## 6 Conclusions  
In conclusion, our review shows that advanced SNOM is a powerful imaging technique with immense potential that has so been only partially realized. With the advent of advanced nanofabrication methods, it is now possible to produce designer c-SNOM tips of varied composition with finely controlled aperture sizes from 100 nm to as small as 20 nm. Studies have shown that SNOM is able to map the complete electromagnetic near-field of nanostructures, even without resorting to specialized tip designs. Access to this unique near-field information has significant potential to improve the design and performance of optoelectronic devices. Imaging near-fields in three dimensions is a  
Figure 15: (**a**) AFM, (**b**) c-SNOM, and (**c**) SEM images obtained for the same area of a copper nanoparticle superlattice; (**d**) c-SNOM scans in the \(z\)-direction for cross sections A–A’ and B–B’ in panels a–c; (**e**) The integrated intensity shown in panel d identifies the exponential decay of the evanescent wave moving away from the surface along the region A–A’ representing an ordered superlattice. Random interference patterns are observed for the randomly disordered area B–B’; (**f**) Light scattering within the superlattices is coherent as the periodic nanoparticles act as a waveguide; (**g**) Randomly distributed nanoparticles result in incoherent scattering and light absorption. Reproduced with permission from [28], Copyright RSC Advances, 2015.  
natural extension on traditional 2D c-SNOM mapping to examine nanostructures, complementing the already robust list of complimentary techniques available including Raman, FTIR, and electromagnetic field imaging. Nanoparticles and nanostructures have the potential to revolutionize device architecture and design by imparting new functionality to already established technologies. 3D SNOM is positioned to encourage this revolution by providing the capability to fully characterize scattered and near-field light from nanoparticles and nanostructures, and exploit them to improve device properties. Examination of the near-field of metal nanoparticles using 3D SNOM has been used to enhance the performance of organic BHJ solar cells through an increased understanding on the forward scattered light field. Efficient control of scattered light in solar cells enabled by 3D SNOM could lead to increased PCE without significant changes to existing solar cell architectures. 3D SNOM has also been shown to have the capability of mapping all components of electric and magnetic fields above PhCW structures using standard circular aperture tips. 3D SNOM is also not limited to mapping of light and electromagnetic near-fields. The sub wavelength resolution of SNOM can be combined with other techniques not covered in this article-such as thermoreflectance-to enhance the resolution beyond the diffraction limit and obtain the nanoscale thermal conductivity. Synergy with an AFM system also allows SNOM to be easily coupled with other nanoscale force microscopies such as Kelvin probe force microscopy or conducting probe AFM. Multiple SNOM systems can be coupled together to simultaneously inject and collect light from nanostructures [58]. Time resolved studies are also possible with switching or chopping of external light sources to examine temporal properties of nanostructured surfaces. Modifications to AFM More exotic modifications can be considered. SNOM has been shown to be well suited for investigation of biological systems where non-destructive and contactless methods are in high demand for nanoscale imaging of live cells [57]. 3D SNOM is envisaged to lead to breakthroughs in the study of biological systems with nanoscale imaging of live cells, as well as improved design and operation of nanoscale light management devices. 3D SNOM is well positioned to augment the study of nanoscale properties of materials, with a bright future ahead for sub-wavelength resolution imaging. **Acknowledgments: [PERSON] acknowledges a MITACS Accelerate Postdoctoral Fellowship.