Modern electronics depend on the interaction of three basic classes of material: metals, semiconductors and insulators. In the decades-long effort to make transistors faster and smaller, semiconductor quality has attracted most of the attention. That focus has produced remarkable advances, particularly in two-dimensional materials whose active layers can be only a few atoms thick. Yet the metal electrodes that inject current into these channels have often been treated as comparatively simple components. At very small dimensions, however, their crystal structure, surface morphology and chemical interface become critical. Structural disorder can scatter carriers, create local variations in electrical potential and produce energy barriers that prevent current from flowing efficiently. As transistor channels shrink, the resistance introduced by the contacts can become larger than the resistance of the semiconductor itself, undermining the benefits of an otherwise ideal channel.

The Step-Eva process is designed to overcome the limitations of conventional metal evaporation. In standard deposition, metal atoms are continuously supplied to a surface. They land, form small nuclei and spread through a competition between additional nucleation and surface diffusion. If new nuclei continue to appear before existing islands can reorganize, the growing film may become polycrystalline, with many differently oriented grains separated by defects and boundaries. The Chinese team’s approach divides deposition into repeated cycles. Each cycle begins with an extremely small, atomic-scale dose of metal, followed by a deliberately prolonged pause. During that pause, the deposited atoms have time to move across the surface, relax into energetically favorable positions and join neighboring domains. By separating the arrival of new atoms from the period of structural rearrangement, Step-Eva creates a controlled kinetic growth window that favors order over disorder.

This timing is central to the method’s operation. Continuous evaporation can drive a surface into a state where nucleation is constantly restarting, producing competing islands before the earlier ones have had time to expand laterally. Step-Eva suppresses that secondary nucleation by temporarily stopping the incoming flux. Surface atoms can then diffuse over longer distances, allowing existing domains to grow outward and merge. The process ultimately supports van der Waals epitaxy, a form of crystal growth in which an overlayer aligns with a substrate through relatively weak interfacial forces rather than conventional chemical bonding. For two-dimensional semiconductors, this is particularly useful because their atomically thin surfaces can provide a clean template without the severe lattice and chemical constraints found in traditional epitaxial systems. The resulting metal film can preserve long-range crystal order while remaining directly integrated with the semiconductor.

The researchers report that the method works with several technologically important metals, including bismuth, silver, indium, gold and palladium. These metals can form single-crystal films on semiconductor surfaces, creating interfaces with less damage and fewer structural irregularities than those produced by conventional processes. The ordered films also exhibit spatially uniform work functions, meaning that the energy required for electrons to move between the metal and semiconductor varies less from one location to another. That uniformity is important because nanoscale devices are highly sensitive to local fluctuations. A rough or chemically disordered interface can generate microscopic patches with different electrical properties, forcing carriers to navigate an uneven potential landscape. By contrast, a cleaner and more uniform interface should make carrier injection more consistent across the device and from one device to the next.

One of the most significant reported effects is the strong reduction of Fermi-level pinning. At many metal–semiconductor interfaces, electronic states created by defects or chemical reactions lock the semiconductor’s Fermi level into a narrow range. This pinning limits the ability of engineers to choose a metal that produces the desired contact behavior. Instead of following the expected relationship between the metal work function and the semiconductor energy bands, the interface develops an unwanted barrier that can impede either electron or hole injection. The single-crystal contacts produced with Step-Eva show much weaker pinning and approach Schottky–Mott behavior, the idealized model in which the energy barrier is determined mainly by the difference between the metal work function and the semiconductor’s electron affinity or ionization energy. This gives designers greater control over whether a contact favors electrons, holes or both.

The electrical measurements suggest that the improvement is not merely structural. Both n-type and p-type two-dimensional transistors fabricated with the contacts achieved on/off current ratios above 10¹⁰, indicating that the devices could strongly distinguish their conducting and nonconducting states. In transistors with channel lengths reduced to 50 nanometers, the on-state current exceeded 1.1 milliamperes per micrometer. The reported contact resistance was as low as 36 ohm-micrometers for n-type devices and 145 ohm-micrometers for p-type devices. Contact resistance is commonly normalized by the width of a transistor, so these values describe how much resistance is associated with injecting carriers through a contact per unit device width. Lower values mean that a larger fraction of the current supplied by the electrode can enter the channel, allowing the semiconductor’s intrinsic properties to influence the circuit rather than being masked by the electrodes.

The films also displayed characteristics that could matter as transistor architectures become more densely packed. According to the researchers, the single-crystal metals remained electrically continuous even when made extremely thin, an important requirement for contacts that must fit within shrinking device geometries. They also showed enhanced thermal stability, which could help preserve performance during fabrication and operation. Heat is a major concern in densely integrated electronics because temperature changes can alter the metal structure, increase resistance or trigger diffusion across the interface. A stable, ultrathin contact could therefore support not only smaller transistors but also more reliable arrays containing millions or billions of devices. The method’s reported compatibility with several different metals further suggests that it may be adaptable to circuits requiring distinct contact properties, although broader manufacturing studies will be needed to determine how consistently the process can be applied over large areas.

The results place the metal electrode, rather than only the semiconductor channel, at the center of the next phase of transistor engineering. Two-dimensional materials have long been viewed as promising candidates for continued miniaturization because their thinness offers strong electrostatic control and may reduce short-channel effects. Yet their potential has been constrained by the difficulty of forming low-resistance, low-damage contacts. Step-Eva offers a way to address that bottleneck by treating metal growth as a carefully timed structural process instead of a simple continuous coating operation. If the approach can be integrated with scalable manufacturing, it could influence future logic, memory, sensing and optoelectronic technologies. The reported performance does not by itself establish a production-ready platform, and questions remain about throughput, uniformity across large substrates and compatibility with industrial processing. Nevertheless, the ability to grow ordered metal contacts directly on semiconductors represents a significant advance toward nanoscale transistors in which both the channel and the electrodes are engineered at the atomic level.