Application of ZnO nanoparticles in influencing the growth rate of Cicer arietinum

In this work, ZnO nanoparticles (NPs) have been synthesised by hydrothermal method. This hydrothermally synthesised product has been characterised by powder X-ray diffraction and field emission scanning electron microscopy (FE-SEM) for the study of crystal structure and morphology/size. FE-SEM image revealed that ZnO NPs are spherical in shape with a diameter of 20–30?nm. The photoluminescence study of these NPs revealed that ZnO NPs consist of three emission peaks at 401, 482 and 524?nm. The UV emission peak at 401?nm is the band edge emission; however, the blue-green emission at 482?nm and green emission at 524?nm is related to defects. These ZnO NPs are used during the seed germination and root growth of Cicer arietinum. The effect of ZnO NPs has been observed on the seed germination and root growth of C. arietinum seeds. The effect of these ZnO NPs on the reactivity of phytohormones, especially indole acetic acid (IAA) involved in the phytostimulatory actions, is also carried out. Due to oxygen vacancies, the oxygen deficient, i.e. zinc-rich ZnO NPs increased the level of IAA in roots (sprouts), which in turn indicate the increase in the growth rate of plants as zinc is an essential nutrient for plants.     

Enhanced field emission from injector-like ZnO nanostructures with minimized screening effect

Injector-like zinc oxide (ZnO) nanostructures have been synthesized on Si substrate by the vapour phase transport method. Samples with different areal densities were obtained by controlling the temperature. The field emission properties of the injector-like ZnO nanostructures showed a clear dependence on the areal density of the nanostructures, which is due to the screening effect. The samples with a needle length of 850?nm and an areal density of 1 × 10(8)?cm(-2) showed the lowest field emission turn-on field of 1.85?V?μm(-1) at a current density of 10?μA?cm(-2), and the current density reaches 1?mA?cm(-2) at an applied field of 4.7?V?μm(-1).     

Position and density control in hydrothermal growth of ZnO nanorod arrays through pre-formed micro/nanodots

Position-?and density-controlled ZnO nanorod arrays (ZNAs) were successfully grown on a Si substrate through a low temperature (90?°C) hydrothermal approach assisted by pre-formed ZnO micro/nanodots. The ZnO dots on Si substrates were prepared by a spin-coating technique, through which the pattern and density of the dots could be easily changed. Accordingly, the position-?and density-controlled growth of ZNAs was achieved. For the resulting density-controlled ZNAs, the density could range from (5.6 ± 0.01) × 10(2) to (1.2 ± 0.01) × 10(2)?rods?μm(-2). The room-temperature photoluminescence (PL) spectrum of ZNAs exhibited excellent UV emission. The water wettability measurements of the ZNAs with different density showed good hydrophobicity, and the ZNAs with the lowest density revealed a superhydrophobic characteristic with a water contact angle of 166.1°.     

Size-tunable Au nanoparticles on MoS(2)(0001)

Ultra-fine Au nanoparticles (NPs) show great application potential in catalysis. Size-tunable Au NPs have been fabricated on MoS(2) covered with monolayer 3,4,5,10-perylene tetracarboxylic dianhydride (PTCDA), and the morphological evolution as a function of Au deposition amount was investigated using scanning tunneling microscopy (STM). The PTCDA molecules act as a surfactant to stabilize ultra-fine Au NPs. Molecular scale STM images show that on MoS(2) the Au NPs with PTCDA molecules on top can be formed with height and lateral size down to 1.3?nm and 3.5?nm, respectively. By controlling the deposition amount and annealing temperature, the size of Au NPs can be tuned. After annealing at 270?°C to remove PTCDA, Au NPs with a linear size ≤5?nm can be obtained on MoS(2)(0001), facilitating the characterization of their intrinsic physical and chemical properties using various analytical techniques. In addition, photoemission spectroscopy data reveal charge transfer from Au NPs to PTCDA, indicating that the NPs possess more reactive chemical properties than bulk Au.     

Direct synthesis of ZnO nanowire arrays on Zn foil by a simple thermal evaporation process

ZnO nanowire arrays were synthesized on zinc foil by a simple thermal evaporation process at relatively low temperature. Morphology and size controlled synthesis of the ZnO nanostructures was achieved by variation of the synthesis temperature, reaction time and the surface roughness of the substrate. A gas-solid and self-catalytic liquid-solid mechanism is proposed for the growth of nanowires at different temperatures. High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction. Photoluminescence exhibited strong UV emission at ～382?nm and a broad green emission at ～513?nm with 325?nm excitation. Raman spectroscopy revealed a phonon confinement effect when compared with results from bulk ZnO. The nanowire arrays also exhibited a field emission property.     

Optical and field-emission properties of ZnO nanostructures deposited using high-pressure pulsed laser deposition

ZnO nanostructures were deposited on GaN (0001), Al2O3 (0001), and Si (100) substrates using a high-pressure pulsed laser deposition (PLD) method. Vertically aligned hexagonal-pyramidal ZnO nanorods were obtained on the Al2O3 and Si substrates whereas interlinked ZnO nanowalls were obtained on the GaN substrates. A growth mechanism has been proposed for the formation of ZnO nanowalls based on different growth rates of ZnO polar and nonpolar planes. Both ZnO nanorods and nanowalls exhibit a strong E2H vibration mode in the micro-Raman spectra. The corresponding fluorescence spectra of ZnO nanorods and nanowalls showed near band emission at 3.28 eV. The ZnO nanorods grown on the Si substrates exhibited better crystalline and optical properties compared with the ZnO structures grown on the GaN and Al2O3 substrates. The high aspect ratio, good vertical alignment, and better crystallinity of the ZnO nanorods with tapered tips exhibited promising field emission performance with a low turn-on field of 2 V/μm, a high current density of 7.7 mA/cm2, and a large field enhancement factor.     

Synergistic effects of SPR and FRET on the photoluminescence of ZnO nanorod heterostructures

Solution-grown ZnO nanorods (NRs) were successfully conjugated with CdSe/ZnS quantum dots (QDs) and Ag nanoparticles (NPs) to suppress intrinsic defect emission and to enhance band-edge emission at the same time. First, high-density and high-crystallinity ZnO NRs of diameter 80–90 nm and length 1.2–1.5 μm were grown on glass substrates using a low-temperature seed-assisted solution method. The as-synthesized ZnO NRs showed sharp photoluminescence (PL) band-edge emission centered at ～377 nm together with broad defect emission in the range of ～450–800 nm. The ZnO NRs were decorated with CdSe/ZnS QDs and Ag NPs, respectively, by sequential drop-coating. The PL of CdSe/ZnS QD||ZnO NR conjugates showed that ZnO band-edge emission decreased by 73.8% due to fluorescence resonance energy transfer (FRET) and charge separation between ZnO and CdSe/ZnS by type II energy band structure formation. On the other hand, Ag NP||CdSe/ZnS QD||ZnO NR conjugates showed increased band-edge emission (by 25.8%) and suppressed defect emission compared to bare ZnO NRs. A possible energy transfer mechanism to explain the improved PL properties of ZnO NRs was proposed based upon the combined effects of FRET and surface plasmon resonance (SPR).     

Study on characteristics of silicon nanocrystals within sol–gel host

In this article, luminescent Si nanocrystalline (NC) powder was uniformly dispersed in dimethyl sulphoxide and then incorporated into the SiO₂ gel matrix. Inorganic precursor tetraethylorthosilane was diluted in ethanol to form a homogenous solution. Dimethylformamide was used as a drying control chemical additive. Absorption and emission spectra of Si NPs in the silica gel with respect to time were recorded systematically at room temperature. The study reveals that the absorption and emission spectra of Si NPs, when doped in sol–gel silica matrix are modified. Influence in the band strengths and their peak positions upon ageing time are discussed. TEM shows existence of Si NPs of size ranges from 5 to 10?nm. Si NCs-doped sol–gel cylindrical rod was prepared and cut at different lengths from 10 to 15?mm to measure the optical gain. Photoluminescence stability of Si NCs in sol–gel is found for several weeks under the UV lamp.     

Enhanced free exciton and direct band-edge emissions at room temperature in ultrathin ZnO films grown on Si nanopillars by atomic layer deposition

Room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 °C, an intensive UV emission corresponding to free-exciton recombination (~3.31 eV) was observed with a nearly complete suppression of the defect-associated broad visible range emission peak. On the other hand, for ZnO films grown at 25 °C, albeit the appearance of the defect-associated visible emission, the UV emission peak was observed to shift by ~60 meV to near the direct band edge (3.37 eV) recombination emission. The high-resolution transmission electron microscopy (HRTEM) showed that the ZnO films obtained at 25 °C were consisting of ZnO nanocrystals with a mean radius of 2 nm embedded in a largely amorphous matrix. Because the Bohr radius of free-exictons in bulk ZnO is ~2.3 nm, the size confinement effect may have occurred and resulted in the observed direct band edge electron-hole recombination. Additionally, the results also demonstrate order of magnitude enhancement in emission efficiency for the ZnO/Si-NP structure, as compared to that of ZnO directly deposited on Si substrate under the same conditions.     

Room-temperature preparation of ZnO nanosheets grown on Si substrates by a seed-layer assisted solution route

A facile route to prepare two-dimensional ZnO nanosheet structures on Si substrates was developed through the adoption of a ZnO seed-layer and suitable growth medium in this work. The characterization results showed that ZnO nanosheets could be grown on Si substrates with a pre-formed ZnO seed-layer at room temperature. The ZnO nanosheets, with thickness of 20-25?nm, were interwoven into networks to form a continuous nanosheet film. Room-temperature measurements of the photoluminescence (PL) spectra and water wettability for the resulting ZnO nanosheet structures showed high intensity ratio of the UV emission to the defect emissions and good hydrophilic property without UV illumination. The present work demonstrates that the adoption of a ZnO seed-layer is an effective approach for room-temperature growth of ZnO nanosheets grown on substrates.     

Synthesis,characterization and growth mechanism of ZnO nanowires on NiCl<Subscript>2</Subscript>-coated Si substrates

Well-crystallized ZnO nanowires have been successfully synthesized on NiCl₂-coated Si substrates via a carbon thermal reduction deposition process. The pre-deposited Ni nanoparticles by dipping the substrates into NiCl₂ solution can promote the formation of ZnO nuclei. The as-synthesized nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The results demonstrate that the as-fabricated nanowires with about 60 nm in diameter and several tens of micrometers in length are preferentially arranged along [0001] direction with (0002) as the dominate surface. Room temperature PL spectrum illustrates that the ZnO nanowires exist a UV emission peak and a green emission peak, and the peak centers locate at 387 and 510 nm. Finally, the growth mechanism of the nanowires is briefly discussed.     

Synthesis and bandgap oscillation of uncapped, ZnO clusters by electroporation of vesicles

A convenient preparation is reported for subnanometre size uncapped ZnO quantum dots, which permits the previously inaccessible live observation of the growth of the clusters in the molecular size regime. The preparation method utilizes electric field-induced transient pore formation (electroporation) in synthetic unilamellar vesicles. This condition allows for facile monitoring of the time-dependent UV spectra associated with the growth of the clusters which are found to initially exhibit novel, oscillating red and blue shifts of the characteristic absorption band, ultimately followed by a monotonic red shift-the latter reflecting cluster growth beyond a size of ～10??. Through a comparison of the observed oscillating transition energies with the corresponding trends found theoretically by others, the wavelengths of the sequential spectral peaks can be assigned to the (ZnO)(1) monomer (5.66?eV), dimer (ZnO)(2) (5.19?eV), (ZnO)(5) (6.21?eV), (ZnO)(12) (5.76?eV), and (ZnO)(15) (6.01?eV). Growth beyond (ZnO)(15) is associated with the customary monotonic red shift of the absorption band (5.59 and 4.95?eV). The reason for oscillation of red and blue shift of the HOMO-LUMO gaps was explained by the structural differences of Zn(i)O(i) (i = 1-15). Under the experimental conditions used, a stable system is reached after 12 days. This solution is estimated to contain 1.4 × 10(17)?(ZnO)(15) particles, each with a greatest dimension of ～10??.     

(101)-oriented ZnO nanoparticles fabricated in Si (100) by Zn ion implantation and thermal oxidation

ZnO nanoparticles (NPs) embedded in Si (100) substrate have been created by Zn ion implantation and post thermal annealing in oxygen atmosphere. Several techniques have been employed to investigate the formation of Zn NPs and their thermal evolution at elevated temperatures. Grazing X-ray diffraction results clearly show that ZnO NPs are effectively formed after 600 °C annealing, and they show a (101) preferential orientation. Cross-sectional transmission electron microscopy observations confirm that ZnO NPs with a narrow size distribution of 2–7 nm are formed within the near-surface region of about 35 nm in thickness. Photoluminescence measurement displays a strong emission band centered at 387 nm in the sample annealed at 600 °C.     

Small angle X-ray scattering and photoluminescence study of ZnO nanoparticles synthesized by hydrothermal process

Polydisperse ZnO nanoparticles have been synthesized by a hydrothermal process. Small-angle X-ray Scattering (SAXS) was performed for particle size distribution analysis of ZnO nanoparticles. Room-temperature photoluminescence measurements revealed that the ZnO nanoparticles have a single visible emission peak ～600?nm, although polydispersity of the sample shows no presence on PL spectrum. It seems the orange emission ～600?nm is due to the presence of Zn(OH)₂ on the surface of ZnO nanoparticles, instead of the commonly assumed interstitial oxygen defect.     

Structure and physical properties of undoped ZnO and vanadium doped ZnO films deposited by pulsed laser deposition

Undoped ZnO films were deposited using pulsed laser deposition technique on Si and glass substrates in different O2 partial pressures (ranging from 10(-5) mbar to 3 mbar) and substrate temperatures. When the substrate temperature is 500 degrees C and O2 partial pressure (pp) approximately 3 mbar, randomly oriented ZnO hexagons were observed on glass substrate, whereas, dense ZnO hexagonal rod like structures (diameter ranging from 200-500 nm) were observed on Si substrate. The photoluminescence (PL) characterization of ZnO film grown on Si exhibited an intense defect free narrow excitonic emission in the UV region (Full width half maximum (FWHM) approximately 11.26 nm) as compared to broad emission (FWHM approximately 57.06 nm) from that grown on glass. The parent film emission was found to shift from UV to blue region on doping ZnO with Vanadium.     

Substrate-free growth, characterization and growth mechanism of ZnO nanorod close-packed arrays

ZnO nanorod close-packed arrays are successfully fabricated in a substrate-free manner by a citric acid assisted annealing process at a low growth temperature of 400?°C. Each nanorod of ZnO nanorod close-packed arrays grows along the [0001] direction and is single crystalline with an average diameter of 50?nm, and an average length of 0.5?μm. The aspect ratio is 10. The ZnO nanorod close-packed arrays show a strong exciton absorption peak at 372?nm in UV-visible absorption spectra, exhibiting a blue-shift relative to the bulk exciton absorption (387?nm). Finally, a new growth mechanism is proposed for the substrate-free preparation of ZnO nanorod close-packed arrays by a citric acid assisted annealing process.     

Template-free solvothermal synthesis of ZnO nanoparticles with controllable size and their size-dependent optical properties

ZnO nanoparticles (NPs) have been synthesized via a facile and template-free solvothermal method. The size of ZnO NPs could be tailored by adjusting the ratio of ethanol to ethylene glycol (EG). Their structure and morphology have been investigated. The as-prepared samples are monodispersed ZnO NPs with controllable sizes of about 24.2, 18.9 and 14.7 nm. The cathodoluminescence (CL) spectra of the samples show that the relative intensity ratio of the visible emission peak at 500-650 nm to the band-edge UV emission peak at 380 nm increases as the particle size decreases. Sample with smaller crystallites would have larger surface area and more oxygen vacancy defects, thus it exhibits higher visible emission peak. The UV-vis absorption spectrum indicates the band gap variation of the ZnO NPs with their size. Moreover, the size-dependent blue shifts of both the CL emission and the UV-vis absorption spectra reveal the effect of quantum confinement.     

Structural and optical properties of single-crystalline ZnO nanorods grown on silicon by thermal evaporation

The growth of perfectly hexagonal-shaped ZnO nanorods, with Zn-terminated (0001) facets bounded with [Formula: see text] surfaces, has been performed on nickel-coated Si(100) substrate via thermal evaporation using metallic zinc powder and oxygen. Detailed structural investigations confirmed that the synthesized nanorods are single crystalline with the wurtzite hexagonal phase and preferentially grow along the c-axis direction. Raman spectra of the as-grown ZnO nanorods showed an optical-phonon E(2) mode at 438?cm(-1), indicating that as-grown nanostructures are in good crystallinity with the wurtzite hexagonal phase. The ZnO nanorods were found to show strong band edge emission with very weak or no deep-level emission, as shown by photoluminescence measurements. The clear observation of free excitons at low temperatures (13-50?K) indicates that the as-grown ZnO nanorods are of high quality.     

Enhanced the structure and optical properties for ZnO/PVP nanofibers fabricated via electrospinning technique

Zinc oxide/polyvinylpyrrolidone (ZnO/PVP) nanocomposite fibers with enhanced structural, morphological and optical properties were purposefully tailored using electrospinning technique. Meanwhile, ZnO nanoparticles (NPs),with particle size of ~50 nm, were synthesized using a co-precipitation method. The nanocomposite fibers were prepared by an electrospun solution of PVP containing ZnO NPs of 2, 4, 6 and 8 wt%. Evidently, the morphological, thermal and optical properties of the ZnO/PVP nanocomposite fibers were enhanced by dispersing ZnO NPs into PVP fibers. Typically, controlling the ZnO NPs content and their dispersibility (0–8 wt%) into PVP fibers result in improved the thermal stability (an increase of onset decomposition temperature by ~120 °C above pure PVP fibers) as well as the UV–Vis protection (reduction in UV transmission by 70%) and the photoluminescence properties (a sharp UV emission around 380 nm) Overall, based on the enhanced properties, the PVP/ZnO nanocomposite fibers can be considered a promise material in optoelectronic sensors and UV photoconductor.     

Silicon-induced oriented ZnS nanobelts for hydrogen sensitivity

Oriented ZnS nanobelts were grown on an Si substrate using hydrogen-assisted thermal evaporation under moist gas conditions. It was found that these ZnS nanobelts had a single crystal hexagonal wurtzite structure growing along the [0001] direction. They had a rectangular cross section with lengths of up to tens of micrometres, a typical width of 50-150 nm, and a thickness of ～40?nm. A silicon-induced vapour-liquid-solid process was proposed for the formation of the ZnS nanobelts and their assembly. These oriented nanobelts have much faster response time to hydrogen gas than that of pure ZnO and Pd-sensitized ZnO, showing excellent hydrogen sensing properties.