Formation and Organization of Amino Terminated Self-assembled Layers on Si(001) Surface

Nanoscale Research Letters, Jun 2007

We have investigated the effects of dipping time, solution concentration and solvent type on the formation of self-assembled monolayers with aminosiloxane molecules (i.e.,N-(3 trimethoxysilylpropyl)diethylenetriamine (TPDA)) on the Si(001) surface. Studies performed with an ellipsometer showed that monolayers with a thickness of about 1.2 nm were formed when the dipping time is about 2 h, while multilayer were observed for longer time periods. The effect of the TPDA concentration on the thickness of the deposited layer was not very profound, however, the contact angle data exhibit importance of concentration on the surface coverage. The type of the solvent used in the formation of the monolayers was found an important parameter. Monolayers were formed with solvent having larger dielectric constants. Relatively thick multilayer was observed when benzene was used as the solvent, due to its quite low dielectric constant (hydrophobicity).

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Formation and Organization of Amino Terminated Self-assembled Layers on Si(001) Surface

G. Demirel 0 M. O. C aglayan 0 B. Garipcan 0 M. Duman 0 E. Piskin 0 0 G. Demirel (&) M. O. C aglayan B. Garipcan M. Duman E. Piskin Department of Chemical Engineering and Division of Bioengineering, Hacettepe University , Beytepe, Ankara 06800, Turkey We have investigated the effects of dipping time, solution concentration and solvent type on the formation of self-assembled monolayers with aminosiloxane molecules (i.e., N-(3 trimethoxysilylpropyl)diethylenetriamine (TPDA)) on the Si(001) surface. Studies performed with an ellipsometer showed that monolayers with a thickness of about 1.2 nm were formed when the dipping time is about 2 h, while multilayer were observed for longer time periods. The effect of the TPDA concentration on the thickness of the deposited layer was not very profound, however, the contact angle data exhibit importance of concentration on the surface coverage. The type of the solvent used in the formation of the monolayers was found an important parameter. Monolayers were formed with solvent having larger dielectric constants. Relatively thick multilayer was observed when benzene was used as the solvent, due to its quite low dielectric constant (hydrophobicity). - Self-assembly has recently emerged as a new approach in chemical synthesis, nanotechnology, polymer science, materials science, and engineering. Molecular self-assembly systems lie at the interface of these disciplines and many self-assembling systems have been developed. Self-assembled monolayers (SAMs) are a class of molecular assemblies that are typically prepared by exposure of a surface to molecules with chemical groups that possess strong affinities for the substrate. The driving force for the formation of the monolayer includes chemisorption of functionalized molecules on the substrate surface, and the intermolecular interactions. Due to their ease of preparation and controllable surface chemical functionality, SAMs represent suitable model systems for studying wetting [13], corrosion [4, 5], adhesion [6, 7], tribology [812], charge transfer through molecules [13], and model surfaces for biochemistry and cell biology [14]. Other applications (resistance to etchants [15] and protein adsorption, modified electrodes for electrochemistry) rely on the ability of SAMs to prevent diffusion of other molecules to the surface of the underlying substrate [16]. The final morphology and thickness of a SAMs are reported to be extremely sensitive to experimental parameters including the type of precursor molecule, concentration, type of solvent and its quality, temperature and reaction time, etc. Despite several experimental investigations dedicated to the grafting of organic molecules to the silicon surface, there are only few description of such grafting and fewer attempts to understand the self-assembly formation. In the present work, SAMs with amino end group were prepared by using N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) molecule on the Si(001) surface. Effects of dipping time, solution concentration and solvent type on the formation of TPDA on Si(001) have been investigated. Subsequently, thicknesses and water contact angle of each film were measured using imaging ellipsometry and contact angle goniometer, respectively. The substrates used in these experiments were Si(001) wafers (n-type, obtained from Shin-etsu, Handoutai, Japan). The substrates were cut into 5 5 mm pieces for further modification. The substrates were first cleaned by repeated rinsing with deionized water and ethanol. They were then further cleaned a mixture of NH3 (25%, v/v), H2O2 (30%, v/v), and deionized water having a volume ratio of 1:1:5 at the temperature of 70 C during 20 min. Afterward, the substrates were washed with ethanol and dried under nitrogen stream. Finally, these substrates were exposed in UV/ozone chamber (Irvine, CA: Model 42, Jelight Company Inc. USA) for 15 min prior to modification in order to remove hydrocarbon and to produce a hydrophilic surface. For this cleaned surface, the water contact angle was about 3 . The lower contact angle obtained is consistent with the presence of increased number of hydroxyl groups on the cleaned surface [17]. Unless otherwise stated, freshly prepared TPDA (Aldrich USA) solutions (0.25, 0.5, 1.0, 2.0, 4.0, and 8.0%, v/ v) in absolute ethanol (Aldrich USA) were used for the monolayer formation. Silicon wafers were dipped in the TPDA solution of particular concentrations and were removed from solution after selected time intervals. Static water contact angles of the sample surfaces were measured at 25 C in ambient air using an automatic contact angle goniometer equipped with a flash camera (model DSA 100, Kruss, Germany) applying the sessile drop method. The volume of the drop used was always 1 lL in all measurements. The contact angles are calculated by using the software of the instrument. All reported values herein are the averages of at least nine measurements taken at three different (...truncated)


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G Demirel, MO Çağlayan, B Garipcan, M Duman, E Pişkin. Formation and Organization of Amino Terminated Self-assembled Layers on Si(001) Surface, Nanoscale Research Letters, 2007, pp. 350, Volume 2, Issue 7, DOI: 10.1007/s11671-007-9071-7