352 



A. FELTYNOWSKI, I. GLASS AND L. GRELEWICZ 



Figs. 1-6 show the difference in grains obtained 

 when six different gelatins are used in emulsions 

 which are otherwise completely similar. 



From this investigation it seems to be impossible 

 to draw a definite conclusion about the relation 

 between silver-grain size and silver-grain colour 

 without taking into account the kind of gelatin used. 



For the ossein gelatin the grains are more compact 

 and more dense in the blue-black pictures, while for 

 the skin-gelatin the effect is just opposite. 



Further work is in progress in order to interpret 

 these different findings while taking into account 

 the physical and chemical properties of the gelatins 

 used. 



We wish to express our sincere appreciation to Messrs. 

 L. de Barcy and P. Frottier of the Entreprises Chimiques 

 et Electriques at Vilvorde for permission to publish this 

 paper. 



References 



1. Ammann-Brass. H., Colloque de Science Photogr., 



Paris 1951. 



2. Arens, H., Z. wiss. Pilot. 43, 120 (1948). 



3. Baker, Th., Photographic Emulsion Technique. Mc 



Millan. 



4. Bradley, D. E., Brit. J. Appl. Phys. 5, 96 (1954). 



5. Chibisov, K. V. and Mikhailova, A. A., Kino Photo 



Chem. Incl. 3, 24 (1937). (In Russian.) 



6. Hall, C. E. and Schoen, A. L., J. Opt. Soc. Am. 31, 



281 (1941). 



7. Hamm. F. a. and Co.mer, J. J., /. Appl. Phvs. 24, 1495 



(1953). 



8. JOHANN, I. and Klein, E., Sc. et Ind. Phot. 27, 91 (1956). 



9. Karpova, a. L. and Moshkovskii, Sc. et liul. Phot. 11, 



346 (1956). 



10. Levenson, G. I. p. and Tabor, J. H., Sc. et Ind. Phot. 23, 



295 (1952). 



11. Pouradier, J., Chim. et Ind. 74, 1175 (1955). 



12. Trivelli, a. p. H. and Smith, W. F., Z. wiss. Phot. 



2,1, 123 (1938); 37, 140 (1938). 



13. Wall, E. Photographic Emulsions. 



The Microstructure of Photoconductive PbTe Layers 

 A. Feltynowski, I. Glass, an<d L. Grelewicz 



Institute of Physics, Polish Academy of Sciences, Warsaw 



1 he microstructure of PbTe layers has been in- 

 vestigated by means of electron diffraction and 

 electron microscopy. These layers are photosensitive 

 in low temperatures and show high sensitivity to the 

 infra-red radiation (2). 



They are usually formed in a glass envelope of the 

 diameter 45 mm and the height 20 mm. The envelope is 

 provided with appropriate electrodes to enable the meas- 

 urements of the photosensitivity. The layers are formed 

 by a twofold evaporation process: in the first stage the 

 substance is evaporated onto a wall without electrodes, 

 whence, in the second stage, it is made to evaporate onto 

 the opposite wall bearing electrodes; the wall on which the 

 PbTe vapour condenses is subjected to intense cooling. 



In order to prepare specimens for electron diffraction 

 and microscopic investigation the envelope was opened 

 after the first evaporation and a thin glass plate (cover- 

 glass) was placed on the wall bearing electrodes. It should 

 be noted that the glass plate covered only a part of the 

 wall; on the remaining part electrodes had been painted 

 with "aquadag" and provided with tungsten leads. To 

 the glass plate the grids of phosphor bronze were attached 

 by a thin formvar film. The envelope had a glass pipe, 

 through which the plate with the grids was placed inside 

 without heating the envelope. Then the envelope was 

 closed and evacuated and the layer evaporated onto the 

 wall bearing the glass plate with the grids. 



The photosensitivity of these cells can be measured. 



The photocell was opened and the grid with PbTe 

 layer adhering to the formvar film was carefully 

 deposited onto the specimen holder. 



PbTe forms crystals of NaCl type cubic struc- 

 ture with the lattice constant 6.34 A (3). 



The diffraction pattern (fig. 1) obtained with the 

 thin layer corresponds to simple cubic structures 



(Table I) with the lattice constant 3.21 A. A similar 

 diffraction pattern was obtained with the PbTe layer 

 evaporated onto the film directly from a tungsten 

 ribbon. 



Such inconsistency in the case of thin layers 

 prepared by evaporation is an indication that a 

 new form of PbTe is present. A possible explanation 

 should be found in random distribution of the 

 tellurium and lead atoms over the lattice points 

 in the thin layer, resulting in extinction of those 



Table 1. 



* Used as standard. 



