Twin boundaries have been exploited to stabilize ultrafine grains and improve mechanical properties of nanomaterials.The production of the twin boundaries and nanotwins is however prohibitively challenging in carbide ...Twin boundaries have been exploited to stabilize ultrafine grains and improve mechanical properties of nanomaterials.The production of the twin boundaries and nanotwins is however prohibitively challenging in carbide ceramics.Using a scanning transmission electron microscope as a unique platform for atomic-scale structure engineering,we demonstrate that twin platelets could be produced in carbides by engineering antisite defects.The antisite defects at metal sites in various layered ternary carbides are collectively and controllably generated,and the metal elements are homogenized by electron irradiation,which transforms a twin-like lamellae into nanotwin platelets.Accompanying chemical homogenization,α-Ti_(3)AlC_(2) transforms to unconventionalβ-Ti_(3)AiC_(2).The chemical homogeneity and the width of the twin platelets can be tuned by dose and energy of bombarding electrons.Chemically homogenized nanotwins can boost hardness by~45%.Our results provide a new way to produce ultrathin(<5 nm)nanotwin platelets in scientifically and technologically important carbide materials and showcase feasibility of defect engineering by an angstrom-sized electron probe.展开更多
The oxygen-related defects in CZ silicon during electron irradiation (1.5 MeV) and subsequent annealing in the range of 150-600 ℃ were investigated by means of FTIR. In the electron irradiation CZ-Si, vacancy-oxygen ...The oxygen-related defects in CZ silicon during electron irradiation (1.5 MeV) and subsequent annealing in the range of 150-600 ℃ were investigated by means of FTIR. In the electron irradiation CZ-Si, vacancy-oxygen complex is one of the dominant defects and its concentration is proportional to electron dose but not related to oxygen concentration. In this work, it was focused on the identification of the weak band at 860 cm-1 which was originated from asymmetrical stretching vibrations of an oxygen atom in the negative VO complex. It exhibits the same thermal stability with neutral VO band at 830 cm-1. In addition, the intensity of 889 cm-1 band has never been observed to exceed that of the A-center, implying that only a partial transformation of VO into VO2 does occur.展开更多
Raman scattering measurements on Se-doped GaAs epitaxial layers and semi-insulating (SI) GaAs irradi-ated by 10 Mev electrons have been investigated. Several defect-related features were observed. We suggestthat the 2...Raman scattering measurements on Se-doped GaAs epitaxial layers and semi-insulating (SI) GaAs irradi-ated by 10 Mev electrons have been investigated. Several defect-related features were observed. We suggestthat the 220 cm ￣-1mode is attribute to As_1 which is associated, at least in part, with EL2 and EL12 defects.For Sedoped samples, the Raman peaks at 205 and 258 cm￣-1 may be due to vibrational modes in small clus-ters of arsenic, and the 77 and 185 ￣-1modes are probably associated with disorder-activated first order Ra-man scattering.Irradiated results show that the small clusters of arsenic and disorder state are increased with in-creasing irradiation fluences. Other Raman peaks will also be discussed in this paper.展开更多
文摘Twin boundaries have been exploited to stabilize ultrafine grains and improve mechanical properties of nanomaterials.The production of the twin boundaries and nanotwins is however prohibitively challenging in carbide ceramics.Using a scanning transmission electron microscope as a unique platform for atomic-scale structure engineering,we demonstrate that twin platelets could be produced in carbides by engineering antisite defects.The antisite defects at metal sites in various layered ternary carbides are collectively and controllably generated,and the metal elements are homogenized by electron irradiation,which transforms a twin-like lamellae into nanotwin platelets.Accompanying chemical homogenization,α-Ti_(3)AlC_(2) transforms to unconventionalβ-Ti_(3)AiC_(2).The chemical homogeneity and the width of the twin platelets can be tuned by dose and energy of bombarding electrons.Chemically homogenized nanotwins can boost hardness by~45%.Our results provide a new way to produce ultrathin(<5 nm)nanotwin platelets in scientifically and technologically important carbide materials and showcase feasibility of defect engineering by an angstrom-sized electron probe.
基金The work was financially supported by the National Natural Science Foundation of China(No.50472034),Natural Science Foundation of Hebei Province(No.E2005000048)and Specialized Research Fundforthe Doctoral Program of Higher Education(No.20050080006).
文摘The oxygen-related defects in CZ silicon during electron irradiation (1.5 MeV) and subsequent annealing in the range of 150-600 ℃ were investigated by means of FTIR. In the electron irradiation CZ-Si, vacancy-oxygen complex is one of the dominant defects and its concentration is proportional to electron dose but not related to oxygen concentration. In this work, it was focused on the identification of the weak band at 860 cm-1 which was originated from asymmetrical stretching vibrations of an oxygen atom in the negative VO complex. It exhibits the same thermal stability with neutral VO band at 830 cm-1. In addition, the intensity of 889 cm-1 band has never been observed to exceed that of the A-center, implying that only a partial transformation of VO into VO2 does occur.
文摘Raman scattering measurements on Se-doped GaAs epitaxial layers and semi-insulating (SI) GaAs irradi-ated by 10 Mev electrons have been investigated. Several defect-related features were observed. We suggestthat the 220 cm ￣-1mode is attribute to As_1 which is associated, at least in part, with EL2 and EL12 defects.For Sedoped samples, the Raman peaks at 205 and 258 cm￣-1 may be due to vibrational modes in small clus-ters of arsenic, and the 77 and 185 ￣-1modes are probably associated with disorder-activated first order Ra-man scattering.Irradiated results show that the small clusters of arsenic and disorder state are increased with in-creasing irradiation fluences. Other Raman peaks will also be discussed in this paper.
