(a) Silicon pattern acquired at 15 keV with the natural unit in pixels. The broad peak of the background is due to the silica capillary. (b) Fitting of equation phkl =(2/m)asin[λ(h2 + k2+ l2)1/2/2a] − (2θ0/m) to the observed position of the peaks in pixel units phkl: a linear relation 2θhkl = mphkl + 2θ0, between phkl and 2θhkl is assumed. λ (Å), m (° pixel−1) and 2θ (°) are the refined parameters. The unit cell of the NIST silicon reference 640c is a = 5.4311946 Å.