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The effect of point defect on mechanical properties of MoSi₂ has been investigated by the first-principles. The elastic constants, mechanical modulus, hardness and thermodynamic properties of MoSi₂ with four different single point defects have been calculated. By comparing with the defect-free MoSi₂, it is found that the bulk modulus/shear modulus ratio (B/G) of MoSi₂ with a single point defect increases slightly while the Debye temperature decreases drastically, which indicates that MoSi₂ with some point defects have relatively good ductility. The calculated three-dimensional (3D) contours of elastic modulus and these projections on the (001) and (010) planes show that the directionality of Young’s modulus and shear modulus is unapparent for MoSi₂ with a point defect (V${}_{\mathrm{\text{Mo}}}$ and Mo${}_{\mathrm{\text{Si}}}$) but it is relatively obvious for MoSi₂ with V${}_{\mathrm{\text{Si}}}$ and Si${}_{\mathrm{\text{Mo}}}$. It suggests that V${}_{\mathrm{\text{Si}}}$ and Si${}_{\mathrm{\text{Mo}}}$ can strengthen the anisotropy in elasticity. The electronic properties of C11${}_{\mathrm{\text{b}}}$ MoSi₂ with different single point defects have been studied to reveal further the influencing mechanism of point defect on mechanical properties. This work should help reveal the interrelation between intrinsic defects and service performance of MoSi₂.

With the plane wave expansion method, we introduced the concept and theory of two-dimensional function photonic crystal, and compared the theoretical difference of two-dimensional function photonic crystal with the conventional photonic crystal. In Numerical calculation, with COMSOL software based on finite element method, we have studied the bandgap structure, defect mode and eigenfield distribution for the two-dimensional function photonic crystal with and without point defect. For the two-dimensional function photonic crystal, the dielectric constant of dielectric column is the space coordinate function, which can be realized by the electro-optic effect and the Kerr effect. In the paper, we studied the dielectric constant function form is $𝜀$(r) = kr + b, and the parameters k and b can be adjusted by changing the electric field or light intensity applied to the dielectric column. By changing the parameters k or b of the dielectric column dielectric constant, we found the two-dimensional function photonic crystal transmission characteristics have the adjustability, i.e., the bandgap structure, the bandgap position and width, the defect mode position, width and number and the defect mode eigenfield distribution can be changed by adjusting the parameters k or b, which can be used to conveniently design the bandgap structure that we need. These conclusions will provide important theoretical basis and methods for optical devices design.

The E′_δ center is one of the most important paramagnetic point defects in amorphous silicon dioxide (a-SiO₂) primarily for applications in the field of electronics. In fact, its appearance in the gate oxide of metal-oxide-semiconductor (MOS) structures seriously affects the proper work of many devices and, often, causes their definitive failure. In spite of its relevance, until now a definitive microscopic model of this point defect has not been established. In the present work we review our experimental investigation by electron paramagnetic resonance (EPR) on the E′_δ center induced in γ-ray irradiated a-SiO₂. This study has driven us to the determination of the intensity ratio between the hyperfine doublet and the main resonance line of this point defect. On the basis of this estimation we have pointed out that the unpaired electron wave function of the E′_δ center is actually delocalized over four nearly equivalent silicon atoms, shedding new light on the microscopic structure of this technologically relevant point defect.

The effect of the surface on edge dislocation glide in the crystal with point defects both on the surface and in the bulk is studied theoretically. It is shown that the drag force of dislocation can be reduced by the image forces to several orders of magnitude in nanoscale region.

In this paper, we investigate the defect modes created by taking a single rod away from the center of the supercell in two-dimensional photonic crystals. Through theoretical calculation, we find that the defect band can exist in the photonic band gaps, and the position of the defect band frequency intensively depends on the position and radius size of the defect rod. When the radius of the defect rod is bigger than that of the normal rods, the frequency of the defect band can be tunable in a wider range by moving the defect position while the doubly degenerate defect modes may split into two nondegenerate defect modes. The investigation provides a theoretical instruction to design the optical resonator with tunable frequency.

The new features of the bound state’s formation due to the defect nonlinearity and stepwise medium nonlinearity are found. The Schrödinger equation containing two terms of different nonlinearity types is solved analytically. The exact solution found is described as the bound state near the nonlinear defect in the nonlinear medium. Properties of the bound state are analyzed in dependence on defect and medium parameters. The bound state existing only near nonlinear defect only is found. It is shown that the influence of a change in the effective defect power is qualitatively equivalent to a change in the defect power up to renormalization, and the effect of the defect nonlinearity is opposite.

Positron annihilation was performed to study the isochronal annealing of wrought (2024, 7075) and casting (AlSi_11.35Mg_0.23, AlSi_10.9Mg_0.17Sr_0.06) aluminum alloys in the temperature range from room temperature to 773 K after they had been deformed at room temperature with 25% deformation. Two annealing stages of microstructures were distinguished which were attributed to recovery in 2024, and AlSi_11.35Mg_0.23, AlSi_10.9Mg_0.17Sr_0.06 due to point and dislocations respectively, and only one due to dislocations in 7075.

Density functional theory has been performed on the step-defect Al₂O₃ film surfaces with the OH, Cl and H₂O molecules coadsorption. Three kinds of step-defect (Al, O2, Al3) surfaces are optimized and the adsorption energy, the binding energies of film and adsorbates are calculated. The energy properties are similar in H₂O or Cl coadsorption configurations, but have obvious differences for the OH group coadsorption configuration due to large numbers of adsorbate species and numbers. After structural relaxation, most of the step-defect surfaces could be easily hydroxylated. The Al3 step-defect surfaces are easier to be corroded by H₂O and coadsorption molecules due to lots of unsaturated dangling bonds, some H₂O molecules are located into the step-defect, surface Al atoms collapse inside the steps and several inner O atoms move outside the film. When the Cl exists in the aqueous solution, it would restrict H₂O molecules from dissociating into OH groups. Moreover, the dissociation and recombination of H₂O molecules could be promoted by OH groups.