.STA'/IC/'.' /, M/'.A'.V ()/■■ ( RVSTM.S U.S 



A1i1h)U,<j;1i about a liair-miiiuk''s c'l(hiii<i; with IS' , liydrolluoric acid rc- 

 moNX's all (juart/ niisoricnted In- more than 45', (|uarl/, misoriciUcd by a 

 smaller angle than this is not entirely removed b}- more than an hour's etch- 

 ing, as indicated by {photographs taken with X-rax'S passing through the 

 plate, a technique to be described later in this paper. The ionization cham- 

 ber and amplifier are not sensitive enough to register the reflection from the 

 small amount of this material left after two minutes' etching. 



The disappearance of the more widely misoriented material in the earlier 

 stages of etching may mean either that this material is j)referentially removed 

 or that there is uniform removal of all the misoriented material with the con- 

 secjuent disa})})earance of that which is smallest in amount. (ieiger-Miiller 

 counter measurements of the mtensity-distribution of the reflections from 

 the misaligned material at various angles at the various stages of etching 

 would indicate which of the two alternatives is true. These measurements 

 are being made by Davisson and Haworth, but are not yet complete. 



2.4 Photography of the Disturbed Surface with a 

 Broad X-Ray Beam 



A second photographic method with the single-crystal spectrometer, used 

 by Berg in 193 P, Gogoberidze in 1940^", and others involves the reflection of 

 a broad monochromatic beam from an appreciable area of the crystal surface 

 (placed at the Bragg Angle, 6) onto a photographic plate or film placed paral- 

 lel to the crystal face. The different reflection-intensities from the variously 

 disturbed parts of the surface of the crystal plate darken the film differently, 

 giving a map-like picture of the distribution of different degrees of dis- 

 turbance over the surface of the plate. One picture produced in this way by 

 Berg is reproduced in Fig. 7. The thin white cross and circle are reference 

 marks scratched on the surface of the rock-salt crystal, the lines being parallel 

 to the cube edges. The two sets of sub-parallel streaks are the traces of do- 

 decahedral { 101 } planes and "show that the crystal structure in these places 

 differed from the ideal lattice". They are interpreted as slip planes (store- 

 benen) in the crystal. C. S. Barrett" has recently refined this technique and 

 broadened its application to the study of a wide variety of metallurgical 

 problems. 



The application of this technique to the study of quartz surfaces might 

 provide useful information on disturbance distribution which is not furnished 

 by the other techniques. 



■' Berg, Wolfgang, "Ubcr cine rontenographischc Mcthode zur fntcrsuchung von 

 Gittcrstorungcn an Kristallen," .\iilun.'issrnscli(iftcn 19 (1<).U), pp. 3')l-v5%. 



"' Gogoljeridzc, D. H., "Investigation of Surface Structure of Crystals by Means of 

 Reflection of a Monochromatic X-Ray Beam, Jour. Exp/l. Pliysic.'i, I'.S.S.R. 10 (1940) p. 

 96 (in Russian). 



" C. S. Barrett; "A New Microscopv and Us I'dtentialities," .\fit,ils Teclnwlo'^y, 

 April, 1945. 



