Metallic glass nanofilms

In this paper, we report for the first time the spontaneous formation of Zr-based metallic glass nanofilms by developed dynamic forced-shear-rupture technique of hat-shaped specimens. The obtained nanofilms have about 100 nm thickness and other two geometrical dimensions can reach micrometer scales. Their glassy nature and structural stability were solidly identified. It was found that electrons with the wavelength of less than 0.165 Å could make the metallic glass nanofilms transparent. Furthermore, it is clearly shown that shear-banding instability still afflicts such 100-nm-thick metallic glass nanofilms.     

Diffusion of the S isotope in soda-lime-silica and sodium trisilicate glass melts

The diffusivity of sulphur in nominal 10 Na₂O-16 CaO-74 SiO₂ (NCS) and 26 Na₂O-74 SiO₂ (NS3) melts was investigated in the temperature range 1273-1473 K using the ³⁵S radioactive isotope in a sandwich setup. Samples were sealed in platinum capsules and run with vertical alignment at 100 MPa confining pressure in an internally heated gas pressure vessel. Using the lowest diffusion coefficient D (m² s^− 1) for each temperature the Arrhenian relations logD = −(4.6 ± 0.3) − (216 ± 7) kJ mol^− 1/RT for NCS and logD = −(6.3 ± 0.6) − (167 ± 17) kJ mol^− 1/RT for NS3 were determined. Viscosity of the melts was used to test the applicability of the Stokes-Einstein (SE) and the Eyring (EY) equations to sulphur diffusion. The SE equation yields unrealistically low radii of the diffusing particles, a consequent of the non-molecular structure of the silicate melts. On the other hand, the Eyring relation yields reasonable jump distances of 550 pm (NCS) and 750 pm (NS3) by fitting the diffusion data to the EY equation. These large values imply that sulphate ions (ionic diameter = 290 pm) migrate as large entities through the silicate network.     

The optical properties of a soda-lime-silica glass in the region from 0.006 to 22 eV

From the measured absorption and reflection spectra, we have determined the optical properties of a well-characterized (with respect to impurities and homogeneity) high-purity 21.3 wt% Na₂O?5.2 wt% CaO?73.5 wt% SiO₂ glass over the energy range 0.006–22 eV. The origins of the absorption spectra are discussed.     

A study of mechanical homogeneity in as-cast bulk metallic glass by nanoindentation

A surface softening effect induced during copper-mould suction casting of bulk metallic glass is investigated as a function of rod diameter and glass fragility index, m, by nanoindentation. A reduction in hardness and reduced modulus at the rod surface is found to be favoured in small diameter castings and in fragile systems, respectively resulting from limited in-situ annealing and from a greater diversity of metastable atomic environments in the potential energy landscape of fragile glasses. Enhanced propensity for shear transformation zone nucleation in the low moduli surface is explained in terms of reduced atomic connectivity arising from a reduction in local co-ordination number and a lowering of the shear modulus. Finally, the structure and mechanical diversity that is possible in as-cast bulk metallic glass rods is explored through a relative quantification of shear modulus and plastic zone size across the whole as-cast state and in a single rod. These findings illustrate the sensitivity of bulk metallic glass to preparation, especially in respect of thermal history, potentially making replication of mechanical data between researchers problematic.     

Precise XPS depth profile of soda-lime-silica glass using C60 ion beam

Ar ion sputtering is one of the most accepted techniques for depth profiling in practical X-ray photoelectron spectroscopy (XPS) analysis, while this technique is known to be inadequate for quantitative analysis of glass including mobile ions such as soda-lime-silica glass. For the precise depth profiling on XPS depth analysis, three methods, (i) coating of conductive thin film on glass surface, (ii) sample cooling at the temperature of −130 °C and (iii) buckminsterfullerene (C₆₀) ion sputtering, were investigated to suppress the migration of mobile ions in glass. In our best knowledge, it is the first time to succeed the precise XPS depth analysis of soda-lime-silica glass (70.4SiO₂, 0.9Al₂O₃, 7.3MgO, 7.8CaO, 13.6Na₂O in mol%) without compositional change by using C₆₀ ion sputtering. The precise analysis revealed that the ion implantation during Ar ion sputtering principally resulted in the compositional change due to the migration of mobile ions.     

Friction memory in the stick-slip of a sheared granular bed

We investigate friction memory effects in the chaotic stick-slip motion of a plate shearing a granular bed. By analyzing separately trajectories' portions having increasing or decreasing instantaneous velocity, it is found that there are two quantitatively distinct granular friction-velocity curves for positive or negative acceleration, which cross one another in the weakening region. Interpreting acceleration dependence as an indirect consequence of contact ageing, we try to explain these effects by including rate-and-state (RS) friction equations in the stochastic model describing the plate motion. Preliminary results on a study case show that the main experimental features can be reproduced in this way, although quantitative agreement is partial. From the value obtained for the RS parameters we conclude that sliding friction decorrelation takes place at the length-scale of the solid-on-solid micro-contacts between grains and plate. In addition, the contemporary presence of noise and RS effects influences the average friction curve at large shear rate.     

Enhancement of field emission in nanotip-decorated ZnO nanobottles

We report a simple fabrication process for the growth of nanotip-decorated ZnO nanobottles with an enhanced field emission property. Well-aligned ZnO nanobottles grown on ITO-coated glass substrates were synthesized by the thermal evaporation technique with the up-side down arrangement of substrate compared with the common method. The hydrothermal growth was carried out to decorate the nanobottles with ZnO nanotips. We demonstrate that the nanobottles decorated with nanotips show a much better field emission property. The improved field emission is attributed to the different local field enhancement factors at the nanobottles tops. Our results confirm the importance of the top morphology of a material in field emission.     

Redox behavior of platinum-group metals in nuclear glass

This study highlights the role of two platinum-group metals, ruthenium and palladium, in the redox equilibria of nuclear waste containment glass. Electrochemical measurements in simplified R7/T7 glass melts were used to develop a thermodynamic model of ruthenium redox equilibrium. The oxygen fugacity at equilibrium, corresponding to the coexistence of ruthenium oxide and ruthenium metal dispersed in the molten glass, was measured at different ratios at temperatures ranging from 1000 °C to 1200 °C. Experiments were carried out on glass with and without Pd, revealing the combined role of palladium and tellurium on redox equilibria in the glass. The formation of palladium-tellurium alloys in nuclear glass was observed to result in oxidation of the elements dissolved in the melt.     

Enhancement of the imprinting effect in cholesterol-imprinted microporous silica

A sol-gel method has been used to fabricate a cholesterol MIP for application in polar solutions. In this study, (cholesteryl propylcarbamate)triethoxysilane and tetraethyl orthosilicate were used as the hydrophobic monomer and crosslinker, respectively. The MIP had a larger pore volume when formation of the polymer was catalyzed at a higher pH than when it was formed at lower pH values, with the pore diameters being 3.5 nm and 2 nm, respectively for materials formed at high and low pH values. Both of these pore volumes were greater than those found for the respective control polymers formed without template. However, only the polymers formed at low pH values showed an imprinting effect. Compared with other methods explored, the sol-gel procedure gave only a small amount of non-specific binding for both the MIP and NIP when synthesized at low pH values. The largest imprinting-induced promotion of binding (IPB) value of the MIP (13 650%) was obtained with [HCl] = 0.01 M in the sol-gel solution. The MIP showed high selectivity towards cholesterol in comparison with other steroid hormones, and also to a lesser extent recognized vitamin D3 in methanol solution containing 5 vol.% water.     

X-ray irradiation-induced coloration of manganese in soda-lime silicate glass

Coloration of Mn in soda-lime silicate glass by X-ray irradiation was investigated as a coloration method suitable for glass recycling. Mn was initially reduced to Mn²⁺ with the addition of Fe, Sn or carbon, and the resultant colorless or near-colorless glasses containing no Mn³⁺ were studied. These glasses turned violet after X-ray irradiation and heat treatment at 200 °C due to formation of Mn³⁺. The color was stable at room temperature and decoloration occurred with heat treatment at 600 °C. The addition of Fe or Sn increased the optical absorption by Mn³⁺ ions. ESR measurement suggests that Mn photo-oxidation occurred through charge transfer from photo-induced hole centers.     

Internal friction analysis of structural relaxation in Si-C-O glass

Forced torsional oscillations has been recorded in Si-C-O glass up to elevated temperatures (≈1900 K). An attempt is shown to extend the measurements into the transformation range where internal friction merely arises from a viscosity-related mechanism and is represented by a background curve, or network contribution (i.e., that component of the internal friction curve which remains after a peak caused by stress-induced anelastic phenomena has been subtracted). Below 2000 K, the internal friction background curve is affected by delayed elasticity. On the other hand, using an approximate expression which relates the tangent of the loss angle to the glass viscosity, it is shown that the frequency dependence of the background internal friction above 2000 K can be simply explained in terms of a Maxwell model. In other words, viscous flow simply represents the high-temperature limiting behavior for the silicon oxycarbide glass, but it is overlapped by an anelastic phenomenon which hampers the full stabilization of its network structure. Some details of the viscoplastic behavior of the material could be obtained by examining internal friction data collected upon cooling.     

Method of measuring depth profile of hydrogen in soda-lime glass

The depth profile of hydrogen in glass, as an indicator for the presence of water, has been determined by two independent techniques. Secondary ion mass spectroscopy (SIMS) gives high spatial resolution measurements of the variation of hydrogen concentration as a function of depth into the glass. These measurements are not absolute, however. Elastic recoil detection analysis (ERDA) provides absolute measurements of the variation of hydrogen concentration with depth, although the spatial resolution is only in the order of 50 nm. The combination of the measurements obtained by these two techniques yields absolute high-resolution data of the depth dependence of hydrogen in glass.     

Optical properties of PbSe quantum dots doped in borosilicate glass

PbSe quantum dots (QDs) were synthesized in borosilicate glass and their optical properties were investigated. The typical quantum confinement effects were clearly observed from the absorption when the average radii of the QDs changed from 1.7 to 3.1 nm. Photoluminescence from PbSe QDs was achieved in 1.1–2.2 μm wavelength region that covers the entire fiber-optic telecommunication window. Borosilicate glasses containing controlled size of PbSe QDs provide potentials for the fiber-optic amplifiers.     

Formation mechanism of nanostructures in soda-lime glass using femtosecond laser

This paper reports on the formation of nanostructures produced in soda-lime glass by controlling the irradiation conditions of a single-beam femtosecond laser. Periodic nanoholes are fabricated in the sample with the lowest diameter of 200 nm (approximately one fourth of the incident light wavelength). Self-organized nanogratings with a period of 120 nm are fabricated for the first time on soda-lime glass surface by applying many pulses at the same spot. We discover that the nanogratings’ period decreases with the increase of the applied pulses. We investigate that the direction of the nanogratings is perpendicular to the direction of laser polarization. Further, it is discovered that the microholes, due to the illumination by many pulses, are elliptical in shape with the major axis perpendicular to the direction of laser polarization. Finally, long distance horizontal and vertical gratings are fabricated by scanning a femtosecond laser beam only in the horizontal direction.     

Estimation of shear-banding resistance in metallic glass containing nano-crystalline particles

Bulk metallic glasses (BMGs) have a variety of excellent properties compared with the majority of conventional crystalline alloys. However, they exhibit limited global plasticity at room temperature because of shear banding. Several methods have been proposed to improve the limited ductility of BMG; one method is the homogeneous distribution of crystalline particles. However, our understanding of the interaction between the crystalline particles and shear bands (SB) is not sufficient. Here, we performed molecular dynamics (MD) simulations of mode II deformation of a notched BMG plate and BMG plates containing one nano-crystalline particle ahead of the notch bottom. To compare the effect of crystalline particle size on the resistance to SB propagation, we used the J-integral. By comparing J-R curves and the deformation behavior of the BMG plates with and without nano-crystalline particles, we found that the resistance to shear banding is efficiently improved by introducing crystalline particles with sufficient size, compared to the SB width.     

Spectroscopic properties and simulation of white-light in Dy-doped silicate glass

Spectroscopic properties of various concentrations Dy³⁺-doped silicate glasses were characterized by excitation and emission spectra. The optimal doping concentration of Dy³⁺ ions was found to be 3.0 wt%, and the nature of resonance energy transfer was confirmed to be electric dipole-dipole interaction according to Huang’s rule. Simulation of white-light for these glasses was also performed by varying the excitation wavelength. The results show that the white-light luminescence color could be tuned to various wavelength excitations, and the present silicate glass is more suitable for generation of white-light for blue LED chips.     

Anomalous temperature dependence of sub-critical crack growth in silica glass

The effects of temperature, water vapor, and stress on the rate of sub-critical crack growth (SCG) in fused silica are reported. The crack velocity was measured using the double-cleavage-drilled compression method. In contrast to other inorganic oxide glasses, crack growth velocities (in region I) were found to decrease with increase in temperature. Hence a small temperature rise has the apparent effect of improving the mechanical strength of a stressed-glass part. Despite the anomalous temperature dependence, SCG in fused silica is still likely governed by the established water-enhanced stress-corrosion mechanism; another competing phenomenon is proposed to cause the observed temperature dependence. Measured crack velocities are described using an empirical model (for region I) and a mass-transport model limited by Knudsen diffusion (for region II).     

Structural implications of water and boron dissolution in albite glass

A combined nuclear magnetic resonance, infrared and Raman spectroscopic study on the effect of water dissolution on the structure of B-bearing aluminosilicate glasses is presented. The base composition was albite (NaAlSi₃O₈) to which different amounts of B₂O₃ (4.8, 9.1, 16.7 wt%) were added. Hydrous glasses containing 4.4 ± 0.1 wt% water were synthesized at pressures of 2000 bar. The results show that B dissolves in both dry and hydrous glasses by forming predominantly trigonal BO₃ groups although some tetrahedral BO₄ is also present. In anhydrous glasses prepared at high pressures (above 10 kbar) the fraction of BO₄ increased. The hydrous glasses contain more BO₄ groups compared to the dry counterparts, suggesting that this species is stabilized by water. The Raman and NMR (¹⁷O, ²⁷Al, ²⁹Si) spectra show that B interacts with the aluminosilicate network by formation of Si-O-B and probably Al-O-B units. In the hydrous glasses the water speciation changes significantly towards higher hydroxyl concentrations with increasing B-content. The NIR peaks, which are related to OH groups and molecular H₂O, develop additional shoulders, suggesting that possibly B-OH complexes are formed.