Figure 2: Writing complex shapes with controlled single continuous crack patterns and details of the crack pattern.

(a) The word ‘CRACK’ and a spiral are written using cracks. Each crack begins from a scribed scratch at the lower section of the image and is guided through straight tracks to each letter-shaped track. White arrows indicate crack starting points and growth directions. The image was taken in the dark-field mode for better visibility. The scale bar represents 400 μm. (b) Cross-sectional scanning electron microscope (SEM) images of a metal interlayer crack sample. Cracks are perpendicular to the substrate without any phase-dependent tilting; no crack through the substrate was observed. Focused ion beam (FIB) milling was used to reveal cross-sections of different segments of the crack pattern. Before FIB milling, a 200-nm Al layer was deposited to reduce the charging effect during milling. The scale bar represents 10 μm; in insets, the scale bars represent 2 μm (c) A FIB-milled initiation notch. The scale bar represents 20 μm (d) Lithographically defined metal extrusion notch pattern, which is composed of 400-nm-thick Al. The scale bar represents 20 μm (e) Optical dark-field microscope image of the sample with scratch via manual scribing and (f) enlarged SEM image. The scale bars represent 40 μm and 5 μm respectively (g) Auto termination at interlayer track endpoint. The scale bar represents 40 μm. (h) Crack is stopped by another crack. The scale bar represents 20 μm. (i) Amplitude and period modulation in a single continuous crack with track width change. The scale bar represents 40 μm. All interlayer materials were 100-nm-thick Al, except (c), which was 100-nm-thick Cu.