Recently, we reported a fullerene modification using neutral-neutral or neutral-ion collision reactions in the two-chamber configuration of the Bio-Nano electron cyclotron resonance ion source (ECRIS). In our methodology, modified fullerenes can be synthesized in vapor-phase in an ECR plasma, or on a surface of a plasma chamber, and can be characterized by on-line mass spectrometric analysis of the ECRIS beam, or by off-line analyses (e.g. time-of-flight mass spectrometry, liquid chromatography mass spectrometry, etc.). So far, we have successfully synthesized a modified C70 with iron (Fe) and chlorine (Cl) atoms using two individual plasmas; Fe-Cl plasma and C70 plasma. In a subsequent experiment, shown in this study, we investigated the ion/electron density distributions in the plasma chamber by using electrostatic probe method. We correlated these results with the off-line synthesized material investigations and also with plasma electron simulations in order to collect more information on the mechanism of the synthesis process.