This year a shaped crystal growth technique has been amazing the crystal growth community: “Saint – Gobain Crystals, USA” announced construction of the new factory “Substrates of High Performance” for production of 6” sapphire substrates of high quality for LED application on the basis of EFG technique [1]. Without any doubt, it is an event of historical significance. Indeed, we know a lot of shaped growth advantages but up to now nobody had believed that their crystal quality can be the best one.

               We would like to use this event to remind a shaped growth history. A priority in applying of a shaper (holes in plates placed onto the melt surface for shaping melt-pulled crystals) belongs to Gomperz [2]. In 1922, he used mica plates floating on melt surfaces to pull Pb, Zn, Sn, Al, Cd, Bi thin filaments through holes in the plates. In 1928, P. Kapitza, later the Nobel Prize rewarded, used this technique for Bi rods growth. In 1929, for Zn single crystalline filaments growth, for the first time, a single crystalline seed was used. Thus, during 1922 – 1931, six papers concerned with a shaper using were published, and the technique was titled as the Czochralski – Gomperz technique.

            A development of shaped crystal growth for industrial application was begun from the set of papers published in 1958 – 1959. The first paper [3] informed that during 1938 – 1941, Russian scientist A. V. Stepanov had carried out experiments concerning pulling of shaped polycrystalline and single-crystalline specimens (sheets, tubes and so on) from melts of some metals, especially aluminum and its alloys. The Second World War interrupted these experiments and they have been continued since 50^th in the Physical and Technical Institute of the USSR Academy of Sciences.

           The very first theoretical analysis of the capillary shaping was reported by the author of this paper at the Internal Russian Conference in April 1967; later it was specified in the set of papers [4] published in the USA. Here is this approach. A crystal grows from a melt meniscus. As the Laplace capillary equation is a second order differential equation, the formulation of the boundary problem for melt meniscus shape calculation requires assignment of two boundary conditions. The first of them (the condition on the crystal-melt interface) is mutual for all techniques of crystal growth and follows from the existence of the growth angle. The second one is determined by a shaper. Shaping is accomplished either on the sharp edges or on the surfaces of the shaper. This corresponds to two different boundary conditions of the capillary boundary problem and as a result – two different techniques of shaped growth: Catching (attachment) and Angle fixation (Wetting) Boundary Conditions. It means that EFG was for the first time formulated in these papers as catching or attachment technique. It was shown that catching (attachment or EFG) boundary condition can be achieved for wetted as well as un-wetted shaper materials by using corresponding melt pressure. This strict formulation of boundary value problems allowed calculation of growth conditions and invention of many practical schemes of shaped crystal growth. But there is a violation in EFG (catching, attachment) boundary condition that never had been mentioned by other researches. The mathematical formulation of the problem requires a fixation of the meniscus edge. But from the physical point of view the melt has to form a wetting angle with the shaper surface. This discrepancy was explained in [5]. The paper contents well-grounded mathematical proof that edge has to be in reality sharp.

        Thus, the real history of shaped crystal growth must be rewrite by the following way. A priority in shaped growth belongs to Gompertz (1922) but strict physical description belongs to the author of this paper who had published the full scheme of shaping (EFG and wetting including) much earlier than LaBelle and Mlavski [6]. 

          In 1971, the very first paper concerning a crystal growth process stability investigation was submitted: Comparative analysis of stability of Czh and EFG techniques [7]. A fundamental result was obtained there – the Czh technique is not stable from capillary point of view, and a shaper can allow a capillary stability of process.

          To resolve contradictions concerning different titles of shaped growth techniques: Czh – Gomperz, Stepanov's, EFG, etc., the author of this paper suggested [8] to use a title TPS (Technique of pulling from shaper). Here is the TPS definition [9]: TPS is the shape crystal growth technique which uses a solid body (shaper) to define a melt meniscus shape by means of either catching (on edges of shaper) or wetting (on surfaces of shaper) capillary boundary condition to obtain the crystal of predominant cross section and impurity distribution as a result of pulling it in a dynamically stable regime.

References:

1.  V. A. Tatartchenko, C. D. Jones, S. A. Zanella, J. W. Locker, F. Pranadi, C – Plane Sapphire Method and Apparatus, USA Patent WO 2008036888 A1, 2006.

2. E. V. Gomperz: Untersuchungen an einkristalldrähten, Zeitschr. für Phys. 8, 184 – 190 (1922).

3.  A. V. Stepanov: A new technique of production of sheets, of tubes, of rods with different cross sections from a melt, J. Tech. Physics 29, 382 – 393 (1959).

4.  V. A. Tatarchenko, A. I. Saet, A. V. Stepanov: Boundary conditions of capillary shaping at crystallization from melts, Bull. Ac. Sc. of the USSR, Phys. Series, 33, 1782 – 1787 (1969).   

5.  V. A.Tatarchenko, V. S. Uspenski, E. V. Tatarchenko, J. Ph. Nabot, T. Duffar, B. Roux: Theoretical Model of Crystal Growth Shaping Process, J. Cryst. Growth 180, 615 - 626 (1997).

6.  H. E. LaBelle: EFG, the invention and application to sapphire growth, J. Cryst. Growth 50, 8 -17 (1980).

7.  V. A. Tatartchenko: Influence of capillary phenomena on the stability of the crystallization process  during  pulling of shaped specimens from the melt, Phys. & Chem. Mater. Treat. №6, 47 – 53 (1973).

8.  V. A. Tatarchenko: Shaped crystal growth (Kluwer Academic Publishers, London, 1993).

9.  V. A. Tatartchenko: Shaped Crystal Growth, In: Springer Handbook of Crystal Growth, Ed. G. Dhanaraj, K. Byrappa, V. Prasad, M. Dudley, pp. 509 – 552 (Springer. Dordrecht, London, New York, 2010).

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/28793 must be provided.

1. Characteristic IR radiation under crystallization, sublimation, and condensation (PeTa effect).