Winter Term with the SEM!

Hi everybody! Chloe here. I’ve been spending my Winter Term at Oberlin doing various things, mainly working with the SEM down on the second floor of Carnegie! Amanda gave a brief introduction on my project during one of our lab meetings in the Rat, but here is a reminder: I’m spending the Winter Term getting to know the SEM and using it to develop a method for giving us quantitative elemental information for materials, such as finding out the bulk compositions of different samples of sediment. I am using samples sent over from the College of Wooster by Meagan Pollack, who did analyses of her own before sending them to me. 

The past two weeks have been a LOT of fun and I’ve learned tons of new things, ranging from how to work the SEM and the theory behind it, to learning how to run sediment samples through HARBIN and even filling the liquid nitrogen detectors in Amanda’s lab and in the SEM. The first week of Winter Term was spent getting to know the Scanning Electron Microscope by taking advantage of the copious information available through the “help” system installed in the Oxford INCA software. I also spent some time reading through a helpful paper that Zeb gave me, titled “Performing elemental microanalysis with high accuracy and high precision by scanning electron microscopy/silicon drift detector energy-dispersive X-ray spectrometry (SEM/SDD-EDS)” by Dale E. Newbury and Nicholas W. M. Ritchie. Zeb also loaned me one of his books, “Modern Analytical Geochemistry: An Introduction to Quantitative Chemical Analysis for Earth, Environmental and Materials Scientists,” which provided further useful information concerning elemental analysis through the use of spectrometry. I spent the rest of the first week getting used to the SEM through hands-on work in order to re-familiarize myself with the machine. I had not used the machine since a couple of weeks before first semester ended when I used it for the Mineral Drawer Project in Mineralogy.

On a side note, for those of you who remember using the SEM in Mineralogy, I am using the machine in “Analyzer” mode instead of “Point & ID” mode. The “Analyzer” mode is different because it can analyze a bigger area than the “Point & ID” mode. It works in a slightly different way, but is just as fun as the “Point and ID” mode!

            The past week was spent collecting data on the SEM using the samples sent over from Wooster by Meagan. I also learned how to prepare and mount these samples, which includes learning how to use the carbon coater machine in the SEM room (which coats the top of the sample in carbon) and further preparing the samples for use in the SEM by putting them on a metal holder and attaching small amounts of copper tape to the sample and the metal holder in order for it to be conductive. I also spent the past week conducting beam stability tests with the SEM, which included taking analyses of the copper tape that is attached to my sample in the SEM and doing quantitative calculations to see how stable the beam current (of electrons that hit the sample) is over a period of time. I’ve learned that it is best to let the machine “warm up” for an hour or two before performing more in-depth analyses on my samples.

            I also spent some time over the past week learning how to make thin sections (with varying degrees of success) with Adrian. This past weekend was spent going over my data and trying to replicate the analyses that Meagan made at Wooster using the same samples. Next week I will conduct more stability tests with the SEM (except by utilizing different timing for the tests, such as leaving the machine on for longer and then doing a quantitative calculation), and work on determining a protocol to use the samples from Wooster as standards for analyzing ground up sediment. Adrian and I have also spent some time going over what we will do for our research project next semester! I’m coming into it with beginner’s knowledge, so I’ve spent a lot of time reading up on papers explaining isotopes such as ¹³⁷Cs and ²¹⁰Pb and their effects on soil erosion and the interpretation of particle size effects on the adsorption of certain isotopes.

            I’ll just sign off here and make another post next week. I hope everybody’s Winter Term projects are going well and everybody in China is having a great time! J

-Chloe