Tip of a growing crystal with border points identified.
Tip of a growing crystal with border points identified.
Tip of a growing crystal with a parabolic fit.
A better fit to the tip can be obtained by including a small fourth-order correction to the parabolic fit.
The fourth-order correction is only useful close to the tip.
Very close to the tip, however, the fourth-order correction is clearly the best fit. For our work, we have found that using points out to a distance of 6 tip radii gives the most robust measurement of the tip size and shape.