Nor Fadilah Chayed

Band Gap Energies of Magnesium Oxide Nanomaterials Synthesized by the Sol-Gel Method

In this work, the band gap energies of magnesium oxide (MgO) were investigated to see if calcination time affects the band gap energies of the MgO. MgO nanomaterials have been prepared by a sol-gel method. MgO precursors produced were calcined at a temperature of 600 °C for 24 hours and 48 hours. The structural characterization of samples is achieved using X-Ray Diffraction (XRD) and the morphology as well as particle size of MgO were examined by Field Emission Scanning Electron Microscopy (FESEM). UV-Vis NIR spectroscopy was used to determine the band gap energies of the materials. From the results, the band gap energy of the MgO with a longer heating time exhibited a higher value.

Optical Band Gap Energies of Magnesium Oxide (MgO) Thin Film and Spherical Nanostructures

Magnesium oxide (MgO) is one of the metal oxides which has unique properties and has great potential applications in industry. In this work, MgO was synthesized by using a sol‐gel and solid state methods. The precursor of MgO was annealed at the temperature of 600 °C for 1 hour and 800 °C for 24 hours for sol‐gel method. For solid state method, magnesium acetate was annealed at the temperature of 800 °C for 24 hours. These samples were characterized by using X‐Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). TEM micrographs show the morphology of the samples of the sol‐gel method are thin film nanostructures whereas sample of the solid state method is spherical shape. The band gap energies of the samples were measured using UV‐Vis NIR Spectrophotometer. The band gap values of the samples were calculated and it was found that there is a difference of band gap energies between samples employing different synthesis route.

Band gap widening and quantum tunnelling effects of Ag/MgO/p-Si MOS structure

MgO films of various thicknesses were fabricated via the pulsed laser deposition method. The MgO thin films obtained have the advantage of high quality mirror finish, good densification and of uniform thickness. The MgO thin films have thicknesses of between 43 to 103 nm. They are polycrystalline in nature with oriented growth mainly in the direction of the [200] and [220] crystal planes. It is observed that the band gap of the thin films increases as the thickness decreases due to quantum effects, however, turn-on voltage has the opposite effect. The decrease of the turn-on as well as the tunnelling voltage of the thinner films, despite their larger band gap, is a direct experimental evidence of quantum tunnelling effects in the thin films. This proves that quantum tunnelling is more prominent in low dimensional structures.

Influence of Carbon Additives on Cathode Materials, LiCoO2 and LiMn2O4

Carbon additives are very important components of cathodes in Li-ion batteries. This is because carbon is an electronic conductor whereas cathode materials are ionic conductors. Without the presence of carbon, the electrons will not be able to flow and there will be space charge built-up in the materials. Carbon therefore facilitates the conductivity of charged species in the cathode materials and help to disperse the negative charge accumulation which may otherwise impede Li-ion diffusion within the cathodes. In this work, two types of carbon, namely, activated carbon (micron sized) and Denka Black (nano sized) were used in conjunction with the cathode materials LiCoO2 and LiMn2O4. The amounts of cathode materials were kept constant while the amounts of carbon additives were varied. Galvanostatic charge-discharge was done over a voltage range of 4.2 V to 3.2 V. Results showed that Denka Black gives improved performance for both cathode material. This is believed to be due to the effect of nano sized particles of Denka Black.

Comparison of experimental and first-principle results of band-gap narrowing of MgO nanostructures and their dependence on crystal structural parameters

From experimental investigations of the bandgaps of magnesium oxide (MgO) nanostructures, the results show that band-gap narrowing occurred as the physical dimension of the MgO crystallites decrease. This is in contrast to other metal oxides such as ZnO. To obtain insights on this observed phenomenon, the first-principle studies using density functional theory were carried out. The strategy used here is different from the normal theoretical studies, such that information of the structural characterization obtained from experimental X-ray diffraction (XRD) data via the Rietveld method was used in the calculations. This is important, because nanostructures do not possess the same crystal parameters as the bulk and accurate real structural parameters should be used in the calculations. Based on these values, the crystal structures were simulated and the electronic band structures were calculated within the density functional theory (DFT). Results from the density of state (DOS) studies shows that the band-gap narrowing is due to the shifting of the valence and conduction bands. From our theoretical results, we can conclude that the narrowing of the bandgaps of MgO nanostructures is a consequence of the increase of their lattice parameters. The calculated results exhibit this trend and are in good agreement with the experimental results.

MgO nanoparticles via a simple solid-state reaction

Normally, nanoparticles were obtained by complex and tedious methods. In this work, magnesium oxide (MgO) nanoparticles were prepared by a simple solid-state reaction method without assistance of any other additives. Magnesium acetate tetrahydrate was used as the starting material and directly annealed at 800 °C for 6 h, 12 h and 24 h. All the samples were characterized using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). All the annealed samples obtained were pure, single phase of cubic structure with space group Fm-3m. SEM results show that all the samples have rounded shape with crystallite size is between 20 to 135 nm. Thus, nanoparticles of MgO can be easily obtained via a simple solid-state reaction method.

MgO Nanostructured Materials Obtained Via the Solid-State Reaction Method

Recently, several synthesis methods have been reported for producing magnesium oxide (MgO) nanostructures such as sol-gel, combustion, thermal evaporation, chemical precipitation, etc. This work describes a simple method to synthesize MgO nanostructures via a conventional solid-state reaction method using magnesium acetate tetrahydrate as a starting material. Magnesium acetate tetrahydrate was directly annealed at a temperature of 600 °C and 800 °C for 24 h. The X-Ray Diffraction (XRD) revealed that the annealed samples were pure while Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) showed different morphologies of MgO. From the results, it is found that TEM may reveal information that cannot be observed in the SEM micrographs.

Effect of Synthesis Method on the Nanostructures of Magnesium Oxide (MgO) and their Band Gap Energies

Magnesium oxide (MgO) is a metal oxide which has many applications in industry and can be synthesized by many different synthesis methods. In this study, MgO was synthesized by using two different methods which were sol-gel and solid-state reaction methods. Both samples were annealed at 800 oC for 24 hours and characterized by using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The band gap energies for both samples were determined by using UV-Vis NIR Spectroscopy. The band gap values of the samples are evaluated from the data. It was found that the band gap energies of the MgO using different synthesis route were not the same.