Synthesis and characterisation of low- dimensional zinc oxide nanostructures by solution-immersion and mist-atomisation / Zuraida Khusaimi

Zinc oxide (ZnO) nanostructures on gold-seeded silicon (Si) substrate were prepared using a low-temperature solution-immersion method. Optimised ZnO structures were then used as a template to grow a second layer of ZnO nanostructures by mistatomisation method. Low-dimensional, vertically-aligned ZnO nanorods were successfully synthesised by the solution-immersion method through optimisation of the reaction parameters, such as concentration of precursor, ratio of stabiliser, alignment of substrate in solution, heating medium, gold-seeded substrates and its thickness, transition metal-seeded substrates, immersion temperature and time, pH of precursor solution, annealing temperature and doping with Mg. SEM, FESEM, TGA, FTIR, XRD, EDX, PL-Raman and I-V were the selected characterisation tools to analyse the structural, morphological, bonding, optical and electrical properties of the nanostructures. TGA and FTIR analyses gave evidence that the prepared ZnO nanostructures were pure with no traces of starting material or contamination. The results give evidence that 6 nm thickness of gold-seeded on Si substrate immersed for 4 hours at 70°C in precursor concentration of 0.005 – 0.05 M zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and hexamethylenetetramine (HMTA) at 1:1 ratio has successfully formed (002) plane, c-axis, aligned ZnO nanorods with diameter of approximately 60 ± 20 nm. The nanorods prepared at low immersion temperatures were found to be readily crystalline with no additional heat treatment. Precursor solution of pH 6.8 and 5 produced ZnO nanorods, while at pH 9 produced ZnO flower-like structures. 1 atomic % of Mg-doped ZnO nanorods were found to produce the highest electrical conductivity relative to as-prepared ZnO, and higher doping content of 3, 5, 7 and 9 atomic %. PL emission spectra of ZnO nanorods consistently produced UV (362-388 nm) and visible emissions (400-800 nm), confirming the formation of a semi-conducting ZnO

Palm oil as the carbon source for the synthesis of carbon nanotubes using floating catalyst - chemical vapour deposition method

CNTs were synthesized using floating catalyst by dual‐furnace thermal chemical vapour deposition method at 800–1000° C. Cooking oil made of palm oil was used as the carbon precursor. Ferrocene in the presence of 0.05 M zinc nitrate and a p‐type silicon wafer was used as a catalyst precursor and a sample target, respectively. The deposition temperature was varied from 800–1000° C. Nitrogen gas was used as a gas carrier with a constant flow rate of 150 sccm/min. Field emission scanning electron micrographs show the formation of CNTs together with other carbons formed on the silicon substrate. Raman spectroscopy studies were also supported the formation of CNTs

Enhancing the performance of self-powered ultraviolet photosensor using rapid aqueous chemical-grown aluminum-doped titanium oxide nanorod arrays as electron transport layer

Aluminum (Al)-doped titanium dioxide nanorod arrays (ATNs) were grown on fluorine-doped tin oxide-coated glass at different Al atomic concentrations ranging from 1 at.% to 5 at.% in a Schott bottle through single-step aqueous chemical growth for self-powered photoelectrochemical cell-type ultraviolet (UV) photosensor applications. X-ray diffraction patterns showed that the grown ATNs exhibited a crystalline rutile structure. The ATNs showed smaller crystallite size and average nanorod diameter and length compared with the undoped sample. The photocurrent measured from the fabricated UV photosensors improved to some extent with increasing Al-dopant concentration. Samples with 2 at.% Al showed the maximum photocurrent of 108.87 μA/cm2 at 0 V bias under UV irradiation (365 nm, 750 μW/cm2). The results show that high-performance UV photosensors can be fabricated and enhanced using ATNs easily prepared in a glass container

The properties of sonicated immersion grown hematite films at various annealing temperatures

In this research, hematite (α-Fe2O3) film was synthesized to study the effect of annealing temperature on its crystallinity, optical and electrical properties. Through a sonicated solution immersion technique, hematite films were deposited on a fluorine-doped tin oxide (FTO) glass substrate. In the synthesis process, 0.2 M ferric chloride (FeCl3·6H2O) was used as a precursor, 0.2 M urea (NH2CONH2) as the stabilizer, and de-ionized (DI) water as a solvent to produce 200 ml of aqueous solution. During the annealing treatment, we varied the temperatures at 350 ºC, 450 ºC and 500 ºC. The X-ray diffraction (XRD) pattern revealed the presence of peaks of 2θ angles between 20° to 90°, corresponding to (104), (110), (214), (125) and (128) planes, which exhibited crystalline structures of rhombohedral with diffraction peaks of hematite phase (α-Fe2O3). Optical characterizations showed that the transmittances of all samples were close to 100% in the high wavelength level of the visible light region, which is close to the infrared spectrum. Absorption of hematite samples was found to be more than 0.6 a.u. in the low wavelength level of the visible light region close to the ultraviolet spectrum and close to 0 in the high wavelength level of the visible light region close to the infrared spectrum. A sample with an annealing temperature of 500 °C has the lowest transmission and the highest absorbance in the visible region due to dim pigments in the hematite film

Effect of different coating layer on the topography and optical properties of ZnO nanostructured

Magnesium (Mg) and aluminum (Al) co-doped zinc oxide (MAZO) thin films were synthesized on glass substrate by sol-gel spin coating method. MAZO thin films were prepared at different coating layers range from 1 to 9. Atomic Force Microscopy (AFM) was used to investigate the topography of the thin films. According to the AFM results, Root Means Square (RMS) of MAZO thin films was increased from 0.747 to 6.545 nm, with increase of number coating layer from 1 to 9, respectively. The results shown the variation on structural and topography properties of MAZO seed film when it's deposited at different coating layers on glass substrate. The optical properties was analyzed using UV-Vis spectroscopy. The obtained results show that the transmittance spectra was increased as thin films coating layer increases

Effect of co-doping process on topography, optical and electrical properties of ZnO nanostructured

We investigated of Undoped ZnO and Magnesium (Mg)-Aluminium (Al) co-doped Zinc Oxide (MAZO) nanostructured films were prepared by sol gel spin coating technique. The surface topography was analyzed using Atomic Force Microscopy (AFM). Based on the AFM results, Root Mean Square (RMS) of MAZO films have rougher surface compared to pure ZnO films. The optical and electrical properties of thin film samples were characterized using Uv-Vis spectroscopy and two point probes, current-voltage (I-V) measurements. The transmittance spectra for both thin samples was above 80% in the visible wavelength. The MAZO film shows the highest conductivity compared to pure ZnO films. This result indicates that the improvement of carrier mobility throughout doping process and possibly contribute by extra ion charge

Structural and electrical properties of ZnO and SiO doped ZnO powder for varistor application

Pure zinc oxide ( ZnO ) and silica (SiO ) doped ZnO nanopowders have been prepared using solid state method. SiO were doped into ZnO at different weight percentage 1 and 3 wt.%. The structural and electrical properties of ZnO and SiO doped ZnO powder have been characterized using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and electro source meter. From the results, the XRD pattern were compatible with ZnO phase structure. Based on the SEM images, the grain size of ZnO varistor is increased when doped with SiO . The obtained value of nonlinear coefficient (α) of undoped ZnO sample is low compared to SiO doped ZnO varistor . The, α value is increased as the content of SiO doped increases. The maximum value of α is at 3 wt.% of SiO doped ZnO which is 1.734 that might be can enhanced the performance of varistor . Thus, the properties of ZnO varistor can be improved when doped with SiO

Effects of Annealing Environments on the Solution-Grown, Aligned Aluminium-Doped Zinc Oxide Nanorod-Array-Based Ultraviolet Photoconductive Sensor

We have fabricated metal-semiconductor-metal- (MSM-) type ultraviolet (UV) photoconductive sensors using aluminium- (Al-) doped zinc oxide (ZnO) nanorod arrays that were annealed in different environments: air, oxygen, or a vacuum. The Al-doped ZnO nanorods had an average diameter of 60 nm with a thickness of approximately 600 nm that included the seed layer (with thickness ~200 nm). Our results show that the vacuum-annealed nanorod-array-based UV photoconductive sensor has the highest photocurrent value of   2.43  ×  10-4 A. The high photocurrent is due to the high concentration of zinc (Zn) interstitials in the vacuum-annealed nanorod arrays. In contrast, the oxygen-annealing process applied to the Al-doped ZnO nanorod arrays produced highly sensitive UV photoconductive sensors, in which the sensitivity reached 55.6, due to the surface properties of the oxygen-annealed nanorods, which have a higher affinity for oxygen adsorption than the other samples and were thereby capable of reducing the sensor’s dark current. In addition, the sensor fabricated using the oxygen-annealed nanorod arrays had the lowest rise and decay time constants. Our result shows that the annealing environment greatly affects the surface condition and properties of the Al-doped ZnO nanorod arrays, which influences the performance of the UV photoconductive sensors