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Nacir Tit

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Michael Wittmann

University of Maine

University of Maryland

Ankur Choudhary

University of Delhi

Shafaa Al-Maqdi

Hamidreza Shojaie

Shahid Beheshti University

Marianne Barnes

José Antonio Chamizo

Universidad Nacional Autónoma de México

Alexei Kojevnikov

University of Lisbon

Joaquín Martínez Torregrosa

Universidad de Alicante

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Papers by Nacir Tit

Misconceptions about Atomic Models Amongst the Chemistry Students

International Journal for Innovation Education and Research, 2018

Bohr’s model is a semi-classical model which involves both classical and quantum principles. Alth... more Bohr’s model is a semi-classical model which involves both classical and quantum principles. Although more sophisticated Schrödinger model has been presented to students, the residual picture in their minds persists to consider Bohr’s model to be the closest to the physical reality. We included few questions about Bohr’s model in tests to assess the students’ understandings of realistic atomic models in general-chemistry courses offered for freshmen in two universities in the Middle-East (namely, Yarmouk University at Irbid, Jordan, and the United Arab Emirates University at Al-Ain, UAE, from both a statistical sample of 687 students was collected). The results reveal the existence of huge misconceptions amongst a large portion of the students’ sample (i.e., ≥ 85%). Alternative solutions are discussed and suggested to draw a strategy to better dissimilate the knowledge in order to overcome the existing learning difficulties.

Magnetic single atom catalyst in C2N to induce adsorption selectivity toward oxidizing gases

Scientific Reports, 2021

Density functional theory (DFT) method is used to study the effect of single-atom catalyst (SAC) ... more Density functional theory (DFT) method is used to study the effect of single-atom catalyst (SAC) of Mn embedded in C2N nanoribbon (C2N-NR) on the adsorption properties as an attempt to achieve selectivity. Many gases (e.g., CO, CO2, H2, H2O, H2S, N2 and O2) of interest to energy and environmental applications were tested. The results show that SAC-Mn alters chemisorption processes with all gas molecules except N2. Clear adsorption selectivity is obtained towards oxidizing CO, CO2 and O2 molecules as evidenced by the enhancements in binding energy and charge transfer and the reduction in magnetization. While the SAC-Mn contributes predominantly to Fermi-energy region with spin-down states, the strong binding to oxidizing molecules introduces there more spin-up states to compromise and reduce the magnetization. Hence, C2N-NR:Mn is proposed to be used as platform for gas sensor (if combined with magnetic sensor) to yield high selectivity toward these latter gases.

Role of defects and dopants in zinc oxide nanotubes for gas sensing and energy storage applications

International Journal of Energy Research, 2020

Spin‐polarized density functional theory (DFT) is employed to study the adsorption of H2 gas mole... more Spin‐polarized density functional theory (DFT) is employed to study the adsorption of H2 gas molecules on zinc oxide nanotubes (ZnO‐NTs) with intrinsic defects (oxygen and zinc vacancies) and dopants (Pd and Pt). Results indicate that defects lead to a strong chemisorption process, associated with strong splitting of the H2 molecule, rendering an irreversible process; that is, desorption is not possible. Such strong chemisorption process results in large adsorption energy and charge transfer between the defective‐ZnO‐NTs and H2 molecules. On the other hand, a weaker chemisorption process, associated with weak splitting of H2 molecule, takes place in the case of Pd or Pt dopants. The chemisorption of H2 on defective sites and dopants changes the energy gap to a large extent, resulting in major changes in the electrical conductivity of the ZnO‐NTs and consequently revealing their relevance for gas sensing applications with an enhancement of sensor response. From a different perspective, Pd ought to be a good dopant for ZnO‐NT based hydrogen storage material as it weakens the adsorption strength between H2 and ZnO‐NT.

Addressing Some Physical Misconceptions in Electrostatics of Freshman Engineering Students

International Journal for Innovation Education and Research, 2020

While the electrostatics is important topic consisting one among the four pillars of electromagne... more While the electrostatics is important topic consisting one among the four pillars of electromagnetic theory, as being represented by Gauss’s law, students persist encountering difficulties in its understanding. Even though the trend looks universal, we triggered an investigation to search for the main reasons behind the students’ misconceptions of electric field and flux aiming to analyze their origins and to search for intervention pathways to make corrections and, thus, to enhance the students learning of these physical concepts. The subject of our statistical sample is a group of 211 freshman engineering students taking the course of “Physics and Engineering Applications II”. Tests were designed for the diagnosis of the origins of students’ struggles in an attempt to find plausible interventional solutions to reduce the effects. Indeed, the statistics of results shows evidence of deviation of students in figuring out the correct answers and characterizes the depths of the misconc...

Relevance of Defects in ZnO Nanotubes for Selective Adsorption of H2S and CO2 Gas Molecules: Ab-initio Investigation

Results in Physics, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Catalyst-induced Gas-sensing Selectivity in ZnO Nanoribbons: Ab-initio Investigation at Room Temperature

Applied Surface Science, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

First principles study on the functionalization of graphene with Fe catalyst for the detection of CO2: Effect of catalyst clustering

Applied Surface Science, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Origins of Negative Differential Resistance in N-doped ZnO Nano-ribbons: Ab-initio Investigation

Scientific Reports, 2019

The electronic transport in low-dimensional materials is controlled by quantum coherence and none... more The electronic transport in low-dimensional materials is controlled by quantum coherence and nonequilibrium statistics. The scope of the present investigation is to search for the origins of negativedifferential resistance (NDR) behavior in N-doped ultra-narrow zigzag-edge ZnO nano-ribbons (ZnO-NRs). A state-of-the-art technique, based on a combination of density-functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism, is employed to probe the electronic and transport properties. The effect of location of N dopant, with respect to the NR edges, on IV-curve and NDR is tested and three different positions for N-atom are considered: (i) at the oxygen-rich edge; (ii) at the center; and (iii) at the Zn-rich edge. The results show that both resistance and top-to-valley current ratio (TVCR) reduce when N-atom is displaced from O-rich edge to center to Zn-rich edge, respectively. After an analysis based on the calculations of transmission coefficient versus bias, band structures, and charge-density plots of HOMO/LUMO states, one is able to draw a conclusion about the origins of NDR. The unpaired electron of N dopant is causing the curdling/localization of wave-function, which in turn causes strong back-scattering and suppression of conductive channels. These effects manifest themselves in the drawback of electric current (or so called NDR). The relevance of NDR for applications in nano-electronic devices (e.g., switches, rectifiers, amplifiers, gas sensing) is further discussed. Although research on zinc oxide (ZnO) commenced as early as 1935 1 , earlier than research on many semiconductors, only the recent few decades have witnessed several breakthroughs paving the way for revolutionary applications that exploit the multifunctional properties of ZnO and making it highly competitive in the market 2-4. Amongst the breakthroughs worth mentioning are: (i) the discovery of p-type doping in ZnO using (Li,N) 5,6 which enhanced the applications of ZnO in electronics; and (ii) the invention of one-atomic thick graphene by Novoselov and Geim 7 which opened the opportunity for many other materials to get synthesized into low-dimensional nanostructures (e.g., ZnO, BN, MoS 2 , silicone, germanene, black-phosphorus, etc.) 8-10. From the perspectives of native properties, ZnO crystallizes into wurtzite structure with a high direct band-gap energy of 3.3 eV and an outstanding excitonic binding energy of 60 meV at room temperature. Adding to its low fabrication cost, it becomes not only more competitive than GaN in optoelectronics but rather comprises much more fields of applications; (iii) the advent in modern growth techniques ranging up to the state-of-the-art flow-rate modulated molecular beam epitaxy (MBE), using which numerous structures have been realized and have long seemed prone to be embryonic 11,12. By nature, ZnO has the tendency to grow into nanorods. Electrons in these systems are free to move in one dimension, but their restricted motion in the other two directions is governed by quantum mechanics, especially when the cross-sectional size of nanorod is at nanometer scale. As a matter of fact, nanorods possess special characteristics completely different from the bulk ones 13. Such properties make them suitable for even broader range of applications for instance in: (a) nano-electronics: ZnO nanorods are utilized as extended gate in MOSFET 14 , and logical circuits 15 ; (b) nano-photonics: ZnO nanorod arrays were used as photonic crystals 16 , as light waveguide 17 , as LED 18 , as radiation detector 19 and in dye-sensitized solar cells 20 ; (c) biomedicine: ZnO nanorods and nanoparticles are utilized in biological and biomedical application (diagnosis and therapy) as to possess high radiative efficiency and least toxicity 21,22 ; (d) Spintronics: Magnetic studies showed that Co-doped ZnO nanorods exhibited room-temperature ferromagnetism with a magnetization increasing with Co content 23 ; (e) Gas-sensing:

Photocatalytic removal of methylene blue using titania- and silica-coated magnetic nanoparticles

Materials Research Express, 2018

The scope of this investigation is the photocatalytic degradation performance of newly synthesize... more The scope of this investigation is the photocatalytic degradation performance of newly synthesized nanoparticles (NPs); namely; Fe 3 O 4 ; Fe 3 O 4 @TiO 2 and Fe 3 O 4 @SiO 2. Non-thermal synthesis methods are used to synthesize the NPs and to explore the ferromagnetic properties of the photocatalysts. The synthesized NPs are characterized using TEM, XRD, FTIR, TGA, VSM, and surface area analysis techniques. The photocatalytic activities of Fe 3 O 4 and Fe 3 O 4 @SiO 2 NPs, put under solar irradiation, and Fe 3 O 4 @TiO 2 NPs, put under UV irradiation, are examined. The efficiency in degradation of Methylene Blue (MB) pollutant is shown to be the best for Fe 3 O 4 @SiO 2 NPs, then in Fe 3 O 4 NPs, and lastly in Fe 3 O 4 @TiO 2 NPs. The silica (SiO 2) coating on Fe 3 O 4 NPs significantly enhances the light absorption and is found to improve the MB degradation rate and the photoinduced charge generation and separation (i.e. it enhances the exciton lifetime). That makes the Fe 3 O 4 @SiO 2 NPs promising candidates for organic pollutants removal in various environment-related applications.

Novel method for synthesis of Fe 3 O 4 @TiO 2 core/shell nanoparticles

Surface and Coatings Technology, 2017

A simple and efficient method has been developed to synthesize Fe 3 O 4 @TiO 2 nanoparticles (NPs... more A simple and efficient method has been developed to synthesize Fe 3 O 4 @TiO 2 nanoparticles (NPs). Firstly, magnetite (Fe 3 O 4) NPs are prepared by co-precipitation method during which an additive coating with polyethylene glycol (PEG) is applied. Then, the core/shell structured NPs are achieved by including the surface coating of Fe 3 O 4 NPs with a thin layer of titania (TiO 2), using modified sol-gel method. The NPs' size, structure, morphology, surface charge, thermal stability, optical and magnetic properties have been investigated by various characterization techniques. The results demonstrate the successful coating of the Fe 3 O 4 NPs surfaces with TiO 2. Fe 3 O 4 @TiO 2 NPs have a spherical shape with an average size of 73 nm. The as-prepared Fe 3 O 4 @TiO 2 NPs exhibit UV wavelengths absorption and visible light emissions. Furthermore, they exhibit excellent magnetic properties suitable for magnetic separation and targeting. Being thermodynamically stable, the characteristics of the NPs can be explored in photonics and further applications like for instance environmental purifications.

Detection of CO2 using CNT-based sensors: Role of Fe catalyst on sensitivity and selectivity

Materials Chemistry and Physics, 2017

The adsorption of CO 2 on surfaces of graphene and carbon nanotubes (CNTs), decorated with Fe ato... more The adsorption of CO 2 on surfaces of graphene and carbon nanotubes (CNTs), decorated with Fe atoms, are investigated using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, neglecting the heat effects. Fe ad-atoms are more stable when they are dispersed on hollow sites. They introduce a large density of states at the Fermi level (N F); where keeping such density low would help in gas sensing. Furthermore, the Fe ad-atom can weaken the C=O double bonds of the chemisorbed CO 2 molecule, paving the way for oxygen atoms to drain more charges from Fe. Consequently, chemisorption of CO 2 molecules reduces both N F and the conductance while it enhances the sensitivity with the increasing gas dose. Conducting armchair CNTs (ac-CNTs) have higher sensitivity than graphene and semiconducting zigzag CNTs (zz-CNTs). Comparative study of sensitivity of ac-CNT-Fe composite towards various gases (e.g., O 2 , N 2 , H 2 , H 2 O, CO and CO 2) has shown high sensitivity and selectivity towards CO, CO 2 and H 2 O gases. Highlights DFTB is used to study Adsorptions of CO 2 molecule on pG and CNT, with Fe catalyst. Armchair CNT-Fe has higher sensitivity to detect CO 2 than zigzag CNT-Fe and pG-Fe. Ac-CNT-Fe is highly sensitive and selective towards CO, CO 2 and H 2 O gases. Keeping Fe ad-atoms dispersed and with low density enhances sensitivity. Our theoretical results corroborate the experimental findings of Ref.[8].

Electronic structure of GaAs with an InAs (001) monolayer

Physical Review B, 1995

<title>Suitability of AlAs/GaAs (001) superlattices for photonic applications</title>

1998 International Conference on Applications of Photonic Technology III: Closing the Gap between Theory, Development, and Applications, 1998

ABSTRACT The effects of (Gamma) X-valley mixing in (AlAs)n(GaAs)n (001) superlattices (SLs) on th... more ABSTRACT The effects of (Gamma) X-valley mixing in (AlAs)n(GaAs)n (001) superlattices (SLs) on the electronic and optical properties are theoretically investigated versus the SL period (n equals 1.25) and the band offsets. The calculations are based on both the empirical sp3s* tight-binding model and the surface Green-function-matching method. The results show that the top state of the valence band is always confined to the GaAs slabs, whereas the bottom state of the conduction band (CB) shows different behaviors as it is sensitive to band mixing and, therefore, can control the optical properties of the superlattice. For large values of n (n &gt;= 9) the SL is found to have a direct bandgap at (Gamma) -point and, thus, forms of type-I heterostructure consisting of multiple quantum wells. Whereas for the ultrathin-layer SLs (n = 26 angstroms.

AB-Initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction

A self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001)... more A self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chosen as an example of the isovalent polar with common-anion lattice mismatched heterojunctions, is presented. The effects of strain are studied by looking at the variation of the VBO versus the inplane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed.

Ali III-Vand II-V Journal of Electronic Materials 10

Ab initio calculation of the band offset at strained GaAs/InAs (001) heterojunctions

Physical Review B, 1993

ABSTRACT We present a self-consistent pseudopotential calculation of the valence-band offset at t... more ABSTRACT We present a self-consistent pseudopotential calculation of the valence-band offset at the GaAs/InAs (001) strained interface which is chosen as an example of isovalent, common-anion, lattice-mismatched heterojunctions. Our results show that the valence-band offset can be tuned by about 0.5 eV going from GaAs to InAs substrates, mainly due to the different effect of strain on the topmost valence-band state of the two bulk materials.

Length-scale-dependent ensemble-averaged conductance of a 1D disordered conductor: Conductance minimum

Physical Review B, 1994

Exact numerical calculation of ensemble averaged length-scale dependent conductance for the ID An... more Exact numerical calculation of ensemble averaged length-scale dependent conductance for the ID Anderson model is shown to support an earlier conjecture for a conductance minimum. Numerical results can be understood in terms of the Thouless expression for the conductance and the Wigner level-spacing statistics.

Strain-induced misfit dislocations in the CdTe/ZnTe (001) superlattices

Physics Letters A, 2004

At the lattice-mismatched heterojunction, the strain may cause one of two results: (i) give one m... more At the lattice-mismatched heterojunction, the strain may cause one of two results: (i) give one more degree of freedom to the novel growth techniques to control the process of bandgap engineering, if the strained layers are kept sufficiently thin, or (ii) cause the occurrence of misfit dislocations, if the strained layers exceed a certain critical thickness. In the present investigation, the electronic band structures of the strained CdTe/ZnTe (001) superlattices (SLs) are investigated using the sp 3 s * tight-binding method, which includes the strain and spin-orbit coupling effects. The calculated band structures are studied versus the biaxial strain, SL layer thicknesses, and valence-band offset (VBO). Special attention has been given to the case of free-standing SLs, which were the most useful structures in interpreting the experimental results. Our theoretical results are compared to the photoluminescence experimental data and shown to be consistent with the strain morphology along the SL growth direction, as well as with the optical and structural qualities of the experimental samples.

Adsorption and splitting of H2S on 2D-ZnO1−xNy: first-principles analysis

Phys. Chem. Chem. Phys., 2014

Based on first-principles calculations, we report novel applications of an inorganic analogue of ... more

$Research paper thumbnail of Evidence for fractional filling in ultrathin GaInN/GaN multiple-quantum wells$

Evidence for fractional filling in ultrathin GaInN/GaN multiple-quantum wells

physica status solidi (a), 2012

SCell representing (InN) 1 (GaN) 7 (001). It contains 32 basis atoms (4 In þ 28 Ga þ 32 N).

Misconceptions about Atomic Models Amongst the Chemistry Students

International Journal for Innovation Education and Research, 2018

Bohr’s model is a semi-classical model which involves both classical and quantum principles. Alth... more Bohr’s model is a semi-classical model which involves both classical and quantum principles. Although more sophisticated Schrödinger model has been presented to students, the residual picture in their minds persists to consider Bohr’s model to be the closest to the physical reality. We included few questions about Bohr’s model in tests to assess the students’ understandings of realistic atomic models in general-chemistry courses offered for freshmen in two universities in the Middle-East (namely, Yarmouk University at Irbid, Jordan, and the United Arab Emirates University at Al-Ain, UAE, from both a statistical sample of 687 students was collected). The results reveal the existence of huge misconceptions amongst a large portion of the students’ sample (i.e., ≥ 85%). Alternative solutions are discussed and suggested to draw a strategy to better dissimilate the knowledge in order to overcome the existing learning difficulties.

Magnetic single atom catalyst in C2N to induce adsorption selectivity toward oxidizing gases

Scientific Reports, 2021

Density functional theory (DFT) method is used to study the effect of single-atom catalyst (SAC) ... more Density functional theory (DFT) method is used to study the effect of single-atom catalyst (SAC) of Mn embedded in C2N nanoribbon (C2N-NR) on the adsorption properties as an attempt to achieve selectivity. Many gases (e.g., CO, CO2, H2, H2O, H2S, N2 and O2) of interest to energy and environmental applications were tested. The results show that SAC-Mn alters chemisorption processes with all gas molecules except N2. Clear adsorption selectivity is obtained towards oxidizing CO, CO2 and O2 molecules as evidenced by the enhancements in binding energy and charge transfer and the reduction in magnetization. While the SAC-Mn contributes predominantly to Fermi-energy region with spin-down states, the strong binding to oxidizing molecules introduces there more spin-up states to compromise and reduce the magnetization. Hence, C2N-NR:Mn is proposed to be used as platform for gas sensor (if combined with magnetic sensor) to yield high selectivity toward these latter gases.

Role of defects and dopants in zinc oxide nanotubes for gas sensing and energy storage applications

International Journal of Energy Research, 2020

Spin‐polarized density functional theory (DFT) is employed to study the adsorption of H2 gas mole... more Spin‐polarized density functional theory (DFT) is employed to study the adsorption of H2 gas molecules on zinc oxide nanotubes (ZnO‐NTs) with intrinsic defects (oxygen and zinc vacancies) and dopants (Pd and Pt). Results indicate that defects lead to a strong chemisorption process, associated with strong splitting of the H2 molecule, rendering an irreversible process; that is, desorption is not possible. Such strong chemisorption process results in large adsorption energy and charge transfer between the defective‐ZnO‐NTs and H2 molecules. On the other hand, a weaker chemisorption process, associated with weak splitting of H2 molecule, takes place in the case of Pd or Pt dopants. The chemisorption of H2 on defective sites and dopants changes the energy gap to a large extent, resulting in major changes in the electrical conductivity of the ZnO‐NTs and consequently revealing their relevance for gas sensing applications with an enhancement of sensor response. From a different perspective, Pd ought to be a good dopant for ZnO‐NT based hydrogen storage material as it weakens the adsorption strength between H2 and ZnO‐NT.

Addressing Some Physical Misconceptions in Electrostatics of Freshman Engineering Students

International Journal for Innovation Education and Research, 2020

While the electrostatics is important topic consisting one among the four pillars of electromagne... more While the electrostatics is important topic consisting one among the four pillars of electromagnetic theory, as being represented by Gauss’s law, students persist encountering difficulties in its understanding. Even though the trend looks universal, we triggered an investigation to search for the main reasons behind the students’ misconceptions of electric field and flux aiming to analyze their origins and to search for intervention pathways to make corrections and, thus, to enhance the students learning of these physical concepts. The subject of our statistical sample is a group of 211 freshman engineering students taking the course of “Physics and Engineering Applications II”. Tests were designed for the diagnosis of the origins of students’ struggles in an attempt to find plausible interventional solutions to reduce the effects. Indeed, the statistics of results shows evidence of deviation of students in figuring out the correct answers and characterizes the depths of the misconc...

Relevance of Defects in ZnO Nanotubes for Selective Adsorption of H2S and CO2 Gas Molecules: Ab-initio Investigation

Results in Physics, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Catalyst-induced Gas-sensing Selectivity in ZnO Nanoribbons: Ab-initio Investigation at Room Temperature

Applied Surface Science, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

First principles study on the functionalization of graphene with Fe catalyst for the detection of CO2: Effect of catalyst clustering

Applied Surface Science, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Origins of Negative Differential Resistance in N-doped ZnO Nano-ribbons: Ab-initio Investigation

Scientific Reports, 2019

The electronic transport in low-dimensional materials is controlled by quantum coherence and none... more The electronic transport in low-dimensional materials is controlled by quantum coherence and nonequilibrium statistics. The scope of the present investigation is to search for the origins of negativedifferential resistance (NDR) behavior in N-doped ultra-narrow zigzag-edge ZnO nano-ribbons (ZnO-NRs). A state-of-the-art technique, based on a combination of density-functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism, is employed to probe the electronic and transport properties. The effect of location of N dopant, with respect to the NR edges, on IV-curve and NDR is tested and three different positions for N-atom are considered: (i) at the oxygen-rich edge; (ii) at the center; and (iii) at the Zn-rich edge. The results show that both resistance and top-to-valley current ratio (TVCR) reduce when N-atom is displaced from O-rich edge to center to Zn-rich edge, respectively. After an analysis based on the calculations of transmission coefficient versus bias, band structures, and charge-density plots of HOMO/LUMO states, one is able to draw a conclusion about the origins of NDR. The unpaired electron of N dopant is causing the curdling/localization of wave-function, which in turn causes strong back-scattering and suppression of conductive channels. These effects manifest themselves in the drawback of electric current (or so called NDR). The relevance of NDR for applications in nano-electronic devices (e.g., switches, rectifiers, amplifiers, gas sensing) is further discussed. Although research on zinc oxide (ZnO) commenced as early as 1935 1 , earlier than research on many semiconductors, only the recent few decades have witnessed several breakthroughs paving the way for revolutionary applications that exploit the multifunctional properties of ZnO and making it highly competitive in the market 2-4. Amongst the breakthroughs worth mentioning are: (i) the discovery of p-type doping in ZnO using (Li,N) 5,6 which enhanced the applications of ZnO in electronics; and (ii) the invention of one-atomic thick graphene by Novoselov and Geim 7 which opened the opportunity for many other materials to get synthesized into low-dimensional nanostructures (e.g., ZnO, BN, MoS 2 , silicone, germanene, black-phosphorus, etc.) 8-10. From the perspectives of native properties, ZnO crystallizes into wurtzite structure with a high direct band-gap energy of 3.3 eV and an outstanding excitonic binding energy of 60 meV at room temperature. Adding to its low fabrication cost, it becomes not only more competitive than GaN in optoelectronics but rather comprises much more fields of applications; (iii) the advent in modern growth techniques ranging up to the state-of-the-art flow-rate modulated molecular beam epitaxy (MBE), using which numerous structures have been realized and have long seemed prone to be embryonic 11,12. By nature, ZnO has the tendency to grow into nanorods. Electrons in these systems are free to move in one dimension, but their restricted motion in the other two directions is governed by quantum mechanics, especially when the cross-sectional size of nanorod is at nanometer scale. As a matter of fact, nanorods possess special characteristics completely different from the bulk ones 13. Such properties make them suitable for even broader range of applications for instance in: (a) nano-electronics: ZnO nanorods are utilized as extended gate in MOSFET 14 , and logical circuits 15 ; (b) nano-photonics: ZnO nanorod arrays were used as photonic crystals 16 , as light waveguide 17 , as LED 18 , as radiation detector 19 and in dye-sensitized solar cells 20 ; (c) biomedicine: ZnO nanorods and nanoparticles are utilized in biological and biomedical application (diagnosis and therapy) as to possess high radiative efficiency and least toxicity 21,22 ; (d) Spintronics: Magnetic studies showed that Co-doped ZnO nanorods exhibited room-temperature ferromagnetism with a magnetization increasing with Co content 23 ; (e) Gas-sensing:

Photocatalytic removal of methylene blue using titania- and silica-coated magnetic nanoparticles

Materials Research Express, 2018

The scope of this investigation is the photocatalytic degradation performance of newly synthesize... more The scope of this investigation is the photocatalytic degradation performance of newly synthesized nanoparticles (NPs); namely; Fe 3 O 4 ; Fe 3 O 4 @TiO 2 and Fe 3 O 4 @SiO 2. Non-thermal synthesis methods are used to synthesize the NPs and to explore the ferromagnetic properties of the photocatalysts. The synthesized NPs are characterized using TEM, XRD, FTIR, TGA, VSM, and surface area analysis techniques. The photocatalytic activities of Fe 3 O 4 and Fe 3 O 4 @SiO 2 NPs, put under solar irradiation, and Fe 3 O 4 @TiO 2 NPs, put under UV irradiation, are examined. The efficiency in degradation of Methylene Blue (MB) pollutant is shown to be the best for Fe 3 O 4 @SiO 2 NPs, then in Fe 3 O 4 NPs, and lastly in Fe 3 O 4 @TiO 2 NPs. The silica (SiO 2) coating on Fe 3 O 4 NPs significantly enhances the light absorption and is found to improve the MB degradation rate and the photoinduced charge generation and separation (i.e. it enhances the exciton lifetime). That makes the Fe 3 O 4 @SiO 2 NPs promising candidates for organic pollutants removal in various environment-related applications.

Novel method for synthesis of Fe 3 O 4 @TiO 2 core/shell nanoparticles

Surface and Coatings Technology, 2017

A simple and efficient method has been developed to synthesize Fe 3 O 4 @TiO 2 nanoparticles (NPs... more A simple and efficient method has been developed to synthesize Fe 3 O 4 @TiO 2 nanoparticles (NPs). Firstly, magnetite (Fe 3 O 4) NPs are prepared by co-precipitation method during which an additive coating with polyethylene glycol (PEG) is applied. Then, the core/shell structured NPs are achieved by including the surface coating of Fe 3 O 4 NPs with a thin layer of titania (TiO 2), using modified sol-gel method. The NPs' size, structure, morphology, surface charge, thermal stability, optical and magnetic properties have been investigated by various characterization techniques. The results demonstrate the successful coating of the Fe 3 O 4 NPs surfaces with TiO 2. Fe 3 O 4 @TiO 2 NPs have a spherical shape with an average size of 73 nm. The as-prepared Fe 3 O 4 @TiO 2 NPs exhibit UV wavelengths absorption and visible light emissions. Furthermore, they exhibit excellent magnetic properties suitable for magnetic separation and targeting. Being thermodynamically stable, the characteristics of the NPs can be explored in photonics and further applications like for instance environmental purifications.

Detection of CO2 using CNT-based sensors: Role of Fe catalyst on sensitivity and selectivity

Materials Chemistry and Physics, 2017

The adsorption of CO 2 on surfaces of graphene and carbon nanotubes (CNTs), decorated with Fe ato... more The adsorption of CO 2 on surfaces of graphene and carbon nanotubes (CNTs), decorated with Fe atoms, are investigated using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, neglecting the heat effects. Fe ad-atoms are more stable when they are dispersed on hollow sites. They introduce a large density of states at the Fermi level (N F); where keeping such density low would help in gas sensing. Furthermore, the Fe ad-atom can weaken the C=O double bonds of the chemisorbed CO 2 molecule, paving the way for oxygen atoms to drain more charges from Fe. Consequently, chemisorption of CO 2 molecules reduces both N F and the conductance while it enhances the sensitivity with the increasing gas dose. Conducting armchair CNTs (ac-CNTs) have higher sensitivity than graphene and semiconducting zigzag CNTs (zz-CNTs). Comparative study of sensitivity of ac-CNT-Fe composite towards various gases (e.g., O 2 , N 2 , H 2 , H 2 O, CO and CO 2) has shown high sensitivity and selectivity towards CO, CO 2 and H 2 O gases. Highlights DFTB is used to study Adsorptions of CO 2 molecule on pG and CNT, with Fe catalyst. Armchair CNT-Fe has higher sensitivity to detect CO 2 than zigzag CNT-Fe and pG-Fe. Ac-CNT-Fe is highly sensitive and selective towards CO, CO 2 and H 2 O gases. Keeping Fe ad-atoms dispersed and with low density enhances sensitivity. Our theoretical results corroborate the experimental findings of Ref.[8].

Electronic structure of GaAs with an InAs (001) monolayer

Physical Review B, 1995

<title>Suitability of AlAs/GaAs (001) superlattices for photonic applications</title>

1998 International Conference on Applications of Photonic Technology III: Closing the Gap between Theory, Development, and Applications, 1998

ABSTRACT The effects of (Gamma) X-valley mixing in (AlAs)n(GaAs)n (001) superlattices (SLs) on th... more ABSTRACT The effects of (Gamma) X-valley mixing in (AlAs)n(GaAs)n (001) superlattices (SLs) on the electronic and optical properties are theoretically investigated versus the SL period (n equals 1.25) and the band offsets. The calculations are based on both the empirical sp3s* tight-binding model and the surface Green-function-matching method. The results show that the top state of the valence band is always confined to the GaAs slabs, whereas the bottom state of the conduction band (CB) shows different behaviors as it is sensitive to band mixing and, therefore, can control the optical properties of the superlattice. For large values of n (n &gt;= 9) the SL is found to have a direct bandgap at (Gamma) -point and, thus, forms of type-I heterostructure consisting of multiple quantum wells. Whereas for the ultrathin-layer SLs (n = 26 angstroms.

AB-Initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction

A self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001)... more A self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chosen as an example of the isovalent polar with common-anion lattice mismatched heterojunctions, is presented. The effects of strain are studied by looking at the variation of the VBO versus the inplane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed.

Ali III-Vand II-V Journal of Electronic Materials 10

Ab initio calculation of the band offset at strained GaAs/InAs (001) heterojunctions

Physical Review B, 1993

ABSTRACT We present a self-consistent pseudopotential calculation of the valence-band offset at t... more ABSTRACT We present a self-consistent pseudopotential calculation of the valence-band offset at the GaAs/InAs (001) strained interface which is chosen as an example of isovalent, common-anion, lattice-mismatched heterojunctions. Our results show that the valence-band offset can be tuned by about 0.5 eV going from GaAs to InAs substrates, mainly due to the different effect of strain on the topmost valence-band state of the two bulk materials.

Length-scale-dependent ensemble-averaged conductance of a 1D disordered conductor: Conductance minimum

Physical Review B, 1994

Exact numerical calculation of ensemble averaged length-scale dependent conductance for the ID An... more Exact numerical calculation of ensemble averaged length-scale dependent conductance for the ID Anderson model is shown to support an earlier conjecture for a conductance minimum. Numerical results can be understood in terms of the Thouless expression for the conductance and the Wigner level-spacing statistics.

Strain-induced misfit dislocations in the CdTe/ZnTe (001) superlattices

Physics Letters A, 2004

At the lattice-mismatched heterojunction, the strain may cause one of two results: (i) give one m... more At the lattice-mismatched heterojunction, the strain may cause one of two results: (i) give one more degree of freedom to the novel growth techniques to control the process of bandgap engineering, if the strained layers are kept sufficiently thin, or (ii) cause the occurrence of misfit dislocations, if the strained layers exceed a certain critical thickness. In the present investigation, the electronic band structures of the strained CdTe/ZnTe (001) superlattices (SLs) are investigated using the sp 3 s * tight-binding method, which includes the strain and spin-orbit coupling effects. The calculated band structures are studied versus the biaxial strain, SL layer thicknesses, and valence-band offset (VBO). Special attention has been given to the case of free-standing SLs, which were the most useful structures in interpreting the experimental results. Our theoretical results are compared to the photoluminescence experimental data and shown to be consistent with the strain morphology along the SL growth direction, as well as with the optical and structural qualities of the experimental samples.

Adsorption and splitting of H2S on 2D-ZnO1−xNy: first-principles analysis

Phys. Chem. Chem. Phys., 2014

Based on first-principles calculations, we report novel applications of an inorganic analogue of ... more

$Research paper thumbnail of Evidence for fractional filling in ultrathin GaInN/GaN multiple-quantum wells$

Evidence for fractional filling in ultrathin GaInN/GaN multiple-quantum wells

physica status solidi (a), 2012

SCell representing (InN) 1 (GaN) 7 (001). It contains 32 basis atoms (4 In þ 28 Ga þ 32 N).