**2.1. Sample preparation and SRIM simulation**

The B+ -ion implantation with the energy of 40 keV, doses from 6.25 × 1014 to 5.0 × 1016 ions/cm2 and current density < 2 μA/cm2 into the optically transparent PMMA plates (1.2 mm thick‐ ness) was performed under a pressure of 10−5 Torr at room temperature by an "ILU-3" ion accelerator at the Kazan Physical-Technical Institute (KPTI, Russia) similar to as it was earlier done for Xe+ and Ag+ ions [34].

For comparative analysis of depth profiles of implanted ions and introduced vacancies in respect to ion mass, SRIM (stopping and range of ions in matter) simulations were carried out for 40 keV He+ , B+ , O+ , P+ , Cl+ , Cu+ , Ag+ , Xe+ , and Au+ ions implanted into PMMA using the free of charge software of version SRIM-2013 [35].

### **2.2. Positron annihilation spectroscopy measurements**

Positron annihilation spectroscopy (PAS) measurements with slow positron beam spectro‐ scopy (SPBS) based on Doppler broadening of positron annihilation gamma-rays as a function of incident positron energy and positron annihilation lifetime at constant positron energy were performed at the National Institute of Advanced Industrial Science and Technology (AIST, Japan) [36]. Doppler broadening spectra (*S*–*E* and *W*–*E*) were measured using a slow positron beamline in the range of positron incident energy *E* from 0 to 30 keV. Positron annihilation lifetime spectra at incident positron energy of 2.15 keV were measured by another slow positron beamline using an electron linear accelerator as an intense source of slow positrons. The details of the SPBS measurements are reported elsewhere [36].

PAS measurements with positron annihilation lifetime spectroscopy (PALS) and Doppler broadening of annihilation line (DBAL) techniques in the temperature range of 50–300 K using helium cryostat (Closed Cycle Refrigerator, Janis Research Company, Inc., USA) and vacuum equipment (Pfeiffer Vacuum, HiCUBE, Germany) were carried out at the Institute of Physics, Slovak Academy of Sciences (IPSAS, Slovakia) [37–39]. The samples were measured in the cycles of heating and cooling with step of 20 K and elapsed time of 4–5 hours per point. At the selected temperatures, the elapsed time was extended for better statistics in the lifetime spectra. For these temperatures, the continuous lifetime analysis technique to obtain the distributions of *ortho*-positronium (*o*-Ps) lifetime (free-volume voids) was employed using maximum entropy lifetime (MELT) program [40]. The positron annihilation lifetime spectra were taken by the conventional fast-fast coincidence method using plastic scintillators coupled to photo‐ multiplier tubes as detectors. The radioactive 22Na positron source (1.5 MBq activity) was deposited in an envelope of Kapton foils and then sandwiched between two samples. This source-sample assembly was placed in a vacuum chamber between two detectors to acquire lifetime spectra at different temperatures. The time resolution (FWHM) of positron lifetime spectrometer was 0.32 ns, measured by defect free Al sample as a standard. Analysis of lifetime spectra was carried out using the PATFIT-88/POSITRONFIT [41] software package with proper source corrections. Three component fitting procedure for PALS data treatment was applied and long-lived lifetime component *τ*<sup>3</sup> and its intensity *I*3, ascribing to the *o*-Ps pick-off annihilation in free-volume spaces, was finally taken into account for analysis. Simultaneously with PALS measurements, the DBAL spectra were recorded using a high-purity Ge detector with energy resolution of 1.9 keV FWHM at the energy 1274 keV. The annihilation line was deconvoluted by Gold algorithm that allows eliminating a linear instability of the measuring equipment if the 1274 keV 22Na peak is measured simultaneously with the annihilation peak, for deconvolution of annihilation peak 511 keV; this procedure permits the measurement of small changes of the annihilation peak with high confidence [42]. The Doppler *S* and *W* parameters were used for analysis of a shape of deconvoluted annihilation peak 511 keV. Their numerical values were defined as the ratio of the central area to the total area of the photon peak for *S* parameter and as the ratio of wings area to the total area of the photon peak for *W* parameter.

#### **2.3. Optical spectroscopy measurements**

Optical UV-visible spectroscopy measurements were performed using a SHIMADZU-UV 3100PC spectrophotometer in the range of 200–800 nm at AIST, Japan [36].

#### **2.4. Raman spectroscopy measurements**

Room temperature Raman spectra were recorded using a Renishaw Raman inVia Reflex spectrometer in the 400–3800 cm−1 range with a spectral resolution of ≤1 cm−1 [43]. The 514 nm Modu-Laser Stellar-REN Pro 514/50 Argon Laser and 785 nm Near Infrared Diode Laser lines were applied as the excitation source. In order to avoid heat-induced effects, the laser power was set at 10 mW. A standard calibration of wavenumber scale with Si plate was used. The Raman spectroscopy measurements were performed at The John Paul II Catholic University of Lublin (KUL, Poland).

#### **2.5. Electrical measurements**

The electrical measuring system was developed at the IPSAS (Slovak Republic) [43]. The measurement of current vs. voltage (*I*–*V*) by transient method or DC method was used in this experiment. The method was selected to check simply presence of the conductivity layer in the material studied. The measuring system includes a cryostat with sample, resistor heating, thermocouple, CSP (charge sensitive preamplifier), excitation circuit of sample, preamplifier, power supply, DAQ (data acquisition) card, and PC (personal computer). The NI PCI 6229 DAQ card was applied [44]. The electrical DC measurement setup used and detail description of basic parameters are reported elsewhere [43].

#### **2.6. Nanoindentation test**

deposited in an envelope of Kapton foils and then sandwiched between two samples. This source-sample assembly was placed in a vacuum chamber between two detectors to acquire lifetime spectra at different temperatures. The time resolution (FWHM) of positron lifetime spectrometer was 0.32 ns, measured by defect free Al sample as a standard. Analysis of lifetime spectra was carried out using the PATFIT-88/POSITRONFIT [41] software package with proper source corrections. Three component fitting procedure for PALS data treatment was applied and long-lived lifetime component *τ*<sup>3</sup> and its intensity *I*3, ascribing to the *o*-Ps pick-off annihilation in free-volume spaces, was finally taken into account for analysis. Simultaneously with PALS measurements, the DBAL spectra were recorded using a high-purity Ge detector with energy resolution of 1.9 keV FWHM at the energy 1274 keV. The annihilation line was deconvoluted by Gold algorithm that allows eliminating a linear instability of the measuring equipment if the 1274 keV 22Na peak is measured simultaneously with the annihilation peak, for deconvolution of annihilation peak 511 keV; this procedure permits the measurement of small changes of the annihilation peak with high confidence [42]. The Doppler *S* and *W* parameters were used for analysis of a shape of deconvoluted annihilation peak 511 keV. Their numerical values were defined as the ratio of the central area to the total area of the photon peak for *S* parameter and as the ratio of wings area to the total area of the photon peak for *W*

Optical UV-visible spectroscopy measurements were performed using a SHIMADZU-UV

Room temperature Raman spectra were recorded using a Renishaw Raman inVia Reflex spectrometer in the 400–3800 cm−1 range with a spectral resolution of ≤1 cm−1 [43]. The 514 nm Modu-Laser Stellar-REN Pro 514/50 Argon Laser and 785 nm Near Infrared Diode Laser lines were applied as the excitation source. In order to avoid heat-induced effects, the laser power was set at 10 mW. A standard calibration of wavenumber scale with Si plate was used. The Raman spectroscopy measurements were performed at The John Paul II Catholic University

The electrical measuring system was developed at the IPSAS (Slovak Republic) [43]. The measurement of current vs. voltage (*I*–*V*) by transient method or DC method was used in this experiment. The method was selected to check simply presence of the conductivity layer in the material studied. The measuring system includes a cryostat with sample, resistor heating, thermocouple, CSP (charge sensitive preamplifier), excitation circuit of sample, preamplifier, power supply, DAQ (data acquisition) card, and PC (personal computer). The NI PCI 6229 DAQ card was applied [44]. The electrical DC measurement setup used and detail description

3100PC spectrophotometer in the range of 200–800 nm at AIST, Japan [36].

parameter.

290 Radiation Effects in Materials

**2.3. Optical spectroscopy measurements**

**2.4. Raman spectroscopy measurements**

of Lublin (KUL, Poland).

**2.5. Electrical measurements**

of basic parameters are reported elsewhere [43].

Nanoindentation test was carried out using an ultra nano hardness tester (UNHT) with a diamond Berkovich indenter at the Lublin University of Technology (LUT, Poland) [45, 46]. Advantages of the new UNHT design applied for nanoindentation test compared to the conventional nano indenter (or NHT) design, both developed by CSM Instruments (Switzer‐ land) [47], allow us to make measurements with high performance. The UNHT experiment was done in a progressive multicycle mode. The details of the progressive multicycle mode parameters used are reported elsewhere [45].
