**1. Introduction**

Ion implantation is a powerful experimental approach for structural modification of materi‐ als. In case of organic media, the interest to ion-irradiated polymers is due to the ion implanta‐ tion being one of the effective technological methods to turn dielectric polymers into semiconductors [1] as well as to improve surface-sensitive mechanical properties of polymers

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for hard-materials applications [2]. Substantial improvements in hardness, wear resistance, oxidation resistance, resistance to chemicals, and electrical conductivity are the main charac‐ teristics attainedbypolymericmaterials aftertheirlow-to-medium-energyionimplantation[3– 7].

The formation of free radicals at lower ion doses (<1016 ions/cm2 ) and carbonization at higher ion doses (>1016 ions/cm2 ) in the most polymeric materials are of general concept [8–10]. In particular, the ion irradiation of polymers leads to the scission and cross-linking of polymer chains, formation of volatile low-molecular fragments, and carbonization of the implanted layer. The carbonization process depends strongly on the implantation dose or/ and ion current density. As ion dose increases, the several stages can be distinguished for carbonization to be occurred. The formation of pre-carbon structures, nucleation, and growth of the carbonenriched clusters, aggregation of the clusters, formation of network of conjugated bonds, and transition to amorphous carbon or graphite-like material are the main stages predicted in literature [8–10]. Despite numerical studies of carbonization processes in polymers, the problem remains to understand better how the carbonaceous phase or carbon nanostructures formed under high-dose ion implantation could be dependent on the type of polymer matrix. In this respect, a lot of efforts have been made by researchers studying the B+ -ion implantation into various polymer matrix such as polycarbonate, Kapton, polyethylene, polyamide, polyimide, poly(ethylene terephthalate), cellulose, polypropylene, polystyrene, polyethersul‐ fone, and others ([2, 4, 5, 11–25] and references therein). At the same time, the B+ -ion implan‐ tation into widely used in practice polymer polymethylmethacrylate (PMMA) was not studied so far.

The interest to B+ -ion implantation of polymers is due to formation of buried carbonaceous layer leading to increasing conductivity [20, 23]. Also, B+ -ion implantation into polymeric matrix results in significant increase of surface-sensitive mechanical properties. So, Lee et al. [4] reported the ion-induced improvement in hardness of Kapton irradiated by three different ion species, He, B, and Si at 200 keV to a dose of 3.5 × 1019 ions/m2 , where boron produced the largest improvement in hardness among the three, not following the increasing trend in atomic number.

The selection of PMMA matrix to be used for B+ -ion implantation is due to an importance of this polymer for construction of many optical components (waveguides, lenses, prisms, etc.), lithography, biomedical applications, etc. ([26–30] and references therein). PMMA was also a subject for implantation with Ag+ -ions [9, 31] to fabricate composite structures with silver nanoparticles for plasmonic applications as well as for implantation with C+ , N+ and Ar+ -ions [29, 30] that may find an extensive application in fabrication of various optoelectronic devices including organic light-emitting diodes, backlight components in liquid crystal display systems, diffractive elements, solar cells, waveguides, microcomponents for integrated optical circuits, etc. The well-known key performance and important characteristics of PMMA such as a long-term stability in outdoor environments, excellent surface hardness, light weight, outstanding transmittance and optical clarity, optical design flexibility and control, etc. [32], and high stability upon positron irradiation at room temperature [33] are also taken into account at the selection of basic polymeric matrix for low-energy ion implantation.

In this chapter, a review of recent results obtained using proper experimental and simulation techniques on the boron-ion-implanted polymethylmethacrylate (B:PMMA) is presented. As a result, the formation of ion-irradiation-induced carbon nanostructures in optoelectronic polymer materials exemplified by B:PMMA is evidently confirmed.
