The growth of crystals from the vapour

Abstract

Central to the successful growth of any crystal from the gas phase is control of the vapour transport, something which has proved to be one of the more intractable problems. Much of this difficulty has stemmed from a failure to appreciate and take advantage of the behaviour of gases flowing through pipes and orifices. Additionally, if crystals of high quality are to be produced, then thermal stresses should be kept to the minimum, in particular, contact with the container wall should be avoided. This paper aims to review some of the physical vapour transport methods, paying particular attention to the ways in which the vapour interacts with the container, and with itself and other gaseous species that may be present. Following a brief description of gas flow in ducts and orifices, the paper will consider in turn, closed tube methods, effusion hole techniques, semi-closed methods and restricted flow technologies. In each case, the discussion will aim to establish the salient features of the method and will discuss the extent to which it provides control of vapour transport and growth free of the container walls.