Characterization of Mesoporous Silica Thin Film by Grazing Incident X-ray
Diffraction and TEM
Pang-Hung Liu (劉邦弘)1, Kuei-Jung Chao (趙桂蓉)1,
Yen-Ru Lee (李彥儒)2, and Shih-Lin Chang (張石麟)2
1
Department of Chemistry and 2Department of Physics, Tsing Hua University, Hsinchu, Taiwan
The combination of high brilliance and high collimation X-ray source from synchrotron
radiation with large diffractometer can simultaneously provide high-energy resolution and high
spatial resolution diffraction information. In this study, the advantages of synchrotron X-ray
diffraction (XRD) are demonstrated in the structural characterization of supported mesoporous
films on silicon wafer. The results have also been confirmed by transmission electron microscopy
(TEM).
A mixture of C16EO10 (C16H33(OCH2CH2)10OH) block copolymer and TEOS in acidic media
was used to prepare templated silica sol. The sol was then dip- or spin-coated on a pre-cleaned Si(0
0 1) wafer to produce a porous SiO2 thin film of 0.3 m in thickness. Heat treatment of baking at 80
~ 110°C and calcining at 500°C were performed. After the template removal by calcination the
well-organized pore arrangement and film texture of mesoporous silica attached to Si(0 0 1) wafer
were clearly shown by XRD performed on the BL17B, Wiggler beamline of NSRRC, Taiwan and
TEM with elelctron diffraction (ED) observed on a JEOL JEM2010 electron microscope.
The structures of the mesoporous thin films were found to be different from that of powdery
analogues and with mesochannels oriented in the direction parallel to the substrate surface by using
grazing incident x-ray diffraction (GIXRD) technique. The diffraction patterns with obvious peaks
were detected using 2-dimensional imaging plates as the detector. The transmission mode XRD was
also employed on a backside-polished dip-coated film but showed only diffraction rings. It indicates
that the mesoporous channels of the grains in the thin film are not aligned well but randomly
orientated around the substrate surface normal.
Two mesoporous structures with elongated elliptical pores in rectangular symmetries have
been observed. Detailed TEM investigations suggest that both the structure of mesoporous silica
and the shear force effect on silica grain growth are direction-dependent during dip-coating, and
grains should have come into contact with each other at the late stage of grain growth. It is
proposed that shearing the precursor sol as well as solvent evaporation affect the resulting
morphology of mesoporous silica films in a dip-coating process.
References:
[1] H. Fan, Y. Lu, A. Stump, S. T. reed, T. Baer, R. Schunk, V. Perez-Luna, G. P. Lopez and C. J.
Brinker, Nature, 405, 56 (2000).
[2] G. Margaritondo, "Elements of Synchrotron Light for Biology, Chemistry and Medical
Research", (2002) Oxford University Press.