Pattern Formation During Nanowear of Gold Films
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Pattern Formation During Nanowear of Gold Films Megan E. Pendergast1, Alex A. Volinsky1, and Xiaolu Pang1,2 1 Department of Mechanical Engineering, University of South Florida, 4202 E. Fowler Ave. ENB118, Tampa, FL, 33620 2 Department of Materials Physics, University of Science and Technology Beijing, 30 Xueyuan Rd, Haidian District, Beijing, Beijing, 100083, China, People's Republic of ABSTRACT The effects of water on the wear resistance of 3 µm thick sputtered gold films on silicon substrate using contact AFM and a scanning nanoindenter was investigated. In performing wear tests on gold samples in the presence of water, a significant increase in depth of the wear area was observed compared to the same tests performed in the ambient atmosphere (~55% humidity). These results were obtained using Hysitron Triboindenter on areas of 10x10 µm2 and an Atomic Force Microscope on areas of 1x1 µm2. Nanowear tests were preformed using silicon nitride cantilevers on the AFM and diamond Berkovich or blunt conical tips on the Hysitron. Normal loads used were 2 µN and 10 µN, respectively. Tests performed in the ambient atmosphere resulted in a slightly reduced surface roughness, while a much higher wear rate was observed in the wear tests performed in water. Additionally, gold surface ripples formed under certain scanning conditions, in water for the Hysitron Triboindenter and in ambient atmosphere for the AFM. Nanoscale stick slip is being investigated as a possible explanation to the rippling phenomenon, and single scan line tests provide valuable information about the mechanisms and progression of the nanoscale wear. INTRODUCTION Wear testing is performed for various reasons, some simply to obtain an idea of longevity, and others to compare materials and different working environments [1]. Gold is used in applications ranging from dentistry to electrical connections, so it naturally evolves that the gold’s response to wear is of vital importance for design [2]. Gold is often deposited in the form of a thin film for economic reasons, and sometimes the thickness is only several nanometers, exacerbating the need to study the wear properties in different environments. Wear progression has been shown to change when comparing results at the macro vs. the nanoscale, and as such requires new explanations. Bulk material physics no longer dictates material reactions, since with the increase of the surface to volume ratio, other forces, such as surface and capillary forces affect materials response [3]. In a typical wear experiment a hard material is scanned over the tested material surface, resulting in a wear rate measurement in terms of the removed material depth as a function of normal applied load and number of wear cycles. Wear experiments performed with Hysitron and AFM are important in adding information to the “scaling down” problem in tribology because of their own relative size differences. Hysitron tests were preformed on 10x10 µm2 areas, while AFM tests were performed on 1x1 µm2 areas. The field of nanoscale tr
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