where the expansion is valid only if (π k B T / d F) ≪ 1. An example value (for φ = 4.5 eV, F = 5 V/nm, T = 300 K) is λ T = 1.024. Normal thinking has been that, in the CFE regime, λ T is always small in comparison with other uncertainties, and that it is usually unnecessary to explicitly include it in formulae for the current density at room temperature.