Robert J. Gulotty

Quantitative Contrast Evaluation of an Industry‐Style Rhodium Nanocatalyst with Single Atom Sensitivity

Aberration‐corrected electron microscopy opens new ways for material characterization. In catalyst research it will enable the observation of single atom arrangements, such as the location of promoter atoms on catalyst particles. However, quantitative procedures must be developed to account for dynamic contrast changes resulting from beam‐sample interactions and incoherent instrument aberrations. We demonstrate that at low acceleration voltage (80 kV), for which knock‐on damage is suppressed, the residual intensity fluctuations can be attributed to the presence of phonons resulting in 3D low frequency atom displacements. For rhodium [110] oriented particles it was found that the catalysts are platelets with an aspect ratio of about 0.2 and a surface roughness of ±1 atom. Observation of single surface atoms requires minimization of phonon‐induced motion.

Nonlinear optical activity of bisphenol A polycarbonate and related copolymers

A series of structurally modified polycarbonates (PC) have been demonstrated to have second-order nonlinear optical (NLO) activity. The dipolar functionality and NLO activity in these polymers are properties of the polymer backbone. d33 values of 0.08-1.35 x 1O esu were determined by second-harmonic generation (SHG) measurements using a Maker Fringe rotation approach. In-situ measurements of the NLO activity as a function of temperature during the parallel plate poling process show that the onset of the NLO activity occurs primarily near the polymer glass transition temperature. A study of the temporal stability of the NLO activity shows persistent NLO activity for at least 640 days after poling. An effective j per polymer repeat unit is calculated from the data and compared to PPP semi-empirical calculations ofj for model molecules. Agreement is shown to be best for carbonate-containing models of the polymer backbone. The approximate agreement of theory and experiment suggests that the orientability of the NLO active segments in the polymer backbone is adequately described by poling theory.