Structure-dependent growth control in nanowire synthesis via on-film formation of nanowires

On-film formation of nanowires, termed OFF-ON, is a novel synthetic approach that produces high-quality, single-crystalline nanowires of interest. This versatile method utilizes stress-induced atomic mass flow along grain boundaries in the polycrystalline film to form nanowires. Consequently, controlling the magnitude of the stress induced in the films and the microstructure of the films is important in OFF-ON. In this study, we investigated various experimental growth parameters such as deposition rate, deposition area, and substrate structure which modulate the microstructure and the magnitude of stress in the films, and thus significantly affect the nanowire density. We found that Bi nanowire growth is favored in thermodynamically unstable films that facilitate atomic mass flow during annealing. A large film area and a large thermal expansion coefficient mismatch between the film and the substrate were found to be critical for inducing large compressive stress in a film, which promotes Bi nanowire growth. The OFF-ON method can be routinely used to grow nanowires from a variety of materials by tuning the material-dependent growth parameters.     

Electrodeposition: a versatile and inexpensive tool for the synthesis of nanoparticles,nanorods, nanowires,and nanoclusters of metals

The synthesis of various nanoscale materials, such as nanoparticles, nanowires of Au, Pt, Ni Co, Fe, Ag etc., by electrodeposition techniques have been demonstrated in this article. Both potentiostatic and galvanostatic methods were employed to carry out the electrodeposition process under different potential ranges, time durations, and current densities. The electrochemical behavior of the deposited nanoparticles on various substrates was investigated by cyclic voltammetric and chronoamperometric techniques. The synthesis of mono-dispersed gold (Au) nanoparticles on indium tin oxide (ITO) coated glass, preparation of Au nanorods on nanoporous anodic alumina oxide (AAO), formation of Au nanoclusters on polypyrrole-modified glassy carbon electrode and one-step electrodeposition of nickel nanoparticle chains embedded in TiO₂ etc. have been highlighted in this article. The potential applications of synthesized nanoparticles such as the role of maghemite (Fe₂O₃) in arsenic remediation, higher electrocatalytic activity of Ag nanoclusters for the reduction of benzyl chloride, and the role of C₆₀ nanoparticle-doped carbon film in fabrication processes are also presented in this article.     

Simple two-step fabrication method of Bi2Te3 nanowires

Bismuth telluride (Bi2Te3) is an attractive material for both thermoelectric and topological insulator applications. Its performance is expected to be greatly improved when the material takes nanowire structures. However, it is very difficult to grow high-quality Bi2Te3 nanowires. In this study, a simple and reliable method for the growth of Bi2Te3 nanowires is reported, which uses post-sputtering and annealing in combination with the conventional method involving on-film formation of nanowires. Transmission electron microscopy study shows that Bi2Te3 nanowires grown by our technique are highly single-crystalline and oriented along [110] direction.     

Ultrathin free-standing close-packed gold nanoparticle films: conductivity and Raman scattering enhancement

A simple filtration technique was developed to prepare large scale free-standing close-packed gold nanoparticle ultrathin films using metal hydroxide nanostrands as both barrier layer and sacrificial layer. As thin as 70 nm, centimeter scale robust free-standing gold nanoparticle thin film was obtained. The thickness of the films could be easily tuned by the filtration volumes. The electronic conductivities of these films varied with the size of the gold nanoparticles, post-treatment temperature, and thickness, respectively. The conductivity of the film prepared from 20 nm gold nanoparticles is higher than that of the film prepared from 40 nm gold nanoparticle by filtering the same filtration volume of their solution, respectively. Their conductivities are comparable to that of the 220 nm thick ITO film. Furthermore, these films demonstrated an average surface Raman scattering enhancement up to 6.59 × 10(5) for Rhodamine 6 G molecules on the film prepared from 40 nm gold nanoparticles. Due to a lot of nano interspaces generated from the close-packed structures, two abnormal enhancements and relative stronger intensities of the asymmetrical vibrations at 1534 and 1594 cm(-1) of R6G were observed, respectively. These robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and hold the potential application for electrodes and surface enhanced Raman detectors. This method is applicable for preparation of other nanoparticle free-standing thin films.     

Morphological control of heterostructured nanowires synthesized by sol-flame method

Heterostructured nanowires, such as core/shell nanowires and nanoparticle-decorated nanowires, are versatile building blocks for a wide range of applications because they integrate dissimilar materials at the nanometer scale to achieve unique functionalities. The sol-flame method is a new, rapid, low-cost, versatile, and scalable method for the synthesis of heterostructured nanowires, in which arrays of nanowires are decorated with other materials in the form of shells or chains of nanoparticles. In a typical sol-flame synthesis, nanowires are dip-coated with a solution containing precursors of the materials to be decorated, then dried in air, and subsequently heated in the post-flame region of a flame at high temperature (over 900°C) for only a few seconds. Here, we report the effects of the precursor solution on the final morphology of the heterostructured nanowire using Co₃O₄ decorated CuO nanowires as a model system. When a volatile cobalt salt precursor is used with sufficient residual solvent, both solvent and cobalt precursor evaporate during the flame annealing step, leading to the formation of Co₃O₄ nanoparticle chains by a gas-solid transition. The length of the nanoparticle chains is mainly controlled by the temperature of combustion of the solvent. On the other hand, when a non-volatile cobalt salt precursor is used, only the solvent evaporates and the cobalt salt is converted to nanoparticles by a liquid–solid transition, forming a conformal Co₃O₄ shell. This study facilitates the use of the sol-flame method for synthesizing heterostructured nanowires with controlled morphologies to satisfy the needs of diverse applications.     

In‐situ formation of metal nanoparticle/acrylic polymer hybrid and its application to miniemulsion polymerization

We present in‐situ formation of metal nanoparticle/acrylic polymer hybrid and its application to prepare hybrid latex particles by miniemulsion polymerization. On the surface of a silver nanoparticle/silica nanoparticle/acrylic polymer hybrid layer formed in‐situ on a polyethylene terephthalate (PET) substrate, a copper film is deposited using electroless copper deposition. Silver nanoparticles, which are formed in‐situ via the reduction of silver ion by radical species and subsequent annealing, work as a catalyst for the electroless deposition. Miniemulsion polymerization via the in‐situ formation of nanoparticles affords nanoparticle/acrylic polymer hybrid latex particles and polymer particles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42675.     

Synthesis and electronic property of platinum nanowire and nanoparticle in mesoporous silica template

Platinum nanowires and nanoparticles were selectively synthesized in mesoporous silicas FSM-16 and HMM-1. The nanowires are 3 nm in diameter and several hundred nm to μm in length with high crystallinity. Pt nanowires and nanoparticles can be isolated by dissolving silica matrix with HF. The Pt wires extracted from organosilica HMM-1 have a nanonecklace structure, while the wires from siliceous FSM-16 have a nanorod structure. The extracted Pt nanoparticles (3 nm in size) on HOPG show the Coulomb staircase phenomena in STM/STS analysis. The mechanism for formation of the Pt nanowires is based on the migration of Pt ions in the mesoporous channels.     

Carbon nanocapsules encapsulating cobalt nanoparticles by pulsed discharge plasma chemical vapor deposition

Silicon coated with a thin film of cobalt [Si/Co (10 nm)] is exposed to the plasma generated using CH₄–H₂ gas mixture by making a discharge between Si/Co substrates and Mo bent plate in pulsed discharge plasma chemical vapor deposition. At high plasma temperature and deposition pressure, carbon nanocapsules encapsulating Co nanoparticles are observed to form. They are investigated using high resolution transmission electron microscopy, scanning electron microscopy, visible Raman spectroscopy and X-ray diffraction. Present study indicates that the formation mechanism of carbon nanocapsules lie in the sputtering of Co thin film by the energetic ions from plasma at high deposition pressure which results in the formation of Co nanoparticles, on surface of which graphitic layers gets deposited at high plasma temperature. Present approach provides a novel strategy for the synthesis of high purity carbon nanocapsules encapsulating metal nanoparticles.     

Synthesis and electronic property of platinum nanowire and nanoparticle in mesoporous silica template

Platinum nanowires and nanoparticles were selectively synthesized in mesoporous silicas FSM-16 and HMM-1. The nanowires are 3 nm in diameter and several hundred nm to μm in length with high crystallinity. Pt nanowires and nanoparticles can be isolated by dissolving silica matrix with HF. The Pt wires extracted from organosilica HMM-1 have a nanonecklace structure, while the wires from siliceous FSM-16 have a nanorod structure. The extracted Pt nanoparticles (3 nm in size) on HOPG show the Coulomb staircase phenomena in STM/STS analysis. The mechanism for formation of the Pt nanowires is based on the migration of Pt ions in the mesoporous channels.     

Micelle-template inducing synthesis of winding ZnS nanowires

Semiconductor single-crystal ZnS nanowires with diameters 40–80 nm and lengths up to tens of micron, which can bend and wind, have been synthesis by the reaction of Zn²⁺ with S²⁻ in reverse micelle for the inducing template. The formation mechanism of ZnS nanowires has been studied. The results indicated that the formation of ZnS nanowires probably was via the process of the directional aggregation and orientated growth of the ZnS nanoparticles.     

Fabrication of polycrystalline silver nanowires via reversed micelle with amphiphilic diblock copolymer and aluminum oxide template at controlled temperature

An amphiphilic diblock copolymer consisting of methyl methacrylate and methacrylic acid was synthesized using atom transfer radical polymerization via a hydrolysis process design. Silver nanoparticles were synthesized by a reverse micelle method using the synthesized diblock copolymer as a surfactant. Silver nanoparticle‐embedded fibers were then fabricated using an anodic aluminum oxide template. Silver nanoparticle‐embedded porous polymer fibers were fabricated by adding unreactive diphenyl sulfide in polymer matrix. They are expected to be applied to recyclable metal catalyst systems. After sintering of silver nanoparticle‐embedded polymer fibers at a relatively lower temperature, silver nanowires were fabricated. Moreover, the surfactant effect on both self assembly of nanoparticle clusters and silver nanowires surface smoothness were compared with the previously reported results. Silver nanoparticles coordinated amphiphilic copolymer was found to reveal higher thermal resistance. POLYM. COMPOS., 31:1352–1359, 2010. © 2009 Society of Plastics Engineers     

Low temperature solution-phase growth of ZnSe and ZnSe/CdSe core/shell nanowires

High quality ZnSe nanowires (NWs) and complementary ZnSe/CdSe core/shell species have been synthesized using a recently developed solution-liquid-solid (SLS) growth technique. In particular, bismuth salts as opposed to pre-synthesized Bi or Au/Bi nanoparticles have been used to grow NWs at low temperatures in solution. Resulting wires are characterized using transmission electron microscopy and possess mean ensemble diameters between 15 and 28 nm with accompanying lengths ranging from 4-10 μm. Subsequent solution-based overcoating chemistry results in ZnSe wires covered with CdSe nanocrystals. By varying the shell's growth time, different thicknesses can be obtained and range from 8 to 21 nm. More interestingly, the mean constituent CdSe nanocrystal diameter can be varied and results in size-dependent shell emission spectra.     

Electrodeposition of cobalt based ferro-magnetic metal nanowires in polycarbonate films with cylindrical nanochannels fabricated by heavy-ion-track etching

Polycarbonate films of thickness 30 μm were irradiated with heavy ions by applying a flux of 10⁸ ions cm⁻² to produce straight tracks perpendicular to the film surface. The tracks were preferentially etched in 6 M aqueous solution of sodium hydroxide to prepare cylindrical nanochannels. The channel diameters were tuned between 200 and 600 nm by varying the etching time. Co₈₁Cu₁₉ alloy nanowires were electrodeposited potentiostatically, while Co/Cu multilayered nanowires, consisting of alternating Co and Cu layers with thickness 10 nm, were synthesized by means of a pulse plating technique in channels of length 30 μm and diameter 200 nm. Co₈₁Cu₁₉ alloy nanowires showed an anisotropic magnetoresistance effect of 0.6%, and the giant magnetoresistance of Co/Cu multilayered nanowires reached up to 8.0%.     

Thermal stability of lead sulfide nanocrystalline films

Thermally stable nanocrystalline films of lead sulfide PbS were prepared using the chemical deposition method. The thickness of the films measured by interferometry was approximately equal to 100 nm, and the average particle size determined from the broadening of the X-ray diffraction reflections was approximately 80 nm. X-ray diffraction analysis revealed that annealing of the film at a temperature of 350°C in air results in the formation of a protective oxide sulfate phase of the composition PbO · PbSO₄ on the surface of the film. It was established that the oxide sulfate phase prevents a further oxidation of the film and serves as an inhibitor of the growth of PbS nanoparticles upon heating up to a temperature of 500°C. The factors responsible for the high thermal stability of the sizes of nanoparticles and the optical properties of the PbS nanocrystalline film were discussed.     

Synthesis and Characterization of Glomerate GaN Nanowires

Glomerate GaN nanowires were synthesized on Si(111) substrates by annealing sputtered Ga₂O₃/Co films under flowing ammonia at temperature of 950 °C. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and Fourier transformed infrared spectra were used to characterize the morphology, crystallinity and microstructure of the as-synthesized samples. Our results show that the samples are of hexagonal wurtzite structure. For the majority of GaN nanowires, the length is up to tens of microns and the diameter is in the range of 50–200 nm. The growth process of the GaN nanowires is dominated by Co–Ga–N alloy mechanism.     

Cadmium selenide nanowires within core-shell cylindrical polymer brushes: Synthesis, characterization and the double-loading process

Cadmium selenide (CdSe) nanowires were successfully in situ fabricated, utilizing amphiphilic core-shell cylindrical polymer brushes (CPB) as well-defined single molecular templates. The hydrophilic polymer brush core acts as the nanoreactor for generating and shaping CdSe nanoparticles into nanowires via the absorption of cadmium ions by carboxylate groups in the core and subsequent introduction of H₂Se gas; the hydrophobic polymer brush shell protects the nanowires from agglomeration and renders the hybrid a soluble material. The formation of 170 nm-long CdSe nanowires proceeds simultaneously with the nucleation, growth and combination of CdSe nanoparticles. After the introduction of CdSe nanowires, the recuperated chemical structure of CPB facilitates a double-loading process, broadening the CdSe nanowire from 7.5 to 9.3 nm on an average. Both hybrids are soluble and stable in organic solvents for one year and a potential candidate of the nanoscale optic and electronic devices.     

Characterization of silica-coated silver nanoparticles prepared by a reverse micelle and hydrolysis–condensation process

Described herein is the synthesis of individually silica-coated silver nanoparticles using a reverse micelle method followed by hydrolysis and condensation of tetraethoxysilane (TEOS). The size of a silica-coated silver nanoparticle can be controlled by changing the reaction time and the concentration of TEOS. By maintaining the size of a silver nanoparticle as a core particle at around 7 nm, the size of a silica-coated silver nanoparticle increased from 13 to 28 nm as the reaction time increased from 1 to 9 h due to an increase in silica thickness. The size of silica-coated silver nanoparticles also increased from 15 to 22 nm as the TEOS concentration increased from 7.8 to 40 mM. The size of a silica-coated silver nanoparticle can be accurately predicted using the rate of the hydrolysis reaction for TEOS. Neither the dispersion nor the film of silica-coated silver nanoparticles exhibited any peak shifting during surface plasmon resonance (SPR) at around 410 nm, whereas, without silica coating, the SPR peak of Ag film shifted to 466 nm.     

Effect of annealing process on the growth and surface properties of Au–ZnO nanowire films grown by chemical routes

Au–ZnO nanowire films have been synthesized by chemical routes, electrochemical deposition (ECD) and chemical bath deposition (CBD) techniques, on zinc foil followed by annealing in air at 400 °C. X-ray diffraction patterns reveal formation of the ZnO wurtzite structure along with binary phases Au₃Zn and AuZn₃. Scanning electron microscopy shows the presence of ZnO nanowires having several micrometers in length and less than 120 nm in diameter synthesized by ECD and in the range of 70–400 nm using the CBD technique. During the annealing process, different surface morphologies originating from different catalytic effects of Au atoms/layers were observed. In addition, the effect of synthesis routes on crystalline quality and optical properties were studied by Raman and photoluminescence spectrometers indicating varying concentration of defects on the films. The Raman results indicate that Au–ZnO nanowire film prepared by chemical bath deposition route had better crystalline quality.     

Aqueous film formation on irregularly shaped inorganic nanoparticles before deliquescence,as revealed by a hygroscopic differential mobility analyzer–Aerosol particle mass system

A hygroscopic tandem differential mobility analyzer (H-TDMA) and a hygroscopic coupled DMA and aerosol particle mass (H-DMA-APM) were coupled to examine aqueous film formation and the deliquescence behavior of inorganic nanoparticles. The two systems complement each other because H-DMA-APM measures mass change, while H-TDMA measures mobility diameter (volume) change of nanoparticles upon water uptake. The former mass change was, in particular, more capable to discern minute particle phase changes than the latter size change at moderate RHs. The mass and diameter changes were used to derive the particle effective density for evaluation of aqueous film formation on the nanoparticle surface before and after deliquescence transition. The measurements further showed that approximately 3–5 and 12–20 monolayer equivalents of water molecules formed on the respective surface of 50- and 100-nm inorganic aerosols (ammonium sulfate and sodium chloride) before deliquescence relative humidity (DRH). These findings support the physical basis of the coated-surface model given by Russell and Ming in 2002, and suggest that the phase transition of inorganic nanoparticles near deliquescence is a gradual process instead of an abrupt change. This phenomenon changed the surface energy values, thus confirming the explanation that the DRH of nanoparticles increases as the particle size decreases. This is the first direct observation of nanoparticle deliquescence phase transition using the H-DMA-APM system, and the detailed characterization of aqueous film formation on inorganic nanoparticles is feasible with the presented measurement systems.

© 2016 American Association for Aerosol Research     

Bi、S共掺杂对TiO_2纳米颗粒的结构和光催化性能的影响

以钛酸丁酯、硝酸铋和硫脲为原料,采用溶胶-凝胶法制备了不同n[Bi(S)]/n(Ti)的Bi、S共掺杂的TiO2光催化剂。采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、激光拉曼光谱(FT-Raman)、紫外-可见漫反射吸收光谱(UV/vis DRS)、微反等方法对光催化材料进行了研究。结果显示,Bi、S元素在TiO2纳米颗粒中分别以Bi2O3和SO42-形式存在,共掺杂未能改变TiO2的锐钛矿结构。Bi掺杂后,通过形成Bi—O—Ti键在TiO2禁带中产生了杂质能级,降低了纳米材料的禁带宽度,从而提高了光吸收效率;而S的引入,增多了催化剂表面的酸性位,有利于光催化活性的提高。Bi、S掺杂能明显改善TiO2纳米颗粒光催化甘油水溶液制氢的性能,3%Bi、S共掺杂TiO2具有最高的产氢速率,在紫外光和模拟太阳光照射下,其产氢速率可分别达到1 514.9和190.2μmol/(h·g)。