David D. Allred received Alumni Professorship Award

Introduction: This study aims to explore the mechanical properties of porous microelectrodes formed from vertically aligned carbon nanotube (CNT) forests. Specifically, we investigate the range of effective CNT-based microelectrode (ME) moduli that can be fabricated and identify moduli within that range that significantly reduce strain on brain tissue during micromotion.Materials and methods: To address these questions, we developed a micromechanical measurement method, known as the dual deflection (DD) test, which is compatible with microelectrode array (MEA) form factors and can measure a wide range of moduli with a 30% uncertainty. Using the DD test with small deflections, we measured the effective Young’s modulus of freestanding CNT microelectrodes (MEs) fabricated with different carbon infiltration times (0, 15, and 30 s) at 900°C. We also developed a static 10 μm deflection finite element analysis (FEA) model to compare the brain tissue strain induced by probes with the maximum (1.7 GPa), median (72 MPa), and minimum (3.9 MPa) measured CNT moduli, along with the modulus of silicon (165 GPa) for comparison.Results: The DD test results showed mean effective moduli of 19.6 ± 14.5 MPa, 67.7 ± 22.7 MPa, and 168 ± 62.3 MPa for arrays fabricated with 0, 15, and 30 s infiltrations, respectively. The FEA model revealed that probes with the maximum CNT modulus induced similar strain to the silicon probes at the tip, while probes with the minimum and median CNT moduli showed minimal strain at the tip.Discussion: These findings suggest that CNT microelectrodes with moduli in the tens of MPa range, achievable through 15 s of carbon infiltration, can significantly reduce brain tissue strain. Additionally, we consistently observed that microelectrodes with 15 s of infiltration were apparently undamaged after deflection, making them mechanically promising candidates for neural probe arrays.

The Extended Murphy Good (EMG) mathematical theory proposed by Richard G. Forbes for Large Area Field Emitters is applied to Patterned As-Grown Carbon Nanotube field emitters as well as existing research for comparison. Patterned As-Grown Carbon Nanotubes (developed by Brigham Young University in collaboration with Varex Imaging) were transferred to titanium substrates by means of a precise thermal process which creates a unique titanium carbide nanostructure as an adhesion mechanism for Patterned As-Grown Carbon Nanotubes. This deposition process is called the VanDyke Deposition Method. Field emission IV curve data was measured from 10 mA to 100 mA and was placed in the EMG calculator. As the EMG data more correctly estimates the vertical axis intercept the EMG results show that As-grown CNTs adhered to titanium can have Formal Emission Areas of 318.9u² & 684.5u² .

Vertically aligned carbon nanotube forest growth uses a thin-film iron catalyst on an alumina support. The iron catalyst thickness (typically, 1–10 nm) strongly affects forest morphology. We explored the use of spectroscopic ellipsometry (SE) as a rapid, sensitive, and nondestructive metrology method for these films. SE does have challenges, however, as it is difficult to break the correlation in the analysis between fitted optical constants and thickness of ultrathin films. Partial oxidation and optical absorption in the iron–iron oxide films add further complexity. We performed a multisample SE analysis of thermally evaporated iron films with target thicknesses of 1–14 nm. To improve sensitivity, we used interference enhancement by incorporating a 350 nm silica film on a silicon substrate beneath the iron film and alumina support. We used a consecutive-layer approach, collecting SE data and fitting the optical constants and thickness of each film before depositing the next. The iron–iron oxide film was modeled with an effective medium approximation layer. The model fit the data well with a mean squared error of 25. From the SE results, we estimated the thickness of the iron film before oxidation (“equivalent iron thickness”). We found that SE is highly sensitive to equivalent iron thickness and yields repeatable thickness measurements (ca. ±0.015 nm). We determined that the equivalent iron thickness variation we observed across different measurement locations on the same sample can be explained by error propagation from uncertainty in the underlying alumina thickness.

Interfacing is a consistent weak point in the manufacturing of microscale gas chromatography columns. Current techniques for interfacing with microfluidic systems often degrade under high temperatures and thermal cycling and suffer from dead volumes. To address these challenges, we fabricated all-metal interfaces that connect 3D-printed microchannels (500 µm diameter) to industry-standard stainless-steel (SS) capillaries. Our fabrication process uses SS binder-jet printing and bronze infiltration to fuse the capillary to the printed part and reduce dead volumes at the interface while utilizing pressure control to prevent the infiltrant from filling the channel or capillary. These interfaces withstood pressures greater than 100 PSI and showed no leakage after thermal cycling to 350 °C. Cross-sections of the interfaces show smooth connections between the channel and capillary with minimal dead volume.