Two-dimensional materials — these extremely thin sheets of atoms — are considered the next big breakthrough in electronics. Yet a study from the University of Vienna reveals a limit at the atomic scale: a tiny gap that, although almost invisible, could ruin the performance of many promising candidates.
Transistors, the electronic switches at the heart of all our electronics and especially microprocessors, rely on a semiconductor material controlled by an electrode. To miniaturize further, the insulator separating these two elements must be reduced to an extremely thin level. Researchers have discovered a problem with certain combinations: the semiconductor and the insulator do not actually touch; an empty space of about 0.14 nanometers (5.5e-9 inches) persists, weakening the capacitive coupling and limiting miniaturization.
The nanometric gap between the 2D conductor and the insulator profoundly alters electronic properties.
Credit: TU Wien This problem stems from the weak van der Waals forces that must bind the layers together, a phenomenon of quantum electrodynamics. As Professor Tibor Grasser explains, this light force is not sufficient to keep the layers well aligned, and always leaves a gap, regardless of the intrinsic quality of the material. The only solution envisioned is to design "zipper-like" materials, where the semiconductor and the insulator fit tightly together, eliminating the gap.
The scientists have therefore established a method to predict which combinations will avoid this trap. For Professor Mahdi Pourfath, the industry must integrate the insulator into the design of future transistors from the very start, at the risk of investing billions in dead ends. This research, published in
Science, redraws the map of viable materials for the chips of tomorrow.
Van der Waals forces: a fragile atomic glue
Van der Waals forces are weak electromagnetic interactions that occur between nearby atoms or molecules. Unlike strong chemical bonds (such as covalent bonds), they do not require sharing electrons. They result from temporary fluctuations in charge that create magnetic dipoles.
In 2D materials like graphene, these forces ensure cohesion between layers. Their intensity depends on distance: the closer the layers, the stronger the attraction. But on surfaces that are not perfectly smooth or identical, a tiny gap (about 0.14 nm or 5.5e-9 inches) persists, reducing adhesion.
This weakness becomes apparent when stacking layers of different natures, such as a 2D conductor and an insulator. The atoms of the two materials cannot align perfectly, and van der Waals forces are insufficient to fill the gaps, creating voids that harm electronic performance.