(Photo by Monika Stawowy on Shutterstock)
Engineers create transparent material with hardness comparable to tungsten metal
AUSTIN, Texas — Imagine a smartphone screen so tough it laughs off keys in your pocket, or eyeglasses that banish annoying glare forever. These desirable attributes that once seemed impossible could soon be reality thanks to a dazzling discovery at The University of Texas at Austin. Researchers have found a way to enhance sapphire with almost superhero-like powers to repel scratches, glare, fog, and even dust.
Modern electronics demand materials that can withstand the daily confrontation with the elements—and sometimes with our own clumsy habits. Among the contestants bidding to become the technology industry’s knight in sparkling armor is sapphire, a material celebrated for its scratch resistance, optical clarity, and robustness in harsh conditions.
“Sapphire is such a high-value material because of its hardness and many other favorable properties,” explains lead researcher Chih-Hao Chang, an associate professor in the Walker Department of Mechanical Engineering, in a statement. “But the same properties that make it attractive also make it difficult to manufacture at small scales.”
This conundrum provided the springboard for Chang and his team to delve into the minute realms of nanostructures, attempting to craft a sapphire that doesn’t just deliver the shine but embraces a tough-as-nails durability. Their innovation? A languid dive into the world of bio-inspired designs, crafting sapphire nanostructures with swiss-army capabilities, boasting anti-glare, anti-fogging, anti-dust, and yes, importantly, scratch resistance.
The Science Deco of Sapphire
Now, if the term ‘nanostructure’ sounds like something out of a futuristic novel, let’s break it down. Think of nanostructures as tiny architectural wonders at a microscopic scale. These structures, despite their minuscule size, pack a punch with features inspired by nature itself—such as the non-reflective eye of a moth.
In their quest to boost sapphire’s already impressive capabilities, the researchers looked to this unlikely insect for inspiration. Much like the moth, these sapphire nanostructures have tapered profiles that allow more light to pass through, reducing glare. “This is very exciting since nanostructures are traditionally seen as being fragile,” notes co-lead author Kun-Chieh Chien, a recent Ph.D. graduate from Chang’s lab who was instrumental in this breakthrough, “but making them in sapphire can solve this problem.”
The fabricated sapphire nanostructures consist of tapered pillars arranged in a precise geometric pattern. Each pillar is about 500 nanometers tall (about 1/100th the width of a human hair) with a width of 240 nanometers, creating an aspect ratio of 2.1—the highest ever reported for sapphire nanostructures. This high aspect ratio is crucial for achieving the desired properties, as it creates a gradual transition in refractive index that reduces reflection and enhances light transmission.
When tested for optical performance, the results were impressive. The nanostructured sapphire showed enhanced light transmission across a broad spectrum of wavelengths, from visible light to near-infrared. At its peak, the double-sided nanostructured sample achieved 95.8% transmission at a wavelength of 1360 nanometers—significantly better than the 85.9% transmission of conventional sapphire.
Perhaps even more remarkable was the material’s anti-fogging capability. When exposed to steam, conventional sapphire immediately fogged up, obscuring vision. The nanostructured sapphire, however, maintained clarity as water condensation formed a thin, uniform film rather than scattered droplets that scatter light. This effect occurs because the nanostructured surface is superhydrophilic (extremely water-loving), causing water to spread evenly rather than beading up.
After chemical treatment to modify the surface properties, the researchers could also make the material superhydrophobic (extremely water-repellent). In this state, water droplets barely touch the surface, maintaining a contact angle of 144.2 degrees—close to the 150 degrees typically defined as superhydrophobic. High-speed camera footage showed water droplets completely rebounding after impact, even at velocities of 1 meter per second. This water-repellent property makes the material self-cleaning, as falling water can easily carry away contaminants.
‘Game-Changer For Space Equipment’
The possibilities this opens up are vast. Picture windows and lenses that stay crystal clear no matter the weather, or windshields that shrug off dust on long drives through the countryside. Sapphire nanostructures also have surfaces that can mimic two natural marvels—the lotus leaf and the moth eye. This dual personality allows them to either soak up water, avoiding fog and condensation, or shed it completely, keeping surfaces clean and dry.
What’s truly impressive is the team’s success in maintaining the ruggedness associated with sapphire, while exponentially expanding its utility. “Our sapphire nanostructures are not only multifunctional but also mechanically robust,” says Mehmet Kepenekci, a key contributor to this ingenious project. This combination of features makes the material ripe for use in situations where durability and enhanced performance are non-negotiable.
Where might that take place? The researchers see this sapphire wonder material playing a pivotal role in our spacefaring dreams, protecting sensitive instruments from space dust—a perennial nuisance in alien landscapes. Andrew Tunell, the researcher who led dust adhesion tests, shares, “Our self-cleaning sapphire surfaces can maintain a 98.7% dust-free area using gravity alone.”
When tested with lunar dust simulant, which consists primarily of oxides with particles averaging around 50 micrometers in size, the nanostructured sapphire showed remarkable resistance to dust adhesion. After application of dust, simply tilting the sample vertically allowed gravity to remove most particles, leaving only 1.3% of the surface covered with dust. In contrast, conventional sapphire retained dust covering 31.8% of its surface under identical conditions—about 24 times more dust residue.
A leap forward from traditional cleaning methods, this dust resistance would be a game-changer for space equipment where water is a precious commodity.
Most crucially, these advanced properties came without sacrificing sapphire’s legendary durability. When subjected to nanoindentation tests, the structured sapphire showed an indentation modulus of 182 GPa and hardness of 3.7 GPa. While these values are lower than those of bulk sapphire (440 GPa and 30 GPa, respectively), they still exceed the properties of conventional glass and match those of scratch-resistant metals like tungsten. Pencil hardness tests further confirmed the material’s scratch resistance.
What’s Next?
The journey doesn’t end here. The energetic team at UT Austin is already busy scaling up production to make these advanced nanostructures available for a wide array of applications. They’re tweaking the design for even greater resilience and exploring new ways our everyday tech—and beyond—can take advantage of sapphire’s updated abilities.
As with any emerging technology, challenges remain. The researchers acknowledge that further optimization could improve properties like the anti-reflective wavelength range and water-repellent performance. Higher aspect ratio structures might enhance optical and self-cleaning properties but could potentially reduce durability—a tradeoff that requires careful engineering.
Thus far from being just a shimmering stone on a ring, sapphire is being propelled into a multitasking marvel with serious potential to transform everything from how we see through our windows to how rockets stay pristine in space.
For now, this sparkling material is poised at the cutting-edge of technological innovation—proving once again that beauty and brains make quite the pair. Diamonds may be forever, perhaps it’s time for sapphire to take its star turn in the spotlight.
Paper Summary
Methodology
The creation process combined several advanced manufacturing techniques. First, the researchers started with high-quality sapphire crystals. Since sapphire is extremely hard and difficult to shape directly, they covered it with a one-micrometer layer of polysilicon to serve as a mask. They then added layers of anti-reflection coating and a light-sensitive material called photoresist. Using a technique called interference lithography, they exposed the photoresist to laser light that created a precise pattern of dots arranged in a grid with 330-nanometer spacing. After developing this pattern, they used plasma etching with different gas mixtures to transfer the pattern through each layer and into the sapphire. A key innovation was using lower power during the silicon etching step, which allowed them to create taller, more defined structures. They repeated the process on both sides of the sapphire to create double-sided nanostructures. To modify how the surface interacts with water, they treated it with oxygen plasma and then added a single-molecule layer of a water-repellent compound through vapor deposition.
Results
The nanostructured sapphire showed several impressive properties. For light transmission, it achieved 92.8% average transmission across a broad range of wavelengths, compared to 86.7% for plain sapphire. This improved transmission worked even when light hit the surface at sharp angles—maintaining about 90% transmission up to 60 degrees, while plain sapphire dropped to 76.4%. In fog tests, the nanostructured sapphire kept over 80% transmission when exposed to steam, while regular sapphire’s transmission fell below 10%. The water-repellent version achieved a contact angle of 144.2 degrees, allowing droplets to bounce completely off the surface. In dust tests, the nanostructured sapphire retained only 1.3% dust coverage after being tilted vertically, compared to 31.8% for regular sapphire—95.9% less dust. Hardness tests showed values that, while lower than pure sapphire, remained similar to regular glass and metals like tungsten that are known for scratch resistance.
Limitations
Despite the impressive results, several limitations exist. The structures created had an aspect ratio (height to width) of 2.1, which could potentially be increased for better performance. The anti-reflection effect worked best in a specific wavelength range (550-1750 nanometers) and was less effective for shorter or longer wavelengths. The water-repellent performance fell slightly short of textbook “superhydrophobicity” (defined as contact angles greater than 150 degrees). The mechanical properties showed some reduction compared to pure sapphire. Sample sizes were limited to 30 mm by 30 mm squares, with edge areas lacking the nanostructures due to manufacturing limitations. The study focused on laboratory demonstration rather than testing long-term durability in real-world conditions or scaling up to commercial production.
Discussion and Takeaways
The researchers emphasize that this work shows how controlling both material composition and surface structure can create materials with multiple useful properties. Future work could focus on optimizing the height, width, and shape of the nanostructures. Taller, thinner structures could improve anti-reflection at longer wavelengths and enhance water-repellent properties, though there may be a trade-off with durability. More gradually tapered structures could create better anti-glare effects. The researchers suggest their process could be adapted for large-scale manufacturing using techniques like nanoimprint lithography. Potential applications include scratch-resistant screen protectors, fog-free windows and mirrors, self-cleaning optical surfaces, and specialized windows for defense and space applications.
Funding and Disclosures
This research was conducted at the University of Texas at Austin using facilities at the Texas Materials Institute, the Nanomanufacturing System for mobile Computing and Energy Technologies, and Texas Nanofabrication Facilities. It received funding from the Army Research Office, NASA, and the National Science Foundation through specific grants. The authors declared no conflicts of interest in their work.
Publication Information
This study, “Scratch-resistant sapphire nanostructures with anti-glare, anti-fogging, and anti-dust properties,” was published in Materials Horizons on February 11, 2025. The research team included Kun-Chieh Chien, Mehmet Kepenekci, Andrew Tunell, and Chih-Hao Chang from the Walker Department of Mechanical Engineering at The University of Texas at Austin. The paper is available online with the identification number DOI: 10.1039/d4mh01844c.
Just in time. Now the young adults have hope. Not.