H.-C. Hansson

A new technique to measure trace elements in individual aerosol particles through scanning proton microprobe

Abstract In atmospheric aerosol research, one key issue is to determine the sources of the airborne particles. Scanning Nuclear Microprobe (SNM) is a new micro analytical technique that gives unique information on individual aerosol particles. In the SNM analyses a 1.0 μm size 2.4 MeV proton beam from the Oxford SNM was used. The trace elements with Z>11 were measured by the Particle Induced X-ray Emission (PIXE) method with detection limits in the 1 to 10 ppm range. Carbon, nitrogen and oxygen are measured simultaneously using Rutherford Back Scattering Spectrometry (RBS). Atmospheric aerosol particles were collected at the Brazilian Antarctic Station and at several biomass burning sites in the Amazon basin tropical rain forest in Brazil. In the Antarctic aerosols samples, the sea-salt aerosol particles were clearly predominating, with NaCl and CaSO4 as major compounds with several trace elements like Al, Si, P, K, Mn, Fe, Ni, Cu, Zn, Br, Sr, and Pb. Factor analysis of the elemental data showed the presence of 4 components: 1) Soil dust particles; 2) NaCl particles; 3) CaSO4 with Sr; 4) Br and Mg. The hierarchical cluster procedure gave results similar to the ones obtained through factor analysis. For the tropical rain forest biomass burning aerosol emissions, biogenic particles with high organic content dominate the particle population, while K, P, Ca, Mg, Zn, and Si are the dominant elements. Zinc at 10 to 200 ppm is present in biogenic particles rich in P and K. It was observed a better source resolution with SNM than with bulk PIXE with receptor modeling. The quantitative aspects and excellent detection limits make SNM analysis of individual aerosol particles a powerful analytical tool.

A new method for measurements of insoluble submicron particles in water

Abstract A new method was developed to determine the size distribution of insoluble particles in e.g., fog water in the particle size range 50 nm p nm. First the water was nebulized and than the droplets dried to form residual aerosol particles. Using a Tandem Differential Mobility Analyser (TDMA), soluble and insoluble particles were separated. The system was calibrated with monodisperse latex particles to determine the loss factor for insoluble particles.

Studies of GaInAs/InP quantum dots processed from aerosol deposited particles

We report a fabrication technology for the production of large quantities of GaInAs/InP quantum dot structures with typical lateral sizes in the range of 20-30 nm. This technique includes the use of sintered aerosol Ag particles as an etching mask in a plasma etching process and epitaxial overgrowth. Transmission electron microscopy shows that the sintered silver particles are almost spherical and monocrystalline. The etching process results in free standing columns with densities around 10/sup 9/ cm/sup -2/. Scanning electron microscopy indicated a narrow deviation in width as well as in height of the columns. Scanning tunneling spectroscopy revealed both electron depletion and a slight widening of the band gap in InP columns. Both as etch and overgrown GaInAs/InP columns were characterized by low-temperature cathodoluminescence. The overgrown dots showed a significant improvement in quantum efficiency as compared to the as etched columns.<<ETX>>

A new method to measure the size distribution of insoluble submicron particles in water

Abstract In the atmosphere, cloud and fog droplets usually contain insoluble material. The role of these insoluble particles is still unknown today, and is of interest to study. To determine the size distribution and number concentration of these particles in water, different techniques are available. The instrumentation, however, to measure nanometer-sized particles down to 50 nm diameter is not known. A new instrument, the Liquid Tandem Differential Mobility Analyser (LTDMA), was developed to measure size distributions of insoluble particles in water in the size range 50–300 nm in diameter. The new method is based on nebulising, e.g. cloud water and forming a residue aerosol consisting of both, insoluble particles with a soluble shell, and pure soluble particles. The insoluble, hydrophobic particles can be separated from soluble, hygroscopic residue particles with a Tandem Differential Mobility Analyser. The system is calibrated with monodisperse latex particles to determine the size-dependent transmission factor of insoluble particles of the Liquid Tandem Differential Mobility Analyser. A size distribution of insoluble particles in cloud water is presented as an application of this new measuring method. The cloud water sample was taken during the field campaign of the EUROTRAC sub project Ground-based Cloud Experiments (GCE) on the Kleiner Feldberg mountain, Germany, in November 1990.

Aerosol deposition and combined dry/wet etching techniques for fabrication of InP-based quantum dot structures

The authors present a novel technology for the fabrication of quantum dots (QDs) structures based on the deposition of ultrafine aerosol Ag particles onto the surface of Ga/sub 0.47/In/sub 0.53/As/InP quantum well structures grown by metal organic vapor phase epitaxy. The quantum well structures consisted of 3 quantum wells (QWs) with nominal thickness of 3, 8 and 18 monolayers with the thinnest QW being on top of the structure. A reference layer of Ga/sub 0.47/In/sub 0.53/As was grown below QWs for lattice matching control. The QWs were separated by 15 nm barriers of InP and the cladding layer was about 66 nm in thickness. Silver particles 40 nm in diameter were used as an etching mask. QW thickness dependence of quenching of QD luminescence was observed.<<ETX>>