Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 313
Fig. (7.15) to (7.19) show the wide scan, and high resolution Na1s, Zn2p, F1s, Te3d,
and O1s XPS spectra respectively, for glass MOF001_v (65TeO2-10Na2O-25ZnF2 mol.
%), melted for 2 hours with fluorinated ZnF2. The quantitative analysis from the high
resolution scans for this glass are shown in table (7.7). Only the O1s peak was
asymmetric for this glass (see fig. (7.19)), with three peaks at 330.7 eV (88.9 % → BOs
and NBOs combined), 532.0 eV (5.8 % → OH), and 535.4 eV (5.3 % Te=O). The F1s
peak was symmetric for this glass, perhaps an indication of batch purity, as the ZnF2 was
fluorinated (far fewer F-Zn-OH species). From table (7.7), the fluorine levels were even
lower for this glass, melted for 2 hours (10.1 at. %), compared to the 1.75 hour melt (11.4
at. %), as a result of volatilisation. The O1s peak (50.4 at. %) was lower than the 1.75
melt by 1.8 at. %. This could be due to experimental error. Fig. (6.28) shows optical loss
plateaus to a minimum of around 10 dB.m -1 at 2900 cm -1 for melting times > 1.75 hours
for glass MOF001. This indicates that self-drying whilst melting has reached
equilibrium, i.e. most of the OH has been eliminated from the glass, therefore fluorine
volatilisation will not proceed as rapidly. If + a few at. % error is considered, the values
of oxygen and fluorine in glass MOF001_v from the XPS spectra are consistent with the
optical loss measurements of this glass series from chapter 6.
For comparison, fig. (7.20) and (7.21) show the wide scan and high resolution O1s
spectra for glass MOF001_v (65TeO2-10Na2O-25ZnF2 mol. %) un-cleaved surface. From
the O1s spectrum (fig. (7.21)), the OH peak at around 532.3 eV (OH) has grown
compared to the cleaved sample (fig. (7.19)). In addition to the peaks seen in the cleaved
sample, a fourth peak at 533.7 eV can be seen. This is likely to be organic (e.g. singly
bonded C-O). The OH peak has grown due to longer exposure to moisture of the un-