We report the production of smooth and well-ordered C(100) surfaces by exposure to a pure hydrogen plasma. A two domain 2×1 surface reconstruction is observed by low energy electron diffraction with half-order spots visible using incident electrons with energies as low as 13 eV. High-resolution electron energy loss spectroscopy reveals a large enhancement in specular reflectivity of low energy electrons following plasma treatment. The hydrogenated surface is stable in air and free of adsorbed hydrocarbons upon insertion into ultrahigh vacuum.
Multiple internal reflection infrared spectroscopy (MIRIRS) and temperature-programmed desorption (TPD) were used to investigate the interaction of oxygen with a diamond (110)-oriented surface. Exposure of the hydrogen-free diamond surface at 90 K to room-temperature O 2 or thermally excited oxygen, O 2 * (produced with a heated iridium filament) resulted in a sharp infrared absorption at 657 cm -1 , which disappeared on heating to 300 K. The 657 cm -1 absorption may indicate a surface peroxide. When the hydrogen-free diamond surface was dosed with O 2 at room temperature, no oxygen adsorption was observed by Auger electron spectroscopy (AES) or TPD. In contrast, dosing the surface with O 2 * at 300 K led to oxygen chemisorption. The room-temperature diamond surface was saturated with oxygen after exposures of >2400 L O 2 *. When the oxidized surface was heated, only CO 2 and CO desorption were observed, with peak maxima at 780 and 870 K, respectively. The peak desorption temperatures for CO 2 and CO did not vary with O coverage, implying first-order desorption kinetics. MIRIR spectra of the oxygen-saturated (110)-oriented surface showed weak absorption modes at 790 and 980 cm -1 . The exposure of the surface at 900 K to O 2 * led to (1) an increase in the coverage of oxygen species stable at high-temperature, (2) narrower, more intense, MIRIRS absorption modes ( 16 O, 770, 934, and 980 cm -1 ; 18 O, 747, 895, and 936 cm -1 ) and (3) a sharp, intense CO desorption peak at 1025 K. These observations imply that the low-temperature adsorption sites were etched away, thus favoring the additional adsorption of oxygen into the adsorption sites that are stable at high temperature. † Part of the special issue "John T. Yates, Jr. Festschrift".
The advent of new educational technologies has stimulated interest in using online videos to deliver content in university courses. We examined student engagement with 78 online videos that we created and were incorporated into a one-semester flipped introductory mechanics course at the Georgia Institute of Technology. We found that students were more engaged with videos that supported laboratory activities than with videos that presented lecture content. In particular, the percentage of students accessing laboratory videos was consistently greater than 80% throughout the semester. On the other hand, the percentage of students accessing lecture videos dropped to less than 40% by the end of the term. Moreover, the fraction of students accessing the entirety of a video decreases when videos become longer in length, and this trend is more prominent for the lecture videos than the laboratory videos. The results suggest that students may access videos based on perceived value: students appear to consider the laboratory videos as essential for successfully completing the laboratories while they appear to consider the lecture videos as something more akin to supplemental material. In this study, we also found that there was little correlation between student engagement with the videos and their incoming background. There was also little correlation found between student engagement with the videos and their performance in the course. An examination of the in-video content suggests that students engaged more with concrete information that is explicitly required for assignment completion (e.g., actions required to complete laboratory work, or formulas or mathematical expressions needed to solve particular problems) and less with content that is considered more conceptual in nature. It was also found that students' in-video accesses usually increased toward the embedded interaction points. However, students did not necessarily access the follow-up discussion of these interaction points. The results of the study suggest ways in which instructors may revise courses to better support student learning. For example, external intervention that helps students see the value of accessing videos may be required in order for this resource to be put to more effective use. In addition, students may benefit more from a clicker question that reiterates important concepts within the question itself, rather than a clicker question that leaves some important concepts to be addressed only in the discussion afterwards.
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