Kinetics of Plasmon-Driven Hydrosilylation of Silicon Surfaces: Photogenerated Charges Drive Silicon- Carbon Bond Formation (original) (raw)
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The Journal of Physical Chemistry C, 2012
As a leading surface-modification approach, hydrosilylation is critical to the practical use of silicon nanocrystals (Si NCs). However, the effect of hydrosilylationinduced surface chemistry on the electronic and optical properties of Si NCs is rather limitedly understood. By means of first-principles calculation at 0 K we show thermodynamically favored surface bonding for hydrosilylation of 1.4 nm Si NCs and the relative reactivity of alkenes and alkynes. The optical properties of hydrosilylated Si NCs are elucidated on the basis of their energy-level schemes and radiative recombination rates. The chain length (up to C12) of ligands hardly affects the absorption and emission of Si NCs. The increase of the surface coverage (up to 29%) of ligands causes the absorption onset to slightly redshift, hardly rendering changes to the light emission from Si NCs. As an added advantage, hydrosilylation may lead to enhanced light emission from Si NCs. Radiative recombination is very sensitive to surface chemistry for Si NCs. Only the coexistence of CC and functional groups at the NC surface significantly modifies the electronic structures and optical behavior of Si NCs.
The initiation mechanisms for surface hydrosilylation with 1-alkenes
Physical Chemistry Chemical Physics, 2011
Hydrosilylation provides a route to form substituted silanes in solution. A similar reaction has been observed in the formation of covalent organic monolayers on a hydrogen-terminated silicon surface and is called thermal hydrosilylation. In solution, the mechanism requires a catalyst to add the basal silicon and saturating hydrogen to the C[double bond, length as m-dash]C double bond. On the silicon surface, however, the reaction proceeds efficiently at 200 °C, initiated by visible light, and more slowly at room temperature in the dark. Such low activation energy barriers for the reactions on a surface relative to that required for solution hydrosilylation are remarkable, and although many explanations have been suggested, controversy still exists. In this work using a constrained molecular dynamics approach within the density functional theory framework, we show that the free energy activation barrier for abstraction of a hydrogen from silicon by an alkene molecule can be overcome by visible light or thermal excitation. Furthermore, we show that by concerted transfer of a hydrogen from the α-carbon to the β-carbon, a 1-alkene can insert its α-carbon into a surface Si–H bond to accomplish hydrosilylation.
Instantaneous Functionalization of Chemically Etched Silicon Nanocrystal Surfaces
Angewandte Chemie, 2016
Remarkable advances in surface hydrosilylation reactions of C=C and C=O bonds on hydride-terminated silicon have revolutionized silicon surface functionalization. However, existing methods for functionalizing hydride-terminated Si nanocrystals (H-SiNCs) require long reaction times and elevated temperatures. Herein, we report a room-temperature method for functionalizing H-SiNC surfaces within seconds by stripping outermost atoms on H-SiNC surfaces with xenon difluoride (XeF 2). Detailed analysis of the reaction byproducts by in situ NMR spectroscopy and GC-MS provided unprecedented insight into NC surface composition and reactivity as well as the complex reaction mechanism of XeF 2 activated hydrosilylation.
Functionalization of the (100) surface of hydrogen-terminated silicon via hydrosilation of 1-alkyne
Materials Science and …, 2003
This work presents an experimental study based on X-ray photoemission spectroscopy (XPS) of hydrosilation of 1-alkyne as a tool for the functionalization of the (100) surface of silicon. In particular, the following processes are considered: (i) hydrogen termination of silicon via HF etching and subsequent exposure to H 2 at high temperature, and (ii) grafting alkene chains to the resulting hydrogen-terminated surface via hydrosilation of 1-octyne. D
Efficient Surface Grafting of Luminescent Silicon Quantum Dots by Photoinitiated Hydrosilylation
Langmuir, 2005
We suggest a method for efficient (high-coverage) grafting of organic molecules onto photoluminescent silicon nanoparticles. High coverage grafting was enabled by use of a modified etching process that produces a hydrogen-terminated surface on the nanoparticles with very little residual oxygen and by carefully excluding oxygen during the grafting process. It had not previously been possible to produce such a clean H-terminated surface on free silicon nanoparticles or, subsequently, to produce grafted particles without significant surface oxygen. This allowed us to (1) prepare air-stable green-emitting silicon nanoparticles, (2) prepare stable dispersions of grafted silicon nanoparticles in a variety of organic solvents from which particles can readily be precipitated by addition of nonsolvent, dried, and redispersed, (3) separate these nanoparticles by size (and therefore emission color) using conventional chromatographic methods, (4) protect the particles from chemical attack and photoluminescence quenching, and (5) provide functional groups on the particle surface for further derivatization. We also show, using 1 H NMR, that the photoinitiated hydrosilylation reaction does not specifically graft the terminal carbon atom to the surface but that attachment at both the first and second atom occurs 10.
Activation of Surface Hydroxyl Groups by Modification of H-Terminated Si(111) Surfaces
Journal of the American Chemical Society, 2012
Chemical functionalization of semiconductor surfaces, particularly silicon oxide, has enabled many technologically important applications (e.g., sensing, photovoltaics, and catalysis). For such processes, hydroxyl groups terminating the oxide surface constitute the primary reaction sites. However, their reactivity is often poor, hindering technologically important processes, such as surface phosphonation requiring a lengthy postprocessing annealing step at 140°C with poor control of the bonding geometry. Using a novel oxidefree surface featuring a well-defined nanopatterned OH coverage, we demonstrate that hydroxyl groups on oxide-free silicon are more reactive than on silicon oxide. On this model surface, we show that a perfectly ordered layer of monodentate phosphonic acid molecules is chemically grafted at room temperature, and explain why it remains completely stable in aqueous environments, in contrast to phosphonates grafted on silicon oxides. This fundamental understanding of chemical activity and surface stability suggests new directions to functionalize silicon for sensors, photovoltaic devices, and nanoelectronics.
Investigation of the Reactions during Alkylation of Chlorine-Terminated Silicon (111) Surfaces
Journal of Physical Chemistry C, 2007
Absorption infrared spectroscopy (IRAS) and Rutherford backscattering (RBS) have been used to investigate the reaction of chlorine-terminated Si(111) surfaces with organometallic molecules (Grignard reagents). Although the predominant reaction leads to alkylation, with formation of covalent Si-C bonds, evidenced by a 678 cm -1 feature assigned to the Si-C stretch mode, solvents typically used during alkylation (tetrahydrofuran and methanol) can also react with Cl/Si(111) surfaces, either during the alkylation reaction or during the rinsing/cleaning process to form Si-OC n H 2n+1 as observed by the presence of a SiO-C stretch mode at 1090 cm -1 . We also address the origin of some silicon oxidation observed after the methylation or ethylation reactions.
Scientific Reports, 2015
Using two different hydrosilylation methods, low temperature thermal and UV initiation, silicon (111) hydrogenated surfaces were functionalized in presence of an OH-terminated alkyne, a CF 3terminated alkyne and a mixed equimolar ratio of the two alkynes. XPS studies revealed that in the absence of premeditated surface radical through low temperature hydrosilylation, the surface grafting proceeded to form a Si-O-C linkage via nucleophilic reaction through the OH group of the alkyne. This led to a small increase in surface roughness as well as an increase in hydrophobicity and this effect was attributed to the surficial etching of silicon to form nanosize pores (~1-3 nm) by residual water/oxygen as a result of changes to surface polarity from the grafting. Furthermore in the radical-free thermal environment, a mix in equimolar of these two short alkynes can achieve a high contact angle of ~102°, comparable to long alkyl chains grafting reported in literature although surface roughness was relatively mild (rms = ~1 nm). On the other hand, UV initiation on silicon totally reversed the chemical linkages to predominantly Si-C without further compromising the surface roughness, highlighting the importance of surface radicals determining the reactivity of the silicon surface to the selected alkynes.
Beilstein Journal of Nanotechnology, 2015
In this letter, we report results of a hydrosilylation carried out on bifunctional molecules by using two different approaches, namely through thermal treatment and photochemical treatment through UV irradiation. Previously, our group also demonstrated that in a mixed alkyne/alcohol solution, surface coupling is biased towards the formation of Si-O-C linkages instead of Si-C linkages, thus indirectly supporting the kinetic model of hydrogen abstraction from the Si-H surface (Khung, Y. L. et al. Chem. -Eur. J. 2014, 20, 15151-15158). To further examine the probability of this kinetic model we compare the results from reactions with bifunctional alkynes carried out under thermal treatment (<130 °C) and under UV irradiation, respectively. X-ray photoelectron spectroscopy and contact angle measurements showed that under thermal conditions, the Si-H surface predominately reacts to form Si-O-C bonds from ethynylbenzyl alcohol solution while the UV photochemical route ensures that the alcohol-based alkyne may also form Si-C bonds, thus producing a monolayer of mixed linkages. The results suggested the importance of surface radicals as well as the type of terminal group as being essential towards directing the nature of surface linkage.