Book reviews

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Book reviews

     

Reactions of formaldehyde and methanol on clean,carburized and oxidized Mo(100) surfaces

The reactions of formaldehyde and methanol have been studied on clean, carburized, and oxidized Mo(100) surfaces using temperature programmed reaction spectroscopy (TPRS). The thermal cracking of ethylene at 550 K and the adsorption of molecular oxygen at 1050 K were used to carburize and oxidize, respectively, the clean surface to saturation. Both the carbide and oxide surfaces showed (1×1) LEED features. Methanol decomposed to give hydrogen atoms and methoxy intermediates upon adsorption on the clean Mo(100) surface at 200 K. The methoxy intermediate was stable up to 340 K. Adsorbed carbon and oxygen suppressed the dissociation of the hydroxyl hydrogen from the alcohol and yielded a significantly different activity and selectivity compared to the very reactive clean surface. The binding energies for both formaldehyde and methanol on the three surfaces were similar, demonstrating the weak sensitivity of donor-acceptor bonds to surface modifiers. The results in this study were very similar to those previously observed for W(100) though different adlayer structures were present. This similarity suggested that the modification in surface reactivity was primarily a compositional effect.     

Hydrodynamic flows in electrowetting

Hydrodynamic flows are generated inside a droplet in electrowetting when an ac voltage is applied. To discover the characteristics and origin of the flows, we investigated the flow pattern for a sessile droplet for various needle-electrode positions, electrolyte concentrations, and applied electrical frequencies. Two distinct types of flows were observed under current experimental conditions. In the typical experimental condition, a quite fast flow appears in the low-frequency range of about 10 Hz to 15 kHz. A different type of flow is observed in the high-frequency range of about 35 to 256 kHz, but this frequency range depends significantly on the electrolyte concentration. Most typically, the flow directions are different for the two flows. A shape oscillation of a droplet was observed in the low-frequency range by a high-speed camera. The flow in the low-frequency range is insensitive to the conductivity of the solution and may be caused by the interfacial oscillation of the droplet. The flow at high frequency is very sensitive to the conductivity of the solution and electrode position, so the high-frequency flow is believed to be caused by some electrohydrodynamic effect.