**Author details**

It should be noted that the (5,0)@(13,0) DWBNNT and (5,0)@(13,0)@(21,0) TWBNNT show different changes in CBM charge densities from those of the SWBNNTs and (13,0)@(21,0) DWBNNT (Figure17). First, the CBM charge densities gradually transfer from boron atoms in the innermost tube to boron atoms in the second innermost tube. This charge delocalization and spreading account for the increase in *E*CBM in the (5,0)@(13,0) DWBNNT and (5,0)@(13,0)@(21,0) TWBNNT during the early stage of the deformation. Then, overlap of the charge densities in curved regions in the second innermost tube is induced with increasing deformation. Consequently, *E*CBM of the (5,0)@(13,0) DWBNNT and (5,0)@(13,0)@(21,0) TWBNNT decreases later in the deformation. It is this mechanism that results in the initial increase and subsequent decrease in *E*<sup>g</sup> in the (5,0)@(13,0) DWBNNT and (5,0)@(13,0)@(21,0) TWBNNT. Because the latter has a larger *η*in than the former under the same *η* (see the atomic positions in the innermost tube at *η* of 0.43 in Figure 17), charge spreading from the first to the second innermost tube is completed earlier in the latter. Therefore, the latter shows an earlier

Micro-Nano Mechatronics — New Trends in Material, Measurement, Control, Manufacturing and Their Applications in

It is evident that a critical chiral index, (*n*c, 0), exists for flattened zigzag MWBNNTs. Consider the innermost tube of a zigzag MWBNNT, denoted as (*n*in, 0). In the case of *n*in > *n*c, *E*<sup>g</sup> decreases monotonically as the flattening deformation increases. In the reverse case (*n*in < *n*c), *E*<sup>g</sup> first increases and then decreases. From the results obtained in this study, *n*<sup>c</sup> is proven to be an integer between 5 and 13. Furthermore, if zigzag BNNTs have the same *n*in, a zigzag BNNT containing more walls shows a more rapid change in *E*<sup>g</sup> (compared with the change in *E*<sup>g</sup> between (13,0) SW and (13,0)@(21,0) DWBNNTs and between (5,0)@(13,0) DW and

In the aforementionedexperimental study on a bentMWBNNT, a notable tendency for a zigzag atomic arrangement and local flattening have been observed [30]. Judging from the HRTEM images, *n*in of the MWBNNT is larger than *n*c. Therefore, it can be said that a possible reason for the change from insulating to semiconducting in the bent MWBNNT is electronic changes, as shown in Figure 16. To the best of our knowledge, there has been no experimental study on deformed BNNTs with *n*in< *n*c, but the results for the (5,0)@(13,0) DWBNNT and (5,0)@(13,0)@(21,0) TWBNNT obtained in this study are expected to be good predictions.

In Section 2, the electronic structures of (*n*,0) zigzag SWBNNTs subjected to tension, torsion, and flattening were investigated by first‐principles DFT calculations. The results revealed that the three deformation modes decrease the energy gaps of the SWBNNTs because of the decrease in the CBM energy caused by an overlap of CBM charge densities between circum‐ ferentially neighboring boron atoms. The key findings of Section 2 are that flattening with a

Bending experiments on BNNTs with *n*in < *n*<sup>c</sup> are greatly anticipated.

shift from increase to decrease in *E*g.

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*3.2.3. Critical diameter of the innermost tube*

(5,0)@(13,0)@(21,0) TWBNNTs in Figure 13).

**4. Summary**

Nobutada Ohno, Dai Okumura and Yusuke Kinoshita

Department of Computational Science and Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Japan

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**Chapter 9**

**Measurement of Frictional Properties on**

Scanning probe microscopes (SPMs) were invented by Binnig and Rohrer in 1980s and have been one of the key methods for measurements and manipulations in nanotechnologies since then [1, 2]. The first SPMs were a scanning tunnelling microscope (STM), which uses a tunnelling current. The vertical resolution of sub‐nm comes from the extremely short length of interaction between the probe and sample surface. If a sharp tip can be prepared, the lateral resolution of sub‐nm is possible. STM can see sample surfaces at an atomic resolution and manipulate a single atom. The concept of STM can be extended to various fields and wide varieties of properties can be measured on the nano scale by changing the interaction between the probe and sample. It should be noted that micro fabrication techniques based on micro‐ machining techniques has been indispensable to the development of SPMs. Atomic force microscopes (AFM) are one of the most successful microscopes in SPMs [3]. As a probe, they use micro cantilevers with a tiny tip, whose apex radius is around several nm. Typical dimensions of the cantilever are 100‐μm long and a few‐μm thick. Micro structures at these dimensions are not easy to fabricate for conventional machining. Therefore, micro fabrication methods have been developed. Micromaching not only improved the performance of SPMs but also made them a popular technology because the fabrication methods were suitable for

SPM have been extending its application to mechanical fields. One of the successful applica‐ tions is a friction force microscope (FFM), which has been a key technology of micro/nano tribology [4]. FFM can measure the local frictional or rheological properties at a micro/nano scale although AFM is limited to measurement of the topography. The performance of micro/ nano mechanical devices, such as micro/nano electro mechanical systems (MEMS/NEMS), computer hard disk drives (HDDs), is dominated by surface forces such as friction and viscous forces rather than volume forces such as gravitational forces. Therefore, the measurement of the local frictional properties is very important for the performance analysis and design of

> © 2013 Fukuzawa; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 Fukuzawa; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

**the Micro/Nanometer Scale**

Kenji Fukuzawa

**1. Introduction**

mass production.

