Edge-defined film-fed growth

A continuous monocrystalline sapphire (A1203) fibre has been prepared as single-crystal fibres by LaBelle and Mlavsky using a modified czochralski puller and radio frequency heating. The technique adopted in this method is called edge-defined film-fed growth (EFG) [18-22], Figure 3.4 shows a schematic of the EFG method. 

Edge defined, film-fed, growth process for making a single-crystal alumina fibre (reproduced by permission of Chapman Hall)56. 

This will be demonstrated for three typical examples representing the most important silicon ribbon growth processes the edge-defined film-fed growth and the string ribbon process where the crystallisation interface moves in line with the ribbon transport direction as typical representatives of type I, and the ribbon growth on substrate technique where the liquid-solid interface moves almost perpendicular to the ribbon transport direction as type II process. 

Edge-Defined Film-Fed Growth (Type I Technology)... 

Fig. 7.2. Schematic drawing of the edge-defined film-fed growth (EFG) technology as an example of a type I process. Liquid silicon is lifted by capillary forces through the die, where the silicon ribbon is pulled (left). Closed forms with 8 or 12 facets (side width 12.5 cm) are used for the shape of the foil in order to avoid edge effects...

Edge-Defined Film-Fed Growth (EFG) - A method for making sheets of polycrystalline silicon (for solar photovlotaic devices) in which molten silicon is drawn upward by capillary action through a mold. 

Saphikon Saphikon 100% AI2O3 3.96 single-crystal a-Al203 125 mono filament edge defined film- fed growth 470 3.5 9 developmental fibers... 

Continuous single crystal fibers can be grown from inviscid melts by two relatively slow processes the edge defined film fed growth (EFG) process [13] and the laser heated float zone (LHFZ) or laser heated pedestal growth (LHPG) process [14]. Both offer growth rates of toO.3-0.7 mm/s [13-14]. 

Edge defined film fed growth (EFG) is a commercial process [13] that facilitates the fabrication of continuous void free single crystal oxide fibers (Figure 16) from tungsten or other growth orifices. 

Figure 16. Edge defined film fed growth process (schematic drawing). Redrawn from J. Monbleau, Single-crystal technology, Product Bulletin, Saphikon Inc., Milford, NH (1994).

Three processes are known to fabricate continuous yttrium aluminum garnet (YAG) fibers. Single crystal YAG fibers are obtained by the edge defined film fed growth process and by the laser heated float zone process (Chapter 4.5). Both are slow processes. Amorphous YAG glass fibers have recently been demonstrated by a containerless laser heated melt process (Chapter 4.4). Polycrystalllne YAG fibers can be obtained with sol-gel and related processes (this chapter). These are potentially fast processes. 

EFG = Edge-Defined Film-Fed Growth. The Time Scales are Defined as Follows According to [30] Tsystem — l-JR, = L /k, ... 

EFG Edge-defined Film-fed Growth technique Crystal "Ir crucible... 

LaBell, Jr., H.E., Growth of Controlled Profile Crystals from the Melt Part II - Edge-Defined, Film-Fed Growth [EFG]. Mat. Res. Bull. 6 581-590 (1971). 

---