Facile template-free fabrication of olive-like ZnO nanoparticles and their photoluminescence properties

A facile template-free solvothermal approach was applied to synthesize olive-like ZnO nanoparticles with an average diameter of about 300 nm and an average length of about 600 nm. XRD, TEM, SEM, SAED, EDX and PL spectra were employed to characterize the crystal phase, morphologies, the chemical compositions, and optical properties of the ZnO nanostructure. The experimental results showed the as-obtained ZnO was single-crystalline nanostructure and the concentration of CH₃COO⁻ solution played a key role in controlling the morphology of ZnO. The growth mechanism of ZnO was tentatively investigated. Besides, the olive-like ZnO nanoparticles exhibit a very strong ultraviolet emission centered at 383 nm and a weak green luminescence emission at around 522 nm.     

The structure of Ta nanopillars grown by glancing angle deposition

Regular arrays of Ta nanopillars, 200 nm wide and 500 nm tall, were grown on SiO₂ nanosphere patterns by glancing angle sputter deposition (GLAD). Plan-view and cross-sectional scanning electron microscopy analyses show dramatic changes in the structure and morphology of individual nanopillars as a function of growth temperature T_s ranging from 200 to 700 °C. At low temperatures, T_s ≤ 300 °C, single nanopillars develop on each sphere and branch into subpillars near the pillar top. In contrast, T_s ≥ 500 °C leads to branching during the nucleation stage at the pillar bottom. The top branching at low T_s is associated with surface mounds on a growing pillar that, due to atomic shadowing, develop into separated subpillars. At high T_s, the branching occurs during the nucleation stage where multiple nuclei on a single SiO₂ sphere develop into subpillars during a competitive growth mode which, in turn, leads to intercolumnar competition and the extinction of some nanopillars.     

HRTEM observations on composites of tin and tin dioxide nanoparticles dispersed on carbon nanotubes by single-atoms-to-clusters method

Nano-composites of tin and tin dioxide particles were synthesized on carbon nanotubes by the single-atoms-to-clusters (SAC) method, and their structures were investigated by high-resolution transmission electron microscopy. By changing the heat-treatment temperature during the SAC process, two different types of samples were obtained. The samples prepared around 450 K were aggregates of 2-4 nm-sized tin dioxide nanoparticles, and their size distributions on carbon nanotubes are in the range 20-40 nm. The other samples formed above 600 K had a core-shell structure of diameter 20-40 nm. The core and shell were made of tin single crystal and disordered oxidized tin, respectively. The thickness of the oxidized layers was ca. 4 nm.     

Defect induced room temperature ferromagnetism in well-aligned ZnO nanorods grown on Si (100) substrate

In this work, we report the fabrication of high quality single-crystalline ZnO nanorod arrays which were grown on the silicon (Si) substrate using a microwave assisted solution method. The as grown nanorods were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photo-luminescence (PL) and magnetization measurements. The XRD results indicated that the ZnO nanorods are well oriented with the c-axis perpendicular to the substrate and have single phase nature with the wurtzite structure. FE-SEM results showed that the length and diameter of the well aligned rods is about ~ 1 μm and ~ 100 nm respectively, having aspect ratio of 20-30. Room-temperature PL spectrum of the as-grown ZnO nanorods reveals a near-band-edge (NBE) emission peak and defect induced green light emission. The green light emission band at ~ 583 nm might be attributed to surface oxygen vacancies or defects. Magnetization measurements show that the ZnO nanorods exhibit room temperature ferromagnetism which may result due to the presence of defects in the ZnO nanorods.     

The growth of nanoscale ZnO films by pulsed-spray evaporation chemical vapor deposition and their structural, electric and optical properties

Great interest in nanoscale thin films (sub-100 nm) has been stimulated by the developing demands of functional devices. In this paper, nanoscale zinc oxide (ZnO) thin films were deposited on glass substrates at 300 °C by pulsed-spray evaporation chemical vapor deposition. Scanning electron micrographs indicate uniform surface morphologies composed of nanometer-sized spherical particles. The growth kinetics and growth mode are studied and the relationship between the film thickness and the electric properties with respect to the growth mode is interpreted. X-ray diffraction shows that all ZnO films grown by this process were crystallized in a hexagonal structure and highly oriented with their c-axes perpendicular to the plane of the substrate. Optical measurements show transparencies above 85% in the visible spectral range for all films. The absorbance in the UV spectral range respects well the Beer-Lambert law, enabling an accurate optical thickness measurement, and the absorption coefficient was measured for a selected wavelength. The measured band gap energies exhibit an almost constant value of 3.41 eV for all films with different thicknesses, which attributed to the thickness-independent crystallite size.     

Monodisperse ceria nanospheres: Synthesis,characterization, optical properties,and applications in wastewater treatment

Monodisperse ceria nanospheres have been synthesized by a facile solvothermal method, and their morphology and microstructures have been revealed by a combination of X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and N₂ adsorption. It is demonstrated that the as-synthesized powders are highly uniform CeO₂ in spherical shape with cubic fluorite structure. HRTEM and XRD studies show that each ceria nanosphere is composed of dozens of nanocrystals with the average size of 8.5 nm. The direct optical band gap of the ceria nanospheres estimated from the ultraviolet–visible absorption spectrum is 2.7 eV, which is evidently red-shifted with respect to the bulk material (E_g = 3.19 eV); the reduced band gap could be resulted from the high concentration of grain boundaries and defects present in the ceria nanospheres. In addition, the ceria nanospheres exhibit a strong blue luminescence at 504 nm and a broad orange luminescence centered at 645 nm. As a result of the large specific surface area, ceria nanospheres are revealed to be an excellent sorbent for the removal of poisonous pollutants present in water, such as chromium ions and rhodamine B. The removal efficiency of chromium ions is as high as ∼94%.     

A template-free alcoholthermal route to Ti(Sn)-doped ZnO nanorods

Ti(Sn)-doped single-crystalline ZnO nanorods with an average diameter of 20 nm and length up to nearly 1 μm were synthesized by a facile ultrasonic irradiation-assisted alcoholthermal method without involving any templates. Photoluminescence spectra of the Ti-doped ZnO nanorods were measured at room temperature and three emitting bands, being a violet emission at 400-415 nm, a blue band at 450-470 nm and a green band at around 550 nm, were detected. The emission intensities of the Ti-doped ZnO nanorods enhance gradually with increasing the doping concentrations. As to the Sn-doped ZnO nanorods, the green emission shifts to 540 nm and the emission intensities increase first but decrease later with increasing the doping concentrations.     

Shape memory effect in Cu nanowires

A rubber-like pseudoelastic behavior is discovered in single-crystalline face-centered-cubic (FCC) Cu nanowires in atomistic simulations. Nonexistent in bulk Cu, this phenomenon is associated primarily with a reversible crystallographic lattice reorientation driven by the high surface-stress-induced internal stresses due to high surface-to-volume ratios at the nanoscale level. The temperature-dependence of this behavior leads to a shape memory effect (SME). Under tensile loading and unloading, the nanowires exhibit recoverable strains up to over 50%, well beyond the typical recoverable strains of 5-8% for most bulk shape memory alloys (SMAs). This behavior is well-defined for wires between 1.76 and 3.39 nm in size over the temperature range of 100-900 K.     

Solvothermal synthesis of nickel nanorods and its magnetic, structural and surface morphological behavior

One-dimensional rod-like nickel nanostructure was fabricated through a simple, efficient and one pot solvothermal approach with hydrazine hydrate and trimethylamine as reducing and morphology directing agents. The phase structure, morphology and magnetic properties of the as-prepared product were extensively characterized by X-ray diffraction, transmission electron microscopy and superconducting quantum interference device magnetometer. X-ray diffraction pattern indicated that the as-synthesized product was nickel with well-crystallized face-centered cubic structure. TEM observation showed that the nickel product consists of rod-like shape with size around 10 nm. Magnetic measurements revealed that the coercive forces of nickel nanorods at 300 K and 4.2 K are 198 Oe and 250 Oe, respectively. Compared with bulk nickel, the nanorods exhibit significant increase in coercive force as a reflection of shape anisotropy. A possible mechanism for the formation of rod-like nanostructure is proposed.     

Vapor phase synthesis of BN ribbons with Sialon ribbons as self-sacrificing templates

Novel polycrystalline BN ribbons (BNRs) with an average width of about 300 nm and a thickness of about 200 nm have been synthesized using Sialon ribbons and ammonia borane as starting materials. We find out that single-crystalline Sialon ribbons can be converted to polycrystalline BNRs upon reacting with the vapors decomposed from ammonia borane at 1450 °C. A template self-sacrificing mechanism has been proposed to account for the growth of BNRs. Our approach can be extended to fabricate other BN nanostructures.     

Single-crystalline Si grown on single-crystalline Gd2O3 by modified solid-phase epitaxy

We investigate molecular beam epitaxial overgrowth of Si template layers produced by different approaches on single-crystalline oxide grown on Si(111). Three approaches based on modified solid-phase epitaxy were found to be suitable for the subsequent Si epitaxial overgrowth. The crystalline quality and interface properties of single-crystalline silicon on single-crystalline oxide grown on Si(111) make the obtained structures suitable for silicon-on-insulator applications. First measurements of electrical properties of p-type samples indicate good electrical properties of the top Si layer. Supplemental investigations demonstrate that Si layers with thickness in the range of 10 nm remain stable during thermal annealing up to 900 °C in an ultra-high vacuum.     

Photoresponse of hydrothermally grown lateral ZnO nanowires

In this paper, a simple self-assembled lateral growth of ZnO nanowires (NWs) photodetector has been synthesized by a hydrothermal method at a temperature as low as 85 °C. The ZnO NWs exhibit single-crystalline wurtzite with elongated c-axis and can be selectively lateral self-assembled around the edges of ZnO seeding layer. The current of ZnO NWs is sensitive to the variation of ambient pressures, i.e. 4.47 μA was decreased to 1.48 μA with 5 V-bias as 1.1 × 10^− 6 Torr changed to 760 Torr, accordingly. Moreover, the current-voltage characteristics of ZnO NWs photodetectors can be evidently distinguished by UV illumination (i.e. λ = 325 nm). The photocurrent of ZnO NWs with UV illumination is twice larger than dark current while the voltage biased at 5 V. Consequently, this faster photoresponse convinces that the hydrothermally grown lateral ZnO NWs devices have a fairly good for the fabrication of UV photodetectors.     

Large-scale synthesis of hexagonal cone-shaped ZnO nanoparticles with a simple route and their application to photocatalytic degradation

We report the large-scale synthesis of hexagonal cone-shaped ZnO nanoparticles by the esterification between zinc acetate and alcohol. The morphology of the ZnO nanoparticles was investigated by transmission electron microscopy, selected area electron diffraction and scanning electron microscopy measurements. The synthesized ZnO nanoparticles are single-crystalline with hexagonal phase and show a strong UV emission at −378 nm due to the excellent crystallinity of particles. A possible formation mechanism of the hexagonal cone-shape structure is proposed. Furthermore, the as-prepared ZnO particles exhibit high photocatalytic activity for the photocatalytic degradation of Rhodamine B, indicating that the ZnO nanostructure is promising as a semiconductor photocatalyst.     

Tin dioxide nanoparticles: Reverse micellar synthesis and gas sensing properties

Tin dioxide (SnO₂) nanoparticles have been synthesized by reverse micellar route using cetyltrimethyl ammoniumbromide (CTAB) as the surfactant. Monophasic tin dioxide (SnO₂) was obtained using NaOH as the precipitation agent at 60 °C, however, when liquor NH₃ was used as precipitating agent then crystalline SnO₂ nanoparticles are obtained at 500 °C. SnO₂ prepared using NaOH show crystallite size of 4 and 12 nm after heating at 60 and 500 °C respectively using X-ray line broadening studies. Transmission electron microscopy (TEM) studies show agglomerated particles of sizes 70 and 150 nm, respectively. The grain size was found to be 6-8 nm after heating the precursor obtained (using liquor NH₃) at 500 °C by X-ray line broadening and the TEM studies. Dynamic light-scattering (DLS) studies show the aggregates of SnO₂ nanoparticles with uniform size distribution. Mössbauer studies show an increase of s-electron density at the Sn sites compared to bulk SnO₂ and a finite quadrupole splitting indicative of lowering of symmetry around tin atoms. The gas sensing characteristics have also been investigated using n-butane which show high sensitivity and fast recovery time.     

Growth of poly-crystalline silicon-germanium on silicon by aluminum-induced crystallization

The formation of poly-crystalline silicon-germanium films on single-crystalline silicon substrates by the method of aluminum-induced crystallization was investigated. The aluminum and germanium films were evaporated onto the single-crystalline silicon substrate to form an amorphous-germanium/aluminum/single-crystalline silicon structure that was annealed at 450 °C-550 °C for 0-3 h. The structural properties of the films were examined using x-ray diffraction, Raman spectroscopy and Auger electron spectroscopy. The x-ray diffraction patterns confirmed that the initial transition from an amorphous to a poly-crystalline structure occurs after 20 min of aluminum-induced crystallization annealing process at 450 °C. The micro-Raman spectral analysis showed that the aluminum-induced crystallization process yields a better poly-crystalline SiGe film when the film is annealed at 450 °C for 40 min. The growth mechanism of the poly-crystalline silicon-germanium by aluminum-induced crystallization was also studied and is discussed.     

Growth of 3C-SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C-SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C-SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH₄ and C₂H₂. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.     

Indium tin oxide films deposited by thermionic-enhanced DC magnetron sputtering on unheated polyethylene terephthalate polymer substrate

Indium tin oxide thin films were deposited onto polyethylene terephthalate substrates via thermionic enhanced DC magnetron sputtering at low substrate temperatures. The structural, optical and electrical properties of these films are methodically investigated. The results show that compared with traditional sputtering, the films deposited with thermionic emission exhibit higher crystallinity, and their optical and electrical properties are also improved. Indium tin oxide films deposited by utilizing thermionic emission exhibit an average visible transmittance of 80% and an electrical resistivity of 4.5 × 10⁻⁴ Ω cm, while films made without thermionic emission present an average visible transmittance of 74% and an electrical resistivity of 1.7 × 10⁻³ Ω cm.     

Observation of magnetic, structural and surface morphological studies of triangle-like nickel nanoplates

Two-dimensional triangle-like nickel nanoplates have been synthesized by solvothermal method in the presence of triethylamine as a structure directing agent. The structure, morphology and magnetic properties of the as-synthesized products were characterized by X-ray diffraction, Atomic force microscopy and Superconducting quantum interference device magnetometer. The as-synthesized products have been confirmed to be phase-pure crystalline nickel with face centered cubic structure on the basis of X-ray diffraction characterization. Atomic force microscopy image demonstrated that the as-prepared nickel product possess two-dimensional triangle-like structure with edge length of about 65-85 nm. Magnetic measurements showed that the coercive forces at 4.2 K and 300 K for nickel nanoplates are 363.3 and 182 Oe, respectively. The nickel nanoplates exhibit a distinct enhanced coercive force due to the presence of shape anisotropy when compared with that of bulk. A possible mechanism for the formation of triangle-like Ni nanoplate structure is proposed.     

Shear banding deformation in Cu/Ta nano-multilayers

Nanoscale Cu/Ta multilayers with individual layer thickness ranging from 3 to 70 nm were deformed under nanoindentation at room temperature. Shear bands can be observed only when individual layer thickness is reduced to 9 nm or below, indicating formation of shear bands in the Cu/Ta multilayers is layer thickness dependent. By observing the cross sectional transmission electron microscope images of the indentation fabricated through focused ion beam technique, shear banding deformation causing a unique layer-morphology with prevalent mismatched laminate structure has been reported for the first time. By capturing and analyzing a series of typical indentation-induced deformed microstructures, a new physical mechanism of shear banding behavior in metallic nano-multilayers is suggested.     

Influences of process parameters on texture and microstructure of NiO films

The experimental result shows that the preferred orientations of NiO thin films are closely related to the working pressure of argon. All of NiO(111), NiO(200), and NiO(220) diffraction peaks are observed in the XRD patterns and exhibited random orientation of NiO film when the film is deposited in low Ar pressure of 0.67 Pa. As the Ar pressure is increased to 2.67 Pa, only the NiO(200) peak appears and shows (200)-textured NiO films. However, the lattice parameter of NiO film deposited in high Ar pressure of 2.67 Pa is 0.426 nm, which is much larger than that of the NiO bulk (0.417 nm). The lattice parameter can be reduced by post-annealing the film because the interstitial Ar atoms are released from the NiO lattice, decreasing continuously from 0.423 to 0.417 nm as the NiO films are annealed by rapid thermal annealing (RTA) from 300 to 600 °C.