Density Of States Research Articles

Electronic structure regulation of Cu-based Ruddlesden-Popper perovskites by cobalt doping for enhanced degradation of oilfield fracturing wastewater in electrocatalytic peroxymonosulfate system

Purification of oilfield fracturing wastewater is the most challenging type of oilfield wastewater treatment. In this work, a heterogeneous electrocatalytic peroxymonosulfate (PMS) system was established to treat oilfield wastewater using Co-doping induced Cu-based Ruddlesden-Popper (RP) perovskites as catalysts. Characterization results illustrated that the obtained catalysts were generated the heterojunction of LaCoO3/La2CuO4 and the Co would transfer electrons to Cu, resulting in a higher chemical oxygen demand (COD) degradation efficiency (> 80 %) of oilfield fracturing wastewater under the neutral environment. Singlet oxygen (1O2) played the main function for COD removal with analysis results of reactive oxygen species (ROS). Experimental results and theoretical calculations indicated that the reduction effect of carbon felt (GF) cathode and the redox cycle of Cu(I)/Cu(II) and Co(II)/Co(III) accelerated the activation of PMS. Moreover, the lattice oxygen participated in the generation of ROS. Significantly, the LaCoO3/La2CuO4 heterojunction displayed a higher total density of states (TDOS) value near the Fermi level, implying their favorable electron transfer for PMS activation. This study opens new avenue for resolving the challenge of oilfield fracturing wastewater pollution.

Structural and dynamical properties of two dimensional disordered metal chalcogenides AB (A [formula omitted] Zn, Cd; B [formula omitted] S, Se): A classical molecular dynamic study

In recent years, the synthesis of two-dimensional (2D) materials, particularly the crystalline and disordered phases of 2D transition metal chalcogenides (TMCs), has gained considerable attention due to their wider electronic band gaps. This distinctive feature is pivotal in shaping their potential applications in solar cells, sensors, field-effect transistors (FETs), and photocatalysis for water decomposition. In the present study, we report molecular dynamics simulation of 2d disordered configuration of ZnX and CdX (X: S, Se) compounds using the Stillinger–Weber potential. We have explored their structural features by calculating their radial distribution functions and ring statistics. These systems are thermodynamically stable. The disordered network with numerous voids in these compounds play a pivotal role in lowering their melting temperature compared to their 2D crystalline counterparts, which falls within the range of 600 K to 700 K. The phonon density of states for all these systems shows a higher number of lower frequency (acoustic) modes than optical modes, which is understandably due to the presence of open regions and 2-fold sites in such systems.

Rapid Detection of Explicit Volatile Organic Compounds for Early Diagnosis of Lung Cancer Using MoSi2N4 Monolayer.

In this study, we investigate the adsorption of MoSi2N4) and MoSi2N4-VNtowards five potential lung cancer volatile organic compounds (VOCs).Density functional theory calculations reveal that MoSi2N4 weakly adsorb the mentioned VOCs, whereas introduction of nitrogen vacancies significantly enhances the adsorption energies ([[EQUATION]]), both in gas phase and aqueous medium. The MoSi2N4-VN monolayers exhibit a reduced bandgap and facilitate charge transfer upon VOCs adsorption, resulting in enhanced [[EQUATION]] values of -0.83, -0.76, -0.49, -0.61, and -0.50 eV for 2,3,4-trimethyl hexane, 4-methyl octane, o-toluidine, Aniline, and Ethylbenzene, respectively. Bader charge analysis and spin-polarized density of states (SPDOS) elucidate the charge redistribution and hybridization between MoSi2N4-VN and the adsorbed VOCs. The work function of MoSi2N4-VN is significantly reduced upon VOCs adsorption due to induced dipole moments, enabling smooth charge transfer and selective VOCs sensing. Notably, MoSi2N4-VN monolayers exhibit sensor responses ranging from 16.2% to 26.6% towards the VOCs, with discernible selectivity. Importantly, the recovery times of the VOCs desorption is minimal, reinforcing the suitability of MoSi2N4-VN as a rapid, and reusable biosensor platform for efficient detection of lung cancer biomarkers. Thermodynamic analysis based on Langmuir adsorption model shows improved adsorption and detection capabilities MoSi2N4-VN under diverse operating conditions of temperatures and pressures.

Strain-modulated intercalated phases of Pb monolayer with dual periodicity in SiC(0001)-graphene interface

Intercalation of metal atoms at the SiC(0001)-graphene (Gr) interface can provide confined 2D metal layers with interesting electronic properties. The intercalated Pb monolayer (ML) has shown the coexistence of the Gr(10 × 10)-moiré and a stripe phase, which still lacks understanding. Using density functional theory calculation and thermal annealing with ab initio molecular dynamics as motivated by experiment, we have studied the formation energy of Gr/Pb/SiC(0001) for different Pb coverages. Near the coverage of a Pb(111)-like ML mimicking the (10 × 10)-moiré, we find a slightly more stable stripe structure, where one half of the structure has compressive strain with Pb occupying the Si-top sites and the other half has tensile strain with Pb off the Si-top sites. This stripe structure along the Gr zigzag direction has a periodicity of 2.3 nm across the [1 2¯ 10] direction agreeing with the previous observations using scanning tunneling microscopy. Analysis with electron density difference and density of states show the tensile region has a more metallic character than the compressive region, while both are dominated by charge transfer from Pb ML to SiC(0001). The small energy difference between the stripe and Pb(111)-like structures means the two phases are almost degenerate and can coexist, which explains the experimental observations.

Magneto-electronic and optoelectronic attributes of half-Heusler VXPt (X = Br, Se) alloys: A first-principles study

High-spin polarized magnetic materials might be useful in spintronics applications. The spin-polarized magnetic, optical, electronic and structural attributes of half-Heusler VXPt (X = Br, Se) alloys were theoretically explored and calculated using the WIEN2k code. The ground states of the structures are optimized, and the bulk moduli and lattice constants are computed. The values obtained from the formation energies show their stability. For VBrPt, an energy gap is present in major and minority spin carriers, while for VSePt, major spin carriers exhibit an energy gap and metallic character is seen in minority spin carriers. The band structures are further illustrated deeply through the investigation of density of states. The electron density graphs depict the ionic bonding in both alloys. The magnetic moments are additionally assessed, and the recorded values support the magnetic characteristics of VBrPt and VSePt. The assessment of how the studied alloys react to light is determined by computing various parameters. The imaginary component and absorption coefficient anticipate substantial light absorption within the visible region. The calculated outcomes unveiled the potential of the examined alloys for applications in spintronics.

Adsorption of Thiotepa on B12N12, Mg12O12, and Si12C12 Fullerene-like Cages: A DFT Study

We examined the adsorption of thiotepa (TTP) on the outer surface of B12N12, Mg12O12, and Si12C12 fullerene-like cages using density functional theory (DFT) calculations. The computations were carried out at the Perdew-Burke-Ernzerhof level with the D3 dispersion correction (PBE-D3) in a water solvent. The adsorption mechanism of TTP through N-head and S-head on the external surface of Si12C12 involves a covalent interaction (binding energy ∼ -1.31 eV) with the carrier surface. In contrast, the adsorption of the TTP molecule through N-head and S-head on the outer surfaces of B12N12 (binding energy ∼ -0.75 eV) and Mg12O12 (binding energy ∼ -0.62 eV) fullerene-like cages is driven by electrostatic interactions. Therefore, due to their low values of recovery time, both B12N12 and Mg12O12 fullerene-like cages can serve as carriers for TTP in the treatment of cancer. Thermodynamic parameters (Gibbs free energy and enthalpy energy) demonstrate that these interactions are exothermic and spontaneous. The results further reveal the significant disparity in the calculated HOMO and LUMO energies at the computational level. The formation of intricate bonds between the drug and the fullerene-like cages is attributed to the charge transfer dynamics that occur during their interactions. Through computational analysis and examination of the total density of state (TDOS) plots, it is evident that B12N12 and Si12C12 fullerene-like cages exhibit a high degree of sensitivity to the TTP drug. The adsorption process can increase the electrical conductivity of B12N12 and Si12C12, while having minimal effect on Mg12O12. This suggests that B12N12 could potentially serve as a suitable biosensor for detecting TTP.

Zr and Y co-doped SrFe0.8Zr0.1Y0.1O3-δ perovskite oxide as a stable, high-performance symmetrical electrode for solid oxide cells

Symmetrical solid oxide cells (SSOCs), which use the same material for both anode and cathode, simplify the cell fabrication process and effectively resist carbon deposition and sulfur poisoning. In this study, Zr, Y co-doped SrFe0.8Zr0.1Y0.1O3-δ (SFZY) perovskite oxide is synthesized and evaluated its properties as an SSOFCs electrode. Density functional theory (DFT) indicates that the local state density of SFZY is lower than that of SrFeO3-δ (SFO). SFZY has good chemical compatibility with La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) electrolyte below cell operating temperature. Zr, Y co-doped SrFe0.8Zr0.1Y0.1O3-δ maintains structural stability in H2 atmosphere. At 750 ℃, the polarization resistance (Rp) of SFZY is 0.11 and 1.06 Ω cm2 in air and hydrogen atmosphere, respectively. During the Rp stability test, SFZY exhibits better stability than that of SrFeO3-δ in air and hydrogen atmosphere. At 750 ℃, the maximum power density of SFZY/LSGM/SFZY fuel cell reaches 420.1 and 258.31 mWcm−2 using H2 and wet C3H8 as fuel, respectively. In electrolytic mode, the current density of SFZY/LSGM/SFZY electrolysis cell reaches -0.55 A cm−2 at 1.3V for electrolysis of pure CO2 at 750 ℃. In summary, SFZY has a great potential as SSOCs electrode.

Sputter-Deposited copper iodide thin film transistors with low Operating voltage

This paper reports on a back-gated p-type thin film transistor (TFT) with copper iodide (CuI) as the channel material, a HfO2 gate dielectric layer, and Al2O3 passivation. The γ-CuI channel was deposited from a CuI target using DC magnetron sputtering at room temperature. Our TFT can be fully shut off by VG = 4 V, with a field-effect channel hole mobility μh ∼ 1.5–2 cm2 V−1 s−1. An anneal in forming gas was performed twice, once at 200 °C, then at 250 °C to improve gate control, yielding a final Ion/Ioff current ratio of ∼ 250. The anneal served two purposes: to reduce the oxygen acceptor density in the CuI channel and reduce the concentration of interface states between the CuI, Al2O3 passivation, and HfO2. A model of the device was built in an industrial TCAD simulator, which reproduces the measured characteristics and allows an estimation of interface state densities and channel doping.

Lead iodide secondary growth and π-π stack regulation for sequential perovskite solar cells with 23.62% efficiency

The sequential deposited perovskite solar cells (PSCs) have received widespread attention due to its application potential in large-scale perovskite module and perovskite/silicon tandem solar cells. However, insufficient reaction between organic ammonium salts and PbI2 leads to residual PbI2 and low crystallinity of perovskite films, and the fragile Pb-I bonds easily creates iodine loss and reduces the stability of PbI6 framework. In this work, the 4-fluorobenzylamine (FBA) with C = O and –NH2 is employed in PbI2 precursor solution to regulate the secondary growth process of PbI2 film. Due to the low Gibbs free energy and high crystallinity of porous PbI2 film, sufficient reaction between organic ammonium salts and PbI2 is promoted, which results in large-grain, low-defect perovskite films. At the same time, through hydrogen bonding and π-π stacking interactions, the stability of the PbI6 skeleton is effectively improved, significantly suppressing non-radiative recombination and reducing defect state density. Finally, this strategy increases the power conversion efficiency (PCE) of PSCs from 22.06 % to 23.62 %, and the target PSCs maintain 96 % of their initial PCE after being placed in nitrogen for 1300 h.

Investigating plasma activated water as a sustainable treatment for improving growth and nutrient uptake in maize and pea plant

In this study, an atmospheric pressure air plasma jet (APAPJ) was employed to generate plasma-activated water (PAW), which was applied to treat maize (monocot) and pea (dicot) seeds for evaluating its influence. This research explored APAPJ diagnostics by varying the air feed rate as 1, 2, and 3 liter per minute (Lpm) through current-voltage characterization, optical emission spectroscopy, electron temperature and density, nitrogen metastable state density, and rotational and vibrational temperature of the plasma. Additionally, various reactive oxygen and nitrogen species (RONS) formed and physicochemical properties of PAW were analyzed by varying plasma treatment time from 0 to 8 min. Furthermore, the water uptake of maize (Zea mays) and pea (Pisum sativum) seeds were examined by the measurement of the contact angle. Results indicated that APAPJ has the capacity of fostering germination, growth, chlorophyll, phosphorus, nitrite, nitrate, ammonium ion and leaf area in plants significantly with an optimized 6 min treated PAW for maize and 2 min treated PAW for peas. Among various categories, seeds soaked in PAW and irrigated with PAW exhibited the most outstanding result in germination and plant growth. Non-thermal plasma showed promising green methods for enhancing plant growth and boosting nutrient content.

Improved Subthreshold Characteristics of Epi-Silicon FinFET via Fin Surface Passivation Technologies

As demand for advanced integrated circuits (ICs) continues to grow, fin field-effect transistors (FinFETs) have remained highly influential in the IC market because of their mature fabrication process and powerful driving capabilities. However, the ion bombardment that occurs during the reactive ion etching (RIE) process used to form the fin structure increases the fin’s surface roughness and results in a high interfacial state density (D it ), which hinders further improvement in the subthreshold swing (SS) of FinFETs. To overcome this issue, this study proposes two oxidative trimming methods for use on the fin structures to improve their interface quality. It is found that conventional thermal oxidation and low-temperature oxidation processes reduced the channel D it by 73.31% vs 71.17%, respectively. Furthermore, the corresponding SS values of the device improved to 72.76 and 71.72 mV dec−1, respectively. The technical solutions proposed in this paper represent a promising approach for performance optimization of FinFETs and other advanced devices.

DFT study of structural, electronic, magnetic, elastic, and thermoelectric properties of Ta-based half-Heusler alloys CsTaX (X = C, Si, and Ge) for spintronics and thermoelectric technologies

The structural, electronic, elastic, magnetic, and thermoelectric characteristics of three novel Ta-based half-Heusler alloys, CsTaC, CsTaSi, and CsTaGe, have been investigated using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method within the density functional theory (DFT). The volume-optimization graphs show that all compounds are stable in the ferromagnetic (FM) phase. Half-Metallicity of these compounds is confirmed by the density of states (DOS) and band structures. The total magnetic moment for CsTaC is 6 μB, and for CsTaX (X = Si, Ge) is 2 μB. The negative pd exchange energy and exchange constants confirm ferromagnetism. The values of Pugh’s ratio (B/G) and Poisson’s ratio (v) reveal that CsTaC is ductile and CsTaX (Si, Ge) is brittle. The thermoelectric response is estimated using the BoltzTraP code, demonstrating that at room temperature, maximum ZT values for CaTaC, CsTaSi, and CsTaGe are 0.99, 0.97, and 0.90, respectively. Consequently, CsTaX (X = C, Si, and Ge) are suitable candidates for spintronic and thermoelectric technologies.

Theoretical design and synthesis of Co30Ni60/CC for high selective methanol oxidation assisted energy-saving hydrogen production

The integration of methanol oxidation reaction (MOR) with hydrogen evolution reaction (HER) represents an advanced approach to hydrogen production technology. Nonetheless, the rational design and synthesis of bifunctional catalysts for both MOR and HER with exceptional activity, stability and selectivity present formidable challenges. In this work, firstly, density functional theory (DFT) was utilized to design and evaluate material models with high performance for both MOR and HER. Secondly, guided by DFT, Co30Ni60/CC (CC, carbon cloth) composites with a leaf-like nanosheet structure were successfully fabricated via electrodeposition. In the MOR process, Ni acts as the predominant active center, while Co amplifies the electrochemically active surface area (ECSA) and enhances the selectivity of methanol oxidation. Conversely, in the HER process, Co serves as the primary active center, with Ni augmenting the charge transfer rate. The electrochemical results demonstrate that Co30Ni60/CC exhibits exceptional performance in both MOR and HER at a current density (j) of 10 mA cm−2, with peak potentials of 1.323 V and −95 mV, respectively. Additionally, it shows remarkable selectivity for the oxidiation of methanol to high value-added formic acid. Thirdly, following a 100 h chronopotentiometry (CP) test, the required potential demonstrates an increase of 4.9 % (MOR) and 8.1 % (HER), signifying the superior stability of Co30Ni60/CC compared to those reported in the literature. The exceptional performance of Co30Ni60/CC can be primarily attributed to that the leaf-like nanosheets structure not only exposes a plethora of active sites but also facilitates electrolyte diffusion, the monolithic structure prepared by electrodeposition enhances its stability, and the transfer of electrons from Co to Ni regulates its electronic structure, as corroborated by X-ray photoelectron spectroscopy (XPS) and density of states (DOS) analyses. Finally, at the same j, the voltage required by the Co30Ni60/CC||Co30Ni60/CC electrolytic cell, powered by an electrochemical workstation, is 198 mV lower than that required for alkaline water-splitting. Meanwhile, at higher j (100 mA cm−2), the electrolytic cell exhibits sustained and stable operation for 150 h, enabling high-efficiency hydrogen production and the synthesis of high value-added formic acid.

Tuning optoelectronic properties of indandione-based D-A materials by malononitrile group acceptors: A DFT and TD-DFT approach.

Indandione-based materials are promising candidates for organic electronics, offering high electron mobility and tunable optoelectronic properties. In this study, we explore the optoelectronic and photovoltaic properties of indandione-based donor-acceptor (D-A) materials, specifically (R1) and (R2), by introducing malononitrile group acceptors into their molecular structure. These strong electron-withdrawing acceptors are designed to enhance charge transfer and overall material performance. The designed molecules (DM1-DM4) exhibit a low optical band gap of approximately 1.77eV, significantly lower than the reference materials (R1 and R2) at around 2.24eV in a solvent environment. Among the designed molecules, DM4 stands out with superior photovoltaic parameters, including a narrow optical band gap (1.77eV), higher electron affinity (3.49eV), an extended excited state lifetime (10.0ns) owing to its low electron and hole reorganization energies (λe ~ 0.13eV and λh ~ 0.24eV), and improved short-circuit current density (Jsc) of ~ 15.73mA/cm2. Notably, DM4 achieves a power conversion efficiency (PCE) of ~ 18.5%, making it an excellent candidate for device applications. A comprehensive computational investigation was carried out on indandione-based D-A materials with malononitrile group acceptors (DM1-DM4) using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, as implemented in Gaussian 16 software. We examined the electronic and optical properties of the proposed molecules through frontier molecular orbital (FMO) analysis, UV-Vis absorption spectra, density of states (DOS), exciton binding energy (Eb), and transition density matrix (TDM) analysis, utilizing GaussView 6.0 and Multiwfn 3.8 software. The photovoltaic parameters and power conversion efficiency (PCE) were evaluated using the Scharber and Alharbi models.

Tunable Electronic, Optoelectronic, and Photocatalytic Properties of MoS2 and GaS Monolayers in the MoS2/GaS Heterostructure

AbstractThe electronic structure calculations show that the GaS and MoS2 monolayer and MoS2/GaS hetero‐bilayer systems are semiconducting materials. It is also justified by the density of states. In the hetero‐bilayer system, the band gap is reduced. It causes an increase in the absorption, compared to their monolayers, of incident light in the visible region. This may be because of the charge transfer and the interlayer interaction between these monolayers in the heterostructure form. The calculated higher extinction coefficient causes the fast absorption of light, hence, the increased absorption coefficient. The heterostructure system makes the refractive index and reflection coefficient of GaS and MoS2 monolayers tuneable. The static reflection coefficient is in the following order GaS < MoS2/GaS < MoS2. It means that the MoS2/GaS heterostructure system can increase the static refractive index of GaS and decrease that of MoS2 monolayers simultaneously. The calculated band edge positions show that the MoS2 and GaS monolayers have excellent water oxidation and reduction capability, respectively. These predictions show that the proposed heterostructure may be a potential candidate for nanoelectronics and optoelectronics.

Theoretical Study of the Adsorption and Sensing Properties of Cr-Doped SnP3 Monolayer for Dissolved Characteristic Gases in Oil

Dissolved gas analysis (DGA) is a vital method for the online detection of transformer operation state. The adsorption performance of a SnP3 monolayer modified by transition metal Cr regarding six characteristic gases (CO, C2H4, C2H2, CH4, H2, C2H6) dissolved in oil was studied. The study reveals the relevant adsorption and gas-sensing response mechanisms through calculations of the adsorption energy, density of states, differential charge density, energy gap, and recovery time. The results display a considerable increase in the adsorption effect of the Cr-SnP3 monolayer on six gases. The CO, C2H2, and C2H4 gases lead to chemical adsorption, and the CH4, H2, and C2H6 gases lead to physical adsorption. Combined with the recovery time, the Cr-SnP3 monolayer has a strong adsorption effect on CO and C2H2 gases at normal temperatures and even high temperatures, and the adsorption is stable. C2H4 gas can be rapidly desorbed from the Cr-SnP3 monolayer at 398 K. Therefore, the Cr-SnP3 monolayer can be expected to serve as a CO and C2H2 gas adsorbent and a resistive gas sensor for C2H4 gas. This research offers a theoretical foundation for the development of the Cr-SnP3 monolayer in gas-sensitive materials.

Investigating the potential of triclinic ABSe3 (A = Li, Na, K, Rb, Cs; B = Si, Ge, Sn) perovskites as a new class of lead-free photovoltaic materials

In recent years, chalcogenide perovskites have emerged as promising candidates with favorable structural, electrical, and optical properties for photovoltaic applications. This paper explores the structural, electronic, and optical characteristics of ABSe3 perovskites (where A = Li, Na, K, Rb, Cs; B = Si, Ge, Sn) in their triclinic crystallographic phases using density functional theory. The stability of these materials is ensured by calculating formation energies, tolerance factors (Tf), and phonon dispersion. The Eform values of all ABSe3 are negative, suggesting favorable thermodynamic stability. The Tf values range between 0.82 and 1.1, which is consistent with stable perovskites. The phonon dispersion analysis of the chalcogenide perovskites revealed no imaginary frequencies in any of the vibrational modes, confirming their stability. The electronic band structures and corresponding density of states are computed to unveil the semiconducting nature of the studied compounds. These perovskites are promising for high-performance solar cells due to their indirect bandgaps (Eg, 1.10–2.33 eV) and a small difference between these indirect and direct gaps (0.149–0.493 eV). The Eg values increase as the ionic radii of A-site elements increase (Li < Na < K < Rb < Cs). At the B-site, Si-based chalcogenides have the largest Eg values, followed by Sn-based and then Ge-based materials. Furthermore, optical properties such as the real part and imaginary part of the dielectric function, refractive index extinction coefficient, optical conductivity, absorption coefficient, reflectivity, and energy loss are predicted within the energy range of 0–50 eV. Several ABSe3 materials, particularly LiGeSe3 and NaGeSe3, demonstrated optical properties comparable to both traditional and emerging materials, suggesting their potential for effective use in solar cells.

An Examination of the Electronic, Optical, and Thermodynamic Properties of Β-Gan

The current work involves the systematic examination of the features of Gallium Nitride (GaN) including the electronic, optical, structural, and thermodynamic features, depending on first principles calculation. This is according to approximations, (LDA), (GGA), and (m-GGA). The bandgap energies of Gallium nitride are (1.85 eV, 1.93 eV, and 2.179 eV), respectively. Furthermore, our study also reveals that GaN has a direct bandgap and is highly stable. Finally, our results indicate that the m-GGA method accurately predicts the bandgap energy of GaN. The m-GGA method outperforms both LDA and GGA methods in accuracy to predict the bandgap energy of GaN, as evidenced by its closest approximation to the experimental value. To determine the orbital nature of the Gallium and Nitrogen atoms, the state density and state partial density of Gallium nitride were simulated. The absorption coefficient of Gallium nitride is computed and analyzed in depth for the optical transitions. The absorption coefficient of Gallium nitride is affected by various factors, including the material's band structure, temperature, doping level, and the energy of the incident photons. In addition to that, the thermodynamic properties that can be calculated like enthalpy, entropy, heat capacity, free energy, and Debye temperature enable us to understand the thermal behavior of the compound better. The heat capacity of α-GaN is detected to be (39.9, 25.5, and 32.4) Jmole-1K-1, and a Debye temperature of 807 K, 1134 K, and 866 K for LDA, GGA, and m-GGA, respectively. This research will offer a detailed interpretation of β-GaN, covering all its basic properties and possible applications in electronic devices and optoelectronic devices. The results of this study are very important and the new technologies that will be developed based on the Cubic phase - GaN research will be very beneficial.

Thermoelectric properties of InGaN/GaN superlattices structure with high indium composition quantum dots

High indium composition InGaN is a promising material for thermoelectric harvesting application, which can work at high temperature and extreme environments. Due to the strong composition segregation, high indium composition InGaN material usually forms localized quantum dots, which advantageously enhances the thermoelectric (TE) properties. In this research, the two-dimensional InGaN/GaN superlattices (SLs) structured TE material with high In composition of 35% quantum dots is first grown and characterized. Using open-circuit voltage measurement, the Seebeck coefficient (S) exhibits a high value of −571 μV/K. Analysis indicates this relatively high S value is related to the increased density of electron states near the Fermi level induced by the reduced dimensionality, resulting in a power factor of 11.83 × 10−4W/m·K2. The dense boundary between InGaN quantum dots also increases the interface phonon scattering, thereby suppressing the heat transportation and leading to a low thermal conductivity (k) value of 19.9 W/m·K. As a result, a TE figure of merit (ZT) value of 0.025 is demonstrated in the sample. This work first clarifies the impact of embedded quantum dots in InGaN/GaN SLs structure on TE properties. It is very conductive for the design and fabrication of low-dimensional GaN based TE device.

Electrical resistivity and magnetic susceptibility of Al-Ni-Co-Cu-Zr high-entropy alloys in solid and liquid states

Electrical resistivity and magnetic susceptibility of Al-Ni-Co-Cu-Zr alloys with different component ratios are studied in a wide temperature range including both solid and liquid states. The abnormal behavior of properties is discovered in the temperature range 700–1200 K. The increase of magnetic atoms concentration (mainly cobalt) in the alloys composition leads to increase of properties anomalies. Some parameters of the electronic structure - paramagnetic Curie temperature, effective magnetic moment and density of electron states at Fermi level - are calculated from the experimental data.