Evaluation of etching on amorphous carbon films in nitric acid

Abstract

Etching on hydrogenated amorphous carbon (a-C:H) films by nitric acid was evaluated in situ using surface plasmon resonance (SPR) device with a multilayer structure consisting of an a-C:H layer on Au. A flow cell was used to introduce the nitric acid onto the a-C:H top layer of the multilayer structure. Nitric acid solutions with various concentrations were injected into the flow cell. The SPR angle was determined as the angle with minimum reflectivity. The obtained SPR angle decreased with increasing duration of nitric acid injection into the flow cell. The observed behavior of the SPR angle indicated that the a-C:H film surface was etched by nitric acid. The thickness of the film was calculated from the SPR angle, and an etching rate of 3.21nm/h was obtained in the case of using 2.0M nitric acid. The obtained shift in the SPR angle depended on the concentration of nitric acid solution. These results indicate that in situ evaluation using the SPR device with a multilayer structure can be used to detect the etching of amorphous carbon films in a liquid.