Brian A. Korgel

We have developed the synthesis of HgTe branched nanorods that exhibit stable infrared (IR) photodetector performance on single-element detector (SED) substrates for more than a year without additional protective coating or packaging. For more than a year, we have been analyzing nanorod films using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), electron microscopy, and grazing incidence small-angle X-ray scattering (GISAXS). After deposition, the films become denser for about a month. The distance between nanorods noticeably decreases without a change in the nanorod size and then stabilizes. Heating of the films leads to similar densification. XPS and TOF-SIMS show that nanorods oxidize at both the film surface exposed to air and the underlying interface with the substrate. This oxidation is self-passivating and slows down enough to retain stable SED performance for more than a year. Tetrahedron-shaped colloidal quantum dots (CQDs) of HgTe were also synthesized and tested as IR photodetector materials for comparison. The CQDs also perform well but degrade after several months.

Indium antimonide (InSb) colloidal quantum dots (CQDs) are attractive heavy-metal-free absorbers for infrared photodetection, yet their synthesis remains challenging because precursor reduction overlaps with nucleation and growth, hindering kinetic control and yielding broad size distributions. Here we employ an automated workflow to achieve precise control over InSb CQD synthesis, leading to improved batch-to-batch reproducibility and narrow size distributions without laborious post-synthetic size-selective precipitation. We find that InSb CQD formation proceeds through a kinetically matched precursor co-reduction pathway, which requires an In-rich environment to compensate for the faster reduction of Sb³⁺ precursor. Within this framework, we tune CQD size by modulating precursor conversion kinetics through In/Sb precursor molar ratio and reducing agent availability. This kinetically guided size control tunes the first excitonic absorption peak of CQDs across 1120-1650 nm in the short-wave infrared. Optimized CQDs with 0.825 eV bandgap exhibit a small Stokes shift of 32 meV, which is among the smallest reported for InSb CQDs.

Hydrogen fuel cells based on proton exchange membrane (PEM) technology are promising as an alternative to fossil fuel-based energy. However, current membrane technology suffers from hydrogen crossover, which represents a significant loss of efficiency. In this work, we demonstrate a scalable, room-temperature coating of ultrathin, polycrystalline boron nitride (BN) via pulsed laser deposition (PLD) that simultaneously increases the conductivity of perfluorosulfonic acid (PFSA)-based membranes while decreasing the crossover, retaining hydrogen on the anode. BN-coated membranes show a 20% increase in beginning of life performance at the operational conditions (1.485 A/cm² at 0.6 V) and a 20% increase in power density (0.965 W/cm²) while exhibiting a maximum crossover current decrease of 32% (3.58 mA/cm²) relative to industry standard Nafion NR-211. The room-temperature direct deposition of ultrathin boron nitride with the PLD method onto a polymer membrane stands as a significant improvement to traditional 2D material transfer-based methods. These observations are practically relevant for the development of PEM technology by enabling more scalable and cost-effective high-performance fuel cell stacks.

Single-element detectors (SEDs) with a room temperature extended short-wave infrared (eSWIR) photoresponse were fabricated with branched nanorods of HgTe. Nanorods with high aspect (length/width) ratios were obtained by using stoichiometric excesses of Hg (i.e., [Hg]/[Te] molar ratios greater than one) and relatively low reaction temperatures, as low as room temperature. The size-tunable optical cutoff wavelengths of the detectors ranged from 2 to 3.5 μm, with specific detectivities as high as 2.4 × 10¹¹ Jones. The devices retained their responsivity for more than a year. Branched nanorods of HgTe are promising materials for IR photodetectors and imagers.

2D assemblies of resonant dielectric particles constitute promising materials for the next generation of photonic devices, thanks to their low optical losses and intense electromagnetic response. However, bottom‐up synthesis methods present many difficulties when targeting metasurface applications, particularly due to the high degree of positional disorder and the size dispersion of the resonant particles. This work presents the fabrication of core–shell silicon@silica particles with multipolar resonances in the visible and near‐infrared. These resonant particles are then assembled at an air–water interface into a semi‐ordered array with islands of crystallinity. The assembly is deposited on quartz and the optical properties are characterized with ellipsometry and optical microscopy. The effective medium of this material appears to display a magnetic resonance with a high‐quality factor at ≈945 nm, as demonstrated by a Lorentzian resonance in the permeability. Thus, this is the first bottom‐up synthesis of silicon particle assemblies known to generate optical magnetism, giving promise for the scalable production of high‐performance metasurfaces, in spite of the imperfections associated with bottom‐up fabrication.

We present the Subset Extended Kalman Filter (SEKF) as a method to update previously trained model weights online rather than retraining or finetuning them when the system a model represents drifts away from the conditions under which it was trained. We identify the parameters to be updated using the gradient of the loss function and use the SEKF to update only these parameters. We compare finetuning and SEKF for online model maintenance in the presence of systemic drift through four dynamic regression case studies and find that the SEKF is able to maintain model accuracy as-well if not better than finetuning while requiring significantly less time per iteration, and less hyperparameter tuning.