Single- or multi-walled carbon nanotube pellicles investigated for NewAthena

Carbon Nanotube (CNT) films are very promising as substrates for thermal and optical filters for X-ray or EUV detectors for space applications. Their spectroscopic and mechanical properties make them very attractive to the scientific community. The current baseline for the thermal and optical blocking filters of the detectors on board the ESA space mission NewAthena foresees the use of a polyimide (PI) membrane coated with an ultrathin aluminum film (30-70 nm). In the last years, we have thoroughly investigated, within ESA-funded contracts, the CNT pellicle technology as a possible alternative to PI for NewAthena. Different parameters can be tuned during the production of CNT pellicles, including Single Walled (SW) vs. Multi Walled (MW), single or multilayer, random or oriented bundle deposition. In this work, we report spectroscopic transmittance measurements to investigate the performance of three types of CNT pellicles, namely randomly oriented dual layer SW, randomly oriented dual layer MW, and oriented multiple layer MW. The geometry of the CNT bundles and their distribution may affect the spectroscopic response and thus impact the filter design for NewAthena. The main purpose of this work is to evaluate the NewAthena in-band (200-1800 eV) and out-of-band (UV-VISMIR) spectroscopic response of aluminum-coated samples of the three types of CNT pellicles and compare these data with mission performance requirements. These experimental campaigns were performed at the Metrologie beamline at SOLEIL synchrotron and at SMaCLab (Spectroscopy and Material Characterization Laboratory) of INAF-OAPA/UNIPA. This work paves the way for selecting the appropriate CNT pellicle. This choice is crucial to properly design a set of representative filter breadboards for the NewAthena X-ray Integral Field Unit instrument that allows the achievement of the Technology Readiness Level 5 before the NewAthena Mission Adoption (June 2027).