Chlorination−Methylation of the Hydrogen-Terminated Silicon(111) Surface Can Induce a Stacking Fault in the Presence of Etch Pits

Solares, Santiago D.; Yu, Hongbin; Webb, Lauren J.; Lewis, Nathan S.; Heath, James R.; Goddard, William A.

doi:10.1021/ja055408g

Cited by 29 publications

(45 citation statements)

References 15 publications

(29 reference statements)

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“…Results for larger chain alkyls indicate that complete coverage is not possible. 27,35 As previously noted by Solares et al 27 and in our previous work, 36 the dihedral angle adopted by the surface methyl groups results from a balance between the steric repulsion of the hydrogen atoms and the torsional strain of the methyl groups with respect to the underlying silicon surface. This balance of forces will be discussed in detail ͑vide infra͒.…”

Section: Introductionsupporting

confidence: 62%

“…[19][20][21][22][23][24][25][26] Recently, organic functionalization involving a two-step chlorination/alkylation has been improved by Lewis and co-workers. [27][28][29] Methyl passivation was found to be effective using a two-step chlorination/ methylation with the Grignard reagent. The resulting surface has been characterized using several experimental methods by Fidelis et al, 30 Yamada et al, 31,32 and by Webb et al 33,34 Methyl passivation stabilizes the silicon ͑111͒ surface to oxidation for long periods of atmospheric exposure ͑Ͼ600 h͒.…”

Section: Introductionmentioning

confidence: 99%

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Collective vibrations in cluster models for semiconductor surfaces: Vibrational spectra of acetylenyl and methylacetylenyl functionalized Si(111)

Ferguson

Raghavachari

2007

The Journal of Chemical Physics

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Section: Introductionsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Collective vibrations in cluster models for semiconductor surfaces: Vibrational spectra of acetylenyl and methylacetylenyl functionalized Si(111)

Ferguson

Raghavachari

2007

The Journal of Chemical Physics

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“…threshold. The optimized structure calculated for both CH 3 -Si(111) and CD 3 The dihedral angle H-C-Si-Si, which defines the orientation of the surface methyl groups, was found to be 37.7 • , which is in excellent agreement with the value (38 • ) obtained by Solares et al 31 using the PBE exchange-correlation functional and by Ferguson et al 20 using the Heyd-ScuseriaErnzerhof (HSE) hybrid functional.…”

Section: Density Functional Perturbation Theory Computational Detailssupporting

confidence: 80%

The interaction of organic adsorbate vibrations with substrate lattice waves in methyl-Si(111)-(1 × 1)

Brown

Hund

Campi

et al. 2014

The Journal of Chemical Physics

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A combined helium atom scattering and density functional perturbation theory study has been performed to elucidate the surface phonon dispersion relations for both the CH3-Si(111)-(1 × 1) and CD3-Si(111)-(1 × 1) surfaces. The combination of experimental and theoretical methods has allowed characterization of the interactions between the low energy vibrations of the adsorbate and the lattice waves of the underlying substrate, as well as characterization of the interactions between neighboring methyl groups, across the entire wavevector resolved vibrational energy spectrum of each system. The Rayleigh wave was found to hybridize with the surface rocking libration near the surface Brillouin zone edge at both the ${\rm \bar M}$M¯-point and ${\rm \bar K}$K¯-point. The calculations indicated that the range of possible energies for the potential barrier to the methyl rotation about the Si-C axis is sufficient to prevent the free rotation of the methyl groups at a room temperature interface. The density functional perturbation theory calculations revealed several other surface phonons that experienced mode-splitting arising from the mutual interaction of adjacent methyl groups. The theory identified a Lucas pair that exists just below the silicon optical bands. For both the CH3- and CD3-terminated Si(111) surfaces, the deformations of the methyl groups were examined and compared to previous experimental and theoretical work on the nature of the surface vibrations. The calculations indicated a splitting of the asymmetric deformation of the methyl group near the zone edges due to steric interactions of adjacent methyl groups. The observed shifts in vibrational energies of the -CD3 groups were consistent with the expected effect of isotopic substitution in this system.

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“…It is likely that the edges and steps are also passivated, possibly by H, if not by -CH 3 groups. 13 The large conductance gap relative to the Si band gap was observed for both the methyl-and ethyl-terminated Si͑111͒ surfaces prepared by the two-step chlorination/ alkylation method. We ascribe this behavior to tip-induced band bending ͑TIBB͒, as identified previously by McEllistrem et al 14 TIBB can only occur for surfaces with relatively low levels of midgap states, so that the bias applied between the tip and the sample drops across the sample, and the Fermi level of the sample becomes unpinned at the surface.…”

mentioning

confidence: 96%

Scanning tunneling spectroscopy of methyl- and ethyl-terminated Si(111) surfaces

Webb

Heath

et al. 2006

Applied Physics Letters

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Methyl-and ethyl-terminated Si͑111͒ surfaces prepared by a two-step chlorination/alkylation method were characterized by low temperature scanning tunneling spectroscopy ͑STS͒. The STS data showed remarkably low levels of midgap states on the CH 3 -and C 2 H 5 -terminated Si surfaces. A large conductance gap relative to the Si band gap was observed for both surfaces as well as for the hydrogen-terminated Si͑111͒ surface. This large gap is ascribed to scanning tunneling microscope tip-induced band bending resulting from a low density of midgap states which avoid pinning of the Fermi levels on these passivated surfaces. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2203968͔Alkylation of Si by a two-step chlorination/alkylation process 1 has been shown to produce surfaces that are passivated both chemically and electrically. 2,3 In common with H-terminated Si surfaces, the alkylated surfaces show extraordinarily low surface recombination velocities. 2,3 However, unlike H-Si͑111͒ surfaces, alkylated surfaces are not susceptible to rapid oxidation in ambient air and do not suffer concomitant degradation of their surface electrical properties. 2,3 Alkylation of Si͑111͒ with methyl groups has been shown by low-energy electron diffraction 4 ͑LEED͒ to produce surfaces with long-range order and by scanning tunneling microscopy ͑STM͒ to produce surfaces with shortrange order. 5,6 Additionally, photoemission and work function measurements 4 in ultrahigh vacuum have shown that CH 3 -terminated Si samples have relatively little band bending, consistent with a low density of band-gap states and in contrast to the fixed charge that is universally present at Si/ SiO 2 interfaces.We report herein scanning tunneling spectroscopy ͑STS͒ data for H-, CH 3 -, and C 2 H 5 -terminated Si͑111͒ surfaces. To date, the only wet chemically prepared Si surface reported to exhibit nearly ideal STS behavior is the H-Si͑111͒ surface. 7 Interestingly, in ultrahigh vacuum ͑UHV͒, this surface exhibits a tunneling gap of Ͼ1.6 eV in which little or no midgap conductance is observed, 8 whereas the band gap of Si is 1.1 eV. The tunneling behavior of CH 3 -Si͑111͒ and C 2 H 5 -Si͑111͒ is thus interesting in this context, given the low midgap density of states expected for such alkylated Si surfaces from macroscopic measurements of such systems. 2,3 Silicon surfaces were functionalized using a two-step chlorination/alkylation procedure. 1 Samples were obtained from ͑111͒-oriented, Sb-doped, 0.005-0.02 ⍀ cm resistivity, n-type Si wafers having a miscut error of ±0.5°. The samples were cleaned and oxidized for 5 min at 80°C in a solution of 1:1:5 ͑vol͒ 30% H 2 O 2 : 30% NH 3 : H 2 O and were then terminated with Si-H bonds by etching for 15 min in 40% NH 4 F͑aq͒. This etching method has been demonstrated to produce large atomically flat terraces. 5 Chlorination was performed by exposure of the samples to a solution of PCl 5 in chlorobenzene. 3,9 A small amount of benzoyl peroxide was added to initiate a radical reaction, and the samples were heated ...

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Chlorination−Methylation of the Hydrogen-Terminated Silicon(111) Surface Can Induce a Stacking Fault in the Presence of Etch Pits

Cited by 29 publications

References 15 publications

Collective vibrations in cluster models for semiconductor surfaces: Vibrational spectra of acetylenyl and methylacetylenyl functionalized Si(111)

Collective vibrations in cluster models for semiconductor surfaces: Vibrational spectra of acetylenyl and methylacetylenyl functionalized Si(111)

The interaction of organic adsorbate vibrations with substrate lattice waves in methyl-Si(111)-(1 × 1)

Scanning tunneling spectroscopy of methyl- and ethyl-terminated Si(111) surfaces

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