Measuring the Size Dependence of Young's Modulus Using Force Modulation Atomic Force Microscopy

Abstract

The dependence of the local Young's modulus of organic thin films on the size of the domains at the nanometer scale is systematically investigated. Using atomic force microscopy (AFM) based imaging and lithography, nanostructures with designed size, shape, and functionality are preengineered, e.g., nanostructures of octadecanethiols inlaid in decanethiol self-assembled monolayers (SAMs). These nanostructures are characterized using AFM, followed by force modulation spectroscopy and microscopy measurements. Young's modulus is then extracted from these measurements using a continuum mechanics model. The apparent Young's modulus is found to decrease nonlinearly with the decreasing size of these nanostructures. This systematic study presents conclusive evidence of the size dependence of elasticity in the nanoregime. The approach utilized may be applied to study the size-dependent behavior of various materials and other mechanical properties.

Measuring radial Young’s modulus of DNA by tapping mode AFM

“…As shown in Figure 4, Young's modulus is 0.1-0.3 GPa under the loaded force. Compared with the previous report on Young's modulus of about 1 GPa for self-assembled thiols [10] , it can be predicted that dsDNA is very soft under the experimental conditions, thus dsDNA is so easy to bend. Furthermore, Young's modulus decreased nonlinearly with increasing loading force.…”

“…Results showed that the reversible deformation of DNA molecules deposited on mica surfaces was able to reach about 50% under external load, with a compression elastic constant of about 0.6 nN/nm. Similar methods have also been applied to other important nanomaterials, such as single-wall carbon nanotubes, cytoskeletal systems, and self-assembled monolayers (SAMs) [9][10][11] . However, there are still many problems pending, including how to deduce the Young's modulus of dsDNA.…”

Size dependence of nanostructures: Impact of bond order deficiency

“…When the measuring temperature rises, the stress drops and changes from tensile to compressive [212]. However, the Y values for the polymer nanostructures drop with size according to the relation Y ¼ 0.014 ln(x) þ 0.903 AE 0.045 [213], with x being the particle size. The Ysuppression indicates the importance of the (T m ÿ T ) contribution in determining the size effect on mechanical strength.…”

Probing physical properties at the nanoscale

“…Researchers have used the method to study the effect of nanostructure geometry on material stiffness for structures as small as 20 nm at a resolution on the order of 10 MPa. 3 Interfacial properties of the tip-surface junction may be similarly probed with contact-mode techniques by adjusting the position of the cantilever to apply compressive or tensile forces to the sample. Reducing the applied load until the tip disengages from the sample yields the system's interfacial energy, or work of adhesion; the spatial resolution is limited by the contact radius of the junction, typically 1-2 nm.…”