A MOS capacitor is fabricated on p-type Si (Silicon) where the metal work function is 4.1 eV and electron affinity of Si is 4.0 eV. E_C-E_F=0.9 eV, where E_C and E_F are the conduction band minimum and the Fermi energy levels of Si, respectively. Oxide ε_r=3.9. ε_o=8.85×10^-14F/cm, oxide thickness t_ox=0.1 μm and electronic charge q=1.6×10^-19 C. If the measured flat band voltage of this capacitor is -1 V. then the magnitude of the fixed charge at the oxide-semiconductor interface, in nC/cm² is