A Chinese research team has broken through one corner of the long-standing "impossible triangle" of one-dimensional metal wires—vacuum stability, robustness, and length. Published online August 20 in *Science* (Vol. 393, Issue 6813, pp. 826–830, DOI: 10.1126/science.aeg0028), a team led by Prof. Li Kuo at the Center for High Pressure Science and Technology Advanced Research (HPSTAR) pushed single-atom-diameter metal wires to the micrometer scale for the first time: individual chains exceed 1 μm, containing more than 4,000 continuously arranged copper atoms—over two orders of magnitude longer than the longest single-metal atomic chains (SMACs) previously reported internationally.
How They Did It: High-Pressure Solid-State Topological Polymerization
For decades, SMACs have been trapped in a trilemma: vacuum requirement, stability, and length—you could only pick two. Solution-synthesized SMACs rarely exceeded 10 atoms; a few nickel chains topped out at 28 before falling apart. Li's team's solution in one sentence: compress first, then lock it in.
The precursor is β-copper phthalocyanine (β-CuPc), the main crystal form of phthalocyanine blue pigment—central copper ions are periodically arranged along the molecular stacking direction, surrounded by 18π-electron unsaturated aromatic rings. When single crystals were compressed to ~0.9 GPa in a diamond anvil cell, β-CuPc underwent a structural phase transition, with the intermolecular slip angle decreasing from 45.5° to 28.6° for denser packing; at 21.5 GPa, the peripheral aromatic rings polymerized with each other; and at 25.0 GPa / 533 K held for 12 hours, a saturated sp³-hybridized carbon skeleton formed a dense protective sheath around the copper atoms, "freezing" the pressure-aligned copper chains for recovery to ambient conditions.
To overcome the tiny sample sizes of diamond anvil cells, the team used a Paris-Edinburgh press at ~40 GPa for bulk synthesis, yielding single crystals up to about 940 × 250 × 50 μm³. X-ray diffraction, selected-area electron diffraction, and HAADF-STEM jointly confirmed a Cu–Cu periodicity of 2.57 Å along the chains with highly ordered alignment.
An acid-assisted ultrasonic exfoliation strategy—3% trifluoroacetic acid—pulled individual chains out of the lattice: exfoliated chains exceeded 1 μm, corresponding to 4,000+ consecutive copper atoms. The chains remained intact even after hours of sonication and prolonged soaking in TFA—credit the sp³ carbon sheath.
The "Sandwich Structure" and Anomalous Electrical Properties
The surprising part isn't the length—it's the physics. Density functional theory calculations and measurements paint this picture: although adjacent copper ions are compressed to 2.57 Å, no significant Cu–Cu chemical bonds form, and the nanowire core constructs a unique one-dimensional antiferromagnetic chain—Curie-Weiss temperature θ_CW = -34.2 K, confirmed by SQUID susceptibility measurements.
The electrical behavior is even more interesting. Measured conductivity along the chain direction is 5.5×10⁻³ S/m (limited by grain boundaries), while DFT predicts up to 2.5×10⁷ S/m for an ideal defect-free structure; perpendicular to the chains it is only 1.2×10⁴ S/m—an anisotropy of more than three orders of magnitude. Crucially, the conducting channels are not Cu-d electrons but p-electrons of the secondary carbon framework—the extreme compression causes p-orbitals along the chain to overlap, forming continuous 1D charge-transport channels. Theorists have summarized this picture as an "insulating sheath + conducting intermediate layer + antiferromagnetic core" sandwich structure.
Generality: Not Just Copper
The team also tested CoPc, NiPc, ZnPc, and metal-free H₂Pc—all precursors produced structurally similar carbon-coated 1D polymeric structures after high-pressure treatment. This means the strategy extends to cobalt, nickel, zinc, and other metals, and could even enable mixed-metal atomic chains and 1D heterostructures—an experimental platform for molecular wires, spintronic devices, and single-electron transistors.
Why This Matters
First, it solves the bottleneck problem that 1D condensed-matter physics has long lacked sufficiently long, stable, and large samples. Classic theories—Peierls transitions, Tomonaga-Luttinger liquids, 1D magnetism—have long suffered from the absence of suitable experimental samples. Now they have one.
Second, it is a genuine "bottom-up" candidate for nanocircuitry. As silicon-based processes approach their physical limits, the road ahead leads toward the 1D limit—and single-atom-diameter metal wires are the material basis of that route.
Third, academician Ho-kwang (Dave) Mao's comment highlights the vision: "Atom-scale ultrathin metal wires promise to offer entirely new material options for next-generation nanocircuits, flexible wearable electronics, and more."
The research was completed by HPSTAR jointly with Nankai University, Peking University, and South China University of Technology; doctoral student Zhang Jie is first author and Li Kuo is corresponding author. The work was funded by the National Key R&D Program and the National Natural Science Foundation of China, with support from the User Facility for Extreme Conditions, Shanghai Synchrotron Radiation Facility beamlines BL17UM/BL14W1, and SPring-8 beamline BL10XU in Japan.
One-dimensional metal wires are no longer "figures in papers"—they are real objects that can be exfoliated, measured, and arrayed.
References: Science online 8/20 (DOI: 10.1126/science.aeg0028), Xinhua 8/21, CCTV News, HPSTAR full-text post, China.com.cn, commentary by academician Ho-kwang Mao, *Science* Vol. 393, Issue 6813, pp. 826–830.