preparation-graphene-supported-microwell-liquid-cells-for-situ

Preparation of Graphene-Supported Microwell Liquid Cells for <em>In Situ</em> Transmission Electron Microscopy

The fabrication and preparation of graphene-supported microwell liquid cells (GSMLCs) for in situ electron microscopy is presented in a stepwise protocol. ...

Friedrich-Alexander University Erlangen-Nürnberg

The multi-junction concept is the most relevant approach to overcome the Shockley-Queisser limit for single-junction photovoltaic cells. The record efficiencies of several types of solar technologies are held by series-connected tandem configurations. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Here we report a generic concept to alleviate this limitation. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. Series/parallel triple-junction cells with organic, as well as perovskite-based subcells may become a key technology to further advance the efficiency roadmap of the existing photovoltaic technologies. 

A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells.

The wing scales of the Green Hairstreak butterfly Callophrys rubi consist of crystalline domains with sizes of a few micrometers, which exhibit a congenitally handed porous chitin microstructure identified as the chiral triply periodic single-gyroid structure. Here, the chirality and crystallographic texture of these domains are investigated by means of electron tomography. The tomograms unambiguously reveal the coexistence of the two enantiomeric forms of opposite handedness: the left- and right-handed gyroids. These two enantiomers appear with nonequal probabilities, implying that molecularly chiral constituents of the biological formation process presumably invoke a chiral symmetry break, resulting in a preferred enantiomeric form of the gyroid structure. Assuming validity of the formation model proposed by Ghiradella H (1989) J Morphol 202(1):69-88 and Saranathan V, et al. (2010) Proc Natl Acad Sci USA 107(26):11676-11681, where the two enantiomeric labyrinthine domains of the gyroid are connected to the extracellular and intra-SER spaces, our findings imply that the structural chirality of the single gyroid is, however, not caused by the molecular chirality of chitin. Furthermore, the wing scales are found to be highly textured, with a substantial fraction of domains exhibiting the <001> directions of the gyroid crystal aligned parallel to the scale surface normal. Both findings are needed to completely understand the photonic purpose of the single gyroid in gyroid-forming butterflies. More importantly, they show the level of control that morphogenesis exerts over secondary features of biological nanostructures, such as chirality or crystallographic texture, providing inspiration for biomimetic replication strategies for synthetic self-assembly mechanisms. 

Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi.

The design and characterization of a new family of multifunctional scaffolds based on bioactive glass (BG) of 45S5 composition for bone tissue engineering and drug delivery applications are presented. These BG-based scaffolds are developed via a replication method of polyurethane packaging foam. In order to increase the therapeutic functionality, the scaffolds were coated with mesoporous silica particles (MCM-41), which act as an in situ drug delivery system. These sub-micron spheres are characterized by large surface area and pore volume with a narrow pore diameter distribution. The solution used for the synthesis of the silica mesoporous particles was designed to obtain a high-ordered mesoporous structure and spherical shape - both are key factors for achieving the desired controlled drug release. The MCM-41 particles were synthesized directly inside the BG-based scaffolds, and the drug-release capability of this combined system was evaluated. Moreover, the effect of MCM-41 particle coating on the bioactivity of the BG-based scaffolds was assessed. The results indicate that it is possible to obtain a multifunctional scaffold system characterized by high and interconnected porosity, high bioactivity, and sustained drug delivery capability. 

Uniform Surface Modification of 3D Bioglass(®)-Based Scaffolds with Mesoporous Silica Particles (MCM-41) for Enhancing Drug Delivery Capability.

Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Ligand-assisted thickness tailoring of highly luminescent colloidal CHNHPbX (X = Br and I) perovskite nanoplatelets.

With the recent advances in instrumentation pushing the limits of in situ transmission electron microscopy, the question of local sample temperature comes into focus again. In this work the applicability of parallel beam electron diffraction to locally measure and monitor the sample temperature in TEM is assessed, with applications for in situ heating experiments in mind. With Au nanoparticles applied to the sample surface, temperature is measured in the range from RT to 890°C by evaluating the change in scattering angle upon thermal expansion. Repeated measurements at constant temperature reveal a statistical precision of the method as good as 2.8K. The applicability to locally measure the temperature is demonstrated mapping the temperature gradient across a heating chip. Owing to instantaneous response of thermal expansion to temperature changes, the method is well suited for monitoring even quick temperature changes, as demonstrated by quenching experiments. In order to enable extensive in situ studies, an evaluation method capable of processing large datasets with high precision is developed. Beam parallelity is identified as crucial experimental prerequisite and a routine is established, optimizing the microscope alignment in terms of beam parallelity. Apart from establishing a procedure for local temperature measurement, the present work demonstrates the unique capabilities of MEMS-based in situ heating equipment.

Local temperature measurement in TEM by parallel beam electron diffraction.

We present a correlative micro-diffraction and differential phase contrast (DPC) study within scanning transmission electron microscopy (STEM) on the determination of mean inner potential (MIP) and explain the origin of subtle beam-specimen interactions at the edge of wedge-shaped crystals using both experiment and simulation. Our measurement of MIP of Si and GaAs resulted in 12.48 ± 0.22 V and 14.15 ± 0.22 V, respectively, from directly evaluating beam refraction in micro-diffraction mode. DPC-STEM measurements gave very similar values. Fresnel fringes within the diffraction disk resulting from interaction of the highly coherent electron beam with the aperture are observed and a numerical simulation scheme is implemented to reproduce the effect of the specimen on the fringe pattern. Perfect agreement between experiment and simulation has been achieved in terms of subtle displacements of the fringes upon approaching the sample edge with the electron probe. The existence of the fringes has minor effect on the DPC-STEM signal, which is well below the noise level of our setup at practically reasonable acquisition times. We suggest the possibility to perform pseudo-contactless probing of weak potential differences in beam sensitive samples by evaluating the subtle displacements of Fresnel fringes quantitatively.

Correlative micro-diffraction and differential phase contrast study of mean inner potential and subtle beam-specimen interaction.

Topological defects in crystalline solids are of fundamental interest in physics and materials science because they can radically alter the properties of virtually any material. Of particular importance are line defects, known as dislocations, which are the main carriers of plasticity and have a tremendous effect on electronic and optical properties. Understanding and controlling the occurrence and behavior of those defects have been of major and ongoing interest since their discovery in the 1930s. This interest was renewed with the advent of two-dimensional materials in which a single topological defect can alter the functionality of the whole system and even create new physical phenomena. We present an experimental approach to directly manipulate dislocations in situ on the nanometer scale by using a dedicated scanning electron microscope setup. With this approach, key fundamental characteristics such as line tension, defect interaction, and node formation have been studied. A novel switching reaction, based on the recombination of dislocation lines, was found, which paves the way for the concept of switches made of a bimodal topological defect configuration.

In situ manipulation and switching of dislocations in bilayer graphene.

Dielectric mirrors based on bilayers of polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene (SEBS) and poly(vinyl alcohol) (PVA)-zirconium dioxide (ZrO) nanocomposites are fabricated for vapor sensing. When exposed to specific solvent vapor, the layers of dielectric mirrors can gradually swell and cause a red-shift of the reflection band. Because PVA solely responds to water and SEBS is sensitive to several different types of organic solvents, the mirrors can respond to a large variety of solvents. The dual-functional hydrophilic ZrO nanoparticles are introduced to not only enlarge the refractive index contrast but also increase the permeability. Time-resolved measurements show that mirrors with nanoparticles have a significantly faster response than those without nanoparticles. Moreover, the dependence on relative humidity is studied for representative solvents, and several types of solvents are selected to show the dependence on the solvent-polymer interaction parameters at typical relative humidity, which allows one to predict the responsivity and selectivity of the sensors.

Time-Resolved Analysis of Dielectric Mirrors for Vapor Sensing.

The growth of silver shells on gold nanorods is investigated by in situ liquid cell transmission electron microscopy using an advanced liquid cell architecture. The design is based on microwells in which the liquid is confined between a thin SiN membrane on one side and a few-layer graphene cap on the other side. A well-defined specimen thickness and an ultraflat cell top allow for the application of high-resolution TEM and the application of analytical TEM techniques on the same sample. The combination of high-resolution data with chemical information is validated by radically new insights into the growth of silver shells on cetrimonium bromide stabilized gold nanorods. It is shown that silver bromide particles already formed in the stock solution play an important role in the exchange of silver ions. The Ag shell growth can be directly correlated with the layer-by-layer dissolution of AgBr nanocrystals, which can be controlled by the electron flux density via distinctly generated chemical species in the solvent. The derived model framework is confirmed by in situ UV-vis absorption spectroscopy evaluating the blue shift in the longitudinal surface plasmon resonance of anisotropic NRs in a complementary batch experiment.

Unravelling the Mechanisms of Gold-Silver Core-Shell Nanostructure Formation by in Situ TEM Using an Advanced Liquid Cell Design.

Clusters in systems as diverse as metal atoms, virus proteins, noble gases, and nucleons have properties that depend sensitively on the number of constituent particles. Certain numbers are termed 'magic' because they grant the system with closed shells and exceptional stability. To this point, magic number clusters have been exclusively found with attractive interactions as present between atoms. Here we show that magic number clusters exist in a confined soft matter system with negligible interactions. Colloidal particles in an emulsion droplet spontaneously organize into a series of clusters with precisely defined shell structures. Crucially, free energy calculations demonstrate that colloidal clusters with magic numbers possess higher thermodynamic stability than those off magic numbers. A complex kinetic pathway is responsible for the efficiency of this system in finding its minimum free energy configuration. Targeting similar magic number states is a strategy towards unique configurations in finite self-organizing systems across the scales.

Magic number colloidal clusters as minimum free energy structures.

We present the preparation and electrochemical analysis of a novel type of positive regenerative fuel cell electrode based on commercially available Ti felts with a Pt/Ir catalyst. Anodic oxidation of the Ti felts leads to the formation of a TiO nanotube layer. The high specific surface area allows for a particularly efficient utilization of the noble metal catalyst. Its loading in the nanoporous system is controlled accurately and minimized systematically by atomic layer deposition. The electrochemical activity towards water splitting of both metals is investigated in acidic media by cyclic voltammetry and steady-state electrolysis for various catalyst loadings. An optimal oxygen evolution reaction is found for a catalyst loading of 76 μg cm resulting in a mass activity of 345 A g at =0.47 V, whereas the simultaneous presence of Pt at the surface is demonstrated by X-ray photoelectron spectroscopy and by the high activity observed for the hydrogen evolution reaction.

Minimization of Catalyst Loading on Regenerative Fuel Cell Positive Electrodes Based on Titanium Felts using Atomic Layer Deposition.

A new in situ synthesis method for the growth of MoO2 nanowires via controlled thermal oxidation of MoS2 flakes is presented, going from a 2D transition metal chalcogenide to a transition metal oxide nanostructure. The wire growth is performed under an optical microscope using a heating stage with adjustable atmospheric conditions. In contrast to prevalent syntheses, this templated growth leads to highly directional wires along defined MoS2 crystallographic directions. We examine the growth kinetics of the wires in dependence of the process temperature. In the temperature regime from 650 °C to 710 °C high quality MoO2 nanowires are formed in a reaction-limited growth process with an activation energy of 596 kJ mol-1. The functional properties of the nanowires are studied by a combination of in situ electron microscopy techniques. Four point measurements in an SEM reveal outstanding metal-like behavior of the nanowires with resistivity values as low as 3.5 × 10-6 Ω m. Surprisingly, junctions between intergrown nanowires show hardly any increase in resistivity which can be attributed to the well-defined orientational relationship of the nanowires resulting from their templated growth on MoS2. Elastic properties of the nanowires are studied by complementary in situ bending and resonance measurements in SEM yielding consistent values of 383 GPa for the Young's modulus. Finally, field emission of single MoO2 nanowires is studied in situ inside the TEM, and an emission current of 500 nA is achieved. The combination of simple synthesis route with outstanding functional properties make the MoO2 nanowires promising candidates for functional devices in the field of novel 1D-oxide/2D-chalcogenide hybrids. The presented synthesis can be generalized and applied to other metal chalcogenides such as WS2, as well.

Article	Year
A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells. Nature communications\| PubMed ID: 26177808	2015
Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 26438839	2015
Uniform Surface Modification of 3D Bioglass(®)-Based Scaffolds with Mesoporous Silica Particles (MCM-41) for Enhancing Drug Delivery Capability. Frontiers in bioengineering and biotechnology\| PubMed ID: 26594642	2015
Ligand-assisted thickness tailoring of highly luminescent colloidal CHNHPbX (X = Br and I) perovskite nanoplatelets. Chemical communications (Cambridge, England)\| PubMed ID: 27928556	2016
Local temperature measurement in TEM by parallel beam electron diffraction. Ultramicroscopy\| PubMed ID: 28049586	2017
Correlative micro-diffraction and differential phase contrast study of mean inner potential and subtle beam-specimen interaction. Ultramicroscopy\| PubMed ID: 28189911	2017
Correlative micro-diffraction and differential phase contrast study of mean inner potential and subtle beam-specimen interaction. Ultramicroscopy\| PubMed ID: 28366352	2017
In situ manipulation and switching of dislocations in bilayer graphene. Science advances\| PubMed ID: 30105305	2018
Time-Resolved Analysis of Dielectric Mirrors for Vapor Sensing. ACS applied materials & interfaces\| PubMed ID: 30264555	2018
Unravelling the Mechanisms of Gold-Silver Core-Shell Nanostructure Formation by in Situ TEM Using an Advanced Liquid Cell Design. Nano letters\| PubMed ID: 30346790	2018
Magic number colloidal clusters as minimum free energy structures. Nature communications\| PubMed ID: 30532018	2018
Minimization of Catalyst Loading on Regenerative Fuel Cell Positive Electrodes Based on Titanium Felts using Atomic Layer Deposition. ChemElectroChem\| PubMed ID: 30775220	2018
Transforming layered MoS into functional MoO nanowires. Nanoscale\| PubMed ID: 31179480	2019

Erdmann Spiecker

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