Iranian Journal of Materials Science and Engineering

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Abstract:

fabricated. Modifications carried out in different parts of the old system in order to control most

of the growth parameters with more accuracy. The fabricated system was used to grow sapphire

single crystals with almost 10 mm in diameter and 50 mm in length. The crystallinity and

structure of the grown crystals were characterized by computer aided single crystal X-ray

diffraction technique.

A Verneuil system, more sophisticated than a conventional one, has been designed and

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Abstract: In this research work, crystallization kinetics of Fe55Cr18Mo7B16C4 alloy was evaluated by X-ray diffraction, TEM observations and differential scanning calorimetric tests. In practice, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates. Results showed that a two -step crystallization process occurred in the alloy in which - Fe phase was crystallized in the first step after annealing treatments. Activation energy for the first step of crystallization i.e. - Fe was measured to be 276 (kj/mol) according to Kissinger model. Further, avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline á – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

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Abstract: Different thickness of Cu2S thin films were prepared by vacuum evaporation under a pressure of 10-6 torr at an evaporation rate of 3Å /sec. Cu2S has direct band gap energy and indirect band gap energy at 1.2eV and 1.8 eV respectively. This paper presents the analysis of structural and optical properties of the Cu2S thin film by X-ray diffractometer (XRD) and UV-Vis-NIR Spectrophotometer. XRD studies showed ploycrystallinity of CuXS thin films at higher thickness. Optical spectra of Cu2S film exhibit high transmittance in the visible region and high absorbance in the near infra-red region. Moreover, the optical property of the film confirms that transmission mainly depends on the thickness of the film. Structural and resistivity property reveals that Cu2S film at higher thicknesses shows slight deviations in stoichiometry. Possible applications of the Cu2S thin films are also discussed.

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Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated using X-ray diffraction, differential scanning calorimetric (DSC) tests and TEM observations in this research work. In effect, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models (i.e. Kissinger- Starink, Ozawa, and Matusita methods). Results showed that a two -step crystallization process occurred in the alloy in which α - Fe and Fe3B phases were crystallized respectively in the structure after heat treatment. Activation energy for the first step of crystallization i.e., α - Fe was measured to be 421 (kj/mol) and 442 (kj/mol) according to both Kissinger- Starink and Ozawa models respectively. Further, Avrami exponent calculated from DSC curves was 1.6 and a two -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. TEM observations reveal that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology

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Boron included aluminium nitride (B-AlN) thin films were synthesized on silicon (Si) substrates through chemical vapour deposition ( CVD ) at 773 K (500 °C). tert-buthylamine (^tBuNH₂) solution was used as nitrogen source and delivered through gas bubbler. B-AlN thin films were prepared on Si-100 substrates by varying gas mixture ratio of three precursors. The structural properties of the films were investigated by X-ray diffraction (XRD) technique and verified the formation of polycrystalline and mixed phases of hexagonal (100), & (110) oriented AlN and orthogonal (002) & cubic (333) oriented BN. The crystallite size was smaller and dislocation density was higher as the deposition was conducted with lowest total gas mixture ratio (25 sccm). Improved surface properties were detected for film deposited using lowest total gas mixture ratio and confirmed by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The composition of films showed the existence of higher concentration of B in the film prepared using lower total gas mixture ratio and confirmed by energy dispersive X-ray Spectroscopy (EDX).

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Copper oxide thin layers were elaborated using the sol-gel dip-coating. The thickness effect on morphological, structural, optical and electrical properties was studied. Copper chloride dihydrate was used as precursor and dissolved into methanol. The scanning electron microscopy analysis results showed that there is continuity in formation of the clusters and the nuclei with the increase of number of the dips. X-ray diffractogram showed that all the films are polycrystalline cupric oxide CuO phase with monoclinic structure with grain size in the range of 30.72 - 26.58 nm. The obtained films are clear blackin appearance, which are confirmed by the optical transmittance spectra. The optical band gap energies of the deposited films vary from 3.80 to 3.70 eV. The electrical conductivity of the films decreases from 1.90.10^-2 to 7.39.10^-3 (Ω.cm)^-1

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Temperature is one of the key factor that affecting the electrical, physical, structural, and morphological properties as well as the crystallinity of the nanomaterials. The current study investigates the effect of annealing temperature on the structural and electrical properties of lanthanum oxide (La2O3) thick films. La2O3 thick films were prepared on a glass substrate using a conventional screen printing technique. In this work, T1 is an unannealed prepared film, whereas T2 and T3 are annealed in a muffle furnace for 3 hours at 350°C and 450°C, respectively. XRD technique was exploited to investigate the crystallization behavior of the films. It was found that the crystal structure of La2O3 thick films are pure hexagonal phase. The annealing temperatures were revealed to have influence on the crystallite sizes of the films. SEM and EDS was used to study the morphology and elemental analysis of the films respectively. The electrical properties of the films were explored by measuring resistivity, temperature coefficient of resistivity (TCR), and activation energy at lower and higher temperatures regions. The film annealed at 450°C has high resistivity, a high TCR, and small crystallite size. The thickness of the La2O3 thick films was also found to decrease as the annealing temperature increased.

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This work aims to prepare and study amorphous carbon nitride (CNx) films. Films were deposited by reactive magnetron radiofrequency (RF) sputtering from graphite target in argon and nitrogen mixture discharge at room temperature. The ratio of the gas flow rate was varied from 0.1 to 1. Deposited films were found to be amorphous. Highest Nitrogen concentration achieved was 42 atomic percent which is very rare and therefore, the highest nitrogen to carbon atomic ratio was 0.76. The incorporation of nitrogen promotes the clustering of diamond-like sites at the expense of graphitic ones leading to the decrease of the disorder. The film surface becomes rough with increasing nitrogen concentration. Films are optically transparent in the 200-900 nm wavelength range with a wide gap varying between 3.59 and 3.63 eV. There is an increase in resistivity from 15 to 87.4 x10^-3Ω.cm for a-CN_x thin films for 0.1< R_F < 0.8 and a less decrease for   R_F > 0.8. Pore size increases in the films, but has little influence on band gaps. On the other hand, increasing the pore size reduces electrical interaction between particles by increasing resistivity.

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