Seung Sae Hong

Scalable fabrication of sub‐20 nm multi‐material nanoarchitectures remains a key challenge due to material incompatibilities and integration complexity. Here, we introduce a cooperative solvent–thermal nanotransfer printing (ST‐nTP) technique that enables single‐step, high‐resolution patterning of compositionally heterogeneous materials. The process exploits a synergistic interplay between solvent‐induced polymer swelling and thermal‐pressure‐driven densification to achieve selective material transfer through partially open shadow masks. When combined with the directed self‐assembly of block copolymers, ST‐nTP produces hierarchical 3D multi‐metal nanoarchitectures with nanoscale precision and spatial material selectivity. As a functional demonstration, these structures are deployed as tunable surface‐enhanced Raman scattering (SERS) platforms. Distinct plasmonic responses across metal–wavelength combinations facilitate multi‐dimensional molecular profiling, enabling the extraction of complementary vibrational signatures from complex biological analytes such as E. coli . This cooperative solvent–thermal nanofabrication strategy expands the design space for integrated nanostructures and offers a versatile route for advanced sensing, diagnostics, and optoplasmonic applications.

Three‐dimensional (3D) printing based on stereolithography (SLA) enables microstructured objects, but sub‐100 nm surface resolution remains difficult because of photopolymerization and resin diffusion. Here, we present a nano‐seed‐assisted SLA method for integrating sub‐50 nm surface nanopatterns with 3D‐printed structures. Si master molds with diverse nanoscale geometries are replicated into polymethyl methacrylate (PMMA) nano‐seed templates, enabling controlled resin infiltration and high‐fidelity pattern transfer from 250 nm to micrometer scales, including dots, holes, waves, and crosses. A conformal ultrathin inorganic barrier layer, such as platinum (Pt) or Ga ₂ O ₃ , suppresses resin‐polymer intermixing, confines curing at the interface, and preserves pattern integrity. The method yields uniform sub‐50 nm nanopatterns over chip‐scale and larger areas up to 45 × 75 mm, verified by high‐resolution TEM and elemental mapping. It integrates decorative or functional nanopatterns with complex 3D objects, exemplified by a 3D‐printed Buddha sculpture. In addition to the hybrid assembly of separately prepared nanopatterned inserts, we further demonstrate the direct fabrication of a monolithic Buddha structure containing a localized nano‐seed‐derived patterned region, confirming that nanoscale surface ornamentation can be incorporated during the SLA printing process without requiring post‐print assembly. Overall, nano‐seed‐assisted SLA offers a scalable route to high‐resolution nanostructuring in 3D‐printed materials.

Topotactic phase transitions between perovskite SrCoO₃ and brownmillerite SrCoO_2.5 have garnered attention for application in energy-efficient neuromorphic computing systems. However, the evolution of local microstructures, crucial for designing topotactic devices and improving switching performance, remains underexplored due to the limitations of epitaxial thin films bound to bulk substrates. Here, we report the synthesis and characterization of topotactic oxide SrCoO_x as a freestanding membrane, successfully stabilizing both perovskite and brownmillerite phases. Plan-view transmission electron microscopy identifies the extraordinary formation of filamentary one-dimensional (1D) domains of SrCoO_2.5 phases during the topotactic phase transition, correlated with the 1D oxygen vacancy channels that facilitate rapid oxygen ion diffusion. These 1D domains serve as direct evidence of the anisotropic nature of the topotactic phase transition, dictated by oxygen diffusion. These findings also underscore the advantages of freestanding membrane geometries for developing a fundamental understanding of phase transitions in complex oxides.

Solid phase epitaxy (SPE) has been widely employed for various thin-film materials, making it valuable for industrial applications due to its scalability. In complex oxides, SPE has been limited to a few materials because of the challenges in maintaining stoichiometric control during growth, particularly when volatile phases are present at high temperatures. Here, we investigate the impact of encapsulation layers on the SPE of complex oxides, using SrRuO3 (SRO) as a model system. An amorphous SRO layer was deposited on a SrTiO3 (STO) substrate, followed by the transfer of a single-crystalline STO membrane as an encapsulation layer in order to suppress the evaporation of volatile species (RuO2) during the SPE process. Whereas both encapsulated and unencapsulated SRO layers were successfully crystallized, the unencapsulated films suffered a substantial loss of Ru ions—exceeding 20%—compared to their encapsulated counterparts. This loss of Ru ions led to a loss of metallicity in the unencapsulated SRO layers, whereas the encapsulated layers retained their metallic ferromagnetic properties. This study demonstrates that the encapsulation provided by oxide membranes effectively suppresses stoichiometric loss during SPE, presenting a new strategy in stabilizing a broader class of functional oxides as epitaxial thin films.

Straining an oxide membrane: Perovskite manganites, such as La _0.7 Ca _0.3 MnO ₃ , have complex phase diagrams with many competing states. Among the knobs that can be used to control their properties are magnetic field and strain. Hong et al. placed membranes of La _0.7 Ca _0.3 MnO ₃ on a flexible polymer layer (see the Perspective by Beekman). Stretching the flexible layer resulted in large strains of up to 8% on the membrane. By varying the magnitude and direction of the strain, the researchers were able to explore the phase diagram of the system and influence its magnetic and transport properties. Science , this issue p. 71 ; see also p. 32

Long-range order and phase transitions in two-dimensional (2D) systems—such as magnetism, superconductivity, and crystallinity—have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO₃, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO₃ membrane lattice collapses below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. The transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices.

We report low-temperature, magnetotransport measurements of ferrocene-doped Bi₂Se₃ nanoribbons grown by vapor–liquid–solid method. The Kondo effect, a saturating resistance upturn at low temperatures, is observed in these ribbons to indicate presence of localized impurity spins. Magnetoconductances of the ferrocene-doped ribbons display both weak localization and weak antilocalization, which is in contrast with those of undoped ribbons that show only weak antilocalization. We show that the observed magnetoconductances are governed by a one-dimensional localization theory that includes spin orbit coupling and magnetic impurity scattering, yielding various scattering and dephasing lengths for Bi₂Se₃. The power law decay of the dephasing length on temperature also reflects one-dimensional localization regime in these narrow Bi₂Se₃ nanoribbons. The emergence of weak localization in ferrocene-doped Bi₂Se₃ nanoribbons presents ferrocene as an effective magnetic dopant source.