Cathodoluminescence Investigations Research Articles

Diagenesis and reservoir properties of Middle Jurassic sandstones, Traill Ø, East Greenland: The influence of magmatism and faulting

The c. 500 m thick Middle Jurassic sandstones of the fluvial Bristol Elv and marine Pelion Formations of the East Greenland Basin are evaluated here in order to improve the understanding of the processes that influenced the diagenetic evolution. The study may help to predict the reservoir properties of sandstones affected by magmatism and faulting, both in general and specifically in undrilled areas on- and offshore East Greenland and, in the Vøring Basin on the Mid-Norwegian shelf. The study shows a variety of authigenic mineral phases dominated by quartz cement, carbonate cement, illite and iron-oxide. One of the clear differences between the two formations is the presence of early carbonate-cemented horizons in the marine sandstones; these horizons are inferred to reflect a primary concentration of biogenic clasts and fossil shells. Intense quartz cementation occurs primarily in the fluvial sandstones but the marine sandstones are also highly quartz-cemented. Two episodes of burial and uplift are recorded in the diagenetic sequence and widespread grain-crushing in coarse-grained intervals is believed to result from overpressure and subsequent compaction due to sudden pressure release along major faults. Maximum burial depths may only have been around 2000–2500 m. Cathodoluminescence analyses show that grain crushing was followed by intense quartz cementation. The quartz cement is to a great deal believed to have formed due to increased surface area from crushing of detrital quartz grains, creating fresh nucleation sites for the quartz. Cathodoluminescence investigations also show that only minor pressure dissolution has taken place between detrital quartz grains and that the ubiquitous quartz cementation displays several growth zones, and was thus in part the result of the introduction of silica-rich extra-formational fluids related to the flow of hot fluids along reactivated faults and increased heat flow and temperature due to magmatism. This interpretation is supported by fluid inclusion homogenization temperatures between 117 and 158 °C in quartz cements. In one of the two study areas, the development of macroscopic stylolites has significantly enhanced quartz cementation, probably in connection with thermal convection flow. As a result of the magmatic and fault-related quartz cementation and illitization, the reservoir quality of the sandstone formations deteriorated and changed drastically.

Strong light scattering and broadband (UV to IR) photoabsorption in stretchable 3D hybrid architectures based on Aerographite decorated by ZnO nanocrystallites

In present work, the nano- and microscale tetrapods from zinc oxide were integrated on the surface of Aerographite material (as backbone) in carbon-metal oxide hybrid hierarchical network via a simple and single step magnetron sputtering process. The fabricated hybrid networks are characterized for morphology, microstructural and optical properties. The cathodoluminescence investigations revealed interesting luminescence features related to carbon impurities and inherent host defects in zinc oxide. Because of the wide bandgap of zinc oxide and its intrinsic defects, the hybrid network absorbs light in the UV and visible regions, however, this broadband photoabsorption behavior extends to the infrared (IR) region due to the dependence of the optical properties of ZnO architectures upon size and shape of constituent nanostructures and their doping by carbon impurities. Such a phenomenon of broadband photoabsorption ranging from UV to IR for zinc oxide based hybrid materials is novel. Additionally, the fabricated network exhibits strong visible light scattering behavior. The developed Aerographite/nanocrystalline ZnO hybrid network materials, equipped with broadband photoabsorption and strong light scattering, are very promising candidates for optoelectronic technologies.

High-Resolution Cathodoluminescence Investigation of Degradation Processes in InGaN Green Laser Diodes

High-Resolution Cathodoluminescence Investigation of Degradation Processes in InGaN Green Laser Diodes

Nanofocus x-ray diffraction and cathodoluminescence investigations into individual core–shell (In,Ga)N/GaN rod light-emitting diodes

Employing nanofocus x-ray diffraction, we investigate the local strain field induced by a five-fold (In,Ga)N multi-quantum well embedded into a GaN micro-rod in core–shell geometry. Due to an x-ray beam width of only 150 nm in diameter, we are able to distinguish between individual m-facets and to detect a significant in-plane strain gradient along the rod height. This gradient translates to a red-shift in the emitted wavelength revealed by spatially resolved cathodoluminescence measurements. We interpret the result in terms of numerically derived in-plane strain using the finite element method and subsequent kinematic scattering simulations which show that the driving parameter for this effect is an increasing indium content towards the rod tip.

Cathodoluminescence investigation of Ge-point defects in silica-based optical fibers

Cathodoluminescence (CL) measurements have been performed on Ge doped and Ge/F co-doped optical fibers, in the aim of studying the spatial distributions of the emitting precursor defects present in the as-drawn optical fiber as well as those of the radiation induced centers generated by the 10keV electron exposure. Using the CL instrument, we recorded different emission bands located in the visible spectral domain (300–750nm) as well as CL imaging of associated defects, with a spatial resolution of about 1µm, along the fiber transverse cross sections. In the pristine fiber, Germanium Lone Pair Centers (GLPCs) emitting at 400nm are the main precursor sites observed in both fibers. Whereas during electron exposure, these centers are converted into other Ge-related defects. In this paper, we studied in situ their bleaching kinetic using CL monochromatic imaging. As expected, our results show that the GLPC signal decreases with the electron fluence, confirming its precursor role. Thanks to the CL abilities, we also demonstrate that the GLPC conversion into radiation induced defects (and then its bleaching kinetic) depends on the germanium concentration, opening the way to a better control of the radiation sensitivity of germanosilicate glass.

Self-Catalyzed Growth of Vertically Aligned InN Nanorods by Metal-Organic Vapor Phase Epitaxy.

Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal-organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorods indicate a self-catalytic vapor-liquid-solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, is necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.

Stacking fault emission in GaN: Influence of n-type doping

We present spatially and spectrally resolved cathodoluminescence investigations on the cross section of semipolar (112¯2) gallium nitride epitaxial layers with high background doping level. The locally varying high carrier concentration leads in emission to a free electron recombination band (FERB) governed on the high energy side by conduction band filling. For the basal plane stacking fault (BSF) of type I1, typically emitting at ≈3.41 eV in low doped GaN, we find a blue shift in emission correlated to the FERB high energy tail. This shift can be perfectly modeled and understood in a quantum well model for the BSF, taking also into account the varying doping level in the barrier region. Thus, the carrier concentration can be finally calculated either from the actual position of the I1 BSF or alternatively from the FERB-related near band edge emission.

Probing plasmons in three dimensions by combining complementary spectroscopies in a scanning transmission electron microscope

The nanoscale optical response of surface plasmons in three-dimensional metallic nanostructures plays an important role in many nanotechnology applications, where precise spatial and spectral characteristics of plasmonic elements control device performance. Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) within a scanning transmission electron microscope have proven to be valuable tools for studying plasmonics at the nanoscale. Each technique has been used separately, producing three-dimensional reconstructions through tomography, often aided by simulations for complete characterization. Here we demonstrate that the complementary nature of the two techniques, namely that EELS probes beam-induced electronic excitations while CL probes radiative decay, allows us to directly obtain a spatially- and spectrally-resolved picture of the plasmonic characteristics of nanostructures in three dimensions. The approach enables nanoparticle-by-nanoparticle plasmonic analysis in three dimensions to aid in the design of diverse nanoplasmonic applications.

Nanoscale Investigation of Degradation and Wavelength Fluctuations in InGaN-Based Green Laser Diodes

We present a study of the optical inhomogeneities and degradation of InGaN-based green laser diodes based on high-resolution cathodoluminescence (CL) investigation of the output facets and inner cross-section of the devices. The results indicate that 1) degradation originates from a diffusion process, which causes an increase in the threshold current. 2) Nanoscale-level CL points out the circular symmetry of the degraded area, which is wider than the ridge and includes not only the quantum wells but also the waveguiding and cladding layers. 3) The yellow luminescence decreases within the degraded region, whereas its intensity increases outside of the degraded region. 4) Wavelength fluctuations are found in both quantum wells and waveguides, which are critically analyzed and ascribed to inhomogeneity in indium concentration. Their possible effect in the filamentation of the laser emission is discussed.

The effect of annealing on properties of europium doped ZnO nanopowders obtained by a microwave hydrothermal method

Europium doped ZnO nanopowders made by microwave hydrothermal method are investigated. As zinc oxide precursor zinc nitrate(V) hexahydrate (Zn(NO3)2·6H2O) was used. Two types of nanopowder samples are examined: as grown and annealed at 750°C in air atmosphere. We investigate the structural, morphological and optical prosperities of europium doped ZnO. Results of scanning electron microscopy, X-ray diffraction, photo- and cathodoluminescence investigations and also CIE1961 chromaticity diagram are presented.

Temperature‐dependent cathodoluminescence investigation of Er‐implanted GaN thin films

In this paper, temperature‐dependent cathodoluminescence (CL) spectra of Er‐implanted GaN thin films were measured. The effects of accelerating voltage and temperature on the CL spectra of Er‐implanted GaN were investigated. In the near band‐edge emission region, the competition mechanism between DAP and D0X was disclosed. A slight blue shift of the DAP emission peak with the increase of accelerating voltage was observed. The temperature dependence of the CL intensity of FX emission reveals a binding energy of ∼32 meV in Er‐implanted GaN. Below 182 K, the 2H11/2 state of Er3+ is not thermally populated and the yellow band luminescence (YL) related to the defects was observed. At higher temperature, the thermal coupling between the two excited state levels of 2H11/2 and 4S3/2 of Er3+ is obvious and the YL is nearly invisible. Even at 373 K, a strong green emission at 537 nm can be observed, which indicates the Er‐doped GaN is promising to be applied in high‐temperature environments.

Carrier-induced refractive index change observed by a whispering gallery mode shift in GaN microrods

Vertical oriented GaN microrods were grown by metal-organic vapor phase epitaxy with four different n-type carrier concentration sections above 1019 cm−3 along the c-axis. In cathodoluminescence investigations carried out on each section of the microrod, whispering gallery modes can be observed due to the hexagonal symmetry. Comparisons of the spectral positions of the modes from each section show the presence of an energy dependent mode shift, which suggest a carrier-induced refractive index change. The shift of the high energy edge of the near band edge emission points out that the band gap parameter in the analytical expression of the refractive index has to be modified. A proper adjustment of the band gap parameter explains the observed whispering gallery mode shift.

Thallium occurrence and partitioning in soils and sediments affected by mining activities in Madrid province (Spain)

Thallium (Tl) and its compounds are toxic to biota even at low concentrations but little is known about Tl concentration and speciation in soils. An understanding of the source, mobility, and dispersion of Tl is necessary to evaluate the environmental impact of Tl pollution cases. In this paper, we examine the Tl source and dispersion in two areas affected by abandoned mine facilities whose residues remain dumped on-site affecting to soils and sediments of natural water courses near Madrid city (Spain). Total Tl contents and partitioning in soil solid phases as determined by means of a sequential extraction procedure were also examined in soils along the riverbeds of an ephemeral and a permanent streams collecting water runoff and drainage from the mines wastes. Lastly, electronic microscopy and cathodoluminescence probe are used as a suitable technique for Tl elemental detection on thallium-bearing phases. Tl was found mainly bound to quartz and alumino-phyllosilicates in both rocks and examined soils. Besides, Tl was also frequently found associated to organic particles and diatom frustules in all samples from both mine scenarios. These biogenic silicates may regulate the transfer of Tl into the soil-water system.

Low-Temperature Cathodoluminescence Investigations of High-Quality Zinc Oxide Nanorods.

We present results of cathodoluminescence (CL) investigations of high-quality zinc oxide (ZnO) nanorods obtained by an extremely fast hydrothermal method on a silicon substrate. A scanning electron microscopy (SEM) system equipped with CL allows direct comparison of SEM images and CL maps, taken from exactly the same areas of samples. Investigations are performed at a temperature of 5 K. An interlink between sample microstructure and emission properties is investigated. CL confirms a very high quality of ZnO nanorods produced by our method. In addition, the presence of super radiation effects in ZnO nanorod arrays is suggested.

Thallium and manganese complexes involved in the luminescence emission of potassium-bearing aluminosilicates

The luminescence emission at 285nm in natural K-feldspar has been studied by Russian groups and associated with thallium ions in structural positions of K+ sites as artificially thallium-doped feldspars display the same emission band. Here attention is focussed on spectra of CL emission bands centered near 285 and 560nm from paragenetic adularia, moscovite and quartz micro-inclusions. With accesorial thallium they show clear resemblances to each other. Associated sedimentary and hydrothermal aluminosilicate samples collected from Guadalix (Madrid, Spain) were analyzed with a wide range of experimental techniques including Environmental Scanning Electron Microscopy (ESEM) with an attached X-Ray Energy-Dispersive Spectrometer (EDS) and a cathodoluminescence probe (CL) and Electron Probe Microanalysis (EPMA), X-Ray Fluorescence Spectrometry (XRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Differential and Thermogravimetric Analyses (DTA-TG), radioluminescence (RL), Mössbauer spectroscopy and X-Ray Photoelectron Spectrometry (XPS). The luminescence emission bands at 285 and 560nm seem to be associated with hydrous thallium–manganese complexes bonded to potassium-bearing aluminosilicates since various minerals such as K-feldspar, moscovite and quartz micro-inclusions display similar CL spectra, accesorial thallium and hydroxyl groups. The presence of iron introduces a brown color which is attributed to submicroscopic iron oxides detectable in the optical and chemical microanalysis, but this does not contribute to the luminescence emission. The XPS Mn 2p spectrum of the adularia sample at room temperature is composed of a spin–orbit doublet plus clear shake-up satellite structure ~4eV above the main photoemision lines and is consistent with Mn2+ in good agreement with the observed luminescence emission at 560nm for aluminosilicates produced by a 4T1(4G)→6A1(6S) transition in tetrahedrally coordinated Mn2+. Moscovite samples display spectral CL bands at 285 and 560nm but only when the electron-beam is directed along the (010) orientation and not along the (001) orientation. The Tl+ versus K+ cation isomorphism anchors the luminogenous hydrous thallium–manganese complexes to the potassium-bearing aluminosilicate surfaces under analyses. The CL emission bands at 285 and 560nm of these complexes together with the EDS detection of thallium are a fast analytical measurement detecting the presence of thallium in further studies involving this toxic element.

Enhanced Cathodoluminescence of KOH-treated InGaN/GaN LEDs with Deep Nano-Hole Arrays

Square lattice nano-hole arrays with diameters and periodicities of 200 and 500 nm, respectively, are fabricated on InGaN/GaN blue light emitting diodes (LEDs) using electron-beam lithography and inductively coupled plasma reactive ion etching processes. Cathodoluminescence (CL) investigations show that light emission intensity from the LEDs with the nano-hole arrays is enhanced compared to that from the planar sample. The CL intensity enhancement factor decreases when the nano-holes penetrate into the multiple quantum wells (MQWs) due to the plasma-induced damage and the residues. Wet chemical treatment using KOH solution is found to be an effective method for light extraction from the nano-patterned LEDs, especially, when the nano-holes penetrate into the MQWs. About 4-fold CL intensity enhancement factor is achieved by the KOH treatments after the dry etching for the sample with a 250-nm deep nano-hole array.

N‐GaN column arrays on the vertical InGaN/GaN blue LEDs formed by maskless dry etching

The InGaN/GaN blue light emitting diodes (LED) structures have been grown on sapphire substrates with a hexagonal array of hemispherical patterns by low‐pressure metalorganic chemical vapor deposition. Vertical LED structures on Cu carriers are fabricated using electroplating and KrF laser lift‐off techniques. After removal of the patterned sapphire substrate, an inductively coupled plasma etching is carried out to expose the n‐GaN layer for n‐metal contact. It is observed that GaN columns are formed at the center of the concave hemispheres after dry etching processes. Cathodoluminescence and wet chemical etching investigations reveal that a high density of dislocations is found to be generated at these specific positions. The possible mechanism for these observations is attributed to the defect distribution and defect‐dependent selective etching of the GaN.

Characterization of dislocations in MOCVD-grown GaN using a high temperature annealing method

In this paper, a high temperature annealing (HTA) method is proposed to characterize dislocations in GaN prepared by metal–organic chemical vapor deposition (MOCVD) on c-plane (0001) sapphire. The templates were each annealed at different temperatures for 5 min. Molten KOH–NaOH eutectic (E) etching was also applied (at 500 °C for 30 min) to test and verify this new method. A comparison between the HTA template and the E etching template was made. The morphology and distribution of HTA pits and E etching pits were examined using scanning electron microscopy (SEM). Atomic force microscopy (AFM) was employed to study the shape of the HTA pits. Transmission electron microscopy (TEM) and cathodoluminescence (CL) investigation were used to further confirm the origin and density of the dislocations.

Optical and Cathodoluminescence Investigations of the Green Microcrystalline (Chrysoprase) Quartz

Gem-quality green cryptocrystalline silica formation is relatively rare in nature, and has an interesting mineralogical crystallization and irradiation response of the fine fibrous silica. Chemical analyses of the green material reveal remarkable concentrations of some trace elements, such as nickel, iron, and chrome. They are certainly responsible for producing of the individual color production and irradiation luminescence response. Optical absorption spectroscopy shows that the dark green coloration is due to light transmittance at 528 nm in the visible region as a result of absorbance peak at 645 nm and about 360-410 nm absorbance band gap. These optical absorbance gaps are due to not only Ni ion content (4600 ppm) but also, Fe ion (13600 ppm) and Cr ion (823 ppm) contents. The cathodoluminescence spectra of the green material were taken into consideration in this study, and they were evaluated using “surpher, grapher, and axum” of the computer programs. In the spectra of alternative current cathodoluminescence with two-dimension, one major spectral emission band appears at readable intensity and magnitude in 90 Hz in the yellow wavelength region at 585 nm. In addition, the two-dimension cathodoluminescence spectra show that only the other major spectral emission band of cathodoluminescence appears at 90 Hz frequency in the green wavelength region at 530 nm.

Cathodoluminescence investigations on quartz cement in the sandstones of Khabour Formation from Iraqi Kurdistan Region, Northern Iraq

The Ordovician deltaic to shallow marine Khabour Formation in Northern Iraq consists mainly of sandstone with minor siltstone and interbedded shale. The sandstones are pervasively cemented by quartz that resulted in very little preserved primary porosity. Cathodoluminescence and petrographic studies showed that the silica cementation occurred in five successive phases which can be distinguished by their luminescence pattern. The precipitations of two phases have predated the major compaction process while the other phases are younger. The successive phases represent a sequence of changes in silica supply which were classified as very early and early, derived from dissolved biogenic silica that precipitated as opal/microquartz, possibly pre-compactional and of non-luminescent quartz overgrowth type. This was followed by phases whose silica supply derived from pressure solution of quartz, dissolution of feldspar, and hydrothermal fluids related to major thrust fault event. These successive quartz cement phases showed an increase in luminescence and the development of complicated zonation pattern in late-stage quartz cementation.