Nicholas Robert Glavin

Performance degradation in electronic devices is caused by nucleation and accumulation of electrically active defects and traps. This spotlight on applications introduces a novel paradigm to actively reverse the damage process with electron wind force (EWF). EWF is a nonintrusive and nonequilibrium mechanism for defect migration at near-ambient average temperatures. Enhancement-mode gallium nitride (GaN) high-electron-mobility transistors (HEMTs) were systematically degraded via high-temperature storage at 310 °C, which induced upto 13% reduction in drain current, 0.2 V negative threshold voltage shift, and 12% reduction in peak transconductance. A brief 1-minute application of EWF achieved full parameter recovery. Crucially, across five consecutive degradation-rejuvenation cycles, the HEMTs maintained excellent resilience, retaining 98.5% of their initial drain current, 97% of peak transconductance, 95% of gate-lag, and 93% of drain-lag responses. These findings indicate that periodic in operando EWF rejuvenation may realize unprecedented reliability of wide-bandgap electronics in mission-critical operations.

Sliding ferroelectricity in vdWs layered systems has emerged as a promising route toward non-volatile nanoscale devices. This work provides insight into the impact of intrinsic disorder and multi-domain kinetics on the ferroelectricity of 3R-TMDs.

The high strength and flexibility of two-dimensional materials enable their use in flexible devices and structures with a high curvature. However, thin films adhered to curved structures can wrinkle, fold, buckle, delaminate, or crack, depending on the curvature, film thickness, film mechanical properties, and film-substrate adhesion. How adhesion relates to 2D film properties such as crystallinity, defects, and substrate interactions is not understood due to the multiphysical, complex interplay between chemistry, structure, and adhesion. Moreover, it is intrinsically challenging to observe 2D materials and their interfaces with substrates laterally with atomic resolution in complex geometries. Here, we address these challenges using customized transmission electron microscopy (TEM) methodology to examine the atomically resolved structures of nanocrystalline few-layer molybdenum disulfide (MoS2) films deposited onto silicon (Si) tips with nanoscale curvature. We observe a transition from conformal film growth to film delamination with a substantial degree of structural defects below a critical tip radius of curvature (Rc) of approximately 5 nm. Continuum mechanics approximations based on membrane bending and stretching energies overestimate Rc and fail to explain the nature of the observed transition. We thus conducted molecular dynamics (MD) simulations of nanocrystalline MoS2 films on nanoscale Si hemispheres. The predicted Rc from MD is in excellent agreement with the experimental findings when the grain size is accounted for. This suggests an interdependence among film mechanical properties, grain size, adhesion, and curvature. In particular, defects, in this case, structural disorder at grain boundaries, enable curvature exceeding that predicted by continuum mechanics-based membrane models.

Covalent organic frameworks (COFs) are a promising class of crystalline organic polymers that can be processed into many different forms, with a majority existing as insoluble powders and thin films. Still, the optimization of crystallinity and orientation of COF thin films, a precondition for many applications, remains particularly challenging. To address this gap, this study employs grazing-incidence wide-angle X-ray scattering (GIWAXS) to examine solvent vapor annealing (SVA) as a postsynthetic method to enhance the structural ordering of imine-linked COF thin films. The SVA process was first systematically optimized for 1,3,5-tris­(4-aminophenyl)­benzene-p-phthalaldehyde (TAPB-PDA) COF thin films through kinetic and thermal studies, with an annealing temperature of 90 °C for 60 min being identified as the optimal treatment condition, which yielded a maximum increase in crystallinity. These optimized conditions were subsequently applied to TAPB-PDA thin films of varying thicknesses and those grown on a diverse range of substrates to evaluate the versatility of the SVA process. These conditions were then utilized for a series of six different COFs with varying chemical compositions and pore sizes. GIWAXS analysis was used to verify the crystalline structure of each COF as well as to obtain a comparative measurement of crystalline volume and orientational order before and after SVA. The SVA process significantly enhances crystallinity in four of the six COFs examined, particularly for those with larger pore sizes (>2.2 nm) and already exhibiting preferential alignment. In particular, 1,3,5-tris­(4-aminophenyl)­benzene-2,5-dihydroxyterephthalaldehyde (TAPB-DHPDA) and TAPB-PDA, both with a pore size of 3.6 nm, demonstrate significant increases in crystalline ordering, with up to a 9-fold increase in intensity and a 61% decrease in full width at half-maximum (FWHM) of the crystalline (100) diffraction peak. The solvent mixture (1,4-dioxane, mesitylene, and 11 M acetic acid) is hypothesized to facilitate this enhancement by enabling imine bond reversibility and creating an environment that promotes crystallite rearrangement. This work demonstrates SVA as an effective method to improve COF thin film quality.

Ferroelectric aluminum scandium nitride (AlScN) is a promising material for use in nonvolatile digital memory operating at temperatures well above the limits of current commercial technology. Ferrodiodes consisting of thin films of AlScN sandwiched between metal contacts exhibit polarization-dependent electrical conduction that can distinguish the on/off memory state with bias voltages below 10 V. However, the reliability and repeatability of key device parameters such as switching voltage and on/off ratio can change significantly with temperature. Understanding the temperature dependence of the material parameters that govern these phenomena is critical to the development of practical memory devices operating reliably at high temperature. We have systematically studied the changes in wake-up-like behavior in 40 nm AlScN films from room temperature to 700 °C. Above 300 °C, an anomalous decrease in device current arises when the applied voltage exceeds the minimum switching voltage. The temperature and rate dependence of the anomalous current loss suggests that thermally activated changes to the interlayer near the top electrode alter the local charged defect compensation. This causes the leakage current to decrease even while the net remnant polarization in the films increases.

We prepare and isolate propylammonium poly-Se(-Te) precursors from a thiol-amine solvent system to produce high quality Se and Se–Te alloy films with bandgaps tunable from 1.2 eV to 1.86 eV for applications in photovoltaics.

Two-step conversion is a promising approach to produce high-quality films of two-dimensional (2D) transition metal dichalcogenides (TMD) from thin metal films. However, the influence of the intermediate metal oxide properties such as oxidation state, stoichiometry, structure, orientation, crystallinity, grain size, and defect density, on the resulting TMD properties have not been well-studied, in part because of the large processing parameter space. Herein, we studied the influence of laser annealing power and scan speed on the structure and chemistry of the metal and metal oxide films, and by extension, on the resulting TMD film. High-throughput processing of a 10 × 11 array on Mo thin films spanning the two processing parameters, complemented with diffraction, Raman, XPS, and ellipsometric mapping allowed us to efficiently optimize the synthesis of MoSe₂. Amorphous, sub-stoichiometric (MoO₂) resulted in the best in-plane (002) aligned MoSe₂ films, which exhibited the highest refractive index >5, comparable to that observed in mechanically exfoliated material and films synthesized through molecular beam epitaxy.