Aromatic‐Diimide‐Based n‐Type Conjugated Polymers for All‐Polymer Solar Cell Applications

All‐polymer solar cells (all‐PSCs) have attracted immense attention in recent years due to their advantages of tunable absorption spectra and electronic energy levels for both donor and acceptor polymers, as well as their superior thermal and mechanical stability. The exploration of the novel n‐type conjugated polymers (CPs), especially based on aromatic diimide (ADI), plays a vital role in the further improvement of power conversion efficiency (PCE) of all‐PSCs. Here, recent progress in structure modification of ADIs including naphthalene diimide (NDI), perylene diimide (PDI), and corresponding derivatives is reviewed, and the structure–property relationships of ADI‐based CPs are revealed.     

Monitoring Nanocrystal Self‐Assembly in Real Time Using In Situ Small‐Angle X‐Ray Scattering

Self‐assembled nanocrystal superlattices have attracted large scientific attention due to their potential technological applications. However, the nucleation and growth mechanisms of superlattice assemblies remain largely unresolved due to experimental difficulties to monitor intermediate states. Here, the self‐assembly of colloidal PbS nanocrystals is studied in real time by a combination of controlled solvent evaporation from the bulk solution and in situ small‐angle X‐ray scattering (SAXS) in transmission geometry. For the first time for the investigated system a hexagonal closed‐packed (hcp) superlattice formed in a solvent vapor saturated atmosphere is observed during slow solvent evaporation from a colloidal suspension. The highly ordered hcp superlattice is followed by a transition into the final body‐centered cubic superlattice upon complete drying. Additionally, X‐ray cross‐correlation analysis of Bragg reflections is applied to access information on precursor structures in the assembly process, which is not evident from conventional SAXS analysis. The detailed evolution of the crystal structure with time provides key results for understanding the assembly mechanism and the role of ligand–solvent interactions, which is important both for fundamental research and for fabrication of superlattices with desired properties.     

Scaffold‐Free Liver‐On‐A‐Chip with Multiscale Organotypic Cultures

The considerable advances that have been made in the development of organotypic cultures have failed to overcome the challenges of expressing tissue‐specific functions and complexities, especially for organs that require multitasking and complex biological processes, such as the liver. Primary liver cells are ideal biological building blocks for functional organotypic reconstruction, but are limited by their rapid loss of physiological integrity in vitro. Here the concept of lattice growth used in material science is applied to develop a tissue incubator, which provides physiological cues and controls the 3D assembly of primary cells. The cues include a biological growing template, spatial coculture, biomimetic radial flow, and circulation in a scaffold‐free condition. The feasibility of recapitulating a multiscale physiological structural hierarchy, complex drug clearance, and zonal physiology from the cell to tissue level in long‐term cultured liver‐on‐a‐chip is demonstrated. These methods are promising for future applications in pharmacodynamics and personal medicine.     

PM‐Composites with Nickel‐Titanium Shape Memory Alloys

Starting from NiTi‐powders, composites of nickel‐titanium shape memory alloys (NiTi‐SMA) and different stainless steels as well as of different NiTi‐SMAs were produced by using the process of hot isostatic pressing (HIP). Metallographic investigations focussed on the interface between NiTi‐SMA and stainless steel with special emphasis placed on the characterization of the typical structure of the diffusion zones in both components.     

Nutzung von Low‐Transformation‐Temperature‐Werkstoffen (LTT) zur Eigenspannungsreduzierung im Elektronenstrahlschweißprozess

Low‐Transformation‐Temperature materials (LTT) were designed to reduce delay as well as residual tensile stress in welds on carbon‐manganese steels. Using the volume expansion effect during a martensitic transformation these materials counteract the volume shrinkage during cooling. While this positive effects on residual stress relief by Low‐Transformation‐Temperature‐alloys has been proven in various studies, these alloys have always been used in large volumes as additional filler material in electric arc welding processes. Modular heat fields initiated by an electron‐beam‐welding‐process offers the potential of a time‐activated initiation of compressive stresses triggered by phase transformation of Low‐Transformation‐Temperature‐alloys. Developing a technology able to reduce residual stress and thus the deformation of complex welded components is the aim. The first approach of Low‐Transformation‐Temperature‐material used in the electron beam process and its behaviour is presented here.     

The influence of low‐plasticity burnishing process on the fatigue life of friction‐stir‐processed Al 7075‐T6 samples

The effects of low‐plasticity burnishing (LPB) on the fatigue life of friction‐stir‐processed (FSP) Al 7075‐T6 plates were examined experimentally and numerically. Aluminum samples were taken from plates to test fatigue response in the presence of heat‐affected zone (HAZ) at different loading magnitudes. Finite element method was employed to numerically evaluate fatigue life of FSPed samples by means of the Smith–Watson–Topper (SWT) model. Through numerical analysis, the FSP and its cooling procedure were modelled on the basis of the arbitrary Lagrangian–Eulerian technique, and then, the effect of the LPB to assess fatigue response of samples was examined. Aluminum samples undergoing friction‐stir process presented lower‐fatigue life as stresses were highly concentrated within FSP regions. Involvement of LPB regained fatigue durability through compressive residual stress induced on the aluminum samples. The higher applied force over the LPB promoted compressive residual stress on the sample surface and improved fatigue life of samples. The predicted life results were found twice more in magnitude than those of experimentally obtained.     

Austrittsarbeitsanalyse von GaN basierten Lateral Polarity Strukturen durch Auger‐Elektronen‐Energie‐Messungen

Work Function Analysis of GaN‐based Lateral Polarity Structures by Auger Electron Energy Measurements Lateral polarity heterostructure (LPH) were grown with adjacent Ga‐ and N‐face domains in order to invert the polarity of the crystal within a periodicity of a few microns. In this study we focus on the analysis of these LPH by Auger electron spectroscopy (AES). Because of the relationship between the Auger electron energy and the Fermi level, AES is a suitable method to identify the domains of a lateral polarity heterostructure. In addition, we discuss the possibility of determining the work function difference of Ga‐ and N‐face GaN. This difference in the work function between Ga‐face and N‐face GaN is found to be 0.25 eV. This difference is caused by a surface band bending.