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Effect of Reactor Pressure on Electrical and Structural Properties of Diamond Films Grown by Hot-Filament CVD

100%
Ullah M., Ahmed E., Rana A.
Acta Physica Polonica A
|
2017
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vol. 131
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issue 6
1419-1425
EN
Polycrystalline diamond films with preferred (111) and (222) facets were fabricated inside hot filament chemical vapour deposition reactor on silicon wafers using a mixture of 1% methane in hydrogen at various reactor pressures ranging from 10 to 50 mbar. Regarding characterization of diamond films, internal texture, surface morphology, quality of diamond and electrical conductivity were investigated using X-ray diffraction, scanning electron microscopy, the Raman spectroscopy and four-point-probe van der Pauw techniques, respectively. Results of these studies demonstrate that polycrystalline diamond structure is grown in random orientation with (111) facet being dominant showing sharp grain boundaries. Moreover, growth rate was found to increase with pressure up to 20 mbar and then decreased for further rise in pressure. That is why grain density is high with relatively smaller grains at higher pressures caused by higher nucleation rates. In contrast, electrical resistivity decreased ≈3 orders of magnitude showing a minimum at 2.9×10⁶ Ω cm as pressure was increased in the reactor. Reactor pressure during film growth resulted in poor surface morphology, absence of sp³ bonds and low resistivity. Hence, decrease of resistivity makes diamond films desirable for many electrical applications in semiconducting/electronic devices.
2
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Study of the Effect of Boron Concentration on Magnetic and Structural Properties of Nd_{7.5}Pr_{2.5}Fe_{90-x}B_x Melt-Spun Alloys

100%
Siddique M., Ahmad I., Kanwal M., Ahmed E.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
353-357
EN
The Mössbauer spectroscopy and X-ray diffraction techniques have been used to investigate the effect of boron concentration on the structural and magnetic properties of as-quenched and heat-treated melt-spun alloys Nd_{7.5}Pr_{2.5}Fe_{90-x}B_x (x=6, 8, 10) produced by melt-spinning technique. X-ray diffraction and Mössbauer spectroscopy results indicate that as-prepared samples are completely amorphous in nature. The X-ray diffraction patterns of samples heat-treated at 700°C are indexed as Fe_{3}B, α -Fe, (NdPr)_{2}Fe_{14}B and Fe_{23}B_{6} phases. The Mössbauer spectra of heat-treated samples are very complex and constituted a number of sextets and a quadrupole doublet. Two main phases are (NdPr)_{2}Fe_{14}B hard and t-Fe_{3}B soft magnetic phases while α -Fe and Nd_{23}Fe_{6} are detected as minor phases. The average internal magnetic field decreases with the increase of boron content; more sharply in as-prepared and comparatively slowly in heat-treated samples. The X-ray diffraction and Mössbauer spectroscopy results are in good agreement with each other.
3
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Thermal Effect of Er³⁺ Ions Embedded in Smart Nano-Composite Oxide Material Prepared by Sol-Gel Technique

88%
Battisha I., Ayoub M., Hashem A., Ahmed E., Amin A.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 4
1277-1283
EN
The phosphosilicate for planar waveguides fabrication by using sol-gel, and particularly erbium-doped waveguide amplifiers, is reviewed. In particular, efforts to use sol-gel to improve molecular homogeneity in Er-doped phosphosilicate-based monolith and thin films will be discussed. A variety of material studies was carried out to investigate and optimize the sample preparation condition for such application. These include X-ray diffraction, the Fourier transform infrared and optical transmittance, absorption and refractive index calculation. The erbium nitrate precursors use is shown to alter the Er³⁺ ions doping in the prepared samples thermally treated in the final monolith glass form, in comparison to the use of thin film phosphosilicate sol-gel sample. Excess heat treatment is used to force prepared samples crystallization, moreover resulting photoluminescence analysis is used to detect the co-operative-up-conversion sample properties before and after heating.
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