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Presenting new results with Spark Ablation in Aerosol Technology

At the European Aerosol Conference 2019 in Gothenburg Sweden, Andreas Schmidt-Ott and Tobias Pfeiffer will present new results on:

  • Producing pure Fe2O3 superparamagnetic powder
  • Transfer of sub 20nm particles from gas to liquid
  • Contacting in electronics with low temparature sintering nanoparticles

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Poster: Transfer of Nanoparticles Smaller than 20 nm from Gas to Liquid Suspension

Poster Session I

Mon 2613:00 - 14:30Location: Expo HallPresented by: Tobias PfeifferTransfer of Nanoparticles Smaller than 20 nm from Gas to Liquid Suspension 


Poster: Aerosol Method of Producing a Pure γ-Fe2O3 Superparamagnetic Powder

Mon 2613:00 - 14:30Location: Expo HallPresented by: Andreas Schmidt-Ott

Aerosol method of producing a pure γ-Fe2O3 superparamagnetic powder

Aerosol Method of Producing a Pure y-Fe2O3 Superparamagnetic Powder

Andreas Schmidt-Ott [Netherlands]1, Justin van Benten [Netherlands]1, Anton J.E Lefering [Netherlands]1

Delft University of Technology1


Superparamagnetic nanoparticles are attracting a lot of attention, partly because of various applications in the biomedical field such as targeted drug delivery in tumor therapy, magnetic resonance imaging, and magnetic hyperthermia.

         We describe a scalable method of producing superparamagnetic powders that does not require any precursors and produces no chemical waste, in contrast to methods described in literature. It is based on spark ablation of Fe electrodes in argon at 1 atmosphere, which leads to spherical primary Fe particles. These coagulate to form agglomerates and are subsequently oxidized by adding a low percentage of oxygen. The particles were collected for characterization by XRD, XPS, TEM, SMPS, MPMS, and Mössbauer spectroscopy.

         The agglomerates had a geometric mean mobility diameter of ca. 55 nm and consisted of 7 nm primary particles. As shown by recording the magnetization curve, they are superparamagnetic at room temperature, which is confirmed by Mösbauer spectoscopy. The saturation magnetization is about 22 Am2/and the blocking temperature is 65 K. XRD. XPS revealed a pure γ-Fe2O3 (maghemite) phase.

         It is not self-evident that the powder formed from these agglomerates is superparamagnetic, because the 7 nm units have interaction with each other. We believe neck formation in the oxidation process makes them rigid aggregates, which increases porosity in the powder and thus limits the magnetic interaction. This way, superparamagnetism is retained and coating is not necessary.

Presentation: Contacting in Electronics by Low Temperature Sintering of Aerosol-produced Nanoparticles

Tue 2711:10Location: F3Synthesis and structuring of functional nanoparticles Presentor: Andreas Schmidt-OttContacting in Electronics by Low Temperature Sintering of Aerosol-produced Nanoparticles

Chair and presentor from VSPARTICLE: Andreas Schmidt-Ott

Joost van Ginkel [Netherlands]1, Max Koole [Netherlands]2, Henk W. van Zeijl [Netherlands]3, Boyao Zhang [Netherlands]3, Guoqi Zhang [Netherlands]3, Andreas Schmidt-Ott [Netherlands]1

Delft University of Technology1, VSParticle B.V.2, Faculty of Electrical Engineering3


The need for replacement of lead-based solder in microelectronics has triggered research on metallic nanoparticles as die-attach material. The advantage of nanoparticles is their low melting point and their even lower sintering temperature.  Pastes containing silver or copper nanoparticles have already been developed for such purposes, but spark ablation could circumvent  a chemical pathway, avoid contaminants and enable direct focussed deposition of 5 nm nanoparticles from the gas phase, drastically lowering the welding temperature with respect to existing pastes, which contain much larger particles.

To prove this concept, ca. 5 nm gold nanoparticles were generated by spark ablation and deposited on Au-coated glass using inertial impaction. Two of such nano-gold layers were compressed to be fused together under rising temperature. The deposits were studied by SEM and four-point-probe resistivity measurements.

Through sintering, the black nano-gold changed into the characteristic golden colour, indicating that the nanostructures disappeared and formed an electric contact. To create such a connection, a deposit of about 100 µg on ca. 1 mm2 was sufficient. A sintering temperature of 200 °C was required. The contact area still retained some porosity and the resistivity was roughly 10 times higher than the resistivity of bulk gold.

            The proof of concept was successful, and further work will concentrate on optimizing the aerosol deposition process defining initial porosity, layer thickness and uniformity. In addition, contact pressure, time and temperature have to be optimized. Replacing gold by copper is the ultimate goal for reasons of cost and compatibility with present electronics materials.

Session: Filtration and Process Analysis - Transfer of Nanoparticles Smaller than 20 nm from Gas to Liquid Suspension

Wed 2810:30 - 12:40Location: F3Filtration and process analysisChairs: Andreas Schmidt-Ott and Andreas GüntnerTransfer of Nanoparticles Smaller than 20 nm from Gas to Liquid Suspension

Chair and presentor from VSPARTICLE: Andreas Schmidt-Ott

Transfer of Nanoparticles Smaller than 20 nm from Gas to Liquid Suspension

Lex Schilperoord [Netherlands]1, Roeland Dijkema [Netherlands]2, Tobias V. Pfeiffer [Netherlands]2, Sana Fateh [Netherlands]3, Andreas Schmidt-Ott [Netherlands]1

Delft University of Technology1, VSParticle B.V.2, Synano Cooling B.V3


Aerosol nanoparticle generation methods may be more suitable for specific applications than liquid phase production even for applications that require liquid suspension. In particular, spark ablation (SA), is an extremely flexible method of producing nanoparticles with properties that can often not be produced by any other technique. Especially in the important field of biomedical research, particles must be suspended in a liquid. Bubbling of aerosols through the liquid is a known method, and theories for the transfer efficiency have been developed. However, a reliable method of measuring the transfer efficiency has not yet been reported for particles smaller than 20 nm, because the bursting bubbles produce nanoparticles from contaminants that all liquids contain and from particles suspended.

An aerosol of spherical gold particles was produced by SA with a lognormal size distribution (relative standard deviation about 1.35), and the generator settings were chosen such that the geometric mean output size was 17 nm. After bubbling this aerosol through a VSParticle bubbler, the reddish colour of gold particles of this size became clearly visible and the respective plasma absorption peak was determined and used as a relative measure of the suspended quantity.

We obtain the trapping efficiency of our bubbler as a function of the liquid volume and conclude that for all particles smaller than 20 nm the collection efficiency is higher than 95% when filled with 50 mL of water. The result can be generalized to be applicable to any bubbler.

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