Today there is more glass in use than ever before. Glass is a critical design component encompassing environmental protection, appearance, safety, light transmission, and thermal management. The increasing importance and sophistication of glass means that more advanced analyses are needed to address manufacturing issues.
Glass development and glass product verification requires the measurement of composition with high accuracy.
Wavelength Dispersive X-ray Fluorescence (WD-XRF) can measure major and minor element glass composition.
WD-XRF: SELECTED COMPOUNDS
Inductively Coupled Plasma Mass Spectrometry (ICP-MS) measures low concentrations and trace level concentrations with high accuracy.
ICP-MS: SELECTED ELEMENTS
INCLUSIONS AND SMALL AREA
Laser Ablation ICP-MS (LA-ICP-MS) measures areas as small as 4 µm. Sampling depth 1 µm.
LA-ICP-MS: SELECTED ELEMENTS
Surface particle and residue contamination can affect appearance, coating adhesion and film integrity.
WASH AND RINSE – Thin film trace level contamination
Adhesion, reliability and appearance of coatings can be affected by surface residue. The efficacy of the cleaning process should be well understood and identification of any residues should be investigated.
Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) has very high sensitivity and a very shallow sampling depth making it ideal for detecting organic and inorganic surface residues.
Residues can have a detrimental effect on coating adhesion, appearance, yields and performance.
TOF-SIMS survery analysis shows:
PARTICLES AND SURFACE DEFECTS
Surface particles, defects, discolorations can affect appearance. Pinholes may affect corrosion of silver layers.
Auger Electron Spectroscopy (Auger) has very shallow sampling depth and can also examine sub-micron features. Auger can examine small particles, stained areas and corrosion sites.
Auger analysis can determine:
Secondary Electron image: appearance of defects
Auger maps: contaminant distribution
Auger spectra: identify contaminants
Exposure of glass surfaces to various treatments can result in a change in surface composition and chemistry. The penetration depth of these changes and the composition can be measured by Secondary Ion Mass Spectrometry (SIMS).
DE-ALKALIZATION BY HYDRATION
Hydration is the process where hydronium ions diffuse into a glass surface and exchange with alkali and other metals. Hydronium concentration and ingress depth can be measured using SIMS. The depletion of alkali concentration at the surface and the depth of depletion can also be measured.
Potassium can be substituted for sodium in the glass matrix using an ion exchange process. The resulting glass is much stronger than before. SIMS concentration profiles of Na and K reveals how far into the material the exchange process has occurred.
SIMS Profile of Mobile Elements
Alkali metals are also called ‘mobile ions’ because they are easily moved by electric fields such as those caused by the SIMS primary ion charged particle beam. With the correct analysis conditions, we can minimize migration caused by SIMS. Here we show a glass cleaved surface profile demonstrating SIMS has caused almost no profile distortions on this fresh fracture surface.
SIMS Profile of a Newly Cleaned Surface
Investigation of the layer structure, identity and composition of an unknown coating system can be done in several ways.
An unknown glass coating structure was profiled by X-ray Photoelectron Spectroscopy (XPS). All layustifers were identified and the composition of each layer was determined. Compositions are accurate. Layer thicknesses are approximate.
An unknown glass coating structure was cross-sectioned and then analyzed by Scanning Transmission Electron Microscopy – Energy Dispersive X-ray Spectroscopy (STEM-EDS). We can observe the layer structure, thickness and uniformity, and all layers were identified. Layer thickness and uniformity is accurate. Composition is approximate.
STEM-EDS Cross Section
TRACE LEVEL AND INTERDIFFUSION
An unknown glass coating structure was depth profiled by SIMS. We can observe the major element profiles along with the trace element profiles including Na diffusion from the substrate glass. Composition can be accurately determined with standards. Trace element concentrations are accurate. Layer thicknesses are approximate, in the absence of correlation to other measurements.
Annealing and tempering of glass will change the glass and coating microstructure and cause interdiffusion between layers. SIMS depth profiling shows diffusion of major and minor elements between layers. TEM shows changes in microstructure.
SIMS shows major diffusion of Na after tempering, from the glass substrate through all of the coating layers and to the surface. Si and N have diffused from the SiAlN layers into the adjoining layers.
TEM shows no change in coating layer thicknesses after tempering. However the interfaces between layers have become more defined and one interfacial layer has disappeared.
Many glass coating systems include a TCO (transparent conductive oxide) layer to make electrical contact with the layer structure. For solar applications, TCO layers need to be optically transparent with a bandgap that minimizes light trapping yet still has high electrical conductivity.
TCO conductivity can be affected by dopants, contaminants, grain size, and grain orientation. GIXRD (Glancing Incidence X-Ray Diffraction) compares 2 TCOs: the red curve is from a low conductivity film while the black is from a higher conductivity film. The textures are quite different.
GI-XRD θ-2θ Scan
THICKNESS/ DENSITY/ ROUGHNESS
TCO thickness, roughness and density can be measured quantitatively without the need for standards using XRR (X-Ray Reflectivity). Critical angle reveals density, the slope after the critical angle reveals roughness, and interference fringes reveals thickness. Comparison of two coatings shows similar thickness and density, but different surface and interface roughness.
Dopants can increase the electrical conductivity of TCOs but dopants can also reduce optical transmission. SIMS depth profiling reveals dopant concentration. The Zn:O ratio was calibrated by RBS (Rutherford Backscattering Spectrometry).
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