A tiny gap with huge consequences
Image Credit: Technische Universität München
Scientific Frontline: Extended "At a Glance" Summary: 2D Materials and the van der Waals Gap in Semiconductors
The Core Concept: When ultrathin 2D semiconductor materials are layered with insulating oxides to build microchips, a minute structural void inevitably forms between them. This interface gap drastically degrades capacitive coupling and establishes a fundamental physical limit on further electronic miniaturization.
Key Distinction/Mechanism: Unlike tightly bonded material combinations, many 2D materials (such as graphene or molybdenum disulfide) and their paired insulators are held together exclusively by weak van der Waals forces. This results in a 0.14-nanometer gap—thinner than a single sulfur atom—preventing the close contact required for the transistor's gate to precisely control the electric fields within the active semiconductor layer.
Major Frameworks/Components:
- 2D Semiconductor Materials: Ultrathin active layers comprising just one or a few atomic layers, previously assumed to be ideal for shrinking electronic components.
- Gate Insulators: Essential oxide layers designed to separate the active semiconductor from the gate electrode in transistors.
- Van der Waals Forces: Weak intermolecular interactions that fail to form a flush, highly conductive bond between the 2D material and the insulator.
- Capacitive Coupling: The electrical modulation mechanism that is severely weakened by the nanometer-scale gap, effectively neutralizing the intrinsic benefits of the 2D materials.
- "Zipper" Materials: A proposed theoretical and material framework where the semiconductor and insulator are designed to structurally interlock from the outset, forming a strong bond that entirely eliminates the interface gap.
Branch of Science: Microelectronics, Materials Science, and Solid-State Physics.
Future Application: This research directs future engineering efforts toward the synthesis of "zipper" materials that bond securely without gaps. Such interlocking components will serve as the architectural foundation for the next generation of highly compact, efficient computer chips and ultra-small electronic devices.
Why It Matters: This discovery acts as a critical corrective measure for the global semiconductor industry. By proving that standard 2D material stacking is fundamentally restricted by the laws of physics at the interface level, it redirects billions of dollars in research and development away from dead-end technologies and toward viable, gapless material integrations.
2D materials are widely seen as a promising path toward better computer chips. Researchers at TU Wien now show some of these materials are unsuitable due to an underestimated effect. But there are alternatives.
The miniaturization of electronic components has been a tremendous success story, driving technological progress for decades. Work is already underway on the next revolution in computer chips: 2D materials—ultrathin layers consisting of just one or a few atomic layers—could be ideally suited for even smaller electronic structures.
However, researchers at TU Wien have now shown that many 2D materials once considered highly promising are in fact unsuitable for this purpose. It is not enough to study the properties of the material itself—interface effects must also be taken into account. When 2D materials are combined with an insulating layer, an extremely thin gap inevitably forms between them, drastically degrading their electronic properties. The good news is that this approach also allows researchers to identify which materials are not affected by this problem—potentially saving the semiconductor industry from investing billions in technologies that are fundamentally limited by the laws of physics.
It’s not just the material—it’s the interface
“For many years, researchers have quite rightly been fascinated by the remarkable electronic properties of novel 2D materials such as graphene or molybdenum disulfide,” says Prof. Mahdi Pourfath, who carried out the research together with Prof. Tibor Grasser at TU Wien’s Institute for Microelectronics. “What is often overlooked, however, is that a 2D material alone does not make an electronic device. We also need an insulating layer—usually an oxide. And this is where things become more complicated from a materials science perspective.”
The basic concept of transistors used in computer chips is simple: the conductivity of a semiconductor—this can also be an ultrathin 2D material—can be modulated between conducting and non-conducting states. Which of these states occurs is controlled by the gate, an electrode that must be separated from the active material by an insulating layer.
Mind the gap!
This insulating layer must be as thin as possible in order to allow precise control of the electric fields in the 2D material, enabling extremely small and compact devices. However, when these structures are analyzed at the atomic scale, a problem emerges that has so far received little attention.
“In many combinations of 2D materials and insulating layers, the bonding between them is relatively weak,” explains Grasser. “They are held together only by so-called van der Waals forces, which provide only a weak attraction between the semiconductor and the insulator. As a result, the two layers do not come into close contact—there is always a gap between them.”
This gap is tiny—only about 0.14 nanometers, thinner than a single sulfur atom—yet it has a major impact on electronic performance. A SARS-CoV-2 virus, for comparison, is roughly 700 times larger. “This gap weakens the capacitive coupling between the layers. No matter how good the intrinsic properties of the materials may be, the gap can become the limiting factor. As long as it exists, it imposes a fundamental limit on how far these devices can be miniaturized.”
The solution: “zipper” materials
“If the semiconductor industry wants to succeed with 2D materials, the active layer and the insulating layer must be designed together from the very beginning,” emphasizes Mahdi Pourfath. There are possible solutions: so-called “zipper materials” combine both aspects. Semiconductor and insulator interlock with each other—they are not just loosely connected by van der Waals forces but form a stronger bond that eliminates the gap.
“Our work is good news for the semiconductor industry,” says Tibor Grasser. “We can predict which materials are suitable for future miniaturization steps—and which are not. But if one focuses only on the 2D materials themselves, without considering the unavoidable insulating layers from the outset, there is a risk of investing billions in an approach that simply cannot succeed for fundamental physical reasons.”
Published in journal: Science
Title: Device-scaling constraints imposed by the van der Waals gap formed in two-dimensional materials
Authors: Mahdi Pourfath, and Tibor Grasser
Source/Credit: Technische Universität München
Reference Number: mcrt042026_01