743 research outputs found
Surface defects repairing of sprayed Ca-P coating by the microwave-hydrothermal method
The increasing interest in decreasing the surface defects of sprayed Ca-P coating deposited on carbon/carbon (C/C) composites to enhance the bonding strength, bioactivity and corrosion resistance of the coating is justified by the growing evidence of its beneficial effect on the bone replacement fields. Microwave-hydrothermal (MH) method detailed in the previous study is successfully used to reduce the above coating defects and the MH mechanism is well studied here. Hence, five different treatment reagents involving calcium and phosphorus solution, sulfuric acid (H2SO4) solution, ammonium hydroxide (NH3·H2O) solution, only Ca2+ solution and deionized water are selected as the precursor solution. The surface, cross-sectional morphologies, phase and composition of the coatings are characterized by the scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), microscopy Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) spectra. Elastic modulus and coating hardness are measured by nanoindentation. Results reveal that the presence of calcium and phosphorus ions, as well as the H2SO4 in the precursor solution during the MH process, have a positive influence on the reduction of sprayed Ca-P coating surface defects. However, the coating treated by other three solutions cannot produce new phases on the basis of sprayed Ca-P coating and the surface defects of it are not decreased. Nevertheless, the elastic modulus and hardness of the coating treated by H2SO4 solution are very weak. MH treated coating by calcium and phosphorus ions in the precursor solution and in NH3·H2O solution, only Ca2+ solution and deionized water own the similar elastic modulus and hardness to that of the sprayed Ca-P coating. To conclude, in the MH process, the surface defects of the sprayed Ca-P coating are only lowered in calcium and phosphorus precursor solution and the coating strength is not dropped, which demonstrates the promoting mechanism of MH process
Crystal Structure Manipulation of the Exchange Bias in an Antiferromagnetic Film
Exchange bias is one of the most extensively studied phenomena in magnetism,
since it exerts a unidirectional anisotropy to a ferromagnet (FM) when coupled
to an antiferromagnet (AFM) and the control of the exchange bias is therefore
very important for technological applications, such as magnetic random access
memory and giant magnetoresistance sensors. In this letter, we report the
crystal structure manipulation of the exchange bias in epitaxial hcp Cr2O3
films. By epitaxially growing twined (10-10) oriented Cr2O3 thin films, of
which the c axis and spins of the Cr atoms lie in the film plane, we
demonstrate that the exchange bias between Cr2O3 and an adjacent permalloy
layer is tuned to in-plane from out-of-plane that has been observed in (0001)
oriented Cr2O3 films. This is owing to the collinear exchange coupling between
the spins of the Cr atoms and the adjacent FM layer. Such a highly anisotropic
exchange bias phenomenon is not possible in polycrystalline films.Comment: To be published in Scientific Reports, 12 pages, 6 figure
Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations
Although many prototype devices based on two-dimensional (2D) MoS2 have been
fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental
nature of 2D MoS2-metal contacts has not been well understood yet. We provide a
comprehensive ab initio study of the interfacial properties of a series of
monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt,
Ni, and Au). A comparison between the calculated and observed Schottky barrier
heights (SBHs) suggests that many-electron effects are strongly suppressed in
channel 2D MoS2 due to a charge transfer. The extensively adopted energy band
calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc
interface. By contrast, an ab initio quantum transport device simulation better
reproduces the observed SBH in the two types of contacts and highlights the
importance of a higher level theoretical approach beyond the energy band
calculation in the interface study. BL MoS2-metal contacts have a reduced SBH
than ML MoS2-metal contacts due to the interlayer coupling and thus have a
higher electron injection efficiency.Comment: 36 pages, 13 figures, 3 table
Does P-type Ohmic Contact Exist in WSe2-metal Interfaces?
Formation of low-resistance metal contacts is the biggest challenge that
masks the intrinsic exceptional electronic properties of 2D WSe2 devices. We
present the first comparative study of the interfacial properties between ML/BL
WSe2 and Sc, Al, Ag, Au, Pd, and Pt contacts by using ab initio energy band
calculations with inclusion of the spin-orbital coupling (SOC) effects and
quantum transport simulations. The interlayer coupling tends to reduce both the
electron and hole Schottky barrier heights (SBHs) and alters the polarity for
WSe2-Au contact, while the SOC chiefly reduces the hole SBH. In the absence of
the SOC, Pd contact has the smallest hole SBH with a value no less than 0.22
eV. Dramatically, Pt contact surpasses Pd contact and becomes p-type Ohmic or
quasi-Ohmic contact with inclusion of the SOC. Our study provides a theoretical
foundation for the selection of favorable metal electrodes in ML/BL WSe2
devices
A Reinforcement Learning-assisted Genetic Programming Algorithm for Team Formation Problem Considering Person-Job Matching
An efficient team is essential for the company to successfully complete new
projects. To solve the team formation problem considering person-job matching
(TFP-PJM), a 0-1 integer programming model is constructed, which considers both
person-job matching and team members' willingness to communicate on team
efficiency, with the person-job matching score calculated using intuitionistic
fuzzy numbers. Then, a reinforcement learning-assisted genetic programming
algorithm (RL-GP) is proposed to enhance the quality of solutions. The RL-GP
adopts the ensemble population strategies. Before the population evolution at
each generation, the agent selects one from four population search modes
according to the information obtained, thus realizing a sound balance of
exploration and exploitation. In addition, surrogate models are used in the
algorithm to evaluate the formation plans generated by individuals, which
speeds up the algorithm learning process. Afterward, a series of comparison
experiments are conducted to verify the overall performance of RL-GP and the
effectiveness of the improved strategies within the algorithm. The
hyper-heuristic rules obtained through efficient learning can be utilized as
decision-making aids when forming project teams. This study reveals the
advantages of reinforcement learning methods, ensemble strategies, and the
surrogate model applied to the GP framework. The diversity and intelligent
selection of search patterns along with fast adaptation evaluation, are
distinct features that enable RL-GP to be deployed in real-world enterprise
environments.Comment: 16 page
Electro-Chemo-Mechanical Failure of Solid Electrolytes Induced by Growth of Internal Lithium Filaments
Growth of lithium (Li) filaments within solid electrolytes, leading to mechanical degradation of the electrolyte and even short circuit of the cell under high current density, is a great barrier to commercialization of solid-state Li-metal batteries. Understanding of this electro-chemo-mechanical phenomenon is hindered by the challenge of tracking local fields inside the solid electrolyte. Here, a multiphysics simulation aiming to investigate evolution of the mechanical failure of the solid electrolyte induced by the internal growth of Li is reported. Visualization of local stress, damage, and crack propagation within the solid electrolyte enables examination of factors dominating the degradation process, including the geometry, number, and size of Li filaments and voids in the electrolyte. Relative damage induced by locally high stress is found to preferentially occur in the region of the electrolyte/Li interface having great fluctuations. A high number density of Li filaments or voids triggers integration of damage and crack networks by enhanced propagation. This model is built on coupling of mechanical and electrochemical processes for internal plating of Li, revealing evolution of multiphysical fields that can barely be captured by the state-of-the-art experimental techniques. Understanding mechanical degradation of solid electrolytes with the presence of Li filaments paves the way to design advanced solid electrolytes for future solid-state Li-metal batteries
- …