Nanoscratch Deformation Response of Carbon Nitride Thin Films
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Nanoscratch Deformation Response of Carbon Nitride Thin Films
C. Charitidis. P. Patsalas, S. Logothetidis Department of Physics, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece
ABSTRACT The mechanical performance of thin carbon nitride (CNx) films deposited onto Si(100) substrate by sputtering, was investigated in the load range of 2-20 mN using nanoindentation and nanoscratch techniques. The microstructure of these films was characterized by the inhomogeneous embedding of crystalline grains into a N-poor amorphous matrix. A load dependent transition was found in both the scratch, as well as the friction responses. Below 5 mN, nanoscratching showed completely elastic behavior of the film, while above 10 mN a mixed elastic-plastic behavior was identified. Testing under a normal load of 20 mN resulted in local grooving at the film surface; however, in-situ profiling of the scratch trace showed no evidence of film failure. Both the coefficient of friction ( ), as well as the plastic deformation of the films were found increasing with the normal load applied following an exponential low.
INTRODUCTION In recent years, nitrogenated amorphous carbon (a-CNx) films have received considerable scientific attention due to the prediction that -C3N4, exhibiting similar crystallographic characteristics with -Si3N4, should have bulk modulus equal to or even higher than diamond [1,2]. Although that a wide variety of techniques has been implemented, there is no clear evidence on the formation of the crystalline stoichiometric phase -C3N4. Up-to-date, only the existence of small -C3N4 crystallites, embedded into an amorphous carbon matrix is reported [3,4]. However, even sub-stoichiometric CNx films, containing nitrogen from 20 up to 40 at.%, exhibit interesting properties such as elevated hardness and elasticity. a-CNx films can be synthesized by various vapor phase deposition techniques [5-8] and find applications in magnetic heads and hard disks for high-density proximity recording, due to their extremely low roughness and their excellent tribological performance. Moreover, the fact that a-CNx films are based on carbon makes them good candidates for biomedical applications [9]. The objective of this work is the investigation of the mechanical performance of thin carbon nitride films deposited onto Si(100) by sputtering with high-energy ion bombardment during deposition (induced by applying a bias voltage Vb=–200 V). The study is mainly focused on the deformation response and the nanotribological behavior of the films and aimed to the better understanding of the mechanisms governing failure of thin films.
EXPERIMENTAL DETAILS CNx films were deposited onto Si(100) substrates by reactive RF magnetron sputtering using a graphite target of 99.999% purity in a deposition chamber with a base pressure better than Q7.19.1
1x10-7 mbar applying sputtering power of 100 W. As sputtering gas N2 of 99.999% purity was used at a partial pressure of 4x10-3 mbar. The cleaning procedure of the substrates included chemical and dr
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