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Imaging surface structure and premelting of ice Ih with atomic resolution

NatureNature·
Read the paperDOI: 10.1038/s41586-024-07427-8

TL;DR

Imagine trying to see the detailed pattern on a delicate snowflake before it melts. It's incredibly difficult. For decades, scientists faced a similar problem trying to see the surface of ice at the smallest possible scale—the level of individual atoms. They knew the surface was important, but couldn't get a clear picture. In this study, researchers used a revolutionary microscope with a tip so fine it's like a record player needle for atoms. By working in an extremely cold, stable environment, they gently 'felt' the surface of the ice without breaking it. They discovered the surface isn't a single, perfect crystal pattern like a tiled floor. Instead, it's a patchwork quilt of two slightly different patterns stitched together. They also witnessed the very first moment of melting, which started right at the 'seams' of this quilt, not everywhere at once.

Ice surfaces are closely relevant to many physical and chemical properties, such as melting, freezing, friction, gas uptake and atmospheric reaction. Despite extensive experimental and theoretical investigations, the exact atomic structures of ice interfaces remain elusive owing to the vulnerable hydrogen-bonding network and the complicated premelting process. Here we realize atomic-resolution imaging of the basal (0001) surface structure of hexagonal water ice (ice Ih) by using qPlus-based cryogenic atomic force microscopy with a carbon monoxide-functionalized tip. We find that the crystalline ice-Ih surface consists of mixed Ih- and cubic (Ic)-stacking nanodomains, forming periodic superstructures. Density functional theory reveals that this reconstructed surface is stabilized over the ideal ice surface mainly by minimizing the electrostatic repulsion between dangling OH bonds. Moreover, we observe that the ice surface gradually becomes disordered with increasing temperature (above 120 Kelvin), indicating the onset of the premelting process. The surface premelting occurs from the defective boundaries between the Ih and Ic domains and can be promoted by the formation of a planar local structure. These results put an end to the longstanding debate on ice surface structures and shed light on the molecular origin of ice premelting, which may lead to a paradigm shift in the understanding of ice physics and chemistry.

  • 1Atomic-resolution imaging of the basal (0001) surface structure of hexagonal water ice (ice Ih) achieved using qPlus-based cryogenic atomic force microscopy.
  • 2The crystalline ice-Ih surface consists of mixed Ih- and cubic (Ic)-stacking nanodomains, forming periodic superstructures.
  • 3Density functional theory reveals the reconstructed surface is stabilized by minimizing electrostatic repulsion between dangling OH bonds.
  • 4The ice surface becomes disordered with increasing temperature, indicating the onset of the premelting process.
  • 5Surface premelting occurs from defective boundaries between Ih and Ic domains and is promoted by planar local structure formation.
Nature·

Over 20,000 precolonial earthworks in the Southwest Amazonia

Imagine flying a special laser scanner over the Amazon jungle that can 'see through' the treetops, like X-ray vision for the ground. When scientists did this, they found over 20,000 geometric shapes — ditches, mounds, and enclosures — built by ancient people long before Europeans arrived. These aren't small things: they're massive earthen structures, like monuments. This means the Amazon rainforest, which most people picture as empty wilderness, was actually home to millions of people who built cities and shaped the landscape. Think of it like discovering that a forest you thought was wild was actually someone's ancient garden on a continental scale.

Nature·

A digitally controlled silicon quantum processing unit

Imagine you want to build a super-powerful calculator that uses the weird rules of quantum physics to solve problems no regular computer can. The trouble is, the tiny quantum pieces — called qubits — are incredibly fragile and need to be kept colder than outer space. On top of that, you need wires and control signals going to every single qubit, and if you have thousands of them, the wiring becomes a nightmare. This team solved part of that puzzle by building their qubits out of silicon (the same stuff in your phone's chip), adding a tiny control computer that works at super-cold temperatures right next to the qubits, and using a special high-density cable to connect everything cleanly. They packed 54 tiny quantum dots onto a chip, arranged 18 of them into working qubits, and showed the qubits work about 10 times better than any previous silicon qubit of this type. They also ran basic error-correction experiments to prove the system is on track for real-world use.

Scientific American·

The 2026 World Cup's grass is an engineering problem

Imagine you're trying to play soccer in 16 different places across the United States, Canada, and Mexico — some in freezing cold, some blazing hot, some in stadiums with roofs that block sunlight. Half of those stadiums normally use fake grass. Now FIFA, the organization that runs the World Cup, wants every single pitch to feel and play exactly the same way, like a video game where every level has identical physics. To do that, they hired grass scientists — yes, that's a real job — who figured out how to grow special grass on thin mats with plastic underneath so it can be transported like a carpet, stitched with synthetic fibers so it doesn't rip when players sprint and tackle, and tested by literally shooting balls at it with a cannon to make sure it bounces right. Different grass species are used depending on whether a stadium is hot, cool, or dark. It's basically a giant, living, high-tech floor installation that has to survive the world's best athletes running on it.

Monthly Notices of the Royal Astronomical Society·

Remarks on the disproof of the unit distance conjecture

Imagine you scatter a bunch of dots on a piece of paper. The question is: how many pairs of those dots can be exactly 1 inch apart? The Erdős unit distance conjecture asked whether there's a specific mathematical formula that limits how often this can happen as you add more and more dots. Think of it like asking how many friendships can exist in a town where friends are defined as people who live exactly one mile apart — there's a suspected maximum, and Erdős guessed what that maximum should be. For decades, no one could prove or disprove his guess. Now, an AI apparently found a specific arrangement of dots (a 'counterexample') that breaks the expected limit, proving Erdős's conjecture was wrong. A team of elite mathematicians then checked and explained the AI's work in this paper.