Study of SEY degradation of amorphous carbon coatings

TL;DR

This study investigates how amorphous carbon coatings used in accelerators degrade their secondary electron yield (SEY) over time when exposed to air, and how annealing can reverse this aging process.

Contribution

It provides new insights into the aging mechanisms of low-SEY carbon coatings and demonstrates annealing as an effective method to recover their properties.

Findings

SEY increases with oxygen surface concentration.

Annealing at 100-200°C reduces aging rate.

Hydrogen desorption is linked to surface segregation.

Abstract

Deposition of low secondary electron yield (SEY) carbon coatings by magnetron sputtering onto the inner walls of the accelerator seems to be the most promising solution for suppressing the electron cloud problem. However, these coatings change their electron emission properties during long term exposure to air. The ageing process of carbon coated samples with initial SEY of about 0.9 received from CERN is studied as a function of exposure to different environments. It is shown that samples having the same initial SEY may age with different rates. The SEY increase can be correlated with the surface concentration of oxygen. Annealing of samples in air at 100-200 {\deg}C reduces the ageing rate and even recovers previously degraded samples. The result of annealing is reduction of the hydrogen content in the coatings by triggering its surface segregation followed by desorption.