Science
Over the past decade, efforts have been made to develop nondestructive techniques for three-dimensional (3D) grain-orientation mapping in crystalline materials. 3D x-ray diffraction microscopy and differential-aperture x-ray microscopy can now be used to generate 3D orientation maps with a spatial resolution of 200 nanometers (nm). We describe here a nondestructive technique that enables 3D orientation mapping in the transmission electron microscope of mono-and multiphase nanocrystalline materials with a spatial resolution reaching 1 nm. We demonstrate the technique by an experimental study of a nanocrystalline aluminum sample and use simulations to validate the principles involved.
关键词:
diffraction;maps;tem
Advanced Materials
Modern methods of in situ transmission electron microscopy (TEM) allow one to not only manipulate with a nanoscale object at the nanometer-range precision but also to get deep insights into its physical and chemical statuses. Dedicated TEM holders combining the capabilities of a conventional high-resolution TEM instrument and atomic force -, and/or scanning tunneling microscopy probes become the powerful tools in nanomaterials analysis. This progress report highlights the past, present and future of these exciting methods based on the extensive authors endeavors over the last five years. The objects of interest are diverse. They include carbon, boron nitride and other inorganic one- and two-dimensional nanoscale materials, e.g., nanotubes, nanowires and nanosheets. The key point of all experiments discussed is that the mechanical and electrical transport data are acquired on an individual nanostructure level under ultimately high spatial, temporal and energy resolution achievable in TEM, and thus can directly be linked to morphological, structural and chemical peculiarities of a given nanomaterial.
关键词:
transmission electron microscopy;nanotubes;nanowires;nanosheets;boron-nitride nanotubes;in-situ tem;filled carbon nanotubes;gan-nanowires;tensile tests;deformation;nanosheets;transport;graphene;nanocontacts
新型炭材料
The overall properties of ordered mesoporous carbons (OMCs) are essentially influenced, by the pore structure. However, neither X-ray diffraction analysis nor transmission electron microscopy (TEM) micrographs can identify the pore structure correctly. Therefore, a three-dimensional (3D) reconstruction method from TEM was carefully developed to investigate the structure and parameters of OMCs. Characteristic pore images of OMCs can be obtained by separately tilting along the two vertical axes using a 3D specimen holder. Pore parameters and a model of their arrangement can be readily obtained by analyzing the geometrical relationship of pore images of OMCs with different azimuths. As an example, OMCs synthesized from resin using an organic template method were investigated. It is concluded that the OMCs have an ordered hexagonal arrangement with a uniform pore size of 11 nm. It is demonstrated that a series of tiltings about two vertical axes can easily confirm Whether the arrangement of OMCs is hexagonal or not. The structure model and parameters of OMCs with hexagonal symmetry can also be easily identified by this method.
关键词:
Ordered mesoporous carbon;Hexagonal model;Transmission electron;microscope;Three-dimensional reconstruction;template
Corrosion Science
The early stages of the evolution of atmospheric corrosion of carbon steels exposed in both a laboratory simulated and a natural atmosphere environment in Shenyang have been observed by in situ scanning electron microscopy. In the case of laboratory cyclic wet-dry tests, even though the chloride content level is very low, filiform corrosion is initiated in the early stage. The filiform corrosion grows in random directions, forming a network of ridges. White nodules nucleate and grow on the ridges during continued corrosion and eventually connect with each other to form the initial corrosion scale. Pits were also found on the surface beneath corrosion products. In the case of a natural atmospheric environment, both filiform corrosion and other localized corrosion, such as pitting and inter-granular attack take place in the initial stage. It is obvious that there is variety of localized corrosion in the initial stage of atmospheric corrosion. (C) 2007 Elsevier Ltd. All rights reserved.
关键词:
steel;atmospheric corrosion;initial stage;localized corrosion;in-situ;iron;electrolyte;thickness
Physical Review B
In the investigation of the optical and magnetic properties of the semiconductors containing transition-metal ions, the one-electron orbital cannot be treated with a pure d orbital because of a strong covalence. This paper presents the energy matrix of the d*(8) and d*(2) (d* means a modified d function) system, in which the covalence is described by two covalent factors. The differences between the matrix diagonal elements of the t(2)(m)e(n) term of the d*(8) system and the t(2)(6-m)e(4-n) term of the d*(2) system vary with m and n. The d(N) electron system can be explained with the d(10-N) hole system because the difference between the energy matrix of the d(N) and d(10-N) systems has a fixed value. However, this kind of simple relation does not exist for the d*(N) and d*(10-N) systems when the covalence is considered. A numerical calculation shows that the variation of the energy levels with the covalence for Ni2+ in the d*(8) electron system is larger than that in the d*(2) hole system. The calculated energy levels obtained from the d*(8) matrix are in good agreement with the experimental data of the Ni2+ ion for ZnS:Ni and ZnSe:Ni. This suggests that the d*(8) electron system instead of the d*(2) hole system should be used in the investigation of optical and magnetic properties of semiconductor containing Ni2+ ions.
关键词:
zns-ni;absorption;vanadium;impurities;spectra;ions
Journal of Materials Research
The results of high resolution transmission electron microscope (HRTEM) observation and image simulation show that Zr4Co4Si7 possesses the same structure type of Zr4CO4Ge7. Addition of Fe or Ni into the Zr4Co4Si7 compound, except that the dimensions changed slightly, does not change the lattice type and coordination in the crystal structure, maintaining the V-phase structure. Also, twins with coherent boundaries and partially coherent interfaces are observed. The image conditions of Zr4Co4Si7 and the structure differences between Zr4Co4Si7 and tetrahedral close-packed phases are also discussed.
关键词:
domain-structures;alloy;hrem
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
