Method For Fabrication Of Devices Research Articles

Vanadium Redox Flow Batteries Fabricated By 3D Printing and Employing Recycled Vanadium Collected from Ammonia Slag

Vanadium redox flow battery (VRFB) is an energy storage system with separately designable power stacks and reservoir. It is one of the most established systems to convert electrical energy to chemical energy, or vice versa, due to its high reversibility, large storage capacity, and the high stability because of the fact that the redox species remain in solution at all times. Currently, the electrolyte for the VRFB is prepared by the electrolytic reduction of vanadium pentoxide (V2O5) in sulfuric acid to produce a vanadium sulfate solution. However, the cost of the whole system exceeds $200/kWh, while the current cost of vanadium is around $ 23-25 Kg-1, which represents around 30% of the overall capital cost of the battery. In order to reduce the cost of the electrolyte, we provide an environmentally–friendly wet process to extract vanadium from industry ammonia slags near the atmospheric conditions (< 100°C). The ammonia slag was treated in a 1.3 M HNO3 solution in a sealed plastic bottle at 95°C for 48 h. After suction–filtrating the insoluble solid, KClO3 was added to the solution to fully oxidize the vanadium species to V5+. Then the solution pH was raised to 6, at which Ca stays dissolved but the others precipitate, by adding a proper amount of a 15 M NaOH solution to obtain Precipitate A. After filtration and washing, Precipitate A was dried in an oven at 50°C overnight, then dissolved in a 1.8 M H2SO4. After that, the solution pH was adjusted to 14 to achieve Precipitate B, which contains the impurities of Mg, Al, Si, Ti, Ni and Fe. Precipitate B was then filtered out and a clear solution remained, in which V still stays. Finally, the solution pH was adjusted to 3 with sulfuric acid and a Precipitate C was formed in the solution after keeping it at 95°C for 12 h. Precipitate C shows a high content of V with a small amount of Na and S observed from EDS, and XRD of this sample indicated presence of NaV6O15 and Na1.2V3O8 as the main components. All of these treatments are done at low temperature (< 100°C) and successfully condensed V from the ammonia slag. Precipitate C and commercial V2O5 (Aldrich) were dissolved to 2 M sulfuric acid to achieve clear yellow solutions of V5+. The vanadium concentration was adjusted to approximately 0.04 M by measuring UV-vis absorption spectra and concentrated to 0.4 M by distillation. A conventional H-cell separated by a Nafion® membrane was used, while two carbon plates served as positive and negative electrodes for the static battery tests. Charging (formation of V5+ and V2+ states) and discharging (V4+ and V3+ states) cycles were nicely achieved with no notable differences between the samples prepared from Precipitate C and reference V2O5 to prove the usefulness of the vanadium resource collected from the ammonia slag for the VFRB application. In this study, we also demonstrated flow battery system, which is designed by CAD and fabricated by a 3D printer. This technique is so powerful that allows us to quickly test different designed parts in order to study optimum cell design using it as the method of device fabrication. Furthermore, our interests are not limited in printing different parts of the cell body, to develop conductive printable materials for micro structured electrode is also very important to maximize the mass transport for the redox media. We have tried to form composites of conductive materials and plastics for that use, and among those carbon fiber-PDMS (Polydimethylsiloxane) composite shows its potential to be the electrode material for RFB. Different flow channels are designed and 3D structured using this composite, which are also tested in the RFB system.

A hybrid paper-based microfluidic platform toward veterinary P-ELISA

This study describes a novel fabrication method to produce a hybrid paper-based microfluidic platform, termed Multi-Pad Paper Plate (MP3) for transfer and optimisation of enzyme-linked immunoassays (ELISA) on paper (P-ELISA). The new fabrication technique is based on a combination of laser micromachining of paper and packaging through thermal lamination. This method is simple, rapid and of high-resolution and can produce robust, versatile and low-cost devices, compatible with a standard 96-well microplate format. The MP3 was used to transfer a sandwich ELISA for detection of bovine haptoglobin (Hp), a marker of inflammation in animals allowing optimisation of the assay in the new format. Using the MP3, a standard curve was generated and the limit of detection achieved was 0.73 μg/ml. The optimised protocol was also applied to the detection of Hp in bovine serum, demonstrating the possibility of using this platform with biological samples. The new platform allowed for a reduction of 93% in time and of 88% in cost for performing the assay and represents a valid alternative to other commonly used device fabrication methods, especially in the context of low-resource settings. It has the potential to translate similar assays into P-ELISA and offers a starting point for achieving animal-side testing.

Microfab in a Microwave Oven: Simultaneous Patterning and Bonding of Glass Microfluidic Devices

We report a new method for fabrication of research-grade glass microfluidic devices using a household microwave oven. The transformative step in this technique is the formation of the microchannel and fusion bonding of the glass layers in a single step. This is demonstrated here using a non-photolithographic technique for both high aspect ratio rectangular and circular cross-section microchannels. In this paper, the microfluidic devices are fabricated utilizing a thin paper cutout as the sacrificial channel layer, glass blanks, and a microwave kiln sold commercially for arts and crafts. Glass microfluidic devices are fabricated in a microwave oven in as short as 2 min.

Evaluation of the Electrical Resistance Response of Insulating Glass Surface to Sense and Classify Humidity and VOCs Vapors

The research on new materials, fabrication processes, and characterization methods aims at obtaining sensors with low cost, high sensibility, and possibility of integration with electronic circuits. Recently, several works have focused on the development of gas sensors based on nanomaterials deposited on insulating platforms due to the remarkable sensing properties of such materials and simple device fabrication methods. However, the interference of such insulating platforms in the sensing properties of a miniaturized sensor becomes non-negligible depending on the dimensions, the type and amount of material, and the gas species analyzed. Thus, this paper proposes the use of interdigital aluminum microelectrodes patterned on a glass substrate to evaluate the influence of adsorption and desorption mechanisms of humidity and volatile organic compounds on this insulating surface. By analyzing the electrical conduction changes when the device is exposed to the mentioned vapors, we demonstrate that this influence is quite significant, as the electrical resistance of the glass insulating platform presented pronounced and fast resistance variation with repeatability and low drift. In addition, the selectivity among the experimented gas species was achieved by applying principal component analysis and supervised linear discriminant analysis classification methodologies, obtaining a success rate of 94% by using a cross-validation technique. The results show that the sensing properties of insulating platforms must be considered in some situations because they can affect the response of sensors based on nanomaterials deposited on insulating substrates.

Perovskites-Based Solar Cells: A Review of Recent Progress, Materials and Processing Methods.

With the rapid increase of efficiency up to 22.1% during the past few years, hybrid organic-inorganic metal halide perovskite solar cells (PSCs) have become a research “hot spot” for many solar cell researchers. The perovskite materials show various advantages such as long carrier diffusion lengths, widely-tunable band gap with great light absorption potential. The low-cost fabrication techniques together with the high efficiency makes PSCs comparable with Si-based solar cells. But the drawbacks such as device instability, J-V hysteresis and lead toxicity reduce the further improvement and the future commercialization of PSCs. This review begins with the discussion of crystal and electronic structures of perovskite based on recent research findings. An evolution of PSCs is also analyzed with a greater detail of each component, device structures, major device fabrication methods and the performance of PSCs acquired by each method. The following part of this review is the discussion of major barriers on the pathway for the commercialization of PSCs. The effects of crystal structure, fabrication temperature, moisture, oxygen and UV towards the stability of PSCs are discussed. The stability of other components in the PSCs are also discussed. The lead toxicity and updated research progress on lead replacement are reviewed to understand the sustainability issues of PSCs. The origin of J-V hysteresis is also briefly discussed. Finally, this review provides a roadmap on the current needs and future research directions to address the main issues of PSCs.

Room‐Temperature Carbon Nanotube Single‐Electron Transistors with Mechanical Buckling–Defined Quantum Dots

AbstractSingle‐electron transistors (SETs) have been proposed as a future alternative to conventional Si‐based electronics. However, their practical applications are strongly limited because most SETs operate at cryogenic temperatures. In this work, room temperature operating SETs are successfully fabricated with the realization of a mechanical buckling–defined quantum dot within a suspended and strained single‐walled carbon nanotube. Clear Coulomb oscillations are observed at room temperature due to the Coulomb blockade effect. The Coulomb charging energy is calculated to be 160 meV, which substantially exceeds the thermal energy. At 10 K, the Coulomb staircases are observed in the current–voltage characteristics with an energy level separation ≈29 meV, confirming that the island behaves as a well‐defined quantum dot for the electrons. This device fabrication method may also help future investigations into the electromechanical properties of nanotube quantum systems.

Assembling 2D Mxene into 3D Ordered Structures for High Power Li-Ion Capacitors

MXenes are a family of two-dimensional (2D) materials with interesting electrical and electrochemical properties and their high potential as electrode materials for Li-ion capacitors has been recently demonstrated. However, the conventional methods for electrode assembly and device fabrication are limiting factors in exploiting the full potential of these electrode materials. The research on the development of electrochemical energy storage devices in the past few years has led to the realization that improved performance can be achieved by assembling the electrode materials into three-dimensional (3D) architectures instead of the conventional 2D “laminate” architecture. In this talk, we present a simple, efficient, and scalable method to assemble 2D Ti3C2 into ordered 3D and porous aerogel structures with high specific capacitances and rate capabilities. MXenes aerogels are fabricated by directional freeze casting and show large specific surface areas. The porous structure of MXene aerogels is dependent on the processing conditions and affect their mechanical and electrochemical properties. MXene aerogels show significantly high specific capacities (1200 mAh/g at 0.05 A/g), excellent rate capability (200 mAh/g at 10 A/g) and outstanding cycling performance for reversible lithium-ion energy storage. We believe that the fabricated 3D MXene structures are promising for a broad range of applications.

Imaging through a projection screen using bi-stable switchable diffusive photon sieves

We designed and demonstrated a liquid crystal (LC) photon sieve (PS) device which can be integrated on a conventional diffusive projection screen and switched to record images. The device fabrication method and assembly of it by using Smectic A (SmA) LC material is also presented. In the PS state, the device comprises diffusive elements, which simultaneously allow to image the scene in front of the device on a camera sensor behind itself and display another image projected onto the device. The image captured using the PS has acceptable visual quality. The projected images, from an external picture source, on the diffusive elements can be observed with a quality comparable to the full scattering state. The projected images are observed with almost no detectable features of the device at the observation distance. The device offers a built-in solution for eye-to-eye video conferencing applications.

A comparative device performance assesment of CVD grown MoS2 and WS2 monolayers

In this study, optical and electronic transport properties of chemical vapor deposition (CVD) grown 2D WS2 and MoS2 based transistors and photodetectors are investigated and compared in ambient air by using 2D flakes grown with the same CVD system. To assess the performance variations between these two materials and understand the underlying mechanisms, it is essential to utilize identical growth methods (i.e. using the same CVD system), identical substrate and dielectric materials with the identical device fabrication methods and geometries. Transistor devices fabricated out of these flakes are examined in terms of their field effective mobility, current ON/OFF ratio, and photoresponsivity. Our results show that the MoS2 based devices have higher mobility and photoresponsivity than the WS2 based devices. However, the hysteresis curve of WS2 based transistors is smaller when compared to that of MoS2 based transistors. The mobilities of MoS2 and WS2 are estimated from measurements as 1.45 and 0.98 cm2 V−1 s−1, respectively. The electronic transport performance of MoS2 based devices (FETs and photodetectors) are found to be unexpectedly better than the WS2 based devices in terms of effective carrier mobility and photoresponsivity at ambient atmosphere and temperature. Our results suggest that WS2 is more sensitive to ambient conditions in comparison to MoS2, in spite of its theoretically estimated superior performance.

Self-Formed Channel Devices Based on Vertically Grown 2D Materials with Large-Surface-Area and Their Potential for Chemical Sensor Applications.

2D layered materials with sensitive surfaces are promising materials for use in chemical sensing devices, owing to their extremely large surface-to-volume ratios. However, most chemical sensors based on 2D materials are used in the form of laterally defined active channels, in which the active area is limited to the actual device dimensions. Therefore, a novel approach for fabricating self-formed active-channel devices is proposed based on 2D semiconductor materials with very large surface areas, and their potential gas sensing ability is examined. First, the vertical growth phenomenon of SnS2 nanocrystals is investigated with large surface area via metal-assisted growth using prepatterned metal electrodes, and then self-formed active-channel devices are suggested without additional pattering through the selective synthesis of SnS2 nanosheets on prepatterned metal electrodes. The self-formed active-channel device exhibits extremely high response values (>2000% at 10 ppm) for NO2 along with excellent NO2 selectivity. Moreover, the NO2 gas response of the gas sensing device with vertically self-formed SnS2 nanosheets is more than two orders of magnitude higher than that of a similar exfoliated SnS2 -based device. These results indicate that the facile device fabrication method would be applicable to various systems in which surface area plays an important role.

Initiated Chemical Vapor Deposition: A Versatile Tool for Various Device Applications

Advances in device technology have been accompanied by the development of new types of materials and device fabrication methods. Considering device design, initiated chemical vapor deposition (iCVD) inspires innovation as a platform technology that extends the application range of a material or device. iCVD serves as a versatile tool for surface modification using functional thin film. The building of polymeric thin films from vapor phase monomers is highly desirable for the surface modification of thermally sensitive substrates. The precise control of thin film thicknesses can be achieved using iCVD, creating a conformal coating on nano‐, and micro‐structured substrates such as membranes and microfluidics. iCVD allows for the deposition of polymer thin films of high chemical functionality, and thus, substrate surfaces can be functionalized directly from the iCVD polymer film or can selectively gain functionality through chemical reactions between functional groups on the substrate and other reactive molecules. These beneficial aspects of iCVD can spur breakthroughs in device fabrication based on the deposition of robust and functional polymer thin films. This review describes significant implications of and recent progress made in iCVD‐based technologies in three fields: electronic devices, surface engineering, and biomedical applications.

Extreme Carrier Depletion and Superlinear Photoconductivity in Ultrathin Parallel‐Aligned ZnO Nanowire Array Photodetectors Fabricated by Infiltration Synthesis

AbstractUltrathin semiconductor nanowires enable high‐performance chemical sensors and photodetectors, but their synthesis and device integration by standard complementary metal‐oxide‐semiconductor (CMOS)‐compatible processes remain persistent challenges. This work demonstrates fully CMOS‐compatible synthesis and integration of parallel‐aligned polycrystalline ZnO nanowire arrays into ultraviolet photodetectors via infiltration synthesis, material hybridization technique derived from atomic layer deposition. The nanowire photodetector features unique, high device performances originating from extreme charge carrier depletion, achieving photoconductive on–off ratios of &gt;6 decades, blindness to visible light, and ultralow dark currents as low as 1 fA, the lowest reported for nanostructure‐based photoconductive photodetectors. Surprisingly, the low dark current is invariant with increasing number of nanowires and the photodetector shows unusual superlinear photoconductivity, observed for the first time in nanowires, leading to increasing detector responsivity and other parameters for higher incident light powers. Temperature‐dependent carrier concentration and mobility reveal the photoelectrochemical‐thermionic emission process at grain boundaries, responsible for the observed unique photodetector performances and superlinear photoconductivity. The results elucidate fundamental processes responsible for photogain in polycrystalline nanostructures, providing useful guidelines for developing nanostructure‐based detectors and sensors. The developed fully CMOS‐compatible nanowire synthesis and device fabrication methods also have potentials for scalable integration of nanowire sensor devices and circuitries.

Homogenous Dispersion of MoS2 Nanosheets in Polyindole Matrix at Air-Water Interface Assisted by Langmuir Technique.

Two-dimensional (2D) inorganic layered materials when embedded in organic polymer matrix exhibit exotic properties that are grabbing contemporary attention for various applications. Here, nanosheet morphology of molybdenum disufide (MoS2) synthesized via one-pot facile hydrothermal reaction are exfoliated in benign aqueous medium in the presence of indole to obtain a stable dispersion. These exfoliated nanosheets then act as host to template the controlled polymerization of indole. The preassembled MoS2-polyindole (MoS2-PIn) nanostructures are reorganized at the air-water interface using the Langmuir method to facilitate maximum interfacial interaction between nanosheet and polymer. This report emphasizes large area, homogeneous dispersion of uniform-sized MoS2 nanosheets (40-60 nm diameter) in the PIn matrix and the formation of stable and uniform film via the Langmuir-Schaefer (LS) method. These self-assembled, MoS2 decorated PIn LS films are characterized using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The fabricated LS films in sandwiched structure Al/MoS2-PIn/ITO as the Schottky diode portrayed remarkable enhancements in charge transport properties. Our study illustrates the potential of the MoS2-PIn LS film in electronic applications and opens a new dimension for uniform dispersion of 2D materials in other polymers via the Langmuir method for device fabrication and enhancement of electrical properties.

Analysis of electrical characteristics and proposal of design guide for ultra-scaled nanoplate vertical FET and 6T-SRAM

In this paper, electrical characteristics of gate-all-around (GAA) nanoplate (NP) vertical FET (VFET) were analyzed for single transistor and 6T-SRAM cell through 3D technology computer-aided design (TCAD) simulation. In VFET, gate and extension lengths are not limited by the area of device because theses lengths are vertically located. The height of NP is assumed in 40 nm considering device fabrication method (top-down approach). According to the sizes of devices, we analyzed the performances of device such as total resistance, capacitance, intrinsic gate delay, sub-threshold swing (S.S), drain-induced barrier lowering (DIBL) and static noise margin (SNM). As the gate length becomes larger, the resistance should be smaller because the total height of NP is fixed in 40 nm. Also, when the channel thickness becomes thicker, the total resistance becomes smaller since the sheet resistances of channel and extension become smaller and the contact resistance becomes smaller due to the increasing contact area. In addition, as the length of channel pitch increases, the parasitic capacitance comes to be larger due to the increasing area of gate-drain and gate-source. The performance of RC delay is best in the shortest gate length (12 nm), the thickest channel (6 nm) and the shortest channel pitch (17 nm) owing to the reduced resistance and parasitic capacitance. However, the other performances such as DIBL, S.S, on/off ratio and SNM are worst because the short channel effect is highest in this situation. Also, we investigated the performance of the multi-channel device. As the number of channels increases, the performance of device and the reliability of SRAM improve because of reduced contact resistance, increased gate dimension and multi-channel compensation effect.

A fast and low-cost microfabrication approach for six types of thermoplastic substrates with reduced feature size and minimized bulges using sacrificial layer assisted laser engraving

Since polydimethylsiloxane (PDMS) is notorious for its severe sorption to biological compounds and even nanoparticles, thermoplastics become a promising substrate for microdevices. Although CO2 laser engraving is an efficient method for thermoplastic device fabrication, it accompanies with poor bonding issues due to severe bulging and large feature size determined by the diameter of laser beam. In this study, a low-cost microfabrication method is proposed by reversibly sealing a 1 mm thick polymethylmethacrylate (PMMA) over an engraving substrate to reduce channel feature size and minimize bulges of laser engraved channels. PMMA, polycarbonate (PC), polystyrene (PS), perfluoroalkoxy alkane (PFA), cyclic-olefin polymers (COP) and polylactic acid (PLA) were found compatible with this sacrificial layer assisted laser engraving technique. Microchannel width as small as ∼40 μm was attainable by a laser beam that was 5 times larger in diameter. Bulging height was significantly reduced to less 5 μm for most substrates, which facilitated leak proof device bonding without channel deformation. Microdevices with high aspect ratio channels were prepared to demonstrate the applicability of this microfabrication method. We believe this fast and low-cost fabrication approach for thermoplastics will be of interest to researchers who have encountered problem with polydimethylsiloxane based microdevices in their applications.

Fully nozzle-jet printed non-enzymatic electrode for biosensing application

The progress in developing the electrochemical sensors for biomolecule detection requires a facile device fabrication method. Herein, we report printing of silver (Ag) precursor and copper oxide nanoparticles (CuO NPs) inks by nozzle-jet technique to fabricate non-enzymatic glucose biosensor on flexible polyethylene terephthalate (PET) substrate. The fully printed CuO NPs/Ag/PET electrodes were characterized using electrochemical techniques for non-enzymatic biosensing of glucose. The fully printed non-enzymatic biosensor exhibited a high sensitivity (1424.2 μA mM−1 cm−2), linear range from 0.1 to 15 mM, low detection limit (0.3 μM; S/N = 3) and fast response time of ∼2 s under a working potential of +0.6 V. Additionally, printed electrodes demonstrated an excellent long term stability, high reproducibility, good selectivity and high accuracy during glucose concentration measurements in human blood and serum samples. These results indicate that the electrode fabrication using nozzle-jet printing can be regarded as a potential technique for the future development of high performance and low cost bio/chemical sensor devices.

Laser-bulge based ultrasonic bonding method for fabricating multilayer thermoplastic microfluidic devices

Ultrasonic bonding is a commonly-used method for fabrication of thermoplastic microfluidic devices. However, due to the existence of the energy director (a convex structure to concentrate the ultrasonic energy), it is difficult to control its molten polymer flow, which may result in a small gap between the bonding interface or microchannel clogging. In this paper, we present an approach to address these issues. Firstly, the microchannels were patterned onto the PMMA sheets using hot embossing with the wire electrical discharge machined molds. Then, a small bulge, which was formed at the edge of the laser-ablated groove (LG), was generated around the microchannel using a CO2 laser ablation system. By using the bulge to concentrate the ultrasonic energy, there was no need for fabricating the complicated and customized energy director. When the bulge was melted, it was able to flow into the LG which overcame the ‘gap’ and ‘clogging’ problems. Here, two types of two-layer microfluidic devices and a five-layer micromixer were fabricated to validate its performance. Our results showed that these thermoplastic microdevices can be successfully bonded by using this method. The liquid leakage was not observed in both the capillary-driven flowing test and the pressure-driven mixing experiments. It is a potential method for bonding the thermoplastic microfluidic devices.

Effect of body bias and temperature on low-frequency noise in 40-nm nMOSFETs

This study investigated the effects of temperature and body bias on drain current flicker noise (1/f) in 40-nm nMOSFETs. The 1/f noise is attributable to the charge number fluctuation correlating with the mobility fluctuation. At 300K, as the depletion width was decreased, 1/f noise decreased with the body bias from −0.5 to +0.5V in the weak inversion; conversely, 1/f noise was independent of the body bias because of the neglected depletion charge capacitance in the strong inversion. When the temperature was below 150K, 1/f noise increased when the drain voltage was low because of the Fermi level toward the band edge, which has a higher trap density and corresponds to the inverse square of the subthreshold swing. However, when the drain voltage was high, 1/f noise was dominated by the mobility fluctuation because a wider strong inversion region at 150K resulted in a lower 1/f noise and insignificant body effect. The analysis of this behavior in 40-nm devices may assist in determining the optimal device fabrication methods and circuit design.

Direct spraying method for fabrication of paper-based microfluidic devices

Direct spraying of hydrophobic materials is an affordable, easy-to-use and equipment-free method for fabrication of flexible microsensors, albeit not yet widely adopted. To explore its application potential, in this paper, we propose and demonstrate two novel hybrid methods to fabricate paper-based components. Firstly, through combing direct spraying with Parafilm embedding, a leak-free paper-based sample preconcentrator for fluorescence sensing was fabricated. The leak-free device worked on the principle of ion concentration polarization (ICP) effect, and achieved enhancement of fluorescent tracer by 220 folds on a paper substrate. Secondly, by using the sprayed hydrophobic patterns, paper-based microsized supercapacitors (mSCs) were fabricated. Vacuum filtration was used to deposit multi-wall carbon nanotubes (MWCNT)-dispersed solution on a porous substrate to form electrodes. A volumetric capacitance of 42.5 mF cm−3 at a current density of 2 mA cm−3 was obtained on the paper-based mSC. Our demonstrations have shown the versatility of direct spraying for the fabrication of integrative paper-based microfluidic devices.

Effect of post-annealing on sputtered MoS2 films

Typical routes for fabricating MoS2-based electronic devices rely on the transfer of as-prepared flakes to target substrates, which is incompatible with conventional device fabrication methods. In this work we investigated the preparation of MoS2 films by magnetron sputtering. By subjecting room-temperature sputtered MoS2 films to post-annealing at mild conditions (450°C in a nitrogen flow), crystalline MoS2 films were formed. To demonstrate the compatibility of the technique with typical device fabrication processes, MoS2 was prepared on epitaxial magnetic oxide films of La0.7Sr0.3MnO3, and the magnetic behavior of the films were unaffected by the post-annealing process. This work demonstrates the possibility of fabricating electronic and spintronic devices based on continuous MoS2 films prepared by sputtering deposition.