quantitative-hardness-measurement-by-instrumented-afm-indentation

Quantitative Hardness Measurement by Instrumented AFM-indentation

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness ...

KoreaTech, Korea University of Technology and Education

The evolutional function of ordered interfacial water near solid surfaces was postulated by Szent-Györgyi: "Life actually, may have started with building these water structures." Here we report their tunability with laser light on both hydrophobic and hydrophilic surfaces. On the former, the light caused their depletion--on the latter, an increase in fluidity--as measured by atomic force acoustic microscopy. Interfacial water layers play a key role in cellular recognition. Their tunability promises to revolutionize various fields in biomedical engineering and life sciences.

Tuning nanoscopic water layers on hydrophobic and hydrophilic surfaces with laser light.

We study nanoindentation and scratching of graphene-covered Pt(111) surfaces in computer simulations and experiments. We find elastic response at low load, plastic deformation of Pt below the graphene at intermediate load, and eventual rupture of the graphene at high load. Friction remains low in the first two regimes, but jumps to values also found for bare Pt(111) surfaces upon graphene rupture. While graphene substantially enhances the load carrying capacity of the Pt substrate, the substrate's intrinsic hardness and friction are recovered upon graphene rupture.

Atomic scale mechanisms of friction reduction and wear protection by graphene.

We combine non-contact atomic force microscopy (AFM) imaging and AFM indentation in ultra-high vacuum to quantitatively and reproducibly determine the hardness and deformation mechanisms of Pt(111) and a Pt57.5Cu14.7Ni5.3P22.5 metallic glass with unprecedented spatial resolution. Our results on plastic deformation mechanisms of crystalline Pt(111) are consistent with the discrete mechanisms established for larger scales: Plasticity is mediated by dislocation gliding and no rate dependence is observed. For the metallic glass we have discovered that plastic deformation at the nanometer scale is not discrete but continuous and localized around the indenter, and does not exhibit rate dependence. This contrasts with the observation of serrated, rate-dependent flow of metallic glasses at larger scales. Our results reveal a lower size limit for metallic glasses below which shear transformation mechanisms are not activated by indentation. In the case of metallic glass, we conclude that the energy stored in the stressed volume during nanometer-scale indentation is insufficient to account for the interfacial energy of a shear band in the glassy matrix.

Article	Year
Tuning nanoscopic water layers on hydrophobic and hydrophilic surfaces with laser light. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 18171094	2008
Atomic scale mechanisms of friction reduction and wear protection by graphene. Nano letters\| PubMed ID: 25375666	2014
Lower nanometer-scale size limit for the deformation of a metallic glass by shear transformations revealed by quantitative AFM indentation. Beilstein journal of nanotechnology\| PubMed ID: 26425424	2015

Arnaud Caron

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