Organic Monolayers onto Oxide-Free Silicon with Improved Surface Coverage: Alkynes versus Alkenes
Scheres, L.M.W. ; Maat, J. ter; Giesbers, M. ; Zuilhof, H. - \ 2010
Langmuir 26 (2010)7. - ISSN 0743-7463 - p. 4790 - 4795.
covalently attached monolayers - acid mediated hydrosilylation - hydrogen-terminated silicon - metal-semiconductor diodes - extremely mild attachment - si(111) surface - porous silicon - visible-light - si - quality
On H-Si(111), monolayer assembly with 1-alkenes results in alkyl monolayers with a Si-C-C linkage to the silicon substrate, while 1-alkynes yield alkenyl monolayers with a Si-C-C linkage. To investigate the influence of the different linkage groups on the final monolayer structure, organic monolayers were prepared from 1-alkenes and 1-alkynes with chain lengths from C12 to C18, and the final monolayer structures were studied in detail by static water contact angles measurements, ellipsometry, attenuated total reflectance infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The thicknesses, tilt angles, and packing densities of the alkyl monolayers are in good agreement with literature values, whereas increased thicknesses, reduced tilt angles, and improved packing densities were observed for the alkenyl monolayers. Finally, the surface coverages for alkyl monolayers were determined to be 50-55% (in line with literature values), while those for the alkenyl monolayers increased with the chain length from 55% for C12 to as high as 65% for C18! The latter value is very close to the theoretical maximum of 69% obtainable on H-Si(111). Such enhanced monolayer quality and increased surface coverage of the alkenyl monolayers, in combination with the oxidation-inhibiting nature of the Si-C-C linkage, significantly increases the chance of successful implementation of organic monolayers on oxide-free silicon in molecular electronic and biosensor devices, especially in view of the importance of a defect-free monolayer structure and the corresponding stability of the monolayer-silicon interface
Self-Assembly of Organic Monolayers onto Hydrogen-Terminated Silicon: 1-Alkynes Are Better Than 1-Alkenes
Scheres, L.M.W. ; Giesbers, M. ; Zuilhof, H. - \ 2010
Langmuir 26 (2010)13. - ISSN 0743-7463 - p. 10924 - 10929.
covalently attached monolayers - metal-semiconductor diodes - extremely mild attachment - alkyl monolayers - si(111) surface - visible-light - molecular electronics - thermal-reactions - si - alkenes
Recently, a new method for the preparation of high-quality organic monolayers with 1-alkynes at room temperature in the dark (i.e., without any external activation) was reported. To pinpoint the precise origin of this self-assembly process and to compare the reactivity of 1-alkenes and 1-alkynes toward hydrogen-terminated Si(111) [H-Si(111)], we followed the gradual formation of both monolayers at room temperature by static water contact angle measurements. Subsequently, attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) were used to obtain detailed information about the structure and quality of the resulting monolayers. Our data clearly demonstrate that 1-alkynes are considerably more reactive toward H-Si(111) than 1-alkenes. 1-Alkynes are able to self-assemble into densely packed hydrophobic monolayers without any external activation (i.e., at room temperature under ambient light and even in the dark) whereas for 1-alkenes under the same conditions hardly any reactivity toward H-Si(111) was observed. The self-assembly of 1-alkynes on H-Si(111) at room temperature is explained by three factors: the higher nucleophilicity of 1-alkynes, which results in a facile attack at the electron-hole pairs at the H-Si surface and easy Si-C bond formation, the stabilization of the ß radical by delocalization over the double bond, and the lower-energy barrier encountered for H abstractions
Self-Assembly of High-Quality Covalently Bound Organic Monolayers onto Silicon
Scheres, L.M.W. ; Arafat, A. ; Zuilhof, H. - \ 2007
Langmuir 23 (2007). - ISSN 0743-7463 - p. 8343 - 8346.
hydrogen-terminated silicon - acid mediated hydrosilylation - extremely mild attachment - alkyl monolayers - porous silicon - si(111) surface - visible-light - si - functionalization - 1-alkenes
A very mild method has been developed to obtain covalently attached alkyl monolayers from the attachment of 1-alkynes onto hydrogen-terminated silicon surfaces at room temperature in the dark. Apart from being the mildest method reported so far for the preparation of such monolayers, their quality, as indicated by water contact angles, XPS, and infrared spectroscopy, equals within experimental error that of the best reported alkyl monolayers on silicon.
Covalently Attached Monolayers on Crystalline Hydrogen-Terminated Silicon: Extremely Mild Attachment by Visible Light
Sun, Q.Y. ; Smet, L.C.P.M. de; Lagen, B. van; Giesbers, M. ; Thüne, P.C. ; Engelenburg, J. van; Wolf, F.A. de; Zuilhof, H. ; Sudhölter, E.J.R. - \ 2005
Journal of the American Chemical Society 127 (2005)8. - ISSN 0002-7863 - p. 2514 - 21523.
self-assembled monolayers - alkyl monolayers - porous silicon - organic monolayers - si(111) surface - alkanethiolate monolayers - functionalized monolayers - mediated hydrosilylation - chemical-modification - nitride surfaces
A very mild method was developed for the attachment of high-quality organic monolayers on crystalline silicon surfaces. By using visible light sources, from 447 to 658 nm, a variety of 1-alkenes and 1-alkynes were attached to hydrogen-terminated Si(100) and Si(111) surfaces at room temperature. The presence and the quality of the monolayers were evaluated by static water contact angles, X-ray photoelectron spectroscopy, and IR spectroscopy. Monolayers prepared by thermal, UV light, or visible light initiation were compared. Additionally, the ability of infrared reflection-absorption spectroscopy to study organic monolayers on silicon was explored. A reaction mechanism is discussed on the basis of investigations of the reaction behavior of 1-alkenes with silicon wafers with varying types and levels of doping. Finally, a series of mixed monolayers derived from the mixed solutions of a 1-alkene and an -fluoro-1-alkene were investigated to reveal that the composition of the mixed monolayers was directly proportional to the molar ratio of the two compounds in the solutions.
Molecular modeling of alkyl monolayers on the Si (100)-2 x 1 surface
Lee, M.V. ; Guo, D. ; Linford, M.R. ; Zuilhof, H. - \ 2004
Langmuir 20 (2004)21. - ISSN 0743-7463 - p. 9108 - 9113.
terminated silicon surfaces - porous silicon - semiconductor surfaces - thermal-decomposition - organic monolayers - si(111) surface - force-field - cycloaddition - chemistry - adsorption
Molecular modeling was used to simulate various surfaces derived from the addition of 1-alkenes and 1-alkynes to Si=Si dimers on the Si(100)-2 × 1 surface. The primary aim was to better understand the interactions between adsorbates on the surface and distortions of the underlying silicon crystal due to functionalization. Random addition of ethylene and acetylene was used to determine how the addition of an adduct molecule affects subsequent additions for coverages up to one molecule per silicon dimer, that is, 100% coverage. Randomization subdues the effect that the relative positions of the adsorbates have on the enthalpy of the system. For ethylene and acetylene, the enthalpy of reaction changes less than 3 and 5 kcal/mol, respectively, from the first reacted species up to 100% coverage. As a result, a (near-)complete coverage is predicted, which is in line with experimental data. When 1-alkenes and 1-alkynes add by [2 + 2] addition, the hydrocarbon chains interact differently depending on the direction they project from the surface. These effects were investigated for four-carbon chains: 1-butene and 1-butyne. As expected, the chains that would otherwise intersect bend to avoid each other, raising the enthalpy of the system. For alkyl chains longer than four carbons, the chains are able to reorient themselves in a favorable manner, thus, resulting in a steady reduction in reaction enthalpy of about 2 kcal/mol for each additional methylene unit.
Covalently attached monolayers on hydrogen-terminated Si (100): Extremely mild attachment by visible light
Sun, Q.Y. ; Smet, L.C.P.M. de; Lagen, B. van; Wright, A. ; Zuilhof, H. ; Sudhölter, E.J.R. - \ 2004
Angewandte Chemie-International Edition 43 (2004)11. - ISSN 1433-7851 - p. 1352 - 1355.
silicon surfaces - alkyl monolayers - si(111) surface - chemical-modification - organic monolayers - porous silicon - dna - functionalization - hydrosilylation - photoreactivity
Covalently Attached Saccharides on Silicon Surfaces
Smet, L.C.P.M. de; Stork, G.A. ; Hurenkamp, G.H.F. ; Qiao-Yu, S. ; Topal, H. ; Vronen, P.J.E. ; Sieval, A.B. ; Wright, A. ; Visser, G.M. ; Zuilhof, H. ; Sudhölter, E.J.R. - \ 2003
Journal of the American Chemical Society 125 (2003). - ISSN 0002-7863 - p. 13916 - 13917.
hydrogen-terminated silicon - alkyl monolayers - si(111) surface - dna - hybridization - chemistry - biosensor - 1-alkenes - acid
This paper presents the first functionalization of silicon surfaces with well-defined, covalently attached monolayers containing saccharides. Two methods were used to this aim: a thermal method (refluxing in mesitylene) and a recently developed, extremely mild photochemical method (irradiation with 447 nm at room temperature). The results were analyzed by FT-IR and angle-resolved X-ray photoelectron spectroscopy. The use of a two-dimensional detector in ARXPS allows for unparalleled, subnanometer resolution in the determination of the elemental composition of monolayers. Even for monolayers with a total thickness of only ~1.5 nm, a clear elemental depth profile can be obtained. Such analyses display for sialic acid-containing monolayers that the mild photochemical attachment does not destroy the (rather fragile) sialic acid moiety and that the sugar is present at the top of the monolayer and thus available for biological interactions.