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Highly sensitive near-infrared (NIR) photodetectors have attracted extensive attention due to their wide applications in thermal imaging, night vision and human health monitoring. Organic phototransistors (OPTs) are an important type of photodetector with three-terminal contact, which provides high sensitivity and tunable gain with an external quantum efficiency (EQE)>100% by controlling unbalanced charge transport through an optically controlled gate terminal. Thus, NIR OPTs are considered as a promising alternative NIR light detecting technology to conventional inorganic NIR phototransistors. The design and fabrication flexibility provided by the organic semiconductors and solution processes also have significant cost benefit, creating next-generation large-area, low-cost and flexible NIR photodetectors. However, now the performance of NIR-OPT is not high enough, which is still far from practical applications. Low field-effect mobility, limited exciton dissociation, and poor NIR light absorption are the main reasons to hamper the performance of NIR OPTs. A key technical development to circumvent this hurdle is to create an organic channel layer with ordered microstructure to provide high field-effect mobility and a smart device design to enhance exciton dissociation. In this work, an air stable conjugated semiconducting polymer of diketopyrrolopyrrole-dithienylthieno[3,2- b ]thiophene (DPP-DTT) with narrow band gap was selected as the NIR light response medium. The DPP-DTT nanowire network was obtained by a solution-processed and scalable approach called polymer-matrix-mediated molecular self-assembly. The matrix polymer of polystyrene (PS) was selectively removed from the resulted DPP-DTT:PS blend film, leaving the pristine DPP-DTT nanowire network thin film as the active channel layer for the NIR OPTs. The electrical properties and NIR response of the OPTs based on DPP-DTT nanowire network were studied. It is found that the pristine DPP-DTT nanowire network layer exhibited a typical p-type field-effect transport, showing the hole mobility of >1 cm2/(V s) and on/off ratio >106. These devices also showed sensitive NIR response with photoresponsivity ( R ) of 336 A/W and specific detectivity ( D *) of 5.6×1012 Jones under NIR light intensity of 8 μW/cm2. To further improve the NIR photodetection of the DPP-DTT nanowire network OPTs, zinc oxide (ZnO) nanoparticles were introduced into the devices as electron acceptor material. A small amount of ZnO nanoparticles (1.0 mg/mL) were spin coated onto the DPP-DTT nanowire network to increase the separation efficiency of photodenerated excitons and then capture the photogenerated electrons in trap sites, thereby minimizing the negative impact of photogenerated electrons on hole transport in the NIR OPTs. As a result, the NIR photodetection of the ZnO-modified OPTs was significantly improved. The photosensitivity of ZnO-modified devices reaches as high as 107, which is increased by about 4 to 5 orders of magnitude compared with the pristine DPP-DTT nanowire network NIR OPTs. Correspondingly, the R and D * of ZnO-modified NIR OPTs have been also enhanced. The maximum R value was increased to 721 A/W, which is more than twice the R value of the pristine DPP-DTT nanowire network NIR OPTs. It is noted that such a large R value has achieved the performance level of conventional inorganic NIR phototransistors. Moreover, the maximum D * of the ZnO-modified NIR OPTs reaches 1.3×1013 Jones under the NIR intensity of 8 μW/cm2. Therefore, this work provides a good idea for the structural design and device performance optimization of high-performance NIR OPTs.

Solution-processed hole-injection layers (HILs) for full-color, inverted quantum-dot light-emitting diodes (QLEDs) are developed by simply incorporating the graphene oxide (GO) into poly(3,4-ethyle...

As the study of topological states witnessed rapid progress and fast development, the current research has been expanded from conventional linear dispersion into high order conditions. In comparison with the linear type, high order topological elements feature multiple exotic properties, such as large topological charge, peculiar Berry phase, and chiral surface states, which could lead to the finding of other new physics. In this study, we present a realistic material candidate hosting an ideal quadratic fermionic point state with multiple band degeneracy. Based on first principles calculation and effective model argument, the origin of the quadratic order is analyzed, and its dispersion conditions are examined. Due to the clean band structure, prominent surface states are observed and they exhibit both large energy variation and broad spatial distribution. These beneficial features are very advantageous for future experimental investigations. This work can significantly enhance the research on high order topological states and, in particular, the proposed material can provide an effective platform for quadratic fermionic point states.

The Au–Al bonding joint was prepared by the parallel gap resistance microwelding. The microstructural evolution of Au–Al bonds was investigated under thermal aging, and the mechanical properties of Au–Al intermetallic compounds (IMCs) were computed by the first-principles calculations. We found that the Au–Al IMCs along with cracks grew during aging time and temperature increasing. The formation of the cracks is explained by the Kirkendall effect, volumetric shrinkages and thermal mismatch. Based on the experimental data, the growth of the IMCs is fitted to the diffusion equation to describe the performance degradation of Au–Al bonds. The Arrhenius relationship is introduced as the acceleration model to describe the effects of thermal stress on lifetime. Furthermore, the Weibull–Arrhenius model is built by the combination of the Weibull distribution and the Arrhenius relationship, which provide a method to estimate the lifetime distribution under work condition.

Improving hole injection is a critical issue for further boosting the brightness and efficiency of quantum dot light-emitting diodes (QLEDs) with an organic-inorganic hybrid structure. In this work, a small molecule of 4,4’-bis-(carbazole-9-yl)biphenyl (CBP) with a deep-lying HOMO level was doped into high mobility polymer of poly(9,9-dioctylfluorene-co-N-(4-(3-methyl- propyl)) diphenylamine) (TFB) to construct an efficient composite TFB:CBP hole transport layer (HTL). Green QLEDs based on such solution-processed composite HTLs exhibited a maximum luminance of 90159 cd/m2, with a peak current efficiency of 21.6 cd/A and power efficiency of 12.3 lm/W. These values were over one-order of magnitude larger than those obtained in the CBP-only devices and also much larger than those in the TFB-only devices.

In this study, we have presented a systematic theoretical study about the electronic, magnetic and structural properties of the full-Heusler compound Fe2CuSi based on first principles calculations. The L21-type structure with ferromagnetic configuration is determined to be the ground state. The calculated electronic band structures show metallic behavior for both spin direction and the obtained total magnetic moment of [Formula: see text]B is mostly contributed from the two Fe atoms, which exhibit strong spin splitting effect as revealed from the partial densities of states. Moreover, both mechanical and dynamic stabilities have been accessed and confirmed for Fe2CuSi under its equilibrium ground-state structure. Besides, multiple mechanical parameters have been calculated and they can provide valuable reference for its practical applications. Lastly, we also evaluate the tetragonal phase by introducing tetragonal strain of [Formula: see text] ratio and results show that the cubic phase maintains the lowest total energy throughout the whole studied strain range, even with [Formula: see text] cell volume variations.

Heusler materials have aroused great scientific research interest during recent years due to their special electronic and magnetic properties. Especially for the equiatomic quaternary Heusler compounds, they exhibit very high composition flexibility and structure tunability. In this work, we have carried out a systematic study on the structural configuration and tetragonal stability for the Heusler compound TiZnMnSi by first-principles calculations. Results reveal the type-A structure with ferromagnetic state possesses the lowest total energy and thus should be the ground state configuration. Based on the equilibrium lattice constant, the electronic band structures and magnetic moments have been computed. The tetragonal phase transformation is then investigated by using the total energy variation under different tetragonal strains, and the stability analysis of the mechanical and dynamic properties indicates that TiZnMnSi exhibits a strong tendency for the tetragonal phase. These findings could provide reference data for relative experiments as well as a very helpful theoretical reference for this fascinating class of materials.

CoFeMnSi has been both experimentally and theoretically proven as a novel spin-gapless semiconductor and resulted in a new research direction in equiatomic full Heusler compounds. Using the first-principles calculation method, we investigated the electronic, magnetic and mechanical properties of CoFeMnSi material in this study. The obtained lattice constant under the LiMgPdSn-type Heusler structure is 5.611 &Aring, and it is fairly consistent with previous experimental results and theoretical calculations. Furthermore, the achieved total magnetic moment of 4 &mu, B follows the Slater&ndash, Pauling rule as Mtotal = Ztotal &minus, 24, where Mtotal is the total magnetic moment per formula unit and Ztotal is the total valence electron number, i.e., 28 for CoFeMnSi material. We have also examined the mechanical properties of CoFeMnSi and computed its elastic constants and various moduli. Results show CoFeMnSi behaves in a ductile fashion and its strong elastic anisotropy is revealed with the help of the 3D-directional-dependent Young&rsquo, s and shear moduli. Both mechanical and dynamic stabilities of CoFeMnSi are verified. In addition, strain effects on the electronic and magnetic properties of CoFeMnSi have been investigated, including both uniform and tetragonal strains, and we found that the spin-gapless feature is easily destroyed with both strain conditions, yet the total magnetic moment maintains a good stability. Furthermore, the specific behaviors under various temperatures and pressures have been accessed by the thermodynamic properties with a quasi-harmonic Debye model, including bulk modulus, thermal expansion coefficient, Gr&uuml, neisen constant, heat capacity and Debye temperature. This comprehensive study can offer a very helpful and valuable reference for other relative research works.

This paper investigates the design of a robust fault detection observer for Wireless Networked Control Systems (WNCS) subject to random packet delays introduced by the wireless communication networks. The concept of input-delay analysis is adopted for analyzing the impacts of the packet delay on the residual generation, and a robust observer design and optimization method is proposed to improve the robustness of fault detection against the network induced delay. For the purpose of realistic simulation, a mixed simulation is carried out, where the control system is simulated in MATLAB and the network-induced delays are achieved by simulating an IEEE 802.11b wireless network at the recently developed OMNeT++ platform. The simulation results validate the proposed robust fault detection observer design approach.