Self-Assembled Gold Nanoparticle/Alkanedithiol Films:  Preparation, Electron Microscopy, XPS-Analysis, Charge Transport, and Vapor-Sensing Properties

Abstract

Gold nanoparticle/alkanedithiol films were prepared via layer-by-layer self-assembly. For the assembly process, dodecylamine-stabilized Au nanoparticles with an average size of 4 nm and alkanedithiols with different alkylene chain lengths (C 6 , C 9 , C 12 , C 16 ) were used. The thickness of the films was determined by AFM and ranged between 26 and 34 nm. FE-SEM and TEM images indicate that the particle size within the film materials was similar to that of the dodecylamine-stabilized particles used for film preparation. The composition of the films was analyzed by XPS. The absence of the nitrogen signal indicated that the dodecylamine ligands were quantitatively exchanged by alkanedithiol molecules during film assembly. Two sulfur signals were observed, which could be assigned to sulfur bound to gold (S-Au) and to free thiol groups (S-H). As indicated by the relative signal intensities, about 60% of the alkanedithiol molecules were bound with both ends to the nanoparticles, whereas 40% were bound with only one thiol group. The C/S ratio was in good agreement with the stoichiometry of the alkanedithiol molecules. All films showed linear current-voltage characteristics. Conductivity measurements at variable temperature were consistent with an Arrhenius-type activation of charge transport. Using an activated tunneling model for describing the charge transport properties, we obtained an electron tunneling decay constant of β N ) 0.61 or 0.71, depending on the method used for data analysis. When the films were dosed with vapors of toluene and tetrachloroethylene, the resistance of the films increased reversibly. This response increased exponentially with increasing length of the alkanedithiol molecules. The chemical selectivity of the films corresponded essentially to the solubility properties of the alkanedithiol molecules.

Spectroscopy-based study on the interaction between gold nanoparticle and poly(vinylpyrrolidone) molecules in a non-hydrocolloid

“…presence of PVP molecules reveals interfacial interaction between the Au NP and PVP molecule [29,31,41,42]. For both samples, a spin-orbit splitting of approximately 3.7 eV confirms reduction of Au 3+ to Au 0 valance state in the reaction medium [7,[29][30][31]. A similar effect has already been reported in the PVP-capped Au NP and Au-metallized polycarbonate [18,31].…”

“…It also helps in knowing the chemical state of Au NPs in the colloid. presence of PVP molecules reveals interfacial interaction between the Au NP and PVP molecule [29,31,41,42]. For both samples, a spin-orbit splitting of approximately 3.7 eV confirms reduction of Au 3+ to Au 0 valance state in the reaction medium [7,[29][30][31].…”

“…Interaction of PVP molecules with metal NPs has been studied by various researchers using UV-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, emission spectroscopy, zeta potential, and X-ray photoemission spectroscopy (XPS) [4][5][6][7]18,19,[25][26][27][28][29][30][31][32][33][34][35][36][37]. Seoudi et al [15] have observed a shift in the band position of C=O and C-N stretching frequencies in the vibrational spectrum of PVP in the presence of Au NPs and ascribed such band shifting to a donor-acceptor-type interaction between the carbonyl group of PVP molecules and Au NP.…”

Intense quenching of fluorescence intensity of poly(vinyl pyrrolidone) molecules in presence of gold nanoparticles

“…A chemical shift of 3.73 eV confirms reduction of Au 3? to Au 0 valance state in the reaction medium (Ram and Fecht 2011;Joseph et al 2003;Patnaik and Li 1998;Abyaneh et al 2007). A negative shift in binding energy of both 4f 7/2 and 4f 5/2 band in GNP with PVP molecules as compared to bulk Au atom reveals an interaction between GNP and PVP polymer molecules (Joseph et al 2003;Patnaik and Li 1998;Abyaneh et al 2007).…”

Impact of the Crosslinker’s Molecular Structure on the Aggregation of Gold Nanoparticles

“…create NP films as vapor-sensing platform [20,21]. Longer dithiol linkers can yield very stable aggregates, that can be moulded into arbitrary shapes as shown in a study by Klajn et al [22].…”