Key Aspects for Implementing ISO/IEC 17025 Quality Management Systems at Materials Science Laboratories

Implementing a quality management system based on the requirements specified in ISO/IEC 17025 standard at materials science laboratories is challenging, mainly due to two main factors: (i) the high technical complexity degree of some tests used for materials characterization and (ii) the fact that most materials science laboratories provide materials characterization tests and also carry out research and development activities. In this context, this chapter presents key subjects while implementing a quality management system at materials science laboratories and some considerations on strategies for effectively implementing such systems

Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS₂

We report a novel mechanical response of few-layer graphene, h-BN, and MoS₂ to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS₂), but it is absent in single-layer graphene and in few-layer mica and Bi₂Se₃. We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed