Homogeneity assessment of YBa_2Cu_3O_(7-x) single crystals by cathodoluminescence microscopy

Cathodoluminescence (CL) of YBa_2Cu_3O_(7-x) single crystals has been investigated in the scanning electron microscope, Some regions of the crystals, generally related to steps or other growth features, show enhanced CL Intensity. Spectra show the presence of two emission bands centered at about 2.85 and 2.3-2.4 eV, respectively. In the regions of higher CL intensity, the 2.3 eV band, which has been attributed to defects in the oxygen sublattice, shows a higher relative intensity. (C) 1996 Americans Institute of Physics

Scanning electron acoustic microscopy observations of twins and grain boundaries in III‐V materials

Polycrystalline GaP and InP have been observed by scanning electron acoustic microscopy. While grain boundaries show a weak contrast, twinned regions are clearly revealed. Results suggest that the contrast observed is related to signal generation by a piezoelectric‐coupling mechanis

Luminescence from growth topographic features in GaN : Si films

Cathodoluminescence (CL) in the scanning electron microscope is used to investigate the nature of defects responsible for the luminescence associated with round and hexagonal-like topographic features of GaN:Si films. Round hillocks of the size of a few microns, which sometimes have a nanopipe related central hole, do not influence the luminescence emission of the film. Hillocks with sizes of several tens of microns show a marked CL contrast at the center and at the border. The origin of the observed contrast is attributed to a growth induced inhomogeneous distribution of point defects and impurities. Radiation with the electron beam of the scanning microscope causes a decrease of the CL intensity without spectral changes

Shape-controlled synthesis and cathodoluminescence properties of elongated α-Fe_2O_3 nanostructures

α-Fe_2O_3 (hematite) nanostructures with various morphologies have been grown by thermal oxidation of compacted iron powder at temperatures between 700 and 900 degrees C. Different thermal treatments have been found to induce the growth of single-crystalline nanowires, nanobelts, nanoplates and featherlike structures, free and caped nanopillars, and pyramidal microcrystals or cactuslike microstructures. The experimental conditions leading to the different morphologies have been systematically investigated, as well as the possible growth mechanisms. The obtained nanostructures have been characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy, x-ray diffraction, and cathodoluminescence (CL) spectroscopy in the SEM. The formation of the nanostructures induces changes in the intensity and spectral distribution of the CL emission, as compared with the bulk material. Ligand to metal charge transfer transitions as well as Fe^(3+) ligand field transitions are thought to be involved in the observed luminescence. The evolution of the panchromatic CL intensity in the visible range as a function of temperature shows some anomalies that may be induced by magnetic ordering effects

Cathodoluminescence from beta-Ga_2O_3 nanowires

ß-Ga_2O_3 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 Ga_2O_3 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 Ga_2O_3 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

Effect of laser irradiation on the luminescence of Mg and Si-doped GaN films

Pulsed laser treatments have been performed in GaN samples of both n- and p-type conductivity. The laser induced changes have been monitored by emissive mode and cathodoluminescence (CL) in a scanning electron microscope. Emissive mode observations indicate a moderate laser induced recrystallization. The luminescent emission has been characterized in both types of samples, GaN:Si and GaN:Mg. Whereas the evolution of CL in the Si doped samples could be explained by the occurrence of laser induced annealing, the luminescent behavior of the Mg doped samples upon irradiation seems to be more complex and a strong relation with the compensation or Mg activation is suggested. Several luminescence bands with maxima ranging from 3.3 to 2.7 eV and their dependence on irradiation conditions have been studied

Effect of α-Hgl_2 epitaxial growth on the defect structure of CdTe:Ge substrates

The aα-HgI_2/CdTe:Ce heterostructures have been studied by cathodoluminescence (CL) in the scanning electron microscope. The alpha-HgI2 expitaxial growth was shown to cause an enhancement of the CL intensity in a layer of the substrate extending up to about 500 mu m from the α-Hgl_2 /CdTe:Ge interface. CL spectra of the layer reveal the appearance of a band related to tellurium vacancies as well as the decrease of the emission attributed to defect complexes involving Ge. The data obtained indicate that Ge-impurity gettering and V-Te generation at the interface take place during α-Hgl_2 epitaxial growth

Cathodoluminescence of defects in sintered tin oxide

Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the luminescence mechanisms in tin oxide. Sintered material prepared from high purity powder has been found to show a strong dependence of the CL emission on the thermal treatments applied during sample preparation. SEM images show the presence of nano and microcrystalline grains. The correlation of the grain size and morphology with the optical emission is analyzed by CL microscopy and spectroscopy. The main emission bands appear centered at about 2.58, 2.25, and 1.94 eV depending on the sintering treatment. CL images reveal that the 2.25 and the 2.58 eV bands are associated at specific crystal faces. The evolution of the luminescence bands with mechanical milling shows a complex evolution of the 1.94 and 2.58 eV emissions which is explained by formation and recovery of defects during milling

Growth and luminescence properties of micro- and nanoneedles in sintered CdSe

Sintering CdSe powder under argon flow at temperatures in the range 800-900 degreesC produces the formation of needles on the sample surface. Bundles of parallel needles of a diameter of about 50 nm give rise to a domain-like appearance in the sample. In addition, rods and needles with a wide range of dimensions up to several microns appear distributed in the surface. The influence of ball milling of the starting powder on the formation of the needles is investigated. Cathodoluminescence in the scanning electron microscope has been used to characterize the sintered samples

Study of structure and luminescence of CdSe Nanocrystals obtained by ball milling

The effect of mechanical milling on the structure and luminescent properties of CdSe powder has been investigated by means of cathodoluminescence (CL) in the scanning electron microscope, transmission electron microscopy (TEM) and x-ray diffraction. The starting powders were ball milled for times between 5 and 20h. TEM of the milled samples reveals the presence of nanocrystals with a wide range of sizes including nanocrystals of 10 nm and smaller. The CL spectra of the untreated samples show the characteristic band edge emission centered at 1.8 eV. In the milled samples a band centered at about 2.5 eV is observed which appears to be associated to the presence of nanocrystals. The evolution of defect structure with milling time has been monitored by recording infrared cathodoluminescence spectra. A partial phase transformation from wurtzite to zinc blende structure also has been observed