In this work, we investigate the adsorption of carbon dioxide on rhodium (Rh) nanocrystals as well as its catalytic reaction with hydrogen, at the nanoscale, using field ion microscopy (FIM), video-field emission microscopy (FEM), and one-dimensional atom probe (1DAP). A FEM pattern-and-brightness analysis during the ongoing dissociation process at 700 K provides information on various facet reactivities and how these facets communicate with each other. Our results show CO 2 dissociative adsorption to be fastest on {012} facets. Initially dark {113} facets transiently appear bright, and we suggest this behavior is due to subsurface oxygen states occupied via spillover from {012} facets. Although local surface reconstructions of individual Rh facets may likewise be encountered, they fail to explain the sequence and time dependence of the observed FEM pattern-andbrightness changes. CO 2 /H 2 coadsorption studies suggest surface and subsurface oxygen can be reacted off as water. The observations are discussed within the context of the reverse water gas shift reaction. Comparative FEM studies are performed with other O-containing molecules. While the adsorption of N 2 O and O 2 leads to similar FEM pattern-and-brightness changes on an otherwise different time scale than those of CO 2 , nondissociative CO adsorption does not produce any noticeable such changes. We conclude that the mechanism of interfacet communication involving subsurface oxygen states is of general importance in reaction studies with oxygen-containing molecules undergoing surface dissociation.

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We employ a simple and reproducible methodology based on thermal gradient crystallization to access forms I and II of acetaminophen. This methodology provides insight into the role of heat flux in the control over polymorphism and phase transitions. We report the crystallization of different polymorphs of acetaminophen as a function of the thermal gradient parameters (magnitude of the gradient, sample velocity) in a thin film geometry. The thin-film samples were displaced at well-defined velocities (1 ≤ v ≤ 75 μm/s) to control both the direction and the rate of crystal growth. We carried out a detailed structural analysis combining polarized optical microscopy and X-ray diffraction (specular and grazingincidence) to characterize the crystalline forms isolated by the thermal gradient technique. The resulting polymorphic forms have been found to exhibit high phase purity and remarkable stability over time. Figure 1. (a) Chemical structure of acetaminophen; (b) schematic representation of the thermal gradient setup. Communication pubs.acs.org/crystal

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