Metal halide perovskites have emerged as a promising new class of layered semiconductor material for light‐emitting and photovoltaic applications owing to their outstanding optical and optoelectronic ...properties. In nanocrystalline form, these layered perovskites exhibit extremely high photoluminescence quantum yields (PLQYs) and show quantum confinement effects analogous to conventional semiconductors when their dimensions are reduced to sizes comparable to their respective exciton Bohr radii. The reduction in size leads to strongly blueshifted photoluminescence and large exciton binding energies up to several hundreds of meV. This not only makes them interesting for optoelectronic devices, but also enables complex architectures based on cascaded energy transfer. Here, an overview of the current state‐of‐the‐art of quantum confinement effects in perovskite nanocrystals is provided, with a focus on synthetic strategies and resulting optical properties, characterization methods, and emerging applications.
Metal halide perovskites have emerged as a promising new class of material for light‐emitting and photovoltaic applications owing to their outstanding optical and optoelectronic properties. This research news provides an overview of the current state‐of‐the‐art of quantum‐confinement effects in perovskite nanocrystals, with a focus on synthetic strategies and resulting optical properties, characterization methods, and emerging applications.
Organometal halide perovskites have recently emerged displaying a huge potential for not only photovoltaic, but also light emitting applications. Exploiting the optical properties of specifically ...tailored perovskite nanocrystals could greatly enhance the efficiency and functionality of applications based on this material. In this study, we investigate the quantum size effect in colloidal organometal halide perovskite nanoplatelets. By tuning the ratio of the organic cations used, we can control the thickness and consequently the photoluminescence emission of the platelets. Quantum mechanical calculations match well with the experimental values. We find that not only do the properties of the perovskite, but also those of the organic ligands play an important role. Stacking of nanoplatelets leads to the formation of minibands, further shifting the bandgap energies. In addition, we find a large exciton binding energy of up to several hundreds of meV for nanoplatelets thinner than three unit cells, partially counteracting the blueshift induced by quantum confinement. Understanding of the quantum size effects in perovskite nanoplatelets and the ability to tune them provide an additional method with which to manipulate the optical properties of organometal halide perovskites.
3D DNA Origami Crystals Zhang, Tao; Hartl, Caroline; Frank, Kilian ...
Advanced materials (Weinheim)
30, Številka:
28
Journal Article
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3D crystals assembled entirely from DNA provide a route to design materials on a molecular level and to arrange guest particles in predefined lattices. This requires design schemes that provide high ...rigidity and sufficiently large open guest space. A DNA‐origami‐based “tensegrity triangle” structure that assembles into a 3D rhombohedral crystalline lattice with an open structure in which 90% of the volume is empty space is presented here. Site‐specific placement of gold nanoparticles within the lattice demonstrates that these crystals are spacious enough to efficiently host 20 nm particles in a cavity size of 1.83 × 105 nm3, which would also suffice to accommodate ribosome‐sized macromolecules. The accurate assembly of the DNA origami lattice itself, as well as the precise incorporation of gold particles, is validated by electron microscopy and small‐angle X‐ray scattering experiments. The results show that it is possible to create DNA building blocks that assemble into lattices with customized geometry. Site‐specific hosting of nano objects in the optically transparent DNA lattice sets the stage for metamaterial and structural biology applications.
A DNA‐origami‐based triangle structure assembles into a 3D rhombohedral crystalline lattice. The accurate assembly of the DNA origami lattice itself as well as the precise incorporation of gold particles is demonstrated by electron microscopy and small‐angle X‐ray scattering experiments.
It is widely recognized that the intrinsic charge transport properties in organic thin-film transistors (OTFTs) depend strongly on the crystal structure of the organic semiconductor layer. Pentacene, ...showing one of the highest charge carrier mobilities among organic semiconductors, is known to crystallize in at least four polymorphs, which can be distinguished by their layer periodicity d (001). Only two polymorphs grow as single crystals, and their detailed crystal structure has been solved. The substrate-induced 15.4 Å polymorph is the most relevant for OTFT applications; however, its crystal structure has remained incomplete as it only grows as a fiber structured thin film. Here we extend the crystal truncation rod X-ray scattering technique to fiber structured thin films. We determined the complete crystal structure of this polymorph grown on technologically relevant substrates. We found that the molecular arrangement within the unit cell is substrate dependent, which may lead to a controlled fine-tuning of intrinsic charge transport properties.
Controlling the domain size and degree of crystallization in organic films is highly important for electronic applications such as organic photovoltaics, but suitable nanoscale mapping is very ...difficult. Here we apply infrared-spectroscopic nano-imaging to directly determine the local crystallinity of organic thin films with 20-nm resolution. We find that state-of-the-art pentacene films (grown on SiO2 at elevated temperature) are structurally not homogeneous but exhibit two interpenetrating phases at sub-micrometre scale, documented by a shifted vibrational resonance. We observe bulk-phase nucleation of distinct ellipsoidal shape within the dominant pentacene thin-film phase and also further growth during storage. A faint topographical contrast as well as X-ray analysis corroborates our interpretation. As bulk-phase nucleation obstructs carrier percolation paths within the thin-film phase, hitherto uncontrolled structural inhomogeneity might have caused conflicting reports about pentacene carrier mobility. Infrared-spectroscopic nano-imaging of nanoscale polymorphism should have many applications ranging from organic nanocomposites to geologic minerals.
Abstract
Silicification of DNA origami structures increases their stability and provides chemical protection. Yet, it is unclear whether the whole DNA framework is embedded or if silica just forms an ...outer shell and how silicification affects the origami’s internal structure. Employing in situ small-angle X-ray scattering (SAXS), we show that addition of silica precursors induces substantial condensation of the DNA origami at early reaction times by almost 10 %. Subsequently, the overall size of the silicified DNA origami increases again due to increasing silica deposition. We further identify the SAXS Porod invariant as a reliable, model-free parameter for the evaluation of the amount of silica formation at a given time. Contrast matching of the DNA double helix Lorentzian peak reveals silica growth also inside the origami. The less polar silica forming within the origami structure, replacing more than 40 % of the internal hydration water, causes a hydrophobic effect: condensation. DNA origami objects with flat surfaces show a strong tendency towards aggregation during silicification, presumably driven by the same entropic forces causing condensation. Maximally condensed origami displayed thermal stability up to 60 °C. Our studies provide insights into the silicification reaction allowing for the formulation of optimized reaction protocols.
Scaffolded DNA origami nanostructures enable the self-assembly of arbitrarily shaped objects with unprecedented accuracy. Yet, varying physiological conditions are prone to induce slight structural ...changes in the nanoscale architecture. Here, we report on high precision measurements of overall shape and interhelical distance of three prototypic DNA origami structures in solution using synchrotron small-angle X-ray scattering. Sheet-, brick-, and cylinder-shaped DNA constructs were assembled and the shape factors determined with angstrom resolution from fits to the scattering profiles. With decreasing MgCl2 concentration electrostatic swelling of both shape cross section and interhelical DNA spacing of the DNA origami structures is observed. The structures tolerate up to 10% interhelical expansion before they disintegrate. In contrast, with increasing temperature, the cylinder-shaped structures show no thermal expansion in a wide temperature window before they abruptly melt above 50 °C. Details on molecular structure of DNA origami can also be obtained using in-house X-ray scattering equipment and, hence, allow for routine folding and stability testing of DNA-based agents that are designed to operate under varying salt conditions.
Halide perovskite nanocrystals (NCs) have shown impressive advances, exhibiting optical properties that outpace conventional semiconductor NCs, such as near-unity quantum yields and ultrafast ...radiative decay rates. Nevertheless, the NCs suffer even more from stability problems at ambient conditions and due to moisture than their bulk counterparts. Herein, we report a strategy of employing polymer micelles as nanoreactors for the synthesis of methylammonium lead trihalide perovskite NCs. Encapsulated by this polymer shell, the NCs display strong stability against water degradation and halide ion migration. Thin films comprising these NCs exhibit a more than 15-fold increase in lifespan in comparison to unprotected NCs in ambient conditions and even survive over 75 days of complete immersion in water. Furthermore, the NCs, which exhibit quantum yields of up to 63% and tunability of the emission wavelength throughout the visible range, show no signs of halide ion exchange. Additionally, heterostructures of MAPI and MAPBr NC layers exhibit efficient Förster resonance energy transfer (FRET), revealing a strategy for optoelectronic integration.
Frequency‐resolved scanning photoresponse microscopy of pentacene thin‐film transistors is reported. The photoresponse pattern maps the in‐plane distribution of trap states which is superimposed by ...the level of trap filling adjusted by the gate voltage of the transistor. Local hotspots in the photoresponse map thus indicate areas of high trap densities within the pentacene thin film.
While the role of crystal facets is well known in traditional heterogeneous catalysis, this effect has not yet been thoroughly studied in plasmon-assisted catalysis, where attention has primarily ...focused on plasmon-derived mechanisms. Here, we investigate plasmon-assisted electrocatalytic CO
reduction using different shapes of plasmonic Au nanoparticles - nanocube (NC), rhombic dodecahedron (RD), and octahedron (OC) - exposing {100}, {110}, and {111} facets, respectively. Upon plasmon excitation, Au OCs doubled CO Faradaic efficiency (FE
) and tripled CO partial current density (j
) compared to a dark condition, with NCs also improving under illumination. In contrast, Au RDs maintained consistent performance irrespective of light exposure, suggesting minimal influence of light on the reaction. Temperature experiments ruled out heat as the main factor to explain such differences. Atomistic simulations and electromagnetic modeling revealed higher hot carrier abundance and electric field enhancement on Au OCs and NCs than RDs. These effects now dominate the reaction landscape over the crystal facets, thus shifting the reaction sites when comparing dark and plasmon-activated processes. Plasmon-assisted H
evolution reaction experiments also support these findings. The dominance of low-coordinated sites over facets in plasmonic catalysis suggests key insights for designing efficient photocatalysts for energy conversion and carbon neutralization.
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