Sashank Shivakumar

This study compares reactive and capillary-driven (non-reactive) ultrafast sintering of simple versus compositionally complex silicides via different kinetic pathways. Four systems, VSi2, (Nb0.273V0.343Cr0.384)Si2, (Mo0.186V0.523Ti0.291)Si2, and (Mo0.081Nb0.197V0.25Cr0.3Ti0.172)Si2, were investigated. The compositionally complex silicides (CCS) were designed to achieve an average melting temperature comparable to that of VSi2 while maximizing configurational entropy under this constraint. For each CCS, capillary-driven ultrafast sintering was performed using pre-synthesized single-phase powders and compared with reactive ultrafast sintering starting from mixtures of three or five binary disilicides. Results indicate that reactive ultrafast sintering resulted in higher sinterability than capillary-driven ultrafast sintering, while increasing compositional complexity generally enhanced densification. Compared with capillary-driven sintering, the reactive process initially suppressed sintering but maintained high densification rates for longer duration, resulting in higher final relative densities. The grain size after ultrafast sintering was found to correlate with the final relative density, regardless of the composition or kinetic pathway.

The formation of uniform, nondendritic seeds is essential to realizing dense lithium (Li) metal anodes and long-life batteries. Here, we discover that faceted Li seeds with a hexagonal shape can be uniformly grown on carbon-polymer composite films. Our investigation reveals the critical role of carbon defects in serving as the nucleation sites for their formation. Tuning the density and spatial distribution of defects enables the optimization of conditions for faceted seed growth. Raman spectral results confirm that lithium nucleation indeed starts at the defect sites. The uniformly distributed crystalline seeds facilitate low-porosity Li deposition, effectively reducing Li pulverization during cycling and unlocking the fast-charging ability of Li metal batteries. At a 1 C rate, full cells using LiNi_0.8Mn_0.1Co_0.1O₂ cathode (4.5 mA h cm^-2) paired with a lithium anode grown on carbon composite films achieve a 313% improvement in cycle life compared to baseline cells. Polymer composites with carbonaceous materials rich in defects are scalable, low-cost substrates for high-rate, high-energy-density batteries.

Objective. Decoding neural activity has been limited by the lack of tools available to record from large numbers of neurons across multiple cortical regions simultaneously with high temporal fidelity. To this end, we developed the Argo system to record cortical neural activity at high data rates. Approach. Here we demonstrate a massively parallel neural recording system based on platinum-iridium microwire electrode arrays bonded to a CMOS voltage amplifier array. The Argo system is the highest channel count in vivo neural recording system, supporting simultaneous recording from 65 536 channels, sampled at 32 kHz and 12-bit resolution. This system was designed for cortical recordings, compatible with both penetrating and surface microelectrodes. Main results. We validated this system through initial bench testing to determine specific gain and noise characteristics of bonded microwires, followed by in-vivo experiments in both rat and sheep cortex. We recorded spiking activity from 791 neurons in rats and surface local field potential activity from over 30 000 channels in sheep. Significance. These are the largest channel count microwire-based recordings in both rat and sheep. While currently adapted for head-fixed recording, the microwire-CMOS architecture is well suited for clinical translation. Thus, this demonstration helps pave the way for a future high data rate intracortical implant.