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Synthesis and characterization of Zn/ZnO microspheres on indented sites of silicon substrate

Ahmed N., Majid A., Khan M. A., Rashid M., Umar Z. A., Baig M. A.

Materials Science Poland

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2018

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Vol. 36, No. 3

501--508

EN

Self-assembled Zn/ZnO microspheres have been accomplished on selected sites of boron doped P-type silicon substrates using hydrothermal approach. The high density Zn/ZnO microspheres were grown on the Si substrates by chemical treatment in mixed solution of zinc sulfate ZnSO4·7H2O and ammonium hydroxide NH4 (OH) after uniform heating at 95 degrees C for 15 min. The Zn/ZnO microspheres had dimensions in the range of 1 pm to 20 pm and were created only on selected sites of silicon substrate. The crystal structure, chemical composition and morphology of as-prepared samples were studied by using scanning electron microscope SEM, X-ray diffraction XRD, energy dispersive X-ray spectroscopy EDS, Fourier transform infrared spectroscopy FT-IR and UV-Vis diffuse reflectance absorption spectra DRS. The energy band gap Eg of about 3.28 eV was obtained using Tauc plot. In summary, this study suggests that interfacial chemistry is responsible for the crystal growth on indented sites of silicon substrate and the hydrothermal based growth mechanism is proposed as a useful methodology for the formation of highly crystalline three dimensional (3-D) Zn/ZnO microspheres.

2

First principle calculations of electronic and magnetic properties of Mn-doped CdS (zinc blende): a theoretical study

Ahmed N., Nabi A., Nisar J., Tariq M., Javid M. A., Nasim M. H.

Materials Science Poland

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2017

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Vol. 35, No. 3

479--485

EN

The electronic structure and magnetic properties of Mn doped zinc blende cadmium sulfide Cd1-xMnxS (x = 6.25 %) have been studied using spin-polarized density functional theory within the framework of Generalized Gradient Approximation (GGA), its further corrections including Hubbard U interactions (GGA + U) and a model for exchange and correlation potential Tran Blaha modified Becke-Johnson (TB-mBJ). Ferromagnetic interactions have been observed between Mn atoms via S atom due to strong p-d hybridization. The magnetic moments on Mn and its neighboring atoms have also been studied in detail using different charge analysis techniques. It has been observed that p-d hybridization reduced the value of local magnetic moment of Mn in comparison to its free space charge value and produced small local magnetic moments on the nonmagnetic S and Cd host sites. The magnetocrystalline anisotropy in [1 0 0] and [1 1 1] directions as well as exchange splitting parameters Noα and Noβ have been analyzed to confirm that ferromagnetism exists. We conclude that the ferromagnetic phase in Mn-doped CdS is not stable in “near” configuration but it is stable for “far” configuration. Mn doped CdS is a p-type semiconductor and the d-states at the top of the valence band edge give a very useful material for photoluminescence and magneto-optical devices.

3

Effects of Triangular Core Rotation of a Hybrid Porous Core Terahertz Waveguide

Ali S., Ahmed N., Alwee S., Islam M., Rana S., Bhuiyan T.

International Journal of Electronics and Telecommunications

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2017

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Vol. 63, No. 1

25--31

EN

In this paper, we investigate the effects for rotating the triangular core air hole arrangements of a hybrid design porous core fiber. The triangular core has been rotated in anticlockwise direction to evaluate the impact on different waveguide properties. Effective Material Loss (EML), confinement loss, bending loss, dispersion characteristics and fraction of power flow are calculated to determine the impacts for rotating the triangular core. The porous fiber represented here has a hybrid design in the core area which includes circular rings with central triangular air hole arrangement. The cladding of the investigated fiber has a hexagonal array of air hole distribution. For optimum parameters the reported hybrid porous core fiber shows a flat EML of ±0.000416 cm⁻¹ from 1.5 to 5 terahertz (THz) range and a near zero dispersion of 0.4±0.042 ps/THz/cm from 1.25 to 5.0 THz. Negligible confinement and bending losses are reported for this new type of hybrid porous core design. With improved concept of air hole distribution and exceptional waveguide properties, the reported porous core fiber can be considered as a vital forwarding step in this field of research.

4

DHI evaluation by combining rock physics simulation and statistical techniques for fluid identification of Cambrian-to-Cretaceous clastic reservoirs in Pakistan

Ahmed N., Khalid P., Shafi H. M. B., Connolly P.

Acta Geophysica

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2017

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Vol. 65, no. 5

991--1007

EN

The use of seismic direct hydrocarbon indicators is very common in exploration and reservoir development to minimise exploration risk and to optimise the location of production wells. DHIs can be enhanced using AVO methods to calculate seismic attributes that approximate relative elastic properties. In this study, we analyse the sensitivity to pore fluid changes of a range of elastic properties by combining rock physics studies and statistical techniques and determine which provide the best basis for DHIs. Gassmann fluid substitution is applied to the well log data and various elastic properties are evaluated by measuring the degree of separation that they achieve between gas sands and wet sands. The method has been applied successfully to well log data from proven reservoirs in three different siliciclastic environments of Cambrian, Jurassic, and Cretaceous ages. We have quantified the sensitivity of various elastic properties such as acoustic and extended elastic (EEI) impedances, elastic moduli (Ksat and Ksat – μ), lambda–murho method (λρ and μρ), P-to-S-wave velocity ratio (VP/VS), and Poisson’s ratio (σ) at fully gas/water saturation scenarios. The results are strongly dependent on the local geo-logical settings and our modeling demonstrates that for Cambrian and Cretaceous reservoirs, Ksat – μ, EEI, VP/VS, and σ are more sensitive to pore fluids (gas/water). For the Jurassic reservoir, the sensitivity of all elastic and seismic properties to pore fluid reduces due to high overburden pressure and the resultant low porosity. Fluid indicators are evaluated using two metrics: a fluid indicator coefficient based on a Gaussian model and an overlap coefficient which makes no assumptions about a distribution model. This study will provide a potential way to identify gas sand zones in future exploration.

5

Probabilistic seismic hazard analysis for the city of Quetta, Pakistan

Rehman S., Lindholm C., Ahmed N., Rafi Z.

Acta Geophysica

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2014

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Vol. 62, no. 4

737--761

EN

Seismic hazard assessment for Quetta is carried out using probabilistic seismic hazard analysis technique based on area sources and augmented by line source used for the first time in Pakistan. Seismic data has been collected and analyzed in spatial and temporal domains. Five Seismic Zones have been modeled in line with tectonics of the region with b-value of 1.14 using regression. The b-value is slightly higher, which is attributed to the fact that aftershocks were not removed as it distorted the dataset. Five fault sources are modeled, with three as reverse and two as strike-slip with 7.8 as maximum magnitude. Mach Structure is included in the tectonics for the first time. The attenuation relation used in the present study is recommended by various researchers. The expected Peak Ground Acceleration for 500-year return period is 4.79 m/s2 for rock outcrop and characterized as very high. Furthermore, variation in spectral acceleration within Quetta city is observed, for which spectral curves are developed for four different places.

6

Fabrication of magnesium aluminum silicate glass ceramics by sintering route

Durrani S. K., Hussain M. A., Hussain S. Z., Hussain S. Z., Akhtar J., Saeed A., Hussain N., Ahmed N.

Materials Science Poland

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2010

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Vol. 28, No. 2

459--466

EN

Magnesium aluminum silicate (MAS) glass ceramic material was prepared by the sintering route. A three-stage heat treatment, consisting of calcination, nucleation and crystallization, was developed with MgF2 as a nucleating agent. The effect of the percentage chemical composition and the sintering temperature on the density of the compacted material was also studied. The thermal stability of MAS was measured by thermogravimetry (TG), differential thermal analysis (DTA). TG/DTA studies revealed that the powder exists as MgO-Al2O3-SiO2-H2O in solid state, and then transforms to MgO-Al2O3-SiO2 via some metastable intermediates above 300 °C. The microstructure and phases were analyzed by X-ray diffractometry (XRD). XRD analysis revealed the formation of various phases such as magnesium silicate, fluorophlogopite, nobergite, siliminite etc. at various processing temperatures.

7

Serum glycoproteins in diabetic and non-diabetic patients with and without cataract

Gul A., Rahman A. M., Ahmed N.

Optica Applicata

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2008

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Vol. 38, nr 3

531-538

EN

This study describes the changes in serum glycoproteins from type 2 diabetic and non-diabetic patients with and without cataract. A total of 85 subjects were selected for the study and divided into four groups. The first group consisted of 21 healthy subjects, the second group consisted of 21 diabetic patients with no chronic complications, the third group consisted of 20 diabetic patients with cataract, and the fourth group had 23 non-diabetic patients with age related cataract. The patients with and without cataract were selected on clinical grounds from the Ziauddin University and Jinnah Postgraduate Medical Centre in Karachi, Pakistan. As expected diabetic patients with and without cataract had significantly higher levels of fasting plasma glucose, glycated haemoglobin, glycated plasma proteins and serum fructosamine. In addition to these parameters, the levels of hexosamine, sialic acid and serum total protein were higher in diabetic compared to non-diabetic subjects with age related cataract and healthy subjects. Analysis of the protein fractions showed that alpha-1-globulins and alpha-2-globulins were higher in diabetic patients without complications compared to non-diabetic subjects with age related cataract and healthy subjects. Serum alpha-1-globulin, alpha-2-globulin, beta globulins and gamma globulins were all significantly higher in diabetic patients with cataract compared to healthy subjects but not serum albumin. In conclusion, the levels of beta globulins and gamma globulins were significantly higher in diabetic patients with cataract and non-diabetic age related patients with cataract compared to healthy subjects. Thus, mechanisms other than hyperglycaemia are responsible for the development of cataract in these patients.