Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 249
7. Surface properties
In this chapter are collected together various studies involving the surface properties of a
number of selected oxide tellurite and fluorotellurite compositions. Specifically: X-ray
photoelectron spectroscopy (XPS), chemical durability to water, acids and alkalis, and
ion exchange. XPS was performed: (i) to asses the effect of fluorination on batch
materials, and (ii) on polished and cleaved bulk tungsten-tellurite and fluorotellurite glass
surfaces for semi-quantitative elemental analysis, to quantify the effect of melt time on
composition of the later system.
Chemical durability was investigated, to choose a possible etchant to ‘clean’ up the
preform surface prior to fibre drawing. The ideal etchant would etch congruently, to leave
a topologically smooth, and non-contaminated surface. Some of this etching was
quantitative by a simple weight loss method, and other results qualitative, describing the
quality of the etch. Environmental durability was also studied as any fibre device will
inevitably come into contact with water. Therefore, it was important to assess the
sensitivity of the glass to water, as the degree of degradation would determine if materials
properties (e.g. mechanical and optical) were significantly affected.
Two methods of ion exchange were investigated for an oxide tellurite composition, in
both cases Ag + for Na + exchange was attempted. This was undertaken to study the
possible manufacture of planar waveguide devices containing a silver rich surface layer
with a potentially higher refractive index than the bulk glass, due to the increased
polarisability of Ag + compared to Na + , 2.40 and 0.41 Å 3 (1 Å 3 = 1×10 -3 nm 3 = 1×10 6
pm 3 ) respectively [1].