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The effects of charge transfer between atoms on an amorphous SiO(sub 2), surface were studied by comparing a model with fixed charge (FQ) and a model that takes into consideration charge transfer by the charge equilibrium (QEq) method. The results suggest that consideration of the charge transfer is essential to reproduce the defect structure of the silica glass surface.

Laser-induced-damage thresholds (LIDT's) with various types of vitreous silica at 1064, 532,355, and 266 nm are investigated. At 1064 nm no difference in the LIDT was observed in any sample. At 1064-355 nm the wavelength dependence of the LIDT of synthetic fused silica (SFS) can be described well by the relation [I.sub.th] = 1.45[[Lambda].sup.0.43], where [I.sub.th] is the LIDT in J/[cm.sup.2] and [Lambda] is the wavelength in nanometers. At 266 nm, however, LIDT's were smaller than half of the calculated value from the relation above. This difference can be explained by the damage mechanism; at 266 nm two-photon absorption-induced defects lower the LIDT as in the case of KrF-excimer-laser-induced defects, whereas at longer wavelengths the two-photon process does not occur. LIDT's of fused quartz (FQ) at 532 and 355 nm and that of SFS containing [approximately]1000 ppm of Cl and no OH at 355 nm were a little lower than those of the other SFS's. This lower LIDT may be related to the absorption of metallic impurities in FQ and dissolved [Cl.sub.2] molecules in SFS. At 266 nm, on the other hand, LIDT's of FQ's were higher than those of most SFS's.

Synthesis of different types of fused silica through vapor-phase axial deposition-soot remelting indicated silica glass deformation from ideal glass networks, while Si-OH and Si-Cl terminal groups decrease highly strained bond amount in the network. Bond breakage was found to be a primary catalyst of laser induced defects for soot-remelted silica with minimal OH and no Cl.

The properties of gamma-ray-induced absorption spectra in oxygen deficient vitreous silica were studied. The spectra were well fitted with five Gaussian absorption bands, the same bands as those found in x-ray- and excimer-laser-induced absorption spectra. Absorption intensity in oxygen deficient silica was much greater than those in silicas with Si-OH or Si-Cl units. The mechanisms for producing radiation-caused defects and the function of terminal structures such as Si-OH and Si-Cl on resisting defect formation were studied.

The linear thermal expansion coefficients of fused quartz with three parts per million of OH generated by electrical melting of natural quartz powder were determined via measurements utilizing an interferometric dilatometer at 300-970 K. The results revealed maxima and minima related to the phase transitions in crystalline silica. The sharp maxima at 500 K was found to be related to the alpha to beta transition temperature of cristobalite. The low- to high-temperature phase transitions of crystalline quartz and tridynamite corresponded to the minima at 850 and 580 K, respectively.

Characteristics of x-ray-induced absorption spectra in various types of synthetic fused silica (SFS) containing 0.1–77×1018 cm-3 of OH were studied up to an irradiation time of 6 h. Induced absorption in the SFS spectra of irradiation with x ray from a Rh target with a dosage of 2×104 C kg-1 h-1 was reproduced by six Gaussian absorption bands, at 3.8, 4.8, 5.0, 5.4, 5.8, and 6.5 eV, respectively. Intensities of these absorption bands increased with power of irradiation time. The intensities of the 5.8, 5.4, and 5.0 eV bands decreased with increasing OH content at an irradiation time shorter than 2 h. At an irradiation time longer than 2 h, on the other hand, the intensities of each absorption band had a minimum at an OH content of ≈5×1018 cm-3, and increased with increasing OH content at higher OH content. The power of the time dependence had a minimum at an OH content of ≈5×1017 cm-3, and increased with increasing OH content for higher OH-containing samples. [ABSTRACT FROM AUTHOR]

Effects of heat treatment on absorption bands in fused quartz produced by melting natural quartz powder containing 2×10[sup 17] cm[sup -3] (sample I) and 1.3×10[sup 19] cm[sup -3] of OH (sample II) were studied. Both samples have an absorption peak at approx. 5.2 eV. Fluorescent spectra and the results of Gaussian peak decomposition suggest that this absorption is associated with the B[sub 2]β band with a peak at 5.15 eV and full width at half maximum of 0.42 eV. The 5.15 eV band and an absorption component at 7.5 eV in sample II were annealed out at 1423 K, whereas almost no change was observed in the absorption spectra of sample I. The decrement of the 5.15 and 7.5 eV bands was proportional to the decrement of the OH content. The annealing mechanism in sample II can be explained using a previously proposed model for OH-containing fused quartz wherein the B[sub 2]β band is the twofold-oxygen-coordinated silicon (=Si:) coordinated with two ≡Si-OH structures. Sample I must have a =Si: structure, but it may not be annealed out because it does not have sufficient OH to form the twofold-coordinated ≡Si-OH on =Si:. The origin of the other absorption bands was also discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the characteristics of γ-ray induced absorption spectra in oxygen deficient vitreous silica. Defect formation in oxygen deficient silica and in hydroxyl free silicas containing chlorine; Role of hydroxide and chlorine on defect formation.