Microgap Structures Research Articles

Regulating microstructure and composition by carbonizing in-situ grown metal-organic frameworks on cotton fabrics for boosting electromagnetic wave absorption

High-temperature carbonized metal-organic frameworks (MOFs) derivatives have demonstrated their superiority for promising electromagnetic wave (EMW) absorbers, but they still suffer from limited EMW absorption capacity and narrow bandwidth. Considering the advantage of microstructure and chemical composition regulation for the design of EMW absorber, hierarchical heterostructured MoS2/CoS2-Co3O4@cabonized cotton fabric (CF) (MCC@CCF) is prepared by growing ZIF-67 MOFs onto CF surface, chemical etching, and carbonization. Aside from the dual loss mechanism of magnetic-dielectric multicomponent carbonized MOFs, chemical etching and carbonization process can effectively introduce abundant micro-gap structure that can result in better impedance matching and stronger absorption capacity via internal reflection, doped heteroatoms (Mo, N, S) to supply additional dipolar polarization loss, and numerous heterointerfaces among MoS2, CoS2, Co3O4, and CCF that produce promoted conduction loss and interfacial polarization loss. Thus, a minimal reflection loss of −52.87 dB and a broadest effective absorption bandwidth of 6.88 GHz were achieved via tunning the sample thickness and filler loading, showing excellent EMW absorption performances. This research is of great value for guiding the research on MOFs derivatives based EMW absorbing materials.

Demonstration of thermal modulation using nanoscale and microscale structures for ultralarge pixel array photothermal transducers

Large-pixel-array infrared emitters are attractive in the applications of infrared imaging and detection. However, the array scale has been restricted in traditional technologies. Here, we demonstrated a light-driven photothermal transduction approach for an ultralarge pixel array infrared emitter. A metal-black coating with nanoporous structures and a silicon (Si) layer with microgap structures were proposed to manage the thermal input and output issues. The effects of the nanoscale structures in the black coating and microscale structures in the Si layer were investigated. Remarkable thermal modulation could be obtained by adjusting the nanoscale and microscale structures. The measured stationary and transient results of the fabricated photothermal transducers agreed well with the simulated results. From the input view, due to its wide spectrum and high absorption, the black coating with nanoscale structures contributed to a 5.6-fold increase in the temperature difference compared to that without the black coating. From the output view, the microgap structures in the Si layer eliminated the in-plane thermal crosstalk. The temperature difference was increased by 340% by modulating the out-of-plane microstructures. The proposed photothermal transducer had a rising time of 0.95 ms and a falling time of 0.53 ms, ensuring a fast time response. This method is compatible with low-cost and mass manufacturing and has promising potential to achieve ultralarge-array pixels beyond ten million.

4D Printing Strain Self-Sensing and Temperature Self-Sensing Integrated Sensor-Actuator with Bioinspired Gradient Gaps.

Integrated sensor–actuators with exciting functionalities, such as action self‐sensing, position self‐sensing, posture self‐sensing, or active sensing, are promising for applications in biomedical device, human–machine interaction, intelligent self‐protection devices, and humanoid robots. Despite recent progress, it remains challenging to achieve a macroscopical integrated sensor–actuator in a material system with microstructures. To address this critical challenge, a 4D printing bioinspired microstructure strategy is reported to design a high‐performance integrated sensor–actuator capable of simultaneous actuation and sensation. Decoupled thermal stimulation and strain sensation is achieved by combining nanocarbon black/polylactic acid composites with bioinspired gradient microgap structures. As a result, printed integrated sensor–actuators can actively touch objects triggered by thermal stimulation and self‐sense the touching state through the resistance change. It is anticipated that the basic design principle underlying this behavior can be used to develop integrated sensor–actuators of various shapes and functionalities to meet desirable applications.

Исследование квантовых точек в мультизеренном слое планарно-торцевой микроструктуры

Quantum dots (QDs) of Cds, PbS, and InSb semiconductors in a multi-grain layer of planar-edge microstructure were studied. A model of the ordered arrangement of CT in the micro-gap structure and the flow of current along the lines of parallel arrangement of QD is proposed. Electronic transport at low voltage values (less than 8 V) is determined by thermal and tunnel emission from the QD into the gap, at high values - by the charge restriction in the QD according to the Coulomb block model. A strong influence of IR and UV radiation on the VAC was found.

Fabrication of Micro-Gap Structure by Reactive Ion Etching Technique (RIE) for Future Reproductivity of Nanogap Biosensor

The important role of reactive ion etching (RIE) technique is to etch the semiconductor surface directionally. The purpose of the current research is to fabricate polysilicon micro-gap structures by RIE technique for future biosensing application. Therefore zero-gap microstructure of butterfly topology was designed by using AutoCAD software and finally the designed was transferred to commercial chrome glass photomask. Ploysilicon wafer samples were selected to achieve high conductivity during electrical characterization measurement. The fabrication process starts from samples resist coating and then by employing photolithography through chrome glass photomask the zero-gap pattern of butterfly topology was transferred to resist coated sample wafer followed by resist stripping from exposed area and finally by reactive ion etching (RIE) technique the open area of polysilicon was etched directionally at different etching time to fabricate micro-gap structure on wafer samples. The spacing of fabricated micro-gap structures will be further shrink by thermal oxidation (size reduction technique) until to nanosize gap spacing. The proposed nanospacing gap will definitely show the capability to detect the bio molecule when inserted into the gap spacing.

Investigation of multiwalled carbon nanotube interconnection geometry and electrical characteristics of an CNT-filled aluminum microgap

In recent years a very large amount of data has been collected regarding devices formed by multiwalled carbon nanotubes (MWCNTs) in polymer matrix as well as single nanotubes. Conversely, very little investigation exists of nanotube networks composed of a small number of MWCNTs. A detailed investigation of the long time stability, adhesion to the surface, and topological structure of the interconnections between MWCNTs is reported here. Three different microscopy techniques, focused ion beam (FIB), scanning electron microscope (SEM), and atomic force microscope (AFM), were used to investigate the interconnection of MWCNTs deposited by electrophoresis on a thermally oxidized silicon wafer with aluminum microgap structures. SEM, AFM, and FIB imaging revealed an interesting interconnection morphology between the drop casted MWCNTs. In particular it was found that in some cases the MWCNTs were connected to each other in a geometry similar to a twisted structure. Furthermore a good stability of the sample in time has been found, proving a strong adhesion of the nanotubes to the oxide surface. Despite the fact that electrical contacts with aluminum to carbon nanotube - based devices are in general not very reliable, using the dielectrophoresis deposition technique with an adequate subsequent annealing procedure, long-term stable temperature sensors with carbon nanotube networks in the aluminum contact microgap were realized. Their temperature dependence can be explained by modeling the internanotube contact resistance.

Fabrication and characterization of a single-bridge nanorod between microgap electrodes

Purpose – The purpose of this study was to investigate the performance of a single-bridge ZnO nanorod as a photodetector. Design/methodology/approach – The fabrication of the design sensor with ∼6-μm gap Schottky contacts and bridging of the ZnO nanorod were based on conventional photolithography and wet-etching technique. Prior to bridging, the ZnO nanorods were grown by the hydrothermal process. The 0.35 M seed solution was prepared by dissolving zinc acetate dihydrate in 2-methoxyethanol, and monoethanolamine, which acts as a stabilizer, was added drop-wise. Before starting the solution deposition, and oxide, titanium (Ti) and gold (Au) layer deposition, p-type (100) silicon substrate was cleaned with Radio Corporation of America (RCA1) and RCA2, followed by dipping in diluted hydrofluoric acid. The aged solution was dropped onto the surface of the Au microgap structure, using a spin coater at a spinning speed of 3,000 rpm for 45 seconds, and then dried at 300°C for 15 minutes, followed by annealing at 400°C for 1 hour. The hydrothermal growth was carried out in an aqueous solution of zinc nitrate hexahydrate (0.025 M) and hexamethyltetramine (0.025 M). Findings – In this study, ZnO nanorods were grown on a SiO2 substrate by the hydrothermal method. Microgap electrodes with ∼6-μm spacing were achieved by using the wet-etching process. After the growth process, an area-selective mask was utilized to reduce the number of rods between the nearby gap areas. The obtained single ZnO nanorod was tested for the UV-sensing application. The single ZnO nanorod photodetector exhibited a UV photoresponse, thereby indicating potential as a cost-effective UV detector. The response and recovery times of the fabricated device were 65 and 95 seconds, respectively. Structural analysis was captured using X-ray Diffraction (XRD), whereas surface morphology was determined using scanning electron microscopy. Originality/value – This paper demonstrates the effect of UV photon on a single-bridge ZnO nanorod between microgap electrodes.

Parametric Study and Thickness Evaluation of Photoresist Development for the Formation of Microgap Electrodes Using Surface Nanoprofiler

A compact nanolaboratory on single chip is one of the challenging tasks for future reproductively of sensitive and selective lab-on-chip. This paper reports a simple and controllable technique for patterning microgap structures on (PR-1 2000A) positive photoresist. For the pattern transformation conventional lithography technique was used integrated with precise resolution mask namely chrome mask. This technique provides an especially simple method for the formation of micro features sizes of gaps onto the photoresist. The thickness of developed microgap structures on photoresist directly relates with the coating speed of spin coater.

Electrical characterization of in-house fabricated polysilicon micro-gap for yeast concentration measurement

Fabrication and electrical characterization of micro-gaps and their properties are discussed with their applications in electrochemical sensors and bimolecular detection. To understand the relationship between the biosensor and micro-structure we have carried out the fabrication and characterization of micro-gap structures for yeast concentration measurement. In this paper two photo mask designs are used. The first mask is for defining the lateral micro-gap and the second one is for the aluminum electrode pattern. Lateral micro-gaps are formed using polysilicon and Al as contact pads. Conventional photolithography techniques are used to fabricate the micro-gap. The electrical measurements were carried out using a Semiconductor Parameter Analyzer to measure the change in capacitance across the micro-gap with the yeast solution drop put across the gap. The measured value of capacitance for each yeast concentration is presented as a function of the gap size. The results indicate that these micro-gaps could possibly be used for yeast sensor applications. Key words: Micro-gap, conductivity, yeast detection, capacity, electrochemical sensor.

Design, fabrication and characterization of nano‐filters in silicon microfluidic channels based on MEMS technology

Since most clinical assays are performed on cell-free serum or plasma, micro-analytical systems for blood tests require integrated on-chip microfluidics for the isolation of plasma or serum from crude blood samples. In this paper, we present a crossflow filtration method using novel silicon nano-filters for plasma separation. The microfluidic chip is made of a silicon substrate containing micropillar arrays, feed channels, side channels and nano-gap structures, sealed with a PDMS-glass compound cover. The design of the silicon filtration structures were optimized using numerical analysis and the optimal MEMS fabrication procedures were obtained. The filtration structures including nano-filters were characterized using SEM and subsequently used to isolate plasma from whole blood in a continuous manner. Compared with micro-gap structures in silicon microfluidic channels, the nano-gap structures have been used to separate plasma from whole blood samples with higher selectivity, where a maximum plasma selectivity of 97.7% has been obtained. Common problems of clogging and jamming in filtration applications have seldom been noticed in our device. The presented microfluidic filtration device for plasma isolation could be integrated into microTAS for point-of-care diagnostics in the near future.

Effect of the drift field on avalanche gain and charge collection in microgap detectors at high pressure

One of the main drawbacks of the use of microgap structures when used at high pressure (6bar) at high count rates (∼106s−1mm−2) is the limited maximum safe gain at which they can be operated. The use of a preamplification device such as the GEM (gas electron multiplier) can overcome this limitation; however, secondary space charge effects due to charge accumulation at the non-metallic surfaces cannot be neglected and should be minimised. These positive charges are due to the intrinsic multiplication of the GEM device and also to the drift of ions from the anode of the main detector. In this study we present data on the variation of the positive ion collection by the drift electrode versus drift field at several pressures up to 6bar using a Kr–CO2 mixture. Data were collected with microgaps having several anode and insulator widths. The influence of the drift field in the pulse rise time is also considered.

Optimization of anode dimensions for microgap detectors at high pressure

The possibility of using microgap structures in pressurized gaseous devices for high rate synchrotron radiation detectors has been presented before; one of their main drawbacks is the limited maximum safe gain at which they can be operated. In this study we present data on the performance of microgap plates with several widths of the anodes (4 to 12 micron) and of the insulating layer (6 to 30 micron). Krypton and xenon based gaseous mixtures were used at pressures of 1, 3 and 6 bar under irradiation by /sup 55/Fe and /sup 109/Cd X-ray sources and an X-ray tube. The dependence of gain on anode voltage is analyzed, as well as the effects of drift field on gain and charge collection. We also present data on the measured safe maximum gain before breakdown versus count rate.