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Investigation of planar arrays of superheated superconducting spheres Meagher, Gail Aileen 1991

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INVESTIGATION OF PLANAR ARRAYS OF SUPERHEATED SUPERCONDUCTING SPHERES By GAIL A I L E E N MEAGHER B.Sc,  Dalhousie University,  1989  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY  OF GRADUATE  DEPARTMENT OF  PHYSICS  We a c c e p t t h i s t h e s i s a s to the required  THE UNIVERSITY  STUDIES  conforming  standard  OF BRITISH COLUMBIA  O c t o b e r 1991  © G a i l A i l e e n Meagher, 1991  72  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department  or  by his  or  her  representatives.  It  is  understood  that  copying or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  Physics  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  October 8, 1991  Abstract  The forward  P l a n a r A r r a y of Superheated as  work h a s of  spheres,  16 mT,  to  of  indium  curves, have  RF-SQUID grain  n e u t r i n o and  c o n c e n t r a t e d on  hysteresis to  a possible  the or  The  fields  in a  was  environment. showed  detector.  of  a  put This  100x100 a r r a y  superheated-supercooled ranging  pumped He  from  the  cryostat  4  Individual  been  superconducting  indium  s a m p l e due  earth's  using to  to  an  normal exposure  gammas. effect  spheres  matter  The  f l i p s were r e c o r d e d w i t h t h e  60 keV  (PASS) h a s  characteristics  f o r magnetic  system.  dark  tin.  been measured  readout  Spheres  a  difference  of  gravity  tested The  where  the  remelting  hysteresis  decreased from  by  on  curves  transition a l l the  shape  arrays  spheres  ii  structure  in  obtained  width,  where t h e y a r e a l l n o r m a l .  and  the  the  microgravity  f o r these  i.e. are  a  of  arrays  temperature  superconducting  to  Table  of Contents  Abstract Table List  i i  of Contents  i i i  of Figures  v  Acknowledgement  viii  1  2  3  Introduction  1  1.1  Superconducting C o l l o i d  1.2  Historical  1.3  Present  1.4  Thesis  Devices  Perspective  1 4  Work  5  Outline  5  Theory  7  2.1  7  G r a i n D e f o r m a t i o n Due t o G r a v i t y  A p p a r a t u s and Sample P r e p a r a t i o n  11  3.1  Cryostat  11  3.2  Data A c q u i s i t i o n  18  3.3  Sample P r e p a r a t i o n  19  3.3.1  Indium A r r a y s  19  3.3.2  T i n Arrays  23  3.4  Size Distribution  25  iii  4  5  6  7  Experiments-Indium Arrays  28  4.1  28  Fast Electronics 4.1.1  Multichannel  Analyzer  29  4.1.2  Digital Oscilloscope  31  4.1.3  F l i p Structure  33  4.2  SQUID Read Out  35  4.3  Radiation Test  37  Experiments - M i c r o g r a v i t y M e l t i n g  40  5.1  Preparation  40  5. 2  Apparatus  41  5.3  Microgravity Flight  47  5.4  H y s t e r e s i s Curves  48  for Flight  Experiments - T i n Arrays  51  6.1  51  Hysteresis  Conclusions  55  Bibliography  58  iv  List  1.1  Phase  diagram  for  a  transition-dotted solid  line,  on a  Forces  3.3  Inner  3.4  SQUID h o u s i n g  3.5  Source  3.6  Indium  cryostat  Tin  3.8  superheated  bulk  transition-  transition-dashed  line.  ..  2  drop  8  13 16  and s h u t t e r arrays, 50x  assembly  (a)  (b)  arrays,  squares,  Superconductor:  assembly  17 jum s e p a r a t e d 3.7  I  line,  sessile  Figures  Type  supercooled  2.2  squares,  of  an  70  (a)  (b)  separated  Indium  array  picture  fed  by  indium  of  40x40  spheres  of  Jim  radius 22  unmelted melted  70 /um,  images, into  array  /urn, 2 0 0 x  an  200x.  radius  unmelted  melted  by  17  tin  of  spheres  4 0 x 4 0 (im of  9 /urn  500x  200x,  frame  array  24  grain  radius  grabber  (b)  1 1 jim image  (a) after  processing  26  4.9  Multichannel analyzer  4.10  Digital  oscilloscope  4.11  Traces  from  oscilloscope. is  trace,  Y axis  1024  counts.  .  setup  30 32  two  different  Both  channels:  1 v/div  sweeps X  is  on 100  digital /us/div,  Y 33  v  4.12  Possible by  4.13  fast  indium g r a i n s  Number  o f indium g r a i n s  Base p l a t e and f l i g h t  5.17  Heating  and  prepared  cooling  curve  ..  39  by r a d i a t i o n  43  f o r sample  in  oven 44 45  (a) s a m p l e s b e f o r e  remelting 46  samples a f t e r r e m e l t i n g  5.20  Sample h o l d e r  5.21  Superconducting radius  indium  (a) t o p v i e w  external f i e l d  Superconducting radius  indium  an e x t e r n a l  diameter  f o r 12  jum  i n microgravity,  in  transition  prepared  B = 12 mT  49  t o normal  transition  grains  prepared  field  B = 12 mT  Superconducting  47  (b) s i d e v i e w  t o normal  grains  t o normal  t i n grains  38  f o r 100x100  f o r jug f l i g h t  Rods i n s a m p l e h o l d e r  6.23  size  36  i n 12 ,um  apparatus  5.19  in  step  flipped  Temperature c o n t r o l box  5.22  B = 4 mT.  t o normal f l i p s  vs  5.18  an  fim  c a u s e d b y gamma r a d i a t i o n .  o f occurrences  5.16  (b)  seen  f o r 12  transition  i n an e x t e r n a l f i e l d  I n d i v i d u a l superconducting  array  flips  34  t o normal  indium g r a i n s  radius 4.15  of individual grain  electronics  Superconducting radius  4.14  structure  in  i n earth's  B = 4 mT  ,um  gravity, 50  transition an  f o r 12  external  f o r 18  nm  field  of 52  vi  Field radius  vs t r a n s i t i o n temperature 9 urn s p h e r e s , s q u a r e s  urn r a d i u s  s p h e r e s , diamonds  vii  for (a)tin  (b)  array  t i n colloid  of  of 7  Acknowledgement I w o u l d l i k e t h a n k my s u p e r v i s o r , D r . B r i a n T u r r e l l , f o r h i s h e l p f u l s u g g e s t i o n s and f o r h i s u n d e r s t a n d i n g . I would a l s o l i k e t o thank Dr. Andrzej K o t l i c k i f o r h i s a s s i s t a n c e , day t o day t o l e r a n c e , a n d h e l p i n t y i n g a l l t h o s e l i t t l e k n o t s . I also a p p r e c i a t e d h i s comments d u r i n g t h e w r i t i n g o f my t h e s i s . I w i s h t o e x p r e s s my a p p r e c i a t i o n t o D r Mark L e G r o s , w i t h o u t whom I w o u l d n e v e r h a v e f o u n d a n y t h i n g , o r b e e n a b l e t o make i t work. I would a l s o l i k e t o acknowledge h i s c o n t r i b u t i o n t o my o p i n i o n o f t h e s i s w r i t i n g . My t h a n k s go o u t t o D r . G e o r g E s k a , f r o m whom I l e a r n e d a great deal i n a short time. I would a l s o l i k e t o thank t h e t e c h n i c a l s t a f f i n t h e p h y s i c s d e p a r t m e n t , who h e l p e d me t h r o u g h my i g n o r a n c e , a n d N S E R C , f o r t h e i r f i n a n c i a l support. T h i s t h e s i s i s b r o u g h t t o b y t h e l e t t e r R , t h e number 4 6 2 , and a s m a l l p i e c e o f s t r i n g .  viii  Chapter  1  Introduction  1.1  Superconducting  Colloid  Superconducting spherical grains, the  same  material,  (B  ,T  (SSCD)  consist  a l l nearly  range  from  one  of  many  a s p o s s i b l e of -  to  one  i n a suitable  dielectric  a type I superconductor. superconducting state  hundred  The g r a i n s  near  t h e phase  ) .  SH' SH'  X  sample  samples and  exhibits  the  different  type I  superconductors  supercooling.  Superheating  superconductivity at a  Similarly,  below  grains  of  thermodynamic  material. state  can  i n a superheated,  superheating  c  detectors  The g r a i n s a r e embedded  Small  T ,  which  a n d a r e made f r o m  are held line  colloid  of a s u i t a b l e metal,  diameter,  micrometers.  Detectors  T ,  c'  a  until  phases.  The  i n t h e SSCD,  transition supercooled T  below  temperature  material  'x' i n f i g u r e 1.1  slightly  occurs  temperature  i s reached.  sc  can  exhibit when  higher  for  the  i s i n the  F i g u r e 1.1  the superheated  than bulk  normal  shows  shows t h e s t a t e  the  the  of the  transition,  but w e l l above s u p e r c o o l i n g . Since exclude  a  the grains i n the detector are superconducting magnetic  field  v i a the  1  Meissner  Effect.  they  When  a  Temperature F i g u r e 1.1: P h a s e d i a g r a m f o r a T y p e I S u p e r c o n d u c t o r : bulk t r a n s i t i o n - d o t t e d l i n e , superheated t r a n s i t i o n s o l i d l i n e , supercooled transition-dashed l i n e .  collision  event  particle,  gamma  converted  t o heat' i n t h e g r a i n .  to  the  occurs  r a y , WIMP e t c . )  transition,  superconducting  i n the grain  the  excludes t h e magnetic  flux  results.  (Superconducting  Quantum  can  field  can  a  neutrino,  be  'flip'  the grain  close  the  grain  i s flipped,  enough from i t no  and a change i n t h e magnetic 'read-out'  Interference  2  alpha  deposited i s mostly  If i ti s sitting  When  longer  This  t h e energy  heat  t o normal.  (with  Device)  by  a  SQUID  magnetometer.  Because  the  grain  i s superheated,  i t remains  normal  after  the  flip. Previous consisted  detectors  of  dielectric,  a  random  e.g.  as a d i p o l e  felt  by  of  grain  felt  the  This results  planar  array  tested  a t UBC.  a  spacing  same. the  of  field,  The  grains  normal  at  field. of  This  in  problem  a  size  to  different  spheres  field  and  shape  magnetic  flip  from  temperatures.  temperatures, been  grain  the  in local  them  has  which  suitable  therefore  variation  slightly  type  superconducting  and  causes  superconducting The  grains  Each  i n a spread of t r a n s i t i o n  applied  set  to  'colloid'  as t h e p o s i t i o n ,  i s different.  superconducting  given  i s different  by  the  o r epoxy.  i n the magnetic  i t neighbours  field  of  suspension  paraffin  acts  each  were  AT ,  addressed  (PASS)  for a  gH  by  the  developed  and  grains are arranged i n a regular array,  between  them  so  that  the  local  fields  Because of the f a b r i c a t i o n p r o c e s s , the s i z e  with  are  and  the  shape o f  g r a i n s a r e more u n i f o r m . The  spread  in  AT  can  be  measured  state  i n an  by  first  putting  the  SH  spheres This 1.5  is K.  i n the done The  superheated by  first  magnetic  field  the  the  i s then  swept up The  magnetic on  from  raised,  w h i l e monitoring both the temperature flux,  value.  to  field,  change i n magnetic  desired  array  earth's  the  to  cooling  applied  the the  order  is  sample  v i a t h e SQUID m a g n e t o m e t e r .  3  of  background  temperature of the  field.  then and  1.2  Historical Perspective  The granules Orsay  1  suggestion as  a  almost  particle twenty  superconducting Significant Faber  of  using  detector  originated  f i v e y e a r s ago.  granules  embedded  s u p e r h e a t i n g was  2 et. a l . .  superheated  a  a  group  to  from  u s i n g type I  dielectric  observed  . superconducting  The  with  They p r o p o s e d in  first  superconducting  material.  i n indium  spheres  . transition  normal  by of  3 granules in  due  to  an  electron  beam was  observed  by  Blot  et. a l .  1974. Many  other  superheated  experiments  have  been  superconducting granules  as have t h e s u g g e s t e d 4 D r u k i e r and V a l e t t e  uses  done  using  (SSG).  a  colloid  These have  of  varied,  o f a d e t e c t o r made o f t h e s e g r a n u l e s .  suggested  that  a  colloid  of  SSG  could  be  5  used  to  suggested  detect  charged  i t s use  as  particles.  a transition  Drukier  radiation  et. a l .  detector.  As  then well,  the  SSC has been proposed as a detector for neutrons , 7 8 9 10 n e u t r i n o s , m a g n e t i c m o n o p o l e s , and c o l d d a r k m a t t e r ' , i n p a r t i c u l a r , weakly i n t e r a c t i n g massive p a r t i c l e s (WIMPs) . 1 1  Results  were  first  reported  on  work  done  by  Le Gros  12 et.  al.  in  1990  superconductors), granules in  in a  transition  than  for  the  on  a new  PASS  (Planar  array  type o f arrangement.  of  By  superheated  fabricating  planar array, using photolithography, the temperatures colloid  was  an  devices.  order  of  Individual  4  magnitude grain  the  spread smaller  flips  were  observed,  and t h e d i s t r i b u t i o n  of f l i p  step sizes  shows a s t r o n g  13 peak a t t h e p o i n t  1.3  of the calculated  m a i n work  testing  of  of this  planar  spheres.  arrays,  them  made  14  making  .  A  larger  'fast  electronics'  determine  system  Pictures  of  microgravity  t o improve  environment.  s a m p l e s were t h e n  the fabrication  indium  new  mask  was  and  more  uniform  15  and  t i n  used  and  the  t o produce  4  arrays  were  the  previously . with  He c r y o s t a t  o u r RF SQUID  and  superheated  than  i n t h e pumped  t h e s i z e and placement  I n an e f f o r t  involved  of  T h e s e a r r a y s were t e s t e d  electronics.  readout  also  16  studied  and to  distribution.  the arrays, The  some were r e m e l t e d  transition  widths  of  in a these  found.  Thesis Outline  In and  thesis  arrays  superconducting  1.4  size  P r e s e n t Work  The  a  step  c h a p t e r two, t h e d e f o r m a t i o n  m i c r o g r a v i t y , when  three,  the  described. outlined. indium  apparatus The  used  procedure  In chapter  arrays  solidifying  are  four,  to to  of a grain  i s calculated.  record fabricate  data the  t h e experiments  discussed.  Chapter  5  due t o g r a v i t y ,  five  in  In the  arrays  lab i s is  performed deals  chapter  also  on t h e  with  the  preparation,  apparatus,  microgravity  flight.  performed  the  on  and  results  Chapter  six  t i n arrays,  while  r e s u l t s and c o n c l u s i o n s .  6  obtained gives  chapter  the seven  from  the  experiments gives  the  Chapter  2  Theory  2.1  Grain  D e f o r m a t i o n Due  Previous the  arrays  gravity To  do  on  a  will  covering  induce  of  metal w i l l  a  However  deformation  grain w i l l  surface,  i t .  density  spherical.  the  flat  The  the  with  molten  solidify  be a  density  which  lighter  metal.  we  need  It  as  density  f l u x used is  in  a  f l u i d on 17  to  fluid,  that  lighter  of  liquid  the  flux,  the  liquid  the  liquid  liquid.  a horizontal surface,  The  earth's  i s much l e s s t h a n  assumed  in  calculate.  drop  . . . i s shown i n f i g u r e 2.2.  a volume v.  grains  the  shape c a l c u l a t e d f o r t h e  of l e s s e r d e n s i t y  a d e n s i t y p , and  melting  approximated  of the  i n the  A s e s s i l e drop of a liquid  Gravity  c a l c u l a t i o n s h a v e b e e n done a s s u m i n g t h e are  this,  to  covered  The  has  drop  a  by has  density,  h  P,  and  i  surrounds the  horizontal symmetry g  unit  surface.  i s given  i s the area,  d r o p e x c e p t where i t i s p u s h e d a g a i n s t  by  The x.  The  a c c e l e r a t i o n due or  radial  interfacial  to  distance  contact  angle  gravity.  tension  7  is  from  the  i s given  The given  surface by  cr.  by  axis 8,  of  while  energy The  the  per  excess  curvature  pressure  a t a depth  z i s given  Ap = 2cr/b +  1/b  by: gz =  (P^PJ)  ( ± + |  where r  i  and  are the p r i n c i p l e  radii  1  (2.1)  cr  2'  1  of curvature,  given  by:  l/r  x  = d0/ds  (2.2)  l/r  2  = sine/x  (2.3)  where s i s t h e a r c l e n g t h . Since  t h e drop  f o r c e s must be  i s i n e q u i l i b r i u m , t h e sum  zero. vp g + 27xxcrsin0  = vp g + Trx Ap 2  h  T h i s c a n be r e d u c e d  equations  can  (2.4)  1  to: V  The  of the v e r t i c a l  (P -P,) h  be  g/cr = Tlx  simplified  factor:  8  2  ( i + i 1 ^ 1 2''  further  by  (2.5) introducing  the  w h i c h c a n make t h e v a l u e s  dimensionless. 3/2  (2.7)  V = VC  1/2  (2.8)  X = XC  z = ZC R  = rc  R  = rc  2.11  1/2  (2.10)  1/2  (2.11)  2  2  t h evalues  (2.9)  I  l  Replacing  1/2  i n equation  2.5  with  2.7  equations  through  gives: (2.12) Calculations  have  been  done  f o r many  different .  1/3  this  equation.  A plot  forms o f  of log X vs log V  f o r various  values  o f x, a m e a s u r e  o f how  18 of  6  c a n be u s e d  much t h e g r a i n the  volume  the  interfacial The  t o estimate  i sflattened.  of the grain,  thevalue Forthis  i t i s necessary  d e n s i t i e s o f t h e metal  t o know  and f l u x , and  t e n s i o n b e t w e e n t h e two.  density  of  a t 231 °C  indium  i s 6 . 9 9 g/cm  and t h e  3  319  density The  of t i na t i t s melting  density  0 . 7 9 g/cm . 3  the  cubed  of  t h e two  not  been  acid  The volume  of the grain  tensions,  Unfortunately,  indium  tension  i n great  o f 232 °C i s 6 . 9 8 g/cm  was d e t e r m i n e d  The i n t e r f a c i a l  surface  studied  99.995% p u r e surface  of abietic  radius.  attraction.  point  i s taken  tension  minus  i s 556 dynes/cm  t o b e 4TT/3  i s equal  force  of abietic  The s u r f a c e  a t i t smelting  o f 99.99% p u r e t i9 n i s 537 dynes/cm  times  to the  t h e adhesion  theproperties detail.  i n t h e l a b t o be  acid  tension 20  point  sum of  have of  . The  a t i t melting  point  .  The i n t e r f a c i a l  451 dynes/cm 10  jLim, t h i s  o r 0 . 4 6 g/cm. gives a value  c = ( 6.99 This allows  tension Taking  will  then  t h e indium  0.79  ) 981 /  the calculation  0 . 4 6 = 1.32x10* cm"  180°. the  With graph.  microscope this  (2.14)  3  = -0.732  1 / 3  (2.15)  Converting  contact  i t was e s t i m a t e d  the value  (2.13)  2  I t was n o t p o s s i b l e t o d e t e r m i n e t h e light  radius as  of:  log V  a  grain  t o be  X = -2.05  of log  angle  exactly.  approximately  was o b t a i n e d  10~  2  g.  value  gravity during Using  of c  =  this  log V  2  cm . -2  (2.16)  i s a small  the m i c r o g r a v i t y  i n equation  1.32xl0  1/3  is  10 nm, t h i s  a grain of radius The  from  back: x = 0 . 7 7 /nm  For  by  of:  V = 6.37xl0"  With  be e s t i m a t e d  2.13  This  distortion.  e x p e r i m e n t w e r e a t most gives  gives  V  t h e much  smaller  6.37xl0 ,  =  - 6  while  •  = -1.73.  obtained.  Again  So f o r t h e  from t h e graph w v a l u e  of log X = -3.95  sphere i n m i c r o g r a v i t y : x = 0 . 0 9 8 jLim  10  (2.18)  Chapter 3  A p p a r a t u s a n d Sample  The  s a m p l e s were t e s t e d i n a pumped H e c r y o s t a t .  link  t h e oven  sample pumped  4  He  nitrogen,  by  a  copper  s e t from  p o t , t o 4.2 K sample  cooled  in  by a s u p e r c o n d u c t i n g pickup  coil  accurate  magnetometer.  an  was  flux  with  t h e oven  placed could  be  of the of the  heating  magnetic  surrounding next  with  connected  temperature  adjustable  solenoid  was  was  through a  t h e temperature  the operating  and above,  sat  i n t h e magnetic  the  field,  t h e sample.  t o t h e sample,  measured  with  a  so very  Cryostat  The  continuous,  been  pumped He c r y o s t a t u s e d t o t e s t 4  constructed  previously  needed.  The placement,  housing,  changed,  which  i n more  the  further  The sample  rod, allowing  1.7 K,  changes  had  then  4  differential  3.1  and  A c o p p e r p l a t e o v e n was f u r t h e r c o o l e d  The  produced  liquid  t o a p o t o f pumped H e .  t o be  sample.  A  with  helium.  thermal to  This  4  precooled liquid  Preparation  RF  resulted  s i g n a l from  t h e SQUID,  22  .  Few  and t u n i n g than  the arrays  . . . modifications o f t h e SQUID  were  a three-fold increase i n  and a t h r e e - f o l d d e c r e a s e  11  were  i n the  noise.  The  shutter  vibrational and  noise  The  teflon  was  i n t o the  consisted  of  a  screws  was  The  inner  attached  to  a  oven, p r o v i d i n g copper  and  heated  external  plate  washers.  by  a  temperature  assumed  to  be  the  was  volume  15.3  scintered  of  silver  prevent clogging The  of  to  reduce  of the  cold  the  the  opening  cryostat  anchored  to  by  a  the  also  of  is  the  pot  piece  by  oven,  oven three  connected  of wire.  resistor,  sample  the  1 K  w h i c h was  filled  with  length  f i l t e r was of the  1 K  The  was  fed  The  by  the  temperature  was  w h i c h was  measured  resistor. by  3  link.  thermally  short  The  that  f i n g e r which  a good t h e r m a l  controller.  cm  47 cm  copper  anchored  cooled  continuously  capillary  portion  T h e y were  same as  o v e n was  inner  both  reliability  thermally  a c a l i b r a t e d germanium The  replaced  improve the  a thermal resistance provided  oven  of  to  was  3.3.  sample  screwed  by  and  c l o s i n g mechanism.  shown i n f i g u r e  by  assembly  pot.  This  pumped by  liquid  4  He  and  0.1  mm  placed  on  the  was  a  by  copper  pot  r o t a r y pump.  It  a  inner end  a  copper  nickel  diameter.  i n t h e He 4  bath  A to  capillary.  magnetic f i e l d  on  the  s a m p l e was  p r o d u c e d by  a  solenoid  23 made  of  443  former epoxy. the  of  Nb-Ti  consisting  of  a  This  area  coated  turns  gave  of the  with  a  epoxy.  cylinder  field  array.  that  The The  wire  was  wound of  12  a  copper  uniform  f o r m e r was  connection  on  2.5  foil  to  cm  diameter  coated  within  0.1%  a c y l i n d e r of copper to  the  solenoid  leads  with over foil was  pumping  line  fill  calibrated germanium thermometer  oven  4-  cold  SQUID  pick-up  line  finger  housing  coil  solenoid  sample  w s o u r c e and shutter  Figure  3.3:  Inner  cryostat  assembly.  13  made by the  screwing  them  solenoid.  These  superconducting magnet  into  n i o b i u m p l a t e s mounted a t  leads  niobium wire.  centimeters  length,  When  1 mA  driven  was  normal,  of  mode.  thermally  sent  which  superconducting field  was  s o l e n o i d t o be in  This  the  the  a  operation  Nb-Ti to  wire, 1 kQ  resistor,  the  persistent The  region  end  of  length  a  changed.  the  by  the  connected  through  allowed  38 Gauss/Amp  shorted  This allowed  i n persistent current  about  were  one  of  of  the  a  few  of  resistor. wire  was  in  the  current  s o l e n o i d produced  where  the  sample  a  was  located. The  sample  sat  homogeneous p a r t the  differential  flux.  A  only  to  because  by  a  at  was  below  coils  the  the  coil  distances  the  6  windings  each,  loop.  pick-up  loop  The  ran  up  arrangement  coil were  close  the  out  loops  one  Two  separated  by  top  wound  other.  coils  y e t a b o v e i t by above t h e  local  is  former.  of  sensitive  the  loops,  is  nearly  The  sample  oppositely 2.2  was  cm,  1.2  5 mm. the  was  the  to  through  most  sample  in  This  very  i n the  the  changes  diameter of the  loop,  to  oppositely  change t h r o u g h pick-up  of  next  change  teflon  solenoid,  two  occur  the  sample s a t i n s i d e t h e the  has  that  the  picked  distance. flux  of  Located  which  opposite  form the p i c k - u p  from  in  large  by  wound  small  middle  field.  coil,  changes  canceled 2 mm  the  differential  separated  the  of  i n the  The  cm,  to so  wires  solenoid  to  SQUID. The  SQUID,  a  very  accurate  14  magnetometer,  was  used  to  detect  t h e changes i n f i e l d  was e n c a s e d against  i n a Niobium  external  superconducting into  magnetic  b e l o w 9 K.  the cables  screwed  into  into  these,  was  less  shielded  each  fields  A 1 mm  end, and t h e w i r e s ,  shield  by t h e p i c k u p  allowing were  entering  the  wires  SQUID c a b l e  inner  t o pass  was a t t a c h e d  hole  was  drilled  wrapped  i n lead  foil  A  piece  a n d t h e SQUID The d i a m e t e r of  was  screwed  allowing  The d o u b l e  t h e Niobium  shielded  tubing.  This  w h i c h was s o l d e r e d t o t h e o u t s i d e  of  cable  shielded  SQUID was h e l d Niobium rods  tube  i n place  by a p i e c e  a n d was s c r e w e d  outside  running  t h e magnet,  of brass  onto  which  t o room  was  shield  temperature.  which  The  encircled the  one o f t h e t h r e e  supplied  was  o f t h e SQUID  the tubing,  t h e two.  to  of teflon  s u r r o u n d e d by l e a d f o i l t h e double  is  through.  diameter  outside  niobium  t o pass  t h e SQUID.  between  shield  the wires  then  end o f t h e tube,  T h e SQUID  i t a good  since  diameter  a s shown i n f i g u r e 3.4. than  coil.  c y l i n d e r w h i c h makes  one e n d o f t h e s h i e l d ,  This  felt  supporting  heatsinking  for  the  SQUID. Our order  tests  to flip  included the grains  temperature. glued  used  •  •  t o a piece •  241  sample  was  was  a  fastened  s h u t t e r was opened, w h i l e  than  small  around  changing  circular  disk of  f o r heat i t .  rays i n  by  •  wire .  exposed  t o gamma  •  of silver  .  Am a l s o h a d t i n f o i l the  t h e sample  by r a d i a t i o n r a t h e r  The s o u r c e  241  Am,  exposing  •  sinking.  .  •  The •  With t h e s h i e l d i n g ,  t o 18 k e V a n d 60 k e V gammas  when t h e  t h e c c - p a r t i c l e s were a b s o r b e d i n t h e  15  teflon  SQUID  teflon  niobium  Figure  foil.  3.4:  SQUID  I t was n e c e s s a r y  needed. sample  The s o u r c e and i n s i d e  was m a c h i n e d  t h e lower  o u t o f copper,  around  a brass  rod.  When  through  source. cryostat,  the This  hole  The t e f l o n using  sample  was  nylon  below t h e A  cylinder  t h e middle, slit  exposed  of the holder.  also  knowledge  through  when n o t  as  and r o t a t e d  s a t on t h e e n d o f t h e t e f l o n  rod could  Two e l e c t r i c a l  placed  rod sat i n this  alpha  thin  operating t h e handle  a slit  blocked  r o d , f o r t h e 'source allowed  with  i n t h e bottom  the  effectively.  the  was  of the solenoid.  The s o u r c e  vertical,  t o be b l o c k e d  assembly  part  A teflon  screw.  a hole  over  f o r the y source  and s h u t t e r  shown i n f i g u r e 3 . 5 .  foil  housing.  be t i l t e d to  the  A piece  particles  thread,  to  of  emitted from  block  source copper by t h e  outside the the  source  c o n t a c t s were made a t t h e b o t t o m o f  open' of  connected  and  the  'source  position  closed' of  the  t o the nylon thread.  16  positions. rod  while  T h e ends o f  the  nylon  other to  thread  were wound  counterclockwise.  either  the  direction  open  on  this  Turning or  handle,  the  closed  one  handle  clockwise,  would  position,  pull  depending  the  the  rod  on  the  turned.  copper  foil  copper  holder  h attachment f o r d e n t a l f l o s s leads  teflon rod  Figure  A  3.5:  second  S o u r c e and  s o l e n o i d was  when a few  wire  solenoid.  I t was  c o n s t r u c t e d on  an  11/8  securely  the  solenoid  holes  were  inch  outer to  made  the  0.2  assembly.  constructed  w i n d i n g s were b r o k e n  diameter  tapped  shutter  f o r the  i n the middle  a brass  In  apparatus,  three  from  one  tests  of the  first  1 inch  inner  former of  diameter.  inches  t i n array  order  to  screw  equally  end.  The  spaced  solenoid 24  was  constructed with  Stycast layer  of  uniform  1266 1.4 by  epoxy, cm  was  reducing  three each  with  added the  l a y e r s of  to  edge  an each  superconducting  turns.  One  of  end,  make t h e  effects. 17  and  average to  This  331  wire  brought  field  more  the  total  turns  t o 1114, a n d g a v e  than  10~  field The  5  over  t h e area  o f 9.33 mT/A,  Data  The  which  of the array.  was  uniform  to greater  The s o l e n o i d  produced  a  o v e r t w i c e a s much a s o u r p r e v i o u s s o l e n o i d .  l e a d s were s e c u r e d  3.2  a magnet  as b e f o r e .  Acquisition  d a t a was c o l l e c t e d  utilizing  a 16 b i t A/D  I/O b o a r d  to a 25  IBM  XT c l o n e  The  computer  SQUID  computer  employing  collected  signal,  two  the Labtech  channels  and t h e d i g i t i z e d  calibrated  germanium  converting  the resistance value  A  file  time  the  the start  files,  plots  digitized  of the resistance of the  A third into  program  channel  was  t h e temperature  o f t h e r u n was could easily  devoted  to  i n Kelvin.  i n Kelvin,  created  and  f o r each  be made.  Sample P r e p a r a t i o n  3.3.1  Indium  The deposition mylar. 20.5  since  From t h e s e  3.3  value  data:  c o n t a i n i n g t h e SQUID r e a d i n g , t e m p e r a t u r e  elapsed run.  resistor.  of  Notebook  Arrays  first  step  of  indium.  This  was  cm d i a m e t e r  in  the  arrays  The s u b s t r a t e u s e d  cleaned copper  making  with  plate.  was  was  the  0.025 urn t h i c k  a l c o h o l and s t r e t c h e d A ring  18  vacuum  was s c r e w e d  into  across  a  the top  of  the plate  indium from  t o hold  shot  was  a starting 6 cm  indium  t h e mylar  evaporated vacuum  flat.  a t an average  of 3xl0~ , and  ranging  from  a thin  layer  9 9 . 9 % pure  shaped,  of 20-30  rate  t o produce  5  i n radius  Tear  circular  1 . 9 /am  k/sec,  layers of 4.8 p  to  in  thickness. The  next  step  required  placed  on t o p o f t h e i n d i u m .  backed  indium  was c u t i n t o  T o make  squares  T h i s was c l e a n e d w i t h i s o p r o p y l a 25 W h a l o g e n of  lamp.  stick  tape  each  o f about  alcohol  sample, 1 . 5 cm  t o be  t h e mylar on a  side.  and a l l o w e d t o d r y under  T h e s a m p l e was t h e n p l a c e d o n t h e p l a t f o r m  t h e s p i n n e r , where  double  of photoresist  i t was  under  held  one  by a  corner.  small A  piece  mixture  of Scotch  of  one  part 26  KPR  thin  film  was  used  as t h e r e s i s t .  the  indium,  layer. hot  aluminum  the  ambient  light  sticking The  squares. make  the array  array  of  on t h e lower  film  resist  of resist  thinner  was a p p l i e d t o  producing a thin,  f o r a few m i n u t e s  uniform  on a  T h e s a m p l e was c o v e r e d w i t h the resist  i n t h e room,  s q u a r e s was d e t e r m i n e d chrome  heated  from  layer  t h e amount o f  of the photoresist  The  i t was  spacing  first  and  t o form  necessary  size  of the  b y a mask made o f a p i e c e o f q u a r t z  side.  An a r r a y  19  a box  on t h e sample.  o f spheres,  squares.  65°C  d e v e l o p i n g due t o  and t o d e c r e a s e  s t e p was t h e e x p o s i n g  To form an  t o prevent  to the resist  next  layer  f o r 1.3 s e c o n d s ,  t h e n spun  foil  KPR t h i n  A thick  to dry the resist.  of  to  t o one p a r t  T h e s a m p l e was t h e n  plate  dust  resist  o f 100x100  squares  with  of size  4 0 x 4 0 am s e p a r a t e d was u s e d , covered given  b y 30 am. was  t h e squares  i n chrome. on  ultraviolet  are clear, Other  different  of  r a d i a t i o n , bonds  As n e g a t i v e  while  sizes  parts  changing i t s s t r u c t u r e . the  used.  an  the  form  the rest spacings  mask.  photoresist  o f t h e mask i s of  squares  When  i n the negative  This allows  were  exposed  to  photoresist,  a p a t t e r n t o b e c r e a t e d on  indium. 27  The just was  s a m p l e was e x p o s e d t o a UV lamp  below t h e b u l b placed  helped  on  press  between  a  to distribute  stage  t h e sample  t h e two.  defined  under  the light  by  evenly  I f space  some o f t h e r e s i s t sharply  covered  with  a  piece  left,  A  toroid  of metal  exposure than  20 urn b e i n g  sample square  was was  evidence. placing  formed.  A  formed, After  exposure,  i t i n the developing which  the pattern  leaving a  was  placed  circles,of  exposure  A  individual,  had n o t been  o f squares  shorter  the size  a 7 mm  smaller  less  I f the b y 7 mm  squares  h a d t o be d e v e l o p e d , This  loosened  exposed  plainly  20  on t h e  radius  increased  e i g h t minutes,  fluid.  less  i n t o t h e sample.  of small  t h e sample  space  develop  edges l e s s w e l l d e f i n e d .  no  which  no  would  minutes.  f o r more t h a n with  T h e sample  leaving  f o r four  longer  a n d made t h e i r  exposed  the r e s i s t  leaving  exposed  resulted i n a pattern  of t h e squares,  away  was  diffuser  foam-wipe  t h e e d g e s o f t h e mask,  pattern.  sample  of  the light  mask t o e n s u r e t h a t t h e mask was p r e s s e d The  evenly.  t o t h e mask,  was  a quartz  by  and r i n s e d  t o t h e UV  visible  in  light,  on t h e indium.  The  s a m p l e was  placed i n the developer f o r ninety  d e v e l o p e r was of  a pipette  then  full  removed  s i n c e water The  etched part  the  of  resist  hotplate by  sample. had  to  The  hotplate.  on  the  The  the  etching  with  are  alcohol,  resistant  making  sample  etching  i t  was  this  array  an  age  relatively under  clear the  of  resist  indium. layer  The due  the  and  the  rinsed ten  the  edges  to  with  minutes,  was  produced,  a r e a between t h e tops  to  also  etch.  squares  The  and  be one  was  on  to  heated  through  quickly  of the  of  indium  four  was  e t c h was It  to  of etch over  see  between  and  procedure  to  removed  process took  full  the  possible  then  e t c h used  The  was  sample.  process.  were e t c h e d u n t i l  an example i s shown i n f i g u r e 3.6a.  etched  The  ethanol.  on t h e t e m p e r a t u r e  With  was  indium  behind.  ten parts  speed  samples  The  depending  rinsed  repeatedly squeezing a p i p e t t e  disappeared,  water.  left  the squares  concentrated HCl,  stirred  and  sample  T h i s a l l o w e d t h e i n d i u m n o t c o v e r e d by r e s i s t  away, l e a v i n g  the  developer  The  f o u n d t o l e a v e t o o much d u s t on t h e  squares  The  d u r i n g t h i s t i m e by t h e f r e q u e n t s q u e e z i n g  o f d e v e l o p e r o v e r t h e sample.  from  was  mild acids.  on  stirred  seconds.  of  the  the  fact  squares  squares that  and  were  chemical  e t c h i n g works e v e n l y i n a l l d i r e c t i o n s t h r o u g h t h e m e t a l . To  melt  the  squares  to  form  (superglue) t o a copper boat. copper  foil  which  was  indentation.  This  gave  spheres,  The  stamped  b o a t was to  approximately  21  the  was  glued  made o f 0.1 mm  thick  make a  1 mm  a  sample  3/8  inch  square  c l e a r a n c e between  >0 o © © © i o © e © o e © o o ©  •  © © © 9 nj © O © ©  0  0 9 O  •• © ©  © ©  ©• O  o 9  •© ©v  o o 9  • o • '#£ • • © O  © ©  Lb (a)  m-.  (b)  750jim  75/um  F i g u r e 3.6: I n d i u m a r r a y s , (a) a n u n m e l t e d a r r a y o f 40x40 am s q u a r e s , 50x ( b ) m e l t e d i n d i u m s p h e r e s o f r a d i u s 17 urn. s e p a r a t e d b y 70 iim, 20Ox.  the  array  contain  and t h e edges o f t h e boat. the flux  added  The  t o t h e sample  boats  were  t o produce  used  to  spheres  on  28 melting wetting not  .  agent.  form  isopropyl sample.  The  flux  Without  spheres.  Abietic  was  and acid  below  abietic  the flux,  The y e l l o w  alcohol  significantly  used  then  a  which  acted  t h e indium melted,  acid few  has a melting  crystals drops  were  were  temperature  157°C m e l t i n g p o i n t 22  acid,  as  a  b u t would  dissolved i n  placed  on t h e  o f about  14 0°C,  o f indium.  The  arrays  were m e l t e d  i n an oven  p l a t e h e a t e d by a r e s i s t o r . integrated current was  circuit  placed  i n this  array  melt was  formed  a temperature  sensitivity.  the voltage  until  t h e squares array  F i g u r e 3.6b shows  m e l t i n g . The a r r a y s  began  resistor was r e a d .  could  165°C.  t o shimmer a n d  had melted,  t h e heat  some o f t h e s p h e r e s o f easily  b e removed  t h e b o a t s a f t e r m e l t i n g b y d i p p i n g them i n l i q u i d  3.3.2  controlled  A 1 kfi l o a d  a c r o s s which  When t h e e n t i r e  lowered.  after  copper  t h e t e m p e r a t u r e was s l o w l y r a i s e d u n t i l  spheres.  slowly  indium  This  circuit,  was w a t c h e d  into  of a  T h e t e m p e r a t u r e was m o n i t o r e d b y a n  s o u r c e w i t h a 1 mA/K  To m e l t a n a r r a y , The  sensor.  consisting  from  nitrogen.  T i nArrays  Some a r r a y s u s i n g t i n i n s t e a d o f i n d i u m were made b y L e a n n e Graham,  a summer s t u d e n t i n t h e l a b . T h i s  substrate  since  mylar  warps  below  required  a  different  232 °C t h e m e l t i n g p o i n t  of  ®29 tin. upper  Kapton  , a dark  working  orange  temperature  polymer,  of  was c h o s e n  250-320 °C.  a s i t has an  When  t i n was  ®  evaporated  onto  t h e kapton  substrate  during  Sputtering  t h e t i n reduced  etching  f i l m s o f 5 am t h i c k n e s s were The very  photolithographic  similar  to that  the t i n film of  the  this  tended  film  problem  to and a  to l i f t form number  o f f the squares. of  t i n  fabricated. fabrication  f o r indium.  23  of the t i n arrays  was  Since t h e m e l t i n g temperature  of  tin  was  far  previously  above  used  constructed.  to  The  thermocouple. square  melted  array  evenly,  a  The  problem  tin  shown  smaller  were  made, is  the  temperature  shapes, is  working range  monitor  The  better  squares  the  in  mask but  that  was  was  in  not  of  integrated  with more  figure  3.7a.  Since  tried. been  very  a  etch  3.7b.  also  have  grains  measured to  shown figure  the  temperature,  seemed  as  of  the  new a  evenly, A tin  Arrays  size  heater  was  cromel-alumel  successfully  small  circuit  are  forming  sample etched of  of  a  more  10x10  melted difficult  fim  yet. to  • B B « « B BI  m m m.mm-ffi ® s i eB.Bmmm9 i  B'B'BB m e m\ G a a B B.B B i I S . i B RI'G i  l l t l . B S.B IB IS SRI •i *j 'is m  I  1  m  ^  «®  1  m  i — i — i — i  0 100 200jnm 0 7511m Figure 3.7: T i n a r r a y s , ( a ) a n u n m e l t e d a r r a y o f 4 0 x 4 0 um s q u a r e s , 200x. ( b ) m e l t e d t i n s p h e r e s o f 9 fim r a d i u s s e p a r a t e d b y 70 /lm, 5 0 0 x .  24  resolve using (125x) . and  our  microscope  T h i s make i t d i f f i c u l t  had  formed  spheres.  seconds a f t e r the  Size  spacing  camera  were  of  eight  left  the  to  a  arrays to  There  software  the  final  w h i c h was  for  melted  only  a  few  s p h e r e s t o move  to  copy  image now  needed t o measure t h e  of  were  then  the  which  was  possible to  the  Data  modified  possible  to  The  DT2853  p i c t u r e s were c u t t o a s e v e n  by  the  threshold  to  and  black  only  lines  less  is  every  completely on  25  in  to  the  than  was  used  colour  in  second  the  help  of  f i g u r e 3.8a,  shown  white.  rounded  analyze.  function as  i s shown  the  take  pictures  Translation  with  video  The  processing  image  was  Canon s t i l l  an  recorded rest  i t  a  size  of  picture  image  the  Using  magnifications.  using  background  grabber  leaving  PC  they  unprocessed  result  frame  at various  package.  as  An  we  microscope,  our  white  an  even  t i n was  array.  spherical grains.  grains,  necessary  Overheating  were m e l t e d ,  of  picture,  magnification  t o j u d g e when t h e  regular  grid  grains.  The  the  grabber.  Image P r o  the  of  transferred  frame  give  arrays  attached  pictures  medium  Distribution  Once t h e and  with  s p h e r e s were f o r m e d c a u s e s t h e  around, d e s t r o y i n g the  3.4  and  It white the  while  figure line  was  the  of  3.8b. the  therefore  lines. original,  This but  •• •B ••••••••1 • • • • • t • # • ,  :::::::: •  o «  (a)  I  (b)  1  1 100  0  100x100 five  pictures  array.  percent  were  Each of  looked  contained  the  at  from  The  200fim  200x, g r a i n r a d i u s grabber (b) i m a g e  fifty-six  array.  1  1 100  0  F i g u r e 3.8: Indium a r r a y images, 11 )Lim (a) p i c t u r e f e d i n t o f r a m e after processing.  Nine  |  200/jm  random grains,  images  were  parts for  a  run  of  the  total  through  of a  . 30 program  developed  shape.  This  each  gave  direction.  between picture.  by us  The  nearest  A.  Kotlicki  the  radius  average  neighbours  The  results  to and  radius <d>  f i t the distance  <R>  and  was  then  gave  <R>  26  data  to  between  the  average  calculated =  a  11.7  ± 0.4  circular grains  in  distance for /urn  each and  <d>  = 70.2  ± 2.2  lira.  These  are  much  better  than  the  values  31 <2R> = 23.2  ± 2.0  nm  and  <d>  e a r l i e r method o f f a b r i c a t i n g  = 81.4  ± 6 |Lim  the arrays.  27  obtained  with  an  Chapter  Experiments  4.1  Fast  The system which  measurements  used  based  t h e SQUID r e a d  c h a n g e A$ o c c u r s  then  amplified This  read  microseconds,  the  with  the fast  electronics  principles  out.  than  An r f p u l s e  due t o a g r a i n  out system The giving  has  pulse  much  two  flip.  With  previous  advantages  are  electronics,  experiments  using  fast  very  t h e number  problems  might  wide  and  of granules be  the  over  the  order  t h e SQUID  of data  possible to  electronics  the  solved  by  the tested colloids,  28  of  pulses  I t was  investigations  at least which  two  i n transition  number  present.  a r r a y s had a t r a n s i t i o n width  narrower than  a  w h i c h c a n n o t be done w i t h t h e SQUID.  was  apparently  on  i t i s also  The s p r e a d  The  when  g i v i n g poor r e s o l u t i o n f o r  problems had been encountered.  these  experiments  i s induced  b e t t e r t i m i n g whereas  the fast  sweep t h e m a g n e t i c f i e l d  exceeded  the  read out  This small pulse i s  major  lengths  i n t h e o r d e r o f 0.1 s e c o n d s ,  flips.  In  Arrays  and shaped o u t s i d e o f t h e c r y o s t a t .  system.  taken  done  on d i f f e r e n t  flux  is  - Indium  Electronics  were  SQUID  4  major widths  greatly  hoped using  that PASS.  an o r d e r o f magnitude should  presumably  make  the  spread  also it  of  transitions  narrower  h a v e a known number o f g r a n u l e s , is  much  more  difficult  to  4.1.1  Multichannel  A  smaller  consisting induction SQUID  of loop  coil.  produce over  the  cracked  piece flux  and  was  on  a 2 mm  out  i t was  A full  a  coil  turns  read  system,  the  The  arrays  colloids  number,  where  making  a  exact.  necessary  soften  i t .  than  i n the  diameter  produced  much  to  approximately  peeled  u n l i k e the  used  100x100 i n d i u m  to  case.  Analyzer  pickup 20  this  know  c o m p a r i s o n t o t h e number o f p u l s e s  the  in  glass rod.  smaller  place  the  a r r a y was  13x27  the  set  up,  Since  the  than  the  signals array  cut with  after  Without  SQUID  putting crazy  directly  in  a scalpel  to  'crazy  glue,  glue'  the  flux  o f f t h e m y l a r when c u t t a k i n g t h e g r a i n s  with  it. One  set  of  experiments  involved using  the  computer  t e m p e r a t u r e was  kept constant  as  an  32 multichannel  analyzer  .  the magnetic  field  swept up  and  1.0  field ramped run. be  Hz.  was up.  In  I t was  in  Runs  were  q u i c k l y swept  obtained  shown  was  each  expected in this  f i g u r e 4.9.  The  also  and  performed  down and  case,  down w i t h  twenty  up  in  before  or  more  r a t e s between  which the  The  T h i s was trace  29  the  made  was per  narrow peak would  actually  obtained  0.1  magnetic  temperature  sweeps were  that a large, reasonably manner.  while  not  the  contained  case a  as  large  amount o f n o i s e partially in  buried  the higher  in  the  i n t h e low e n e r g y r e g i o n ,  total  of  three  counts  noise,  energy r e g i o n .  region  distinguish  in this  with  them.  eight  the The  counts  i n the  m  making  peaks  higher  peak.  well five  above counts  was  peaks  to  occur  difficult  the  noise  i n one  thought  1885 LI: ieee  i  broad  seemed  i t very  I t was  hump t h a t  small,  Most o f t h e f l i p s  p e r sweep,  l&t:  }ff  and two v e r y  noise,  two  a broad  to  had  peak, that  a  and these  IH i  i  •  A.  l I M H i 258 = lineal it), F i g u r e 4.9: M u l t i c h a n n e l  57 Cntsj m analyzer  30  1624 | ffl 512|  trace, Y axis  1024  counts  peaks  could  diameter  In  were  done  the  the  which  others  These  t o reduce at  3.45  counts  lower  to  K,  were  due  were  and  low  above then  temperatures.  showed b e t w e e n 20 this  grains  to  a  etching  energy  that  the  noise,  critical  runs  in  was  not  of  5000  temperature  s u b t r a c t e d from  The  residual  30 c o u n t s p e r sweep.  peak  similar at  I t was  number  of  flips.  An  However,  average  of  the  less  result  than  40  was  low  of runs  energy  expected  that  4.1.2  Digital  The  expected scale,  33  to  constant  at  magnetic  field  sweeps  .  The  obtain  giving a  showed  a  p u l s e s was  setup a  high  ranging  was  then  that  the  A  is  large  narrow,  value  same t i m e s . given  lower  than  per  sweep  were  grains.  Oscilloscope  o t h e r method o f c o l l e c t i n g  oscilloscope  of  much  counts  r e c o r d e d , w h i l e t h e sample c o n t a i n e d o v e r 340  is  microns  s u b t r a c t i o n p r o c e d u r e would n o t have as a c c u r a t e a count  expected.  the  few  consistent. attempt  at  to  than  an  indium. done  due  larger  completely  sweeps  be  sample  i n f i g u r e 4.11.  . in  shown  number  of  peak. from  swept up grain  the data u t i l i z e d  from  flips  o f two  flips  to  in  3.45  different  much more t h a n e x p e c t e d .  The  short  K.  occurred at  the  a  time  was  The  mT.  was time kept  applied  Repetitive  almost  traces  digital It  temperature  0 t o 24.3  However,  31  f i g u r e 4.10.  The  1.7  a  exactly  showing  spread  this  of  a l l the  p u l s e s a l s o had  varying  energies,  and tended  PICKUP COIL PREAMP  AMP  t o occur  i n groups.  3.25 lis DELAY  GATE COMPUTER (MCA) COMPUTER LABTECH  F i g u r e 4.10:  Digital  oscilloscope  32  setup.  F i g u r e 4.11: oscilloscope. 1 v/div.  4.1.3  Flip  One  T r a c e s f r o m two d i f f e r e n t sweeps on d i g i t a l Both channels: X i s 100 / i s / d i v , Y i s  Structure  possible explanation  f o r t h e above r e s u l t s i s t h a t  each read  g r a i n does n o t f l i p  a t once.  The t i m e s c a l e w i t h t h e SQUID  out  compared  to the fast  electronics.  i s seen w i t h  t h e SQUID i s made up  i s very  possible  that  large each  flip  that  33  It is  of  many  normal  smaller in  why read the  pulses out.  The  would  A SQUID  integrate  o f lower  noise.  sized pulses  would  possible reads  occur grain  out data  over these  energy  The m a j o r i t y  low e n e r g y  different  This  stages.  f i g u r e 4.12. therefore  flips.  would  on t h e d i g i t a l  flip  is  every  are recorded  also  grain  steps.  of the pulses This  i f a  becomes  shown  0.1 s e c o n d ,  This  would  then  explain  loop  be b u r i e d i n  the grouping of  oscilloscope trace.  100 150 TIME [usee] F i g u r e 4.12: P o s s i b l e s t r u c t u r e o f i n d i v i d u a l g r a i n f l i p s s e e n by f a s t e l e c t r o n i c s .  34  and  explain  i n the induction  would  in  250  4.2  SQUID Read  A grain  Out  100x100 radius  array  of  12  were  obtained  for  from  0.05  the  mT,  of  Indium  microns. several  squares  was  prepared,  Superconducting different  earth's  field,  to  magnetic to  with  Normal  fields,  12 mT.  a  curves ranging  Indium  has  a  34 critical  field  following  s t e p s were  1)  the to  2)  of  heater 1.7  K,  4)  the  the 5)  reaching was the  transition  3.4  input  signal,  lowering  and  temperatures,  zero  curves,  the  sample t o  cool  1 K  pot,  c u r r e n t , making s u r e  magnet  was  raised  by  The AT  the  t o normal a  preset  a l l the  state.  increased  and  to  supply  the  application  time  of  a  slow  controller. were  The  recorded  for  transition.  temperature, the  sample  through  to  the  temperature  constant,  ramp the  at  was  which  the  reversed,  normal  to  SQUID slowly  supercooled  fields.  normal  lower, ,  of  temperature,  f o r low  superheated K,  allowing the  superconducting  i n the  the  signal  The  i n the  superheated  upon  these  field.  to  SQUID  obtain  zero,  set to  t e m p e r a t u r e was  ramp  To  the temperature of the  current  desired  .  set to  t h e magnet was  the  mT  taken:  was  grains are 3)  28.3  and  occurred  transition broader for  35  higher  occurred spread field  between  in  2.6  transition  values.  An  example  of  the  f i g u r e 4.13. observed  The  for  transition  hysteresis  occurred  pot.  can  n o t be r e a c h e d  in  less within  At higher  f i g u r e 1.1.  prepared  normal  fields  1 K  with  to  new  B = 4 mT  4.0 mT,  fields  at  which  the temperature,  were  shown  point  range  found  widths to  be  in were the  of the  the superconducting  in transition  mask  is  transitions  o p e r a t i n g temperature  magnetic  spread  for  supercooled  than  by s w e e p i n g  The the  curve  state  a s c a n be f o r the  seen  sample  narrower  than  35 previously  found  w i t h o l d samples.  In that  case the spread i n  1 .  -8  .  I  1  2  2.5  Figure  4.13:  1  3 TEMPERATURE [K]  Superconducting  t o normal  1  3.5  4  transition for  12 ura r a d i u s i n d i u m g r a i n s i n an e x t e r n a l  36  1  field  B = 4  mT.  AT  for a field  o f 4 mT  was  20 mK,  w h e r e a s t h e new  sample had  SH  a  spread  AT  of  15 mK,  which  was  the  noise  level  i n the  SH  temperature  4.3  reading.  Radiation  Test  T e s t s were a l s o made t o f l i p magnet  was  adjusted  to give  t e m p e r a t u r e was t h e n  raised  t h e g r a i n s by r a d i a t i o n .  15.2 mT to just  at  The  low t e m p e r a t u r e .  below t h e t r a n s i t i o n  The point,  241  when  the shutter  noise size  level  was  was  opened,  approximately  o f 260 mV.  exposing 100 mV,  The r u n l a s t e d  three  l o n g p e r i o d o f t i m e was n e c e s s a r y grain The  flips.  step  A  sample  of these  furthest left  correspond  t o more  flips  one g r a i n  Am  below  source.  hours.  t o observe  i s shown  flipping,  flipping  The  t h e expected  and a h a l f  i n order  i s one g r a i n  than  the  step This  individual  i n f i g u r e 4.14. the larger  at nearly  steps  t h e same  time. The a  data  program  collected  which  counted  sizes.  As  shown  0.25 V,  indicating  Progressively value,  When t h e a r e a in  a  large peaks  sweep was  of steps  this  showed  number  of  single  are  found  at  a  37  large  grains  using step  peak  at  flipping.  multiples  e a c h p e a k was t o t a l e d , 9,015  Some o f t h e m i s s i n g  analyzed  of d i f f e r e n t  2, 3, 4, and 5 g r a i n s f l i p p i n g  under  5,886 s t e p s .  t h e number  i n f i g u r e 4.15,  smaller  indicating  i n the thermal  of  this  simultaneously. grains  flipped  985 g r a i n s may h a v e  flipped  during be  t h e SQUID r e s e t s ,  a problem  every  10 o r s o v o l t s .  i n a p p l i c a t i o n s such  lower c o u n t i n g r a t e s  a r e expected.  38  as d e t e c t i n g  This  would n o t  WIMPs s i n c e  much  F i g u r e 4.15: Number o f o c c u r r e n c e s v s s t e p s i z e f o r 100x100 a r r a y o f i n d i u m g r a i n s f l i p p e d by r a d i a t i o n .  Chapter 5  Microgravity  5.1  Preparation  A  to  gravity. shape  was  conduct  an  In t h i s  environment  Space  a i r p l a n e which  experiment  and t h e i r  Agency  arranged  five  minute  flight break.  a l l have  fabricate  the effects  for a  pattern  of gravity  on t h e  be r e d u c e d . on  flies  around  1.8 g .  10  parabolas i n  experiments.  Each  parabola a t an  by about  65 s e c o n d s  by a  40 p a r a b o l a s consists  of  acceleration  .  .  i n approximately  N e g a t i v e g i s sometimes e x p e r i e n c e d d u r i n g t h e p a r a b o l a .  Each p a r a b o l a i s s l i g h t l y the  KC 135  10 p a r a b o l a s , f o l l o w e d  i n 'microgravity',  g, f o l l o w e d  The  The p l a n e i s used  -2  of  NASA's  i s repeated u n t i l  completed.  20 s e c o n d s  i n low  flight  as r u n s c i e n t i f i c  Space  arrays  conditions.  the plane f l i e s This  been  approximately  to  t o t h e Canadian  i s a m o d i f i e d B o e i n g 707 w h i c h  a s t r o n a u t s as w e l l  On e a c h  made  m e t a l l u r g y would  a i rt o simulate microgravity  to train  in  application  of the grains  Canadian  the  for Flight  successful  Agency  Melting  pilots  (who  are the  different same  p i g g y backs t h e space s h u t t l e ) . around these  ones  and depends on t h e s k i l l who  f l y the plane  of  which  The e x p e r i m e n t must be d e s i g n e d  conditions.  40  5.2  Apparatus  The  aim  100x100  of  arrays  indium  the of  spheres,  indium  in  way  supply  of  of  s a m p l e s i n an w o u l d be  for  Because o n l y  was  apparatus minute  experiment Canadian trouble also  up  was  spots  The  floor  so  c o o l the the  Some  pass  experiment  was  T h i s was  the the  f r e e as  larger  this,  samples  i t  was  quickly,  temperature,and  way  of  containing since  20  a the  arrays  the  was  NASA's  during  sets  parabolas.  in  be  very  of The  designed securely cabin.  equipment t o ,  the  to  The  as w e l l  components.  41  advice  or  Large  to  the five The  of  the  potential  1.8  safety  g.  It  was  regulations  KC-135.  f i t on  bolted  the  pinpointing  strict  u s e d on  possible,  changed  simple.  sought  necessary  A l l equipment  Wherever  between very  i t was  possible.  piece. be  airplane's  some e l e c t r i c a l  solidify  single  also required,  i t could  kept  apparatus could  of  as  t h a t might occur i n m i c r o g r a v i t y  base t o a t t a c h sink  second  Agency  aluminum p l a t e . the  a  breaks  to  and  accomplish  were p l a n n e d ,  trouble  also  Space  the  flights  as  flight  well  monitoring  above.  remelt  flight.  designed  necessary  before  the  two  with  was  level  and  each  experiment  backed  as To  o r d e r l y f a s h i o n was  h e a t e d on  make t h e  spheres,  to  o v e n , t o h e a t and  controlling  power  was  microgravity.  n e c e s s a r y t o h a v e an some  experiment  a  to the  26x26x1/2 i n c h 20  aluminum as  inch grid gave  a  secure  a l a r g e mass t o  handles  were  on  heat  placed  on  three  sides  handles  to  also  a i d the operator  gave  a  measure  during the transition The  of  during  the flight.  protection  to  the  These equipment  from m i c r o g r a v i t y t o h y p e r g r a v i t y .  apparatus consisted  o f f o u r major  parts:  t h e oven, t h e  36 temperature holder.  controller,  These  the  battery  a r e shown on t h e b a s e  pack plate  ,  and  the  i n f i g u r e 5.16.  c a b l e c o n n e c t i o n s t o e a c h box were s u p p o r t e d u n d e r n e a t h pieces The  of metal  tool  make  digital  screwdrivers,  repairs  was a l s o  monitored  oven  inch  hot  plate.  plate.  and h e l d  On  be n e c e s s a r y  the flight.  T h e two  thermocouple  on t h e  i n place  four P e l t i e r top  controller.  T h e o v e n was made o f a  T h e N i C r w i r e was f o l d e d  of  by c e r a m i c .  the  plate  also  on t h e s i d e s  placed  t h e temperature.  of the plate  T h e o v e n was e n c a s e d  were  under t h e  A l o n g t h e edges o f  e l e m e n t s were p l a c e d ,  and an IC t o m o n i t o r  place.  I t held  diameter NiCr wire coated i n  elements.  thermocouple placed  which might  type K  on t h e t e m p e r a t u r e  1 square  copper p l a t e ,  and v e l c r o .  meters,  a n d c o o l e d by P e l t i e r  copper p l a t e ,  s t e p p e d on.  t o run t h e apparatus without these  was h e a t e d b y 0.3 mm  copper  by s m a l l  backup.  ceramic,  the  a  were  The  t h e second b e i n g a  using only the l i g h t s The  cloth  during  O n l y one m e t e r was u s e d , possible  i f they  and wrenches,  and adjustments 37  thermometers  oven p l a t e . It  damage  c o n t a i n e r was made o f h e a v y  a l i e n keys, to  t o minimize  sample  t o cool the a  type K  C l a s p s were  to hold  t h e sample i n  i n an aluminum b o x .  A h o l e was c u t  42  I  e  1  battery pack  digital thermometer controller •  o  o  o  •  Ih sample holder  oven  ©  ©  F i g u r e 5.16:  in  the  top  of  B a s e p l a t e and f l i g h t  the  box,  so  that  the  apparatus.  sample  could  be  observed.  T h i s h o l e was  covered with a p l e x i g l a s s  sheet t o minimize  from  oven.  were  the hot  plate.  A  narrow  The  slit  sheet  was  machined  n e x t t o t h e window, t h r o u g h The  apparatus  allowed  and  the  box  bolted  out of the side  to the of the  w h i c h t h e s a m p l e s c o u l d be sample  43  to  be  heated  danger base box  inserted.  and  cooled  rapidly,and  f i g u r e 5.17  a thermocouple  shows  the  temperature  recorded  by  on a c o p p e r b o a t i n a h e a t - c o o l c y c l e .  200 i  .  0 I 0  1  1  1  1  i  i  i  i  i  i  10  20  30  40  50  60  70  80  90  100  110  TIME Tsl F i g u r e 5.17: H e a t i n g and c o o l i n g o v e n p r e p a r e d f o r jLig f l i g h t .  c u r v e f o r sample i n  The  controller  box  f i g u r e 5.18. before  the  for The  flight  the heater so  l o w e r t e m p e r a t u r e was with  temperature and  t h e upper 35°C.  t h e h e a t e r and c o o l e r  on t h e l e f t  cooler  current  temperature  Fine adjustments off dials.  o f t h e box, c o n t r o l l e d  44  is  shown  s e t were was  160°C  in  adjusted and t h e  o f t h e s e were made  A heat/off/cool  the temperature.  switch,  HEATER OFF TEMP.SET  o  HEAT  OFF  COOLER OFF TEMP.SET  COOL  Figure  The was  batteries than  limited The  A  producing  and  e a c h one The  the  and  protect  were  yet  over had  access,  of  tight  cork  unreliable  the  to  are  one  box  designed  A  samples  before  Only fuse  side.  was  box  strip from  i n t o the  shown  the in  that  to  was  hold  used  could was  used  the  rather on be  the used  connected a  time  in  zero  hypergravity  part  the  i n the  wide  slits  metal  was  left  trodden  back o f  samples  between  source  a battery  two  being  the  power  and  at  in i t s circuit.  had of  were  e a c h one  battery  f o r easy access  remelting, hold  Batteries  so  batteries  foam p l a c e d  indicated that  11 V.  The  with  f i t .  somewhat  also allow  box.  four rechargable  a 10 Amp  parabola.  used  a  and  r o d s were s c r e w e d samples  sheets  g r e e n LED  sample  front  held  b a t t e r i e s were w i r e d  and  of  container  obtain  separately.  gravity  Temperature c o n t r o l  thin  to  the  plane.  5.18:  with  COOLER CURRENT SET  o  battery  lined  HEATER CURRENT SET  the  other on  f i g u r e 5.19.  45  on  box,  samples  cut in  i n t o the the  rod, The  middle  to  accidentally.  Two  one  the  for holding  f o r afterwards.  the  top  while green  The  clasps  allowing rod  held  easy the  u n m e l t e d s a m p l e s a n d i t s c l a s p was d e s i g n e d t o p r e v e n t i n s e r t i o n of  a  sample  washer  were p l a c e d  forward, rod  allowing  stored  samples  while  the  allowing  i t s easy  on t h e b a c k the last  samples  t o be p u t on  of this  few t o be  after  removal.  r o d t o push easily  remelting  i t readily,  A  and  spring the  removed.  plastic  f i g u r e 5.20. the  teflon  larger drilled  handles. The  screw  diameter  The  samples placed  than  were  sample pushed  holders into  i n the handle.  that  of  the  into the handles of holders  rod  A  i n the  f o r easy  mm  shown  in  as  of a sample  f a r as slightly box  storage.  (a)  (b) F i g u r e 5.19: Rods i n sample h o l d e r (a) s a m p l e s remelting (b) s a m p l e s a f t e r r e m e l t i n g .  46  The  t o 0.65  are  t h e oven hole  allowed  removed.  s a m p l e s were g l u e d t o c o p p e r b o a t s w h i c h were r i v e t e d thick  samples The r e d  i t s clasp  but not e a s i l y  and  before  was  PLASTIC  TEFLON NUT AND SCREW  COPPER  1  I (a)  (P~ < T  HOLE  Figure  5.3  near  5.20:  Sample h o l d e r  (a) t o p v i e w  (b) s i d e  view  Flight  experiment  t h e Johnson  days,  INDENTATION TO HOLD SAMPLE  RIVETS  Microgravity  The  (b)  was  Space  for a total  flown Center  of forty  from  Ellington  i n Houston,  parabolas,  A i r Force  Texas.  o r twenty  Base,  I t flew  two  samples.  The  batteries  were  p r o c e d u r e was a s f o l l o w s . When connected cooled  level  flight  and t h e oven  properly.  preparation.  was  estimated  the  by  was  turned  After  NASA  listening to  cool  was  sure  placed  This then  into  and a f r e s h  47  the start  point by  the  t h e o v e n was t u r n e d  and  i n t h e oven i n  was  the  of t h e engines.  t e n seconds  to the receptacle  i t heated  before  on.  director,  t o t h e sound  about  was  seconds  turned  test  entering hypergravity,  was removed  five  the  t o make  sample  Approximately the heater  obtained,  tested  The f i r s t  microgravity,  experimenter  was  of  first  flyer The  /  oven  microgravity.  o f f , t h e sample  sample  was p l a c e d i n  the  oven.  This  procedure  had  to  be  followed  without  head  movement! It  had  parabolas, sample. very  been  but  The  rapidly  operator.  planned  to  complete  i n the event r e q u i r e d  small once  This  mass o f t h e removed  left  from  time  one  only  copper  enjoy  one  boat  t h e oven,  to  sample  two  p a r a b o l a f o r each  allowed  w i t h no  the  every  i t to  danger  unique  cool  to  the  experience  of  microgravity!  5.4  Hysteresis  Curves  Once  samples  the  necessary  to  remelting  had  measured smaller  at  f i g u r e 5.21,  with 12  cryogenic  made  fixed  transition  difference  prepared  do  in  the  any  width  the grain  tests  for than  widths  lab.  centers  returned on  from  them  difference.  fields  t h e sample  i n the  were  can  melted Both  arrays  s e p a r a t e d by  mT.  48  discover  samples.  previously  i n aq,  to  Hysteresis  three  be  Houston,  easily and have 70 /am,  seen  and  i f  the were  showed  arrays. by  f i g u r e 5.22, grain  was  curves  They  tested  i t  a The  comparing a  sample 12  am  were m e a s u r e d  at  radius  of  —20 ' 2.1  1  1  2.2  1  2.3  1  2.4  1  1  1  2.5 2.6 2.7 T E M P E R A T U R E [K]  1  2.8  1  2.9  3  3.1  F i g u r e 5.21: Superconducting t o normal t r a n s i t i o n f o r 12 nm r a d i u s i n d i u m g r a i n s p r e p a r e d i n m i c r o g r a v i t y , i n an e x t e r n a l f i e l d B = 12 mT.  It  i s not completely  transition gravity. structure  width A  occurs  possible  changes,  understood  when  a  o v e r t h e volume o f t h e g r a i n . which nucleate  the array  reason  . . giving  why  is  much  such  change  i s melted  that  more  a  the  homogeneous  49  t o normal  lesser  polycrystalline  T h i s would produce  the superconducting  in a  i n the  structure  fewer  transition.  39  defects  5  _25  ' 2.1  1  1  2.2  2.3  1  2.4  1  1  1  2.5 2.6 2.7 T E M P E R A T U R E [K]  1  1  2.8  1  2.9  3  F i g u r e 5.22: Superconducting t o normal t r a n s i t i o n f o r 12 urn r a d i u s i n d i u m g r a i n s p r e p a r e d i n e a r t h ' s g r a v i t y , i n an e x t e r n a l f i e l d B = 12 mT.  50  3.1  Chapter  Experiments  It if  was  not  which  hoped t h a t  better  than  the  indium  under  other, enough  flatten  p r e s s u r e when i n the than  i t .  field,  and  mT  28.3  future, light  Tin  magnetic  will  Tin  has  two  K  arrays  f o r the  pressure  also  3.72  has and  f o r indium.  work, t h i s  In  results  a  final from  higher  30.3  mT  the  are  stacked  fingertips  on  of  Indium  is  easily  temperature  range  to  top  can  f o r t i n compared  temperature  It is a likely  detector.  critical  good  to  and  3.41  i n which  i n a steeper B vs T curve r e s u l t i n g  K we  in a  temperatures.  Hysteresis  A  100x100  array  of  18 /nm  diameter  t i n spheres  f o l l o w i n g t h e same p r o c e d u r e s u s e d t o i n v e s t i g a t e A  as  properties  so t h e spheres a r e l e s s  many  lower spread i n the t r a n s i t i o n  6.1  ones.  w o u l d be  make i t b e t t e r t h a n i n d i u m f o r u s e a s a d e t e c t o r .  deform  soft  - Tin Arrays  the t i n a r r a y s produced  much h a r d e r m e t a l t h a n i n d i u m ,  each  6  visual  examination  that  the q u a l i t y  for  the  later  with  of t h i s indium  the  microscope  a r r a y was  arrays,  not  there  51  at  was  tested  indium  arrays.  125 power  as good as t h a t being  a  fair  showed  obtained  amount  of  scatter  in  the  placement  of  the  spheres  with  some  completely  missing. H y s t e r e s i s c u r v e s were m e a s u r e d f o r m a g n e t i c f i e l d s from  0.05  the curves The of  mT  (Earth's f i e l d )  obtained  cryogenic transition  than  to  16 mT.  An  i s shown i n f i g u r e 6.23  quality  of  temperatures  that of the  up  indium  the  sample  which  example  i s about  of  for a field  i s reflected 30 mK,  ranging one  of  of 4  mT.  i n the  spread  a value  larger  samples p r e p a r e d p r e v i o u s l y  4 0  .  3  0.5  1  1  3.41  3.42  1  3.43  1  1  1  1  3.44 3.45 3.46 3.47 T E M P E R A T U R E [K]  1  3.48  1  3.49  1  F i g u r e 6.23: Superconducting t o normal t r a n s i t i o n f o r 18 jim d i a m e t e r t i n g r a i n s i n an e x t e r n a l f i e l d o f B = 4  52  3.5  mT.  Although transition found in  scale  into sphere  tin  sample  temperatures,  f i g u r e 6.24,  take the  to  the  w i t h magnetic  a  to  the  much  midpoint field  as  i n which the magnetic  consideration due  the  had  of  the  expected. field  the higher f i e l d higher  broader  density  of  transition This  i s scaled  felt  spread  at the  magnetic  in was  i s shown by  3/2  to  equator  of  flux  found  T E M P E R A T U R E [K] F i g u r e 6.24: F i e l d vs t r a n s i t i o n temperature, squares: t i n a r r a y o f r a d i u s 9 jam s p h e r e s , diamonds: t i n colloid o f 7 /am r a d i u s s p h e r e s .  53  there.  Also  shown a r e d a t a  points  for a colloid  of t i n spheres  41 o f a v e r a g e r a d i u s 7 jim curve.  Note t h a t  uncertainty  An the  t i n sample.  slightly  i n lower  i n higher  fields,  fields  on t h e same  has a  greater  due t o t h e l a r g e r  spread  temperatures.  attempt  calculated  The p o i n t s a p p e a r t o f a l l  the t r a n s i t i o n  than that  in transition  .  was  made t o r e c o r d  This  t o be a r o u n d  proved 0.1 V  individual  unsuccessful a t B = 12 mT,  g r e a t e r t h a n 0.1 V.  54  as  grain  flips  with  the  flips  were  while  the noise  was  Chapter  7  Conclusions  The  pumped He c r y o s t a t u n d e r w e n t m i n o r m o d i f i c a t i o n s w h i c h 4  significantly the  SQUID  reduced  signal.  the vibrational A  new  a r r a y s , which gave b o t h and  a lowering  mask  n o i s e and g r e a t l y improved  was  used  i n the production  b e t t e r s i z e and placement  i n the spread  of transition  of  distributions,  temperatures  f o r the  array. Using an  array  this  c r y o s t a t and a f a s t  o f 13x27  indium  energy peak expected the  pulses  Observing  sweep  showed a s e r i e s in  time.  actually  This  g r a i n s was s t u d i e d .  read  o u t system,  The w e l l  defined  i n t h e MCA s p e c t r u m d i d n o t a p p e a r , most o f  appearing a  electronic  t o have  of  the  of small suggests  b e composed  a  lower  field  on  energy  the d i g i t a l  p u l s e s , many  i n groups  that the steps  o f many  smaller  than  oscilloscope  and spread o u t  seen w i t h  steps  predicted.  t h e SQUID may  associated with the  g r a i n becoming normal i n s t a g e s . A  full  studied  100x100  with  array  the  of  12 u.m  cryostat  radius and  indium SQUID  spheres  was  electronics.  Superconducting-supercooling  h y s t e r e s i s c u r v e s were o b t a i n e d f o r  magnetic  0.05 mT t o 12 mT.  fields  transition  ranging  from  c o u l d n o t be o b s e r v e d  for fields  55  The s u p e r c o o l i n g  of 4  mT  or greater  since  they  occurred a t a temperature  temperature transition grain  rays  an extended  time  that  t h e step size  size  Indium  grain  microgravity Hysteresis centers  separated  arrays  array  i nthe lab.  the in  i t does a f f e c t  individual  crystals  thecrystals  8  These  were  melted  aboard with  by a  steps  were  that  by  between s i n g l e and  and  NASA's  solidified KC-135  12 lira r a d i u s  factor  since  similar slight  structure,  nucleation  Fewer  making defects  centers,  which  temperatures.  a r r a y s o f 100x100 s p h e r e s , w i t h g r a i n  More work n e e d s t o b e done t o i m p r o v e  a  they are very small, but  a n d more r e g u l a r .  centers separated  with  i n transition  has only a  thepolycrystalline  g i v e fewer  airplane.  o f two t h a n  gravity  in a  spheres  t h e spread  The l e s s e r  larger  would a l s o  a n d 13 /nm, w i t h  Single  o f occurrences o f steps  would a l s o d e c r e a s e the spread i n t r a n s i t i o n Tin  field.  I t was f o u n d  t o discriminate  on t h e shape o f t h e g r a i n  presumably  observed.  b y 70 /am i n d i c a t e d  was n a r r o w e r  affect  applied  period.  f o r a sample  temperatures melted  t h e spreads i n  events.  environment  curves  with  were  1.7 K, t h e o p e r a t i n g  expected,  a n d t h e number  i t was p o s s i b l e  simultaneous m u l t i p l e  As  increased  d u e t o gamma  over  observing  pot.  temperatures  flips  counted  of  of the 1 K  below  radii  b y 70 lira, w e r e the quality  o f between also  made.  of the arrays  s i n c e some s p h e r e s a r e m i s s i n g w h i l e o t h e r s h a d moved d u r i n g t h e melting the  process.  cryostat  with  An a r r a y  o f 9 urn. r a d i u s  t h e SQUID  setup.  56  s p h e r e s was t e s t e d i n  Hysteresis  curves  were  obtained the  for various  grains  fields.  scales with  The  field,  width of the  as  expected.  transition  of a l l  However, t h e  spread  i n t r a n s i t i o n temperatures are wider than those indium The  B-T  arrays,  a  reflection  p h a s e d i a g r a m was  that previously obtained to  record  estimated  of  s i z e was  poor  q u a l i t y of  mapped f r o m 0.05  to  for a t i n colloid.  discrete transitions step  the  of the  of  individual  same o r d e r  57  measured f o r  16 mT. 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Gonzalez-Mestres and D. P e r r e t - G a l l i x , Editions Frontieres, Gif-sur-Yvette, (1989) p . 417. 23  Supercon, core/copper: 2  4  see  . Inc. superconducting wire, type .005"/.0065", insulation: Formvar.  T48B,  diameters  #7.  25 Labtech Notebook Version 4.1, Laboratory Technologies C o r p o r a t i o n , 2 5 5 B a l l a r d v a l e S t r e e t , W i l m i n g t o n , MA 0 1 8 8 7 .  59  26  KPR t h i n f i l m r e s i s t ( c a t a l o g u e number 7 0 5 ) , KPR t h i n f i l m r e s i s t thinner ( c a t a l o g u e number 7 1 5 ) , and KTFR d e v e l o p e r (catalogue number 749) f r o m M.G. C h e m i c a l s . 27 Blak-ray long wavelength u l t r a v i o l e t 100 W l o n g w a v e m e r c u r y s p o t b u l b .  lamp  f r o m UVP  Inc. using  28 M. L e G r o s , A. Da S i l v a , B.G. T u r r e l l , A. K o t l i c k i D r u k i e r , i n Low Temperature Detectors for Neutrinos Matter III, e d . L . B r o g i a t o , D.V. Camin and E. F i o r i n i F r o n t i e r e s , G i f - s u r - Y v e t t e , 1990) p a g e 91. 29 . Kindly  a  and A.K. and Dark (Editions  s u p p l i e d by DuPont Canada.  30  . M. L e G r o s , G. Meagher, A. K o t l i c k i , B.G. T u r r e l l , and A.K. D r u k i e r , Proceedings of the 2nd London Conference on PositionSensitive Detectors, S e p t . 4-7 1990, I m p e r i a l College, London. 31 M. L e G r o s , A. Da S i l v a , D r u k i e r , A p p l . Phys. L e t t .  B. G. T u r r e l l , A. K o t l i c k i , 5 6 , 2234 ( 1 9 9 0 ) .  and  A.  K.  32 ACE  M u l t i c h a n n e l A n a l y z e r , v e r s i o n 4.03,  EG&G O r t e c .  33 SCC-1220 D i g i t a l S t o r a g e O s c i l l o s c o p e , F e r n a n d o , C a l i f o r n i a , 91340-1597.  Soltec  Corporation,  San  34 C. J . S m i t h e l l s , Metals Reference Book Volume III, C h a u c e r P r e s s , S u f f o l k , G r e a t B r i t a i n (1967) F o u r t h E d i t i o n , p a g e 747. 35 . . M. L e G r o s , A. Da S i l v a , B.G. T u r r e l l A. K o t l i c k i and A.K. D r u k i e r , i n Low temperature Detectors for Neutrinos and Dark Matter, e d s . L. G o n z a l e z - M e s t r e s and D. P e r r e t - G a l l i x , Editions F r o n t i e r e s , G i f - s u r - Y v e t t e , (1990) p . 91. 36 The t e m p e r a t u r e c o n t r o l l e r and b a t t e r y p a c k were d e s i g n e d and constructed by t h e t a l e n t e d technicians i n t h e UBC physics e l e c t r i c a l and m a c h i n e s h o p s . 37  . . Digi-sense, parmer.  model  no.  9528-40,  type  K  38 R e c h a r g a b l e b a t t e r y NP6-12, f r o m Y u a s a ,  60  thermocouple,  12 v o l t s ,  6.0  from  Ah.  Cole  J.J. Favier, J . Berthier, Ph. A r r a g o n , K h r y a p o v , a n d I.V. B a r m i n , A c t a A s t r o n a u t i c a ,  Y. M a l e j a c , V.T. 9, 255 ( 1 9 8 2 ) .  40 M. L e G r o s , A. Da S i l v a , B.G. T u r r e l l A. K o t l i c k i a n d A.K. Drukier, i n Low Temperature Detectors for Neutrinos and Dark Matter, e d s . L . G o n z a l e z - M e s t r e s a n d D. P e r r e t - G a l l i x , E d i t i o n s F r o n t i e r e s , G i f - s u r - Y v e t t e , (1990) p . 91. 41 A. Da S i l v a , I n v e s t i g a t i o n of a Superheated Superconducting Colloid, M.A.Sc. t h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1988.  61  

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