SUPPLEMENTAL INFORMATION

X-ray irradiation induced effects on the chemical and electronic properties of MoO3 thin films

X. Liao,1,* A.R. Jeong,1 R.G. Wilks,1,2 S. Wiesner,1 M. Rusu,1

and M. Bär1,2,3,*

1Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany

2Energy Materials In-situ Laboratory Berlin (EMIL), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin,

Germany3Brandenburgische Technische Universität Cottbus-Senftenberg, Institut für Physik und Chemie, Platz der Deutschen Einheit 1, 03046 Cottbus, Germany

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Fig. S1 Mo 3d XPS (Mg K, 30 W) detail spectra of a MoO3 thin film before (“pristine MoO3”) and after 420 min hours of UV (He I) exposure.

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Fig. S2 XPS survey spectra of MoO3 thin films after UV (He I) and Mg Kα exposure using a source power of (a) 300 W, (b) 100 W, and (c) 30 W.

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Fig. S3 Fits of selected Mo 3d spectra after different Mg Kα exposure times using a source power of 100 W. The residuum (difference between data and fit) is shown under each fit.

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Fig. S4 Fits of selected Mo 3d spectra after different Mg Kα exposure times using a source power of 30 W. The residuum (difference between data and fit) is shown under each fit.

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In order to confirm the Mg Kirradiation – induced reduction of MoO3, we consult the O 1s

spectra. With increasing exposure time, the O 1s spectra broaden (the 300 W data is

exemplary shown in Fig. S5). In detail, the O 1s metal oxide component at low binding

energies (530.31 ± 0.05 eV eV) decreases in intensity while the contribution at high binding

energies (531.60 ± 0.05 eV eV) increases in intensity as indicated by the arrows. Neglecting

the oxygen species related to the high binding energy O 1s contribution that can be associated

with a surface hydroxide/carbonate [1] or with an oxygen deficient chemical environment [2],

the intensity of the low binding energy O 1s contribution (see also Fig. S6 for a detailed fit

analysis) that is attributed to molybdenum oxide [3] is used to estimate an O/Mo ratio

evolution assuming that the highest intensity presents the nominal O/Mo ratio characterizing

MoO3. If this O 1s derived “O/Mo ratio” is arbitrarily connected to the O/Mo ratio evolution

determined from the Mo 3d fits (see Fig. 3) such that the data points at an Mg K irradiation

of 453 min agree (see Fig. S5(b)), a reasonable agreement can be observed. Based on this, we

conclude that the primary mechanism for the beam damage induced changes observed for

MoO3 thin films during Mg K irradiation is the creation of oxygen vacancies with a

corresponding reduction of Mo, rather than a purely morphological or structural change.

Fig. S5 (a) O 1s spectra measured after different Mg K (300 W) exposure times and (b)

O/Mo ratio derived from the O 1s and Mo 3d spectra as a function of Mg K (300 W) exposure. Note that the O 1s derived O/Mo ratio is arbitrarily set agree with the Mo 3d-based ratio at an exposure time of 453 minutes.

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526528530532534536

78153228303378453528603678753828903978

Inte

nsity

(a.u

.)

Binding energy (eV)

exposure time (min) (a) O 1sMg K

300W

0 200 400 600 800 1000

2.70

2.75

2.80

2.85

2.90

2.95

3.00

derived from Mo 3d derived from O1s (oxide)

O/M

o ra

tio (%

)

exposure time (min)

(b)

Fig. S6 Fits of selected O 1s spectra after different Mg K (300 W) exposure times. The magnified residuum (difference between data and fit) is shown under each fit.

References

[1] B. Brox, I. Olefjord, Surf. Inter. Anal. 13 (1988) 3.

[2] W. Li, S. Zhao, B. Qi, Y. Du, X. Wang, M. Huo, Appl. Catal. B: Environ. 92 (2009), 333.

[3] M. Vasilopoulou, A.M. Douvas, D.G. Georgiadou, L.C. Palilis, S. Kennou, L. Sygellou, A. Soultati, I. Kostis, G. Papadimitropoulos, D. Davazoglou, P. Argitis, J. Am. Chem. Soc. 134 (2012) 16178.

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