Young's modulus measurements on ultra-thin coatings

Abstract

The determination of the mechanical properties of ultra-thin coatings has become more and more important because of the increasing number of applications using such films. However, an accurate mechanical testing of coatings with a thickness down to some nanometers is still a challenge, despite the improvements of existing measurement techniques. Nanoindentation is an often used mechanical nanoprobe. Using the conventional test method with a sharp Berkovich indenter, the problem of the influence of the substrate on the results arises with decreasing film thickness. Therefore, it is nearly impossible to measure the modulus of films with a thickness less than 100-200 nm. The problem can be overcome by using spheri cal indenters in combination with an analytical solution for the Hertzian contact of coated systems. It allows a separation of film and substrate properties from the load-displacement curve of the compound. Indentation measurements were done at a 44 nm TiN film and at diamondlike carbon coatings in the thickness range between 4.3 nm and 125 nm on Si substrates. Several corrections were applied to obtain wholly elastic force-displacement curves with high accuracy. It is shown in more detail how zero point and thermal drift corrections are used to obtain statistical depth errors below 0.2 nm. Laser-acoustic measurements based on ultra sonic surface waves were chosen as second method, which also measures the Youngs modulus in this thickness range. Although the indentation technique is a local probe and the laser-acoustic technique gives an integrated value for a surface range of some millimetres, the results agree well for the investigated samples. In contrast, it was impossible to get the correct Youngs modulus results by co nventional indentation measurements with Berkovich indenter, even for ultra-low loads

Synchrotron X-ray diffraction study of load partitioning during elastic deformation of bovine dentin

“…Many fewer studies have been performed for the case of ceramics. However, it has been shown that diamond-like carbon thin films undergo a decrease in elastic modulus as their thickness decreases [92][93][94]. This decrease can be as much as 44% of the elastic modulus (360 GPa at 6 nm vs. 640 GPa at 125 nm thickness) [92].…”

“…However, it has been shown that diamond-like carbon thin films undergo a decrease in elastic modulus as their thickness decreases [92][93][94]. This decrease can be as much as 44% of the elastic modulus (360 GPa at 6 nm vs. 640 GPa at 125 nm thickness) [92]. Using semi-continuum models on platelike nanomaterials a 27% decrease in the modulus for NaCl was predicted for thin films with less than 10 atomic layers [95].…”

A variable temperature mechanical analysis of ZDDP-derived antiwear films formed on 52100 steel

“…It is generally accepted that for thin films on a substrate, if the indentation exceeds ∼10% of the film thickness, the measured hardness may be affected by the substrate properties [37]. No such rule has been applied for the Young's modulus; however several groups have tried to derive empirical formulas for effective modulus and compliance as a function of elastic properties of both materials [38][39][40][41]. Problems arise when testing the mechanical properties of the ZDDP tribofilms due to the fact that these films are extremely thin and may vary in thickness.…”

Effect of trypan blue staining on the elastic modulus of anterior lens capsules of diabetic and nondiabetic patients

“…Because nanoindentation elastically deforms the sample at small strains, Poisson's ratio of the lens capsule was assumed to be 0.5. The Poisson's ratio and Young's modulus (n i and E i , respectively) of the sapphire flat punch indenter were obtained from Chudoba et al 23 By substituting these values into equation 2, 19 the Young's modulus from each indent was calculated.…”