Narrow Results

Using thermodynamics approach, the present work analytically studies the effect of mismatch strains on the material properties of ferroelectric thin films. A one-dimensional model is first developed to illustrate the physical picture and the procedure of the theoretical approach. Then, the effect of non-equal mismatch strains is investigated by using the same theoretical approach.

It is well known that a circular hole in a blanket thin film causes strain concentration near the hole edge when the thin film is under tension. The increased strain level can be as high as three times of the applied tension. Interestingly, we show that, by suitably patterning an array of circular holes in a thin film, the resulting strain in the patterned film can be decreased to only a fraction of the applied tension, even at the hole edges. The strain deconcentration in the film originates from the following deformation mechanism: while initially planar, the film patterned with circular holes elongates by deflecting out of plane, so that a large tension induces only small strains. Using finite element simulations, we investigate the effects of geometric parameters (i.e., hole size, spacing, and pattern) and loading direction on the resulting strain in patterned thin films under tension. The large deformability of the patterned film is independent of materials and length scale, and thus sheds light on a potential architecture concept for flexible electronics.

This paper presents alternative analysis methodologies to extract the elastic modulus and hardness of the ultra-thin films from nanoindentation load-displacement data, especially when the film thickness is only few hundred nanometers or less. At such film thickness, the conventional analysis methods for nanoindentation usually do not give accurate film properties due to the substrate effect. The new methods are capable to show how to determine the film-only properties and how the substrates affect the nanoindentation measurement, especially for ultra thin films. These methods give accurate results for nanoindentation of various metallic, ceramic and polymeric films. It also reveals the differences between the use of high-resolution nanoindentation set-up and normal nanoindentation set-up on the same films. The relationships between the mechanical properties and film thickness are also discussed.

Gold and copper thin films are widely used in microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) devices. Nanoindentation has been developed in mechanical characterization of thin films in recent years. Several researchers have examined the effect of surface roughness on nanoindentation results. It is proved that the surface roughness has great importance in nanoindentation of thin films. In this paper, the surface topography of thin films is simulated using the extracted data from the atomic force microscopy (AFM) images. Nanoindentation on a rough surface is simulated using a three-dimensional finite-element model. The results are compared with the results of finite-element analysis on a smooth surface and the experimental results. The results revealed that the surface roughness plays a key role in nanoindentation of thin films, especially at low indentation depths. There was good compatibility between the results of finite-element simulation on the rough surface and those of experiments. It is observed that on rough films, at low indentation depths, the geometry of the location where the nanoindentation is performed is of major importance.