SiO2 Single Crystals Research Articles

α–β Phase Transition in the Impurity Phase of a SiO2 Single Crystal

α–β Phase Transition in the Impurity Phase of a SiO2 Single Crystal

Adsorption of alcohols on a two-dimensional SiO2 single crystal – Alcohol adsorption on silicatene

The adsorption kinetics of alcohols (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol) was studied on monoatomic, two-dimensional SiO2 single crystals (silicatene) using thermal desorption spectroscopy (TDS). Silicatene was grown on Mo(112) at ultra-high vacuum. In contrast to Mo, the alcohols physisorb molecularly on the hydrophobic SiO2/Mo surface. Zero coverage binding energies vary from 46.5 to 65.5kJ/mol and increase with molecular size. Silicatene was characterized by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and water TDS.

UV-Blue Emitting SiO2 Sintered Glass for Radiation Dosimetry

Phosphor materials are often used in radiation measurement as a converter, from ionizing radiation to light. In dosimetry, a phosphor material absorbs and accumulates the incident radiation energy over a certain period of time as electronic charges trapped at localized centres. A recombination of these charges can be stimulated externally by light exposure or heat, followed by light emission. The latter emission intensity is proportional to the incident radiation dose accumulated, hence the radiation dose can be indirectly measured. Today, such phosphor materials are used in a variety of scenes, for example, personnel dose monitoring, radiation therapy, and medical imaging. In this study, we have synthesized bulk SiO2 glasses and characterized for dosimetry applications. The samples were prepared by spark plasma sintering (SPS), which is a unique way to obtain a bulk SiO2 glass. First, radioluminescence (RL) spectrum was measured for both the prepared sample and SiO2 single crystal. The glass sample showed a broad emission feature from 300 to 500 nm while the crystal sample showed a narrower emission around 450 nm. The RL measurement at low temperatures revealed that the broad emission by glass consists of two components with the peaks at 385 nm and 511 nm. The origin of the former emission seems to be a pair of silylene centres generated by sintering process while the latter is due to a presence of dioxasilirane and sililene. Moreover, it was found that the sample shows a strong thermally-stimulated luminescence (TSL) after X-ray irradiation. The glow curve indicates strong emissions at the temperatures of approximately 140 °C and higher than 300 °C. In contrast, SiO2 single crystal shows much weaker signal at lower temperature (~90 °C). The luminescent centres responsible for TSL are the silylene-silylene pair emitting at 385 nm. With a use of TSL in our SiO2 glass sample, a detectable X-ray dose range is at least 1 - 10000 mGy, which is a comparable sensitivity to commercial dosimeter.

Structural and optical characterization of SiO2 under irradiation with swift heavy ions

SiO2 single crystals irradiated with 600keV, 4 and 5MeV Kr ions using the 320kV High Voltage Experimental Platform (IMP, Lanzhou) were investigated with infrared, fluorescence spectroscopes and TEM. In the low-energy regime, single ion tracks are well separated and the damage process is dominated by the formation of simple color centers such as F+ and F2 centers. For the high energy ions, the energy density in ion tracks produced at a high stopping power is larger, and consequently the defect concentration increases significantly. At higher defect densities, the distance between single defects is smaller facilitating the aggregation of individual electron center to defect cluster and defect annihilation by recombination of hole and electron centers. The latter process determines the limited efficiency of color-center creation under heavy-ion irradiation. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes.

Color center creation in SiO2 under irradiation with swift heavy ions: Dependence on energy loss and fluence

SiO2 single crystals irradiated with 600keV, 2MeV, 4MeV and 95MeV Ar ions using 320kV high voltage Experimental platform (IMP, Lanzhou) and the HIRFL-SFC (Heavy Ion Research Facility in Lanzhou) facility in Lanzhou were investigated by Infrared spectra and fluorescence spectroscopes. PL spectra peaks of silicon dioxide irradiated with 600keV, 2MeV, 4MeV and 95MeV Ar ions were located at 445nm (F2 color center), 570nm (F4 color center) and 650nm (F2+ and F3+ color centers) emission band etc. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses derived from the reciprocity approach, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes.

Raman scattering analysis of silicon dioxide single crystal treated by direct current plasma discharge

Low-k materials such as silicon dioxide (SiO2) play an important role in the semiconductor industry. Plasma has become indispensable for advanced materials processing. In this work a treatment of SiO2 single crystal by direct current plasma discharge is studied in detail. Offline metrology is conducted for silicon dioxide wafers by Raman scattering, energy-dispersive x-ray spectroscopy, and ellipsometry. Broad Raman peak at around 2800 cm−1 is observed for the treated SiO2 wafers. Effects of plasma treatment on position of this peak are reported in the paper. An analysis of this correlation could be a framework for creating virtual etch rate sensors, which might be of importance in managing plasma etching processes.

Study of angular width of an X-ray beam fully pumped from quartz single crystal in the presence of temperature gradient

We investigate the cross section of transmitted X-ray beam diffracted by reflecting atomic planes (10–11) of a SiO2 single crystal in Laue geometry for different values of temperature gradient applied to the crystal. It is shown that the angular width of a fully pumped X-ray beam depends on the distance between the source and the studied sample and decreases with the increase in this distance.

Anisotropy of dielectric losses in Al2O3 and SiO2 single crystals

The procedure and results of measurements of the dielectric loss tangent using the dielectric resonator technique on azimuthal modes of the HE (quasi-E) and EH (quasi-H) types are considered. The measurements were performed for uniaxial anisotropic single crystals of Al2O3 (at a frequency of 11 GHz) and SiO2 (at 39 GHz) in a temperature range of 80–373 K and for an isotropic single crystal of Y3Al5O2 (YAG) at room temperature in a frequency range of 9–15 GHz. The proposed method revealed the anisotropy of dielectric losses in Al2O3 and SiO2 single crystals in the temperature range studied. According to this, losses along the optical axis of these crystals are lower than in the transverse plane. In the YAG crystal, the Q values for modes of the two types with the same frequency are close, which corresponds to isotropic losses. The dielectric losses in YAG increase in proportion to the frequency.

A multi-exciton model for the electronic sputtering of oxides

Three models are examined for the electronic sputtering by high energy heavy ions. It is found that the charged fraction of the sputtered particles is small (less than 10% in this study) and hence, Coulomb explosion model is unsound. According to the thermal spike model, rapid thermal quenching of the melted zone is anticipated, implying amorphisation of SiO2 single crystal (c-SiO2). X-ray diffraction results indicate no amorphisation of c-SiO2, suggesting no melting. Moreover, the electronic sputtering yields of both c-SiO2 and amorphous-SiO2 (a-SiO2) have been found to be the same. With these results and thermal properties of both c-SiO2 and a-SiO2, thermal spike model is examined further and appears to be unfavorable. A multi-exciton model is suggested for the electronic sputtering.

Si X-Ray Absorption Near Edge Structure(XANES) in X-Ray Fluorescence Spectra

Abstract Silicon K X-ray fluorescence spectra of Si and SiO2 single crystals are measured using a wave dispersive X-ray fluorescence spectrometer. It is demonstrated that the fine structures in the line shape of the low energy tail of the Kα characteristic X-ray fluorescence spectra resemble those of the K X-ray absorption near edge structure(XANES).

Crystal structure of lead(II) dipivaloylmethanate

The volatile complex of lead(II) with 2,2,6,6-tetramethylheptane-3,5-dione is investigated by X-ray diffractometry. Crystal data: a = 10.901(2), b = 21489(4), c = 10.203(2) a, space group Pccn (N 56), V = 2503.4(8) a3, M = 573.74, Z = 4, dcalc = 2.522 g/cm3. The crystal structure is of molecular type; the molecule of the complex has a nonplanar structure. The lead atom is coordinated by four oxygen atoms of the two bidentate ligands. Films of the complex on substrates of Si and SiO2 single crystals, melted quartz, and glass were obtained by thermal evaporation in vacuum. X-Ray diffraction analysis of the polycrystals and films of the complex showed that the films are distinctly textured along the b axis.

Adhesion of Thin Metal Films to Vacuum-Cleaved SiO2, Al2O3, and MgO Substrates

ABSTRACTThe adhesion of Au, Ag, Pb, Sn, In, Cu, Cd, Mg, Ca films to vacuum-cleaved Al2O3, MgO and SiO2 single crystals has been studied. It is shownf -4hat for botn Al2O3 and MgO the level of adhesion is slightly higher than that for SiO2 and tends to increase with chemical activity of deposited metals. As a result, the adhesion varies from the level of van der Waals forces to the level of chemical interaction.

Unidirectional Solidification of Bi<sub>2</sub>O<sub>3</sub>(Nb<sub>2</sub>O<sub>5</sub>)-6Bi<sub>2</sub>O<sub>3</sub>⋅SiO<sub>2</sub> Eutectic by Double Crucible Method

An eutectic melt in the system (Bi2O3)0.85(Nb2O5)0.15-6Bi2O3⋅SiO2(Ref. 1) was unidirectionally solidified in double crucibles, in which a pin hall was made at the center of the bottom of the upper one and a seed crystal was placed at the center of the bottom of the lower one (Fig. 1). A temperature gradient of 100°C/cm and a solidification rate of 0.5mm/h were maintained during the solidification in a temperature gradient furnace having SiC heating elements at the top and a water-cooled copper jacket at the bottom. The obtained ingot showed a uniform structure throughout the ingot, in which fibrous crystals of δ-(Bi2O3)0.85(Nb2O5)0.15 3.8μm in diameter were embedded in parallel in a matrix of γ-6 Bi2O3⋅SiO2 single crystal (Figs. 2 and 3). This structure was in contrast to that obtained with a single crucible (Ref. 1), in which orientation of the fibrous crystals varied depending on the location (Fig. 2b). A transverse thin section of the ingot obtained with the double crucibles showed a high optical transmission like an optical fiber array (Fig. 5). Then, this may be useful for applications such as screen of a cathode ray tube of high resolution.