Search

In nano-crystalline and multi-crystalline silicon, grain boundaries (GBs) and their properties may dominate the overall material performance. With a hybrid Monte Carlo and molecular dynamics (MC/MD) approach capable of reproducing the natural formation process of silicon (001) small angle twist GBs, the misorientation and temperature dependence of GB properties were examined at the atomic level. The GB structures and energies show various transition characteristics around three critical misorientation angles. Structure–property correlations are established by converting the three critical misorientation angles to the corresponding dislocation spacings, which are equal to 6-, 2-, and 1-times dislocation core radius. Stress fields and elastic strain energies agree well with the Continuum theory, and their effects on the dislocation structures and defect sink are discussed. This work also reports the variations of GB structures and energies are governed by a critical temperature at around 800 K, where the GB energies reach the minimum and the dislocation dissociations are suppressed.

FeOCl has attracted much attention for its good photo-Fenton properties. However, there are still some limitations to the removal efficiency of organic pollutants. Visible-light-responsive FeOCl/CdS quantum dot composites were prepared by calcination to overcome their flaws, and their catalytic activity was explored by the degradation of acid orange II (AO-II). The experimental results showed that the FeOCl/CdS composites exhibited better catalytic performance than pure components. The F1Cd0.5composite (mass ratio of FeOCl to CdS is 1:0.5) achieved 98.5% removal efficiency of AO-II, which is 14.8 times higher than that of FeOCl+CdS under similar experimental conditions; moreover, the F1Cd0.5composite still exhibits a high stability after five cycles. According to the characterization and experimental results with density functional theory calculations together, it is proposed that the type II carrier transfer-separation mechanism plays a leading role in enhancing the photodegradation performance of the photo-Fenton catalysts. This study provides a new idea to further improve the catalytic efficiency of the photo-Fenton technology for organic pollutant degradation.

The degradation of inverted metamorphic four-junction (GaInP/GaAs/In0.3Ga0.7As/In0.58Ga0.42As, IMM4J) solar cells irradiated by 1-MeV electrons was investigated via their spectral responses and the characterization of their electrical properties. As in the case of traditional three-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties (Isc, Voc, and Pmax) decrease with the logarithmic change of the electron fluence. The degradation of open-circuit voltage (Voc) is slightly more pronounced than that of Isc in IMM4J solar cells because of the sum rule for Voc and the limit rule for Isc. The spectral response analysis showed that an In0.3Ga0.7As subcell was the most damaged subcell in the irradiated IMM4J solar cell, but an In0.58Ga0.42As subcell had the lowest initial short-circuit current density (Jsc), which was maintained throughout the irradiation test. We therefore focused on the In0.58Ga0.42As subcell. Deep-level transient spectroscopy (DLTS) experiments were realized to study emission and capture processes in two special full configurations of In0.58Ga0.42As and In0.3Ga0.7As subcells of the IMM4J solar cell. DLTS measurements reveal a dominant electron trap at 0.52 eV below the conduction band (Ec) of In0.58Ga0.42As, and the electron trap gradually evolved into Ec-0.46eV and Ec-0.58eV after 1-MeV electron irradiation. Based on the first-principles calculation, Ec-0.46 eV and Ec-0.58 eV can be assigned as ${\bf V}_{{\bf Ga}}^{\bf 0}/{\bf V}_{{\bf Ga}}^{{\rm{ - }}1}$ and ${\bf V}_{{\bf In}}^{\bf 0}/{\bf V}_{{\bf In}}^{{\bf - 1}}$, respectively. However, only one shallow level Ec-0.03eV was observed within the bandgap of In0.3Ga0.7As after irradiation with DLTS detection. We summarize the issues faced for the space application of IMM4J solar cells by comparing the spectral responses of IMM3J, IMM4J, and TJ solar cells. Finally, the optimization of the design and fabrication of IMM solar cells are proposed.

Grain boundary (GB) is the fundamental issue enabling the high performance of multicrystalline materials. However, structural multiplicity within some macroscopic GB characters may significantly affect their microscopic properties. In this paper, the natural formation process of a Si [001] small angle (1.15°) symmetric tilt GB is reproduced via molecular dynamics, where we find three dislocation types and six GB-dislocation structures. The dislocations are observed as the sink of defects during the GB formation, and their formation probabilities are strongly correlated with the elastic strain energy. For more potential structural multiplicity, a lower misorientation angle is energetically favorable. The validity of our results is confirmed by the continuum theory.