The surface structure and termination of α-Al2O3 plays a key role in its performance as substrate to grow other materials and catalyst support as discussed earlier. The termination could be affected by many environmental factors like O2 pressure, temperature and so on. In this work, we are interested in how water adsorption will affect the termination of α-Al2O3(11-20) which is one of the three most thermodynamic stable cuttings but less studied.
With SFG technique, we successfully probed the spectra change in the Al-O vibrations at the range 900- 1200 cm-1 of samples that prepared in UHV (clean and water dissociatively adsorbed) and in ambient. By probing the surface phonon vibration rather than OH stretching vibrations as most people did in previous work, the signal takes advantage of being not influenced by the interfacial water side which always makes the assignment SFG response of OH much difficult. We are able to obtain the vibrational information purely from the substrate involved side and learn the termination of alumina. By combining the SFG results (the resonance information extracted by global fitting) and theoretical calculations of normal modes of three surfaces, we are able to make such a conclusion as: it is O-I termination for UHV prepared clean α-Al2O3(11-20) where the surface is composed by Al2O and Al3O with ratio 1:2, while in ambient the fully protonated surface is O-III terminated which is composed of AlO, Al2O and Al3O with ratio 1:1:1. This dramatical change of surface termination happens fast when clean α-Al2O3(11-20) is transformed from UHV to ambient conditions which also suggests the O-I terminated (11-20) surface is very hydrophilic and active with water adsorption in ambient with water pressure 10-2 bar. Sample that acted with water in UHV chamber under pressure 10-10 bar won’t result in O-III termination. Therefore, the reconstruction from O-I to O-III of (11-20) surface is water pressure dependent.
Before, people who investigated water/α-Al2O3(11-20) always focused on the already fully protonated surface (in ambient or with liquid water) and found that it was terminated by AlO, Al2O and Al3O. Our work study the termination of α-Al2O3(11-20) from UHV to ambient conditions, which allows an insight into how the O-I terminated clean surface gets reconstructed into O-III termination in ambient. Now we know that O-III termination is the product of reaction between O-I and water adsorption: the top most two O layers of O-III are from water.
The above findings of α-Al2O3(11-20) termination is of crucial importance when we want to discuss the surface macro-properties like charges which further affect the reactions with other species; what is more, the termination change from water free environment to ambient should be much considered especially when it is used as substrate to grow thin films or catalyst in inductry since this may change the growth of the first atomic layer of the film due to the lattice change.
In addition, the SFG approach as implemented in this work to probe the surface phonon vibrations can be extended to other surfaces of α-Al2O3 and other metal oxides/water interfaces to learn their termination change or reconstruction that induced by water adsorption.
5.8 References
1. S.H. Behrens; Borkovec, M., Electrostatic interaction of colloidal surfaces with variable charge. The Journal of Physical Chemistry C, 1999. 103: p. 2918-2928.
2. Kosmulski, M., pH-dependent surface charging and points of zero charge. III. Update. J Colloid Interface Sci, 2006. 298(2): p. 730-41.
3. Finne, A.P., et al., An intrinsic velocity-independent criterion for superfluid turbulence. Nature, 2003.
424(6952): p. 1022-5.
4. Henrich, V.E.C., P. A. , The surface science of metal oxides 1996, england: Cambridge University Press. 5. Ago, N.I.H., Crystal plane dependent growth of aligned single-walled carbon nanotubes on sapphire.
Journal of the American Chemical Society, 2008. 130(30): p. 9918-9924.
6. Nehasil, V., et al., The interaction of carbon monoxide with Rh/α-Al2O3 model catalysts: influence of the support structure. Surface Science, 1999. 433-435: p. 215-220.
7. Bolt, P.H., et al., The interaction of thin NiO layers with single crystalline α-Al2O3(11-20) substrates.
Surface Science, 1995. 329(3): p. 227-240.
8. Kotula, P.G., et al., Kinetics of thin-film reactions of nickel oxide with alumina: I, (0001) and (11-
20)reaction couples. Journal of the American Ceramic Society, 1998. 81(11): p. 2869-2876.
9. Bolt, P.H., et al., Interfacial reaction of NiO with Al2O3(11-20) and polycrystalline α-Al2O3. Applied
Surface Science, 1995. 89(4): p. 339-349.
10. Meinander, K. and J.S. Preston, A DFT study on the effect of surface termination in CdTe (111)/α-
Al2O3(0001) heteroepitaxy. Surface Science, 2015. 632: p. 93-97.
11. Gutekunst, G., et al., Atomic structure of epitaxial Nb-Al2O3 interfaces I. Coherent regions. Philosophical Magazine A, 1997. 75(5): p. 1329-1355.
12. Kurita, T., K. Uchida, and A. Oshiyama, Atomic and electronic structures of α-Al2O3 surfaces. Physical
Review B, 2010. 82(15).
13. Liu, Y., et al., Termination, stability and electronic structures of α-Al2O3(0114) surface: An ab initio study. Applied Surface Science, 2014. 303: p. 210-216.
14. Wirth, J., et al., Characterization of water dissociation on α-Al2O3((1-102): theory and experiment.
Physical Chemistry Chemical Physics, 2016. 18(22): p. 14822-32.
15. Kirsch, H., et al., Experimental characterization of unimolecular water dissociative adsorption on α-
alumina. The Journal of Physical Chemistry C, 2014. 118(25): p. 13623-13630.
16. Heiden, S., et al., Water dissociative adsorption on α-Al2O3(11-20) is controlled by surface site undercoordination, density, and topology. The Journal of Physical Chemistry C, 2018. 122(12): p. 6573-
6584.
17. Li, F., et al., X-ray radiation induces deprotonation of the bilin chromophore in crystalline d. radiodurans
18. Trainor, T.P., et al., Crystal truncation rod diffraction study of the α-Al2O3(1-102) surface. Surface
Science, 2002. 496: p. 238-250.
19. Tanwar, K.S., et al., Surface diffraction study of the hydrated hematite surface. Surface Science, 2007.
601(2): p. 460-474.
20. Shen, Y.R., Surface properties probed by second-harmonic and sum-frequency generation Nature, 1989.
337: p. 519-525.
21. Sung, J., Y.R. Shen, and G.A. Waychunas, The interfacial structure of water/protonated α-Al2O3(11-20) as a function of pH. Journal of Physics: Condensed Matter, 2012. 24(12): p. 124101.
22. Boulesbaa, A. and E. Borguet, Vibrational dynamics of interfacial water by free induction decay sum
frequency generation (FID-SFG) at the α-Al2O3(11-20)/H2O Interface. The Journal of Physical Chemistry
Letters, 2014. 5(3): p. 528-533.
23. Tuladhar, A., et al., Spectroscopy and ultrafast vibrational dynamics of strongly hydrogen bonded OH
species at the α-Al2O3(11-20)/H2O interface. The Journal of Physical Chemistry C, 2016. 120(29): p.
16153-16161.
24. Kirsch, H., et al., Experimental characterization of unimolecular ater dissociative Adsorption on α-
alumina. The Journal of Physical Chemistry C, 2014. 118(25): p. 13623-13630.
25. Sung, J., et al., Surface structure of protonated R-sapphire (1-102) studied by sum-frequency vibrational
spectroscopy. Journal of the American Chemical Society, 2011. 133(11): p. 3846-53.
26. Tong, Y., et al., Optically probing Al-O and O-H vibrations to characterize water adsorption and surface
reconstruction on alpha-alumina: an experimental and theoretical study. The Journal of Chemical
Physics, 2015. 142(5): p. 054704.
27. DeLong, K.W., et al., Frequency-resolved optical gating with the use of second-harmonic generation. Journal of the Optical Society of America B, 1994. 11(11): p. 2206-2215.
28. Kane, D.J., Real-time measurement of ultrashort laser pulses using principal component generalized
projections. IEEE Journal of Selected Topics in Quantum Electronics, 1998. 4(2): p. 278-284.
29. Kane, D.J., et al., Simultaneous measurement of two ultrashort laser pulses from a single spectrogram in
a single shot. Journal of the Optical Society of America B, 1997. 14(4): p. 935-943.
30. Doll, A. and G. Jeschke, Fourier-transform electron spin resonance with bandwidth-compensated chirp
pulses. Journal of Magnetic Resonance, 2014. 246: p. 18-26.
31. Elu, U., et al., High average power and single-cycle pulses from a mid-IR optical parametric chirped
pulse amplifier. Optica, 2017. 4(9): p. 1024-1029.
32. Porto, S.P.S.K., R. S., Raman effect of corundum. The Journal of Chemical Physics, 1967. 47(3): p. 1009- 1012.
33. Hirose, C.E., Naotoshiakamatsu ; Kazunaridome, Formulas for the analysis of the surface spectrum and
transformation coefficients cartesian SFG tensor components Applied Spectroscopy, 1992. 46.
34. Becker, T., et al., Microstructure of the α-Al2O3(11-20)surface. Physical Review B, 2002. 65(11).
35. Catalano, J.G., Relaxations and interfacial water ordering at the corundum (110) surface. The Journal of Physical Chemistry C, 2010. 114: p. 6624–6630.