Thermal Stability of Organic Monolayers Covalently Grafted on Silicon Surfaces

Yang, F.; Allongue, P.; Ozanam, F.; Chazalviel, Jean-Noel

doi:10.1002/9781119117711.ch1

Cited by 2 publications

(6 citation statements)

References 217 publications

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“…Therefore, the alkene formation involves two silicon atoms and not only one as proposed in the literature (see eq ). − A reaction involving only one silicon atom would have a very low probability for long alkyl chains because after the breaking of the Si–C bond, the molecule is pushed away from the surface. As shown in eq , only for the ethyl monolayer we rarely observed the formation of an ethylene molecule involving only one Si atom.…”

Section: Resultsmentioning

confidence: 99%

Thermal Stability of Organic Monolayers Grafted to Si(111): Insights from ReaxFF Reactive Molecular Dynamics Simulations

Soria¹,

Zhang

Duin

et al. 2017

ACS Appl. Mater. Interfaces

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We used the ReaxFF reactive molecular dynamics simulations to investigate the chemical mechanisms and kinetics of thermal decomposition processes of silicon surfaces grafted with different organic molecules via Si-C bonds at atomistic level. In this work, we considered the Si(111) surface grafted with n-alkyl (ethyl, propyl, pentyl, and decyl) layers in 50% coverage and, Si-CH, Si-CCCH and Si-CHCHCH layers in full coverage. Si radicals primarily formed by the homolytic cleavage of Si-C bonds play a key role in the dehydrogenation processes that lead to the decomposition of the monolayers. Contrary to commonly proposed mechanisms that only involve a single Si atom center, we found that the main decomposition pathways require two Si lattice atoms to proceed. The ability of surface silyl radicals to dehydrogenate the organic molecules depends on the flexibility of the carbon backbones of the organic molecules as well as on the C-H bond strength. The dehydrogenation of n-alkyl chains mainly involves the H atoms of the β-carbon (leading to 1-alkene desorption). However, as the surface coverage decreases, the flexibility of the alkyl chains allows for the dehydrogenation of any methylene group and even the terminal methyl group of the long decyl layer. On the contrary, the rigid carbon backbone of the Si-CCCH and Si-CHCHCH moieties hinders the dehydrogenation of the terminal methyl group, which confers these layers a higher thermal stability. For all layers, the surface ends up mostly hydrogenated as Si-C bonds break and new Si-H bonds are formed during the dehydrogenation reactions.

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Section: Resultsmentioning

confidence: 99%

Thermal Stability of Organic Monolayers Grafted to Si(111): Insights from ReaxFF Reactive Molecular Dynamics Simulations

Soria¹,

Zhang

Duin

et al. 2017

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

show abstract

“…Silicon is the most important material in modern technology, and the functionalization of bulk and nanostructured silicon surfaces is critical for many device applications. The attachment of organic molecules to Si surfaces via Si–C bonds has distinctive advantages due to its high chemical and thermal stabilities . Understanding the structure and reactivity of the grafted silicon surface is required for reliable device manufacturing.…”

Section: Introductionmentioning

confidence: 99%

“…The importance of the surface chemistry of grafted silicon has motivated a series of investigations regarding the mechanisms of decomposition of alkylated silicon surfaces . Sung et al .…”

Section: Introductionmentioning

confidence: 99%

“…The attachment of organic molecules to Si surfaces via Si−C bonds has distinctive advantages due to its high chemical and thermal stabilities. 1 Understanding the structure and reactivity of the grafted silicon surface is required for reliable device manufacturing. High-coverage monolayers grafted to silicon form a passivating layer, which avoids its oxidation, 2−4 an important step in the development of photovoltaic devices.…”

Section: Introductionmentioning

confidence: 99%

“…8 The importance of the surface chemistry of grafted silicon has motivated a series of investigations regarding the mechanisms of decomposition of alkylated silicon surfaces. 1 Sung et al 9 studied the thermal stability of octadecyl monolayers in ultrahigh vacuum and found that the characteristic vibrational modes of the grafted layer stay unchanged up to about 327 °C. At higher temperature, the signals of characteristic modes decrease, while the Si−H vibrational modes appear simultaneously.…”

Section: Introductionmentioning

confidence: 99%

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Si/C/H ReaxFF Reactive Potential for Silicon Surfaces Grafted with Organic Molecules

et al. 2018

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In this work, we developed Si/C/H ReaxFF force field for the study of the functionalization and decomposition of alkyl monolayers on silicon surface. The parameterization was performed based on the main reactions involved in the decomposition of alkyl layers on small silicon clusters. The decomposition mechanisms observed in the molecular dynamics (MD) simulations were validated by the comparison of ReaxFF energy barriers for the elementary steps of the main mechanisms with density functional theory (DFT) calculations. Activation energy barriers obtained from the MD simulations from Arrhenius plots are in excellent agreement with the values calculated from DFT. The trends in the pre-exponential factor with the alkyl chain length follow the predictions of transition state theory. The results confirm that the main decomposition mechanism of the alkyl chains is the alkene elimination to the gas phase after a β-hydride abstraction by silyl radicals, which are formed in a previous step. The ReaxFF force field was used to comparatively investigate the alkyl surface coverage of Si(111), Si(100)–2 × 1 and “half-flat” Si(100) surfaces as a function of the alkyl chain length, showing good agreement with reported experimental values. Both the DFT and ReaxFF MD calculations predict that decyl monolayers with coverages as high as 0.8 are thermodynamically stable at moderate temperatures.

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Thermal Stability of Organic Monolayers Covalently Grafted on Silicon Surfaces

Cited by 2 publications

References 217 publications

Thermal Stability of Organic Monolayers Grafted to Si(111): Insights from ReaxFF Reactive Molecular Dynamics Simulations

Thermal Stability of Organic Monolayers Grafted to Si(111): Insights from ReaxFF Reactive Molecular Dynamics Simulations

Si/C/H ReaxFF Reactive Potential for Silicon Surfaces Grafted with Organic Molecules

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