Cost-effective Fabrication Process Research Articles

Efficient surface enhanced Raman scattering substrates based on complex gold nanostructures formed by annealing sputtered gold thin films

Surface enhanced Raman scattering (SERS) has attracted great attention of scientists in the last few decades due to its wide range of applications, especially in detecting chemical compounds even at single molecular level. In this research, we combine sputtering and post annealing method to prepare gold nanoparticles with uniform distribution on cover glass substrates, which work as efficient SERS substrates. This work studies the effect of gold thickness on the formation of nanoparticles during annealing process. The effect of size, inter-distance and morphology of gold NPs on plasmon properties was studied by scanning electron microscope and absorption spectroscopy. The enhancement capability of different morphologies was also verified by using Finite Different Time Domain (FDTD) technique. The as-prepared gold nanoparticles arrays are efficient surface enhanced Raman scattering substrates as demonstrated by the ability to detect methylene blue at concentration as low as 10−10 M. The facile, cost-effective fabrication process is convenient to scale up for mass production of high sensitivity surface enhanced Raman substrates.

All solution processed flexible p-NiO/n-CdS rectifying junction: Applications towards broadband photodetector and human breath monitoring

Solution processable flexible devices meet the rising demand of sensors in wearable electronics owing to their cost-effective fabrication process with large area and throughput. This report demonstrates the multifunctional sensor based on p-NiO/n-CdS rectifying junction on ITO coated PET flexible substrate using low-temperature all solution processed deposition technique for UV–vis photodetection and breath monitoring applications. Under UV and visible light, the fabricated device exhibited strong current rectifying activity of approximately four orders. The responsivity (R) of the device underneath UV and visible illuminations found to be ~40.43 mAW−1 and ~25.96 mAW−1, respectively. Further, the device showed a response time of ~3.2 sec and detectivity of 1.4 × 1010 Jones under UV illumination. The internal electric field created at the p-NiO and n-CdS interface due to the formation of excellent rectifying junction assists in the efficient separation of photo-generated electron-hole pairs, thus improving the responsivity. Furthermore, the fabricated device was used as a breath sensor, and it was evaluated for different breath patterns of an individual. Interestingly, the device was able to distinguish between the different breath patterns (slow, fast, deep, etc.) The fabricated device displayed a negligible change in performance even after harsh deformations, indicating the flexibility and robustness of the device.

Analysis of Grain Boundary Dependent Memory Characteristics in Poly-Si One-Transistor Dynamic Random-Access Memory.

A capacitorless one-transistor dynamic random-access memory cell with a polysilicon body (poly-Si 1T-DRAM) has a cost-effective fabrication process and allows a three-dimensional stacked architecture that increases the integration density of memory cells. Also, since this device uses grain boundaries (GBs) as a storage region, it can be operated as a memory cell even in a thin body device. GBs are important to the memory characteristics of poly-Si 1T-DRAM because the amount of trapped charge in the GBs determines the memory's data state. In this paper, we report on a statistical analysis of the memory characteristics of poly-Si 1T-DRAM cells according to the number and location of GBs using TCAD simulation. As the number of GBs increases, the sensing margin and retention time of memory cells deteriorate due to increasing trapped electron charge. Also, "0" state current increases and memory performance degrades in cells where all GBs are adjacent to the source or drain junction side in a strong electric field. These results mean that in poly-Si 1T-DRAM design, the number and location of GBs in a channel should be considered for optimal memory performance.

Practical Evaluation of Printed Strain Sensors Based on Long-Term Static Strain Measurements.

Recent progress in printable electronics has enabled the fabrication of printed strain sensors for diverse applications. These include the monitoring of civil infrastructure, the gradual aging of which raises concerns about its effective maintenance and safety. Therefore, there is a need for automated sensing systems that provide information on the performance and behavior of engineering structures that are subjected to dynamic and static loads. The application of printed strain sensors in structural health monitoring is of growing interest owing to its large-area and cost-effective fabrication process. Previous studies have proven the suitability of printable strain sensors for dynamic strain measurements on bridges; however, the analysis of the long-term stability of printed sensors during static strain measurements is still lacking. Thus, this study aims to assess the long-term stability of printed strain sensor arrays and their suitability for the static strain analysis of large civil structures. The developed sensors and a dedicated wireless data acquisition system were deployed inside a gravity dam, which was selected as the field test environment. This test environment was chosen owing to the relatively stable temperature inside the dam and the very slow static strain changes associated with periodic water level changes. The results exhibited an average signal drift of 20 over 127 days. One of the sensor arrays was installed on a small crack in the dam structure; it showed that the sensors can track static strain changes owing to variations in the crack opening, which are related to the water level changes in the dam. Overall, the results of the developed sensors exhibit good strain sensitivity and low signal drift. This indicates the potential suitability of printed sensors for applications in the static strain analysis of engineering structures.

Optical modulation frequency mediated tunable response time and responsivity in graphene-PbS QD based hybrid photodetectors

Graphene/lead sulfide (PbS) quantum dot (QD) hybrid infrared photodetectors have gained a lot of attention in recent times due to their high resolution and cost effective fabrication process. In spite of exhibiting remarkably high responsivity, such hybrid detectors are slow as a result of their internal gain mechanism process. In this work, we present a convenient strategy to modulate the correlation between their responsivity and response time giving access to high resolution fast photodetectors in the broadband wavelength range for imaging purpose. Using a layer-by-layer deposition technique including simultaneous ligand exchange and surface passivation at each layer, homogeneous PbS QD films on chemical vapour deposition grown single layer graphene could be achieved. The obtained hybrid phototransistors exhibit a high responsivity of 108 A W−1 and sensitivity down to 0.1 pW incident light power in the near-infrared wavelength range. By modulating the incident light at a modulation frequency up to 50 kHz, we achieve a response time as low as 5 μs while preserving a much higher responsivity (144 A W−1) compared to existing commercial room temperature infrared photodetectors.

Scalable synthesis of multicomponent multifunctional inorganic core@mesoporous silica shell nanocomposites

Integrating multiple materials with different functionalities in a single nanostructure enables advances in many scientific and technological applications. However, such highly sophisticated nanomaterials usually require complex synthesis processes that complicate their preparation in a sustainable and industrially feasible manner. Herein, we designed a simple general method to grow a mesoporous silica shell onto any combination of hydrophilic nanoparticle cores. The synthetic strategy, based on the adjustment of the key parameters of the sol-gel process for the silica shell formation, allows for the embedment of single, double, and triple inorganic nanoparticles within the same shell, as well as the size-control of the obtained nanocomposites. No additional interfacial adhesive layer is required on the nanoparticle surfaces for the embedding process. Adopting this approach, electrostatically stabilized, small-sized (from 4 to 15 nm) CeO2, Fe3O4, Gd2O3, NaYF4, Au, and Ag cores were used to test the methodology. The mean diameter of the resulting nanocomposites could be as low as 55 nm, with high monodispersity. These are very feasible sizes for biological intervention, and we further observed increased nanoparticle stability in physiological environments. As a demonstration of their increased activity as a result of this, the antioxidant activity of CeO2 cores was enhanced when in core-shell form. Remarkably, the method is conducted entirely at room temperature, atmospheric conditions, and in aqueous solvent with the use of ethanol as co-solvent. These facile and even “green” synthesis conditions favor scalability and easy preparation of multicomponent nanocomposite libraries with standard laboratory glassware and simple benchtop chemistry, through this sustainable and cost-effective fabrication process.

A cost-effective and solderability stretchable circuit boards for wearable devices

Soft/stretchable electronics accompanied by the nature of matching nonplanar and dynamic surfaces have wide application prospects in the fields of information, energy, medical, and national defense. Current soft/stretchable electronics suffer from high cost, low yield, and poor solderability due to the limitation of fabrication process capabilities of soft electronic materials. We thus present a cost-effective and solderable fabrication process for manufacturing stretchable circuit boards (SCBs). The excellent solderability of the SCBs is demonstrated. The shaped polyimide (PI) layers, which served as solder masks and support layers, allow electronic components with different packages to solder onto the SCBs. The feasibility of the SCBs for application in wearable embedded systems is demonstrated by developing a soft wireless pressure monitoring prototype and a soft posture detection and control system on the SCBs. The tests of stretchability and durability of SCBs and SCB-based embedded systems are carried out. The results reveal that SCBs and SCB-based embedded systems are robust enough for application in wearable systems. The proposed process has been demonstrated as a novel, state-of-the-art manufacturing process for SCB fabrication. It has the potential to extend to other types of soft wearable embedded systems.

Antiseptic povidone-iodine encapsulating edible phospholipid gels

Lecithin-based gels are generally made by adding water or water/surfactant systems into lecithin dissolved solvents, a process known as organogel formation. Organogels are stable viscoelastic micellar phospholipid aggregates with drug encapsulating capabilities. In this work, we demonstrate an alternative approach in which soy lecithin/alginate (1:1) gels were fabricated from aqueous solutions by divalent cationic crosslinking without using any solvents. As a model drug, we used a common antiseptic, povidone iodine complex (PVPI) that has been recently demonstrated to be effective and fast acting against SARS-CoV-2 virus. Rheological characteristics of gelling dynamics were studied with isothermal oscillation shear measurements. The gels were shown to encapsulate PVPI complex (7 wt%), during ionic cross-linking. Soy lecithin significantly minimized antiseptic loss during crosslinking. At the end of 1 h of gelling process, lecithin free gels lost 20% of the loaded drug whereas composite gels lost about 12% back into the crosslinking solution. In water, drug release from the composite gels was slower compared to lecithin-free gels. This effect was more pronounced in simulated gastric fluid, indicating that the composite gels could act as slow dissociating matrices for hydrophilic drugs in gastric fluid. Optical density (600 nm) measurements showed that PVPI loaded composite gels effectively disinfected aqueous media contaminated with both gram-negative and gram-positive bacteria. This cost-effective fabrication process can be easily scaled up with potential applications such as wet tissue ulcer treatment and biodegradable field water purification additives targeting not only bacteria but also virulent water borne pathogens.

Extrusion-Based 3D Printing Applications of PLA Composites: A Review

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as mechanical weakness, water solubility rate, etc. FDM is a simple and more cost-effective fabrication process compared to other 3D printing techniques. Unfortunately, there are deficiencies of the FDM approach, such as mechanical weakness of the FDM parts compared to the parts produced by the conventional injection and compression molding methods. Preparation of PLA composites with suitable additives is the most useful technique to improve the properties of the 3D-printed PLA parts obtained by the FDM method. In the last decade, newly developed PLA composites find large usage areas both in academic and industrial circles. This review focuses on the chemistry and properties of pure PLA and also the preparation methods of the PLA composites which will be used as a raw material in 3D printers. The main drawbacks of the pure PLA filaments and the necessity for the preparation of PLA composites which will be employed in the FDM-based 3D printing applications is also discussed in the first part. The current methods to obtain PLA composites as raw materials to be used as filaments in the extrusion-based 3D printing are given in the second part. The applications of the novel PLA composites by utilizing the FDM-based 3D printing technology in the fields of biomedical, tissue engineering, human bone repair, antibacterial, bioprinting, electrical conductivity, electromagnetic, sensor, battery, automotive, aviation, four-dimensional (4D) printing, smart textile, environmental, and luminescence applications are presented and critically discussed in the third part of this review.

Fabrication and Materials Integration of Flexible Humidity Sensors for Emerging Applications.

In the past decade, humidity measurements have ubiquitously gained consideration in the wide range of application paradigms such as industrial predictive maintenance, instrumentation, automation, agriculture, climate monitoring, healthcare, and semiconductor industries. Accurate humidity measurements and cost-effective fabrication processes for large-volume and high-performance sensors with flexible form factors are essential to meet the stringent performance requirements of the emerging application areas. To address this need, recent efforts focus on development of innovative sensing modalities, process technologies, and exploration and integration of new materials to enable low-cost, robust, and flexible humidity sensors with ultrahigh sensitivity and linearity, large dynamic range, low hysteresis, and fast response time. In this review paper, we present an overview of flexible humidity sensors based on distinct sensing mechanisms, employed processing techniques, and various functional sensing layers and substrate materials for specific applications. Furthermore, we present the critical device design parameters considered to be indicative of sensor performance such as relative humidity range, along with a discussion on some of the specific applications and use cases.

Porous Silicon Optical Devices: Recent Advances in Biosensing Applications.

This review summarizes the leading advancements in porous silicon (PSi) optical-biosensors, achieved over the past five years. The cost-effective fabrication process, the high internal surface area, the tunable pore size, and the photonic properties made the PSi an appealing transducing substrate for biosensing purposes, with applications in different research fields. Different optical PSi biosensors are reviewed and classified into four classes, based on the different biorecognition elements immobilized on the surface of the transducing material. The PL signal modulation and the effective refractive index changes of the porous matrix are the main optical transduction mechanisms discussed herein. The approaches that are commonly employed to chemically stabilize and functionalize the PSi surface are described.

MTM- and SIW-Inspired Bowtie Antenna Loaded with AMC for 5G mm-Wave Applications

This paper investigates a feasible configuration of slotted bowtie antenna based on MTM and SIW properties for 5G millimeter-wave applications. To realize the proposed slotted bowtie antenna in a compact dimension with high performances, the MTM and SIW concepts are implemented by applying the trapezoidal slots on the top surface of the antenna and metallic via holes through the substrate layer connecting the top surface to the ground plane. The antenna has been fed with a simple microstip-line which is connected to a waveguide-port. It is shown that the slotted bowtie antenna with a small dimension of 30 × 16 × 0.8 mm3 operates over a measured wideband of 32–34.6 GHz with the fractional bandwidth, average gain, and radiation efficiency of 7.8%, 3.2 dBi, and 50%, respectively. To improve the antenna's performance, the artificial magnetic conductor (AMC) properties have been employed on the ground plane by loading vertical and linear slots with various lengths. The AMC slots are aligned under the trapezoidal slots on the top surface to transfer the maximum electromagnetic signals to them for optimum radiation. The proposed method enlarges the antenna’s effective aperture area, keeping constant its physical dimensions. The proposed AMC-loaded antenna covers wider frequency range of 30–37 GHz in measurement, which corresponds to 21% fractional bandwidth. The average experimental gain and radiation efficiency have been increased to 5.5 dBi and 66.5%, respectively, which illustrate the effectiveness of the proposed AMC-loaded antenna. The results confirm that the proposed slotted bowtie antenna with advantages of compact dimension, wide bandwidth, high gain and efficiency, low profile, being cost-effective, simple design, and easy fabrication process, which makes it applicable for mass production, can be a good candidate for 5G millimeter-wave applications.

Fabrication of Highly Flat, Flexible Mesh Electrode for Use in Photovoltaics

Metal mesh-based flexible transparent conductive electrodes have attracted much interest as one alternative to conventional indium tin oxide electrodes. In addition to ongoing efforts to develop scalable and cost-effective fabrication processes for high-resolution mesh patterns, the high surface roughness of the mesh which can cause short circuiting and current leakage in optoelectronic devices must be solved. Herein, high-resolution (below ~ 10 μm) mesh patterns with various thicknesses are fabricated by scalable, selective transfer printing and then stably and sufficiently sintered under delicately controlled flash irradiation. A polyethylene terephthalate (PET) film is laminated on the patterns overlaid with a UV-curable resin and then peeled off after UV curing, which produces mesh patterns strongly bonded to the cured resin to be separated in a fully embedded form. The final, highly flat, flexible mesh with a low sheet resistance of 1.7 Ω sq−1, a high optical transparency of 88.6%, excellent mechanical flexibility, and strong adhesion to the substrate is successfully implemented in a flexible perovskite solar cell with a high power conversion efficiency (PCE) of 14.92%.

Floating Gate Schottky Junction Solar Cells With Improved Output Power

In this article, the concept of floating gate Schottky junction (FGSJ) solar cell with improved photovoltaic properties, compared to those of the conventional Schottky junction solar cell, is proposed. The floating gate junction is electrically isolated from the current collection junction in order to prevent reduction in the barrier height at the floating gate contact from load voltage. The unaffected barrier height at the floating gate junction leads to a more effective separation of photo-generated electron-hole pairs, and therefore, a better photovoltaic response. Single junction FGSJ solar cells based on n -type GaAs with different doping concentration levels and gate contact layer materials were fabricated, and their electrical and optical properties were characterized under standard 1-sun illumination condition. The measurement results show a notable improvement in both diode-like and photovoltaic properties of FGSJ solar cells compared to those of the conventional Schottky solar cells, which includes higher short-circuit current density, open-circuit voltage, and maximum output power. This is due to a higher equivalent Schottky barrier height in FGSJ solar cells compared with nonfloating gate devices. Moreover, the proposed floating gate structure can be used in metal/ n -type semiconductor Schottky junctions to eliminate the use of highly p -doped wide bandgap semiconductors in p–n junctions. Also, the simpler and more cost-effective fabrication process of the FGSJ solar cells, compared to the p–n junction solar cells, could reduce the total production cost; therefore, making them financially viable for large-scale development of high-efficiency photovoltaic panels.

Apparent differences between single layer molybdenum disulphide fabricated via chemical vapour deposition and exfoliation

Innovative applications based on two-dimensional solids require cost-effective fabrication processes resulting in large areas of high quality materials. Chemical vapour deposition is among the most promising methods to fulfill these requirements. However, for 2D materials prepared in this way it is generally assumed that they are of inferior quality in comparison to the exfoliated 2D materials commonly used in basic research. In this work we challenge this assumption and aim to quantify the differences in quality for the prototypical transition metal dichalcogenide MoS2. To this end single layers of MoS2 prepared by different techniques (exfoliation, grown by different chemical vapour deposition methods, transfer techniques and as vertical heterostructure with graphene) are studied by Raman and photoluminescence spectroscopy, complemented by atomic force microscopy. We demonstrate that as-prepared MoS2, directly grown on SiO2, differs from exfoliated MoS2 in terms of higher photoluminescence, lower electron concentration and increased strain. As soon as a water film is intercalated (e.g. by transfer) underneath the grown MoS2, in particular the (opto)electronic properties become practically identical to those of exfoliated MoS2. A comparison of the two most common precursors shows that the growth with MoO3 causes greater strain and/or defect density deviations than growth with ammonium heptamolybdate. As part of a heterostructure directly grown MoS2 interacts much stronger with the substrate and in this case an intercalated water film does not lead to the complete decoupling, which is typical for exfoliation or transfer. Our work shows that the supposedly poorer quality of grown 2D transition metal dichalcogenides is indeed a misconception.

Simple Amphoteric Charge Strategy to Reinforce Superhydrophilic Polyvinylidene Fluoride Membrane for Highly Efficient Separation of Various Surfactant-Stabilized Oil-in-Water Emulsions.

Long-term efficient separation of highly emulsified oily wastewater is challenging. Reported herein is the preparation of a reinforced superhydrophilic, underwater superoleophobic membrane with demulsification properties using active iron nanoparticles in situ generated on a polydopamine (PDA)/polyethylenimine (PEI)-modified polyvinylidene fluoride (PVDF) membrane surface. A stable zwitterionic structure is fabricated on the membrane surface and provides it with an excellent capability of binding a hydration layer, leading to enhanced superhydrophilic/underwater superoleophobic properties. The interaction between the membrane surface and water is quantified using the relaxation time of water. After iron nanoparticles in situ anchoring, the superhydrophilic, underwater superoleophobic PDA/PEI modified PVDF membrane shows more stable flux behaviors, higher oil separation efficiency, demulsification, and excellent antioil-fouling properties for various anionic, nonionic, and cationic surfactant-stabilized oil-in-water emulsions in a crossflow filtration system. The reinforced hydration layer and the amphoteric charged demusification properties of the membrane play important roles in enhancing the membrane separation performance. The reinforced membrane also exhibits excellent cleaning and reusability performance in long-term operations. The outstanding separation performance, as well as the simple and cost-effective fabrication process of the membrane with various favorable properties, highlight its promise in practical emulsified oily water applications.

Direct-writing of organic field-effect transistors on plastic achieving 22 MHz transition frequency

Organic field effect transistors are considered among the key enablers of flexible, wearable, lightweight and portable electronics. The possibility to fabricate polymer-based devices from solution with high throughput processes makes organic electronics suitable for low cost mass-production of new and diverse applications. Nevertheless, the investigation of the dynamic behaviour of these devices, i.e. their operational frequency, is still limited and the reported operational speed remains low, especially on flexible substrates, limiting their applicability in many circuitry applications. In this work, we report downscaled p-type polymer field effect transistors (FETs), fabricated on both rigid and flexible polymer substrates, by a combination of coating and direct-writing techniques, achieving radio-frequency operation. FETs with the shortest channel of 1.2 µm can operate up to 22 MHz at a relatively low bias voltage of −12 V, as measured by scattering parameters. Such a transition frequency (fT) is the highest so far recorded for organic transistors fabricated on flexible substrates. In terms of fT normalized by the applied gate-to-source voltage (fT/VGS), the achieved 1.83 MHz V−1 is the highest for solution-processed organic transistors on plastic. This result paves the way to the implementation of polymer radio-frequency devices with cost-effective fabrication processes on flexible substrates.

Solid oxide fuel cells with zirconia/ceria bilayer electrolytes via roll calendering process

Solid oxide fuel cell (SOFC) with yttria-stabilized zirconia (YSZ)/gadolinium-doped ceria (GDC) bilayer electrolytes has been considered one of representative types of high-performance intermediate-temperature SOFCs, because it enables to apply highly active cathode materials. However, the processing of fully dense bilayer electrolytes with good interfacial structure, which are essential for high-performance and secure operation, has not yet been successfully achieved. Here, we present a simple and cost-effective roll calendering process for fabrication of SOFCs with YSZ/GDC bilayer electrolytes. From understanding on the correlation between processing conditions of roll calendering and microstructure of bilayer electrolytes, the roll calendering process is optimized, and in turn, the bilayer electrolytes with overall thickness of 8.0 μm, relative density above 98%, and enhanced interfacial connectivity of 69% is obtained by co-sintering at reduced temperature of 1250 °C. This excellent structural enhancement in comparison with conventional uniaxial pressing process is explained by a shear force applied during roll calendering process, which presumably facilitates particle rearrangement within bilayer electrolytes. The optimized cell yields promising electrochemical performance of 1.45 W/cm2 at current density of 2 A/cm2 and low ohmic resistance of 0.046 Ω cm2 at 800 °C.

A Self-Powered Biosensor for Monitoring Maximal Lactate Steady State in Sport Training

A self-powered biosensor for monitoring the maximal lactate steady state (MLSS) during exercise has been developed for intelligently assisting training system. It has been presented to create poly (vinylidene fluoride) (PVDF)/Tetrapod-shaped ZnO (T-ZnO)/enzyme-modified nanocomposite film through an efficient and cost-effective fabrication process. This sensor can be readily attached to the skin surface of the tester. Due to the piezoelectric surface coupling effect, this biosensor can monitor/sense and analyze physical information in real-time under the non-invasive condition and work independently without any battery. By actively outputting piezoelectric signals, it can quickly and sensitively detect body movements (changes of joint angle, frequency relative humidity during exercise) and physiological information (changes of lactate concentration in sweat). A practical application has been demonstrated by an excellent professional speed skater (male). The purpose of this study is to increase the efficiency of MLSS evaluation, promote the development of piezoelectric surface coupling effect and motion monitoring application, develop an intelligently assisting training system, which has opened up a new direction for human motion monitoring.

Enhancing visible-light-driven water splitting of ZnO nanorods by dual synergistic effects of plasmonic Au nanoparticles and Cu dopants

Converting solar energy into chemical fuels is important to develop renewable energy. Here, Cu-doped ZnO nanorods (NRs) decorated with Au nanoparticles (NPs) are used as an efficient semiconductor catalyst for visible-light-driven water splitting. Doping Cu into ZnO NRs narrows the bandgap and shifts the absorbance toward red light; decorating Au NPs onto the ZnO:Cu NRs enhances the absorbance in the visible region and improves the solar energy conversion. The band gap of the ZnO:Cu NRs is optimized at 3% Cu doping, which presents a minimum value of 3.09 eV. Furthermore, the surface plasmon resonance effect, which is caused by decorating 10-nm Au NPs on the Cu-doped ZnO NRs, enhances the optical absorption and improves the photoelectrochemical water splitting performance. The presence of Au NPs on the surface of the NRs also reduces charge recombination, increasing the photocurrent. Under visible illumination (λ > 420 nm), the considerable photocurrent density of this device reaches 10.2 μA cm−2 at 0.581 V, which is about 7.3 times higher than that of a pure ZnO NRs sample. The simple and cost-effective fabrication process of this design provides an innovative approach for water splitting and future optoelectronic devices.