Quorum Technologies, market and technology leaders in electron microscopy coating and cryogenic preparation products, report on the use of their PP3010T cryo SEM preparation system which is being used to understand the formation of ice crystals in high altitude clouds. 

Dr Nate Magee is an associate Professor of Physics at The College of New Jersey (TCNJ) where he leads a team working to advance the understanding of the physical role of ice crystals in processes with high altitude clouds. Cirrus clouds are primarily composed of ice crystals that interact with solar radiation and IR radiation from the ground, and they play a significant, but still poorly understood role in Earth's climate. The precise shapes and textures of these cirrus ice crystals largely determine how solar radiation interacts with the clouds (i.e. reflection & scattering angles) but the microscale structure is still fairly uncertain. Dr Magee is working with the Quorum cryo preparation system to make high-resolution images, 3D reconstructions and statistical measurements of ice crystals that are grown in the lab under cirrus conditions as well as ice crystals that are collected and recovered directly

A cryo preparation system is vital to the success of these studies. Describing the work, Dr Magee says, “Keeping ice crystals very cold (sub -150 °C) means that their vapour pressure will be sufficiently low that their shape and surface structure can be "locked" in place as we image and analyse the ice particles. Working at Peltier cooling stage temps (maybe to -50 °C) would not make this possible. The Quorum PP3010T transfer and interlock setup on our Hitachi SEM (with a few custom modifications on our part) has made it possible to transfer crystals from our lab systems directly into the SEM for imaging without exposing them to warmth or excess water vapour.” 

So why did Dr Magee select the Quorum cryo-preparation package? “I have used Peltier cooling stages with FEI SEMs, which actually do have a few advantages for some types of in-situ ice growth experiments. However, as I have said, we required sub -150 °C temperatures for this study so, after considering what was available, we chose to work with Quorum. Their full cryo temperature range and interlock prep chamber works very well for transfer experiments. We are still working to develop its functionality for in-situ dynamic experiments on growing ice.” 

This work is being presented in July at the International Conference on Clouds and Precipitation in Manchester.

The Quorum PP3010T is a highly automated, easy to use, column-mounted, gas-cooled cryo preparation system suitable for most makes and models of SEM, FE-SEM and FIB/SEM. Highly efficient cooling allows temperatures of down to -190 °C to be routinely achieved. The PP3010T includes facilities for rapid freezing and handling pre-frozen samples, cold fracturing, controlled sublimation and high resolution sputter coating. The typical process time for samples is between five and ten minutes. 

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