First-principles investigation of functionalization-defects on silicon surfaces (original) (raw)
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Chemical Physics Letters, 2004
The reaction of the bifunctional organic molecule 1-dimethylamino-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations on a one-dimer cluster model. We found that, once in the physisorbed dative bonded well (À22.1 kcal mol À1), DMAP can proceed to react via a number of pathways. We first considered the cycloaddition of the C"C triple bond, leading to Si-C di-r bonded product (À58.6 kcal mol À1), computing an energy barrier of 33.1 kcal mol À1. We considered also possible dissociative pathways of dative bonded DMAP, i.e., methylene C-H, methyl C-H or N-CH 3 bond cleavage.
Si/C/H ReaxFF Reactive Potential for Silicon Surfaces Grafted with Organic Molecules
The Journal of Physical Chemistry C, 2018
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 preexponential 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.
Molecular Modeling of Alkyl Monolayers on the Si(100)−2 × 1 Surface
Langmuir, 2004
Molecular modeling was used to simulate various surfaces derived from the addition of 1-alkenes and 1-alkynes to SidSi 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.
Competitive Chemisorption of Bifunctional Carboxylic Acids on H:Si(100): A First-Principles Study
The Journal of Physical Chemistry C, 2008
We investigate competitive chemisorption processes of bifunctional R-carboxy ω-alkenes and ω-alkynes on fully hydrogenated H:Si(100), using first-principles density functional theory, in extended surface simulations. We study the structural properties and quantify the energetics and activation barriers, analyzing the reaction paths. Our results reveal that, if the plain, unactivated chemisorption reaction is always achieved through high barriers, once realized the configurations are very stable, ensuring robustness and reliability of the functionalized interface. We identify the conditions where disordered configurations are more likely to arise, with both functionalities offered at the free surface. For all stable configurations, a thorough analysis of the electronic properties and the extent of hybridization in the functionalized interface allows us to identify promising candidates for applications in molecular electronics.
Ab initio investigation of the adsorption of organic molecules at Si(111) and Si(100) surfaces
Surface Science, 2003
To investigate the early stages of SiC growth on silicon, we performed an ab initio study of the adsorption of C 2 H 2 and other small organic molecules on different Si surfaces. Our calculations, based both on geometry optimization and on finite-temperature molecular dynamics simulations, show that for all the molecules that we have considered the preferred adsorption sites at low temperature are confined at the surface, with no sub-surface penetration. Adsorption occurs through the formation of Si-C bonds, accompanied by a distortion of the adsorbed molecule to adapt the Si-C distance to the SiC bulk bond length. We discuss similarities and differences upon changing the organic molecule and the crystal face. To complete the study with the computation of directly measurable quantities, we analyze the optical reflectance anisotropy of one simulated structure.
Cluster model study of the chemisorption of atomic carbon on Si(100) surfaces
Journal of Crystal Growth, 1997
Structural parameters for chemisorption of atomic carbon above a Si(100) surface have been obtained through a Si35H 32 cluster model and a MINDO/3 hamiltonian. The most stable position has been found to be the bridge one when considering the unrelaxed surface. The stability increases about 14 kcal/mol when relaxation of the surface is allowed. Further research has been carried out using a reduced cluster model (SigH i2) at the ab initio Hartree-Fock level of calculation. Results confirm the increase of stability of the relaxed system. At this level, the binding energy is 90 kcal/mol for the unrelaxed surface and the stabilization when the surface is relaxed is of about 20% with respect to the non-relaxed surface.
The Journal of Physical Chemistry B, 1998
The understanding and control of silicon surfaces is of great importance in the production of silicon-based electronic devices made from semiconductor materials and constructed on silicon single-crystal substrates. This is the first study to see the effect of surface etching by fluorine on the stability of the unreconstructed Si(100) surface using periodic density functional calculations. All the possible fluorine substitution sites are considered, and the results are compared with the existing experimental observation in terms of suitability of fluorine substitution on the surface. The results are compared with H-terminated surfaces to prove the efficiency of fluorine in stabilizing the unreconstructed Si(100) surface. Oxidation of the Si(100) surface for both Hand F-terminated surfaces were also studied to propose the plausible mechanism of oxidation. Two kinds of experimental situations were mimicked for oxidation; (1) oxidation on the surface, i.e., generation of the Si-O-H bond, and (2) oxidation on the bridging bond between two silicons, i.e., generation of Si-O-Si, were compared to show the feasibility of Si-O-Si bond formation. Oxidation through atomic oxygen was followed throughout the calculation. The calculations were performed with smaller clusters using density functional methodology to validate and rationalize the current understanding. The results were further supported by molecular electrostatic potential maps generated from periodic density functional calculation results.
Chemical Physics Letters, 1997
The structure of chemisorbed acetylene on the Si(001)-(2 × 1) surface is investigated based on ab initio molecular-dynamics simulations according to the Car-Parrinello method and within the local-density approximation (LDA) to densityfunctional theory. The calculations reveal that the Si-Si dimer bond is stable upon acetylene chemisorption resulting in the formation of a four-member disilacyclobutene ring. Coadsorption of two hydrogen atoms together with the acetylene molecule onto the Si-Si dimer bonds results in cleavage of the Si-Si bond and separation of the two silicon atoms by a distance equal to the second-nearest neighbor distance in bulk crystalline silicon.
Spontaneous dissociation of a conjugated molecule on the Si(100) surface
The Journal of Chemical Physics, 2002
The adsorption mechanism of ␣-sexithiophene ͑␣-6T͒ on the clean Si(100)-(2ϫ1) surface has been investigated using scanning tunneling microscopy ͑STM͒ and first principles electronic structure calculations. We find that at submonolayer coverage, the ␣-6T molecules are not stable and dissociate into monomers. We observe two different configurations of the monomers and have discussed the corresponding adsorption geometries based on theoretical calculations. The calculations elucidate how the fragments are absorbed on the surface, giving rise to the observed STM images. With increasing coverage, the STM images show the existence of complete ␣-6T molecules. In addition, results of the adsorption behavior of ␣-6T molecules on the H-passivated Si(100)-(2ϫ1) surface are reported. On this surface the molecules are highly mobile at room temperature due to the weak molecule-substrate interaction. The STM results also indicate that they can easily be anchored at the defect sites.
Surface Science, 2011
Partially H-terminated silicon surface Adsorption of organic molecules Nudged elastic band method (NEB) Adsorption properties of 4-bromostyrene (Br-Sty) on the Si(001)-(1 × 2) surface are investigated by ab initio calculation based on density functional theory (DFT). For the adsorption of Br-Sty molecule on the Si (001)-(1 × 2) surface, we have assumed two possible cases within: (i) binding on the partially Hterminated surface and (ii) binding on the clean surface. For the first case, we have estimated two different binding sides: (i) Bromine-terminated bindings and (ii) Carbon-terminated binding. The adsorption energies of Br-terminated and C-terminated binding were found as 0.36 eV and 3.76 eV, respectively. In the same manner, we have also assumed two possible binding sides for the clean surface: (i) Br-terminated binding and (ii) ring-shaped binding. We have found adsorption energies for Br-terminated and ringshaped binding as 0.14 eV and 1.10 eV on the clean surface, respectively. Moreover, the nudged elastic band method (NEB) was used to reveal the adsorption pathway of these binding models. These results serve to understand the possibility of the adsorption of Br-Sty molecules onto different kind of silicon surfaces into different reaction conditions.