Orientation‐dependent nanostructuring of titanium surfaces by low‐energy ion beam erosion

Regular nanoscopic ripple and dot patterns are fabricated on poly-crystalline titanium samples by irradiation with 1.5 keV argon ions at normal incidence. The morphology of the nanostructures is investigated by scanning electron microscopy and scanning force microscopy. The ripple structures exhibit a saw-tooth cross-section profile. Electron backscatter diffraction experiments are performed to analyze the local grain structure. The study suggests a distinct correlation of the nanostructure morphology to the crystallographic orientation of the titanium surface

The mechanical response of cellular materials with spinodal topologies

The mechanical response of cellular materials with spinodal topologies is numerically and experimentally investigated. Spinodal microstructures are generated by the numerical solution of the Cahn-Hilliard equation. Two different topologies are investigated: "solid models," where one of the two phases is modeled as a solid material and the remaining volume is void space; and "shell models," where the interface between the two phases is assumed to be a solid shell, with the rest of the volume modeled as void space. In both cases, a wide range of relative densities and spinodal characteristic feature sizes are investigated. The topology and morphology of all the numerically generated models are carefully characterized to extract key geometrical features and ensure that the distribution of curvatures and the aging law are consistent with the physics of spinodal decomposition. Finite element meshes are generated for each model, and the uniaxial compressive stiffness and strength are extracted. We show that while solid spinodal models in the density range of 30-70% are relatively inefficient (i.e., their strength and stiffness exhibit a high-power scaling with relative density), shell spinodal models in the density range of 0.01-1% are exceptionally stiff and strong. Spinodal shell materials are also shown to be remarkably imperfection insensitive. These findings are verified experimentally by in-situ uniaxial compression of polymeric samples printed at the microscale by Direct Laser Writing (DLW). At low relative densities, the strength and stiffness of shell spinodal models outperform those of most lattice materials and approach theoretical bounds for isotropic cellular materials. Most importantly, these materials can be produced by self-assembly techniques over a range of length scales, providing unique scalability

Canonical Effective Subalgebras of Classical Algebras as Constructive Metric Completions

We prove general theorems about unique existence of effective subalgebras of classical algebras. The theorems are consequences of standard facts about completions of metric spaces within the framework of constructive mathematics, suitably interpreted in realizability models. We work with general realizability models rather than with a particular model of computation. Consequently, all the results are applicable in various established schools of computability, such as type 1 and type 2 effectivity, domain representations, equilogical spaces, and others

Evaluation of Mobile Phones for Large Display Interaction

Large displays have become more and more common in the last few years. While interaction with these displays can be conducted using standard methods such as computer mouse and keyboard, this approach causes issues in multi-user environments, where the various conditions for providing multiple keyboards and mice, together with the facilities to employ them, cannot be met. To solve this problem, interaction using mobile phones was proposed by several authors. Previous solutions were specialized interaction metaphors only for certain applications. To gain more insight into general interaction patterns realizable with smart phones, we created a set of general test cases using a well-known taxonomy for interactions. These test cases were then evaluated in a user study, comparing smart phone usage against the traditional keyboard/mouse-combination. Results (time and user satisfaction) show strengths and weaknesses when using the new interaction with the smart phone. With further evaluations we draw conclusions on how to improve large display interaction using smart phones in general

Humidity-Dependent Flaw Sensitivity in the Crack Propagation Resistance of 3D-Printed Nano-Ceramics

Abstract 3D-printed nano-architected ceramic metamaterials currently emerge as a class of lightweight materials with exceptional strength and stiffness. However, their application is hampered by the lack of knowledge on their mechanical reliability. Characteristics like the fracture strength and their dependency on environmental conditions are unknown. We herein present and discuss a nanoindentation pillar splitting method to measure fracture toughness, elastic modulus, and hardness of 3D-printed nano-ceramics. We show that two photon polymerization-derived pyrolytic carbon achieves improved fracture toughness over macroscopic forms of vitreous carbon, with values up to 3.1 MPam0.5. However, experiments at different humidity levels reveal that only few, nanometer-sized, surface cavities can cause embrittlement from liquid diffusion, which promotes earlier crack propagation. While comparable effects are less relevant in macro-size ceramics, this study demonstrates that reliability and durability of micro- and nano-architected ceramic metamaterials and devices requires toughening design approaches that focus on size-dependent surface effects

Reactive ion beam figuring of optical aluminium surfaces

Ultra-smooth and arbitrarily shaped reflective optics are necessary for further progress in EUV/XUV lithography, x-ray and synchrotron technology. As one of the most important technological mirror optic materials, aluminium behaves in a rather difficult way in ultra-precision machining with such standard techniques as diamond-turning and subsequent ion beam figuring (IBF). In particular, in the latter, a strong surface roughening is obtained. Hence, up to now it has not been possible to attain the surface qualities required for UV or just visible spectral range applications. To overcome the limitations mainly caused by the aluminium alloy structural and compositional conditions, a reactive ion beam machining process using oxygen process gas is evaluated. To clarify the principle differences in the effect of oxygen gas contrary to oxygen ions on aluminium surface machining, we firstly focus on chemical-assisted ion beam etching (CAIBE) and reactive ion beam etching (RIBE) experiments in a phenomenological manner. Then, the optimum process route will be explored within a more quantitative analysis applying the concept of power spectral density (PSD) for a sophisticated treatment of the surface topography. Eventually, the surface composition is examined by means of dynamic secondary ion mass spectrometry (SIMS) suggesting a characteristic model scheme for the chemical modification of the aluminium surface during oxygen ion beam machining. Monte Carlo simulations were applied to achieve a more detailed process conception

Environmental reliability and crack propagation resistance of 3d-printed ALD-coated nano-ceramics

3D-printed micro- and nano-architected ceramic metamaterials currently emerge as a class of lightweight materials with exceptional strength and stiffness. However, their application is hampered by the lack of knowledge of their mechanical reliability. Recently, the sensitivity of nano-ceramics’ crack propagation resistance to environmental conditions, triggered by the unavoidable presence of surface flaws introduced by the TPP-DLW 3D printing and pyrolization post-processing, has been evidenced [1], with a reduction of 20% in the average fracture toughness value reported at high relative humidity levels of testing ( ൐ 60%) from the generally performed low-humidity-based testing. Please click Download on the upper right corner to see the full abstract