Multilayer hexagonal boron nitride (h-BN) is an ideal insulator for two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides, because h-BN screens out influences from surroundings, allowing one to observe intrinsic physical properties of the 2D materials. However, the synthesis of large and uniform multilayer h-BN is still very challenging because it is difficult to control the segregation process of B and N atoms from metal catalysts during chemical vapor deposition (CVD) growth. Here, we demonstrate CVD growth of multilayer h-BN with high uniformity by using the Ni-Fe alloy film and borazine (BHN) as catalyst and precursor, respectively. Combining Ni and Fe metals tunes the solubilities of B and N atoms and, at the same time, allows one to engineer the metal crystallinity, which stimulates the uniform segregation of multilayer h-BN. Furthermore, we demonstrate that triangular WS grains grown on the h-BN show photoluminescence stronger than that grown on a bare SiO substrate. The PL line width of WS/h-BN (the minimum and mean widths are 24 and 43 meV, respectively) is much narrower than those of WS/SiO (44 and 67 meV), indicating the effectiveness of our CVD-grown multilayer h-BN as an insulating layer. Large-area, multilayer h-BN realized in this work will provide an excellent platform for developing practical applications of 2D materials.

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The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, _ " ", lower than 10 À10 s À1 and low temperature ranging from 0:32T m to 0:43T m . It was found that the creep behavior in this region depends strongly on grain sizes and impurity concentrations. For high-purity aluminum (5 N Al) with an average grain size, d g > 1600 mm, nearly the wire diameter of the spring sample, where the role of grain boundary during creep deformation can be negligible, the stress exponent was n $ 5 and the activation energy was Q c ¼ 32 kJ/mol. Microstructural observation showed the formation of large dislocation cells ($10 mm) and tangled dislocations at the cell walls. For high-purity aluminum (5 N Al) with d g ¼ 24 mm, the stress exponent was n $ 1 and the activation energy was Q c ¼ 15 kJ/mol. On the other hand, for commercial low-purity aluminum (2 N Al) with d g ¼ 25 mm, the stress exponent was n ¼ 2 and the activation energy was Q c ¼ 25 kJ/mol. Microstructural observations revealed dislocations emitted from grain boundaries, those dislocations interacting with intragranular dislocations and the formation of dislocation cells in the grains. Based on those experimental results, the low-temperature creep mechanisms in pure aluminum at _ " " < 10 À10 s À1 have been discussed.

We performed the three-dimensional visualization of dislocations through serial sectioning and use of SEM electron channeling contrast (ECC) images for a crept nickel-based alloy. We successfully reconstructed a volume of approximately 7.5 lm 3 , including dislocation arrangements, by performing calculations based on the continuous tomograms of ECC images. By incorporating the information on crystal orientation obtained by the electron back-scattered diffraction, we verified that the three-dimensional arrangement of dislocations, such as slip plane, was accurately reflected in the three-dimensional volume.A transmission electron microscope (TEM) has usually been used for observing dislocations. However, it has been recently reported that dislocations can be observed using a scanning electron microscope (SEM) through electron channeling contrast (ECC) utilizing the channeling phenomena of electron beam [1-6]. Observation of SEM-ECC images utilizing the channeling phenomena of electron beam is possible by using the contrast caused by the difference in the penetration depth of electron beam, depending on the angles between their incident directions and the crystal orientation, when irradiating crystalline samples. If dislocations exist in crystals, it is possible to observe them in ECC images under appropriate conditions because the disorder in crystal structures causes the scattering conditions of electron beam to vary in their vicinity.In a TEM observation, it is possible to obtain a threedimensional volume of the microstructure using the electron tomography method for obtaining several images by intermittently tilting a sample to large angles in a microscope. A three-dimensional visualization of dislocation arrangements has recently been performed using the electron beam tomography method by tilting samples while maintaining proper diffraction condition [7][8][9]. In contrast, the serial sectioning method [10,11] is a well-known technique for the three-dimensional visualization of the microstructure using a SEM. In the serial sectioning method, three-dimensional volumes are obtained by acquiring continuous tomographic images by cutting samples, mainly using the focused ion beam (FIB) equipment and alternately and continuously observing the SEM images, followed by reconstruction and performing calculations. While the TEM tomography method utilizes thin films or nanopillar-like samples, the SEM serial sectioning method has the advantage that a wider range of information about the microstructures can be derived in a form that is close to the bulk interior because it enables the use of bulk materials. Although it is possible, in principle, to three-dimensionally observe and analyze dislocation arrangements existing within a space of approximately 1000-100,000 lm 3 by combining the ECC dislocation imaging and the SEM serial sectioning method, there is no report on this method. Dislocation arrangements of materials subjected to plastic deformation may be non-uniform on a micrometer scale, and it can be easily imagined ...

Quenched martensitic steels are known to show the characteristic feature of stress-strain relations, with extremely low elastic limits and very large work-hardening. The continuum composite approach is one way to express this characteristic feature of stress-strain curves. Although the overall stress-strain curves, as a function of alloy chemistries of steels, were well represented by this approach, the relationship between the macroscopic deformation behaviors and microstructural information is yet to be clarified. A highspatial-resolution digital image correlation analysis was conducted to demonstrate the possible unit size corresponding to the microstructure. The continuum composite approach model was also modified to consider the size effect of the microstructure on the stress-strain curves of the as-quenched martensitic steels. Strain concentrations were observed at various boundaries, including lath boundaries, and the characteristic microstructural size was also predicted by the present model, which is smaller than the reported spacing between adjacent strain-concentrated regions.