First reveal the damage of nano-scale glass! The field of glass science is expected to usher in great development

According to the international research team, spectroscopy technology has revealed for the first time the sub-surface structure changes of silica glass caused by nano-scale wear and damage, which is expected to improve glass products such as electronic display screens and automobile windshields.

Seong Kim said that one of the main research areas of my group is glass surface science, which mainly studies the relationship between glass properties, structure and mechanical and chemical properties, especially mechanical durability and chemical durability. He is the Distinguished Professor of Chemical Engineering at Pennsylvania State University and the co-lead author of the “Journal of Materials” (“Subsurface structural change of silica upon nanoscale physical contact: Chemical plasticity beyond topographic elasticity”) study. One of the techniques we have been using is vibrational spectroscopy. But the challenge of performing nanoscale structural analysis on glass surfaces is that many of the widely used spectroscopy techniques do not work here.

Through hyperspectral near-field optical mapping, the infrared beam can show nano-scale defects and damage that weaken the glass sample. (Photo: Elizabeth Flores-Gomez Murray, Pennsylvania State University)

Infrared spectroscopy can only detect surface defects to a certain extent. If the defects generated on the glass surface are smaller than 10 microns, which is lower than the wavelength of 10 microns in the infrared spectrum, correct analysis or imaging cannot be performed. Raman spectroscopy and other analytical techniques used in the field of glass research work better in terms of spatial resolution, but they are still insufficient for nano-scale structural analysis.

Kim’s team wanted to create a technique to discover the structural changes that occur in nano-scale dents on the glass surface. As part of the research, they used a tiny tip to make indentations on the glass surface, which could create nano-indents several hundred nanometers deep and one to two micrometers wide. It is important to find structural changes even at small damage levels, because these infinitesimal defects can affect the strength of the glass.

Gorilla Glass produced by Corning is an example. It is mainly used for display glass of electronic products such as mobile phones, and recently also used for windshields of cars and airplanes. This glass is very strong when it leaves the factory, but when it reaches the manufacturer, the glass becomes weak. This is due to small scratches and other damages caused by physical contact such as paper contact, truck vibration, packaging, and frequent collisions during unloading during transportation. The defects may not be obvious, but they are enough to weaken the glass performance.

In addition, glass can also be corroded. This corrosion is different from metal corrosion. In glass corrosion, some of the constituent elements are lost on the glass surface, and the chemical properties of the glass change, which will also weaken the glass.

So, how to describe this invisible structural damage? Kim said that this is a very important field of glass science, because in theory, glass should be as strong as steel. However, the strength of glass is not as good as steel, and one of the main reasons is surface defects.

When Kim’s team left tiny dents on the glass, they wanted to see what structural changes would occur in and around the dents due to damage to the glass.

Therefore, since the maximum size of the dent is only a few microns, we need high spatial resolution infrared spectroscopy to characterize this, Kim said.

To overcome this challenge and “see” the damage to the glass, Kim contacted his colleague Slava V. Rotkin, a leading professor of engineering science and mechanics at Pennsylvania State University, who used a new instrument technology called “Hyperspectral near-field optical mapping”. This technology provides optical spectral resolution and high spatial resolution, and uses a scattering scanning near-field optical microscope manufactured by Neaspec gmh, a German nanoimaging and spectrometer company.

Until recently, research like Seong was either indirect, because you couldn’t really image tiny things happening on the nanoscale, or they would come into contact with physical substances such as atoms or molecules instead of optical properties, Rotkin said, so , Our instrument is very unique because it allows you to conduct optical research on a very small scale, which was impossible in the past.

Glass is mainly silicon oxide, which is in principle the same as sand or crystal quartz in watches, but there is an obvious difference: the degree of defects. Sand is like a stone with many surface defects, crystal quartz is a perfect crystal, and glass is somewhere in between. This makes it difficult to “see” glass at the nanometer scale because there are too many inhomogeneities. However, hyperspectral near-field optical mapping technology allows researchers to focus and observe the impact of scratches on glass, even beyond topographic damage.

It’s like looking down at a large forest from above. There are many, many trees, bushes, mushrooms, flowers, etc. You don’t know what to look at. Rotkin said that the students left scratches on the glass, and you see These scratches are very interesting and conspicuous, just like if you cut down trees in the forest to open up a clearing, it will be very conspicuous. When you clear the tree, it may push the bush to the ground, and due to some damage, it will change the color of the leaves in some way. Maybe the observation instrument you use can’t see these, but with our instrument, you can see a single shrub, not only that, but you can also see the leaves turning red.

This is an important step in glass science. In principle, the papers we published provide a new way to understand how these glass inhomogeneities occur and the physical principles behind them. Rotkin said that we have seen mechanical changes, scratches are producing physical changes, chemical changes and Changes in optical performance. This is very interesting.

It is important to understand this, because accuracy is important for many types of equipment. The camera on the Mars rover can measure the spectral characteristics of the Martian surface, but scratches on the glass will not only affect the optical properties, but also the mechanical and chemical properties, which are very important for truly accurate measurements. In addition, nano-scratches on the glass of the mobile phone camera will not only change the transparency, but also change the color coding, resulting in lower photo quality.

Kim said that this research is more about understanding what happened to glass. This is something we have never done before and have not understood. A process or product can be improved through trial and error. But a better method is based on knowledge development or processing. So, if we can’t understand what kind of defects are caused by physical contact, how can we make the glass surface better, more perfect, and more durable, both mechanically and chemically.

With this information, Kim believes that glass science is likely to make new progress.

By understanding the nano-surface damage of multi-component glass materials using this technology, we can significantly improve our basic understanding of glass science, Kim said.