Electronic Properties Of Materials Research Articles

First principles study of structural and electronic properties of Ce substituted Ti2O3 slabs with compositions TixCe4-xO6 where x = 0, 1, 2, 3, 4

This study employs Density-functional theory (DFT) to investigate the structural and electronic properties of Ce2O3–Ti2O3 alloys. We systematically examined the structural and electronic properties of the two dimensional (2D) alloys, thereby exploring the impact of Ce substitution in Ti2O3 in full alloy range. The study of charge transfer and bonding analysis revealed the series of materials have dominant ionic character and it decreases linearly with an increase of Ce percentage. Initially, we observed that the parent material Ti2O3 exhibited semiconducting behavior with a narrow band gap of 0.29 eV. However, upon further incorporating Ce substitution into the pristine crystal structure, all the prepared alloys showed an increase of population of states in the band structure. Notably, the band gap of Ti3CeO6 alloy decreased to 0.13 eV and eventually reduced to zero. This trend was consistent across other metallic alloy systems, including Ti2Ce2O6, TiCe3O6, Ce2O3. Moreover, our results revealed that an increased concentration of Ce atoms led to the emergence of magnetic behaviour in the alloys. The work function of all materials to check the reactivity of the studied alloys is also reported. Further, the DFT + U method is employed to include the Hubbard U correction for electronic properties of materials.

Lithium-Ion Dynamic and Storage of Atomically Precise Halogenated Nanographene Assemblies via Bottom-Up Chemical Synthesis.

Graphene has received much scientific attention as an electrode material for lithium-ion batteries because of its extraordinary physical and electrical properties. However, the lack of structural control and restacking issues have hindered its application as carbon-based anode materials for next generation lithium-ion batteries. To improve its performance, several modification approaches such as edge-functionalization and electron-donating/withdrawing substitution have been considered as promising strategies. In addition, group 7A elements have been recognized as critical elements due to their electronegativity and electron-withdrawing character, which are able to further improve the electronic and structural properties of materials. Herein, we elucidated the chemistry of nanographenes with edge-substituted group 7A elements as lithium-ion battery anodes. The halogenated nanographenes were synthesized via bottom-up organic synthesis to ensure the structural control. Our study reveals that the presence of halogens on the edge of nanographenes not only tunes the structural and electronic properties but also impacts the material stability, reactivity, and Li+ storage capability. Further systematic spectroscopic studies indicate that the charge polarization caused by halogen atoms could regulate the Li+ transport, charge transfer energy, and charge storage behavior in nanographenes. Overall, this study provides a new molecular design for nanographene anodes aiming for next-generation lithium-ion batteries.

Coupled Dynamic Characteristics of Mobile Ions in Halide Perovskites.

Mixed perovskites show immense promise for diverse applications owing to their exceptional compositional flexibility and outstanding optoelectronic performance. Nevertheless, a significant hurdle in their widespread use is their susceptibility to compositional instability. Some mixed perovskites exhibit a tendency to segregate into regions with varying halide content, negatively impacting the material's electronic properties and impeding its overall advancement. This study focuses on investigating the lattice and A-site cation dynamics in mixed-halide perovskites as well as the relationship between the stability and dynamic properties of mixed-halide perovskites. Our findings reveal an intrinsic link between the kinetics of organic molecules and halogen ion migration. The stability of halide ions is linearly positively correlated with the radius, number of H atoms, and moment of inertia of the organic molecules. Organic molecules with lower rotational kinetics effectively suppress the overall cationic kinetic activity, enhancing lattice dynamic stability in mixed perovskite systems. This inhibition further impedes the migration of halogen ions and hinders the halide segregation process. The presence of dominant I/MA vacancies in perovskites accelerates the rotation of MA and the migration of halogen ions. The coupled dynamic behavior of varying vacancy concentrations in A-site cations/X-site anions within the inorganic framework significantly impacts the photovoltaic performance of these halide perovskites.

Analytical investigation of thermodynamic properties of power electronic semiconductor materials

Analytical investigation of thermodynamic properties of power electronic semiconductor materials

An ultrasensitive electrochemical sensor based on boron-doped porous graphene for efficient detection of nitrite in food

Boron (B) doping plays a critical role in adjusting the electronic properties of carbon materials. In this work, B-doped porous graphene (B-PG) was successfully prepared by a simple strategy and used as an advanced electrode material for the detection of nitrite (NO-2) in food. The scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize this B-PG. Due to the ideal doping of boron atoms, the material has good conductivity and exhibits excellent electrochemical catalytic performance. NO-2 was used as the representative analytes to demonstrate the sensing performance of B-PG. It is found that the B-PG modified GCE exhibited a linear response over the concentration range from 3 μM – 3 mM and 3 mM – 15 mM, with a detection limit of 1.1 μM. The designed electrochemical sensor has good analytical performance, such as high sensitivity, good reproducibility and acceptable accuracy, and can be successfully applied to the accurate and precise detection of residual NO-2 in food.

Toward coupling across inorganic/organic hybrid interfaces: polyaniline-coated gold nanoparticles with 4-aminothiophenol as gold-anchoring moieties

AbstractThe chemical binding between metal nanoparticles and (semi-)conductive polymer layers is essential to control the (opto-)electronic properties of such hybrid materials. Current approaches that achieve a conjugated binding of organic (semi-)conductive ligands to metal nanoparticles demonstrated promising functional properties, but are based on tedious multi-step organic synthesis to incorporate the required binding moieties at the chain ends of targeted macromolecular species. Herein, we explore the pre-functionalization of gold nanoparticles with p-aminothiophenol and subsequent surfactant-assisted formation of a poly(aniline) (PANI) shell as a means to access gold/PANI core–shell-type nanoparticles with enhanced conductive properties. Controlled surface deposition of these hybrid nanoparticles is achieved via template-assisted self-assembly. For these surface-deposited nanoparticles, charge transport properties are characterized at the nanoscale by conductive atomic force microscopy measurements and show a significant conductivity increase of our core–shell particles as compared to reference particles formed by conventional surfactant-assisted PANI-shell formation. Graphical Abstract

Gas-Induced Electrical and Magnetic Modulation of Two-Dimensional Conductive Metal-Organic Framework.

Controlled modulation of electronic and magnetic properties in stimuli-responsive materials provides valuable insights for the design of magnetoelectric or multiferroic devices. This paper demonstrates the modulation of electrical and magnetic properties of a semiconductive, paramagnetic metal-organic framework (MOF) Cu3(C6O6)2 with small gaseous molecules, NH3, H2S, and NO. This study merges chemiresistive and magnetic tests to reveal that the MOF undergoes simultaneous changes in electrical conductance and magnetization that are uniquely modulated by each gas. The features of response, including direction, magnitude, and kinetics, are modulated by the physicochemical properties of the gaseous molecules. This study advances the design of multifunctional materials capable of undergoing simultaneous changes in electrical and magnetic properties in response to chemical stimuli.

Coherent potential approximation study of impurity effect on monolayer hexagonal boron phosphide

Impurity doping is a necessary technology for the application of semiconductor materials in microelectronic devices. The quantification of doping effects is crucial for controlling the transport properties of semiconductors. Here, taking two-dimensional (2D) hexagonal boron phosphide semiconductor as an example, we employ coherent potential approximation method to investigate the electronic properties of 2D semiconductor materials at low doping concentrations, which cannot be exploited with conventional density function theory. The results demonstrate that the positive or negative impurity potential in 2D semiconductors determines whether it is p-type or n-type doping, while the impurity potential strength decides whether it is shallow-level or deep-level doping. Impurity concentration has important impacts on not only the intensity but also the broadening of impurity peak in band gap. Importantly, we provide the operating temperature range of hexagonal boron phosphide as a semiconductor device under different impurity concentrations and impurity potentials. The methodology of this study can be applied to other 2D semiconductors, which is of great significance for quantitative research on the application of 2D semiconductors for electronic devices.

Structural, Dielectric and Magnetic Properties of MFeNbO6 materials (M=Ti , Zr, Hf)

We study the structural, magnetic and electronic properties of MFeNbO6 materials (where A = Ti, Zr or Hf). TiFeNbO6 crystallises with the disordered rutile structure with the P42/mnm space group. Increasing the ionic radii of the M4+ cation going from Ti4+ (0.605 Å) to Zr4+ (0.72 Å) and Hf4+ (0.710 Å) results in a buckling of the octahedral chains with these materials crystallising with the disordered α-PbO2 structure (space group Pbcn). In contrast, with previous reports for TiFeNbO6 we find no evidence of relaxor ferroelectric behaviour with all three materials instead exhibiting Maxwell-Wagner-like relaxation. Impedance spectroscopy confirms semiconductor behaviour. Magnetically, all three materials can be described by infinite irregular antiferromagnetic S = 5/2 chains with weak ferromagnetism below 10 K. These chains have random directions of propagation between nearest Fe-Fe neighbours consistent with the disordered nature of these materials. We observed a negative imaginary part of the ac susceptibility related to the defect magnetic topology.

Effect of Changing and Combining Trivalent Metals in the Structural and Electronic Properties of Cu-Based Crystal Delafossite Materials

Cu-based ternary oxides with delafossite structure have received considerable attention in recent years for their versatility in a wide range of applications, among which is the possibility to use them in heterostructure solar cells as hole transport layers, due to their promising behavior as p-type conducting oxides. Ab initio calculations have been performed with density functional theory to investigate the role of the trivalent metal within the CuMO2 structure and the dependence of structural and electronic properties with the species (M = Al, Ga, In, Fe, Cr, Co, Sc, Y) occupying the site of the metal. Generalized Gradient Approximation also including a Hubbard term and nonlocal Heyd–Scuseria–Enzerhof screened hybrid functional schemes were tested and their results were compared. Excellent agreement with experimental lattice parameters and measured gaps have been found. The use of hybrid functionals in HSE approximation considerably improves the bandgaps when compared with the experimental results but takes considerable time to converge, hence the need to explore less demanding methodologies. Trends in the geometry as well as in the electronic properties are discussed, and the effect of mixing different metals (CuMxN1−xO2, M, N being the aforementioned elements) in the geometry and electronic properties of these delafossite materials is investigated. Due to the high cost of HSE calculations, especially when supercells are needed to model several x concentrations, statistical models and techniques based on machine learning have also been explored to predict HSE bandgap values from GGA and structural information.

2D Cadmium(II) Coordination Polymer Based on 2,5-Furandicarboxylate and 1,4-Bis(1H-imidazol-1-yl)butane Linkers: Synthesis, Characterization and DFT Studies

AbstractAs a result of hydrothermal synthesis of 2,5-furandicarboxylate (fdc2−), Cd(II) ion and bis(imidazole) derivative 1,4-bis(1H-imidazole-1-yl)butane (bib) ligand, a novel two-dimensional Cd(II) coordination polymer {[Cd(µ-fdc)(H2O)(µ-bib)]·H2O}n (1) was synthesized. According to the results of single crystal X-ray diffraction analysis, the complex was crystallized in the monoclinic system and in the P21/n space group. In addition, the thermal, luminescence and optical properties of the complex were investigated. The complex emits a maximum at 509 nm and also shows semi-conductor properties according to the solid-state UV–Vis diffuse reflection spectra results. To determine chemical structure, vibrational properties and some chemical properties of complex, theoretical calculations were carried out. All theoretical computations were performed using the DFT method at the B3LYP/LanL2DZ level of theory. The obtained experimental results were in good agreement with theoretical results. To calculate HOMO–LUMO energy values, which provided insights into the material's electronic properties, DFT calculations were used. Detailed information about the local and global chemical activity, as well as the electrophilic and nucleophilic nature of the complex, were also obtained.

Exploration of the electronic structure and thermoelectric properties of the carbon-doped bulk GaN materials by first-principles calculations

As a common impurity, carbon was related to the physical properties of GaN-based materials closely. By using density functional theory and Boltzmann transport theory, the electronic structure and thermoelectric properties of carbon doped GaN were studied. The band structure, electronic density of states and thermoelectric properties were calculated. Comparing with the intrinsic bulk-GaN, (1) It was found that the Fermi level moves down, and the band gap becomes narrow for GaN with CN point defects. (2) Power factors become decrease, while thermal conductivity decreases more significantly. Therefore, electrical thermoelectric figure of merit (ZTe) increases, especially, the ZTe increase up to 1.150 at 500 K for GaN with CN point defects. The research could provide reference for experimental studies of GaN-based materials.

Enhanced Electrical Transport Properties of Molybdenum Disulfide Field-Effect Transistors by Using Alkali Metal Fluorides as Dielectric Capping Layers.

The electronic properties of 2D materials are highly influenced by the molecular activity at their interfaces. A method was proposed to address this issue by employing passivation techniques using monolayer MoS2 field-effect transistors (FETs) while preserving high performance. Herein, we have used alkali metal fluorides as dielectric capping layers, including lithium fluoride (LiF), sodium fluoride (NaF), and potassium fluoride (KF) dielectric capping layers, to mitigate the environmental impact of oxygen and water exposure. Among them, the LiF dielectric capping layer significantly improved the transistor performance, specifically in terms of enhanced field effect mobility from 74 to 137 cm2/V·s, increased current density from 17 μA/μm to 32.13 μA/μm at a drain voltage of Vd of 1 V, and decreased subthreshold swing to 0.8 V/dec The results have been analytically verified by X-ray photoelectron spectroscopy (XPS) and Raman, and photoluminescence (PL) spectroscopy, and the demonstrated technique can be extended to other transition metal dichalcogenide (TMD)-based FETs, which can become a prospect for cutting-edge electronic applications. These findings highlight certain important trade-offs and provide insight into the significance of interface control and passivation material choice on the electrical stability, performance, and enhancement of the MoS2 FET.

Fully Screen‐Printed, Flexible, and Scalable Organic Monolithic Thermoelectric Generators

AbstractEnergy‐harvesting technologies offer a sustainable, maintenance‐free alternative to conventional energy‐storage solutions in distributed low‐power applications. Flexible thermoelectric generators (TEGs) can generate electric power from a temperature gradient, even on complex surfaces. Organic materials are ideal candidates for flexible TEGs due to their good solution‐processability, natural abundance, low weight, and flexibility. Electronic and thermoelectric properties of organic materials have steadily progressed, while device architectures leveraging their advantages are largely missing. Here, a design and fabrication method are proposed for producing fully screen‐printed, flexible monolithic organic TEGs scalable up to m2, compatible with any screen‐printable ink. This approach is validated, along with its scalability, by printing TEGs composed of two different active inks, in three configurations, with up to 800 thermoelements, with performances well matching simulations based on materials parameters. It is demonstrated that by using an additive‐free graphene ink, a remarkable power density of 15 nW cm−2 at ΔT = 29.5 K can be achieved, with an estimated weight‐normalized power output of 1 µW g−1, highlighting a strong potential in portability. Owing to such power density, only limited areas are required to generate microwatts, sufficient for operating low‐power electronic devices such as sensors, and wearables.

Exploring the Regulatory Mechanism of ZnS Materials under Stress and Re Doping: Insights from Density Functional Theory

The application prospects of ZnS stress luminescent materials cover many fields such as high‐precision structural monitoring, smart materials, biomedical imaging, and new sensor technologies, which bring broad application prospects and significance to them in the fields of engineering, medicine, and scientific research. In this article, the electronic structure and optical properties of ZnS materials are successfully regulated by applying pressure and doping rare earth metals (Re), and it is found that the regulation of the luminescence properties of ZnS is the result of stress and doping interactions. Specifically, when pressure is applied or Re metal doping, the lattice structure is deformed and the atomic spacing is adjusted, which affects the electronic energy level distribution and optical properties of ZnS materials. Computational analysis of density functional theory (DFT) reveals the microscopic mechanisms behind these changes, including changes in lattice parameters, adjustment of bond length, and changes in band structure. This study provides theoretical guidance for the design and synthesis of high‐performance and high‐stability ZnS light‐emitting materials, and is of great significance for expanding the application of ZnS in the field of lasers and sensors.

Composition-Dependent Phonon and Thermodynamic Characteristics of C-Based XxY1−xC (X, Y ≡ Si, Ge, Sn) Alloys

Novel zinc-blende (zb) group-IV binary XC and ternary XxY1−xC alloys (X, Y ≡ Si, Ge, and Sn) have recently gained scientific and technological interest as promising alternatives to silicon for high-temperature, high-power optoelectronics, gas sensing and photovoltaic applications. Despite numerous efforts made to simulate the structural, electronic, and dynamical properties of binary materials, no vibrational and/or thermodynamic studies exist for the ternary alloys. By adopting a realistic rigid-ion-model (RIM), we have reported methodical calculations to comprehend the lattice dynamics and thermodynamic traits of both binary and ternary compounds. With appropriate interatomic force constants (IFCs) of XC at ambient pressure, the study of phonon dispersions ωjq→ offered positive values of acoustic modes in the entire Brillouin zone (BZ)—implying their structural stability. For XxY1−xC, we have used Green’s function (GF) theory in the virtual crystal approximation to calculate composition x, dependent ωjq→ and one phonon density of states gω. With no additional IFCs, the RIM GF approach has provided complete ωjq→ in the crystallographic directions for both optical and acoustical phonon branches. In quasi-harmonic approximation, the theory predicted thermodynamic characteristics (e.g., Debye temperature ΘD(T) and specific heat Cv(T)) for XxY1−xC alloys. Unlike SiC, the GeC, SnC and GexSn1−xC materials have exhibited weak IFCs with low [high] values of ΘD(T) [Cv(T)]. We feel that the latter materials may not be suitable as fuel-cladding layers in nuclear reactors and high-temperature applications. However, the XC and XxY1−xC can still be used to design multi-quantum well or superlattice-based micro-/nano devices for different strategic and civilian application needs.

Phonon-mediated ultrafast energy- and momentum-resolved hole dynamics in monolayer black phosphorus.

The electron-phonon scattering plays a crucial role in determining the electronic, transport, optical, and thermal properties of materials. Here, we employ a non-Markovian stochastic Schrödinger equation (NMSSE) in momentum space, together with abinitio calculations for energy bands and electron-phonon interactions, to reveal the phonon-mediated ultrafast hole relaxation dynamics in the valence bands of monolayer black phosphorus. Our numerical simulations show that the hole can initially remain in the high-energy valence bands for more than 100fs due to the weak interband scatterings, and its energy relaxation follows single-exponential decay toward the valence band maximum after scattering into low-energy valence bands. The total relaxation time of holes is much longer than that of electrons in the conduction band. This suggests that harnessing the excess energy of holes may be more effective than that of electrons. Compared to the semiclassical Boltzmann equation based on a hopping model, the NMSSE highlights the persistence of quantum coherence for a long time, which significantly impacts the relaxation dynamics. These findings complement the understanding of hot carrier relaxation dynamics in two-dimensional materials and may offer novel insights into harnessing hole energy in photocatalysis.

Combining linear-scaling quantum transport and machine-learning molecular dynamics to study thermal and electronic transports in complex materials

We propose an efficient approach for simultaneous prediction of thermal and electronic transport properties in complex materials. Firstly, a highly efficient machine-learned neuroevolution potential (NEP) is trained using reference data from quantum-mechanical density-functional theory calculations. This trained potential is then applied in large-scale molecular dynamics simulations, enabling the generation of realistic structures and accurate characterization of thermal transport properties. In addition, molecular dynamics simulations of atoms and linear-scaling quantum transport calculations of electrons are coupled to account for the electron-phonon scattering and other disorders that affect the charge carriers governing the electronic transport properties. We demonstrate the usefulness of this unified approach by studying electronic transport in pristine graphene and thermoelectric transport properties of a graphene antidot lattice, with a general-purpose NEP developed for carbon systems based on an extensive dataset.

Chirality-enhanced 2D conductive polymer for flexible electronics and chiral sensing applications

Chiral two-dimensional (2D) conductive polymers, encompassing chiral, 2D, flexible, and conductive properties, constitute a novel class of material that remains largely unexplored. The infusion of chirality into 2D conductive polymers taps into the unique characteristics associated with chirality, presenting opportunities to enhance or tailor the electronic, optical, and structural properties of materials for specific technological applications. In this study, we synthesized a chiral 2D PEDOT:PMo11V nanofilm through interfacial polymerization, effectively integrating a chiral monolayer, conductive polymer, and inorganic cluster. The inclusion of inorganic cluster serves to enhance the conductivity of the resulting chiral nanofilm. Furthermore, we demonstrated the chiral nanofilm as a capable electrochemical sensor for detecting drug enantiomers. The inherent flexibility of the chiral nanofilm also lays the groundwork for the development of chiral flexible/wearable devices.

Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration.

Metal-semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe2) nanophase within the nanocrystalline ternary skutterudite (Co(Ge1.22Sb0.22)Te1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase's role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ∼ 1.30) is attained with CGST-7 wt. % CoTe2 nanocomposite film at 655 K compared to that of pristine CGST.