Dr. Ming Chen
Photons for Engineering and Manufacturing Group
5232 Villigen PSI
Ming Chen is a postdoctoral researcher in the Photons for Engineering and Manufacturing group (PEM). He received his Ph.D. at Materials department of ETH Zurich under supervision of Prof. Ralph Spolenak and Dr. Jeffrey M. Wheeler in 2020. During his Ph.D. study, he focused on studying micromechanical properties of brittle semiconductors, i.e. diamond, Silicon and Germanium, over a wide range of temperatures. He conducted micro-pillars compressions and transmission electron microscopy to investigate defects behavior and size effects in diamond-structured crystals as a function of temperature and size. From July 2020, he joined PEM group to work as a postdoctoral researcher to study 3D printing of alloys using operando synchrotron X-ray. He also works with mechanical testing with multi-axial loading to explore the effect of loading paths on deformation behavior.
Within the PEM-group, Ming Chen is responsible for the experiments and maintenance of miniSLM machines and bi-axial tensile machine with synchrotron X-ray tests.
Ming Chen’s present research work focus on two aspects, i.e. manufactory and testing of materials. During his previous studies, he conducted mechanical testing from macro- to micro-scales to study materials properties. After that, deformation microstructures were characterized by using electron microscopy to investigate defect behavior, such as dislocations and twins, as a function of temperature and specimen size. In his postdoctoral work at PEM, he also want to address the manufactory aspect of materials by studying 3D printing of Ti and Al alloys using operando synchrotron X-ray to understand selective laser melting process of metallic powders. In addition, he also works with mechanical testing with multi-axial loading to explore the effect of loading paths on deformation behavior of materials.
For an extensive overview we kindly refer you to our publication repository DORA (includes publications since joining PSI).
(Only first author papers here, complete list at Google Scholar)
Achieving micron-scale plasticity and theoretical strength in Silicon, Ming Chen, Laszlo Pethö, Alla S Sologubenko, Huan Ma, Johann Michler, Ralph Spolenak, Jeffrey M Wheeler, Nature Communications, Volume 11, Pages 1-10 (2020). At ambient temperature, the brittleness of Si limits its mechanical application in devices. Here, we demonstrate that Si processed by modern lithography procedures exhibits an ultrahigh elastic strain limit, near ideal strength (shear strength ~4 GPa) and plastic deformation at the micron-scale, one order of magnitude larger than samples made using focused ion beams, due to superior surface quality. This extended elastic regime enables enhanced functional properties by allowing higher elastic strains to modify the band structure. Further, the micron-scale plasticity of Si allows the investigation of the intrinsic size effects and dislocation behavior in diamond-structured materials. This reveals a transition in deformation mechanisms from full to partial dislocations upon increasing specimen size at ambient temperature. This study demonstrates a surface engineering pathway for fabrication of more robust Si-based structures.
Size-dependent plasticity and activation parameters of lithographically-produced silicon micropillars, Ming Chen, Juri Wehrs, Alla S Sologubenko, Jacques Rabier, Johann Michler, Jeffrey M Wheeler, Materials & Design, Volume 189, Pages 108506 (2020). Silicon is brittle at ambient temperature and pressure, but using micro-scale samples fabricated by focused ion beam (FIB) plasticity has been observed. However, typical drawbacks of this methodology are FIB-damage and surface amorphization. In this study, lithographic etching was employed to fabricate a large number of 〈100〉-oriented Si pillars with various diameters in the micro-scale. This allowed quantitative study of plasticity and the size effect of FIB-free Si in the brittle temperature range (25–500 °C) by conducting monotonic and transient microcompression in situ in the scanning electron microscope. Lithographic pillars achieved the ideal strength in temperature range of 25–100 °C and displayed significantly higher strengths (30–60%) than FIB-machined pillars because of the undamaged surface and the oxide layer confinement. The activation energy of deformation revealed a transition in dislocation mechanisms as a function of temperature. Strain rate sensitivity and activation volume measured from strain rate jump and stress relaxation tests indicated the surface nucleation of kink-pairs associated with the constricted dislocation motion in Si during deformation at temperatures below the brittle-ductile transition. A modified analytical model is proposed to accurately evaluate the size-dependent strength of covalent crystalline Si.
Influence of helium ion irradiation on the structure and strength of diamond, Ming Chen, James P Best, Ivan Shorubalko, Johann Michler, Ralph Spolenak, Jeffrey M Wheeler, Carbon, Volume 158, Pages 337-345 (2020). Microfabrication of synthetic single crystal diamond using accelerated helium ions beams has significant potential for functional applications, such as high precision optical devices, through tailoring of the optical properties via diamond graphitization. The use of helium ion microscopes (HIM) with nano-scaled focused ion beam spot sizes also allows for precision nano-patterning of the diamond surface through post-exposure selective etching of the generated graphitic phase. It is observed that ⟨123⟩ orientation was notably more sensitive to ion irradiation as sp3 bonds transition to sp2 bonds at lower fluence compared to other orientations. In situ uniaxial compression of SC diamond micro-pillars revealed the strength of ⟨123⟩-oriented pillars is strongly dependent on the ion fluence, and thus is tunable by ion irradiation. Notably, ⟨100⟩-oriented pillars exhibit a better damage resistance as a small strength degradation due to its higher ion channeling efficiency. The irradiation damage of energetic helium ions on the structure and strength of diamond is therefore highly orientation-dependent.
High-Temperature In situ Deformation of GaAs Micro-pillars: Lithography Versus FIB Machining, Ming Chen, Juri Wehrs, Johann Michler, Jeffrey M Wheeler, JOM, Volume 68, Issue 11, Pages 2761-2767 (2020). The plasticity of silicon-doped GaAs was investigated between 25°C and 400°C using microcompression to prevent premature failure by cracking. Micropillars with diameters of ~2.5 μm were fabricated on a ⟨100⟩-oriented GaAs single crystal by means of both conventional lithographic etching techniques and focused ion beam machining and then compressed in situ in the scanning electron microscope (SEM). A transition in deformation mechanisms from partial dislocations to perfect dislocations was found at around 100°C. At lower temperatures, the residual surface layer from lithographic processing was found to provide sufficient constraint to prevent crack opening, which resulted in a significant increase in ductility over FIB-machined pillars. Measured apparent activation energies were found to be significantly lower than previous bulk measurements, which is mostly attributed to the silicon dopant and to a lesser extent to the size effect.