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Alkali metal halides have recently received great attention as additives in the chemical vapor deposition (CVD) process to promote the growth of transition metal dichalcogenides (TMDs). However, the multi-faceted role of these halide salts in modulating the properties and quality of TMD monolayers remains mechanistically unclear. In this study, by introducing excessive gaseous sodium chloride (NaCl) into the CVD system, we demonstrate that preferential NaCl deposition along the monolayer edges causes large in situ strain that can invoke localized domains of high defect density and 2H to 1T phase transition. High-resolution scanning transmission electron microscopy, Raman mapping and molecular dynamics simulations revealed that higher NaCl concentrations can promote the coalescence of independent local strain domains, further increasing the 1T/2H phase ratio and defect density. Furthermore, excessive NaCl was also proven by density functional theory calculations to convert thermodynamic growth to kinetic growth, accounting for the unique cloud-shaped MoS2 crystals acquired. Compared with post-growth strain processing methods, this one-step approach for phase and defect engineering not only represents a deeper understanding of the role that NaCl plays in the CVD process, but also provides a convenient means to controllably synthesize conductive/defect-rich materials for further electrocatalysis and optoelectronic applications.

Person re-identification (ReID) is an important problem in intelligent monitoring. Recently, with the development of deep learning, convolutional neural networks have achieved state-of-the-art performance on person ReID problems. However, the deep neural network models used by these methods tend to have large number of parameters and high computational cost, thereby hindering their deployment on resource-constraint devices or real-time applications. In this study, we propose a method that distills the knowledge to a pruned model to reduce the parameters, which can be divided into two stages: one is to apply unstructured pruning method on over-parameterized models, whereas the other is to carry out representation and metric learning-based knowledge distillation on the model after pruning to improve performance. Finally, the proposed method can effectively reduce the total number of parameters by 8.4 with only 0.1% drop of rank-1 accuracy on the Market1501 dataset and no drop of rank-1 accuracy on the DukeMTMC-reID dataset.

With the explosion of data traffic, the use of caching technology to offload data traffic is a very effective way to alleviate network pressure, especially in high-speed train (HST) scenarios. And when users participate in the caching game, the costs of data offloading are greatly reduced. However, current research on users’ participation in data traffic offloading is not much; and there are user security and data reliability issues in the cache of device-to-device (D2D) network. Therefore, in this paper, we propose a novel scheme that user terminals (UTs) cooperatively cache wireless services to the intelligent routing relay (IRR) side in HST scenarios; and we establish a reverse auction model to motivate UTs to collaborate and cache. In this model, IRR acts as the purchaser of the wireless services and UTs are suppliers and consumers. We propose a synchronous reverse auction strategy (S-RAS) to maximize the social incomes at first. However, UTs often have to wait for a long time before the auction begins. Then, we adopt an asynchronous reverse auction strategy (A-RAS) to minimize UTs’ waiting time. Ultimately, in order to minimize UTs’ waiting time while maximizing social incomes, we propose the popularity based hybrid reverse auction strategy (PB-H-RAS) considering both the advantages of S-RAS and A-RAS. Simulation and experiment results verify the effectiveness of the proposed PB-H-RAS strategy; and they also show that the performances of PB-H-RAS strategy are better than the other two strategies in terms of final incomes and completion rate.

Bismuth-antimony (BiSb) alloy combines the low volume expansion of Bi with the high theoretical capacity of Sb and very suitable for application for energy storage. However, the low reversible capacity and poor conductivity of BiSb are still a challenge for promoting their potassium (K) storage properties. Herein, the homogeneous BiSb nanoconfined in three-dimensional (3D) carbon framework were synthesized by NaCl-template assisted method. In the as-constructed architecture, the nano-sized BiSb alloy particles not only shorten the electronic transport route, but also offer adequate K-storage active sites by virtue of the interface between binary alloy and graphene-like coating layers, which were theoretically validated by the density functional theory simulations. Furthermore, the carbon structure can effectively alleviate the internal stress of BiSb during the charging and discharging processes due to the robust integrated structure, i.e. graphene-like layer coated BiSb that embedded into 3D carbon architecture. As a result, the composite electrode exhibits a stable cycling of 303.5 mA h g−1 after 1000 cycles at 500 mA g−1, and a high-rate performance of 246.8 mA h g−1 at 2 A g−1. This work indicates that the enhancement of interfacial K-storage through biphasic synergistic effect will serve as a reference for the development of other energy storage materials.

The interface doping with transition metal elements (TM = Ti, Cr, Co, Ni) has been experimentally proved to be an effective pathway to improve the weak interface bonding of graphene/copper (Gr/Cu) composites. In this paper, the microscopic influencing mechanism of TM doping on the interface interaction and mechanical properties of Gr/Cu was investigated by the first-principles calculations. The sandwich model with graphene embedded in Cu matrix was adopted here to simulate the TM-doped interfaces. It is revealed that the introduction of TM doping elements can significantly improve the work of separation, which relates to the electronegativity difference between TM and Cu elements based on the analysis of the interface electronic structure. Then, the mechanical properties of the clean and TM-doped interfaces were studied by the rigid stretching and the relaxed stretching. We found that, in rigid case, the theoretical tensile strengths of different interfaces are positively correlated with the work of separation, and the electronegativity is also a main factor affecting the mechanical properties. Furthermore, a fitting function containing the element electronegativity was applied to get the stress–strain relationship curve, and the quantitative relationship between the interface bonding and mechanical properties determined in this work can be served as a favorable support for the experimental design of Gr/Cu composites.

The surface reconstruction and its effect on the oxygen vacancy (VO) formation and OER performance of CoO (111) surface are studied using the first principles calculations. The surface reconstruction from the CoO6 octahedrons to the CoO4 tetrahedrons is revealed at CoO (111) surface, which enhances the OER activity and the stability of VO at the surface of CoO (111). The existence of VO changes the electron accumulation around the Co atoms and the bonding state between Co and O atoms, and thus, affects the adsorption of OH and deprotonation process. By analyzing the electron structure, the nature of the activity changes at Co sites due to the surface reconstruction and the introduction of VO is revealed. Our investigation provides a theoretical basis for the design and application of Co-based OER catalysts.

While many metal compounds have been widely studied as electrocatalysts for hydrogen evolution reaction (HER), the mechanism of HER on these materials is still not well understood nor why one compound is more electrocatalytically active than another. Here, we report our findings in synthesis and characterization of several Co compounds (CoP, CoS and Co3O4) with similar morphology and uniform size but dramatically different HER activities. Electrochemical measurements indicate that CoP has the best HER activity, achieving an overpotential of 80 mV at 10 mA cm−2, which is much smaller than those for CoS and Co3O4. DFT-based computations suggest that electron delocalization resulting from the p-d orbits coupling at the surfaces facilitates HER charge transfer kinetics and an optimal balance between the surface adsorption of H atom and desorption of H2. Both experimental and computational analyses reveal that the HER activity of the Co compounds is correlated closely with the energy gap between the anion p-band and the Co d-band centers, which can be used as an effective descriptor for HER activity. This work offers the scientific basis for rational design of more efficient metal compound electrocatalysts with high HER activity.

The poor wettability of alumina surface greatly limits the interface binding between alumina and iron in alumina reinforced iron matrix composites. In this work, the active elements (Ti and Ni) additives are introduced into the interface to enhance the adhesion of the interface, and the activation mechanism is studied. Through the analysis of the embedding ability of activating elements Ti or Ni in Al2O3/Fe interface and their influence on adhesion of interfaces, it is revealed that Ti is prone to segregation at the interface and has a great improvement on the strength and stability of interface binding. However, Ni hardly enhances interface interaction and even causes interface deterioration. Electron structures analysis shows that 4 s, 3p, 3d coupling of Ti results in more electrons involved in the interface interaction, and the formation of Ti-Fe and Ti-O bonds essentially determines the increase of the work of adhesion. The activation mechanism of Ti and Ni well explains the experimentally reported different existence forms and action modes of Ti and Ni.

We investigated the atomic and electronic structures and interface interaction of graphene/copper interface with rare earth elements (REEs) modified using density functional theory. The effect of interface interaction enhancement induced by interfacial modification is revealed, which results in significant improvement of the mechanical properties of graphene/copper. Thereby, we applied a novel strategy to incorporate Y element at the interface of graphene nanoplatelets/copper (GNPs/Cu) to improve mechanical properties of composites. Tensile tests demonstrated that the yield strength of composites increases by 95.4% via very low fraction (0.2 wt. %) of Y modification with elongation comparable to Cu, which exhibits excellent matched relationship between strength and ductility. Simultaneously, the composite equips with improved electrical conductivity compared with that of the matrix. We illustrated the strengthening effects of REEs modification at the interface that give rise to the effective load transfer, in consistence with the theoretical predication. Furthermore, the GNPs/Cu composites with the interface Ce/Sc elements modified were also fabricated, both of which showed excellent strength-ductility combination. Therefore, the universality of the present method is verified for the preparation of metal matrix composites with excellent mechanical properties through interface modification with REEs.

Diamond reinforced metal matrix composites are considered as a promising thermal management material. The interface between diamond and metal matrix determines the properties of the material to some extent. In this paper, the atomic structure, work of adhesion and binding characteristics of diamond (1 1 1)/Al (Cu) (1 1 1) clean interface are studied using first principles calculations. The influence of Mo doping on the interface interaction, tensile properties and thermal conductivity of diamond (1 1 1)/Al (Cu) (1 1 1) interface is discussed. It is revealed that the work of adhesion of diamond/Al interface is much higher than that of diamond/Cu interface and the magnetic moments also prove this point of view. Mo doping increases the binding of diamond/Al interface and diamond/Cu interface, with an increase rate of 7.2% and 28.4%, respectively. The tensile strength is decreased due to the Mo doping, but the breaking elongation of diamond/Al (Cu) composites is effectively improved, which is intimately related to the charge density distribution and the localization of density states at the Fermi level. Furthermore, Mo is a good additive element to improve the thermal conductivity of diamond/Cu interface, which gives an interpretation of the reported experimental results through the view of the atomic and electronic structures.

Interface plays a crucial role to enhance the mechanical properties of metal-matrix composites. Here, we investigated and modulated the intrinsic characteristics of Al2O3/Al interface through interfacial doping by the first-principles calculations. The Al-terminated Al2O3 (0 0 0 1)/Al (1 1 1) interface with OT stacking was found to be the most stable structure by calculating works of adhesion and interface energies. Then, the first principles tensile experiments were performed on the stable interfacial structure, and the tensile strength and elongation were calculated. It is revealed that there is no direct correlation between tensile properties and the work of adhesion or the interface energy. Systematical analysis on electronic structure indicates that the incorporation of doping elements will redistribute the electrons at the interfaces, and there is the interplay between the uniform electron distribution and the tensile properties, especially the elongation. It is found that Mg-doped and Cu-doped interface systems with more uniform electron distribution show better mechanical properties. Therefore, the interface intrinsic strengthening mechanism caused by the interfacial microstructure has a significant impact on the mechanical properties of the composite materials, and complements the load transfer mechanism in metal matrix composites.