Nurhanna Badar

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.

Solid Solutions of LiCo1-xNixO2(x=0,0.1,...,0.9) Obtained via a Combustion Synthesis Route and Their Electrochemical Characteristics.

Pure, single-phase and layered materials with good cation ordering are not easy to synthesize. In this work, solid solutions of (x = 0, 0.1, …, 0.9) are synthesized using a self-propagating combustion route and characterized. All the materials are observed to be phase pure giving materials of hexagonal crystal system with R-3m space group. The RIR and R factor values of stoichiometries of (x = 0.1, 0.2, 0.3, 0.4, and 0.5) show good cation ordering. Their electrochemical properties are investigated by a series of charge-discharge cycling in the voltage range of 3.0 to 4.3 V. It is found that some of the stoichiometries exhibit specific capacities comparable or better than those of LiCoO2, but the voltage plateau is slightly more slopping than that for the LiCoO2 reference material.

Mn Substitution with Co in LiCo(1-X)MnxO2 Cathode Materials and their Charge-Discharge Characteristic

LiCoO2 has been used as a cathode material in commercial Li-ion batteries. This is due to advantageous properties of the LiCoO2 like ease of preparation and good electrochemical characteristics. However, the high cost and toxicity of Co has limited its use. Therefore, the substitution of Co in the LiCoO2 by non-toxic and inexpensive transition metallic element is needed. Mn is considered as one of the promising candidates to fulfill all the requirements. Partial substitution of Co by Mn has also been considered to enhance the stability of LiCoO2 lattice, minimize capacity fading and increase cycle life of the Li-ion battery. LiCo(1-x)MnxO2 (x= 0.1, 0.2, 0.3) were prepared by using a self-propagating combustion (SPC) method. X-ray diffraction (XRD) of the samples were carried out for phase analysis and showed that all the materials are pure. The samples were also analyzed using the Field Emission Scanning Electron Microscope (FESEM) to study its morphology and particle size. Finally cathodes were fabricated and assembled in an inert gas-filled fabrication box. Discharge profiles of the materials were carried out in the voltage range of 4.3 V – 3 V. The materials obtained were phase pure and improved the capacity fading of the materials compared to LiCoO2. All of the materials exhibited less than 10% capacity loss even though it does not improve the first cycle discharge capacity.

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.

Characterization of Al2O3 thin films deposited by PLD

Aluminium Oxide (Al2O3) thin films have been widely used in many kinds of applications due to their excellent properties such as good mechanical strength, high abrasive and insulating characteristics. In this work, Al2O3 thin films are deposited on silicon (100) substrates using pulsed laser deposition (PLD). The deposition is done using different chamber environments. The crystal structure of the thin films is investigated using Grazing Incidence Diffraction (GID). The surface morphology and thicknesses of the thin films are studied by Field Emission Scanning Electron Microscopy (FESEM). The electrical current-voltage (I-V) characteristics of the thin films are measured using Signaton H150 Probe Station with Keithly 302 source measurement. It was found that the different process parameters greatly influenced the characteristics of the thin films obtained. FESEM images show high quality, smooth and dense films obtained using the PLD method. Generally, all films show rectifying behaviour.

Synthesis and Characterization of Fe2O3 Prepared Via Sol-Gel Method

Fe2O3 was synthesized via a sol-gel method. Pure, single phase materials were obtained at 300 °C and 800 °C heated for 24 hours. The conductivies of the materials were investigated using a.c. impedance spectroscopy. It was found that the material annealed at a lower temperature gives better conductivity value of about two orders of magnitude higher.

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.

Synthesis and Characterization of Al2O3 by Using a Combustion Synthesis Method

Aluminium oxide is one of the metal oxides that can exist in many phases such as α, θ, η etc. All the phases obtained are affected by annealing temperature and synthesis route. In this research the Al2O3 powders were synthesized by the combustion method using triethanolamine as fuels. A pure η phase as well as a mixed α and η phases were obtained. The size and morphology of Al2O3 particles were studied using scanning electron microscopy (SEM).

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.