High‐Quality Alkyl Monolayers on Silicon Surfaces

Abstract

Covalent attachment of functionalized monolayers onto silicon surfaces (see Figure for examples) is presented here as a strategy for surface modification. The preparation and structure of both unfunctionalized and functionalized alkyl‐based monolayers are described, as are potential applications, for example, in the surface passivation of Si solar cells and for photopatterning of silicon surfaces.

Wet chemical routes to the assembly of organic monolayers on silicon surfaces via the formation of Si–C bonds: surface preparation, passivation and functionalization

“…capping agents required 51 ); (c) harsh deprotection reactions required; 33,49 (d) non-quantitative coupling yields; 51,127 (e) surface segregation 232 of acid and alkyl chain in mixed decyl/10-carboxydecyl mixed layers; 233 and (f) long term oxidation of the silicon substrate starting from defects sites in the monolayer. 107,117 To address some or all of the above concerns is a precondition if both the structural 78,89,119 and electronic 95 properties of the unoxidized crystalline silicon surface are to be retained upon the formation of an organicpassivated interface, that does not possess significant defect sites, 66,114,117,124,234,235 but rather increases the chemical stability of the interface. 32,115,147,152 3.4 Reactivity of olefin-and acetylene-terminated monolayers It is intuitive that issues on functional group incompatibilities with hydride terminations, as mentioned above, could be easily addressed by employing a symmetrical a,o-bifunctional molecule in the hydrosilylation step.…”

Molecules on Si: Electronics with Chemistry

“…Hydrosilysation [75] of SiÀH with neat alkene was first reported in 1993 [76] and several other methods were reported since then. Excellent reviews on the chemistry of wet [77][78][79] and gas-phase [10,31,80,81] adsorption have been published. The SiÀH bond needs to be activated for the reaction, which can be done by heating (150À200 8C), [44,71] UV illumination, [31,69] Lewis acid-mediated initiators, [42] or electrochemistry.…”

“…Therefore, while a C 1 (ÀCH 3 ) layer can have nearly 100% coverage, [84] longer alkyl chains form monolayers with a density of adsorbed molecules of about 1:2, [85] with the remaining Si atoms bound to H. [77,85] The longer the alkyl chain is, the stronger is the intermolecular (van der Waals) interaction and the less commensurate is the monolayer structure with the original Si surface. Indeed, we could not detect evidence for lateral order, with low-energy electron diffraction (LEED), spot profile analysis (SPA)-LEED or grazing angle X-ray diffraction (GAXRD), in monolayers made of C 10 or longer alkyls.…”

Monolayer Doping of Si with Improved Oxidation Resistance

“…Surface functionalization greatly increases the oxidation resistance of Si. 25 To ascertain the stability of the "click" functionalized samples towards ambient conditions, substrates were left exposed to ambient conditions (air, 20 °C) for periods of time ranging from 24 h to one month. Prior to analysis the samples were rinsed with chloroform to remove adventitiously adsorbed material from the surface.…”