Growth Of One-dimensional Nanostructures Research Articles

Simple Preparation of Ceramic-Like Materials Based on 1D-Agx(x=0, 5, 10, 20, 40 mM)/TiO2 Nanostructures and Their Photocatalysis Performance

Vertical Agx/TiO2 nanorods were successfully grown by a simple oxidation method of a Ti-Ag coating. The samples were grown in the phase of ceramic-like materials, which can be reusable for many cycles for photocatalysis applications. These ceramic-like Agx/TiO2 nanostructures were prepared by the spin-coating of silver nitrate onto Ti sheets. The presence of silver on the surface of the Ti sheet during the oxidation process helped in the growth of one-dimensional nanostructures. The physical properties of the fabricated ceramic-like nanostructures were studied by varying the concentration of silver on the Ti-sheet before the oxidation. One-dimensional nanostructures with an average size varying within the range of 200–500 nm were grown. The presence of silver made the nanostructure vertically directed. The nanorods were dense at the low and medium concentrations of 5, 10, and 20 mM of silver in contrary to high silver concentrations, where the nanorods were very sparse at 40 mM. Structural analysis showed the anatase and rutile structure of pure TiO2 with distinguishing diffraction lines A(101) and R(110); however, Agx/TiO2 showed a dominant orientation of A(101), confirming the 1D growth. Raman spectra confirmed the presence of TiO2 via the observation of its corresponding phonon modes. The photocatalysis properties of the fabricated ceramic-like nanostructures were performed on methylene blue (MB) as a known target dye. The low- and medium-silver-concentration samples showed a high photocatalytic activity compared to the pure and high-silver-concentration samples.

Snow-Ice-Inspired Approach for Growth of Amorphous Silicon Nanotips.

The growth of one-dimensional nanostructures without a metal catalyst via a simple solution method is of considerable interest due to its practical applications. In this study, the growth of amorphous silicon (a-Si) nanotips was investigated using an aqueous solution dropped onto the Si substrate, followed by drying at room temperature or below for 24 h, resulting in the formation of a-Si nanotips on the Si substrate. Typically, the a-Si nanotips were up to 1.6 μm long, with average top and middle diameters of 30 and 80 nm, respectively, and contained no metal catalyst in their structure. The growth of a-Si nanotips can be explained in terms of the liquid–solid mechanism, where the supercritical Si solution (liquid) generated on the Si substrate (after reaction with the aqueous solution) promotes the nucleation of solid Si (acting as seeds) on the roughened surface, followed by surface diffusion of Si atoms along the side wall of the Si seeds. This is very similar to the phenomenon observed in the growth of snow ice crystals in nature. When photoexcited at 265 nm, the a-Si nanotips showed blue luminescence at around 435 nm (2.85 eV), indicating feasible applicability of the nanotips in optoelectronic functional devices.

Lateral growth of ZnO nanorod arrays in polyhedral structures for high on-current field-effect transistors.

Lateral growth of one-dimensional nanostructures is crucial for high performance field-effect transistors (FETs) which can drive a high on-current that is proportional to the number of nanorods (NRs) aligned between electrodes. Hence, it is strongly required to laterally and directly grow a large number of NRs between electrodes. For the first time, we propose a polyhedral-type FET (PH-FET) based on laterally-grown ZnO NRs, which includes circle, square and triangle configurations. The PH-FET structure not only provides a larger contact area than that of the planar parallel-type FET so that a great number of ZnO NRs are aligned between electrodes, but also generates a high on-current in the mA range (i.e., 5.5-6.8 mA). The high on-current PH-FET opens up a new range of applications for power devices where large currents have to be switched.

High index, reactive facet-controlled synthesis of one-dimensional single crystalline rare earth hydroxide nanobelts

Nanomaterials that are enclosed by high index, reactive facets exhibit a significantly enhanced chemical reactivity, leading to superior performances in electronics, photonics, energy conversion and storage, as well as interfacing with living cells for various biological purposes. This article investigates the formation of single crystalline rare earth hydroxide nanobelts with selective control of high energy surfaces. Combining experimental and theoretical efforts, a carboxylic group and carbon–carbon double bond of oleic acid molecules are found to reduce the (0001) surface energy by 60%, leading to the growth of nanobelts and the stabilization of their high energy surfaces. These findings shed light on the growth of one-dimensional nanostructures that exhibit a simultaneous control over the crystallographic facets, shapes, and sizes. Our results engender a versatile synthesis method for nanomaterials that exhibit enhanced physical and chemical properties by overcoming their energy barrier to grow with high energy surfaces.

Growth of One‐Dimensional Nanostructures in Porous Polymer‐Derived Ceramics by Catalyst‐Assisted Pyrolysis. Part II: Cobalt Catalyst

Via catalyst‐assisted pyrolysis, Si3N4 and SiC nanowires were produced on the cell walls of polymer‐derived ceramic foams. The pyrolysis atmosphere and temperature were the main parameters affecting their development: silicon nitride single‐crystal nanowires formed under nitrogen, while silicon carbide ones were produced under argon, and their amount increased with the increasing pyrolysis temperature. Brunauer–Emmett–Teller analysis showed that the presence of the nanowires afforded high specific surface area (SSA) values to the macroporous ceramic foams, ranging from 10 to 110 m2/g. Co‐containing samples developed higher SSA values, especially after pyrolysis at 1400°C in N2, than samples containing Fe as a catalyst. The differences were explained in terms of morphology (diameter and assemblage), which depended on the processing conditions and the catalyst type (Co or Fe).

The temperature-controlled growth ofIn2O3 nanowires, nanotowers and ultra-long layered nanorods

Indium oxide (In2O3) nanowires (with diameters of 25–90 nm and lengths of 10–50 µm), nanotowers (with diameters 100–150 nm and lengths below 10 µm) and long layered nanorods (with diameters of 200–400 nm and lengths of 20–50 µm) are grown through carbothermal reduction ofIn2O3 powder by varying the source temperature in a CVD horizontal furnace. At875 °C sourcetemperature, In2O3 nanowires were formed by a VLS (vapor–liquid–solid) mechanism. The growth is changed to VS(vapor–solid)-initiated growth on the substrate surface when the source temperature is raised to950 °C due to high saturation vapor pressure. Meanwhile, alternate VLS–VS grown nanotowerscan be obtained at the bottom of the substrates. Growth of one-dimensionalnanostructures with different structures and variation in growth mechanism from asingle precursor with the confinement of vapor pressure enables the diversity ofIn2O3 nanostructure synthesis. The morphologies and crystalline structures are characterized byx-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) andhigh-resolution transmission electron microscopy (HRTEM). The growth mechanisms ofthese structures are discussed.

Chemical tension and global equilibrium in VLS nanostructure growth process: from nanohillocks to nanowires

We formulate a global equilibrium model to describe the growth of one-dimensional nanostructures in the VLS process by including also the chemical tension in addition to the physical tensions, i.e. surface energies. The chemical tension derives from the Gibbs free energy change due to the growth of a crystal layer of an elementary thickness. The system global equilibrium is arrived at via the balance of the static physical tensions and the dynamic chemical tension. The model predicts and provides conditions for the growth of nanowires of all sizes exceeding a lower thermodynamic limit. The model also predicts the conditions distinguishing the growth of nanohillocks from nanowires. These predictions will allow the verification of the model by future experiments specifically designed for this purpose.