Low-Cost, Compact Quadrupole Mass Filters with Unity Mass Resolution via Ceramic Resin Vat Photopolymerization.

This study reports novel, compact, and additively manufactured quadrupole mass filters (QMFs) with adequate filtering performance for practical mass spectrometry applications. The QMFs are monolithically fabricated via vat photopolymerization of glass-ceramic resin using 57 µm × 57 µm × 100 µm voxels, and selective electroless plating of nickel-boron. Experimental characterization of QMF prototypes at 1.74 MHz using FC-43 yields 131 Da peaks with 0.50 Da full width at half maximum (260 resolution), surpassing the resolution of reported miniaturized counterparts under similar conditions, and being on par with commercial, non-miniaturized, heavier devices. The sensitivity of the 3D-printed devices is estimated at 0.13 mA Torr-1 (comparable to that of optimized, commercial counterparts), while the devices attained up to 250 Da of mass range (limited by the driving electronics). The work is of interest to low-cost, capable mass spectrometry, 3D-printed instruments, and in-space manufacturing of complex instrumentation.

Ultrathin Ceramic Piezoelectric Films via Room-Temperature Electrospray Deposition of ZnO Nanoparticles for Printed GHz Devices.

High-frequency devices are key enablers of state-of-the-art electronics used in a wide and diverse range of exciting applications such as inertial navigation, communications, power conversion, medicine, and parallel computing. However, high-frequency additively manufactured piezoelectric devices are yet to be demonstrated due to shortcomings in the properties of the printed transducing material and the attainable film thickness. In this study, we report the first room-temperature-printed, piezoelectric, ultrathin (<100 nm) ceramic films compatible with high-frequency (>1 GHz) operation. The films are made of zinc oxide (ZnO) nanoparticles via near-field electrohydrodynamic jetting, achieving film piezoelectricity, without high-temperature processing, through a novel mechanism that is controlled during the deposition. Optimization of the printing process and feedstock formulation results in homogeneous traces as narrow as 213 µm and as thin as 53 nm as well as uniform field films as thin as 91 nm; the printing technique can be used with flexible and rigid, conductive and insulating substrates. The crystallographic orientation of the imprints toward the (100) plane increases if the rastering speed during printing is augmented, resulting in a larger piezoelectric response. The resonant frequency of film bulk acoustic resonators increases monotonically with the rastering speed, achieving transmission values as high as 4.99 GHz, which corresponds to an acoustic velocity of 2094 m/s, similar to the expected transverse value in high-temperature-grown ZnO films. Piezoresponse force microscopy maps of printed field films show local variation in the piezoelectric behavior across the film, with an average piezoelectric response as high as 21.5 pm/V, significantly higher than the d33 piezoelectric coefficient of single-crystal, high-temperature-grown ZnO, and comparable with reported values from ZnO nanostructures.

Microfluidic Model for Evaluation of Immune Checkpoint Inhibitors in Human Tumors.

Presented is the first demonstration of real-time monitoring of the response of resident lymphocyte populations in biopsied tumor tissue to immunotherapeutic agents in a perfused tumor microenvironment. This technology comprises a microfluidic tumor trapping device constructed from a novel 3D-printed, transparent, noncytotoxic substrate. The 3D-printed device sustains viability of biopsied tissue fragments under dynamic perfusion for at least 72 h while enabling simultaneous administration of various drug treatments, illustrating a useful tool for drug development and precision medicine for immunotherapy. Confocal microscopy of the tumor tissue and resident lymphocytes in the presence of fluorescent tracers provides real-time monitoring of tumor response to various immunotherapies. Devices are additively manufactured in Pro3dure GR-10 (i.e., a relatively new, high-resolution stereolithographic resin with properties suitable for biomedical applications), allowing integration of a set of finely featured functional components into a monolithically constructed platform. The presented platform comprises a new methodology for modeling and analyzing tumor response for the improved prediction of patient-specific immunotherapy efficacy. It is acknowledged that this is the first report of human tumor fragments cultured in a dynamic perfusion system capable of testing the effect of circulating immune checkpoint inhibitors on resident tumor-infiltrating lymphocytes.

3D printed multiplexed electrospinning sources for large-scale production of aligned nanofiber mats with small diameter spread.

We report the design, fabrication, and characterization of novel, low-cost, and modular miniaturized nanofiber electrospinning sources for the scalable production of non-woven aligned nanofiber mats with low diameter variation. The devices are monolithic arrays of electrospinning emitters made via stereolithography; the emitters are arranged so each element has an independent line of sight to a rotating collector surface. Linear and zigzag emitter packing were evaluated using a PEO solution with the aim of maximizing the throughput of nanofibers with the smallest diameter and narrowest distribution. Current versus flowrate characterization of the devices showed that for a given flowrate a zigzag array produces more current per emitter than a linear array of the same emitter pitch and array size. In addition, the data demonstrate that larger and denser arrays have a net gain in flow rate per unit of active length. Visual inspection of the devices suggests uniform operation in devices with as many as 17 emitters with 300 µm inner diameter and 1.5 mm emitter gap. Well-aligned nanofiber mats were collected on a rotating drum and characterized; the 17-emitter device produced the same narrow nanofiber distribution (∼81 nm average diameter, ∼17 nm standard deviation) for all tested flow rates, which is strikingly different to the performance shown by 1-emitter sources where the average fiber diameter significantly increased and the statistics notably widened when the flowrate increases. Therefore, the data demonstrate that massively multiplexing the emitters is a viable approach to greatly increase the throughput of non-woven aligned nanofiber mats without sacrificing the statistics of the nanofibers generated. The production of dry nanofibers by the 17-emitter array is estimated at 33.0 mg min-1 (1.38 mg min-1 per mm of active length), which compares favorably with the reported multiplexed electrospinning arrays with emitters distributed along a line.

Electrospray-printed nanostructured graphene oxide gas sensors.

We report low-cost conductometric gas sensors that use an ultrathin film made of graphene oxide (GO) nanoflakes as transducing element. The devices were fabricated by lift-off metallization and near-room temperature, atmospheric pressure electrospray printing using a shadow mask. The sensors are sensitive to reactive gases at room temperature without requiring any post heat treatment, harsh chemical reduction, or doping with metal nanoparticles. The sensors' response to humidity at atmospheric pressure tracks that of a commercial sensor, and is linear with changes in humidity in the 10%-60% relative humidity range while consuming <6 µW. Devices with GO layers printed by different deposition recipes yielded nearly identical response characteristics, suggesting that intrinsic properties of the film control the sensing mechanism. The gas sensors successfully detected ammonia at concentrations down to 500 ppm (absolute partial pressure of ∼5 × 10(-4) T) at ∼1 T pressure, room temperature conditions. The sensor technology can be used in a great variety of applications including air conditioning and sensing of reactive gas species in vacuum lines and abatement systems.

Multiplexing and scaling-down of nanostructured photon-triggered silicon field emitter arrays for maximum total electron yield.

Femtosecond ultrabright cathodes with spatially structured emission are a critical technology for applications such as free-electron lasers, tabletop coherent x-ray sources, and ultrafast imaging. In this work, the optimization of the total electron yield of ultrafast photon-triggered field emission cathodes composed of arrays of nanosharp, high-aspect-ratio, single-crystal silicon pillars is explored through the variation of the emitter pitch and height. Arrays of 6 nm tip radius silicon emitters with emitter densities between 1.2 and 73.9 million tips cm(-2) (hexagonally packed arrays with emitter pitch between 1.25 and 10 µm) and emitter height between 2.0 and 8.5 µm were characterized using 35 fs 800 nm laser pulses. Three-photon electron emission for low-energy (<0.3 µJ) light pulses and strong-field emission for high-energy (>1 µJ) light pulses was observed, in agreement with the literature. Of the devices tested, the arrays with emitter pitch equal to 2.5 µm produced the highest total electron yield; arrays with larger emitter pitch suffer area sub-utilization, and in devices with smaller emitter pitch the larger emitter density does not compensate the smaller per-emitter current due to the electric field shadowing that results from the proximity of the adjacent tips. Experimental data and simulations suggest that 2 µm tall emitters achieve practical optimal performance as shorter emitters have visibly smaller field factors due to the proximity of the emitter tip to the substrate, and taller emitters show marginal improvement in the electron yield at the expense of greater fabrication difficulty.

Parallel nanomanufacturing via electrohydrodynamic jetting from microfabricated externally-fed emitter arrays.

We report the design, fabrication, and characterization of planar arrays of externally-fed silicon electrospinning emitters for high-throughput generation of polymer nanofibers. Arrays with as many as 225 emitters and with emitter density as large as 100 emitters cm(-2) were characterized using a solution of dissolved PEO in water and ethanol. Devices with emitter density as high as 25 emitters cm(-2) deposit uniform imprints comprising fibers with diameters on the order of a few hundred nanometers. Mass flux rates as high as 417 g hr(-1) m(-2) were measured, i.e., four times the reported production rate of the leading commercial free-surface electrospinning sources. Throughput increases with increasing array size at constant emitter density, suggesting the design can be scaled up with no loss of productivity. Devices with emitter density equal to 100 emitters cm(-2) fail to generate fibers but uniformly generate electrosprayed droplets. For the arrays tested, the largest measured mass flux resulted from arrays with larger emitter separation operating at larger bias voltages, indicating the strong influence of electrical field enhancement on the performance of the devices. Incorporation of a ground electrode surrounding the array tips helps equalize the emitter field enhancement across the array as well as control the spread of the imprints over larger distances.

Nanostructured ultrafast silicon-tip optical field-emitter arrays.

Femtosecond ultrabright electron sources with spatially structured emission are an enabling technology for free-electron lasers, compact coherent X-ray sources, electron diffractive imaging, and attosecond science. In this work, we report the design, modeling, fabrication, and experimental characterization of a novel ultrafast optical field emission cathode comprised of a large (>100,000 tips), dense (4.6 million tips·cm(-2)), and highly uniform (<1 nm tip radius deviation) array of nanosharp high-aspect-ratio silicon columns. Such field emitters offer an attractive alternative to UV photocathodes while providing a direct means of structuring the emitted electron beam. Detailed measurements and simulations show pC electron bunches can be generated in the multiphoton and tunneling regime within a single optical cycle, enabling significant advances in electron diffractive imaging and coherent X-ray sources on a subfemtosecond time scale, not possible before. At high charge emission yields, a slow rollover in charge is explained as a combination of the onset of tunneling emission and the formation of a virtual cathode.