Molecular conformation of n-alkyl monolayers covalently bonded to Si(1 1 1) probed by infrared–visible sum-frequency spectroscopy

Ishibashi, Teru; Ara, Masato; Tada, Hayato; Ōnishi, Hiroshi

doi:10.1016/s0009-2614(02)01713-x

Cited by 18 publications

(35 citation statements)

References 25 publications

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“…It is possible to attribute this band to FR(CH 2 ), but this would violate the selection rule. 34 We are cautiously attributing this band to the asymmetric stretch of CH 2 (d ω -) instead, consistent with the assignment of the C-H stretching vibrations of octadecylsiloxane on glass by Chow et al 24 In our case, there are two different types of d -stretches, 2930 and 2902-5 cm -1 ; the former can be attributed to trans-gauche defects in the backbone chains, which has been observed by Ishibashi et al 36 Since no 2902-5 cm -1 band was observed for n-alkyl monolayers on silicon, 26,27 this peak must be related to CH 2 groups adjacent to the carboxyl group (Figure 3). All peak assignments for the ester-terminated monolayers on silicon before and after hydrolysis are summarized in Tables 3 and 4. The spectrum of dodecyl monolayers on silicon (Figure 4a) is composed of three major bands, 2873 cm -1 (r + ), 2940 cm -1 (FR), and 2962 cm -1 (r -).…”

Section: Resultssupporting

confidence: 93%

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Structure and Reactivity of Alkoxycarbonyl (Ester)-Terminated Monolayers on Silicon: Sum Frequency Generation Spectroscopy

et al. 2006

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Carboxylic acid-terminated monolayers on crystalline silicon surfaces can be readily modified with biological macromolecules for the fabrication of semiconductor-based biosensing devices. They were prepared by acidcatalyzed hydrolysis of alkoxycarbonyl (ester)-terminated monolayers and studied by vibrational sum frequency generation (SFG) spectroscopy. The C-H vibration region of the SFG spectra consists of strong methyl bands with significant contributions from methylene stretching modes, indicating that these monolayers are generally ordered but with considerable gauche defects in the alkyl chains in comparison with n-alkyl monolayers. After hydrolysis, the methylene stretching modes prevail, with "residues" of the methyl bands, indicating incomplete hydrolysis and disruption of the monolayer structure. This work demonstrates that SFG is capable of providing quantitative information on structure-reactivity correlations in organic monolayers.

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Section: Resultssupporting

confidence: 93%

“…32 All SFG spectra had signal-to-noise ratios comparable to those reported in the literature. [25][26][27] 3.1. Peak Assignments and Structure Evaluation.…”

Section: Resultsmentioning

confidence: 99%

Structure and Reactivity of Alkoxycarbonyl (Ester)-Terminated Monolayers on Silicon: Sum Frequency Generation Spectroscopy

et al. 2006

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“…All spectra exhibited features thatcorrespondtodenselypackedandwell-orientedmonolayers. 10,12,25 Specifically, contributions from methylene (CH 2 ) stretching modes were negligible, and the spectral features were dominated by the contributions from the methyl (CH 3 ) groups: methyl symmetric stretch (r…”

Section: Alkyl Monolayers On Siliconmentioning

confidence: 99%

Probing the Molecular Conformation of Self-Assembled Monolayers at Metal/Semiconductor Interfaces by Vibrational Sum Frequency Generation Spectroscopy

et al. 2009

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The conformation of self-assembled monolayers (SAMs) buried at metal-semiconductor interfaces plays a crucial role in the functioning of the molecular junctions thus formed. We have studied by vibrational sum frequency generation (SFG) spectroscopy the influence of deposited gold films on the molecular orientation of a series of n-alkyl monolayers that are covalently bonded to silicon(111) via Si-C linkages (≡Si-C n H 2n+1 , n ) 10, 12, 14, and 18). The SFG spectra indicate that the gold contacts (overlayers) introduce significant gauche defects within the initially highly oriented alkyl chains. The methyl tilt angles of the buried n-alkyl monolayers depend on the gold deposition method (vacuum evaporation vs sputtering) and the alkyl chain length. These observations are supported by solid-state electrical measurements.

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“…SFG vis IR 2 (9) In this equation, the resonant contribution of mode q to the susceptibility is given by (10) In this article, we report the recent development of a program for the simulation and the interpretation of SFG signatures and its application in the probing of the structure of organic layers at silicon interfaces. The general method that has been developed combines density functional theory (DFT) calculations to evaluate the molecular properties with a threelayer approach to determine the macroscopic response of the interface.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The covalent attachment can be performed through coupling reactions between the chemically activated surfaces and molecules. Among the systems of interest, silicon is one of the most widely used semiconductors in modern technology, and organic monolayers covalently bonded to silicon surfaces have gained much attention since their introduction, owing to their well-defined structures and the possibility of introducing diverse electrical and optical functionalities into the system. ,− Nevertheless, the lack of control of such processes at the molecular level might result in the formation of multilayers in which the molecules have lost active conformation or orientation. − …”

Section: Introductionmentioning

confidence: 99%

Theoretical Investigation of Vibrational Sum-Frequency Generation Signatures of Functionalized H—Si(111)

2015

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Developments toward a general approach for simulating and interpreting the sum-frequency generation signatures of functionalized surfaces are reported. This approach encompasses two steps: (1) The molecular properties (vibrational frequencies, IR and Raman quantities) are evaluated using first-principles approaches implemented in standard quantum chemistry programs, and (2) the macroscopic optical responses (second-order nonlinear optical susceptibility tensor) of the adsorbate on its substrate are determined within the three-layer model of the interface. A homemade code was written to carry out this second step, including (1) the evaluation of the Fresnel factor and (2) the determination of the molecular orientation in the laboratory frame. This approach and program allow for the generation of the SFG spectra for different combinations of molecular orientations and experimental setups, as well as the identification of the vibrational modes to facilitate their analysis. Then, the approach is illustrated in the case of a decyl chain covalently bonded to hydrogen-terminated Si(111) [ Si(CH 2 ) 9 CH 3 ]. The simulated ppp spectrum agrees closely with experiment, whereas the agreement gets worse when parts of the chain are frozen, demonstrating that the SFG signature originates from a large part of the decyl chain. Calculations were also performed for the other sets of polarizations (sps, ssp, and pss), highlighting the fact that the spectral profile varies considerably from ppp to ssp, sps, and pss, which is attributed to the combined effects of the Fresnel factors and the structure of the χ (2),R tensor. The impact of the orientation of the alkyl chain (tilt and rotation angles) on the ppp SFG intensity was then monitored by reducing the system to an isolated decane molecule and determining the changes in the SFG spectral pattern related to the orientation of the IR dipole moment.

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Molecular conformation of n-alkyl monolayers covalently bonded to Si(1 1 1) probed by infrared–visible sum-frequency spectroscopy

Cited by 18 publications

References 25 publications

Structure and Reactivity of Alkoxycarbonyl (Ester)-Terminated Monolayers on Silicon: Sum Frequency Generation Spectroscopy

Structure and Reactivity of Alkoxycarbonyl (Ester)-Terminated Monolayers on Silicon: Sum Frequency Generation Spectroscopy

Probing the Molecular Conformation of Self-Assembled Monolayers at Metal/Semiconductor Interfaces by Vibrational Sum Frequency Generation Spectroscopy

Theoretical Investigation of Vibrational Sum-Frequency Generation Signatures of Functionalized H—Si(111)

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