In very shallow silicon transistor, it has been required to detect individual dopant atoms. High angle annular dark field (HAADF) image is a powerful tool for composition analysis at an atomic level, but it has been two-dimensional information. Recently, aberration corrected electron microscope has been developed, which enable us to have an electron probe with large convergent angle. Such a probe has been pointed out to improve not only transverse resolution but also depth resolution on a nanometer scale. We found that the column intensity in the HAADF image depended on the z-position of arsenic (As) dopant atoms on the condition that the specimen was very thin and the incident electron beam was irradiated along the  direction of the silicon crystal. It means that the position of As dopant atom can be determined three-dimensionally. This is an advantage of obtaining three dimensional distribution of As dopant atoms in the silicon crystal and also finding which type of dopant cluster is formed.
Most functional materials (ceramics, semi-conductor and metallic alloys) contain not only heavier elements but also light elements, such as oxygen, nitrogen and carbon. It is important to know the atomic arrangement of these elements. However, High angle annular dark field (HAADF) images of those materials usually do not produce any contrast from the light element columns, because the contrast in the image is approximately proportional to the square of the atomic number. Annular bright field (ABF) imaging by Scanning transmission electron microscope (STEM) has recently been found as a novel technique to visualize light elements and heavier elements in the same image. The recent theoretical study by Findley et al7,8) reveals that ABF imaging produces robust dark contrast on atomic columns which is non-oscillating: independent of sample thickness and of the focus of its image. This characteristic of the ABF imaging results in easily interpretable images unlike STEM BF imaging. This paper describes experimental details about results of the visualization of light elements for three ceramics (two oxides and one nitride) using an ABF imaging technique.
Combination of transmission electron microscopy and computed tomography (TEM-CT) is a powerful technique to characterize three-dimensional nature of materials. In this paper, its principle and application are described in detail. In addition, as an example, TEM and TEM-CT was applied on TiN-Ag nanocomposite synthesized by dc arc-plasma method. Microstructures of TiN-Ag nanocomposite were carefully characterized by TEM, and nano-morphologies by TEM-CT. It was found that the surface of nanocrystalline TiN matrix was covered by finely dispersed Ag nanoparticles, and it was found that they were physically attached but not chemically bonded. From these experimental results, formation mechanisms are also predicted.
Magnetic structures in advanced functional materials were studied by electron holography and Lorentz microscopy, both of which are the methods of magnetic imaging based on transmission electron microscopy. The microscopy observations revealed that anti-phase boundaries (APBs: planar lattice imperfections) formed in a ferromagnetic shape memory alloy provided significant pinning sites for the magnetic domain walls. The width of magnetic domain walls trapped by APBs was only 10 nm, which was considerably smaller than the width of conventional 180° walls formed in cubic systems: this narrow wall width was reasonably explained by the depression of ferromagnetism within APBs. We also report on the original method to determine magnetic parameters, related to the exchange stiffness and the magnetocrystalline anisotropy, by using only electron microscopy observations.
Recent development of spherical aberration correctors for transmission electron microscopes (TEM) and scanning TEM (STEM) has enabled atomic-resolution imaging of nanocarbon materials even at relatively low electron acceleration voltages around and below 100 kV. In this article, we review some recent studies on carbon nanotubes (CNTs) and fullerene nanopeapods using aberration-corrected TEM/STEM. Local structure of each individual CNT can be visualized in details including point defects such as atomic vacancies and adatoms in aberration-corrected TEM images. Atomic-level structures of fullerene molecules and their orientation inside a CNT can be unambiguously observed. Identification of single metal atoms such as calcium and lanthanides in nanopeapods by using STEM-EELS operated at 60 kV is also presented.
Aberration-corrected scanning transmission electron microscopy is becoming a very powerful tool to directly image dopant atoms within buried crystalline interfaces. Here, we demonstrate direct imaging of individual dopant atoms in an alumina interface. The focused electron beam transmitted through the off-axis crystals clearly highlights the individual yttrium atoms located on the monoatomic layer interface plane. Not only is their unique two-dimensional ordered positioning directly revealed with atomic precision, but local disordering at the single atom level, which has never been detected by the conventional approaches, is also uncovered. The ability to directly probe individual atoms within buried interface structures will be powerful for characterizing internal interfaces in many advanced materials and devices.
For successful application of low-voltage, ultra-high resolution scanning electron microscopy for nano-surface analysis, sample surface preparation is of key importance. Here, this is demonstrated through the examination of fine inclusions in a type 304 stainless steel. Inclusions are mostly MnS, TiO2, Al2O3 and TiN; they are present either in isolation or forming clusters of two, three, or four features. With the use of mirror-finished surfaces, prepared by mechanical polishing using a suspension of colloidal silica, these inclusions were not revealed clearly due to the presence, at the surface, of thin contaminant layers. After removal of such contaminant layers by radio-frequency-powered glow discharge sputtering, however, inclusions were revealed at the clarity never seen before. By sputtering, thin contaminant layers are removed successfully, without formation of new altered surface layers. Simultaneously, sputtering generates fine textures over the surface of inclusions that are directly related to their compositions. Through the use of such sputter-induced textures, compositional variations in mixed inclusions of sizes even below 50 nm can be revealed clearly and at a high lateral resolution of ∼1 nm.
For the characterization of the materials under a wide range of different ambient atmospheres and temperatures, we have developed an environmental TEM based on a 300 kV TEM, which employs high resolution objective lens. The microscope column is differentially pumped using three sets of high speed turbo molecular pumps with a pumping speed of 260 l/s. In order to improve the experimental capability of the environmental TEM, we have developed an environmental cell. The developed environmental cell is a side entry type with a built-in specimen heater of a spirally shaped tungsten wire, which is used as the standard heater for high temperature specimen heating in principle. The developed holder is possible to use in the high resolution objective lens pole-piece. The gas pressure inside the environmental cell can be continuously controlled from 10−5 Pa to atmospheric pressure in the normally evacuated specimen chamber.