# 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
No films other than the Ni films exhibited the same type of inverted dewetting, nor did any films exhibit delamination to the same extent. Other films containing some portion of Ni are discussed below, showing some delamination immediately adjacent to the laser path. As the pitch is lowered to 40 \(\upmu\)m in Figure 4b, the dewetted bead becomes nearly symmetrical around the non-melted film to form a \"dumbbell\" cross-section created out of two adjacent laser scans. The unprocessed film in between the 40 \(\upmu\)m pitch ridges is also delaminated and, due to the small pitch, it extends all the way across to the next ridge formation. The ridges themselves appear to stay adhered and reside in small indentations within the Par-C surface that were most likely created during the dewetting action. Both cross-sections also exhibit a sub-micron porosity formed in the ridges of the dewetted material. No other investigated material exhibited such a porosity. The voids that are observed in both sets of Ni linear arrays most likely arise from the degradation or outgassing of the polymer at the interface, as no voids are visible in the original, non-dewetted and displaced Ni film. The gas evolution from the surface of the polymer may play an important role by protecting the Par-C from the intense heat of melting Ni through the presence of a thermally insulating gas, similar in consequence to the Leidenfrost effect [38]. In addition, the gas formation may be responsible for the aforementioned \"delamination\" of the film from the surface prior to melting. In the future, it would be of interest to observe and possibly verify this process through an in-situ characterization. To achieve well-defined dewetted structures in metal films deposited on polymer substrates, the preservation of the polymer substrate emerges as one of the major hurdles. This is especially true when processing high-melting point metal films. Par-C has a relatively low degradation temperature of 290 \({}^{\circ}\)C compared to the 1455 \({}^{\circ}\)C melting point of Ni; therefore, there is a large risk of substrate degradation during the dewetting process. While optical micrographs do not show any apparent charring or degradation within the exposed polymer, some deformation of the substrate surface may be expected due to the polymer's thermoplastic behavior, in addition to the aforementioned evidence of surface vaporization. Profilometry scans (Figure 2b) and cross-section micrographs (Figure 4b) on the 40 \(\upmu\)m pitched array demonstrate the existence of deformation of the polymer surface via the wavy appearance in the trench area between the dewetted nickel ridges. Similar heat induced deformations are not observed in the profiles of the 100 \(\upmu\)m pitched array (Figure 2a), likely due to a lower overall heat concentration and greater thermal conductivity of the larger remaining metal digits. In the case of short-pitched laser scans, higher concentrations of heat accumulate, expose the Par-C to higher peak temperatures, and lead to the deformation observed in the 40 \(\upmu\)m pitch vs. the 100 \(\upmu\)m pitch. Increasing the wait time between the laser passes, or alternating the scans may provide a greater amount of cooling; however, a more effective solution would be to use a lower power setting beyond the capabilities of the present laser system.