In this paper, the investigation of boron delta layers by atom probe tomography is used to demonstrate that a sub nanometer resolution (0.9 nm full-width at half-maximum, FWHM) can be achieved. This resolution is surprisingly lower than the intrinsic resolution observed in silicon (0.2 nm). Reconstruction artifacts are suggested. In this paper, the extent of reconstruction artifacts is evaluated using a model that reproduces the field evaporation of the sample and the image reconstruction. It is shown that reconstruction artifacts can only account for half of the resolution degradation, suggesting an actual physical depth of delta doped B layer of about 0.5 nm.