Showing papers on "Cathodoluminescence published in 2005"
TL;DR: In this paper, a direct correlation has been established between stacking faults in a-plane GaN epilayers and luminescence peaks in the 3.29-3.41 eV range, where the structural features of stacking faults were determined by diffraction-contrast transmission electron microscopy, while the optical emission characteristics were observed by highly spatially resolved monochromatic cathodoluminescence.
Abstract: A direct correlation has been established between stacking faults in a-plane GaN epilayers and luminescence peaks in the 3.29–3.41 eV range. The structural features of the stacking faults were determined by diffraction-contrast transmission electron microscopy, while the optical emission characteristics were observed by highly spatially resolved monochromatic cathodoluminescence. The studies were performed in the exact same regions of thinned foils. We find that stacking faults on the basal plane are responsible for the strong emission at ∼3.14eV. Luminescence peaks at ∼3.33 and ∼3.29eV are associated with the presence of stacking faults on prismatic a planes and partial dislocations at the stacking fault boundaries, respectively.
328 citations
TL;DR: In this article, boron nitride nanotubes (BNNTs) may be dissolved in organic solvents by wrapping them with a polymer, and a band gap ranging from 5.2 to 5.5 eV was documented for the BNNTs independent of their geometrical characteristics.
Abstract: We report for the first time that boron nitride nanotubes (BNNTs) may be dissolved in organic solvents by wrapping them with a polymer. Transmission electron microscopy and cathodoluminescence studies indicate the strong π−π interactions between BNNTs and the polymer. A band gap ranging from 5.2 to 5.5 eV was documented for the BNNTs independent of their geometrical characteristics by using ultraviolet−visible absorption experiments on composite films and thin BNNT films prepared from solutions.
247 citations
TL;DR: In this paper, a conversion from ohmic to rectifying behavior is observed for Au contacts on atomically ordered polar ZnO surfaces following remote, room-temperature oxygen plasma treatment.
Abstract: A conversion from ohmic to rectifying behavior is observed for Au contacts on atomically ordered polar ZnO surfaces following remote, room-temperature oxygen plasma treatment. This transition is accompanied by reduction of the “green” deep level cathodoluminescence emission, suppression of the hydrogen donor-bound exciton photoluminescence and a ∼0.75eV increase in n-type band bending observed via x-ray photoemission. These results demonstrate that the contact type conversion involves more than one mechanism, specifically, removal of the adsorbate-induced accumulation layer plus lowered tunneling due to reduction of near-surface donor density and defect-assisted hopping transport.
239 citations
TL;DR: In this paper, the emission properties of nonpolar a-plane GaN layers grown on r -plane sapphire were investigated and temperature-, excitation-density-, and polarization-dependent photoluminescences and spatially resolvable spatial resolvability was obtained.
Abstract: We report on the emission properties of nonpolar a -plane GaN layers grown on r -plane sapphire. Temperature-, excitation-density-, and polarization-dependent photoluminescences and spatially resol ...
193 citations
TL;DR: In this paper, high-pressure pulsed-laser deposition (PLD) was used to grow MgxZn1−xO nanowires on gold-covered sapphire single crystals.
Abstract: MgxZn1−xO nanowires with Mg-content x from 0 to 0.2 have been grown by high-pressure pulsed-laser deposition (PLD) on gold-covered sapphire single crystals. The PLD process allows for a unique wide-range control of morphology, diameter, and composition of the MgxZn1−xO nanowires. The diameter of single ZnO wires could be varied between about 50 and 3000 nm, and the Mg content x of MgxZn1−xO wire arrays was controlled via the PLD gas pressure. The microscopic homogeneity of Mg content is displayed by cathodoluminescence (CL) imaging of the excitonic peak energy. The fluctuation of CL peak energy between individual wires is about an order of magnitude smaller than the alloy broadening.
191 citations
TL;DR: In this article, single-phase wurtzite Zn1−xMgxO alloy films with 0.45x=0.45 were successfully grown on (1 − 1 − 1)-oriented Si substrates by molecular beam epitaxy.
177 citations
TL;DR: In this paper, single crystalline TiO 2 nanowires have been successfully grown on alumina substrates using a high-frequency (350-KHz) dielectric heater at 1050-°C by a two-step of thermal evaporation method without using any catalyst.
167 citations
TL;DR: An original time-resolved cathodoluminescence set-up is applied to describe carrier dynamics within single gallium-arsenide-based pyramidal nanostructures with a time resolution of 10 picoseconds and a spatial resolution of 50 nanometres.
Abstract: Picosecond and femtosecond spectroscopy allow the detailed study of carrier dynamics in nanostructured materials1. In such experiments, a laser pulse normally excites several nanostructures at once. However, spectroscopic information may also be acquired using pulses from an electron beam in a modern electron microscope, exploiting a phenomenon called cathodoluminescence. This approach offers several advantages. The multimode imaging capabilities of the electron microscope enable the correlation of optical properties (via cathodoluminescence) with surface morphology (secondary electron mode) at the nanometre scale2. The broad energy range of the electrons can excite wide-bandgap materials, such as diamond- or gallium-nitride-based structures that are not easily excited by conventional optical means. But perhaps most intriguingly, the small beam can probe a single selected nanostructure. Here we apply an original time-resolved cathodoluminescence set-up to describe carrier dynamics within single gallium-arsenide-based pyramidal nanostructures3 with a time resolution of 10 picoseconds and a spatial resolution of 50 nanometres. The behaviour of such charge carriers could be useful for evaluating elementary components in quantum computers4,5, optical quantum gates6 or single photon sources7,8,9 for quantum cryptography10.
160 citations
TL;DR: In this paper, spherical SiO2 particles have been coated with Y2O3:Eu3+ phosphor layers by a Pechini sol-gel process, and the obtained core-shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution.
Abstract: Spherical SiO2 particles have been coated with Y2O3:Eu3+ phosphor layers (SiO2@Y2O3:Eu3+) by a Pechini sol-gel process. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, and cathodoluminescence spectra were utilized to characterize the SiO2@Y2O3:Eu3+ core-shell-structured phosphor particles. The obtained core-shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution. The thickness of Y2O3:Eu3+ shell could be easily controlled by changing the number of deposition cycles (60nm for three deposition cycles). The SiO2@Y2O3:Eu3+ core-shell particles show a strong red emission corresponding to D05-F27 (611nm) of Eu3+ under the excitation of ultraviolet (250nm) and low-voltage electron beams (2–6kV), which have potential application for field emission displays.
143 citations
TL;DR: In this article, micro-Auger electron spectroscopy, cathodoluminescence (COMS) spectrograms, and work function measurements in copper indium gallium diselenide polycrystalline solar cell films cleaved in ultrahigh vacuum were used to confirm theoretical predictions that polar GB interfaces are stabilized by massive removal of Cu atoms.
Abstract: We have used micro-Auger electron spectroscopy, cathodoluminescence spectroscopy, and work function measurements in copper indium gallium diselenide polycrystalline solar cell films cleaved in ultrahigh vacuum. We establish that, relative to the grain interior, the grain boundary shows (1) a Cu composition decrease, as large as a factor of two, (2) a work function decrease of up to 480 meV, and (3) no additional radiative recombination centers despite a high concentration of grain boundary (GB) defects. These results confirm theoretical predictions that (i) polar GB interfaces are stabilized by massive (∼50%) removal of Cu atoms, leading to (ii) a valence band offset between GB and grain interiors that (iii) repels holes from the GB, thus likely reducing GB electron-hole recombination and improving photovoltaic (and other photonic) device operation.
125 citations
TL;DR: In this article, aligned TiO2 nanowire arrays were fabricated onto Si wafers by a simple thermal deposition (PVD) method, and the as-prepared nanowires are single-crystalline and of high purity.
Abstract: Aligned TiO2 nanowire arrays were fabricated onto Si wafers by a simple thermal deposition (PVD) method. Scanning electron microscopy and high-resolution transmission electron microscopy observations confirm that the as-prepared TiO2 nanowires are single-crystalline and of high purity. Field emission measurements showed that the TiO2 nanowire arrays could provide stable, high-current electron emission at a low voltage. The emission current monitored over a period of 24 h fluctuated gently but did not show degradation. The cathode-luminescence (CL) images captured by a CCD camera were very bright and their CL intensity was homogeneous. This remarkable performance reveals that TiO2 nanowire arrays are well suited for commercial use in electron devices, particularly flat panel displays.
TL;DR: In this paper, room-temperature monochromatic cathodoluminescence images at the redshifted peak reveal spatially nonuniform emission similar to that observed in In(Al)GaN alloys and attributed to compositional inhomogeneity.
Abstract: AlGaN samples grown by plasma-assisted molecular-beam epitaxy on sapphire (0001) substrates, with 20%–50% Al content and without the use of indium, show intense room-temperature photoluminescence that is significantly redshifted, 200–400meV, from band edge. This intense emission is characterized by a long room-temperature lifetime (∼375ps) comparable to that seen in low defect density (∼108cm−2) GaN. Room-temperature monochromatic cathodoluminescence images at the redshifted peak reveal spatially nonuniform emission similar to that observed in In(Al)GaN alloys and attributed to compositional inhomogeneity. These observations suggest that spatial localization enhances the luminescence efficiency despite the high defect density (>1010cm−2) of the films by inhibiting movement of carriers to nonradiative sites.
TL;DR: In this article, pegmatite quartz from several localities in Norway and Namibia were investigated by cathodoluminescence (CL) microscopy and spectroscopy, electron paramagnetic resonance (EPR) measurements, and trace-element analysis (ICP-MS) to obtain information about their structure and luminescence characteristics.
Abstract: Samples of pegmatite quartz from several localities in Norway and Namibia were investigated by cathodoluminescence (CL) microscopy and spectroscopy, electron paramagnetic resonance (EPR) measurements, and trace-element analysis (ICP-MS) to obtain information about their structure and luminescence characteristics. The defect structure and trace-element composition of the pegmatite quartz samples that were studied differ from those of quartz of other origin (hydrothermal, igneous and metamorphic quartz). EPR measurements reveal an almost complete lack of intrinsic lattice defects associated with O or Si vacancies (e.g., E′ center, O 3− 2 center), whereas some trace elements (Al, Ti, Ge, Li) are apparently enriched and form paramagnetic centers. The results indicate that there possibly is a redistribution of alkali ions during electron irradiation. The diamagnetic [AlO 4 /M + ] 0 center transforms into the paramagnetic [AlO 4 ] 0 center, while the compensating ions diffuse away and may be captured by the diamagnetic precursor centers of [GeO 4 ] 0 and [TiO 4 ] 0 to form paramagnetic centers ([TiO 4 /Li + ] 0 , [GeO 4 /Li + ] 0 ). These defects result in a specific luminescence behavior, which is very similar for all samples. In general, quartz from pegmatites shows homogeneous CL without growth zoning or internal structures suggesting constant physicochemical conditions during crystal growth. The CL emission is dominated by a transient bluish-green CL, which disappears after 60–100 s of electron irradiation. The two main emission bands centered at 505 nm (2.45 eV) and 390 nm (3.18 eV) are probably related to alkali-compensated, trace-element centers in the quartz structure. Other CL emission bands, which are characteristic features of igneous, metamorphic, or hydrothermal quartz (e.g., at 450 nm = 2.75 eV, 580 nm = 2.14 eV, 650 nm = 1.91 eV) are almost completely lacking. This fact indicates that the defects responsible for these CL emissions are absent in pegmatite quartz.
TL;DR: In this paper, the results of sintering Ga2O3 powder under argon flow have been investigated by cathodoluminescence in the scanning electron microscope and the results showed that the violet-blue emission characteristic of Ga 2O3 and a red emission at 1.73 eV dominant in the nanowires and other nano- and microstructures formed during the sinter treatment.
Abstract: β‐Ga2O3 nano- and microwires with diameters ranging from tens of nanometers to about one micron and lengths of up to tens of microns, have been obtained by sintering Ga2O3 powder under argon flow. The structures have been investigated by cathodoluminescence in the scanning electron microscope. The samples showed the violet-blue emission characteristic of Ga2O3 and a red emission at 1.73 eV dominant in the nanowires and other nano- and microstructures formed during the sintering treatment. At temperatures below 210 K, this band exhibits sharp peaks separated by 20 meV. This observation suggests the exchange of phonons in the recombination process.
TL;DR: In this paper, a reproducible growth of GaN nanowires is demonstrated by pulsed low pressure metalorganic chemical vapor deposition using self-assembled Ni nanodots as nucleation sites on (0001) sapphire substrates.
Abstract: Controlled and reproducible growth of GaN nanowires is demonstrated by pulsed low-pressure metalorganic chemical vapor deposition Using self-assembled Ni nanodots as nucleation sites on (0001) sapphire substrates we obtain nanowires of wurtzite-phase GaN with hexagonal cross sections, diameters of about 100nm, and well-controlled length The nanowires are highly oriented and perpendicular to the growth surface The wires have excellent structural and optical properties, as determined by x-ray diffraction, cathodoluminescence, and Raman scattering The x-ray measurements show that the nanowires are under a complex strain state consistent with a superposition of hydrostatic and biaxial components
TL;DR: In this article, a microwave plasma assisted chemical vapour deposition (MWPACVD) has been successfully used on high-pressure high-temperature (HPHT) (100) substrates.
TL;DR: Porous boron carbonitride nanotubular fibers with BCN stoichiometry and homogeneous B, C, and N species distribution were fabricated via the CVD method, suggesting the characteristics of a semiconductor with a band gap of 3.89 eV.
Abstract: Porous boron carbonitride nanotubular fibers with BCN stoichiometry and homogeneous B, C, and N species distribution were fabricated via the CVD method. Spatially resolved cathodoluminescence measurements on individual nanostructures revealed intense ultraviolet emission centered at 319 nm, suggesting the characteristics of a semiconductor with a band gap of 3.89 eV. It is believed that the present nanostructures may have a variety of applications in ultraviolet optical devices, hydrogen storage systems, and field emission apparatus.
TL;DR: In this paper, the influence of ball milling of the starting powder on the formation of tubes is investigated and the local cathodoluminescence measurements show a different defect structure in the tubes than in the sample background.
Abstract: Sintering SnO2 under argon flow at temperatures in the range of 1350–1500°C causes the formation of wires, rods, and tubes on the sample surface. At high temperatures of the mentioned range, microwires with lengths of hundreds of microns are formed. At lower temperatures the formation of micro- and nanorods as well as micro- and nanotubes takes place. The influence of ball milling of the starting powder on the formation of tubes is investigated. The local cathodoluminescence measurements show a different defect structure in the tubes than in the sample background.
TL;DR: In this article, single-crystalline nanowire-type nanostructures were synthesized on silicon by thermal chemical vapor deposition without catalysts through a two-step pressure-controlled vapor-reflected process at a low temperature of 550°C where self-organized hexagonal crystalline or porous nanowires arrays were grown on nanorods.
Abstract: ZnO single-crystalline nanowire-type nanostructures were synthesized on silicon by thermal chemical vapor deposition without catalysts through a two-step pressure-controlled vapor-reflected process at a low temperature of 550 °C where self-organized hexagonal crystalline or porous nanowire arrays were grown on nanorods. The nanowire diameter is around 20 nm and number of nanowires is selected by the nanorod size. Cathodoluminescence spectra exhibit strong green emissions, indicative of high oxygen-vacancy density, which sheds a light on further applications for multichannel nanoconductors in nanodevices.
TL;DR: In this paper, an almost cylindrical shape and an average diameter of about 30-50 nm for the smallest nanowire was reported. But the authors did not find any evidence of near band edge transition.
TL;DR: In this article, a transparent glass ceramics containing CaF2 nano-crystals co-doped with Er-Yb were developed by heat treatment of glasses in the system SiO2-Al2O3-CaF2-LnF3 (Ln=Er, Yb).
Abstract: Transparent glass ceramics containing CaF2 nano-crystals co-doped with Er–Yb were developed by heat treatment of glasses in the system SiO2–Al2O3–CaF2–LnF3 (Ln=Er, Yb). The crystal size of CaF2 increased with increasing heat-treatment temperature. Upconversion emission intensities at 660 and 540 nm increased dramatically with increasing heat-treatment temperature. The cathode luminescence mapping indicates that the visible Er-luminescence arises mainly from the precipitated CaF2 nano-crystals with a phonon energy lower than that of a silicate matrix. It is concluded that both Er and Yb were concentrated in the CaF2 nano-crystals, and the quantum efficiency of Er3+-luminescence and the energy transfer efficiency from Yb3+ were considerably improved after ceramization.
TL;DR: In this article, ZnO nanopushpins with very thin and flat cap on top of the nanorods and regular hexagonal nanotubes were obtained in the same run of growth in different regions.
Abstract: ZnO nanostructures with peculiar morphology were synthesized in large quantities via catalyst-free thermal evaporation. Both ZnO nanopushpins with very thin and flat cap on top of the nanorods, and regular hexagonal nanotubes, can be obtained in the same run of growth in different regions. The ZnO nanopushpins and nanotubes were characterized by using scanning electron microscopy and transmission electron microscopy. Cathodoluminescence measurements revealed that the emission from oxygen vacancy overwhelmed that of the near band gap in the as-grown ZnO nanotube arrays.
TL;DR: In this paper, the as-synthesized TiSi2 nanowires were investigated using x-ray diffraction, scanning electron microscopy, transmission electron microscope, and Raman scattering.
Abstract: TiSi2 is a high-melting compound with excellent conductivity ∼severalμΩcm. TiSi2 nanowires were fabricated in large scale by a simple vapor phase deposition method. The as-synthesized TiSi2 nanowires were investigated using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman scattering. Field emission property of TiSi2 nanowires was studied and an emission current density of 5mA∕cm2 was obtained and no obvious degradation was observed in a life stability experiment period for over ∼40h. The cathodoluminescence images were very bright and homogenous. The remarkable performance reveals that the TiSi2 nanowires can serve as a good candidate for commercial application in vacuum microelectronic devices, particularly flat panel displays.
TL;DR: In this article, an almost cylindrical shape and an average diameter of about 30-50 nm for the smallest nanowires are reported. But the results of the X-ray diffraction investigations exclude the presence of spurious phases.
Abstract: 0.1–0.3 mm thick entanglements of quasi-one-dimensional semiconducting Tin dioxide nanocrystals, in form of nanowires and nanobelts, are successfully grown by low cost Chemical Vapour Deposition directly on large area (100 mm2) Al2O3, SiO2 and Si substrates. Their lateral size ranges from 50 to 700 nm and their length can achieve several hundreds of micrometers. Transmission Electron Microscopy reveals either the nanowires and the nanobelts grow in the tetragonal Rutile structure. Diffraction contrast analyses and selected area diffraction investigations show the nanowires are single crystals without defects while the nanobelts sometimes present twins inside. An almost cylindrical shape and an average diameter of about 30–50 nm for the smallest nanowires is reported. X-ray diffraction investigations exclude the presence of spurious phases. A broad band structured in two emissions peaked at about 450 nm and 560 nm is revealed by large area Cathotoluminescence, while single nanocrystal spectroscopy shows that the reduction of the lateral dimension of the nanobelts from 1000 nm to 50 nm blue-shifts the main emission band at 560 nm of about 40 nm (at room temperature). These preliminary results suggest a possible role of oxygen vacancies and of the surface/volume ratio on the origin and the blue shift of Cathodoluminescence spectra. The near band edge emission, typical of bulk tin dioxide (∼320 nm), is not found in nanobelts narrower than 1000 nm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, Li-doped Y2O3:Eu and Gd2O-3-Eu phosphors have been studied as potential red phosphors for application to field emission displays.
TL;DR: In this paper, the synthesis and characterization of Zn 2 SiO 4 :Mn phosphor layers on spherical silica spheres, i.e., core-shell particles, are described.
Abstract: The synthesis and characterization of Zn 2 SiO 4 :Mn phosphor layers on spherical silica spheres, i.e., core-shell particles of Zn 2 SiO 4 :Mn@SiO 2 are described in this paper. First, monodisperse silica spheres with an average size around 750 nm have been obtained via the Stober method by the hydrolysis and condensation of telraethoxysilane Si(OC 2 H 5 )4 under base condition (using NH 4 OH as the catalyst). Second, the silica spheres are coated with Zn 2 SiO 4 :Mn phosphor layers by a sol-gel process. The resulting core-shell particles are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscopy, photoluminescence, low-voltage cathodoluminescence, as well as kinetic decay. The results confirm that the 1000°C-annealed sample consists of crystalline Zn 2 SiO 4 :Mn shells and amorphous SiO 2 cores with spherical morphology and narrow size distribution. The Zn 2 SiO 4 :Mn@SiO 2 particles show the green emission at 521 nm corresponding to 4 T 1 ( 4 G)- 6 A 1 ( 6 S) transition of Mn 2 + under the excitation of UV (250 nm), vacuum UV (172 nm), and electron-beams (1-6 kV). The luminescence intensity has been studied as a function of coating number, accelerating voltage, and filament current, respectively.
TL;DR: In this article, the results of photoluminescence (PL) studies on Cu(In,Ga)Se2 thin films with varying Ga contents were reported and the defect depth was found to increase with increasing Ga content, as expected from the hydrogen model.
TL;DR: In this article, the effect of different surface orientations on the defect structure of TiO2 single crystals and the evolution of the luminescence properties under plastic deformation are investigated by cathodoluminescence microscopy.
Abstract: In this work, the effect of different surface orientations on the defect structure of TiO2 single crystals and the evolution of the luminescence properties under plastic deformation are investigated by cathodoluminescence (CL) microscopy. The main features of the spectra are an infrared band at 1.53 eV, and a complex band in the visible range, whose peak position depends on the electron beam energy, and is attributed to oxygen vacancy related defects. Comparison of the intensity of these bands in the spectra recorded at low electron beam voltage indicates that the Ti3+ defects present a higher concentration at the (110) surface, whereas the (100) surface presents a more complex defect structure related to the oxygen vacancies. Competition is observed between the visible and the infrared emission centres during plastic deformation of the samples in agreement with the different diffusion mechanisms of the defects involved in the emissions.
TL;DR: In this article, the cathodoluminescence properties of ZnO films were investigated with respect to deposition temperature (Ts) and air flow rate (f), and the best films had three emissions: near ultra-violet (UV) band gap peak at 382 nm, a blue-green emission at 520 nm and a red emission at 672 nm.