Nanodiamond photocathodes for MPGD-based single photon detectors

TL;DR

This work assesses hydrogenated nanodiamond (HND) photocathodes as robust, high-potential alternatives to CsI for MPGD-based single-photon detectors. It combines HND hydrogenation, pulsed-spray coating onto THGEMs, and integration with Micromegas in Ar-based gas mixtures to evaluate quantum efficiency and durability under ion bombardment. Key findings show HND coatings achieve measurable QE at VUV wavelengths and exhibit roughly an order of magnitude greater resistance to ion-induced aging than CsI, with THGEM performance largely unaffected by the coatings. The results imply that HND can enable more durable, efficient gaseous-photodetectors and motivate further optimization of coatings and gas environments for practical radiation-detection applications.

Abstract

This study investigates the suitability of Hydrogenated NanoDiamond (HND) materials as an alternative for CsI in MPGD-based photon detectors. The research focuses on characterizing HND photocathodes coupled with THGEM + Micromegas-based detectors. The HND grains were prepared via hydrogenation and stored in water for more than two years. They were then coated on PCB discs or THGEMs using a pulsed spray technique. The resulting quantum efficiency (QE) values (~4% at 122 nm) were found to be within a factor of 10 of the best freshly hydrogenated samples reported in the literature ( ~40% at 120 nm). The robustness of reflective HND photocathodes against ion bombardment was measured to be about 10 times larger than the corresponding CsI one after the same charge accumulation. Furthermore, THGEM characterization indicates minimal alteration in response after HND coatings. These results suggest that HND holds potential as a more robust photocathode for gaseous detectors, offering improved performance in single-photon detection applications.

Figures (8)

• Figure 1: Scheme of the R&D protocol followed for ND characterization.
• Figure 2: QE response of CsI and HND photocathodes as a function of charge accumulation in $\sim 10^{-6}$ mbar vacuum.
• Figure 3: QE vs. wavelength response of HND photocathodes coated on PCB substrate in vacuum ($\sim 10^{-5} mbar$).
• Figure 4: SEM images of HND photocathodes coated on stainless steel substrate with (a) 5, (b) 20, (c) 30 and (d) 50 spray shots.
• Figure 5: Transmittance spectra of bare and HND coated $Cr-MgF_{2}$ window as a function of wavelength.