Cathodoluminescence Investigations Research Articles

High-resolution spectrometric analysis of rare earth elements-activated cathodoluminescence in feldspar minerals

Cathodoluminescence (CL) investigations of igneous, metamorphic and sedimentary feldspars indicate that rare earth elements (REE)-activated CL in feldspars is more common than previously assumed. Hot-cathode CL microscopy combined with high-resolution spectrometric analysis of CL emission allow to detect some REE below the detection limits of electron microprobe and proton-induced X-ray emission analysis (PIXE) and reveal variations in the REE distribution within single feldspar crystals. Differently luminescing zones can reflect changes during feldspar crystallization and/or element fluctuations during secondary alteration processes which are not discernible using conventional polarizing microscopy. The results of the study document Eu 2+, Sm 3+, Dy 3+, Tb 3+, and Nd 3+-activated CL in feldspars of different origin. The influence of the crystal field on shape and position of REE luminescence spectra significantly differs for divalent and trivalent REE ions. Whereas Eu 2+ shows a broad band emission (∼420 nm) which is influenced by the local crystal field, trivalent ions of the rare earth show narrow emission lines which reflect the transitions between excited state wave functions lying inside closed electronic shells. The positions of these peaks and the characteristic energies are described for the different REE 3+.

Near-Field Cathodoluminescence (NF-CL) Investigations on Semiconducting Materials

Near-Field Cathodoluminescence (NF-CL) Investigations on Semiconducting Materials

Scanning near‐field cathodoluminescence investigations

AbstractBy implementing a scanning near‐field optical microscope into the analysis chamber of a scanning electron microscope, the light emitted due to cathodoluminescence can be locally detected in the near‐field using tapered, coated optical fibers. In addition to the ability to perform contactless measurements of local diffusion lengths, the achievable spatial resolution can be increased to about 50 nanometers.

Near-field detection cathodoluminescence investigations

To make near-field detection cathodoluminescence investigations with a resolution in the nanometre regime feasible, a scanning near-field optical microscope (SNOM) has been implemented in the chamber of a scanning electron microscope. Two different modes of operation which can yield complementary information on the specimen can be carried out in our set-up. In the first mode, the SNOM probe position remains unchanged while the primary electron beam is scanned in raster fashion over the sample surface. In the second mode, the sample is homogeneously irradiated by the electron beam while being raster scanned underneath the SNOM probe. Whereas in the first mode specimen properties such as diffusion lengths are accessible, the achievable spatial resolution in the second mode depends only on the size of the aperture at the apex of the SNOM probe. A spatial resolution of well below 50 nm has been achieved on bulk YAG specimens in the second mode using commercially available probes.

Investigation of luminescence properties of GaN single crystals grown on 3C-SiC substrates

Cathodoluminescence (CL) and photoluminescence (PL) investigations of single crystal GaN grown on 3C-SiC(100) substrates by metalorganic vapor-phase epitaxy are reported. The GaN grown on 3C-SiC substrates shows distinct crystal facets. We identified the square facet and inclined facet as cubic GaN and hexagonal GaN, respectively. We studied the luminescence properties from the square facet or from the inclined facets separately by CL. For the cubic GaN, a sharp excitonic transition and a weak DA pair transition were observed from the square facet. On the other hand, an emission line at 3.293eV was obtained from the inclined facets. By studying its temperature dependence, we suggest that the 3.293eV emission is due to the free electron to acceptor transition of hexagonal GaN.

Cathodoluminescence investigation of isotope effects in diamond

We report high-resolution cathodoluminescence (CL) measurements near the indirect gap of isotopically modified diamonds. From the energies of intrinsic phonon-assisted peaks, as well as the no-phonon recombination of boron-bound excitons, we determine the contribution of isotope disorder to the frequencies of various phonons with nonzero wave vector. The results confirm calculations of the phonon self-energy based on ab-initio lattice dynamics. For some modes we predict an asymmetric variation of the disorder-induced shift with the 13C concentration which is observed in second-order Raman spectra. The no-phonon emission from boron-bound excitons (D 0 and D 0 ′ lines) exhibits a fine structure which arises from a splitting of the neutral boron acceptor ground state (2 meV) and the initial bound excitons (3.3 meV). When varying the 13C content all components shift with a slope of (14.6 ± 0.5) meV/amu.

Graded InxGa1−xAs/GaAs 1.3 μm wavelength light emitting diode structures grown with molecular beam epitaxy

In this study 1.1–1.3 μm wavelength light emitting diode (LED) structures with InxGa1−xAs compositionally graded buffers were grown on GaAs substrates with molecular beam epitaxy and characterized using microstructure and discrete device characterization techniques. The growth temperature and design of the graded buffer greatly affect the luminescence properties of the active device region above the graded buffer. These effects were most prominent in LED structures which incorporated a quantum well in the active device region. In quantum well devices, bright luminescent bands in the 〈110〉 directions are revealed under cathodoluminescence investigation and the number of bands and their intensity depend on grading rate. This study shows that a high threading dislocation density generated at or above the quantum well region has an adverse effect on the I–V characteristics of the diodes, but did not hinder luminescence from the quantum well LEDs.

Cathodoluminescence Investigation of Electron Irradiation Damage in Insulators.

Abstract Cathodoluminescence (CL) is the luminescent emission from a material which has been irradiated with electrons. Cathodoluminescence microanalysis (spectroscopy and microscopy) in an electron microscope complements the average defect structure information available from complementary techniques (e.g. Photoluminescence, Electron Spin Resonance spectroscopy). CL microanalysis enables both pre-existing and irradiation induced local variations in the bulk and surface defect structure to be characterized with high spatial (lateral and depth) resolution and sensitivity. This is possible as electron beam parameters such as the beam energy, may be varied to finely control the penetration depth of the incident electrons and hence the local volume of specimen probed. Irradiation with charged and neutral energetic radiation produces defects in radiation sensitive materials. The energetic electron beam in an electron microscope may also induce defects in the specimen. Cazaux has characterized the electric field produced by electron irradiation of a insulator with a conductive surface coating

Study of copper aggregations at dislocations in Gaas

In copper diffused gallium arsenide cathodoluminescence investigations were combined with analytical and transmission electron microscopy in order to interpret the occurrence of bright or dark dislocation contrasts. Various structures of Cu agglomerations were found in dependence on diffusion temperature and cooling rate. Bright dislocation contrasts are related to the enrichment of solute Cu Ga acceptors, whereas dark contrasts are mainly due to non-radiative recombination of Cu-As precipitates or clouds of small dislocation loops.

Photoluminescence and Cathodoluminescence Investigation of Optical Properties of InP-Based InGaAs Ridge Quantum Wires Formed by Selective Molecular Beam Epitaxy

Optical properties of InP-based InGaAs ridge quantum wires formed by selective molecular beam epitaxy (MBE) growth were characterized in detail by using cathodoluminescence (CL) and photoluminescence (PL). Both the CL and PL spectra had strong emission peaks with narrow widths. Spot-excited CL images confirmed that these peaks originated from ridge quantum wires. Depending on the excitation power, emission peaks showed energy shift and half-width change due to band filling. Temperature dependence of the PL emission peak followed that of the energy gap. The PL intensity decreased with increasing temperature, but was still fairly intense at room temperature. The behavior of PL intensity change with temperature was found to be the same for wires and reference wells, indicating the presence of a common nonradiative recombination mechanism.

REE-activated cathodoluminescence of calcite and dolomite: high-resolution spectrometric analysis of CL emission (HRS-CL)

Cathodoluminescence (CL) investigations of Phanerozoic marine limestones, sinter calcites and saddle dolomites of hydrothermal veins indicate that in contrast to previous knowledge rare earth element (REE)-activated CL in sediments is common. The methods of high-resolution spectrometric analysis of CL emission (HRS-CL) combined with ‘hot-cathode’ CL microscopy are able to prove qualitatively some REE below the detection limits of electron microprobe and proton-induced X-ray emission analysis (PIXE). Our investigations document Sm 3+, Dy 3+, Tb 3+ and probably Ho 3+-activated CL in calcite and Eu 3+-activated CL in a saddle dolomite of hydrothermal veins. Sometimes the REE-activated CL is hidden by dominant Mn 2+ emission. In such cases the REE emission spectrum may be obtained by subtracting a spectrum of luminescence produced only by Mn 2+. The occurrence of only one REE in natural samples is uncommon. In all observed samples REE are present in groups.

Correlation of the electrical, thermal, and optical properties of CVD diamond films by scanning microscopy techniques

Abstract Scanning electron microscopy (SEM) and scanning probe techniques (SFM, STM, SThM) were used to analyse microwave plasma-deposited polycrystalline CVD diamond films grown from C/H and C/H/O gas mixtures. Wavelength- and time-resolved cathodoluminescence (CL) and electron beam-induced current (EBIC) investigations were done in modified scanning electron microscopes. High lateral resolution analysis was carried out by scanning force (SFM) and scanning tunnelling (STM) microscopy. STM-EBIC investigations using a modified SFM in contact current mode (CCM-SFM) and thermal profiling (SThM) resulted in high-resolution images of the electrical and thermal properties of the diamond films. The various methods used allowed us to measure morphological, electrical and thermal properties of polycrystalline diamond, to detect defects, special features and structures of the grains and the grain boundaries and to connect the results with the preparation conditions, e.g. the composition of the CVD gas phase.

Cathodoluminescence investigation of SiGe quantum wires fabricated on V-groove patterned Si substrates

Cathodoluminescence (CL) imaging and spectroscopy have been used to characterize SiGe quantum wires grown by gas source molecular beam epitaxy (GS-MBE) on V-groove patterned substrates. CL spectra recorded at T ≈ 5 K contained three separate SiGe no-phonon luminescence features and their transverse optic phonon replicas. Monochromatic CL imaging recorded in cross section reveals that the three different luminescence features are related to the SiGe(100) quantum wells, SiGe(111) quantum wells and the SiGe quantum wire. CL images from the SiGe(100) reveal that the low temperature ( T = 5–30 K) images are broadened by exciton diffusion, whereas at higher temperatures ( T = 30–70 K) the CL images become sharper due to non-excitonic recombination.

Cathodoluminescence investigations of three-dimensional island formation in [formula omitted] quantum wells

When a growth interruption is applied to the top interface of a nominally 3 monolayers (ML) thick InAs quantum well (QW), grown on an InP substrate, the InAs layer relaxes by formation of three-dimensional (3D) islands. The emission from the QW is split into at least 8 peaks. Each peak corresponds to an integral number of MLs of InAs. Using cathodoluminescence imaging and photoluminescence excitation spectroscopy, we demonstrate that the emission originates in 3D islands with a lateral extension of less than 1 μm. Furthermore, most of the 3D islands are completely isolated, separated by InP, even though there are 3D islands of different thicknesses that are connected. A conclusion from our investigation is that the whole InAs layer, rather than just the top ML, is involved in the 3D island formation.

Panchromatic cathodoluminescence investigation of defects in CdTe bulk crystals and homoepitaxial layers

Scanning electron microscopy panchromatic cathodoluminescence has been used to investigate extended crystal defects in (111) CdTe bulk crystals and homoepitaxial layers grown by liquid phase epitaxy. Good defect images have been obtained by a very simple experimental setup using a Si photodiode at room temperature. The bulk crystals have been found to be affected by dislocations arranged in cellular structures, lineages roughly parallel to the [110] directions, [110] slip bands, and precipitates. The homoepitaxial layers exhibited dislocations, precipitates, and inclusions of growth solution. The wavy morphology typical of the layers grown by liquid phase epitaxy did not give rise to cathodoluminescence contrast.

Cathodoluminescence of single quantum wires and vertical quantum wells grown on a submicron grating

We present cathodoluminescence (CL) investigations of a corrugated GaAs/AlGaAs single quantum well (QW) structure grown on a submicron grating. The CL spectra have four distinct emission peaks. Using plan-view and cross-sectional CL imaging together with cross-sectional transmission electron microscope imaging, we have assigned the four peaks: They originate in the nominal QW, a quantum wire (QWR), a vertical quantum well (VQW), and the barrier, respectively. We have CL-imaged and -characterized single QWRs and VQWs.

Zircon zonation patterns as revealed by cathodoluminescence and backscattered electron images: Implications for interpretation of complex crustal histories

Zircon exhibits an extraordinary memory. Its stability, durability, low solubility and low elemental diffusivities combine to preserve in it a record of most of the important events that have affected it, its host rocks, and the crust of which it is a part. Zonation in zircon grains delineates the boundaries of discrete geochemical packages formed at different times, each effectively a closed system. The elemental and isotopic compositions of these packages reflect the timing and conditions of growth events, and the morphology of the zonation indicates qualitatively the nature of both growth and intervening degradation events. Cathodoluminescence (CL) and backscattered electron (BSE) imaging reveals detailed zonation patterns that are commonly invisible or barely visible with conventional transmitted and reflected light microscopy. Characteristic patterns are visible in almost all zircons that serve to distinguish igneous from metamorphic growth, to distinguish truncation surfaces of different types (e.g., sedimentary fracturing vs. resorption), and possibly to identify ancient metamictization. Zircons from many rocks record multistage histories that reflect two or more events; those from rocks such as peraluminous granites and high-grade paragneisses are especially likely to reveal long and complex histories. Studies of zonation patterns in zircons provide a clear, though qualitative, history of a rock and its heritage. Furthermore, they provide the basis for a quantification of that history. Elemental and isotopic compositions can reveal the environment in which a zone grew. U-Pb analysis of a zone provides an age for its growth. shrimp analyses that are not guided by detailed knowledge of zonation can straddle two (or more) zones and a discordant U-Pb result from such an analysis may falsely suggest Pb loss, and important growth zones may be missed entirely. Thus, the combined use of CL, BSE, electron microprobe and ion probe methods can elucidate complex crustal histories.

IR Cathodoluminescence Investigations on La-Doped Barium Titanate Ceramics

IR Cathodoluminescence Investigations on La-Doped Barium Titanate Ceramics

Luminescence Spectra of the CuAlSe2 Single Crystals Doped by the Elements of the II Group

Single crystals of CuAlSe2 were prepared by the iodine vapour transport technique and annealed in the atmosphere of Zn, Cd, Cd+Al. The cathodoluminescence investigations were carried out at 77 and 300 K. The obtained results suggest the possibility of using this material in light-emitting devices.

The Recombination in Zn, Cd and Hg-Doped CuAlS2

Single crystals of CuAlS2 were grown by the chemical vapour transport using iodine as a transporting agent and doped by the elements Zn, Cd and Hg in the growth process or in atomosphere of vapour. The cathodoluminescence investigations of annealed samples at the temperatures 77 and 300 K allowed to determine the recombination mechanism. The outlook of this material for light-emitting devices is presented.