This paper describes a novel chemical etching method to fabricate high quality near-field optical antennas-tapered metallic tips-from gold wire in a reproducible way for optically probing a specimen on the nanoscale. A new type of an electrochemical cell is introduced and different dc and ac etching regimes are studied in detail. The formation and dynamics of a meniscus around a gold wire immersed in an electrolyte when supplying a square wave voltage are considered. We show that in situ etching current kinetics allows one to improve a yield of tips with a well-defined geometry up to 95% by filtering these on the basis of a cutoff current and a power spectrum of etching current fluctuations. As a quantitative measure for estimating the yield we introduce a probability to find tips with curvature radii falling in the range of interest. Testing the tips for a plasmonic effect is implemented with tip-enhanced Raman spectroscopy and sub-wavelength imaging of a thin fullerene film.

Particulate matter (PM) emitted during laser additive manufacturing with stainless steel powder materials has been studied in detail. Three different additive manufacturing techniques were studied: selective laser melting, direct metal deposition and laser cladding. Gas flow and temperature fields accompanying the processes were numerically modeled for understanding particle growth and oxidation. Transmission and scanning electron microscopy were used for primary particle and PM characterization. The PM collected in the atmosphere during manufacturing consisted of complex aggregates/agglomerates with fractal-like geometries. The overwhelming number of particles formed in the three processes had equivalent projected area diameters within the 4–16 nm size range, with median sizes of 8.0, 9.4 and 11.2 nm. The primary particles were spherical in shape and consisted of oxides of the main steel alloying elements. Larger primary particles (> 30 nm) were not fully oxidized, but where characterized by a metallic core and an oxidic surface shell.

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