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Nanomechanical and nanotribological characterization of noble metal-coated AFM tips for probe-based ferroelectric data recording

Probe-based data recording is being developed as an alternative technology for ultrahigh areal density. In ferroelectric data storage, a conductive atomic force microscope (AFM) probe with a noble metal coating is placed in contact on lead zirconate titanate (PZT) film, which serves as the ferroelectric material. A crucial mechanical reliability concern is tip wear during contact of the ferroelectric material with the probe. To achieve high wear resistance, the mechanical properties (such as elastic modulus and hardness) of the metal-coated probe should be high. Nanoindentation experiments were performed in order to evaluate the mechanical properties of four commercial noble metal coatings, namely, Pt, Pt–Ni, Au–Ni and Pt–Ir, deposited on AFM probes. The effective hardness and elastic modulus were evaluated, using a contact mechanics model that accounts for the effect of the underlying silicon substrate. The Pt–Ir coating was found to exhibit the highest hardness, highest elastic modulus and lowest creep resistance. Nanoscratch studies reveal that the noble metal coatings are removed primarily by plastic deformation. The Pt–Ir and Pt coatings show the highest and lowest scratch resistance, respectively, which is consistent with results obtained from wear tests of the noble metal-coated AFM probes on a PZT surface.