Watching Ions Move: Scanning Probe Microscopy on Perovskite Solar Cells

Engineering von Proteinen an Oberflächen: Von komplementärer Charakterisierung zu Materialoberflächen mit maßgeschneiderten Funktionen

Preparation and Photochemistry of Dendrimers with Isolated Stilbene Chromophores

In addition to the model compounds 4a and 4b, the dendrimers 11 and 14 with trans-stilbene chromophores in the core and on the periphery of the dendrons were prepared and their photochemistry was studied in solution and in neat films. Due to the flexibility of the arms, intramolecular and intermolecular CC bonds are formed on irradiation. Thus, the generation of nanoparticles, which represent small oligomers, is much more likely than for the cross-linking of rigid, cross-conjugated stilbenoid dendrimers. The photoreactions in solution were studied by UV and NMR spectroscopy, the transformation of the films was studied by AFM. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 200…

Removal of Surface Oxygen Vacancies Increases Conductance Through TiO(2) Thin Films for Perovskite Solar Cells

[Image: see text] We report that UV–ozone treatment of TiO(2) anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV–ozone-treated TiO(2) anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO(2) anatase thin films results in a 2% increase of the average power conversion efficiency (PCE) of methylammonium lead iodide-based perovskite solar cells. PCE values up to 19.5% for mesoporous solar cells are realized. The additional UV–ozone treatment results in a reduced number of oxygen…

Two-Dimensional Aggregation of Organogelators Induced by Biaxial Hydrogen-Bonding Gives Supramolecular Nanosheets

Light-induced charge separation in a donor–chromophore–acceptor nanocomposite poly[TPA-Ru(tpy)2]@ZnO

The synthesis and characterisation of a new donor–chromophore–acceptor system based on poly(vinyltriphenylamine) as the electron donor and a glycine-functionalised bis(2,2′;6′,2′′-terpyridine)ruthenium(II) complex acting both as a chromophore and as an anchor group attached to ZnO nanorods as the electron acceptor are described. The TPA-containing block copolymer was synthesised by Reversible Addition Fragmentation Chain Transfer (RAFT) polymerisation and the ruthenium complex glycine conjugates prepared by Solid Phase Peptide Synthesis (SPPS) were attached via post-polymerisation esterification. GPC, NMR, IR and UV-Visible spectroscopy were used to characterise the multifunctional chromoph…

Nanowear on Polymer Films of Different Architecture

In this paper, we describe atomic force microscope (AFM) friction experiments on different polymers. The aim was to analyze the influence of the physical architecture of the polymer on the degree and mode of wear and on the wear mode. Experiments were carried out with (1) linear polystyrene (PS) and cycloolefinic copolymers of ethylene and norbornene, which are stabilized by entanglements, (2) mechanically stretched PS, (3) polyisoprene-b-polystyrene diblock copolymers, with varying composition, (4) brush polymers consisting of a poly(methyl methacrylate) (PMMA) backbone and PS side chains, (5) PMMA and PS brushes grafted from a silicon wafer, (6) plasma-polymerized PS, and (7) chemically c…

Engineering Proteins at Interfaces: From Complementary Characterization to Material Surfaces with Designed Functions

Abstract Once materials come into contact with a biological fluid containing proteins, proteins are generally—whether desired or not—attracted by the material's surface and adsorb onto it. The aim of this Review is to give an overview of the most commonly used characterization methods employed to gain a better understanding of the adsorption processes on either planar or curved surfaces. We continue to illustrate the benefit of combining different methods to different surface geometries of the material. The thus obtained insight ideally paves the way for engineering functional materials that interact with proteins in a predetermined manner.

Hydrogen peroxide sensors for cellular imaging based on horse radish peroxidase reconstituted on polymer-functionalized TiO2 nanorods

We describe the reconstitution of apo-horse radish peroxidase (apo-HRP) onto TiO2 nanorods functionalized with a multifunctional polymer. After functionalization, the horse radish peroxidase (HRP) functionalized TiO2 nanorods were well dispersible in aqueous solution, catalytically active and biocompatible, and they could be used to quantify and image H2O2 which is a harmful secondary product of cellular metabolism. The shape, size and structure of TiO2 nanorods (anatase) were analyzed by transmission electron microscopy (TEM), high resolution TEM (HRTEM), electron diffraction (ED) and X-ray diffraction (XRD). The surface functionalization, HRP reconstitution and catalytic activity were con…

Rupture Force of Single Small Drug Molecule Binding a Split Aptamer

Aptamers are specific oligonucleotides (DNA or RNA) which bind small inorganic or organic molecules, large proteins or cells. In particular, the high affinity of aptamers is expected to lead to a new class of therapeutic reagents. Thus the detection and characterization of binding strength of small molecules is important for drug and medical research. Atomic force spectroscopy (AFS) with a force resolution in the piconewton range is a valuable tool for studying interactions on a single molecular level. The detection of very small target molecules less than 500 Dalton is characterized by only a few hydrogen interactions between the aptamer and the target molecules. Thus tiny rupture forces w…

Synthesis, characterization, and hierarchical organization of tungsten oxide nanorods: spreading driven by Marangoni flow.

Tungsten oxide nanorods were synthesized by a soft chemistry approach using tungsten alkoxide and trioctyl amine and oleic acid as the surfactants. The optical properties of the nanorods were studied. The nanorods were found to be soluble in a wide range of solvents like chloroform, cyclohexane, and so on. Upon solvent evaporation, the nanorods formed hierarchically organized solid state structures. Depending on the solvent used, the nanorods organized in different mesostructures. Moreover, the organization of the nanorods from mixtures of polar and nonpolar solvents was studied. Here, the Marangoni effect resulting from differences in the surface tensions of the two solvents was found to p…

Local Current Imaging through TiO2 Thin Films

Surface Coatings Based on Polysilsesquioxanes: Solution-Processible Smooth Hole-Injection Layers for Optoelectronic Applications

Optoelectronic devices usually consist of a transparent conductive oxide (TCO) as one electrode. Interfacial engineering between the TCO electrode and the overlying organic layers is an important method for tuning device performance. We introduce poly(methylsilsesquioxane)-poly(N,N-di-4-methylphenylamino styrene) (PMSSQ-PTPA) as a potential hole-injection layer forming material. Spin-coating and thermally induced crosslinking resulted in an effective planarization of the anode interface. HOMO level (-5.6 eV) and hole mobility (1 × 10(-6)  cm(2)  · Vs(-1) ) of the film on ITO substrates were measured by cyclovoltammetry and time-of-flight measurement demonstrating the hole injection capabili…

Adaptive Wetting-Adaptation in Wetting

Many surfaces reversibly change their structure and interfacial energy upon being in contact with a liquid. Such surfaces adapt to a specific liquid. We propose the first order kinetic model to describe dynamic contact angles of such adaptive surfaces. The model is general and does not refer to a particular adaptation process. The aim of the proposed model is to provide a quantitative description of adaptive wetting and to link changes in contact angles to microscopic adaptation processes. By introducing exponentially relaxing interfacial energies and applying Young's equation locally, we predict a change of advancing and receding contact angles depending on the velocity of the contact line…

Enzyme-Mediated Deposition of a TiO2Coating onto Biofunctionalized WS2 Chalcogenide Nanotubes

A chemically specific and facile method for the biofunctionalization of WS2 nanotubes (NT-WS2) is reported. The covalent modification strategy is based on the affinity of the nitrilotriacetic acid (NTA) side chain, which serves as a ligand for the surface binding to NT-WS2 and simultaneously as an anchor group for the binding of His-tagged proteins to the polymer backbone. The polymer functionalized WS2 nanotubes can be solubilized either in water or organic solvents; they are stable for at least one week. The probes were characterized by FT-IR and UV-vis spectroscopy. The immobilization of silicatein, a hydrolytic protein encountered in marine sponges, was visualized by scanning force micr…

Measuring single small molecule binding via rupture forces of a split aptamer.

The rupture force of a split (bipartite) aptamer that forms binding pockets for adenosine monophosphate (AMP) was measured by atomic force spectroscopy. Changes in the rupture force were observed in the presence of AMP, while this effect was absent when mutant aptamers or inosine were used. Thus, changes in the rupture force were a direct consequence of specific binding of AMP to the split aptamer. The split aptamer concept allowed the detection of nonlabeled AMP and enabled us to determine the dissociation constant on a single-molecule level.

Stability of a Split Streptomycin Binding Aptamer

Here we investigated the stability of an aptamer, which is formed by two RNA strands and binds the antibiotic streptomycin. Molecular dynamics simulations in aqueous solution confirmed the geometry and the pattern of hydrogen bond interactions that was derived from the crystal structure (1NTB). The result of umbrella sampling simulations indicated a favored streptomycin binding with a free energy of ΔGbind° = −101.7 kJ mol–1. Experimentally, the increase in oligonucleotide stability upon binding of streptomycin was probed by single-molecule force spectroscopy. Rate dependent force spectroscopy measurements revealed a decrease in the natural off-rate (koff-COMPLEX = 0.22 ± 0.16 s–1) for the …

Photoinduced Charge Separation of Self-Organized Semiconducting Superstructures Composed of a Functional Polymer-TiO2 Hybrid

Redox active polymers with phenothiazine moieties for nanoscale patterning via conductive scanning force microscopy

Redox active polymers with phenothiazine moieties have been synthesized by Atomic Transfer Radical Polymerization (ATRP). These novel polymers reveal bistable behaviour upon application of a bias potential above the oxidation threshold value. Using conductive Scanning Force Microscopy, two distinguishable conductivity levels were induced on a nanoscale level. These levels were related to a high conducting “On” and a low conducting “Off” state. The “On” state is generated by the oxidation of the phenothiazine side chains to form stable phenothiazine radical cations. The formation and stability of the radical sites was examined by cyclic voltammetry, electron spin resonance and optical spectr…

Electrodeposition of ZnO nanorods on opaline replica as hierarchically structured systems

We present a new method to prepare hierarchical structures by using ZnO replica and ZnO-coated PMMA opals as electrodes in an electrodeposition process of ZnO nanorods. Depending on the approach the nanorods can be either grown exclusively on top of the replica or inside the replica structures. Therefore two types of systems are accessible: 3D photonic crystals with a hierarchically structured surface consisting of nanorods and macroporous ZnO structures with an increased surface area.

Chemical Mimicry: Hierarchical 1D TiO2@ZrO2 Core−Shell Structures Reminiscent of Sponge Spicules by the Synergistic Effect of Silicatein-α and Silintaphin-1

In nature, mineralization of hard tissues occurs due to the synergistic effect of components present in the organic matrix of these tissues, with templating and catalytic effects. In Suberites domuncula, a well-studied example of the class of demosponges, silica formation is mediated and templated by an axial proteinaceous filament with silicatein-α, one of the main components. But so far, the effect of other organic constituents from the proteinaceous filament on the catalytic effect of silicatein-α has not been studied in detail. Here we describe the synthesis of core-shell TiO(2)@SiO(2) and TiO(2)@ZrO(2) nanofibers via grafting of silicatein-α onto a TiO(2) nanowire backbone followed by …

Mechanical Properties of Single Molecules and Polymer Aggregates

This chapter deals with the mechanical properties of single polymer chains, aggregates, and supramolecular complexes. The topics discussed cover a broad range from fundamental statistical mechanics of the equilibrium elastic properties of single polymer chains to details of the behavior of binding pockets in biomolecular assemblies as observed by force spectroscopy. The first section treats the equilibrium mechanical properties of single polymer chains in various environments, investigated via extensive simulations employing coarse-grained models that have proven extremely successful in many branches of polymer physics, namely the bond-fluctuation model and the self-avoiding walk model. Apa…

Mapping of local conductivity variations on fragile nanopillar arrays by scanning conductive torsion mode microscopy.

A gentle method that combines torsion mode topography imaging with conductive scanning force microscopy is presented. By applying an electrical bias voltage between tip and sample surface, changes in the local sample conductivity can be mapped. The topography and local conductivity variations on fragile free-standing nanopillar arrays were investigated. These samples were fabricated by an anodized aluminum oxide template process using a thermally cross-linked triphenylamine-derivate semicondcutor. The nanoscale characterization method is shown to be nondestructive. Individual nanopillars were clearly resolved in topography and current images that were recorded simultaneously. Local current−…

Humidity-Induced Grain Boundaries in MAPbI3 Perovskite Films

Methylammonium lead halide perovskites (MAPbI3) are very sensitive to humid environments. We performed in situ scanning force microscopy and in situ X-ray diffraction measurements on MAPbI3 films to track changes in the film morphology and crystal structure upon repeated exposure to a high relative humidity environment (80%). We found that the appearance of monohydrate (MAPbI3·H2O) Bragg reflections coincided with the appearance of additional grain boundaries. Prolonging the exposure time to humidity induced more grain boundaries and steps in the MAPbI3 films, and the peak intensities of the monohydrate MAPbI3·H2O increased. The monohydrate was not stable under dry atmosphere and could be r…

Vitamin C Loaded Polyethylene: Synthesis and Properties of Precise Polyethylene with Vitamin C Defects via Acyclic Diene Metathesis Polycondensation

A polyethylene-like polymer with an in-chain vitamin C group was synthesized by olefin metathesis polymerization. Here, we describe both the synthesis and a comprehensive physical characterization. Because of the olefin metathesis synthesis, the vitamin C groups are equidistantly arranged in the polyethylene (PE) main chain. Their separation was adjusted to 20 CH2 units. After hydrogenation, a semicrystalline polymer is obtained that is soluble in polar solvents. Because of its size and steric effect, the vitamin C acts as a chain defect, which is expelled from the crystal lattice, yielding a lamellar crystal with a homogeneous thickness corresponding to the interdefect distance. The physic…

Local Time-Dependent Charging in a Perovskite Solar Cell

Efficient charge extraction within solar cells explicitly depends on the optimization of the internal interfaces. Potential barriers, unbalanced charge extraction, and interfacial trap states can prevent cells from reaching high power conversion efficiencies. In the case of perovskite solar cells, slow processes happening on time scales of seconds cause hysteresis in the current-voltage characteristics. In this work, we localized and investigated these slow processes using frequency-modulation Kelvin probe force microscopy (FM-KPFM) on cross sections of planar methylammonium lead iodide (MAPI) perovskite solar cells. FM-KPFM can map the charge density distribution and its dynamics at intern…

Growth of fibrous aggregates of silica nanoparticles: Fibre growth by mimicking the biogenic silica patterning processes

We describe the self-assembly of discrete SiO2 nanofibers via grafting of silicatein side chains to a polymer backbone. The covalent binding of silicatein to the backbone of the polymer is based on the affinity of the nitrilotriacetic acid (NTA) side chain, which serves as a ligand for the immobilization of His-tagged silicatein. The surface charge and the bulkiness of the protein moieties prevent the entropically favoured coil formation of the polymer and force it to adopt an open chain structure after hydrolysis of the silica precursors. The probes were characterized by scanning force microscopy (SFM) and optical light microscopy. Surface complexation of the resulting silica nanoparticles…

Ferroelastic Fingerprints in Methylammonium Lead Iodide Perovskite

Methylammonium lead iodide (MAPbI3) perovskite shows an outstanding performance in photovoltaic devices. However, certain material properties, especially the possible ferroic behavior, remain unclear. We observed distinct nanoscale periodic domains in the piezoresponse of MAPbI3(Cl) grains. The structure and the orientation of these striped domains indicate ferroelasticity as their origin. By correlating vertical and lateral piezoresponse force microscopy experiments performed at different sample orientations with X-ray diffraction, the preferred domain orientation is suggested to be the a1–a2-phase. The observation of these ferroelastic fingerprints appears to strongly depend on the film t…

Temperature dependence of surface reorganization characteristics of amphiphilic block copolymer in air and in water studied by scanning force microscopy

We have investigated the surface reorganization characteristics of a novel amphiphilic diblock copolymer, poly(acetic acid-2-(2-(4-vinyl-phenoxy)-ethoxy)-ethylester)-block-polystyrene (PAEES-b-PS), in response to varying interfaces from air to water and vice-versa at various temperatures. The surface reorganization characteristics of the block copolymer films was monitored by scanning force microscopy, in order to delineate the kinetically controlled morphological process of surface reorganization of a diblock copolymer, with a particular emphasis on the phase contrast signal which allowed the determination of local composition patterns of PAEES-b-PS at the surface. Upon heating a water-an…

Self-cleaning antimicrobial surfaces by bio-enabled growth of SnO2 coatings on glass.

Conventional vapor-deposition techniques for coatings require sophisticated equipment and/or high-temperature resistant substrates. Therefore bio-inspired techniques for the fabrication of inorganic coatings have been developed in recent years. Inspired by the biology behind the formation of the intricate skeletons of diatoms orchestrated by a class of cationic polyamines (silaffins) we have used surface-bound spermine, a naturally occurring polyamine, to promote the fast deposition of homogeneous, thin and transparent biomimetic SnO2 coatings on glass surfaces. The bio-enabled SnO2 film is highly photoactive, i.e. it generates superoxide radicals (O2˙(-)) upon sunlight exposure resulting i…

Pulicaria glutinosa plant extract: a green and eco-friendly reducing agent for the preparation of highly reduced graphene oxide

The environmentally friendly synthesis of nanomaterials using green chemistry has attracted tremendous attention in recent years due to its easy handling, low cost, and biocompatibility. Here we demonstrate a facile and efficient route for the synthesis of highly reduced graphene oxide (PE-HRG) by the green reduction of graphene oxide (GRO) using the Pulicaria glutinosa plant extract (PE). The phytomolecules present in the P. glutinosa extract are not only responsible for the reduction of GRO, but also for the functionalization of the surface of the PE-HRG nanosheets and stabilize them in various solvents, thereby limiting the use of any other external and harmful chemical reductants and su…

Hockeypuck-Micellen aus Oligo(p-benzamid)-b-PEG-Stab-Knäuel-Blockcopolymeren