5.3 Experimental validation of the concept 83
parameters were the same as described earlier for the pure MnO2 lms with the
exception that for the last 5 nm, Mn and Ti were co-deposited in a ratio corresponding
to 4:1. The concentration value is on a total metal basis, i.e. Ti
Ti+Mn.
The substrates were QCMs and Au polycrystalline samples which were kept at
200 oC during deposition. A schematic of the mixed thin lm samples can be
seen in gure 5.5.
Figure 5.5: Schematic showing the layered structure of the thin lm samples. The
lowest layer, in teal, is a quartz oscillator which is used for the frequency measurement.
A gold layer, in yellow, is deposited for electronic contact to the catalytic layer.
Between the quartz and the gold a thin titanium layer is deposited for adhesion but
this is not shown on the gure. On top of the gold layer a 35 nm thin MnO2 lm is
deposited, shown in blue. Finally the last 5 nm consist of mixed Ti-MnO2 deposited
by co-sputtering, shown in lighter blue with a shadow line.
The deposition rates of Mn and Ti were calibrated with an in-chamber QCM
to match 20 % Ti ratio and this was conrmed by X-ray Photoelectron Spectroscopy,
XPS. XPS measurements were conducted before and after electrochemical
test for a set of samples and Mn2p and Ti2p peaks were used for
quantication. In gure 5.6a-d the XPS data can be seen for both peaks before
and after testing. A simple integration of the peaks was used to obtain atomic
percentage values. Both before and after test, the Mn:Ti ratios were approximately
4:1. The XPS measurements were also used to conrm that the Mn3s
multiplet and Mn2p1
2 satellite positions were consistent with a MnO2 stoichiometry,
as for the pure lms described in chapter 4. This was indeed the case and
in this chapter the thin lms will be denoted as Ti-MnO2 and MnO2.
The morphologies of these lms were investigated with Scanning Electron
Microscopy, SEM. Four dierent samples were used, MnO2 and Ti-MnO2 as
prepared and after electrochemical testing. In this way, dierences introduced
by titanium modication could be investigated as well as from the stability tests.
To facilitate comparison among the tested lms, all the samples for SEM were
deposited on EQCM substrates, which were then broken into smaller pieces and