Quantum-Well-Metasurface to Maximize Nonlinear Polarization

arXiv (Cornell University) · 2026-04-16

Nonlinear frequency conversion unlocks technologies ranging from telecommunications to quantum computation; however, weak nonlinearities and architectures that resist miniaturization currently limit devices. Here, we combine a bandstructure-engineered GaAs/AlGaAs heterostructure with a high quality factor dielectric metasurface to simultaneously tailor the intrinsic nonlinear susceptibility and optimize the electromagnetic field within the heterostructure. By engineering a resonant interband transition, we realize a large second-order nonlinear tensor element, 1.6 nm/V at 1.57 um wavelength. We then make it free-space-accessible and boost the effective nonlinearity to ~ 14 nm/V using a metasurface patterned on the material. Our proof-of-concept experiment establishes that interband transition engineering and metasurfaces accessing otherwise unusable nonlinear tensor elements enable giant effective nonlinearities in the near-infrared to visible spectrum. This addresses material and device-level constraints in nonlinear photonics, providing a scalable route to compact, efficient devices.

High-efficiency Pt75Au25-based spintronic terahertz emitters

Applied Physics Letters · 2026-02-23

Spintronic terahertz emitters (STEs) generate broadband THz radiation via ultrafast spin–charge conversion in magnetic multilayers, offering spectral coverage beyond that of photoconductive antennas and nonlinear optical crystals. Here, we demonstrate STEs based on a PtxAu100−x alloy that achieve significantly higher THz output power than widely used Pt-based devices. Alloy composition and layer thickness tuning yield Pt75Au25 as the optimal alloy, providing a 30% increase in THz power in CoFeB/Pt75Au25 bilayer STEs compared to the optimized CoFeB/Pt reference STE. In W/CoFeB/Pt75Au25 trilayer STEs, we observe a 10% higher THz power than in the optimized W/CoFeB/Pt trilayer. The STE efficiency is reduced upon annealing for both Pt75Au25- and Pt-based STEs due to the formation of interfacial alloys. Our results establish Pt75Au25 as a promising platform for high-performance STEs, where its giant spin Hall effect significantly enhances efficiency over conventional Pt-based devices.

Electrocatalytic Upcycling of Plastic Waste to Organonitrogen Chemicals via Intercepting Carbon Intermediates

Nano Letters · 2025-06-21 · 10 citations

) as C and N sources, respectively. Furthermore, amides were synthesized with real-world PET plastic waste as the C source, indicating the potential practical application of this proof-of-concept work.

A cation-exchange approach to tunable magnetic intercalation superlattices

Nature · 2025-06-25 · 21 citations

Dimensionally resolved nanostructures of an atomically precise and optically active 1D van der Waals helix

ChemRxiv · 2025-06-10 · 1 citations

Inorganic freestanding helices are rare and are sought-after for their unusual physical states endowed by chirality. To this end, III-VI-VII solids have emerged as a distinct class of ternary 1D van der Waals (vdW) crystals which bear atomically precise helical motifs. However, the physical understanding of the instrinsic and size-dependent properties of these materials is limited by the lack of synthetic strategies to directly access freestanding nanocrystals in high volumes. Using GaSI as a representative phase, we present a bottom-up strategy to grow high yields of ultrathin nanostructures based on this helical materials class. With this strategy, we were able to grow single crystals of 1D nanowires with thicknesess in the 10 to 100 nm range at high temperature conditions, as well as quasi-2D nanoribbons at lower temperatures. We establish the band gap of the nanowires in the UV region and demonstrate the persistence of nonlinear optical behavior originating from the non-centrosymmetric crystal structure of GaSI. Inspired by these results, we probe the effect of chirality on the electronic structure of hypothetical single chains of GaSI from first principles and show the pronounced handedness-dependent and chirality-driven spin polarization at the single helix regime.

Ternary-containing Al_0.7InAsSb digital alloys on InP and InP-on-Si [Invited]

Optical Materials Express · 2025-09-22 · 1 citations

Al x In 1−x As y Sb 1−y is a promising multiplier for avalanche photodiodes (APD) on InP for near-infrared applications. In this work, we investigated the potential of two different ternary-containing layer stacks for the growth of AlInAsSb digital alloys on InP and InP-on-Si templates with applications in future photodetectors. STEM measurements confirmed high-quality material and interfaces on both substrates with no evidence of phase separation. Low dark currents and high gains were measured from PIN diodes grown on both substrates, with slightly higher dark currents observed in the Si-based device due to defects resulting from lattice mismatch in the template.

Revealing the Role of Individual Metal-Support Interactions in Hydrogen Production for Heterogeneous Photocatalysts via 4DSTEM Techniques

Microscopy and Microanalysis · 2025-07-01

Atomic-scale imaging of frequency-dependent phonon anisotropy

Nature · 2025-09-17 · 5 citations

Direct Observation of Rh and La Dopant Positions in SrTiO ₃ Nanoparticles with Atomic-Scale Electron Microscopy

ACS Applied Materials & Interfaces · 2025-11-10 · 1 citations

Doped SrTiO3 nanoparticles constitute a leading materials platform for solar hydrogen production. One of the most ubiquitous and efficient SrTiO3 materials utilizes Rh and La as dopants, designed to improve both visible-light absorption and charge separation ability. Typically, dopant positions in the SrTiO3 lattice are assigned using ionic size and charge or ensemble-averaged techniques such as power X-ray diffraction or Raman spectroscopy. Direct observations of dopant locations in the SrTiO3 lattice have not been previously reported. Here, we apply atomic-scale scanning transmission electron microscopy (STEM) coupled with image processing to directly elucidate dopant locations in 2% Rh-doped SrTiO3 (Rh:SrTiO3) and 2% La, 2% Rh codoped SrTiO3 (La,Rh:SrTiO3). Ensemble measurements were first performed to quantify aggregate properties across many particles of each type. Measurements of H2 using in-line mass spectrometry suggest that the materials have different quantum yields for photocatalytic H2 evolution, and Raman spectroscopy suggest that the concentration of dopants in the B-site (Ti site) differs. Simultaneous atomic-scale STEM, energy-dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) were performed on individual nanoparticles to directly determine dopant locations. Results indicate that in Rh:SrTiO3, Rh occupies both the A-site and the B-site, which is unexpected because ionic radii argument suggests Rh will occupy only the B-site. In La,Rh:SrTiO3, La primarily occupies the A-site and Rh primarily occupies the B-site. Precise knowledge of dopant positions is used to inform density functional theory (DFT) simulations for each doped lattice’s electronic structure. These combined results suggest that La codoping can hinder photocatalytic H2 evolution activity when Rh dopants exist in B-site recombination centers. The methods presented here demonstrate the effectiveness of correlating ensemble measurements, atomic-scale STEM imaging, and DFT simulations to establish structure–performance relationships for doped SrTiO3 nanoparticles.

Unveiling the Atomic Vibrational Anisotropy and Electron-Phonon Coupling via Momentum-Selective Electron Microscopy

Microscopy and Microanalysis · 2025-07-01 · 1 citations