Low Threshold Electric Field Research Articles

Microarray Chip and Method for Simultaneous and Highly Consistent Electroporation of Multiple Cells of Different Sizes.

Cell electroporation is an important cell manipulation technology to artificially transfer specific extracellular components into cells. However, the consistency of substance transport during the electroporation process is still an issue due to the wide size distribution of the natural cells. In this study, a cell electroporation microfluidic chip based on a microtrap array is proposed. The microtrap structure was optimized for single-cell capture and electric field focusing. The effects of the cell size on the cell electroporation in the microchip were investigated through simulation and experiment methods using the giant unilamellar vesicle as the simplified cell model, and a numerical model of a uniform electric field was used as a comparison. Compared with the uniform electric field, a lower threshold electric field is required to induce electroporation and produces a higher transmembrane voltage on the cell under a specific electric field in the microchip, showing an improvement in cell viability and electroporation efficiency. The larger perforated area produced on the cells in the microchip under a specific electric field allows a higher substance transfer efficiency, and the electroporation results are less affected by the cell size, which is beneficial for improving substance transfer consistency. Furthermore, the relative perforation area increases with the decrease of the cell diameter in the microchip, which is exactly opposite to that in a uniform electric field. By manipulating the electric field applied to the microtrap individually, a consistent proportion of substance transfer during electroporation of cells with different sizes can be achieved.

Electric Switching Behaviors and Dielectric Relaxation Properties in Ferroelectric, Antiferroelectric, and Paraelectric Smectic Phases of Bent-Shaped Dimeric Molecules.

This study reports the electric switching behaviors and dielectric properties of the ferroelectric smectic-A (SmAPF), anti-ferroelectric smectic-A (SmAPA), anti-ferroelectric SmCAPA, and smectic-A (SmA) phases formed by mixing the bent-shaped dimeric molecules, α,ω-bis(4-alkoxyanilinebenzylidene-4'-carbonyloxy)pentanes. These four phases each show characteristic features. The SmAPF shows a low threshold electric field for ferroelectric switching and a large dielectric strength due to the collective fluctuation mode of dipoles at around 500 Hz. Both the threshold electric field and dielectric strength are strongly dependent on the cell thickness. The threshold field decreases to 0.1 V μm-1, and the dielectric strength increases up to a huge value of 10,000 as the cell thickness increases up to 80 μm. The SmAPA also shows a similar collective mode at around 2 kHz with a relatively small dielectric strength (around 200), which may be induced by the anti-phase rotation of dipoles in adjacent layers. In these collective modes, the dielectric strength is found to be inversely proportional to the switching threshold field. On the other hand, another anti-ferroelectric SmCAPA as well as the paraelectric SmA show only the non-collective mode (i.e., rotational relaxation of individual molecules around their short axes) at a high frequency of around 100 kHz.

Microwave breakdown of sub-atmospheric argon gas in the vicinity of a microgap

The microwave electric field at breakdown for argon gas in a microgap (generally, gap size <1 mm) over a wide range of pressures and gap sizes was found to exhibit two behavioral pressure regimes. A high microwave electric field was established in the gap of a re-entrant mode resonator. By slowly raising the microwave electric field level, a breakdown level is reached where impact ionization induces low pressure argon gas to breakdown preferentially outside of the gap. At high pressure, breakdown is found to occur preferentially inside the gap, but only after the pressure is high enough for impact ionization to produce breakdown there. Impact ionization has a lower threshold electric field than the boundary-controlled processes, such as secondary electron emission, that would eventually produce breakdown inside the microgap if impact ionization did not occur first. Thus, the lower pressure regime is characterized by breakdown outside of the gap, while in the high-pressure regime, breakdown occurs inside the gap, in both cases by impact ionization. The transition pressure PT between these two pressure regimes depends on the gap size dgap, roughly as PT ∝ dgap−2. Consistent with the model developed here, this corresponds to the full-amplitude of electron oscillation in the gap field being commensurate with the gap size.

MoS2 nanosheet arrays grown on Mo foils for high-performance field emission

Free-standing molybdenum disulfide (MoS2) nanosheets with different morphologies on molybdenum (Mo) foil were synthesized through hydrothermal method using thiourea as the sulphur source and Mo foil as the Mo source. The effect of the concentration of thiourea in the reaction solution on the morphology and field emission (FE) properties of MoS2 nanosheets were investigated. The vertically aligned MoS2 nanosheets exhibit a low turn-on (∼1.90 V/μm) and threshold electric field (∼2.51 V/μm), along with good emission stability. The results are attributed to the high geometrical field enhancement factor (∼1979) and the sturdy structure of the MoS2 grown on highly conductive Mo substrate.

Direct synthesis of micropillars of vertically aligned carbon nanotubes on stainless-steel and their excellent field emission properties

Vacuum micro/nano-electronics can greatly benefit from the improved emission current density and temporal stability of the electron beam due to the morphological control and direct contact of cold field-emitters on a conducting substrate. In this work, high-performance vertically aligned carbon nanotube (VACNT) pillar-based field-emitter arrays (VACNT-P-FEAs) were synthesized directly on stainless-steel (SS) via plasma-enhanced chemical vapor deposition. Nanosphere lithography was employed to limit the growth sites of VACNTs and form VACNT-P-FEAs of different sizes on the SS substrate. The field emission (FE) properties of the VACNT-P-FEAs were dependent on the size of the pillar emitters. Remarkable FE properties, such as low turn-on electric field (ETo = 1.57 V/μm), low threshold electric field (ETh = 2.94 V/μm), high field enhancement factor (β = 4977), and high emission current density (∼33 mA/cm2 at a field of 4 V/μm) were observed from the VACNT-P-FEAs grown using polystyrene microspheres (450 nm diameter) for lithography. The excellent FE performance can be ascribed to the inherent properties of the sample, such as the high conductivity of the SS substrate, low contact resistance between the SS substrate and VACNTs, the suitable number of active VACNT pillar field-emitters, and the reduced screening effect between the VACNT pillars.

Density control of vertically aligned carbon nanotubes and its effect on field emission properties

Vertically aligned carbon nanotubes (VACNTs) were synthesized directly on stainless steel substrate and their surface densities were tuned by an order of magnitude via growing them at different temperatures. The surface density of the VACNTs was correlated with the surface evolution of the substrate, a process in which catalyst nano hills were generated at different growth temperatures in the presence of reducing gas environment. Enhanced field emission (FE) properties including low turn-on electric field (ETurn-on = 0.66 V μm-1), low threshold electric field (ETh = 1.07 V μm-1), high field enhancement factor (β = 4084), and high FE stability for 600 min were obtained from VACNT arrays synthesized at 650 °C. It is speculated that the inherent features of our sample such as the conductive substrate, the low contact resistance between the substrate and the VACNTs, the uniform length and the appropriate spacing between the VACNTs have contributed to the excellent field emission properties. Simulation on the electrostatic field of various VACNT arrays was performed and the result is in good agreement with the experimental data.

Improving field emission properties of vertically aligned carbon nanotube arrays through a structure modification

Vertically aligned carbon nanotube (VACNT) emitters were synthesized directly on stainless steel substrate using DC plasma-enhanced chemical vapor deposition. Remarkable field emission (FE) properties, such as low turn-on electric field (ETO = 1.40 V/μm) and low threshold electric field (ETH = 2.31 V/μm), were observed from VACNT arrays with long length and moderate density. The FE performance was significantly enhanced by a uniquely bundled structure of VACNTs formed through a simple water treatment process. The FE properties of VACNTs were further improved by coating the exterior of CNTs with a uniform layer of crystalline SnO2 nanoparticles; the ETO and ETH were reduced to 1.18 and 2.01 V/μm, respectively. The enhancement of FE properties by SnO2 coating can be attributed to the morphological change of VACNTs caused by the solution phase coating process. The coated samples also exhibited an improved FE stability which is attributed to the enhancement of the mechanical strength and chemical stability of the VACNTs after the SnO2 coating. The VACNT emitters with characteristic features such as a conductive substrate, low contact resistance between the VACNTs and the substrate, uniform coating, and bundled morphology can be ideal candidates for FE devices.

The high performance of field electron emission from sandwich-like carbon nanotubes/carbon nanoparticles film/vertically aligned carbon nanotubes on silicon substrate

We prepare the sandwich-like carbon nanotubes/carbon nanoparticles film/vertically aligned carbon nanotubes on silicon substrate (CNTs/CNPs/VACNTs/silicon) by pyrolysis of FePC at 880 °C. The field emission properties of the CNTs/CNPs/VACNTs/silicon are investigated. The lower turn-on electric field of 0.78 V/μmat a current density of 20μA/cm2, lower threshold electric field of 1 V/μmat a current density of 1 mA/cm2and good emission current stability are observed. The unique structure not only provides large field enhancement factor but also strongly reduces the field-screening effect. The above results make CNTs/CNPs/VACNTs/silicon an effective field emitter.

Growth of Wafer-Scale ReS2 with "Tunable" Geometry toward Electron Field-Emission Application.

Despite high potential, the promise of 2D materials has not been realized practically because of limits of tiny grown size and difficult manipulation of the active spot. The utilization of 2D layers is the ultimate approach, which should be supported by large-scale production. In this very first report, we demonstrate the wafer-scale production of ReS2 using the conventional sputtering method. The controllability of ReS2 geometry has been investigated to form typical thin films or vertically aligned layers that are further applied for field emission. The vertically aligned ReS2 layers exhibit ultralow turn-on electric field (0.6 V μm-1) with the current density (0.6 mA cm-2) and significantly low threshold electric field (0.8 V μm-1), respectively, along with outstanding emission stability. The results are attributed to weakly coupled ReS2 layers and the high geometrical field enhancement factor (∼1.08 × 105). Further, Kelvin probe force microscopy measurements confirm that lowering the work function is not solely responsible to achieve the ultralow operative field. Moreover, finite element simulation suggests that not only the length, width, and separation of the nanostructures but also the local slope plays an important role in suppressing screening effects.

Comparative study of electron field emission from randomly-oriented and vertically-aligned carbon nanotubes synthesized on stainless steel substrates

Randomly-oriented carbon nanotubes (CNTs) and vertically-aligned CNTs have been synthesized by a thermal chemical vapor deposition (CVD) process and a plasma enhanced CVD process, respectively, on stainless steel substrates without any external catalyst. Surface topography studies reveal that polishing and chemical etching result in favorable catalytic conditions for nucleation and growth of CNTs. Scanning electron microscopy and transmission electron microscopy observations reveal the growth of CNTs with catalyst particle at the tips. In comparison to randomly-oriented CNTs, vertically-aligned CNTs demonstrate better field emission properties with lower turn-on electric field of ∼2.0 V/μm, lower threshold electric field of ∼3.2 V/μm, and a 2.5-fold increase in the field enhancement factor. The vertical alignment of the emitters benefits the emission process by reducing the screening effect and streamlining the path of ejected electrons directly onto the anode. Vertically-aligned CNTs on conducting substrates are promising emitters in cold cathode vacuum electronics because of their direct contact with the substrate and efficient performance at low operating voltages.

Observation of field emission from carbon nanoparticles film coating on top of vertically aligned carbon nanotubes on silicon substrate

The carbon nanoparticles film coating on top of vertically aligned carbon nanotubes on silicon substrate (CNPs/CNTs/silicon) has been prepared by the pyrolysis of FePC at 960 °C. The surface morphologies and structure of the prepared sample are characterized by Scanning Electron Microscope, X-ray energy dispersive spectroscopy and Raman Spectroscopy. The field electron emission (FEE) properties of the CNPs/CNTs are also measured. A low turn-on electric field of 1.3 V/μm at a current density of 10 μA/cm2, low threshold electric field of 1.8 V/μm at a current density of 1 mA/cm2, a high emission density and good field emission stability are obtained. The above results make CNPs/CNTs/silicon an effective field emitter.

Electrospinning on a plucked string

Preparation of high-quality nanofibers by electrospinning with low applied voltage and industrial scales remains challenging. A novel differential electrospinning technology for nanofiber preparation was proposed, with which multiple jets are generated from the string by plucking. The spinning principles were investigated, and the operation parameters were optimized. Results showed that lower threshold electric field was required for jets generation by plucked string electrospinning compared with the conventional needleless electrospinning. The finest average diameter of nanofibers with a narrow distribution range of 143 ± 16 nm was obtained at an applied voltage of 25 kV, a PVA concentration of 8 wt%, a rotational speed of 150 rpm and a spinning distance of 7 cm. The maximum yield for single string was as high as 2.64 g h−1 at a PVA concentration of 12 wt%. It was demonstrated that the proposed technology is feasible for manufacturing of nanofibers with lower voltage and high productivity as the string could be modularly extended.

(Invited) 2D MoS2 Memristors with Variable Switching Characteristics

Memristors has been extensively studied as an important candidate device structure for realizing non-Von Neumann computers, neuromorphic and analog computing systems. The conventional memristors are made from transition metal oxides such as TiOx, TaOx, WOx, and HfOx.1 The conductance states of such memristors can be adjusted through modulating the distribution of oxygen vacancies in the oxide channels. Recently, memristor-like transport behaviors have been also observed in the electronic devices made from emerging 2D-layered transition metal dichalcogenides (TMDCs, such as MoS2 and WSe2).2 Such emerging 2D-material-based memristors could be used for constructing novel neural networks with a significantly improved level of connectivity and enabling bio-realistic emulation of brain neuron functions. Therefore, it is highly desirable to further perform nanofabrication and nanoelectronics research to fully explore the applicability and advantage of 2D-TMDC-based memristors for practical neuromorphic applications. Here, we present a study on the nanofabrication and characterization of memristive devices based on mechanically printed few-layer MoS2 structures. This work shows that mechanically printed MoS2 memristors with critical thicknesses exhibit a very low threshold electric field for initiating memristive-switching processes, which is essential for the successful construction and operation of energy-efficient memristor-based neural networks. More importantly, such MoS2 memristors exhibit both analogue (i.e., gradient) and discrete switching characteristics, which could be further exploited for making reconfigurable memristors for both analog and digital computing applications. This work leveraged the unique transport properties of 2D layered MoS2 for memristor-related applications and advanced the scientific/technical knowledge for controlling memristive switching behaviors.

Synthesis and field electron emission properties of multi-walled carbon nanotube films directly grown on catalytic stainless steel substrate

The multi-walled CNT films were directly grown on stainless steel substrates using an oxidation-reduction treatment with chemical vapor deposition. Microstructure and field emission properties of the as-received CNT films were detailedly investigated. The results indicate that the CNTs have originally random orientation with relative high density, good crystalline perfection and large diameter. Besides, the CNT films exhibit superior field electron emission performances with low threshold electric field (∼4.2 V/μm) and very high emission current density (∼24 mA/cm2). Importantly, the CNTs directly grown on stainless steel substrates have remarkable long-term stability with ∼3.4% fluctuation over 50 h continuous measurement under high current density, ∼10 mA/cm2. The perfect graphitization, large field enhancement factor, low contact resistance, good adhesion and high thermal conductivity are believed to be principally responsible for their superior field emission properties, which make them very promising application as an electron source in microthrust space electric propulsion neutralizer.

Effect of lead content on the performance of niobium‐doped {100} textured lead zirconate titanate films

AbstractNiobium‐doped, {100} textured, gradient‐free, lead zirconate titanate (PZT) films were fabricated from solutions with different lead contents. Film lead content was controlled through changes in the average solution lead excess from 14.7% to 17 at.%. The low field dielectric response as well as the polarization‐electric field hysteresis loops were not a strong function of lead content. However, films with lower lead contents in the precursor tended to withstand higher poling fields than films prepared from more lead‐rich precursors. Although no residual PbO was observed at the grain boundaries, films prepared from more lead‐rich solutions had higher levels of grain‐boundary porosity, lower breakdown strengths, and lower threshold electric fields at which cracking was observed.

Field emission properties and strong localization effect in conduction mechanism of nanostructured perovskite LaNiO3

We report the potential field emission of highly conducting metallic perovskite lanthanum nickelate (LaNiO3) from the nanostructured pyramidal and whisker shaped tips as electron emitters. Nano particles of lanthanum nickelate (LNO) were prepared by sol-gel route. Structural and morphological studies have been carried out. Field emission of LNO exhibited high emission current density, J = 3.37 mA/cm2 at a low threshold electric field, Eth = 16.91 V/μm, obeying Fowler–Nordheim tunneling. The DC electrical resistivity exhibited upturn at 11.6 K indicating localization of electron at low temperature. Magnetoresistance measurement at different temperatures confirmed strong localization in nanostructured LNO obeying Anderson localization effect at low temperature.

Effectively Improved Field Emission Properties of Multiwalled Carbon Nanotubes/Graphenes Composite Field Emitter by Covering on the Si Pyramidal Structure

The composite nanostructure emitter of multiwalled carbon nanotubes and graphenes was deposited on pyramidal silicon substrate by the simple larger scale electrophoretic deposition process. The field emission (FE) properties of the composite/pyramidal Si device were greatly improved compared with that of the composite/plain Si. The low turn-ON electric field, the low threshold electric field, and the larger enhancement factor were obtained using the pyramidal structure. The better FE performances of the composite/pyramidal Si were a combined effect of the field enhancement from the composite emitter and the pyramidal Si structure. The numerical simulation of the electric field distribution on composite/pyramidal cathode was used to illuminate the improved FE properties by using the pyramidal substrate. These studies indicate that constructing composite/pyramidal structure is one of the efficient ways to improve the FE properties.

Characterization of field-emission cathodes based on graphene films on SiC

The properties of a point field-emission cathode representing a structure in the form of a silicon carbide tip coated with a thin graphene film are assessed. For the point cathode with the graphene coating, the current–voltage characteristics are constructed in the Fowler–Nordheim coordinates; the work functions φ of the point cathode are calculated by their slope. The possibility of forming heavily doped n+-SiC on the point surface by the sublimation of low-threshold field emission cathodes with low threshold electric fields and field-emission currents is shown.

Radial AlN nanotips on carbon fibers as flexible electron emitters

A facile catalyst-free approach using a simple thermal transport method has been developed to fabricate high-density AlN nanotips on flexible carbon cloth at large scales for use as field emission (FE) emitters. The AlN nanotips exhibit good performance as flexible cold-cathode electron emitters, with a very low turn-on electric field of 1.1–2.3Vμm−1, a low threshold electric field of 1.5–2.5Vμm−1, and a high emission current density. The excellent field emission properties of the AlN nanotips are attributed to the large field enhancement factor of 6895 as well as the combined effect of the tip profile of the AlN nanostructures and the excellent electron transport path of the conductive carbon cloth substrate.

Field emission behavior of carbon nanotube field emitters after high temperature thermal annealing

The carbon nanotube (CNT) field emitters have been fabricated by attaching a CNT film on a graphite rod using graphite adhesive material. The CNT field emitters showed much improved field emission properties due to increasing crystallinity and decreasing defects in CNTs after the high temperature thermal annealing at 900 °C in vacuum ambient. The CNT field emitters showed the low turn-on electric field of 1.15 V/μm, the low threshold electric field of 1.62 V/μm, and the high emission current of 5.9 mA which corresponds to a current density of 8.5 A/cm2. In addition, the CNT field emitters indicated the enhanced field emission properties due to the multi-stage effect when the length of the graphite rod increases. The CNT field emitter showed good field emission stability after the high temperature thermal annealing. The CNT field emitter revealed a focused electron beam spot without any focusing electrodes and also showed good field emission repeatability.