Strain turns Ångström-thin semiconducting bismuth right into a metallic, increasing choices for reconfigurable electronics

Two-dimensional (2D) supplies, sparked by the isolation of Nobel-prize-winning graphene in 2004, has revolutionized trendy supplies science by exhibiting {that electrical}, optical, and mechanical behaviors may be tuned just by adjusting the thickness, pressure, or stacking order of such 2D supplies. From transistors and versatile show to neuromorphic chips, the way forward for electronics is predicted to be considerably empowered by 2D supplies.

In a brand new examine printed in Nano Letters titled “Strain-Pushed Metallicity in Ångström-Thickness 2D Bismuth and Layer-Selective Ohmic Contact to MoS₂,” researchers led by SUTD have found {that a} light squeeze is sufficient to make bismuth—one of many heaviest parts within the periodic desk—change its electrical character.

Utilizing state-of-the-art density purposeful concept (DFT) simulations, the workforce confirmed that when a single layer of bismuth, only some atoms thick, is compressed or “squeezed” between surrounding supplies, the atoms reorganize from a barely corrugated (or buckled) construction into a superbly flat one. This structural flattening, although refined, has dramatic digital penalties: it eliminates the vitality band hole and permits electrons to maneuver freely, turning the fabric metallic.

“As soon as the bismuth sheet turns into utterly flat, the digital states overlap, and the fabric all of the sudden conducts electrical energy like a metallic. The transformation is totally pushed by mechanical stress,” mentioned Dr. Shuhua Wang, a postdoctoral analysis fellow at SUTD.

Explaining a latest experimental shock

Earlier in 2025, a landmark Nature paper reported that when bismuth was squeezed between two layers of molybdenum disulfide (MoS₂) right down to the Ångström-thickness restrict, it behaved as a metallic, in sharp distinction to the semiconducting character predicted by a long time of theoretical research and former experiments on freestanding monolayers.

That surprising commentary posed an open query: Why does confined bismuth conduct electrical energy when its unconfined counterpart doesn’t?

This analysis gives the lacking theoretical rationalization. By linking stress, construction, and digital habits, the workforce demonstrated that van der Waals squeezing flattens the atomic lattice of bismuth, thus triggering the exact structural and digital transition wanted for metallicity.

A brand new strategy to rewire present

The researchers additional proposed a MoS₂-Bi-MoS₂ trilayer heterostructure, the place the atomically skinny bismuth acts as a metallic bridge sandwiched between two semiconducting layers.

Their simulations revealed a placing asymmetry: one MoS₂ layer varieties a low-resistance (Ohmic) contact with the metallic Bi, whereas the opposite varieties a higher-resistance (Schottky) barrier. By making use of an exterior electrical discipline perpendicular to the stack, the workforce confirmed that this Ohmic contact may be switched between the highest and backside layers, thus permitting electrical present to be steered between layers on demand.

This mechanism, termed a layer-selective Ohmic contact, marks a brand new milestone in 2D electronics. It generalizes the acquainted metallic–semiconductor interface right into a layer-dependent, field-controllable contact—the essence of layertronics, a tool idea that exploits the layer diploma of freedom in 2D supplies for information processing and storage.

“Conventional circuits are wired as soon as and stuck perpetually,” mentioned Assistant Professor Yee Sin Ang, the challenge lead and Kwan Im Thong Hood Cho Temple Early Profession Chair Professor in Sustainability at SUTD. “In MoS₂-Bi-MoS₂ trilayer heterostructure, we are able to reconfigure the place the present flows just by tuning an electrical discipline. Meaning the identical gadget can carry out a number of features with none bodily rewiring. It is a key step towards reprogrammable, energy-efficient nanoelectronics.”

Such advances could assist tackle one of many biggest challenges in trendy electronics: integrating ultrathin transistors and interconnects with out sacrificing contact efficiency. The flexibility to fine-tune contact habits by way of mechanical or electrical fields gives a robust, sustainable pathway towards the following era of versatile, low-power, and reconfigurable computing chips.