Quantum Capacitance of 2D Material - II
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Now we have seen the shift in the Fermi energy is :math:`\delta E_F = e\delta \phi_e + \frac{\delta N}{D_0}`.
If the geometrical capacitance of the sheet per unit area is :math:`C_0`, :math:`\delta \phi_e  = C_0 \delta \sigma` 
where :math:`\delta \sigma` is the charge density per unit area, :math:`\delta \sigma = e \delta N`.