Corning Code Research Articles

Influence of Amorphous Silica Matrices on the Formation, Structure, and Chemistry of Iron and Iron Oxide Nanoparticles

Fe(CO)(5) physisorbs onto Corning's code 7930 porous Vycor glass (PVG) and dried (<or=200 degrees C), base-catalyzed (NH(3)) tetramethoxysilane/methanol/water xerogels. Although chemically and structurally similar matrices, 488-nm photolysis of the physisorbed complex yields ca. equal amounts of Fe(0) and Fe(2)O(3) in PVG, but only Fe(2)O(3) in the xerogel. Mossbauer, EXAFS, and XANES results give no indication the photoproducts bind to either silica matrix, and consolidation of the PVG matrix leads to Fe(0)-Fe(2)O(3) nanoparticle formation with little change in the Fe(0)/Fe(III) ratio. PVG serves as a template defining the particle diameter and interparticle spacing, whereas consolidation of the xerogel does not result in nanoparticle formation. Instead, ca. 20% of the octahedrally coordinated Fe(III) converts to tetrahedral coordination during consolidation. The photoproducts within these porous silica matrices reflect a competition between aggregation and oxidation, where the extent and most likely the rate of aggregation are functions of the correlation lengths of these amorphous matrices. With a correlation length of 22 +/- 1 nm, aggregation exceeds oxidation in PVG and limits oxidation to the outer periphery, thereby creating particles whose Fe(0)/Fe(III) ratio is unaffected by air or water released during consolidation of the silica matrix. The correlation length of the xerogel, <or=1 nm, limits aggregation of the primary photoproduct and favors smaller particles. As a result, the primary photoproducts in the xerogel do not achieve sufficient size to limit oxidation to the outer periphery of the particle, and the primary photoproduct oxidizes, forming only Fe(2)O(3). Desorption of decomposition products derived from the xerogel precursors creates a dynamic surface that limits nanoparticle growth during annealing. Desorption also disrupts the growing silicate matrix, creating sites that facilitate the change from octahedrally to tetrahedrally coordinated Fe(III) in the xerogel.

Importance of Crystallization Hierarchies in Microstructural Evolution of Silicate Glass–Ceramics

Quench studies of in‐house melted glasses were used to study the microstructural evolution in Macor‐type and Corning Code 9606‐type glass–ceramics to elucidate the microstructures of the commercial products. They reveal that phase separation initiates crystallization in both systems which then proceeds via formation of several phases at different scales of size, the first phases to form being those containing the most rapidly diffusing species. This study highlights the concept of crystallization hierarchies whereby crystals form, sometimes simultaneously, sometimes sequentially, on heating glasses, but at different length scales. This is illustrated by the simultaneous nucleation of μ‐cordierite nanocrystals and ∼0.2 μm MgAl2Ti3O10 rosettes in Corning 9606‐type compositions and of ∼0.3 μm chondrodite and 3–4 μm fluorophlogopite laths in Macor‐type compositions.

Bulk diffusion measurements to study the effectiveness of barrier layers: II. Exchange of sodium between liquid crystal display glass substrates with different barrier layers

Na-22 tracer diffusion experiments were performed to study the exchange of Na ions between liquid crystal display glass substrates (Corning Code 1737) separated by different types of layers. Different types of layers were generated (i) by RCA cleaning, (ii) by preannealing in wet air, and (iii) by low pressure chemical vapor deposition. A sandwich configuration was used to study the effect of such layers between two glass substrates on the exchange of Na ions between these substrates. The sandwiches were of the type substrate 1 (containing Na-22 tracer)/layer/substrate 2. Diffusion annealing of such sandwiches led to a redistribution of the sodium tracer. This redistribution was analyzed experimentally with regard to the sodium tracer diffusion coefficient in the bulk and the rate of the sodium tracer transfer across the layer. It was found that all three types of layers considered act as barrier layers, i.e., they suppress the exchange of Na ions between glass substrates.

Thermal dimensional stability of glass substrates for poly‐Si TFT‐LCD application

Abstract— Thermal dimensional stability of Fusion‐drawn Corning Code 1737 glass was investigated at simulated thermal cycles for low‐temperature poly‐Si TFT fabrication. For low‐temperature poly‐Si TFT processes between 550 and 600°C, annealed Code 1737 is required to meet a typical thermal shrinkage requirement of less than 20 ppm. For super‐low‐temperature poly‐Si TFT processes between 400 and 450°C, Code 1737 meets the requirement in the unannealed state. Code 1737 glass having a high strain point of 666°C provides thermal capabilities as a substrate for low‐temperature poly‐Si TFT‐LCD applications.

Microcrystalline‐silicon thin films by physical vapor deposition for wide‐area low‐temperature polysilicon production

Abstract—A sputtered microcrystalline‐silicon thin film deposited on unannealed Corning Code 1737 glass has been shown to transform to polycrystalline material after excimer‐laser annealing at low energy densities, and below the full‐melt threshold. The homogeneous large‐grain polysilicon films obtained show promise for high‐yield manufacturing of large‐area LTPS displays. The material properties of the films will be presented and the properties of devices fabricated in the films will be discussed.

On The Formation Of Diffusion Layer Between Cr Film And Glass

Abstract Chromium films are commonly used as a metal “glue” layer because of good adhesion to glass. It is believed that an intermediate oxide layer is formed during deposition, since Cr has a very strong affinity for oxygen. For example, a graded Cu/Cr/CrOx/SiO2 structure ensures excellent adhesion of Cu to glass, whereas Cu exhibits poor adhesion to most dielectrics. In our recent study, however, a diffusion layer, Cr2O3+SiOy, was observed between CrOx and SiO2 (glass) substrate. It is quite likely that this diffusion layer is responsible for the good adhesion of Cr film to glass. The relative compositions of the major components across the interface are shown in Fig 1. A Cr film was evaporated on Corning Code 1737 glass (Al2O3-B2O3-SiO2 with ˜67at.% Si02) substrate at room temperature (RT) and subsequently covered with about lOnm Cu. A 5nm'wide diffusion layer is seen. The corresponding regions are also indicated in Fig 2, an Annular Dark Field (ADF) image whose contrast is approximately proportional to the density if the thickness is assumed uniform.

Polycrystalline silicon thin films formed by metal-induced solid phase crystallization of amorphous silicon

Metal-induced solid phase crystallization (MISPC) was performed on plasma-enhanced chemical vapor deposited a-Si:H films which were deposited at substrate temperatures between 100 and 320 °C on bare or SiNx-coated Corning code 7059 glass substrates. The nickel or palladium layers used in the MISPC were thermally evaporated on the a-Si:H film surfaces to thicknesses of 5, 10, or 15 Å. We then examined the MISPC kinetics and its dependence on the precursor a-Si:H deposition temperature, the substrate coating, and the metal layer thickness. For the metals used in this study, it is found that the crystallization time and the microstructure and size of grains in the MISPC polycrystallization silicon (poly-Si) films are independent of the precursor a-Si:H deposition temperature, the metal layer thickness, and the substrate coating; however they are dependent on the metal type. It is argued that the formation of silicides and the solubility of metal in silicon, during the annealing, play important roles in enhancing crystallization. It is also found out that the diffusion of metal impurities into silicon from the metal layer used in the MISPC is detrimental to the electrical properties of the forming poly-Si and to the characteristics of thin film transistors fabricated in the poly-Si.

Internal Friction in Lithium Aluminosilicate Glass‐Ceramics

This paper describes the results of an investigation of the anelastic behavior of two glass‐ceramic materials with similar compositions, one nucleated with TiO2 and the other with ZrO2. The influence of the grain size, residual glass fraction, and composition was examined. A low‐frequency torsion pendulum was constructed for this purpose. The as‐received TiO2‐nucleated. Corning Code 9608 ceramic exhibits an attenuation peak at about 750°C; when heat‐treated at 1200°C for 167 h, the attenuation peaks at approximately 850°C. The ZrO nucleated glass‐ceramic showed no such peak. Our results indicate that this anelastic behavior is due to grain boundary sliding, but the rates and magnitude of sliding are strongly dependent on boundary chemistry.

Structural characteristics of as-deposited and crystallized mixed-phase silicon films

In this work, we report on the structural characteristics of as-deposited and crystallized mixed-phase silicon films prepared by thermal decomposition of silane in a low pressure chemical vapor deposition reactor. Mixed-phase films consist of crystallites embedded in an amorphous matrix. The size of these crystallites depends upon the surface diffusion length, a parameter quantitatively expressing the potential of adsorbed silicon atoms for surface diffusion. The density of the pre-existing crystallites can be related to the maximum density of critical nuclei, which develops during the deposition of the film. Both variables were quantitatively related to the deposition temperature and rate via physical models reflecting the experimental observations. Values for the parameters associated with these models were extracted by fitting the experimental data to the theoretical equations. Our theoretical analysis is the first to relate quantitatively the structural characteristics of as-deposited mixed-phase films to the prevailing deposition conditions. Mixed-phase films can crystallize in a much shorter time than as-deposited amorphous films, due to the combination of the growth of the pre-existing crystallites and the higher nucleation rate of new crystallites within the amorphous matrix of the mixed-phase film. The crystallization time and final grain size of crystallized mixed-phase films were found to decrease with increasing density of pre-existing crystallites. However, we showed that if composite films are deposited, consisting of a mixed-phase layer and an amorphous layer, the grain size after crystallization could be comparable to that of crystallized as-deposited amorphous films, with the crystallization time of such composite films about threefold shorter. The structure of both as-deposited and crystallized single and composite mixed-phase films was found to be identical for films deposited on both oxidized silicon and Corning Code 1735 glass substrates.

Hybrid ceramic matrix composites

A model hybrid glass-matrix composite has been studied. The system investigated was Corning Code 1723 glass matrix (an alkaline earth aluminosilicate glass) with silicon carbide whiskers and Nicalon® fibres. It was found that a 10 wt % whisker loading of the matrix gave optimum composite properties. The optimized hybrid composite, when compared to an optimized non-hybrid composite, showed increases in microcrack yield stress from 330 to 650 MPa, interlaminar shear strength from 47 to 130 MPa, and transverse strength from 12 to 50 MPa, while the ultimate strength decreased from 965 to 900 MPa.

Laser-recrystallized silicon thin-film transistors on expansion-matched 800°C glass

Laser-recrystallized silicon thin-film transistors (TFT's) have been fabricated, for the first time, on a novel, potentially low-cost glass substrate, The 0.5-µm-thick silicon films were deposited along with appropiate dielectric layers on Corning Code 1729 glass substrates and recrystallized using an argon ion laser. The n-channel enhancement-mode transistors were made using conventional IC device fabrication procedures modified to have a maximum processing temperature of 800°C. Transistor's made in the recrystallized silicon show field-effect electron mobilities as high as 270 cm2/V.s, approximately 15 times that of comparable devices made in as-deposited polycrystalline-silicon films. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do comparable polycrystalline-silicon devices.

Cl(-)-selective microelectrodes: sensitivity to anionic Cl- transport inhibitors.

Cl(-)-selective microelectrodes, containing Corning code 477315 or 477913 liquid ion exchangers, are often used to measure extra- and intracellular Cl- activities in the presence of Cl- transport inhibitors such as furosemide, bumetanide, and the stilbene sulfonic acid derivative 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). Because these inhibitors are anions in the physiological pH range and have relatively high lipid solubilities, they would be expected to interfere with the response to Cl- of these microelectrodes. Preliminary reports have confirmed this expectation. We examined the effect of furosemide, bumetanide, and SITS on the Cl(-)-selective barrels of double-barreled microelectrodes containing Corning code 477315 liquid anion exchanger and suitable for impaling small cells (e.g., epithelial cells). The results showed that at pH 8.2 in pure solutions of furosemide and bumetanide, these microelectrodes gave linear responses to the logarithm of furosemide or bumetanide concentrations ranging from 1 X 10(-2) to 1 X 10(-4) M. In the physiological pH range both these inhibitors (in concentrations of 0.1 mM) interfered significantly with the response of the microelectrodes to Cl- (in concentrations ranging from 100 to 1 mM). Calculated electrode sensitivities, relative to Cl-, were approximately 150 for both these compounds. Microelectrodes of this type appeared to be approximately 1,000 times as sensitive toward SITS as they were toward Cl-.

Materials and Processes For Silicon TFT's On Aluminosilicate Glass: An Alternative Soi Technology

AbstractAs-deposited polycrystalline silicon and argon ion laser recrystallized silicon thin film transistors (TFT's) have been fabricated on Corning Code 1729 glass substrates. This novel aluminosilicate glass has an expansion coefficient matched to that of silicon and a chemical durability comparable to that of fused silica. N-channel enhancement mode transistors were made using conventional IC device fabrication procedures (including thermal oxidation to form the gate insulator) modified to have a maximum processing temperature of 800 C. The- polycrystalline silicon TFT's exhibit leakage currents of less than 2x10-11 A/ μm; of channel width and good stability and reproducibility. Transistors made in the recrystallized silicon show field effect electron mobilities as high as 270 cm2/V s, approximately 15 times the mobility of comparable devices made in as-deposited polycrystalline silicon. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do the comparable polycrystalline silicon devices. Major advantages of this TFT technology include the use of a novel, potentially low cost glass substrate and the simultaneous processing of both polycrystalline and recrystallized silicon devices on the same substrate material. This approach represents a new avenue for the incorporation of active devices into a variety of applications including integrated active matrix displays.

Direct Observation of the Phase Separated Microstructure of a Sodium Borosilicate Glass and Its Development During Heat Treatment

By treating Corning code 7740 sodium borosilicate glass (composition by weight 80.5% SiO2, 13% B2O3, 3.8% Na2O, 2.2% Al2O3, 0.4% K2O) with a process consisting of heat treatment within the immiscibility region followed by a chemical etch, it is possible to produce a thin surface layer on the glass giving a low total optical reflectivity over the entire visual spectrum. In the course of a full investigation into this phenomenon, an attempt has been made to fully characterize the nature and development of the two-phase structure produced by the heat treatment.Coupons of glass 3 x 3 x 0.125 inches, as received from Corning Glass Works, were heated for times ranging between 1-1/2 and 1000 hours at 600°C (well below the phase transition temperature, about 650°C for this glass). It is known that a three-hour heat treatment maximizes the antireflective property. Electron microscope specimens were conventionally prepared by mechanical grinding and ion thinning. However, after ion thinning, specimens were chemically etched by floating them on a drop of 0.1 wt% NH4.HF in 1.6N HNO3 solution, for typically 2 to 5 minutes. Specimens were rinsed by repeated flushing with distilled water, dried, and then carbon coated to prevent charging effects.

Stress profile determination in chemically strengthened glass using scattered light

A method is described for determining stress profiles in thin specimens of chemically strengthened glass by progressively etching away the surface compressive layer and measuring the change in magnitude of the centre tensile stress using the scattered light technique. The profile is derived from the relationship between thickness change and centre tension change. Some specimen results are presented for a commercial glass (Corning Code 0319) and other chemically strengthened glasses.

Trace chemical analysis of high-purity glass

Trace-element impurities in high-purity silica (Corning Code 7940 fused silica and J. T. Baker Ultrex silicon dioxide), 96% silica glass (Corning Code 7913), borosilicate glasses (Corning Code 7740 and Owens-Illinois KG-33) and doped optical waveguide glass have been determined by spark-source mass-spectrometry, optical-emission spectrography, neutron-activation analysis, atomic-absorption and plasma emission spectrometry, spectrophotometry, voltammetry and chemical methods. Particular care was taken to prepare samples and carry out analyses in a clean environment with ultrapure reagents. In most cases some 30 elements as well as water were determined by two or more of the techniques indicated. The impurity level for many elements in the high-purity silica and optical waveguide glass is in the ng/g range and in theμg/g range for the other glasses. Spark-source mass-spectrometry and neutron-activation analyses were carried out not only on samples prepared by a hydrofluoric acid dissolution-evaporation procedure but also on undissolved samples for volatile elements such as B, P, S, As and Hg. Results obtained are discussed with respect to application of the materials as well as to the analytical methods developed.

Precision Measurements of the Dimensional Stability of Four Mirror Materials.

There are several glasses and glass-ceramics available today which have low coefficients of thermal expansion - some near zero. For this reason they often serve as substrates for massive mirrors in orbit. In order for such a mirror to enjoy a lifetime of 5 years or more of diffraction-limited service, the substrate must be dimensionally stable and thereby preserve the original figure. Early in l967, it was decided that the National Bureau of Standards and Corning Glass Works would undertake a joint effort to measure the lengths of small samples of such materials over a period of years. These measurements were completed in 1971. The average length changes in parts per million of the four materials selected are as follows: Corning Code 9623 a glass ceramic- 0.30Corning Code 7971 a titanium silicate- 0.37Corning Code 7940 a vitreous silica- 0.47Corning Code 9622 a glass-ceramic- 1.03.

Glass fiber hermetic seals using a CO_2 laser

Glass fibers of approximately 0.13-mm diam have been hermetically sealed through windows of Corning Code 7740 glass and Code 7052 glass, and into B(2)O(3)-3SiO(2) glass as well. The seals were made with a 50-W CO(2) laser at a power level of about 5 W. Transmission loss tests show a transit loss of <0.2 dB for a B(2)O(3)-3SiO(2) clad fused silica fiber through a Corning Code 7740 glass window.

Spectral Remote Sensing of Temperature Distribution in Semitransparent Solids Heated by an External Radiation Source

A spectral remote sensing method for recovering the temperature distribution in semitransparent solids from remotely sensed spectral emission data is studied. An analytical model that relates the emerging spectral intensity from a plane layer of solid heated by an external radiation source to the temperature distribution, spectral radiation properties, radiation characteristics of the interfaces of the solid, and the source is formulated. The temperature profile is expressed in the form of a finite series of Legendre polynomials; and the coefficients are obtained using an optimization scheme that, by iteratively solving the expressions for emerging intensity, reconstructs the distribution that best fits the spectral emission data. The validity and accuracy of the remote sensing method is evaluated by comparing the recovered temperature with independent measurements in two different experiments; one using surface thermocouples only and the other a Mach-Zehnder interferometer. Experimental results are reported for PPG clear float glass and Corning Code 7940 fused silica using a Perkin-Elmer spectrometer and Barnes Spectralmaster radiometer to measure the emerging spectral radiant energy. For clear float glass, the recovered temperatures were a maximum of 1.5% higher than those measured with surface thermocouples. For fused silica, the linear recovered and interferometrically measured temperature profiles agreed well, with the maximum deviation never exceeding approximately 2% up to about 1000 K.

Development and Evaluation of a Remote Sensing Technique for Determining the Temperature Distribution in Semitransparent Solids

A technique is presented for recovering the temperature profile in semitransparent solids from remotely sensed spectral emission data. The temperature distribution is determined by iteratively solving the equation governing the emerging spectral emission to recover the profile to best match the emission data. The technique is evaluated using both analytical and experimental emission data. Analytical results show the effect of data error, number of data points, method of representing the temperature profile, and optical thickness range. The method is verified experimentally using Corning Code 7940 fused quartz by comparing recovered temperature profiles with those predicted by a combined conduction-radiation heat-transfer analysis.