Mustafa S Omar - Academia.edu (original) (raw)

Papers by Mustafa S Omar

Innovaciencia Facultad de Ciencias Exactas Físicas y Naturales, 2019

Introduction: The Al 85-Ni15 alloy with 99.99% purity of Al and Ni were prepared by an arc meltin... more Introduction: The Al 85-Ni15 alloy with 99.99% purity of Al and Ni were prepared by an arc melting technique system. The annealing effect onthe microstructure properties, phase transformation and micro-hardness for the Al-Ni alloy system were investigated. Material and Methods:The alloys were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Differential Thermal Analysis (DTA) as well as Vickers micro-hardness measurement. Results and Discussion: The quantitative results confirm that the chemical composition of the alloys is very close to compositions and the microstructures are in typical lamellar morphology. Mechanical properties for the as-prepared samples and subsequently heat-treated samples were measured by a Vickers indenter. Values of the micro-hardness (HV) Conclusions: According the XRD pattern analysis a multi phases produced, such as Al, AlNi3in room temperature, Al3Ni2, Al0.42Ni0.58 at 200ºC, Al1.1Ni0.9 at 300ºC and Al 0.802Ni0.198, AlNi3...

Bulletin of Materials Science, 2020

Theoretical calculations are performed on lattice thermal conductivity (LTC) and related paramete... more Theoretical calculations are performed on lattice thermal conductivity (LTC) and related parameters for the zinc blende and wurtzite structure of InAs nanowires (NWs) with diameters of 50, 63, 66, 100 and 148 nm through the Morelli-Callaway model. For the model to be efficiently applicable, the longitudinal and transverse modes are considered. The melting point of the various-sized NWs is considered to estimate the Debye and phonon group velocities. The impacts of Grüneisen parameter, dislocations and surface roughness are also successfully utilized to address the calculated and measured LTC of the semiconductor under investigation. Results show that the Grüneisen parameter increases with decreasing NW diameter and that phonon confinement leads to an observable deviation of the calculated LTC curve from that of the experimental one in the case of bulk InAs. We assume that NW boundaries, dislocations and imperfections are responsible for the scattering of phonons along with electrons and other phonons because of normal and Umklapp processes. Therefore, at a specified temperature, LTC depends on the size and crystal structure of the semiconductor. As such, the thermal and mechanical parameters of InAs can be greatly modified by decreasing the size and dimension of the semiconductor as a result of the quantum-confinement effect.

Sādhanā, 2018

This study investigates the effect of size on bulk modulus and its related parameters, including ... more This study investigates the effect of size on bulk modulus and its related parameters, including melting temperature and mass density based on the ratio number of surface atoms to that of its internal. The equation of bulk modulus in the bulk state B(?) is modified to include the related size-dependent parameters without any adjustable parameter, and is applied to Si nanocrystals. The bulk modulus B(r) decreases from 9.8 9 10 10 N m 2 for the bulk state to 5.93 9 10 10 N m 2 for a 5 nm diameter of Si nanoparticles. An inherent relation between bulk modulus and change of the lattice parameter in nanocrystals obtained from the variation in the surface to volume ratio, this leads to increase in the mean bond length. The effect of mass density and melting temperature on bulk modulus are also discussed. Calculated results for bulk modulus are verified by experimental as well as the available computer simulation data.

International Journal of Thermophysics, 2016

We report an equation free from fitting parameters as a direct calculation of size-dependent mean... more We report an equation free from fitting parameters as a direct calculation of size-dependent mean bond length for group IV and compounds from the III–V and II–VI binary groups. Size-dependent melting temperature and thermal expansion are also investigated for some materials forming the groups mentioned above. The empirical relation, which is obtained from fitting experimental data of melting enthalpy, is used to recalculate their values as well as entropy. The nanosize dependence of lattice thermal expansion for elements forming group IV is analyzed according to the hard sphere model, while mean ionicity is used for groups III–V and II–VI.

Materials Research Bulletin, 1990

The compounds Cu2GeS 3, Cu2SiS 3 and Cu2SiSe 3 were dissolved in the ternary compound CuGe2P 3. A... more The compounds Cu2GeS 3, Cu2SiS 3 and Cu2SiSe 3 were dissolved in the ternary compound CuGe2P 3. A modified Bridgman technique was used in the preparation, and good quality single crystals were grown for single phase samples. A complete solid solution for the system CuGe2P3-Cu2GeS 3 was found, with lattice parameters changing from 5.3678~ to 5.2895~ for 90% CuGe2P 3 and obeying Vegards law. In the CuGe2P3-Cu2GeSe 3 system the existence of the solid solution appears in the region of 0.25~x~0.9 when x is CuGe2P 3. However, the compound CuGe2P 3 does not form any solid solution with the compounds Cu2SiS 3 and Cu2SiSe 3.

International Journal of Thermophysics, 2010

A model for calculating the lattice thermal expansion is modified to be applicable to binary defe... more A model for calculating the lattice thermal expansion is modified to be applicable to binary defect tetrahedral compounds that belong to the III 2-VI 3 group. The number of valence electrons for the expected missing atom as a vacancy is used to correlate the deviations caused by the ionicity of this group of compounds. The ionicity effects which are due to the different numbers between vacancy atom types, which in this case is the group III element, and the element itself, were also added to the correlation equation. In general, the lattice thermal expansion for a compound semiconductor can be calculated from a relation containing the melting point, the mean atomic distance, and the number of valence electrons for the atoms forming the compound. For compounds that undergo a structural change during heating, the phase transition temperature has the same role as the melting point for calculating the lattice thermal expansion that belongs to the related structure phase. The value of the mean ionicity for this group of compounds is also calculated and found to be equal to 0.416.

Crystal Research and Technology, 1988

is measured in the temperature range from 180 t o 550 K and the standard molar enthalpies and ent... more is measured in the temperature range from 180 t o 550 K and the standard molar enthalpies and entropies relative t o 298.15 K are calculated on the basis of these data. From a comparison of the temperature variation of the apparent Debye temperatures in CuGeaP, and

Crystal Research and Technology, 1994

ABSTRACT CuSi2P3 is a semiconductor having sphalerite structure with the space group F33m with ra... more ABSTRACT CuSi2P3 is a semiconductor having sphalerite structure with the space group F33m with random distribution of the copper and silicon atoms on the cation sites. Silicon is soluble in CuSi2P3 upto 3 moles to form CuSi2 + xP3 (x = 1, 2, 3) compounds in single phase. In continuation of our work on thermal expansion of ternary semiconductors, CuSi3P3 crystals have been grown by a modified Bridgman method. Using a Unicam high temperature camera, the precision lattice parameter and the coefficient of thermal expansion (CTE) of CuSi3P3 at various high temperatures have been evaluated from X-ray diffraction data. It has been found that the lattice parameter increases non-linearly while the coefficient of thermal expansion increases linearly with temperature. The results on thermal expansion of various semiconductors have been discussed in terms of their ionicities.

The existence of various ternary adamantine compounds is discussed. Normal and defect ternary ada... more The existence of various ternary adamantine compounds is discussed. Normal and defect ternary adamantine compounds have been a subject of discussion, p a r t icu la r ly from a structural point of view. Rules for the formation of adamantine compounds are explained and related to each other. A home-made DTA apparatus was operated to detect the melting point and phase change from room temperature up to 1300 °C for the materials investigated. The group I-IV2-V3 compounds were the main subject o f this research. CuGe2 Ps and CuSi2 P3 were the only compounds found to grow in this family. The f i r s t was chosen for study in more d e ta i l , mainly because of i ts lower melting point. CuGe2 P3 was compared to other compounds, part icu la r ly structural aspects, and solid solutions were tr ied for twenty-two d iffe ren t materials. This investigation shows s im ila r ity with group 1 2 -IV-Vs compounds, such as CuzGeSs, and new alloys were found with Cu2 Ge$3 . Stoichiometric Cu2 GeS3 d...

physica status solidi (b), 1984

The ternary compound CuGe2P3 is a semiconductor which crystallizes in the sphalerite structure wi... more The ternary compound CuGe2P3 is a semiconductor which crystallizes in the sphalerite structure with a random distribution of the copper and germanium atoms on the cation sites /1, 2/. Results of e a r l i e r investigations regarding phase diagram properties, microhardness, thermal conductivity, and gap energy have been reviewed in /3/. Recently, thermal expansion data and a detailed study of the elastic constants of CuGe2P3 have been published /4/. In the present communication infrared reflectivity spectra of CuGe2 P3 are reported for the first time. F r o m an analysis of the spectra the optical effective m a s s of the holes and the parameters of the optical lattice mode a r e derived.

Progress in Crystal Growth and Characterization, 1984

ABSTRACT CuGe2P3 is a p-type semiconductor with a zinc blende structure. Even when doped with Zn ... more ABSTRACT CuGe2P3 is a p-type semiconductor with a zinc blende structure. Even when doped with Zn or S it is heavily p-type with p = 1020cm-3 and μp = 3cm2v-1s-1. DTA studies show that it melts at 830°C and shows no structural change. Single crystal samples have been grown using a Bridgman method and a steep temperature gradient. X-ray powder photographs reveal a lattice parameter of 5.3678 Å and a coefficient of expansion of 8.2 10-6.

Journal of Materials Science Letters, 1990

Recently it has been established that the ternary compounds Cu2GeS3 and CuGezP3 form a continuous... more Recently it has been established that the ternary compounds Cu2GeS3 and CuGezP3 form a continuous series of solid solutions over the whole composition range [1]. On the basis of X-ray powder diffraction studies of (Cu2GeS3)~_x(CuGe2P3)x solid solutions with compositions x = 0.2, 0.5 and 0.8 it has been argued that these alloys crystallize in the zinc blende structure with a random distribution of the copper and germanium atoms on the cation sites and of the sulphur and phosphorus atoms on the anion sites [l-3]. The zinc blende structure with a random distribution of the copper and germanium atoms on the cation sites has also been reported for CuGe2P3 by various researchers [4-6]. However, in the case of Cu2GeS 3 it follows from X-ray structure studies on single crystals [7] as well as from infrared lattice vibration investigations in the frequency range of both the fundamental lattice modes [8] and the two-phonon combination modes [9] that this compound crystallizes in a monoclinic lattice with an ordered distribution of the ,copper and germanium atoms on the cation sites. In principle it cannot be completely excluded that (Cu2GeS3)~_x(CuGe2P3)x alloys with small x values crystallize in a non-cubic lattice, too, since it is known from X-ray structure studies of Cu2GeS3 that the reflections characteristic of the monoclinic structure are very weak, indistinct or even absent in powder diffraction diagrams [10, l 1]. In view of this fact it is obvious that careful X-ray diffraction measurements o n (C u 2 Q e S 3) I x (C u G e z P 3) x

Advanced Materials Letters, 2012

Theoretical calculations of the magnitude and temperature variation of the measured thermal condu... more Theoretical calculations of the magnitude and temperature variation of the measured thermal conductivity of undoped and doped GaAs nanobeams will present. The calculations have been performed by employing modified Callaway's theoretical model. In the model, both longitudinal and transverse modes are explicitly taken into account. Scattering of phonons is assumed to be by nanobeam boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. A method is used to calculate the Debye temperature and phonon group velocities for undoped and doped nanobeams from their related melting points. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. The drop in thermal conductivity of doped nanobeams compared to that of the undoped beams arises from electronphonon scattering and additional phonon scattering from a large number of point impurities due to the presence of dopant atoms. Effect of Gruneisen parameter, surface roughness, and dislocations are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves.

Sadhana, 2010

The effects of nanoscale size dependent parameters on lattice thermal conductivity are calculated... more The effects of nanoscale size dependent parameters on lattice thermal conductivity are calculated using the Debye-Callaway model including transverse and longitudinal modes explicitly for Si nanowire with diameters of 115, 56, 37 and 22 nm. A direct method is used to calculate the group velocity for different size nanowire from their related calculated melting point. For all diameters considered, the effects of surface roughness, defects and transverse and longitudinal Gruneisen parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the reported experimental curve. The obtained fitting value for mean Gruneisen parameter has a systematic dependence on all Si nanowire diameters changing from 0•791 for 115 nm diameter to 1•515 for the 22 nm nanowire diameter. The dependence also gave a suggested surface thickness of about 5-6 nm. The other two parameters were found to have partially systematic dependence for diameters 115, 56, and 37 nm for defects and 56, 37 and 22 nm for the roughness. When the diameters go down from 115 to 22 nm, the concentration of dislocation increased from 1•16 × 10 19 cm −3 to 5•20 × 10 19 cm −3 while the surface roughness P found to increase from 0•475 to 0•130 and the rms height deviation from the surface changes by about 1•66 in this range of diameter. The diameter dependence also indicates a strong control of surface effect in surface to bulk ratio for the 22 nm wire diameter.