The synthesis and characterization of 15, 25, 50, and 70 nm thin iron films having chemical impurities below the detection limit of various analytical techniques is reported. As established herein, the films are chemically pure and formed by electron beam deposition from inexpensive and readily available iron sources of 3N5 purity. Chemical purity of the thin films was achieved using mean deposition rates of 0.3 nm/s or higher, at which point the melting point of iron is reached at the iron source surface and a shutter is opened, from which point on the rate of transfer of impurities present in the source to the target is low enough that they are not observed in the film as confirmed via X-ray photoelectron spectroscopy (XPS), reported here for energies between 0 and 1200 eV. Nanoindentation measurements indicate the iron films to be 14 times harder than bulk iron. The iron films are shown by XPS to be coated with a 3 nm thin overlayer of Fe 3+ , which is possibly present in the form of Fe 3 O 4 , even though other forms of iron oxide are likely to be present as well, as indicated by Raman and XPS spectroscopy. Grazing incidence angle X-ray diffraction experiments indicate the presence of crystalline Fe 0 with low index faces exposed but no crystallinity of the iron oxide overlayer. Atomic force microscopy of the iron film surfaces indicates narrowing and shifts to lower heights in the height distribution of nanoscale features formed during the film deposition process as the film thickness decreases. Second harmonic generation is then used to determine that the interfacial charge density of the thinnest iron film is −0.007(3) C/m 2 at pH 7.
The classroom exercise outlined here is a self-directed assignment that connects students to the environmental contamination problem surrounding the DePue Superfund site. By connecting chemistry knowledge gained in the classroom with a real-world problem, students are encouraged to personally connect with the problem while simultaneously developing skills in data management and interpretation. Designed for first-year undergraduate, general chemistry students, each of the four primary exercises builds upon the skills developed in those before it. This approach makes it easy to tailor this assignment to the needs of individual classrooms. This assignment was given as the first laboratory course assignment to a pilot group of 178 general chemistry undergraduate students at Northwestern University. Students enrolled in this course had already completed the first of two accelerated general chemistry courses. Over 75% of students scored in the 85% to 100% grade range, illustrating that the majority of students who completed this assignment demonstrated a high level of comprehension.
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