Optical Transport Properties Research Articles

In-plane anisotropic electronic properties in layered α′-In2Se3

In2Se3 polymorphs have been extensively studied because of their diverse physical properties such as piezoelectricity, photoelectricity, and ferroelectricity, thereby showing plentiful promising applications in integrated electronic devices. These diverse properties are strongly dependent on or affected by their atomic bonding arrangement in the crystal phases. Combining lattice symmetry and local atomic perturbation, we demonstrate a novel layered α′-In2Se3 phase by using the first-principles calculations, which is reconstructed from the inverted tetrahedral bonding configuration by the in-plane displacive middle layer Se atom. The optimized structure of monolayer α′-In2Se3 has triple degenerated atomic configurations with different Se atom orientations. We noted that these degenerated atomic configurations exhibit a moderate switching barrier (about 61 meV/f.u.) between them. To further explore this atom-oriented anisotropic property in α′-In2Se3, the electronic properties were studied with an orthorhombic unit cell. The comparative results for the orthogonal Se atom orientations suggest that the nonbonding orbital coupling of the displacive Se atoms induces large in-plane anisotropic optical absorption and electrical transport properties. This study of the layered α′-In2Se3 phase can extend the realm of switchable anisotropic optoelectronic applications in future electronic devices.

Strain engineering and thermal conductivity of a penta-BCN monolayer: a computational study

Two-dimensional (2D) pentagonal nanostructures have been caught research attention down to their electronic, optical, mechanical and thermal transport properties. Among them, the newly proposed ternary penta-BCN monolayer shows a great potential for piezoelectric materials according to intrinsic piezoelectricity and spontaneous polarization. Nevertheless, the effect of strain toward these properties of the penta-BCN has not been elucidated. In this study, using density-functional theory with the Perdew–Burke–Ernzerhof (PBE) functional, we have investigated the impact of a uniform biaxial strain on the electronic structure and the thermal conductivity of the semiconducting penta-BCN single sheet. The strain-free penta-BCN monolayer is mechanically and dynamically stable with an indirect band gap of 1.70 eV. The sheet is rather soft as judged from the low in-plane Young’s moduli. The pentagonal structure is preserved up to the yielding point of 18.4%, beyond this point the irreversible transition into the dynamically unstable, honeycomb-like system is observed. In contrast, the penta-BCN has dynamically instability under the compressive strain as small as −4%. The PBE band gap of the penta-BCN monolayer could be tuned within a range of 1.36–1.70 eV, falling into the infrared spectrum. The calculated lattice thermal conductivity of penta-BCN is around 97 W m−1 K−1 at temperature of 300 K, and decreases with increasing temperature.

Effect of sulfur-doped graphene quantum dots incorporation on morphological, optical and electron transport properties of CH3NH3PbBr3 perovskite thin films

Effect of sulfur-doped graphene quantum dots incorporation on morphological, optical and electron transport properties of CH3NH3PbBr3 perovskite thin films

Defect Passivation in Lead-Halide Perovskite Nanocrystals and Thin Films: Toward Efficient LEDs and Solar Cells.

Lead‐halide perovskites (LHPs), in the form of both colloidal nanocrystals (NCs) and thin films, have emerged over the past decade as leading candidates for next‐generation, efficient light‐emitting diodes (LEDs) and solar cells. Owing to their high photoluminescence quantum yields (PLQYs), LHPs efficiently convert injected charge carriers into light and vice versa. However, despite the defect‐tolerance of LHPs, defects at the surface of colloidal NCs and grain boundaries in thin films play a critical role in charge‐carrier transport and nonradiative recombination, which lowers the PLQYs, device efficiency, and stability. Therefore, understanding the defects that play a key role in limiting performance, and developing effective passivation routes are critical for achieving advances in performance. This Review presents the current understanding of defects in halide perovskites and their influence on the optical and charge‐carrier transport properties. Passivation strategies toward improving the efficiencies of perovskite‐based LEDs and solar cells are also discussed.

Exploring the potential of thin films made from poly(imide-amide-sulfone)s for engineering applications

This work focuses on the thorough investigation of structure–assisted multifunctional properties of some poly(amide-imide-sulfone) films specifically designed to meet the technological needs. In this respect, the influence of structural parameters onto mechanical, optical, dielectric and gas transport properties was deeply explored along with some general characteristics, like chemical integrity, thermal stability and solid-state packing. The understudy tough and flexible films featuring amorphous state displayed good mechanical behavior, withstanding repeating bending or rolling. The sulfone groups reduced the charge transfer complex formation, and in some cases, increased transparency. The permittivity, dielectric loss and conductivity and their variation with frequency and temperature were studied along with γ and β secondary relaxations originating from small- and large-scale segmental motions. The permeability of CO2, O2 and N2 through these dense films along with diffusion and solubility coefficients and respective selectivities were measured and discussed in relation with the structural parameters.

Molecular Structure‐Property Relationships of the Asymmetric Thienoacenes: Naphtho[2,3‐b]thieno[2,3‐d]thiophene, Anthra[2,3‐b]thieno[2,3‐d]thiophene, and their Thienyl Derivatives

AbstractPolycyclic aromatic compounds are attractive candidates for organic semiconductor materials whose optical and charge transport properties are significantly influenced by the molecular and packing structures. In this work, we investigated the crystal structure and physical properties of asymmetric bent‐shaped thienoacenes, which have a thieno[3,2‐b]thiophene unit at the end of the fused aromatic ring core, and their thienyl extended‐type derivatives. Among the naphthalene‐based analogs, naphtho[2,3‐b]thieno[2,3‐d]thiophene and its thienyl derivative gave an antiparallel slip‐stack structure. In contrast, among the anthracene‐based analogs, anthra[2,3‐b]thieno[2,3‐d]thiophene produced an antiparallel slip‐stack structure, while its thienyl derivative gave a layered structure with a large molecular orbital overlap. In extended conjugated systems, molecular symmetry of the long axis and dispersion forces were improved, resulting in the formation of crystal structures with large intermolecular interactions. These results suggest the importance of both the extension and molecular symmetry of a conjugated system to controlling the molecular structure.

Electronic, optical, and thermoelectric properties of Janus In-based monochalcogenides

Inspired by the successfully experimental synthesis of Janus structures recently, we systematically study the electronic, optical, and electronic transport properties of Janus monolayers In2 XY (X/Y = S, Se, Te with X ≠ Y) in the presence of a biaxial strain and electric field using density functional theory. Monolayers In2 XY are dynamically and thermally stable at room temperature. At equilibrium, both In2STe and In2SeTe are direct semiconductors while In2SSe exhibits an indirect semiconducting behavior. The strain significantly alters the electronic structure of In2 XY and their photocatalytic activity. Besides, the indirect–direct gap transitions can be found due to applied strain. The effect of the electric field on optical properties of In2 XY is negligible. Meanwhile, the optical absorbance intensity of the Janus In2 XY monolayers is remarkably increased by compressive strain. Also, In2 XY monolayers exhibit very low lattice thermal conductivities resulting in a high figure of merit ZT, which makes them potential candidates for room-temperature thermoelectric materials.

Theoretical investigation of novel half Heusler compounds MRhSb (M = Nb & Ta): For optoelectronic and thermoelectric applications

AbstractThe main objective of this work is to make a detailed study on a new class of half heuslers which possess a 19 valence electron and which are sought for perpetually because of their thermoelectric performances. The mechanical, electronic structures, optical, and electrical transport properties are studied using full potential linearized augmented plane wave (LAPW) + local orbitals (lo) scheme, in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) for the purpose of exchange correlation energy functional. The electronic structure is treated by the TB‐mBJ exchange‐correlation potentials. The independent elastic constants and the related mechanical properties are investigated. From the energy bands and density of states it is observed that the 3d‐states of Nb, Ta, and Rh atoms contribute mainly to the conduction band, which results in increase in electrical and thermal conductivity of NbRhSb and TaRhSb . The optical constants as the dielectric function, refractive index, optical reflectivity, and absorption coefficient were calculated and discussed in detail. The dependence of Seebeck coefficient, electrical conductivity, and power factor on the Fermi level is investigated.

Radiative transfer in a Solar CPC Photoreactor using the First-Order Scattering Method

Abstract This manuscript analyzes the suitability of a recently proposed numerical method, the First-Order Scattering Method (FOS), to describe radiation transfer in a Solar Compound Parabolic Collector Photoreactor (CPCP). The study considers five different irradiance conditions ranging from fully diffuse to fully direct solar radiation, with 90 and 45° angled rays. Three photocatalysts at different loadings were considered: Evonik P25, Graphene Oxide, and Goethite, selected due to (1) their relevance in photocatalytic applications and (2) the availability of optical transport properties in the open literature. The study shows that the method is efficient and free of statistical noise, while its accuracy is not affected by the boundary condition’s complexity. The method’s accuracy is very high for photocatalysts with low to moderate albedos, such as Goethite and Graphene Oxide, displaying Normalized Absoluted Mean Error below 3%, i.e., comparable to the Monte Carlo (MC) Method’s statistical fluctuations.

First-principles investigation of electronic, optical, mechanical and heat transport properties of pentadiamond: A comparison with diamond

Pentadiamond is a carbon allotrope consisting of hybrid sp2 and sp3 atoms, which has been predicted to be stable and synthesizable. In this work we employ first-principles calculations to explore the electronic structure, optical characteristics, mechanical response and lattice thermal conductivity of pentadiamond, performing a direct comparison with the corresponding properties in diamond. The HSE06 density functional predicts indirect electronic band gaps for pentadiamond and diamond with values of 3.58 eV and 5.27 eV, respectively. Results for optical characteristics reveal pentadiamond’s large absorption in the middle UV region, where diamond does not absorb light, consistent with the smaller band gap of pentadiamond. The elastic modulus and tensile strength of pentadiamond are found to be 496 GPa and 60 GPa, respectively, considerably lower than the corresponding values for diamond. The lattice thermal conductivity is examined by solving the Boltzmann transport equation, with anharmonic force constants evaluated via state-of-the-art machine-learning interatomic potentials. We predict a thermal conductivity of 427 W/m-K for pentadiamond, less than one fifth of the corresponding quantity for diamond. Our results provide a useful vision of the intrinsic properties of pentadiamond, but also highlight some of its disadvantages in mechanical strength and heat conduction when compared to diamond.

Comparison of mechanical, optical and electronic transport properties of ‎isotropic and anisotropic borophosphene

In this research, mechanical, optical and electronic transport properties of two phases of graphene-like borophosphene are investigated using density functional theory. Graphene-like borophosphene, a honeycomb structure with equal ratio of boron and phosphorus atoms, is introduced in two isotropic and anisotropic phases. For this purpose, band structure, partial density of states, Young’s modulus, Poisson ratios, dielectric function, and current-voltage characteristics are calculated and compared. The results show that the anisotropic phase of graphene-like borophosphene is semimetal and the isotropic phase is a semiconductor with a direct energy gap of 0.9 eV. Moreover, the Young’s modulus has the highest values for both phases in the zigzag and armchair directions of crystal, and the Poisson ratio has the lowest values in these two directions. Besides, optical properties of these two structures include electron energy loss spectroscopy, refractive index, extinction coefficient, optical conductivity and reflection coefficient for parallel and perpendicular polarization of electric fields respect to the sheets are computed by real and imaginary parts of dielectric function using random phase approximation. Plasmon’s energies are obtained 2.24 and 8.88 eV in the armchair direction and 9.01 eV in the zigzag direction for the anisotropic phase and for the isotropic phase, 3.38 and 9.12 eV are obtained in both directions. Both phases are transparent respect to visible light polarized in the perpendicular direction to the crystal, and the reflection and absorption are zero. Due to the selective transmission / absorption / reflection of the electromagnetic wave in the crystals, this material is suggested as a suitable candidate in the fabrication of nano optoelectronic devices. Furthermore, Ohmic behavior is observed in current-voltage characteristics of the isotropic phase after the threshold bias voltage of 0.9 V. As a result of the high Fermi velocity of charge carriers in the anisotropic phase of borophosphene ( ), this material can be used in nanoelectronic devices.

The influence of localized states on the optical absorption and carrier transport properties of acylamino hybrid perovskites with tunable electronic structures

Organic-inorganic hybrid perovskite solar cells have excellent optoelectronic properties, but their low thermal and chemical stabilities limit their commercial applications. In this paper, a new type of organic-inorganic hybrid perovskite is proposed. Malondiamide (MA,CH2(CONH2)2) and propionamide (PA, CH3CH2CONH2) were used as organic layers, with Pb-I octahedral inorganic layers to form quasi three-dimensional (3D) perovskites. The crystal structure, stability, electronic structure, and optical properties of MAPbI4 and PAPbI4 perovskites were investigated, and the results showed that there were localized states that corresponded to the number of acyl groups in the two perovskites. Energy band calculations showed that the localized states of the two perovskites rose above the bottom of the conduction band. This can be used to regulate the band gap of the two perovskites, which affects the electronic properties and optical absorption characteristics of the two perovskites. Compared with PAPbI4, MAPbI4 has a lower formation energy, lower band gap, lower effective mass of electrons and holes, wider energy range, and larger absorption coefficient, which indicates that MAPbI4 is more suitable for use in solar cells. This study provides guidance for obtaining efficient and stable photovoltaic materials.

Optical properties of a waveguide-mediated chain of randomly positioned atoms.

We theoretically study the optical properties of an ensemble of two-level atoms coupled to a one-dimensional waveguide. In our model, the atoms are randomly located in the lattice sites along the one-dimensional waveguide. The results reveal that the optical transport properties of the atomic ensemble are influenced by the lattice constant and the filling factor of the lattice sites. We also focus on the atomic mirror configuration and quantify the effect of the inhomogeneous broadening in atomic resonant transition on the scattering spectrum. Furthermore, we find that initial bunching and persistent quantum beats appear in photon-photon correlation function of the transmitted field, which are significantly changed by the filling factor of the lattice sites. With great progress to interface quantum emitters with nanophotonics, our results should be experimentally realizable in the near future.

Interface Chemical Modification between All-Inorganic Perovskite Nanocrystals and Porous Silica Microspheres for Composite Materials with Improved Emission.

In recent years, there has been rapid progress in the development of photonic devices based on lead halide perovskite nanocrystals since they possess a set of unique optical and charge transport properties. However, the main limiting factor for their subsequent application is poor stability against exposure to adverse environmental conditions. In this work, a study of a composite material based on perovskite CsPbBr3 nanocrystals embedded in porous silica microspheres is presented. We developed two different approaches to change the interface between nanocrystals and the surface of the microsphere pores: surface treatment of (i) nanocrystals or (ii) microspheres. The surface modification with tetraethylorthosilicate molecules not only increased stability but also improved the optical responses of the composite material. The position of the emission band remained almost unchanged, but its lifetime increased significantly compared to the initial value. The improvement of the optical performance via surface modification with tetraethylorthosilicate molecules also works for the lead-free Bi-doped Cs2AgInCl6 double perovskite nanocrystals leading to increased stability of their optical responses at ambient conditions. These results clearly demonstrate the advantage of a composite material that can be used in novel photonic devices with improved performance.

The bimetallic and the anchoring group effects on both optical and charge transport properties of hexaphyrin amethyrin

Bimetallic Cu(ii)-hexaphyrin amethyrin proposed as a molecular switch operated by the application of an external magnetic field.

Efficient Bilayer Light-Emitting Diode Based on Distyrylarylene-Containing Polymers: Numerical and DFT Simulation

In this article, we report a combined experimental and theoretical study on the optoelectronic properties of two semi-conducting polymers containing different <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -conjugated sequences [distyrylphenylene (P-DSP) and distyrylbithiophene (P-DSBT)]. Theoretical calculations were conducted, based on time-dependent density functional theory and Marcus theories, to predict the optical, electronic, and charge transport properties of the studied polymers. These results were compared with the experimental ones measured using UV–vis and photoluminescence (PL) spectroscopies. The P-DSBT polymer shows good absorption with a maximum absorption wavelength of 426 nm and a green emission with a maximum wavelength of 508 nm. Besides, the calculated characteristics showed that P-DSBT has better electron and hole mobilities of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.9\times 10^{-6}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-2}\,\,\text{V}^{-1}\,\,\text{s}^{-1}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.4\times 10^{-6}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-2}\,\,\text{V}^{-1}\,\,\text{s}^{-1}$ </tex-math></inline-formula> , respectively. A numerical simulation of ITO/polymer/Al device using the Silvaco Tecad simulator was reported and fitted to the experimental data and the results reveal an excellent overlap with the experimental ones. Moreover, the simulation of ITO/polymer/Alq <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Al bilayer organic light-emitting diode (OLED) has been performed and electrical behavior enhancement was evidenced compared with the monolayer device with a maximum current decrease from 9 to 49 mA, using P-DSBT polymer.

Nonlinear optical control of chiral charge pumping in a topological Weyl semimetal

Solids with topologically robust electronic states exhibit unusual electronic and optical transport properties that do not exist in other materials. A particularly interesting example is chiral charge pumping, the so-called chiral anomaly, in recently discovered topological Weyl semimetals, where simultaneous application of parallel DC electric and magnetic fields creates an imbalance in the number of carriers of opposite topological charge (chirality). Here, using time-resolved terahertz measurements on the Weyl semimetal TaAs in a magnetic field, we optically interrogate the chiral anomaly by dynamically pumping the chiral charges and monitoring their subsequent relaxation. Theory based on Boltzmann transport shows that the observed effects originate from an optical nonlinearity in the chiral charge pumping process. Our measurements reveal that the chiral population relaxation time is much greater than 1 ns. The observation of terahertz-controlled chiral carriers with long coherence times and topological protection suggests the application of Weyl semimetals for quantum optoelectronic technology.

Spin-dependent rare-earth-based MgPr2X4 (X = S, Se) spinels investigations for spintronic and sustainable energy systems applications

In this paper, density functional theory (DFT) calculations are performed to investigate the spin-dependent mechanical, electronic, magnetic, optical, and thermal transport properties of rare-earth-based chalcogenides MgPr2X4 (X = S, Se) spinels. The mechanical properties are obtained by employing the modified Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA). Also, the modified Becke and Johnson (mBJ) potential is engaged in examining the electronic, magnetic, optical, and transport properties. Structural stability in the ferromagnetic (FM) phase is confirmed by calculating the energy difference between the FM and non-magnetic states. Besides, the formation energies are computed for thermodynamic stability. The strong hybridization near the Fermi level comes from chalcogenides 2p-states and f-states of rare-earth metals, which results in the total magnetic moments. The in-depth optical properties are evaluated in terms of dielectric constant and refraction. Lastly, electronic thermal coefficients, such as Seebeck coefficient, electrical and thermal conductivity, and power factor, are also probed and suggested studied spinels as promising sustainable energy materials.

Perfluorodioxolane Polymers for Gas Separation Membrane Applications.

Since the discovery of polytetrafluoroethylene (PTFE) in 1938, fluorinated polymers have drawn attention in the chemical and pharmaceutical field, as well as in optical and microelectronics applications. The reasons for this attention are their high thermal and oxidative stability, excellent chemical resistance, superior electrical insulating ability, and optical transmission properties. Despite their unprecedented combination of desirable attributes, PTFE and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene and perfluoropropylvinylether are crystalline and exhibit poor solubility in solvents, which makes their processability very challenging. Since the 1980s, several classes of solvent-soluble amorphous perfluorinated polymers showing even better optical and gas transport properties were developed and commercialized. Amorphous perfluoropolymers exhibit, however, moderate selectivity in gas and liquid separations. Recently, we have synthesized various new perfluorodioxolane polymers which are amorphous, soluble, chemically and thermally stable, while exhibiting much enhanced selectivity. In this article, we review state-of-the-art and recent progress in these perfluorodioxolane polymers for gas separation membrane applications.

Optical and hidden transport properties of BaFe1.91Ni0.09As2 film

Optical spectroscopy was used to study the electrodynamics and hidden transport properties of a BaFe1.91Ni0.09As2 thin superconducting (SC) film. We analyzed the normal state data using a Drude–Lorentz model with two Drude components: one narrow (D1) and another broad one (D2). In the SC state, two gaps with –2.0 and –4.3 are formed from the narrow component D1 while the broad component D2 remains ungapped. The calculated total DC resistivity of the film and the low-temperature scattering rate for the narrow Drude component show a hidden Fermi-liquid behavior. The change of total electron–boson coupling (λ tot) and representative energy (Ω0) in the normal state with respect to the SC state is typical of other iron-based materials as well as high-temperature superconducting (HTSC) cuprates.