Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 256
where σ is the photoelectric cross-section, ζ the fraction of photoelectric events which
take place without intrinsic plasmon excitation, λ the mean free-path in the sample, η the
kinetic energy dependent spectrometer transmission, and I the area of the peak [3]. Cross-
sections are well known from theoretical calculations by Scofield [4], the mean free path
can be estimated from a universal curve, which depends on the energy of the incident
beam, not the atomic number of the sample, and η is inversely proportional to the kinetic
energy. Due to the superimposition of intrinsic and extrinsic plasmon events, ζ is difficult
to estimate. Often the entire loss tail is assigned to extrinsic events, i.e. ζ = 1. This can
introduce in significant errors into quantification, as ζ is not necessarily the same for two
individual elements in a compound [3].
7.1.2. Chemical and environmental durability
7.1.2.1. Method
For the chemical durability etching studies glass samples (of dimensions 3 × 5 × 5 mm,
polished as described in section 6.1.1.1.) were immersed in a solution of 50 ml of the
etchant, in a Pyrex beaker (250 ml capacity). For samples etched at 15 or 21°C, the
beaker containing the etchant was surrounded by a constant temperature water bath, and
the experiment begun (i.e. the sample was immersed) when the etchant had reached the
appropriate temperature, measured with a mercury thermometer. For some samples
(where stated) these were removed from the water bath to a sonic bath and agitated
ultrasonically at room temperature (measured), to ensure homogeneous etching on all