Browsing by Subject "Electronic properties"

Now showing 1 - 20 of 45

Open Access
Ab initio study of electronic properties of armchair graphene nanoribbons passivated with heavy metal elements
(Elsevier, 2019) Narin, P.; Abbas, J. M.; Atmaca, G.; Kutlu, E.; Lisesivdin, S. B.; Özbay, Ekmel
In this study, electronic properties of graphene nanoribbons with armchair edges (AGNRs) have been investigated with Density Functional Theory (DFT). Effects of heavy metal (HM) elements, including Zinc (Zn), Cadmium (Cd) and Mercury (Hg) atoms on electronic behavior of AGNRs have been calculated by passivating for both one and two edges of AGNRs in detail. To explain the electronic behavior of investigated AGNRs, the electronic band structure, the density of states (DOS), total energy have been calculated. Energetically favorable structures have been determined using calculated binding energy values. The obtained bandgap values of investigated structures changes between 0.30 and 0.64 eV. Increasing atomic number of passivation atoms have led to an increment in the bandgap of AGNRs.
Open Access
Ab initio study of Ru-terminated and Ru-doped armchair graphene nanoribbons
(Taylor and Francis, 2012) Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, Ekmel
We investigate the effects of ruthenium (Ru) termination and Ru doping on the electronic properties of armchair graphene nanoribbons (AGNRs) using first-principles methods. The electronic band structures, geometries, density of states, binding energies, band gap information, and formation energies of related structures are calculated. It is well founded that the electronic properties of the investigated AGNRs are highly influenced by Ru termination and Ru doping. With Ru termination, metallic band structures with quasi-zero-dimensional, one-dimensional and quasi-one-dimensional density of states (DOS) behavior are obtained in addition to dominant one-dimensional behavior. In contrast to Ru termination, Ru doping introduces small but measurable (12.4 to 89.6meV) direct or indirect band gaps. These results may present an additional way to produce tunable band gaps in AGNRs.
Open Access
Analysis of strain fields in silicon nanocrystals
(American Institute of Physics, 2009) Yilmaz, D. E.; Bulutay, C.; Çaǧın, T.
Strain has a crucial effect on the optical and electronic properties of nanostructures. We calculate the atomistic strain distribution in silicon nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon dioxide matrix. A seemingly conflicting picture arises when the strain field is expressed in terms of bond lengths versus volumetric strain. The strain profile in either case shows uniform behavior in the core, however, it becomes nonuniform within 2-3 Å distance to the nanocrystal surface: tensile for bond lengths whereas compressive for volumetric strain. We reconcile their coexistence by an atomistic strain analysis.
Open Access
Effect of chalcogens on electronic and photophysical properties of vinylene-based diketopyrrolopyrrole copolymers
(American Chemical Society, 2015) Dhar, J.; Mukhopadhay, T.; Yaacobi-Gross, N.; Anthopoulos, T. D.; Salzner, U.; Swaraj, S.; Patil, S.
Three vinylene linked diketopyrrolopyrrole based donor−acceptor (D−A) copolymers have been synthesized with phenyl, thienyl, and selenyl units as donors. Optical and electronic properties were investigated with UV−vis absorption spectroscopy, cyclic voltammetry, near edge X-ray absorption spectroscopy, organic field effect transistor (OFET) measurements, and density functional theory (DFT) calculations. Optical and electrochemical band gaps decrease in the order phenyl, thienyl, and selenyl. Only phenyl-based polymers are nonplanar, but the main contributor to the larger band gap is electronic, not structural effects. Thienyl and selenyl polymers exhibit ambipolar charge transport but with higher hole than electron mobility. Experimental and theoretical results predict the selenyl system to have the best transport properties, but OFET measurements prove the thienyl system to be superior with p-channel mobility as high as 0.1 cm2 V−1 s −1.
Open Access
Electronic and elastic properties of the multiferroic crystals with the Kagome type lattices -Mn3V2O8 and Ni3V2O8: First principle calculations
(Taylor & Francis, 2019-08-16) Koç, H.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
The electronic, mechanical, and optical properties of the Kagome staircase compounds, Mn3V2O8 and Ni3V2O8, have been investigated using the VASP (Vienna ab-initio Simulation Program) that was developed within the density functional theory (DFT). The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The electronic band structures for both compounds and total and partial density of states corresponding to these band structures have been calculated. Spin up (spin down) Eg values for Mn3V2O8 and Ni3V2O8 compounds are 0.77 eV indirect (3.18 direct) and 1.58 eV indirect (0.62 eV) direct, respectively. The band gaps of both compound is in the d-d character. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropic factors, sound velocity, and Debye temperature were calculated and interpreted.
Open Access
Electronic and magnetic properties of zinc blende half-metal superlattices
(A I P Publishing LLC, 2004) Fong, C. Y.; Qian, M. C.; Pask, J. E.; Yang, L. H.; Dag, S.
Zinc blende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. We explore layered materials, consisting of alternating layers of zinc blende half-metals, by first principles calculations, and find that superlattices of (CrAs)1(MnAs)1 and (CrAs)2(MnAs)2 are half-metallic with magnetic moments of 7.0mB and 14.0mB per unit cell, respectively. We discuss the nature of the bonding and half-metallicity in these materials and, based on the understanding acquired, develop a simple expression for the magnetic moment in such materials. We explore the range of lattice constants over which half-metallicity is manifested, and suggest corresponding substrates for growth in thin film form.
Open Access
Electronic and optical properties of black phosphorus doped with Au, Sn and I atoms
(Taylor and Francis, 2018) Kutlu, E.; Narin, P.; Lisesivdin, S. B.; Özbay, Ekmel
In this study, the electronic and the optical properties of monolayer black phosphorus (BP) doped with Gold (Au), Tin (Sn) and Iodine (I) atoms have been investigated by the density-functional theory (DFT) method. In the calculations, the electronic and the optical properties of monolayer BP have been substantially changed with doping. Monolayer BP has a narrow bandgap as 0.85 eV, BP doped with these atoms, results in a metallic behaviour and nearly spin gapless band gap behaviour. The dielectric constant of BP which shows anisotropic optical properties due to different edge states as zigzag and armchair has been changed with doping especially with Au.
Open Access
Electronic properties of Li-doped zigzag graphene nanoribbons
(Elsevier B.V., 2016) Narin, P.; Kutlu, E.; Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, Ekmel
Zigzag graphene nanoribbons (ZGNRs) are known to exhibit metallic behavior. Depending on structural properties such as edge status, doping and width of nanoribbons, the electronic properties of these structures may vary. In this study, changes in electronic properties of crystal by doping Lithium (Li) atom to ZGNR structure are analyzed. In spin polarized calculations are made using Density Functional Theory (DFT) with generalized gradient approximation (GGA) as exchange correlation. As a result of calculations, it has been determined that Li atom affects electronic properties of ZGNR structure significantly. It is observed that ZGNR structure exhibiting metallic behavior in pure state shows half-metal and semiconductor behavior with Li atom.
Open Access
Electronic properties of polypyrrole/polyindene composite/metal junctions
(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.
Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.
Open Access
Electronic properties of spin excitation in multiferroics with a spinel structure: first principles calculation
(Taylor & Francis, 2019-06-04) Koç, H.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the structural, electronic and mechanical properties of LiVCuO4 and LiCu2O4 spinel type multiferroics have been investigated by means of first principles calculations. The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The structural optimization of these multiferroics compounds has been performed by using VASP-code, and the lattice parameters and magnetic moments have been calculated. From our calculation, it has been determined that the LiVCuO4 compound is a narrow band gap semiconductor, while the LiCu2O4 compound is metallic in nature. Considering the spin states from the electronic band structure and density of the state (DOS) of the LiVCuO4 compound, it has been identified that Eg=1.87 eV for spin up and Eg=0.37 eV for spin down. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work.
Open Access
Electronic properties of zigzag ZnO nanoribbons with hydrogen and magnesium passivations
(Elsevier, 2018) Abbas, J. M..; Narin, P.; Kutlu, E.; Lisesivdin, S. B.; Özbay, Ekmel
In this study, the electronic properties of ZnO nanoribbons with zigzag edges (ZZnONr) have been investigated with Density Functional Theory (DFT). After a geometric optimization, the electronic band structures, the density of states (DOS) of ZZnONr passivated with Hydrogen (H) and Magnesium (Mg) atoms were calculated ZZnONr. It is shown that the increasing width of ZZnONrs has led to a decrement in energy band gap of the studied structures. While ZZnONr passivated with Mg for Zn-rich edge have not been shown a spin dependency, the structure passivated with Mg for O-rich edge have exhibited spin-dependent band structure. The energetically most stable structures have been determined as ZZnONr passivated with Mg for Zn-rich edge. ZZnONr passivated with Mg atoms for both edges have a graphene-like band structure especially for 8 and 10 atom width structures and this property of ZZnONrs could be important in terms of the electron transport for ZZnONrs.
Open Access
Electronic structure of conducting organic polymers: insights from time-dependent density functional theory
(John Wiley & Sons Ltd., 2014) Salzner, U.
Conducting organic polymers (COPs) became an active field of research after it was discovered how thin films rather than insoluble infusible powders can be produced. The combination of the properties of plastics with those of semiconductors opened the research field of organic electronics. COPs share many electronic properties with inorganic semiconductors, but there are also major differences, e.g., the nature of the charge carriers and the amount of the exciton binding energy. Theoretical analysis has been used to interpret experimental observations early on. The polaron model that was developed from one-electron theories is still the most widely used concept. In the 1990s, time-dependent density functional theory (TDDFT) became available for routine calculations. Using TDDFT, electronic states of long oligomers can be calculated. Now UV spectra of neutral and oxidized or reduced species can be compared with in situ UV spectra recorded during doping. Likewise states of cations can be used to model photoelectron spectra. Analysis of states has resolved several puzzles which cannot be understood with the polaron model, e.g., the origin of the dual absorption band of green polymers and the origin of a 'vestigial neutral band' upon doping of long oligomers. DFT calculations also established that defect localization is not crucial for spectral changes observed during doping and that there are no bound bipolarons in COPs.
Open Access
Electronic structure of conventional slater type antiferromagnetic insulators: AIrO3 (A=Sr, Ba) perovskites
(Institute of Physics, 2022) Koc, Husnu; Mamedov, Amirullah M.; Özbay, Ekmel
The structural, mechanical, and electronic properties of Perovskite BaIrO3 and SrIrO3 compounds based on the density functional theory (DFT) have been examined in four different structures (C2/c, R-3m, P6_3/mmc and Pm-3m) and Pnma structure, respectively. The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. As a result of spin polarized calculations, it has been observed that BaIrO3 compound showed magnetic properties in C2/c and R-3m structures, but not in Pm-3m and P6_3/mmc structures. SrIrO3 compound also shows magnetic properties in Pnma structure. The elastic constants have been calculated using the strain-stress method and the other related quantities (the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, sound velocities, and Debye temperature) have also been estimated. In electronic band structure calculations, while Pm-3m and P6_3/mmc structures of NaIrO3 compound are metallic and semiconductor (Eg = 1.190 eV indirect), respectively, while C2/c and R-3m structures showing magnetic properties are metallic in spin down state and semiconductor (Eg=0.992 eV indirect and Eg=0.665 eV direct, respectively) in the spin up state. The Pmna structure in the SrIrO3 compound is a semiconductor in both spin states (Eg=0.701 eV “0.632 eV” indirect in the spin up “spin down”). © 2022 Institute of Physics Publishing. All rights reserved.
Open Access
Experimental and theoretical investigations of electronic and atomic structure of Si-nanocrystals formed in sapphire by ion implantation
(IOP, 2008) Wainstein, D.; Kovalev, A.; Tetelbaum, D.; Mikhailov, A.; Bulutay, Ceyhun; Aydınlı, Atilla
The semiconductor nanocomposites based on Si nanocrystals in dielectric matrices attract a great amount of attention due to their ability for luminescence in visible and near-IR part of the electromagnetic spectrum. Si nanocrystals in sapphire matrix were formed by Si+ ion implantation with doses from 5×1016 to 3×1017 cm -2 at an accelerating voltage 100 kV and post-implantation annealing at 500-1100 d̀C for 2 hours. Depth distribution of lattice defects, impurities and Si nanocrystals, the peculiarities of interband electronic transitions were investigated by XPS and HREELS. The molecular orbitals and local electronic structure of the Al2O3 matrix with Si nanocrystals was calculated using an atomistic pseudopotential technique. The electronic structure of Si nanocrystals as determined from HREELS measurements is in good agreement with the theoretically calculated electronic structure for Si nanocrystals.
Open Access
First-principles calculations of Pd-terminated symmetrical armchair graphene nanoribbons
(Elsevier, 2013) Kuloglu, A. F.; Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, Ekmel
The effects of Palladium (Pd) termination on the electronic properties of armchair graphene nanoribbons (AGNRs) were calculated by using ab initio calculations. After a geometric optimization process, the electronic band structures, density of states, and binding energies of AGNRs with Na = 5-15 were calculated. Pd-termination was found to significantly influence the electronic properties of AGNRs. In DOS, many Q0D and Q1D type states were observed. Binding energy (BE) for single-side or both-side Pd-terminated structures represents characteristic drops with the increasing GNR width. With the increasing GNR width, the BEs of these structures become similar to hydrogenated structures. Because of the GNR width, dependent BE also gave information on the possible stiffness information, in which all of this information can be used in studies where controlled binding to graphene is required.
Open Access
Functionalization of group V monolayers and their compounds: alloying, doping and surface modification
(2020-11) Kanlı, Muammer
There has been growing interest during the last decade in two-dimensional (2D) materials due to their important roles in various scientific and technological applications such as detectors, lasers and light emitting diodes. In this thesis we present a theoretical investigation of a couple of such 2D materials from group V monolayers and their compounds. Firstly, ordered alloys of GaxAl1−xN hexagonal monolayer are studied and the effect of Al content on mechanical, electronic, thermal and optical properties are investigated. The optimized lattice constants and band gaps change in accordance to Vegard’s Law. Low barrier energies and favorable substitution of Ga by Al may show feasibility of fabrication. Segregation is also checked with mixing energy calculations. The dynamical stability of alloys is shown by phonon spectrum analysis and MD simulations. GaxAl1−xN alloys give lower in-plane stiffness than h-BN or graphene, but higher Poisson’s ratio than most realized 2D systems. Heat capacity of alloys delivers a decrease with Al content at low temperatures but it converges to the classical limit at high temperatures. The absorption onset of GaxAl1−xN alloys remain in the near UV range and prominent absorption peaks blue-shifts with increasing x in compliance with the variation of the band gap. The considered systems, in regard to their stability and tunable fundamental properties seem to be very promising 2D semiconductors for wide range of applications at reduced scales. Then, the interaction of alkali metal atoms (Li, Na, and K) with single layer and periodic structures of hb-As and sw-As phases are revealed by first-principles methods. Arsenene phases are considered to be used as electrodes (anode) for ion-batteries. Strong alkali-electrode binding and low diffusion energy barriers gives out better cycling stability and faster diffusion, respectively. hb-As shows better storage capacity than sw-As. However, deviations from ordered pattern and decline of formation energy with increasing doping level point out a possible structural transformation. By MD calculations, crystalline to amorphous phase transition is seen even for low concentrations level at ambient temperature. The average open-circuit voltages of 0.68-0.88 V (0.65-0.98 V) with specific capacity up to 715 mAhg−1 (358 mAhg−1) are calculated for single layer (periodic) configurations. Overall, non-crystalline phases are calculated to offer more favorable structures than crystalline configurations and they provide more coherent results when compared with experimental data. The obtained voltage profile together with low diffusion barriers and strong metal-electrode binding suggests arsenene as a promising anode material to be used in for alkali-ion battery applications. Lastly, the formation of dumbbell (DB) geometry upon adsorption of Ga, N adatoms to GaN monolayer is investigated. While Ga-N DBs are unstable, Ga-Ga and N-N DB geometries are predicted to form in an exothermic and spontaneous scheme. Cohesive energy of hexagonal GaN monolayer decreases when a DB is formed on its surface. Electronic structures for Ga-Ga DBs for 2×2, 3×3, 4×4 and 5×5 phases show spinpolarized and degenerate bands mainly contributed by p-orbitals of the atoms in impurity zone. Degenarated bands are not observed for N-N dumbbell for HDP, TDP, 2×2 and 3×3 phases. Upon DB formation, semiconductor GaN monolayer become spin-polarized semiconductor with varying band gap, where this functionalization allows electronic structure to be tuned substantionally. This would be highly desired for nanoscale electronic and optical devices. These Ga-Ga and N-N DB geometries may also be used for the synthesis of layered GaN structures.
Open Access
Functionalized carbon nanotubes and device applications
(IOP, 2004) Çıracı, Salim; Dağ, Sefa; Yıldırım, T.; Gülseren, Oğuz; Senger, Ramazan Tuğrul
Carbon nanotubes, in which the two-dimensional hexagonal lattice of graphene is transformed into a quasi-one-dimensional lattice by conserving the local bond arrangement, provide several structural parameters for engineering novel physical properties suitable for ultimate miniaturization. Recent interest in nanoscience and nanotechnology has driven a tremendous research activity in carbon nanotubes, which has dealt with a variety of problems and produced a number of new results. Most of the effort has gone into revealing various physical properties of nanotubes and functionalizing them in different ways. This paper covers a narrow region in this enormous research field and reviews only a limited number of recent studies which fit within its scope. First, we examine selected physical properties of bare carbon nanotubes, and then study how the mechanical and electronic properties of different tubes can be modified by radial strain, structural defects and adsorption of foreign atoms and molecules. Magnetization of carbon nanotubes by foreign atom adsorption has been of particular interest. Finally, we discuss specific device models as well as fabricated devices which exploit various properties of carbon nanotubes.
Open Access
Growth of ∼3-nm ZnO nano-islands using Atomic layer deposition
(IEEE, 2016) El-Atab, N.; Chowdhury, F. I.; Ulusoy, Türkan Gamze; Ghobadi, Amir; Nazirzadeh, Amin; Okyay, Ali Kemal; Nayfeh, A.
In this work, the deposition of 3-nm dispersed Zinc-Oxide (ZnO) nanislands by thermal Atomic Layer Deposition (ALD) is demonstrated. The physical and electronic properties of the islands are studied using Atomic Force Microscopy, UV-Vis-NIR spectroscopy, and X-ray Photoelectron Spectroscopy. The results show that there is quantum confinement in 1D in the nanoislands which is manifested by the increase of the bandgap and the reduction of the electron affinity of the ZnO islands. The results are promising for the fabrication of future electronic and optoelectronic devices by single ALD step.
Open Access
Hybrid functional calculated optical and electronic structures of thin anatase TiO2 nanowires with organic dye adsorbates
(Elsevier, 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtioğlu, Ş.; Mete, E.
The electronic and optical properties of thin anatase TiO2 (1 0 1) and (0 0 1) nanowires have been investigated using the screened Coulomb hybrid density functional calculations. For the bare nanowires with sub-nanometer diameters, the calculated band gaps are larger relative to the bulk values due to size effects. The role of organic light harvesting sensitizers on the absorption characteristics of the anatase nanowires has been examined using the hybrid density functional method incorporating partial exact exchange with range separation. For the lowest lying excitations, directional charge redistribution of tetrahydroquinoline (C2-1) dye shows a remarkably different profile in comparison to a simple molecule which is chosen as the coumarin skeleton. The binding modes and the adsorption energies of C2-1 dye and coumarin core on the anatase nanowires have been studied including non-linear solvation effetcs. The calculated optical and electronic properties of the nanowires with these two different types of sensitizers have been interpreted in terms of their electron-hole generation, charge carrier injection and recombination characteristics.
Open Access
Intimate relationship between structural deformation and properties of single-walled carbon nanotubes
(Cambridge, 2002) Yıldırım, Taner; Gülseren, Oğuz; Çıracı, Salim
Carbon nanotubes continue to surprise scientists with their novel properties. Recently we have discovered many intimate relationships between structural deformation and the properties of single-walled nanotubes (SWNT), that could be important in technological applications. From first-principles we show that by using pressure, carbon nanotubes can be covalently joined to form one and two-dimensional networks of interlinked nanotubes. We also find that the band gap of an insulating nanotube can be engineered by elliptical distortion, which is found to be in the elastic range. This could allow the fine-tuning of the properties of SWNTs via reversible deformation and ultimately lead to variable quantum devices. Finally, we have very recently shown that the chemical reactivity of nanotubes can be tuned by elliptical deformation, which may provide a way to attach various atoms such as H and metals to a specific location on a nanotube.