Atomic-Scale Dynamic Deformation Behavior of BN Thin Films
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Atomic-Scale Dynamic Deformation Behavior of BN Thin Films Chihiro Iwamoto1, Hangsheng Yang2, and Toyonobu Yoshida2 1 Engineering Research Institute, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan 2 Department of Materials Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan ABSTRACT Deformation behavior of the BN film was dynamically observed by high-resolution transmission electron microscopy. BN thin films were deposited on a narrow edge of Si flakes, using inductively coupled plasma-enhanced chemical vapor deposition. High-resolution observation of the sample revealed that the BN film was possibly deposited on the edge of the Si thinned to less than 10 nm in thickness, whose morphology varied depending on the thickness of the Si edge. Intriguing mechanical properties of the BN films, especially relating their dynamic behavior, were clearly verified by the high-resolution observation with piezo-ceramic tube for three-axis positioning of an indenter.
INTRODUCTION Among several polymorphs of boron nitride, cubic boron nitride (c-BN), which has a sp -bonded zinc-blende structure, has been intensively studied due to the significant potential of its mechanical, electrical and optical properties: especially its hardness is second to that of diamond. On the other hand, graphitic BNs such as hexagonal BN (h-BN) and turbostratic BN (t-BN), which have layered structures of sp2-bonded BN sheets with the van der Waals interaction between the adjacent sheets, have been rarely attracted attention. However, the t-BN deserves much more attention, because it is always formed in the BN films deposited using the ion-assisted methods, which is the most promising technique to obtain c-BN films of good quality. In the case of c-BN film growth on a Si substrate, an amorphous layer is formed, and then a t-BN layer grows, followed by formation of a c-BN layer [1-11]. Though elimination of the amorphous layer was found to be possible recently by appropriate pre-treatment applying positive bias [12], a t-BN layer of less than 10 nm is still formed prior to c-BN growth [13,14]. Therefore, the mechanical properties of the polymorphs are worth examining, even if our prime interests are in the properties of the c-BN films. Motivated by the above situation, we examined mechanical properties of the BN film by cross-section high-resolution observation during indentation. Cross-section observation of the BN film permitted us to analyze the mechanical properties of each BN polymorph layer during film deformation. In this report, we focused on the preparation process of the samples for the real time observation of their deformation behavior. 3
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EXPERIMENTAL DETAILES In the conventional sample preparation process of a BN film for a cross-section transmission electron microscope (TEM) observation, two Si substrates, on which the BN film was deposited, have been attached by glue so that the BN films were face to face, to prevent th
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