Cathodoluminescence Detection Research Articles

Characterization of Individual GaAs/AlGaAs Self-Standing Nanowires by Cathodoluminescence Technique using Transmission Electron Microscope

Cathodoluminescence (CL) spectra and monochromatic CL images of GaAs/AlGaAs self-standing nanowires were observed using a transmission electron microscope combined with a CL detection system. Individual nanowires were resolved in monochromatic CL images, and the CL spectra taken from those wires by focused beam illumination showed emission peaks at different energies. Double peaks were sometimes observed to appear in the CL spectrum from a single nanowire. From the line-scan spectrum measurement and CL image observation of tilted angle illumination, it was found that a quantum-dot-like structure is formed along the nanowire.

Polarized cathodoluminescence study of InP nanowires by transmission electron microscopy

Cathodoluminescence (CL) spectra and polarized monochromatic CL images of InP nanowires were studied using a transmission electron microscope combined with a CL detection system. Emission spectra from individual nanowires showed a broad single peak with a peak energy of 1.6 eV, which is higher than expected from the quantum confinement effect for an average nanowire with a diameter of 20 nm. An individual nanowire could be resolved in the monochromatic CL images. The emission is highly polarized along the wire axis with a degree of polarization of more than 50%.

Carrier diffusion lengths in (In,Ga)(As,N)/GaAs quantum wells studied by spatially resolved cathodoluminescence

We have directly measured the carrier diffusion length Ld of dilute nitride single quantum wells (QWs) by means of spatially resolved cathodoluminescence (CL) spectroscopy as a function of the CL detection energy (E ) for different temperatures. While Ld (E ) of a GaAs/(Al,Ga)As reference sample does not vary with E , Ld (E ) of (In,Ga)(As,N)/GaAs QWs is significantly reduced with increasing E . The qualitative difference of Ld (E ) between the binary and quaternary QWs is explained in terms of different transport mechanisms (hopping versus tunnelling, respectively) in conjunction with the presence of localized states. Ld of (In,Ga)(As,N) QWs decreases rapidly with increasing temperature. Ld can be significantly reduced by the presence of extended defects even at low temperatures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Imaging of Cathodoluminescence Zoning in Calcite by Scanning Electron Microscopy and Hyperspectral Mapping

Abstract Imaging of cathodoluminescence (CL) emission from carbonate minerals by scanning electron microscopy (SEM) is problematic owing to the slow rate at which CL decays from each point as the electron beam is scanned over an area (the phenomenon of phosphorescence). Using SEM-CL and a newly developed electron probe–based technique of hyperspectral mapping, we have evaluated methods that have been proposed to overcome phosphorescence. With the dwell-time technique, the duration of time that the electron beam is static is increased such that CL emission from a given point makes a negligible contribution to the total signal from subsequent points. The dwell-time required to form sharp SEM-CL images of calcite that has a high intensity of luminescence at orange wavelengths is equal to or greater than 6.4 milliseconds, whereas calcite that luminesces predominantly at ultraviolet to blue wavelengths can be imaged using submillisecond dwell times. By using longer dwell times (> 1000 ms), CL and X-ray spectra can also be acquired from each point to form hyperspectral maps. The limited-wavelength imaging technique employs optical filters to excise slowly decaying long-wavelength emission so that the image is formed only using the more rapidly decaying ultraviolet to blue wavelengths, allowing shorter dwell times to be used. Both techniques have some disadvantages. The main drawback of the dwell-time technique is the long period of time required to acquire high-resolution images whereas the success of limited-wavelength imaging may depend on the sensitivity of the CL detector being used. CL images and emission spectra acquired by hyperspectral mapping also show that there is a nonlinear relationship between luminescence intensity variations at ultraviolet to blue wavelengths and intensity variations at orange wavelengths, indicating that short-wavelength emission is an imperfect proxy for zoning at longer wavelengths. Additionally, we have been unable to identify the controls on spatial variations in the intensity of ultraviolet to blue luminescence, although our data discount Fe2+ concentrations as being the sole determinant. By using hyperspectral mapping in combination with electron-probe microanalysis to obtain CL and X-ray spectra from the same micrometer-sized volume of a material, it is now possible to understand and quantify the controls on activation and quenching of CL in calcite and other minerals such as apatite and zircon.

Effect of Zr addition on the microstructure of the alumina scales on FeCrAlY-alloys

The effect of Zr-addition on the alumina scale formation on an FeCrAlY-alloy was studied by FEG-SEM equipped with EBSD and cathodo-luminescence detectors. The Zr imparted modifications of the alumina structure result in a higher scale growth rate, which decreases after the Zr in the bulk alloy is depleted. The effect of Zr thus depends on the Zr reservoir in the alloy i.e., on specimen thickness.

Cathodoluminescence imaging for identifying uptaken fluorescence materials in Kupffer cells using scanning electron microscopy

Cathodoluminescence (CL) is the light that is emitted from a material irradiated by an electron beam. The present study was undertaken to show the applicability to biological studies of a scanning electron microscope (SEM) equipped with a high-sensitive cathodoluminescence detection system. For this purpose, we injected inorganic fluorescent powders (P43) suspended in phosphate buffered saline into rat blood circulation, fixed the animals with glutaraldehyde within a day, and observed the hepatic tissues with a SEM. Our instrument enabled the simultaneous collection of both secondary electron (SE) and CL images of these tissues. Backscattered electron (BSE) images of the same portion were also able to be obtained with this microscope. SE and BSE images clearly showed the three-dimensional structure of the hepatic tissues including hepatocytes, Kupffer cells, Ito cells, and sinusoidal epithelial cells, while CL images visualized cathodoluminescence signals emitted from P43 as bright spots. We observed non-coated tissues under a low-vacuum condition and metal-coated tissues under a high-vacuum condition, and found that the high-vacuum observation of metal-coated tissues provided high quality CL images of P43 in the Kupffer cells. The superimposition of the CL images onto the corresponding SE or BSE images revealed that bright spots in the CL images were produced by the fluorescent powders uptaken by Kupffer cells. These findings indicate that the detection of CL as well as SE or BSE signals by SEM all provide us with useful information on the distribution of fluorescent tracers in tissues and cells in three-dimensional images.

Development of new TEM specimen holder for cathodoluminescence detection.

A simple, new TEM specimen holder to detect cathodoluminescence (CL) in a transmission electron microscope has been developed. This holder accommodates a flat light-collecting reflector below the specimen and CL signals are guided to an optical spectrometer outside of the microscope through a quartz optical fibre. The compact system requires no modification of the microscope itself and allows large-angle specimen tilting and easy combination with other associate analytical tools. Test data are presented to aid the future application of the holder.

Cathodoluminescence study of apatite crystals

Cathodoluminescence (CL) spectrometry represents a promising technique for the analysis of trace-element concentrations and distributions in minerals. However, a higher precision and a standardization of the recording conditions are required to use CL spectral data quantitatively. A significant step towards a more quantitative treatment of CL spectra is presented in this study. A procedure to correct the spectra for the various efficiencies as a function of the wavelength of the CL detector is proposed using low-pressure mercury-vapor and quartz-iodine lamps. CL spectra presented in this study are thus corrected for the system response. Apatite CL spectra, which are commonly composed of two broad bands centered at 3.5 and 2.2 eV, are deconvoluted to isolate component bands and determine their areas. The crystallographic control by prismatic or basal sections of apatite on spectral intensities is significant and only prismatic sections should be used. Signal decrease associated with electron bombardment (electron beam aging) is exponential and appears drastic in the first hundred seconds but continues even after 15 minutes of beam bombardment. All observed CL bands could be correlated with a specific activator [rare earth elements (REE) or manganese]. The 3.5 eV band is composed of three bands at 3.59 eV, 3.29 eV, and 2.87 eV. Ion microprobe results and comparison between CL and photoluminescence data support Ce 3+ activation for the origin of these bands. The relationship between CL band intensity and REE concentration measured by ion microprobe analysis demonstrates that CL also can provide semi-quantitative data for Gd 3+ , Ce 3+ , Dy 3+ , and Sm 3+ when recording conditions are strictly controlled.

Fluid inclusion petrography

A procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed (microthermometry and spectroscopic) analysis. An overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms ‘primary’ and ‘secondary’ fluid inclusions. Some principles of fluid inclusion modification are explained. Cathodoluminescence (CL) studies of quartz with the optical high-power CL-microscope and the electron microprobe provided with a CL detector are an important help in ‘fluid petrography’. CL textures are subdivided in primary, growth textures and a wide variety of secondary microtextures, which are in part induced by fluid inclusions. The latter is grouped in textures indicative of local lower crystal order (increasing defect structures) and microtextures indicative of local quartz healing (reduction of the defect structures). Microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post-entrapment changes of fluid inclusions and therewith testify their geological relevance.

Prediction of macrofracture properties using microfracture information, Mesaverde Group sandstones, San Juan basin, New Mexico

A better understanding of relationships between microfractures and macrofractures is prerequisite to the extrapolation of observed microfracture properties as a basis for inferring properties of associated macrofractures. The hypothesis that micro- and macrofractures represent different size fractions of the same fracture sets, and consequently have linked attributes, was tested on sandstones of the Mesaverde Group, San Juan basin, New Mexico. The use of a cathodoluminescence detector attached to a Scanning Electron Microscope (SEM) allowed observation of microfractures not readily visible using conventional microscopic techniques. The orientations of microfractures reproduce the orientations recorded at the macroscopic scale from cores and outcrops. Fracture size distributions are best modeled using power laws, and extrapolation of microfracture frequencies to the scale of macrofractures successfully predicts the macrofracture frequencies. Fracture-size distributions change at the length scale of the thickness of the mechanical layer, typically by increasing the exponent of their power-law distribution. This change is independent of censoring biases and reflects changes in sampling topology and/or fracture growth mechanisms.

Cathodoluminescence microscopy and spectroscopy of plagioclases from lunar soil

Cathodoluminescence (CL) microscopy and spectroscopy of single plagioclase grains from lunar soil show that plagioclases from Luna 20 (highland) have more or less homogeneous CL with both blue or green colors, whereas plagioclase grains sampled by Luna 24 (mare) luminesce dominantly green with partially distinct oscillatory zoning. The three main emission bands in the blue (~450 nm), green (~560 nm), and red-IR (~690 nm), mimic the most common emission bands in terrestrial feldspars. Mn 2+ is the most important activator element in lunar plagioclases. Variations in the amount of structurally incorporated Mn 2+ cause variations in the intensity of the green emission band at 560 nm, in some cases resulting in zoning of the CL intensity within single crystals. Calculations by a combination of quantitative spectral analysis of CL emission and PIXE measurements yield Mn concentrations of 7-47 ppm. The intense intrinsic emission band at 450 nm (probably an Al-O - -Al center), which was especially prominent in Luna 20 plagioclases, causes their blue CL color. The occurrence of a CL emission band at ~690 nm in plagioclases from Luna 24 samples confirms that Fe 3+ -activated CL is common in these grains. The results indicate that at least some of the Fe in Luna 24 plagioclases is Fe 3+ , whereas all Luna 20 plagioclases have Fe 3+ -near the CL detection limit of about 0.1 ppm.

Cathodoluminescence Imaging of n-Type Porous Silicon

Cathodoluminescence (CL) from n-type porous silicon (PS) was studied using a transmission electron microscope (TEM) equipped with the CL detection system. Two luminescence peaks at wavelengths of 660 nm and 420 nm were observed from a cross-sectional sample. The monochromatic CL images clearly reveal the spatial distribution of these luminescences along the depth direction; the 660 nm luminescence is mainly from near the top surface of the PS layer and the 420 nm luminescence the interface between the PS layer and Si substrate. The increase of the 420 nm luminescence intensity upon removal of the Si substrate suggests that the excited carriers in the residual Si matrix of the PS take part in the 420 nm luminescence.

Design and characterisation of a single‐reflection, solid‐state detector with high discrimination against backscattered electrons for cathodoluminescence microscopy

AbstractAportable solid‐state detector (SSD) for cathodoluminescence (CL) has been constructed and tested. The detector geometry utilises a parabolic reflector to direct light towards the solid‐state detection element. The photo‐sensitive area of the solid‐state photodiodes is situated at a level in line with or sightly below the top surface of the specimen to minimise the collection of backscattered electrons (BSEs) coming directly from the beam impact point. The components have been integrated into a single unit to enhance portability. In comparison with a commercial CL detection system, the new geometry shows excellent efficiency in rejecting BSE contribution during CL operation. A light collection solid angle close to 1.97π steradian is realised in this geometry, higher than other SSD‐CL systems. A method for characterising CL detection system performance has been developed.

Optoelectronic material analysis and device failure analysis using SEM cathodoluminescence

Abstract This paper reports on a portable Cathodoluminescence (CL) system which was developed and its applications to optoelectronic material analysis and device failure analysis. The portable CL detector was made from a solid-state photodiode which was mounted onto a specimen stage adaptor. Its portability allows it to be retrofitted to practically any standard scanning electron microscope (SEM) chamber stage without requiring any modifications to the SEM. The CL detector system was used to investigate non-radiative material defects in light emitting diodes (LEDs). Panchromatic CL micrographs of a degraded GaAs 0.72 P 0.28 LED and a AlGaAs epilayer grown by molecular beam epitaxy (MBE) containing various material defects are presented. A case study on the application of the SEM CL mode to the failure analysis of extra junctions in a LED device is also presented. The CL micrographs indicated the presence of an anomalous p-n-p-n structure which was verified by the current-voltage (I–V) characteristic.

Characterization of Crystal Defects by Cathodoluminescence Detection System Combined with TEM

Characterization of Crystal Defects by Cathodoluminescence Detection System Combined with TEM

Observations of Hg0.7Cd0.3Te epilayers by infrared cathodoluminescence detection

AbstractExtension in wavelength detection of cathodoluminescence (CL) toward the infrared is an area attracting interest regarding its development potential. This article describes our progress in CL characterization of Hg1−xCdxTe epilayers intended for optoelectronic array applications in the 3–5 μm radiation window. We present a description of the equipment set‐up, experimental procedure, and difficulties encountered in this study. We present preliminary observations performed at liquid helium temperatures of CL contrast variations from liquid phase epitaxial layers of Hg0.7Cd0.3Te lattice matched to Cd0.96Zn0.04Te substrates.

Cathodoluminescence and polarization studies from individual dislocations in diamond

Abstract A cathodoluminescence detector attached to a transmission electron microscope has been used to record visible optical-emission spectra from individual dislocations of known type in type IIb diamond over a range of temperatures. The polarization of the emission has also been determined from individual dislocations and this information correlated with the type and degree of dissociation of the dislocations. It was found that the dislocation emission at 435 nm was polarized along the dislocation line (independent of the Burgers vector) and had maximum intensity at 170 K. The emission spectrum was independent of dislocation type, and showed a broad (0·416 eV f.w.h.m.) band. All luminescent dislocations were dissociated, and one non-luminescent dislocation was found which was undissociated within the resolution of the weak-beam technique (∼ 15 A). Non-luminescent dissociated dislocations were also found. Curved dislocations were less luminescent than straight ones. A one-dimensional donor-acceptor mod...

A cathodoluminescence detection system for TEM/STEM

The ability to correlate near-atomic resolution TEM images of defects with their cathodoluminescence (CL) spectra holds promise as a powerful technique for the study of the electronic structure of defects in semiconductors. We have constructed a CL detection instrument fitted to a Philips 400T electron microscope, similar to that described by Roberts, as shown in Fig. 1. The instrument uses an ellipsoidal mirror for light collection allowing operation in the TEM, STEM and REM modes in a relatively clean vacuum, and is compatible with the ELS and EDS modes. The ellipsoidal mirror was designed to collect the maximum amount of emitted light within the limitations of the spacing between the specimen holder and the upper pole piece of the twin lens, as shown in Fig. 2 and 3. The length of the major axis is 61.2 mm and that of the minor axis is 12.1 mm.

The identification of pollen grains using cathodoluminescence in the scanning electron microscope

AbstractA scanning electron microscope fitted with a sensitive cathodoluminescence detector system has been used for the identification of pollen grains stained with acridine orange or unstained. This approach provides a means of identifying and studying the morphological details of pollens. Cathodoluminescence detection can, in principle, extend the limits of resolution beyond those obtainable with the fluorescence microscope.

Detection of aluminum oxide and polyethylene wear particles from joint endoprostheses using cathodoluminescence and x-ray analysis in SEM.

A highly sensitive method to localize aluminum oxide or polyethylene wear particles in biological tissues is presented. Using the scanning electron microscope (SEM) with a special cathodoluminescence detector system, small amounts of these foreign materials can be visualized in simple frozen sections by their bright luminescence, even at low magnifications (200X). At higher magnifications, a differentiation of free as well as phagocytized aluminum oxide and polyethylene particles can be made due to their different behavior in light emission. In addition, aluminum oxide such as other metals can be identified by x-ray microprobe analysis. This combination of SEM with microprobe analysis and with the highly sensitive cathodoluminescence mode enables to detect and identify wear products from all the materials, commonly used in manufacturing artificial joint replacements.