Anomalous X-ray Diffraction Studies for Photovoltaic ApplicationsGrisel Rivera Batista

Science Undergraduate Laboratory Internship Program

August 12, 2010.

Advantages of AXRD

Sensitive to: Neighboring

elements in the periodic table.

Specific crystallographic phase.

Specific crystallographic site in a phase.

AXRD – Combination of Structural & Chemical TechniqueStructural (XRD) Chemical (XAS)

X-rays diffract from specific

planes

Diffraction peak

Near resonant absorption

energy

X-raysabsorbed

RESULT

Diffracted peak intensity ↓ depending on elements present on diffracting planes

0.0

0.2

0.4

0.6

0.8

1.0

2.182.23

2.28

9600 9650 9700 9750 9800

Inte

nsi

ty, I

(a.

u.)

Misra, S., Bettinger J., Anomalous X-ray Diffraction (AXRD), 5thAnnual SSRL School on Synchrotron X-ray Scattering Techniques in Materials and Environmental Sciences: Theory and Application. June 1st, 2010

fn = f0(Q) + f ′(E) + i f ′ ′(E)

f0(Q) = normal (E

independent)

f ’(E) = anomalous (E

dependent)

f ’’(E) = absorption (E

dependent)

atoms

n

lzkyhxinlkh

nnneEfF1

2),,( )(

• fn is the atomic scattering factor

• xn, yn, zn are the (fractional) positions of the nth

atom

• Atomic scattering strength (fn) varies near X-ray absorption edge

• Varying X-ray energy near absorption edge → total intensity changes

• fn depends on oxidation state of the elementVariation for Zn

Energy, E (eV)

9000 9200 9400 9600 9800 10000 10200

Sca

tter

ing S

tren

gth

10

12

14

16

18

20

22

24

Sca

tter

ing S

tren

gth

0

2

4

6

8

10

f0+ f'

f''

Anomalous X-ray Diffraction (AXRD)

2

hklhkl FI

Misra, S., Bettinger J., Anomalous X-ray Diffraction (AXRD), 5thAnnual SSRL School on Synchrotron X-ray Scattering Techniques in Materials and Environmental Sciences: Theory and Application. June 1st, 2010

ZnO loaded with Gallium

Zinc

oxygen

Tetrahedral sites in ZnO cell

Q (Å -1)

2.0 2.5 3.0 3.5 4.0

Inte

nsity

(a.u

.)

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18(101)

(002)

(102)

(110)

(100)

(103)

(200)

(112)

(201)

ZnO loaded with Ga

Peak 100

Spinel: ZnCo2O4

Zn, Co

Oxygen

Spinel Inversion

Inversion determines the amount of each cation found on either the tetrahedral or octahedral site, and has a big effect on the electrical properties.

MixedSpinel

(0 <n < 1)

Normal spinel ( n = 0)

(Co) (Zn) (Co)

B A B

Inverse spinel ( n = 1)

(Co) (Co) (Zn)

B A B

Degree of Inversion Continuum

Peak 311

Conclusion

AXRD is an effective technique to characterize bulk and nanomaterials.

Acknowledgments

U.S. Department of Energy, Office of Science, through the Summer Undergraduate Laboratory Internship Program (SULI)

Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC National Accelerator Laboratory.

My mentors Michael Toney, Sumohan Misra, and Joanna Bettinger for their guidance during the realization of my project.

Stephen Rock and all the SULI staff at SLAC for give me the opportunity to work during this summer under their program.

References

Bettinger, J., Misra, S. Anomalous X-ray Diffraction (AXRD), California. 2010.  Bettinger, J. Probing the Effects of Dopants, Defects, and Crystal Structure in

Spinel Transparent Conducting Oxides for Photovoltaic Applicationsi, California.  Granqvist, C. G., Transparent conductors as solar energy materials: A

panoramic review, Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, Uppsala, Sweeden. 2007.

  Introduction to X-ray Diffraction, Materials Research laboratory, University of

California, Santa Barbara. 2010.  Thomas, R.K., Simple Solids and their Surfaces [Online]. Available:

http://rkt.chem.ox.ac.uk/tutorials/surfaces/solids.html  Pecharsky, V. K., Zavalij, P.Y., Fundamentals of Powder Diffraction and

Structural Characterization of Materials, Page 146-152, Springer, New York. 2005.

Cullity, B.D., Stock, S.R., Elements of X-Ray Diffraction, Page 31-47, Prentice Hall, New Jersey. 2001.

Questions?