite sizes for nanoparticles were determined to be about 27 nm before and 37 nm after annealing, and residual stresses for annealed particles were omitted. The morphology of the annealed sample was investigated by TEM and the mean particle size was determined to be about 30 nm. The final stoichiometry of the sample after annealing showed good agreement with the initial stoichiometry using atomic absorption spectrometry. Magnetic properties of the annealed sample such as saturation magnetization, remanence magnetization, and coercivity measured at room temperature were 70 emu/g, 14 emu/g, and 270 Oe, respectively. The Curie temperature of the sample was determined to be 350 °C using AC-susceptibility technique.     

Effects of metal layer morphology to silicon nanostructure formation in metal-assisted etching

This study presents a rapid and simple approach for creating silicon nanostructures using metal-assisted etching. The thickness of the metal layer was found to be a key process parameter affecting the surface morphology of silicon nanostructures. Au and Ag layers with a thickness of 3 nm, 5 nm, and 10 nm were used to study the effects of metal catalyst thickness on silicon nanostructure morphology. The experimental results show that the surface morphology of metal has a significant influence on the silicon nanostructure morphology, such that the silicon nanostructures transform from porous silicon surfaces into filament nanostructures or silicon nanowire with increasing thicknesses of both the Au and Ag metal layers.     

Catalytic activity of a soft composite material: Nanoparticle location–activity relationship

A nanostructure, fiber-shaped morphology of a conjugated polymer (poly-5 amono-ortho-cresol, PAOC) has been synthesized using palladium acetate as the oxidizing agent. A one pot, in situ chemical synthesis approach has been utilized in which palladium acetate was reduced during the polymerization process of 5-amono-o-cresol (AOC) and formed well dispersed palladium nanoparticles in the polymer fibers. The resultant composite material was characterized by means of optical, thermo and micro-analytical techniques. The elemental identity of the nanoparticles was determined by means of electron energy loss spectroscopy (EELS) mapping using analytical transmission electron microscopy (TEM). Subsequently, the sample was used as a catalyst for a model gas-phase hydrogenation reaction. The activation and deactivation behaviour of the catalyst as a function of temperature is discussed in the light of different phase transition points of the polymer as well as the orientation of the palladium nanoparticles. The fact that palladium nanoparticles (2 nm) were uniformly distributed throughout the polymer matrix makes the composite material an excellent hybrid structure.     

Effects of process conditions on the properties of silicon nanoparticles synthesized by gas phase reactions using inductive coupled plasma

Silicon nanoparticles were synthesized by passing monosilane through a quartz tube wrapped with Inductive Coupled Plasma (ICP) coil. Microstructures of synthesized silicon nanoparticles were investigated with various process conditions. To research the effects of process parameters on the properties of nanoparticles, we verified the partial pressure of monosilane, the plasma power and the working pressure. The highly crystalline silicon nanoparticles were only achieved at the proper partial pressure of the reactive gas and plasma power. Partial pressure determined not only the particle size but also the crystallinity of the nanoparticles. The plasma power was controlled from 50 to 100 W which determined not the particle size but the crystallinity of nanoparticles. Especially, too low a power resulted in amorphous particles with an average sizes of 5.25 nm. As the working pressure increased, the amount of produced nanoparticles linearly increased and the maximum production yield was at 76 mg/hr. Controlling those parameters, we achieved monodispersed single crystalline silicon nanoparticles with an average diameter of 7.52 nm. Silicon nanoparticles in this study can be applied to light absorbing material for solar cells and the wavelength down-converter material of Light Emitting Diode (LED).     

Preparation of protein nanoarray on silicon surface by atomic force microscopy nanofabrication

Atomic force microscopy (AFM) with bias control is employed to fabricate oxidized nanopatterns on a silicon surface with a feature size as low as 50 nm. Nanopatterns made by a Pt/Ir coating probes have larger feature size than these made by the probe without, but the patterning speed is fast, 0.1 s per dot. 20 nm gold nanoparticles are immobilized on oxide nanopatterns to elucidate the dimensions of the nanoparticles on an oxide nanopattern. These patterning conditions are utilized to prepare a nanoarray for the immobilization of biotins to interact with free streptavidins. The resultant height of the biotin labeled on oxidized nanopattern is 0.93 +/- 0.1 nm and the combined height of biotin-streptavidin is 5.14 +/- 0.45 nm, as determined using the imaging functions of AFM. Based on the experimental results, a nano biochip of silicon dioxide can be utilized to monitor molecular interactions on the nanometer scale under static conditions and without the labeling of fluorescence dyes.     

Micro-porous silicon structure with low optical reflection

A porous silicon structure with good physical and optical characteristics was made by a novel method. In this method, an amorphous silicon film with many fine grains was used as micro-mask. When the sample was subjected to etching process, the presence of fine grain boundaries resulted in selective etching on the surface of silicon wafer. The completed sample showed a low-reflective silicon wafer with a complex morphology. When a light illuminated on this proposed structure, there was nearly no optical reflection to be detected. This indicates that the new porous silicon structure can act as a good light-trapper.     

Design and fabrication of a photosensing nanodevice structure with CdSe and Au nanoparticles on a silicon chip

A newly developed four-layered photosensing nanodevice was fabricated by integrating nanoparticles (NPs) on a silicon substrate. Through ionic interaction, negatively charged Au NPs (/spl sim/15 nm) were assembled in alternate layers with positively charged CdSe NPs (/spl sim/5 nm) on the silicon oxide surface between the two Al electrodes. The silicon oxide surface after each step of the fabrication process was observed and evaluated by images obtained from the scanning electron microscope. By applying voltage biases across the electrodes, the currents were measured in the dark and under illumination using a 375-nm laser. It was found that a constant photocurrent increment can be obtained for different voltage biases, and the nanodevice structure with a longer length had less conductivity but a larger increment of photocurrent after illumination. In addition, the efficiency rate of photocurrent generation is much higher in comparison to that obtained from CdSe thin film. The fabrication process integrated a newly developed model of a diode-resistor array of semiconductor-metal junctions between CdSe and Au NPs (nano-Schottky-diode structures), which can successfully explain the measured results. While nanotechnology has unprecedented advantages over the traditional silicon electronics, its technology presents physical challenges. However, the success of the fabrication of the multilayered photosensing nanodevice directly on the silicon chip paves the way for further applications and research.     

Kinetic studies on water-soluble gold nanoparticles coordinated to poly(vinylpyrrolidone): isotropic to anisotropic transformation and morphology

The growth kinetics, isotropic-to-anisotropic transformation, structural properties and surface morphology of polyvinylpyrrolidone (PVP)-coordinated gold nanoparticles are reported in this work. The reduction of gold ions, kinetics, and growth mechanism of gold nanoparticles, and the coordination between PVP and gold are explored for the first time in this single report. The layer-by-layer growth mechanism (adsorption of gold ions to the nuclei and their subsequent reduction) was observed in the growth of isotropic nanoparticles during the initial stage of the reaction, whereas the Ostwald ripening mechanism (growth of larger particles at the expense of smaller particles) was observed in the growth of the anisotropic nanoparticles in the later stage of the reaction. The surface plasmon resonance band for the anisotropic nanoparticles (average size for a typical sample was ca. 9 nm) was blue-shifted (20 nm) toward that of the isotropic nanoparticles (whose average size is much smaller than that of the anisotropic nanoparticles). The increased effective electron density on the surface of anisotropic particles was the cause of this blue shift. The resultant gold colloids were very stable because the PVP molecules were coordinated through both the C–N and C=O groups, instead of the C=O group alone. The positions of the surface plasmon band and morphology of the gold products were strongly dependent on the amount of PVP.     

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene polymer waveguide

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene (BCB) waveguide were investigated. The silicon nanoparticles, of a size varying from 6 to 25?nm, were prepared by vapor condensation. The transmission modes and losses were examined by the prism coupler and cut-back methods. A He-Ne laser beam with a wavelength of 6328?? was used to measure the effective index and thickness of the waveguide. Laser light could be efficiently coupled into the BCB waveguide when the embedded Si nanoparticles were smaller than 6?nm. The film thickness and effective index of the Si-embedded BCB waveguide were measured to be 1.825?μm and 1.565, respectively. The optical transmission losses of the pure BCB and Si-embedded ridge waveguides measured by the cut-back method were 0.85 and 1.63?dB?cm(-1), respectively. Although the optical loss was increased by the embedded Si, the disturbance of the output contour was quite small. This result demonstrates that the nanoparticle-embedded polymer waveguide may be used for optoelectronic integrated circuits.     

Biocompatible nanotemplate-engineered nanoparticles containing gadolinium: stability and relaxivity of a potential MRI contrast agent

In this article, we use a nanotemplate engineering approach to prepare biodegradable nanoparticles composed of FDA-approved materials and possessing accessible gadolinium (Gd) atoms and demonstrate their potential as a Magnetic Resonance Imaging (MRI) contrast agent. Nanoparticles containing dimyristoyl phosphoethanolamine diethylene triamine penta acetate (PE-DTPA) were prepared using 3.5 mg of Brij 78, 2.0 mg of emulsifying wax and 0.5 mg of PE-DTPA/ml from a microemulsion precursor. After the addition of GdCl3, the presence of Gd on the surface of nanoparticles was characterized using inductively coupled plasma atomic emission spectroscopy and Scanning Transmission Electron Microscopy (STEM). The in vitro relaxivities of the PE-DTPA-Gd nanoparticles in different media were assessed at different field strengths. The conditional stability constant of Gd binding to the nanoparticles was determined using competitive spectrophotometric titration. Transmetallation kinetics of the gadolinium ion from PE-DTPA-Gd nanoparticles with zinc as the competing ionic was measured using the relaxivity evolution method. Nanoparticles with a diameter of approximately 130 nm possessing surface chelating functions were made from GRAS (Generally Regarded As Safe) materials. STEM demonstrated the uniform distribution of Gd3+ on the surface of the nanoparticles. The thermodynamic binding constant for Gd3+ to the nanoparticles was approximately 10(18) M(-1) and transmetallation studies with Zn2+ yielded kinetic constants K1 and K(-1) of 0.033 and 0.022 1/h, respectively, with an equilibrium constant of 1.5. A payload of approximately 10(5) Gd/nanoparticle was achieved; enhanced relaxivities were observed, including a pH dependence of the transverse relaxivity (r2). Nanoparticles composed of materials that have been demonstrated to be hemocompatible and enzymatically metabolized and possessing accessible Gd ions on their surface induce relaxivities in the bulk water signal that make them potentially useful as next-generation MRI tumor contrast enhancement agents.     

铜掺杂纳米二氧化钛颗粒的相变研究

采用溶胶-凝胶法制备铜掺杂的纳米二氧化钛颗粒。应用X射线衍射(XRD)、透射电子显微镜(TEM)、扫描透射电子显微镜(STEM)、X射线光电子能谱(XPS)和紫外-可见分光光度计(UV-Vis)技术对纳米二氧化钛颗粒的物相组成、平均晶粒尺寸、微观结构、化学态及光吸收性能进行表征。结果表明:Cu掺杂抑制TiO_2的相变,在650℃时Cu的氧化物CuO在TiO_2颗粒表面出现,掺杂的Cu离子以Cu^+的形式存在。掺杂Cu的TiO_2光吸收带边显著红移,随着Cu掺杂量的提高,样品光吸收度提高,随着温度的升高,样品紫外-可见光光谱吸收带边红移。     

Synthesis and field electron emission properties of hybrid carbon nanotubes and nanoparticles

Hybrid ZnO-carbon nanotubes as well as nanodiamond-carbon nanotubes were synthesized via a straightforward process of plasma enhanced chemical vapor deposition. For the former, ZnO nanoparticles were instantly coated on the tube surface in the final growing process of carbon nanotubes, while for the latter diamond nanoparticles were grown using pretreatment of a silicon substrate with Ni(NO(3))(2)·6H(2)O/Mg(NO(3))(2)·6H(2)O alcohol solution prior to deposition and a high H(2)/CH(4) gas flow ratio in the deposition process. The morphology and microstructure of the obtained hybrid materials were characterized by transmission electron microscopy. Both hybrid ZnO-carbon nanotubes and nanodiamond-carbon nanotubes exhibited excellent field emission properties.     

Comparative Studies of Microwave and Sol–Gel-Assisted Combustion Methods of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanostructures: Synthesis,Structural, Morphological,Opto-magnetic,and Antimicrobial Activity

Nickel ferrite NiFe₂O₄ nanoparticles (NPs) were successfully synthesized by using nickel nitrate, ferric nitrate, citric acid, and ethyl cellulose as a surfactant by a simple sol–gel-assisted combustion method (SACM) and microwave-assisted combustion method (MACM). Structural, morphological, optical, and magnetic properties of the obtained powder were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL) spectroscopy, and vibrating sample magnetometry (VSM). XRD results show that the resultant powder was pure crystalline with cubic structure. The average crystalline size was found to be 18.8 and 10.2 nm synthesized by SACM and MACM, respectively. FT-IR spectra indicate the type of bonds between Ni–O and Fe–O (metal and oxygen). SEM images show that the morphology of the powder consists of well-defined structure. VSM results showed a ferromagnetic behavior of the sample. Antimicrobial activity of NiFe₂O₄ nanoparticles was performed. Both sample 1 (SACM) and sample 2 (MACM) show good inhibition in the zone 100 μg/ml. While comparing, sample 2 shows high inhibition than sample 1.