# Nano- and Micropatterning on Optical Fibers by Bottom-Up Approach: The Importance of Being Ordered
## 5 Conclusions
Post-processing treatments can be used to reduce the number of defects and increase the order but maybe it is equally important to define how much defectivity can be tolerated by the system, more than aiming at perfect ordered patterns. Periodic order is important in establishing photonic resonances (i.e., guided resonances) and plasmonic resonances (exploited in SPR and SERS probes). A \"strong\" deviation from the order can surely affect the formation of such resonances, but a \"weak\" deviation can only slightly change their spectral characteristics (i.e., slight spectral shifting or decreasing of the resonance Q-factor can be expected). Several order quantification methods are available both for batch-to-batch quality control and for an immediate evaluation of the self-assembly process, as summarized in Table 2. For example, an order evaluation tool like the Debye ring can be applied directly to the sample while it is forming or immediately after its preparation, without damaging it, and therefore can be used in the optimization steps to find the  
Figure 7: (**a**) SEM micrographs of different binary assemblies obtained by adjusting the size ratio \(\mathrm{R_{S}}\) and the number ratio \(\mathrm{R_{N}}\) between the small and the large particles (i–iv), and possible metal nanotriangle arrays obtainable by NSL with binary assemblies (v). Scale bars are 1 \(\upmu\)m for (i–iv) and 400 nm for (v). Reproduced from Ref. [109] with permission from 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim, Germany. (**b**) Structural model of AB-type binary superlattice (top) and corresponding binary superlattice self-assembled from 13.2 nm LaF\({}_{3}\) nanodisks and CdSe/CdS nanorods (bottom). Reproduced from Ref. [110] with permission from the 2015 American Chemical Society. conditions that allow obtaining the most ordered structures which are achievable by the technique employed. Another important aspect related to periodic order (and related defects) pertains to reproducibility and uniformity. Ordered structures are in general more effective than the random ones both in terms of reproducibility and of efficiency of the photonic response. When the photonic structures are created by NSL and the outcome is SERS detection, for example, the density of plasmonic structures strongly affects the SERS activity of the substrate since, by increasing it, an increment in the number of hot spots is produced. In addition, the periodicity of ordered nanostructures leads to a uniform distribution of hot spots over the sample. In turn, the deviation from the order affects the possibility to get repeatable quantitative measurements. A systematic evaluation of the degree of order is often missing whilst the assessment of the degree of order is an important best practice useful to push the proposed self-assembly methods to a mature technological level. Definitively, nanofabrication of highly ordered nanostructures by bottom-up methods demonstrated great potentialities in terms of reproducibility and repeatability for OF probes development. Even if each technique presents some limitations or a reduced versatility with respect to classical nanofabrication tools, the described self-assembly methods collectively represent an alternative tool to integrate advanced materials with the OF in order to attain advanced lab-on-fiber devices. The growth margins of the self-assembly processes are still enormous. Further research efforts are required to overcome current limitations and fully exploit the potentialities through the rigorous assessment of the fabrication processes. M.P. and F.G.Writing--original draft, review & editing. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The authors declare no conflict of interest.