Noor Hamizah Khanis

Structural- and optical-properties analysis of single crystalline hematite (α-Fe2O3) nanocubes prepared by one-pot hydrothermal approach

High quality single crystal hematite (α-Fe2O3) nanocubes with average dimensions of 40 nm were successfully synthesized by a facile one-pot hydrothermal method. Systematic analyses were performed to investigate the morphological-, structural- and optical-properties of the as-synthesized α-Fe2O3 nanocubes. Continuous formation and hourly monitoring towards proper arrangement of single crystal α-Fe2O3 nanocubes was observed throughout the hydrothermal heating process of 180 °C from 4 h to 12 h. The probable growth mechanism on the formation of cubic nanostructures is also proposed. Electron micrographs show the cubic α-Fe2O3 synthesized at the most optimum 8 h hydrothermal heating duration are indeed produced in high-yield with a well-defined cubical shape. The typical rhombohedral structure of cubic α-Fe2O3 was evident from the XRD pattern. The SAED pattern indicates that the α-Fe2O3 nanocubes are single-crystalline in nature, with lattice-fringes and a d-spacing value of 3.6 A. The optical characterization reveals that α-Fe2O3 nanocubes show strong visible-light absorption with a band gap energy of ∼2.1 eV while the photoluminescence emission spectra depicts a mono-peak centered at ∼590 nm. Both the SAED pattern and UV-vis spectra show a strong correlation with the standard α-Fe2O3. The as-synthesized α-Fe2O3 single crystal is of high quality that potentially could be used as a visible-light active nanomaterial in renewable energy device applications.

Self-assembly and secondary nucleation in ZnO nanostructures derived from a lipophilic precursor

The influence of organically capped nucleation on morphogenesis of zinc oxide (ZnO) as a technologically important iono-covalent material has been extensively investigated. However, the effect of lipid–lipid interactions on selective adsorption and the mechanism of growth is largely unknown. Here, we demonstrate a novel route toward synthesis of various ZnO nanostructures using zinc stearate, a metal soap, rather than the commonly utilised polar-soluble salts. Study of a variety of amphiphilic ligands suggests that during decomposition, secondary carboxylic acids substitute primary aliphatic tails in the precursor. In this regard, saturated and unsaturated fatty acids appear to influence the rate of progression quite differently. On the other hand, in the early stages of growth, amine adsorbates are inhibited by lipophilic tails of carboxylic acids, leading to a multi-step growth. The subsequent self-assembly of these nanorods into bundles is accompanied by recrystallisation of their stems and formation of planar defects which promote random secondary nucleation.

Investigations on the Role of N2:(N2 + CH4) Ratio on the Growth of Hydrophobic Nanostructured Hydrogenated Carbon Nitride Thin Films by Plasma Enhanced Chemical Vapor Deposition at Low Temperature

Nanostructured hydrogenated carbon nitride (CNx:H) thin films were synthesized on a crystal silicon substrate at low deposition temperature by radio-frequency plasma-enhanced chemical vapor deposition (PECVD). Methane and nitrogen were the precursor gases used in this deposition process. The effects of N2 to the total gas flow rate ratio on the formation of CNx:H nanostructures were investigated. Field-emission scanning electron microscopy (FESEM), Auger electron spectroscopy (AES), Raman scattering, and Fourier transform of infrared spectroscopies (FTIR) were used to characterize the films. The atomic nitrogen to carbon ratio and sp2 bonds in the film structure showed a strong influence on its growth rate, and its overall structure is strongly influenced by even small changes in the N2:(N2 + CH4) ratio. The formation of fibrous CNx:H nanorod structures occurs at ratios of 0.7 and 0.75, which also shows improved surface hydrophobic characteristic. Analysis showed that significant presence of isonitrile bonds in a more ordered film structure were important criteria contributing to the formation of vertically-aligned nanorods. The hydrophobicity of the CNx:H surface improved with the enhancement in the vertical alignment and uniformity in the distribution of the fibrous nanorod structures.

SnO2 Nanoparticles Decorated 2D Wavy Hierarchical Carbon Nanowalls with Enhanced Photoelectrochemical Performance

Two-dimensional carbon nanowall (2D-CNW) structures were prepared by hot wire assisted plasma enhanced chemical vapor deposition (hw-PECVD) system on silicon substrates. Controlled variations in the film structure were observed with increase in applied rf power during deposition which has been established to increase the rate of dissociation of precursor gases. The structural changes resulted in the formation of wavy-like features on the 2D-CNW, thus further enhancing the surface area of the nanostructures. The FESEM results confirmed the morphology transformation and conclusively showed the evolution of the 2D-CNW novel structures while Raman results revealed increase in ratio indicating increase in the presence of disordered domains due to the presence of open edges on the 2D-CNW structures. Subsequently, the best 2D-CNW based on the morphology and structural properties was functionalized with tin oxide (SnO2) nanoparticles and used as a working electrode in a photoelectrochemical (PEC) measurement system. Intriguingly, the SnO2 functionalized 2D-CNW showed enhancement in both Mott-Schottky profiles and LSV properties which suggested that these hierarchical networks showed promising potential application as effective charge-trapping medium in PEC systems.

The Effect of Hydrogen Dilution on the Morphology of Carbon Nanowalls Decorated Carbon Nanotubes Deposited by Hot-Wire r.f. Plasma Enhanced Chemical Vapour Deposition

An investigation on the effects of hydrogen (H2) gas dilution on the morphology and growth of carbon nanowalls (CNWs) decorated carbon nanotubes (CNTs) by hot-wire r.f. plasma enhanced chemical vapour deposition technique is presented. With the assistance of nickel nanoparticle catalyst, CNWs decorated CNTs formed only under the presence of 25% of H2 gas, relative to the methane (CH4) gas precursor. By varying the amount of H2 incorporated with CH4, the role of H2 dilution in the development of CNWs decorated CNTs was studied. Based on the FESEM and HRTEM results, it is hypothesized that H2 density and relative carbon radical concentration are the important parameters for the deposition of CNWs decorated CNTs. The effect of H2 dilution on the formation of CNWs decorated CNTs is presented.