arXiv subjects

Dmytro Nykypanchuk

Publications and source records attributed to Dmytro Nykypanchuk.

4 recordsLinked to original sources

arXiv2026

Valence-free open nanoparticle superlattices

A cornerstone of advanced materials design is establishing a framework for assembling nanoparticle superstructures with tailored symmetries. A longstanding challenge has been assembling diamond-like superstructures for photonic devices. Traditionally, such open superstructures require functionalized nanoparticles with directional or anisotropic interactions, reminiscent of valence bonding in a diamond. Here, we present a robust strategy for assembling valence-free nanoparticles into a broad array of cubic superstructures. By grafting nanoparticles with oppositely charged, end-functionalized water-soluble polymers of adjustable molecular weight, we gain control over electrostatic interactions and conformational constraints. This unified approach yields lattices analogous to rock salt, CsCl, zinc-blende, diamond, and the rare simple cubic phase, with tunable lattice constants. Theoretical models and simulations elucidate the underlying interactions, providing a framework for engineering valence-free nanoparticle superlattices.

cond-mat.mtrl-sci↗

arXiv2025

Direct Imaging of Hydrogen-Driven Dislocation and Strain Field Evolution in a Stainless Steel Grain

Hydrogen embrittlement (HE) poses a significant challenge to the durability of materials used in hydrogen production and utilization. Disentangling the competing nanoscale mechanisms driving HE often relies on simulations and electron-transparent sample techniques, limiting experimental insights into hydrogen-induced dislocation behavior in bulk materials. This study employs in situ Bragg coherent X-ray diffraction imaging to track three-dimensional dislocation and strain field evolution during hydrogen charging in a bulk grain of austenitic 316 stainless steel. Tracking a single dislocation reveals hydrogen-enhanced mobility and relaxation, consistent with dislocation dynamics simulations. Subsequent observations reveal dislocation unpinning and climb processes, likely driven by osmotic forces. Additionally, nanoscale strain analysis around the dislocation core directly measures hydrogen-induced elastic shielding. These findings experimentally validate theoretical predictions and offer mechanistic insights into hydrogen-driven dislocation behavior. The quantified nanoscale phenomena serve as critical inputs for multiscale modeling frameworks to predict bulk material responses and accelerate the development of HE-resistant alloys.

cond-mat.mtrl-sci↗

arXiv2025

Single crystalline orthorhombic GdAlGe as a rare earth magnetic Dirac nodal-line metal

Crystal engineering is a method for discovering new quantum materials and phases, which may be achieved by external pressure or strain. Chemical pressure is unique in that it generates internal pressure perpetually to the lattice. As an example, GdAlSi from the rare-earth ($R$) $R$Al$X$ ($X =$ Si or Ge) family of Weyl semimetals is considered. Replacing Si with the larger isovalent element Ge creates sufficiently large chemical pressure to induce a structural transition from the tetragonal structure of GdAlSi, compatible with a Weyl semimetallic state, to an orthorhombic phase in GdAlGe, resulting in an inversion-symmetry-protected nodal-line metal. We find that GdAlGe hosts an antiferromagnetic ground state with two successive orderings, at $T_\mathrm{N1}$ = 35 K and $T_\mathrm{N2}$ = 30 K. In-plane isothermal magnetization shows a magnetic field induced metamagnetic transition at 6.2 T for 2 K. Furthermore, electron-hole compensation gives rise to a large magnetoresistance of $\sim 100\%$ at 2 K and 14 T. Angle-resolved photoemission spectroscopy measurements and density functional theory calculations reveal a Dirac-like linear band dispersion over an exceptionally large energy range of $\sim$ 1.5 eV with a high Fermi velocity of $\sim 10^6$ m/s, a rare feature not observed in any magnetic topological materials.

cond-mat.mtrl-sci↗

arXiv2024

Revealing the Origin and Nature of the Buried Metal-Substrate Interface Layer in Ta/Sapphire Superconducting Films

Despite constituting a smaller fraction of the qubits electromagnetic mode, surfaces and interfaces can exert significant influence as sources of high-loss tangents, which brings forward the need to reveal properties of these extended defects and identify routes to their control. Here, we examine the structure and composition of the metal-substrate interfacial layer that exists in Ta/sapphire-based superconducting films. Synchrotron-based X-ray reflectivity measurements of Ta films, commonly used in these qubits, reveal an unexplored interface layer at the metal-substrate interface. Scanning transmission electron microscopy and core-level electron energy loss spectroscopy identified an approximately 0.65 \ \text{nm} \pm 0.05 \ \text{nm} thick intermixing layer at the metal-substrate interface containing Al, O, and Ta atoms. Density functional theory (DFT) modeling reveals that the structure and properties of the Ta/sapphire heterojunctions are determined by the oxygen content on the sapphire surface prior to Ta deposition, as discussed for the limiting cases of Ta films on the O-rich versus Al-rich Al2O3 (0001) surface. By using a multimodal approach, integrating various material characterization techniques and DFT modeling, we have gained deeper insights into the interface layer between the metal and substrate. This intermixing at the metal-substrate interface influences their thermodynamic stability and electronic behavior, which may affect qubit performance.

cond-mat.mtrl-sci↗