Facile Synthesis of Hollow MgO Spheres and Their Fluoride Adsorption PropertiesRead the full article
Advances in Condensed Matter Physics publishes research on the experimental and theoretical study of the physics of materials in solid, liquid, amorphous, and exotic states.
Chief Editor, Professor Ulloa, is based at Ohio University and is a condensed matter theorist. His research is focussed on the electronic properties of nanostructures including quantum dots and nanowires, as well as proximity effects in 2D crystals.
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A Novel Elastic Metamaterial with Multiple Resonators for Vibration Suppression
In this paper, two models of elastic metamaterial containing one and two resonators are proposed to obtain the bandgaps with the aim of providing broadband vibration suppression. The model with one DOF is built by assembling several unite cells in which each unite cell consists of a rectangular frame as the base structure and a rack-and-pinion mechanism that is joined to the frame with a linear spring on both sides. In the second model with two DOF, a small mass is added while its center is attached to the center of the pinion on one side and the other side is connected to the rectangular frame via a linear spring. In the first mechanism, the pinion is considered as the single resonator, and in the 2DOF model, on the other hand, the pinion and small mass acted as multiple resonators. By obtaining the governing equations of motion for a single cell in each model, the dynamic behavior of two metastructures is thoroughly investigated. Therefore, the equations of motion for the two models are written in matrix form, and then, the dispersion relations are presented to analyze the influences of system parameters on the bandgaps’ starting/ending frequencies. Finally, two models are successfully compared and then numerically simulated via MATLAB-SIMULINK and MSC-ADAMS software. With the aid of closed-form expressions for starting/ending frequencies, the correlation between the system parameters and bandgap intervals can be readily recognized.
Stress-Driven Evolution on Mismatched Ca2Co2O5 Oxide Material: From Geometry to the Electronic States
The geometrical structures, phase stabilities, electron energy band structures, electron density of states, and atom recombination together with the electron conduction behaviors of the sandwiched Ca2Co2O5 with external stress of 1 GPa are intensively studied by the density functional theory method. The studying results show that the symmetry remains undisturbed; the strain to the stress response is anisotropic. The strain of microarchitecture induced by external stress is also anisotropic. There is stronger covalent binding between Co and O. The binding between Co and O within CdI2 like CoO2 is very much even covalent, and it is weakened under external stress. But the covalent Co-O binding within the rock salt like CaCoO layer is enhanced. The Ca-O binding strength is insensitive to external stress. An energy gap of 0.1 eV below Fermi level for the spin-up electron band disappears, and the two energy gaps are narrowed for the spin-down electron bands. The p orbital electrons form primarily the bands below Fermi level and the d orbital electrons form primarily the bands above Fermi level. The transitions from p orbital electrons to d orbital electrons produce the conduction. The CdI2 like CoO2 layer has been enhanced in terms of participating in the conduction properties with external stress of 1 GPa, and the capability of Co is enhanced while the capability of O is decreased.
Molecular Dynamics Simulation of the Coalescence and Melting Process of Cu and Ag Nanoparticles
The coalescence and melting process of different sizes and arrangements of Ag and Cu nanoparticles is studied through the molecular dynamics (MD) method. The results show that the twin boundary or stacking fault formation and atomic diffusion of the nanoparticles play an important role in the different stages of the heating process. At the beginning of the simulation, Cu and Ag nanoparticles will contact to each other in a very short time. As the temperature goes up, Cu and Ag nanoparticles may generate stacking fault or twin boundary to stabilize the interface structure. When the temperature reaches a critical value, the atoms gain a strong ability to diffuse and eventually melt into one liquid sphere. The coalescence point and melting temperature increase as cluster diameter increases. Moreover, the arrangement of Cu and Ag nanoparticles has a certain effect on the stability of the initial joint interface, which will affect subsequent coalescence and melting behavior.
Micropyramid Vertical Ultraviolet GaN/AlGaN Multiple Quantum Wells LEDs on Si(111)
Micropyramid vertical GaN-based ultraviolet (UV) light-emitting diodes (LEDs) on Si(111) substrate have been fabricated by selective area growth to reduce threading dislocations and the polarization effects. There is no-light emission at the bottom and six planes of the pyramid at lower current due to the leakage current and nonradiative recombination of the dislocation at the bottom and the 90° threading dislocations (TDs) at six planes of the pyramid, and the top of the pyramid is the high-brightness region. The micropyramid UV LED has a high optical output intensity under a small current injection, and the series resistance of unit area is only a quarter of the conventional vertical LEDs, so the micropyramid UV LED would have a high output power under the drive circuit. The reverse leakage current of a single micropyramid UV LED is 2 nA at −10 V.
Microwave Vitrification of Uranium Tailings: Microstructure and Mechanical Property
In this work, the dense glass matrix of uranium tailings was successfully fabricated via microwave sintering process with Na2CO3 as a sintering aid. The effects of Na2CO3 additive and sintering temperature on the microstructure and mechanical properties of as-prepared solids were systematically investigated. XRD results confirmed the vitrified forms can be achieved at 1200°C within 30 min with 20 wt.% Na2CO3 addition. Importantly, the Na2CO3 additive significantly reduced the firing temperature from 1500°C to 1200°C and promoted densification. FT-IR analysis demonstrated that the main characteristic peaks of the sintered samples were attributed to the vibration of Si-O-Si. Microstructural studies presented the homogeneous distribution of glass phases. The results of mechanical properties of the sintered forms show that bulk density and Vickers hardness increased with increasing Na2CO3 content as well as sintering temperature, and the highest bulk density (2.45 ± 0.01 g/cm3) and Vickers hardness (823 ± 25 HV) were obtained at the temperature of 1300°C with 20 wt.% Na2CO3 addition, the heating rate of 20°C/min, and the soaking time of 30 min. It implied that the combination of microwave sintering with the appropriate addition of Na2CO3 would provide an efficient method for the immobilization of radionuclides in uranium tailings.
Tuning Electronic Properties of GaSe/Silicane Van der Waals Heterostructure by External Electric Field and Strain: A First-Principle Study
The electronic structure of GaSe/silicane (GaSe/SiH) van der Waals (vdW) heterostructure in response to a vertical electric field and strain was studied via first-principle calculations. The heterostructure had indirect band gap characteristics in the range [−1.0, −0.4] V/Å and direct band gap features in the range [−0.3, 0.2] V/Å. Furthermore, a type-II to type-I band alignment transition appeared at −0.7 and −0.3 V/Å. Additionally, the GaSe/SiH vdW heterostructure had a type-II band alignment under strain, but an indirect to direct band gap semiconductor transition occurred at −3%. These results indicated that the GaSe/SiH vdW heterostructure may have applications in novel nanoelectronic and optoelectronic devices.