Preparation of Highly Ordered Mesoporous Thin Film with Alkyltrimethylammonium(CnTMA + )
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ABSTRACT We synthesized the highly ordered mesoporous thin films with alkyltrimethyl-ammonium (CnTMA+). The arrangement of mesopores was depend on the Si/surfactant ratio. The hexagonal(P6mm) arrangement was observed, when Surfactant/Si ratio was 1/10. Increasing the Surfactant/Si ratio to 1.6/10, the cubic (Pm3n) arrangements were observed. A steel vessel for the measurement of the nitrogen adsorption isotherms of thin film on the substrate was designed. It was found that mesopore arrangements in the film is more regular than that in the powder samples prepared by the same acidic synthesis conditions.
INTRODUCTION Recently developed mesoporous materials such as FSM-16[1], MCM-4112,3] are expected to realize new field of nano-material science. The mesopore structure is controllable in nanometer range and accessible for outer guest molecules. We can use mesopore space as a Host to make nano-sized materials. Same efforts have done in the field of crystalline aluminosilicate, zeolites. Zeolites can be a host material to make sub-nanometer clusters such as CdS[4], K[5], and so on. But, zeolites are difficult to form thin film configuration with no crack or defect. That is coming from the nature of zeolite crystal. On the contrary, mesoporous materials has amorphous wall structure and periodic pore structures and continuous film formation is expected. Former work in this area by Ogawa with sol-gel method could make optically transparent mesoporous silicate thin films, but in micron-range it has many defects and low stability[6]. In this work, we try to make mesoporous silica thin film structure without defects and cracks. Another important point of Host material, orientation control must be required. Many efforts have been done with various technique[7-101. We developed relatively simple one based on the nature of template micell.
EXPERIMENT All
thin films have been made with surfactants
alkyltrimethylammonium
chloride
Cx-TMA-Cl (e.g. Cethyl-Trimethyl-ammonium-chloride) with chain length x of 12-18. As a silica source, tetramethylorthosilicate(TMOS) was used. At first, organic/silica complex solution as precursor for thin films has prepared in the molar ratio of 0.1 TMOS, 0.25 HO and
0.0002 HCL. The mixture has stirred for 1 hour. Then surfactants (0.01-0.02 mol) were added with stirring under control of pH in the range 1-3 for 10 minutes. Finally water (30-50mi) added to decrease viscosity. The thickness could be changed in the range of 100-500nm by
423 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
viscosity and dipping speed. This organic/silica complex solution was transparent and stable for about 3 days. This organic/silica complex solution could be coated on various substrates by dip-coating or spin-coating method. For example, mesoporous silica film has prepared on glass plate ( coaning 7059 ) with dip-coating at room temperature. To remove surfactants, samples were dried at 373K for 1 hour and calcined at 773K in air for 6 hours. The pore orientation on a substrate could be contr
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