Advanced Materials

The cover shows a silver patchy particle produced via a template-free one-pot colloidal route (Communication by Bao et al., p. 2644) developed within the Cluster of Excellence “Engineering of Advanced Materials” (University of Erlangen-Nuremberg, Germany). Such asymmetric particles are synthesized into blueprints generated by topology optimization techniques with the aim to design advanced “heat management” pigments, which scatter near-infrared radiation whilst being transparent to visible light. Contributions from theory to the design of colorant particles are discussed in the Progress Report by Klupp Taylor et al. (p. 2554). Image: Chenting Tian/Robin Klupp Taylor/Gerd Beck

The FEI Titan³ 80–300, a world-class transmission electron microscope (TEM) purchased by the Cluster of Excellence “Engineering of Advanced Materials” (EAM) at the University of Erlangen-Nuremberg, offers significant advantages for the analysis of materials at the atomic scale. The inside cover shows a high-resolution TEM image of a tin-doped indium oxide nanoparticle, a fundamental building block of transparent electrodes in printable electronic devices being developed at EAM. Due to its aberration-corrected electron optics and suite of analytical tools the Titan³ microscope can reveal, in unprecedented clarity, the internal atomic structure of such nanoparticles, as well as structural and compositional details of particle surfaces, coatings and contact points, key issues in several EAM projects. Image: Erdmann Spiecker/Gerd Beck.

In hybrid plasmonic-photonic crystals the metal and dielectric components are spatially separated in order to preserve their individual properties, but positioned in close vicinity to each other to warrant their efficient interaction. This design approach broadens the functionality of hybrid materials by relying on different resonance mechanisms for light transfer and ensures wide tuneability of the optical properties. These topics are explored in the Review by Romanov et al. (p. 2515).

Inhybrid plasmonic-photonic crystals the metal and the dielectric components are spatially separated in order to preserve their individual properties, but they are positioned in close vicinity to each other to warrant their efficient interaction. This design approach extends the functionality of hybrid crystals by relaying on different resonance mechanisms in light transfer and ensures wide tuneability of the hybrid's optical properties.

Carbon nanotubes and graphene are outstanding materials of the 21st century with a broad spectrum of potential applications. However, major challenges are faced such as the intrinsically low solubility of these carbon allotropes. A promising approach to overcome this hurdle is non-covalent functionalization, which is summarized in the Progress Report by Backes et al. on p. 2588, with a special focus on the interaction of the carbon nanomaterials with perylene bisimide based surfactants.

Minkowski tensors are a novel method to quantify morphology and anisotropy of complex materials. These robust shape indices are relevant for structure-property relationships of tensor-valued or orientation-dependent physical properties. An introduction to Minkowski tensors is given and illustrated by applications to SFM images of copolymeric films, tomography of open-cells foams, and of granular matter, defect detection in simulations of copper and orientation-correlations in cellular partitions.

Particle-based colorants are ubiquitous materials of the modern world. Many are the result of exhaustive empirical experimentation. At the same time, fundamental theoretical understanding of the influence of nanostructure on optical properties has been developed. This Progress Report gives an overview of the structure–property relationship of particle-based colorants and indicates how it is being inverted in order to design enhanced and multifunctional materials.

Materials that make use of thin ionic liquid (IL) films as functional layers open up new possibilities in heterogeneous catalysis. We review recent progress towards an understanding of such systems at the microscopic level using a surface science type of approach, with a special focus on model systems for supported ionic liquid phase (SILP) and solid catalysts with ionic liquid layer (SCILL) materials.

Noncovalent functionalization of sp² carbon allotropes by designed π-surfactants constitutes a highly feasible and versatile route for solubilization and tailoring of surface properties by supramolecular self-assembly. In this regard the potential of perylene bismides as novel substance class to provide an exceptional anchor unit is outlined.

Hierarchical zeolitic materials have attractive properties, such as superior mass/heat transfer characteristics, lower restriction of the diffusion of the reactants in the mesopores, and low pressure drop. Our Progress Report provides general information about the recent advances in the preparation and characterization of hierarchical zeolitic structures combining two (e.g., micro–meso, micro–macro) or even three (micro–meso–macro) levels of porosity.

The preparation of hierarchical large-pore cage-type periodic mesoporous organosilicas is reported in a Communication by Zhou et al. (on p. 2627). The hydrophobicity and structure of these novel materials are benefi cial for lipase entrapment and provide signifi cantly enhanced activity and stability compared to the native enzyme.

Ionic liquids (ILs), such as [BMIM][Tf₂N], on well-defined SCILL model catalysts are able to replace weakly adsorbed CO. On Pt, on-top CO remains adsorbed under the ionic liquid layer, but its IR signal red-shifts by over 30 cm⁻¹. IL–adsorbate interactions are mediated by the noble metal and similar to ligands.

Intrinsically strong avidin-neutravidin bonds can exhibit ultraweak adhesion mediated by transiently bound domains and can undergo a transition to a stable strong adhesion by locally increasing bond density.

A group of hierarchically ordered PMOs with large cage-like pores are prepared with organosilica units including ethylene, ethenylene, and phenylene-bridged silanes. The structure and hydrophobicity of these materials are shown to offer significant advantages for the physical adsorption of lipase from aqueous media and also markedly enhance its activity.

The dependence of linear-elastic prop­erties on effective density is studied for porous network solids, by voxel-based finite element methods. The same dependence is found for solid structures derived from Poisson-Voronoi processes and from confocal microscopy images of collagen scaffolds. We recover the power-law for the bulk modulus for low densities and suggest a functional form for the cross-over to a high-density porous solid.

Adsorption of PTCDI induces a bandgap opening on graphene, due to the specific electronic structure of PTCDI, characterized by a LUMO energetically located in the vicinity of the Dirac point. The approach is highly versatile for bandgap engineering, tuning the bandgap by modifying the adsorption geometry, the active adsorbate coverage, or by chemical modifications of the adsorbate.

The one-pot synthesis of patchy particles with morphologically tunable optical properties by the heterogeneous nucleation and growth of silver onto colloidal silica particles is described. Heat treatment of the silica and coating reaction conditions can be optimized in order to produce full yields of patchy particles. Dissolution of the cores leads to stable silver cages.

The optimization and manufacturing of an auxetic structure is presented. An inverse homogenization method is used to obtain the optimized geometry shown in the figure. The resulting structure is then produced using selective electron beam melting. The numerically predicted properties are experimentally verified.

X-ray imaging is an established tool for materials characterization even though it usually has the drawback of not being a quantitative method. This drawback can be overcome by energy-sensitive X-ray imaging methods such as the basis material decomposition method presented in this paper, which can provide quantitative results for materials characterization.

Various nanostructures are directly written by electron-beam-induced deposition using dimethyl-gold(III)-acetylacetonate as the precursor gas. After purification, their potential applications include plasmonic devices and metamaterials. Carbon contamination of the as-written structures can be completely removed by low-temperature ozone treatment, leaving polycrystalline pure gold structures (see figure). This treatment reduces the size of the nanostructures but does not substantially alter their functional shape.

Micro-structured materials with a negative Poisson ratio are termed auxetic. In a Research News (p. 2669), Mitschke et al. demonstrate how the geometric analysis of periodic tessellations or tilings can help identify novel auxetic material designs. At least some of the tessellations that are auxetic in a “skeletal structure” model are also auxetic when realized as a linear-elastic cellular structure, produced for example by selective electron beam melting. ADMA23-22-23-Frontispice.indd 3 6/9/11 1:56:44 AM

Accumulative roll bonding (ARB) is a very attractive process for processing nanostructured materials and composites with tailored properties in large quantities. Strengthening with nanoparticles is a very promising way to improve the properties and accelerate grain refining during the severe plastic deformation process. Graded Al laminates have been produced by combining different Al alloys to obtain composites with optimized properties, i.e., high strength and good surface quality.

Tessellations or tilings can be exploited as designs for regular cellular solids. By a search of several classes of planar tessellations, a novel auxetic structure is found, with Poisson's ratio ν_ss = −1 when realized as a skeletal structure of stiff struts, and ν_{LE ≈} −0.75 when realized as a linear-elastic cellular structure, by selective electron beam melting.

The development of up-conversion (UC)materials, that is, phosphors doped with rare-earth (RE) ions, is reviewed, in particular recent progress for solar cell applications New trends in RE-ion-doped phosphors from the authors’ lab at the University of Erlangen–Nürnberg, among them trivalent RE-ion-doped UC materials for organic solar cell applications, are also discussed.

Pressure-assisted melt-infiltration of magneto-optical (MO) glasses into microcapillaries or photonic crystal fibers (PCFs) enables straightforward generation of very complex waveguide architectures from unusual combinations of glasses. This promises not only the implementation of as-to-yet-unsuited but strongly magnetoactive glass candidates into MO fiber waveguides, but also the fabrication of MO PCFs.

Recent developments of self-assembled monolayer (SAM) applications in organic electronic devices, are described, following the increasing complexity of molecules and applications. The applications range from simple supporting layers, functional device mono- and multilayers (top in figure), and multifunctional device layers (bottom left) to the new trend of mixed monolayers (bottom right).