This Thesis describes ultralow temperature studies of helium quantum crystals. Owing to the surrounding superfluid, small latent heat of crystallization and correspondingly short relaxation times, which are unreachable in ordinary crystals, helium crystals offer a unique and clean modeling system to study surface phenomena in a solid. The measurements of the crystal shape and growth rates are essential in providing the microscopic understanding of crystal growth.
Optical observations are probably the most direct way to quantify the surface of crystals.
The optical investigations on 3 He crystals revealed altogether eleven types of facets at temperatures well below 1 mK, while previously only three facet types have been seen. The growth rates of rough and smooth surface states were explored and show significant anisotropy. The measured growth velocities of different facet types indicate that the main growth mechanism is spiral growth in the regime of suppressed mobility. Important thermodynamic parameters of an interface such as the width of an elementary step and the step free energy were directly deduced from the observed growth kinetics. Measurements of the spiral growth of the c- facet on 4 He crystals in the presence of a small number of 3 He atoms were also conducted.