Nanomanufacturing

A low-voltage alternating current (AC) field (20 V peak-to-peak, 1 kHz) was superimposed on a conventional direct current (DC) electrospinning configuration in order to test whether the shape of that perturbation measurably alters fiber formation. A function generator delivered sinusoidal, pulsed (square), ramp and arbitrary (noise) waveforms to a foil-covered flat collector, while a standard DC high-voltage source (20 kV) drove the jet from the spinneret. Polyvinylpyrrolidone (PVP) nanofibers were characterized by scanning electron microscopy (SEM), fiber-diameter distribution analysis (FIJI/ImageJ), quantitative orientation analysis and contact profilometry. One-way analysis of variance across the six conditions was significant (F(5.594) = 5.56, p = 5.1 × 10⁻⁵) but the associated effect size was small (η² = 0.045). Relative to the connected control (237 ± 52 nm), the ramp (205.5 ± 43.9 nm), noise (201.3 ± 48.6 nm) and pulse (212.6 ± 70.0 nm) waveforms yielded significantly finer fibers (Tukey HSD, p = 0.0008, 0.0001 and 0.022, respectively); relative to the grounded control (215 ± 47 nm), no waveform reached significance. The ramp waveform produced the narrowest diameter distribution but, unexpectedly, the roughest mat of the four AC conditions (Ra = 1.95 µm against 0.74 µm for the grounded control), while the noise waveform gave both the smallest mean diameter and the smoothest mat (Ra = 0.61 µm); with a single profile per scan direction, these roughness values are descriptive rather than statistically compared. Quantitative orientation analysis using two independent estimators (structure tensor and fast Fourier transform) returned Herman orientation factors of S ≤ 0.13 for every condition, against S = 0.81 for a partially aligned reference population: no condition exceeded the isotropic noise floor of the FFT estimator (S95 = 0.141), and the three conditions that marginally exceeded the structure-tensor floor (S95 = 0.104) included the connected control, which received no oscillating signal. No waveform, including the pulsed waveform, produced fiber alignment attributable to the AC field. The applied AC amplitude corresponds to approximately 0.05% of the DC voltage, and the associated oscillating field (±50 V m⁻¹) is approximately three orders of magnitude smaller than the mean DC field (~1 × 10⁵ V m⁻¹); the electrohydrodynamic mechanisms discussed here are therefore presented as hypotheses requiring direct measurement rather than as established explanations. Within these limits, low-voltage waveform modulation is a simple, safe and retrofittable route to modest control of nanofiber diameter and mat uniformity in a single-polymer system, but it does not induce fiber alignment.

We present a dual-wavelength analysis of nitrogen-vacancy (NV) center quantum magnetometry enhanced by uniformly coated gold nanoparticles (AuNPs). An ensemble-averaged model is developed to analyze the AuNP-enhanced stimulated absorption at the 532 nm excitation wavelength and the spontaneous emission at 637 nm. The resulting detected optically magnetic resonance (ODMR) signal profiles are simulated for both enhancement mechanisms. We find that the enhanced stimulated absorption at 532 nm significantly amplifies the ODMR signal intensity without broadening the linewidth, thereby improving the signal-to-noise ratio (SNR) without sacrificing the magnetic field sensing resolution. Conversely, enhancing the 637 nm spontaneous emission increases the total photo emission rate but simultaneously broadens the ODMR detection linewidth due to the direct reduction in the effective spin coherence time of excited states by the enhanced spontaneous rate. The dual-wavelength analysis provides valuable design guidance for the development of low-cost spin-coated AuNP-enhanced NV-center quantum magnetometry technologies.

Historically, TEM prep has been an artisan craft without a systematic workflow that ensures quantified control over TEM sample thickness. Over- and under-thinning is a significant problem in the TEM prep process. A direct measurement process was demonstrated to control the final thickness of the TEM lamella. Final lamella thickness was controlled by directly measuring lamella thickness in real time using a 10–15 kV SEM while performing secondary electron imaging at the mill position, allowing for (human-mediated) closed-loop processing. We demonstrated the utility of this technique by systematically thinning five TEM samples to discretely target thicknesses ranging from 100 nm down to 28 nm. We demonstrated the repeatability and simplicity of the process by fabricating 10 STEM lamella with a targeted thickness of 32 nm. We demonstrate the ability to fabricate an engineered multi-layered structure that acts as a lamella thickness measurement feature that is independent of sample type, allowing a broader implementation of in-line lamella thickness monitoring. We applied our thickness measurement technique to three thin-film materials (Au, Ag, and Cu) to obtain TEM lamella thickness target values needed to achieve electron transparency for each material. Having knowledge of a target thickness parameter prevents the over- and under-thinning problem in TEM prep.