Cathodoluminescence Method Research Articles

Integrated textural and geochemical analysis of igneous zircon by atom probe tomography

Mechanisms relating to growth and/or compositional modification of zircon occur at the atomic scale. For felsic igneous systems, processes responsible for growth patterns in zircon have previously remained elusive as the volume of material needed to analyze these compositional features using traditional in-situ methods is considerably larger than the typical sub-micron scale distribution of trace elements. To illuminate some of these driving forces, we characterize and quantify minor and trace element concentrations in igneous zircon grains by combining methods of cathodoluminescence (CL) imaging, electron microprobe microanalysis (EMPA) elemental maps for Hf, Y, Yb and U or Th, and atom probe tomography (APT). We focus on igneous zircon from the Chon Aike Silicic Large Igneous Province (Patagonia) that provide novel insights into (1) dissolution and re-crystallization during crustal anatexis, (2) crystallization to produce oscillatory zonation patterns that are typical of igneous zircons, and (3) the incorporation of trace element impurities (e.g., P, Be, and Al) at the nanoscale. Significantly, these APT volumes provide nanoscale sampling of boundaries between oscillatory growth zones in an igneous zircon to reveal compositional zoning of Y and, to a lesser extent P, which appear as high-angle, planar features. These concentration boundaries measured on the order of 10 to 12 nm are difficult to reconcile with proposed mechanisms for generating fine-scaled oscillations. Lastly, we fit diffusional profiles to measured Y concentrations to provide an estimate on the maximum timescales of zircon growth prior to eruption, as a function of the temperature at which diffusion occurred. When combined with known pressure-temperature-time paths for the magmatic system considered, these extremely short diffusion profiles that are resolvable by APT provide a powerful method to constrain timescales of crystal growth.

Local symmetry of manganese ions in MgAl2O4 optical nanoceramics

Optically transparent nanoceramics of the composition Mg1-xMnxAl2O4(x = 0.005) with a grain size of 15–40 nm were obtained by thermobaric synthesis in a toroid-type high-pressure chamber in the range P = 4–9 GPa at a temperature of 600 °C. EPR spectroscopy indicates the presence of divalent manganese ions with a characteristic HFS signal. In addition, the signal from F+ centers were registered in the EPR spectrum. It has been established that in the HFS of impurity Mn2+ there is an additional contribution from manganese centers split in the field of rhombic symmetry. Photoluminescence spectroscopy methods revealed the presence of optically active centers based on Mn3+ and Mn4+. With an increase in the synthesis pressure, the conversion of manganese ions localized in octa- and tetra-positions occurs, accompanied by a change in valence. It has been found that some manganese ions with a valence of 2+ can be localized in an octahedral oxygen environment, occupying anti-site positions with reduced point symmetry. The formation of F-type centers, as well as polyvalent manganese centers, was confirmed by the cathodoluminescence method. Changing the synthesis parameters makes it possible to control the ratio of valence manganese ions in the corresponding sites of the spinel crystal lattice, thereby expanding the methodological base of defect nanoengineering.

Optical properties of Zn0.75Mg0.25O:Mn ceramics

Mn-doped ZnO, MgO and Zn0.75Mg0.25O samples ([Mn] = 0.1 at.%) were produced by conventional solid-state technique and investigated by means of XRD, EPR, absorption, photocurrent, photo- and cathodoluminescence methods. It was shown that Zn0.75Mg0.25O solid solution with hexagonal structure has the bandgap of Eg ∼3.65 eV. The quenching of host defect-related luminescence in ZnO:Mn and in hexagonal Zn0.75Mg0.25O:Mn was observed, while the Mn-related emission being absent. The energy level of MnZn2+ center in hexagonal Zn0.75Mg0.25O:Mn was found to be at 2.16 eV below conduction band (c-band) bottom and all excited states of MnZn2+ ions, including the lowest one, reside in c-band, as it takes place in ZnO:Mn. It is concluded that the necessary condition to obtain Mn-related light emission in Mn-doped alloys is to make deeper the lowest excited level of MnZn2+ ions. One of the solutions is to produce Zn1-xMgxO:Mn solid solution with the bandgap energy larger than 4.0 eV using nonequilibrium fabrication approaches.

An Experimental Study of Dislocation Dynamics in GaN.

The dynamics of dislocations introduced through indentation or scratching at room temperature into a few GaN layers that were grown using the HVPE, MOCVD and ELOG methods and had different dislocation densities were studied via the electron-beam-induced current and cathodoluminescence methods. The effects of thermal annealing and electron beam irradiation on dislocation generation and multiplication were investigated. It is shown that the Peierls barrier for dislocation glide in GaN is essentially lower than 1 eV; thus, it is mobile even at room temperature. It is shown that the mobility of a dislocation in the state-of-the-art GaN is not entirely determined by its intrinsic properties. Rather, two mechanisms may work simultaneously: overcoming the Peierls barrier and overcoming localized obstacles. The role of threading dislocations as effective obstacles for basal plane dislocation glide is demonstrated. It is shown that under low-energy electron beam irradiation, the activation energy for the dislocation glide decreases to a few tens of meV. Therefore, under e-beam irradiation, the dislocation movement is mainly controlled by overcoming localized obstacles.

Current mode of photomultiplier tube operation for the detection of the kinetics of small optical signals

Subject of study. The possibility of using the nonlinear current mode of operation of a photomultiplier tube for measurements of luminescence kinetics was investigated. Aim of study. This study aimed to validate the possibility of using the nonlinear current mode of operation of a photomultiplier tube to determine the kinetic properties of small luminescence signals of condensed media, including the signals that cannot be detected in a linear current mode. Method. The signal arriving at a high-impedance (1 MΩ) input of a digital oscilloscope from a photomultiplier tube via a coaxial cable was measured. This signal is a convolution of a photocurrent pulse with a kinetic instrument function determined by the discharge of capacitance in the measurement circuit of the photomultiplier tube. The bandwidth of the circuit was determined by the lowest frequency of its elements instead of the characteristic time of the instrument function. The real photocurrent signal was reconstructed by the deconvolution of the digital convoluted array. The pulsed cathodoluminescence method was used to detect the kinetics. Main results. A method for measuring the kinetics of small optical signals in the current mode of operation of a photomultiplier tube connected to a high-impedance input of a digital oscilloscope was presented. The results of using this method to measure the kinetics of pulsed cathodoluminescence of impurity and intrinsic centers in ceramic and monocrystalline samples of yttrium aluminum garnet were presented. The direct determination of characteristic decay times by approximating the convoluted curves without deconvolution was demonstrated for an exponential luminescence decay profile. Practical significance. The proposed method for the characteristic time detection of luminescence kinetics enables comprehensive analysis of luminescence that can be applied in various sectors of the national economy.

Synthesis and crystal and defect structures of polycrystalline Cu2SrSnS4 and Cu1.9SrSnS4 powders

The polycrystalline samples of Cu2 – δSrSnS4 with a trigonal structure were prepared by solid-phase ampoule synthesis with a long annealing time (1944 h), and their crystal lattice parameters were refined and Raman spectra were obtained. For the first time, the effect of defect structure on the lifetimes of photogenerated current carriers in the polycrystalline powders was examined by combining time-resolved microwave photoconductivity and cathodoluminescence methods. A significant increase in the lifetimes during the conversion of Cu2SrSnS4 into Cu1.9SrSnS4 was found, which was probably due to changes in the defect structure.

Post-depositional history of the lower Palaeocene interval using petrographic, CL and geochemical data in the East Tethys: Kopet-Dagh Basin, northeast Iran

AbstractThis study investigates the Danian siliciclastic successions in the East Tethys in the Kopet-Dagh Basin, NE Iran, which are composed of conglomerates, sandstones, shales and mudstones. The studied interval includes significant changes in sedimentary environments from alluvial to fluvial systems. The Danian siliciclastic formation is sandwiched between two marine carbonate sequences. The effects of the late Palaeocene sea transgression can be traced back to the precipitation of several types of carbonate cement in the studied siliciclastic formation. Several diagenetic features have been identified in the studied successions. The most observed features comprise physical and chemical compaction, cementation, alteration, dissolution, fractures and fillings. Some of the mentioned diagenetic processes, such as cementation, may be seen in a range of diagenetic environments and phases, such as early meteoric, low depth and deep burial, and late meteoric after the tectonic uplifting. The calcite cements considered in this study have been subdivided into four types. Some of the calcite cements, such as the rim, gravity pendant and meniscus, are classified as type one. They have formed around the rock grains and show no luminescence. The blocky and poikilotopic types have been grouped in type two. They are deposited between grains and exhibit dark luminescence. Type three cement consists of some of the blocky and poikilotopic cements that have formed amid grains and present a bright luminescence. Finally, type four comprises filled fractures which display a dark luminescence (blocky cement). Geochemical data revealed that the categorized cement types were precipitated in three diagenetic environments: early meteoric; burial; and late meteoric after the uplifting. The meteoric diagenetic environment is subdivided into vadose and phreatic meteoric. The burial diagenetic environment is subdivided into shallow burial and deeper burial. The qualitative petrographic method contributed to the initial recognition of the diagenetic features. The semi-quantitative cathodoluminescence method, the quantitative major and trace elements, and oxygen and carbon stable isotope analysis were utilized to evaluate the exact diagenetic processes and environments. Finally, the diagenetic sequence was reconstructed and depicted as diagenetic models and a paragenesis sequence. The data of this study can lay the foundation for future studies on the siliciclastic diagenesis in the studied basin.

Simultaneous Nanoscale Excitation and Emission Mapping by Cathodoluminescence.

Free-electron-based spectroscopies can reveal the nanoscale optical properties of semiconductor materials and nanophotonic devices with a spatial resolution far beyond the diffraction limit of light. However, the retrieved spatial information is constrained to the excitation space defined by the electron beam position, while information on the delocalization associated with the spatial extension of the probed optical modes in the specimen has so far been missing, despite its relevance in ruling the optical properties of nanostructures. In this study, we demonstrate a cathodoluminescence method that can access both excitation and emission spaces at the nanoscale, illustrating the power of such a simultaneous excitation and emission mapping technique by revealing a subwavelength emission position modulation as well as by visualizing electromagnetic energy transport in nanoplasmonic systems. Besides the fundamental interest of these results, our technique grants us access into previously inaccessible nanoscale optical properties.

Exciton-dielectric mode coupling in MoS2 nanoflakes visualized by cathodoluminescence

Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDCs), possessing unique exciton luminescence properties, have attracted significant attention for use in optical and electrical devices. TMDCs are also high refractive index materials that can strongly confine the electromagnetic field in nanoscale dimensions when patterned into nanostructures, thus resulting in complex light emission that includes exciton and dielectric resonances. Here, we use cathodoluminescence (CL) to experimentally visualize the emission modes of single molybdenum disulfide (MoS2) nanoflakes and to investigate luminescence enhancement due to dielectric resonances in nanoscale dimensions, by using a scanning transmission electron microscope. Specifically, we identify dielectric modes whose resonant wavelength is sensitive to the shape and size of the nanoflake, and exciton emission peaks whose energies are insensitive to the geometry of the flakes. Using a four-dimensional CL method and boundary element method simulations, we further theoretically and experimentally visualize the emission polarization and angular emission patterns, revealing the coupling of the exciton and dielectric resonant modes. Such nanoscopic observation provides a detailed understanding of the optical responses of MoS2 including modal couplings of excitons and dielectric resonances which play a crucial role in the development of energy conversion devices, single-photon emitters, and nanophotonic circuits with enhanced light-matter interactions.

Study of Glass Ceramics with YNbO-=SUB=-4-=/SUB=- : Tb-=SUP=-3+-=/SUP=- Crystallites Synthesized at Different Temperatures

The optimal temperature regime for the synthesis of glass ceramics with YNbO4 : Tb3+ crystalline inclusions has been established. Glass ceramics were synthesized on the basis of a sodium borate matrix from oxide precursors. It has been established that synthesis at a temperature of 950oC is optimal, since at this temperature only one crystalline phase YNbO4 : Tb3+ is formed in the glass and its content is maximum. The spectra of crystalline inclusions and the glass matrix were obtained by the method of local cathodoluminescence, the phase composition of glass ceramics was studied by X-ray phase analysis. Keywords: YNbO4, luminescence, terbium ion, glass ceramics.

Исследование стеклокерамики с кристаллитами YNbO-=SUB=-4-=/SUB=- : Tb-=SUP=-3+-=/SUP=-, синтезированной при разных температурах

The optimal temperature regime for the synthesis of glass ceramics with YNbO4 : Tb3+ crystalline inclusions has been established. Glass ceramics were synthesized on the basis of a sodium borate matrix from oxide precursors. It has been established that synthesis at a temperature of 950°C is optimal, since at this temperature only one crystalline phase YNbO4 : Tb3+ is formed in the glass and its content is maximum. The spectra of crystalline inclusions and the glass matrix were obtained by the method of local cathodoluminescence, the phase composition of glass ceramics was studied by X-ray phase analysis.

Low-Temperature Synthesis of Glass-Ceramics with YNbO-=SUB=-4-=/SUB=- : Tb-=SUP=-3+-=/SUP=- Crystallites

The main aim of this work was to perform low-temperature synthesis of glass-ceramics with YNbO4 : Tb3+ crystalline inclusions and study the structural and luminescent properties of the samples synthesized. In the framework of this work, inclusions crystallized in the system B2O5-Na2O-Y2O3 -Nb2O5-Tb4O7 (Bura). It was shown that in this system, regardless of the precursors in the samples, YNbO4 : Tb3+ in an amount of more than 70% of the total crystalline component. The most promising system for the synthesis of activated glass-ceramics with YNbO4 proved to be synthesized from oxide precursors; it crystallized more than 95% YNbO4 : Tb3+ of the total crystalline component. The luminescent properties of crystalline inclusions were studied using the local cathodoluminescence method. The composition and structure of glass ceramics were studied by methods X-ray spectral microanalysis and X-ray diffraction phase analysis. Keywords: YNbO4 : Tb3+, luminescence, glass-ceramics.

Luminescence features of bulk crystals β-(Ga-=SUB=-x-=/SUB=-Al-=SUB=-1-x-=/SUB=-)-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

This work is devoted to the study of the luminescence inhomogeneity nature of bulk (GaxAl1-x)2O3 samples grown by the Czochralski method. In the study of sample cleavages by the local cathodoluminescence method, regions with different luminescence were observed. To determine the cathodoluminescence contrast nature, we studied the uniformity of the aluminum distribution, the surface topography, and compared the luminescence spectra and the kinetics of emission bands for different regions of the sample. Also, to determine the luminescence bands nature, the crystal was annealed in air at 1000oC. This made it possible to observe the change in luminescence for the same region of the sample. Based on the studies performed, it was concluded that inhomogeneous luminescence is associated with the distribution of point defects. Upon annealing in air, the transformation of nonradiative recombination centers into luminescent centers was observed. Keywords: gallium oxide, luminescence, point defects.

Detection and Localization of Eu on Biosilica by Analytical Scanning Electron Microscopy

Abstract Algae like diatoms are widely studied as a means to remediate anthropogenically contaminated sites. In the present study, CL (cathodoluminescence) and EDX (energy-dispersive X-ray) spectroscopy in an SEM (scanning electron microscope) were optimized for the detection of Eu(III) sorbed on diatom biosilica. The required stability of biosilica under a focused electron beam was extensively investigated. Using experimentally determined data of thermal properties, the temperature increase within biosilica exposed to an electron beam was simulated by finite element calculations based on results from Monte Carlo simulations of electron scattering. Complementary thermogravimetric studies substantiated a chemical stability of biosilica in a wide temperature range, confirming its suitability for long-lasting SEM investigations. In subsequent EDX measurements, characteristic Eu lines were detected. Eu was found to preferentially accumulate and aggregate on silica fragments. CL spectra were obtained for the Eu(III) reference material, EuCl3. For Eu-loaded biosilica, even parts without detectable Eu signal in the EDX spectra show significant Eu(III) signals in the CL spectra. This highlights the sensitivity of CL in studying f-element sorption. CL data showed that Eu(III) was distributed on the entire surface. In conclusion, this work demonstrates the merit of CL and EDX methods for sorption studies on biogenic materials.

Three-dimensional mapping of the optical centers in the bulk of natural diamond by photoluminescent spectroscopy

Optically active defects in natural diamonds form specific spectral bands in the optical absorption and luminescence spectra and are called optical centers. Optical centers in the visible spectral range and their corresponding defects are called color centers. Spectral absorption and luminescence bands usually occupy several tens of nanometers in the spectral range and often have a complex structure. This spectral structure is unique to each optical center. The stationary broadband UV-MIR characterization of the set of optically active defects in the bulk of natural diamond with a widely varying concentration of impurities was carried out in this work. Comparison of the initial and modified impurity-defect structures of near-surface diamond layers was carried out by the method of cathodoluminescence and cathodoluminescence topography.

Chiral Light Emission from a Sphere Revealed by Nanoscale Relative-Phase Mapping.

Circularly polarized light (CPL) is currently receiving much attention as a key ingredient for next-generation information technologies, such as quantum communication and encryption. CPL photon generation used in those applications is commonly realized by coupling achiral optical quantum emitters to chiral nanoantennas. Here, we explore a different strategy consisting in exciting a nanosphere—the ultimate symmetric structure—to produce CPL emission along an arbitrary direction. Specifically, we demonstrate chiral emission from a silicon nanosphere induced by an electron beam based on two different strategies: either shifting the relative phase of degenerate orthogonal dipole modes or interfering electric and magnetic modes. We prove these concepts both theoretically and experimentally by visualizing the phase and polarization using a fully polarimetric four-dimensional cathodoluminescence method. Besides their fundamental interest, our results support the use of free-electron-induced light emission from spherically symmetric systems as a versatile platform for the generation of chiral light with on-demand control over the phase and degree of polarization.

Rapid identification of rare earth element bearing minerals in ores by cathodoluminescence method

In mineral ores, the identification of monazite, bastnäsite, and xenotime, which are currently exploited rare earth element bearing minerals, is important for the development of the mines that reserve rare earth elements. A conventional method for their identification, an electron probe microanalysis, is time-consuming. Here a method to rapidly identify these minerals is presented by acquiring cathodoluminescence (CL) images and spectra. Monazite, xenotime, and bastnäsite emitted red, blue-green, and red luminescence in their CL images, respectively. We detected CL peaks related to some rare earth elements, such as Ce, Tb, Pr, Sm, and Nd for monazite; Gd, Ce, Tb, Er, Tm, Dy, Sm, and Nd for xenotime; and Pr, Sm, and Nd for bastnäsite using our custom CL spectrometer. Monazite, bastnäsite, and xenotime are distinguishable from other minerals that coexist with these three minerals based on their CL colors, intensities, peak wavelengths, and peak intensity ratios. The analysis time to acquire the CL images and spectra was within 100 s. Therefore, the acquisition of CL images and spectra contributes to the development of the rare earth element reserving mines and the sustainable supply thereof.

Comparative Study of Optical and Electrical Properties of Grown-In and Freshly Introduced Dislocations in GaN by SEM Methods

Electrical and optical properties of grown-in and freshly introduced dislocations in GaN have been studied by the electron beam induced current and cathodoluminescence methods. It is observed that the recombination properties of grown-in and freshly introduced basal plane and threading dislocations are comparable. That allows to assume the intrinsic nature of dislocation recombination activity in GaN. It is demonstrated that the recombination properties of basal plane dislocations weakly depend on their type. The behavior of dislocation-related luminescence at 3.1 eV is more complex. It can be observed not in all GaN crystals even when dislocations are introduced in the similar conditions. Besides, it is not observed on basal plane and threading grown-in dislocations. This luminescence is not produced by freshly introduced basal plane dislocations. These observations can be explained assuming that the dislocation-related luminescence is associated with point defects generated by dislocations gliding in pyramidal or prismatic slip planes.

Strong Coupling of Excitons in Hexagonal GaN Microcavities

The GaN planar hexagonal microcavities are grown by the selective vapor-phase epitaxy technique. The spectra are measured by the low-temperature cathodoluminescence method using a scanning electron microscope. The obtained spectra show a huge Rabi splitting (~100 meV). Numerical simulation of the spatial distribution of the intensities of modes in a hexagonal cavity is carried out. Certain modes can have a high spatial localization leading to strong coupling with the exciton and huge Rabi splitting. The fraction of excitons in polariton modes, which correlates with the intensity of exciton radiation associated with these modes, is theoretically calculated for hexagonal-shaped microcavities. Thus, the form of the dependence of the radiation probability on the eigenfrequencies of the structure is obtained.

Сильная связь экситонов в микрорезонаторах GaN гексагональной формы

The GaN planar hexagonal microcavities were grown by a selective vapor phase epitaxy. The spectra were measured by the low-temperature cathodoluminescence method in-situ scanning electron microscope. The obtained spectra show a huge Rabi splitting (in order of 100 meV). Numerical simulation of the spatial distribution of the modes’ intensities of a hexagonal resonator is shown. Some modes can have strong spatial localization, leading to strong coupling with the exciton and huge Rabi splitting. Theoretically, we calculated the fraction of excitons in polariton modes, which correlates with the intensity of exciton radiation associated with these modes, for microcavities of a hexagonal shape. Thus, we have obtained the form of the dependence of the radiation probability on the eigenfrequencies of the structure.