High-resolution limited-angle phase tomography of dense layered objects using deep neural networks.

We present a machine learning-based method for tomographic reconstruction of dense layered objects, with range of projection angles limited to [Formula: see text] Whereas previous approaches to phase tomography generally require 2 steps, first to retrieve phase projections from intensity projections and then to perform tomographic reconstruction on the retrieved phase projections, in our work a physics-informed preprocessor followed by a deep neural network (DNN) conduct the 3-dimensional reconstruction directly from the intensity projections. We demonstrate this single-step method experimentally in the visible optical domain on a scaled-up integrated circuit phantom. We show that even under conditions of highly attenuated photon fluxes a DNN trained only on synthetic data can be used to successfully reconstruct physical samples disjoint from the synthetic training set. Thus, the need for producing a large number of physical examples for training is ameliorated. The method is generally applicable to tomography with electromagnetic or other types of radiation at all bands.

Electron transmission through suspended graphene membranes measured with a low-voltage gated Si field emitter array.

We experimentally demonstrate the transmission of electrons through different number (1, 2, and 5) of suspended graphene layers at electron energies between 20 and 250 eV. Electrons with initial energies lower than 40 eV are generated using silicon field emitter arrays with 1µm pitch, and accelerated towards the graphene layers supported by a silicon nitride grid biased at voltages from -20 to 200 V. We measured significant increase in current collected at the anode with the presence of graphene, which is attributed to the possible generation of secondary electrons by primary electrons impinging on the graphene membrane. Highest output current was recorded with monolayer graphene at approximately 90 eV, with up to 1.7 times the incident current. The transparency of graphene to low-energy electrons and its impermeability to gas molecules could enable low-voltage field emission electron sources, which often require ultra-high vacuum, to operate in a relatively poor vacuum environment.

Nanoscale silicon field emitter arrays with self-aligned extractor and focus gates.

Out-of-plane focusing is essential for electron beam collimation in gated field emission sources. The focus electrode redirects electrons emitted by the tip with a wide angle towards the central axis, resulting a small focal spot at the anode. Here, we demonstrate for the first time, very high density (108 emitters/cm2) arrays of double-gated field emission electron sources with self-aligned apertures and integrated nanowire current limiters. Release of the emitters after fabrication required the combination of a highly selective dry-etch and an isotropic wet-etch to avoid the loss of the insulator between the two gates. The aperture diameters are ∼360 nm and ∼570 nm for the extractor gate and focus gate, respectively. The turn-on voltage was low (15-20) V and anode currents of 400 nA were measured at 25 V. We compared devices with different extractor gate thicknesses resulting from planarization non-uniformity, and demonstrate the influence of the focus gate on anode current. The focal spot size was measured, using a low energy phosphor screen, to be around 700 µm for a 500 µm device when the [Formula: see text] ratio was 0.35.

A Multifunctional Microfluidic Platform for High-Throughput Experimentation of Electroorganic Chemistry.

Electroorganic synthesis is a promising tool to design sustainable transformations and discover new reactivities. However, the added setup complexity caused by electrodes in the system impedes efficient screening of reaction conditions. Herein, we present a microfluidic platform that enables automated high-throughput experimentation (HTE) for electroorganic synthesis at a 15-microliter scale. Two HTE modules are demonstrated: 1) the rapid electrochemical reaction condition screening for a radical-radical cross-coupling reaction on micro-fabricated interdigitated electrodes, and 2) measurements of kinetics for mediated anodic oxidations using the microliter-scale cyclic voltammetry. The presented modular approach could be deployed for a range of other electroorganic chemistry applications beyond the demonstrated functionalities.

Fabrication of nanostructured transmissive optical devices on ITO-glass with UV1116 photoresist using high-energy electron beam lithography.

High-energy electron beam lithography for patterning nanostructures on insulating substrates can be challenging. For high resolution, conventional resists require large exposure doses and for reasonable throughput, using typical beam currents leads to charge dissipation problems. Here, we use UV1116 photoresist (Dow Chemical Company), designed for photolithographic technologies, with a relatively low area dose at a standard operating current (80 kV, 40-50 µC cm-2, 1 nAs-1) to pattern over large areas on commercially coated ITO-glass cover slips. The minimum linewidth fabricated was ∼33 nm with 80 nm spacing; for isolated structures, ∼45 nm structural width with 50 nm separation. Due to the low beam dose, and nA current, throughput is high. This work highlights the use of UV1116 photoresist as an alternative to conventional e-beam resists on insulating substrates. To evaluate suitability, we fabricate a range of transmissive optical devices, that could find application for customized wire-grid polarisers and spectral filters for imaging, which operate based on the excitation of surface plasmon polaritons in nanosized geometries, with arrays encompassing areas ∼0.25 cm2.

Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry.

A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal-insulator-metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850 nm based on Ag (25 nm) and MgF2 (75-250 nm). Maximum spectral transmittance is measured at ∼70% with a Q-factor of ∼20.

A novel split mode TFBAR device for quantitative measurements of prostate specific antigen in a small sample of whole blood.

Easy monitoring of prostate specific antigen (PSA) directly from blood samples would present a significant improvement as compared to conventional diagnostic methods. In this work, a split mode thin film bulk acoustic resonator (TFBAR) device was employed for the first time for label-free measurements of PSA concentrations in the whole blood and without sample pre-treatment. The surface of the sensor was covalently modified with anti-PSA antibodies and demonstrated a very high sensitivity of 101 kHz mL ng-1 and low limit of detection (LOD) of 0.34 ng mL-1 in model spiked solutions. It has previously been widely believed that significant pre-processing of blood samples would be required for TFBAR biosensors. Importantly, this work demonstrates that this is not the case, and TFBAR technology provides a cost-effective means for point-of-care (POC) diagnostics and monitoring of PSA in hospitals and in doctors' offices. Additionally, the accuracy of the developed biosensor, with respect to a commercial auto analyser (Beckman Coulter Access), was evaluated to analyse clinical samples, giving well-matched results between the two methods, thus showing a practical application in quantitative monitoring of PSA levels in the whole blood with very good signal recovery.

Microfluidic electrochemistry for single-electron transfer redox-neutral reactions.

Electrochemistry offers opportunities to promote single-electron transfer (SET) redox-neutral chemistries similar to those recently discovered using visible-light photocatalysis but without the use of an expensive photocatalyst. Herein, we introduce a microfluidic redox-neutral electrochemistry (µRN-eChem) platform that has broad applicability to SET chemistry, including radical-radical cross-coupling, Minisci-type reactions, and nickel-catalyzed C(sp2)-O cross-coupling. The cathode and anode simultaneously generate the corresponding reactive intermediates, and selective transformation is facilitated by the rapid molecular diffusion across a microfluidic channel that outpaces the decomposition of the intermediates. µRN-eChem was shown to enable a two-step gram-scale electrosynthesis of a nematic liquid crystal compound, demonstrating its practicality.

Split resonances for simultaneous detection and control measurements in a single bulk acoustic wave (BAW) sensor.

A self-referenced resonator consisting of two distinct areas of the top electrode made from Mo and a thin (5-30 nm) functional Au layer is shown. The fundamental frequencies for both the shear (∼1 GHz) and longitudinal (∼2 GHz) modes are split in two, such that mass attachment on the functional layer region causes frequency shifts in only one of the resonances, allowing a new approach of using the difference between the two frequencies to be used to measure mass attachment; this reduces the importance of device-to-device variability in absolute resonant frequency as a result of device fabrication.

Author Correction: Nanofabrication of Conductive Metallic Structures on Elastomeric Materials.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Nanofabrication of Conductive Metallic Structures on Elastomeric Materials.

Existing techniques for patterning metallic structures on elastomers are limited in terms of resolution, yield and scalability. The primary constraint is the incompatibility of their physical properties with conventional cleanroom techniques. We demonstrate a reliable fabrication strategy to transfer high resolution metallic structures of <500 nm in dimension on elastomers. The proposed method consists of producing a metallic pattern using conventional lithographic techniques on silicon coated with a thin sacrificial aluminium layer. Subsequent wet etching of the sacrificial layer releases the elastomer with the embedded metallic pattern. Using this method, a nano-resistor with minimum feature size of 400 nm is fabricated on polydimethylsiloxane (PDMS) and applied in gas sensing. Adsorption of solvents in the PDMS causes swelling and increases the device resistance, which therefore enables the detection of volatile organic compounds (VOCs). Sensitivity to chloroform and toluene vapor with a rapid response (~30 s) and recovery (~200 s) is demonstrated using this PDMS nano-resistor at room temperature.

Nanostructured plasmonic metapixels.

State-of-the-art pixels for high-resolution microdisplays utilize reflective surfaces on top of electrical backplanes. Each pixel is a single fixed color and will usually only modulate the amplitude of light. With the rise of nanophotonics, a pixel's relatively large surface area (~10 µm2), is in effect underutilized. Considering the unique optical phenomena associated with plasmonic nanostructures, the scope for use in reflective pixel technology for increased functionality is vast. Yet in general, low reflectance due to plasmonic losses, and sub-optimal design schemes, have limited the real-world application. Here we demonstrate the plasmonic metapixel; which permits high reflection capability whilst providing vivid, polarization switchable, wide color gamut filtering. Ultra-thin nanostructured metal-insulator-metal geometries result in the excitation of hybridized absorption modes across the visible spectrum. These modes include surface plasmons and quasi-guided modes, and by tailoring the absorption modes to exist either side of target wavelengths, we achieve pixels with polarization dependent multicolor reflection on mirror-like surfaces. Because the target wavelength is not part of a plasmonic process, subtractive color filtering and mirror-like reflection occurs. We demonstrate wide color-range pixels, RGB pixel designs, and in-plane Gaussian profile pixels that have the potential to enable new functionality beyond that of a conventional 'square' pixel.

Gravimetric sensors operating at 1.1 GHz based on inclined c-axis ZnO grown on textured Al electrodes.

Shear mode solidly mounted resonators (SMRs) are fabricated using an inclined c-axis ZnO grown on a rough Al electrode. The roughness of the Al surface is controlled by changing the substrate temperature during the deposition process to promote the growth of inclined ZnO microcrystals. The optimum substrate temperature to obtain homogeneously inclined c-axis grains in ZnO films is achieved by depositing Al at 100 °C with a surface roughness ~9.2 nm, which caused an inclination angle of ~25° of the ZnO c-axis with respect to the surface normal. Shear mode devices with quality-factors at resonance, Q r and effective electromechanical coupling factors, [Formula: see text], as high as 180 and 3.4% are respectively measured. Mass sensitivities, S m of (4.9 ± 0.1) kHz · cm2/ng and temperature coefficient of frequency (TCF) of ~-67 ppm/K are obtained using this shear mode. The performance of the devices as viscosity sensors and biosensors is demonstrated by determining the frequency shifts of water-ethanol mixtures and detection of Rabbit immunoglobin G (IgG) whole molecule (H&L) respectively.