Characterizing Multi- layer thin films Janez Kosir

X-ray photoelectron spectroscopy (XPS) We can determine the chemical composition and film thickness A depth profile can be constructed by tilting the sample Changes in the chemical composition indicate a new layer S. Geng, S. Zhang, H. Onishi; XPS Applications in Thin Films Research Evans Analytical Group; Physical and Chemical Characterization of Thin Films

Nanoindentation We can measure hardness and elastic modulus Properties change with depth/layer Film properties adapt to one another Thin films have different properties than bulk Agilent Technologies; Nanotribology of Hard Thin Film Coatings: A Case Study Using the G200 Nanoindenter – Application Note B. Bhushan, X. Li; A review of nanoindentation continuous stiffness measurement technique and its applications

Nano-scratch testing We can measure the adhesion, surface roughness, friction, wear, elastic and plastic deformation At the point of failure the depth and friction coefficient rapidly increase. We can also see delamination, chipping or blistering A. C. Fischer-Cripps; Nanoindentation Micro Materials; Nano-Scratch & Wear

Nano-scratch testing When does the coating fail? Which coating fails? Thin films below the surface exhibit residual stress C. Kang, H. Huang; Mechanical load- induced interfacial failure of a thin film multilayer in nanoscratching and diamond lapping Agilent Technologies; Scratch Testing of Multilayered Metallic Film Stacks – Application Note

Conclusions All characterization methods for mono-layer thin films can be applied to multi-layer thin films Multi-layer thin films combine properties of each individual film The results must be interpreted based on the fact that there are multiple layers It is also important to know the exact parameters (maximum load, scratch speed, penetration rate) at which the characterization was performed

Questions?

Information Slides XPS can be used to determine the chemical compositions of thin films X-rays knock out electrons from atoms. Based on the electron energy we can determine the element (each electron in a specific element has a specific energy) The penetration depth of the x-rays depends on their wavelength By tilting the sample we can control the penetration depth relevant to the substrate That way we can construct a depth profile of the chemical composition of our thin film and also measure the film thickness

Information Slides In nanoindentation we press a hard (diamond) tip into the surface of the sample (usually the shape of a Berkovich pyramid). At the same time we measure the load and displacement of the tip By applying a small oscillating force to the tip we can measure the hardness and elastic modulus of the sample as a function of depth A nanoindenter can measure forces as low as a few nN and distances of 0,1 nm making it a good characterization method for thin films The thin film hardness and elastic modulus will adapt to one another and the substrate resulting in different properties than they would have if they were in bulk form

Information Slides In nano-scratch testing, the tip is pressed into the surface while at the same time the sample moves in a predetermined direction The force of the tip can be constant (roughness, wear) or can linearly increase (adhesion, elastic and plastic deformation) In multilayer thin films, films below the surface exhibit residual stress due to the pressure from other films above them. This can cause the film to crack and fail It is important to know that a film can fail before our tip reaches it which is why we must also analyse which coating failed The film can fail either by delamination, chipping or blistering

References S. Geng, S. Zhang, H. Onishi; XPS Applications in Thin Films Research; Materials Technology, vol. 17, no. 4 (2002) Evans Analytical Group; Physical and Chemical Characterization of Thin Films; (2007) D. P. Cole, H. A. Bruck; Nanoindentation Characterization of Graded Shape Memory Alloy and Multilayer Thin Films; Society for Experimental Mechanics (2009) Agilent Technologies; Nanotribology of Hard Thin Film Coatings: A Case Study Using the G200 Nanoindenter – Application Note; (2013) B. Bhushan, X. Li; A review of nanoindentation continuous stiffness measurement technique and its applications; Materials Characterization, 2001, vol.48, no. 1, pp R. H. Dauskardt, M. Lane, Q. Ma, N. Krishna; Adhesion and debonding of multi-layer thin film structures; Engineering Fracture Mechanics, vol. 61, no. 1, pp. 141 – 162 (1998) A. C. Fischer-Cripps; Nanoindentation; vol. 3, Springer, 2011, ISBN-13: Micro Materials; Nano-Scratch & Wear C. Kang, H. Huang; Mechanical load-induced interfacial failure of a thin film multilayer in nanoscratching and diamond lapping; Journal of Materials Processing Technology, vol. 229, pp. 528 – 540 (2016) Agilent Technologies; Scratch Testing of Multilayered Metallic Film Stacks – Application Note; (2010)