Molecular Assemblies on Silicon Surfaces via Si−O Linkages

Abstract

Monolayer assemblies on silicon surfaces are of interest for a number of technological reasons. Here, we present a novel, two-step strategy for assembly formation directly on silicon surfaces. In the first step, a H-terminated Si(100) or Si(111) surface reacts with Cl2 to give a Cl-capped surface. In the second step, the Cl-Si surface is immersed in an alcohol/isooctane solution for monolayer formation via Si-O linkages, with the removal of surface Cl likely in the form of HCl. This reaction mechanism is confirmed by X-ray photoelectron spectroscopy. X-ray reflectivity measurement shows that the thickness of the monolayer film is close to molecular dimension and the density is about 85% of that in crystalline paraffine. Fourier transform infrared spectroscopy and water contact angle measurements suggest that the alkyl chains within the monolayer possess, to a limited degree, conformational order. Atomic force microscopy image with molecular lattice resolution shows intermolecular distance corresponding to close packing of alkyl chains. The monolayer coatings show both chemical and mechanical stability. The possible mechanism for monolayer assembly formation on covalent Si surfaces is discussed.

Plasma‐Assisted Synthesis of Silicon Nanocrystal Inks

“…[26,27] X-ray photoelectron spectroscopy (XPS) was performed to verify the presence of oxygen. The oxygen-related satellite peak at 103 eV of the Si2P peak at 99.3 eV [28] could not be observed, suggesting that the EPR feature in Figure 3c is not oxide-related. Still, the EPR signal intensity clearly decreases after liquid-phase post-treatment, meaning that the density of dangling bonds decreases, which is likely the reason for the improvement of the optical properties.…”

“…Alcohols are also known to react with silicon surfaces, but they have a low reactivity with hydrogen terminated surfaces. [28] Surprisingly, hexane also bonds with the silicon nanocrystals. This is very likely due to the higher species reactivity in the non-thermal plasma system as compared to the thermally activated system.…”

Chlorination of hydrogen-terminated silicon (111) surfaces

“…[20][21][22][23][24][25] These chlorination methods start from the wet-chemically prepared H-terminated silicon surface. Wet chemical silicon chlorination methods have been described in the liquid phase using phosphorus pentachloride ͑PCl 5 ͒ and a radical initiator as a Cl radical source.…”

“…Wet chemical silicon chlorination methods have been described in the liquid phase using phosphorus pentachloride ͑PCl 5 ͒ and a radical initiator as a Cl radical source. [21][22][23][24][25][26] Gas phase methods, either in the dark 27 or using UV light in a low pressure chamber, 24 have also been demonstrated. Relatively little structural characterization has been performed to date on such chlorinated Si surfaces.…”

Monolayer formation of hydrocarbons with various reactive groups via photochemical reaction on Si(111)-H surface

“…The monolayer formation with unsaturated groups of acetylene, alcohols and thiols has been reperted. And the modifications of Si-H with halogenations and click reaction have been also reported [5,6]. In this way, Si-H surfaces can be modified by various methods, but the modification was not investigated in the unified treatment [7][8][9][10].…”