Hot Electrons Print Metals in 3D at Nanoscale Precision

By Samudrapom DamReviewed by Susha Cheriyedath, M.Sc.Jun 30 2026

A femtosecond laser-driven method fuses metal nanocrystals into intricate 3D structures, pointing to cleaner, lower-energy routes for nanoscale manufacturing.

Paper: 3D nanoprinting of metals by spatiotemporally confined hot electrons via multiple-electron excitations in nanocrystals. Image credit: AI-generated image created using ChatGPT/OpenAI 

A paper recently published in the journal Nature Communications demonstrated a metal-printing method that uses spatiotemporally confined hot electrons to enable high-precision metal printing with low pulse energy. This method provides a polymer-free approach for flexible nanoscale metal printing at relatively low processing temperatures.

Challenges in Metal Nanoprinting

Metal three-dimensional (3D) printing is used to produce end-use components in the energy, aerospace, automotive, and medical sectors. Yet, achieving nanoscale resolution remains difficult, as it requires rigorous control over the growth, coalescence, and nucleation of metal atoms.

Most existing methods rely on additives such as ligands, resists, or polymers to preserve structural integrity and guide deposition. However, these additives hinder the formation of pure metal and limit the achievable material properties unless they are removed by pyrolysis at high temperatures.

Electrically stimulated reactions or focused energetic beams can be used to directly deposit metals from ionic or atomic precursors in polymer-less methods.

Yet, methods such as focused electron beam-induced deposition, two-photon decomposition without polymer additives, and localized pulsed electrodeposition suffer from limitations such as limited scalability, slow growth rates, a requirement for ultrafast laser pulses, and limited resolution.

While nanoscale metal printing methods employing molds or masks increase throughput, these approaches depend on prefabricated molds or masks, which hinder the production of free-form, arbitrary metal nanostructures.

Different laser-beam modulation approaches, including spatiotemporal modulation, have demonstrated their potential to enhance printing throughput while retaining the flexibility of maskless strategies.

In nanoscale 3D printing of metals, mask-based strategies offer high throughput, and maskless methods provide greater flexibility. In maskless methods, achieving high-quality, flexible metal printing is an active research field, as it requires effective control over nanoparticle assembly or atomistic coalescence while limiting the use of excessive energy, additives, or polymers that degrade printing quality.

The Proposed 3D Nanoprinting Approach

In this work, researchers at Texas A&M University demonstrated an approach for 3D nanoprinting of metals with depth and lateral resolution of <250 nm. They introduced a metal printing approach employing spatiotemporally confined hot electrons for high-precision metal printing using low pulse energy.

The team used commercial gold, silver, and platinum nanocrystal (NC) inks, while copper, nickel, and cobalt NCs were synthesized in-house under a nitrogen atmosphere. All chemicals were used as received and handled in a glove box.

Printing of Structures

Researchers synchronized an x-y-z axis piezo stage using a two-dimensional (2D) galvo scanner for fabricating arbitrary 3D objects to show the 3D printing of nanostructures.

Both free-space direct printing and layer-by-layer stacking were employed to ensure flexibility in printing different structures and compatibility with common methods used in commercial 3D printing.

Typical parameters for 3D nanoprinting included 50–270 µW laser powers, 1 kHz to 10 MHz repetition rates, and 1–10 µm s^-¹ scan speeds. Researchers printed a 10 × 10 array of spiral structures that demonstrated exceptional uniformity throughout.

Additionally, they fabricated volumetric complex 3D architectures, including a hierarchical mechanical metamaterial (HMM), a miniature Statue of Liberty, a dome-shaped architecture, and an Eiffel Tower-like structure, to assess the abilities of the nanoprinting method.

Boat-shaped complex structures were also fabricated using several metals, including gold, platinum, silver, copper, nickel, and cobalt, to evaluate the reliability and versatility of the demonstrated nanoprinting system.

Effectiveness of the Approach

Researchers successfully demonstrated 3D nanoprinting of metals with depth and lateral resolution below 250 nm. The method employed femtosecond laser-induced hot electrons spatiotemporally confined within NCs to enable nonlinear multi-electron absorption, ligand desorption, and NC fusion.

It operated at a pulse energy approximately 100 times lower than simultaneous multi-photon processes, avoided polymer additives while using ligands that were desorbed during printing, and remained compatible with free-space and layer-by-layer printing.

Printing of multiple metals was demonstrated, with mechanical strengths comparable to those of pure metals, along with functional optical and mechanical metamaterials.

To evaluate the mechanical performance of the printed structures, researchers fabricated a cubic body-centered gold HMM and performed scanning electron microscopy (SEM)-based quasi-static in situ uniaxial compression testing.

SEM images showed localized buckling and unit-cell distortion under maximum compressive displacement while preserving overall structural integrity. During unloading, the HMM recovered its geometry without collapsing or fracturing, with peak compressive strain of 25% and 40.7% recovery, demonstrating dense structural integrity and high printing consistency.

The measured Young's modulus for printed silver, gold, platinum, nickel, cobalt, and copper was 22.3, 33.3, 86.0, 65.5, 71.6, and 39.5 GPa, corresponding to 26%, 45%, 51%, 33%, 34%, and 31% of their respective bulk values. These values indicate strong mechanical performance but also show that stiffness remained below that of bulk metals.

Notably, the HMM was tested in its as-printed state, while the single nanopillars used for Young’s modulus measurements were post-sintered at 350 °C for five minutes before testing.

In conclusion, the demonstrated technology allows customizable 3D nanoprinting of metals for advanced applications in metamaterials, semiconductor manufacturing, biotechnology, sensors, and nanorobotics.

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