Abstract In situ sensing in extreme environments requires waveguide media that can withstand ultrahigh temperatures, intense radiation, and large mechanical strains. Here, [100]-, [110]-, and [111]-oriented magnesium aluminate spinel (MgAl2O4) single-crystal fibers (SCFs) were fabricated by the laser-heated pedestal growth (LHPG) method for the first time, with diameters down to 50 μm and lengths exceeding 1 m. High-temperature exposure produces extensive surface deposition together with aligned linear features and triangular faceted surface features. Sapphire-tube protection markedly suppresses surface deposition and reduces both high-temperature and irreversible attenuation, identifying external deposits as a major source of optical loss. The triangular features remain compositionally close to the MgAl2O4 matrix, whereas Ar treatment produces isolated Mg-depleted, Al-rich faceted crystallites. Furthermore, MgAl2O4 SCF Bragg gratings (MFBGs) were fabricated by femtosecond-laser inscription and evaluated for high-temperature sensing. The [111]-oriented MFBG exhibits a temperature sensitivity of 39.54 pm/°C at 1600 °C and no observable Bragg wavelength drift after γ-ray irradiation to 21.6 kGy. The MFBGs also exhibit a stable strain response, with a sensitivity of 1.63 pm/με at 1600 °C under strains up to 1440 με. These results demonstrate the potential of MgAl2O4 SCFs and the corresponding MFBGs for multi-parameter sensing in extreme environments.
Abstract This study investigated the structure−property relationship of DNA-functionalized gold nanoparticle (DNA-AuNP) colloidal single crystals composed of ordered superlattices using small-angle X-ray scattering (SAXS) and rotational crystallographic analysis. We obtained colloidal single crystals suitable for single-crystal SAXS measurements using heavy water (D2O) as an alternative growth medium. The crystal enlargement is discussed in terms of suppressed early-stage nucleation, reduced nanoparticle diffusion, and possible isotope effects on DNA duplex stability. The increase in crystal dimensions enabled the detailed structural characterization of the internal lattice arrangement and three-dimensional order of the DNA-AuNP superlattice. The diffraction profiles exhibited well-defined Bragg reflections, which allowed the quantitative assessment of lattice broadening and internal lattice coherence under different growth conditions. The D2O-grown DNA-AuNP superlattice crystals exhibited measurable surface-enhanced Raman scattering (SERS) activity using rhodamine B as a probe molecule. Boundary element method simulations showed that the average integrated |E|4 enhancement remained comparable over the investigated range of lattice disorder, whereas the spatial distribution and variability of the electromagnetic hotspots changed with the gSC-factor. These results demonstrate the SERS functionality of the DNA-AuNP superlattice crystals and suggest that moderate structural disorder mainly affects hotspot uniformity rather than the average electromagnetic enhancement. These findings clarify the relationship between the structural characteristics of DNA-AuNP superlattices and their optical functionality, and provide insights into the development of DNA-programmed plasmonic superlattices with tunable structural and optical properties.
Abstract Hexagonal lutetium ferrite (h-LuFeO3) is a promising multiferroic material, but its low Néel temperature (TN ≈ 130 K) limits its room-temperature applications. Herein, we demonstrate that epitaxial strain engineering enables robust tuning of its structural, ferroelectric, and magnetic properties. High-quality h-LuFeO3 thin films were epitaxially grown on yttria-stabilized zirconia (YSZ) (111) and Al2O3 (0001) substrates, introducing tensile and compressive strain, respectively. Atomic-scale scanning transmission electron microscopy analysis reveals that tensile strain reduces the c/a ratio of the h-LuFeO3 crystal lattice, while compressive strain increases the c/a ratio. Combined first-principles calculations and Monte Carlo simulations elucidate that tensile strain weakens the antiferromagnetic exchange interaction, lowering TN to approximately 50 K, whereas compressive strain strengthens the exchange coupling, raising TN to approximately 200 K. The strain-induced variation of TN follows a linear correlation with the c/a ratio. These results establish the c/a ratio as a quantitative structural descriptor, demonstrating that strain engineering is a powerful strategy to tailor the multiferroic properties of h-LuFeO3, with compressive strain offering a promising route toward room-temperature multiferroic applications.
Abstract Balancing a wide optical band gap with large birefringence remains a key challenge in the design of short-wavelength birefringent materials. Herein, two Sb(III)−Nb(V) oxyfluorides, Rb4(SbF4)2(NbOF5) (I) and Cs8Sb4Nb5O5F35 (II), were investigated in terms of their crystal structures and optical properties. Compound I contains spatially isolated Sb- and Nb-centered units, whereas II features multiple inequivalent Sb−O/F and Nb−O/F coordination environments assembled into finite heterometallic aggregates. Both compounds exhibit relatively wide optical band gaps of 4.60 and 4.46 eV, respectively, while their birefringences reach 0.078 and 0.154 at 546 nm. Structural and theoretical analyses show that II contains a highly asymmetric [SbF3O] unit with pronounced local polarizability anisotropy, together with differentiated Nb−O/F coordination environments and a distinct organization of the anisotropic Sb- and Nb-centered units. These structural characteristics are consistent with its larger birefringence. These findings provide insight into the relationship between local coordination environments and optical properties in Sb(III)−Nb(V) oxyfluorides.
N-polar InGaN provides an attractive route to long-wavelength optoelectronic devices. However, the growth of N-polar InGaN quantum wells with high In composition is still limited by the trade-off between In incorporation and crystalline quality. Although underlayer strain engineering has been widely used to address this trade-off in metal-polar InGaN, its role in N-polar InGaN growth remains insufficiently understood. In this work, first-principles calculations are employed to elucidate the effects of biaxial strain in the underlying N-polar GaN on In-related adsorption and incorporation during InGaN growth. Our calculations show that tensile strain stabilizes InGaN adsorption relative to GaN adsorption at both step terminations without altering their distinct step selectivities, thereby promoting In incorporation through a GaN-dominated step-flow pathway without aggravating alternating-step attachment asymmetry. After lattice incorporation, tensile strain generally weakens In segregation, with this tendency also modulated by surface reconstruction. A quantitative strain-composition relationship is further established for N-polar InGaN under MOCVD conditions based on a cooperative multi-In incorporation pathway. Importantly, this relationship reproduces the experimentally observed strain dependence of In composition. This work provides atomic-scale insights into strain-modulated N-polar InGaN growth and offers guidance for high-quality InGaN quantum wells with high In composition.
