SEM-EDX Analysis of Aerosol Samples

One of the important environmental issues in upstate New York is the acid rain problem in the Adirondack Mountains, which is associated with atmospheric aerosols. As a part of a systematic study to understand the transport, transformation, and effects of airborne pollutants in the Adirondack Mountains, we are performing an analysis of atmospheric aerosols collected at Piseco Lake. In previous work, we used proton induced X-ray emission (PIXE) [1] spectrometry to measure the concentrations of elements in aerosol samples as a function of the size of the particulate matter. The results of the PIXE analysis indicate significant concentrations of sulfur in small particles that can travel great distances and may contribute to acid rain. Here we report on the investigation of the small-particle aerosol samples using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) to obtain elemental information on individual particles. Many of the particles contain large concentrations of sulfur and oxygen that may indicate the presence of sulfur oxides from industry and coal combustion that are known contributors to acid rain, but they are not always in the same ratio. There are also many particles that contain significant concentrations of elements commonly found in soil (Al, Si, K, and Ca)

Spin Seebeck effect at low temperatures in the nominally paramagnetic insulating state of vanadium dioxide

The low temperature monoclinic, insulating phase of vanadium dioxide is ordinarily considered nonmagnetic, with dimerized vanadium atoms forming spin singlets, though paramagnetic response is seen at low temperatures. We find a nonlocal spin Seebeck signal in VO2 films that appears below 30 K and which increases with decreasing temperature. The spin Seebeck response has a non-hysteretic dependence on in-plane external magnetic field. This paramagnetic spin Seebeck response is discussed in terms of prior findings on paramagnetic spin Seebeck effects and expected magnetic excitations of the monoclinic ground state.Comment: 11 pages, 3 figures, + 11 pages and 10 figures of supplemental materia

The challenges of measuring spin Seebeck noise

Just as electronic shot noise results from the granularity of charge and the statistical variation in the arrival times of carriers in driven conductors, there are predictions for fundamental noise in magnon currents due to angular momentum being carried by discrete excitations. The advent of the inverse spin Hall effect as a transduction mechanism to convert spin current into charge current raises the prospect of experimental investigations of such magnon shot noise. Spin Seebeck effect measurements have demonstrated the electrical detection of thermally driven magnon currents and have been suggested as an avenue for accessing spin current fluctuations. We report measurements of spin Seebeck structures made from yttrium iron garnet on gadolinium gallium garnet. While these measurements do show an increase in measured noise in the presence of a magnetic field at low temperatures, the dependence on field orientation suggests an alternative origin for this signal. We describe theoretical predictions for the expected magnitude of magnon shot noise, highlighting ambiguities that exist. Analysis in terms of the sample geometry dependence of the known inverse spin Hall transduction of spin currents into charge currents implies that magnon shot noise detection through this approach is strongly suppressed. Implications for future attempts to measure magnon shot noise are discussed.Comment: 20 pages, 3 figures, + 7 pages/6 figures of supplementary materia