We report on the fabrication of molybdenum (Mo) nanopillar (NP) arrays with NP diameters down to 75 nm by means of deep-reactive ion etching at cryogenic temperatures. A variable-thickness Mo metal layer sputtered onto a Si₃N₄/Si substrate makes possible NPs with different lengths in a controllable manner. We demonstrate how our fabrication strategy leads to tunable cross-sections with different geometries, including hexagonal, cylindrical, square and triangular shapes, by using electron beam lithography on hydrogen silsesquioxane negative tone resist. To ensure well-defined facets and surfaces, we employ deep-reactive ion etching in a gas mixture of SF₆ and O₂ at cryogenic temperatures in an inductively coupled plasma reactive ion etching (ICP-RIE) system. These results represent an attractive route towards the realization of high-density Mo NP arrays for applications from nanoelectronics to quantum sensing and hydrogen evolution reaction catalysis.

Ultra-low-noise transition edge sensors (TES) with noise equivalent power lower than 2 × 10^{- 19} W/Hz^{1 / 2} have been fabricated by SRON, which meet the sensitivity requirements for the far-infrared SAFARI instrument on space infrared telescope for cosmology and astrophysics. Our TES detector is based on a titanium/gold (Ti/Au) thermistor on a silicon nitride (SiN) island. The island is thermally linked with SiN legs to a silicon support structure at the bath temperature. The SiN legs are very thin (250 nm), narrow (500 nm), and long (above 300 μ m); these dimensions are needed in leg-isolated bolometers to achieve the required level of sensitivity. In this paper, we describe the latest fabrication process for our TES bolometers with improved sensitivity.