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“Background Multiferroic materials exhibit see more some unique characteristics with the

co-existence of at least two kinds of long-range ordering among ferroelectricity (or antiferroelectricity), ferromagnetism (or antiferromagnetism), and ferroelasticity. Single-phase compounds in which both ferromagnetism and ferroelectricity arise independently and may couple to each other to give rise to magneto-electric interactions are ideal materials for novel functional device applications but are unfortunately rare in nature [1]. BiFeO3 (BFO) is one of the most important multiferroic materials so far discovered, which has a ferroelectric Curie temperature of 1,103 K [2, 3] and an antiferromagnetic Néel temperature of 643 K [4]. In addition to its interesting optical properties [5], strong coupling between ferroelectric and magnetic orders is observed in BFO at room temperature, making it a strong candidate for realizing room-temperature multiferroic devices [6, 7]. However, while most of the researches have been concentrated on the abovementioned magneto-electric characteristics of BFO, researches on the mechanical characteristics of this prominent functional LY2090314 chemical structure material have been largely ignored. In particular, since the mechanical properties of materials are size-dependent, the properties obtained from thin films may substantially deviate from those of the bulk material. In view of the fact that most practical

applications of functional devices are fabricated with Dolichyl-phosphate-mannose-protein mannosyltransferase thin films, it is desirable to carry out precise measurements of the mechanical properties of BFO thin films. Because of its high sensitivity, Tubastatin A cost excellent resolution, and easy operation,

nanoindentation has been widely used for characterizing the mechanical properties of various nanoscale materials [8, 9] and thin films [10–12]. Among the mechanical characteristics of interest, the hardness, Young’s modulus, and the elastic/plastic deformation behaviors of the interested material can be readily obtained from nanoindentation measurements. For instance, by analyzing the load–displacement curves obtained during the nanoindentation following the methods proposed by Oliver and Pharr [13], the hardness and Young’s modulus of the test material can be easily obtained. In general, in order to avoid the complications arising from the substrate material, the contact depths of the indenter need to be less than 10% of the film thickness to obtain intrinsic film properties [14]. On the other hand, it is very difficult to obtain meaningful analytical results for indentation depths less than 10 nm because of the equipment limitations. Hence, for films thinner than 100 nm, it is almost impossible to obtain results without being influenced by responses from the substrate. In order to gain some insights on the substrate influences and obtain the intrinsic properties for films thinner than 100 nm, it is essential to monitor the mechanical properties as a function of depth.