Performance Improvement of Graphenic Carbon X-ray Transmission Windows

TL;DR

This paper reports on the fabrication and performance of graphenic carbon x-ray transmission windows that outperform traditional materials in transmission and stability, with new fabrication techniques enabling thicker, more durable windows.

Contribution

It introduces a two-step growth process for fabricating thicker GC windows, enhancing their mechanical stability and x-ray transmission capabilities.

Findings

GC windows withstand 6.5 bars pressure

40% transmissivity at 0.677 keV for 650 nm thickness

Two-step growth enables up to 6 μm thickness

Abstract

Graphenic carbon (GC) x-ray transmission windows for EDX and XRF applications with a high transparency for x-rays below 2.5 keV have been fabricated on 6 inch wafers with a CMOS-compatible CVD process. GC windows with an open diameter of 7.4 mm and a thickness of 770 nm withstand up to 6.5 bars of differential pressure. A high transmissivity of 40 % for fluorine K{\alpha} (0.677 keV) radiation is demonstrated for a GC thickness of 650 nm. The GC membranes outperform beryllium (Be) windows, in terms of higher x-ray transmission and better mechanical stability while avoiding the toxicity of Be. Optical profilometry has been employed to visualize a large deformation of the GC layer during the window fabrication. This seems to limit the thickness of the GC windows that can currently be fabricated. A two-step growth process can overcome these limitations and windows with a thickness of up to 6 {\mu}m have been realized.