Omar M S

• PhD
• Professor (Full) at Salahaddin University-Erbil

Modified Callaway Model with that of Murnghan and Clapeyron equations were used to calculate the hydrostatic pressure effect on lattice thermal conductivity (LTC) in Si nanofilms. The pressure-off calculations of temperature dependence LTC were obtained in a way that fits the experimental data for 7 film sample thicknesses from 3000 nm down to 20 n...

A geometrical approach is constructed to explain the dependence of lattice thermal conductivity (LTC) in InAs/GaAs multi-layered superlattice structures (SLs). The Morelli–Callaway model is applied to calculate the LTC of InAs/GaAs SLs with the assumption of InAs+GaAs thickness as a grain boundary and the total layer thickness as the sample size. C...

The hydrostatic pressure effect on lattice thermal conductivity (LTC) in CdSe bulk, nanowires, and thin films was calculated. Values of LTC obtained through Callaway with that of Clapeyron equations are used to correlate those of the experimentally measured curves. Frequency-dependent relaxation time approximation of phonon-scattering processes was...

Systematic empirical relations were established for the nanosize-dependent surface roughness, ε(D) , dislocations, ND(D) , and effective length to examine their effects on the temperature-dependent lattice thermal conductivity (LTC) within the framework of the Morelli-Callaway model for In0.53Ga0.47As alloy films with thicknesses ranging from 10 to...

Debye–Callaway model in combination with the Murnaghan and Clapeyron equations was used to calculate the hydrostatic pressure effects on lattice thermal conductivity (LTC) of wurtzite gallium nitride. The calculations are for the longitudinal and transverse phonon modes. The results are efficiently fitted with the whole temperature (1–400) of the e...

Lattice thermal conductivity (LTC) for In0.53Ga0.47As alloy films, with thicknesses ranging from 10 nm to 1.4 μm, was investigated under pressures of up to 11 GPa and temperatures between 1 and 450 K, utilizing the modified Debye-Callaway model. The effects of structural and thermodynamical parameters, as well as phonon interactions, on LTC were ex...

Lattice structure based model to calculate nanosize dependence of melting temperature

An approach is made to calculate and analyze the combination of Lindemann’s role for melting and Debye temperature \(\left({\uptheta }_{D}\right)\) with that of lattice structure to examine ionicity and the structure factor for elements and compounds forming IV, III-V, II-VI, II-IV-V2 and I-III-VI2 tetrahedral group semiconductors. The results were...

This study presents a green method for synthesizing lead oxide nanoparticles (PbO NPs) using green tea leaf extract and explores their potential as an eco-friendly agent for water purification. The PbO NPs were characterized using UV–vis spectroscopy, SEM-EDX, and XRD, revealing their purity, stability, crystalline structure and composition. This p...

The specific heat for Si nanoparticles is calculated from the nanosize dependence of the Gruneisen parameter using the Gruneisen equation, which includes lattice thermal expansion, lattice volume, and bulk modulus. The results were comparable to the size dependent lattice volume under hydrostatic pressure. The reduction in specific heat from its bu...

The shift in lattice thermal conductivity of multilayer hexagonal boron nitride is studied as a function of layer thickness, hydrostatic pressure, and temperature. A Morelli-Callaway model is used for pressures ranging from zero to 7 GPa and temperatures scale from 2 to 350 K. Hydrostatic pressure and size parameters such as the mean bond length, m...

The Morelli–Callaway model was used to calculate the lattice thermal conductivity (LTC) of indium arsenide in both zinc blende and wurtzite phases of bulk and nanowire (NW) forms under applied hydrostatic pressures. Calculations were performed for NWs with diameters of 50, 63, 66, 100, and 148 nm in the temperature range of (0–400) K. The melting t...

Modified Callaway Model with that of Murnghan and Clapeyron equations were used to calculate the hydrostatic pressure effect on lattice thermal conductivity (LTC) in Si nanofilms. The pressure-off calculations of temperature dependence LTC were obtained in a way that fits the experimental data for 7 film sample thicknesses from 3000 nm down to 20 n...

The lattice thermal conductivity (LTC) of silicon nanowires (NWs) with diameters of 115, 56, 37 and 22 nm in the temperature range of 2–300 K for different pressures ranging from 0 to 10 GPa, was calculated by employing a modified Callaway model. Both longitudinal and transverse modes were explicitly considered within the model. A strategy is utili...

The modified Callaway model is used to calculate Lattice Thermal Conductivity (LTC) for (20-nm) silicon nanowires diameter in the temperature range from 2K to 800K. Acoustic phonon mode and group velocity in the calculations are modified by spatial confinement of phonons with that of the boundary effects. All important scattering rates such as Umkl...

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...

Mathematical modeling has been extended to simulate some physical systems to calculate some parameters that may need a sophisticated cost or may have some obstacles to be measured directly with an experimental method. In this study, the Modified Callaway Model has been used to calculate size dependence lattice thermal conductivity (LTC), and the in...

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...

Theoretical formalism based on the orthogonalized plane wave method supplemented by a potential scaling scheme was used to predict the temperature dependence of energy gap of CuSi 2 P 3 semiconductor. A computer code in Pascal was used to perform the variation of fundamental energy gap with temperature in the range of 150 K to 800 K. The dependence...

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, a...

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, a...

The size-dependent cohesive energy, melting temperature, Debye temperature and lattice heat capacity are investigated using density functional theory within generalized gradient approximation of Sn nanoparticles. The analyses of the obtained total energies are presented by considering effect of mean bond length and the ratio number of surface atoms...

Lattice thermal conductivity (LTC) of Si bulk and nanowires (NWs) with diameter 22, 37, 50, 56, 98 and 115 nm was investigated in the temperature range 3–300 K using a modified Callaway model that contains both longitudinal and transverse modes. Using proper equations, mean bond length, lattice parameter, unit cell volume, mass density, melting tem...

The size effects on the Grüneisen parameter was calculated which based on the ratio number of surface atoms to that of its internal, using the bulk Grüneisen parameter γ(∞) modified to include its related size dependent parameters and applied to Si. It was found that the nanoscale size values of Grüneisen parameter γ(r) dropped when the size decrea...

This study investigates the effect of size on mass density and its subsequent influence on the other physical parameters of zirconia nanoparticles in the structural forms of cubic, tetragonal and monoclinic. The general equations for these calculations are established based on the variation of lattice parameter model and surface internal atoms rati...

Surface and internal Crystal structure, melting point, lattice dislocation, dynamical properties of solids, thermal expansion, thermal conductivity, lattice bonding and ionicity are the subject of this talk

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 obtain...

Modified Callaway's theory was used to calculate lattice thermal conductivity (LTC) of Germanium nanowires. Results are compared to those of experimental values of the temperature dependence of LTC for nanowire diameters of 62, 19, and 15nm. In this calculation, both longitudinal and transverse modes are taken into account. Scattering of phonons is...

A model for calculating size dependent lattice volume of nanoparticles with that of the model for calculating size dependence melting point are applied to calculate nanoparticles structure parameters for Au in its critical size range smaller than 3 nm. From the method of trial and error for the melting temperature Tm, size dependence curve fitting...

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 phon...

A model, based on the ratio number of surface atoms to that of its internal, is derived to calculate the size dependence of lattice volume of nanoscaled materials. The model is applied to Si, Sn and Au nanoparticles. For Si, that the lattice volume is increases from 20 Å3 for bulk to 57 Å3 for a 2 nm size nanocrystals. A model, for calculating melt...

A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phon...

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 phon...

Investigation of the physical properties on an n- type GaP single crystal semiconductor compound is given. The magneto-optical properties, magneto photoconductivity, Hall effect as well as Seebeck and Nernst effects are measured for the same sample. A constructed basic experimental set-up for conducting these measurements is shown. An optical cryos...

A model for calculating the lattice thermal expansion is modified to be applicable to binary defect tetrahedral compounds that belong to the III2-VI3 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...

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 calcul...

The temperature dependence of magneto-optical and magneto-photoconductivity measurements were carried out in the range of (200-330) K. A home made optical cryostat was used for the measurements. The measured room temperature value of the energy gap was found to be 2.211 eV. The temperature coefficient of energy gap was found to be -5.48 x 10 -4 eV/...

The room-temperature dependence on composition of the energy gap is measured for the ternary alloy system In 1−x Ga x P semiconductors. The cross-over point from the direct to indirect optical transition energy gap is found at x = 0.718. An em-pirical relation for the alloy system energy-gap dependence is found for both direct and indirect transiti...

Modified formulas were used to calculate lattice thermal expansion, specific heat and Bulk modulus for Si nanowires with diameters of 115, 56, 37 and 22 nm. From these values and Gruneisen parameter taken from reference, mean lattice volumes were found to be as 20.03 Å3 for the bulk and 23.63, 29.91, 34.69 and 40.46 Å3 for Si nanowire diameters men...

A general empirical formula was found for calculating lattice thermal expansion for compounds having their properties extended for compound groups having different mean ionicity as well as more than one type of cation atoms with that of different numbers of them such as I{sub 2}-IV-VI{sub 3} and I{sub 3}-V-VI{sub 4}. The difference in the valence e...

A suitable simple optical cryostat for optical, magneto-optical, electrical and thermo-electrical measurements was designed. It is suitable for use in a magnetic pool gap as narrow as less than 1 cm. Throughout a long period of time, the heat diffusion process of the cryostat can be easily operated at slow increase in sample temperature in a range...

A Seebeck and a magneto‐Seebeck coefficients were measured for a single crystal of GaP and found to be in the range of 200 to 1800 μ V/K and 0.2×10−2 to 5×10−2cm2 /K s in the temperature range from 203 to 320K. A mobility as high as 1000cm2/V s was observed. The density of state effective mass was calculated in the same temperature range above. By...

The cubic root of the deviation of the lattice thermal expansion from that of the expected value of diamond for group IV semiconductors, binary compounds of III–V and II–VI, as well as several ternary compounds from groups I–III–VI2, II–IV–V2 and I–IV2V3 semiconductors versus their bonding length are given straight lines. Their slopes were found to...

Burstein and Moss formulas were used to calculate the optical energy gaps for five n-type compound semiconductors. The room-temperature intrinsic energy gaps were found to increase from 2% for ZnO to about 7 times of its value for InSb. The room temperature critical Burstein point of carrier concentration nm for five compounds of InSb, InAs, GaAs,...

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 cry...

The infrared reflectivity spectra were recorded at room temperature in the wavenumber range ν=180 to 4000 cm −1 using incident radiation polarized parallel to the respective crystal axes and perpendicular to the plane of incidence. The resulting spectra for the two polarization directions E∥a 0 and E∥b 0 are shown for the wavenumber range ν=180 to...

Infrared reflectivity spectra of (CuGe2P3)1−x(6 Ge)x mixed crystals with compositions in the range x = 0.07–0.33 are measured at room temperature in the wavenumber range from 180 to 4000 cm−1. An analysis of the spectra reveals six vibrational modes. The composition dependence of the mode frequencies and of the free carrier concentration and mobili...

Infrared reflectivity spectra of CuGe2P3 single crystals are measured at room temperature in the wavenumber range from 180 to 4000 cm−1. From an analysis of the spectra the parameters of five vibrational modes are determined. The results are discussed in terms of the Keating model and are compared with lattice vibrational data for ZnGeP2, CdGeP2, a...

Infrared reflectivity and transmission spectra of Cu2GeS3 are measured at room temperature in the wavenumber range from 180 to 4000 cm−1. From an analysis of the spectra the parameters of the fundamental infrared active lattice modes and of the two-phonon combination modes are determined. From a comparison of the experimental data with group theore...

Infrared reflectivity spectra of (Cu2GeSe3)1−x(CuGe2P3)x mixed crystals with x = 0.1 and 0.2 are measured in the wave-number range from 180 to 4000 cm−1. An analysis of the spectra reveals contributions from five vibrational modes and from free carriers to the reflectivity. The results are compared with previous measurements for Cu2GeSe3 and CuGe2P...

CuGe 2 P 3 est un semi-conducteur type p cristallisant dans F43m; dans la maille elementaire, les atomes de Ge et Cu sont repartis au hasard sur les sites cationiques. Pour Cu 2 GeS 3 , differentes structures ont ete etablies, a temperature ambiante. Dans ces 2 composes, les sites anioniques sont occupes respectivement par des atomes de P et S. Des...

The molar heat capacity at constant pressure of Ag6Ge10P12 is measured in the temperature range from 180 to 550 K and the standard molar enthalpies and entropies relative to 298.15 K are calculated on the basis of these data. From a comparison of the temperature variation of the apparent Debye temperatures in CuGe2P3 and Ag6Ge10P12 it is concluded...

The heat capacity at constant pressure of CuGe2P3 is measured in the temperature range from 180 to 550 K. Standard enthalpies and entropies relative to 298.15 K are calculated from the heat capacity data. The Debye temperature in the high-temperature limit is estimated to be about 710 K. Die Wärmekapazität bei konstantem Druck wurde für CuGe2P3 im...

Infrared reflectivity spectra of Cu2GeSe3 are measured at room temperature in the wavenumber range from 180 to 4000 cm−1. From an analysis of the spectra the parameters of four vibrational modes are determined. The experimental results are compared with predictions from group theory. From a comparison of the results for Cu2GeSe3 with the vibrationa...

To ascertain how the increased germanium content influences the elastic properties, the elastic constants and their hydrostatic pressure derivatives of a single crystal of CuGe//4P//3 have been measured. The extent of the pressure induced acoustic mode stiffening for the near zone centre modes has been quantified by computation of the Gruneisen par...

Infrared reflectivity spectra of p-type Ag6Ge10P12 single crystals were measured at room temperature in the wavenumber range from 180 to 4000 cm-1. Fits to a dielectric function including contributions from lattice oscillators and free carriers gave the parameters of five lattice vibrational modes and an effective hole mass of mp/mo = 2.3.

A single crystal has been grown of CuGe2P3, a ternary semiconductor with a zincblende structure in which the copper and germanium atoms are randomly distributed on the cation sites. The second order elastic constants measured by the ultrasonic pulse echo overlap technique (C11 = 13.66, C12 = 6.17, C44 = 6.66 and bulk modulus B = 8.67 in units of 10...

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 rev...