Fabrication of freestanding Pt nanowires for use as thermal anemometry probes in turbulence measurements

Abstract

We report a robust fabrication method for patterning freestanding Pt nanowires for use as thermal anemometry probes for small-scale turbulence measurements. Using e-beam lithography, high aspect ratio Pt nanowires (~300 nm width, ~70 µm length, ~100 nm thickness) were patterned on the surface of oxidized silicon (Si) wafers. Combining wet etching processes with dry etching processes, these Pt nanowires were successfully released, rendering them freestanding between two silicon dioxide (SiO2) beams supported on Si cantilevers. Moreover, the unique design of the bridge holding the device allowed gentle release of the device without damaging the Pt nanowires. The total fabrication time was minimized by restricting the use of e-beam lithography to the patterning of the Pt nanowires, while standard photolithography was employed for other parts of the devices. We demonstrate that the fabricated sensors are suitable for turbulence measurements when operated in constant-current mode. A robust calibration between the output voltage and the fluid velocity was established over the velocity range from 0.5 to 5 m s−1 in a SF6 atmosphere at a pressure of 2 bar and a temperature of 21 °C. The sensing signal from the nanowires showed negligible drift over a period of several hours. Moreover, we confirmed that the nanowires can withstand high dynamic pressures by testing them in air at room temperature for velocities up to 55 m s−1.

Charged Particle-Induced Surface Reactions of Organometallic Complexes as a Guide to Precursor Design for Electron- and Ion-Induced Deposition of Nanostructures

“…Platinum nanostructures have applications in electronic devices, 46,47 sensors, 48,49 and catalysts. 50−53 FEBID and FIBID allow for controlled fabrication of metal nanostructures with subnanometer spatial resolution.…”

“…Platinum nanostructures have applications in electronic devices, , sensors, , and catalysts. − FEBID and FIBID allow for controlled fabrication of metal nanostructures with subnanometer spatial resolution . In general, FEBID studies have targeted means to fabricate highly pure metal deposits.…”

Batchelor Prize Lecture: Measurements in wall-bounded turbulence

“…Subminiature probe development The development of NSTAP probes has obviously had a positive impact on our ability to measure turbulence at high Reynolds number. Le-The et al (2021) have recently constructed a similar set of free-standing probes with = 70 µm, w ≈ 300 nm and t ≈ 100 nm, and Baradel et al (2021) have fabricated comparable probes with = 60 µm, w ≈ 200 nm and t ≈ 1.5 µm. We can therefore expect to see a growing use of such small probes in the coming years as they become more readily available.…”

“…Le-The et al. (2021) have recently constructed a similar set of free-standing probes with m, nm and nm, and Baradel et al. (2021) have fabricated comparable probes with m, nm and m.…”

Investigation of properties of superfluid He4 turbulence using a hot-wire signal

“…Hot-wires can be designed to have suitable temporal and spatial resolution, (see, e.g., Refs. [6][7][8][9]), but the interpretation of their signal in He II is a challenge [1,10]. The main stumbling block is the apparition of a spectral bump at high frequency.…”