Spectroscopic Studies of the Modification of Crystalline Si(111) Surfaces with Covalently-Attached Alkyl Chains Using a Chlorination/Alkylation Method

Bansal, Ashish; Li, Xiuling; Yi, Sang I.; Weinberg, W. H.; Lewis, Nathan S.

doi:10.1021/jp010284p

Cited by 180 publications

(249 citation statements)

References 77 publications

(166 reference statements)

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“…This peak was assigned as the C-H symmetric bending, or "umbrella", mode of the methyl group. 22,27 This mode is expected to be normal to the surface if CH 3 replaces Cl on Si(111) as shown in Chart 1.…”

Section: Resultsmentioning

confidence: 99%

“…3 A few grains of benzoyl peroxide were added as a radical initiator, and the reaction solution was heated at 95°C for 45 min. The sample was then removed from the reaction solution, rinsed with tetrahydrofuran (THF) and CH 3 OH, and then finally rinsed again with THF, which was allowed to evaporate off the wafer.…”

Section: Methodsmentioning

confidence: 99%

“…3 Excess THF was added to the reaction solution to allow for solvent loss. The reaction was heated at 75°C for 3 h for n ) 1 and for 5 h for n ) 2.…”

Section: Methodsmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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

et al. 2006

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“…3 Extensive work in our laboratory has focused on the use of a two-step chlorination/alkylation procedure to produce well-defined, alkylated Si surfaces. 4,5 Such surfaces have been shown to exhibit very low surface recombination velocities, indicating relatively few electrically active defect sites on the functionalized surface. 1,5 Consistently, no silicon oxides are detectable by surface-sensitive X-ray photoelectron spectroscopy on such initially prepared alkylated Si surfaces.…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Soft X-ray Photoelectron Spectroscopic Studies and Scanning Auger Microscopy Studies of the Air Oxidation of Alkylated Silicon(111) Surfaces

et al. 2006

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High-resolution soft X-ray photoelectron spectroscopy was used to investigate the oxidation of alkylated silicon(111) surfaces under ambient conditions. Silicon(111) surfaces were functionalized through a two-step route involving radical chlorination of the H-terminated surface followed by alkylation with alkylmagnesium halide reagents. After 24 h in air, surface species representing Si + , Si 2+ , Si 3+ , and Si 4+ were detected on the Cl-terminated surface, with the highest oxidation state (Si 4+ ) oxide signal appearing at +3.79 eV higher in energy than the bulk Si 2p 3/2 peak. The growth of silicon oxide was accompanied by a reduction in the surface-bound Cl signal. After 48 h of exposure to air, the Cl-terminated Si(111) surface exhibited 3.63 equivalent monolyers (ML) of silicon oxides. In contrast, after exposure to air for 48 h, CH 3 -, C 2 H 5 -, or C 6 H 5 CH 2 -terminated Si surfaces displayed <0.4 ML of surface oxide, and in most cases only displayed ≈0.20 ML of oxide. This oxide was principally composed of Si + and Si 3+ species with peaks centered at +0.8 and +3.2 eV above the bulk Si 2p 3/2 peak, respectively. The silicon 2p SXPS peaks that have previously been assigned to surface Si-C bonds did not change significantly, either in binding energy or in relative intensity, during such air exposure. Use of a high miscut-angle surface (7°vs e0.5°off of the (111) surface orientation) yielded no increase in the rate of oxidation nor change in binding energy of the resultant oxide that formed on the alkylated Si surfaces. Scanning Auger microscopy indicated that the alkylated surfaces formed oxide in isolated, inhomogeneous patches on the surface.

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“…The disappearance of the Si-H stretch mode (2082 cm -1 ) upon chlorination was expected. 20 The most striking feature is the appearance of a unique azide symmetric stretching mode at 2168 cm -1 , which is blue-shifted by ca. 122 and 63 cm -1 with respect to either azides in solution (see SI) or organic azides 18,21 with nitrogen bonded to a carbon atom, respectively.…”

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confidence: 99%

Azidation of Silicon(111) Surfaces

Cao

Heath

2008

J. Am. Chem. Soc.

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Spectroscopic Studies of the Modification of Crystalline Si(111) Surfaces with Covalently-Attached Alkyl Chains Using a Chlorination/Alkylation Method

Cited by 180 publications

References 77 publications

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

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

High-Resolution Soft X-ray Photoelectron Spectroscopic Studies and Scanning Auger Microscopy Studies of the Air Oxidation of Alkylated Silicon(111) Surfaces

Azidation of Silicon(111) Surfaces

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