## 3 Results and Discussion  
### Material Characterization  
SEM was used to characterize the surface morphology of the sputtered carbon coatings that were deposited at three different throw distances (4, 12, 20 cm). As shown in Figure 1, coatings produced at the 4 cm throw distance were more porous than the other two. We attribute this substantial difference in morphology to the directionality (or lack thereof) of the sputtering process. Based on previous calculations [18], the mean free path for carbon atoms in this process is 1.32 cm. Accordingly, at a throw distance of 12 or 20 cm, the process should be non-directional. However, at a 4 cm throw distance, carbon atoms only have to travel three mean free paths, which should lead to a more directional process. This directional sputtering results in a highly porous morphology. Due to the greater porosity of the fibers produced with the 4 cm throw distance, only these fibers were considered in this study. The thicknesses of sputtered coatings were measured by SEM (see Supplementary Materials Figure S1). The small globules/spots in Figure 1d provide visual evidence for PDMS deposition on the sputtered carbon coating. In addition, as was the case in our previous study [20], spectroscopic ellipsometry provided an average thickness of the PDMS coating of 16 nm on witness silicon shards. XPS and WCA goniometry were also used to analyze the elemental compositions and hydrophobic natures of the surfaces, respectively. However, because of their small size, sputtered SPME fibers are difficult to characterize using XPS and WCA goniometry. Thus, the same deposition processes were replicated on witness silicon shards, which were then \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**CTC PAL Parameters**} \\ \hline \multicolumn{2}{c}{**HS/DI Modes**} \\ \hline \multicolumn{2}{c}{**Conditioning temperature**} & 280 \({}^{\circ}\)C \\ \multicolumn{2}{c}{**Conditioning time**} & 60 s \\ \multicolumn{2}{c}{**Preconditioning**} & Yes \\ \multicolumn{2}{c}{**Post conditioning**} & No \\ \multicolumn{2}{c}{**Vial penetration depth**} & 35 mm \\ \multicolumn{2}{c}{**Inconbution/extraction temperature**} & 300 s \\ \multicolumn{2}{c}{**Inconbution/extraction time**} & 120 s \\ \multicolumn{2}{c}{**Injector penetration depth**} & 50 mm \\ \multicolumn{2}{c}{**Desorption time**} & 60 s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: HS/DI–SPME parameters. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Agilent 7890B/5977B GC–MS Parameters**} \\ \hline \multicolumn{2}{c}{**Column**} & Rxi-624 Sil MS–30 m \(\times\) 0.25 mm \(\times\) 1.4 μm (Cat# 13868) \\ \multicolumn{2}{c}{**Injection**} & See CTC PAL Parameters \\ \multicolumn{2}{c}{**Mode**} & Split (50:1) \\ \multicolumn{2}{c}{**Liner**} & Topaz 0.75 mm ID Straight/SPME Intel Liner (Cat# 23434) \\ \multicolumn{2}{c}{**Injector temperature**} & 280 \({}^{\circ}\)C \\ \multicolumn{2}{c}{**Purge flow**} & 3 mL/min \\ \multicolumn{2}{c}{**Oven**} & 50 \({}^{\circ}\)C (hold 1 min) to 150 \({}^{\circ}\)C by 15 \({}^{\circ}\)C/min to 280 \({}^{\circ}\)C (hold 5 min) \\ \multicolumn{2}{c}{**by 25 \({}^{\circ}\)C/min**} \\ \multicolumn{2}{c}{**Carrier gas**} & He \\ \multicolumn{2}{c}{**Flow rate**} & 1.4 mL/min (Constant Flow) \\ \multicolumn{2}{c}{**Detector**} & HES-MS \\ \multicolumn{2}{c}{**Mode**} & Full Scan \\ \multicolumn{2}{c}{**Transfer line temp.**} & 300 \({}^{\circ}\)C \\ \multicolumn{2}{c}{**Source temp.**} & 325 \({}^{\circ}\)C \\ \multicolumn{2}{c}{**Quad temp.**} & 200 \({}^{\circ}\)C \\ \multicolumn{2}{c}{**Solvent delay**} & 1 min \\ \multicolumn{2}{c}{**Acquisition range**} & 35–350 m/z \\ \multicolumn{2}{c}{**Frequency**} & 4.5 scans/sec \\ \hline \hline \end{tabular}
\end{table} 
Table 3: GC–MS parameters. characterized by XPS and WCA goniometry. Figure 2 shows the XPS survey spectra [42] of a bare silicon wafer, carbon sputtered on a silicon wafer, and PDMS deposited on a sputtered carbon surface. The expected changes in the elemental compositions of the materials are evident.