Transmission FTIR spectra of -alkanethiol SAMs on GaAs(001): octadecanethiol , hexadecanethiol , tetradecanethiol , dodecanethiol , and decanethiol . stretching modes: asymmetric (a), symmetric (b), and stretching modes (c). Spectra are differential, baselined with an etched GaAs reference substrate.
Component analysis of FTIR spectra. Data (circles) and component fit (lines) using fixed and -dependent C–H stretching mode assignments referenced by peak position in : 2959 (navy), 2955 (orange), 2932 (violet), 2924 (red), 2917 (blue), 2902 (olive), 2889 (gray), 2876 (magenta), 2862 (dark cyan), 2854 (wine), and 2850 (dark yellow). See Table I for details.
asymmetric mode peak frequency as a function of the modal analysis scale factor; continuous model (line) and component fit results (circles) illustrating the correspondence of amplitude and peak position in the -scaling model. Fitting of the spectrum was not possible within the model and its position is estimated only.
asymmetric mode amplitude as a function of the methylene group number (circles). Linearization used to derive the absorption coefficient (line). Amplitude scaling model parameterized by the scale factor to a linear mapping of (dotted line). Data at are predicted for indicating a loss of SAM integrity and marks the assigned threshold -value.
Example liquid phase stretching mode spectra: (a) , (b) , and (c) , according to measured layer thickness. Absorption coefficients are derived from the asymmetric mode peak amplitudes, e.g., and . The ratio of points (i) and (ii) verify the linear dependence of absorbance on layer thickness, in this case for .
Enhancement factor observed for the SAM phase absorption coefficient relative to Beer–Lambert measurements in bulk material. Data at evaluated from the spectrum of for polycrystalline in Ref. 21. The dotted line is used for trend visualization only.
Assignment of C–H modal parameters (adapted from Refs. 21 and 28) and scaling indicator for the spectral components of SAMs on GaAs(001).
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