Thermally treated GO foil dielectric properties under low and medium vacuum conditions

The dielectric properties of thermally treated graphene oxide (GO) foils under low and medium vacuum conditions were investigated at room temperature. The thermal treatment consisted of successive heating at different temperatures (50°C, 100°C, 150°C) under vacuum conditions ranging from low vacuum (0.5 mbar for heating at 50°C and 100°C) to medium vacuum (3×10−2 mbar for heating at 150°C). The dielectric properties, i.e. the real part ε1 of permittivity, the imaginary part ε2 of permittivity, the loss tangent tanδ and the ac electrical conductivity σac, of the investigated GO foils were analyzed as a function of frequency at room temperature in the (102 ÷ 106) Hz range using a LCR meter. The dielectric response is confirmed by the ATR-FTIR spectrum performed at room temperature at each treatment temperature. At 50°C and under low vacuum an oxidation of GO foil occurs as confirmed by the observed decrease in ε1 and ε2; a poorly resolved dielectric loss peak is also observed only in tanδ. At 100°C, under low vacuum conditions, a slight increase in ε1 and in ε2 was revealed in agreement with the beginning of both the removal of water from interlayer and the decomposition of some oxygen containing functional groups observed in the relative ATR-FTIR spectrum. At this temperature a poorly resolved dielectric loss peak is also observed in ε2 and better defined in tanδ but at a higher frequency than that for the GO 50C foil. Based on the literature and ATR-FTIR data, an origin is proposed for this dielectric loss peak. At 150°C and at a pressure of 3×10−2 mbar, a partial but greater removal of water and oxygen containing groups occurs as observed in the relative ATR-FTIR spectrum and GO changes in partially reduced GO. This change is confirmed by greater values observed at 3 kHz for ε1, ε2, tanδ and σac, this last increasing by over two orders of magnitude.