Formation of Single Micro‐ and Nanowires with Extreme Aspect Ratios in Microfluidic Channels

Shown here is the site‐specific formation of single extraordinarily long metal–organic micro‐ and nanowires using a microfluidic device made of poly(dimethylsiloxane) (PDMS). This approach exploits two concepts, i) the diffusion of organic precursor molecules through PDMS and ii) the use of microfluidic channels as a growth template. To initiate wire formation, metal and organic precursor solutions are filled into different supply channels that are separated by PDMS. As the precursor diffuses through PDMS, and thereby infiltrates the adjacent channel, the growth of micro‐ and nanowires starts at the side walls of this adjacent channel. The formation yields single wires with sizes ranging from several hundreds of micrometers to millimeters at diameters of 0.5–2 µm. The principles of this formation pathway are demonstrated with the reaction of tetrathiafulvalene (TTF) and gold(III) ions that yields Au‐TTF wires. The influence of various reaction parameters including the choice of solvents and the chip fabrication protocol on the reaction are evaluated. Based on these findings, a further microfluidic device design with orthogonally arranged channels is developed, and the formation of single wires in a channel‐defined pattern is demonstrated. Moreover, the possibility of pulsed precursor supply allows for advanced control over the growth of the wires.