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differences between precursors were, in fact, minor. The differences in the surface densities are due to the different sizes of the ligands and the size of the whole precursor molecule. Comparison of two precursors of different size, viz. AAPS and APTS, on the SiO2 surface, clearly shows that the larger precursor molecule AAPS covers a greater surface area and overlaps more silanols on the surface than does the smaller molecule APTS (Figure 15). Figure 15. Relative sizes of AAPS and APTS molecules monodentately attached to the surface of β-cristobalite (111). VII Greater differences in the surface densities of mono-, bi-, and trifunctional precursors have been observed in the liquid-phase depositions of silanes on silica. This is because bidentate and especially tridentate precursor molecules are hydrolyzed before deposition and give rise to polymer-structured multilayers. Thus, denser layers were obtained with trifunctional alkylchlorosilanes 132 and aminosilanes 130,131 than with monofunctional precursors. A surface density of 3.9 N/nm 2 was obtained when trifunctional APTS and bifunctional APDMS were deposited in an organic solvent on a planar substrate. A single surface-saturated molecular layer was achieved only with monofunctional APDEMS. 130,131 4.2.1.2 Effect of reaction temperature As shown above, silica is saturated with vaporized aminopropylalkoxysilane molecules when deposition is at relatively low temperature, that is, near 150 °C. The effect of higher reaction temperatures, i.e. 200-300 °C, on the surface species on silica is discussed for trifunctional APTS, III-V,VII but APTMS and AAPS behave in a similar way. As can be seen in Figure 16, 39
mono- and bidentate bonding modes of APTS on silica appear in the 29 Si CP/MAS NMR spectrum as chemical shifts at δ=–53 ppm and δ=–59 ppm, respectively, regardless of the deposition temperature, i.e. 150-300 °C. In addition to the main reaction of the alkoxy groups with the silanols, the amino group is also observed to react with the surface, forming Si-N bonds. When the deposition temperature is raised from 150 °C to 300 °C, new peaks appear or small peaks increase in intensity in the 29 Si CP/MAS NMR spectra. At the reaction temperature of 150 °C, a completely new resonance appears at –40 ppm. This resonance has not been observed in the 29 Si NMR spectra of APTS samples deposited on silica from the liquid phase. The peak represents the region where the silicon atom of the silane molecule is surrounded by three unreacted oxygen atoms of ethoxy groups. Free APTS molecules are unlikely to be physisorbed onto the pores of silica at such a high reaction temperature and with subsequent nitrogen purging of any physisorbed molecules. The resonance of liquid APTS in deuterated chloroform (CDCl3) in the solution-state 29 Si NMR spectrum is seen in the same region, viz. –45.4 ppm. 133 It seems likely, therefore, that APTS molecules are bound through the amino end of the molecule, while all three alkoxy groups remain unreacted on the surface. In addition, at the deposition temperatures of 200 and 300 °C a group of new bands appear at –33, –26, and –20 ppm. Very faint peaks at the same positions are also seen at the deposition temperature of 150 °C. These bands and the above-mentioned band at –40 ppm are due to the reaction of amino groups with the ethoxy groups of APTS molecules on silica. One possible surface structure of APTS is shown in Figure 16; the others are depicted in publications IV and V. In addition to reacting with the alkoxy groups, the amino groups were also observed to react with the silanol groups of silica. The presence of O3-Si-N surface species, seen at approximately –80 to –90 ppm, confirms the reaction. 134 O3-Si-N species are seen even at deposition temperature 150 °C, and more so at higher deposition temperatures, i.e. at 200 and 300 °C. Part of the SiO4 species at about –100 to –110 ppm are then shifted to higher frequency due to the substitution of one oxygen for a nitrogen. The silanediol (i.e. geminal silanol), silanol, and siloxane groups on silica are generally seen in the 29 Si NMR spectra as broad peaks at –90.6, –99.8, and –109.3 ppm, respectively. 135 Reaction of amino groups with the silica surface at 300 °C was further observed as the appearance of a new band in the N-H region of the DRIFT spectrum. III When the aminosilylated silica samples deposited at 300 °C were treated with water, the peaks due to 40
Page 1 and 2: Helsinki University of Technology I
Page 3 and 4: Distribution: Helsinki University o
Page 5 and 6: PREFACE The experimental work of th
Page 7 and 8: THE AUTHOR’S CONTRIBUTION TO THE
Page 9 and 10: MTES Methyltriethoxysilane MTMS Met
Page 11 and 12: 1. INTRODUCTION There is growing in
Page 13 and 14: 2. GENERAL BACKGROUND As background
Page 15 and 16: Figure 2. Gas-phase deposition of
Page 17 and 18: 3-Bromopropyltrichlorosilane Glass
Page 19 and 20: the number of cycles applied. Adjac
Page 21 and 22: announced ALD to be the method-of-c
Page 23 and 24: precursor molecules compared to the
Page 25 and 26: Figure 5. Distilled water was used
Page 27 and 28: 3.2.2 Deposition of several surface
Page 29 and 30: 4. RESULTS AND DISCUSSION The effec
Page 31 and 32: Wave number/ cm -1 Figure 8. DRIFT
Page 33 and 34: Table 3. Results from TG and 1 H MA
Page 35 and 36: Various signal-processing technique
Page 37 and 38: 450 °C, the sharp peak due to free
Page 39: only monodentately bound, but also
Page 43 and 44: The reaction of the amino groups of
Page 45 and 46: APTS molecules/ nm 2 Carbon atoms/
Page 47 and 48: Figure 20. Deposition of pyromellit
Page 49 and 50: 5. CONCLUSIONS Because ALD growth i
Page 51 and 52: 6. REFERENCES 1. Vansant, E.F., Van
Page 53 and 54: 64. Haller, I., J. Amer. Chem. Soc.
Page 55 and 56: 135. Maciel, G.E. and Sindorf, D.W.

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