Size-Selective 2D Ordering of Gold Nanoparticles Using Surface Topography of Self-Assembled Diamide Template

Size-selective organization of ∼2 nm dodecanethiol stabilized gold nanoparticles (AuNPs) into periodic 1D arrays by using the surface topographical features of a soft template is described. The template consists of micrometer length nanotapes organized into nanosheets with periodic valleys running along their length and is generated by the hierarchical self-assembly of a diamide molecule (BHPB) in cyclohexane. The AuNP ordering achieved simply by mixing the preformed template with the readily available ∼2 nm dodecanethiol stabilized AuNPs is comparable to those obtained using programmable DNA and functional block copolymers. The observed periodicity of the AuNP arrays provided valuable structural clues about the organization of nanotapes into nanosheets. Self-assembling BHPB molecules in the presence of AuNPs by heating and cooling the two components led to a comparatively disordered organization because the template structure was changed under these conditions. Moreover, the template could not order larger AuNPs (∼5 nm) into a similar 1D array, owing to the steric restriction imposed by the dimension of the valleys on the template. Interestingly, this geometric constraint led to AuNP size sorting when a polydisperse sample (2.5 ± 0.9 nm) was used for organization, with AuNPs attached to the template edges being larger (≥2.2 ± 0.9 nm) than those associated to the inner valleys (1.6 ± 0.8 nm). This is a unique example of size-sorting induced by the surface topographical features of a soft template

Controlling the Growth of Silver Nanoparticles on Thin Films of an n‑Type Molecular Semiconductor

Nucleation and growth of silver nanoparticles were studied on the surface of an n-type organic semiconductor (<i>N</i>,<i>N</i>′-bis­(<i>n</i>-octyl)­dicyanoperylene-3,4:9,10-bis­(dicarboximide) (N1400)) as a function of the deposition rate τ and the substrate temperature <i>T</i>_s. Electron tomography was used to probe the bulk diffusion of Ag in the N1400 layers. No Ag nanoparticles (NPs) are formed in the bulk of N1400 even for high substrate temperatures, <i>T</i>_s = 125 °C, indicating that Ag diffusion in the organic semiconductor is marginal. The NP distribution on the surface of N1400 is essentially determined by the surface roughness of the N1400 films. A transition in the nucleation mode of Ag NPs on N1400 is evidenced as a function of <i>T</i>_s: for <i>T</i>_s ≤ 50 °C, Ag NPs form random patterns, whereas, for <i>T</i>_s ≥ 75 °C, linear arrays of aligned NPs are observed. Such arrays result from step edge decoration of the N1400 terraces. The surface density of Ag NPs is thermally activated, but the activation energy depends on the structure of the N1400 films: the smaller the crystal size of the N1400 grains, the larger the activation energy

Effect of the Alkyl Chain Length of Secondary Amines on the Phase Transfer of Gold Nanoparticles from Water to Toluene

In the present paper we describe a phase transfer of aqueous synthesized gold nanoparticles (AuNPs) from water to toluene using secondary amines: dioctylamine, didodecylamine, and dioctadecylamine. The effect of the hydrocarbon chain length and amount of amines on the transfer efficiency were investigated in the case of nanoparticles (NPs) with three different sizes: 5, 9, and 13 nm. Aqueous colloids were precisely characterized before the transfer process using UV–vis spectroscopy, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Nanoparticles were next transferred to toluene and characterized using UV–vis and DLS techniques. It was found that dioctadecylamine provides the most effective transfer of nanoparticles. No time-dependent changes in the NP size were observed after 12 days, showing that the dioctadecylamine-stabilized nanoparticles dispersed in toluene were stable. This indicates that long hydrocarbon chains of dioctadecylamine exhibit sufficiently hydrophobic properties of nanoparticles and consequently their good dispersibility in nonpolar solvent