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Controlling water droplet motion on a surface is important for facilitating or improving the efficiency of many processes. Irrespective of the external force inducing the motion, surface wettability plays a vital role in this process. In this work, we study the effect of changing the length scale of chemical heterogeneities on wetting and droplet dynamics during the impact and condensation on surfaces with alternating, equal sized hydrophilic and hydrophobic stripes. We show that as the width of the stripes decreases to nanoscale, the surface shows near isotropic wettability. Specifically, we demonstrate that the difference between the advancing contact angle, sliding angle, and contact angle hysteresis measured parallel and perpendicular to the stripes is negligible for the nano-striped surface. Moreover, we show that the droplet dynamics during the impact and condensation on the nano-striped surfaces are similar to those observed on a chemically homogeneous surface with equivalent wettability.

A dry single-step process for enhancing the surface area of a silicon microcantilever is described. In this process, a flat microcantilever is irradiated with ∼100-femto-second-long laser pulses. The silicon surface melts and rapidly cools, resulting in the formation of nanoscale pillars. The shape and size of these nanostructures can be tuned by changing the energy of the pulses. Resonance measurements on surface-enhanced microcantilevers show that the irradiation process reduces the stiffness and the resonance frequency of the cantilevers. Fluidic dissipation measurements provide an estimate for the surface area increase. Both the enhanced surfaces and the fluidic characteristics of these microcantilevers may be useful in bio-chemical sensing applications.

An inert, precursor free, argon jet is used to control the growth rate of electron beam induced deposition. Adjustment of the jet kinetic energy/inlet temperature can selectively increase surface diffusion to greatly enhance the deposition rate or deplete the surface precursor due to impact-stimulated desorption to minimize the deposition or completely clean the surface. Physical mechanisms for this process are described. While the electron beam is also observed to generate plasma upon interaction with an argon jet, our results indicate that plasma does not substantially contribute to the enhanced deposition rate.

Superhydrophobic surfaces (SHSs) show promise as promoters of dropwise condensation. Droplets with diameters below ∼10 μm account for the majority of the heat transferred during dropwise condensation but their growth dynamics on SHS have not been systematically studied. Due to the complex topography of the surface environmental scanning electron microscopy is the preferred method for observing the growth dynamics of droplets in this size regime. By studying electron beam heating effects on condensed water droplets we establish a magnification limit below which the heating effects are negligible and use this insight to study the mechanism of individual drop growth.

Amorphous carbon deposited via electron beam induced deposition (EBID) is frequently used to make a low-temperature Ohmic contact with low electrical resistance and improved mechanical characteristics of the multiwall nanotube (MWNT) substrate or MWNT-MWNT interface. However, influence of the MWNT on the EBID process has not been quantified. In this work, we experimentally and theoretically investigate the growth dynamics of EBID of residual hydrocarbons in presence of a MWNT. We demonstrate that the properties of MWNT do not impact amorphous carbon deposition process.