We have studied the alignment of colloidal gold nanorods, deposited from solution onto well-defined substrates in the presence of an AC electric field generated by micrometer spaced electrodes. The field strengths employed in our experiments are sufficiently large to overcome Brownian motion and induce accumulation and alignment of the nanorods in the region near the electrodes with their long axis parallel to the field. However, despite the large fields, we find that the degree of alignment is considerably smaller than what was previously reported for field-induced nanorod alignment in suspension. We show that hydrodynamic interactions and capillary effects during drying, as well as friction of nanorods on the substrate surface, to not play a major role. The limited alignment of nanorods is ascribed to the different experimental configuration and the correspondingly larger density of nanorods. The mutual interactions of nanorods give rise to a disturbance of the local electric field and therewith their orientation. For sufficiently large field strengths, these interactions lead to the formation of nanorod chains that ultimately bridge the electrode gap. Furthermore, for small electrode spacing, the nanorods accumulate on the electrode surface, and the screening of their mutual interactions results into considerably improved alignment.

Aeromonas strains (187) from human diarrhoeal stools and from drinking water (263) in The Netherlands were typed by three different methods. Biotyping alone was found to be of little value for epidemiological studies because 84% of all strains belonged to only 10 biotypes. Common biotypes could be further differentiated by serotyping. Gas-liquid chromatography of cell wall fatty acid methyl esters (FAME) was useful for species identification as well as for typing: 86% of all strains could be identified to the species level, and within this group 92% of all identifications corresponded with the biotype. Cluster analysis and principal component analysis of FAME profiles could be used for comparison of strains from different sources and gave the same general conclusions as bio- and serotyping. There was little overall similarity between Aeromonas strains from human (diarrhoeal) faeces and from drinking water, differences being most pronounced for Aeromonas caviae and least for A. sobria.

The combination of angle-resolved X-ray photoelectron spectroscopy (ARXPS) and a modified Levenberg-Marquardt (LM) fit procedure has been used to study a native oxide layer on a clean Si(100) substrate. Numerical calculations show that with an aperture of 3 o or 9 o of the electron analyser, the photoelectron takeoff angle should not exceed 80 o or 70 o, respectively, as compared to normal takeoff angles. At larger photoelectron takeoff angles, the effect of the aperture on the photoelectron energy distribution may not be neglected. We show how absolute ARXPS measurements in which the same XPS feature is considered at several electron takeoff angles are an alternative for relative ARXPS film thickness measurements, avoiding large errors in the quantitative results. Models for the composition and thickness of the oxide layer have been developed. Also, the errors in the parameters of these models have been calculated. It can be concluded that the native oxide layer on silicon is 27 + 1 (:t: 5%) ,~ thick and that the ratio of the silicon atom concentration in the substrate to that in the native oxide layer is 3.7 :t: 0.3 (:t:8%), values that agree well with the literature. This report shows that the combination of ARXPS and a LM fit procedure is well suited to study ultra-thin layers and gives reliable results.

We demonstrate a simple and versatile way to achieve high yield synthesis of shape- and size-controlled multi-branched gold nanoparticles (MBNPs). Control over the shape of the MBNPs was achieved by varying the ratio of gold to the mild reducing agent ascorbic acid, using a seed-mediated growth approach. Higher ascorbate concentrations resulted in the smoothing of branches, leading to the yield of relatively more isotropic particles. Furthermore, we found that using much higher silver concentrations in the growth solution resulted in the formation of rod-shaped micro-features together with MBNPs; we postulate them to be cetyltrimethyl ammonium silver bromide crystals. The as-prepared MBNPs show interesting tunable optical properties that are strongly influenced by the particle shape. The results are discussed in terms of plasmon coupling between the core and branches of the MBNPs.

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