Citation
Techane, S. D.; Gamble, L. J.; & Castner, D. G. (2011). Multitechnique Characterization of Self-Assembled Carboxylic Acid-Terminated Alkanethiol Monolayers on Nanoparticle and Flat Gold Surfaces. Journal of Physical Chemistry C, 115(19), 9432-9441.Abstract
Gold nanoparticles (AuNPs) with 14, 25, and 40 nm diameters were functionalized with different chain length (C6, C8, C11, and C16) carboxylic acid terminated alkanethiol self-assembled monolayers (COOH-SAMs). X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to examine the changes in surface chemistry as both AuNP diameter and SAM chain length were varied. COOH-SAMs on flat gold surfaces were also examined and compared to the COOH-SAM on AuNP results. For a given surface, as the COOH-SAM chain length increased the XPS C/Au atomic ratio increased due to an increased number of carbon atoms per molecule in the overlayer and an increased attenuation of the Au substrate signal. For the C16 COOH-SAMs, as the size of AuNPs decreased the XPS C/Au atomic ratio and the apparent SAM thickness increased due to the increased curvature of the smaller AuNPs. The C16 COOH-SAMs on the flat Au had the lowest XPS C/Au atomic ratio and apparent SAM thickness of any C16 COOH-SAM covered Au surface. The effective takeoff angles of the COOH-SAMs were also calculated by comparing the apparent thickness of COOH-SAMs with literature values. The effective takeoff angle for C16 COOH-SAM on 14-, 25-, and 40-nm diameter AuNPs and flat Au were found to be 57 degrees, 53 degrees, 51 degrees, and 39 degrees, respectively, for data acquired in a mode that collects a wide range of photoelectron takeoff angles. The effective takeoff angle for C16 COOH-SAM on 14 nm AuNP and flat Au decreased to 52 and 0 degrees, respectively, for data acquired in a mode that collects a narrow range of photoelectron takeoff angles. The ToF-SIMS results showed similar changes in surface chemistry with COOH-SAM chain length and AuNP size. For example, the ratio of the sum of the C(1-4)H(x)O(y)), positive ion intensities to the sum of the Au-containing positive ions intensities increased with decreasing AuNP size and increasing COOH-SAM chain length. Fourier transform IR spectroscopy in the attenuated total reflectance mode (FTIR-ATR) was used to characterize the crystallinity of the COOH-SAMs. The CH(2) stretching frequencies decreased with increasing COOH-SAM chain length on flat Au. The C16 COOH-SAM on the 14 nm AuNPs exhibited a crystalline-like CH2 stretching frequency. The size, size distribution, shapes, and solution stability of AuNPs were investigated with transmission electron microscopy (TEM) and UV/vis spectroscopy. As the average diameter of the AuNPs decreased, the size distribution became narrower, and the shape became more spherical.Keyword(s)
auger-electron-spectroscopycluster moleculesdetermining overlayer thicknession mass-spectrometryparticlesprincipal component analysisquantitative xpsray photoelectron-spectroscopysizethin-filmsNotes
761UVTimes Cited:22
Cited References Count:53