Enhanced field emission property of a novel Al2O3 nanoparticle-decorated tubular SiC emitter with low turn-on and threshold field

We report a novel Al(2)O(3) nanoparticle-decorated tubular SiC nanostructure, which shows a remarkable enhanced field emission property with low turn-on and threshold field. The formation of Al(2)O(3) nanoparticle-decorated tubular SiC on Si substrates is achieved in one-step via simple heating evaporation process for the first time. The nanostructure consists of tubular SiC and the Al(2)O(3) nanoparticles, which homogeneously decorate on the surface of the tubular SiC with an average diameter of 7.8 nm and narrow diameter distribution. Moreover, compared with the same density and sized bare tubular SiC, the Al(2)O(3) nanoparticle-decorated tubular SiC nanostructure has an obvious reduction in turn-on (from 8.8 to 2.4 V μm(-1)) and threshold field (from 23.5 to 5.37 V μm(-1)). The very low turn-on and threshold field is also comparable to that of carbon nanotubes, which indicates the Al(2)O(3) nanoparticle-decorated tubular SiC is of huge potential application in future field emission display devices.     

Synthesis of open and closed metallacages using novel tripodal ligands: unusually stable silver(I) inclusion compound

The tripodal ligand 1,3,5-(CH3)3C6[CH2OCH2C(pz)3]3 (L1, pz=pyrazolyl ring) reacts with AgBF4 to yield ([L12Ag3(CH3CN)](BF4)3).(CH3CN)4, an inclusion complex in which the encapsulated acetonitrile cannot escape the triangular cage unit in either the solid or solution phase. The analogous hexatopic ligand C6[CH2OCH2C(pz)3]6 forms a 2-dimensional polymer composed of similar triangular cage units, again with the encapsulation of one acetonitrile molecule, linked by the additional tris(pyrazolyl)methane units. In contrast, the complex formed with L1 and Cd2+ has a double, open cage structure holding two diethyl ether molecules.     

Two types of carbon nanocomposites: Graphite encapsulated iron nanoparticles and thin carbon nanotubes supported on thick carbon nanotubes, synthesized using PECVD

In this work, graphite encapsulated Fe nanoparticles and thin carbon nanotubes (CNTs) supported on the pristine CNTs, respectively, were synthesized using plasma enhanced chemical vapor deposition via efficiently controlling the flow rate of discharging CH₄ and H₂ gas. The properties of the obtained hybrid materials were characterized with superconducting quantum interference and field emission measurements. The results showed that the encapsulated Fe nanoparticles had diameters ranging from 1 to 30 nm, and this hybrid nanocomposite exhibited a ferromagnetic behavior at room temperature. Thin CNTs with an average diameter of 6 nm were attached to the surface of the prepared CNTs, which exhibited a lower turn-on field and higher emission current density than the pristine CNTs. The Fe nanoparticles either encapsulated with graphite or used as catalyst for thin CNTs growth were all originated from the pyrolysis of ferrocene.     

Surfactant-resisted assembly of Fe-containing nanoparticles for site-specific growth of SWNTs on Si surface

This paper describes a facile approach to the site-specific growth of single-walled carbon nanotubes (SWNTs) on silicon surfaces by chemical vapor deposition (CVD). The approach is based on the use of a surfactant as a resist to define patterns of silicon oxide nanodomains onto which nanoparticles of iron hydroxide (Fe(OH)3), 1-5 nm diameter, could be deposited. In base growth mode, the SWNTs can grow from the oxide nanodomains. By controlling the location of oxide nanodomains, site-specific growth could be obtained. The iron hydroxide nanoparticles were prepared by hydrolysis of ferric chloride (FeCl3). Patterned hydroxylated silicon oxide nanodomains were created by scanning probe oxidation (SPO) of silicon substrates modified with aminopropyltrimethoxysilane (APTMS, H2N(CH2)3Si(OCH3)3). Due to electrostatic interaction, Fe(OH)3 nanoparticles can be selectively deposited on hydroxyl groups present on silicon oxide nanodomains. To inhibit the assembly of the nanoparticles on a APTMS-coated silicon surface, sodium dodecyl sulfate (SDS) was introduced, which restricted deposition to the hydroxylated nanodomains. A model mechanism for the selective deposition mechanism has been proposed. It was possible to convert the patterned Fe(OH)3 nanoparticles to iron oxide, which served as a catalyst for the site-specific growth of SWNTs. Raman spectroscopy and AFM were used to characterize the nanotubes on the Si substrate. This will offer the possibility for future integration with conventional microelectronics as well as the development of novel devices.     

Liquid gallium columns sheathed with carbon: Bulk synthesis and manipulation

It is impossible to fabricate isolated gallium nanomaterials due to the low melting point of Ga (29.8 degrees C) and its high reactivity. We report the bulk synthesis of uniform liquid Ga columns encapsulated into carbon nanotubes through high-temperature chemical reaction between Ga and CH4. The diameter of filled Ga liquid columns is approximately 25 nm, and their length is up to several micrometers. The thickness of the carbon sheaths is approximately 6 nm. Simultaneous condensation of a Ga vapor and carbon clusters results in the generation of Ga-filled carbon nanotubes. A convergent 300 kV electron beam generated in a field emission high-resolution electron microscope is demonstrated to be a powerful tool for delicate manipulation of the liquid Ga nanocolumns: they can be gently joined, cut, and sealed within carbon nanotubes. The self-organization of a carbon sheath during the electron-beam irradiation is discussed. The electron-beam irradiation may also become a decent tool for Ga-filled carbon nanotube thermometer calibration.     

Kinetic and thermodynamic assessments of the mediator-template assembly of nanoparticles

The understanding of kinetic and thermodynamic factors governing the assembly of nanoparticles is important for the design and control of functional nanostructures. This paper describes a study of the kinetic and thermodynamic factors governing the mediator-template assembly of gold nanoparticles into spherical assemblies in solutions. The study is based on spectrophotometric measurements of the surface plasmon (SP) resonance optical property. Gold nanoparticle cores ( approximately 5 nm) encapsulated with tetraoctylammonium bromide shells were studied as a model system. The mediator-template assembly involves a thioether-based multidentate ligand (e.g., MeSi(CH2SMe)3) which functions as a mediator, whereas the tetraoctylammonium bromide capping molecules function as template agents. On the basis of the temperature dependence of the SP optical property in the mediator-template assembly process, the kinetic and thermodynamic parameters such as the reaction rate constant and reaction enthalpy have been determined. The results led to two important findings. First, the mediator-template assembly of nanoparticles is an enthalpy-driven process. Second, the enthalpy change (-1.3 kcal/mol) is close to the magnitude of the van der Waals interaction energy for alkyl chains and the condensation energy of hydrocarbons. Implications of the findings to the understanding of the interparticle interactions have also been discussed.     

Preparation, microstructure characterization and catalytic performance of Cu/ZnO and ZnO/Cu composite nanoparticles for liquid phase methanol synthesis

Stearate@Cu/ZnO nanocomposite particles with molar ratios of ZnO?∶?Cu = 2 and 5 are synthesized by reduction of the metal-organic Cu precursor [Cu{(OCH(CH(3))CH(2)N(CH(3))(2))}(2)] in the presence of stearate@ZnO nanoparticles. In the case of ZnO?∶?Cu = 5, high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) combined with electron-energy-loss-spectroscopy (EELS) as well as attenuated total reflection Fourier transform infrared (ATR-IR) spectroscopy are used to localize the small amount of Cu deposited on the surface of 3-5 nm sized stearate@ZnO particles. For ZnO?∶?Cu = 2, the microstructure of the nanocomposites after catalytic activity testing is characterized by HAADF-STEM techniques. This reveals the construction of large Cu nanoparticles (20-50 nm) decorated by small ZnO nanoparticles (3-5 nm). The catalytic activity of both composites for the synthesis of methanol from syn gas is evaluated.     

Organosilica nanotubes: large-scale synthesis and encapsulation of metal nanoparticles

In this communication we have demonstrated the synthesis of organosilica nanotubes with inner diameter of ～6 nm and their carbonization to form carbon/silica composite nanotubes. Pd nanoparticles. encapsulated in the organosilica and carbon/silica nanotubes show different catalytic activities in the hydrogenation of cyclohexene.     

Synthesis of Fe@C nanoparticles containing sulfo groups on their surfaces and study of their aggregation behavior in aqueous media

Russian Chemical Bulletin - Magnetic iron nanoparticles (MNPs) encapsulated in a carbon shells and containing sulfo groups on the surface (Fe@C-SO3H) were synthesized. The aggregative stability of...     

Controlled self-assembly of filled micelles on nanotubes

We have used coarse-grained molecular dynamics simulations to show that hydrated lipid micelles of preferred sizes and amounts of filling with hydrophobic molecules can be self-assembled on the surfaces of carbon nanotubes. We simulated micelle formation on a hydrated (40,0) carbon nanotube with an open end that was covered with amphiphilic double-headed CH(3)(CH(2))(14)CH(((CH(2)OCH(2)CH(2))(2)(CH(2)COCH(2)))(2)H)(2) or single-headed CH(3)(CH(2))(14)CH(2)((CH(2)OCH(2)CH(2))(2)(CH(2)COCH(2)))(4)H lipids and filled with hexadecane molecules. Once the hexadecane molecules inside the nanotube were pressurized and the lipids on its surface were dragged by the water flowing around it, kinetically stable micelles filled with hexadecane molecules were sequentially formed at the nanotube tip. We investigated the stability of the thus-formed kinetically stable filled micelles and compared them with thermodynamically stable filled micelles that were self-assembled in the solution.     

温控离子液体/有机两相体系中纳米Rh催化烯烃氢甲酰化反应

将具有"高温混溶、室温分相"功能的离子液体[CH3(OCH2CH2)16N+Et3][CH3SO3–](ILPEG750)与甲苯-正庚烷组成的两相体系用于纳米Rh催化的烯烃氢甲酰化反应中,在优化的反应条件下,1-辛烯转化率和醛收率分别为99%和91%.催化剂经简单分相即可与产物分离,且可连续使用8次,其活性基本保持不变.     

Gold nanoparticles generated by thermolysis of "all-in-one" gold(I) carboxylate complexes

Consecutive synthesis methodologies for the preparation of the gold(I) carboxylates [(Ph(3)P)AuO(2)CCH(2)(OCH(2)CH(2))(n)OCH(3)] (n = 0-6) (6a-g) are reported, whereby selective mono-alkylation of diols HO(CH(2)CH(2)O)(n)H (n = 0-6), Williamson ether synthesis and metal carboxylate (Ag, Au) formation are the key steps. Single crystal X-ray diffraction studies of 6a (n = 0) and 6b (n = 1) were carried out showing that the P-Au-O unit is essentially linear. These compounds were applied in the formation of gold nanoparticles (NP) by a thermally induced decomposition process and hence the addition of any further stabilizing and reducing reagents, respectively, is not required. The ethylene glycol functionalities, providing multiple donating capabilities, are able to stabilise the encapsulated gold colloids. The dependency of concentration, generation time and ethylene glycol chain lengths on the NP size and size distribution is discussed. Characterisation of the gold colloids was performed by TEM, UV/Vis spectroscopy and electron diffraction studies revealing that Au NP are formed with a size of 3.3 (±0.6) to 6.5 (±0.9) nm in p-xylene with a sharp size distribution. Additionally, a decomposition mechanism determined by TG-MS coupling experiments of the gold(i) precursors is reported showing that 1(st) decarboxylation occurs followed by the cleavage of the Au-PPh(3) bond and finally release of ethylene glycol fragments to give Au-NP and the appropriate organics.     

Dye-labeled silver nanoshell-bright particle

Silica beads with average diameters of 40-600 nm were prepared, and Ru(bpy)3(2+) complexes were incorporated into the beads. These beads were coated by silver layer by layer to generate porous but continuous metal nanoshells. The thicknesses of these metal shells were 5-50 nm. The emission band from the dyes in the silica cores was more narrow and the intensity was enhanced with growth of silver shell thickness due to coupling of the emission light from Ru(bpy)3(2+) in the cores with the metal plasmon from the silver shells. The enhancement of emission intensity was also dependent on the size of the silica core, showing that the enhancement efficiency decreased with an increase in the size of the silica beads. Lifetime measurements support the coupling mechanism between the dye and metal shell. This study can be used to develop novel dye-labeled metal particles with bright and narrow emission bands.     

Production of palladium nanoparticles supported on multiwalled carbon nanotubes by gamma irradiation

Palladium nanoparticles were produced and supported on multiwalled carbon nanotubes (MWCNT) by gamma irradiation. A solution with a specific ratio of 2:1 of water-isopropanol was prepared and mixed with palladium chloride and the surfactant sodium dodecyl sulfate (SDS). The gamma radiolysis of water ultimately produces Pd metallic particles that serve as nucleation seeds. Isopropanol is used as an ion scavenger to balance the reaction, and the coalescence of the metal nanoparticles was controlled by the addition of SDS as a stabilizer. The size and distribution of nanoparticles on the carbon nanotubes (CNT) were studied at different surfactant concentrations and radiation doses. SEM, STEM and XPS were used for morphological, chemical and structural characterization of the nanostructure. Nanoparticles obtained for doses between 10 and 40 kGy, ranged in size 5-30 nm. The smaller nanoparticles were obtained at the higher doses and vice versa. Histograms of particle size distributions at different doses are presented.     

Enhanced anode performances of the Fe3O4-carbon-rGO three dimensional composite in lithium ion batteries

A three dimensional composite was constructed by anchoring Fe(3)O(4) nanoparticles encapsulated within carbon shells onto reduced graphene oxide sheets, which exhibited enhanced anode performances in lithium ion batteries with a specific capacity of 842.7 mAh g(-1) and superior recycle stability after 100 cycles.     

Tailored core-shell-shell nanostructures: sandwiching gold nanoparticles between silica cores and tunable silica shells

Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.     

1R,3S-1,2,2-三甲基-1,3-环戊二胺为配体的铂髤配合物的合成、表征和抗肿瘤活性

本文合成了9种含有由天然D( )鄄樟脑衍生的1R,3S鄄1,2,2鄄三甲基鄄1,3鄄环戊二胺(A)为配体的铂髤配合物[Pt髤AX]{其中,X=(CH2)3C(COO-)2(1,1鄄环丁烷二羧酸根),2CH3OCH2COO-,2CH3CH2OCH2COO-,2CH3(CH2)3OCH2COO-,[OCH(CH3)COO]2-(乳酸根),(OCH2COO)2-(乙醇酸根),2CH3OCH2CH2OCH2COO-,2CH3CH2OCH2CH2OCH2COO-和2CH3(CH2)3OCH2CH2OCH2COO-}。通过元素分析、热重分析、红外光谱、1H核磁共振谱和电喷雾质谱等对配合物进行了表征。体外生物活性测试表明,部分配合物对A549人肺癌细胞和HCT鄄116人结肠癌细胞具有较强的抗肿瘤活性。     

A novel nanostructure of nickel nanotubes encapsulated in carbon nanotubes

A novel nanostructure of Ni nanotubes encapsulated in carbon nanotubes has been obtained via the pyrolysis of C2H2 on an array of Ni nanotubes in an alumina membrane support and a possible mechanism has been proposed.     

Synthesis and characterization of water-soluble silsesquioxane-based nanoparticles by hydrolytic condensation of triethoxysilane derived from 2-hydroxyethyl acrylate

A new family of silsesquioxane-based nanoparticles was synthesized by hydrolytic condensation of a triethoxysilane precursor, R-Si(OCH2CH3)3, R = -CH2CH2CH2N(CH2CH2COOCH2CH2OH)2, derived from 2-hydroxyethyl acrylate. Condensation of the triethoxysilane precursor proceeded as a homogeneous system in methanol in the presence of hydrofluoric acid (HF) to afford water-soluble silsesquioxane-based nanoparticles, as confirmed by NMR, FT-IR, and elemental analyses. Scanning force microscopy (SFM) measurements indicated the formation of nanoparticles having a relatively narrow size distribution with an average particle diameter of less than 2.0 nm without aggregation. The size of the nanoparticles (1.7 nm) was determined by X-ray diffraction (XRD). The narrow polydispersity (Mw/Mn = 1.08) and a reasonable molecular weight (Mn = 3300), corresponding to species having 6-12 silicon atoms, were also confirmed by size-exclusion chromatography. Co-condensation of tetraethoxysilane (TEOS) with the triethoxysilane precursor was carried out under different feed ratios, and water-soluble products were obtained in the cases of TEOS molar ratios up to 70%. Thermal stability and the char yield were found to increase with increasing TEOS content in the feed, as determined by thermogravimetric analysis. The isolated nanoparticles distributed homogeneously without any aggregation were visualized by SFM, when the product was prepared at TEOS/triethoxysilane precursor = 50/50 mol %.     

Ultrasonic approach for formation of erbium oxide nanoparticles with variable geometries

Ultrasound (20 kHz, 29 W·cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (μs) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.