This Letter studies the relationship between the elastic constants and the microstructure of nanocrystalline diamond thin films deposited by the chemical vapor deposition method doping various concentration of N2 gas. The elastic constants were measured by resonant ultrasound spectroscopy and picosecond laser ultrasounds. The increase of N2 gas decreases the diagonal elastic constants, but increases the off-diagonal elastic constants. The micromechanics calculation can explain this unusual elastic behavior, and it predicts thin graphitic phases at grain boundaries.

This letter studies the relationship between the off-diagonal elastic constant C12 and bond configuration in nanocrystalline-diamond (NCD) thin films deposited by the nitrogen-doped chemical vapor deposition method. The film thickness was varied between 2.4 and 11.3μm. The elastic constants were measured by resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. The diagonal elastic constants C11 and C44, and Young’s modulus in NCD films are smaller than those of the bulk polycrystalline diamond and microcrystalline-diamond (MCD) thin films, and they decrease as the film thickness decreases. However, the off-diagonal elastic constant of the NCD films is significantly larger than that of the bulk diamond, while that of the MCD films is smaller. Micromechanics calculations revealed that this exceptional enhancement of C12 occurs when the material includes randomly distributed thin graphitic plates in the isotropic diamond matrix. Thus, this result indicates that the NCD films consist of sp3-bonded diamond grains and sp2-bonded grain boundaries.

This study clarifies that the initial scale structure affects the transformation behavior of wüstite. The initial scale structure is controlled by limiting the temperature of nitrogen gas before the transformation of wüstite. The bilayer scale of magnetite and wüstite transforms from the magnetite/wüstite interface, while the monolayer scale of wüstite alone generates magnetite precipitates at the scale/steel interface preferentially. Furthermore, the monolayer scale takes longer to transform compared with the bilayer scale. These results indicate that the transformation behavior of wüstite can be controlled by the initial scale structure.

Thermal conductivities of iron oxide scales have been determined in a temperature range of room temperature to 1 176 K by the laser flash method, where the interfacial thermal resistance between FeO and iron has been corrected for each temperature. Two series of samples were prepared from iron plates with 99.99% purity. One was samples with FeO scale only and the other was samples with multi-layered scale of Fe 2 O 3 /Fe 3 O 4 /FeO. The laser flash method was applied to measure apparent thermal diffusivities, which were converted to apparent thermal conductivities. Apparent thermal conductivities obtained are contaminated by the interfacial thermal resistance between scale and iron, and are in linear proportion to scale thickness. Using apparent thermal conductivities at room temperature, thermal conductivities of scale have been derived from the slope of the linearity as 2.4 Wm − 1 K − 1 for FeO scale and 1.8 Wm − 1 K − 1 for multilayered scale, and interfacial thermal resistances have been derived from the intercept as 7.3 × 10 − 6 m 2 KW − 1 for the interface at FeO/iron and 6.4 × 10 − 6 m 2 KW − 1 for the interface at multi-layered scale/iron. The interfacial thermal resistance between FeO and iron decreases with increasing temperature. Considering these temperature-dependent interfacial thermal resistances, thermal conductivity values of FeO scale have been determined as a function of temperature. The values are roughly 2.2 Wm − 1 K − 1 up to 1 176 K except 6.9 Wm − 1 K − 1 at 674 K where the decomposition of FeO tends to take place.

Understating elastic properties of thin films is a matter of deep interest both in scientific and industrial fields. In this paper, we propose a combination of resonant-ultrasound spectroscopy coupled with the laser-Doppler interferometry and pump-probe photoacoustics for measuring anisotropic elastic constants of deposited thin films. Among the five independent elastic constants, the resonant-ultrasound spectroscopy is sensitive to the in-plane elastic constants, C 11 , C 13 , and C 66 , and pumpprobe photoacoustics to the out-of-plane elastic constant, C 33 . We apply this to Cu thin films deposited on monocrystalline Si substrates by the magnetron-sputtering method. Cu thin films show elastic anisotropy, C 33 > C 11 . The cause of this elastic anisotropy is attributed to the textured structure and the columnar structure. These effects are estimated by X-ray diffraction measurements and micromechanics calculations.