In this work, there are two major factors to develop; one is the design and construction of a nano-fabrication system operating inside the SEM, and the other is the development of the fabrication cantilevers.
Figure 1 shows a schema of the experimental procedure of nano-mechanical fabrication with AFM mechanics. By indenting a cutting edge fixed on the cantilever tip against the material surface and then raster scanning relatively between the cutting edge and the surface, the material of a square region of the surface can be removed. To observe the nano-cutting process, a view angle from the diagonal direction to the front of the cantilever must be maintained.
Figure 2 shows a special SEM stage integrating a nano-fabrication system. These are uniquely designed to avoid interference with the SEM lens system and to preserve an observation angle. The system has to be installed in a vacuum chamber, so a non-resonant ultrasonic actuator is applied to reduce the mechanical drive system.
Figure 3 shows a cantilever for fabrication with a sharpened tip made of CVD diamond. This tip is formed by using a pyramidal silicon mold which is fabricated by anisotropic etching. Until now, as a cutting edge, single diamond abrasive grain has been used, fixed on the cantilever tip. However, the irregularity of the grain shape causes unevenness in fabrication performance, and thereby it was quite difficult to identify the cutting points . The sharpened cutting edges we have formed have a geometrically regular shape with a tip apex of 30 nm in radius, resulting in a good cutting performance.
Figure 4 shows a SEM image of a cantilever cutting edge after nano-cutting experiment and the periphery. By the cutting, the material surface is partially removed, and many cutting chips are left on the surface. Figure 5 shows still images captured from movie recorded in the nano-cutting process. Several grooves, shown in Figure 5(e), are formed by fabricating toward right with stepwise increasing normal-load applied to the cutting edge; it is clearly seen that the depth of the grooves increases gradually. The cutting action is done at the edge toward the front of the cantilever (visible edge side in pictures). The cutting depth can be estimated to be approximately 100 nm from the pitch of the line feed of scanning.
The single crystal silicon used is a comparatively hard material, usually referred to as one of the "brittle" materials. In macro-scale mechanical fabrication, it behaves as a fragile material like glass. However, our experimental results demonstrate that, in nano-cutting fabrication, the ductile-mode cutting is performed even for brittle materials as well as the usual metallic materials. Thus, we have experimentally confirmed that the nano-mechanical fabrication is applicable to a variety of materials, such as metal and glass, because single crystal silicon is harder than the usual metallic materials.