# Atomic Layer Deposition of Inorganic Thin Films on 3D Polymer Nanonetworks
## 4 Application of 3D Inorganic Nanonetworks  
### Organic-Inorganic Hybrid Nanocomposites  
The resulting material produced through polymer template-assisted ALD is a structured composite with a polymer core and an inorganic shell deposited through ALD. In this case, the inorganic shell may serve to alter the surface properties of the original polymer template, or to complement its mechanical or optical properties. A representative example of the former can be found in nanofluidic devices. [PERSON] et al. reported that a polymer template with densely packed, inch-length horizontal nanochannels possessing a diameter of 200 nm and a period of 400 nm was fabricated by performing PnP near the diffraction limit [23]. The template material was epoxy-based SU-8, with a hydrophobic surface. To utilize this unique nanochannel array as a nanofluidic filter for water treatment, it is necessary to change its surface to hydrophilic. However, it is very challenging to coat inch-length high-aspect-ratio pores  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**ALD Type**} & **Template Preparation** & **Template Structure** & \multirow{2}{*}{**Precursor**} & **Reactant/ Plasma** & **Temperature** & **Deposited Materials** & **Ref. ** \\  & **Method** & **Regularity** & & **Gas** & (°C) & **Materials** & **Ref. ** \\ \hline Thermal & Electrospinning & Irregular & DEZ & H\({}_{2}\)O & 200 & ZnO & [69] \\ \hline Thermal & Electrospinning & Irregular & DEZ & H\({}_{2}\)O & 200 & ZnO & [71] \\ \hline Thermal & Nonwoven fabric & Irregular & DEZ & H\({}_{2}\)O & 125-155 & ZnO & [92] \\ \hline Thermal & BCP lithography & Regular & TIC\({}_{4}\) & H\({}_{2}\)O & 150 & TiO\({}_{2}\) & [10] \\ \hline Thermal & D\(\mathrm{\ddot{\mathrm{\mathrm{o}}}}\)T lithography & Regular & DEZ & H\({}_{2}\)O & 50 & ZnO & [9] \\ \hline Thermal & D\(\mathrm{\ddot{\mathrm{\mathrm{o}}}}\)T\(\mathrm{\ddot{\mathrm{\mathrm{o}  
of 200 nm diameter with a hydrophilic material uniformly. In this study, the authors successfully converted the nanochannels from hydrophobic to hydrophilic by conformally coating the TiO\({}_{2}\) thin film through a thermal ALD process with a long supply time of precursors and reactants (Figure 6a). As the number of ALD cycles increased, a reduction in the size of the nanochannel was also observed. This TiO\({}_{2}\)-coated polymer nanochannel array was integrated into a microfluidic device and used as a high-throughput device that can stretch DNA or filter out sub-100-nm nanoparticles. An example of modulating material properties through polymer template-assisted ALD can be found in interpenetrating network composites. Recently, [PERSON] et al. developed a new type of 3D continuous ceramic nanofiller-inserted polymer composite by filling an index-matched polymer in an Al\({}_{2}\)O\({}_{3}\)-coated 3D polymer nanonetwork prepared through the combination of PnP and ALD (Figure 6b) [26]. The content of the ceramic nanofiller, relative to the polymer matrix, can be finely controlled through the ALD cycle. Unlike conventional discrete ceramic nanoparticle-polymer composites, continuous interpenetrating network composites enable high loading above 15 vol\(\%\), owing to the absence of an aggregation of nanoparticles. The resulting composite film with a thickness of \(\sim\)11 \(\upmu\)m is not only optically transparent (\(>\)85\(\%\) at 600 nm), but also mechanically flexible, because it has a structure in which the 3D nanostructured ultrathin (\(\sim\)60 nm) Al\({}_{2}\)O\({}_{3}\) layer is embedded in the polymer matrix. The film can withstand bending strain without fracture, and can recover its original shape after relaxation. In addition, the continuous Al\({}_{2}\)O\({}_{3}\) nanonetwork in the composite film provides an efficient heat transfer path for rapid heating and cooling. Thus, this composite can be used as a mechanically reinforced multifunctional optical film (Figure 6c).