A-Indentation for non-destructive elastic moduli measurements of supported ultra-hard ultra-thin films and nanostructures
Abstract
During conventional nanoindentation measurements, the indentation depths are usually larger than 1-10 nm, which hinders the ability to study ultra-thin films (< 10 nm) and supported atomically thin two-dimensional (2D) materials. Here, we discuss the development of modulated A-indentation to achieve sub-A indentation depths during force-indentation measurements while also imaging materials with nanoscale resolution. Modulated nanoindentation (MoNI) was originally invented to measure the radial elasticity of multi-walled nanotubes. Now, by using extremely small amplitude oscillations ( 1 A) at high frequency, and stiff cantilevers, we show how modulated nano/A-indentation (MoNI/AI) enables non-destructive measurements of the contact stiffness and indentation modulus of ultra-thin ultra-stiff films, including CVD diamond films (modulus 1000 GPa), as well as the transverse modulus of 2D materials. Our analysis demonstrates that in presence of a standard laboratory noise floor, the signal to noise ratio of MoNI/AI implemented with a commercial atomic force microscope (AFM) is such that a dynamic range of 80 dB - achievable with commercial Lock-in amplifiers - is sufficient to observe superior indentation curves, having indentation depths as small as 0.3 A, resolution in indentation < 0.05 A, and in normal load < 0.5 nN. Being implemented on a standard AFM, this method has the potential for a broad applicability.