Silicon Nanocluster in Silicon Dioxide: Cathodoluminescence, Energy Dispersive X-Ray Analysis and Infrared Spectroscopy Studies

Abstract

This chapter is extended to various electronical and optical modifications of amorphous silica (a-SiO 2) layers as they are applied in microelectronics, optoelectronics, as well as in the forthcoming photonics. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR) and cathodoluminescence (CL) have been used to investigate thermally grown pure amorphous silicon dioxide and ion-implanted layers with thickness d ox =100-500 nm. The main luminescent centers in silicon dioxide layers are the red luminescence (650 nm; 1.85 eV) of the non-bridging oxygen hole center (NBOHC; ≡Si-O•), a blue (460 nm; 2.7 eV) and a ultra violet luminescence (290 nm; 4.3 eV) of the oxygen deficient centers (ODC's; ≡Si•••Si≡), and a yellow luminescence (570 nm; 2.2 eV) appears especially in hydrogen treated silica indicating water molecules, and on the other hand, in silicon excess samples indicating higher silicon aggregates. A quite different CL dose behavior of the red luminescence is observed in dry and hydrogen-treated samples due to dissociation and re-association of mobile hydrogen and oxygen to radicals of the silica network. Additionally implanted hydrogen diminishes the red luminescence in wet oxide but maintains the blue and the UV bands. Thus hydrogen passivates the NBOHC and keeps the ODC's in active emission states. A model of luminescence center transformation is proposed based on radiolytic dissociation and re-association of mobile oxygen and hydrogen at the centers as well as formation of interstitial H 2 , O 2 , and H 2 O molecules. Non-stoichiometric SiO x layers produced by direct ion implantation or reactive sputtering are used to investigate whether the different luminescent centers are related to oxygen or to silicon. Oxygen implantation as well as direct silicon implantation led to an oxygen surplus as well as an oxygen deficit, respectively. The related luminescence damages provide direct evidence to the nature of the defects. Oxygen-deficient thin silica layers SiO x with different stoichiometric degree 1≤x≤2, were prepared by thermal evaporation of silicon monoxide in vacuum and in ambient oxygen atmosphere of varying pressure onto crystalline silicon substrates. The chemical composition has been calibrated and determined by FTIR spectroscopy. The CL spectra of the oxygen-deficient layers shows the development of typical silica luminescence bands at the composition threshold x≤1.5 onwards to x=2. The

A multi-spectroscopic study for the characterization and definition of production techniques of German ceramic sherds

“…LIF spectroscopy is used in this research to explore the potentiality of this technique to investigate ceramic materials exploiting the mineral luminescence and carrying on fast analyses in a non-destructive and non-invasive way. Luminescence in minerals and glaze ceramic depends on activator elements, such as impurity ions and lattice defects, on composition and structure of the glass [20,51]. It has to be considered that interpretation of LIF spectra can be difficult due to the characteristic fluorescence broad bands and the lack of studies regarding its application on archaeological and historical ceramic and glass materials.…”

“…6(a)) show bands in UV, blue and green regions may be due to Pb ++ doped silicas [15]. In the UV region the fluorescence may be also due to Al 3+ , Li + , K + and Na + doped SiO 2 [20]. LIF band at~450 nm can be attributed to cobalt blue pigments, which shows a characteristic fluorescence signal at 442 nm [52].…”

“…This technique offers the advantages to be sensitive and non-destructive spectroscopic technique, remote, portable, and has been used as a diagnostic tool for artworks with successful results [16][17][18]. The fluorescence in minerals is sensitive to activator elements, impurity ions, defects, as well as chemical composition and crystal lattice [19,20]. LIF analyses can be useful to detect trace elements in minerals [21,22] and in the present study was applied to obtain indication of both ceramic glaze and matrix composition.…”

Nucleation-controlled vacancy formation in light-emitting wide-band-gap oxide nanocrystals in glass

“…4a and b) and lifetime value (few ns) allow us to preliminary identify the kind of point defects potentially responsible for the fast violet component among the possible defect configurations compatible with a silica-based and germanosilicate glass matrix. 31 In Ge-containing silica-based glass, light emission in the violet spectral region is mainly expected from oxygen deficient defects consisting in twofold coordinated O-Ge-O sites. [31][32][33] However, in such defects, the emission is ascribed to triplet-to-singlet transitions with a decay time of 0.1 ms, 32 incompatible with the observed fast decay in the ns domain.…”

“…31 In Ge-containing silica-based glass, light emission in the violet spectral region is mainly expected from oxygen deficient defects consisting in twofold coordinated O-Ge-O sites. [31][32][33] However, in such defects, the emission is ascribed to triplet-to-singlet transitions with a decay time of 0.1 ms, 32 incompatible with the observed fast decay in the ns domain. Instead, violet luminescence with few ns of lifetime is typical of alkali-germanates and alkali-silicates, 34,35 arising from non-bridging groups 3ORT-O-M with T = Si, Ge and M = Li, Na.…”