# Direct-Write Dewetting of High Melting Temperature Metals on Flexible Substrates
## 3 Results  
### Directed-Dewetting of Ni and Ag on Par-C Substrates  
#### 3.1.1 Nickel  
A typical set of metallic lines fabricated from 640 nm Ni thin films on Par-C substrates are pictured in Figure 2. Examples of similar Ni films deposited to only 320 nm onto borosilicate glass or Par-C can be found in Figure S1 of the Supplementary Material. 100 \(\upmu\)m and 40 \(\upmu\)m pitch lengths were scanned into the films revealing dewetted trenches and bordering ridges as a result of the movement of the molten metal along the polymer surface. Associated profilometry scans of the two sets of lines reveal the characteristic film-ridge-trench-ridge-film profile, similar to that observed in earlier studies focused on low-melting temperature metal films [20]. The low trenches represent the surface of Par-C exposed after the rastering laser induced complete dewetting of the molten Ni. The morphology of the ridges created by the displaced material located alongside the trenches parallel to the motion of the laser beam is, in large part, uniform; however, there are signs of a continued morphological evolution along the ridge into a series of beads. Three-dimensional mapping (Figure 3) of the linear structures provides evidence of Ni dewetting rather than ablation. Any material displaced above the baseline surface of the Ni film is tallied as a \"positive\" volume. The volume is then compared to the voids occurring below the baseline surface, which are tallied as a \"negative\" volume. For the 100 \(\upmu\)m pitched array, only 11.5% of the positive volume remained unaccounted for, suggesting that the clear majority of the Ni film is conserved. The excess positive volume is most likely due to minor shadowing effects from the shape of the probe and the shape of the features, where the negative volume remains unmeasured. Figure 2: Optical micrographs (upper) and profilometry (lower) of Ni digits for pitch lengths of (**a**) 100 \(\upmu\)m and (**b**) 40 \(\upmu\)m. Optical micrographs have been aligned with the profiles for comparison. Yellow shading has been used to demark the polymer substrate in the profile; grey shading has been used to demark the native Ni-film layer. The evolution of the Ni films after dewetting were achieved by a FESEM analysis of Ar ion cross sectioned samples embedded in Ag epoxy. The FESEM analysis (Figure 4) of the 100 \(\upmu\)m array reveals the evolution of the Ni films after the dewetting action. Each FESEM image displays an area of newly exposed substrate surrounded by an accumulation of the dewetted Ni material ridge, with no residual Ni present in the dewetted area. The reader is directed back to Figure 1 for a general schematic of the structure cross-section. Figure 4: Cross-sectional FESEM images of Ni dewetted arrays for **(a)** 100 \(\upmu\)m and **(b)** 40 \(\upmu\)m pitched arrays. Ni is highlighted in red. The conductive epoxy used to pot the samples contained flakes of Ag, which appear above and around the film structures. The Par-C polymer substrate is the black area at the bottom of each image. The magnified areas are composed of the displaced dewetted Ni, which has cooled as beads along the laser pathway, which is perpendicular to the plane of the image. Figure 3: 3D profilometry mapping of a Ni linear array formed by directed dewetting with a spacing of 100 \(\upmu\)m. “Negative” and “Positive” relate to the surface of the original Ni film. Of the accounted volume, an 11.5% excess positive volume remains unaccounted for after the dewetting process. This is attributed to shadowing effects from the measurement and the shape of the features. The solidification of the dewetted and displaced nickel occurs underneath the remaining film. The partial delamination of the film at the edge of the laser path can be observed in Figure 4a, but it is unclear whether the delamination occurs before or after the melting occurs. This results in bead formation underneath the film rather than on top--a sharp contrast to the morphology of other dewetting thin film examples [20; 37].