Journal of Electronic Materials最新文献

A theoretical prediction of the contribution to the thermo-electromotive force (thermo-EMF) of a thermocouple due to the minority charge carriers in both legs is presented. This prediction is made on the assumption that, at any time, the electrical conductivity of the majority charge carriers (sigma _M) remains very large compared to the electrical conductivity of the minority carriers (sigma _m) ((sigma _Mgg sigma _m)). The expression has also been analyzed in order to find strategies to reduce its negative impact on the thermo-EMF of the thermocouple. Finally, calculations were carried out in the case of the thermocouple made of silicon thermoelements. The results show that the presence of minority carriers in the thermocouple legs can either positively or negatively affect the generated thermo-EMF. Whenever the contribution is negative, its magnitude may be reduced by widening the bandgap of the N-type leg and/or narrowing that of the p-type leg, adjusting the length of the legs, or intensifying recombinations on the surfaces of the P-type leg

The existence of a variety of two-dimensional (2D) carbon allotropes with different carbon frameworks has provided an unprecedented platform to explore novel properties and potential applications beyond graphene. In this work, the strain effects on the structural, electronic, and thermal transport properties of the γ-graphyne and twin graphene sheets have been systematically clarified through first-principles calculations. Regardless of the geometrical similarities of the two considered 2D carbon allotropes, our results indicate that the acetylenic linkages in the γ-graphyne and the AA-stacked aromatic rings in the twin graphene are capable of resulting in the notable deviations in their electronic and thermal transport properties, as well as the strain-dependent behaviors. Both of the two sheets possess an intrinsic semiconducting nature with a tunable direct bandgap that depends on the biaxial strains. The thermal conductivity of the γ-graphyne is significantly suppressed compared to the twin graphene counterpart. Moreover, the heat transfer of the two sheets can be further enhanced by the tensile strains, and a dramatic increase can be obtained in the strained γ-graphyne sheet. Thus, the effectively tunable electronic and thermal transport properties revealed in this work imply the great potential of the two 2D carbon allotropes, and the comparative study also uncovers the structural effect of the carbon networks on their novel properties and strain responses.

Due to its elemental abundance, nontoxic nature, and suitable optical-electrical properties, copper oxide is a valuable p-type semiconductor for photovoltaic (PV) applications. However, synthesizing copper oxide films for PV devices with a band gap close to the Shockley–Queisser limit (1.4 eV) using a one-step deposition process is important for maximum efficiency and synthesis simplification. In this work, cathodic cage plasma deposition (CCPD) of copper oxide (CuO + Cu₂O) films on glass was performed to evaluate the microstructural, morphological, chemical, and band gap changes as a function of treatment time (2 h, 3 h, 4 h, and 5 h). The samples were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, x-ray diffraction, and Raman spectroscopy to identify the morphology, chemical composition, and crystalline phases of the deposited films, and diffuse reflectance spectroscopy was used to calculate the band gap width. The films showed characteristics of absorbing material in the visible region with band gap values from 1.43 eV to 1.5 eV. However, the sample treated for 3 h had a compact coating with a thickness of 1.46 µm and band gap energy of 1.43 eV, showing the applicability of the CCPD technique for synthesizing copper oxide absorber layers with an optimum band gap in a single deposition step.

Nano-size spinel ferrite CoFe₂O₄ (CFO), ferroelectric BaTiO₃ (BTO), and their nanocomposites BTO@CFO (BTO nanoparticles are added during the synthesis of CFO) and CFO@BTO (CFO nanoparticles are added during the synthesis of BTO) were synthesized using a combination of chemical co-precipitation and sol–gel routes, respectively. The phase formation and crystallinity of the bare CFO and BTO and their nanocomposites were verified via x-ray diffraction (XRD) patterns. High-resolution transmission electron microscopy (HRTEM) revealed the formation of the nanocomposites. Magnetization measurements confirmed the ferromagnetic behavior of all the samples except BTO, in which superposition of a weak ferromagnetic and diamagnetic response occurred due to its nanostructure. Magnetization versus temperature (M–T plot) measurements showed an anomaly near the ferroelectric-to-paraelectric phase transition of BTO. Also, the dielectric constant (ε′) and loss tangent (tanδ) with respect to frequency (10²–10⁶ Hz) and temperature (300–700 K) were examined. The ε′–T curve of the nanocomposites exhibited an anomaly at the same temperature as observed in the M–T plot, indicating the inherent magnetoelectric coupling in the nanocomposites. The energy storage properties of BTO and the nanocomposites were examined via P–E loop analysis and confirmed that the CFO@BTO sample exhibits maximum energy storage efficiency.

Semiconductors, with their exceptional properties, have diverse applications across fields such as photovoltaics, sensing, and catalysis. In the present study, nickel pyro-vanadate compounds of high purity and homogeneity, with the chemical formula A₂NiV₂O₇ (where A = Na, Ag), were synthesized under precisely controlled stoichiometric conditions. The primary focus is to investigate the optical and electronic properties of these compounds using a combination of experimental techniques and theoretical modeling. Initially, insights into the chemical structure and morphology of the synthesized semiconductor were obtained through powder x-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A₂NiV₂O₇ were found to be homogeneous, crystalline in nature, and isotypic with Κ₂CoV₂O₇, exhibiting alternating layers of NiV₂O₇ and Ag/Na. Moreover, absorption spectra obtained from UV–Vis diffuse reflectance spectroscopy (DRS) showed direct optical bandgaps of 1.83 eV for Na₂NiV₂O₇ and 1.92 eV for Ag₂NiV₂O₇, affirming their semiconductor properties. Further characterization was performed using density functional theory (DFT) and hybrid-DFT methods. These advanced techniques provide detailed understanding of the electronic structure and properties across different sodium–silver ratios. The computed electronic structures demonstrate the separation of the conduction band (CB) and valence band (VB) around the Fermi level, with bandgaps of 0.44 eV and 1.76 eV for Na₂NiV₂O₇, and 0.56 eV and 1.60 eV for Ag₂NiV₂O₇, as determined using the Perdew–Burke–Ernzerhof (PBE) and DFT+U methods, respectively. This comprehensive investigation offers valuable insights into the optical and electronic dynamics of nickel pyro-vanadate compounds, establishing a foundation for their potential applications in various fields, including optoelectronics, photocatalysis, and energy storage.

Graphical abstract

Cuprous oxide (Cu₂O) thin films grown by radio-frequency magnetron sputtering were post-annealed at 700°C under various oxygen partial pressures (PO₂). Reduction and oxidation of oxygen were found in thin films annealed under PO₂ of 0.1 Pa and 2.0 Pa, respectively. We investigated the photoluminescence characteristics of the Cu₂O thin films measured at low temperature (30 K) and room temperature (300 K). When post-annealed at PO₂ of 0.3 Pa and 0.7 Pa, Cu₂O films presented dominant PL lines originating from transitions of excitons and doubly charged oxygen vacancies at low temperature, and solely excitonic recombination at room temperature. The temperature-dependent exciton spectra were well modeled in terms of phonon-assisted recombination of ortho-excitons. On the other hand, a broad luminescence band around 2.2 eV dominated in oxygen-deficient and over-oxidized Cu₂O thin films. By comparing the results of grazing-incident x-ray diffraction and luminescence spectra, we believe that the origin of this band, however, involves extrinsic bands induced by structural imperfections.

In this paper, we study the effects of spinning speed on the electrical, optical, structural, morphological, and gas sensing properties of thin films deposited on glass substrates by sol–gel spin coating, using copper acetate dihydrate as the precursor. The deposition of the films was carried out at varying spinning speeds from 1500 rpm to 2500 rpm to achieve different thicknesses ranging from 157 nm to 470 nm, respectively. The results revealed that the resistivity of the films decreased from 75.5 Ω·m to 42.5 Ω·m with the decrease in spinning speed. X-ray diffraction (XRD) studies demonstrated that the crystallite size varied in the range of 18.14–27.48 nm. The band gap of the samples was found to vary from 2 eV to 1.69 eV, revealing that these samples were suitable for gas sensing applications. Field-emission scanning microscopy (FESEM) studies showed that the prepared samples were porous in nature and were suitable for H₂S gas detection. The films were examined at different operating temperatures with different concentrations of H₂S gas. The results showed that the response toward hydrogen sulfide gas varied with varying thickness of the samples. The CuO thin films showed the highest response toward hydrogen sulfide gas at a temperature of 25°C.

The emergence of new functionalities in transition metal oxides and their interfaces poses an important challenge. Many recent discoveries regarding the polar/nonpolar interface between perovskite oxides open new avenues for modern applications. SrTiO₃/LaCrO₃ heterostructures are particularly intriguing due to a polar discontinuity along the [001] direction, giving rise to two distinct and controllable interface structures, TiO₂-LaO and SrO-CrO₂, which exhibit new and promising electronic and thermoelectric transport properties. Through a combination of first-principles simulations based on density functional theory and the Boltzmann transport equation, we have calculate and discuss the structural, electronic, valence band offset, and thermoelectric properties of SrTiO₃, LaCrO₃, and SrTiO₃/LaCrO₃ heterostructures. The temperature dependence of the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and figure of merit is determined. Furthermore, we highlight the effect of the interface between the polar perovskite LaCrO₃ and the nonpolar SrTiO₃(001) on the thermoelectric properties, wherein we observed a change in the metal–semiconductor transport behavior. These results constitute an important advancement in our understanding of the thermoelectric properties at polar/nonpolar perovskite oxide interfaces.

A triboelectric nanogenerator (TENG) working on a contact electrification and electrostatic induction principle is a promising energy source for fulfilling the energy demand of low power electronic devices by converting the ambient mechanical energy to useful electrical energy. Here, a polymer nanocomposite film-based triboelectric nanogenerator has been designed by embedding reduced graphene oxide (rGO) nanosheets in a polyvinylidene fluoride (PVDF) matrix as one of the friction layers. The PVDF nanocomposite film-based TENG was constructed and examined for structural, electrical, and surface properties with varied weight percentages of rGO nanofillers (0.0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%). The experimental results demonstrate that the addition of rGO in a PVDF matrix considerably increased the output performance of the TENG device. The TENG device with 1.5 wt% of rGO can deliver the maximum output voltage and current of 95.9 V, and 16.8 μA, respectively, which are ~ 3 and ~ 7 times the voltage and current produced by pristine PVDF film-based TENG. The enhanced performance of the nanogenerator is attributed to the addition of conductive nanofillers in the polymer matrix which improves the surface charge density of polymer nanocomposite films by forming a conduction network, resulting in more effective charge transfer. Moreover, the output of the nanogenerator is stored in the capacitor and used to drive commercial LEDs, revealing the TENGs' potential applications for designing self-powered electronic devices.

Recently discovered twisted and coiled polymer actuators (TCPAs) show huge potentials in the field of soft robots due to advantages of low cost, large deformation and force, high energy density, long life, compact size, and easy to drive. To realize practical applications of the TCPA in soft robots, the study on its dynamic modeling is necessary. However, the TCPA has an obvious hysteresis nonlinearity, bringing obstacles to its modeling. Although some hysteresis models for the TCPA have been established, the study on its rate-dependent hysteresis modeling is still insufficient. To address this issue, a compound model has been established, in which the thermomechanical model is developed by cascading the backlash-like model and a dynamic linear system to depict the relationship between the output force and temperature. In addition, a thermoelectric model has been developed based on the first law of thermodynamics, whose function is to depict the relationship between the temperature and excitation current. All fitness values in the model validation of the compound model are larger than 87.949%. Hence, the compound model has a good generalization performance.