Polar plot representation of time-resolved fluorescence.

Measuring changes in a molecule's fluorescence emission is a common technique to study complex biological systems such as cells and tissues. Although the steady-state fluorescence intensity is frequently used, measuring the average amount of time that a molecule spends in the excited state (the fluorescence lifetime) reveals more detailed information about its local environment. The lifetime is measured in the time domain by detecting directly the decay of fluorescence following excitation by short pulse of light. The lifetime can also be measured in the frequency domain by recording the phase and amplitude of oscillation in the emitted fluorescence of the sample in response to repetitively modulated excitation light. In either the time or frequency domain, the analysis of data to extract lifetimes can be computationally intensive. For example, a variety of iterative fitting algorithms already exist to determine lifetimes from samples that contain multiple fluorescing species. However, recently a method of analysis referred to as the polar plot (or phasor plot) is a graphical tool that projects the time-dependent features of the sample's fluorescence in either the time or frequency domain into the Cartesian plane to characterize the sample's lifetime. The coordinate transformations of the polar plot require only the raw data, and hence, there are no uncertainties from extensive corrections or time-consuming fitting in this analysis. In this chapter, the history and mathematical background of the polar plot will be presented along with examples that highlight how it can be used in both cuvette-based and imaging applications.

Nanoscale dynamic behavior of surface magnetic domains on a La0.7Sr0.3MnO3 thin film.

An oscillating magnetic tip can be used to induce the striped magnetic ripple pattern with alternating up-and-down striped magnetic domains on a ferromagnetic La0.7Sr0.3MnO3 (LSMO) thin film surface. Magnetic force microscopy (MFM) images show that the surface magnetic domains (SMDs) can be aligned in a well-ordered alternating up-and-down c(2 x 2) structure on the stripe magnetic domains, indicating that the oscillating magnetic tip turns the ferromagnetic LSMO surface into a canted antiferromagnetic state. The orientation of the SMDs is determined by their discrete phase distribution. A three-dimensional (3D) SMD orientation model is built to understand dynamic behavior of the SMDs.

Effective photoluminescence in a large-area array of Ta2O5 nanodots.

We describe here the synthesis of a large-area Ta2O5 nanodot array by utilizing the hot filament metal vapor deposition technique. The Ta2O5 nanodots arranged in a large-area array on a Si wafer had an average diameter of -8 nm. X-ray photoemission spectroscopy (XPS) revealed the stoichiometric Ta and O compositions of the Ta2O5 nanodots. Raman spectroscopy showed the Ta2O5 nanodots to be of orthorhombic (beta) crystal. Photoluminescence (PL) spectroscopy showed the green and red light emissions of the beta-Ta2O5 nanodots at room temperature.