Metals, semiconductors and insulators are fundamental components of modern electronics. However, efforts to improve device performance have focused mainly on semiconductor quality, while metal crystallinity has received much less attention. As transistor dimensions continue to scale down, structural disorder in metals and at metal–semiconductor interfaces increasingly hinders carrier injection and transport. Metals therefore need a level of structural order comparable to that of single-crystal semiconductors. This is essential for pushing device performance toward its physical limits.

To address this challenge, a research team led by Prof. CHU Junhao at the Shanghai Institute of Technical Physics, Chinese Academy of Sciences, developed Step-Eva, an atomic-scale stepwise evaporation method that enables the direct in situ growth of single-crystal metal films. The study was published in Science on Aug. 27.

Step-Eva divides metal deposition into repeated cycles consisting of an atomic-scale deposition dose followed by a prolonged stabilization pause. By temporally separating deposition from structural relaxation, the method creates a distinct growth-kinetic window that suppresses disordered secondary nucleation, promotes atomic diffusion and facilitates lateral domain coalescence. In this way, Step-Eva overcomes the competition between continuous nucleation and atomic diffusion inherent to conventional evaporation, enabling high-quality van der Waals epitaxial growth of long-range ordered single-crystal metals.

Step-Eva is broadly applicable to a range of metals, enabling the growth of high-quality single-crystal bismuth (Bi), silver (Ag), indium (In), gold (Au), and palladium (Pd). The resulting single-crystal metals form clean, low-damage metal–semiconductor interfaces and exhibit well-defined, spatially uniform work functions with minimal local potential fluctuations.

The resulting single-crystal metal contacts for 2D semiconductors exhibit strongly suppressed Fermi-level pinning, near-ideal Schottky–Mott behavior, and ultralow contact resistance. Both n-type and p-type 2D transistors exhibit on/off current ratios exceeding 10¹⁰, while devices with channel lengths scaled to 50 nm deliver on-state currents above 1.1 mA μm^-1, and the contact resistances of N-type and P-type transistors are as low as 36 Ω·μm and 145 Ω·μm, respectively, demonstrating highly efficient carrier injection and transport.

In addition, the single-crystal metals exhibit excellent dimensional scalability, retain continuous electrical conduction at ultrathin thicknesses, and show enhanced thermal stability. Such attributes could support further device scaling and high-density integration, providing a promising materials foundation for next-generation energy-efficient electronic and optoelectronic systems.

Figure 1.Growth mechanism of single-crystal metals via Step-Eva. Schematic illustration of the Step-Eva process and the resulting single-crystal Bi growth.

Figure 2. Generality of single-crystal metal growth via Step-Eva. Demonstration of diverse single-crystal metals, their well-defined work functions, and the electrical performance of n-type and p-type transistors.

Contact：

WANG Xudong E-mail:wxd0130@ mail.sitp.ac.cn