The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Controlled Preparation of Amino-Functionalized Surfaces on Porous Silica by Atomic Layer Deposition

Satu Ek (née Härkönen)

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Chemical Technology for public examination and debate in Auditorium KE 1 at Helsinki University of Technology (Espoo, Finland) on the 11th of December, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7446-9)   [695 KB]
Dissertation is also available in print (ISBN 951-22-7403-5)


The aim of the research was to study the preparation of amino-functionalized silicon dioxide surfaces from the gas-phase by atomic layer deposition (ALD) technique. ALD and other gas-phase techniques have rarely been used for the deposition of organic precursors, in this case various γ-aminopropylalkoxysilanes. Thermogravimetry (TG) and diffuse reflectance infrared Fourier spectroscopy (DRIFTS) with multivariate calibration, i.e. projections to latent structures by means of partial least squares (PLS), were applied for the first time to study of the surface species on various porous silicon dioxide, i.e. silica, samples. The gas-solid reactions of aminopropylalkoxysilane precursors on porous silica were investigated at various deposition temperatures by depositing a single surface-saturated molecular layer of precursors by ALD. Study was also made of the effects of pretreatment temperature of silica and type of precursor, and the effect of using sequential aminopropylalkoxysilane/water cycles on the surface density of amino groups on silica. As an example of the growth of organic multilayered structures on aminosilylated silica, the deposition of polyimide structures was demonstrated. The basic principles of ALD on porous substrates and a review of the literature on the use of silanes in gas-phase processes are presented by way of background.

The study showed TG to be a simple and relatively fast technique for determination of the total number of silanol groups on silica. Combined DRIFTS/PLS procedure also enabled fast determination of the total number of silanols after calibration with the results from TG measurements. Separate determination of the different types of silanols was not possible with these methods, however. For reference and practical purposes, the numbers of isolated and hydrogen-bonded silanols were also determined by 1H MAS (magic angle spinning) NMR, but this is a slower and more expensive technique.

Trifunctional γ-aminopropyltrimethoxysilane (APTMS), γ-aminopropyltriethoxysilane (APTS), and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPS); bifunctional γ-aminopropyldiethoxymethylsilane (APDMS); and monofunctional γ-aminopropyldimethylethoxysilane (APDMES) were used as precursors for the deposition of amino-functionalized surfaces on silica. The aminosilylated silica surfaces were characterized by DRIFTS, solid-state 29Si and 13C nuclear magnetic resonance (NMR), and elemental analyses.

According to the results, homogeneous aminosilylated silica surfaces can be prepared by ALD at low temperatures (≤ 150 °C) in a reproducible way by a solvent-free procedure. The deposition of a single surface-saturated molecular layer on silica led to densities between 1.0 and 2.1 amino groups/nm2 depending on the pretreatment temperature of silica (200-800 °C) and the precursor. The highest amino group density was achieved with the bifunctional precursor, APDMS, on silica pretreated at 200 °C. The use of relatively high deposition temperatures, i.e. 150-300 °C, led to side-reactions between the amino groups of bi- and trifunctional precursors and silanol groups or alkoxy groups of other precursor molecules on silica. The amino group density could be better controlled when sequential reactions of trifunctional aminopropylalkoxysilanes and water were applied. Thus, depending on the number of APTS/-, APTMS/-, or AAPS/water cycles, surface densities from 1.5-1.9 to 2.8-3.0 terminal amino groups/nm2 were achieved. After four cycles the surface was saturated and a constant surface density of nitrogen and carbon atoms was achieved. The deposition of a monolayer on the surface was thus achieved.

This thesis consists of an overview and of the following 7 publications:

  1. Ek, S., Root, A., Peussa, M., and Niinistö, L., 2001. Determination of the hydroxyl group content in silica by thermogravimetry and a comparison with 1H MAS NMR results. Thermochimica Acta 379, numbers 1-2, pages 201-212.
  2. Peussa, M., Härkönen, S., Puputti, J., and Niinistö, L., 2000. Application of PLS multivariate calibration for the determination of the hydroxyl group content in calcined silica by DRIFTS. Journal of Chemometrics 14, numbers 5-6, pages 501-512.
  3. Ek, S., Iiskola, E. I., and Niinistö, L., 2003. Gas-phase deposition of aminopropylalkoxysilanes on porous silica. Langmuir 19, number 8, pages 3461-3471.
  4. Ek, S., Iiskola, E. I., Niinistö, L., Pakkanen, T. T., and Root, A., 2003. New bonding modes of gas-phase deposited γ-aminopropyltriethoxysilane on silica studied by 29Si CP/MAS NMR. Chemical Communications 2003, number 16, pages 2032-2033.
  5. Ek, S., Iiskola, E. I., Niinistö, L., Vaittinen, J., Pakkanen, T. T., and Root, A., 2004. A 13C and 29Si CP/MAS NMR study of bi- and trifunctional γ-aminopropylalkoxysilanes deposited onto porous silica in the gas phase. Journal of Physical Chemistry B 108, number 31, pages 11454-11463.
  6. Ek, S., Iiskola, E. I., Niinistö, L., Vaittinen, J., Pakkanen, T. T., Keränen, J., and Auroux, A., 2003. Atomic layer deposition of a high-density aminopropylsiloxane network on silica through sequential reactions of γ-aminopropyltrialkoxysilanes and water. Langmuir 19, number 25, pages 10601-10609.
  7. Ek, S., Iiskola, E. I., and Niinistö, L., 2004. Atomic layer deposition of amino-functionalized silica surfaces using N-(2-aminoethyl)-3-aminopropyltrimethoxysilane as a silylating agent. Journal of Physical Chemistry B 108, number 28, pages 9650-9655.

Keywords: gas-phase deposition, gamma-aminopropylalkoxysilane, polyimide, modification of silica, silylation of silica, atomic layer deposition, amino-functionalized surface

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© 2004 Helsinki University of Technology

Last update 2011-05-26