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We evaluated the accuracy of the standard m-line method in the description of the refractive index profile of ion-exchanged waveguides by comparing its results with those from energy dispersion spectroscopy and direct near-surface/extended Brewster–Pfund (DNS-B) Method. Looking at a few single and double-exchange processes, the comparison shows three major situations: (i) the m-line accuracy is validated by the other two methods; (ii) discontinuity of ion-concentration does not allow the assumption of a continuous refractive index profile; or (iii) although the overall m-line profile is compatible with results from the other two methods, these significantly depart by a near-surface inflection-in which case, the DNS-B can be used together with the m-line experimental data to produce a more accurate index profile. [Copyright &y& Elsevier]

Graphical abstract Highlights • Thin films derived from d -limonene are deposited by plasma polymerization. • Fast deposition in seconds timescale is achieved. • Relationship between deposition time and resulting thickness is non-linear. • Fabricated films contain polar groups that were not present in the precursor. • Surface of the thin film is smooth, pinhole free and levels the substrate's defects. Abstract Thin films made from natural precursors are an environmentally friendly alternative for conventional synthetic materials. This work describes the deposition of thin films derived from d -limonene, a product extracted from waste orange peels, using plasma polymerization technique. The effect of deposition time on the resulting thickness, the chemical composition, and the surface morphology were studied. Results show that the film thickness depends on the processing time, with fast deposition during the first seconds, reaching its limit when the precursor ends. An optically transparent film with thickness of 83 ± 1 nm with a smooth surface (average roughness of 0.48 ± 0.02 nm) is achieved after 3 s of deposition. The precursor and the film have distinct chemical composition. The latter contains bond heterogeneity, which indicates an amorphous and cross-linked structure, and new polar moieties caused after exposure of the coating to air. Surface chemical analysis shows that the topmost layer is composed by 89.68% of carbon and 10.32% of oxygen. Plasma-polymerized d -limonene films are smooth and pinhole free regardless of the substrate polishing marks, thus, presenting leveling properties. The fast one-step deposition of thin films derived from d -limonene proved to be an alternative for thin film production, with renewable precursors, for organic electronics and optoelectronics. [ABSTRACT FROM AUTHOR]