Molecular Modeling of Covalently Attached Alkyl Monolayers on the Hydrogen-Terminated Si(111) Surface

Sieval, Alexander B.; Hout, Bram van den; Zuilhof, and Han; Sudhölter, Ernst J. R.

doi:10.1021/la001494g

Cited by 159 publications

(239 citation statements)

References 31 publications

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“…Our observation of non-exfoliation phenomenon is presumably due to the additional energy needed to overcome partially or fully interdigitated interactions between the alkyl chains of the intercalates (Fig. 3b) 30,32,33 .…”

Section: Resultsmentioning

confidence: 82%

Tandem intercalation strategy for single-layer nanosheets as an effective alternative to conventional exfoliation processes

et al. 2015

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Simple and effective generation of transition metal chalcogenides (TMCs) in a single-layer form has been a challenging task. Here we present a tandem molecular intercalation (TMI) as a new exfoliation concept for producing single-layer TMCs from multi-layer colloidal TMC nanostructures in solution phase. TMI requires tandem Lewis base intercalates, where short 'initiator' molecules first intercalate into TMCs to open up the interlayer gap, and the long 'primary' molecules then bring the gap to full width so that a random mixture of intercalates overcomes the interlayer force. Spontaneous exfoliation then yields single-layer TMCs. The TMI process is uniquely advantageous because it works in a simple one-step process under safe and mild conditions (that is, room temperature without sonication or H 2 generation). With the appropriate intercalates, we have successfully generated single-layer nanostructures of group IV (TiS 2 , ZrS 2 ), group V (NbS 2 ) and VI (WSe 2 , MoS 2 ) TMCs.

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Section: Resultsmentioning

confidence: 82%

Tandem intercalation strategy for single-layer nanosheets as an effective alternative to conventional exfoliation processes

et al. 2015

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“…Third, the relative quantity of species II and IV in Si2p increased during this photon induced oxidation, thus both peak positions of A and B would be moved towards higher binding energies. Transmission IR experiments on thermal hydrosilyation of porous silicon shows that the maximum coverage coverage of alkyl chain on porous silicon is 0.3-0.5 ML (monolayer) [48]. This suggests that a substantial fraction of the surface atoms of the Si-QDs are bound to hydrogen.…”

Section: Photoluminescence Spectroscopymentioning

confidence: 99%

Soft X‐ray induced oxidation on acrylic acid grafted luminescent silicon quantum dots in ultrahigh vacuum

Chao

Wang

Pietzsch

et al. 2011

Physica Status Solidi (a)

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Water soluble acrylic acid grafted luminescent silicon quantum dots (Si-QDs) were prepared by a simplified method. The resulting Si-QDs dissolved in water and showed stable strong luminescence with peaks at 436 and 604 nm. X-ray photoelectron spectroscopy (XPS) was employed to examine the surface electronic states after the synthesis. The co-existence of the Si2p and C1s core levels infers that the acrylic acid has been successfully grafted on the surface of silicon quantum dots. To fit the Si2p spectrum, four components were needed at 99.45, 100.28, 102.21 and 103.24 eV. The first component at 99.45 eV (I) was assigned to Si-Si within the silicon core of the Si-QDs. The second component at 100.28 eV (II) was from Si-C. The third at 102.21 eV (III) was a sub-oxide state and the fourth at 103.24 eV (IV) was from SiO 2 at Si-QDs surface. With an increase in exposure to soft X-ray photons, the intensity ratio of the two peaks within the Si2p region A and B increased from 0.5 to 1.4 while the peak A intensity decreased, and eventually a steady state was reached. This observation is explained in terms of photon-induced oxidation taking place within the surface dangling bonds. As the PL profile for Si-QDs is influenced by the degree of oxidation within the nanocrystal structure, the inducement of oxidation by soft X-rays will play a role in the range of potential applications where such materials could be used -especially within biomedical labelling.

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“…The area under this peak corresponded to a coverage of surface Si-H bonds of 14% of the freshly etched surface, indicating that a substantial portion of atop Si atoms are bonded to ethyl groups, and that only a small amount of the surface is terminated with H groups. Extensive work is ongoing in our laboratory to quantify further the full coverage of ethyl groups on the (111) surface, and to determine how an alkyl group with a van der Waals diameter of 5.4-5.0 Å 35,36 can pack to such high extent on a surface with an internuclear Si atop site distance of 3.8 Å. 37 Upon close inspection of the low-wavenumber region of this surface, a feature at 627 cm -1 was apparent at both IR beam incident angles ( Figure 6).…”

Section: Tirs Peak Area (Cmmentioning

confidence: 99%

Transmission Infrared Spectroscopy of Methyl- and Ethyl-Terminated Silicon(111) Surfaces

et al. 2006

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Transmission infrared spectroscopy (TIRS) has been used to investigate the surface-bound species formed in the two-step chlorination/alkylation reaction of crystalline (111)-oriented Si surfaces. Spectra were obtained after hydrogen termination, chlorine termination, and reaction of the Cl-Si(111) surface with CH 3 MgX or C 2 H 5 MgX (X ) Cl, Br) to form methyl (CH 3 )-or ethyl (C 2 H 5 )-terminated Si(111) surfaces, respectively. Freshly etched H-terminated Si(111) surfaces that were subsequently chlorinated by immersion in a saturated solution of PCl 5 in chlorobenzene were characterized by complete loss of the Si-H stretching and bending modes at 2083 and 627 cm -1 , respectively, and the appearance of Si-Cl modes at 583 and 528 cm -1 . TIRS of the CH 3 -terminated Si(111) surface exhibited a peak at 1257 cm -1 polarized perpendicular to the surface assigned to the C-H symmetrical bending, or "umbrella" motion, of the methyl group. A peak observed at 757 cm -1 polarized parallel to the surface was assigned to the C-H rocking motion. Alkyl C-H stretch modes on both the CH 3 -and C 2 H 5 -terminated surfaces were observed near 2900 cm -1 . The C 2 H 5 -terminated Si(111) surface additionally exhibited broad bands at 2068 and 2080 cm -1 , respectively, polarized perpendicular to the surface, as well as peaks at 620 and 627 cm -1 , respectively, polarized parallel to the surface. These modes were assigned to the Si-H stretching and bending motions, respectively, resulting from H-termination of surface atoms that did not form Si-C bonds during the ethylation reaction. I. IntroductionAlkylation of silicon(111) surfaces has attracted significant recent attention due to the potential for obtaining molecular level control over the electrical, electrochemical, and chemical properties of Si surfaces. 1-5 Hydrogen-terminated Si(111) surfaces have a very low surface electron-hole recombination velocity, 6 but oxidize rapidly in ambient air, forming a large number of surface electronic trap states. 2 In contrast, alkylated Si surfaces prepared through a two-step chlorination/alkylation procedure show excellent chemical stability and low surface charge carrier recombination rates for extended time periods, even as they are exposed to ambient air. 1,2 Methyl moieties are the only saturated hydrocarbon group which can sterically form a Si-C bond to every atop site on an unreconstructed Si(111) surface, because van der Waals interactions between neighboring methylene units should prevent C 2 H 5 -and other alkyls from terminating every Si atop site. 7 Furthermore, the sp 3 -hybridized Si-C bond on the Si(111) surface should orient the methyl groups on the CH 3 -terminated surfaces normal to the surface plane, as shown in Chart 1. This orientation should produce diagnostic signatures and polarizations in the vibrational spectrum of such surfaces. Recent scanning tunneling microscopy 8 and low-energy electron diffraction studies 9 have revealed both short-range and long-range order on CH 3 -terminated Si surfaces. However, at pr...

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Molecular Modeling of Covalently Attached Alkyl Monolayers on the Hydrogen-Terminated Si(111) Surface

Cited by 159 publications

References 31 publications

Tandem intercalation strategy for single-layer nanosheets as an effective alternative to conventional exfoliation processes

Tandem intercalation strategy for single-layer nanosheets as an effective alternative to conventional exfoliation processes

Soft X‐ray induced oxidation on acrylic acid grafted luminescent silicon quantum dots in ultrahigh vacuum

Transmission Infrared Spectroscopy of Methyl- and Ethyl-Terminated Silicon(111) Surfaces

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