Then, the indenter was completely click here removed from the material. In this study, constant strain rate was chosen in order to avoid the strain-hardening effects. At least 20 indentations were performed on each sample, and the distance between the adjacent indents was kept at least 10 μm apart to avoid interaction. In nanoindentation tests, the hardness is defined as the applied indentation load divided by the projected contact area as follows: (2) where A p GF120918 research buy is the projected contact area between the indenter and the sample surface at the maximum indentation load, P max. For a perfectly sharp Berkovich indenter, the projected area A p is given by with

h c being the true contact depth. The elastic modulus of the sample can be calculated based on the relationships check details developed by Sneddon [17]: . Here S is the contact stiffness of the material, and β is a geometric constant with β = 1.00 for the Berkovich indenter, respectively. The reduced elastic modulus, E r, can be calculated from

the following equation: (3) Here v is Poisson’s ratio, and the subscripts i and f denote the parameters for the indenter and the BFO thin films, respectively. For the diamond indenter tip, E i = 1,141 GPa and v i = 0.07, and v film = 0.25 is assumed for BFO thin films in this work. It is generally accepted that the indentation depth should never exceed 30% of the film thickness to avoid the substrate effect on hardness and modulus measurements [18]. Our samples

and test methodology were considered Chloroambucil as adequate based on this concept. In addition, because of the fact that it enters as in the calculation of E, an error in the estimation of Poisson’s ratio does not produce a significant effect on the resulting value of the elastic modulus of thin films [19]. Results and discussion Figure 1 shows the XRD results of BFO thin films obtained with deposition temperatures of 350°C, 400°C, and 450°C, respectively. It is evident that the intensity and the full width at half maximum (FWHM) of the BFO(110) diffraction peak are both improved with the increasing deposition temperature, indicating a tendency of better film crystallinity and increased grain size. The grain size, D, can be estimated according to Scherrer’s equation [20]: (4) where λ, B, and θ are the X-ray wavelength, the FWHM of the BFO(110) diffraction peak, and the corresponding Bragg’s diffraction angle, respectively. The estimated grain sizes for BFO thin films deposited at 350°C, 400°C, and 450°C are 24.5, 30.6, and 51.2 nm, respectively. As can be seen below, consistent results were obtained from the AFM examinations. Figure 1 XRD patterns of BFO thin films deposited at various deposition temperatures. (a) 350°C, (b) 400°C, and (c) 450°C. As shown in Figure 2, the AFM observations reveal that the R RMS values for BFO thin films deposited at 350°C, 400°C, and 450°C are 6.5, 9.4, and 14.8 nm, respectively.