Probing elastic properties of soft materials with AFM: Data analysis for different tip geometries

Abstract

It has become increasingly common to use atomic force microscopy measurements to probe mechanical properties at the nano-micro level. The data obtained from these measurements, however, must be subjected to specific models for deconvolution of the effect of the probe's tip size and shape. While analytical models have been developed to assist in this endeavor, a thorough understanding of the limits of these models is essential to fitting data accurately. In this report, we explore the relationship between three different analytical tip shape models for the AFM tip (spherical, parabolic, and conical indenters) and present an analysis of mechanical testing on selected materials. Along with this, we present a simple numerical method for computing the contact radius for true spherical contact. The role of tip size (large vs small radius) on the limitations of data analysis and the benefits and drawbacks inherent to different tip sizes is discussed. Our analysis demonstrates the ability to accurately apply multiple models to a given data set, while also showing the limitations of simple analytical models to accurately describe tip-sample interactions outside of certain indentation regimes.

Adhesion and Mechanical Properties of PDMS-Based Materials Probed with AFM: A Review

“…The model works with conical AFM tips when the indent is significantly higher than the radius of curvature of the tip apex. It is vitally important to precisely monitor and control sample deformation, especially for very soft materials where the nature of the tip-sample contact geometry can change due to increasing penetration, or in the case of a thin film on top of a stiff substrate which could increase apparent modulus [80].…”

“…Significant adhesion phenomena were observed where flexible cantilevers were used, but they were effectively controlled carrying out an easy preliminary hydrophobic treatment of tips. Data analysis for different tip geometries probing soft materials was performed by Chyasnavichyus et al [80]. They explored the relationship between three different analytical AFM tip shape models (spherical, parabolic, and conical indenters) and presented an analysis of mechanical testing on selected materials and developed a simple numerical method for computing the contact radius for true spherical contact.…”

Bimorph Silk Microsheets with Programmable Actuating Behavior: Experimental Analysis and Computer Simulations

“…All moduli were determined fitting a minimum of 10 force distance curves to a parabolic indentation model using an in-house analysis software. 34 SEM images were collected on a Hitachi S-3400-II microscope at a voltage of 10 kV. For the preservation the 3D shape, the samples were frozen with liquid nitrogen, and then freezedried for 24 hrs within freeze dryer (SF Scientific).…”

The Next Generation of Colloidal Probes: A Universal Approach for Soft and Ultra‐Small Particles

“…The colloidal probe technique is utilized in many laboratories worldwide and typical applications range from determining adhesion behavior, to mechanical properties, or colloidal interaction forces . Nevertheless, the essential preparation procedure for colloidal probes has not seen significant changes in the last 30 years: Shortly, a colloidal particle is placed by means of a micromanipulator (or the AFM) at the end of a tipless cantilever, where it is immobilized permanently, either by glue or by a sintering procedure .…”