Cathodoluminescence (CL) microanalysis provides high-sensitivity spectra and high-resolution images associated with impurity and structural defects at the nanoscale and from luminescent materials including minerals, semiconductor, and dielectric/insulating materials. Cathodoluminescence is the non-incandescent emission of light (photons) emitted from materials excited by an electron beam. CL photons (UV-VIS-NIR) are produced as a result of electronic transitions between the conduction and valence band and may also involve electronic transitions associated with defect levels within the band gap. Microscopic defects such as imperfections and impurities influence the optical, electrical, and mechanical properties of scientifically and technologically important materials. CL microanalysis is therefore a useful microanalytical technique for characterizing these properties with high sensitivity and spatial resolution. CL image resolution can range from sub-10 nm to microns, dependent on experimental arrangement (STEM-CL, SEM-CL, optical CL microscopy), electron beam parameters, specimen configuration, carrier diffusion, etc. The sensitivity of CL microanalysis is dependent on the specimen and, in the absence of self-absorption and competitive recombination centers, can be several magnitudes more sensitive than X-ray microanalysis. In particular, quantitative CL microanalysis of trace impurity concentrations while challenging has recently been shown to be possible for a range of minerals.

Hyperspectral cathodoluminescence imaging provides spectrally and spatially resolved information on luminescent materials within a single dataset. Pushing the technique toward its ultimate nanoscale spatial limit, while at the same time spectrally dispersing the collected light before detection, increases the challenge of generating low-noise images. This article describes aspects of the instrumentation, and in particular data treatment methods, which address this problem. The methods are demonstrated by applying them to the analysis of nanoscale defect features and fabricated nanostructures in III-nitride-based materials.

The Monte Carlo software CASINO has been expanded with new modules for the simulation of complex beam scanning patterns, for the simulation of cathodoluminescence (CL), and for the calculation of electron energy deposition in subregions of a three-dimensional (3D) volume. Two examples are presented of the application of these new capabilities of CASINO. First, the CL emission near threading dislocations in gallium nitride (GaN) was modeled. The CL emission simulation of threading dislocations in GaN demonstrated that a better signal-to-noise ratio was obtained with lower incident electron energy than with higher energy. Second, the capability to simulate the distribution of the deposited energy in 3D was used to determine exposure parameters for polymethylmethacrylate resist using electron-beam lithography (EBL). The energy deposition dose in the resist was compared for two different multibeam EBL schemes by changing the incident electron energy.

BaFCl:Sm3+ is an efficient photoluminescent storage phosphor for ionizing radiation. Cathodoluminescence (CL) microanalysis enables the Sm2+ and Sm3+ oxidation states of samarium doped BaFCl to be easily identified, provides information about electron-beam and X-ray induced modification of BaFCl:Sm, and enables the synthesis dependent spatial distribution of samarium dopants of <100 ppm concentration to be determined with sub-100 nm resolution at 295 K. CL spectroscopy of BaFCl:Sm particles reveals broad CL emissions at ∼360 and ∼500 nm associated with Vk(Cl−) and oxygen-vacancy defects in the BaFCl host lattice and fine structure CL emissions associated with major 4GJ → 6HJ (Sm3+) and 5DJ → 7FJ (Sm2+) transitions. CL microanalysis shows samarium dopants are uniformly distributed in conventional sintered microcrystalline BaFCl:Sm. In contrast, CL investigations reveal that for BaFCl:Sm nanoparticles, which have been prepared using a co-precipitation method, with greatly improved Sm3+ → Sm2+ conversion efficiency, the samarium dopants are concentrated near the particle surface resulting in a BaFCl:Sm3+ shell surrounding the BaFCl core, which is stable to energetic irradiation.

The measurement of near-infrared (NIR) cathodoluminescence (CL) with sufficient sensitivity to allow full spectral mapping has been investigated through the application of optimized grating spectrometers that allow the ultraviolet (UV), visible, and NIR CL spectra to be measured simultaneously. Two optical spectrometers have been integrated into an electron microprobe, allowing simultaneous collection of hyperspectral CL (UV-NIR), characteristic X-rays, and electron signals. Combined hyperspectral CL spectra collected from two natural apatite (Ca5[PO4]3[OH,F]) samples from Wilberforce (Ontario, Canada) and Durango (Mexico) were qualitatively analyzed to identify the emission centers and then deconvoluted pixel-by-pixel using least-squares fitting to produce a series of ion-resolved CL intensity maps. Preliminary investigation of apatite has shown strong NIR emissions associated primarily with the rare-earth element Nd. Details of growth and alteration were revealed in the NIR that were not discernable with electron-induced X-ray mapping. Intense emission centers from Nd3+ and Sm3+ were observed in the spectra from both apatites, along with minor emissions from other 3+ rare-earth elements. Quantitative electron probe microanalysis was performed on points within the mapped area of the Durango apatite to produce a calibration line relating cathodoluminescent intensity of the fitted peak centered at 1,073 nm (1.156 eV) to the Nd concentration.

Previously, imaging and analysis with cathodoluminescence (CL) detectors required using high accelerating voltages. Utilization of lower accelerating voltage for microanalysis has the advantages of reduced beam-specimen interaction volume, and thus better spatial resolution, as well as reduction in electron beam induced damage. This article will highlight recent developments in field emission gun–scanning electron microscope technology that have allowed acquisition of high spatial resolution CL images at very low accelerating voltages. The advantages of low kV CL imaging will be shown using examples of a geological specimen (shale) and a specimen of an industrial grade diamond.

Ionoluminescence (IL) is the emission of light from a material due to excitation by an ion beam. In this work, a helium ion microscope (HIM) has been used in conjunction with a luminescence detection system to characterize IL from materials in an analogous way to how cathodoluminescence (CL) is characterized in a scanning electron microscope (SEM). A survey of the helium ion beam induced IL characteristics, including images and spectra, of a variety of materials known to exhibit CL in an SEM is presented. Direct band-gap semiconductors that luminesce strongly in the SEM are found not do so in the HIM, possibly due to defect-related nonradiative pathways created by the ion beam. Other materials do, however, exhibit IL, including a cerium-doped garnet sample, quantum dots, and rare-earth doped LaPO4 nanocrystals. These emissions are a result of transitions between f electron states or transitions across size dependent band gaps. In all these samples, IL is found to decay with exposure to the beam, fitting well to double exponential functions. In an exploration of the potential of this technique for biological tagging applications, imaging with the IL emitted by rare-earth doped LaPO4 nanocrystals, simultaneously with secondary electron imaging, is demonstrated at a range of magnifications.

We have developed a fiber-based confocal optical microscope that operates inside of a commercial scanning electron microscope (SEM) instrument (JEOL 6400; JEOL Ltd., Tokyo, Japan) enabling the excitation of a sample either by a laser or by electron beam, and hence combining the complimentary techniques of photoluminescence and cathodoluminescence. The instrument uses single-mode fibers that enter the SEM by vacuum feedthroughs. The illumination and collection fibers operate as effective pinholes providing, in combination with a microscope objective (NA = 0.3), high spatial resolution (~2 μm) and excellent collection efficiency. The high spatial resolution ensures that the light collected from the sample is in a region of optimal laser beam and electron beam overlap. The capabilities of this instrument are tested by experiments involving the excitation of europium ions in situ doped in GaN thin films.

Cathodoluminescence (CL) microscopy and spectroscopy are luminescence techniques with widespread applications in geosciences. Many rock-forming and accessory minerals show CL characteristics, which can be successfully used in geoscientific research. One of the most spectacular applications is the visualization of growth textures and other internal structures that are not discernable with other analytical techniques. In addition, information from CL imaging and spectroscopy can be used for the reconstruction of processes of mineral formation and alteration to provide information about the real structure of minerals and materials, and to prove the presence and type of lattice incorporation of several trace elements. In the present article, an overview about CL properties of selected minerals is given, and several examples of applications discussed. The presented data illustrate that best results are achieved when luminescence studies are performed under standardized conditions and combined with other analytical techniques with high sensitivity and high spatial resolution.

Color centers in selected micro- and nanodiamond samples were investigated by cathodoluminescence (CL) microscopy and spectroscopy at 298 K [room temperature (RT)] and 77 K [liquid-nitrogen temperature (LNT)] to assess the value of the technique for astrophysics. Nanodiamonds from meteorites were compared with synthetic diamonds made with different processes involving distinct synthesis mechanisms (chemical vapor deposition, static high pressure high temperature, detonation). A CL emission peak centered at around 540 nm at 77 K was observed in almost all of the selected diamond samples and is assigned to the dislocation defect with nitrogen atoms. Additional peaks were identified at 387 and 452 nm, which are related to the vacancy defect. In general, peak intensity at LNT at the samples was increased in comparison to RT. The results indicate a clear temperature—dependence of the spectroscopic properties of diamond. This suggests the method is a useful tool in laboratory astrophysics.

The 49 type I natural pink diamonds examined exhibit color restricted to lamellae or bands oriented along {111} that are created by plastic deformation. Pink diamonds fall into two groups: (1) diamonds from Argyle in Australia and Santa Elena in Venezuela are heavily strained throughout and exhibit pink bands alternating with colorless areas, and (2) diamonds from other localities have strain localized near the discrete pink lamellae. Growth zones are highlighted by a blue cathodoluminescence (CL) and crosscut by the pink lamellae that emit yellowish-green CL that originates from the H3 center. This center probably forms by the recombination of nitrogen-related centers (A-aggregates) and vacancies mobilized by natural annealing in the Earth's mantle. Twinning is the most likely mechanism through which plastic deformation is accommodated for the two groups of diamonds. The plastic deformation creates new centers visible through spectroscopic methods, including the one responsible for the pink color, which remains unidentified. The differences in the plastic deformation features, and resulting CL properties, for the two groups might correlate to the particular geologic conditions under which the diamonds formed; those from Argyle and Santa Elena are deposits located within Proterozoic cratons, whereas most diamonds originate from Archean cratons.

Hyperspectral cathodoluminescence mapping is used to examine a carbonado diamond. The hyperspectral dataset is examined using a data clustering algorithm to interpret the range of spectral shapes present within the dataset, which are related to defects within the structure of the diamond. The cathodoluminescence response from this particular carbonado diamond can be attributed to a small number of defect types: N-V0, N2V, N3V, a 3.188 eV line, which is attributed to radiation damage, and two broad luminescence bands. Both the N2V and 3.188 eV defects require high-temperature annealing, which has implications for interpreting the thermal history of the diamond. In addition, bright halos observed within the diamond cathodoluminescence, from alpha decay radiation damage, can be attributed to the decay of 238U.

A comparative cathodoluminescence (CL) spectroscopic study of extraordinarily well-preserved versus diagenetically altered Turonian (∼92 Ma before present) calcitic and aragonitic microfossils was performed to document the cathodoluminescence characteristics of two common Cretaceous carbonate producers, foraminifera and calcareous dinoflagellates. Unaltered specimens reveal a conspicuous peak in the blue CL band at ∼400 nm that has rarely been previously reported for biogenic carbonates. We interpret this luminescence as an indicative feature of the primary bio-mineralized shells of calcareous dinoflagellates and foraminifera. Orange luminescence as the second important CL emission band (∼620 nm) in calcite generally increases with diagenetic cement overgrowth and recrystallization but can also be present in unaltered material. Thus, orange CL of biogenic calcite is not an unequivocal diagenetic indicator. Accordingly, spectroscopic investigation of both the ∼400 and ∼620 nm peaks represents a more objective criterion to evaluate the degree of diagenetic alteration. The ratio of relative intensities of the blue CL versus orange CL can provide a semiquantitative measure with relative intensity ratios blue:orange >2 occurring in the least diagenetically altered microfossils. Comparison of unaltered specimens of separate species reveals elemental differences that potentially indicate species-specific biomineralization or habitats.

This article concerns application of cathodoluminescence (CL) spectroscopy to volcanic quartz and its utility in assessing variation in trace quantities of Ti within individual crystals. CL spectroscopy provides useful details of intragrain compositional variability and structure but generally limited quantitative information on element abundances. Microbeam analysis can provide such information but is time-consuming and costly, particularly if large numbers of analyses are required. To maximize advantages of both approaches, natural and synthetic quartz crystals were studied using high-resolution hyperspectral CL imaging (1.2–5.0 eV range) combined with analysis via laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Spectral intensities can be deconvolved into three principal contributions (1.93, 2.19, and 2.72 eV), for which intensity of the latter peak was found to correlate directly with Ti concentration. Quantitative maps of Ti variation can be produced by calibration of the CL spectral data against relatively few analytical points. Such maps provide useful information concerning intragrain zoning or heterogeneity of Ti contents with the sensitivity of LA-ICPMS analysis and spatial resolution of electron microprobe analysis.

We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity.

A method for obtaining quantitative mean atomic number images in a scanning electron microscope for different kinds of samples has been developed. The backscattered electron signal is monotonically increasing with the mean atomic number Z, and accordingly Z can be given as a function of the image gray levels. From results obtained from Monte Carlo simulations, an exponential function is fitted to convert the backscattered registered gray levels into a Z image map. Once this fitting was performed, the reproducibility of the Z determination was checked through the acquisition of backscattered electron images from metal and mineral standards. The developed method can be applied to any unknown sample, always controlling the experimental conditions, as shown here for a thin section of a rock in which several unknown mineral phases are present; the results obtained herein are compared to quantitative assessments performed with X-ray spectra from each mineral phase.

In this article, we demonstrate the application of a new compressed sensing three-dimensional reconstruction algorithm for electron tomography that increases the accuracy of morphological characterization of nanostructured materials such as nanocrystalline iron oxide particles. A powerful feature of the algorithm is an anisotropic total variation norm for the L1 minimization during algebraic reconstruction that effectively reduces the elongation artifacts caused by limited angle sampling during electron tomography. The algorithm provides faithful morphologies that have not been feasible with existing techniques.

Nonwoven materials are found in a gamut of critical applications. This is partly due to the fact that these structures can be produced at high speed and engineered to deliver unique functionality at low cost. The behavior of these materials is highly dependent on alignment of fibers within the structure. The ability to characterize and also to control the structure is important, but very challenging due to the complex nature of the structures. Thus, to date, focus has been placed mainly on two-dimensional analysis techniques for describing the behavior of nonwovens. This article demonstrates the utility of three-dimensional (3D) digital volumetric imaging technique for visualizing and characterizing a complex 3D class of nonwoven structures produced by hydroentanglement.

In this study the nanomorphology of P3HT:PC61BM absorber layers of organic solar cells was studied as a function of the processing parameters and for P3HT with different molecular weight. For this purpose we apply scanning transmission electron microscopy (STEM) at low electron energies in a scanning electron microscope. This method exhibits sensitive material contrast in the high-angle annular dark-field (HAADF) mode, which is well suited to distinguish materials with similar densities and mean atomic numbers. The images taken with low-energy HAADF STEM are compared with conventional transmission electron microscopy and atomic force microscopy images to illustrate the capabilities of the different techniques. For the interpretation of the low-energy HAADF STEM images, a semiempirical equation is used to calculate the image intensities. The experiments show that the nanomorphology of the P3HT:PC61BM blends depends strongly on the molecular weight of the P3HT. Low-molecular-weight P3HT forms rod-like domains during annealing. In contrast, only small globular features are visible in samples containing high-molecular-weight P3HT, which do not change significantly after annealing at 150°C up to 30 min.

A gray cast iron specimen was investigated by color and chemical etching with optical and atomic force microscopy, and the effect of grain orientation on the effectiveness of etching was examined. It was proven that the grain orientation dependence of chemical and color etching is just the opposite, and that the specimen surface after color etching is not uniformly smooth. Explanation for the layer structure of the color etched iron specimen is given.