Wide-band dielectric spectroscopy of small-molecule glass-forming liquids and insulating thin films

Abstract

This thesis describes the application of broadband dielectric spectroscopy in the frequency range 1 mHz - 1.8 GHz to two main topics; (i) the glass transition and relaxation features of supercooled liquids and glasses, and; (ii) the characterisation of insulator films for use as low dielectric constant (low-k) dielectrics. The first two chapters provide background information on dielectric theory of materials and the glass transition. The remainder of the thesis covers four main areas of study. The dielectric spectra of pure and 1.0 mol% LiCl04 solutions of supercooled liquid and glassy 1-propanol and 0.5-1.0 mol% LiCl04 solutions of 5-methyl-2-hexanol were measured. Analysis of the spectra showed three relaxations (process I, II, and III) in the frequency range 1 mHz - 1 MHz which persist on addition of the salt. The effect of ions on the dielectric properties is discussed. Arguments against the assignment in the literature of process II as the a-relaxation (with process I being unrelated to viscous flow) are given. The crystallisation of supercooled liquid D-sorbitol was investigated by holding samples isothermally for several hours at different temperatures, and observing the evolution of the dielectric spectra.