Acoustic one-way manipulations have recently attracted significant attention due to the deep implications in many diverse fields such as biomedical imaging and treatment.However,the previous mechanisms of asymmetric m...Acoustic one-way manipulations have recently attracted significant attention due to the deep implications in many diverse fields such as biomedical imaging and treatment.However,the previous mechanisms of asymmetric manipulation of airborne sound need to use elaborate heavyweight structures and only work in certain frequency ranges.We propose a mechanism for designing an ultra-lightweight and optically transparent structure with asymmetric transmission property for normally incident plane waves.Instead of fabricating solids into complicated artificial structures with limited bandwidth and heavy weight,we simply use xenon to fill a spatial region of asymmetric shape which allows the incident plane wave to pass along one direction while reflecting the reversed wave regardless of frequency.We demonstrate both analytically and numerically its effectiveness of producing highly-asymmetric transmission within an ultra-broad band.Our design offers new possibility for the design of one-way devices and may have far-reaching impact on various scenarios such as noise control.展开更多
Radiation-induced defect annealing in He<sup>+</sup> ion-implanted 4H-SiC via H<sup>+</sup> ion irradiation is investigated by Raman spectroscopy. There are 4H-SiC wafers irradiated with 230 ke...Radiation-induced defect annealing in He<sup>+</sup> ion-implanted 4H-SiC via H<sup>+</sup> ion irradiation is investigated by Raman spectroscopy. There are 4H-SiC wafers irradiated with 230 keV He<sup>+</sup> ions with fluences ranging from cm<sup>?2</sup> to cm<sup>?2</sup> at room temperature. The post-implantation samples are irradiated by 260 keV H<sup>+</sup> ions at a fluence of cm<sup>?2</sup> at room temperature. The intensities of Raman lines decrease after He implantation, while they increase after H irradiation. The experimental results present that the magnitude of Raman line increment is related to the concentration of pre-existing defects formed by He implantation. A strong new peak located near 966 cm<sup>?1</sup>, which is assigned to 3C-SiC LO () phonon, is found in the He-implanted sample with a fluence of cm<sup>?2</sup> followed by H irradiation. However, for the He-implanted sample with a fluence of cm<sup>?2</sup> followed by H irradiation, no 3C-SiC phonon vibrations are found. The detailed reason for H irradiation-induced phase transformation in the He-implanted 4H-SiC is discussed.展开更多
The influence of strain field on defect formation energy and threshold displacement energy （Ed） in body-centered cubic tungsten （W） is studied with molecular dynamics simulation. Two different W potentials （Fikar...The influence of strain field on defect formation energy and threshold displacement energy （Ed） in body-centered cubic tungsten （W） is studied with molecular dynamics simulation. Two different W potentials （Fikar and Juslin） are compared and the results indicate that the connection distance and selected function linking the short-range and long-range portions of the potentials affect the threshold displacement energy and its direction-specific values. The minimum Ed direction calculated with the Fikar potential is （100） and with the Juslin potential is （111）. Nevertheless, the most stable seff-interstitial configuration is found to be a （111）-crowdion for both the potentials. This stable configuration does not change with the applied strain. Varying the strain from compression to tension increases the vacancy formation energy while decreases the self-interstitial formation energy. The formation energy of a seff-interstitial changes more significantly than a vacancy such that Ed decreases with the applied hydrostatic strain from compression to tension.展开更多
Ti_3AlC_2 samples are irradiated in advance by 3.5 MeV Fe-ion to the fluence of 1.0×10^（16） ion/cm^2,and then are implanted by 500 keV He-ion with the fluence of 1.0×10^（17） ion/cm^2 at room temperature....Ti_3AlC_2 samples are irradiated in advance by 3.5 MeV Fe-ion to the fluence of 1.0×10^（16） ion/cm^2,and then are implanted by 500 keV He-ion with the fluence of 1.0×10^（17） ion/cm^2 at room temperature.The irradiated samples are investigated by grazing incidence x-ray diffraction（GIXRD） and transmission electron microscopy（TEM）.GIXRD results show serious structural distortion,but without amorphization in the irradiated samples.Fe-ion irradiation and He-ion implantation create much more serious structural distortion than single Fe-ion irradiation.TEM results reveal that there are a large number of defect clusters in the damage region,and dense spherical He bubbles appear in the He depositional region.It seems that the pre-damage does not influence the growth of He bubbles,but He-ion implantation influences the pre-created defect configurations.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 91426301,11605256 and 11405231
文摘Acoustic one-way manipulations have recently attracted significant attention due to the deep implications in many diverse fields such as biomedical imaging and treatment.However,the previous mechanisms of asymmetric manipulation of airborne sound need to use elaborate heavyweight structures and only work in certain frequency ranges.We propose a mechanism for designing an ultra-lightweight and optically transparent structure with asymmetric transmission property for normally incident plane waves.Instead of fabricating solids into complicated artificial structures with limited bandwidth and heavy weight,we simply use xenon to fill a spatial region of asymmetric shape which allows the incident plane wave to pass along one direction while reflecting the reversed wave regardless of frequency.We demonstrate both analytically and numerically its effectiveness of producing highly-asymmetric transmission within an ultra-broad band.Our design offers new possibility for the design of one-way devices and may have far-reaching impact on various scenarios such as noise control.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11005130,11475229 and 91026002the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDA03010301
文摘Radiation-induced defect annealing in He<sup>+</sup> ion-implanted 4H-SiC via H<sup>+</sup> ion irradiation is investigated by Raman spectroscopy. There are 4H-SiC wafers irradiated with 230 keV He<sup>+</sup> ions with fluences ranging from cm<sup>?2</sup> to cm<sup>?2</sup> at room temperature. The post-implantation samples are irradiated by 260 keV H<sup>+</sup> ions at a fluence of cm<sup>?2</sup> at room temperature. The intensities of Raman lines decrease after He implantation, while they increase after H irradiation. The experimental results present that the magnitude of Raman line increment is related to the concentration of pre-existing defects formed by He implantation. A strong new peak located near 966 cm<sup>?1</sup>, which is assigned to 3C-SiC LO () phonon, is found in the He-implanted sample with a fluence of cm<sup>?2</sup> followed by H irradiation. However, for the He-implanted sample with a fluence of cm<sup>?2</sup> followed by H irradiation, no 3C-SiC phonon vibrations are found. The detailed reason for H irradiation-induced phase transformation in the He-implanted 4H-SiC is discussed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11375242,91026002,91426301 and 11405231the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDA03010301the support of the Office of Fusion Energy Sciences,U.S.Department of Energy under Contract DE-AC05-76RL01830
文摘The influence of strain field on defect formation energy and threshold displacement energy （Ed） in body-centered cubic tungsten （W） is studied with molecular dynamics simulation. Two different W potentials （Fikar and Juslin） are compared and the results indicate that the connection distance and selected function linking the short-range and long-range portions of the potentials affect the threshold displacement energy and its direction-specific values. The minimum Ed direction calculated with the Fikar potential is （100） and with the Juslin potential is （111）. Nevertheless, the most stable seff-interstitial configuration is found to be a （111）-crowdion for both the potentials. This stable configuration does not change with the applied strain. Varying the strain from compression to tension increases the vacancy formation energy while decreases the self-interstitial formation energy. The formation energy of a seff-interstitial changes more significantly than a vacancy such that Ed decreases with the applied hydrostatic strain from compression to tension.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11405231 and 91426301
文摘Ti_3AlC_2 samples are irradiated in advance by 3.5 MeV Fe-ion to the fluence of 1.0×10^（16） ion/cm^2,and then are implanted by 500 keV He-ion with the fluence of 1.0×10^（17） ion/cm^2 at room temperature.The irradiated samples are investigated by grazing incidence x-ray diffraction（GIXRD） and transmission electron microscopy（TEM）.GIXRD results show serious structural distortion,but without amorphization in the irradiated samples.Fe-ion irradiation and He-ion implantation create much more serious structural distortion than single Fe-ion irradiation.TEM results reveal that there are a large number of defect clusters in the damage region,and dense spherical He bubbles appear in the He depositional region.It seems that the pre-damage does not influence the growth of He bubbles,but He-ion implantation influences the pre-created defect configurations.
