Search

Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) provides spatially resolved chemical information down to the atomic scale. However, studying radiation-sensitive specimens such as organic–inorganic composites remains extremely challenging. Here, we analyzed metal–organic framework nanoparticles (nanoMOFs) at low-dose (10 e–/Å2) and liquid nitrogen temperatures, similar to cryo-TEM conditions usually employed for high-resolution imaging of biological specimens. Our results demonstrate that monochromated STEM-EELS enables damage-free analysis of nanoMOFs, providing in a single experiment, signatures of intact functional groups comparable with infrared, ultraviolet, and X-ray data, with an energy resolution down to 7 meV. The signals have been mapped at the nanoscale (<10 nm) for each of these energy spectral ranges, including the chemical features observed for high energy losses (X-ray range). By controlling beam irradiation and monitoring spectral changes, our work provides insights into the possible pathways of chemical reactions occurring under electron exposure. These results demonstrate the possibilities for characterizing at the nanoscale the chemistry of sensitive systems such as organic and biological materials.

Whispering-gallery mode resonators host multiple trapped narrow-band circulating optical resonances that find applications in quantum electrodynamics, optomechanics, and sensing. However, the spherical symmetry and low field leakage of dielectric microspheres make it difficult to probe their high-quality optical modes using far-field radiation. Even so, local field enhancement from metallic nanoparticles (MNPs) coupled to the resonators can interface the optical far field and the bounded cavity modes. In this work, we study the interaction between whispering-gallery modes and MNP surface plasmons with nanometric spatial resolution by using electron-beam spectroscopy with a scanning transmission electron microscope. We show that gallery modes are induced over a selective spectral range of the nanoparticle plasmons, and additionally, their polarization can be controlled by the induced dipole moment of the MNP. Our study demonstrates a viable mechanism to effectively excite high-quality-factor whispering-gallery modes and holds potential for applications in optical sensing and light manipulation.

Hybrid/moiré interlayer and intralayer excitons have been realized in twisted two-dimensional transition metal chalcogenides (2D-TMD) due to variation in local moiré potential within a moiré supercell. Though moiré excitons have been detected in TMD heterostructures by macroscopic spectroscopic techniques, their spatial distribution is experimentally unknown. In the present work, using high-resolution scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS), we explore the effect of the twist angle in MoS2/WSe2heterostructures. We observe weak interaction between the layers at higher twist angles (>5°) and stronger interaction for lower twist angles. The optical response of the heterostructure varies within the moiré supercell, with a lower energy absorption peak appearing in regions with the AAstacking.

Silver, king among plasmonic materials, features low inelastic absorption in the visible-infrared (vis-IR) spectral region compared to other metals. In contrast, copper is commonly regarded as too lossy for actual applications. Here, we demonstrate vis-IR plasmons with quality factors >60 in long copper nanowires (NWs), as determined by electron energy-loss spectroscopy. We explain this result by noticing that most of the electromagnetic energy in these plasmons lies outside the metal, thus becoming less sensitive to inelastic absorption. Measurements for silver and copper NWs of different diameters allow us to elucidate the relative importance of radiative and nonradiative losses in plasmons spanning a wide spectral range down to <20 meV. Thermal population of such low-energy modes becomes significant and generates electron energy gains associated with plasmon absorption, rendering an experimental determination of the NW temperature. Copper is therefore emerging as an attractive, cheap, abundant material platform for high-quality plasmonics in elongated nanostructures.

Atomic vibrations and phonons are an excellent source of information on nanomaterials that we can access through a variety of methods including Raman scattering, infrared spectroscopy, and electron energy-loss spectroscopy (EELS). In the presence of a plasmon local field, vibrations are strongly modified and, in particular, their dipolar strengths are highly enhanced, thus rendering Raman scattering and infrared spectroscopy extremely sensitive techniques. Here, we experimentally demonstrate that the interaction between a relativistic electron and vibrational modes in nanostructures is fundamentally modified in the presence of plasmons. We finely tune the energy of surface plasmons in metallic nanowires in the vicinity of hexagonal boron nitride, making it possible to monitor and disentangle both strong phonon–plasmon coupling and plasmon-driven phonon enhancement at the nanometer scale. Because of the near-field character of the electron beam–phonon interaction, optically inactive phonon modes are also observed. Besides increasing our understanding of phonon physics, our results hold great potential for investigating sensing mechanisms and chemistry in complex nanomaterials down to the molecular level.

Idiopathic kidney stones originate mainly from calcium phosphate deposits at the tip of renal papillae, known as Randall’s plaques (RPs), also detected in most human kidneys without stones. However, little is known about the mechanisms involved in RP formation. The localization and characterization of such nanosized objects in the kidney remain a real challenge, making their study arduous. This study provides a nanoscale analysis of the chemical composition and morphology of incipient RPs, characterizing in particular the interface between the mineral and the surrounding organic compounds. Relying on data gathered from a calculi collection, the morphology and chemical composition of incipient calcifications in renal tissue were determined using spatially resolved electron energy-loss spectroscopy. We detected microcalcifications and individual nanocalcifications found at some distance from the larger ones. Strikingly, concerning the smaller ones, we show that two types of nanocalcifications coexist: calcified organic vesicles and nanometric mineral granules mainly composed of calcium phosphate with carbonate in their core. Interestingly, some of these nanocalcifications present similarities with those reported in physiological bone or pathological cardiovascular biominerals, suggesting possible common formation mechanisms. However, the high diversity of these nanocalcifications suggests that several mechanisms may be involved (nucleation on a carbonate core or on organic compounds). In addition, incipient RPs also appear to present specific features at larger scales, revealing secondary calcified structures embedded in a fibrillar organic material. Our study proves that analogies exist between physiological and pathological biominerals and provides information to understand the physicochemical processes involved in pathological calcification formation.

Control over the optical properties of atomically thin two-dimensional (2D) layers, including those of transition metal dichalcogenides (TMDs), is needed for future optoelectronic applications. Here, the near-field coupling between TMDs and graphene/graphite is used to engineer the exciton line shape and charge state. Fano-like asymmetric spectral features are produced in WS2, MoSe2, and WSe2van der Waals heterostructures combined with graphene, graphite, or jointly with hexagonal boron nitride (h-BN) as supporting or encapsulating layers. Furthermore, trion emission is suppressed in h-BN encapsulated WSe2/graphene with a neutral exciton red shift (44 meV) and binding energy reduction (30 meV). The response of these systems to electron beam and light probes is well-described in terms of 2D optical conductivities of the involved materials. Beyond fundamental insights into the interaction of TMD excitons with structured environments, this study opens an unexplored avenue toward shaping the spectral profile of narrow optical modes for application in nanophotonic devices.

A variety of advanced (scanning) transmission electron microscopy experiments, carried out in aberration-corrected equipment, provide direct evidence about subtle structural changes taking place at nanometer-sized Au||ceria oxide interfaces, which agrees with the occurrence of charge transfer effects between the reduced support and supported gold nanoparticles suggested by macroscopic techniques. Tighter binding of the gold nanoparticles onto the ceria oxide support when this is reduced is revealed by the structural analysis. This structural modification is accompanied by parallel deactivation of the CO chemisorption capacity of the gold nanoparticles, which is interpreted in exact quantitative terms as due to deactivation of the gold atoms at the perimeter of the Au||cerium oxide interface.

Single-walled carbon nanotubes substitutionally doped with the light-element phosphorus are synthesized and are investigated by electrical and nuclear magnetic resonance measurements. Decreased spin−lattice relaxation times compared to undoped tubes point toward enhanced spin-sensitive scattering. Temperature dependence of the zero-bias conductance shows step-like features, a signature of scattering from a very low density (few sites per nanotube) of localized spin moments at oxidized phosphorus sites, consistent with density functional calculations. This supports recent predictions that localized magnetic moments must be indirectly magnetically coupled through the nanotube conduction electrons.

We present a density functional theory study on the shape and arrangement of small BN domains embedded into single-walled carbon nanotubes. We show a strong tendency for BN hexagon formation at the simultaneous inclusion of B and N atoms within the walls of carbon nanotubes. The work emphasizes the importance of a correct description of the BN−C frontier. We suggest that a BN−C interface will be formed preferentially with the participation of N−C bonds. Thus, we propose a new way of stabilizing the small BN inclusions through the formation of nitrogen-terminated borders. The comparison between the obtained results and the available experimental data on the formation of BN plackets within the single-walled carbon nanotubes is presented. The mirror situation of inclusion of carbon plackets within single-walled BN nanotubes is considered within the proposed formalism. Finally, we show that the inclusion of small BN plackets inside the CNTs strongly affects the electronic character of the initial systems, opening a band gap. The nitrogen excess in the BN plackets introduces donor states in the band gap, and it might, thus, result in a promising way for n-doping single-walled carbon nanotubes.

Simple epitaxial growthof a cyano‐bridged coordination network on different core particles can lead to core–multishell nanoparticles. Shell growth is controlled on the nanometer scale and can be repeated with different metal ions. Particles can be prepared with a distinct composition in each layer (see images), and synergy is observed between their magnetic properties.

Epitaxiales Aufwachseneines Koordinationsnetzwerks mit Cyanidbrücken auf Kernpartikeln erzeugt Kern‐Schale‐Nanopartikel. Die Schalendicke lässt sich im Nanometerbereich einstellen, und der Prozess kann mit unterschiedlichen Metallionen wiederholt werden, um Partikel mit mehreren Schalenschichten und kombinierten magnetischen Eigenschaften zu erhalten (siehe Bilder).

Multiwalled boron- and nitrogen-doped carbon nanotubes (C xB yN z) have been synthesized using both low and high temperature synthesis methods namely an aerosol-assisted chemical vapor deposition process and a laser vaporization process, respectively. Degrees of purity, homogeneity, and yield have been estimated from a systematic inspection of the sample by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Spatially resolved electron energy loss spectroscopy (EELS) measurements in a dedicated scanning transmission electron microscope (STEM) have been performed in order to correlate spectroscopic information with structural features at a nanometer scale on nanotubes and nanoparticles that originates their growth. As a result, spatially resolved analyses have shown a clearly defined segregation of BN-regions from CN-rich regions, indicating that separate nanodomains of boron nitride and carbon nitride may exist with different arrangements in carbon nanotubes as a function of the synthesis method.

By using a combination of transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) techniques, we have followed in detail the structural and chemical changes occurring on the very surface layers of powder CexPr1-xO2mixed oxides, used as supports, during the preparation of rhodium-supported catalyst by wet impregnation techniques. Results demonstrate the occurrence of Pr3leaching out of the Ce−Pr solid solution during the impregnation step, which promotes a severe spatial redistribution of lanthanide cations at the surface of the mixed oxide. A highly heterogeneous surface composition is reached after the metal deposition. Mobilization of the support also affects the features of the final surface structure of the metal-supported nanoparticles, which become decorated by patches of support material. All these facts seem crucial to properly understand the redox and catalytic behavior of this kind of materials.

The spontaneous stabilization of 6.5 nm bimetallic Ni–Cr cyanide bridged nanoparticles was achieved in water. Dispersible particles were recovered from solution using two different coating agents. The magnetic studies of the particles in the powder form show either a superparamagnetic or a spin glass like behaviour depending on the isolation technique used.

By the use of electron energy‐loss spectroscopy performed in a scanning transmission electron microscope (STEM‐EELS), detailed spatial information is obtained concerning the amount and nature of carbonaceous deposits formed inside the crystals of the zeolite ferrierite (FER) during the reaction of n‐butene to isobutene. In all cases, gradients in coke concentration over the crystal have been observed and quantified. An extensive accumulation of coke is observed at the entrance of the eight‐membered‐ring (MR) pores, while less coke is present at the entrances of the ten‐MR channels. At a higher coke content, further filling up of the complete micropore system occurs and the eight‐MR pores become fully blocked. The ten‐MR channels remain partially accessible for n‐butene, with alkyl‐aromatic species deposited near the inlets of these channels. With regard to the selective transformation of n‐butene into isobutene, this supports the view that the catalytic action takes place in the pore mouths of the ten‐MR channels. Overall it is demonstrated that the major benefit of STEM‐EELS is the possibility to simultaneously determine the position‐resolved amount and nature of carbonaceous deposits on intact zeolite crystals.

By the use of electron energy-loss spectroscopy performed in a scanning transmission electron microscope (STEM-EELS), detailed spatial information is obtained concerning the amount and nature of carbonaceous deposits formed inside the crystals of the zeolite ferrierite (FER) during the reaction of n-butene to isobutene. In all cases, gradients in coke concentration over the crystal have been observed and quantified. An extensive accumulation of coke is observed at the entrance of the eight-membered-ring (MR) pores, while less coke is present at the entrances of the ten-MR channels. At a higher coke content, further filling up of the complete micropore system occurs and the eight-MR pores become fully blocked. The ten-MR channels remain partially accessible for n-butene, with alkyl-aromatic species deposited near the inlets of these channels. With regard to the selective transformation of n-butene into isobutene, this supports the view that the catalytic action takes place in the pore mouths of the ten-MR channels. Overall it is demonstrated that the major benefit of STEM-EELS is the possibility to simultaneously determine the position-resolved amount and nature of carbonaceous deposits on intact zeolite crystals.

Structural, electronic, and chemical nanoscale modifications of transition metal dichalcogenide monolayers alter their optical properties. A key missing element for complete control is a direct spatial correlation of optical response to nanoscale modifications due to the large gap in spatial resolution between optical spectroscopy and nanometer-resolved techniques. Here, we bridge this gap by obtaining nanometer-resolved optical properties using electron spectroscopy at cryogenic temperatures, specifically electron energy loss spectroscopy for absorption and cathodoluminescence for emission, which are then directly correlated to chemical and structural information. In an h-BN/WS2/h-BN heterostructure, we observe local modulation of the trion (X–) emission due to tens of nanometer wide dielectric patches. Trion emission also increases in regions where charge accumulation occurs, close to the carbon film supporting the heterostructures. The localized exciton emission (L) detected here is not correlated to strain above 1%, suggesting point defects might be involved in their formation.

Numerous fullerenes were synthesized in various B-C-N materials by in-situ electron beam irradiation in a high-resolution transmission analytical electron microscope JEM-3000F. Boron-doped graphitic carbons, hexagonal and rhombohedral boron nitrides, and ternary B-C-N turbostratic materials served as the starting materials for irradiation. The transformation to fullerene-like morphology from originally flat or curled and jumbled graphene-like sheets or polygonal particles takes place through a solid-state phase transition by rearrangement of atoms, which is drastically enhanced by thermal and irradiation-induced diffusion. The scale of generated fullerenes ranges from ∼1 nm (single-shelled objects) to 50 nm (giant nested objects having up to 75 shells). Fullerene symmetry and chemical composition were clarified by high-resolution transmission electron microscopy and electron energy loss spectroscopy, respectively. Finally, 3-D fullerene models were developed which particularly emphasize icosahedral symmetry for B-C and B-C-N fullerenes, and octahedral symmetry for BN fullerenes.