Room-temperature, atmospheric-pressure microsputtering of dense, electrically conductive, sub-100 nm gold films.

In this study, we investigate the effects of deposition parameters (i.e. gas flow rates, bias voltages, and nozzle-to-substrate separation) on the microstructure of <100 nm thick gold deposits made with a room-temperature, atmospheric-pressure, ion-drag microsputterer. Without resorting to the use of vacuum or substrate heating, optimization of the printing process yields dense, continuous deposits (96.5% coverage) with low electrical resistivity (45 µΩ cm). Using statistical analysis, we developed a simple model that provides insight into the dynamics of such a printing method; based on this model, we identify electrostatic effects as the most important factor that influences the deposition process.

Additively manufactured MEMS multiplexed coaxial electrospray sources for high-throughput, uniform generation of core-shell microparticles.

This study reports the first MEMS multiplexed coaxial electrospray sources in the literature. Coaxial electrospraying is a microencapsulation technology based on electrohydrodynamic jetting of two immiscible liquids, which allows precise control with low size variation of the geometry of the core-shell particles it generates, which is of great importance in numerous biomedical and engineering applications, e.g., drug delivery and self-healing composites. By implementing monolithic planar arrays of miniaturized coaxial electrospray emitters that work uniformly in parallel, the throughput of the compound microdroplet source is greatly increased, making the microencapsulation technology compatible with low-cost commercial applications. Miniaturized core-shell particle generators with up to 25 coaxial electrospray emitters (25 emitters cm-2) were fabricated via stereolithography, which is an additive manufacturing process that can create complex microfluidic devices at a small fraction of the cost per device and fabrication time associated with silicon-based counterparts. The characterization of devices with the same emitter structure but different array sizes demonstrates uniform array operation. Moreover, the data demonstrate that the per-emitter current is approximately proportional to the square root of the flow rate of the driving liquid, and it is independent of the flow rate of the driven liquid, as predicted by the theory. The core/shell diameters and the size distribution of the generated compound microparticles can be modulated by controlling the flow rates fed to the emitters.

Fabrication of large arrays of high-aspect-ratio single-crystal silicon columns with isolated vertically aligned multi-walled carbon nanotube tips.

This paper describes the fabrication of large arrays (10(6) units in 1 cm(2)) of 100 µm tall, single-crystal silicon columns with submicron tip cross-sections. The columns are formed using thin film deposition and growth, reactive ion etching, and deep reactive ion etching. The columns can be either slightly tapered or have pencil-like morphology with nanoscaled tip diameter (41 nm). Conformal thin film coating was used to substantially and uniformly modify the porous structure and, thus, vary by orders of magnitude the fluid permeability of the structure. Gaps between the vertical pillars were varied between 9 µm and 50 nm. Isolated 45 nm diameter, 5 µm tall plasma enhanced chemical vapour deposited multi-walled carbon nanotubes (MWNTs) were grown on the top surface of the columns using a 7 nm thick evaporated Ni film as catalyst. Field emission characterization of the resulting structure was conducted and it is in agreement with scanning electron micrographs of the MWNTs.