Cathodoluminescence Emission Research Articles

Si and Ge nanocluster formation in silica matrix

High resolution transmission electron microscopy, scanning transmission electron microscopy, and cathodoluminescence have been used to investigate Si and Ge cluster formation in amorphous silicon-dioxide layers. Commonly, cathodoluminescence emission spectra of pure SiO2 are identified with particular defect centers within the atomic network of silica including the nonbridging oxygen hole center associated with the red luminescence at 650 nm (1.9 eV) and the oxygen deficient centers with the blue (460 nm; 2.7 eV) and ultraviolet band (295 nm; 4.2 eV). In Ge+ ion-implanted SiO2, an additional violet emission band appears at 410 nm (3.1 eV). The strong increase of this violet luminescence after thermal annealing is associated with formation of low-dimension Ge aggregates such as dimers, trimers, and higher formations, further growing to Ge nanoclusters. On the other hand, pure silica layers were modified by heavy electron beam irradiation (5 keV; 2.7 A/cm2), leading to electronic as well as thermal dissociation of oxygen and the appearance of under-stoichiometric SiOx. This SiOx will undergo a phase separation and we observe Si cluster formation with a most probable cluster diameter of 4 nm. Such largely extended Si clusters will diminish the SiO2-related luminescence and Si-crystal-related luminescence in the near IR.

Comparison of UV-IR radioluminescence and cathodoluminescence spectra of a potassium feldspar

This paper reports on the cathodoluminescence (CL) and radioluminescence (RL) emission properties of well-characterised K-rich feldspar ( K 0.98 Na 0.02 Al 1.02 Si 2.98 O 8 ) . Both CL and RL spectra display three groups of components in the: (i) UV (290 nm); (ii) green (570 nm) and (iii) red-IR (640 nm) region. As observed in other aluminosilicates, the emission peaked at lower wavelengths (290 nm) can be associated with structural defects located in the twin-domain boundaries related to the recombination process in which the Na + ion diffusion-limited is involved; green and red emissions are, respectively, associated with the presence of Mn 2 + and Fe 3 + ions. The ratio between the relative intensities peaked at 290 and 570 nm is about 3:7 for CL and 1:7 for RL; this fact indicates that the efficiency of recombination centres changes depending on the type of radiation, i.e., X-rays to obtain the RL spectra and electron beams for the CL emission.

Identification of cathodoluminescence activators in zoned alkali feldspars by hyperspectral imaging and electron-probe microanalysis

Cryptoperthitic alkali feldspars within the Proterozoic Klokken syenite have been pervasively altered deuterically to patch perthites whose constituent subgrains display very fine-scale zoning in optical cathodoluminescence (CL). Electron-probe analyses and hyperspectral maps were acquired from several areas of patch perthite to potentially identify the centers responsible for CL emission and to access information that the subgrains might provide about the late-stage geological evolution of the pluton. Each hyperspectral map is composed of tens of thousands of CL spectra covering a wavelength range of 350-850 nm, and images can be formed from any desired wavelength band. The patch perthite subgrains have two emission bands: one in the blue (similar to 460 nm) and the other at red to infrared wavelengths (similar to 690-725 nm). Cathodoluminescence images formed using both bands show that the optically visible zoning is developed only at blue wavelengths. Comparisons of emission intensities with electron-probe analyses show that the blue band is activated by Ti3+ and less than similar to 25 ppm of the trace element is required for optically detectable luminescence. Adjacent Ab- and Or-rich subgrains can have identical patterns of zoning at blue wavelengths, indicating that they crystallized from the deuteric fluid simultaneously, but in most cases, differences in zoning within any one area of patch perthite indicate that subgrains grew at different times and slowly relative to the frequent changes in concentrations of Ti within the deuteric fluid. The red to infrared CL emission band is inferred to be activated by Fe3+. Ab-rich feldspar with the greatest intensities of long-wavelength emission and FeO concentrations crystallized from a late-stage and relatively low-T fluid that obtained a proportion of its Fe from mafic grains. The generally poor correlation between variations in intensities of the two emission bands within any one subgrain indicates that concentrations of Ti and Fe in the deuteric fluid varied independently of each other, and one trace element has no sensitizing or quenching effect on emission from the other center. The maximum length of zones within individual subgrains (similar to 0.5 mm) and maximum separation of subgrains with similar zoning patterns (similar to 1 mm) helps to constrain the length and interconnectivity of the thin films of deuteric fluid that mediated alteration.

Sol-Gel Synthesis and Characterization of SiO2 @ NaGd ( WO4 ) 2 : Eu3 + Core-Shell-Structured Spherical Phosphor Particles

Monodisperse, core-shell-structured particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL), and low-voltage cathodoluminescence (CL) as well as time-resolved PL spectra and lifetimes. PL and CL study revealed that the core-shell-structured particles show strong red emission dominated by the transition of at with a lifetime of . The PL and CL emission intensity can be tuned by the coating number of phosphor layers on and by accelerating voltage and the filament current, respectively.

Cathodoluminescence as a method for the study of degradation of polysilanes

The paper presents a unique cathodoluminescent (CL) method suitable for studying polysilane properties and the first CL characteristics of the material being investigated. Poly[methyl(phenyl)silylene] (PMPSi) was selected as a typical representative of polysilanes. The PMPSi study is based on the measurement of the intensity of CL emission after passing through the specimen. The major problem of this study is the susceptibility of the material being investigated to the degradation by electron beam. PMPSi degradation strongly decreases the CL intensity. Therefore, detection in the synchronous mode was used to eliminate the influence of the background and of the noise. It was found that the degradation process is partly reversible. A partial recovery of intensity was attributed to reverse recombination reactions of silyl radicals in a vacuum after 20h of annealing at room temperature. Understanding of the physical and chemical mechanisms of the degradation and of the reversible process of the PMPSi CL emission is interesting for science as well as the application (e.g. resist in electron beam lithography or molecular scale electronic devices).

Cathodoluminescence Measurements and Thermal Activation of Rare Earth Doped (Tb<sup>3+</sup>, Dy<sup>3+</sup> and Eu<sup>3+</sup>) a-SiC Thin Films Prepared by rf Magnetron Sputtering

We present comprehensive cathodoluminescence measurements from thin amorphous a- SiC films doped with rare earths. The a-SiC films were prepared by rf magnetron sputtering using a high purity SiC wafer in high purity argon atmosphere (5N, pressure approx. 0.2 mbar). The rare earth doping (Tb, Dy and Eu concentrations were below 2%) was performed by placing respective rare earth metal pieces of appropriate size onto the Silicon Carbide wafer. The rare earth ion emissions cover the colors green (Tb), yellow (Dy) and red (Eu). The optical and related structural properties of the films are correlated by means of high resolution transmission electron microscopy in combination with cathodoluminescence measurements in a scanning electron microscope. In addition, the corresponding compositions are determined by energy-dispersive x-ray analysis. The cathodoluminescence spectra of the rare earth 3+ ions are recorded in the visible at 20°C in the asgrown condition and after annealing treatments in the temperature range from 300°C to 1050°C by steps of 150°C. The anneal-related changes in the cathodoluminescence emission spectra and in the microstructure of the films are addressed. The SiC films show amorphous structure almost independent of the annealing treatment. Optimal annealing temperature for emissions of Tb3+ doped a-SiC were derived to be 600°C whereas Dy3+ and Eu3+ emissions increase at least up to 1050°C.

Electron-beam irradiation effects on luminescence properties in subsurface regions of single-crystalline sapphires treated with and without hydrogen plasma exposures

Electron irradiation effects on various insulating sapphires treated with and without hydrogen plasma have been investigated mainly by means of cathodoluminescence (CL) measurements. The samples examined included Be-diffusion-treated natural sapphire (BNS) and two types of synthetic sapphires grown by Verneuil and Czochralski methods. For all the samples examined, on one hand, their CL intensities of the F +-center-related emission peaked at ≈3.8 eV rapidly increased with increasing the fluences of keV electrons, and were represented roughly by exponentially saturating curves. There occurred slight blue-shifts of the F +-center luminescence other than the intensity increases for some of the electron-irradiated specimens, suggesting possible presence of two components for the F +-center luminescence. On the other hand, a hydrogen plasma exposure to these sapphires resulted in sample-dependent changes in the optical property and in the beam-irradiation effect on the F +-center CL emission. Such variations were induced most strongly in the BNS sample, whose color changed from orange to pink due to substantial decreases in the absorbance after the hydrogen plasma treatment. Furthermore, the energy positions of both the Cr 3+-center luminescence peaked at ≈1.8 eV and its satellite peaks were found to slightly shift for the untreated and H-plasma-treated BNS samples after the electron beam irradiations. Possible origins of these observations are discussed.

Emission properties from dense exciton gases in diamond

AbstractA systematic study of cathodoluminescence (CL) emission arising from free exciton recombination in diamond is given. CL spectra of free exciton emission from diamond under high excitation conditions were used to characterize properties of ultradense exciton gases at quasi‐thermal equilibrium. Theoretical spectra of excitonic emission from diamond were calculated based on Bose–Einstein (BE) statistics, taking into account collision of excitons in an indirect semiconductor like diamond. The calculated spectra agreed well with the observed spectra over a wide temperature range for high‐quality homoepitaxial chemical vapor deposition diamond thin films. The analysis showed that a high density of excitons of over 1018 cm−3 could be achieved under thermodynamic quasi‐equilibrium by continuous electron beam excitation, at which BE condensation can be expected at low temperature. These results indicate that diamond is a perfect material for the generation and detection of BE condensation which is the most characteristic features of BE statistics. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sharp, Long Wavelength Cathodoluminescence Emission from Undoped Semi-insulating GaAs

Cathodoluminescence investigations on bulk undoped semi-insulating GaAs (SI GaAs) samples taken from different sources reveal the presence of a sharp, long wavelength emission at 0.9 eV (at 10 K), with a very narrow full-width at half-maximum of 7 meV, which shows a redshift and thermal broadening upon increasing the temperature. At 10 K, the liquid encapsulated Czokralski grown undoped SI GaAs samples show an additional lower energy emission at 0.89 eV, which is absent in the vertical gradient freeze grown undoped SI GaAs samples. Systematic temperature dependent and beam parameter dependent studies indicate that, the probable origin for the 0.9 eV emission maybe some quantum-dot/nano-cluster like structures present inside the SI GaAs crystal lattice.

Luminescence and epitaxy of ion-implanted α-quartz

Ion implantation is a promising route for doping quartz with luminescent impurity atoms and growing photoactive nanoparticles of them. The present work focuses on cathodoluminescence (CL) and epitaxy during or after Na, Rb, Cs, Ge, and Ba ion implantation as well as Rb/Ge double implantation in crystalline α-quartz, under the conditions of dynamic, chemical or laser epitaxy. In addition to the known intrinsic sub-bands in the CL spectra, which have been associated with specific defects in the silica matrix, very intense blue or violet bands were found. They are correlated with the implanted ion species and follow their thermal behaviour. The quantum efficiency and possible origins of the blue/violet CL emission for various ions and processing treatments will be discussed. The case of double Rb/Ge implantation appears to be very promising with respect to a combination of a high CL output and full chemical epitaxy.

Experimental and natural cathodoluminescence in the shell of Crassostrea gigas from Thau lagoon (France): ecological and environmental implications

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 317:143-156 (2006) - doi:10.3354/meps317143 Experimental and natural cathodoluminescence in the shell of Crassostrea gigas from Thau lagoon (France): ecological and environmental implications D. Langlet1,4*, M. Alunno-Bruscia2,5, M. Rafélis1, M. Renard1, M. Roux3, E. Schein3, D. Buestel2,6 1JE Biominéralisations & Paléoenvironnements, FRE CNRS 2400 Case 116, Université Pierre & Marie Curie, 4 Place Jussieu, 75252 Paris Cedex 05, France 2IFREMER-LCM (Laboratoire Conchylicole de Méditerranée), BP 171, 34200 Sète Cedex, France 3Laboratoire des Sciences de la Terre, Université de Reims, Centre de Recherches sur l’Environnement et l’Agronomie, UMR CNRS 5561, Biogéosciences, 2 Esplanade Roland Garros, 51100 Reims, France 4Present address: Section de Pétrographie-Minéralogie-Géochimie, Musée Royal de l’Afrique Centrale, Leuvensesteenweg 13, 3080 Tervuren, Belgium 5Present address: CRELA (Centre de Recherche sur les Ecosystèmes Littoraux Anthropisés ), UMR 6217 CNRS, IFREMER & Université de La Rochelle, Place du Séminaire, BP 5, 17137 L’Houmeau, France 6Present address: IFREMER-COP (Centre Océanologique du Pacifique), BP 7004, 98719 Taravao, Tahiti, French Polynesia *Email: dlanglet@africamuseum.be ABSTRACT: We present a cathodoluminescence (CL) study of growth layer deposition in the shell of the oyster Crassostrea gigas. CL is based on the physical properties of lattice-bound manganese (Mn2+), which is the main activator in calcium carbonate. Our study involved chemical marking by immersing individuals in seawater to which manganese chloride had been added, and subsequent reading of the shell with CL microscopy coupled with numeric treatment of microphotographs; CL emission was analyzed using a scanning electron microscope coupled to a spectrometer. Since the marking did not harm the oysters, repeated markings were possible, allowing validation of the inferences made from analysis of the shell rings. Oysters reared in a French Mediterranean lagoon (Thau lagoon) were marked in June and October 1999, i.e. at the beginning and end of the main shell growth period, respectively. In a few specimens sacrificed 24 h immediately after marking, we observed a bright marking line, suggesting rapid coprecipitation of Mn2+. In oysters collected from March to July 2000, we found 3 luminescent lines (with an emission peak at 620 nm peak) that corresponded to the 3 successive markings. The shells also exhibited weak background Mn2+-induced luminescence, which contrasted with the marking lines both in intensity and color. This background signal varied in intensity over time at 3 distinct scales, i.e. seasonal and daily scales plus an intermediate scale that might reflect tidal patterns. The luminescence intensity was clearly positively correlated with seawater temperature. We postulate that the temperature of the lagoon, combined with abiotic and biotic factors, may control both Mn2+ uptake by the bivalve through a stimulation of biomineralization processes, and Mn2+ bioavailability in water through biogeochemical processes. Our study confirmed the usefulness of Mn marking coupled with CL analysis to reveal (1) the complex functioning of the mantle epithelium with respect to carbonate deposition on a microscale, and (2) the relationship between the bivalve and its environment. KEY WORDS: Oyster · Cathodoluminescence · Shell growth · Carbonate biomineralization · Manganese marking · Mediterranean lagoon Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 317. Online publication date: July 18, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Cathodoluminescence microscopy and spectroscopy of GaN epilayers microstructured using surface charge lithography

Cathodoluminescence (CL) microscopy and spectroscopy have been used to investigate the optical properties of GaN microstructures patterned by Ar+ ion irradiation and subsequent photoelectrochemical (PEC) etching. Monochromatic CL images and CL spectra reveal an enhancement of several defect-related emission bands in a 10μm wide area around each microstructure. In addition, columnar nanostructures and nanoetch pits were found in the PEC etched areas. CL emission of the nanocolumns is dominated by free electron to acceptor transitions, while excitonic luminescence prevails in the rest of the etched GaN layers. Investigation of the sidewalls of the microstructures reveals that a CL emission band centered at about 3.41eV, attributed to excitons bound to structural defects, is effectively suppressed after PEC etching only in the observed nanocolumns.

Different behaviors of F + centers due to electron beam irradiations between synthetic sapphire and Be-diffusion-treated natural sapphire

Cathodoluminescence (CL) intensities of F + centers in Be-diffusion-post-treated natural sapphire (BNS) and synthetic sapphire have been found to substantially increase under continuous irradiations of 15-keV electrons with constant incident currents ranging from 0.1 to 2 μA and to be represented approximately by an exponential saturation function of the electron fluence. The efficiency of F +-center CL emissions at room temperature (RT) was higher in the synthetic sapphire than in the BNS specimen. Whereas the CL intensity of the BNS sample had little temperature dependence, that of the synthetic sapphire decreased by approximately one order of magnitude with decreasing the specimen temperatures from RT to 85 K. In addition, time-resolved photoluminescence data measured for the 420-nm emission evidence a relatively shorter lifetime of the BNS specimen. These facts indicate that the natural sapphire which was successfully post-treated with Be diffusion had a slightly but substantially poorer crystalline quality than synthetic sapphire. Possible origins of these observed differences are discussed.

Carrier dynamics of optical emission from two‐dimensional electron gas in undoped AlGaN/GaN single heterojunctions

AbstractThe strucutral and optical properties of undoped AlGaN/GaN single heterojunctions (HJs) were studied by means of high‐resolution x‐ray diffraction, photoluminescence (PL), cathodoluminescence (CL), and time‐resolved PL spectroscopy. An additional two‐dimensional electron gas (2DEG)‐related PL and CL emission appeared at about 40 meV below the GaN band‐edge emission energy and persisted up to about 100 K, while this peak disappeared when the top AlGaN layer was removed by reactive ion etching. Depth‐resolved CL spectra reveal the presence of a 2DEG at the heterointerface. The additional PL and CL emission below the GaN band‐edge emission is attributed to the recombination between photogenerated holes and electrons confined at 2DEG states in the triangular‐shaped interface potential. For the 2DEG emission, we observed an about 50‐ps delayed rise time than the GaN and AlGaN emissions by using time‐resolved PL, indicating effective carrier transfer from the GaN flatband and AlGaN regions to the heterointerface. From the results, we explained the optical properties and carrier recombination dynamics of 2DEG, GaN, and AlGaN emissions in undoped AlGaN/GaN single HJs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of stacking on optical characteristics of GaN/AlN self‐organized quantum dots

AbstractThe effect of stacking on the optical properties of self‐organized GaN/AlN quantum dots (QDs) grown by plasma‐assisted molecular beam epitaxy was investigated by photoluminescence (PL), PL excitation (PLE), and cathodoluminescence (CL) spectroscopic techniques. With an increase in the number of the GaN QDs stacking layer, we observed a red shift in the main QD PL peaks. A Stokes‐like shift was observed between PL emission and PLE absorption edge for all the samples. From the depth‐resolved CL of a 200‐period GaN QD sample, we observed that the main QD CL emission peak energy position does not change much, while the higher‐energy side CL peak around ∼3.7 eV shows a variation of its peak position with the accelerating voltage probably due to the change in either distribution of QD size/shape or wetting layer properties during the growth of multiple stacking of GaN QDs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Multiple growth and characterization of thick diamond single crystals using chemical vapour deposition working in pulsed mode

In this paper, the fast growth of three thick diamond single crystals using the chemical vapour deposition (CVD) method working in a pulsed mode is reported. After 48 h, a total of half a carat of uncoloured synthetic diamond was obtained. These crystals, exhibiting thicknesses of 430, 570 and 900 μm, were then thoroughly analysed by a wide range of characterization techniques, such as Raman spectroscopy, UV and IR absorption, photoluminescence (PL) and cathodoluminescence (CL). All three samples turned out to be of relatively high quality but small differences in purity and quality could be detected. These appeared to be directly related to the slight inconsistence of the substrate temperature during growth that ranged from 800 to 900 °C due to non-uniformity in the radial distribution of gas temperature. A higher contamination by residual nitrogen impurities has been evidenced for the two samples that were grown with the lowest temperature as confirmed by the PL and UV absorption spectra, as well as a lower free excitonic emission in CL. Finally a 900 °C growth temperature was shown to be more favourable to good quality and fast growth rate.

Luminescence properties of sol–gel derived spherical SiO 2@Gd 2(WO 4) 3:Eu 3+ particles with core–shell structure

Monodisperse, core–shell structured SiO 2@Gd 2(WO 4) 3:Eu 3+ particles were prepared by the sol–gel method. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL) and low-voltage cathodoluminescence (CL). PL and CL study revealed that the core–shell structured SiO 2@Gd 2(WO 4) 3:Eu 3+ particles show strong red emission dominated by the 5D 0– 7F 2 transition of Eu 3+ at 615 nm with a lifetime of 0.89 ms. The PL and CL emission intensity can be tuned by the coating number of Gd 2(WO 4) 3:Eu 3+ phosphor layers on SiO 2 particles, the size of the SiO 2 core particles, and by accelerating voltage and the filament current, respectively.

Origin of the fluctuations in the luminescence emission in InGaN quantum wells

InGaN single quantum wells grown by metal organic vapour phase epitaxy were studied by spectrally resolved cathodoluminescence (CL) and transmission electron microscopy (TEM). Spatial fluctuations of the intensity and peak wavelength at submicrometric scale in the CL emission were observed. The correlation of CL data with structural analysis carried out by TEM shows that such fluctuations are related to threading dislocations that cross the full structure and modify In concentration and thereafter the piezoelectric field and the non-radiative recombination efficiency.

Cathodoluminescence characterization of SnO 2 nanoribbons grown by vapor transport technique

Cathodoluminescence (CL) was used to characterize the tin dioxide (SnO 2) nanoribbons grown by vapor transport technique. The CL emission at the room temperature showed two broad bands centered at 2.02 eV (orange band) and 2.70 eV (blue-green band). The orange band may be related to the oxygen vacancies. The CL spectra did not change along the longer axis of the nanoribbons, while they varied across the nanoribbons. The variation across the nanoribbons was classified into three categories. The phenomena may be related to the different facets at the growth front of the nanoribbons.

Blue-green-red LEDs based on InGaN Quantum Dots by Plasma-assisted MBE using GaN QDs for Dislocation Filtering

ABSTRACTIn this paper, we report the development of blue-green-red LEDs based on InGaN quantum dots (QDs) and quantum wells in the active region, and GaN QDs in the nucleation layer for dislocation filtering, by plasma assisted molecular beam epitaxy. Self-assembled InGaN QDs and GaN QDs were grown in the Stranski-Krastanov mode. For the GaN QDs grown at 770 °C, the height distribution of the dots shows a bimodal distribution, which can be attributed to the interaction of the GaN QDs with the threading dislocations. TEM and XRD studies indicate that GaN QDs in the nucleation region help threading dislocations to deviate and annihilate. The average dot height, diameter and density of the InGaN QDs were estimated to be 3 nm, 30 nm and 7×1010 cm−2, respectively. The cathodoluminescence emission peak of the InGaN/GaN multiple layer quantum dots (MQDs) was found to red shift 330 meV with respect to the emission peak of the uncapped single layer of InGaN QDs due to Quantum Confined Stark effect. Blue LEDs based on InGaN/GaN multiple quantum wells (MQWs) as well as green and red LEDs based on InGaN MQDs emitting at 440 nm, 560 nm and 640 nm with FWHM of 30 nm, 87 nm and 97 nm, respectively, were grown and fabricated. The electroluminescence peak positions of both the green and red InGaN MQD LEDs are shown to be more blue-shifted with increasing injection current than that of the blue InGaN/GaN MQW LEDs.