# Direct-Write Dewetting of High Melting Temperature Metals on Flexible Substrates
## 3 Results
### Complex Pattern Direct Dewetting of Ni and Ag Films  
Ultimately, the advantage of using the scan-system in the dewetting process manifests in the ability to quickly fabricate complicated and free-form shapes, such as one would want for microelectrodes or microfluidic channels. To demonstrate such effectiveness, inter-digit electrode (IDE) pairs were both patterned into single-layer sets of films. By measuring the electronic resistivity between the two electrodes, we can characterize the extent to which dewetting occurs, while also demonstrating a moderately complex pattern design. Figure 11 presents an example of such an IDE created in Ag films. Each electrode was connected to 45 inter-digits, with 30 \(\upmu\)m spacing and an 80 \(\upmu\)m width. The spacing between the digits represents a single pass of the laser. The resistance within the unprocessed area was measured using an ohmmeter at various points throughout the film prior to processing to establish the film's connectivity. After processing the film into the dewetted IDE, two-wire resistance measurements across the two electrode pads generated values > 1 G-Ohm. Therefore, it is concluded  
Figure 10: Cross section EDS maps of the dewetted and displaced “ridge” portion of **(a–c)** Bi-Ag layered films and **(d–f)** Ni-Ag layered films after the dewetting process described in the text. The EDS shows a contrast in the elemental distributions. A segregated displaced layer of Ni (**f**) is shown to encapsulate the displaced Ag shown in **(e)** during the dewetting process of the Ni/Ag films. This is in contrast to the mixed phase of Bi with Ag for the dewetted Bi/Ag films. The arrow indicates the dewetted and displaced metal “ridge”. The other Ag is from the conductive epoxy utilized for the specimen preparation. that the dewetting action proceeds completely and does not leave any percolated conductive metal or by-products. The EDS maps presented in Figure 9 also confirm the lack of any significant amount of residual metal within the trench area after processing. An inspection under an optical microscope and under SEM (Figure 11a) appeared to show that all the inter-digits were continuous; however, electrical conductivity was not confirmed via direct-measurement due to the small size of the features. The lift-off of the Par-C polymer substrate from the glass slide backbone produced an IDE patterned onto a flexible, free-standing polymer, as seen in Figure 11b,c. The use of the scanner allowed for successively shifted, overlapping passes of the laser beam within a single pattern. This type of scanning induces a buildup of displaced metal along the dewetting front. Previous work on Bi and Sn thin films demonstrated that this buildup can be manipulated via different scanning geometries to produce structures many times thicker than the original deposited film [19]. Attempts to perform such \"push\" dewetting on Ni films were realized, but within certain limitations. Figure 12b diagrams the laser scanning procedure, where three scans are carried out with partial overlap in the specified numerical order. The thickness measurements (Figure 12a) demonstrate a designated preferential dewetting to one side of the exposure trenches. For example, a single laser pass across a 0.64 um Ni film resulted in displaced Ni ridge heights ranging between 3.6 um and 4.3 um, while a multi-pass process will result in ridge heights between 5.3 um and 7.1 um, approximately 10X the value of the original Ni film thickness. A side effect of the pushing procedure manifests as a smoothing of the edge profile of the trench/ridge interface. This is most pronounced in Figure 12b, where the non-pushed edge appears slightly scalloped on the left, while the built-up edge at the end of the dewetting front on the right (boxed) presents as relatively smooth. Figure 11: An inter-digit electrode composed of 45 pairs of digits with 30 μm spacing and an 80 μm width formed from a scanning laser dewetted Ag film deposited upon a Par-C polymer, imaged using (**a**) FESEM.