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Title: Studies of thin films at liquid helium temperatures using an electron diffraction camera
Author: Mascall, Anthony James
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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An electron diffraction camera incorporating a liquid helium cryostat has been used to study the properties of various materials at about 4.2°K. Section I. Thin films of solid hydrogen and solid deuterium obtained by condensation from the vapour at about 4.5°K were studied by reflection electron diffraction. The diffraction patterns from hydrogen contained sharp rings from a face-centred cubic structure with ao = 5.29 ± 0.05 A, and broad rings from a hexagonal close-packed structure with the same intermolecular spacing. The patterns from deuterium contained sharp rings from a face-centred cubic structure with ao= 5.07 0.05 A. The results are discussed with reference to the recently discovered structural transformations found in these elements below 4°K. Section II. Solid binary mixtures of argon-krypton and argon-neon were formed by condensing the pre-mixed gases at about 7°K. The argonkrypton mixtures formed a crystalline structure at all concentrations, the lattice parameter being dependent on the relative concentration. No evidence was seen of the phase separation which has been predicted by other workers. The behaviour of the argon-krypton mixtures is compared with that predicted from a theoretical model of such solutions. The argon-neon mixtures formed an amorphous structure at all concentrations; at the higher neon concentrations the deposits also contained separate crystallites of pure neon. This behaviour is in accord with the predicted insolubility of argon and neon in the solid state. Section III. An electron beam shadow technique was used to study the mixed state and the occurrence of flux trapping in a thin film sample of Nb3Sn, a typical type II superconductor. The same technique was used to show that thin films of beryllium condensed at about 5°K are superconducting, confirming the results of Lazarev (1960). Diffraction patterns from the beryllium films showed that a disordered structure was formed on condensation. Thin films of iron condensed at the same temperature were not superconducting.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available