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.

Carbon nanotubes (CNTs) possess many unique properties that make them ideal for field emission. However, screening due to high density and poor substrate adhesion limits their application. We tested the field emission of various patterned vertically aligned carbon nanotube (VACNT) arrays adhered to copper substrates using carbon paste. After many fabrication steps to improve uniformity, we found that the field emission was dominated by individual CNTs that were taller than the bulk VACNT arrays. After testing a sample with silver epoxy as the binder, we found that the failure mechanism was adhesion to the substrate. Using energy dispersive x-ray spectroscopy, we found that the carbon paste migrated into the VACNT bulk volume while the silver epoxy did not. The migration of carbon paste into the volume may explain why the carbon paste had greater adhesion than the silver epoxy.

This paper introduces a neural network-based calibration for low-force sensors that operate in the sub-newton regime $(0-1 \mathrm{N})$ for wearable applications. The proposed calibration utilizes a fully-connected neural network to digitally reduce the sensor nonlinearity. The neural network is trained using data from a custom low-force measurement system with a novel compliant mechanism. Detailed study explores the tradeoffs between the neural network size and activation function with calibration accuracy. Measurement results demonstrate 4X improvement in the force sensor linearity, achieving errors less than 0.005 N. The proposed calibration is well-suited for wearable applications requiring precise low-force measurements.

Hollow cathodes are a common type of vacuum ultraviolet (VUV) light source with a wide range of design and application. We determined the VUV (58.4 nm) intensity distribution of a hollow cathode as a function of current and pressure. Our model describes the intensity distribution of a McPherson 629-like hollow cathode helium plasma within the range of 0.50–1.00 A and 0.50–1.00 Torr as a ring with a center peak. We found that for all pressures and currents considered, the ring emits more VUV light than the center peak. We also found that the center peak has a minimum VUV light emission near 0.9 Torr.

High-temperature microfluidic devices (such as gas chromatography microcolumns) have traditionally been fabricated using photolithography, etching, and wafer bonding which allow for precise microscale features but lack the ability to form complex 3D designs. Metal additive manufacturing could enable higher complexity microfluidic designs if reliable methods for fabrication are developed, but forming small negative features is challenging-especially in powder-based processes. In this paper, the formation of sealed metal microchannels was demonstrated using stainless-steel binder jetting with bronze infiltration. To create small negative features, bronze infiltrant must fill the porous part produced by binder jetting without filling the negative features. This was achieved through sacrificial powder infiltration (SPI), wherein sacrificial powder reservoirs (pore size similar to 60 mu m) are used to control infiltrant pressure. With this pressure control, the infiltrant selectively filled the small pores between particles in the printed part (pore size similar to 3 mu m) while leaving printed microchannels (700 mu m and 930 mu m) empty. To develop the SPI method, a pore filling study was performed in this stainless-steel/bronze system with 370 mu m, 650 mu m, and 930 mu m microchannel segments. This study enabled SPI process design on these length scales by determining variations in pore filling across a sample and preferential filling between different sized pores.

Windows for vacuum ultraviolet (VUV) sources are valuable for many applications but difficult to fabricate due to most materials being too absorptive at VUV wavelengths. We have designed, fabricated, and characterized a carbon nanotube (CNT) collimator as a window with high (VUV) transmission and significant differential pumping. The CNT collimators are arrays of square channels of various dimensions and height with sidewalls composed of vertically aligned CNT forests. The CNT collimators in this work exhibited peak intensity transmissions for VUV light (58.4 nm) of 18%–37% of that reported for the same system without a collimator present [S. Olsen, D. Allred, and R. Vanfleet, J. Vac. Sci. Technol. A (2024)]. Further analysis found that the peak intensity transmissions were lowered due to carbon deposition on the phosphor viewing screen from contaminants. The CNT collimator also had significant sidewall reflection in the VUV range (R=0.21±0.08 in the VUV range for angles 15.6 degrees and below). Pressure ratios (low pressure over high pressure) in the VUV transmission experiment were dominated by leaks in the alignment mechanism. Additional experiments demonstrated the CNT collimator’s reflection and superior differential pumping with pressure ratios less than 0.001.

Estimating the elastic modulus and strength of heterogeneous films requires local measurement techniques. For local mechanical film testing, microcantilevers were cut into suspended many-layer graphene using a focused ion beam. An optical transmittance technique was used to map thickness near the cantilevers, and multipoint force-deflection mapping with an atomic force microscope was used to record the compliance of the cantilevers. These data were used to estimate the elastic modulus of the film by fitting the compliance at multiple locations along the cantilever to a fixed-free Euler-Bernoulli beam model. This method resulted in a lower uncertainty than is possible from analyzing only a single force-deflection. The breaking strength of the film was also found by deflecting cantilevers until fracture. The average modulus and strength of the many-layer graphene films are 300 and 12 GPa, respectively. The multipoint force-deflection method is well suited to analyze films that are heterogeneous in thickness or wrinkled.

Journal Article Mechanisms for Chemical Vapor Deposition Carbon Nanotube Growth by Surface Modification of 316L Stainless Steel Get access Joshua Hancock, Joshua Hancock Department of Physics, Brigham Young University, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Felipe Rivera, Felipe Rivera Department of Physics, Brigham Young University, Provo, UT, United StatesElectron Microscopy Facility, Brigham Young University, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Brian Jensen, Brian Jensen Department of Mechanical Engineering, Brigham Young University, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Richard Vanfleet Richard Vanfleet Department of Physics, Brigham Young University, Provo, UT, United States Corresponding author: richard_vanfleet@byu.edu Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 759–761, https://doi.org/10.1093/micmic/ozad067.375 Published: 22 July 2023

Understanding processing-structure-property (PSP) linkages of solid-phase microextraction (SPME) coating materials is crucial for the rational design and advancement of these new materials. As SPME is a diffusion-based extraction technique, analyzing the morphology of its coating materials is important for optimizing its performance. In this study, we assess the morphological evolution of micro/mesoporous amorphous silicon (a-Si) thin films sputtered at an oblique angle onto silicon, which serve as models for support materials in SPME devices. The contrast of scanning transmission electron microscopy (STEM) images is enhanced via ZnO infiltration by atomic layer deposition (ALD). Various metrics, including physical descriptors and two-point statistics methods, are employed to follow the films' evolution. Analysis of the two-point correlation function reveals a simple ellipse/spherical local pore geometry in contrast to the long-range irregular arrangement of pores identified by a range of traditional and novel metrics. Additionally, analyzing the internal structure of the pores through homology metrics aligns well with the theoretical understanding of morphological evolution in oblique sputtered films. These analyses show that the "average ratio of principal moment of inertia", "Betti numbers", and "two-point statistics" based metrics can capture valuable information during film growth. The morphological analysis approach proposed in this study can be applied to analyze any nanoporous medium as a first step towards developing structure-property relationships that tie back to a given preparation method. Ultimately, a more extensive experimental and/or simulation-based study should confirm the correlations between these metrics and actual diffusion properties as the basis for process-structure-properties relations for improved design and optimization of this film.

A miniaturized short-wavelength infrared spectrometer for use with diffuse light was created by combining a thin form factor carbon nanotube composite collimator, a linear variable filter, and an InGaAs photodiode array. The resulting spectrometer measures 3 mm x 4 mm x 14 mm and shows a significant improvement in resolution over a spectrometer without the collimator when used with diffuse light. Its small size and high throughput make it ideal for applications such as wearable optical sensing, where light from highly scattering tissue is measured. Plethysmographic measurements on the wrist were demonstrated, showing rapid data collection with diffuse light.

Journal Article Simultaneous HAADF & EELS Data Acquisition for Relative Quantification of Temperature and Thickness Effects on Thermal Diffuse Scattering in STEM Get access Paul S Minson, Paul S Minson Brigham Young University, Electron Microscopy Facility, Provo, UT, United StatesBrigham Young University, Physics and Astronomy, Provo, UT, United States Corresponding author: paul.minson@byu.edu Search for other works by this author on: Oxford Academic Google Scholar Felipe Rivera, Felipe Rivera Brigham Young University, Electron Microscopy Facility, Provo, UT, United StatesBrigham Young University, Physics and Astronomy, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Richard Vanfleet Richard Vanfleet Brigham Young University, Physics and Astronomy, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 358–360, https://doi.org/10.1093/micmic/ozad067.167 Published: 22 July 2023

In the last two decades, advances in the dark field detectors and microscopes of scanning transmission electron microscopy (STEM) have inspired a resurgence of interest in quantitative STEM analysis. One promising avenue is the use of STEM as a nanothermometric probe. In this application, thermal diffuse scattering, captured by a CCD camera or an annular dark field detector, acts as an indirect measurement of the specimen temperature. One challenge with taking such a measurement is achieving adequate sensitivity to quantify a change in scattered electron signal on the order of 1% or less of the full electron beam. Another difficulty is decoupling the thermal effect on electron scattering from scattering changes due to differing specimen thicknesses and materials. To address these issues, we have developed a method using STEM, combined with electron energy loss spectroscopy (EELS), to produce a material-specific calibration curve. On silicon, across the range 89 K to 294 K, we measured a monotonically increasing HAADF signal ranging from 4.0% to 4.4% of the direct beam intensity at a thickness-to-mean-free-path ratio of 0.5. This yielded a calibration curve of temperature versus full-beam-normalized, thickness-normalized HAADF signal. The method enables thermal measurements on a specimen of varying local thickness at a spatial resolution of a few nanometers. We demonstrated the potential of the technique for testing electron scattering models by applying single-electron scattering theory to the data collected to extract a measurement of the mean atomic vibration amplitude in silicon at 294 K. The measured value, 0.00738 +/- 0.00002 nm, agrees well with reported measurement using X-rays.

Some of the least reflective materials are vertically aligned carbon nanotubes (VACNTs). However, VACNT films are extremely fragile, restricting the range of applications where they can be used. Here, we have formed VACNT/carbon composite films with greater than 500x stiffness and 50x strength compared to as-grown VACNTs while maintaining ultralow reflectance. This is achieved using an infiltration process that coats the individual nanotubes with a thin layer of nanocrystalline carbon, locking the nanotubes together, and then adding lateral subwavelength surface topography to the tops of the VACNTs with an oxygen plasma etch to reduce the reflectance. While still a delicate material, these composites are robust enough to be exposed to water and handled. We demonstrated that these composites can be transferred from the growth substrate to other surfaces resulting in a reflectance of less than 0.1%.

Hollow cathode plasmas are common extreme ultraviolet (EUV) lamps used for material characterization. However, the relatively high pressure of the plasma can affect downstream instruments, as well as absorb the EUV. EUV windows are difficult to fabricate due to EUV's strong interaction with all materials. We present a carbon nanotube (CNT) microfabricated window composed of multiple high aspect-ratio columns in parallel. The open areas allow wide bandpass transmission, while the walls restrict gas flow. We model the CNT window transmission as a weight function on the light from of a Mcpherson 629-like hollow cathode helium plasma in visible wavelengths. We model the CNT window differential pumping as a series of columns between two chambers of different pressures.

Traditional collimators typically require large optics and/or long pathlengths which makes miniaturization difficult. Carbon nanotube templated microfabrication offers a solution to pattern small 3D structures, such as parallel hole collimators. Here we present the characterization of a carbon nanotube parallel hole collimator design and its efficacy in visible and short wavelength infrared light. Comparison to geometric and far field diffraction models are shown to give a close fit, making this a promising technology for miniaturized diffuse light collimation.

Several electrical devices are formed by growing vertically aligned carbon nanotube (CNT) structures directly on a substrate. In order to attain high aspect ratio CNT forest growths, a support layer for the CNT catalyst, usually alumina, is generally required. In many cases, it has been found that current can pass from a conductive substrate, across the alumina support layer, and through the CNTs with minimal resistance. This is surprising in the cases where alumina is used because alumina has a resistivity of ρ>1014 Ω cm. This paper explores the mechanism responsible for current being able to cross the alumina support layer with minimal resistance following CNT growth by using scanning transmission electron microscopy imaging, energy dispersive x-ray spectroscopy, secondary ion mass spectroscopy, and two-point current-voltage (I-V) measurements. Through these methods, it is determined that exposure to the carbonaceous gas used during the CNT growth process is primarily responsible for this phenomenon.