Nanoindentation and pico-indentation based on atomic force microscopy (AFM) are commonly used for the evaluation of material mechanical properties using the depth-loading profile measured at a specific location of the material. However, the interpretation of the measurement results largely relies on the parameters of indentation such as the tip shape and material of the indenter, the indentation environment, and the indenting speed. Contact models are commonly adopted to deduce the mechanical properties of the materials by best fit of the indentation depth-loading profile. However, determination on the correct contact model is not unambiguously determined by the local depth-loading profile. This ambiguity can be removed by using the extra data of the non-local deformation of materials.
Here, we develop a method that can reconstruct the non-local deformation of materials by combining nanodiamond orientation sensing and the AFM-nanoindentation. The method exploits the superb sensitivity of diamond vector magnetometry and the high spatial resolution of AFM indentation. Loading on the material is carried out by the AFM tip. The material deformation upon an AFM indentation is then reconstructed by measuring the rotation of nanodiamonds (NDs) docked on the surface in the vicinity of the indentation location.
Figure 1. Experimental setup. Left: AFM-confocal correlation microscopy. Right upper: Photo of the setup during measuringment. Right lower: Scheme of the nanoindentation on a gelatin particle.
In the proof-of-the-concept demonstration, we reconstruct the deformation of a polydimethylsiloxane (PDMS) film with a 5 nm precision in the loading direction and an in-plane spatial resolution limited by the ND size (which is ~200 nm in the present experiments). We further apply this technique to investigate the mechanical properties of a gelatin particle in water. Elastocapillary effects at the gelatin/water interface are disclosed by the non-local deformation sensing.
The work holds promises for investigation of mechanical properties/mechano-response of soft materials. The low cytotoxicity and high photo-stability of NDs make NDs especially attractive for live cell investigations.
Read the full article in Nature Communications here: https://rdcu.be/bLg2m