4D Printing at the Microscale

3D printing of adaptive and dynamic structures, also known as 4D printing, is one of the key challenges in contemporary materials science. The additional dimension refers to the ability of 3D printed structures to change their properties—for example, shape—over time in a controlled fashion as the result of external stimulation. Within the last years, significant efforts have been undertaken in the development of new responsive materials for printing at the macroscale. However, 4D printing at the microscale is still in its early stages. Thus, this progress report will focus on emerging materials for 4D printing at the microscale as well as their challenges and potential applications. Hydrogels and liquid crystalline and composite materials have been identified as the main classes of materials representing the state of the art of the growing field. For each type of material, the challenges and critical barriers in the material design and their performance in 4D microprinting are discussed. Importantly, further necessary strategies are proposed to overcome the limitations of the current approaches and move toward their application in fields such as biomedicine, microrobotics, or optics.     

Core–Shell Nanoparticle Interface and Wetting Properties

Latex colloids are among the most promising materials for broad thin film applications due to their facile surface functionalization. Yet, the effect of these colloids on chemical film and wetting properties cannot be easily evaluated. At the nanoscale, core–shell particles can deform and coalesce during thermal annealing, yielding fine‐tuned physical properties. Two different core–shell systems (soft and rigid) with identical shells but with chemically different core polymers and core sizes are investigated. The core–shell nanoparticles (NPs) are probed during thermal annealing in order to investigate their behavior as a function of nanostructure size and rigidity. X‐ray scattering allows to follow the re‐arrangement of the NPs and the structural evolution in situ during annealing. Evaluation by real‐space imaging techniques reveals a disappearance of the structural integrity and a loss of NP boundaries. The possibility to fine‐tune the wettability by tuning the core–shell NPs morphology in thin films provides a facile template methodology for repellent surfaces.     

Biotic and abiotic determinants of the ascent behaviour of adult Atlantic salmon transiting passable waterfalls

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temperature, and barometric pressure) factors. The Norwegian river Numedalslågen is interrupted by natural waterfalls ranging in height from 2 to 6 m. We tagged 113 Atlantic salmon with radio transmitters in the estuary and used stationary radio telemetry stations to track fish. Ninety‐one salmon were recorded in Numedalslågen, 39 of which remained in the river for spawning. Large salmon moved farther and faster upriver but also delayed longer and had lower daily probability to pass the second waterfall. Delay below and passage probability at the final, largest waterfall was affected by water discharge, wherein passage occurred when discharge was declining. Barometric pressure also influenced daily probability of ascent, albeit in opposite directions for each waterfall. Importantly, we also found that salmon with surgically implanted radio transmitters moved farther upriver on average and delayed less time below one of the waterfalls than those with externally attached transmitters. Although there is variance in timing arising from individual decision‐making, we showed that natural waterfalls delay progress of Atlantic salmon on their spawning migration and that both biotic (i.e., size) and abiotic (i.e., barometric pressure and discharge) factors influenced the salmon's decisions to pass waterfalls that they encounter.     

Human factors methods for early evaluation of control room systems – guidelines for use in practice

Formative human factors (HF) evaluation is an important activity in control room design. Its purpose is to provide design feedback in the development process, preferably early so as to lower the risk of late and sub-optimal design changes. Early evaluation requires assessment of higher level design decisions due to the gradual specificity of design decisions made as the development process progresses. There is also a need to further develop HF methods that are applicable in practice. The purpose of this article is to seek understanding of, and base guidelines on, the practical use of HF methods for formative assessment of higher level design decisions in control rooms. Evaluations in three development projects at a Swedish nuclear power plant were studied, identifying 18 method guidelines. The guidelines related to: 1) the method’s ability to define, adapt, focus and balance; 2) execution of the evaluation workshops; 3) the communicative purpose of the evaluation activity. Comparing the identified guidelines with literature showed similarities, but also highlighted unique guidelines. The compiled results can be used to further develop methods for early formative evaluation of control rooms in practice.     

Sift‐proofness of Dangerous Goods Packagings – An Incompletely Defined Requirement

Sift‐proofness is a requirement for different types of dangerous goods packagings for solid substances according to the international Dangerous Goods Regulations. In these regulations, a sift‐proof packaging is defined as a packaging that is completely impermeable to dry contents. This means indirectly that absolutely no mass transport of solid substances is allowed. Moreover, this requirement applies both to the original filling substance and to fine solid material generated during transport. Further specifications, test conditions or tolerable limit values are not given. This is in contrast to physical principles and the usual practice in other fields of technology in which sift‐proofness is relevant. This paper shows the necessary steps for how the requirements for sift‐proofness of dangerous goods packagings can be defined more precisely. Physical basics of the term ‘sift‐proofness’ are explained. A qualitative as well as a quantitative approach is possible. In any case, it is essential to carry out appropriate vibration tests to assess the sift‐proofness. There is a need for systematical investigations of the sift‐proofness of dangerous goods packagings. Copyright © 2017 John Wiley & Sons, Ltd.     

A facile co-precipitation synthesis of heterostructured ZrO<Subscript>2</Subscript>|ZnO nanoparticles as efficient photocatalysts for wastewater treatment

ZrO₂-decorated ZnO (ZrO₂|ZnO) nanoparticles (NPs) have been synthesized by a facile co-precipitation method in the presence of cetyltrimethylammonium bromide (CTAB) surfactant. The ZrO₂ amount in the NPs has been varied from 1.0, 2.0, 4.9, to 9.3% by weight. The resulting NPs are heterostructured and consist of a crystalline ZnO core (wurtzite phase) surrounded by an amorphous ZrO₂ layer. X-ray diffraction analyses support this observation. The NPs show a narrow size distribution and are slightly elongated. Compared to pure ZnO NPs, the hybrid ZrO₂|ZnO ones show enhanced photocatalytic activity toward the degradation of Rhodamine B under UV–Vis light. Such enhancement has been partly attributed to the increased amount of oxygen vacancies when ZrO₂ is incorporated into the NPs, as shown by X-ray photoelectron spectroscopy analyses.     

Quantum Confinement of Dirac Quasiparticles in Graphene Patterned with Sub-Nanometer Precision

Quantum confinement of graphene Dirac-like electrons in artificially crafted nanometer structures is a long sought goal that would provide a strategy to selectively tune the electronic properties of graphene, including bandgap opening or quantization of energy levels. However, creating confining structures with nanometer precision in shape, size, and location remains an experimental challenge, both for top-down and bottom-up approaches. Moreover, Klein tunneling, offering an escape route to graphene electrons, limits the efficiency of electrostatic confinement. Here, a scanning tunneling microscope (STM) is used to create graphene nanopatterns, with sub-nanometer precision, by the collective manipulation of a large number of H atoms. Individual graphene nanostructures are built at selected locations, with predetermined orientations and shapes, and with dimensions going all the way from 2 nm up to 1 µm. The method permits the patterns to be erased and rebuilt at will, and it can be implemented on different graphene substrates. STM experiments demonstrate that such graphene nanostructures confine very efficiently graphene Dirac quasiparticles, both in 0D and 1D structures. In graphene quantum dots, perfectly defined energy bandgaps up to 0.8 eV are found that scale as the inverse of the dot’s linear dimension, as expected for massless Dirac fermions.     

热等静压烧结制备细晶粒Ce,Y:SrHfO3闪烁陶瓷

Ce:SrHfO₃陶瓷因具有高密度和高有效原子序数, 对高能射线具有很强的阻止能力。同时, Ce:SrHfO₃陶瓷还具有快衰减和高能量分辨率等优异的闪烁性能, 引起了研究人员的广泛关注。由于传统的烧结方法难以实现非立方结构Ce:SrHfO₃陶瓷的透明化, 本研究采用真空长时烧结和短时真空预烧结合热等静压烧结(Hot Isostatic Pressing, HIP)方法制备Ce,Y:SrHfO₃陶瓷。以金属氧化物和碳酸盐为原料, 1200 ℃下煅烧8 h可以获得平均粒径为152 nm的纯相Ce,Y:SrHfO₃粉体。1800 ℃真空烧结20 h获得平均晶粒尺寸为28.6 μm的不透明的Ce,Y:SrHfO₃陶瓷, 而两步烧结法可以制备光学透过率良好的Ce,Y:SrHfO₃陶瓷。本研究详细分析了陶瓷致密化过程中微结构的演变, 探究了预烧结温度对Ce,Y:SrHfO₃陶瓷密度、显微结构和光学透过率的影响。真空预烧(1500 ℃×2 h)结合HIP后处理(1800 ℃×3 h, 200 MPa Ar)所获得的Ce,Y:SrHfO₃陶瓷在800 nm处的最高直线透过率为21.6%, 平均晶粒尺寸仅为3.4 μm。在X射线激发下, Ce,Y:SrHfO₃陶瓷在400 nm处产生Ce³⁺ 5d-4f发射峰, 其XEL积分强度比商用锗酸铋(BGO)晶体高3.3倍, Ce,Y:SrHfO₃陶瓷在1 μs门宽下的光产额约为3700 ph/MeV。良好的光学和闪烁性能可以拓宽Ce,Y:SrHfO₃陶瓷在闪烁探测领域的应用。     

A Facet‐Specific Quantum Dot Passivation Strategy for Colloid Management and Efficient Infrared Photovoltaics

Colloidal nanocrystals combine size‐ and facet‐dependent properties with solution processing. They offer thus a compelling suite of materials for technological applications. Their size‐ and facet‐tunable features are studied in synthesis; however, to exploit their features in optoelectronic devices, it will be essential to translate control over size and facets from the colloid all the way to the film. Larger‐diameter colloidal quantum dots (CQDs) offer the attractive possibility of harvesting infrared (IR) solar energy beyond absorption of silicon photovoltaics. These CQDs exhibit facets (nonpolar (100)) undisplayed in small‐diameter CQDs; and the materials chemistry of smaller nanocrystals fails consequently to translate to materials for the short‐wavelength IR regime. A new colloidal management strategy targeting the passivation of both (100) and (111) facets is demonstrated using distinct choices of cations and anions. The approach leads to narrow‐bandgap CQDs with impressive colloidal stability and photoluminescence quantum yield. Photophysical studies confirm a reduction both in Stokes shift (≈47 meV) and Urbach tail (≈29 meV). This approach provides a ≈50% increase in the power conversion efficiency of IR photovoltaics compared to controls, and a ≈70% external quantum efficiency at their excitonic peak.