We describe a number of microfluidic components that have been formed by laer micromachining and incorporated in a picoliter droplet dispenser. The laser micromachined structures include an adhesive interface between macrofluidic and microfluidic regions, a particle filter, a fluid manifold, channels, and nozzles. Both excimer laser and C0<sub>2</sub> laser processes are used.
We show a correlation between the surface roughness of tantalum heaters in water with the temperature at which nucleation occurs at a set of fixed sites on the heater surface. The smoothest heater displayed the highest nucleation and vapor sheet formation temperatures. Experiments using degassed water indicate that some of the specific surface sites are due to air entrapped in small crevices in the tantalum. The high temperature (> 272 degree(s)C) for the nucleation indicate that the air entrapment sites are on the order of 1 - 4 nm in diameter.