Proceedings of the 10th DoD El ectromagnetic Windows Symposium

N

o rf ol

k, Vi rgi n i a , May 2004



### A Century of Sapphire Cry stal Growth

Daniel C. Harris *

Naval Air System s Com m a nd, China Lake, California

ABSTRACT

Abstract: In Paris around 1890, A. V. L. Verneuil developed a flam e fusion process to produce ruby and sapphire. By 1900 there was brisk dem a nd for ruby

m a nufactured by Verneuil’s m e thod, which was used with little alteration for 50 years. From 1932-1953, S. K. Popov in the Soviet Union established a capability

for m a nufacturing high quality sapphire by the Verneuil process. In the U.S., under governm e nt contract during W o rl d W a r II, Linde Air Products Co.

im plem ented the Verneuil process for m a king jewel bearings for precision

instrum e nts. In the 1960s and 1970s, th e Czochralski process was im plem ented by Linde and its successor, Union Carbide, to m a ke higher quality crystals f o r ruby lasers. Stim ulated by a governm e nt c ontract for structural fibers in 1966, H. LaBelle invented edge-defined film -fed growth (EFG). The Saphikon com p any, owned now by Saint-Gobain, evolved from this effort. Stepanov independently developed edge-defined film -fed growth in the Soviet Union. In 1967 F. Schm id

and D. Viechnicki at the Arm y Materials Research Lab grew sapphire by the heat exchanger m e thod (HEM). Schm id later established Crystal System s, Inc. around this technology. Rotem Industries, founded in Israel in 1969, perfected the growth of sapphire hem i spheres and near-net-shape dom es by gradient solidification. In the U.S., growth of near-net-shape sapphire dom es was dem onstrated by both the EFG and HE M m e thods in the 1980s but neither

m e thod becam e com m e rcial. Today, dom es in the U.S. are m a de by “scooping” sapphire boules with diam ond-im pregnate d cutting tools. Com m e rcial m a rkets for sapphire, especially in the sem i conduc tor industry, are healthy and growing at

the dawn of the 21 st century.

Introduction and Prehistory

Com m e rcial production of synthetic sapphire is now 100 years old. 1 Sapphire is a readily available crystal product used as an optical wi ndow for industrial and m ilitary applications in

which the window m u st withstand extrem e e nvironm ents. Sapphire transm its from the ultraviolet through the visible and into the m i dwav e (3-5 μm ) infrared regions. It withstands high tem p erature, rapid heating and cooling, hi gh pressure, and resists chem ical corrosion. Sapphire is the abrasion-resistant window in bar c ode scanners and the scratch-proof crystal face of expensive wristwatches. High crystal perfec tion, low reactivity, and appropriate unit cell size

m a ke sapphire an excellent substrate in the sem i conductor industry for blue light-em itting diodes

* Daniel.Harris@navy.m il; phone 1-760-939-1649; fax 1-760-939-1617

C l eared for pubi c rel ease; di st ri but i on unl i m i t e d.

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Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std Z39-18and diode lasers. Sapphire is also used for equipm ent to

m a nipulate sem i conductor wafers during processing in extrem e environm ents. Sapphire and its cousin, ruby, are em ployed as jewel bearings in precision m echanical instrum e nts.

5 4 3 1 2

Sapphire is also known as cor undum , the natural crystal of

alum inum oxide, Al 2 O 3 (Figure 1). It is stable up to its m e lting

tem p erature of 2050oC. Its hardne ss of 9 on the Mohs m i neral scale is second only to that of diam ond. The 3-fold sym m e try axis of the trigonal crystal, designated c , is also called the optical axis. Two-fold sym m e try axes designated a and m are found perpendicular to the 3-fold axis . Pure corundum is clear and colorless. Natural sapphire has a variety of colors. Blue sapphire

contains iron and titanium im purities whose charge transf er transition (Fe 2+ ,Ti 4+ → Fe 3+ ,Ti 3+ ) absorbs red light and im parts blue color to the crystal. 2 The red color of ruby com e s from Cr 3+

in corundum , which gives rise to el ectronic transitions that absorb visible light. Figure 1: Natural sapphire (1, 2), natural ruby (3), and synthetic sapphire (4, 5).

Early in the 19 th century, it was thought that sapphire a nd ruby were oxides of the elem ents

alum inum and silicon. 1 In 1817, J. L. Gay-Lussac found that pure alum inum oxide (also called

alum ina) could be prepared by ther m a l decom position of am m onium alum

, (NH 4 )Al(SO 4 ) 2 • 12H 2 O

. Alum ina prepared by this route rem a ins as the raw m a terial for m a king sapphire today. In 1840 H. Rose showed that silicon observed in sapphi re was an im purity introduced from the agate

m o rtars used to grind sapphire for chem ical anal ysis. Once the true com position of sapphire was known, m a ny chem ists sought to m a ke the valuab le crystal. In the period 1837-1840, H. Gaudin

used a torch to fuse alum ina prepared from a m m onium alum to prepare sm all hexagonal platelets

of corundum . Mixing alum with chrom i um salts prior to fusion produced sm all, strained, hard red particles whose density was less than that of natural ruby because of trapped gas. Gaudin

believed he had m a de a glass, but m odern work suggests that he m a de crystalline ruby. 1 I n 1851, H. Senarm ont m a de m i croscopic rhom bohedral crystals by heating solutions of alum inum

chloride to over 350oC in sealed tubes. In 1848, J. J. Ebelm a n prepared ruby by fusing alum ina

and boric acid with chrom i um oxide. Ebelm a n and F. Parm antier prepared crystals from alum ina dissolved in fused salts at high tem p erature. Other investigations were carried out by R. Boettger, W

. Bruhns, A. Brun, H. Debray, H. St.-C. Deville, H. Caron, Daubré, C. Doelter, L. Elsner, G. Friedel, H. Grandeau, P. Hautefeu ille, M. Houdard, H. Loyer, J. W

. Mallet, G. Medanich, S. Meunier, H. Moissan, J. Morozewi cz, C. F. W

. A. Oetling, H. Perrey, L. Schuch,

and E. W e inschenk. 1, 3

, 4 None of this work produced m o re than m i croscopic crystals.

More successful investigations were led by Edm ond Frém y (1814-1894) at the Museum of Natural History in Paris. 1 Frém y and his assistant, Charles Feil, published a paper in 1877 in which they obtained sm all, clear, red ruby crystals . Fireclay crucibles with 20-kg charges were held at red heat for periods up to 20 days. Lead oxide (Pb 3 O 4 ) was converted to lead alum inate, which reacted with silica to give lead silicat e plus corundum . Ruby wa s obtained by adding 2-3 wt% potassium dichrom a te to the reaction. After Feil died in 1876, Frém y’s new assistant was Auguste V. L. Verneuil (1856-1913), who had applied to work with Frém y at the age of 17.

Clear

2ruby crystals up to 3 m m in diam eter and

0.3 carat in m a ss (1 carat = 0.2 gram s) were grown from alum ina in a potassium hydroxide/barium fluoride flux in a ceram ic

crucible at 1500oC. In unsuccessful

attem p ts to increase the size of the ruby crystals, flux growth was scaled up at the Saint-Gobain glass factory and then in 50- liter crucibles at the Appert glass f actory. Although Frém y thought he was crystallizing alum ina from the flux, Kurt

Nassau 1 suggests that alum ina and barium fluoride give gaseous alum inum fluoride.

Alum inum fluoride reacts with water vapor that diffuses through the porous crucible to give alum ina, which crystallizes in m a ny locations with little chance to grow into larger crystals. Frém y sum m a rized his investigations in a book in 1891. 5 He retired in 1892 and died in 1894. Figure 2, reproduced from Nassau, 6 was taken from

Frém y’s book. Figure 2: Crystal growth storage cabinet from

Frém y’s lab. 5,6

Flame Fusion and the Verneuil Process

In 1885 rubies selling for $1000-2500 per carat fr om an unknown source appeared in Geneva and were purported to be natural gem s

. 1 Investigation of the crystals at the Sorbonne in Paris and at Tiffany in New York found m i croscopic gas bubbles suggestive of a high-tem p erature synthetic process. The French Syndicate of Diam onds and Precious Stones ruled that the crystals had to be m a rketed as “artificial,” which reduced their price to $25-40 per carat. Modern investigation of “Geneva” rubies by Na ssau suggests a 3-stage flam e fusion synthetic

process. 1 In the first stage, alum ina plus a chrom i um salt are fused on a ceram ic support to form a tiny crystalline ball. The ball is then turned upside down and growth of a larger crystalline ball is continued by adding fresh m a terial to the flam e. The final stage appears to require 2 torches to enlarge the growing crystal to its final dim e ns ions. The proposed m echanism is supported by 2

discontinuities in chrom i um concentration insi de “Geneva” rubies. One of the people who

exam ined “Geneva” ruby in 1886 was the m i neralogi st, P. M. E. Jannettaz at the Museum of Natural History in Paris. He concluded that fu sion was involved in the creation of the “Geneva” ruby and he discussed his findings with his colleague, Verneuil.

W h ile working with Frém y, Verneuil had earned hi s bachelor, m a sters, and doctoral degrees.

W h en Frém y retired in 1892, Verneuil becam e profe ssor of applied chem istry at the Museum of Natural History in Paris. In 1886, following hi s introduction to the “Geneva” ruby by Jannettaz, Verneuil and G. A. Terreil used a hydrogen-oxygen torch to fuse alum ina powder with som e added chrom i um salt. They obtained tiny partic les, which Jannettaz identified as ruby. From this experim e nt, Verneuil began in earnest in 1888 to develop flam e fusion growth of ruby.

3W o rking with his student, Marc Paquier, Vern euil developed the flam e fusion process well enough to write the details in a sealed report whic h he deposited at the Paris Academ y of Science

in 1891. After further im provem e nt in decreas ing growth stress, Verneuil deposited a second

sealed docum ent at the Academ y of Science in 1892. Marc Paquier, presum ably the sam e person who assisted Verneuil, displayed ruby crystals at the W o rld Fair in Paris in 1900. The crystals,

for which there was brisk dem a nd, appear to have been m a de by the Verneuil process, not the Geneva process, and com m e rcial producti on had already begun by 1900. In 1902, Verneuil announced that he had developed a flam e fusi on process for m a king ruby and he published full

details in 1904. 7

Figure 3 is taken from one of Ve rneuil’s two U.S. patents. To m a ke feed powder, am m onium

alum inum sulfate and am m onium chrom i um sulf ate were each recrystallized 4-5 tim es and a

m i xture of the two was calcine d at 1000-1200oC to give a m i xture of the oxides. Ground powder was placed in container B in Figure 3 and deliv ered into tube K by the tapping ham m e r D. Oxygen was also delivered through tube K and illu m i nating gas was delivered through tube S.

The flam e burned inside the ceram ic m u ffle insu lator M whose inside diam eter was 25 m m and whose inside height was 105 m m

. An alum ina pe destal L held by a platinum tube could be lowered away from the flam e by crank P as th e crystal grew on the pedestal. A m i ca window covered by a steel shutter, neither of which is shown in Figure 3, enabled the operator to view the growing crystal inside the m u ffle.

The crystal growth process described in Verneuil’ s patent is shown in Figure 4. Powder falling through the flam e was heated just below its m e lting point. The initial powder built up a conical pile in which the hot particles sintered together to m a ke a rigid “sinter cone.” The upper tip of

the cone becam e m o lten when the cone got sharp enough. Fresh powder landing on the m o lten

ball would m e lt and enlarge the crystal. Only the upperm ost skin of the growing crystal was

m o lten. As the crystal grew in a vertical direc tion, the pedestal was lowered to keep the top of the crystal at the correct location in the flam e. Flam e tem p erature during crystal growth was regulated by controlling the flow of oxygen. At th e end of a growth run, the flam e was shut and,

if there was not too m u ch strain, the crystal woul d not shatter. Even so, crystals had so m u ch strain that a light tap at the end would split the crystal lengthwise into two halves. A typical growth tim e of 2 hours produced a 15 carat cylinde r with a diam eter of 6 m m and length of 25

mm.

In 1909 Verneuil was appointed chief chem ist at the Paris laboratory of the New York jewelry

com p any, L. Heller and Sons. His charge was to grow blue sapphire for jewelry. The origin of

the blue color was not known until chem ical anal yses by Verneuil showed that natural blue sapphire always contained both iron and titanium . Arm e d with this knowledge, Verneuil was able to grow deliberately doped blue sapphire. The Paris laboratory was closed in 1911 with the

successful com p letion of the project.

Ruby and sapphire m a nufacturing by the Verneu il process had begun in Europe prior to Verneuil’s publication of 1904. 1 One of the largest Verneuil operations was that of Industrie de Piérres Scientifiques, Hrand Djévahirdjian in France and Switzerland. The com p any had a room with approxim a tely 100 Verneuil torches operating around 1920. Heller Com p any had planned

to m a nufacture blue sapphire in the U.S. but f ound that labor costs were too high to com p ete with European m a nufacturing. Blue sapphire was grown for Heller by Baikovsky Brothers in

4France.

Powder

feed

Water cooling j acket

Flame and growing

cry s t a l Figure 3: Diagram of Verneuil’s apparatus for growing sapphire. From U.S. Patent 1,004,505, Septem ber 26, 1911.

B. container of feed powder

D

. h a mme r G. rotating cam O. oxygen feed tube

H. illum i nating gas f eed tube

K inner tube carries oxygen

S. outer tube carries illum i nating gas

M. m u ffle (insulation) surrounding downward-pointing flam e
L. ceram ic pedestal

P. crank for lowering pedestal to keep crystal at correct height in flam e

Mechanism to lower crystal to keep growth

surface at correct

elevation in the flame

Figure 4: Method of growing sapphire

described in Verneuil’s
U.S. Patent 1,004,505.

Baikovsky had 3 torches in 1903, 80 in 1914, 400 in 1919, and 1600 torches in 1980. By 1980 there were approxim a tely six large Verneuil m a nuf acturers with a total capacity of 10 9 carats/yr. Most sapphire was cut into jewel bearings for watches and precision instrum e nts. The process of cutting jewels wastes approxim a tely 99% of the as-grown boule.

5In the Soviet Union, S. K. Popov (1903-1953) be gan experim e nts with the Verneuil m e thod in

1932. 4 By 1938 he had produced a sem i -autom a tic growth apparatus which enabled the

m a nufacturing of long thin rods suitable for m a ki ng jewels for watches and instrum e nts. From 1938 until his death, Popov worked at the Institu te of Crystallography of the Academ y of

Sciences of the USSR. In 1945-50 he im prove d the equipm ent for m a king ruby rods, solving such problem s as accurate supply of powder and uni form heating of the growing crystal. In 1951-53 he developed a new use for sapphire as a durable fiber guide in the textile industry. He also devised equipm ent for bending corundum rods into shapes. A com m e ntary written by N. N. Sheftal’ in 1959 stated that Popov’s equipm ent was m o re advanced than that of W e stern Europe and that the crystal quality produced in the S oviet Union was higher than that available

elsewhere. 4

Birth of the Sapphire Industry in the United States

Prior to the publication by Verneuil in 1904, industr ial production of ruby began in the town of Hoquiam , W a shington in the period 1903-1904. The story pieced together by Nassau 1 states that two entrepreneurs, Polson and Ninem i re, who ha d accum u lated wealth in the lum b er industry,

hired an assistant of Verneuil to establish a flam e fusion facility to grow ruby for jewelry. It was necessary to send boules to New York for cutting and the venture as a whole was not

econom ical. The arrival of less expensive Ve rneuil ruby from Europe ended any hope of

Am erican production.

There was no further U.S. pr oduction of ruby or sapphire until Am erica was cut off from European supplies of jewel bearings in W o rld W a r II. The U.S. governm e nt issued developm ent contracts which led to production by Linde Air Pr oducts Co. in Indiana in 1942. One advantage that Linde had for sapphire produc tion was that Linde was a m a jor supplier of industrial gases, including those used for the Verneuil torch. Li nde was later acquired by Union Carbide Corp. After the war, the U.S., again, could not co m p ete with Europe for econom y in sapphire production. In the late 1940s Linde developed a process for m a king star sapphire and star ruby,

which contain needles of titanium dioxide, for je welry. Another m a rket for sapphire was fiber guides in the textile industry. The Linde pl ant in Indiana was closed in 1974 and Union Carbide’s Linde Crystal Products Division con centrated on Czochralski crystal growth in

California and W a shington State. In 1999 the Crystal Products Division was acquired by Bicron,

a division of the French com p any, Saint-Goba in. In 2000 the division was renam e d “SaintGobain Crystals and Detectors”.

Cz ochralski Sapphire Crystal Grow th

Verneuil’s flam e fusion process, perfected in 1892, hardly changed in the 70 years in which it was the only significant production m e thod for sa pphire. There is still significant dem a nd for

Verneuil m a terial at the dawn of the 21 st century because the m e thod is the least expensive way

to m a ke sapphire and ruby whose quality is ade quate for m a ny applications. However, higher crystal quality dem a nded by electronic and optical applications, and the need f o r sizes and shapes that cannot be m a de by flam e fusion, spar ked the developm ent of other ways to m a ke sapphire after 1960.

6The Czochralski crystal growth m e thod wa s applied to sapphire in the early 1960s. 8 Then other growth m e thods were invented later in the 1960s. Edge-defined film -fed growth was developed in the U.S and the related Stepanov m e thod was applied to sapphire in the U.S.S.R. The heat exchanger m e thod was developed in the U.S. and gradient solidification was introduced in Israel.

A resurgence of interest in r uby arose with the invention of the ruby laser in 1960 using a Verneuil boule grown by Union Carbide in 1959. It was quickly discovered that the optical quality of Verneuil boules was not adequate for

lasers. This dilem m a led to the developm ent of sapphire growth by the Czochralski m e thod at Union Carbide in the 1960s. In this process, alum ina is m e lted in an iridium

crucible in an atm o sphere of 98% N 2 / 2% O 2 . A seed crystal is then dipped into the liquid a nd withdrawn at a rate of 6-25

m m / h while rotating at a rate up to 30 rpm

. As the seed is withdrawn, alum ina from the m e lt crystallizes onto the seed.

The diam eter of the boule could be controlled by the rate of

withdrawal of the seed. Boul e diam eters up to 11 cm could

be obtained from a 15-cm -diam e ter crucible. Saint-Gobain

in W a shington State and Crysta r Research (a division of Johnson Matthey) in Vancouver, Canada both produce sapphire today by the Czochralski m e thod. Ir idium

cr ucible

Figure 5: Czochralski

cr y stal g rowth.

Edge-Defined Film-Fed Grow th

Harold LaBelle, Jr. was a talented technician with only a high school diplom a who joined Tyco

Laboratories in W a ltham , Massachusetts in 1962. Previously, he served as a Navy weather

observer at W h ite Sands Proving Ground and attende d New Mexico State University. His early experience at Tyco was in the growth of sem i conductor crystals by gradient freeze and “traveling

solvent” m e thods, from which he gained an unde rstanding of solid-liquid interface control. In 1965 he began work on an Air Force contract whose goal was to m a ke sapphire fibers for

reinf o rcem ent of m e tal m a trix com posites. 9

, 10

, 11 By analogy with silicon growth at other laboratories, LaBelle found that if he plunged a cold tungsten rod into m o lten alum ina, sm all, crystalline alum ina dendrites grew from the tungs ten, which served as a seed. However, the longest dendrites were only 3 m m
, which was m u ch shorter than required. In an attem p t to
im prove tem p erature stability, Labelle m e lted alum ina in a tungsten boat in a vacuum evaporator. W h en a 0.25 m m tungsten wire was di pped into the m e lt and carefully lifted out, a sapphire crystal grew on the tungsten wire “seed”. This process was essentially a Czochralski crystal growth that produced a carrot shaped sapphire crystal with the tapered tip attached to the last drop of m o lten alum ina (Figure 6).

The final diam eter of the sapphire depended on the diam eter of the liquid drop rem a ining in Figure 6. LaBelle reasoned that a droplet of the right cross section would produce a filam e nt of

the desired cross section. A m e thod was needed to feed liquid with a constant cross section from a reservoir so that long filam e nts could be pr oduced. Therefore, Labelle floated a m o lybdenum washer on top of m o lten alum ina and drew a fibe r by Czochralski-like growth through the orifice of the washer (Figure 7). Several 1-m m

- diam eter crystals up to 30 cm long were grown in this

m a nner. These results were im pressive enough to secure additional funding for the project.

7Figure 6. Czochralski-like growth of sapphire from m o lten alum ina using tungsten wire as a “seed crystal”.

Redrawn from reference 10. Figure 7. Sapphire crystal growth by the floating orifice technique. Redrawn

from reference 10.

For several m onths, LaBelle grew crystals by th is floating orifice technique. Eventually, he concluded that floating dense m o lybdenum on le ss dense alum ina was too delicate for use in

m a nufacturing. It then occurred to him that “a m o lybdenum capillary projecting out of the m e lt

m i ght yield the positive result that the f l oati ng orif ice had, yet represent m e chanical, and

theref ore, therm a l stability as well.” 10 T h e self-filling tube in Figure 8 provided filam e nts with

m o re regular surfaces and 3-4 tim es as m u ch strength as from filam e nts grown earlier. 10

, 12 T h e capillary in Figure 9, m a de from concentric m o lybdenum tubes, produced the first sapphire tubes. Many tubes and ribbons were grown from self-filling tubes in 1967.

Figure 8. Self -f

illing capillary tube f o r filam e nt growth. Redrawn from

reference 13. Figure 9. Self -f

illing capillary tube for tube growth. Redrawn

from reference 10.

8In a key observation, LaBelle noticed that som e tim es the sapphire diam eter grew larger than that

of the orifice from which it was drawn. The difference depended on the angle of the upper

surface of the orifice. If the top surface of the m o lybdenum were flat, the liquid would spread to the edge and then stop. A crystal grown from such a capillary would be just as wide as the outer

diam eter of the m o lybdenum . LaBelle and his assistant, John Bailey, built the die in Figure 10, which easily produced a tube whose outer diam et er was equal to the outer diam eter of the

m o lybdenum . Because the dim e nsions of the sa pphire tube grown in Figure 10 were controlled by the m o lybdenum die, Labelle’s supervisor, Ed Mlavsky coined the term “edge-defined film

fed growth,” or “EFG.”

Figure 10. First edge-defined film -fed growth of a sapphire tube whose wall dim e nsions were equal to the dim e nsions of the m o lybdenum die.

Redrawn from reference 10. Figure 11. Die used to prove that the edges of the m o lybdenum die defined the edges of the sapphire crystal.

Redrawn from reference 10.

To distinguish between edge-def ined film -fed growth and self -filling tube growth, the die in Figure 11 was constructed. If the top surface of the m o lybdenum die controlled the shape of the crystal, then a uniform tube would grow from the m o lten alum ina fed through the four capillary openings. Sure enough, the die produced a tube w ith uniform walls. “The uniqueness of EFG in shaping was therefore established ... since the capilla ries were of totally different cross-sectional shape than the growing crystal.” 10 LaBelle suggested calling the new process “continuous shaped film propagation,” but Mlavsky’s “e dge-defined film -fed growth” prevailed.

The purpose of the Air Force contract at Tyco Laboratories was to gr ow long filam e nts of sapphire. To accom p lish this, LaBelle had to inve nt clever m echanism s to guide the growing fiber and to pull long lengths with a sm all m achin e. Fibers grown in the Air Force program in 1965-66 were nearly opaque and there was no im m e diate dem a nd for the product. However, in
the 1970s, transparent m a terial could be grown in m a ny shapes. 11,12, 13 An application with a significant m a rket was 12.5 × 12.5 × 0.6 m m wi ndows for erasable program m a ble read-only

m e m o ry chips. EFG growth of transparent sapphire optical fibers for high tem p erature
environm ents was stim ulated in the 1980s by funding from the Departm e nt of Energy.

9Concurrent with the work of LaBelle in the 1960s, Stepanov independently applied his shaped growth m e thod to sapphire in the Soviet

Union. 14

, 15 His m e thod was originally used in the late 1930s to grow shaped m e tal crystals. 16

The Stepanov m e thod uses wettable or nonwettable aids to shape the m e lt colum n which, in turn, dictates the shape of the grown crystal (Figure 12). 13 By contrast, in edgedefined film -fed growth, th e shape of the die, not the shape of the m e lt colu m n , controls the shape

of

the crystal.

In 1970 Tyco created the Saphikon Division to produce EFG sapphire in W a ltham . In 1978 the Saphikon Division m oved to Milford, New

Ham p shire. In the 1970s and 1980s Saphikon received the bulk of its revenue by licensing the EFG process to com p anies such as Kyocera, RCA, Corning, and Allied Signal, all of whom

saw com m e rcial potential for sapphire substrates for the newly developing silicon-on-sapphire electronics technology. In 1982, Joseph Gaziano, the president of Tyco, died. The new president, John Fort, sought to sell the Saphikon Division, which had less than two m illion dollars per year in revenue. Eventually he m a de a d eal with LaBelle that was “too good to refuse”. LaBelle purchased Saphikon in 1985 and resold it at a profit in 1987. Saphikon rem a ined independent until 2000 when Saint-Gobain purch ased the com p any and the rights to m a ke sheets, rods, tubes, and 3-dim e nsional shapes. The newly form ed, independent com p any Photran retained exclusive rights to m a nufacture sapphire fibers. Figure 12. W e ttable shaping aid used in Stepanov growth. The dim e nsions of the crystal are determ ined by the dim e nsions of the liquid feed colum n . Redrawn from

reference 13.

Kyocera in Japan acquired EFG technology from Saphikon and further developed the process. Kyocera sells r -, a -, or c -plane sheets up to 20 cm wide x 30 cm long x 0.02-2 cm thick. Kyocera also sells c -axis rods and tubes.

Heat Exchanger Method

The Heat Exchanger Method (HEM) for growing large sapphire boules was invented by Fred

Schm id and Dennis Viechnicki at the Arm y Materials Research Lab in W a tertown,

Massachusetts in 1967. 17

, 18 Fresh out of college in the early 1960s, Schm id worked in

m a nufacturing at the W a tertown Arsenal, wher e he gained experience in the directional

solidification of m e tals and with a helium

- cooled arc furnace for casting titanium . He then went to Northeastern University to earn a m a sters de gree in m a terials science. Returning to the

W a tertown Lab in 1967, Schm id set to work with Viechnicki on directional solidification of an

alum ina m e lt onto a sapphire seed crystal.

10The m odern im plem entation of Schm id and Vi echnicki’s heat-exchanger m e thod at Crystal System s in Salem

, Massachusetts is shown in Figur e 13. A sapphire seed crystal is placed at the

bottom of a m o lybdenum crucible which is then loaded with pure alum ina crackle, a byproduct of the Verneuil process. The furnace is evacuated and resistively heated to m e lt the crackle while keeping the seed just below its m e lti ng point by passing helium gas through the heat exchanger beneath the center of the crucible. Heat and vacuum help purify the alum ina by vaporizing som e im purities. Af ter partial m e lting of the seed, helium f

l ow is increased to cool the seed and initiate crystallization of alum ina ont o the seed. The furnace is held at constant

tem p erature during growth of the crystal, which proceeds out from the seed in 3 dim e nsions. After crystallization is com p lete, the furnace tem p erature and the helium flow are decreased and the boule is slowly annealing in situ . The long slow cooldown produ ces sapphire of the highest crystal quality. Boules with a diam eter of 34 cm and a m a ss of 65 kg ar e routinely produced and boules up to 38 cm have been grown.

Single crystals of sapphire were grown in an 18-m m

- diam eter crucible in 1967 at W a tertown. By 1969, after about 50 attem p ts, crack-free sapphire with a diam eter of 76 m m was grown. By

1971 the diam eter was up to 152 m m

. The first pate nt for the process, which was then known as

the Schm id-Viechnicki technique, was issued in 1969.

( a ) ( b )

( c )

Figure 13: ( a ) Furnace used at Crystal System s to grow sapphire by the Heat Exchanger Method. ( b ) The first sapphire boule grown at W a tertown in 1967. ( c ) Production-quality 34-

cm -diam e ter sapphire boule. Courtesy Crystal System s, Inc.

11By early 1971, Schm id was convinced that th e new m e thod was a breakthrough and wanted to

find a com m e rcial m a rket for the product. He f ound interest at Inselec and Insaco in obtaining sapphire wafers for silicon-on-sapphire electronics. Schm id persuaded a sailing buddy and an accountant to invest in creating the com p any, Crystal System s, of which Schm id would own

51%. The com p any was incorporated in Augus t 1971 after Schm id had purchased a scrapped

furnace from Raytheon in July. He began refurb ishing the furnace in his garage and soon m oved the operation to Shetland Industrial Park in Salem

. For the first year of the com p any, Schm id held his old job at W a tertown and worked on the furnace at night. By July 1972 he grew his first

152-m m

- diam eter boule, from which 51-m m cores were drilled for silicon-on-sapphire substrate wafers. In. Septem ber 1972 Schm id resigned from W a tertown to devote full attention to Crystal System s. He hired his first helper (who was “just getting out of high school”) and his wife handled advertising. First-year sales were less th an fifty thousand dollars. Shortly after the first advertising went out in 1974, Schm id received a letter from Union Carbide indicating that Crystal System s was infringing on their patent a nd offering to license Union Carbide technology.

This claim led Schm id to clarify the difference between the processes and to obtain a patent for his technique, whose nam e he changed to “h eat-exchanger m e thod” because of its unique, controllable heat exchanger.

In the m i d 1970s Crystal System s began to hire full-tim e em ployees. Schm id developed a fixedabrasive slicing technique using a diam ond-im pre gnated blade or wire to slice wafers from a cylinder with m i nim a l loss of m a terial. Th e National Aeronautics and Space Adm i nistration selected HEM sapphire for use in satellites because of its extrem ely low optical scatter. In 1978

the com p any m oved to its current, larger quarter s in the sam e industrial park. In 1979 Crystal System s received a contract to grow laser-qua lity ruby in one of the first actions of the

governm e nt’s new Sm all Business Innovative Re search program . In 1987-89, titanium -doped sapphire for lasers was com m e rcialized. M ilitary and com m e rcial m a rkets for sapphire expanded greatly in the 1980s. In 1974 Crystal Sy stem s got its first governm e nt contract to grow silicon and in 1977 Chandra Khattak at Crys tal System s used the heat-exchanger m e thod to grow crack-free polycrystalline silicon ingots in hi gh purity silica crucibles for the first tim e. HEM silicon for photovoltaics and equipm ent for growing silicon are currently m a jor products of Crystal System s, in addition to sapphire a nd crystal slicing equipm ent. HEM silicon ingots weighing 240 kg with a cross section of 69 × 69 cm are routinely produced.

Sapphire Domes

One of the m o st dem a nding applications for an infrared window m a terial is the seeker dom e on an infrared-guided m i ssile. The dom e m u st withst and stress from very rapid heating and it m u st survive collisions with raindrops, sand particles, and insects in the air. Am ong the infraredtransparent m a terials available in the 1980s, sapphi re was clearly the m o st durable with respect

to therm a l stress and particle im pact. However, the cost of growing sapphire was high and the

cost of f

a bricating it into an optically polishe d hem i sphere was even higher. To decrease the cost, the governm e nt invested in two efforts to grow near-net-shape dom es which would require relatively little m achining af ter growth.

12One Navy-funded effort at Saphikon led to a Manufacturing Technology contract in 1989- 92. A curved sapphire seed crystal was placed in contact with a curved slit at the top

of a m o lybdenum die for EFG growth. The seed was slowly withdrawn in a path thattraced an arc in space. The result was an asgrown dom e, such as that in Figure 14, which could be ground and polished into a finished

dom e. However, the crystal quality was not as high as desired and the m a nufacturing
process was never optim ized. 19

, 20 Figure 14: As-grown EFG sapphire

p roduced by Saphikon. 19,20

Another Navy Sm all Business Innovative Research c ontract was conducted at Crystal System s.
W o rk done in the m i d to late 1980s used the appara tus shown at the left in Figure 15 to grow the
near-net-shape dom es at the right. 21

, 22

, 23 Two hem i spheric m o lybdenum m a ndrels were inserted into the crucible in which sapphire was grown. After a boule was grown and cracked apart, sapphire that crystallized in the volum e between the two m a ndrels had a hem i spheric shape.

This m e thod suffered from cracks extending in to the boule and it was never taken beyond an

initial dem onstration.

Figure 15: Molybdenum apparatus at left was used at Crystal System s to grow near-net-shape sapphire dom es at right. 21-23 Photos courtesy Crystal System s.

Dom e s were form erly produced from sapphi re boules by m achining each dom e out of a cylindrical piece of m a terial, as shown at the left in Figure 16. This process wastes valuable

m a terial and requires a great deal of m achining. A cost effective m e thod for m a king dom es—the process used today in the U.S.—is called scooping . Shown at the m i ddle of Figure 16, 7 nested

dom es could be taken from the sam e volum e of m a terial that produced 3 dom es by conventional

m achining. Diam ond-im pregnated cutting tools show n at the right of Figur e 16 are used to cut

out first the inner surface and then the outer surface of consecutive dom es. In the cutting process, the sapphire is rotated in one direction while the tool is rotated against it in the opposite

13direction. At the end of th e scooping, neighboring dom es are connected by a sm all cylinder of

m a terial at the apex. The dom es are broken apart by tapping and then they are ground and polished to their final finish.

Figure 16: Line drawings com p are conventional use of a boule to m a ke 3 dom es and scooping to

m a ke 7 dom es from the sam e volum e. Phot ograph shows diam ond-im pregnated scooping tools used at Crystal System s for scooping sapphire. Photo courtesy Crystal System s.

Rotem Industries, which was founded in 1969, provides sapphire products for defense applications. The gradient solidification m e thod for sapphire growth was developed at Rotem to produce high quality, near-net-shape dom es. 24

, 25

, 26

, 27

, 28 In Figure 17, alum ina is loaded into a

hem i spheric m o lybdenum crucible containing a sapphi re seed at the bottom

. The crucible is

heated in vacuum to produce a gradient of tem p erat ure, with the highest tem p erature at the top.

W h en the seed has partially m e lted, the tem p erat ure is lowered in a carefully controlled m a nner so that crystallization proceeds out from the seed crystal. An as-grown hem i spheric dom e and a

solid hem i sphere are shown in Figure 18.

Seed

Vacuum

sy st em Power

control 3-phase graphite heating element

Mo crucible Sa pp hire Crucible lid Mo radiation shield P y romete r

Figure 17: Apparatus for growing sapphire by gradient solidif ication at

Rotem Industries in Israel.

14In the heat-exchanger m e thod, highest crystal quality is produced when growth takes place along

the a -axis of the crystal. For the boule in Figure 13( c ), the a -axis is the cylindrical axis. The optical axis of sapphire (the c -axis) is perpendicular to a and com e s out the curved side of the

boule. To m a ke c -axis dom es, a cylindrical core is drilled from the side of the boule and dom es are scooped out from the core. In Rotem ’ s grad ient solidification m e thod, the therm a l m a ss is low enough to perm it the growth of good quality c -axis boules and dom es, as well as a -axis

ma t e r i a l

.

c -axis or a

As-grown boule Polished As-grown dome

Figure 18: Sapphire produced at Rotem Industries by gradient solidif ication. W h en a c -axis flat or dom e is viewed through crossed polarizers, as shown at the left, crystal im perfections and grain boundaries appear as irregularities in the circular f r inges and characteristic cross. The sym m e try of the pattern in the photo at the

lef t is evidence of high crystal quality. Each line of the black cross, referred to in optics as an isogyre, is

p arallel or perpendicular to the direction of a polarizer,

and occurs from extinction of either p - or s -polarized light when only light of that polarization is incident on the crystal. Photos courtesy Atara Horowitz. Dome viewed through crossed polarizers

Outlook

Current issues for sapphire production for windows and dom es include: (1) The cost of sapphire is high. Much of the cost is in m achining a nd polishing. (2) There is a need for larger area

windows. The EFG m e thod can m a ke inherently large windows. The Heat Exchanger m e thod has been scaled up to 38-cm -diam e ter, but larger sizes would be desirable. Materials System s, Inc. has dem onstrated a way to bond sapphire pa nes to each other to m a ke large windows, but the bond lines are not as strong as sapphire a nd they provide an optical discontinuity. 29 (3) Optical fabrication is not well enough controlled to give reproducible m echanical properties. It is virtually im possible to know the m echanical st rength of a particular sapphire part unless it is proof tested. In the absence of proof testing, designs m u st be conservative to be reliable.

15Acknow ledgements

A great deal of sapphire history is presented in the wonderful book, Gems Made by Man by Kurt

Nassau. I am indebted to the following peopl e who shared their knowle dge with m e : Fred

Schm id and Chandra Khattak of Crystal System s; Herb Bates, Cy Gregg and Tim Davis,

form erly of Saphikon; Larry Rothrock of Photra n and Union Carbide; and Atara Horowitz of

Rotem

.

References

1. K. Nassau, Gems Made by Man , Chilton Book Com p any, Radnor, PA, 1980.

2. K. Nassau, Gemstone Enhancement , 2nd ed, Butterworth-Heinem a nn, Oxford, 1994, p. 38;

G. Lehm ann and H. Harder, “Optical Spectra of Di- and Trivalent Iron in Corundum ,” Amer.

Min

. 55 , 98-105 (1970).

3. P. Chirvinskii, Artificial Production of Minerals in the Nineteenth Century [i n Russi an], Kiev, 1903-1906.

4. S. K. Popov, “Growing Synthetic Corundum as Rods and Boules” in Growth of Crystals

, Vol. 2 (A. V. Shubnikov and N. N. Sheftal’, Eds.), English translation by Consultants Bureau, New York, 1959, pp 103-135.

5. E. Frém y, Synthèse du Rubis , Libraire des Corps Nationaux, Paris, 1891.

6. K. Nassau, “Dr. A. V. L. Verneuil: The Man and the Method,” J. Cryst. Growth 13/14 , 12- 18 (1972). A m o re detailed biography appears in K. Nassau and J. Nassau, “Dr. A. V. L. Verneuil and the Synthesis of Ruby and Sapphire,” Lapidary J

., 24 , 1284-96, 1442-47, 1524- 32 (1971).

7. A. Verneuil, “Mem oire sur la Reproduction du Rubis par Fusion,” Ann. Chim. Phys

. Ser 8, 3 : 20-48 (1904).

8. T. B. Reed and R. E. Fahey, “Resistance Heated Crystal l Puller for Operation at 2000o C,”

Rev. Sci. Instr

. 37 , 59 (1966).

9. Final report for Air Force contract AFML-TR-66-246 (1966). 10. H. E. LaBelle, “Experim e ntal W o rk Leading to EFG,” Am. Assoc. Crystal Growth

Newsletter , July 1984. 11. H. E. LaBelle, J. Serafino, and J. J. Fitzgibbon, “Recent Developm ents in Growth of Shaped Sapphire Crystals,” Proc. SPIE 683 , 36-40 (1986).

12. B. Chalm e rs, H. E. LaBelle, Jr., and A. I. Mlavsky, “Edge-Defined, Film -Fed Crystal Growth,” J. Cryst. Growth 13/14 , 84-87 (1972). 13. H. E. LaBelle, Jr., “EFG, The Invention and Application to Sapphire Growth,” J. Cryst.

Growth 50 , 8-17 (1980). 14. P. I. Antonov, S. P. Nikanorov, and V. A. Tatarchenko, “The Growth of Controlled Profile Crystals by Stepanov’s Method,” J. Cryst. Growth 42 , 447-452 (1977). 15. P. I. Antonov, “Shape and Properties of Crystals Grown from the Melt by the Stepanov Techniques” in Growth of Crystals , Vol. 13 (E. I. Givargizov, Ed.), English translation by Consultants Bureau, Plenum , New York, 1986, p 198; V. A. Borodin, T. A. Steriopolo, and V. A. Tatarchenko, “Growing Profiled Sapphire Crystals by Variational Shaping” in Growth of Crystals , Vol. 15 (E. I. Givargizov and S. A. Grinberg, Eds.), English translation by Consultants Bureau, Plenum , New York, 1988, p 183. 16. A. V. Stepanov, “Method of Producing Articles (Sheets, Tubes, Rods, Various Sections, etc.) Directly from Liquid Metal. I.,” Soviet Phys. Tech. Phys

. 4 , 339 (1959).

1617. F. Schm id and D. Viechnicki, “Growth of Sapphire Disks from the Melt by a Gradient Furnace Technique,” J. Am. Ceram. Soc

. 53 , 528 (1970).

18. F. Schm id, A Dream That Came True: Reminiscences of Fred Schmid on the Occasion of Crystal Systems 25 th Aniversary , Crystal System s, Salem

, Massachusetts, 1997.

19 J. W

. Locher, H. E. Bates, W

. C. Severn, B. G. Pazol, and A. C. DeFranzo, “80 m m EFG Sapphire Dom e Blanks Yield High Qua lity, Low Cost Single Crystal Dom e s,” Proc. SPIE

1760 , 48-54 (1992).

20. J. W

. Locher, H. E. Bennett, P. C. Archibal d, and C. T. Newm yer, “Large Diam eter Sapphire

Dom e : Fabrication and Characterization,” Proc. SPIE 1326 , 2-10 (1990).

21. C. P. Khattak and F. Schm id, “Production of Near-Net-Shaped Sapphire Dom e s Using the Heat Exchanger Method (HEM),” Proc. SPIE 1760 , 41-47 (1992).

22. F. Schm id and C. P. Khattak, “Current Status of Sapphire Technology for W i ndow and

Dom e Applications,” Proc. SPIE 1112 , 25-30 (1989). 23. C. P. Khattak, A. N. Scoville, and F. Schm id, “Recent Developm ents in Sapphire Growth by Heat Exchanger Method (HEM),” Proc. SPIE 683 , 32-40 (1986). 24. A. Horowitz, S. Biderm an, G. Ben Am ar, U. Laor, M. W e iss and A. Stern, “The Growth of Single Crystals of Optical Materials By the Gradient Solidification Method”, J. Cryst.

Growth 85 , 215-222 (1987).

25. S. Biderm an, G. Ben Am ar, Y. Einav, A. Horo witz, U. Laor, M. W e iss and A. Stern, “Crystal Growth of Optical Materials by the Gradient Solidification Method”, Proc. SPIE 819 , 157 (1987).

26. S. Biderm an, A. Horowitz, Y. Einav, G. Ben Am ar, D. Gazit, A. Stern and M. W e iss, “Production of Sapphire Dom e s by the Growth of Near-Net-Shape Single Crystals”, Proc.

SPIE 1535 , 27-34 (1991). 27. A. Horowitz, S. Biderm an, D. Gazit, Y. Einav, G. Ben Am ar and M. W e iss, “The Growth of

Dom e Shaped Sapphire Crystals by the GSM Method” J. Cryst. Growth 128 , 824-828 (1993). 28. A. Horowitz, S. Biderm an, Y. Einav, G. Ben Am ar, and D. Gazit, “Im p roved Control of Sapphire Crystal Growth”, J. Cryst. Growth 167 , 183 (1996).

29. R. Gentilm an, P. McGuire, D. Fiore, K. Os treicher, and J. Askinazi, “Large Area Sapphire

W i ndows,” Proc. SPIE 5078 , 54-60 (2003); P. McGuire, B. Pazol, R. Gentilm an, J. Askinazi, and J. Locher, “Large Area Edge-Bonded Flat and Curved Sapphire W i ndows,”

Proc. SPIE 4375 , 12-19 (2001).

171A Century ofSapphireCrystal Growth10th DoD Electromagnetic Windows SymposiumDan HarrisNaval Air Systems CommandChina Lake, CaliforniaDaniel.Harris@navy.milMay 2004SovietVerneuilRubyCirca 1950HomeAgenda2Ruby red color comes from severalpercent Cr3+substituted for Al3+Blue sapphire color comes from a combination of Fe2++ Ti4+impuritiesFe2++ Ti4+Fe3++ Ti3+λmax≈600 nmCharge-transferabsorption bandPure Al2O3is colorless, but...Sapphire, also called corundum, is Al2O33Sapphire CrystalMelting point = 2050°CMohs hardness = 94•1800: Ruby and sapphire were thought to consistof Al2O3and SiO2•1817: Gay-Lussac:•1840: Rose: Found SiO2in sapphire is fromagate mortar used for grinding•1837-72: Gaudin: Fused alum + Cr salt with torch→hard red particles•1800s: Other corundum reports:Senarmont, Ebelman, Moissan,Parmantier, Boettger, Bruhns,Brun, Debray, Deville, Caron, Daubré, Doelter,Elsner, Friedel, Grandeau,Hautefeuille, Houdard,Loyer, Mallet, Medanich, Meunier, Morozewicz, Oetling,Perrey, Schuchand Weinschenk•1877: Edmund Frémy (1814-1894), Museum of Natural History, ParisHistory of artificial ruby and sapphire:Kurt Nassau,“Gems Made by Man”(Chilton Book Co., 1980)Lead oxide→lead aluminateLead aluminate + silica→lead silicate + thin, fragile corundum crystalsAddition of 2% K2Cr2O7to reaction→ruby crystalsAmmonium alumHeat(NH4)Al(SO4)2•12H2O pure Al2O3Joseph Louis Gay-Lussac1778-18505Auguste V. L. Verneuil, age 19(1856-1913)At age 17, Verneuil applied to work with Frémyat the Museum of Natural History, Paris. Verneuilwas hired to work on flux growth of ruby.Verneuil earned bachelors, masters, and Ph.Dwhile working for Frémy.1892-1905: Professor of Applied Chemistry atMuseum of Natural History. Interests:•chemistry of selenium•phosphorescence of zinc blende•rare earth elements•purification of glycerin•high-refractive-index glass for telescopes•growth of ruby and sapphireNassau,Gems Made by ManSee also K. Nassau,J. Crystal Growth1972,13/14, 126Crystals up to 1/3 carat(1 carat = 200 mg)Crystallization of Al2O3+ K2Cr2O7from flux ofKOH and BaF2at 1500°C in porous 800-mLcrucible3BaF2+ Al2O3→2AlF3(g) + 3BaO (1)2AlF3(g) + 3H2O→Al2O3+ 6HF (2)2HF + BaO→3BaF2+ H2O (3)In attempts to increase crystal size, work wastransferred to large ovens of Saint-Gobain andAppert glass factories with 50-L cruciblesVapor phase nucleation in reaction (2) occurs inmany small cavities and prevents growth of largecrystals1891: Frémy publishes book summarizing fluxgrowth of rubyFrémy retired in 1892 and died in 18941876-1892: Frémy and Verneuil - Flux Growth of Ruby10 mmNassau,Gems Made by Man7Flux-grown rubyFrémy and VerneuilFlux GrowthJewelry with synthetic rubyFrémy’s storage cabinet (1891)Nassau,Gems Made by Man8Geneva Ruby•1885: Rubies of quality worth $1000-$2500/carat appeared on market from Geneva•1886: Prof. F. Friedel of Sorbonne observed gas bubbles in Geneva ruby andconcluded that stone was made byhigh-temperature fusion process•1886: French Syndicate of Diamonds and Precious Stones rules Geneva ruby isman-made and must be sold as“artificial”⇒price drops to $25-$40/carat•1886: G. F. Kunz of Tiffany examined Geneva ruby and concluded (probablyincorrectly) that it was made by Frémy/Verneuil flux growth process•1904: Geneva ruby production ceases when Verneuil published his processNassau,Gems Made by Man9Geneva Ruby Growth Process as Reconstructed by Kurt NassauA. Tiny boule grown at tip of sinter conefrom pure Al2O3powder + Cr saltB. Break off and turn boule overC. Further growthD. Complete growth with 2 torches androtation of boule supportDiscontinuities in Cr contentof Geneva ruby correspondto different stages of growthprocess

Cr (wt %)MillimetersNassau,Gems Made by Man10•1886: Mineralogist P. M. E. Jannettaz at Museum of NaturalHistory, Paris, examined Geneva ruby and concludedthat fusion was involved in its fabrication. Jannettazdiscussed his observations with Verneuil.•1886: Verneuil and G. A. Terreil fused alumina powder plus Cr salt to producemicroscopic single-crystal ruby, as confirmed by Jannettaz.•1888: Verneuil begins to investigate solidification of molten Al2O3as an alternative toflux growth. The only practical way to obtain 2050°C needed to melt Al2O3was H2-O2torch or gas-O2blow torch.•1891: Working with his student, M. Pacquier, Verneuil had developed most of whatwe now call Verneuil flame-fusion crystal growth. Verneuil deposited details ofthe process in a sealed document at the Paris Academy of Science. Crystalcracking was main unsolved problem.Origins of Flame Fusion (Verneuil) Crystal GrowthNassau,Gems Made by Man11•1892: Verneuil eliminated crystal cracking by making contact area between rubycrystal and sinter cone as small as possible. A second sealed document withdetails was deposited at Paris Academy of Science.•1900: Pacquier exhibits ruby crystals at Paris World’s Fair. Source of rubies wasunknown, but it was reported that the Paris manufacturer made ruby by thenew Verneuil process (not the Geneva process) and“was able to sell all of hisproduction to France and Germany.”•1902: Verneuil announces details of flame fusion process•1904: Full publication: A. Verneuil,“Memoire sur la reproduction du rubis parfusion,”Annales de Chimie et de PhysiqueSer. 8, 3: 20-48 (1904)SinterconeInitial fused region wheretiny crystal begins to growNassau,Gems Made by ManInitial stages ofVerneuil-grown rubyin Museum of Artsand Sciences, Paris12Verneuil’s Flame Fusion ApparatusMuffle furnacecrystal growthzoneNassau,Gems Made by ManPowderfeedTorch pointingdownMechanism tolower crystalduring growth13B. Container filled with feed powder andscreen on lower end(NH4)Al(SO4)2•12H2O+(NH4)Cr(SO4)2•12H2OAl2O3+Cr2O31200°CRecrystallized 4-5×Feed powderD. Tapping hammerG. Rotating camO. Oxygen inletK. Inner tube carries powder plus oxygenH. Fuel (illuminating gas) inletS. Outer tube carries fuelM. Downward pointing flameL. Alumina ceramic pedestal held by Pt tubeP. Crank lowers pedestal during growthNassau,Gems Made by ManVerneuil ApparatusUS Patent 1,004,505–September 26, 1911FlameandfurnacePowderfeedWatercoolingjacketMicawindowMechanism forlowering thegrowing crystalFlame14SinterconeInitial fused region wheretiny crystal begins to grow1. Hot, almost melted powderfalls on alumina pedestaland builds up sinteredcone2. Uppermost tip of conemelts3. Molten drop enlargesVerneuil Flame Fusion ProcessNassau,Gems Made by ManVerneuil-grown ruby in Museumof Arts and Sciences, Paris1 2 3 4 564. Molten drop enlarges5. Pedestal is lowered tomaintain molten region atconstant height6. Flame shutoff time iscritical to avoid cracking15Cut Verneuil rubyCurved growth striations seen inalmost all Verneuil crystalsEarly Verneuil boule grownon natural ruby seed crystalNassau,Gems Made by ManTypical ruby boule: tapered cylinder~25 mm long and 6 mm diameterweighing 15 caratsAfter growth, ruby boule is tapped andit splits in half lengthwise.16First U.S. Synthetic Ruby:Hoquiam RubyNassau,Gems Made by Man•1903-1904: Lumber businessmen Polson and Ninemire set up factory tomanufacture ruby in Hoquiam, Washington.•Kurt Nassau argues that technology was probably provided by one of Verneuil’sFrench assistants.•Surviving Hoaquiam rubies are low quality material made by Verneuil process.Rubies are small, strained, and have many gas bubbles•Rubies had to be sent to New York for cutting•Within a few years, cheaper, higher quality Verneuil ruby from Europe ended theHoquiam venture.17Auguste V. L. VerneuilAge 55 in 1911•1905: Verneuil becomes Professor of“lime, cement, ceramics, andglassmaking”at NationalConservatory of the Arts andSciences, Paris•1909: Verneuil becomes chief chemist inParis laboratory of L. Heller and Sonsof New York (later Heller-Hope Co.)Sets up factory to produce ruby andblue sapphireBy analyzing natural, blue sapphire,Verneuil discovered that the bluecolor is associated with Fe + TiimpuritiesNassau,Gems Made by Man18Heller Laboratory in Paris, 1910with Verneuil torchesProf. VerneuilNassau,Gems Made by ManBy 1907, several manufacturerswere producing synthetic ruby ata total rate of 5 million carats/yr19Verneuil growth room with almost 100 torches in 1920Industrie de Piérres Scientifiques, Hrand Djévahirdjian, SwitzerlandNassau,Gems Made by Man20Verneuil Growth Room of DjévahirdjianPlant with 270 Torches (~1970s)Nassau,Gems Made by Man21Savva K. Popov: Soviet Pioneer in Ruby and Sapphire GrowthS. K. Popov (1903-1953)1932: Began work on Verneuil crystal growth1938: Produced semi-automatic growthapparatus to make long thin rodssuitable for watch jewels1945-50: Improved device for making ruby rods1951-53: Developed new use for corundum rods•fiber guide for making artificial fibers•flame polishing of corundum•method of bending corundum rodsInstitute of Crystallography, Academy of Sciences of USSRS. K. Popov inGrowth of Crystals(A. V. Shubnikov and N. N. Sheftal’, eds), Chapman & Hall, London, 1959, pp 104-1351959 assessment by N. N. Sheftal’:Popov made more uniform crystals byoptimizing feed and heating conditions.Equipment and crystal quality betterthan those in Western Europe221939 195050 mmRuby boules circa 1950S. K. Popov inGrowth of Crystals(A. V. Shubnikov and N. N. Sheftal’, eds), Chapman & Hall, London, 1959, pp 104-135Popov’s work23Nassau,Gems Made by ManLinde history hereLinde Air Products Co. Verneuil Ruby and Sapphire in U.S.•No synthetic ruby/sapphire production in U.S. after Hoquiam•With European sources of jewel bearings cut off in World War II, U.S.government issued development contracts•Linde Air Products Co. begins Verneuil production in East Chicago, IN.Linde was a compressed gas producer•After World War II, Linde could not compete with lower European laborcosts. Linde developed automated process for making 81 cm x 5 mm rodsthat could be efficiently cut into jewel bearingsLinde Verneuil growth in 196024Nassau,Gems Made by Man•Partial melting of feed powder occurs in flame, with complete melting only in thinlayer on top of boule. 30-40% of feed powder is lost and cannot be re-used.•Boule is lowered at 1 cm per hour•Flame is shut suddenly at end of run.“If the boule does not shatter in the nextten seconds, then the remaining stress will be relieved by a light tap with ahammer, which causes the boule to split in half.”Verneuil Crystal Growth in 1979Corundum grown alongdifferent crystal directionshas different cross sections25Nassau,Gems Made by Man1960: Demand for Ruby Crystals for Lasers SpurredDevelopment of Larger Verneuil Boules andEventually Led to Czochralski Crystal Growth43-cm-long Linde Verneuilruby weighing 4500 carats19-cm-long earlyCzochralski rubyfrom Linde120-carat rubyfrom Linde1974: Linde East Chicago facilitycloses and U.S. ruby growth ceasesLinde Crystal Products Divisionbecomes part of Union Carbide andfocuses on Czochralski growth26Nassau,Gems Made by ManCzochralski Crystal Growth of Corundum•In 1979, Verneuil ruby and sapphire was least expensive variety and was usedfor gems, watch and instrument bearings, thread guides in weaving machines,balls in ball-point pens, and phonograph needles (remember those?)•Higher crystal quality was needed for lasers•Czochralski crystal growth•Pure Al2O3is melted in iridiumcrucible just above 2050°C•Sapphire seed crystal is dippedinto melt. If temperature is too low,melt crystallizes. If temperature istoo high, seed melts.•Seed is rotated (up to 30 rpm) andpulled out of melt at 6-25 mm/h•Atmosphere is typically 98%N2-2%O2•Careful control of pull rate requiredfor constant diameter boule•11-cm-diameter crystals can bepulled from 15-cm crucible27Nassau,Gems Made by ManUnion Carbide Czochralski Crystals4.2 kg ruby10 kg sapphireCzochralski sapphire applications in 1980s:Infrared and ultraviolet windowsWindows for xenon lampsSodium lamp tubesHigh-pressure cell opticsPhotomultiplier tube face platesUltracentrifuge cell windowsCorrosion-resistant cells, crucibles, tubesHigh-power laser opticsSemiconductor wafer carrier platesPhotomasks and platesRadiation light pipesTransparent electronic substratesOptical flatsMicrowave output windowsHigh-temperature process windows---From Union Carbide product literature28Union Carbide Sapphire Plant inWashougal, Washington, 19881999: Union Carbide Crystal Products Division acquired by Bicron.Bicron was the successor to Harshaw Chemical Co, aproducer of optical crystals. Bicron had been acquired bySaint-Gobain in 1990.2000: Sapphire division renamed“Saint-Gobain Crystals andDetectors”2003: Czochralski sapphire is still produced at Washougal plant29Nassau,Gems Madeby Man•Melt Al2O3in molybdenum crucible•Melt wets surface of molybdenum die and movesup by capillary attraction•Dip sapphire seed crystal into melt on top of die•Pull seed crystal to draw out crystallizing Al2O3EFG-drawn sapphire(Tyco Labs)EFGGrowth Method:Edge-DefinedFilm-FedGrowth•Research at Tyco Laboratories, Waltham, MA, funded by Air Force in 1965 todevelop EFG continuous sapphire filament for reinforcement of metal matrixcomposite (Report AFML-TR-66-246,1966)•EFG method invented at Tyco by Harold E. LaBelle, a technician without a collegeeducation. Patent issued to LaBelle in 197130Sapphirecrystalfilament1. Czochralski-like growth ofsapphire from molten aluminausing tungsten wire as a“seed crystal”. Diameter ofcrystal is related to diameterof remaining liquid dropGenesis of EFG Crystal Growth2. Floating orifice: Mowasher floats on liquidalumina. Diameter of crystal filament isgoverned by diameter of orifice. Method isnot stable enough for manufacturing.313. Self-filling capillary tube forsapphire filament growth.Mo no longer floats on meltGenesis of EFG Crystal Growth4. Self-filling capillary for growthof sapphire tube325. First Edge-Defined Film-Fed Growthof sapphire filament. Diameter ofdie, not diameter of melt column,dictates diameter of filamentGenesis of EFG Crystal Growth6. Experiment proved that the edgesof the Mo die defined the edges ofthe sapphire crystal.Moltenalumina• LaBelle suggested the name “continuous shaped filmpropagation”• His boss, Ed Mlavsky, called it “edge-defined film-fed growth”33•1970: Tyco Laboratories created Saphikon Division in WalthamMA and moved it to Milford NH 1978•1970s-1980s: Saphikon revenue mainly from licensing EFGtechnology to companies such as Kyocera, RCA, Corning, AlliedSignal. Licensees saw potential for silicon-on-sapphire products•1982: Tyco president Joe Gaziano dies and John Fort becomespresident•Saphikon Division had less than $2M/yr revenue. Fort tried to sell Saphikon butfound no taker•Fort sold Saphikon to Harry LaBelle in 1985 in a deal“too good to refuse”.LaBelle’s intention was to resell Saphikon•1985: Department of Energy funded project for optical fiber for high temperatureand corrosive conditions•Saphikon purchased by Cy Gregg in 1987. Tim Davis was President/CEO in 1990s•2000: Saint-Gobain buys Saphikon to manufacture sheets, rods, tubes,3-dimensional shapes. Gregg forms Photran which retains exclusive right tomanufacture sapphire fibers (for optical and structural applications)Saphikon Company HistoryInformation from Cy Gregg, Tim Davis, Herb Bates. EFG sapphire photo from Chalmerset al.,J. Cryst. Growth1972,13/14, 84Early EFGSapphire34Saphikon EFG Sapphire Sheets[Photos courtesy John Locher]mc35•EFG sapphire fiber uses•Optical fibers for Er-YAG lasers for medical use•Proprietary structural composites(Fibers grown for ceramic/ceramic compositesfor National AeroSpace Plane in 1980s)•EFG bulk sapphire uses•Bar code scanners - largest application•Substrates for blue LEDs and laser diodes•Semiconductor manufacturing equipmentTubes for plasma applicatorsWindows for high temperature/corrosive environmentsElectrostatic chuck to hold wafer in place during processingEnd effector on robotic arm - grabs wafer and moves it during processing•Laser material•Scalpels and ceramic parts used inside the body•Infrared sensors components•Kyocera EFG sapphire products available in 2003•r, a, or c-plane sheets up to 20 cm wide x 30 cm long x 0.02-2 cm thick•c-axis rods 0.05 to 2 cm diameter up to 1 m long•c-axis tubes•Violet sapphire jewelsInformation from Cy Gregg,Tim Davis and Kyocera web siteGreentrafficlight36Stepanov Independently DevelopedShaped Sapphire Crystal Growth in USSR in 1960sGrowth of shaped corundumbegan in early 1970sEffusion cells formolecular beam epitaxySodium lamp envelops andboats for making ultrapure materialsP. I. Antonov inGrowth of Crystals, Vol 13 (E. I. Givargizov, ed), Plenum,New York, 1986; V. A Borodin et al. inGrowth of Crystals, Vol 15 (E. I.Givargizov and S. A. Grinberg, eds), Plenum, New York, 1988SeedEdgedefinerMoltencharge37Stepanov Crystal GrowthEFG Crystal Growth• Stepanov method: wettable ornonwettable aids shape the meltcolumn which shapes of the crystal• EFG: shape of die, not shape of meltcolumn, controls shape of crystalDifference Between Stepanov and EFG Crystal Growth38•Crucible with seed crystal at bottom isloaded with Verneuil crackle•Evacuate and heat to melt charge.Seed is cooled by He flow through heatexchanger•After some melting of seed, increaseflow of He to initiate crystal growth•When solidification is complete,decrease He flow and anneal in situ byslow cooldownSapphire Growth byHeat-ExchangerMethod (HEM)Crystal Systems39Fred Schmid and Dennis Viechnickiin early days of HEM developmentat Army Materials Research Lab in 1960sOrigins of theHeatExchangerMethod•Early 1960s: Lafayette mechanicalengineer Fred Schmid worked inmanufacturing at Watertown Arsenal•Directional solidification of metals•He-cooled arc furnace for casting Ti•After Arsenal closed, Schmid worked forprecision casting company and decidedto go to Northeastern for MS in MaterialsScience•1967: Schmid returned to AMRL andconceived He-cooled heat exchanger.Worked with D. Viechnicki on directionalsolidification of alumina•1967: single-xtal Al2O3in 3/4′′crucible•1969: crack-free 3′′xtal after 50 tries•1969: first HEM patent issued•1971: 6′′diameter boule grownCrystal Systems401970J. Am. Ceram. Soc.1970,53, 528Thermocouple41First sapphire grown in Watertown Larger boule in crucibleCrystal SystemsCrystals grown 1972/73 were largest diametersapphire ever grown at that timeWindow made from6′′diameter hexagons42• “By early 1971 I was convinced that the...Schmid-ViechnickiTechnique...was a breakthrough and felt that I would need tofind a market for sapphire”•Interest in sapphire was expressed by Inselec and Insaco forSOS (silicon-on-sapphire)•Schmid convinces sailing buddy, Larry Ingber, andaccountant, Dick Kanter, to invest in Crystal Systems,in which Schmid would hold 51% interest•July 1971: Schmid purchases scrapped CVD furnace from Raytheon for $1750•Aug 1971: Crystal Systems incorporated.Schmid works on furnace in his garage•Furnace moved into space at Shetland Industrial Park in Salem• “All this time I still had my job at AMRL and was working...between 18 and 20hours a day”•July 1972: 6′′boule grown and 2′′cores drilled for SOS wafers.“All the bouleswere stressed and loaded with gas nearthe outside periphery because I didn’tunderstand the growth process.”•Sept 1972: Schmid leaves AMRL to work full time with 1 helper“just getting outof high school.”1st year sales <$50K to Inselec and Insaco•Sept 1973: CSI hires 1st full-time employee; Judy Schmid handles advertisingOrigin of Crystal Systems, Inc as told by Fred Schmid43• “I sent our first advertising piece out as a news release...and shortly after it waspublished (mid-1974) I got a letter from Union Carbide indicating I was infringingon their patent and offering to license their [Czochralski] technique to me.”•1975: CSI obtains patent for bubble-free sapphire and names technique“HeatExchanger Method”because of unique controllable heat exchanger•1973-78: Schmid developsFixedAbrasiveSlicingTechnique for cutting sapphirewafers with diamond abrasive on a blade combined with rocking workpiece•1974: NASA selects HEM sapphire for satellites because of low optical scatter•1975: CSI gets government contract to grow silicon by HEM•1977: Chandra Khattak hired fromBrookhaven to work on Si. 1stcrack-free silicon grown by HEM•1978: CSI moves to current quartersand grows 1st 12′′boule•1979: SBIR program initiated andCSI gets one of 1st contracts forlaser-quality ruby•1980-82: HEM Si for photovoltaics•1987-89: Ti:sapphire commercializedFred Schmid’s Story, continuedCrystal Systems44Crystal SystemsManagement in 1996Peggy Mulane, Vicky Herman,Fred Schmid, Chandra Khattak,Mark Felt, Henry Rogers,Maynard SmithHEM FurnacesCSI products•sapphire(boules up to 15′′diameter)•polycrystalline Si•HEM furnaces•crystal slicing machinesCrystal Systems45FixedAbrasiveSlicingTechniqueCrystal SystemsShaped wire reduceskerf loss to 150μmDiamond abrasiveplated onto Winter wire46Growth of Near-Net-Shape Sapphire Domes by EFG MethodNavy manufacturing technologyContract at Saphikon 1989−199247Polished EFG near-net-shape domesviewed through crossed polarizersHigh-quality single-crystalsapphire dome viewed throughcrossed polarizers48Molybdenum preformsplaced in molten aluminacharge for HEM growthat Crystal SystemsGrowth of Near-Net-Shape Sapphire Domes by HEM MethodNavy contract 1985-86As-grown blanks Polished dome and as-grown blank49Once upon a time,one dome washogged out of onecylinder of sapphireThen scooping wasinvented and manymore domes could betaken from the samevolumeCrystal SystemsPrecision Lapping and Optical Co.50Diamond-impregnated scooping toolsScooped dome blanks•Rotate sapphire rod and scooping toolin opposite directions to cut out insidediameter with the small scooping toolwhose outside edge is the activecutting surface•Then use larger tool to cut outerdiameter of the dome. Inside edgeof tool is active cutting surface•Small cylindrical plug is left at apexof dome connecting it to next domein stack. Light force breaks domesapart at end of scoopingScooping domes at Crystal Systems51HottestCoolestGradient SolidificationSapphire Growthat Rotem Industries, IsraelFounded in 1969PyrometerMo radiation shieldCrucible lidSapphireMo crucible3-phase graphiteheating elementPowercontrolVacuumsystemSeedcrystalAtara Horowitz52Atara HorowitzRotem furnacesPolishedAs-grown domeDome throughcrossed polarizersRotemSapphireSapphiredomeAs-grown boulec-axis or a-axis53S & R Rubicon SapphireRussian American Company, IllinoisHorizontal directional solidification(Bridgman growth)Stepanov (EFG) growthVerneuil growthS & R Rubicon also usesKyropoulos growth methodfor highest crystal quality54Sapphire from AtlasRussian Research and Production CompanyKyropoulos growth method, also called GOI in Russia55Verneuil Sapphire from AtlasRussian Research and Production Company56Acknowledgements:•Kurt Nassau,Gems Made by ManBell Labs•Fred Schmid and Chandra KhattakCrystal Systems•Herb Bates, Cy Gregg, and Tim DavisSaphikon•Larry RothrockPhotran and Union Carbide•Atara HorowitzRotemIf he didn’t talk somuch, he wouldhave finished hisice cream by now