Origin of diameter-dependent growth direction of silicon nanowires

A nucleation thermodynamic model was developed to clarify the diameter-dependent crystallographic orientation of silicon nanowires (SiNWs) grown via the vapor-liquid-solid (VLS) mechanism with an Au catalyst. The calculated critical energies (E(r*)) and corresponding critical radii (r*) of the SiNWs with <111> and <110> orientations as a function of Au-catalyst size (D(Au)) revealed that the 110-oriented SiNW with r is preferred below D(Au) = approximately 25 nm, but the preferred direction changes to <111> above D(Au) = approximately 25 nm. The model indicated that the nucleated SiNW with a radius (r) above r is stable and continues to grow until the diameter becomes equal to D(Au) but that the crystallographic orientation is maintained. Thus, the predicted growth direction of the final SiNW with a size of D(Au) is <110> for D(Au) < approximately 25 nm and <111> for D(Au) > approximately 25 nm, which is in excellent agreement with reported experimental results.     

Ion-induced elongation of gold nanoparticles in silica by irradiation with Ag and Cu swift heavy ions: track radius and energy loss threshold

Systematic investigations of the energy loss threshold above which the irradiation-induced elongation of spherical Au nanoparticles occurs are reported. Silica films containing Au nanoparticles with average diameters of 15-80 nm embedded within a single plane were irradiated with 12-54 MeV Ag and 10-45 MeV Cu ions at 300 K and at normal incidence. We demonstrate that the efficiency of the ion-induced nanoparticle elongation increases linearly with the electronic energy transferred per ion track length unit from the energetic ions to the silica film. Ion beam shaping occurs above a threshold value of the specific electronic energy transfer. Three relevant regions are identified with respect to the original size of the Au nanoparticles. For 15 and 30 nm diameter particles, elongation occurs for electronic stopping power larger than 3.5 keV nm(-1). For Au nanoparticles with 40-50 nm diameter an electronic stopping power above 5.5 keV nm(-1) is required for elongation to be observed. Elongation of Au nanoparticles with 80 nm diameter is observed for electronic stopping between ～ 7-8 keV nm(-1). For all combinations of ions and energies, the ion track temperature profiles are calculated within the framework of the thermal spike model. The correlation between experimental results and simulated data indicates a thermal origin of the increase in the elongation rate with increasing the track diameter.     

Physical vapor deposition of metal nanoparticles on chemically modified graphene: observations on metal-graphene interactions

The growth of metallic nanoparticles formed on chemically modified graphene (CMG) by physical vapor deposition is investigated. Fine control over the size (down to ～1.5 nm for Au) and coverage (up to 5 × 10(4) μm(-2) for Au) of nanoparticles can be achieved. Analysis of the particle size distributions gives evidence for Au nanocluster diffusion at room temperature, while particle size statistics differ clearly between metal deposited on single- and multilayer regions. The morphology of the nanoparticles varies markedly for different metals (Ag, Au, Fe, Pd, Pt, Ti), from a uniform thin film for Ti to a droplet-like growth for Ag. A simple model explains these morphologies, based only on consideration of 1) the different energy barriers to surface diffusion of metal adatoms on graphene, and 2) the ratio of the bulk cohesive energy of the metal to the metal-graphene binding energy. Understanding these interactions is important for controlling nanoparticle and thin-film growth on graphene, and for understanding the resultant charge transfer between metal and graphene.     

Electrochemiluminescent metallopolymer-nanoparticle composites: nanoparticle size effects

Metallopolymer-gold nanocomposites have been synthesized in which the metal complex-Au nanoparticle (NP) mole ratio is systematically varied by mixing solutions of 4-(dimethylamino) pyridine protected gold nanoparticles and a [Ru(bpy)(2)PVP(10)](2+) metallopolymer; bpy is 2,2'-bipyridyl and PVP is poly-(4-vinylpyridine). The impact of changing the gold nanoparticle diameter ranging from 4.0 ± 0.5 to 12.5 ± 1 nm has been investigated. The photo induced emission of the metallopolymer undergoes static quenching by the metal nanoparticles irrespective of their size. When the volume ratio of Au NP-Ru is 1, the quenching efficiency increases from 38% to 93% on going from 4.0 ± 0.5 to 12.5 ± 1 nm diameter nanoparticles while the radius of the quenching sphere remains unaffected at 75 ± 5 ?. The conductivity of thin films is initially unaffected by nanoparticle incorporation until a percolation threshold is reached at a mole ratio of 4.95 × 10(-2) after which the conductivity increases before reaching a maximum. For thin films of the nanocomposites on electrodes, the electrochemiluminescence intensity of the nanocomposite initially increases as nanoparticles are added before decreasing for the highest loadings. The electrochemiluminescence intensity increases with increasing nanoparticle diameter. The electrochemiluminescence (ECL) emission intensity of the nanocomposite formed using 12.5 nm particles at mole ratios between 5 × 10(-3) and 10 × 10(-3) is approximately 7-fold higher than that found for the parent metallopolymer. The application of these materials for low cost ECL-based point of care devices is discussed.     

Quantitative characterization of gold nanoparticles by field-flow fractionation coupled online with light scattering detection and inductively coupled plasma mass spectrometry

An analytical platform coupling asymmetric flow field-flow fractionation (AF(4)) with multiangle light scattering (MALS), dynamic light scattering (DLS), and inductively coupled plasma mass spectrometry (ICPMS) was established and used for separation and quantitative determination of size and mass concentration of nanoparticles (NPs) in aqueous suspension. Mixtures of three polystyrene (PS) NPs between 20 and 100 nm in diameter and mixtures of three gold (Au) NPs between 10 and 60 nm in diameter were separated by AF(4). The geometric diameters of the separated PS NPs and the hydrodynamic diameters of the Au and PS NPs were determined online by MALS and DLS, respectively. The three separated Au NPs were quantified by ICPMS and recovered at 50-95% of the injected masses, which ranged between approximately 8-80 ng of each nanoparticle size. Au NPs adhering to the membrane in the separation channel was found to be a major cause for incomplete recoveries. The lower limit of detection (LOD) ranged between 0.02 ng Au and 0.4 ng Au, with increasing LOD by increasing nanoparticle diameter. The analytical platform was applied to characterization of Au NPs in livers of rats, which were dosed with 10 nm, 60 nm, or a mixture of 10 and 60 nm nanoparticles by intravenous injection. The homogenized livers were solubilized in tetramethylammonium hydroxide (TMAH), and the recovery of Au NPs from the livers amounted to 86-123% of their total Au content. In spite of successful stabilization with bovine serum albumin even in alkaline medium, separation of the Au NPs by AF(4) was not possible due to association with undissolved remains of the alkali-treated liver tissues as demonstrated by electron microscopy images.     

Precise control over shape and size of iron oxide nanocrystals suitable for assembly into ordered particle arrays

Here we demonstrate how monodisperse iron oxide nanocubes and nanospheres with average sizes between 5 and 27 nm can be synthesized by thermal decomposition. The relative importance of the purity of the reactants, the ratio of oleic acid and sodium oleate, the maximum temperature, and the rate of temperature increase, on robust and reproducible size and shape-selective iron oxide nanoparticle synthesis are identified and discussed. The synthesis conditions that generate highly monodisperse iron oxide nanocubes suitable for producing large ordered arrays, or mesocrystals are described in detail.     

Au-MgF2复合纳米颗粒薄膜的制备和微结构

用射频磁控共溅射法制备了Au体积分数分别为6%、15%、25%、40%、50%和60%的Au-MgF2复合纳米颗粒薄膜.用X射线衍射、透射电镜、X射线光电子能谱对薄膜的微结构和组分进行了测试分析,分析结果表明:制备的Au-MgF2复合纳米颗粒薄膜由fcc-Au晶态纳米微粒镶嵌于主要为非晶态的MgF2陶瓷基体中构成,当Au体积百分含量由15%增至60%时,其平均晶粒尺寸由5.1nm增大到21.2 nm,晶格常数由0.399 84nm增大到0.407 43nm;随Au体积百分含量由6%增至50%,其颗粒平均粒径则由9.8nm增至21.4 nm.名义组分为vol.60%Au-MgF2样品中Au的体积百分含量约为62.6%,与设计值基本一致.     

Gold nanowires fabricated by immersion plating

The growth mechanism of oriented Au nanowires fabricated by immersion plating was investigated. Both n-type crystal Si (c-Si) and amorphous Si (a-Si) with an electron-beam (E-beam) patterned resist nanotrench were immersed into the plating bath HAuCl(4)/HF. For the Au nanowires fabricated on c-Si, voids, nanograins, and clusters were observed at various plating conditions, time and temperature. The voids were often found in the center of the Au nanowires due to there being fewer nucleation sites on the c-Si surface. However, Au can easily nucleate on the surface of a-Si and form continuous Au nanowires with grain sizes about 10-50?nm. The resistivities of Au nanowires with width 105?nm fabricated on a-Si are about 4.4-6.5?μΩ?cm. After annealing at 200?°C for 30?min in N(2) ambient, the resistivities are lowered to about 3.0-3.9?μΩ?cm, measured in an atomic force microscope (AFM) in contact mode. The grain size of Au is in the range of ～50-100?nm. A scanning electron microscope (SEM) examination and grazing incident x-ray diffraction (GIXRD) analysis were also carried out to study the morphology and crystalline structure of the Au nanowires.     

FAB mass spectrometry of Au25(SR)18 nanoparticles

The molecular ion of the nanoparticle Au 25(SCH 2CH 2Ph) 18 (A 25(SR) 18) is observed at 7394 Da in fast atom bombardment (FAB, Xe atoms) ionization mass spectrometry using a 3-nitrobenzyl alcohol matrix. A distinctive pattern of positive fragment ions is evident in the mass interval 5225-7394 Da, where peaks are seen for successive mass losses equivalent to R 2S entities. Because the Au 25(SCH 2CH 2Ph) 18 nanoparticle structure is crystallographically known to consist of a centered Au 13 icosahedral core surrounded by six Au 2(SR) 3 semirings, the R 2S loses are proposed to represent serial rearrangements and decompositions of the semiring structures. Mass losses equivalent to R 2S 2 and R 2 entities also appear at the lower end of this mass interval. The most intense spectral peak, at m/ z = 5246 Da, is assigned to the fragment Au 25S 10, from which all of the CH 2CH 2Ph organic units have been cleaved but from which no gold atoms have been lost. A different pattern of fragmentation is observed at lower masses, producing ions corresponding to serial losses of one gold atom and varied numbers of sulfur atoms, which continues down to a Au 9S 2 fragment. FAB mass spectra of the Au nanoparticle are much easier to interpret than laser desorption/ionization spectra, but they show more extensive fragmentation than do electrospray and low laser pulse intensity MALDI spectra. The loss of R 2S fragmentation in FAB is distinctive and unlike that seen in the other ionization modes. The FAB spectrum for the nanoparticle Au 25(S(CH 2) 9CH 3) 18 is also reported; its fragmentation parallels that for Au 25(SCH 2CH 2Ph) 18, implying that this nanoparticle has the same surprising stellated (staples) structure.     

Controlled Growth of Platinum Nanoparticles on Strontium Titanate Nanocubes by Atomic Layer Deposition

With an eye toward using surface morphology to enhance heterogeneous catalysis, Pt nanoparticles are grown by atomic layer deposition (ALD) on the surfaces of SrTiO₃ nanocubes. The size, dispersion, and chemical state of the Pt nanoparticles are controlled by the number of ALD growth cycles. The SrTiO₃ nanocubes average 60 nm on a side with {001} faces. The Pt loading increases linearly with Pt ALD cycles to a value of 1.1 × 10^?6 g cm^?2 after five cycles. Scanning electron microscopy images reveal discrete, well‐dispersed Pt nanoparticles. Small‐ and wide‐angle X‐ray scattering show that the Pt nanoparticle spacing and size increase as the number of ALD cycles increases. X‐ray absorption spectroscopy shows a progression from platinum(II) oxide to metallic platinum and a decrease in Pt? O bonding with an increase in Pt? Pt bonding as the number of ALD cycles increases.     

Synthesis of dendrimer-stabilized gold-polypyrrole core-shell nanoparticles

Core-shell composite nanoparticles consisting of a gold core and polypyrrole shell were prepared and stabilized with the poly(amidoamine) dendrimer. An in situ redox polymerization technique was used in which pyrrole reduced Au3+ to Au and then oxidized to polypyrrole. The presence of gold nanoparticles as a core was characterized by its surface plasmon absorption peak at 534 nm. Fourier transform infrared spectroscopy confirmed the presence of polypyrrole on the nanoparticle surfaces. The average diameter of the core-shell nanoparticle is 8.7 +/- 1.8 nm with a shell thickness of approximately 1.5-2.0 nm as estimated from the transmission electron microscopy image. Dissolution of the Au core using KCN enabled the formation of hollow polymer nanospheres.     

Size-dependence of surface plasmon resonance and oxidation for Pd nanocubes synthesized via a seed etching process

Pd nanocubes between 8 and 50 nm in size were synthesized at the same concentration of Na2PdCl4 precursor by controlling the number of seeds formed in the nucleation stage. Increasing the concentration of FeCl3, an oxidative etchant for Pd, reduced the number of seeds and led to formation of larger Pd nanocubes. The larger nanocubes exhibited surface plasmon resonance peaks in the visible region, the locations of which matched with the results of the discrete dipole approximation calculation. While the nanocubes of 25 and 50 nm in size oxidized in air to form Pd@PdO core-shell structures, the 8-nm nanocubes were stable in air for over 90 days.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Ag+-assisted heterogeneous growth of concave Pd@Au nanocubes for surface enhanced Raman scattering (SERS)

AgNO3 is often used in the preparation of Au nanostructures since Ag-based substances (AgBS) can selectively be adsorbed on Au(100) and significantly modulate the growth of Au nanocrystals.High-index-faceted Au nanostructures have demonstrated excellent performance in catalysis and surface enhanced Raman scattering (SERS),thus attracting the interest of many researchers in the past several decades.Herein,high-index-faceted Pd@Au concave nanocubes (CNCs) were prepared using AgBS as growth-directing agents in the heterogeneous growth of Au on Pd nanocubes (NCs).During the growth of Pd@Au CNCs,Au atoms are initially deposited on the Pd{100} facets leading to the formation of thin Au shells,and then AgBS are quickly adsorbed on the formed Au(100),favoring the growth along 〈111〉 and the formation of Pd@Au CNCs.Transmission electron microscopy (TEM),high resolution transmission electron microscopy (HRTEM),energy dispersive spectroscopy (EDS),high angle annular dark field (HAADF),and scanning transmission electron microscopy EDS (STEMEDS) were used to systematically investigate the growth of Pd@Au CNCs.We also demonstrated that the high-index-faceted Pd@Au CNCs exhibited excellent SERS performances.     

Biomimetic synthesis of PbS nanocubes in the lysozyme solution

Cubic phase PbS nanocubes were fabricated using lysozyme as template by biomimetic synthesis method at room temperature. The prepared nanocubes are uniform and monodispersed with homogeneous size around 45 nm. The interaction of Pb²⁺/PbS with the lysozyme was studied through Fourier transform infrared (FTIR) spectroscopy, and the shift of characteristic IR peaks of the lysozyme suggesting that Pb²⁺/PbS can react with − OH and − NH groups of the lysozyme. Optical properties of the obtained PbS nanocubes were investigated by photoluminescence (PL) spectroscopy. PbS nanocrystals exhibit a well-defined emission feature at 470 nm excited by 300 nm wavelength (λ_ex). The experimental results indicated that the lysozyme not only induced nucleation, but also inhibited the further growth of PbS crystals and play an important role in formation of PbS nanocubes.     

Analytical evidence for the monolayer-protected cluster Au225[(S(CH2)5CH3)]75

The Brust synthesis of thiolate-protected gold clusters has been modified to produce identifiable proportions of a hexanethiolate-protected Au225 core nanoparticle that display quantized double layer charging voltammetry consistent with a Au225 core dimension. Transmission electron microscopy (TEM) and thermogravimetric results indicate an average nanoparticle formula of Au225[(S(CH2)5CH3)]75. A simulated pulse voltammogram that accounts for the TEM nanoparticle dispersity matches reasonably well with that of the polydisperse synthetic sample containing the Au225 component. In confirmation of the size determination, an HPLC analysis using ratiometric absorbance and electrochemical detectors gives a core radius of 1.0 nm for the Au225 nanoparticle.     

Self-construction of SnO2 cubes based on aggration of nanorods

The SnO₂ cubes with the rutile structure have been successfully synthesized without using any catalyst. Their morphology and microstructure were studied by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and elected area electron diffraction (SAED). It is revealed that the SnO₂ nanocubes exhibit high crystalline quality. The size of the nanocubes ranges from 100 nm to 300 nm. The side surfaces of nanocubes are {110} planes, while their cube axes are [001] direction. The growth mechanism of SnO₂ nanocubes was discussed and we suggested vapor-solid process should dominate the growth. These SnO₂ nanostructures represent an important example of spontaneous organization.     

Palladium and gold nanoparticle array films formed by using self-assembly of block copolymer

The well-arrayed Pd and Au nanoparticle thin films were successfully prepared by making use of self-assembled PS-b-P4VP block copolymer (BCP) as a mask for the reduction of PdCl2 deposited on glass substrate. The films consisted of spherialcal nanoparticles with an average diameter of about 45 nm. For monitoring the size, shape and array formation of Pd nanopaticle films, this procedure was proved better to the conventional process in which PdCl2 impregnated in the channels of self assembled BCP film is reduced to form nanoparticle array. This observations of Pd nanoparticle array film formation is supported by the AFM and UV-VIS studies of Au nanoparticle array films formed by conventional method.     

Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

Au／SiO2复合纳米颗粒膜及SiO2纳米线的制备

室温下用磁控溅射法在Si（111）衬底上生成Au／SiO2复合纳米颗粒膜,并分不同温度进行退火处理。1000℃退火时自组装生成空间分布均匀（直径约为70nm）的Au纳米点,从而用自组装生长方法制备了生长一维纳米材料的模板,然后,将Au催化剂模板在1100℃下退火处理,生成纳米线,SEM和TEM测试,制备的SiO2纳米线直径约为100nm,长度约为4μm,表面光滑,直且粗细均匀。