3.2 Characterization techniques 49
are features that depend on the stoichiometry. References have been reported
and compared by Gorlin et al. 151 and the values can be seen in table 3.1.
Sample Reference E2p1
2 eV E3s eV
MnO 151 11.8 4.5
MnO 192 11.9 4.5
Mn3O4 151 10.0 5.1
Mn3O4 192 10.5 5.4
Mn2O3 151 6.0 6.0
Mn2O3 192 5.4 6.1
MnO2 151 10.5 6.0
MnO2 192 11.3 5.3
Table 3.1: Reference values for the Mn2p1/2 satellite distance and Mn3s multiplet
splitting.
The XPS system used throughout the project has been a ThetaProbe Instrument
from Thermo Scientic, where the base pressure was 5 x 10��10 mbar. The Xray
source was monochromatized AlK (1486.7 eV). All XPS measurements have
been conducted by Kenneth Nielsen or Paolo Malacrida at CINF DTU.
3.2.2 X-ray Diraction
X-Ray Diraction is another routinely used technique that can provide crucial
information about catalytically active samples 46. The technique is based
on the principles of Bragg's Law, which states the conditions that must be
fullled to observe constructive interference of radiation scattered by the atoms
in a crystalline specimen. In a crystalline material all the atomic positions can
be described by a simple set of vectors that forms the crystal lattice. It is
the interaction between the incoming radiation and a large number of crystal
planes that can lead to strong constructive interference observable in X-Ray
Diractograms. This eect is illustrated in a simple schematic in gure 3.4.
The condition described by Bragg states that for a given wavelength, , and
interplanar distance, d, constructive interference is possible at an angle given
by:
n = 2d sin ; n = 1; 2; ::: (3.3)
Besides identifying crystalline phases, the XRD method can be used to estimate
the mean size of sub-micrometer ordered domains, or crystallites, . This is
done by using the Scherrer equation 194:
=
K
cos
(3.4)