Illustrating the formation of metal nanoparticles with a growth concept based on colloidal stability.

A large number of scientific contributions is dedicated to syntheses, characterization and applications of metal nanoparticles. In contrast, only few studies on their formation mechanisms have been reported. In general, concepts to describe particle growth processes are rare. Commonly used models are not able to explain the influences of reaction parameters on the growth and the final particle size. In this contribution it is shown how the growth of colloidal metal nanoparticles can be illustrated using an approach based on colloidal stability. In the first part, investigations of various syntheses of colloidal nanoparticles (including Rh, Pd, Pt, Cu, Ag and Au) show that growth due to aggregation and coalescence is the governing principle of nanoparticle formation if the monomer supply is faster than the actual growth. In the second part of this contribution, the influences of various parameters on the growth of Au nanoparticles are studied and it is demonstrated how the colloidal stability approach can illustrate the impact of synthesis parameters on the final particle size.

Size dependent catalysis with CTAB-stabilized gold nanoparticles.

CTAB-stabilized gold nanoparticles were synthesized by applying the seeding-growth approach in order to gain information about the size dependence of the catalytic reduction of p-nitrophenol to p-aminophenol with sodium borohydride. Five different colloidal solutions of stabilized gold nanoparticles have been characterized by TEM, AFM, UV-Vis, SAXS, and DLS for their particle size distributions. Gold nanoparticles (mean sizes: 3.5, 10, 13, 28, 56 nm diameter) were tested for their catalytic efficiency. Kinetic data were acquired by UV-Vis spectroscopy at different temperatures between 25 and 45 °C. By studying the p-nitrophenol to p-aminophenol reaction kinetics we determined the nanoparticle size which is needed to gain the fastest conversion under ambient conditions in the liquid phase. Unexpectedly, CTAB-stabilized gold nanoparticles with a diameter of 13 nm are most efficient.

X-ray-assisted formation of gold nanoparticles in soda lime silicate glass: suppressed Ostwald ripening.

The in situ formation of gold nanoparticles in soda lime silicate glass under constant x-ray irradiation is compared with the ex situ formation in preirradiated glasses. The ASAXS measurements confirm that pure Au particles are formed. The comparison shows that the number of particles nucleated under irradiation is about an order of magnitude higher than of those nucleated with preirradiation. The radius, R, remains slightly below 1 nm under in situ conditions and the Ostwald ripening stage is slowed down. Under ex situ conditions Ostwald ripening is clearly observed and R grows up to 3 nm.

Ultrasonic force microscopy on strained antimony nanoparticles.

Ultrasonic force microscopy (UFM) is used to resolve the elastic nanostructure of strained antimony (Sb) particles. These nanoparticles were formed by aggregation and spontaneous rapid crystallization of thermally deposited Sb onto the (0001) basal planes of highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS(2)). UFM reveals clear contrast within individual nanoparticles, which can be attributed to differences in the local stiffness. This interpretation is confirmed by transmission electron microscopy (TEM) images, in which bending contours prove the existence of strained regions within the nanocrystals.

Quantitative NMR spectroscopy for gas analysis for production of primary reference gas mixtures.

Due to its direct correlation to the number of spins within a sample quantitative NMR spectroscopy (qNMR) is a promising method with absolute comparison abilities in complex systems in technical, as well as metrological applications. Most of the samples studied with qNMR are in liquid state in diluted solutions, while gas-phase applications represent a rarely applied case. Commercially available NMR equipment was used for purity assessment of liquid and liquefied hydrocarbons serving as raw materials for production of primary reference gas standards. Additionally, gas-phase studies were performed within an online NMR flow probe, as well as in a high-pressure NMR setup to check feasibility as verification method for the composition of gas mixtures.

Self-assembly of gold nanoparticles on deep eutectic solvent (DES) surfaces.

Self-assembly of gold nanoparticles was obtained by sputter deposition on DES. SAXS and TEM investigations reveal the formation of spherical nanoparticles with a mean diameter of 5 ± 0.5 nm. For extended sputtering times, the number density of AuNPs increases linearly and a very pronounced 1st and 2nd shell ordering is observed.

Vibrational and electronic characterization of ethynyl derivatives grafted onto hydrogenated Si(111) surfaces.

Covalent grafting of ethynyl derivatives (-C triple bond C-H, -C triple bond C-CH3, -C triple bond C-aryl) onto H-terminated Si(111) surfaces was performed by a one-step anodic treatment in Grignard electrolytes. The electrochemical grafting of such ethynyl derivatives, which tends to form ultrathin polymeric layers, can be controlled by the current and charge flow passing through the Si electrode. The prepared ultrathin layers cover the Si surface and had a thickness up to 20 nm, as investigated by the scanning electron microscopy (SEM) technique. Exchanging Cl for Br in the ethynyl Grignard reagent leads to very thin layers, even under the same electrochemical conditions. However, for all ethynyl derivatives, high-resolution synchrotron X-ray photoelectron spectroscopy (SXPS) investigations reveal the incorporation of halogen atoms in the organic layers obtained. Moreover, it was observed that the larger the end group of the ethynyl derivative, the thinner the thickness of the ultrathin polymeric layers as measured by both SXPS and SEM techniques after low and high current flow respectively. For the first time, these new types of ultrathin organic layers on Si surfaces were investigated using infrared spectroscopic ellipsometry (IRSE). The different possible reaction pathways are discussed.