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<jats:p>The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases (3DEGs) at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional (2D)–three-dimensional (3D) channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure (DH:Si/C). Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure (SH:C). There are fast, medium, and slow trap states in DH:Si/C, while only medium trap states exist in SH:C. The time constant/trap density for medium trap state in SH:C heterostructure are (11 μs–17.7 μs)/(1.1 × 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>–3.9× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>) and (8.7 μs–14.1 μs)/(0.7× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>–1.9× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>) at 300 K and 500 K respectively. The time constant/trap density for fast, medium, and slow trap states in DH:Si/C heterostructure are (4.2 μs–7.7 μs)/(1.5× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>–3.2× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>), (6.8 μs–11.8 μs)/(0.8× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>–2.8× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>), (30.1 μs–151 μs)/(7.5× 10<jats:sup>12</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>–7.8× 10<jats:sup>12</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>) at 300 K and (3.5 μs–6.5 μs)/(0.9× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>–1.8× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>), (4.9 μs–9.4 μs)/(0.6× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>–1.7× 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>), (20.6 μs–61.9 μs)/(3.2× 10<jats:sup>12</jats:sup> cm<jats:sup>−2</jats:sup> · eV<jats:sup>−1</jats:sup>–3.5× 10<jats:sup>12</jats:sup> cm<jats:sup>−2</jats:sup>·eV<jats:sup>−1</jats:sup>) at 500 K, respectively. The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.</jats:p>

<jats:p>The piezoelectric, ferromagnetism, and magnetoelectric response of BiFeO<jats:sub>3</jats:sub>–BaTiO<jats:sub>3</jats:sub> ceramics with the compositions around the morphotropic phase boundary (MPB) of the solid solution are systematically investigated after the ceramics have been quenched from a high temperature. We find that the ferromagnetism of the quenched ceramics is greatly enhanced. An enhanced piezoelectric response <jats:italic>d</jats:italic> <jats:sub>33</jats:sub> larger than 200 pC/N, which could be sustained up to 350 °C, is measured. As a result of enhanced ferromagnetism and piezoelectric response, a large magnetoelectric response ∼ 1.3 V/cm·Oe (1 Oe = 79.5775 A·m<jats:sup>−1</jats:sup>) is obtained near the mechanical resonance frequency of the quenched ceramic samples. Our research also shows that in addition to the ferromagnetism and piezoelectric response, the mechanical quality factor is another important parameter to achieve high magnetoelectric response because the physical effects are coupled through mechanical interaction in BiFeO<jats:sub>3</jats:sub>-based materials. Our work suggests that quenching is an effective approach to enhancing the magnetoelectric response of BiFeO<jats:sub>3</jats:sub>-based materials and the materials belong to single-phase multiferroic materials with high magnetoelectric response.</jats:p>

<jats:p>The electrocaloric effect of ferroelectric ceramics has been studied extensively for solid-state caloric cooling. Generally, most ferroelectric ceramics are poor thermal conductors. In this work, the possibility of enhancing the thermal conduction of ferroelectric ceramics through the electrocaloric effect is studied. A multilayer ceramic structure is proposed and the proper sequential electric field is applied to each ceramic layer. The result shows that the thermal conduction of the multilayer structure is significantly enhanced because of the electrocaloric effect of the ferroelectric ceramics. As a result, the work finds an alternatively way of applying the electrocaloric effect, prompting thermal conduction.</jats:p>

<jats:p>Inhomogeneous electroluminescence (EL) of InGaN green LEDs grown on mesh-patterned Si (111) substrate had been investigated. Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed the inhomogeneous EL in the low current density range. Near-field EL emission intensity distribution images depicted that inhomogeneity in the form of premature turn-on at the periphery of the LED chip, results in stronger emission intensity at the edges. This premature turn-on effect significantly reduces the luminous efficacy and higher ideality factor value due to locally current crowding effect. Raman measurement and fluorescence microscopy results indicated that the partially relaxed in-plane stress at the edge of the window region acts as a parasitic diode with a smaller energy band gap, which is a source of edge emission. Numerical simulations showd that the tilted triangular n-AlGaN functions like a forward-biased Schottky diode, which not only impedes carrier transport, but also contributes a certain ideality factor.</jats:p>

<jats:p>Ge–Ga–S thin films were deposited by magnetron sputtering with mean coordination number (MCN) ranging from 2.46 to 2.94. The physical properties of the Ge–Ga–S films, including optical band gap, refractive index, and thickness, vary with the time of heat treatment. Based on the analysis of the topology model, it is concluded that the Ge–Ga–S thin films with components close to the stoichiometric ratio can form the most Ga–S bonds and Ga–S bonds, and the physical properties of the Ge<jats:sub>27.3</jats:sub>Ga<jats:sub>6.3</jats:sub>S<jats:sub>66.3</jats:sub> (MCN = 2.62) film are the most stable. This is an important reference for thin film photonic devices.</jats:p>

<jats:p>Transport properties and the associated structural heterogeneity of room temperature aqueous ionic liquids and especially of super-concentrated electrolyte aqueous solutions have received increasing attention, due to their potential application in ionic battery. This paper briefly reviews the results reported mainly since 2010 about the liquid–liquid separation, aggregation of polar and apolar domains in neat RTILs, and solvent clusters and 3D networks chiefly constructed by anions in super-concentrated electrolyte solutions. At the same time, the dominating effect of desolvation process of metal ions at electrode/electrolyte interface upon the transport of metal ions is stressed. This paper also presents the current understanding of how water affects the anion–cation interaction, structural heterogeneities, the structure of primary coordination sheath of metal ions and consequently their transport properties in free water-poor electrolytes.</jats:p>

<jats:p>Graphene and black phosphorus have attracted tremendous attention in optics due to their support of localized plasmon resonance. In this paper, a structure consisted of graphene–black phosphorus heterostructure is proposed to realize terahertz anisotropic near-perfect absorption. We demonstrate that strong plasmonic resonances in graphene–black phosphorus heterostructure nanoribbons can both be provided along armchair and zigzag directions, and dominated by the distance between the graphene and black phosphorus ribbons. In particular, the maximum absorption of 99.6% at 10.2 THz along armchair direction can be reached. The proposed high performance anisotropic structure may have promising potential applications in photodetectors, biosensors, and terahertz imaging.</jats:p>

<jats:p>The microstructure and Ge-V photoluminescent properties of diamond particles treated by microwave oxygen plasma are investigated. The results show that in the first 5 min of microwave plasma treatment, graphite and disordered carbon on the surface of the particles are etched away, so that diamond with regular crystal plane, smaller lattice stress, and better crystal quality is exposed, producing a Ge-V photoluminescence (PL) intensity 4 times stronger and PL peak FWHM (full width at half maximum) value of 6.6 nm smaller than the as-deposited sample. It is observed that the cycles of ‘diamond is converted into graphite and disordered carbon, then the graphite and disordered carbon are etched’ can occur with the treatment time further increasing. During these cycles, the particle surface alternately appears smooth and rough, corresponding to the strengthening and weakening of Ge-V PL intensity, respectively, while the PL intensity is always stronger than that of the as-deposited sample. The results suggest that not only graphite but also disordered carbon weakens the Ge-V PL intensity. Our study provides a feasible way of enhancing the Ge-V PL properties and effectively controlling the surface morphology of diamond particle.</jats:p>

<jats:p>We demonstrate a piezoelectric vibration energy harvester with the ZnO piezoelectric film and an improved synchronous electric charge extraction energy harvesting circuit on the basis of the beam-type mechanical structure, especially investigate its output performance in vibration harvesting and ability to generate charges. By establishing the theoretical model for each of vibration and circuit, the numerical results of voltage and power output are obtained. By fabricating the prototype of this harvester, the quality of the sputtered film is explored. Theoretical and experimental analyses are conducted in open-circuit and closed-circuit conditions, where the open-circuit mode refers to the voltage output in relation to the ZnO film and external excitation, and the power output of the closed-circuit mode is relevant to resistance. Experimental findings show good agreement with the theoretical ones, in the output tendency. It is observed that the properties of ZnO film achieve regularly direct proportion to output performance under different excitations. Furthermore, a maximum experimental power output of 4.5 mW in a resistance range of 3 kΩ–8 kΩ is achieved by using an improved synchronous electric charge extraction circuit. The result is not only more than three times the power output of classic circuit, but also can broaden the resistance to a large range of 5 kΩ under an identical maximum value of power output. In this study we demonstrate the fundamental mechanism of piezoelectric materials under multiple conditions and take an example to show the methods of fabricating and testing the ZnO film. Furthermore, it may contribute to a novel energy harvesting circuit with high output performance.</jats:p>

<jats:p>To enhance the potential application of thermally activated delayed fluorescence (TADF) molecular materials, new functions are gradually cooperated to the TADF molecules. Aggregation induced emission can effectively solve the fluorescence quenching problem for TADF molecules in solid phase, thus aggregation-induced delayed fluorescence (AIDF) molecules were recently focused. Nevertheless, their luminescent mechanisms are not clear enough. In this work, excited state properties of an AIDF molecule DMF-BP-DMAC [reported in <jats:italic>Chemistry–An Asian Journal</jats:italic> <jats:bold>14</jats:bold> 828 (2019)] are theoretically studied in tetrahydrofuran (THF) and solid phase. For consideration of surrounding environment, the polarizable continuum method (PCM) and the combined quantum mechanics and molecular mechanics (QM/MM) method were applied for solvent and solid phase, respectively. Due to the increase of the transition dipole moment and decrease of the energy difference between the first single excited state (S<jats:sub>1</jats:sub>) and the ground state (S<jats:sub>0</jats:sub>), the radiative rate is increased by about 2 orders of magnitude in solid phase. The energy dissipation of the non-radiative process from S<jats:sub>1</jats:sub> to S<jats:sub>0</jats:sub> is mainly contributed by low-frequency vibrational modes in solvent, and they can be effectively suppressed in aggregation, which may lead to a slow non-radiation process in solid phase. Both factors would induce enhanced luminescence efficiency of DMF-BP-DMAC in solid phase. Meanwhile, the small energy gap between S<jats:sub>1</jats:sub> and triplet excited states results in high reverse intersystem crossing (RISC) rates in both solvent and solid phase. Therefore, TADF is confirmed in both phases. Aggregation significantly influences both the ISC and RISC processes and more RISC channels are involved in solid state. The enhanced delayed fluorescence should be induced by both the enhanced fluorescent efficiency and ISC efficiency. Our calculation provides a reasonable explanation for experimental measurements and helps one to better understand the luminescence mechanism of AIDF molecules.</jats:p>