排序方式: 共有94条查询结果,搜索用时 31 毫秒
21.
E. Pelucchi S. Watanabe K. Leifer B. Dwir E. Kapon 《Physica E: Low-dimensional Systems and Nanostructures》2004,23(3-4):476
We report on the growth and optical properties of various configurations of sub-micron pitch dense arrays of pyramidal quantum dots (QDs) grown by organometallic chemical vapour deposition on patterned substrates. We show that the effective growth rate of these QDs is influenced by the ratio between the free {1 1 1}B area and {1 1 1}A exposed facets surrounding them. This provides a powerful technique for engineering the energy level structure of ordered QD arrays by means of geometrical patterning of the growth template. Such technique should be particularly useful for applications in photonic crystals incorporating QDs with tailored absorption and/or emission properties. 相似文献
22.
The main luminescent centers in SiO2 films are the red luminescence R (1.85 eV) of the nonbridging oxygen hole center (NBOHC) and the oxygen deficient center (ODC) with a blue B (2.7 eV) and a UV band (4.4 eV). By means of a new “track-stop” technique we have investigated especially the initial luminescence behavior at the beginning of irradiation. Thus the blue-emitting center is produced under irradiation, but from existing precursors. Contrary to that, the dose behavior of the red (R) luminescence in wet and dry oxide is quite different, decreasing in wet oxide from a high initial level and increasing in dry oxide from almost zero. We propose a model of luminescence center transformation based on radiolytic dissociation and the reactions of mobile oxygen and hydrogen. 相似文献
23.
Raffaella Ruffini Alessandro Borghi Roberto Cossio Filippo Olmi Gloria Vaggelli 《Mikrochimica acta》2002,139(1-4):151-158
Quartz is a common phenocryst in acidic volcanic rocks but rarely contributes to the understanding of the magmatic or eruptive
processes due to its apparent chemical homogeneity. Cathodoluminescence studies indicate that volcanic quartz is strongly
zoned with respect to the trace elements. The determination of this zoning can help to elucidate the crystallisation history
of the magmatic rock. Polished thin sections from rhyolitic and dacitic volcanic rocks were examined by cathodoluminescence
mounted on an optical microscope and analysed by electron probe microanalysis. X-ray mapping of the trace elements incorporated
in the zoned quartz was also performed. The interpretation of the data obtained from these different analytical methods provides
useful information on the chemical zoning of single crystals and therefore on the chemico-physical conditions of the melt
from which the quartz crystallised. Quartz from dacitic rock shows a complex cathodoluminescence oscillatory zoning, consisting
of large red-brown and blue bands concentric to a resorbed core. Quartz from rhyolite shows simpler cathodoluminescence zoning,
consisting of dark to bright blue luminescent bands. The EMPA analyses and the X-ray maps combined with the cathodoluminescence
images suggest a clear correlation between the concentrations of some trace element (mainly Al and Ti, acting as activators
of luminescence) and the cathodoluminescence colours pattern zoning. The incorporation of these trace elements during the
growth of the crystals is linked to small variations in the thermo-chemical properties of the magma such as temperature and
chemical composition. 相似文献
24.
Electrochemical/chemical synthesis of highly-oriented single-crystal ZnO nanotube arrays on transparent conductive substrates 总被引:1,自引:0,他引:1
Guangwei She Xiaohong Zhang Wensheng Shi Xia Fan Jack C. Chang 《Electrochemistry communications》2007,9(12):2784-2788
Arrays of ZnO nanotube (ZNT) were prepared by a two-step electrochemical/chemical process on a transparent, conductive substrate from an aqueous solution at 85 °C. The as-grown ZNTs are single crystals with wurtzite structure and have good crystalline state. The tubular morphology was formed by the proton generated from anodic splitting of water and defect-selective etching of the electrodeposited ZnO nanorod (ZNR) along the c-axis. The photoluminescence and cathodoluminescence spectra of the ZNT arrays show two emission bands located in the ultraviolet (UV) and visible region, respectively. It was found that the PL intensity in the UV band as well as the ratio of Iuv/Ivisible increased with increasing of the excitation intensity. 相似文献
25.
Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC
Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors. 相似文献
26.
Natural fibrous crystals of bavenite (Ca4Be2Al2Si9O26(OH)2) collected in intra-granitic pegmatite bodies of Bustarviejo (Madrid, Spain) have been examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron microprobe (EMPA) and inductively coupled plasma-mass spectrometry (ICP-MS). The strong luminescence emissions of bavenite using thermoluminescence (TL), cathodoluminescence (CL) and its thermal stability have been recorded, looking for new physical properties and new phosphor or dosimetric uses. The bavenite luminescence takes place in the 5d electron shell that interacts strongly with the crystal field; the spectra bands assignment are Gd3+ (319 nm), Sm3+ (562 and 594 nm), Dy3+ (572 nm) and Tb3+ (495 nm). A Mn2+ band at about 578 nm in Ca2+ sites is present as a broad band that overlaps with the Dy3+, Sm3+ and Tb3+ bands. Mn2+ is a transition metal ion that has an electron configuration of 3d5 and interacts strongly with the crystal field (d → d) transition. Stability tests at different temperatures show clearly that the TL glow curves at 400 nm in both irradiated and non-irradiated bavenite samples track the typical pattern of a system produced by a continuous trap distribution. The ICP-MS analyses show concentrations of Yb = 29.7 ppm, Dy = 22.7 ppm, Sm = 9.45 ppm, Nd = 8.95 ppm and Gd = 8.15 ppm in the bavenite lattice. 相似文献
27.
Cathodoluminescence (CL) spectra for the Si nanocrystallites embedded in a matrix of silicon oxide films are measured at room temperature. The CL spectra consist of two principal bands whose peak energies are in a near-infrared (NIR) region (<1.6 eV) and in a blue region (2.6 eV), respectively. The spectral feature of the NIR CL band is similar to the corresponding PL spectra. The strong correlation between the presence of Si nanocrystallites and the formation of the NIR CL band are found as well as the PL spectrum. The peak energy of the blue CL band is slightly lower than that of the luminescence band originating from oxygen vacancies (≡Si–Si≡) in SiO2. Therefore, the blue CL band is considered to come from Sin clusters with n3 in the oxide matrix. Under irradiation of electron beams, degradation of the intensity is observed for both the CL bands but the decay characteristics are different. 相似文献
28.
Hyung-Wook Choi Beom-Joo Hong Seung-Kyu Lee Kyung-Hwan Kim Yong-Seo Park 《Journal of luminescence》2007,126(2):359-364
The zincgallate (ZnGa2O4) phosphor thin film was grown using RF magnetron sputtering system at various process parameters. A ZnGa2O4 phosphor thin film was deposited on Si(1 0 0) substrate and annealed by a rapid thermal processor (RTP). The X-ray diffractometer (XRD) patterns indicate that the Mn-doped ZnGa2O4 phosphor thin film shows a (3 1 1) main peak and a spinel phase. A ZnGa2O4 phosphor thin film has better crystallization due to increased substrate, annealing temperature and deposition time. Also the ZnGa2O4:Mn phosphor thin film shows green emission (510 nm, 4T1→6A1), and the ZnGa2O4:Cr phosphor thin film shows red emission (705 nm, 4A2→4T2). 相似文献
29.
Sturm R 《Micron (Oxford, England : 1993)》2004,35(8):681-684
In the past, investigations of mineral growth were routinely carried out by the application of light-microscopic methods and, later on, by the production of single crystal sections and their documentation using specific imaging techniques (CL, BSEI, etc.). In the present work, a method is described which enables the precise sectioning of elongate crystals parallel and perpendicular to their longest axis. By examining backscattered electron images of parallel and perpendicular sections of the same grain, growth of all faces may be evaluated without major geometric correction. The new technique is applied to zircon crystals of a granitoid exposed in the southwestern Bohemian Batholith, Austria. For the studied zircon population, pyramidal and prism development during crystal growth is worked out very clearly by the imaging procedure. Besides its significance in crystal studies, the introduced method could also find a use in material science for the growth study of synthetic mineral phases. 相似文献
30.
Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6 kV, 3-5 μA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (<10 ns) and a slow one in the range of 200 μs. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6 eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom)0-[AlO4]+ that is formed after the trapping of an electron and a hole by Li+ (or Na+) and AlO4. 相似文献