<title>Mechanical properties of fullerite and diamondlike carbon films using surface acoustic waves and nanoindentation</title>

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ABSTRACT C60 and amorphous diamond-like carbon (DLC) films have been grown by thermal evaporation and laser ablation tech-niques at different substrate temperatures and on various substrates. The elastic modulus and the hardness of the films havebeen investigated by surface acoustic waves and nanoindentafion. Both methods are completely new and designed for in-vestigations ofvery thin films. For homogeneous C60films the Young's modulus was found to be 14 GPa and the Poisson'sratio of 0.2. The measured nanohardness of 167 MPa corresponds with the microhardness value of 130 MPa. There is acorrelation between deposition techniques and hardness as well as Young's modulus for DLC films.Keywords: amorphous carbon films, C films, deposition techniques, scanning force microscopy, nanoindentation, sur-face acoustic waves, Young's modulus. 1. INTRODUCTION Structural and mechanical properties of molecular soft C60 films are different from those of amorphous or crystalline carbonfilms. Both types of carbon films have potential applications in hard and/or optical coatings. These materials are also con-sidered to be biocompatible with applications as coating materials in environmental techniques and on medical devices,implants, grafts or other biological systems.Fullerene films contain C60 molecules, which form a solid fcc structure by van der Waals forces. They can be grown ondifferent substrates. The growth mode is very different and depends on the mobility of single Co molecules on the surfaceand their adherence to the substrate. Generally the growth mode is an island growth, however they can be also grown layerby layer on suitable substrates with a very low molecular surface roughness. These fullerene films are then epitaxial. Cofilms can be grown to a few monolayers but also to thick films of a few aim. They represent a soft material which can beused as interlayer in hard coatings or in combination with biomaterial.The structure and morphology of different carbon films 2 is responsible for their physical properties and depends on thedeposition technique and several process parameters. Hard carbon coatings can include hydrogen. The investigated samplesin this paper are free from hydrogen and charactensed by a certain portion of sp2 and sp3 bonds. Hard diamond-like (DLC)carbon films contain a high amount of strong sp3 bonds and have a high hardness estimated wear treatment, scratch testingand density and Young's modulus measurements. Because of internal stress the films cannot be grown to a thickness ofmore than 500 am without any additional treatment. Thus microhardness measurements are not straightforwardly applica-ble.The classification of carbon films is not a simple procedure. Investigations with scanning force microscopy (SFM) charac-tense the surface morphology and grain size distribution including the roughness of the film surface. The same tip for scan-mng the surface to obtain an image can be used to make indents and scratches on the surface by application of forces in therange of it-Newtons and rn-Newtons. That very recent method gives hardness values on narioscale and can be applied tothin films. From the load-depth relation the elastic part can be separated which gives the Young's modulus of the film.