*Article*

## **On the Importance of Combined Scratch/Acoustic Emission Test Evaluation: SiC and SiCN Thin Films Case Study**

#### **Jan Tomastik 1,\*, Radim Ctvrtlik 2,\*, Martin Drab 3 and Jan Manak 4**


Received: 9 April 2018; Accepted: 21 May 2018; Published: 22 May 2018

**Abstract:** The scratch test, as probably the most widespread technique for assessment of the adhesive/cohesive properties of a film–substrate system, fully depends on reliable evaluation based on assessment of critical loads for systems' failures. Traditionally used evaluation methods (depth change record and visual observation) may sometimes give misleading conclusions about the failure dynamics, especially in the case of opaque films. Therefore, there is a need for another independent evaluation technique with the potential to complete the existing approaches. The nondestructive method of acoustic emission, which detects the elastic waves emitted during film cracking and delamination, can be regarded as a convenient candidate for such a role even at nano/micro scale. The strength of the combination of microscopic observation of the residual groove and depth change record with the acoustic emission detection system proved to be a robust and reliable approach in analyzing adhesion/cohesion properties of thin films. The dynamics of the gradual damage taking place during the nano/micro scratch test revealed by the combined approach is presented for SiC and SiCN thin films. Comparison of critical load values clearly reflects the higher ability of the AE approach in detecting the initial material failure compared to the visual observation.

**Keywords:** scratch test; acoustic emission; thin films; silicon carbide
