Ahmad Radzi Mat Isa

An Improved Study of Electronic Band Structure and Optical Parameters of X-Phosphides (X=B, Al, Ga, In) by Modified Becke—Johnson Potential

We report the electronic band structure and optical parameters of X-Phosphides (X=B, Al, Ga, In) by first-principles technique based on a new approximation known as modified Becke—Johnson (mBJ). This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as: Eg(mBJ-GGA/LDA) > Eg(GGA) > Eg(LDA). Optical parametric quantities (dielectric constant, refractive index, reflectivity and optical conductivity) which based on the band structure are also presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4–9 eV, 4–7 eV, 3–7 eV, and 2–7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AlP, GaP, and InP show significant optical conductivity in the range 5.2–10 eV, 4.3–8 eV, 3.5–7.2 eV, and 3.2–8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.

Electronic band structure and optical parameters of spinel SnMg 2O 4 by modified Becke - Johnson potential

The electronic band structure and optical parameters of SnMg2O4 are investigated by the first-principles technique based on a new potential approximation known as modified Becke—Johnson (mBJ). The direct band gap values by LDA, GGA and EV-GGA are underestimated significantly as compared to mBJ-GGA, which generally provides the results comparable to the experimental values. Similarly, the present band gap value (4.85 eV) using mBJ-GGA is greatly enhanced to the previous value by EV-GGA (2.823 eV). The optical parametric quantities (dielectric constant, index of refraction, reflectivity, optical conductivity and absorption coefficient) relying on the band structure are presented and examined. The first critical point (optical absorptions edge) in SnMg2O4 occurs at about 4.85 eV. A strong absorption region is observed, extending between 5.4 eV to 25.0 eV. For SnMg2O4, static dielectric constant e1(0), static refractive index n(0), and the magnitude of the coefficient of reflectivity at zero frequency R(0) are 2.296, 1.515 and 0.0419, respectively. The optoelectronic properties indicate that this material can be successfully used in optical devices.

First principle investigations of the physical properties of hydrogen-rich MGH2

Hydrogen being a cleaner energy carrier has increased the importance of hydrogen-containing light metal hydrides, in particular those with large gravimetric hydrogen density like magnesium hydride (MgH 2 ). In this study, density functional and density functional perturbation theories are combined to investigate the structural, elastic, thermodynamic, electronic and optical properties of MgH 2 . Our structural parameters calculated with those proposed by Perdew, Burke and Ernzerof generalized gradient approximation (PBE-GGA) and Wu‐Cohen GGA (WC-GGA) are in agreement with experimental measurements, however the underestimated band gap values calculated using PBE-GGA and WC-GGA were greatly improved with the GGA suggested by Engle and Vosko and the modified Becke‐Johnson exchange correlation potential by Trans and Blaha. As for the thermodynamic properties the specific heat values at low temperatures were found to obey the T 3 rule and at higher temperatures Dulong and Petit’s law. Our analysis of the optical properties of MgH 2 also points to its potential application in optoelectronics.

An Insight into the Structural, Electronic and Transport Characteristics of XIn2S4 (X = Zn, Hg) Thiospinels using a Highly Accurate All-Electron FP-LAPW+Lo Method

The highly accurate full-potential linearized augmented plane wave plus local orbital method is employed to calculate the structural, electronic and transport properties of HgIn2S4 and ZnIn2S4. For ZnIn2S4, the calculated In—S bond length is in good agreement with the experimental data. Bulk moduli results suggest that ZnIn2S4 can afford more compressional effects than HgIn2S4. The present study confirms that both HgIn2S4 and ZnIn2S4 are indirect band gap materials with band gap values of 0.705 eV and 1.533 eV respectively. The localized region existing in the most bottom valance band of both materials splits into states by 1 eV energy difference under the spin orbital coupling effect. Contour plots of charge density predict that chemical bonding in these compounds is a mixture of ionic and covalent characteristics. Effective mass results reveal that mobility of charge carriers in ZnIn2S4 is greater than that in HgIn2S4.

AB INITIO Study of optoelectronic properties of spinel ZnAl 2O4 beyond GGA and LDA

Electronic band structure and optical parameters of ZnAl2O4 are investigated by first-principles technique based on a new potential approximation, known as modified Becke–Johnson (mBJ). This method describes the excited states of insulators and semiconductors more accurately The recent direct band gap result by EV-GGA is underestimated by about 15% compared to our band gap value using mBJ-GGA. The value of the band gap of ZnAl2O4 decreases as follows: Eg(mBJ-GGA/LDA) > Eg(GGA) > Eg(LDA). The band structure base optical parametric quantities (dielectric constant, index of refraction, reflectivity and optical conductivity) are also calculated, and their variations with energy range are discussed. The first critical point (optical absorptions edge) in ZnAl2O4 occurs at about 5.26 eV in case of mBJ. This study about the optoelectronic properties indicates that ZnAl2O4 can be used in optical devices.

First principles study of the physical properties of pure and doped calcium phosphate biomaterial for tissue engineering

Calcium phosphate biomaterials are under extensive study owing to their excellent biocompatibility and identical chemical composition to natural teeth and bones. Calcium phosphate compounds can be used in tissue engineering (TE) as a good alternative to biocompatible ceramics to fabricate scaffolds to accommodate and lead to the growth of living cells and tissue reformation in three dimensions. Tricalcium phosphate (TCP) and hydroxyapatite (HA) bioceramics can be used in TE to increase bone reformation by employing strategies to encourage adhesion, endogenous osteoblast, osteoinduction, and osteoconduction by growth factors. However, due to defects in mechanical strength of existing scaffolds, which are manufactured using undoped TCP and HA materials in three dimensions for TE, they show a lower efficiency than optimal for real clinical applications. A theoretical overview about the mechanical properties and doping with some trace elements such as zinc, magnesium, strontium, and silicon is also given. We explore the future prospects of said compounds and expected revolutionary effects in TE applications.

Interdependencies of Critical Radius, Critical Energy and Surface Energy (CRESE) in Silicon Self-Assembled Nanodots

The interdependence parameters in the growth of silicon self-assembled nanodots are investigated. Accordingly, the critical radius, critical energy change and surface energy can be interpreted in terms of cubic function, where it produced a critical surface energy NS* and the corresponding r* and G*, called a CRESE point at a fixed growth temperature T when solved mathematically. It is defined as a limiting point at which equilibrium of the critical parameters take place at a constant temperature. Experiments were performed on the samples of amorphous silicon nanodots fabricated onto different non-crystalline substrates. A further analysis on the NS*-T plots revealed inverse linear relationships which converged at a CID point (o*,T*) when projected near the solidification temperature of silicon. The results suggested strong influence of atomic bonding at the nucleus-surface interface combined with higher surface roughness. In conclusion, there exists an equilibrium condition among the growth parameters which stabilizes the growth of amorphous silicon nanodots, as well as the existence of CRESE’s ideal destination (CID).

The effect of annealing process on the colloidal golds and gallium arsenide nanowires

Nanowires as a one dimensional building block have generated a lot of interests due to their unique physical properties and potential to revolutionize broad areas of nanotechnology. For successful applications, precise knowledge about the effect of the various growth parameters is essential. In this study, we report the effects of annealing process on colloidal gold and GaAs nanowires using metal‐organic chemical vapor deposition. AFM observation showed that the annealing process of colloidal gold, the substrate surface was attacked with a pit left behind where Au and Ga dissolved to form eutectic alloy. The morphological studies using FE‐SEM of the as‐annealed GaAs nanowire showed the direction of the GaAs nanowire to be 35° inclined from the surface but grown almost perpendicular to the substrate when the annealing process was omitted from the MOCVD growth process flow. TEM studies showed that the GaAs nanowires grown on orientation substrate without annealing process have less crystal latti...