Department of Condensed Matter Physics (1982 - Present)
Physics
, Greece, Greece
Physics
, Oregon, U.S.A
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We investigated structural, electronic, and optical properties of Sb/PtTe2 van der Waals heterostructure using density functional theory. Four different configurations were chosen to investigate the band structures and find the most stable configuration. Due to the distance between two individual layers (3.59??) and calculations of vdW-corrections the interface interactions of Sb/PtTe2 are controlled by vdW forces. Our wannierized band structure calculations along with the band alignment of the most stable configuration show that the nature of valence band maximum and conduction band minimum are contributed by PtTe2 resulting a type I band alignment with an indirect bandgap (1.05?eV), making efficient recombination of the photo
In this article, the structural, electronic, and optical properties of antimonene/palladium ditelluride van der Waals heterostructure were investigated using density functional theory. Our results revealed the Sb/PdTe2 heterostructure in its most stable configuration is an indirect semiconductor with energy bandgap of 0.49 eV and a type-I band alignment. We also studied the impact of strain and external electric field on the structural and electronic properties of this heterostructure. Our results indicate that the band alignment of this heterostructure could be controlled by changing the external electric field and strain parameters to make type-I or type-II semiconductors or a conductor with energy bandgap between 0 eV and 0.55 eV.
High crystalline order, large grains and low defects are important parameters to enhance the structural and optoelectrical properties of a thin film. Here, it was found that these parameters affected by substituting ionic radius in the crystal structure of a thin film. In this report, three ionic radii of Cr2+, Cr3+ and Zn2+ ions were compared to get the optimum structural and optoelectrical properties represented in the CZTS, CCr2+TS and CCr3+TS thin films. Among the highest properties are the crystalline order, absorption coefficient, refractive index, dielectric constants and polarizability to the light. So, the authors believe that the CCr2+TS thin film can be used as an absorber layer instead of CZTS thin film for thin-film solar cell
Rich physical properties of ferrite nanoparticles, which exhibit a spinel structure, are sensitive to the distribution of cations in tetrahedral and octahedral sites as well as the crystal field effect, both of which can modify the electronic structure. Here, using a hydrothermal method, we incorporated Co+2 ions into nickel ferrite (NiFe2O4) nanoparticles to synthesize Ni1-xCoxFe2O4 (x?=?0.0, 0.5, 1) nanoparticles and studied how their structural, electronic, and electrochemical properties are influenced by the Co+2 content. We found that the employed surfactant agent (here, CTAB) is critically important and affects the size and the specific surface area of the nanoparticles. X-ray diffractometry indicated that the obtained nanoparticles h
Graphene oxide nanosheets were coated on thin films of vertical ZnO nanorods and incrementally reduced into rGO by the photocatalytic effect of ZnO for different times. The photocatalytic reduction (1) slightly decreased bandgap, considerably increased the ultraviolet absorption, and significantly enhanced the charge carrier separation in rGO–ZnO, while (2) increased the defects in rGO sheets. We tested the rGO/ZnO thin films for ultraviolet sensing and found that 60-min reduction is the optimal case. We discussed the result based on competition between the above (1) and (2) findings.
Predicting the realistic bandgap of a semiconductor is critical to its applications. A relatively new two-dimensional semiconducting structure with few experimental reports is graphene-like ZnO (g-ZnO). Although the bandgaps of various bulk structures of ZnO are well-known experimentally and theoretically, there is not yet any experimental report on the bandgap of g-ZnO. On the other hand, the standard density functional theory (DFT) grossly underestimates the bandgap of metal oxides, especially in the case of the bulk wurtzite ZnO with the predicted bandgap of ∼0.72 eV as compared to the experimental bandgap of ∼3.3 eV. There are two widely used approaches to partly resolve the problem of DFT: (1) the computationally expensive use
Strong excitonic effects is a very subtle issue in pristine hexagonal boron nitride (h-BN) and h-BN nanoribbons (h-BNNRs) due to large band gaps and reduced dimensionality. One of the reasons for such a large exciton binding energy (as large as 2.5 eV) is weak dielectric screening. Employing first-principles calculations in conjunction with the constrained random-phase approximation, we determine the strength of the Coulomb matrix elements for pristine h-BN and h-BNNRs with armchair and zigzag edges. Due to the nonconventional screening, the calculated off-site U parameters for passivated h-BNNRs turn out to be rather sizable. Coulomb interaction is weakly screened at short distances and antiscreened at intermediate distances. Transition fr
Using a first-principles study, we investigated structural, electronic, and optical properties of a heterostructure (HTS) composed of graphene-like zinc oxide (g-ZnO) and alpha-phase platinum dioxide (α-PtO2) monolayers and studied how the properties are influenced by perpendicular electric fields applied across the HTS. The formation of the vdW HTS significantly narrowed the wide bandgaps of the individual components (3.3 and 3.23?eV for g-ZnO and α-PtO2 monolayers, respectively) to 0.47?eV with a type-II (staggered) band alignment and large valence band and conduction band offsets. Furthermore, band structure calculations showed that the charge densities corresponding to the valence band maximum and the conduction band minimum lie compl
By using a facile hydrothermal method, we synthesized Ni 1− x Mn x Fe 2 O 4 nanoparticles as supercapacitor electrode materials and studied how the incremental substitution of Ni with Mn would affect their structural, electronic, and electrochemical properties. X-ray diffractometry confirmed the single-phase spinel structure of the nanoparticles. Raman spectroscopy showed the conversion of the inverse structure of NiFe 2 O 4 to the almost normal structure of MnFe 2 O 4. Field-emission scanning electron microscopy showed the spherical shape of the obtained nanoparticles with a size in the range of 20–30 nm. Optical bandgaps were found to decrease as the content of Mn increased. Electrochemical characterizations of the samples indicated t
Manganese ferrite (MnFe2O4) nanoparticles were synthesized via a hydrothermal method and combined with exfoliated MoS2 nanosheets, and the nanocomposite was studied as a supercapacitor. X-ray diffractometry and Raman spectroscopy confirmed the crystalline structures and structural characteristics of the nanocomposite. Field-emission scanning electron microscopy images showed the uniform and dense distribution of MnFe2O4 nanoparticles (~ 10 nm) on few-layer MoS2 nanosheets (~ 2 to 3 ?m in width). UV-visible absorption photospectrometry indicated a decrease in the bandgap of MnFe2O4 by MoS2, resulting in a higher conductivity that is suitable for capacitance. Electrochemical tests showed that the incorporation of MoS2 nanosheets largely incre
Recently, quaternary Cu2ZnSnS4 (CZTS) semiconductor has been garnering attention in CZTS thin film solar cells. In order to improve the physical properties of CZTS semiconductor which in turn enhancing the conversion efficiency of CZTS thin film solar cells, Fe+3 has been incorporated into CZTS semiconductor using the solvothermal method. The experimental results of effecting Fe+3 showed that the Fe+3 had stronger hybridization and more effective on energy storage than Fe+2 thus it's more convenient than Fe+2. XRD pattern revealed the crystal structure was high crystallinity and low distortion. Raman analysis indicated the structural transition from kesterite Cu2ZnSnS4 to stannite Cu2FeSnS4 occurred in the Cu2(Zn1-xFex)SnS4 samples with Fe3
Few-layer exfoliated MoS2 nanosheets were easily composited with ZnO nanorods. It was found that MoS2 nanosheets could enhance the sunlight-induced photocatalytic activity rate of ZnO by 74%. In addition, we showed that under UV-blocked sunlight irradiation, MoS2 weakens the photocatalytic activity rate of ZnO by 33%. Finally, we discussed the mechanisms behind the enhanced (weakened) photocatalytic activity under sunlight (UV-blocked sunlight) irradiation based on the UV-Vis absorption and photoluminescence spectra as well as the potential band diagrams of the ZnO/MoS2 composite.
Ag nanoparticles were deposited on a hydrogenate amorphous carbon (a-C:H) thin film as a host by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) for various deposition times. We observed that as the sputtering time increases, the particle shape of the deposited nanostructures changes to a cluster shape. AFM images show that the accumulation of the nanoparticles on each other leads to the vertical growth of the nanoclusters. According to X-ray diffraction patterns, the crystalline structure is formed for the nanocluster shape. The Fourier-transform infrared (FTIR) spectroscopy showed that bonds are formed between Ag ions and free hands of carbons on the surface of the a-C:H film. The peak related to carbid
Electronic and magnetic properties of the heavily H-doped LaFeAsO 1 − x H x ( x ∼ 0.5 ) were studied in the framework of the density functional theory combined with the dynamical mean field theory. We found a stripe-like-ordered structure of hydrogen and oxygen atoms, as the ground state, in a 2 a ? 2b ?c supercell, with the same configuration as the antiferromagnetic order. The new configuration could explain the existing experimental results related to the heavily H-doped LaFeAsO 1 − x H x, such as the in-plane electronic anisotropy and the nonuniform magnetic behavior. A significant anisotropy was observed between Fe-3d x z (xz) and Fe-3d y z (yz) orbitals in the ground state in the absence of the pseudogap resulting from the spin
In this report for the first time, the Cu2Zn1-xBixSnS4 (CZBiTS) semiconductor at (0 ≤ x ≤ 1) has been synthesized using the solvothermal and spin coating methods. The structural, optical, morphological and electrical properties of CZBiTS semiconductor were investigated. It was found that the Cu2BiSnS4 (x = 1) (CBiTS) thin film was better than the Cu2ZnSnS4 (x = 0) (CZTS) and CZBiTS (x = 0.25, 0.5 and 0.75) thin films due to its optimum features like higher absorption coefficient (>104 cm−1), higher optical conductivity, lower transmittance and lower band gap (1.25 eV). Furthermore, the CBiTS thin film was more uniform, improved and had large grains so; it was observed the number of grains in the CBiTS film, 0
In this regard for the first time, the multicomponent chalcogenide Cu2(Zn1-xCrx)SnS4 (CZCrTS) nanocrystals at (0 ≤x ≤ 1) were synthesized by the solvothermal method. Improvement of structural, optical and electrical properties in Cr-doped Cu2ZnSnS4 thin film deposited on SLG substrate by spin coating technique has been investigated. It was observed that introduced the Cr element into the Cu2ZnSnS4 nanocrystal led to increasing the disorder of cations distribution within the unit cell through increasing the tensile strain inside the unit cell resulting in a decline the unit cell volume accompanied by a decrease the particle size and also the crystallite size. It has been found that the optical band gap of the CZCrTS nanocrystals ra
Graphene quantum dots (GQDs) were simply synthesized by pyrolysis of citric acid, and zinc oxide nanorods (ZnO NRs) were grown on pre-seeded glass substrates by a solvothermal method. Finally, the GQDs were dropped on the ZnO NR thin film. It was found that the incorporation of GQDs eliminated the photoluminescence (PL) intensity of the ZnO NR thin film, suggesting that electrons of ZnO can be readily transferred to GQDs, contributing to the passing current. Finally, the ethanol sensing analysis was performed, showing that the incorporation of GQDs enhanced the sensitivity of ZnO NR thin film to ethanol gas, and the mechanism behind the enhancement was discussed.
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