Humidity effects on the determination of elastic properties by atomic force acoustic microscopy

Abstract

We have investigated how ambient humidity can affect quantitative measurements of elastic properties on the nanoscale. Using an emerging technique called atomic force acoustic microscopy ͑AFAM͒, two samples were examined: a thin film of fluorosilicate glass and a section of borosilicate glass. When experimental results were analyzed using a simple model of the atomic force microscope cantilever dynamics, values of the tip-sample contact stiffness k* increased approximately linearly with relative humidity. The effect is believed to be due to the presence of a humidity-dependent layer of water on the sample. To account for this, the data analysis model was extended to include viscoelastic damping between the tip and the sample. A damping term proportional to the relative humidity was used. The revised values for k* showed virtually no dependence on humidity. Thus, the subsequent calculations of the indentation modulus M from k* yielded similar values regardless of measurement humidity. These results indicate that environmental conditions can influence quantitative nanoscale measurements of elastic properties, at least in some materials.

Elasticity mapping of precipitates in nickel-base superalloys using atomic force acoustic microscopy

“…Hertz contact model can be effectively used for metallic materials as the adhesion forces are much smaller than the elasticity forces [46] and hence adhesion can be neglected. However, the adhesion forces may influence the results significantly for soft materials [47].…”

Acoustic Scanning Probe Microscopy: An Overview

“…Efforts have been made to take into account as many experimental parameters as possible when describing the cantilever [76,77]. From the simplest model where the tip-sample contact is modeled as an elastic spring of constant k * and the cantilever mass is assumed to be concentrated in a single point, subsequent improvements have introduced the description of the cantilever as a beam with distributed mass, the tip not placed at the very end of the beam, nonzero tip height, cantilever and tip inclination, normal damping at the contact by a dashpot γ * in parallel with k * [78,79], and the effect of lateral forces by a parallel lateral contact stiffness k lat and lateral dashpot γ lat [76,77]. Finally, a nonuniform cantilever cross section along the axis can be taken into account [80][81][82][83].…”

Contact resonances of U-shaped atomic force microscope probes

“…(27) with the one given in Eq. (28) shows that the natural frequency and damping factor can be found in terms of the real and imaginary parts of the eigenvalues. They are thus defined as…”

“…More recently, Yuya et al 10,18 developed a method to find the viscoelastic properties of a sample from experiment by following a similar approach. CR-AFM is becoming well accepted for analyzing the properties of a wide variety of materials such as polymers, [11][12][13][14]16,18,23 biological materials, 16,25,26 composite materials, 27 dielectric materials, 28 metallic glass, 29 and metals. 6,8,9 It has shown great promise for many interesting problems especially those involving the interfaces of a multi-phase material.…”