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A technique for producing large single crystals of lead telluride Cannon, G. Harry (George Harry) 1954

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A TECHNIQUE FOR PRODUCING LARGE SINGLE CRYSTALS OF LEAD TELLURIDE  by George Harry Cannon  A Thesis Submitted i n P a r t i a l Fulfilment of the Requirements f o r the Degree of MASTER OF SCIENCE i n the Department of Physics  We accept this thesis as oonforming to the standard required from candidates f o r the degree of MASTER OF SCIENCE  Members of th® Department of Physics THE UNIVERSITY OF BRITISH COLUMBIA October, 1954  Abstract  The growing  steps  to  single  taken  crystals  Two t h e o r i e s The  be  record  in  are  the  a technique  of  outlined.  on c r y s t a l  of  developing  growth  are  experimental  lightly  work done  treated.  includes  the  following. i in  The a furnace  1400°C  is  developsient to  operate  to ± 1 $ ? i s  the  temperature  temperature  ranges  gradient 600°C  to  with time  to  control  the  temperature  of  this  developed.  A recording tions  an a x i a l  discussed. A controller  furnace  in  of  (or  unit  to  record  with position  in  the  temperature  the  furnace)  varia-  is  incorporated. The PbTe lines  considerations  are  discussed.  of  tellurium,  This  for  preparing  include  compiled from  a table the  and of  testing  the  I-l.I.T. Table  pure  spectral of  Wavelengths. A  technique  The described.  for  attempts  The  degrees  to of  producing produce success  a  single  a single  crystal  crystal  and f a i l u r e  are  of  is  outlin  PbTe  are  discussed.  Acknowledgements  I would whose  help  like  to  success  in  t e n d e r my t h a n k s this  to  undertaking  the  would  following, not  have  without  been  possible.  financed of  The D e f e n c e  Research Board  the  and  project  has  of Canada which  employed the  author  has  for  the  summer  1953.  The D e p a r t m e n t British  Columbia  for  and f o r  employing the  o f P h y s i c s and  encouragement author  for  D r . A . II. C r o o k e r f o r wholehearted during  the  to  in  summer  of  the  of  undertaking  1954.  c o n t i n u a l encouragement  overcoming the  many  and  difficulties  work.  Hr. own t i n e  cooperation  University  in starting  the  his  the  John Lees f o r aid  the  author  his with  unselfishness the  in giving  glassxvork.  of  his  T a b l e o f Contents Chapter I  I n t r o d u c t i o n t o the Problem  Chapter I I  Theory  Chapter I I I  Experimental C o n s i d e r a t i o n s A.  General  B.  Equipment ( i ) Furnace ( i i ) Control ( i i i ) Recording  C.  Materials ( i ) General ( i i ) Preparation ( i i i ) Testing  D.  Technique ( i ) General ( i i ) P r o d u c t i o n Runs  Chapter IV  Results  Chapter V  Discussions  A TECHNIQUE FOR  PRODUCING LARGE SINGLE  CRYSTALS OF LEAD TELLUR3DE  Chapter I. Introduction Research i n f i e l d s of physics such as spectroscopy, electronics, etc. often needs large crystals free from flaws with special physical properties f o r making observations and measurements.  In some cases these c r y s t a l s may  be obtained from nature  but more often they must be prepared a r t i f i c i a l l y i n the  labora-  tory either because of short supply of the former or because of special properties found only i n the l a t t e r . In the case of large single c r y s t a l s of lead t e l l u r i d e they must be prepared a r t i f i c i a l l y .  Crystals of lead t e l l u r i d e  are of interest because of t h e i r semi-conductor properties t h e i r photo-electric response i n the infra-red region. that observation  and  In order  and measurement of physical c h a r a c t e r i s t i c s of  lead t e l l u r i d e may  be made without the complications caused by  c r y s t a l boundaries and interfaces, and also be made on a macroscopic scale, a large single c r y s t a l i s needed.  To develop a  technique f o r the production of large single c r y s t a l s was problem undertaken i n the work reported  the  on i n t h i s t h e s i s .  Laboratory techniques f o r growing c r y s t a l s are many and varied (1) depending on the substance from which the growth must -tic  take place.  These methods include growth^ of c r y s t a l s from  -  2 -  solution, s o l i d state, and from the melt, etc..  The method  which i s selected f o r making the lead t e l l u r i d e crystals i s the l a s t one mentioned; i . e . from the melt. Again, the melt method of producing c r y s t a l s has been performed with many techniques, each one successful f o r the material used.  For producing lead t e l l u r i d e crystals i t was decided to  use the Stockbarger method having two furnaces i n cascade at d i f f e r e n t temperatures with a sharp temperature ating them.  gradient separ-  By lowering a boule through t h i s s t a t i c temperative  program at the correct rate i t should be possible to produce a single c r y s t a l throughout the melt. The problem then resolves i t s e l f into three parts: (1) To produce; ( i ) a controlled furnace with the proper static;, temperature program along i t s axis, ,  ( i i ) a c o n t r o l l e r which w i l l maintain the temperature program with a tolerance set down l a t e r i n t h i s t h e s i s , ( i i i ) a lowering mechanism and stand to permit lowering of the boule through the temperature  program,  ( i v ) a recording device to measure and record the temperature the furnace.  program i n  - 3 -  (2) To prepare; ( i ) the raw materials used i n the process, ( i i ) a method of checking f o r purity and, i f necessary, a method of producing the materials i n the laboratory. (3) To develop a technique f o r growing the c r y s t a l s . The following pages w i l l report on what steps have been taken; what results have been achieved; and what i s suggested f o r further investigation.  - 4 -  Chapter  II  Theory Two on  other,  crystal  an a t o n i c  Volmer,  the  Kossel,  growth of In  the  ing  an  In  two p h a s e s  the  first. a fluid  is  a minimum.  that  this  condition  unit  the  have  its  volume as  volume.  a constant  early  resides  the  way f o r  the to  on the the  stability  free  the  and  has been latter  others. developed  considers  the  free  the  made  use  growth of  surface  o f an  a crystal  the  small  conditions govern-  in  inside  its  drop  area,  equilibrium  and  pressure,  energy w i l l  volume f r e e crystal,  a  separating  isolated  energy, and hence  Gibbs  throughout  a  second phase  temperature  Taking  from  theory Gibbs  i n a mist  constant  that  start  and a p p l i e d  surface  implies  a given  the  its  f o r m a t i o n of for  This  tfulff  One,  crystal.  droplets  surroundings at  minimum f o r  must  In a s i m i l a r  its  growth,  energy which  retards  is  with  crystal  of  drops  The c o n d i t i o n  of  Curie,  perfect  liquid  The f r e e  the  by G i b b s ,  c o n s i d e r a t i o n of  growth of water  crystal.  been propounded.  S t r a n s k i and o t h e r s .  a crystal  analogy of  the  g r o w t h have  is  theory  ideally  general,  beginning. of  of  thermodynamical grounds  The by  theories  be  a  energy  the  per  condition  becomes n \  Q  i  F i = minimum  (1)  1 where ith  face  of  ^ area  is  the  surface  free  F_. o n a c r y s t a l  energy per  unit  bounded by n f a c e s .  area  of  Thus  the those  faces  will  energy  for  Wulff the  develop which a given extended  energies  of  perpendicular total  theory  V of  the  pyramids  with  P as  total  of  V  free  by showing the a crystal  P within  f r o m P on t h e  volume  the  a minimum t o t a l  surface  free  and  relation  the  between  relative  surface  faces.  a point  Therefore  and  this  the  Considering  to  volume.  G i b b s e q u i l i b r i u m shape  free  the  lead  i t h face  crystal  will  vertex  and  n r —  1  =  energy  the  crystal, of  let  p ^ be  .  Then  area  be  equal  to  the  the  faces  as  bases.  the the  volumes  of  (2)  p . p .  is (3)  E  (J—. F .  = > "TT  Now the  i f  change  one  set  of  i n volume  1  1  faces  grows  d V may b e  at  the  xvritten  expense  of  another  as  (4) dV  = £ ^  F.dP.  1  and  from  (2)  dV  If  we k e e p  =  the  1  3"  (5)  n ? L—  (F-dp. l * i  volume  constant  p.dF.) * i i  df  B  0 a n d we h a v e  (4) a n d (5)  t  p .l d F . l  o 0  (6)  from  -  From  (1) if-, t h e  neglecting  total  any v a r i a t i o n  6  free  energy  <J  of  -  with  is  constant  we h a v e  F  n  Thus f r o m possible  to  (7)  ( 6 ) and  equations  (7) the  v a r y F - i n d e p e n d e n t l y must  faces  be  n  so  for  the  perpendicular proportional This growth  picture  of  for  is the  only If  not  to  grow i f  If  energy  crystal  will  the of  a step  melt  (due  the  re-entry  are  appropriate  the  surface  to  crystal,  velocities  of growth of  theory  free  faces.  of  normals  are  energies.  the  crystal  a crystal  in  crystal  will  we c a n c o n s i d e r t h a t  evaporation i s plus  on the  temperature)  energy,  growth can take  melt continually  of  solid  an i d e a l  along which  the  But i f  to  rate  interface  energy  melt.  specific  the  the  d i r e c t i o n s of  applicable only  latter  and e n t e r i n g  binding  evaporation  is  of  the  the  surroundings.  is  a solid,  leaving  the  its  there  i n the  any f i n i t e  c o n s i d e r i n g the  agitation.  plus  for  energies  on a c r y s t a l  appropriate  criterion  with  free  that  faces  the  true  Gibbs  we h a v e  are  implies  is  that  a polyhedron such that  a point P, within  specific  different  equilibrium In  the  from  it  ( 8 )  should form  distances to  proportional This  crystal  which  situated  Pi^Gcrr Therefore,  by  the  the  energy  other is  less  crystal  due  to  greater of  place. molecules  thermal than  the  re-entry,  the  hand,  the  energy  than  the  binding  will  grow.  of  Consider  energy the  binding faces  e n e r g y t o be  are  being  energy w i l l So  that  be  i f the  energies  along  a t t r a c t e d by  adjacent  g r e a t e r than with the  the  greater  step  are  i s due  t h a t f o r c r y s t a l growth as  a seed  and  We  should  next  the there  a supercooled consider  commonly, n u c l e a t i o n .  Ey  molecular  l a y e r depends on  molecular  island  the  large the  given  cooling  result  nuclei.  grow.  will  of  take degree  use In  up  the  be  a single  T h u s , i f we  can  be  small  binding  face  The  only.  only.  on  liquor.  of  If  this  disappear  the  out  of  a single large  nuclei! will  island.  i s small  a l a r g e degree  be  this  grow f a s t e r t h a n a s m a l l  produce  the  l a y e r can  size  place  we  s e e d s o r more  of s u p e r c o o l i n g .  take  The  Thus  mother  a molecular  a l a r g e degree  of  started  the  move the  for  supercooling  at a r a t e not  the  crystal,  single crystal  melt.  the  a face  of the  volume of a m e l t , a s i n g l e c r y s t a l w i l l  the  attracted.  super-  nucleus and  the  crystal.  produce  we  being  a s t e p formed  a snail  crystal,  binding  supercooling.  place.  t h i s manner, t h e n ,  A l l other  three  available material starving  i n a s m a l l volume s h o u l d  t h a t may  degree  production  i s large i t w i l l  will  the  a crystal  t h a n on  should  or  of a s t e p ,  a step  volume i n w h i c h g r o w t h may  nucleus  small  the  face  t h a n on  supercooling,  upon w h i c h g r o w t h nay  i f two  s o l u t i o n f o r the  the  deposited  If  one  advancing  along to  then  molecules,  only  g r o w t h i s by  energy of r e - e n t r y  face  -  a f u n c t i o n of a r e a ;  Thus g r o w t h i s more l i k e l y  see  7  rest  faster will  of the  supercooling grow.  melt  than the  If,  i n t o the  growth r a t e  grow t h r o u g h o u t the  in having region of  whole  -  This single nucleation first  8  -  then depends on the two  that the degree of s u p e r c o o l i n g  minimum value  and  conditions,  reaches at l e a s t to some  second, that the volume i n which c r y s t a l  growth i s t a k i n g place Thus, i n theory  i s smaller  than some maximum.  i t w i l l be p o s s i b l e to grow a s i n g l e c r y s t a l  throughout the whole melt i f the n u c l e a t i o n requirements of a large s u p e r c o o l i n g  i n a very  small volume can be  met.  Chapter III 1  Experimental  A. General j I  The Stockbarger (2) method of growing crystals has  been successfully used f o r growing many types of single crystals.  In this method a s t a t i c temperature  program  i s set up on a v e r t i c a l axis through two furnaces, one above the other.  The upper section of the program ( i n  the top furnace) i s set about 50°C above the melting point of the material being used.  The lower section  (in the bottom furnace) i s about 50°C below the melting point.  The temperature gradient between the two sections  should be about 100°C i n one inch.  The temperature i n  the lower section should be reasonably constant f o r several inches of length along the a x i s .  The time v a r i a t i o n of  <r°c temperature should be better than  (£3^ over a t h i r t y  minute period or longer. When a suitable program i s developed a crucible i s lowered through the freezing point a f t e r the contents: has been well melted i n the upper furnace. To start a single c r y s t a l growing the amount of supercooling i s adjusted by setting the temperature of the plateau i n the lower furnace to the number of degrees below the freezing point to produce a single nucleus. The following are the steps taken i n attempting to  -10 f u l f i l the requirements  stated above.  B. Equipment. ( i ) FURNACE The f i r s t furnace used was fourteen inches i n diameter and fourteen inches high, outside dimensions.  It  consisted of an alundum core one and one half inches inside diameter and one and three quarters inches outside diameter around which was wound a platinum heating element. surrounded  with a bulk insulation made by  This was  Johns-Manville  c a l l e d S i l - 0 - C e l C - 3 which was contained i n a cylinder of sixteen guage galvanized i r o n .  The bottom of the cylinder was  a piece of quarter inch t r a n s i t e , fourteen inches outside diameter and two inches inside diameter.  The top of the S i l - 0 - C e l  was surmounted by a layer of f i r e - b r i c k sawed to form a segment disc and a disc of quarter inch transite with a f i v e inch hole i n the centre.  A plug of porous f i r e brick closed  the top of the alundum core and a shaped f i r e brick f i t t e d the brick and transite superstructure.  into  Each of these plugs  was bored to permit passage of a nickel lowering wire. The heating element consisted of number twenty two Brown and Sharpe guage platinum wire wound two and  one  quarter turns per inch f o r the top seven inches and two turns per inch f o r the bottom seven inches at the point between the two windings a c h i l l ring was placed.  This consisted of half  inch thick Alpha brass twelve inches i n diameter with a two one half inch centre hole.  and  The space between the c h i l l ring and  11 and the furnace core i s f i l l e d with a c o i l of nichrome wire. Opposite the c h i l l ring and inside the furnace i s a s i l i c a diaphragm one quarter inch thick, one and one half inches outside diameter, and f i v e eighths inch inside, diameter which separates the two sections of the furnace. D i r e c t l y below the s i l i c a diaphragm the c o n t r o l l e r thermocouple (Pt - Pt 10% RL) i s inserted.  The bottom of the  furnace tube was blocked by a piece of fine b r i c k . The temperature  program was charted by lowering  a thermocouple down through the furnace, measuring the T - C output on a Rubicon potentiometer, and converting this to temperature.  The program shown on graph 1 with unbroken  l i n e was measured f o r the furnace described above. This program was not considered s a t i s f a c t o r y ; f i r s t , because the gradient was not steep enough; second, because the temperature  i n the upper chamber was not pro-  perly distributed; and f i n a l l y , because the plateau i n the lower furnace was not long enough.  Coupled with the above  three objections the time v a r i a t i o n i n temperature  at any  one pint was too large, as shown by the spread indicated on the curve.  To reach a proper program i t was intended to  attempt to correct the temperature dotted l i n e on graph 1.  traverse to follow the  - 12 F i r s t a s i l i c a tube was. inserted into the lower furnace to increase the heat content.  In this way  i t i s intended to reduce the time variations of temperature to a minimum.  Second, a s t a i n l e s s s t e e l tube was i n -  serted i n the upper furnace. This was also to increase the heat content of the upper furnace f o r better temperature control.  But more than that, i t was intended to cause a re-  generation i n the furnace by conducting some of the heat downwards.  F i n a l l y by blocking the bottom of the furnace  to reduce updrafts, thermal currents were reduced. The result of these changes i s shown i n graph 2.  F i r s t , the plateau i n the lower furnace has been exten-  ded to an acceptable minimum length.  Then the gradient has  been steepened to 85°C i n one inch and the maximum temperature i n the upper furnace has been reduced by 40°C, resulting i n a better temperature d i s t r i b u t i o n i n the upper furnace. And f i n a l l y , the time variations of temperature have been reduced from  at lOOOOC to  at 1000°C.  This new program was considered to be just acceptable.  To improve on t h i s program i t was considered  necessary to rewind the heating c o i l which would require new platinum wire since the present material was baked on with alundum cement and could not be reclaimed as wire. It was decided at this stage to make an attempt  - 13 to produce a c r y s t a l .  This attempt w i l l not be described  further at t h i s point but w i l l come under further sections of t h i s chapter, such as "materials" and "technique".  But,  i t i s s u f f i c i e n t to say that the attempt to produce a crys t a l was delayed by the furnace element open c i r c u i t i n g . This was due to an expansion of the alundum core when the s t a i n l e s s s t e e l insert corroded at the high to which i t was  subjected.  temperatures  An oxide layer was  deposited  between the tube and the core which produced the pressure to break the alundum core. Thus, a second furnace was b u i l t .  It was  intended to use the experience of the f i r s t furnace to improve the program to something approximating curve on graph 1.  the dotted  To do t h i s , no extreme changes i n design  were requied, except to change the d i s t r i b u t i o n of the heating c o i l to introduce the power into the furnace i n a more favorable fashion. This change was not calculated, but a judicious guess from inspecting graphs 1 and 2 suggested that more power was needed from the nine inch mark to the fourteen inch mark and from the four inch mark to the seven inch mark.  To do t h i s the new winding was distributed on the  core such that at the bottom of the c o i l i t was two turns per inch reducing gradually to one and three quarter turns  - 14 per inch at the seven inch mark.  Then the c o i l increased  to two and three quarters turns per inch reducing gradually to two and one quarter turns per inch at the top.  At the  seven inch nark a space of three quarters of an inch was l e f t on the core without winding on i t . the c h i l l ring was  At t h i s position  to be placed and the c o n t r o l l e r thermo-  couple inserted. The platinum was not baked on with alundum cement this time but was  tacked to the core at several  places with Saureisen porcelain cement.  The core used to  support the winding was again made of RA 98 Norton Alundum but this time i t had an inside diameter of one and one half inches and an outside diameter of two inches with a length of fourteen inches. before.  The furnace was now reassembled  as  In addition the lower furnace had inserted i n i t ,  in place of the s i l i c a tube, f i r s t a piece of alundum tubing then a piece of monel tubing.  This was a l l held up  in place by a s i l i c o n plug that closed completely the bottom of the tube producing, e s s e n t i a l l y , a dead a i r space in the furnace.  In the upper furnace the same inserts as  in the lower furnace were made.  These inserts were to both  increase the heat content of the furnace and provide regeneration i n the furnace and thus a more even temperature distribution. The new temperature program i s recorded now  on  - 16 graph 3 .  I t i s seen f i r s t that i n the lower furnace  there i s a plateau at least three inches long, of a constant temperature. the furnace.  This w i l l be the annealing section of  The gradient i s approximately  degrees i n one inch.  one hundred  For about four inches i n the upper  furnace the variation of temperature i s approximately t h i r t y degrees, or e s s e n t i a l l y constant f o r the melting section of the furnace.  The large drop i n temperature  in the f i r s t three inches and the l a s t two inches i s an effect which could have been compensated f o r to some extent with a wiser choice of taper on the heater windings. The time variation of temperature has also been reduced with the increase i n heat content of the furnace by adding the inserts and increasing the thickness of the alundum core.  The measured differences i n temperature at  nine hundred degrees i s now t- 1.5°C over a period of s i x minutes f o r the cycle.  The problem of improving t h i s w i l l  be discussed under controls i n the next s e c t i o n . A Dexion rack was b u i l t to hold the furnace and a n c i l l a r y equipment such as the dropping mechanism. The rack was mounted on rubber casters to reduce shock. The dropping mechanism was made from an e l e c t r i c clock. It was mounted on a flange which was attached to a moveable p l a t e .  This plate was mounted on another moveable  plate that could be moved at right angles to the f i r s t and  also locked.  The whole was mounted on the top of the  Dexion rack.  (See photograph 1 ) . F i r s t , the whole mechanism could be moved to  give a rough p o s i t i o n a l adjustment.  Then a f i n e adjustment  can be made with the moving of the two plates at right angles such that any position i n the ^"Yplane may be selected. In t h i s way the crucible can be positioned exactly i n the furnace to drop a x i a l l y down the furnace without having contact with the sides.  This again i s to reduce mechanical  shock to a minimum, ( i i ) CONTROL To control the furnace temperature two essent i a l s are necessary.  F i r s t , f o r the s t a t i c program the  temperature must be able to be held constant. The time v a r i a t i o n i n temperature about the median should be less than -©35^ over a period of a half hour or longer.  Second,  the temperature must be able to be reduced at a controlled rate f o r annealing a f t e r the c r y s t a l i s made.  To do both  of these a Wheelco Potentiotrol, which was available, was used. The essential p r i n c i p l e of t h i s control i s electronic i n nature.  The output of a Pt - Pt 10$ Rh  thermocouple which i s inserted i n the furnace i s applied to a moving c o i l galvanometer.  (See diagram 1). A metal  - 11 f l a g i s fastened to the c o i l and swings so that i t passes through the pickup c o i l s , varying the inductance.  This  causes variations to an electronic tube (presumably a D.C. amplifier) which i n turn operates a relay which i s cascaded with a micro switch, and this operates the on - off relay of the furnace. As the temperature increases, the output of the thermocouple increases, swinging the metal f l a g .  When  the preset temperature and the temperature of the thermocouple coincide the f l a g varies the coupling so that the tube operates the relays cutting off the current.  When  the temperature of the thermocouple i s reduced due to radiation and conduction the f l a g swings out from the pickup c o i l s varying the inductance, operating the e l e c t r o n i c tube, actuating the relays and turning on the current i n the furnace heaters. The s e n s i t i v i t y of t h i s control i s s u f f i c i e n t f o r c o n t r o l l i n g the furnace to the s p e c i f i c a t i o n s l a i d down but f o r the i n e r t i a l e f f e c t .  This i s to say, the  temperature of the furnace tends to swing past the l i m i t s set by the c o n t r o l l e r causing a larger v a r i a t i o n i n temperature than that at which the c o n t r o l l e r reacts.  This i s  due when heating to the temperature difference between the element and the furnace averaging out as a function of t h e i r heat capacities.  When cooling t h i s i s due to a f i n i t e heating  time being necessary f o r the element and the surrounding volume.  - 18 This v a r i a t i o n i n temperature was  evident  on the f i r s t boule when i t resulted i n rings being made on the outside of the boule (see photograph 1 ) . correct f o r this the following procedure was  To  adopted.  A rheostat was placed across the points of the current c o n t r o l l i n g r e l a y .  Then, with the  furnace  temperature at the operating point, the Variac which controls the current across the heating c o i l i s reduced so that the heater w i l l not quite increase the temperature of the furnace.  The Variac then i s adjusted so that  the current i s about one half ampere above this point. Then the rheostat i s adjusted so that the current i s one half ampere below this point with the relay open. w i l l give a control of the temperature to within  This 1°C at  90C-OC. This v a r i a t i o n follows the cycle of one and  one  half minutes at high current with t h i r t y to f o r t y minutes at low current, depending on the temperature of the room which varies throughout the night as the heat was  turned  off i n the b u i l d i n g . In the i n i t i a l heating of the furnace, to the temperature c o e f f i c i e n t of resistance of the voltage across the furnace must be kept low.  due  platinum, But  as  the temperature of the furnace increases and thus the resistance increases i t i s necessary to raise the voltage  so  that the power input to the furnace i s s u f f i c i e n t to keep the temperature increasing.  This i s accomplished by  having  - 19 a Variac across the input, thus the voltage across the c o i l s can be adjusted.  The maximum current i n the  coils  should not exceed ten amperes. Precautions must be taken i n the event of the furnace being up to temperature and the power f a i l i n g , to ensure that the current does not exceed ten amperes i f the furnace has cooled when the power comes back on.  To do t h i s  a c i r c u i t (see diagram 2) using two relays was made so that one relay held the other relay i n while the current was But on a power f a i l u r e  on.  the relays dropped out and must be  reset by hand before the power w i l l come back on.  If the  power has been off f o r too long a period, the Variac can be readjusted to keep the current below 10 amperes. The disadvantage  of t h i s c i r c u i t was that,  when drop i n the line voltage f o r a few seconds took place, the furnace would be unnecessarily shut down.  To avoid  t h i s d i f f i c u l t y a new c i r c u i t (see diagram 3) was  devised  using an amperite delay switch. The amperite thermal delay switch took approximately time to open.  t h i r t y seconds to close and about the same The c i r c u i t was devised so that the manual  switch across the points of the thermal delay when placed at START would close a l l relays.  When the thermal switch  closed this wculd act as a holding device f o r the others. Now  the manual switch should be placed at RUN.  I f the  power f a i l e d and came back on within thirty seconds, the thermal delay would not have opened so that whole c i r c u i t xtfould s t i l l be operative.  In t h i s time the furnace would  not have cooled s u f f i c i e n t l y to cause a large increase i n current.  But i f the power f a i l e d and stayed off f o r more  than t h i r t y seconds, the thermal delay would open, open c i r c u i t i n g the unit and closing down the furnace. Since several power f a i l u r e s were experienced during this work i t i s suggested that a further addition be made to this control u n i t .  If the power f a i l s i t would be  advantageous'to automatically change over to an a u x i l i a r y supply such as the e x i s i t i n g D.C. supply i n the b u i l d i n g . The suggested c i r c u i t i s shown on diagram 4.  A s t a r t has  been made on this change but has not been completed at t h i s writing. The second essential f o r the control was to be able to reduce the temperature at some predetermined rate.  Again, the Wheelco Potentiotrol w i l l do t h i s .  The  setting of the temperature at which this unit., w i l l control i s done by moving an arm through an arc of several inches. This arm can be locked i n any desired position or can ride on a cam which i s driven by a small synchronous motor. The radius of the cam at any point determines the temperature at which the control operates f o r that s e t t i n g .  The  motor i s geared down so that the cam makes one revolution every twenty four hours.  - 21 The cans are made from sixteenth inch thick aluminum.  A one inch hole i s made i n the centre of the cam  and a key slot i s f i l e d i n the edge of the hole.  The cooling  program i s scribed onto the plate and then the cam i s cut out. The edge of the cam i s then f i l e d smooth. To scribe a cooling program onto the cam two methods were used.  F i r s t , a piece of graph paper was glued  to the aluminum and the curve was l a i d out on the graph paper.  Then the resulting curve was cut out on a band saw.  Since the rate of cooling was continuous i t was found more advantageous to make a j i g out of brass to which the aluminum plate i s clamped.  A post i s placed i n the centre which has  a circumference equal to the differences i n r a d i i of the start and f i n i s h of the cam. Around this post i s wound a piece of fine wire to which a stylus has been attached. The length of the wire i s adjusted to have the stylus at the largest radius on the rotation around the post and the shortening of the wire due to being wound on the post describes a s p i r a l of constant reduction i n radius.  This gives  the type of cooling curve used i n the production of the crystals. No cooling curve f a s t e r than the normal rate with the power turned off i s p o s s i b l e . This i s the one l i m i t on choice of cooling programs.  With any other cooling  program i t i s necessary to reduce the current i n the heating  c o i l (by lowering the Variac) as the temperature i s reduced so as to keep the duty cycle approximately 50%.  This i s  also necessary to maintain the current through the c o i l below the ten ampere maximum, ( i i i ) RECORDING EQUIPMENT Measurement of the temperature programs i n the furnace was made by dropping a thermocouple through the furnace i n place of the c r u c i b l e .  The thermocouples used  were either type S (Pt - Pt 10% Rh) or Type R (Pt - Pt 13% Rh).  The measurement of the potentials generated was  either by a Rubicon or Leeds Northrup potentiometer. The thermocouples were lowered one inch at a time and the pot e n t i a l measurement was taken.  The f i r s t programs were  measured i n this way-and plotted on a graph.  In order  that the programs could be measured i n a way which would more approximate the actual conditions a dynamic method was devised. A Brown recording potentiometer was converted so that the chart drive was four and one half inches per hour and the s e n s i t i v i t y was f u l l scale def l e c t i o n i n 3 seconds. was 0 - 1 0 mv.  The scale on t h i s potentiometer  This was used i n conjunction with a type  S thermocouple which would measure 0° - 1040° C  -  f o r 0 - 10 av range. wheel which was  23  -  The thermocouple was  suspended from a  rotated by means of the dropping mechanism.  The rate of dropping of the thermocouple was  one inch per hour.  A l l the l a t t e r programs were measured and recorded manner.  Then the information was  in this  transferred to the graph  paper. It was  intended  to replace the suspension wire f o r  the crucible by a tube of n i c k e l so that a thermocouple core could be inserted and the thermocouple dropped coincident with the c r u c i b l e .  In this way  the crucible saw  a more exact record of the program  could be made. At the time of t h i s writing  this has not been done. C. Materials. ( i ) GENERAL One  of the main problems i n growing c r y s t a l s i s  obtaining the proper materials from which the c r y s t a l must grow.  The considerations i s , i n most cases, one of purity  of the material.  I f i t i s i n t e n t i o n a l to add a s l i g h t trace  of impurity i t i s a problem to make the material homogeneous. In the case of lead t e l l u r i d e purity i s what we are concerned with. Prepared lead t e l l u r i d e was purchased along with tellurium metal and lead. gram was  As a preliminary check a spectro-  taken comparing the lead t e l l u r i d e against the lead  and tellurium (see photograph2.).  Prom t h i s spectrogram i t i s  evident that the prepared lead t e l l u r i d e contains impurities. So i t was  decided to produce the lead t e l l u r i d e i n the laboratory.  24  -  (ii)  PREPARATION To d o t h i s  and  t e l l u r i u m are  tube of  and  the  the  mixed  contents  tube  action  is  whole  are  heating  evacuated.  the  exothermic  out  glassware  mixture  and  of  the  must  process  be w e l l  used  was  i n a fume  start  upon b e i n g  tongs  i f  be  The  placed at  the  reaction.  started  lead  tube.  is  travels  taken  to  keep  high purity  is  to  cleaned.  closet.  Each  The t a b l e  with for  must  the  end  The  re-  through  a glass  top  h a n d l i n g the  a l l  be  contamin-  gained.  The c l e a n i n g p r o c e s s immersions  sulphuric acid  water.  covered  Glass  glass  A flame to  was s u c c e s s i v e  sodium h y d r o x i d e ,  distilled  quartz  of  mixture.  was f i n a l l y  acid  stoichiometric proportions  in a clean  Precaution ation  -  and  then  s t e p was f o l l o w e d on w h i c h which  the  also  acid, in  chronic  by a washing  preparation was w e l l  m a t e r i a l were  which  in nitric a boiling  A l l  was  in  made  cleaned.  made b y t h e  glass  blower. The subject the only the  to  glass  a l l the tongs  consisted first  first  precautions  had n o t of  attempt  product  been  of  the  laboratory  l i s t e d above.  made  and  the  cleaning  a boiling  i n chromic a c i d .  was  a lead  still  For  The  t e l l u r i d e which  was  not  instance, process result  of  contained  impurities. A second was m a d e .  This  time  attempt  at  producing lead  a l l precautions  were  taken  as  telluride listed  above.  -  25  -  Besides t h i s , a flame was played on the mixture at the end of the evacuation process to heat i t gradually and thus t r y to drive any trapped a i r out. The second attempt at making the lead t e l l u r i d e was successful.  According to the spectrogram  taken, a high degree of purity had been gained, ( i i i ) TESTING The method of testing f o r p u r i t y was spectroscopic.  From the H.I.T. Tables of Wavelength of Spectral Lines  two separate tables were compiled;  Table 1, the Spectral Lines  of Lead and Table 2, the Spectral Lines of Tellurium. These were used along with the P r i n c i p a l Spectral Lines of the elements from the K.I.T. Tables f o r checking the purity. The spectrograms  were taken on a Hilger Spectro-  graph with FII Spectroscopic plates. in a cored carbon open arc.  The material was excited  The current through the arc was  adjusted to a constant to .give approximately the same excitation f o r each sample.  For c a l i b r a t i o n the iron spectrum was  photographed. The methods used f o r checking f o r impurities were by comparison.  On the f i r s t plate Lead, Lead Telluride  (purchased), and Tellurium spectrin  were placed side by side.  The lead t e l l u r i d e was checked f o r l i n e s that did not appear in lead and tellurium separately. l i n e s were checked against  The wavelengths of these  principal  l i n e s of elements.  t h i s way the impurities were i d e n t i f i e d .  In  As a further check  the  lists  of  spectral  and  2 established  i f  pared  and  lead  each  2 is  prepared  4 and  other  5 compare  and  against  I  -  print  plate  IV -  2;  print  5;  group  tially  free  crystal D.  of  telluride  the  (i)  plate  Growing  the  lead  to  a method  up  3;  V -  print  6.  lead  these  plate  plates  lead  T h i s was  things  it  to  and  pre-  also  tellurium.  PbTe's  1 - 5  against  III  it  are -  the  shown  print  is  seen  telluride  is  material  is  It  as  4;  that  the  essen-  used  withstand with  the  also  necessary  to  lead  telluride.  To d o  this  variables  is  very  to  contain  to It  the  the  in  the  must  having  was  the  intended  a minimum. with  melt  oxygen  i n an i s made  or b e t t e r . be  and  develop  Because  capsule  1200°C  to  it  reactive  highly toxic.  from which  temperatures  furnace,  now o n l y r e m a i n s  crystal.  reduce  is  an a c c e p t a b l e  it  telluride  The m a t e r i a l  react  produced  g r o w i n g the  temperature.  capsule.  not  laboratory  Technique,  Lead  to  lead,  PbTe.  print  telluride,  for  able  against  process.  technique  two  tellurium.  telluride;  of plates  prepared  or  1  GENERAL  prepared  high  lead  prepared  -  of  lead  iron  against  prints  from i m p u r i t i e s .  Having  set  to  3 compares  purchased  II  laboratory  growing  Crystal  Plate  purchased  On i n s p e c t i o n second  belong  two l a b o r a t o r y  plate  t e l l u r i u m i n Tables  a c a l i b r a t i o n of  Photographic Plate  and  did not  against lead  lead  telluride.  telluride  laboratory Plates  lead  of  a line  Plate tellurium  lines  26  able  to  of  these  evacuated must It  be  at  be  must evacuated  . and  sealed  after  was u s e d .  1 cm d i a m e t e r this  into  75°  to  and  then  or  cone.  were  sealing. inch  bore  It  the on  99% SiC>2 a n d  about  d r a w n down t o  tip  with  had s t r a i g h t  about  walls  1 mm d i a m e t e r  again  to  called  tubing  an a n g l e for  with  of  about  about  bore  1 cm d i a m e t e r  t e l l u r i d e was g r o u n d i n t o It  was a b o u t  capsules,  hours  at  they  500°C.  was t h e n  put  two t h i r d s  other to  sealed  off  assist  in  were  This  cases  into  full.  attempt  and a  placed  was t o  a flame to  After  to  3  inches  permit  for  another  drive  ring  of  so was  In  of  the  case  a l l oxygen out  quartz  a  that joined the  first several  of  the  capsule.  capsule  for  several  out.  b e i n g x-rell e v a c u a t e d ,  small  capsule  The c a p s u l e  was p l a y e d on t h e  is  the  capsule  attached  to  is  the  top  to  lowering. is  a c h i e v e d by suspending  from  a nichrome wire eighteen  from  a cord  which  rotated  b y means  hours.  In  this  is of  would a clock  inches  around  so f a r  were  motor;  controlled. from  .96  long.  a small  way b y c h a n g i n g t h e  o f d r o p p i n g c a n be  vestigated  the  a powder w i t h  i n an o v e n and b a k e d f o r  d r i v e a l l oxygen  Lowering  rate  telluride.  The g l a s s b l o w e r f o r m e d  a v a c u u m s y s t e m and pumped d o w n .  minutes  lead  comes as  1 mm w a l l .  increased  and p e s t l e .  the  the  so.  three  In  is  with  specifications a material  The c a p s u l e  The b o r e  capsule to  -  having a pointed  Lead mortar  these  and  capsules  the  27  h a v i n g been f i l l e d  To m e e t Vitreosil  -  one  The w i r e drum.  of  The r a t e s hour  to  capsule is  suspended  The drum  revolution in  diameter  cm p e r  the  the  is  twelve drum  the  of dropping i n .48  cm p e r  hour.  - 28 -  Seven  runs  have  been In  up t o of  with  preparing  temperature  twenty-four  section  of  the  hours  after  the  is  p o s i t i o n the  with  any p a r t  This  is  reason  to  the  of  the  cord  used  the  is  placed  capsule  that  the  to  annealing  is  started  furnace  the  section  c a n be  c a n be  and  section  of  the  After  the  is  period  is  charged  hottest  twenty-four  to  started, that  melt  capsule  for  rack. any  it  to  completely  necessary is  p e r i o d of  to  act  made  the  drop.  For this as  a  same  shock  absorber.  vertical position a  In  time. i n the  stopped  is  no c o n t a c t  a minimum.  suspension  later  this  way t h e  This  is  p o s i t i o n of  essential  melting section  while  s t i l l  metal  in  so of  the  the  furnace. capsule  the  has  been  clockmotor.  watched  done  over a  i n the  material  to  positioned  with  by s t a r t i n g  at  brought  furnace  of from  throughout- the  furnace  start  This  the  checked  now s h o u l d be  minimum. of  on t h e  capsule  furnace  the  is  begin.  i n the  To a d j u s t scale  a period  mechanical shock  is  itself  positioned  dropping i s  furnace  furnase  Then the  d r o p p i n g mechanism so  reduce  the  is  Again  d r o p p i n g may  the  stabilize  allowed for  Before to  a run  hours.  capsule  furnace.  forty-eight which  forty-eight  and  the  for  and a l l o w e d to  to  a capsule  made.  so-that  by a d j u s t i n g  well  melted,  The t e m p e r a t u r e variations  the  are  "high" and  dropping of  kept  "low"  the to  a  currents  furnace.  of  the  When t h e  capsule  has  a l l reached  furnace,  w h i c h may t a k e  from  the  fourteen  annealing to  twenty-  .four  hours*  position the  the  motor  while  the  stopped.  furnace  is  is  controlled.  recording  A sample  Potentiometer After  ture  the  wheel  and  single  capsule the  is  is  the  is  The  capsule  the  cooling  curve  furnace  removed.  If  left  in  so  that  measured  this cam o n  the  cooling  on t h e  Brown  8.  h a s "been  The q u a r t z  is  A prepared  setting  shown on g r a p h  removed.  boule  .  cooled slowly.  Nheelco P o t e n t i o t r o l adjusts  rate  To  is  29 -  cooled to is  cut  off  successful,  this  room  tempera-,  with  a  will  diamond be  a  crystal.  recapitulate  the  steps  taken:  (1)  The c a p s u l e  is  filled,  (2)  The f u r n a c e  i s brought  evacuated, up t o  and  sealed.  temperature  and a l l o w e d  to  stabilize. (3) A r e c o r d be  taken  the  of  the  at  this  furnace  temperature point  program i n the  by d r o p p i n g a  and r e c o r d i n g  its  furnace  thermocouple  output  on a B r o w n  should through  recording  potentiometer. (4)  The f u r n a c e  is  charged  (5)  The c a p s u l e  is  p o s i t i o n e d and l e f t  will (6)  completely  The c a p s u l e at and  a constant stopped  (7)  The f u r n a c e  (8)  The b o u l e  (ii)  is  is  with  the  capsule. so  that  the  boule  melt. dropped  rate  through  into  the  the  temperature  annealing part  of  gradient the  furnace  there. goes  through  a controlled cooling  program.  extricated,  P R O D U C T I O N RUNS The  first  three  capsules  were  filled  from  a common  source  material,  evacuating to  drive  same put  they  out  evacuated, were  placed  a l l trapped  conditions the  furnace,  reducing  one  variable. Since  the  i n an  the  the  it  be  the  were  for  this  several  for  each  the  being-  thus  each  run,  attempt.  becomes  hours  to  before  identical  reset  While  subject  that  are  be  in level  time.  500°C f o r  assumed  mast  changed,  same  they  capsules  furnace  p r o g r a m may c h a n g e  d i s t r i b u t i o n cannot  Since  c a n be  three  at  oven at  oxygen.  throughout,  into  temperature  and s e a l e d  another  the  But  as  fixed  factor. With upper furnace, complete. long  the  respect only  To e n s u r e  down l a t e r desirable  to  the  effect  is  possible  capsules problems  hut  to  m e l t i n g of  is  been  complete  used so  each  next  repeat  finding  the  the  is  proper  of  that  it  This it  in  the  must  be  an  could  extra be  s h o u l d have  cut no  un-  long.  another  rate  boule  i n a l l cases  desired but  step  the  time.  i n p r o d u c t i n n by b e i n g  variable  is  dropping f o r  dropping rate  is  encountered. subsequent  one  of  the  major  encountered. Finally,  striction  it  minimum i f  In^the It  the  r e s t r i c t i o n on t h i s  that  m e l t i n g p e r i o d has  to  on i t .  It  the  must  annealing program only  not  he  too  is  slow at  two h o u r  cooling  period which  creasing  i n rate  (see  sufficiently  long  to  graph be  Thus w i t h  8)  i t  neglected the  first  fast. the  was f e l t as  a  In  has  one  selecting  a  b e g i n n i n g and  that  the  reseventy i n -  annealing  was  variable.  capsules  the  only  two  varying  -  conditions  were  the In  tribution graph  constant  be  and  -  of drop  dropping  on g r a p h  must  rate  31  the  and  first  4 was p l o t t e d  corrected  for  s h o u l d be  the  mately the in  first 35°C.  degree  run  to  of  empirically.  the  the  the  remains was it  a  is  liquid  heat  This  about  .5  By  adding  points  the  and  and  as  "off"  but  close of  This  only  to  current  is  a  905°C,  approxi-  drop, are  not  remains must  so  Since defined  combination  that  the  interface  at  the  same  be  s l o w enough  away and  level  the  in  so  interface  The r a t e  of  .76  cm p e r  results  of  the  first  hour boule  correct.  rings  were  was f o u n d  to  found be  and  to  to the  was p o s s i b l e  to  second  run followed  the  dropping time first,  first  the  keep  make same  it  constant.. relay  rather  this  and c o o l i n g  than  effect  pattern  a better  boule  variations  control  "low" current  it  were;  on the  due  in parallel with  two changes  is  hour.  such  carried  the  This  This  cm p e r  right  c o n t r o l l e r attempted  The m e l t i n g t i m e , The  from  the  rate  c a n be  having a "high"  The first.  the  a l l times.  resistance  thus  phases  3).  22°C.  telluride  of  be  dis-  readings.  .76  rate  to f i n d  say,  boule  the  the  (Step  supercooling is  was  drop must  solid  series  mm a p a r t .  temperature  of  to  reasonably  in  same.  is  i n the  A  "on"  and  j u d i c i o u s guess be  drop used  necessary  h o r i z o n t a l at  must  of  The r a t e  furnace.  that  maximum d e g r e e . o f  s u p e r c o o l i n g and it  lead  of  supercooling.  temperature  process  a l l graph of  of  the  room t e m p e r a t u r e  added  The r a t e  any l i m i t s  between  the  degree  capsule  i n the  The m e l t i n g p o i n t for  the  rate  as  negligible. the  were  stabilized  the  - 32 temperature  and  second, The  of  the  rheostat  s w i n g was a t o t a l period.  The  degrees  at  that,  of  the  the  of f i f t y  critical It  is  was  time  felt  resulting  out  drop found  large  whole  that  freezing  ten  The  third  made,  but  to  at  by a  possible  was a t  through effect  about  the  on t h e  i n the  not  one  and  a  gradient. boule  degree  upon e x t r a c t i o n from but  6 A.M.  open c i r c u i t  This  a change  crystals  before  for  the lead  the  furnace  of  the  capsule  extending  replaced  furnace.  was  then  at  the  was  keep  the  for  which  had  not  passed  to  that  through-  at  a l l .  it  The  removing the find  temperature  the  after  cooled,  was  the was  circuited  stable set  through  at  and the  thermocouple capsule  new s e t t i n g  needed.  it  open  furnace  that  without  necessary  in  intermittently  to  telluride  and  arrive  than  capsule  was r e p a i r e d  to  fifteen  r u n was u n f o r t u n a t e  temperature  point  controller  reduced  line  minutes.  c o n t r o l thermocouple  In f a c t ,  It  on the  was p a s s i n g  "Wheelco P o t e n t i o t r o l  a much h i g h e r recorded.  minute  melt.  the  the  temperature  way p e r m i t t i n g  had an u n d e s i r a b l e  single  the  in a fifty  ( d i a g r a m 2j) t o  The r e s u l t i n g b o u l e  had been  causing  drop  i n a d i s l o c a t i o n due  up i n t o  the  this  boule  was  addition  degrees.  Circuit about  degrees  in this  voltage  for  supercooling.  s t a b i l i z e d by the  furnace  centigrade  when t h e  that  nucleation. broke  off  the  level  Eains Control  furnace  was  of  when p r o p e r l y a d j u s t e d  of  annealing  A large the  degree  two c e n t i g r a d e  temperature  supercooling  caused  a larger  temperature  such  -  To do  from  the  on  the  this  a  - 33 thermocouple and  was  adjustments  touched opened  the the  removing the  were  capsule  made. near  to  of  the  done  of  w h i c h was  inserted  into  the  the  reaction  furnace.  furnace  was  done  Then by  rest  of  the  by  heating PbTe  was  chanber.  used  product.  were  for  a flame  for  tried  on t h e  separated  made,  the  This  d e s i g n was tip  capsule,  p r e s u m a b l y b y some  1200°C the  new c a p s u l e s  with  the  and c l e a n i n g them.  a temperature  prepared  ball  parts  The m a t e r i a l  c u a t i n g was  round  and  of  sealed.  capsule  tip  decontamination  Three  in  the  The  moveable  alongside  The t h e r m o c o u p l e  melt  out  laboratory  furnace  d i s c h a r g i n g the  furnace  and  i n the  capsule  the  evaporated  inserted  filled,  filling  time  was  the  the  heating  a shorter  period.  i n that  one  from  evacuated first  while A  departure  was b u i l t w i t h  the  main capsule  eva-  a  small  by  a  constriction. Run 4 was similar five the  to  graph 4,  centigrade rate  being  of  done  This  fast  that  cooling Run  solid  dotted aimed  line  line at  to  i n the the  .96  on g r a p h  in building  a possible  cm p e r  hour.  quickly  While i n the  had a d e t r i m e n t a l  It  is  5.  This  is  the  furnace.  r u n was the  of  increase  annealing  the  The p r o d u c e d  note  "ideal"  was  being  on the  d i s t r i b u t i o n as to  thirty-  850°C t o  effect  interesting a plot  to  equipment  c o o l e d from  a temperature 5.  distribution  s u p e r c o o l i n g of  in this  power r e s u l t e d  furnace  5 had  a temperature  The c h a n g e  may h a v e  on g r a p h  with  give  degrees.  a drop  down s o  the  which  dropping  shut  set  500°C. boule.  plotted also  in  the  program  distribution  compares  -  favorably  with  was  used.  the  freezing  was  essentially  the  "ideal".  For  Run 5 the  The a n n e a l i n g point.  due  to  large  control  as  with  centigrade  rate  was a d j u s t e d  interrupted perature was it  6.  to  due  to  set  for  Run the  line  gives  ,48 cm'per  furnace  back  to  to  normal.  This  turning  been  made  This  off  supply and  installed.  p r o g r a m was a d j u s t e d plateau  freezing point.  hour.  The  The c o o l i n g  i n the  minimize  hour.  a mains  an a n a e a l i n g  a power f a i l u r e  below  2.  voltage,  temperature  tip  degrees  . 7 6 cm p e r  ( d i a g r a m 3 ) has  This  on the  dropping  curve  so  that  An a u x i l i a r y  sudden  twenty-  was  The c o o l i n g  area  the  and  drop  to  was  the  tem-  D.C. s u p p l y  6 0 ° and  d r o p may h a v e  bring  affected  the  growth.  up i n  used.  was  60° i n a few m i n u t e s .  For the  The  material filled, of  a delay  t e m p o r a r i l y h o o k e d up  crystal  this  ball  Brown R e c o r d i n g P o t e n t i o m e t e r .  dropped  quickly  in  the  55 c e n t i g r a d e  against  degrees b e l o w the  on t h e  with  was  p r o g r a m as  Run 6 a  on g r a p h  five  recorded  same  a precaution  For plotted  plateau  fluctuations  circuit  capsule  The d r o p p i n g r a t e  the As  -  34  furnace.  capsule  which  temperature  program of  dropping rate  w h i c h was  sealed  the  time  .76  d r o p p e d was f i l l e d  first  and  of  produced  in  the  i n the  same  this  writing  graph  cm p e r with  7 was  hour  the  remaining  laboratory.  way a s  the  was  second  It  was  group  capsules. At  been  made  been  taken  research  The  had been  evacuated  three  Run 7 the  to  produce  single  of  crystals  over  t o make  crystals  i n the  nuclear  resonance  of  no f u r t h e r  of PbTe. other  work.  attempts  The e q u i p m e n t  substances  needed  have  has in  - 35 -  Chapter  IV  Results Of  the  seven  a reasonable very in  poor  amount  success,  a single The  experience  of  that  temperature is  between  quartz  showed  made.  two  It  and  tain  impurities.  It  nucleation  and  quartz,  each  further  these  melts  these  were is  presumably  capsule  tion.  The  top  of  the  discolored  due  to  impurities.  discoloration  d i d not  was  considered  be  the  success  i n part  material  that  used.  for In  In  show u p ,  an  attempt is  had resulted  case  to  a  were  the  of  the  grow  a  reaction  of  numbers  with a material that  the  impurities  the  7. con-  could  structure. place  on  the  showed a  last  first  four  the  first  impurity. blamed  Run 4 i t  Thus  may a l s o  a  was  this  PbTe  on the  as  discolora-  melts  two r u n s ,  In  the  impurity depositing  since  7 is  took  itself  of  4 and  known t o  a poly crystalline  measurable  case  this  a measurement  discoloration  Runs 4 and the  two  No m e l t  In  there  success  i n each  without  had  1100°C.  The b o u l e  boule  and  for  by a v o l a t i l e  wall.  success,  w a s R u n 3.  showed  a heavy  work three  boule.  before  considered  on the  to  whole  performed  caused  some  time  thus produce  capsules  this  completed.  necessity  sludge  of  the  completed the  had  never  runs w i t h very poor  of  of  was  during  one  alundum above  Both  both  not  distribution  crystal  cause  one  throughout  was  gained  attempted success,  and  crj^stal  one  The  melts  sludge used  the  lack  impurity be  that  of the  dropping crystal is  rate faces  one  the  attempt  the  large  crystal core. the  rate  nuclei  suggesting  of  the  impurity  melt. showed  to  be  of  the  some with  success a small This  w a s R u n 5. pilot  melt  long  resulted  the  The r e a s o n  i m p u r i t i e s , but in  the  the  for  was  joined  in a  to  single  a polycrystalline  polygonal p i l l a r s growing  boule  capsule  This  capsule  polygonal pattern  showing i m p u r i t i e s again but  the  produced  that  the  i m p u r i t i e s were  through  of  dis-  presumably pushed  ahead  a polycrystalline structure  also  may b e  due  to  several  small  sphere  and  a l l growing,  at  may  seed not  one. the  note  which melt  was  c a n be  three  that  had  ities  one  slower  rode  the  done  at  in  rotating  these  of  them,  and,  reasonable  R u n 6, w a s made But the  the  others.  It  interface  between  the  than  the  one  is  sections through  time it  crystal.  is  with  with  lead  considered this  light  surface  these is  is  interesting  telluride  that  of  the  which  this impur-  possibly  On c l e a v i n g , t h i s  good cleavage  indicating a  it  dropping rate  two p h a s e s ,  an i n c i d e n t  In fact,  success  presumed  slower dropping rate.  planes  indeed,  a single  with  purity.  several  o n l y maximum a t faces  capsules  a questionable  resulted  for  top  present  to  d i s c o l o r a t i o n of  1 mm t h i c k g r o w i n g a r o u n d  seems  drop  being  Of to  about  is  back  boule,  by a c o n s t r i c t i o n .  On t h e  of  the  a capsule  interface.  refer  just  use  core  coloration  the  to  that  -  Run 7 shows  fast.  Ttfhole  melt  shell  melt.  the  the  one  The  too  throughout  throughout The  of  was  36  of  planes. the at  boule  On  reflection least  is  parallel  to  be  single planes  as  used  as  justification  for  considering The These  other  were  higher  a large  single  two r e a s o n a b l e  produced  degree  c r y s t a l has  of  at  single  impurity  to  auxiliary  the  that  furnace  the  through the  to  is  capsules  whole melt  interesting pure  affect  is  from  cleavage the  square;  another,  millimetres  to  the  for  result  several  note  s t i l l  there  was n o t  In-both  cases It  is  caused  was n o t  large  slightly  These  R u n 6.  that-..both in-large  d i d not  of  the  plane  boule  one, three  square.  amount  of  compound were  ci~ystal  that  contain  the the  coolin  considered the  a single  single crystal  single  crystals  of  boules  making  of  Run S.  throughout  These  results  supercooling, used w i t h the  of  the  the  melt would  sealing.  by  cm w i d e h a s  means of  long  that  four  a centimeter  correct  present result.  This  been  sizeable up  into  millimetres  long  and 5  indication that dropping rate  furnace,  did  manner.  Run 2 b r o k e  and  g i v e an  a  layer  suggesting  obvious  The b o u l e  quarters  after  The  a thin  i n any  This  a centimeter  but  or a s i l i c a t e  .75  containing  crystals.  sludge,  capsule  crystal  the  single  tellurate  1 cm l o n g  c r y s t a l was p r o d u c e d . crystals;  pure  and a  improper annealing  oxygen i n the  growth  several  correct  cases  some  the  A flat  single  R u n 1 a n d R u n 2.  R u n 6.  because  than  compound p r o b a b l y a  there  cleaved  faster  but  for  nucleation.  PbTe r e s u l t e d  i n both  yellow  not  so  were  melt.  relatively  that  done  shatter  the  It  of  was  crystals  strainscset'-up^iby  crystals  up  cause  produced.  dropping rate  supercooling than  in large  of  successes  a faster  resulted  bean  etc.,  a  i f and  the a  single  - 38  -  Chapter  V  Discussion Probably from  the  troller can  be  have the  the  most  work done have  made  It  has  to  be  been  is  important that  been  a furnace  constructed  of m a t e r i a l s seen  (see  i n which  that  from  considered  conclusion that  have  the  d i a g r a m 5)  large  work that  four  i n producing large  and  single  melting points  drawn con-  crystals  under  1400°C.  important  factors  single  crystals  from  melt. • The  used.  first  First,  important the  factor  source  is  materials  one  of p u r i t y  must  be  reached  by c o n s i d e r i n g the  record  o f Runs  5,  7,  during  If  material  made  this  the  during  the  of  the  production i t  a  r e f i n i n g s u c h as  was  presumably  zone  Run 6.  end by  the  This built way  chemistry  work.  In  better  linked  indicates  with  the  need  crj/stal  the  cleanliness can  the  between  c o n t r o l of  Contamination  the  the of  growing i s  to  purity  due  conclusion  2 versus  is  not  Runs  made  4,  pure  made p u r e  experiencedby  the  by  boule  moved a l o n g t o  r e f i n i n g furnace be  carried  material w i l l  i n h a n d l i n g the place  materials  the  phases. a zone  source  This  can be  i m p u r i t i e s are  problem of  take  1,  the  of  the  material  to  on.  be  In  be this  possible.  source during  insufficient  to  material  is  productbn.  care  in  handling  materials. Still  take  manner  interface  i f further  Along  the  this  of  pure.  is  of  c a n be  considering purity  precautions  of p a s s i b l e  of  the  melt,  it  is  chemical reactions  necessary d u r i n g the  to process.  -  Looking  at  the  cleanliness material  before  the  w i t h oxygen. the  be  regarded,  It  PbTe  2 where  a reaction  is  possible  should  be  precautions  and where  the  materials.  for  and  a suitable  purity  took then  done  over  checked  the  these  melt  locations The  place that  of  towards  the  during  the  source the  while passing  material  run  mixture a  warm  R e a c t i o n w i t h the  affects  points  can  of  produce  next in  the  the  large  a  of  also  used  of  dropping.  In  time  is  small,  rate  that  the  single  order of  nucleus  in  capsule  making  that  o n l y one  cooling these  large  and  enough,  dropping  two f a c t o r s  must  be  degree  of  of  other  must  be  be  s m a l l enough  And so are  arrived  be  and  the  increases  by  adjusting  nucleus  production that  of  the  of  the  c r y s t a l l i z i n g at  any  This for  That  criterion  the is  the  produced  wc f i n d  that  factor,  one  grow.  growth.  are  a large  small.  small is  dis-  supercooling,  so  this  volume  impurities  nucleation  of  on the the  crystal  considered  But  which w i l l  rate  the  done.  a nuclei will  can e x i s t .  the  the  be  since  which produces  supercooling  that drop  is  to  in  production  c a n be  c r y s t a l l i z i n g volume  cooling  of  the  c r y s t a l l i z i n g volume  a large  the  necessary  The r a t e  dependent  rate  the  One,  degree  crystal  is  have  nucleation.  supercooling  single  nucleus  that  technique.  rate  degree•of  forming  are  auxiliary nucleation  two f a c t o r s  e x p o n e n t i a l l y w i t h the the  precaution  or p o l y c r y s t a l l i n e structures  variables  of  1 and  capsule. All  in  Runs  c l o s e l y checked,  atmosphere  also  of  strictly  producing  hydrogen must  were  was  presumably  capsules  -  39  production  to  say,  degree  of  which i s  degree  of  i f super-  so  large  super-  interdependent.  The v a l u e s  at  But,  empirically.  it  is  of  -  40-  c o n s i d e r e d from the e x p e r i m e n t a l r e s u l t s t h a t the r a t e of drop f o r PbTe w i t h t h i s f u r n a c e s h o u l d be l e s s than The  .5 cm per hour.  f i n a l f a c t o r which must be c o n s i d e r e d i s t h a t of  annealing.  S i n c e the s t r u c t u r e of the c r y s t a l depends on  i n t e r n a l f o r c e s i n the c r y s t a l , a n n e a l i n g i s i m p o r t a n t .  the The  p o i n t here i s t h a t the c o o l i n g w h i l e i n the s o l i d phase can be too slow.  But on the o t h e r hand, i f i t i s too f a s t  are s e t up i n s i d e the c r y s t a l which may  main not  strains  d i s t o r t the c r y s t a l , r e -  d u c i n g i t to a p o l y c r y s t a l l i n e from a s i n g l e c r y s t a l s t r u c t u r e . As an example of t h i s i n Runs 1 and 2 the a n n e a l i n g was due  to power t r o u b l e .  i n s t e a d of one s i n g l e  too q u i c k  Thus, s e v e r a l l a r g e c r y s t a l s were produced crystal.  I n r e s p e c t to the equipment t h a t has been made, s e v e r a l p o i n t s are worth n o t i n g . now  The  temperature d i s t r i b u t i o n of the  compares f a v o r a b l y to the proposed program.  furnace  T h i s can be  seen  i f we check the a c t u a l d i s t r i b u t i o n (the s o l i d l i n e on graph 5) w i t h the proposed program ( d o t t e d l i n e on graph 5 ) . ment c o u l d be made on a f u t u r e f u r n a c e  An  improve-  (a) i f more power was  i n t r o d u c e d a t the ends to reduce end e f f e c t and  (b) i f the  ratio  of power i n t r o d u c e d i n t o the upper f u r n a c e to the power i n t r o d u c e d i n t o the lower f u r n a c e was The  l a r g e r t o produce a s t e e p e r g r a d i e n t .  temperature c o n t r o l i s v e r y s a t i s f a c t o r y , b e i n g  «^  /°C  v a r i a t i o n over a p e r i o d of f i f t y minutes when a d j u s t e d p r o p e r l y . To i n c r e a s e t h i s c o n t r o l w i t h the e x i s i t i n g equipment i t i s necessary  to i n c r e a s e the r a t i o of the heat c o n t e n t of the  t o the heat c o n t e n t of the h e a t i n g element.  furnace  I t i s considered  that in  very  little  improvement  c a n be  drastic  changes  design. Finally,  large  single  in respect crystals  to  were  the  Success  i n producing  whole  was  met  proper  melt  technique.  discussed,  c a n be  not  is  It  due is  followed  prodiiced w i t h  the  attempts  produced  attempts.  as  made w i t h o u t  to  accidental  a single equipment  make  in. three  a single  concluded  to  that  of  single the  crystal  crystal  the  six  from  proper  throughout  described  completed  throughout  variations i f  crystals,  in this  the  the  technique:,, the  melt  thesis.  -  42  Table  -  I  S P E C T R A L L I N E S OF L E A D C o m p i l e d f r o m M I T 'T a b l e o f W a v e l e n g t h  Intensity CUT) Arc Spark  Class  Intensity (MIT) Arc Spark  8 20hl  100 10 2  7229.11 7193 .6 7165.1 7114.7 7099.78  II II II II  40 50 2 10 15  7050.7 7013 .2 6872.0 6790.8 6785.9  II  '20  II II  3  500 25 15 25 35  6660.0 6569.4 6558.7 .6527.8 6518.2  2 25  6433 . 6 6422.9 6345.0 6342.0 6339.8  50  10  3  3 15 40 20 50 5d od 30 lOh 50 15hl 2d  6311.5 6235.44 6229.7 6203.7 6198.8 6181.9 6169.4 6160 6110.78 6094.0  •  Band head II II Band head II  II II  10 3h  6007.5C  II  20 6  Class  •  5910.7 5895.70 5857.67 5767.9 5713.8  Bandhead I II II  40 8 40 25 25 lOh 40  5544.6 5523 .5 5472.4 5372.5 5372.1  40 20 2h 2  5367.3 5353 .8 5306.8 5201.44 5191.4  20 25 8 25 4h  5189.2 5163.8 5162.3 5155.8 5143 . 1 4  II Band head II  5138.2 5109.6 5081.2 5074.6 5070.7  Band head II II II II  3 6 6 40 . 40  II  II II  6001.88  10  Wavelength  5692.26 5660.1 5617.7 5608.8 5545 .1  3  II II  6075.8 6041.4 5011.98  2 20 40 10  4  II II II II II  200 3 5d 25hl 40hl  Wavelength  10 35 20 4  5063.1 5049.3 5032.2 5005.43 4983 .8  II Band II  head  II I II II II Band head II II  I II II Band  head  -  Intensity  (Km  Arc  Wavelength  43  Class  Spark  -  Intensity (JUT) Arc Spark  Wavelength  Class  3 10 5 10 5  4195.5 4168.045 4152.93 4141.42 4128.21  II  4 5 5 2 20  4113.27 4110.77 4094.68 4077.61 4062.144  II II  300r 6 5 30 5 Oh  4057.820 4019.639 3 9G7.5 3 971.3 3 951.94  I  3 2 6 5  4912.7 4895.6 4836.3 4833 .7 4816.9  8 10 20 5 6  4804.5 4802.23 4798.52 4798.4 4788.1  II  I II  20  5 5 2 10 4  4684.9 4665.5 4605.43 4582.34 4581.3  II II  2000r 6  10 7 2  4579.15 4571.72 4557.2 4553 .7 4544.8  II I II Band head II  5 2 2 40 2  3943 .80 3927.79 3925.23 3909.17 3896.9  2  4534.69 4476.3 4428.7 4410.4 4386.0  II II Band head II  5 2 2 100 5h  3894.6 3874.65 3872.64 3854.053 3341.91  10 3 6 7 30  4352.7 4351.5 4296.71 4293.34 4272.63  II II II  60 50 2 20 lOh  3841.62 3832.83 3829.2 3827.2 3786.243  2 10 2 2  4272.55 4242.47 4242.20 4232.43  II II II II  10 60h 10 20  3784.0 3739.947 3734.8 3723.83  II  2  3723.87  I  4 5 3 2  4229.0  II II II II Band head  20  II II  T  Band  150  head  II  II II I  II II II I  II II II  II I  -  Intensity (MIT) Arc Spark  300 50  300  200  44  -  Wavelength  Class  Intensity (MIT) A r c Spark  10 10 401 5 2  3714.05 3699.2 3689.309 3689.201 3639.0  II II II  50 2 7 70 2  3683.471 3674.95 3671.503 3671.39 3665,485  I  2 5Oh 5 20 30  3665.05 3639.580 3620.35 3601.8 3593.12  I I  3 40 20 20 5  3592.921 3S89.92 3586.44 3572.734 3567.1  20 2 5 5 10  3562.89 3533.91 3530.35 3505.15 3501.9  30bh 30 2 50 2  3485.7 3483.39 3476.25 3463.6 3453.0  II II  3118.92 2 3118.19 lOOea 3117.7 2sx 3111.38 10 3102.874  10 80 10 10  3451.90 3451.70 3451.619 3450.0  I II II II  30 20 10 lOsx  3089.093 3087.039 3068.5 3062.44  10  3437.36  I  2sx  3061.13  II  II  II  2 5 29bhl lOea 15sx  3431.35 3429*6 3401.9 3389.4 3361.58  15ea lOsx 5hkl 60sx  3309.2 3279.33 3276.44 3276.19 3262.353  2sx 50ea 40sx  3261.21 3251.0 3242.86 3232.353 3231.23  20h  30kl lOsx 5sx  I  5h  Class  II II I II  15ea 2sx 2  3227.08 3220.538 3217.9 3190.89 3190.06  II  lOOkl 2ea lOsx lOOkl 3sx  3176.54 3173.5 3145.60 3137.83 3129.63  I II I I I  50h  II  Wavelength  I I II  -  Intensity  Wavelength  Class  3 043.90 3031.65 3025.61 3017.46 3 016*4  I  (JUT)  Arc  Spark  100 20sx 2sx 10  -  25ea 2sx 10gs 20ea  3010.19 3 002.74 2986.9 2980.16 2973.00 .  125 lOea 10gs lOOr  2948.719 2926.646 2914.5 2887.19 2873.316  20ea 5 60 2sx 2ea  2873.0 2868.148 2864.257 2860.64 2S45.2  20  2840.66 2833.069 2823.189 2802.003 2772.71  2 2kl  2hkl  500r 150r 250rh 2 20ea 2hsx 15wh 5 3-00wh lOOkl  2717.5 2717.37 2697.527 2684.76 2663.166  5hsx 2 20ea  2650.4 2650.26 2637.72 2634.3  50hz  2628.263  45  Intensity OUT) Arc Spark  200r 50r 100  2614.178 2613.653 2608.4 2577.263 2576.55  10 100 2sx 2sx 2sx  2568.43 2562.28 2550.29 2534.78 2527.03  lOOgs 5sx 2sx 2sx  2526.62 2508.90 2500.50 2495.58 2476.379  20sx  lOOw lOhkl  2461.51 2446.188 2445.1 2443.838 2428.644  75hz 50 35 2500 40  2411.735 2401.946 2399.583 23 9 3 . 7 9 4 2388.774  5ea lOOwh II  II II  II II II 150wh  1 5 Own 2ea II II I I II II  II  Wavelength  60  4  3 3 2h  2359.58 2332.426 2296.85 2280.85 2257.50  II  40 3 Or 15 50w  2253.95 2246.888 2242.610 2237.426  II  50  2218.08  Class  -  Intensity (KITT Arc Spark 5000r 50 6 40w lOOOr 15 3 Or 15 20w 3 Or 12  201g  8r 12 5  Wavelength  2203.505 2187.85 2181.66 2175.58 216S.994  Class  II II I  2159.52 2115.02 2112.03 2111.74 2088.43 2087.58 2074.0 2061.74 2053 .32 2022.07  I  46  -  Intensity OUT)  Wavelength  Class  - 47 Table II SPECTRAL LINES OF TELLURIUM Compiled from KIT Table of Wavelength Wavelength  Class  18 35 5 30 15  7280.9 7191.08 7144.61 7135.34 7103.43  I I  5  70  Intensity (MIT) Arc Spark  5 70 50 15 — i  o  Intensity (MIT) Arc Spark  Wavelength  15 5 30 100 15  6659.80 6658.07 6649.72 6648.52 6640.59  7097.57 7049.68 7038.95 7015.89' 6959.08  50 50 181 5 30  6637.00 6628.7 6613.4 6603.04 6596.32  6930.51 6924.66 6913.18 6885.04 6877.94  30 15 30 501 121  6584.93 6587.63 6574.50 6563.95 6553.5  5 30 100 5 15  6546.59 6541.89 6537.01 6528.35 6491.81  30 30 50 5w 5 501 70 50w  6870.56 6867.53 6854.7 6843.94 6837.65  30 5 5 30 50  6832.46 6796.66 6782.54 6761.34 6751.40  70 30 3L 7 5  6487.09 6474.28 6469.13 6462.9 6457.80  30 30 5 5 7w  673 6.32 6708.34 6688.49 6687.36 6686.7  15w 5 1000 70  6456.7 6446.7 6437.06 6422.96 6409.4  30 70 5 50 30  6686.03 6676.01 6672.70 6670.6 6661.06  18 50 15 70 5  6405.9 6396.46 6390.19 6367.10 6363.93  I I I  Class  I I I I  - 48 -  Intensity (JUT) Arc Spark  Wavelength  30 5 5 30 3  6345.51 633 0.04 6324.38 6298.64 6277.7  18s 70 30 30 12  6273.41 6266.21 . 6260.51 6259.44 6255.9  150 15 300 50 30  6245.61 6243 .24 6230.80 - 6221.48 6211.49  Class  I  I •-  /  1  Intensity (MIT) Arc Spark  Wavelength  15 30 50 5L 100  6106.55 " 6082.45 6073.35 6055.82 6047.44  30 7w 30 100 3L  6022.06 6020.8 6019.51 6014.49 6013.49  30 15 15 75 75  6008.62 6007.97 6001.34 5993.94 5993.12  75 250 50 25 75  5985.64 5974.70 5972.64 5954.96 5936,21  15 70 5 5 50  6203.29 6202.29 6195.05 6187.56 6183.39  30  I  5 15 100  6180:58 6181.94 6171.83 6167.24 6166.84  15 8L 25 15 8  5 932.22 5925.25 5896.65 5891.43 5888.89  3w 12w 15 70 2  6162.4 6160.2 6155.16 6153.89 6148.1  I I I  3s 15 15 8 50  5874.6 5871.80 5866.11 5859.7 5858.55  5 30 30 15 70  6146.57 6144.32 6142.24 6140.28 6136.31  I  75 8 25 15 25  5851.09 5845.02 5843.31 5835.16 5828.63  Class  I I  Intensity  OUT)  Wavelength  Arc Spark  Class  Intensity  OUT)  Wavelength  Arc Spark  50 50 50 9 8  5826.45 5824.19 5803.07 5789.22 5787.05  8 50 15 75 8  5480.83 5479.13 5465.17 544 9.82 5426.05  8 15 35 6 70  5785.23 5777.25 5770.92 5769.1 5765.25  25 25 15 8 8  5410.41 5366.91 5366.28 5350.41 5321.02  25 15 250 8 8  5763.92 5762.60 5755.87 5746.31 5745.75  25 15 25 8 15  5304.99 5303.72 5256.36 5244.21 5238.07  70 8 8 25 15  5741.66 5733.5 5692.96 5679.71 5672.24  8 15 8 8 8  5219.46 5172.99 5164.00 5149.90 5148.7  15 50 25 25 25  5667.86 5666.26 5655.15 5652.06 5651.51  8 15 8 8 8  5133.23 5130,99 5112.12 5065,74 5060.44  250 25 , 25 15 15  5649.30 5630.66 5618.47 5592.90 5582.77  15 8 25 15 30  5037,97 5020.44 5000.87 4925.25 4919.12  8 15 8 25 50  5580.46 5569.38 5565.57 5536.73 5488.07  15 30 150 70 15  4912.05 4901,14 4894.94 4893.58 4875.53  Class  - 50 Intensity (JUT) Arc Spark  Wavelength  Class  Intensity (MIT) Arc Spark  Wavelength  800 50 800 50 800  4866.22 4865.13 4864.10 4842.88 4831.29  15 50 50 15 30  4550.36 4546.64 4537.07 4535.83 4529.54  50 70 70 50 30  4827.14 4796.10 4784.85 4771.56 4769.73  15 30 50 30 30  4522.22 4514.05 4498.59 4489.33 4485.77  150 15 50 70 50  4766.03 4765.03 4738.67 4731.27 4729.83  800 15 70 50 50  4478.73 4455.28 4434.96 4411.78 4410.95  15 70 70 300 15L  4726.91 4711.16 4706.53 4686.95 4681.06  15 100 70 100 70  4405.49 4401.89 43 98.45 4396.00 4377.10  15 30 800 15 70  4676.88 4670.11 4654.38 4645.22 4641.19  50 30 400 50 30  4373.00 4368.09 43 64.02 43 61.27 4349.29  50 15 800 15 70  4630.57 4621.27 4602.37 4586.98 4569.71  15 15 30 30 30  4346.86 4332.54 4325.77 4323.79 4321.96  15 300 30 50 15  4562.45 4557.84 4555.27 4552.10 4551.04  70 70 70 15 50  4294.25 4293.35 4285.84 4279.48 4276.68  Class  -  Intensity (MIT) Arc Spark  Wavelength  Class  51  Intensity (MIT) Arc Spark  Wavelength  70 30 300 50 70  4273.40 4264.32 4261.08 4256.10 4251,15  5 350 15 15 5  3589.78 3585.34 3552.15 3521.27 3480.28  15 50 100 15 15  4246.47 4238.46 4229.42 4211.32 4197.22  10 5 10 10 15  3456.84 3449.57 3442.22 3438.73 3406.77  30 50 30 15 15  4183.99 4163.53 4127.34 4127.04 4113.60  25 15 50 10 5  3374.10 3365.17 3362.83 3358.12 3356.89  50 3 00 70 15 15  4101.07 4073.57 4048.89 4047.18 4029.73  35 5 35 25 15  3352.11 3350.68 3345,93 3340.07 3323.06  30 100 5 10 10  4011.68 4006.50 3988.33 3981.74 3 975.90  5 5 10 10 15  3301.48 3301.18 3282.67 3278.77 3277.50  10" 10 5 5 5  3969.18 3 947.93 3936.21 3 931.43 3918.50  35 25 5 35 5  3256.81 3229.52 3228.27 8211.20 3201.06  10 25 25 5 5  3644.46 3644.27 3617.55 3612.90 3611.77  10 10 10 5 10  3194,41 3193.59 3193.12 3189.87 3188.37  Class  -  Intensity tar) Arc Spark  Wavelength  Class  52  -  Intensity (MIT) Arc Spark  Wavelength  5 10L 10L 5. 5  3186.46 3159.31 3158.23 3154.24 3152.81  100 350 20 5 25  3023.29 3017.51 3015.09 3013.63 3012.05  15 10 5 5 10  3151.46 3145.18 3141.62 3136.15 3132.58  5 50 10 10 50  3009.96 3006.35 3004.87 2998.89 2997.05  15 10 10 25 15  3128.74 3125.91 3120.36 3117.99 3112.00  15 5 10 15 10  2995.67 2990.73 2988.97 2985.47 2983.24  5 10 5L 5L 10  3105.95 3104.41 3101.45 3097.33 3 087.52  15 30 100 50 300  2980.02 2 977-. 94 2975.91 2973.69 2976.21  5L 5 25 100 10  3085.40 3083.91 3 076.57 3073.53 3073.01  25 10 10 15 100  2959.43 2955.55 2954.82 2951.48 2949.52  10 5 10 35 350  3063.18 3 052.44 3050.01 3049.36 3047.00  5 100L 5 15 5  2 944.96 2942.16 2 940; 95 2937.90 2936i77  5 10 5 5 15  3040.46 3034.62 3033.35 3029.90 3028.45  5 10 15 25 15  2931.88 2930.17 2928.23 2925.37 2924.02  Class  -  Intensity (JUT) Arc Spark  Wavelength  Class  53  Intensity (JUT) Arc Spark  Wavelength  5 50 10 5 15  2 921.97 2919.96 2911.35 2908.36 2906.98  30 50 25 5 15  2724.25 2711.61 2703.54 2700.17 2697 .,67  10 30 5 10 100  2900.52 2893.27 2872.18 2869.72 2868.86  50 15 10 5 30  2695.55 2694.55 2689.06 2686.48 2684.52  5 2 30 10 10  2867.67 2842.02 2841.18 2839.02 2831.48  5 10 5 25 30  2683.76 2680.60 2677.16 2662.11 2661.13  15 5 5 10 300  2827.20 2821.57 2813.96 2809.90 2793.24  10 15 10 5 10  2657.72 2649.80 2648.61 2644.84 2642.09  30 10 5 10 5  2791.95 2778.08 2772.64 2767.16 2759.51  15 5 350 10 15  2640^35 2639.17 2635.55 2628.24 2625.12  10 10 10 5L 25  2753.64 2752.21 2751.59 2746.38 2745.57  15 5 10 5  2622.26 2616.91 2608.18 2605.89 2595.33  10 5L 25 5 30  2740.37 2738.50 2737.90 2736;84 2726.36  30 15 15 50 25  2591.35 2586.04 2581.05 2579.24 2577.57  O  Class  -  Intensity (MIT) Arc Spark  10 10  Wavelength  Class  54  -  Intensity (MIT) Arc Spark 10 50 5 5 30  Wavelength  2412.06 2411.38 2410.88 2407.54 2403.66  15 15 150 10 25  2573.14 2568il3 2564.58 2562.28 2559.71  5 5 5 10 30  2549.21 2544.89 2537.19 2533.05 2530.70  10 300 10 15 15  2500.88 2499.75 2499.22 2494.67 2490.33  30 10 50 10 5  2374.94 2372.86 2369.92 2367.00 2361.64  100 10 10 5 300  2489.20 2485.24 2481.22 2479.85 2469.62  5 10 5 5 5  2359.53 2358.23 2356.60 2355.08 2354.90  50 5 5 10 5  2467.72 2456.90 2455.54 2452.53 ' 2447.92  5 10 15 5 15  2348.74 2343.83 2336.15 2334.91 2332.32  25 25 15 10 10  2438.80 2436.63 2434.73 2434.35 2433.82  50 25 5 5 10  2329.12 2327.45 2326.22 2322.22 2320.09  15 10 100 2 50  2431.78 2431.45 2426.39 2420.14 2415.59  5 10L  2311.81 2304.29 2288.90 2287.84 2286.71  ".'  I  I I  600 500  100 10 25 300 300  ^2403.00 2401.81 2389.79 2385.76 2383.25  Class  - 55 Intensity (MIT) Arc Spark  10 200 50 5 5 10 100  600  100 100  400 5 3 00 5 50 600 30  15 5 2  15 150 25 10 10 30 10 5 15 30 5  5  Wavelength  2226.07 2216.61 2209.45 2208.83 2207.17 2196.07 2187.22 2178.13 2159.79 2148.04 2147.19 2143.54 2142.75 2121.75 2117.46 2109.83 2107.63 2107.20 2101.74 2081.88 .2081.03 2067.94 2066.49 2061.03 2044.22 2039.79 2024.20 2002.72 2001.59 2000.2  Class  Intensity (MIT) Arc Spark  Wavelength  Class  -  56  -  Table  III  RECORD OP RUNS A T T E M P T E D  Run  Dropping Rate cm/hr  Supercooling  Success  1  .76  350  good  2  .76  50°  good  3  .76  —  4  .56  35°  poor  5  .76  55°  fair  6  .48  25°  good  7  .76  45°  poor  incomplete  BIBLIOGRAPHY  Crystal Growth. John W i l e y and Sons I n c . This reference includes a comprehensive coverage of the r e f e r e n c e s on c r y s t a l g r o w t h to 1951  (1)  B u c k l e y H . E.  (2)  Stockbarger  Also  referred  (3)  Venaer A .  (4)  D a v e y P. D .  A Study of and i t s  (5)  L a w s o n W. D .  A Ilethod of Growing C r y s t a l s o f PbTe PbSe. J . A . P . 22, 1444,  D.  to  P,  R.S.I.  7,  133,  1936  Crystal  Growth and  were:  J.  Dislocations,  Crystal Structure Applications Single and 1951.  Oxygen F r e e S i n g l e C r y s t a l s of PbTe, PbSe, and P b S . J . A . P . 2 3 , 4 9 5 , 1952 (6)  R. Smith  Hopkins  C h a p t e r s i n the C h e m i s t r y of Less F a m i l i a r Elements.  -  - -  - -- -Ii bo  - -  -  --  -  -  -—  -  -  -  |  - -T  -  H_  *•  A r  /  IB  s  /  \J?  I  1  ft \  *  --  -  1  1  \  V  '}\  *  %  1  E  J  fi ~  1. 1  1 T  •  900  -  -  !  7  -  1  ?  q7 T-e7 V  r f~t  >  *-  j  J  * -  7  |  J  _j —• L I — —4  /  i  I  %  F— \ 7 •  <,  \ \  300  L  s  1  \ r  \ >  1  l  \  J _  7cc  1  •  v.  -\  600  1 I" _  5 op  1 1 T  1 1  t  —  f  8  to  IZ.  i  1  \j... 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