Bioanalytical imaging techniques have been employed to investigate cellular composition at the single-cell and subcellular regimes. Four imaging modes have been performed sequentially in situ to demonstrate the utility of a more integrated approach to imaging cells. The combination of bright-field, scanning ion, and fluorescence microscopy complements TOF-SIMS imaging of native biomolecules. Bright-field microscopy provides a blurred visualization of cells in frozen-hydrated samples, while scanning ion imaging provides a morphological view of freeze-fractured cells after TOF-SIMS analysis is completed. With the use of selective fluorescent labels, fluorescence microscopy allows single mammalian cells to be located in the complex ice matrix of freeze-fractured samples, a task that has not been routine with either bright-field or TOF-SIMS. A fluorescent label, DiI (m/z 834), that does not interfere with the mass spectra of membrane phosphatidylcholine, has been chosen for fluorescence and TOF-SIMS imaging of membrane phospholipids. In this paper, in situ fluorescence microscopy allows the distinction of single cells from ice and other sample debris, previously not possible with bright-field or scanning ion imaging. Once cells are located, TOF-SIMS imaging reveals the localization of membrane lipids, even in the membrane of a single 15-microm rat pheochromocytoma cell. The utility of mapping lipids in the membranes of single cells using this integrated approach will provide more understanding of the functional role of specific lipids in functions of cellular membranes.

We observe terahertz emission by optical rectification of an intense 1.5-eV, 50-fs pulse in single-crystal iron thin films grown by molecular beam epitaxy. The azimuthal dependence of the emission indicates the presence of a magnetic nonlinearity and a nonmagnetic surface nonlinearity.

We have conducted an experimental investigation into molecular desorption stimulated by 8 keV Ar + ions. The investigated systems are comprised of aromatic molecules (benzene and phenol) adsorbed to an Ag(111) surface. Resonance-enhanced laser ionization coupled with time-of-flight mass spectrometry provide the ability to obtain quantum state resolved kinetic energy distributions of the desorbed molecules. Our results indicate that the desorption mechanisms for the molecules are dictated by the molecular coverage and determine if the molecules are desorbed in an internally excited state. We use specific mechanisms observed in molecular dynamics simulations reported in the literature to describe our experimental observations. In the low coverage regime, ballistic collisions between dislocated silver substrate atoms and the adsorbed molecules lead to the emission of energetic molecules. A collision between a single substrate atom and an adsorbed molecule leads to the emission of translationally and internally hotter molecules. A collision between an adsorbed molecule and several substrate atoms with similar momentum leads to the emission of slower, internally cooler molecules. In multilayer systems, a gentler mechanism, such as a molecular collision cascade or localized heating, generates the emission of translationally slow molecules. Temperature-programmed desorption studies allow characterization of the benzene film structure and show how the emission characteristics of the desorbed molecules change concomitantly with changes in the film structure. In general, we provide a framework describing the collision events responsible for stimulated molecular desorption.

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