Dr.-Ing. Patrick Herre
The mechanical response of homogeneous bulk materials to external stimuli is well described by the constitutive laws of continuum mechanics. However, the small scale deformation behavior of (sub-) micron-sized particles is fairly distinct from the bulk due to internal and external interfaces as the size dimensions are close to the characteristic length scale (e.g. dislocation spacing) of underlying physical (deformation) processes. Especially in the field of particle technology, where particle-particle and particle-substrate interactions govern the final product properties, the mechanical deformation behavior of individual (sub-) micron-sized particles in contact (and ensembles thereof) is of great interest and relevance [1,2].
In this context, structurally and morphologically well-defined particulate material systems are characterized by complementary in situ compression experiments in the scanning as well as transmission electron microscope. Particle synthesis is realized by either wet chemical sol-gel synthesis of metal-oxide particles , or solid/liquid state dewetting of thin metallic layers on ceramic substrates yielding pure and/or solid solution metallic particles of defined morphology and texture (see Fig.1) . Mechanical testing of these structures is performed in a SEM-supported manipulation device , allowing for a statistical evaluation of mechanical quantities such as Young’s modulus and breakage probability. Moreover, the mode of deformation and/or fracture can be directly imaged at high resolution. Complementary in situ TEM experiments help deciphering the underlying mechanisms of deformation.
Fig.1: (A) preparation of pure metallic and solid solution metallic micron-sized particles by solid state dewetting. (B) SE top-view image of a dewetted pure Ni thin film. (C) SE top-view image of a dewetted Ni-Au bilayer film. (D) stress-strain data obtained from in situ compression experiments in the SEM.
 J. Paul et al., Advanced Powder Technology 25 (2014) 136.
 J. Paul et al., Powder Technology 286 (2015) 706.
 S. Tanaka et al., Journal of Colloid and Interface Science 334 (2009) 188.
 D. Mordehai et al., Acta Materialia 59 (2011) 5202.
 S. Romeis et al., Review of Scientific Instruments 83 (2012) 95105.