Akademisk avhandling--Stockholm. Högskolan. / Bibliography: p. 125-131.

Thesis (Ph. D.)--University of Iowa, 1923. / Reprinted from the Journal of the Optical society of America and review of scientific instruments, v. 10, no. 6, June, 1925.

A study of the growth of monocrystals of tellurium and selenium-tellurium alloys by the Czochralski method has been made, together with measurements of the photoconductivity in such materials. In tellurium, it was found that large temperature gradients occur within a growing ingot which cause an increase in the concentration of lattice defects. This concentration can be reduced by subsequent annealing. An etch pit orientation effect was observed enabling the growth direction of an ingot to be determined, arising from a correspondence between preferential growth and etching planes. Photoconductivity in tellurium at 77 K was found to be decreased by abrasive polishing of the samples and increased by annealing. Transient photoconductivity was found to be characterized approximately by two time constants, one of the order of microseconds and the other tens of microseconds. The largest D* detectivity measured on the samples was 1.3 x 10('11) cm Hz(' 1/2)w('-1) at 3.5 (mu)m. Crystals of Se(,x)Te(,1-x) were prepared by the Czochralski method for Te-rich and Se-rich compositions with 0.1 > x > 0.95. For intermediate compositions with 0.1 < x < 0.95 it was not possible to obtain Czochralski-ingots due to a meniscus rupture problem arising from excess selenium at the growing interface. In this case crystallographically aligned samples were obtained by a slow cooling method. Measurements on the Se(,x)Te(,1-x) alloys showed a continuous wavelength displacement of the photoconductivity maximum from 3.7 to about 0.8 (mu)m in going from tellurium to selenium. This was accompanied by an increase of some 5 orders of magnitude in the photoresponse, in the photoconductive decay time constants and in the electrical resistivity. From the results the estimated energy gaps were found to change continuously from tellurium to selenium with a possible change of slope starting near 40 at.% Se.

No description available.

<p> The nature of the coloured solutions of selenium and tellurium in sulfuric acid has been investigated using mainly cryoscopic, conductimetric, and spectrophotometric techniques. Evidence has been obtained for the new species Se₈²⁺ and Se₄²⁺ in the green and yellow solutions of selenium respectively. Evidence on red solutions of tellurium seems consistent with the formulation Te₄²⁺. Solid compounds analysing as Se₄S₄O₁₃, Se₄(HS₂O₇)₂ and TeO(HS₂O₇)₂ have been prepared and characterised. </p> <P> Solutions of some selenium(IV) and selenium(VI) compounds have been examined. It is shown that a number of phosphates and arsenates ionise in sulfuric acid to give the P(OH)₄⁺ and As(OH)₄⁺ ions respectively. Ammonium metavanadate and vanadium pentoxide ionise to give the complex acid H[VO(HSO₄)₄]. Potassium chromate and dichromate ionise to give the compound CrO₂(HSO₄)₂ and potassium permanganate ionises to give the non-electrolyte MnO₃∙SO₄H. </p> / Thesis / Doctor of Philosophy (PhD)

<p> The preparation of compounds containing polyatomic cations of sulphur, selenium and tellurium has been investigated by using oxidising agents such as AsF5, SbF5, S2O6F2 and SO3. New compounds, containing polyatomic cations Se8 2+, Se4 2+, Te3n n+, Te4 2+ Ten n+, S16 2+, S8 2+ and S4 2+, and anions of very strong acids such as Sb2F11- and AsF6- were isolated and characterised by a combination of the stoichiometry of the preparation reactions, UV-visible spectrophotometry, Infrared and Raman spectroscopy and magnetic susceptibility measurements.</p> <p> Solutions of sulphur in various concentrations of oleum were investigated in detail by UV-visible spectrophotometry and e.s.r. spectroscopy. Evidence is presented for the formation of the sulphur cations S16 2+, S8 2+ and S4 2+ in these media, and for the presence of low concentrations of the radical cations S8+ and S4+.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.