*This chapter has been submitted to Surf. Sci. Spectra for review (David S. Jensen, Supriya S. Kanyal, Michael A. Vail, Andrew E. Dadson, Hussein Samha, Mark Engelhard, and Matthew R. Linford) Chapter 10: XPS of Al 2 O 3 e-Beam Evaporated onto Silicon (100)/SiO 2 * 10.1. Abstract We report the XPS characterization of a thin film of Al 2 O 3 (35 nm) deposited via e-beam evaporated onto silicon (100). The film was characterized with monochromatic Al Kα radiation. An XPS survey scan, an Al 2p narrow scan, and the valence band were used to characterize the material. The Al 2 O 3 thin film is used as a diffusion barrier layer for templated carbon nanotube (CNT) growth in the preparation of microfabricated thin layer chromatography plates. 1-3 10.2. Introduction The Al 2 O 3 film, deposited by e-beam evaporation is used as a diffusion barrier layer for the catalytic growth from iron nanoparticles of templated carbon nanotube (CNT) forests in the preparation of microfabricated thin layer chromatography plates. 1-3 The present spectra are from a study by Jensen et al., the entirety of the study can be found in Ref 4. 4 The characteristics of the deposited Al 2 O 3 barrier films are important because the ability to catalytically grow CNTs is dependent upon the catalyst, Fe, not being poisoned by silicide formation. 5-7 Accordingly, we have used XPS to characterize the thin (35) Al 2 O 3 barrier film. The survey spectrum (Figure 10.1) shows that the material is composed of Al, O, and C, where C is presumably adventitious contamination (Figure 10.1). The narrow scans of Al 2p and O 1s give an Al/O atom% ratio of 0.41 which is not the expected value of 0.67 for Al 2 O 3 . A possible reason for this discrepancy (i) the C 1s narrow scan shows an oxidized carbon peak and (ii) it is common for the Al 2 O 3 film after exposure to air to have some adsorbed hydroxyls. The narrow Al 2p scan (Figure 10.2) shows a peak at 75.9 eV (Figure 10.3), indicating that the aluminum is oxidized. The narrow
Transcript
*This chapter has been submitted to Surf. Sci. Spectra for review (David S. Jensen, Supriya S.
Kanyal, Michael A. Vail, Andrew E. Dadson, Hussein Samha, Mark Engelhard, and Matthew R.
Linford)
Chapter 10: XPS of Al2O3 e-Beam Evaporated onto Silicon (100)/SiO2*
10.1. Abstract
We report the XPS characterization of a thin film of Al2O3 (35 nm) deposited via e-beam
evaporated onto silicon (100). The film was characterized with monochromatic Al Kα radiation.
An XPS survey scan, an Al 2p narrow scan, and the valence band were used to characterize the
material. The Al2O3 thin film is used as a diffusion barrier layer for templated carbon nanotube
(CNT) growth in the preparation of microfabricated thin layer chromatography plates.1-3
10.2. Introduction
The Al2O3 film, deposited by e-beam evaporation is used as a diffusion barrier layer for
the catalytic growth from iron nanoparticles of templated carbon nanotube (CNT) forests in the
preparation of microfabricated thin layer chromatography plates.1-3
The present spectra are from
a study by Jensen et al., the entirety of the study can be found in Ref 4.4 The characteristics of
the deposited Al2O3 barrier films are important because the ability to catalytically grow CNTs is
dependent upon the catalyst, Fe, not being poisoned by silicide formation.5-7
Accordingly, we
have used XPS to characterize the thin (35) Al2O3 barrier film. The survey spectrum (Figure
10.1) shows that the material is composed of Al, O, and C, where C is presumably adventitious
contamination (Figure 10.1). The narrow scans of Al 2p and O 1s give an Al/O atom% ratio of
0.41 which is not the expected value of 0.67 for Al2O3. A possible reason for this discrepancy (i)
the C 1s narrow scan shows an oxidized carbon peak and (ii) it is common for the Al2O3 film
after exposure to air to have some adsorbed hydroxyls. The narrow Al 2p scan (Figure 10.2)
shows a peak at 75.9 eV (Figure 10.3), indicating that the aluminum is oxidized. The narrow
2
scan of the O 1s region shows a symmetric peak centered at 533.1 eV (Figure 10.3). The valence
band spectrum is in reasonable agreement with the valance band spectra of alumina found in the
literature (Figure 10.4).8-11
The Al2O3 layer described herein is an essential part of the materials deposited in the
preparation of microfabricated thin layer chromatography (TLC) plates.1-3
Indeed, submissions to
Surface Science Spectra have been made on the XPS and SIMS characterization of the key
materials in this microfabrication, including the silicon substrate,12, 13
an alumina barrier layer on
the Si/SiO2 substrate (the current submission and one on ToF-SIMS14
), the Fe film on the
alumina layer,15, 16
the Fe film after annealing in H2 to create Fe nanoparticles,17, 18
and the
carbon nanotube forest grown on the Fe nanoparticles.19, 20
10.3. Instrumental Parameters
XPS and valence band spectroscopy were performed on an as received bare Si (100)
wafers coated with thin film of e-beam evaporated Al2O3 (35 nm). This work was performed at
the Pacific Northwest National Laboratory (PNNL) in the Environmental Molecular Sciences
Laboratory (EMSL) using a Physical Electronics Quantera Scanning X-ray Microprobe. This
system uses a focused, monochromatic Al Kα X-ray (1486.7 eV) source for excitation, a
spherical section analyzer, and a 32 element multichannel detection system. A 98 W X-ray beam
focused to 100 μm (diameter) was rastered over a 1.3 mm x 0.1 mm rectangle on the sample. The
X-ray beam is at normal incidence to the sample and the photoelectron detector is at 45° off-
normal. High energy resolution spectra were collected using a pass-energy of 69.0 eV with a step
size of 0.125 eV. For the Ag 3d5/2 line, these conditions produced a FWHM of 1.2 eV. All
3
samples were analyzed as received. All XPS spectra were charge referenced to the maximum in
the carbon C 1s narrow scan, taken as 285.0 eV.
10.4. Acknowledgments
We thank Diamond Analytics, a US Synthetic company (Orem, UT), for funding this
study. Part of this research was performed at EMSL, a national scientific user facility sponsored
by the Department of Energy’s Office of Biological and Environmental Research and located at
Pacific Northwest National Laboratory.
10.5. References
1. Song, J.; Jensen, D. S.; Hutchison, D. N.; Turner, B.; Wood, T.; Dadson, A.; Vail, M. A.;
Linford, M. R.; Vanfleet, R. R.; Davis, R. C., Adv. Funct. Mater. 2011, 21 (6), 1132-1139.
2. Jensen, D. S.; Kanyal, S. S.; Miles, A. J.; Davis, R. C.; Vanfleet, R.; Vail, M. A.; Dadson,
A. E.; Linford, M. R., Submitted to J. Vac. Sci. Technol., B 2012, - (-), -.
3. Jensen, D. S.; Kanyal, S. S.; Gupta, V.; Vail, M. A.; Dadson, A. E.; Engelhard, M.;
Vanfleet, R.; Davis, R. C.; Linford, M. R., J. Chromatogr., A 2012, 1257 (0), 195-203.
4. Jensen, D. S.; Kanyal, S. S.; Handcock, J. M.; Vail, M. A.; Dadson, A. E.;
Shutthanandan, V.; Zhu, Z.; Vanfleet, R.; Engelhard, M.; Linford, M. R., Submitted to Surf.
Interface Anal. 2012, - (-), -.
5. Homma, Y.; Kobayashi, Y.; Ogino, T.; Takagi, D.; Ito, R.; Jung, Y. J.; Ajayan, P. M., J.
Phys. Chem. B 2003, 107 (44), 12161-12164.
6. Ci, L.; Ryu, Z.; Jin-Phillipp, N. Y.; Rühle, M., Diamond Relat. Mater. 2007, 16 (3), 531-
8. Thomas, S.; Sherwood, P. M. A., Anal. Chem. 1992, 64 (21), 2488-2495.
9. Rotole, J. A.; Sherwood, P. M. A. In Valence band x-ray photoelectron spectroscopic
studies to distinguish between oxidized aluminum species, Baltimore, Maryland (USA), AVS:
Baltimore, Maryland (USA), 1999; pp 1091-1096.
10. Rotole, J. A.; Sherwood, P. M. A., Fresenius J. Anal. Chem. 2001, 369 (3), 342-350.
11. Snijders, P. C.; Jeurgens, L. P. H.; Sloof, W. G., Surf. Sci. 2002, 496 (1–2), 97-109.
12. Jensen, D. S.; Kanyal, S. S.; Engelhardt, H.; Linford, M. R., Submitted to Surf. Sci.
Spectra
2012, - (-), -.
13. Kanyal, S. S.; Jensen, D. S.; Zhu, Z.; Linford, M. R., Submitted to Surf. Sci. Spectra
2012, - (-), -.
14. Kanyal, S. S.; Jensen, D. S.; Zhu, Z.; Linford, M. R., Submitted to Surf. Sci. Spectra
2012, - (-), -.
15. Jensen, D. S.; Kanyal, S. S.; Engelhard, M.; Linford, M. R., Submitted to Surf. Sci.
Spectra
2012, - (-), -.
16. Kanyal, S. S.; Jensen, D. S.; Zhu, Z.; Linford, M. R., Submitted to Surf. Sci. Spectra
2012, - (-), -.
17. Jensen, D. S.; Kanyal, S. S.; Engelhard, M.; Linford, M. R., Submitted to Surf. Sci.
Spectra
2012, - (-), -.
18. Kanyal, S. S.; Jensen, D. S.; Zhu, Z.; Linford, M. R., Submitted to Surf. Sci. Spectra
5
2012, - (-), -.
19. Jensen, D. S.; Kanyal, S. S.; Engelhard, M.; Linford, M. R., Submitted to Surf. Sci.
Spectra
2012, - (-), -.
20. Kanyal, S. S.; Jensen, D. S.; Zhu, Z.; Linford, M. R., Submitted to Surf. Sci. Spectra
2012, - (-), -.
6
Figure 10.1. Survey spectrum of thermally evaporated Al2O3 thin film (35 nm) on a Si (100) wafer. The spectrum shows O 2s (ca. 30 eV), Al 2p (ca. 77 eV), Al 2s (ca. 120 eV), C 1s (ca. 285 eV), O 1s (ca. 530), O KLL (ca. 980 eV) and, C KLL (ca. 1230 eV) signals.
1200 1000 800 600 400 200 00
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Figure 10.2. Narrow scan of the Al 2p peak of thermally evaporated Al2O3 (35 nm) on a Si (100) wafer.
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Figure 10.3. O 1s narrow scan of thermally evaporated Al2O3 (35 nm) on a Si (100) wafer.
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Figure 10.4. Valence band spectrum of thermally evaporated Al2O3 (35 nm) on a Si (100) wafer.
