Hydrogen-air mixtures are highly flammable. Hydrogen sensors are therefore of paramount importance for timely leak detection during handling. However, existing solutions do not meet the stringent ...performance targets set by stakeholders, while deactivation due to poisoning, for example by carbon monoxide, is a widely unsolved problem. Here we present a plasmonic metal-polymer hybrid nanomaterial concept, where the polymer coating reduces the apparent activation energy for hydrogen transport into and out of the plasmonic nanoparticles, while deactivation resistance is provided via a tailored tandem polymer membrane. In concert with an optimized volume-to-surface ratio of the signal transducer uniquely offered by nanoparticles, this enables subsecond sensor response times. Simultaneously, hydrogen sorption hysteresis is suppressed, sensor limit of detection is enhanced, and sensor operation in demanding chemical environments is enabled, without signs of long-term deactivation. In a wider perspective, our work suggests strategies for next-generation optical gas sensors with functionalities optimized by hybrid material engineering.
Several concepts for platinum-based catalysts for the oxygen reduction reaction (ORR) are presented that exceed the US Department of Energy targets for Pt-related ORR mass activity. Most concepts ...achieve their high ORR activity by increasing the Pt specific activity at the expense of a lower electrochemically active surface area (ECSA). In the potential region controlled by kinetics, such a lower ECSA is counterbalanced by the high specific activity. At higher overpotentials, however, which are often applied in real systems, a low ECSA leads to limitations in the reaction rate not by kinetics, but by mass transport. Here we report on self-supported platinum-cobalt oxide networks that combine a high specific activity with a high ECSA. The high ECSA is achieved by a platinum-cobalt oxide bone nanostructure that exhibits unprecedentedly high mass activity for self-supported ORR catalysts. This concept promises a stable fuel-cell operation at high temperature, high current density and low humidification.
The integration of dissimilar materials in heterostructures has long been a cornerstone of modern materials science—seminal examples are 2D materials and van der Waals heterostructures. Recently, new ...methods have been developed that enable the realization of ultrathin freestanding oxide films approaching the 2D limit. Oxides offer new degrees of freedom, due to the strong electronic interactions, especially the 3d orbital electrons, which give rise to rich exotic phases. Inspired by this progress, a new platform for assembling freestanding oxide thin films with different materials and orientations into artificial stacks with heterointerfaces is developed. It is shown that the oxide stacks can be tailored by controlling the stacking sequences, as well as the twist angle between the constituent layers with atomically sharp interfaces, leading to distinct moiré patterns in the transmission electron microscopy images of the full stacks. Stacking and twisting is recognized as a key degree of structural freedom in 2D materials but, until now, has never been realized for oxide materials. This approach opens unexplored avenues for fabricating artificial 3D oxide stacking heterostructures with freestanding membranes across a broad range of complex oxide crystal structures with functionalities not available in conventional 2D materials.
A new platform is developed for assembling freestanding oxide thin films with different materials and orientations into artificial stacks of heterointerfaces. The heterointerfaces can be tailored by controlling the stacking sequences, as well as the twist angle between the constituent layers with atomically sharp interfaces, leading to distinct moiré patterns.
2D materials are by definition just a few atomic layers thick. They are therefore ideal samples for transmission electron microscopy, in the plan‐view geometry. However, 2D materials are typically ...placed or grown on substrates, which in some cases requires analysis to be performed on cross sections. In this case focused ion beam preparation is often the technique of choice for producing thin lamellae, but damage to the surface of 2D material during imaging and milling must be mitigated. Herein, it is demonstrated that the typically applied electron beam‐assisted deposition of platinum and carbon prior to milling does not provide sufficient protection, and results in significant damage. Instead, it is found that arc‐evaporated carbon—deposited with a standard carbon coater designed for scanning electron microscopy (SEM) samples—can provide sufficient protection, enabling cross‐sectional analysis without detectable damage to monolayer or bilayer samples subsequently prepared by standard focused ion beam preparation procedures.
Preparing exposed 2D material surfaces for atomic level cross‐sectional investigations requires surface damage to be minimized. This work presents a simple procedure for eliminating the surface damage, measurable with transmission electron microscopy, scanning transmission electron microscopy, and electron energy‐loss spectroscopy, during focused ion beam preparation of lamella of exposed MoS2 on gold using evaporated carbon.
We study the surface plasmon (SP) resonance energy of isolated spherical Ag nanoparticles dispersed on a silicon nitride substrate in the diameter range 3.5–26 nm with monochromated electron ...energy-loss spectroscopy. A significant blueshift of the SP resonance energy of 0.5 eV is measured when the particle size decreases from 26 down to 3.5 nm. We interpret the observed blueshift using three models for a metallic sphere embedded in homogeneous background material: a classical Drude model with a homogeneous electron density profile in the metal, a semiclassical model corrected for an inhomogeneous electron density associated with quantum confinement, and a semiclassical nonlocal hydrodynamic description of the electron density. We find that the latter two models provide a qualitative explanation for the observed blueshift, but the theoretical predictions show smaller blueshifts than observed experimentally.
The dependence of surface plasmon coupling on the distance between two nanoparticles (dimer) is the basis of nanometrology tools such as plasmon rulers. Application of these nanometric rulers ...requires an accurate description of the scaling of the surface plasmon resonance (SPR) wavelength with distance. Here, we have applied electron energy-loss spectroscopy (EELS) and scanning transmission electron microscopy (STEM) imaging to investigate the relationship between the SPR wavelength of gold and silver nanosphere dimers (radius R) and interparticle distance (d) in the range 0.1R < d < R. The choice of EELS enables probing the SPRs of individual dimers, whose dimensions and separation distances are measured in situ with subnanometer resolution using STEM. We find that the decaying exponential description of the fractional SPR wavelength shift with d/2R holds valid only over a limited range of d. Instead, within the range 0.1R < d < R the fractional SPR wavelength shift is found to be related to (2R/d) n , with n ∼ 0.9 determined for both gold and silver dimers. Despite this common power dependence, consistently larger SPR wavelength shifts are registered for silver for a given change in d, implying silver dimers to be more sensitive plasmon rulers than their gold counterparts.
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