M. V. Zamoryanskaya

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.

Cathodoluminescence properties of yttrium aluminum garnet doped with Eu2+ and Eu3+ ions

Yttrium aluminium garnet (YAG) doped with Eu2+ and Eu3+ ions is very interesting as a phosphor for conversion of light-emitting diode light for white light sources. The europium ion occupies the structural position of yttrium in yttrium aluminium garnet and has valence state Eu3+. Our sample was doped with Zr4+, which is why some of the europium ions had valence state Eu2+. As a rule, luminescence of Eu3+ ions is observed in the orange and red range of spectrum. The luminescence of Eu2+ in yttrium aluminum garnet is characterized by an intensive broad band with maximum of intensity at about 560 nm (green color). In this work, we studied the intensity and decay time dependences on europium concentration, and the influence of excitation power density on the cathodoluminescence of the sample. The most interesting result is the change of visible cathodoluminescence color in dependence on the density of the exciting power.

Synthesis and Study of 239Pu-Doped Gadolinium-Aluminum Garnet

Garnet solid solutions, Y 3 A1 5 O 12 -Gd 3 A1 5 O 12 -Gd 3 Ga 5 O 12 (YAG-GAG-GGG), are being considered as prospective durable host phases for the immobilization of actinide-containing waste with complex chemical compositions. Garnet samples with the suggested simplified formula: (Gd,Ce…) 3 (Al,Ga,Pu,…) 5 O 12 containing from 3.4 to 5.3 wt.% 239 Pu and 3.6-5.5 wt.% Ce have been synthesized through melting of oxide starting materials in air using a hydrogen torch. Calcium and Sn were added to increase the Pu incorporation into the garnet lattice through ion charge and size compensation for Pu 4+ . Polycrystalline materials obtained in the experiments consist of garnet, perovskite and other phases and were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). Our results confirmed that the use of compensating elements such as Ca and Sn allow for significant incorporation of Pu and Ce (not less than a few wt.%) into the garnet structure. The preliminary conclusions thus so far indicate that garnet solid solution compositions may incorporate simultaneously trivalent and tetravalent actinides in significant quantities because they occupy different positions in the garnet structure

Modification of Silicon Oxide by High Energy Electron Beam

During interaction between thin film SiO2 and electron beam with high power density, amorphous silicon dioxide modifies. Silicon nanoclusters are formed in radiated area. Result of this interaction is formation of Si/SiO2 nanocomposite. We studied modified SiO2 by TEM, microdiffraction and cathodoluminescence.

Cathodoluminescence study of silicon oxide-silicon interface

In this paper, the local cathodoluminescence method was used to study the characteristics of the SiO2-Si interface, the change of its properties during oxidation, and the influence of the type of silicon conductivity on its properties. This research shows that the first phase of silicon oxidation is the formation of amorphous silicon layers on the silicon surface and the appearance of silicon clusters in the natural silicon oxide. Cathodoluminescence gives the possibility of finding the presence of point defects in silicon oxide and silicon and of studying the distribution of such defects on the surface and in the depth.

Quartz microtubes based on macroporous silicon

The conditions under which quartz microtubes 5–10 µm in diameter are formed in the course of structuring oxidized macroporous silicon are reported. It is shown that microtubes with a closed bottom can be fixed in a vertical position at equal distances from one another in correspondence with the “lattice” of macroporous silicon and may be of interest as test tubes for a single-chip microlaboratory. In a disordered state, long, thin quartz microtubes form a “glass wool.” It is found that the microtubes and the glass wool exhibit high-intensity photo-and cathodoluminescence with the highest intensity in the green spectral range.

The use of cathodoluminescence for the development of durable self-glowing crystals based on solid solutions YPO4-EuPO4

Local cathodoluminescence spectroscopy has been suggested for the development of durable self-glowing crystals based on crystalline solid solutions (Y, Eu)PO4. Nonradioactive ions of Eu3+ in these crystals cause strong luminescence in the visible range, initiated by small admixture (less than 1 wt %) of α-radioactive 238Pu. The intensity of self-glowing depends on the Y: Eu ratio and the 238Pu content. The optimal Y: Eu ratio responsible for the most intensive luminescence has been identified. The principal features of cathodoluminescence emission in (Y, Eu)PO4 crystals of various chemical compositions are being discussed.

The Employment of Cathodoluminescent Method for Characterization of Silicon Oxide - Silicon Interface

In this work we studied the cathodoluminescence (CL) of thin silicon oxide and natural silicon oxide grown on different types of silicon substrates (p-silicon and n-silicon with different content of boron and phosphor). At the same time we studied the distribution of intrinsic defects on depth for thermal silicon oxide films with depth resolution 10-20 nm. The method of local cathodoluminescence was used for definition the structure defects in SiO2 think layer and control of the quality of SiO2-Si interface.

Fabrication and Optical Properties of Photonic Crystals Based on Opal-GaP and Opal-GaPN Composites

Nanocrystalline GaP and amorphous GaPN solid solution have been synthesized in voids of artificial opal. The opal-GaP and opal-GaPN composites obtained clearly demonstrate properties of photonic crystals. The reflection spectra of the opal-GaPN composite exhibit specific features related to multiple Bragg diffraction on two systems of {111} planes, parallel and nonparallel to the surface of the photonic crystal. The study of photoluminescence spectra revealed a considerable modification of the emission band of the opal-GaPN composite, which was attributed to the influence of the photonic band gap.

Optical and electrical properties of 4H-SiC irradiated with Xe ions

Structures with aluminum-ion-implanted p+-n junctions formed in 26-μm-thick chemicalvapor-deposited-epitaxial 4H-SiC layers with an uncompensated donor concentration Nd−Na = (1–3) × 1015 cm−3 are irradiated with 167-MeV Xe ions at fluences of 4 × 109 to 1 × 1011 cm−2 and temperatures of 25 and 500°C. Then as-grown and irradiated structures are thermally annealed at a temperature of 500°C for 30 min. The as-grown, irradiated, and annealed samples are analyzed by means of cathodoluminescence, including the cross-sectional local cathodoluminescence technique, and electrical methods. According to the experimental data, radiation defects penetrate to a depth in excess of several tens of times the range of Xe ions. Irradiation of the structures at 500°C is accompanied by “dynamic annealing” of some low-temperature radiation defects, which increases the radiation resource of 4H-SiC devices operating at elevated temperatures.