Paul W. Wang

Structural role of lead in lead silicate glasses derived from XPS spectra

Abstract The X-ray photoelectron spectroscopy (XPS) spectra of lead silicate glasses with different PbO content were measured and analyzed and the structural role of lead in the glass is discussed. It was found that the binding energy of Pb4f 7/2 decreases with the increase of PbO content before the concentration of PbO reaches 40 mol% and is maintained at a low constant when the PbO content is higher than 40 mol%. It was inferred that the polarizability of Pb is concentration-dependent and grows with the increase of PbO content in the glass. This suggests an increase in the covalent degree of PbO bond, which accounts for the formation of the PbO 4 pyramid polymeric chain network. It is proposed that in the low PbO content region (PbO 2 is the main glass former and the three-dimensional network built by SiO 4 tetrahedra is still maintained, with PbO increase in the glass. PbO 4 pyramids tend to assemble together to form another structure network. In the high PbO content region (PbO > 40 mol%), the three-dimensional network built by SiO 4 tetrahedra is seriously destroyed; the PbO 4 pyramid polymeric chains connect together through SiO 4 tetrahedra to form the glass structure network skeleton.

Formation of silver colloids in silver ion-exchanged soda-lime glasses during annealing

The structural and compositional changes of the soda-lime glasses during the formation of the silver colloids were analyzed by the X-ray Photoelectron Spectroscopy (XPS) in order to examine the silver colloid formation mechanism. The in situ behavior of silver and SiO2 networks on the surfaces of silver ion-exchanged soda-lime glasses during heating and cooling processes in ultra-high vaccum was monitored. The results showed that silver diffuses toward the surface, precipitates, and crystallizes during heating and the total silver surface concentration is slowly increased during cooling. The concentration changes of oxidized and neutral Ag, a new non-bridging oxygen species (NBO*), and a new silicon species (Si[a]) were applied to deduce a disappropriation reaction mechanism of Ag+ on the surface during annealing. The SiO2 network is modified at temperatures below 350°C to accommodate more silver on the surface and to balance the extra charge carried by the Ag+. That the SiO2 network polymerizes during annealing was deduced from the results of the higher binding energies of Si2p and O1s after annealing. This observation suggests that the reduction of the Gibbs free energies and the relaxation of tensile stress result in the formation of the silver colloids under thermal annealing.

Aluminum nitride and alumina composite film fabricated by DC plasma processes

Abstract Composite films of aluminum nitride and alumina were fabricated on aluminum 6061 alloys in a DC plasma chamber. Samples were treated by three main processes. These were: (1) Ar plasma etching, (2) NH 3 /Ar plasma with low pressure and low current density, and (3) NH 3 plasma with high pressure and high current density. The oxygen-free Al surface was obtained after 10 min 2.8 keV Ar + sputtering in an ultrahigh vacuum analysis chamber after the sample was treated by processes 1 and 2. Composite films of aluminum nitride and alumina were obtained on samples treated by processes 1, 2 and 3. The surface compositions and bonding environments of the composite films were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. the thicknesses of the films were determined by argon sputtering in the ultra-high vacuum chamber. The surface morphologies of samples after fabrication processing in DC plasma were investigated by scanning electron microscopy. Al with the composite film not only shows a much better corrosion resistance in 1N HCl solution but also exhibits six times higher hardness than that of untreated Al. A possible formation mechanism of the composite film is proposed.

Some effects of 5 eV photons on defects in SiO2

The effects of 5 eV photons on the optical absorption bands and paramagnetic centers produced by a prior γ-ray irradiation of type III and IV silicas have been measured. Silica samples obtained from two commercial sources were irradiated with 137Cs γ-rays to a dose of ∼108 R at an ambient temperature of ∼35°C. The samples were then exposed to 5 eV photons supplied by a pulsed KrF excimer laser. The samples were exposed to pulses from 100 to 11 500 with 150 mJ per pulse per cm−2. Sample temperatures during exposure were <40°C. Optical absorption spectra were measured with a double beam spectrometer in the 1–6 eV range at a temperature of 22°C. Electron paramagnetic resonance (EPR) spectra were measured with a homodyne spectrometer at 9.7 GHz, room temperature and 110 K and at various power levels. After 100 pulses, a band with a peak at 5.5 eV was bleached in the spectra of type III samples. No additional bleaching was observed after 1500 pulses. After 11 500 pulses, a decrease in absorption at 5.8 eV was observed. In the EPR spectra, the E′ center concentration increased by a factor of 1.8 and the concentration of the non-bridging oxygen centers (NBOHCs) did not change after 100 pulses. No additional changes were observed after 1500 pulses. After 11 500 pulses, a decrease of the order of 69% in the E′ center concentration and a decrease of the order of 26% in the NBOHCs was observed. In the spectra of the type IV samples, a band with a peak at ∼4.85 eV was bleached by the first 100 pulses and no additional changes were observed up to 1500 pulses. A band with a peak at ∼5.8 eV decreased with exposure to 11 500 pulses. The E′ center concentration increased by a factor of 1.5 after 100 pulses, did not change after 1500 pulses and decreased by 84% after 11 500 pulses. The peroxy radical molecule ion concentration decreased to below detectability after 800 pulses and a new paramagnetic state grew with increasing number of pulses up to 1500 pulses, after which no additional increase was observed. No oxygen-related center was detected for any exposure in the type III samples. It is concluded that there are at least three bands absorbing at ∼5.8 eV, the E′ center, the E″ center and another band. The 4.8 absorption bleached by 5 eV photons is attributed to the peroxy radical. The absorption at ∼5.5 eV bleached by 5 eV photons is not attributed to any of the paramagnetic states.

Ion beam assisted deposition of diamond-like nanocomposite films in an acetylene atmosphere

Abstract In recent years, doped diamond-like carbon (DLC) coatings have been shown to solve some intrinsic application difficulties of DLC, esp. reducing internal stresses and improving thermal stability. Diamond-like nanocomposite (DLN), by incorporating an amorphous Si-O network into the DLC, is a special class of modified DLC coatings, which have many excellent properties and wide applications. In this paper, a diamond-like nanocomposite film was synthesized by an ion beam assisted deposition method in an acetylene atmosphere. The composition and microstructure of the DLN film were investigated by various spectroscopic analyses, including Fourier transform infrared absorption spectroscopy, Rutherford backscattering spectroscopy. Raman scattering spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible absorption spectroscopy.

XPS investigation of electron beam effects on a trimethylsilane dosed Si(100) surface

A trimethylsilane covered Si(100) surface at temperature −120°C was bombarded by 1.3 keV electrons for various time intervals. The core level Si2p and C1s electrons were studied after each electron bombardment by use of X-ray photoelectron spectroscopy. The spontaneous dissociation of TMSiH on the Si(100) surface was observed judging from the formation of CC bonds. The CC and CSi bonds increased initially and then saturated after ∼ 20 min of electron exposure. The binding energy of C1s in CC and CSi bonds and that of Si2p in SiC bonds showed an opposite behavior under electron irradiation. The former increased and the latter decreased at the beginning of the irradiation and then both increase rate and decrease rate reduced. From the previous results of electron stimulated desorption and temperature programmed desorption, and the variation of electron density distribution around C and Si, it is concluded that the de-hydrogenation in CHn and SiCHm bonds was induced and new SiC and CSi bonds were formed by electron irradiation on TMSiH covered Si(100) surface.

Evaluation of refractive-index and material dispersion in fluoride glasses.

The relationships between the refractive-index and material dispersion of fluoride glasses and their compositions have been studied. A set of parameters was established that can be used to calculate approximately the refractive-index and material dispersion of fluoride glasses. The calculated and measured results agree well.

Thermal stability of silver in ion‐exchanged soda lime glasses

X‐ray photoelectron spectroscopy was used to study the thermal stability of silver in ion‐exchanged sodium calcium silicate glasses during heat treatment in ultrahigh vacuum. The changes in concentration, in line shape, and in binding energy as functions of sample temperature show that silver diffuses toward the surface and the chemical structure of the sample surface changes. Judging from a comparison of the line shapes and the binding energies of the samples to those of pure silver and silica, the concentration variations in bridging and nonbridging oxygens, and the binding energy shifts of nonbridging oxygens, it is concluded that the SiO2 glass network starts breaking up during Ag+ diffusion at sample temperatures below 200 °C, metallic silver clusters form, and nonbridging oxygens originally surrounded by silver atoms reconnect to silicon atoms at sample temperatures above 200 °C. The relaxation of surface stress introduced by the exchange process and the net reduction of Gibbs free energy cause the surface diffusion and segregation of silver and the reconnection between oxygen and silicon. The estimated activation energy of the silver surface diffusion is 0.16 eV.X‐ray photoelectron spectroscopy was used to study the thermal stability of silver in ion‐exchanged sodium calcium silicate glasses during heat treatment in ultrahigh vacuum. The changes in concentration, in line shape, and in binding energy as functions of sample temperature show that silver diffuses toward the surface and the chemical structure of the sample surface changes. Judging from a comparison of the line shapes and the binding energies of the samples to those of pure silver and silica, the concentration variations in bridging and nonbridging oxygens, and the binding energy shifts of nonbridging oxygens, it is concluded that the SiO2 glass network starts breaking up during Ag+ diffusion at sample temperatures below 200 °C, metallic silver clusters form, and nonbridging oxygens originally surrounded by silver atoms reconnect to silicon atoms at sample temperatures above 200 °C. The relaxation of surface stress introduced by the exchange process and the net reduction of Gibbs free energy cause the ...

Surface modification of lead silicate glass under X-ray irradiation

Abstract Radiation-induced changes in the microstructure of lead silicate glass were investigated in-situ under MgKα irradiation in an ultra-high vacuum (UHV) environment by X-ray Photoelectron Spectroscopy (XPS). Lead-oxygen bond breaking to result in pure lead formation was observed. The segregation, growth kinetics and the structure relaxation of lead, plus the corresponding changes of oxygen and silicon on the glass surfaces were all studied by measuring the time-dependent changes in concentration, binding energy, and the full-width at half-maximum. A bimodal distribution of the oxygen XPS signal, caused by bridging and non-bridging oxygens, was found during the relaxation process. All experimental data indicate a reduction of the oxygen, a phase separation of lead from the glass matrix, and the metallization of lead during and after X-ray irradiation.

Optical phenomena observed in low‐energy ion and electron bombardment of silica surfaces

Optical spectroscopy has been used to characterize the interaction of ionizing radiation with glasses, including ions with energies in the 3–10 keV range, and electrons with energies ranging from 320 to 640 eV. Characteristic line emission spectra of desorbed excited atoms, as well as luminescence spectra from the near‐surface bulk, were observed. A search for possible changes in desorption mechanisms as a function of radiation dose was carried out by observing the time dependence of integrated intensity and spectral linewidth for desorbed silicon and the trace element calcium. Defect formation in the near‐surface bulk was monitored by spectrally resolved, time‐dependent measurements of the bulk luminescence and by electron paramagnetic resonance spectroscopy. These spectroscopic observations are correlated with identifiable differences in the manufacturing processes of several silicas, and thus can be related to one particular kind of surface radiation damage, namely, ion‐ and electron‐induced desorption.