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Dislocations in perovskite oxides have important impacts on their physical and chemical properties, which are determined by their unique atomic environments. In the present study, the structure of dislocations in a 10° low-angle grain boundary of SrTiO3 that was fabricated in an N2 annealing atmosphere is characterized by spherical aberration-corrected scanning transmission electron microscopy and spectroscopy. We find that the dislocation cores are deficient in titanium (Ti) due to Sr substitution and under Ti occupancy. This differs from previously reported dislocation cores fabricated in an air annealing atmosphere, which show Ti enrichment. The presence of oxygen vacancies and partially reduced Ti are also detected in these Ti-deficient dislocation cores. These findings indicate that atomic structures of dislocations can be very different even when they have the same Burgers vectors. Controllable element segregation in the dislocations and grain boundaries via bicrystal engineering should be very useful for designing devices with novel functions. [ABSTRACT FROM AUTHOR]

In ultra-short pulse laser machining and micro/surface processing, accurate simulation of laser ablation is important for understanding laser-target interaction and improving ablation performance, but it remains challenging. This work aims to develop a numerical model to improve the accuracy of the ablation depth calculation. A grid deformation scheme is proposed based on energy conservation and considering contributions to instant material removal from both the electron and lattice subsystems. By incorporating this scheme with the two-temperature model (TTM), a reasonable prediction of the instant target surface profile during laser ablation has been achieved. In the case of single-pulse femtosecond laser ablation of Ti6Al4V, the calculated ablation depth ranges from 0.06 to 0.56 μm for laser energy from 1.0 to 10.0 μJ. For single-pulse picosecond laser ablation of stainless steel, as laser energy increases from 6.0 to 18.5 μJ, the predicted ablation crater deepens accordingly from 40 to 87 nm. In addition, for multi-pulse picosecond laser ablation of stainless steel, a linear dependence of the ablation depth on the pulse number is observed up to a depth of about 803 nm at 6.0 μJ and 20 pulses. In all the above-mentioned cases, the calculation results are in better agreement with experimental measurements than conventional TTM or other material removal schemes, validating the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Helium ion microscope (HIM) has presented an outstanding ability to image and nanofabricate thin film and two-dimensional materials with high precision. However, the concomitant damage and implantation induced by focused helium ion beam should influence the imaging quality and nanomachining efficiency inevitably, especially for bulk samples. In this work, the authors investigated the generation process of damages at nanoscales in single crystalline bulk silicon caused by ions implantation in HIM using transmission electron microscopy. The dependence of implantation and damage on ion dose, ion energy, and beam current was also discussed and analyzed. It was found that the damage should be originated from the local defects caused by ion implantation and the crystal structure could be gradually destroyed and transform into amorphous silicon with the generation and growth of subsurface nanobubbles as ion dose increased. The local concentration of implanted helium ion was found as a universal factor to impact on the damage level and the size of nanobubbles directly. These findings not only shed lights on the effective imaging and nanofabrication of HIM but also provide a further understanding in the nuclear irradiation area. [ABSTRACT FROM AUTHOR]

We measured thermal conductivity and electrical conductivity in organic/inorganic composites with Ag nanowires (NWs) embedded in a poly(vinylidene fluoride) matrix. High thermal and electrical conductivities of 8.43 W / ( mK ) and 1.02 × 10 6 S / m are achieved, respectively, when the volume fraction of Ag NWs reaches 28.34 %. Both measured electrical and thermal conductivities obey the universal power law commonly described in the percolation theory. The percolation behaviors of thermal and electrical conductivities are clearly observed when the volume fraction of Ag NWs is above the critical volume fraction (2.25%), due to the formation of a percolation spanning cluster. Further calculations on the Lorenz number as a function of Ag NW volume fraction also confirm the percolation behaviors. The power-law exponent for the thermal percolation is slightly smaller than that for the electrical percolation, which is likely due to the “dead-end” structures that do not contribute to electrical percolation. To understand the effect of contact resistance between Ag NWs, we modeled the electron contribution to the electrical and thermal resistance at the contact. The non-ideal contact will cause the interfacial thermal resistance increase much more than the electrical contact resistance. The interfacial Lorenz number will decrease from the Sommerfeld value to a much lower value if the contact is non-ideal. Our work can shed some light on the thermal percolation in composite materials. [ABSTRACT FROM AUTHOR]