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Measuring growth kinetics of nanoscale ice crystals using Spectroscopic ellipsometry and environmental scanning electron microscopy

Faculty Mentor: Nathan Magee

Student: Andrew Miller

We studied the optical properties of ice crystals using environmental scanning electron microscopy (ESEM).  The ESEM allowed us to image the mesoscopic surface of ice crystals, and rough surface topography (including linear strands, crevasses, islands, and steps) was discovered at an unprecedented level of magnification: 10,000x.  We used an ESEM because light microscopy – a competing way to study ice crystals surface structure and shape — has proved to be a limiting factor in studying the mesoscopic surface of ice crystals, for the light prevents any visible roughness to be seen.  Other scientists have seen surface architecture using an ESEM, but they either limited their observations to a certain face of the ice crystals, or confined their observations to a narrow range of morphologies, substrate selections, temperature s, and nucleation and growth rates.  We believe that these scientists misinterpreted their data due, in part, to the effects of the angle from which the ice is viewed, as well as the brightness and contrast setting on the ESEM.  A better understanding of the mesoscopic surface of ice crystals could lead to improved light scattering models of ice crystals – currently a chief problem in atmospheric science – and a more thorough account of thunderstorm electrification: how ice crystals collide and interact to become charged and create lightning, essentially.  Additionally, our results represent the beginning of a quantitative catalog for the prevalence, scale, shapes, and symmetry of these surface features.  This catalog is absolutely necessary for climate change science due to a long history of conflicting satellite observations, aircraft measurements, and modeling of cirrus and mixed-phase clouds.