Showing papers on "Cathodoluminescence published in 2009"
TL;DR: Light emitting diodes based on n-ZnO nanorods combined with different technologies (hybrid technologies) are suggested and the recent electrical, as well as electro-optical, characteristics of these LEDs are shown and discussed.
Abstract: Zinc oxide (ZnO), with its excellent luminescent properties and the ease of growth of its nanostructures, holds promise for the development of photonic devices. The recent advances in growth of ZnO nanorods are discussed. Results from both low temperature and high temperature growth approaches are presented. The techniques which are presented include metal?organic chemical vapour deposition (MOCVD), vapour phase epitaxy (VPE), pulse laser deposition (PLD), vapour?liquid?solid (VLS), aqueous chemical growth (ACG) and finally the electrodeposition technique as an example of a selective growth approach. Results from structural as well as optical properties of a variety of ZnO nanorods are shown and analysed using different techniques, including high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), photoluminescence (PL) and cathodoluminescence (CL), for both room temperature and for low temperature performance. These results indicate that the grown ZnO nanorods possess reproducible and interesting optical properties. Results on obtaining p-type doping in ZnO micro-?and nanorods are also demonstrated using PLD. Three independent indications were found for p-type conducting, phosphorus-doped ZnO nanorods: first, acceptor-related CL peaks, second, opposite transfer characteristics of back-gate field effect transistors using undoped and phosphorus doped wire channels, and finally, rectifying I?V characteristics of ZnO:P nanowire/ZnO:Ga p?n junctions. Then light emitting diodes (LEDs) based on n-ZnO nanorods combined with different technologies (hybrid technologies) are suggested and the recent electrical, as well as electro-optical, characteristics of these LEDs are shown and discussed. The hybrid LEDs reviewed and discussed here are mainly presented for two groups: those based on n-ZnO nanorods and p-type crystalline substrates, and those based on n-ZnO nanorods and p-type amorphous substrates. Promising electroluminescence characteristics aimed at the development of white LEDs are demonstrated. Although some of the presented LEDs show visible emission for applied biases in excess of 10 V, optimized structures are expected to provide the same emission at much lower voltage. Finally, lasing from ZnO nanorods is briefly reviewed. An example of a recent whispering gallery mode (WGM) lasing from ZnO is demonstrated as a way to enhance the stimulated emission from small size structures.
606 citations
TL;DR: The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% wurtzite are presented in this paper.
Abstract: The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% wurtzite are presented. A variety of shorter and longer segments of zinc-blende or wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random short period superlattices existent in these nanowires, assuming a staggered band offset between wurtzite and zinc-blende GaAs. The latter is confirmed also by time-resolved measurements. The extremely local nature of these optical transitions is evidenced also by cathodoluminescence measurements. Raman spectroscopy on single wires shows different strain conditions, depending on the wurtzite content which affects also the band alignments. Finally, the occurrence of the two crystallographic phases is discussed in thermodynamic terms.
457 citations
TL;DR: In this article, the thickness of hexagonal boron nitride (h-BN) nanosheets can be tuned in a range of 25−50 nm, revealing a strong and narrow cathodoluminescence emission in the ultraviolet range.
Abstract: Bulk quantities of hexagonal boron nitride (h-BN) nanosheets have been synthesized via a simple template- and catalyst-free chemical vapor deposition process at 1100−1300 °C. Adjusting the synthesis and chemical reaction parameters, the thickness of the BN nanosheets can be tuned in a range of 25−50 nm. Fourier transform infrared spectra and electron energy loss spectra reveal the typical nature of sp2-hybridization for the BN nanosheets. It shows an onset oxidation temperature of 850 °C for BN nanosheets compared with only about 400 °C for that of carbon nanotubes under the same conditions. It reveals a strong and narrow cathodoluminescence emission in the ultraviolet range from the h-BN nanosheets, displaying strong ultraviolet lasing behavior. The fact that this luminescence response would be rather insensitive to size makes the BN nanosheets ideal candidates for lasing optical devices in the UV regime. The h-BN nanosheets are also better candidates for composite materials in high-temperature and hazar...
177 citations
TL;DR: In this article, a three-layer staggered InGaN quantum wells (QWs) light-emitting diodes (LEDs) emitting at 520-525 nm were grown by metal-organic chemical vapor deposition by employing a graded growth-temperature profile.
Abstract: Three-layer staggered InGaN quantum wells (QWs) light-emitting diodes (LEDs) emitting at 520–525 nm were grown by metal-organic chemical vapor deposition by employing graded growth-temperature profile. The use of staggered InGaN QW, with improved electron-hole wave functions overlap design, leads to an enhancement of its radiative recombination rate. Both cathodoluminescence and electroluminescence measurements of three-layer staggered InGaN QW LED exhibited enhancements by 1.8–2.8 and 2.0–3.5 times, respectively, over those of conventional InGaN QW LED.
172 citations
TL;DR: In this article, a soft-chemical approach is used for the first time for this purpose, which is otherwise accomplished with high-temperature techniques, and a careful analysis of the product and intermediate states of the synthesis reveals that one of the reaction intermediates with sheet-like morphology acts as a self-sacrificing template and induces such unexpected and novel growth.
Abstract: Homogenous crystallization in solution, in the absence of external influences, is expected to lead to growth that is symmetric at least in two opposite facets. Such was not the case when we attempted to synthesize ZnO nanostructures by employing a solvothermal technique. The reaction product, instead, consisted of bullet-shaped tiny single crystals with an abrupt hexagonal base and a sharp tip. A careful analysis of the product and the intermediate states of the synthesis reveals that one of the reaction intermediates with sheet-like morphology acts as a self-sacrificing template and induces such unexpected and novel growth. The synthesis was further extended to dope the nanobullets with nitrogen as previous studies showed this can induce p-type behavior in ZnO, which is technologically complementary to the naturally occurring n-type ZnO. Herein, a soft-chemical approach is used for the first time for this purpose, which is otherwise accomplished with high-temperature techniques. Cathodoluminesce (CL) investigations reveal stable optical behavior within a pure nanobullet. On the other hand, the CL spectra derived from the surfaces and the cores of the doped samples are different, pointing at a N-rich core. Finally, even though N-doped ZnO is known to have high electrical conductivity, the study now demonstrates that the field-emission properties of ZnO can also be greatly enhanced by means of N doping.
160 citations
TL;DR: In this article, a detailed theoretical analysis is presented that successfully explains the measured cathodoluminescence (CL) signal based upon interference of transition radiation directly generated by electron impact and SPPs launched by the electron and outcoupled by the grating.
Abstract: The surface plasmon polariton (SPP) field intensity in the vicinity of gratings patterned in an otherwise planar gold surface is spatially resolved using cathodoluminescence (CL). A detailed theoretical analysis is presented that successfully explains the measured CL signal based upon interference of transition radiation directly generated by electron impact and SPPs launched by the electron and outcoupled by the grating. The measured spectral dependence of the SPP yield per incoming electron is in excellent agreement with rigorous electromagnetic calculations. The CL emission is shown to be similar to that of a dipole oriented perpendicular to the surface and situated at the point of electron impact, which allows us to establish a solid connection between the CL signal and the photonic local density of states associated to the SPPs.
150 citations
TL;DR: A red shift of the exciton of ZnO nanowires is efficiently produced by bending strain, as demonstrated by a low-temperature (81 K) cathodoluminescence (CL) study ofZnO Nanowires bent into L- or S-shapes.
Abstract: A red shift of the exciton of ZnO nanowires is efficiently produced by bending strain, as demonstrated by a lowtemperature (81 K) cathodoluminescence (CL) study of ZnO nanowires bent into L- or S-shapes. The figure shows a nanowire (Fig. a) with the positions of CL measurements marked. The corresponding CL spectra - revealing a peak shift and broadening in the region of the bend - are shown in Figure b. (Figure Presented).
134 citations
TL;DR: In this article, a vectorial description of induced field is given, which complements the information obtained from experiments, and the results of radiative emission under electron excitation show an excellent agreement with experiments.
Abstract: Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out-of-plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25 nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.
130 citations
TL;DR: In this paper, a combination method of sol-gel process and electrospinning was used to combine one-dimensional CaWO4 and CaWOWO4:Tb3+ nanowires and nanotubes, and the results of X-ray diffraction, scanning electron microscopy (SEM), TEM, high-resolution transmission electron microscope (HRTEM), photoluminescence, and time-resolved emission spectra, as well as kinetic decays were used to characterize the resulting samples.
Abstract: One-dimensional CaWO4 and CaWO4:Tb3+ nanowires and nanotubes have been prepared by a combination method of sol-gel process and electrospinning. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low voltage cathodoluminescence (CL) and time-resolved emission spectra, as well as kinetic decays were used to characterize the resulting samples. The results of XRD, FT-IR, TG-DTA indicate that the CaWO4 and CaWO4:Tb3+ samples begin to crystallize at 500 °C with the scheelite structure. Under ultraviolet excitation and low-voltage electron beams excitation, the CaWO4 samples exhibit a blue emission band with a maximum at 416 nm originating from the WO42−groups, while the CaWO4:Tb3+ samples show the characteristic emission of Tb3+ corresponding to 5D4–7F6,5,4,3 transitions due to an efficient energy transfer from WO42− to Tb3+. The energy transfer process was further studied by the time-resolved emission spectra as well as kinetic decay curves of Tb3+ upon excitation into the WO42−groups. Furthermore, the PL emission colour of CaWO4: x mol %Tb3+ can be tuned from blue to green by changing the concentrations (x) of the Tb3+ ion, making the materials have potential applications as fluorescent lamps and field emission displays (FEDs).
128 citations
TL;DR: In this paper, the structural, cathodoluminescence and field-emission properties of one-dimensional Cds micro/nanostructures with different morphologies are systematically investigated.
Abstract: High-quality, uniform one-dimensional Cds micro/nanostructures with different morphologies-microrods, sub-microwires and nanotips-are fabricated through an easy and effective thermal evaporation process. Their structural, cathodoluminescence and field-emission properties are systematically investigated. Microrods and nanotips exhibit sharp near-band-edge emission and broad deep-level emission, whereas sub-microwires show only the deep-level emission. A significant decrease in a deep-level/near-band-edge intensity ratio is observed along a tapered nanotip towards a smaller diameter part. This behaviour is understood by consideration of defect concentrations in the nanotips, as analyzed with high-resolution transmission electron microscopy. Field-emission measurements show that the nanotips possess the best field-emission characteristics among all 1D Cds nanostructures reported to date, with a relatively low turn-on field of 5.28 V mu m(-1) and the highest field-enhancement factor of 48.19. The field-enhancement factor, turn-on and threshold fields are discussed related to structure morphology and vacuum gap variations under emission.
126 citations
TL;DR: In this paper, white cathodoluminescence was achieved by co-doping Tm3+ and Dy3+ with appropriate ratios in the LaOCl single host lattice, which can be used as backlights.
Abstract: Blue, yellow and white light emissive LaOCl:Tm3+, LaOCl:Dy3+ and LaOCl:Tm3+,Dy3+ nanocrystalline phosphors were synthesized through the Pechini-type sol-gel process. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. Under UV radiation (229 nm) and low-voltage electron beam (0.5–5 kV) excitation, the Tm3+-doped LaOCl phosphor shows a very strong blue emission corresponding to the characteristic transitions of Tm3+ (1D2, 1G4 → 3F4, 3H6) with the strongest emission at 458 nm. The cathodoluminescent color of LaOCl:Tm3+ is blue to the naked eye with CIE coordinates of x = 0.1492, y = 0.0684. This phosphor has better CIE coordinates and higher emission intensity than the commercial product Y2SiO5:Ce3+. Notably, for the first time, white cathodoluminescence was realized by co-doping Tm3+ and Dy3+ with appropriate ratios in the LaOCl single host lattice, which can be potentially used as backlights. Luminescence mechanisms were proposed to explain the observed phenomena.
TL;DR: In this article, the luminescence properties of single-crystalline erbium-doped yttria nanoparticles with an average diameter of 80 nm, synthesized by a molten salt method, are reported.
Abstract: In this paper, the luminescence, including photoluminescence, upconversion and cathodoluminescence, from single-crystalline erbium-doped yttria nanoparticles with an average diameter of 80 nm, synthesized by a molten salt method, is reported. Outstanding luminescent properties, including sharp and well-resolved photoluminescent lines in the infrared region, outstanding green and red upconversion emissions, and excellent cathodoluminescence, are observed from the nanocrystalline erbium-doped yttria. Moreover, annealing by the high power laser results in a relatively large increase in photoluminescent emission intensity without causing spectral line shift. These desirable properties make these nanocrystals promising for applications in display, bioanalysis and telecommunications.
Journal Article•
TL;DR: In this article, a low-temperature (81 K) cathodoluminescence (CL) study of ZnO nanowires bent into L- or S-shapes is presented.
Abstract: A red shift of the exciton of ZnO nanowires is efficiently produced by bending strain, as demonstrated by a lowtemperature (81 K) cathodoluminescence (CL) study of ZnO nanowires bent into L- or S-shapes. The figure shows a nanowire (Fig. a) with the positions of CL measurements marked. The corresponding CL spectra - revealing a peak shift and broadening in the region of the bend - are shown in Figure b. (Figure Presented).
Posted Content•
TL;DR: The results of radiative emission under electron excitation show an excellent agreement with experiments, and a complete vectorial description of induced field is given, which complements the information obtained from experiments.
Abstract: Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out of plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.
TL;DR: The emission colors of CaMoO(4):Ln( 3+) nanofibers can be tuned from blue-green to green, yellow, and orange-red easily by changing the doping concentrations of Ln(3+) ions, making the materials have potential applications in fluorescent lamps and field emission displays (FEDs).
Abstract: One-dimensional CaMoO(4):Ln(3+) (Ln = Eu, Tb, Dy) nanofibers have been prepared by a combination method of sol-gel and electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and low voltage cathodoluminescence (CL) as well as kinetic decays were used to characterize the resulting samples. SEM and TEM analyses indicate that the obtained precursor fibers have a uniform size, and the as-formed CaMoO(4):Ln(3+) nanofibers consist of nanoparticles. Under ultraviolet excitation, the CaMoO(4) samples exhibit a blue-green emission band with a maximum at 500 nm originating from the MoO(4)(2-) groups. Due to an efficient energy transfer from molybdate groups to dopants, CaMoO(4):Ln(3+) phosphors show their strong characteristic emission under ultraviolet excitation and low-voltage electron beam excitation. The energy transfer process was further studied by the emission spectra and the kinetic decay curves of Ln(3+) upon excitation into the MoO(4)(2-) groups in the CaMoO(4):x mol % Ln(3+) samples (x = 0-5). Furthermore, the emission colors of CaMoO(4):Ln(3+) nanofibers can be tuned from blue-green to green, yellow, and orange-red easily by changing the doping concentrations (x) of Ln(3+) ions, making the materials have potential applications in fluorescent lamps and field emission displays (FEDs).
Abstract: The oxygen vacancy in BiFeO3 is calculated to be a double donor with states 0.6 eV below the conduction band edge, consistent with cathodoluminescence and electronic conductivity data. The atomic configurations were relaxed using the local density approximation plus Hubbard U (LDA+U) to the electron-correlation energy for each defect charge state to ensure that the oxide had a nonzero band gap. The defect formation energies were calculated using the screened exchange (sX) functional.
TL;DR: In this article, the point defect structure of clear natural α-quartz at 295 K was investigated and the observed CL emissions were identified with a range of native and impurity defect centres including: interstitial molecular O at 0.968 eV, a charge-compensated substitutional Fe 3+ impurity centre at ∼1.65 eV; a non-bridging oxygen hole centre (NBOHC) at 1.9 eV), an NBOHC with OH -probability 1.95 eV and neutral relaxed O vacancy at 4.
Abstract: Cathodoluminescence (CL) spectroscopy in an SEM has been used to investigate the point defect structure of clear natural α-quartz at 295 K. Cathodoluminescence processes and experimental factors that influence the CL spectra from α-quartz are investigated. Electron irradiation may induce changes in the average local crystal microstructure of quartz, locally transforming it to a less dense, amorphized state. The observed CL emissions are identified with a range of native and impurity defect centres including: interstitial molecular O at 0.968 eV; a charge-compensated substitutional Fe 3+ impurity centre at ∼1.65 eV; a non-bridging oxygen hole centre (NBOHC) at 1.9 eV; an NBOHC with OH - precursor at 1.95 eV; an NBOHC with a non-bridging impurity (e.g. Li + , Na + or K + ) precursor at ∼1.9 eV; a radiative recombination of the self-trapped exciton (STE) associated with an E′ centre in electron-irradiation-amorphized quartz at 2.3 eV; a radiative recombination of the STE associated with the E 1 ′ centre in α-quartz at 2.7 eV; a charge-compensated substitutional Al3+ impurity centre at 3.3 eV; and a neutral relaxed O vacancy at 4.3 eV. In addition, unresolved contributions from O-deficient defects in electron-irradiation-amorphized SiO 2 are likely at ∼2.7 and 4.3 eV.
TL;DR: In this article, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (CL) spectra were utilized to characterize the synthesized phosphors.
Abstract: LaAlO3:Tm3+ and LaAlO3:Tb3+ phosphors were prepared through a Pechini-type sol−gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence, and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphors. The XRD results reveal that the fully crystalline pure LaAlO3 phase can be obtained at 800 °C. The FE-SEM image indicates that the phosphor samples are composed of aggregated spherical particles with sizes ranging from 40 to 80 nm. Under the excitation of ultraviolet light (230 nm) and low-voltage electron beams (1−3 kV), the LaAlO3:Tm3+ and LaAlO3:Tb3+ phosphors show the characteristic emissions of Tm3+ (1D2→3H6,4,3F4 transitions) and Tb3+ (5D3,4→7F6,5,4,3 transitions), respectively. The CL of the LaAlO3:Tm3+ phosphors have high color purity and comparable intensity to the Y2SiO5:Ce3+ commercial product, and the CL colors of Tb3+-doped LaAlO3 phosphors can be tuned from blue to green by changing the doping concentration of Tb...
TL;DR: Using newly developed parallel-detection-mode CL-STEM, it is shown that optical properties can vary within a single nanowires heterostructure as a function of nanowire morphology.
Abstract: Direct correlation of structural and optical properties on the nanoscale is essential for rational synthesis of nanomaterials with predefined structure and functionality. We study optical properties of single III-V nitride nanowire radial heterostructures with measured spatial resolution of <20 nm using cathodoluminescence (CL) technique coupled with scanning transmission electron microscopy (STEM). Enhanced carrier recombination in nanowire quantum wells and reduced light emission from regions containing structural defects were directly observed. Using newly developed parallel-detection-mode CL-STEM, we show that optical properties can vary within a single nanowire heterostructure as a function of nanowire morphology.
TL;DR: No crystal-orientation dependence is observed while releasing the AlN/GaN nanomembranes from the Si substrate indicating that the driving stress mainly originates from the zipping effect among islands during growth.
Abstract: Ultrathin AlN/GaN crystalline porous freestanding nanomembranes are fabricated on Si(111) by selective silicon etching, and self-assembled into various geometries such as tubes, spirals, and curved sheets. Nanopores with sizes from several to tens of nanometers are produced in nanomembranes of 20-35 nm nominal thickness, caused by the island growth of AlN on Si(111). No crystal-orientation dependence is observed while releasing the AlN/GaN nanomembranes from the Si substrate indicating that the driving stress mainly originates from the zipping effect among islands during growth. Competition between different relaxation mechanisms is experimentally revealed for different nanomembrane geometries and well-described by numerical calculations. The cathodoluminescence emission from GaN nanomembranes reveals a weak peak close to the GaN bandgap, which is dramatically enhanced by electron irradiation.
TL;DR: In this paper, the effects of GaN nanowire coalescence were investigated on a local scale by combining high-resolution transmission electron microscopy imaging with spatially resolved cathodoluminescence measurements.
Abstract: The effects of GaN nanowire coalescence have been investigated on a local scale by combining high-resolution transmission electron microscopy imaging with spatially resolved cathodoluminescence measurements. Coalescence induces the formation of a network of boundary dislocations, above which I1-type basal-plane stacking faults are nucleated. The former contributes to the reduction in the crystalline quality at the bottom of coalesced nanowires while the latter leads to intense excitonic radiative transitions at 3.42 eV in their center. Despite coalescence, the top of coalesced nanowires presents a very high crystalline quality, resulting in strong radiative recombinations of donor bound excitons at 3.47 eV.
01 Jan 2009
TL;DR: In this paper, backscatter diffraction (EBSD) is employed as an additional characterization technique to a scanning electron microscope (SEM), enabling individual grain orientations, local texture, point-to-point orientation correlations, and phase identification and distributions to be determined routinely on the surfaces of bulk polycrystals.
Abstract: Electron backscatter diffraction (EBSD), when employed as an additional characterization technique to a scanning electron microscope (SEM), enables individual grain orientations, local texture, point-to-point orientation correlations, and phase identification and distributions to be determined routinely on the surfaces of bulk polycrystals. The application has experienced rapid acceptance in metallurgical, materials, and geophysical laboratories within the past decade (Schwartz et al. 2000) due to the wide availability of SEMs, the ease of sample preparation from the bulk, the high speed of data acquisition, and the access to complementary information about the microstructure on a submicron scale. From the same specimen area, surface structure and morphology of the microstructure are characterized in great detail by the relief and orientation contrast in secondary and backscatter electron images, element distributions are accessed by energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), or cathodoluminescence analysis, and the orientations of single grains and phases can now be determined, as a complement, by EBSD.
29 May 2009
TL;DR: In this paper, the SnO 2 nanowires were synthesized on alumina substrates and formed into an ultraviolet (UV) photodetector, which exhibited a rapid photo-response as a UV lamp was switched on and off.
Abstract: SnO 2 nanowires can be synthesized on alumina substrates and formed into an ultraviolet (UV) photodetector. The photoelectric current of the SnO 2 nanowires exhibited a rapid photo-response as a UV lamp was switched on and off. The ratio of UV-exposed current to dark current has been investigated. The SnO 2 nanowires were synthesized by a vapor–liquid–solid process at a temperature of 900 °C. It was found that the nanowires were around 70–100 nm in diameter and several hundred microns in length. High-resolution transmission electron microscopy (HRTEM) image indicated that the nanowires grew along the [200] axis as a single crystallinity. Cathodoluminescence (CL), thin-film X-ray diffractometry, and X-ray photoelectron spectroscopy (XPS) were used to characterize the as-synthesized nanowires.
TL;DR: The resonant whispering gallery modes of plasmonic subwavelength ring cavities defined by circular grooves patterned into a gold surface are resolved, allowing us to assess the symmetry, ordering, degree of confinement, and near-field enhancement of the modes with unprecedented detail.
Abstract: We resolve the resonant whispering gallery modes of plasmonic subwavelength ring cavities defined by circular grooves patterned into a gold surface. An interesting interplay is observed between subwavelength confinement and guiding along the groove. Full spatial and spectroscopic information is directly obtained using cathodoluminescence, including details of the nanoscale intensity distribution (spatial resolution 11 ( 8 nm). Excellent agreement between measurements and rigorous electromagnetic theory is obtained, thus allowing us to assess the symmetry, ordering, degree of confinement, and near-field enhancement of the modes with unprecedented detail. Surface plasmons (SPs) are hybrid electromagnetic and conduction electron excitations 1 that allow matching the micrometer-sized wavelength of light at optical frequencies with nanoscopic dimensions of patterned metallic structures. In particular, the interplay between localized and propagating surface plasmons has been intensely investigated with a view to integrated plasmonic devices like plasmon waveguides 2-4 and plasmon lasers. 5 However, exploiting the field concentration that is offered by such nanostructures requires a probe of the plasmonic modes at nanometer scale resolution. Scanning near-field optical microscopy (SNOM) provides a resolution down to ∼50 nm, although a coated tip can interact with the local modes thus producing distorted information. In contrast, fast electrons constitute a noninvasive probe of metal structures with the potential for true nanometer spatial resolution to retrieve spectral information through induced light emission (cathodoluminescence, CL) 6 or via the analysis of electron energy loss in the case of thin samples. 7 The field of a moving electron 8 diverges close to its trajectory. The interaction of the electron with the photonic structure being probed is governed by this divergent field. Consequently, there is no limit to the resolution, which in experiment is only limited by the finite size of the electron beam. In this Letter, we investigate whispering gallery plasmon excitations 9-13 supported by grooves of annular shape that share a unique combination of features associated to both standing wave modes and propagating modes. We pattern the grooves in a single-crystal gold surface and study the spatial and spectral evolution of the modes with unprecedented detail by using cathodoluminescence spectroscopy and boundary element method (BEM) calculations. We report excellent agreement between experiment and theory, which allows us to classify plasmon modes according to their azimuthal symmetry and radial order. We formulate a dispersion model relating circular grooves to straight grooves that explains satisfactorily the detailed dependence of mode frequencies and spatial distributions on ring radius and groove depth.
TL;DR: In this paper, the energy transfer process from Ce3+ to Tb3+ in LaPO4:Ce3++ nanofibers was further studied by the time-resolved emission spectra.
TL;DR: In this paper, the results of the cathodoluminescence and Raman spectroscopy studies indicate that the type of the Y-rich oxide phases after heat-treatment can be correlated with the content and/or reservoir of metallic Y in the coating.
Abstract: SEM cathodoluminescence (CL) imaging and Raman spectroscopy were used to study the compound type, distribution and morphology of Y-rich oxide particles in MCrAlY-coatings at various stages of the manufacturing and oxidation exposure. Compared to conventional SEM/EDX, CL allows easy detection of Y-rich oxides at a high, sub-µm resolution with a fast image acquisition. Furthermore, phase analysis of the Y-rich oxide compounds based on the wavelength resolved Raman spectra and in some cases also using CL-spectra is possible. The presented results of the cathodoluminescence and Raman spectroscopy studies indicate that the type of the Y-rich oxide phases after heat-treatment can be correlated with the content and/or reservoir of metallic Y in the coating. Hence, these analytical methods have potential to be applied as (non-destructive) quality control methods in the manufacturing of MCrAlY-coatings. The distribution of the Y-rich oxide precipitates formed during manufacturing has been shown to affect the growth rate and mechanical stability of the alumina scales during service. Y-oxide distribution in the MCrAlY-coatings, therefore, represents a factor, which influences the lifetime of overlay and TBC-coatings.
TL;DR: Cathodoluminescence real-color imaging and spectroscopy were employed to study the properties of Ga(2)O(3) nanowires grown with different Sn/Ga ratios, showing large spectral emission variation, ranging from blue to red, with a green transition zone.
Abstract: Cathodoluminescence real-color imaging and spectroscopy were employed to study the properties of Ga2O3 nanowires grown with different Sn/Ga ratios. The structures grown under Sn-rich conditions show large spectral emission variation, ranging from blue to red, with a green transition zone. Spectral emission changes correlate with changes in the chemical composition and structure found by energy dispersive spectroscopy and electron diffraction. A sharp transition from green to red emission correlates with a phase transition of β-Ga2O3 to polycrystalline SnO2. The origin of the green emission band is discussed based on ab initio calculation results.
TL;DR: It was found as expected that the emission of GaAs/In(x)Ga(1-x)As/GaAs heterostructures is localized and this work is important for the use of an external catalyst-free growth of complex axial heterostructure and related opto-electronic devices that facilitates its possible integration in the device or system fabrication processes.
Abstract: Self-catalyzed growth of axial InxGa1-xAs/GaAs heterostructures has been realized by molecular beam epitaxy. The growth of the wires is achieved from gallium/indium alloy droplets that are nucleated in situ. By variation of the In/Ga beam flux during the growth it was possible to vary the effective indium content up to x = 5%, as deduced from photoluminescence measurements. We have analyzed the dependence of the alloy concentration on the growth conditions and present a simple model for the growth. The heterostructures grown with the method presented were spatially mapped along the wires with confocal microphotoluminescence and cathodoluminescence. It was found as expected that the emission of GaAs/InxGa1-xAs/GaAs heterostructures is localized. This work is important for the use of an external catalyst-free growth of complex axial heterostructures and related opto-electronic devices that facilitates its possible integration in the device or system fabrication processes.
TL;DR: Ni-doped ZnO nanostructures were synthesized in situ through a pulsed-electrodeposition-assisted chemical bath deposition method, and the optical and magnetic properties of the nanostructure were studied as mentioned in this paper.
Abstract: Ni-doped ZnO nanostructures were synthesized in situ through a pulsed-electrodeposition-assisted chemical bath deposition method, and the optical and magnetic properties of the nanostructures were studied. It was found that the morphology of the nanostructures evolved from a rodlike to a sheetlike structure because of the different growth modes, and a growth mechanism is proposed to explain these findings. A relatively strong UV emission was observed for the nanorods, whereas a relatively strong visible emission was seen for the nanosheets. Ni was successfully doped into the ZnO wurtzite lattice structure as revealed by X-ray diffraction and X-ray photoelectron spectroscopy and also verified by the cathodoluminescence characterization. Room-temperature ferromagnetism was also observed in the Ni-doped ZnO nanostrucures. The results are helpful to tailor the physical properties of ZnO by changing its morphology and composition.
TL;DR: In this article, a Pechini-type solgel process was used to synthesize LaInO3: Sm3+, LaIn O3: Pr3+ and LaIn o3: Tb3+ phosphors.