Cathodoluminescence Techniques Research Articles

Dielectric Sphere Oligomers as Optical Nanoantenna for Circularly Polarized Light.

Control of circularly polarized light (CPL) is important for next-generation optical communications as well as for investigating the optical properties of materials. In this study, we explore dielectric-sphere oligomers for chiral nanoantenna applications, leveraging the cathodoluminescence (CL) technique, which employs accelerated free electrons for excitation and allows mapping the optical response on the nanoscale. For a certain particle-dimers configuration, one of the spheres becomes responsible for the left-handed circular polarization of the emitted light, while right-handed circular polarization is selectively yielded when the other sphere is excited by the electron beam. Similar patterns are also observed in trimers. These phenomena are understood in terms of optical coupling between the electric and magnetic modes hosted by the dielectric spheres. Our research not only expands the understanding of CPL generation mechanisms in dielectric-sphere oligomer antennas but also underscores the potential of such structures in optical applications. We further highlight the utility of CL as a powerful analytical tool for investigating the optical properties of nanoscale structures as well as the potential of electron beams for light generation with switchable CPL parities.

Effect of MgO/ZnO ratio on the formation process of MgxZn1-xO ceramics

The structural characteristics, chemical composition, and element spatial distribution in MgxZn1-xO ceramics were investigated using X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, energy-dispersive X-ray spectroscopy, and cathodoluminescence techniques. The study revealed that the morphology of the ceramic samples, as well as the mechanism of solid solution formation, depend on the relative contribution of both oxides in the charge. It was discovered that hexagonal and cubic phases of the solid solution were found to form simultaneously. An increase in the MgO content in the charge results in the magnesium content rise in the hexagonal grains continuously, reaching approximately 13 at.%. It was discovered an enrichment of grain boundaries with zinc and magnesium playing a significant role in doping ZnO and MgO grains. Obtained results allowed to propose two mechanisms involved in the formation of solid solution ceramics: i) diffusion of Mg and Zn along grain boundaries, followed by their incorporation into ZnO or MgO grains, respectively, and ii) interdiffusion of Mg into ZnO and Zn into MgO due to direct contact of ZnO and MgO grains. The second mechanism appears to dominate when both ZnO and MgO contribute comparably, increasing the probability of their direct contact. This study significantly advances the understanding of the process of the formation of MgxZn1-xO ceramics under thermodynamic conditions. These insights are crucial for optimizing the doping process and improving the material properties, thereby promoting innovations in the ceramics industry.

Ruthenium-doped ZnO nanostructures: Growth, characterization, and applications in waveguides and light-emitting devices

ZnO based materials are gaining importance due to its potential applications. In many of these applications, the size, shape and dopability of the structures grown play a determinant role. In the present work, ZnO nano- and microstructures doped with Ru have been grown using the Vapour-Solid (VS) method. Among the different growth parameters, gas flux and initial dopant content seem to play the major role to determine both shape and size of the structures. The main morphologies obtained are self-arranged triangular grids and elongated structures. Based on microscopic observations a simplified growth model is proposed for the grids. An exhaustive characterization has been performed. X-Ray diffraction (XRD) investigations demonstrate good crystallinity and texturing related to preferential growth direction changes due to doping. Luminescence characterization through photo- and cathodoluminescence (PL and CL) techniques reveals typical ZnO near band edge and deep level emission bands at 3.2 and 2.3 eV, respectively. The potential use of elongated structures as waveguides and optical cavities, Fabry-Pèrot resonators, is explored.

Momentum-resolved EELS and CL study on 1D-plasmonic crystal prepared by FIB method.

We investigate a one-dimensional plasmonic crystal using momentum-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) techniques, which are complementary in terms of available optical information. The plasmonic crystal sample is fabricated from large aluminum grains through the focused ion beam method. This approach allows curving nanostructures with high crystallinity, providing platforms for detailed analysis of plasmonic nanostructures using both EELS and CL. The momentum-resolved EELS visualizes dispersion curves outside the light cone, confirming the existence of the surface plasmon polaritons and local modes, while the momentum-resolved CL mapping analysis identified these surface plasmon polaritons and local modes. Such synergetic approach of two electron-beam techniques offers full insights into both radiative and non-radiative optical properties in plasmonic or photonic structures.

Diagenesis and lateral sealing types of fault zones in the Lishu Depression, Songliao Basin, NE China

The Lishu Depression in the Songliao Basin is characterized by well-developed faults, and the accumulation of oil and gas is closely related to fault sealing. However, there remains a dearth of comprehensive investigation into the diagenesis of fault zones and their influence on lateral sealing. This study employed electron probe analysis, cathodoluminescence, and carbon and oxygen isotope techniques to investigate the diagenetic processes in fault zones. This research also reconstructed the evolution of porosity and displacement pressure of fault rocks, and identified the lateral sealing characteristics of fault zones and their impact on oil and gas accumulation. The majority of faults in the study region formed earlier, and the fault zones experienced intricate diagenesis, characterized by compaction, cementation, replacement, and dissolution. The displacement pressure of fault rocks is higher during fault intermittent and static periods compared to active periods, and it is influenced by diagenesis. Late-stage calcite and pore-filling chlorite were deposited subsequent to the period of fault activity, filling dissolution pores. This led to relatively higher displacement pressure and improved lateral sealing of fault zone. The kaolinite cement exhibits a relatively elevated potassium concentration, due to its connection with the dissolution of feldspar, resulting in lower displacement pressure and poor sealing of fault zone. Based on the evolutionary characteristics of displacement pressure in fault rock and reservoir during various transportation stages, this study identified six types of lateral sealing of fault zones. Notably, the sealing types characterized by "fault core and damage zone sealing during static periods" and "fault core and damage zone sealing during intermittent and static periods" exhibit superior lateral sealing properties, effectively controlling the accumulation of oil and gas in the sand bodies on either side of the fault zone.

Synthesis of Plasmonically Active Titanium Nitride Using a Metallic Alloy Buffer Layer Strategy.

Titanium nitride (TiN) has emerged as a highly promising alternative to traditional plasmonic materials. This study focuses on the inclusion of a Cr90Ru10 buffer layer between the substrate and thin TiN film, which enables the use of cost-effective, amorphous technical substrates while preserving high film quality. We report best-in-class TiN thin films fabricated on fused silica wafers, achieving a maximum plasmonic figure of merit, -ϵ'/ϵ″, of approximately 2.8, even at a modest wafer temperature of around 300 °C. Furthermore, we delve into the characterization of TiN thin film quality and fabricated TiN triangular nanostructures, employing attenuated total reflectance and cathodoluminescence techniques to highlight their potential applications in surface plasmonics.

High-Resolution Cathodoluminescence Images of Igneous and Metamorphic Monazite.

Monazite is one of the most important dating accessory minerals for deciphering geological processes. The growth history of monazite can be identified by its internal structure; thus, high-resolution imaging is necessary for in situ U-Th-Pb dating. In this study, cathodoluminescence (CL) techniques were optimized via the key parameters of working distance, accelerating voltage, and beam current and were then applied to monazites from igneous and metamorphic rocks. The CL images of igneous monazites show concentric oscillatory zoning, whereas those of metamorphic monazites clearly show homogeneous, patchy, or core-rim structures. CL imaging is a more effective approach than back-scattered electron (BSE) imaging for the observation of the internal structure of monazite and may yield additional information. CL can add to the interpretation of X-ray maps and the two techniques that may complement each other. The CL spectra of monazite consist of broad peaks and sets of narrow emission rare earth element 3+ (REE3+) peaks (Gd3+, Tb3+, Dy3+, and Sm3+). The microstructures observed via CL imaging techniques can show a certain relationship between light REE (LREE) and U, Th, and Si in some igneous monazites and heavy REE (HREE) variation in some metamorphic monazites.

Diagenesis of continental carbonates linked to the evolution of the flexural margin of the Triassic Sorocayense-Hilario rift sub-basin, Argentina

The lithostratigraphic units that conform the Sorocayense Group and fill the Sorocayense-Hilario sub-basin represent an alluvial-fluvial-lacustrine succession with significant volcanic supply during its deposition. They are namely the Cerro Colorado del Cementerio, Agua de los Pajaritos, Monina, Hilario and El Alcázar formations and present several carbonate levels. The genesis, diagenesis, and main controlling factors on continental carbonates present a means to understand basin evolution through the study of their petrography and chemical elemental composition through cathodoluminescence techniques. We have identified six microfacies: a) homogeneous micrite, b) bioclastic micrite, c) dolomicrite, d) laminated micrite, e) oncolitic packstone, and f) sparitic carbonate. Among these microfacies, six cementation and alteration phases have been identified: a) micritization, b) mechanical compaction, c) calcitic cementation, d) sparitic cementation, e) microsparitic cementation, and f) chemical compaction. This analysis allowed establishing a chronology of the diagenetic modifications undergone by the carbonates. Results support diagenesis was controlled mainly by tectonics showing major impact in carbonate facies identified at the flexural margin of the rift. The effect would have been linked to exertion of a paleohydrological effect favoring lateral meteoric water migration through faulting. The presence of dolomite in some of the microfacies is linked to the presence of montmorillonite as the dominant Mg-rich-phyllosilicate in clay assemblages most likely acting as the potential source. In turn, Mg is more likely to be replaced by Mn leading to luminescent carbonate microfacies.

Plasmonic Nanopyramid Array Enhancing Luminescence of MoS2 Investigated by Cathodoluminescence

AbstractTransition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS2) have unique optical properties such as strong luminescence and a tunable bandgap. However, the small interaction distance due to the atomically thin nature of these materials is a limitation for applications. In this study, a significant enhancement of the A‐ and B‐exciton emission in MoS2 flakes through coupling with plasmonic Au nano‐pyramid arrays fabricated by a colloidal lithography technique is reported. This study experimentally maps local emission enhancement from the structure with a nanometer spatial resolution by cathodoluminescence (CL) technique. Strongly enhanced emission intensity within the MoS2‐Au pyramids is achieved due to the localized surface plasmon resonance confined in nano‐pyramids and its interaction with the periodicity‐based resonance of the array structure. The results provide an approach to significantly improve the luminescence intensity of MoS2 through optical interaction with the local plasmonic field, which is promising for applications in optoelectronic devices and nanophotonics.

Decay kinetics in single crystals and ceramics based on yttrium aluminum garnet doped with rare earth ions

The paper is devoted to the study of cathodoluminescence decay kinetics in ceramics and single crystals of YAG:Nd and YAG:Eu. The decay kinetics of Nd and Eu cathodoluminescence bands were found to be double exponential. The decay kinetics dependence on the electron beam penetration depth was studied. The cathodoluminescence technique allowed varying the proportion of surface area in the excited region depending on the energy of the electron beam. The electron beam depth penetration calculation was performed using Monte Carlo method. In single crystals the second decay component appeared to be only on the surface of the samples, whereas in ceramics the second decay component was constant over electron beam penetration depth. Double exponential kinetics as assumed are connected with two types of RE ions – luminescent centers.

Fine core structure and spectral luminescence features of freshly introduced dislocations in Fe-doped GaN

Dislocations introduced by Vickers tip microindentation of an a-plane free-standing semi-insulating Fe-doped GaN halide vapor phase epitaxy (HVPE) crystal were investigated by means of cathodoluminescence and scanning transmission electron microscopy techniques. Detailed combined analyses of both spectral properties and the core structure of the introduced a-screw dislocations revealed that Fe-doped GaN exhibit not only dislocation-bound emission at ∼3.35 eV of perfect a-screw dislocations previously found in such kind of samples but also luminescent bands at 3.1–3.2 and 3.3 eV due to dissociated a-screw dislocations and extended dislocation nodes previously observed only in low-resistance n-GaN. For the first time, all these luminescent bands were observed together in the same sample. Structural studies revealed the coexistence of the dislocations with the dissociated and the perfect core as well as with extended dislocation nodes, thus establishing a correlation between previously observed luminescence bands and a fine dislocation core structure.

Regeneration Growth as One of the Principal Stages of Diamond Crystallogenesis

Revealing the internal structure of diamonds is key to understanding the general regularities of crystal growth and dissolution. This paper presents and summarizes data on the internal structure of diamonds of different morphological types, colors and defect-impurity composition. In order to provide a comprehensive explanation of the stages of diamond growth, crystals and plates were observed, and panchromatic cathodoluminescence and photoluminescence techniques were applied. This article considers the mechanism of tangential growth from existing surfaces (regeneration growth) as an intermediate stage between normal and tangential crystal growth. The regeneration growth is very fast due to the absence of the limiting stage-nucleation of a new atomic layer. Cuboid diamonds were refaceted to stepped octahedrons by the regeneration growth mechanism. A schematic model of crystal habit transformation due to regeneration growth explains the internal structure of crystals in connection with their morphology and thermal history. The main variants of regeneration stage and its morphological manifestations were demonstrated. Most diamonds pass through the regeneration stage, and in many cases, it was a stage of growth termination.

Non-destructive imaging of residual strains in GaN and their effect on optical and electrical properties using correlative light–electron microscopy

We demonstrate a non-destructive approach to understanding the growth modes of a GaN thin film and simultaneously quantify its residual strains and their effect on optical and electrical properties using correlative scanning electron microscopy techniques and Raman microscopy. Coincident strain maps derived from electron backscatter diffraction, cathodoluminescence, and confocal Raman techniques reveal strain variations with similar magnitude and directions, especially in the proximity of dislocations. Correlating confocal Raman imaging with electron channeling contrast imaging suggests that the dislocations organize themselves to form a distinctive pattern as a result of the underlying growth mask, where some of them align along the [0001] growth direction and some are inclined. The methodology presented in this work can be adopted to investigate any heteroepitaxial growth, in particular, those using selective masks on the growth substrates, where the morphology influences the subsequent growth.

X-ray peaks profile analysis, optical and cathodoluminescence investigations of cobalt-doped ZnO nanoparticles

Effects of Co doping on the structural and optical properties of ZnO oxide nanoparticles (NPs) prepared by a solvothermal method are reported. X-ray diffraction examinations using Rietveld refinement confirms the hexagonal wurtzite symmetry ZnO phase nanostructure belonging to P63mc space group. No segregated secondary phases or Co rich clusters were detected. The X-ray diffraction peaks shifts towards higher angle gradually as the concentration of nominal Co content increases in ZnO. This shifting in peak position reflect that Co is well replaced Zn in ZnO matrix. With increasing the Co content to 3%, both lattice parameters a and c of the hexagonal ZnO tended to gradually decrease, suggesting substitutional doping of Co at the tetrahedral Zn2+sites. For Co loading of5%, these trends reversed and the lattice showed a gradual expansion, which is explained by additional interstitial incorporation of Co. The Williamson-Hall (W–H) method with various models i.e. uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM), as well as size-strain plot (SSP) method, and the morphological observations using transmission electron microscopy (TEM) image were used to evaluate the crystallite size as well as the lattice strain. Optical studies carried out by diffuse reflectance spectroscopy (DRS) indicated a decrease in the value of the band gap from 3.238 eV to 2.993 eV with increasing Co doping concentration. The obtained results are confirmed by cathodoluminescence technique.

Study of radioluminescence and cathodoluminescence of artificial diamond single crystals as prospective durable core material for nuclear electric batteries

This work provides further step in considering artificial diamond crystals doped with beta-emitter 14C as chemically durable and environmentally friendly material to be applied as a core of nuclear electric photo-voltaic batteries. In order to investigate features of diamond radioluminescence the metallic radioactive technetium 99Tc and electron beam treatment have been used as external sources of beta-radiation simulating diamond self-glowing from admixture of 14C. Three types of commercially produced artificial diamonds have been applied: Ib, IIa and IIb. Intensive radioluminescence and cathodoluminescence have been observed for two diamond types: IIa and IIb, which can be suggested for further doping by 14C. It had been demonstrated that simulation of diamond self-glowing from 14C using 99Tc and electron beam were insufficiently different due to technical aspects of the experiment, not the difference in the excitation energy. Cathodoluminescence technique can be used in the future for the study of diamonds when optimizing it spectral properties.

Valley-Polarized Plasmonic Edge Mode Visualized in the Near-Infrared Spectral Range.

Valley polarization has recently been adopted in optics, offering robust waveguiding and angular momentum sorting. The success of valley systems in photonic crystals suggests a plasmonic counterpart that can merge topological photonics and topological condensed matter systems, for instance, two-dimensional materials with the enhanced light-matter interaction. However, a valley plasmonic waveguide with a sufficient propagation distance in the near-infrared (NIR) or visible spectral range has so far not been realized due to ohmic loss inside the metal. Here, we employ gap surface plasmons for high index contrasting and realize a wide-bandgap valley plasmonic crystal, allowing waveguiding in the NIR-visible range. The edge mode with a propagation distance of 5.3 μm in the range of 1.31-1.36 eV is experimentally confirmed by visualizing the field distributions with a scanning transmission electron microscope cathodoluminescence technique, suggesting a practical platform for transferring angular momentum between photons and carriers in mesoscopic active devices.

Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus‐Olivine‐Assemblages in chondrites

AbstractThe geochemistry and textures of phosphate minerals can provide insights into the geological histories of parental asteroids, but the processes governing their formation and deformation remain poorly constrained. We assessed phosphorus‐bearing minerals in the three lithologies (light, dark, and melt) of the Chelyabinsk (LL5) ordinary chondrite using scanning electron microscope, electron microprobe, cathodoluminescence, and electron backscatter diffraction techniques. The majority of studied phosphate grains appear intergrown with olivine. However, microtextures of phosphates (apatite [Ca5(PO4)3(OH,Cl,F)] and merrillite [Ca9NaMg(PO4)7]) are extremely variable within and between the differently shocked lithologies investigated. We observe continuously strained as well as recrystallized strain‐free merrillite populations. Grains with strain‐free subdomains are present only in the more intensely shocked dark lithology, indicating that phosphate growth predates the development of primary shock‐metamorphic features. Complete melting of portions of the meteorite is recorded by the shock‐melt lithology, which contains a population of phosphorus‐rich olivine grains. The response of phosphorus‐bearing minerals to shock is therefore hugely variable throughout this monomict impact breccia. We propose a paragenetic history for P‐bearing phases in Chelyabinsk involving initial phosphate growth via P‐rich olivine replacement, followed by phosphate deformation during an early impact event. This event was also responsible for the local development of shock melt that lacks phosphate grains and instead contains P‐enriched olivine. We generalize our findings to propose a new classification scheme for Phosphorus‐Olivine‐Assemblages (Type I–III POAs). We highlight how POAs can be used to trace radiogenic metamorphism and shock metamorphic events that together span the entire geological history of chondritic asteroids.

Photoabsorption Imaging at Nanometer Scales Using Secondary Electron Analysis.

Optical imaging with nanometer resolution offers fundamental insights into light-matter interactions. Traditional optical techniques are diffraction limited with a spatial resolution >100 nm. Optical super-resolution and cathodoluminescence techniques have higher spatial resolutions, but these approaches require the sample to fluoresce, which many materials lack. Here, we introduce photoabsorption microscopy using electron analysis, which involves spectrally specific photoabsorption that is locally probed using a scanning electron microscope, whereby a photoabsorption-induced surface photovoltage modulates the secondary electron emission. We demonstrate spectrally specific photoabsorption imaging with sub-20 nm spatial resolution using silicon, germanium, and gold nanoparticles. Theoretical analysis and Monte Carlo simulations are used to explain the basic trends of the photoabsorption-induced secondary electron signal. Based on our current experiments and this analysis, we expect that the spatial resolution can be further improved to a few nanometers, thereby offering a general approach for nanometer-scale optical spectroscopic imaging and material characterization.

Impact of petrographic characteristics on reservoir quality of tight sandstone reservoirs in coal‐bearing strata: A case study in Lower Permian Shihezi Formation in northern Ordos Basin, China

The lower Shihezi Formation in the Sulige gas field is the main gas exploitation target in the Ordos Basin and is crucial in finding high‐quality reservoirs for further exploration. Using X‐ray diffraction, cathodoluminescence (CL), and scanning electron microscope (SEM) techniques, the eighth member of lower Shihezi Formation (He8) sandstones are characterized as fine‐ to coarse‐grained quartzarenite and litharenite with good sorting, which are controlled by different sources and depositional faces. Four types of sandstones are recognized according to varied petrographic characteristics, among which fine‐grained sandstones (type I) has the poorest reservoir quality and coarse‐grained sandstones with chlorite coating (type II) are the best reservoirs. The complicated diagenetic process mainly includes intense compaction, two‐stage dissolution, quartz and calcite cementation, which is closely associated with the thermal evolution of coals. The increased ductile fragments account for low reservoir quality in type I sandstones. Due to the absence of feldspar, the influence of other detrital components on the reservoir quality has increased. Sandstones with abundant volcanic fragments (type II) usually formed grain‐coating chlorite, which inhibit tight compaction and quartz cementations. Quartz overgrowth originated from feldspar dissolution as well as pressure dissolution of detrital quartz are frequently observed in medium‐ to coarse‐grained quartzarenite (type III). The high‐quality reservoir exits when the ductile grains content is about 4%, according to the negative relationship between quartz cement and ductile content. Although there are a lot of dissolution pores in medium‐ to coarse‐grained litharenite (type IV), the reservoir quality did not improve much due to the diagenetic minerals filling in the secondary pores.

Dolomitization models in the Sibzar Formation (Middle Devonian), Binalood Mountains (NE Iran): Based on the petrographic and geochemical evidence

Lithostratigraphically, Sibzar Formation (Middle Devonian) in the Kharv section (Binalood Mountains, NE Iran) with a thickness of 334 m consists of three units (in ascending order): dolostone with intercalations sandstone, middle basaltic sill, and upper dolostone. Three types of dolomite have been identified based on crystal size and shape. Fine crystalline dolomite (D1; finer than 30 μm) consist of Nonplanar-a dolomites. Fine to medium crystalline dolomite (D2; 20 to 150 μm) consist of mostly Nonplanar-a dolomites and some dolomites are Planar-s and Planar-e. Vein dolomites (Vd; 40 to 700 μm) have a very diverse crystalline texture and are mostly Planar-s, Planar-e and some Nonplanar-a. Cathodoluminescence technique studies also showed that most of these dolomites have dull red luminescence, in some veins with bright red luminescence and zoning. Based on the X-ray diffraction (XRD) and ICP-OES, all dolomites are nearly stoichiometric dolomite and relatively well ordered. Elemental analysis and stable isotope studies show that the concentration of minor elements such as sodium (D1: 822–1365 ppm; D2: 1016–1241 ppm; Vd: 971–1072 ppm), strontium (D1: 257–963 ppm; D2: 134–1334 ppm; Vd: 144–379 ppm), manganese (D1: 560–3675 ppm; D2: 1039–2168 ppm; Vd: 1818–3454 ppm), and iron (D1: 15997-30080 ppm; D2: 8288–18456 ppm; Vd: 19304-25618 ppm) in these dolomites were high and the values of the stable isotope of oxygen (D1: -9.1 to −5.9‰; D2: -7.6 to −6.1‰; Vd: -11.1 to −7.2‰) and carbon (D1: -3.5 to −2.5‰; D2: -5.2 to −1.3‰; Vd: -2 to −1.6‰) were low. The high values of iron and manganese and depletion of the carbon and oxygen isotopes can be related to the effects of high-temperature diagenetic fluids caused by basaltic sill during the burial. These dolomites formed in tidal environment and burial diagenesis in this Formation. Seawater, connate seawaters, saline basinal fluid, and magnesium-rich hypersaline fluids are the main source of magnesium ion (Mg2+) for dolomites of this Formation.