Formation Of ZnO Particles Research Articles

Morphological, structural, electrical, and piezoelectric analysis of hydrothermally grown ZnO nanowires on various substrates

In this present work, we have successfully fabricated a piezoelectric structure based on ZnO nanowires (ZnO NWs) using a simple, low cost and environmentally friendly hydrothermal method. This structure forms the basis to fabricate vertically integrated nanogenerator device. This paper attempts to study the effect of several parameters such as the seed layer morphology, seed layer roughness, seed layer annealing temperature, growth temperature, and growth time on three different substrates, which are silicon substrate with a gold & platinum film as lower metal contact, and stainless steel. The structure and morphology of the seed layer and the as-obtained nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). SEM analysis shows that the non-aqueous seed solution must be stirred to avoid the formation of the two phases (milky and translucid) and thus the formation of ZnO particles with different sizes and morphologies. In addition, the annealing temperature influences the diameter of the ZnO seed layer and thus ZnO nanowires diameter. This work also shows that the length of the nanowires increases with the growth duration without affecting ZnO diameter (70 ± 30 nm). HR-TEM and XRD studies show the high crystalline quality of the one-dimensional nanomaterials deposited on stainless steel and confirm their high density along the c-axis direction. In this paper, we have also investigated the electrical and piezoelectric performances of the structure obtained. Indeed, the I-V curves exhibit nonlinear and asymmetric electrical characteristics, which confirms the formation of Schottky contacts between the metal and ZnO NWs. According to the piezo-response force microscope, an effective piezoelectric coefficient d33 between 5 and 7 pm/V as a function of the substrate was measured.

Application of Modified PANI-ZnO Composites for NH3Gas Sensor at Ambient Temperature

Polyaniline and zinc oxide nanoparticles were successfully synthesized through inverse emulsion polymerization method and hydrothermal method respectively. For ammonia gas sensing using LCR meter thin film of the composite was fabricated by using spin coater. The functional groups, morphological, optical, structural properties of zinc oxide nanoparticles, polyaniline (emeraldine salt) and composites were investigated by FTIR spectroscopy, Scanning electron microscopy (SEM), UV- Visible spectroscopy and XRD analysis. The formation of ZnO particles of different shapes in the nano range was confirmed from UV-visible and XRD analysis. UV visible spectrum shows the formation of nanoparticles of ZnO. Thin film of Polyaniline/zinc oxide composites were deposited on the surface of copper interdigitated electrode. The fabricated device showed sensitivity to ammonia gas (NH3) at ambient temperature (300 K). It was observed that the resistance is decreases with the increase of volume of ammonia gas. The electrical properties were also investigated of the different concentration of nanocomposite. Optimum sensing response was achieved with PANI in the presence of 50 wt% ZnO nanoparticles. It may also be inferred from this study that the solution mixing process to produce composites has promising future if handled carefully.

OPTOELECTRONIC PROPERTIES OF ZnO NANOPARTICLES DEPOSITION ON POROUS SILICON

In this work, a colloid of nanocrystalline ZnO particles was prepared by chemical method, and sprayed on porous silicon (PS) substrate which was prepared by electrochemical etching under a current density of 15 mA/cm2 for 10 min. The initial radius of the ZnO particles was found to be (2.2 nm). FTIR spectra exhibit the presence of Zn – O bond which indicates the formation of ZnO particles. Also spectra reveals the formation of SiH x(x = 1–2) and Si – O bond which indicates the presence of porous layer. High-performance rectification was obtained, with high photoresponsivity of 0.54 A/W at 400 nm. The corresponding quantum efficiency was 166.7%. The results show that ZnO on PS structures act as good candidates for making highly efficient photodiodes.

Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate

Formation of ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate in air atmosphere has been investigated using XRD, DTA, FT-IR, and FE-SEM as experimental techniques. ZnO as a single phase was produced by direct heating at ≥200 °C. DTA in air showed an endothermic peak at 195 °C assigned to the ZnO formation and exothermic peaks at 260, 315 and 365 °C, with a shoulder at 395 °C. Exothermic peaks can be assigned to combustion of an acetylacetonate ligand released at 195 °C. ZnO particles prepared at 200 °C have shown no presence of organic species, as found by FT-IR spectroscopy. Particles prepared for 0.5 h at 200 °C were in the nanosize range from ∼20 to ∼40 nm with a maximum at 30 nm approximately. The crystallite size of 30 nm was estimated in the direction of the a 1 and a 2 crystal axes, and in one direction of the c-axis it was 38 nm, as found with XRD. With prolonged heating of ZnO particles at 200 °C the particle/crystallite size changed little. However, with heating temperature increased up to 500 or 600 °C the ZnO particle size increased, as shown by FE-SEM observation. Nanosize ZnO particles were also prepared in two steps: (a) by heating of zinc acetylacetonate monohydrate up to 150 °C and distillation of water and organic phase, and (b) with further heating of so obtained precursor at 300 °C.

Influence of synthesis route on the formation of ZnO particles and their morphologies

The formation and microstructure of ZnO particles, obtained by mixing concentrated aqueous Zn(NO 3) 2 and NaOH solutions, were monitored by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM) and specific surface area measurement (BET). At 160 °C and a pH near 6, plate-like Zn 5(OH) 8(NO 3) 2(H 2O) 2 particles were formed at the beginning of the precipitation process, then quickly transformed into ZnO via a dissolution/reprecipitation mechanism. ZnO particles of different geometrical shapes, based on the hexagonal prism, were produced. Precipitation at 20 °C and pH near 6 yielded plate-like Zn 5(OH) 8(NO 3) 2(H 2O) 2 particles which were present up to 6 months of aging. Autoclaving of the precipitation system at 160 °C up to 72 h and a pH near 7 yielded only ZnO particles as pseudospheres, hexagonal dipyramids and an open form of the hexagonal pyramid. All these particles were made up of much smaller ZnO units. Only ZnO particles precipitated at 160 or 20 °C and a pH near 13. All ZnO particles, thus obtained, were plate-like and their size depended on the temperature and time of aging. BET measurements can be related with the size of ZnO particles, as inspected with FE-SEM. The FE-SEM inspection did not show any formation of microporous ZnO particles. The spectral shape of the corresponding FT-IR spectra can also be related to the geometrical shapes and size of ZnO particles.