Covalently bound organic monolayers on hydrogen-terminated silicon surfaces = covalent gebonden organische monolagen op waterstof-getermineerde siliciumoppervlakken

A.B. Sieval

Research output: Thesisinternal PhD, WU

Abstract

<p>Monolayers of 1-alkenes and 1-alkynes can be prepared on hydrogen-terminated Si(100) and Si(111) surfaces by a reaction between the organic compound and the Si surface. This reaction, which is schematically depicted below, results in the formation of densely packed, covalently bound, and well-ordered monolayers of the organic compound on the hydrogen-terminated Si surface, that inhibit the oxidation of the underlying Si surface.</p><div align="center"><img src="/wda/abstracts/i2968.gif" width="443" height="85" alt="Inline Image" border="0"/></div><p>In this research, several aspects of this surface modification have been investigated. The scope of the reaction has been explored by using a variety of functionalized and nonfunctionalized alkenes. The results show that many functional groups can be used, provided that: a) the functional group is properly protected, and b) the formation of well-ordered monolayers is not disturbed by too much steric hindrance between these functional groups, once they are in the monolayer. A very interesting property of the resulting functionalized monolayers is that the functional groups can be deprotected and/or further modified, without damaging the monolayer or the underlying Si substrate. This gives access to functionalized monolayers that so far could not be prepared by other methods.</p><p>The method for the preparation of the monolayers has been improved by showing that the reaction can also be done using solutions of the 1-alkenes and 1-alkynes in aromatic solvents. The best solvent was found to be mesitylene (1,3,5-trimethylbenzene). In this solvent monolayers are formed that are at least as good as those prepared using neat 1-alkenes/1-alkynes, even at concentrations as low as 0.1 M. This is an important improvement, as it considerably reduces the amount of 1-alkene/alkyne needed in the surface modification.</p><p>In the case of the hydrogen-terminated Si(100) surface, there are two hydrogen atoms on each Si surface atom. Upon reaction of this surface with a 1-alkyne, not just one, but two covalent Si-C bonds are formed per organic molecule, as had been demonstrated by a combination of IR spectroscopy, X-ray reflectivity measurements, and quantum chemical calculations. This type of reactivity has so far not been observed for 1-alkynes on other H-terminated (crystalline) Si surfaces.</p><p>To get more insight in the structure of the monolayers on a molecular level, they have been investigated by molecular modeling simulations. Large modified Si surfaces, with &gt;30 alkyl chains attached to the Si surface, were investigated, using the approach of two-dimensionally repeating boxes. Calculations without this repeating box approach failed completely, as did calculations using small boxes (&lt;30 alkyl chains). The results show that: a) there is a good correlation between the structure as observed in the simulations and the structure as deduced from a combination of experimental data, and b) that the currently obtained substitution percentage of the Si-H for Si-alkyl groups is close to the maximum substitution percentage that can be reached. This latter conclusion shows that the obtained monolayers are (almost) as densely packed as possible, as desired.</p><p>The possibility to use the monolayers for silicon surface passivation has been investigated, determining the effective lifetimes of the minority charge carriers in p-type Si wafers modified with 1-alkenes. The passivating properties of the monolayers are found to be comparable to those of HF and iodine/ethanol solutions, two methods commonly used in semiconductor technology, but the monolayer-modified surfaces are far more stable than these two systems. This shows that these monolayers provide an interesting alternative for Si surface passivation.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Sudhölter, E.J.R., Promotor, External person
  • Zuilhof, J.T., Promotor, External person
Award date20 Apr 2001
Place of PublicationS.l.
Publisher
Print ISBNs9789058083845
Publication statusPublished - 2001

Keywords

  • silicon
  • unimolecular films
  • interphase
  • semiconductors
  • surface phenomena
  • preparations

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