Hala Alhashim - Academia.edu (original) (raw)
Papers by Hala Alhashim
Symmetry
Given that one of the most critical operations in the oil and gas industry is to instantly determ... more Given that one of the most critical operations in the oil and gas industry is to instantly determine the volume and type of product passing through the pipelines, in this research, a detection system for monitoring oil pipelines is proposed. The proposed system works in such a way that the radiation from the dual-energy source which symmetrically emits radiation, was received by the NaI detector after passing through the shield window and test pipeline. In the test pipe, four petroleum products—ethylene glycol, crude oil, gasoil, and gasoline—were simulated in pairs in different volume fractions. A total of 118 simulations were performed, and their signals were categorized. Then, feature extraction operations were started to reduce the volume of data, increase accuracy, increase the learning speed of the neural network, and better interpret the data. Wavelet features were extracted from the recorded signal and used as GMDH neural network input. The signals of each test were divided ...
Buildings
A supplemental pozzolanic material such as fly ash may result in a reduction in the concrete’s ad... more A supplemental pozzolanic material such as fly ash may result in a reduction in the concrete’s adverse environmental effect by reducing the discharge of carbon dioxide throughout the cement production procedure. This pozzolanic material also enhances the mechanical characteristics as well as the durability of concrete material. Considering the boundless passion for utilizing fly ash and conducting extensive research studies, the extent to which this supplement can be added to concrete has a limitation equal to almost one-third of cement material’s weight. In the current study, a model based on the Radial Basis Function (RBF) is developed to estimate the compressive strength of concrete containing various amounts of fly ash at any arbitrary age. Having parameters used as inputs in ANN modeling such as concrete additives and characteristics of fly ash, the output was compressive strength. It was concluded that the estimated results agree well with the experimental measurements with an...
Electronics
Transient electronics can be gradually dissolved in a variety of liquids over time. The short-liv... more Transient electronics can be gradually dissolved in a variety of liquids over time. The short-lived nature of such electronics has promoted their implementation in prospective applications, such as implantable electronics, dissolvable devices for secure systems, and environmentally biodegradable electronics. The amorphous metal tungsten nitride (WNx) has the remarkable ability to scale down to the nano-scale, allowing the fabrication of sub-1 volt nano-electromechanical (NEM) switches. When compared to silicon, amorphous WNx has a greater density and electrical conductivity, making it an even more appealing material for the design of accelerometers and resistive temperature detectors. Kinetic hydrolysis is observed by the dissolution of amorphous WNx in ground water. To better understand the kinetics of hydrolysis, in this paper, samples are dissolved in different solutions under different conditions over time. NEM switches immersed in ground water, de-ionized (DI) water, and salty ...
Processes
As time passes, scale builds up inside the pipelines that deliver the oil or gas product from the... more As time passes, scale builds up inside the pipelines that deliver the oil or gas product from the source to processing plants or storage tanks, reducing the inside diameter and ultimately wasting energy and reducing efficiency. A non-invasive system based on gamma-ray attenuation is one of the most accurate diagnostic methods to detect volumetric percentages in different conditions. A system including two NaI detectors and dual-energy gamma sources (241Am and 133Ba radioisotopes) is the recommended requirement for modeling a volume-percentage detection system using Monte Carlo N particle (MCNP) simulations. Oil, water, and gas form a three-phase flow in a stratified-flow regime in different volume percentages, which flows inside a scaled pipe with different thicknesses. Gamma rays are emitted from one side, and photons are absorbed from the other side of the pipe by two scintillator detectors, and finally, three features with the names of the count under Photopeaks 241Am and 133Ba o...
Separations
Loss of energy, decrement of efficiency, and decrement of the effective diameter of the oil pipe ... more Loss of energy, decrement of efficiency, and decrement of the effective diameter of the oil pipe are among the consequences of scale inside oil condensate transfer pipes. To prevent these incidents and their consequences and take timely action, it is important to detect the amount of scale. One of the accurate diagnosis methods is the use of non-invasive systems based on gamma-ray attenuation. The detection method proposed in this research consists of a detector that receives the radiation sent by the gamma source with dual energy (radioisotopes 241Am and 133Ba) after passing through the test pipe with inner scale (in different thicknesses). This structure was simulated by Monte Carlo N Particle code. The simulation performed in the test pipe included a three-phase flow consisting of water, gas, and oil in a stratified flow regime in different volume percentages. The signals received by the detector were processed by wavelet transform, which provided sufficient inputs to design the ...
Mathematics
Over time, oil pipes are scaled, which causes problems such as a reduction in the effective diame... more Over time, oil pipes are scaled, which causes problems such as a reduction in the effective diameter of the oil pipe, an efficiency reduction, waste of energy, etc. Determining the exact value of the scale inside the pipe is very important in order to take timely action and to prevent the mentioned problems. One accurate detection methodology is the use of non-invasive systems based on gamma-ray attenuation. For this purpose, in this research, a scale thickness detection system consisting of a test pipe, a dual-energy gamma source (241Am and 133Ba radioisotopes), and two sodium iodide detectors were simulated using the Monte Carlo N Particle (MCNP) code. In the test pipe, three-phase flow consisting of water, gas, and oil was simulated in a stratified flow regime in volume percentages in the range from 10% to 80%. In addition, a scale with different thicknesses from 0 to 3 cm was placed inside the pipe, and gamma rays were irradiated onto the pipe; on the other side of the pipe, the...
Processes
As the oil and petrochemical products pass through the oil pipeline, the sediment scale settles, ... more As the oil and petrochemical products pass through the oil pipeline, the sediment scale settles, which can cause many problems in the oil fields. Timely detection of the scale inside the pipes and taking action to solve it prevents problems such as a decrease in the efficiency of oil equipment, the wastage of energy, and the increase in repair costs. In this research, an accurate detection system of the scale thickness has been introduced, which its performance is based on the attenuation of gamma rays. The detection system consists of a dual-energy gamma source (241 Am and 133 Ba radioisotopes) and a sodium iodide detector. This detection system is placed on both sides of a test pipe, which is used to simulate a three-phase flow in the stratified regime. The three-phase flow includes water, gas, and oil, which have been investigated in different volume percentages. An asymmetrical scale inside the pipe, made of barium sulfate, is simulated in different thicknesses. After irradiatin...
Mathematics
Setting up pipelines in the oil industry is very costly and time consuming. For this reason, a pi... more Setting up pipelines in the oil industry is very costly and time consuming. For this reason, a pipe is usually used to transport various petroleum products, so it is very important to use an accurate and reliable control system to determine the type and amount of oil product. In this research, using a system based on the gamma-ray attenuation technique and the feature extraction technique in the frequency domain combined with a Multilayer Perceptron (MLP) neural network, an attempt has been made to determine the type and amount of four petroleum products. The implemented system consists of a dual-energy gamma source, a test pipe to simulate petroleum products, and a sodium iodide detector. The signals received from the detector were transmitted to the frequency domain, and the amplitudes of the first to fourth dominant frequency were extracted from them. These characteristics were given to an MLP neural network as input. The designed neural network has four outputs, which is the per...
InAs/GaAs quantum-dot intermixing: comparison of various
Materials Science in Semiconductor Processing, 2021
Spinel ferrites with configuration Co 1-x Ba x Fe 2 O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were cre... more Spinel ferrites with configuration Co 1-x Ba x Fe 2 O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were created by sol-gel technique. X-ray diffraction pattern showed that the entire specimen possessed singular phase. The standards of lattice constant increased, while densities as well as porosity decreased with the increment of barium ions. The room temperature resistivity and activation energy increased with the addition of barium ions. The temperature dependent resistivity presented the decreasing trend with the increase of barium ions which proves its semiconducting nature. The magnetization decreased while coerecivity was increased with the substitution of barium ions, as applied field changed from − 2 KOe to +2 KOe. Dielectric properties were also measured from 3 MHz to 1 G Hz. Due to high value of dc resistivity and low dielectric loss, these samples might be suitable for highfrequency devices.
Ceramics International, 2021
The development of materials in two-dimensions has been established as an effective approach to i... more The development of materials in two-dimensions has been established as an effective approach to improve their thermoelectric performance for renewable energy production. In this article, we generated monolayers of the orthorhombic structured lead-chalcogenides PbX (X = S, Se, and Te) for room-temperature thermoelectric applications. The Density functional theory and semiclassical Boltzmann transport theory-based computational approaches have been adopted to carry out this study. The band structures of PbX monolayers exhibited narrow indirect bandgaps with a large density of states corresponding to their bandgap edges. Accordingly, substantial electrical conductivities and Seebeck coefficients have been obtained at moderate level doping that has caused significant thermoelectric power factors (PFs) and figures-of-merit (zT) ~1. The single-layered PbX showed anisotropic dispersion of electronic states in the band structure. A relatively lighter effective mass of charge carriers has been extrapolated from the bands oriented in the y-direction than that of the x-direction. As a result, the electrical conductivities and PFs have been observed larger in the y-direction. The optimum PFs recorded for single-layered PbS, PbSe, and PbTe in y-direction amounts to 9.90 × 10 10 W/mK 2 s at 1.0 eV, 10.40 × 10 10 W/ mK 2 s at 0.82 eV, and 10.80 × 10 10 W/mK 2 s 0.66 eV respectively. Moreover, a slight increase in p-type doping is found to improve the x-component of the PF, whereas n-type doping has led to improvement in the y-component of PF. Our results show an improved thermoelectric response of PbX monolayer (PbTe in particular) than their bulk counterparts reported in the literature, which indicates the promise of PbX monolayers for nanoscale thermoelectric applications at room temperature.
Materials Chemistry and Physics, 2021
Abstract We present a comprehensive first-principles study on the physical properties of the lead... more Abstract We present a comprehensive first-principles study on the physical properties of the lead-free double perovskites halides, Cs2LiYX6 (X = Br, I). Our calculated results of lattice constants (a0) of both compounds are in nice agreement with the reported experimental and theoretical investigations. The predicted band structures of both compounds show that both compounds are wide and direct bandgap materials at T-point. Similarly, our computed results of elastic analysis predict that the investigated materials are elastically anisotropic, mechanically stable, and of ductile nature. The results of optical parameters such as absorption coefficients, refractive index, optical conductivity, optical reflectivity, electron energy loss, and extinction coefficients for an energy range of 0–14 eV are calculated and analyzed as well. The analysis of obtained results of wide and direct band gaps as well as optical parameters particularly absorption coefficients reflect the suitability of both compounds for ultraviolet high-frequency device applications.
International Journal of Energy Research, 2020
Rechargeable sodium-ion batteries are facing the challenge of highly electrochemical active anode... more Rechargeable sodium-ion batteries are facing the challenge of highly electrochemical active anode for their realization. In this study, we report a dual coating strategy of CoS 2 with metallic Co particles and carbon to boost the charge transfer and stability. The phase of CoS 2 and the existence of Co metallic particles were confirmed using x-ray diffraction (XRD). x-ray photoelectron spectroscopy (XPS) results corroborate the presence of carbon and Co S bonding. The prepared CoS 2 @Co@C anode reveals high performance where it shows a capacity of 712 mA h g −1 at 0.05 C rate. The CoS 2 @Co@C electrode exhibits exceptional high rate capability where it exhibits a capacity of 260 mA h g −1 at elevated rate of 10.0 C. The cyclability of CoS 2 @Co@C anode is tested at 0.05 C and 0.5 C rates where the electrode shows 78% and 45% capacity retention of stabilized capacity. The reaction mechanism of the CoS 2 @Co@C electrode is determined using x-ray absorption spectroscopy (XAS) and the results show reversibility of the material. K E Y W O R D S anode, CoS 2 @co@C, dual coating, sodium-ion batteries, x-ray absorption spectroscopy 1 | INTRODUCTION Recently, rechargeable sodium-ion batteries (SIBs) have emerged as the strongest candidates as an alternative to the existing lithium-ion batteries (LIBs). This is due to the extensive usage of energy storage gadgets from small (electronics) to medium (electric vehicles) to large (energy storage system) scale applications. Currently, it seems difficult to replace LIBs from electronic devices and electric vehicles, however, their use in the energy storage system is obstructed due to the high cost and inadequate sources. 1,2 In comparison, SIBs have the
Optical Materials Express, 2018
Self-assembled nanowires are posed to be viable alternatives to conventional planar structures, i... more Self-assembled nanowires are posed to be viable alternatives to conventional planar structures, including the nitride epitaxy for optoelectronic, electronic and nano-energy applications. In many cases, current injection and extraction at the nanoscopic scale are essential for marked improvement at the macroscopic scale. In this investigation, we study the mechanism of nanoscale current injection and the origin of improvement of the flow of charged carriers at the group-III nitride semiconductor surface and metal-semiconductor interfaces. Conductive atomic force microscopy (c-AFM) and Kelvin probe force microscopy (KPFM) enable a rapid analysis of the electrical and morphological properties of single and ensemble nanostructures. The surface potential and current injection of AlGaN nanowirebased LEDs are spatially mapped before and after surface treatment with KOH solution. Treated-nanowires showed an improved current spreading and increased current injection by nearly 10×, reduced sub-turn-on voltage (as low as 5 V), and smaller series resistance. The reduced contact potential confirms the lower semiconductor/metal barrier, thus enabling larger carriers flow, and correlates with the 15% increase in injection efficiency in macroscopic LEDs. The improvement leads to the normalization of nanoscale electrical conducting properties of UV AlGaN-based nanowire-LEDs and lays the foundation for the realization of practical nanowire-based device applications.
IEEE Photonics Journal, 2015
We report on a flat-top and ultrawide emission bandwidth of 125 nm from In-GaAsP/InP multiple qua... more We report on a flat-top and ultrawide emission bandwidth of 125 nm from In-GaAsP/InP multiple quantum-well (MQW) superluminescent diode with antireflection coated and tilted ridge-waveguide device configuration. A total output power in excess of 70 mW with an average power spectral density of 0.56 mW/nm and spectral ripple 1:2 AE 0:5 dB is measured from the device. Wall-plug efficiency and output power as high as 14% and 80 mW, respectively, is demonstrated from this batch of devices. We attribute the broad emission to the inherent inhomogeneity of the electron-heavy-hole (e-hh) and electron-light-hole (e-lh) recombination of the ground state and the first excited state of the MQWs and their simultaneous emission.
Bandgap Engineering of 1300 nm Quantum Dots/Quantum Well Nanostructures
AIP Advances, 2020
Characterization of epitaxial titanium nitride mediated single-crystal nickel oxide grown on MgO-... more Characterization of epitaxial titanium nitride mediated single-crystal nickel oxide grown on MgO-(100) and Si-(100) AIP Advances 10, 065318 (2020);
Electronics Letters, 2015
Impurity free vacancy disordering induced highly intermixed InAs/ GaAs quantum-dot lasers are rep... more Impurity free vacancy disordering induced highly intermixed InAs/ GaAs quantum-dot lasers are reported with high internal quantum efficiency (>89%). The lasers are shown to retain the device characteristics after intermixing and emitting in the important wavelength of ∼1070-1190 nm. The non-coated facet Fabry-Pērot post-growth wavelength tuned lasers exhibits high-power (>1.4W) and high-gain (∼50 cm −1), suitable for applications in frequency doubled greenyellow-orange laser realisation, gas sensing, metrology etc.
Optical Engineering, 2015
We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser str... more We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO 2 and Si 3 N 4 films, HfO 2 and SrTiO 3 dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175 nm (>148 meV) is obtained for HfO 2 capped sample. Likewise, investigation of TiO 2 , Al 2 O 3 , and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ∼1060─1200 nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green-yellow-orange coherent light generation, as well as addressing photonic integration via areaselective, and postgrowth bandgap engineering.
Symmetry
Given that one of the most critical operations in the oil and gas industry is to instantly determ... more Given that one of the most critical operations in the oil and gas industry is to instantly determine the volume and type of product passing through the pipelines, in this research, a detection system for monitoring oil pipelines is proposed. The proposed system works in such a way that the radiation from the dual-energy source which symmetrically emits radiation, was received by the NaI detector after passing through the shield window and test pipeline. In the test pipe, four petroleum products—ethylene glycol, crude oil, gasoil, and gasoline—were simulated in pairs in different volume fractions. A total of 118 simulations were performed, and their signals were categorized. Then, feature extraction operations were started to reduce the volume of data, increase accuracy, increase the learning speed of the neural network, and better interpret the data. Wavelet features were extracted from the recorded signal and used as GMDH neural network input. The signals of each test were divided ...
Buildings
A supplemental pozzolanic material such as fly ash may result in a reduction in the concrete’s ad... more A supplemental pozzolanic material such as fly ash may result in a reduction in the concrete’s adverse environmental effect by reducing the discharge of carbon dioxide throughout the cement production procedure. This pozzolanic material also enhances the mechanical characteristics as well as the durability of concrete material. Considering the boundless passion for utilizing fly ash and conducting extensive research studies, the extent to which this supplement can be added to concrete has a limitation equal to almost one-third of cement material’s weight. In the current study, a model based on the Radial Basis Function (RBF) is developed to estimate the compressive strength of concrete containing various amounts of fly ash at any arbitrary age. Having parameters used as inputs in ANN modeling such as concrete additives and characteristics of fly ash, the output was compressive strength. It was concluded that the estimated results agree well with the experimental measurements with an...
Electronics
Transient electronics can be gradually dissolved in a variety of liquids over time. The short-liv... more Transient electronics can be gradually dissolved in a variety of liquids over time. The short-lived nature of such electronics has promoted their implementation in prospective applications, such as implantable electronics, dissolvable devices for secure systems, and environmentally biodegradable electronics. The amorphous metal tungsten nitride (WNx) has the remarkable ability to scale down to the nano-scale, allowing the fabrication of sub-1 volt nano-electromechanical (NEM) switches. When compared to silicon, amorphous WNx has a greater density and electrical conductivity, making it an even more appealing material for the design of accelerometers and resistive temperature detectors. Kinetic hydrolysis is observed by the dissolution of amorphous WNx in ground water. To better understand the kinetics of hydrolysis, in this paper, samples are dissolved in different solutions under different conditions over time. NEM switches immersed in ground water, de-ionized (DI) water, and salty ...
Processes
As time passes, scale builds up inside the pipelines that deliver the oil or gas product from the... more As time passes, scale builds up inside the pipelines that deliver the oil or gas product from the source to processing plants or storage tanks, reducing the inside diameter and ultimately wasting energy and reducing efficiency. A non-invasive system based on gamma-ray attenuation is one of the most accurate diagnostic methods to detect volumetric percentages in different conditions. A system including two NaI detectors and dual-energy gamma sources (241Am and 133Ba radioisotopes) is the recommended requirement for modeling a volume-percentage detection system using Monte Carlo N particle (MCNP) simulations. Oil, water, and gas form a three-phase flow in a stratified-flow regime in different volume percentages, which flows inside a scaled pipe with different thicknesses. Gamma rays are emitted from one side, and photons are absorbed from the other side of the pipe by two scintillator detectors, and finally, three features with the names of the count under Photopeaks 241Am and 133Ba o...
Separations
Loss of energy, decrement of efficiency, and decrement of the effective diameter of the oil pipe ... more Loss of energy, decrement of efficiency, and decrement of the effective diameter of the oil pipe are among the consequences of scale inside oil condensate transfer pipes. To prevent these incidents and their consequences and take timely action, it is important to detect the amount of scale. One of the accurate diagnosis methods is the use of non-invasive systems based on gamma-ray attenuation. The detection method proposed in this research consists of a detector that receives the radiation sent by the gamma source with dual energy (radioisotopes 241Am and 133Ba) after passing through the test pipe with inner scale (in different thicknesses). This structure was simulated by Monte Carlo N Particle code. The simulation performed in the test pipe included a three-phase flow consisting of water, gas, and oil in a stratified flow regime in different volume percentages. The signals received by the detector were processed by wavelet transform, which provided sufficient inputs to design the ...
Mathematics
Over time, oil pipes are scaled, which causes problems such as a reduction in the effective diame... more Over time, oil pipes are scaled, which causes problems such as a reduction in the effective diameter of the oil pipe, an efficiency reduction, waste of energy, etc. Determining the exact value of the scale inside the pipe is very important in order to take timely action and to prevent the mentioned problems. One accurate detection methodology is the use of non-invasive systems based on gamma-ray attenuation. For this purpose, in this research, a scale thickness detection system consisting of a test pipe, a dual-energy gamma source (241Am and 133Ba radioisotopes), and two sodium iodide detectors were simulated using the Monte Carlo N Particle (MCNP) code. In the test pipe, three-phase flow consisting of water, gas, and oil was simulated in a stratified flow regime in volume percentages in the range from 10% to 80%. In addition, a scale with different thicknesses from 0 to 3 cm was placed inside the pipe, and gamma rays were irradiated onto the pipe; on the other side of the pipe, the...
Processes
As the oil and petrochemical products pass through the oil pipeline, the sediment scale settles, ... more As the oil and petrochemical products pass through the oil pipeline, the sediment scale settles, which can cause many problems in the oil fields. Timely detection of the scale inside the pipes and taking action to solve it prevents problems such as a decrease in the efficiency of oil equipment, the wastage of energy, and the increase in repair costs. In this research, an accurate detection system of the scale thickness has been introduced, which its performance is based on the attenuation of gamma rays. The detection system consists of a dual-energy gamma source (241 Am and 133 Ba radioisotopes) and a sodium iodide detector. This detection system is placed on both sides of a test pipe, which is used to simulate a three-phase flow in the stratified regime. The three-phase flow includes water, gas, and oil, which have been investigated in different volume percentages. An asymmetrical scale inside the pipe, made of barium sulfate, is simulated in different thicknesses. After irradiatin...
Mathematics
Setting up pipelines in the oil industry is very costly and time consuming. For this reason, a pi... more Setting up pipelines in the oil industry is very costly and time consuming. For this reason, a pipe is usually used to transport various petroleum products, so it is very important to use an accurate and reliable control system to determine the type and amount of oil product. In this research, using a system based on the gamma-ray attenuation technique and the feature extraction technique in the frequency domain combined with a Multilayer Perceptron (MLP) neural network, an attempt has been made to determine the type and amount of four petroleum products. The implemented system consists of a dual-energy gamma source, a test pipe to simulate petroleum products, and a sodium iodide detector. The signals received from the detector were transmitted to the frequency domain, and the amplitudes of the first to fourth dominant frequency were extracted from them. These characteristics were given to an MLP neural network as input. The designed neural network has four outputs, which is the per...
InAs/GaAs quantum-dot intermixing: comparison of various
Materials Science in Semiconductor Processing, 2021
Spinel ferrites with configuration Co 1-x Ba x Fe 2 O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were cre... more Spinel ferrites with configuration Co 1-x Ba x Fe 2 O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were created by sol-gel technique. X-ray diffraction pattern showed that the entire specimen possessed singular phase. The standards of lattice constant increased, while densities as well as porosity decreased with the increment of barium ions. The room temperature resistivity and activation energy increased with the addition of barium ions. The temperature dependent resistivity presented the decreasing trend with the increase of barium ions which proves its semiconducting nature. The magnetization decreased while coerecivity was increased with the substitution of barium ions, as applied field changed from − 2 KOe to +2 KOe. Dielectric properties were also measured from 3 MHz to 1 G Hz. Due to high value of dc resistivity and low dielectric loss, these samples might be suitable for highfrequency devices.
Ceramics International, 2021
The development of materials in two-dimensions has been established as an effective approach to i... more The development of materials in two-dimensions has been established as an effective approach to improve their thermoelectric performance for renewable energy production. In this article, we generated monolayers of the orthorhombic structured lead-chalcogenides PbX (X = S, Se, and Te) for room-temperature thermoelectric applications. The Density functional theory and semiclassical Boltzmann transport theory-based computational approaches have been adopted to carry out this study. The band structures of PbX monolayers exhibited narrow indirect bandgaps with a large density of states corresponding to their bandgap edges. Accordingly, substantial electrical conductivities and Seebeck coefficients have been obtained at moderate level doping that has caused significant thermoelectric power factors (PFs) and figures-of-merit (zT) ~1. The single-layered PbX showed anisotropic dispersion of electronic states in the band structure. A relatively lighter effective mass of charge carriers has been extrapolated from the bands oriented in the y-direction than that of the x-direction. As a result, the electrical conductivities and PFs have been observed larger in the y-direction. The optimum PFs recorded for single-layered PbS, PbSe, and PbTe in y-direction amounts to 9.90 × 10 10 W/mK 2 s at 1.0 eV, 10.40 × 10 10 W/ mK 2 s at 0.82 eV, and 10.80 × 10 10 W/mK 2 s 0.66 eV respectively. Moreover, a slight increase in p-type doping is found to improve the x-component of the PF, whereas n-type doping has led to improvement in the y-component of PF. Our results show an improved thermoelectric response of PbX monolayer (PbTe in particular) than their bulk counterparts reported in the literature, which indicates the promise of PbX monolayers for nanoscale thermoelectric applications at room temperature.
Materials Chemistry and Physics, 2021
Abstract We present a comprehensive first-principles study on the physical properties of the lead... more Abstract We present a comprehensive first-principles study on the physical properties of the lead-free double perovskites halides, Cs2LiYX6 (X = Br, I). Our calculated results of lattice constants (a0) of both compounds are in nice agreement with the reported experimental and theoretical investigations. The predicted band structures of both compounds show that both compounds are wide and direct bandgap materials at T-point. Similarly, our computed results of elastic analysis predict that the investigated materials are elastically anisotropic, mechanically stable, and of ductile nature. The results of optical parameters such as absorption coefficients, refractive index, optical conductivity, optical reflectivity, electron energy loss, and extinction coefficients for an energy range of 0–14 eV are calculated and analyzed as well. The analysis of obtained results of wide and direct band gaps as well as optical parameters particularly absorption coefficients reflect the suitability of both compounds for ultraviolet high-frequency device applications.
International Journal of Energy Research, 2020
Rechargeable sodium-ion batteries are facing the challenge of highly electrochemical active anode... more Rechargeable sodium-ion batteries are facing the challenge of highly electrochemical active anode for their realization. In this study, we report a dual coating strategy of CoS 2 with metallic Co particles and carbon to boost the charge transfer and stability. The phase of CoS 2 and the existence of Co metallic particles were confirmed using x-ray diffraction (XRD). x-ray photoelectron spectroscopy (XPS) results corroborate the presence of carbon and Co S bonding. The prepared CoS 2 @Co@C anode reveals high performance where it shows a capacity of 712 mA h g −1 at 0.05 C rate. The CoS 2 @Co@C electrode exhibits exceptional high rate capability where it exhibits a capacity of 260 mA h g −1 at elevated rate of 10.0 C. The cyclability of CoS 2 @Co@C anode is tested at 0.05 C and 0.5 C rates where the electrode shows 78% and 45% capacity retention of stabilized capacity. The reaction mechanism of the CoS 2 @Co@C electrode is determined using x-ray absorption spectroscopy (XAS) and the results show reversibility of the material. K E Y W O R D S anode, CoS 2 @co@C, dual coating, sodium-ion batteries, x-ray absorption spectroscopy 1 | INTRODUCTION Recently, rechargeable sodium-ion batteries (SIBs) have emerged as the strongest candidates as an alternative to the existing lithium-ion batteries (LIBs). This is due to the extensive usage of energy storage gadgets from small (electronics) to medium (electric vehicles) to large (energy storage system) scale applications. Currently, it seems difficult to replace LIBs from electronic devices and electric vehicles, however, their use in the energy storage system is obstructed due to the high cost and inadequate sources. 1,2 In comparison, SIBs have the
Optical Materials Express, 2018
Self-assembled nanowires are posed to be viable alternatives to conventional planar structures, i... more Self-assembled nanowires are posed to be viable alternatives to conventional planar structures, including the nitride epitaxy for optoelectronic, electronic and nano-energy applications. In many cases, current injection and extraction at the nanoscopic scale are essential for marked improvement at the macroscopic scale. In this investigation, we study the mechanism of nanoscale current injection and the origin of improvement of the flow of charged carriers at the group-III nitride semiconductor surface and metal-semiconductor interfaces. Conductive atomic force microscopy (c-AFM) and Kelvin probe force microscopy (KPFM) enable a rapid analysis of the electrical and morphological properties of single and ensemble nanostructures. The surface potential and current injection of AlGaN nanowirebased LEDs are spatially mapped before and after surface treatment with KOH solution. Treated-nanowires showed an improved current spreading and increased current injection by nearly 10×, reduced sub-turn-on voltage (as low as 5 V), and smaller series resistance. The reduced contact potential confirms the lower semiconductor/metal barrier, thus enabling larger carriers flow, and correlates with the 15% increase in injection efficiency in macroscopic LEDs. The improvement leads to the normalization of nanoscale electrical conducting properties of UV AlGaN-based nanowire-LEDs and lays the foundation for the realization of practical nanowire-based device applications.
IEEE Photonics Journal, 2015
We report on a flat-top and ultrawide emission bandwidth of 125 nm from In-GaAsP/InP multiple qua... more We report on a flat-top and ultrawide emission bandwidth of 125 nm from In-GaAsP/InP multiple quantum-well (MQW) superluminescent diode with antireflection coated and tilted ridge-waveguide device configuration. A total output power in excess of 70 mW with an average power spectral density of 0.56 mW/nm and spectral ripple 1:2 AE 0:5 dB is measured from the device. Wall-plug efficiency and output power as high as 14% and 80 mW, respectively, is demonstrated from this batch of devices. We attribute the broad emission to the inherent inhomogeneity of the electron-heavy-hole (e-hh) and electron-light-hole (e-lh) recombination of the ground state and the first excited state of the MQWs and their simultaneous emission.
Bandgap Engineering of 1300 nm Quantum Dots/Quantum Well Nanostructures
AIP Advances, 2020
Characterization of epitaxial titanium nitride mediated single-crystal nickel oxide grown on MgO-... more Characterization of epitaxial titanium nitride mediated single-crystal nickel oxide grown on MgO-(100) and Si-(100) AIP Advances 10, 065318 (2020);
Electronics Letters, 2015
Impurity free vacancy disordering induced highly intermixed InAs/ GaAs quantum-dot lasers are rep... more Impurity free vacancy disordering induced highly intermixed InAs/ GaAs quantum-dot lasers are reported with high internal quantum efficiency (>89%). The lasers are shown to retain the device characteristics after intermixing and emitting in the important wavelength of ∼1070-1190 nm. The non-coated facet Fabry-Pērot post-growth wavelength tuned lasers exhibits high-power (>1.4W) and high-gain (∼50 cm −1), suitable for applications in frequency doubled greenyellow-orange laser realisation, gas sensing, metrology etc.
Optical Engineering, 2015
We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser str... more We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO 2 and Si 3 N 4 films, HfO 2 and SrTiO 3 dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175 nm (>148 meV) is obtained for HfO 2 capped sample. Likewise, investigation of TiO 2 , Al 2 O 3 , and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ∼1060─1200 nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green-yellow-orange coherent light generation, as well as addressing photonic integration via areaselective, and postgrowth bandgap engineering.