STUDY OF THE GROWTH-KINETICS OF FACETS IN A FREE-GROWING HE-4 CRYSTAL

The growth of a free-growing He-4 crystal is studied in a temperature range from 1.5 K to 0.5 K at overpressures up to 1000 dyne/cm(2). A method is developed to grow crystals with a minimal amount of dislocations. The anisotropy of the coefficient of the kinetic growth of the crystal is measured directly by the crystal form. Below the temperatures of both roughening transitions the crystal grows with its form retained which Is to say that the growth rates for all free facets are proportional and the growth mechanism is single for basal and lateral facets and the equivalent faces under equal conditions have the growth rates differed by a factor of 2, suggesting a significant influence of surface defects on the crystal growth. A threshold is observed In the overpressure dependence of facet growth rate. The results pre explained qualitatively In the framework of the layer-by-layer crystal growth model by which the creation of a new layer is controlled by the Frank-Read sources and surface defects.