# Direct-Write Dewetting of High Melting Temperature Metals on Flexible Substrates
## 2 Materials and Methods  
Pre-cleaned borosilicate glass microscope slides were coated with a 22 \(\upmu\)m thick layer of Par-C via CVD methods, as previously described [20]. These coated slides served as substrates for a number of single and multi-layered metal films. Ni films were sputtered at thicknesses of 320 nm and 640 nm. Ag films were evaporated onto the described substrates at a thickness of 405 nm. Multi-layered films were created by evaporating 45 nm of Bi onto 405 nm of Ag. Additional multi-layered films were created by sputtering 45 nm of Ni onto 405 nm of Ag.  
All film processing was conducted with an integrated laser processing system consisting of a near-infrared (NIR) laser (SPI redPOWER R4-HS), an in-line camera system (uEye GigE), a galvanometer-driven scanner (Scanlab IntelliSCAN 20) with an f-theta telecentric lens (115 mm effective focal length) and a custom-made sample stage. The sample stage allowed for the manual adjustment of the \(z\)-axis as well as tilt-leveling around the x- and \(y\)-axis. The telecentric optics ensured a consistent laser intensity through a flat focal plane. Laser exposure was conducted in both the pulsed-mode and in the continuous-wave exposure, depending on the chemistry of the target film and substrate. While in the pulsed-mode, the laser ran at 10 W, with pulse lengths of 2.5 \(\upmu\)s and an exposure frequency of 100 kHz. The beam waist was \(\sim\)34 \(\upmu\)m in diameter under these conditions, as calculated by Equation (2), where \(M^{2}\) is the beam quality factor (\(<1.1\)), \(\lambda\) is the wavelength (1060 nm), \(f\) is the effective focal length (115 mm), \(r_{i}\) is the beam radius as it enters the lens (2.535 mm), and \(r_{0}\) is the radius of the beam at the focal point.  
\[r_{0}=\frac{M^{2}\lambda f}{\pi r_{i}} \tag{2}\]  
With this beam spot, the processing parameters resulted in a pulse fluence of 2.75 J/cm\({}^{2}\). At speeds of 0.2 m/s, the normalized scan energy was calculated to be 12.5 J per meter scanned. Under a continuous wave (CW) operation, scan speeds were increased an order of magnitude to 2.0 m/s to  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**M.P.**} & \multicolumn{2}{c}{**Surface Energy/Tension**} & \multirow{2}{*}{**Inherent**} & \multirow{2}{*}{**Thermal**} & \multirow{2}{*}{**Electrical**} \\  & & **[m/m\({}^{2}\)]** & & & **Absorptivity at** \\  & & & **Solid** & **Liquid** & **1064 nm [\%]** & **[W/(m-K)]** & **[G\(\upmu\)m]** \\ \hline Borosilicate Glass & 821 [29] (soften) & 253.0 [30] & - & \(<3\)[31] & 1.05 & \(8\times 10^{8}\) \\ Parylene-C & 290 [32] & 19.6 [32] & - & \(<15\)[33] & 0.082 & \(1\times 10^{15}\) \\ Polyimide & 400 (soften) & 53 & - & \(<10\)[34] & 0.15 & \(1.5\times 10^{15}\) \\ PTFE & 327 & 20 & - & \(<10\)[34] & 0.26 [35] & \(1\times 10^{23}\) \\ Bi & 271.5 [35] & 446 [36] & 378 [36] & 32 \({}^{1}\) & 7.87 [35] & \(107\times 10^{-8}\)[35] \\ Sn & 2319.3 [35] & 661 [36] & 560 [36] & 54 \({}^{1}\) & 66.6 [35] & \(11.5\times 10^{-8}\)[35] \\ Ni & 1455 [35] & 2080 [36] & 1763 [36] & 28 \({}^{1}\) & 90.7 [35] & \(6.93\times 10^{-8}\)[35] \\ Ag & 962 [35] & 1086 [36] & 920 [36] & \(<5\) \({}^{1}\) & 429 [35] & \(1.587\times 10^{-8}\)[35] \\ \hline \hline \end{tabular}  
\({}^{1}\) Calculated from optical constants.  
\end{table}
Table 1: Physical attributes of various substrate or target film chemistries.  
compensate for the lack of cooling between the pulses. With an output power of 25 W, the normalized scan energy remained at 12.5 J per meter scanned for the CW operation, but retained higher laser intensities to overcome high reflectivity barriers, such as in the case of Ag films. Layered films were dewetted with a laser power of 10 W and speeds of 1 m/s and 3 m/s, which resulted in scan energies of 10 J and 3.33 J per scanned meter, respectively.