A Low-Cost Apparatus for Laboratory Exercises and Classroom Demonstrations of Geometric Optics

Current trends in research towards the teaching of geometric suggest a constructivist approach. Student experimentation dealing directly with student misconceptions through repetition of examples in many contexts to confront conflicting reasoning allow students to construct definitions with their experiences and observations. Developing the scientific method of observation, prediction/experimental design, conducting experiments and repeating is reinforced with these techniques. Cataloguing student misconceptions and redesigning course material and laboratory experiments in their context has only recently begun. Use of technology has also been shown to increase student interest in course material and 3D printers have recently become common tools in schools. Additionally, experiments that lend themselves towards computer modeling are sought after as an interface to reconcile conflicting reasoning in student misconceptions. An apparatus and set of experiments is described that deal with student misconceptions in iterative experiments. Overall cost of the system is decreased by 3D printing expensive optical components. The system highlights complex interactions of propagating light waves and seeks to explain the effects of media on image formation

An Efficient, Movable Single-Particle Detector for Use in Cryogenic Ultra-High Vacuum Environments

A compact, highly efficient single-particle counting detector for ions of keV/u kinetic energy, movable by a long-stroke mechanical translation stage, has been developed at the Max-Planck-Institut f\"ur Kernphysik (Max Planck Institute for Nuclear Physics, MPIK). Both, detector and translation mechanics, can operate at ambient temperatures down to $\sim$ 10 K and consist fully of ultra-high vacuum (UHV) compatible, high-temperature bakeable and non-magnetic materials. The set-up is designed to meet the technical demands of MPIK's Cryogenic Storage Ring (CSR). We present a series of functional tests that demonstrate full suitability for this application and characterise the set-up with regard to its particle detection efficiency.Comment: 12 pages, 9 figures, version accepted for publication in Review of Scientific Instrument

Rapid Assembly of Small Materials Building Blocks (Voxels) into Large Functional 3D Metamaterials

Herein, various 3D additive manufacturing approaches are reviewed in terms of two important figures of merit: maximum voxel printing rate and minimum voxel size. Voxel sizes from several 100 µm down to the 100 nm scale are covered. Original results on multifocus two‐photon printing at around voxel printing rates of 107 voxels s−1 are presented in this context, which significantly surpass previous best values. These advances are illustrated by and applied to the making of microstructured 3D (chiral) mechanical metamaterials that are composed of more than one‐hundred‐thousand unit cells in three dimensions. Previous best values for unit cells of similar complexity are smaller by two orders of magnitude

Multi‐Photon 4D Printing of Complex Liquid Crystalline Microstructures by In Situ Alignment Using Electric Fields

An approach is presented to align the direction of liquid crystal networks or elastomers in situ during multi-photon laser printing for each voxel in three dimensions by applying a quasi-static electric field with variable orientation. This approach enables the making of 3D micro-heterostructures operating under ambient conditions that show large-amplitude elastic actuation, with temperature serving as the stimulus (“4D microstructures”). The approach involves two novelties. First, a dedicated sample cell with a variable height suitable for laser printing is introduced. It is based on optically transparent electrodes and allows to apply arbitrary electric field vectors in three dimensions, for example, parallel or normal to the substrate plane. Second, a variable optical phase plate combined with a pivotable half-wave plate warrants a single well-defined laser focus for nearly all possible quasi-static electric field vectors. Without the latter, one generally obtains two spatially separated laser foci, an ordinary and an extraordinary one, due to the optical birefringence of the medium induced by the alignment of the liquid crystal director via the applied quasi-static electric field. The versatility of the approach is illustrated by manufacturing and characterizing several exemplary architectures

Influence of alloying elements on the mechanical properties, especially fracture toughness, of the WB2-z base system

Transition metal diborides are an emerging class of thin film materials with promising properties ranging from ultra-low compressibility, high thermal stability, super hardness to superconductivity. These properties allow an application as protective coating in harsh environments. Our recent ab initio calculations suggest an attractive combination of both, high hardness and relatively high fracture toughness, for WB2. This is enabled by a stabilization of the α-structure (space group 191, AlB2-prototype, P6/mmm) over the intrinsic more stable ω-structure due to omnipresent point defects in physical vapor deposited coatings (i.e. boron and metal vacancies) [1]. However, those point defects in turn lower the thermal stability as the are affected by recovery events, leading to phase transformation into the ω-type. Further calculations point towards a stabilization of the α-type with the addition of Ta (which diboride is stabilized in the α-structure without the need of vacancies) at—compared to other transition metals investigated—low cost on ductility. Within this study we deposited various W1-xMxB2-z solid solution coatings with different alloying element contents and examined them for mechanical properties and thermal stability. It was found for M=Ta that the hardness increases ~4 GPa (from 40.8±1.5 to 45.0±2.0 GPa) together with an improvement of the thermal stability (a change of the phase transformation temperature from ~800-1000 °C to over 1400 °C was observed) [2,3]. Besides these characteristics, in various applications a certain amount of damage tolerance (crack initiation and propagation) is required to prevent premature failure. To assess this behavior, we determined the fracture toughness of these coatings by performing micromechanical experiments by means of single cantilever bending tests within the framework of specifications given by Matoy et al. and Brinckmann et al. [4–6]. At the same time of the increase in hardness and thermal stability, we observe a decrease (in agreement with our DFT calculations) in fracture toughness (from 3.7±0.3 MPaÖm for to 3.0±0.2 MPaÖm) with the addition of tantalum up to a maximum content of 26 at% on the metal sublattice. [1] V. Moraes, H. Riedl, C. Fuger, P. Polcik, H. Bolvardi, D. Holec, P.H. Mayrhofer, Sci. Rep. (2018). [2] V. Moraes, C. Fuger, V. Paneta, D. Primetzhofer, P. Polcik, H. Bolvardi, M. Arndt, H. Riedl, P.H. Mayrhofer, Scr. Mater. 155 (2018) 5–10. [3] C. Fuger, V. Moraes, R. Hahn, H. Bolvardi, P. Polcik, H. Riedl, P.H. Mayrhofer, MRS Commun. (2019) 1–6. [4] K. Matoy, H. Schönherr, T. Detzel, T. Schöberl, R. Pippan, C. Motz, G. Dehm, Thin Solid Films 518 (2009) 247–256. [5] S. Brinckmann, C. Kirchlechner, G. Dehm, Scr. Mater. 127 (2017) 76–78. [6] S. Brinckmann, K. Matoy, C. Kirchlechner, G. Dehm, Acta Mater. 136 (2017) 281–287