Insulated gate bipolar transistor (IGBT) is a kind of power switching device owns the advantage of gate voltage control and high power capacity, while remaining the problem of potential catastrophic failures in high voltage. A novel structure of IGBT combined with a vacuum field emission transistor (VFET) and a bipolar junction transistor (BJT) was introduced which exhibits high blocking voltage, high frequency characteristics and excellent robustness toward catastrophic failure such as latch-up and gate oxide breakdown. A pulsing current overshooting effect due to the gate-cathode capacitance of VFET was observed to expedite the switching process, offering a novel approach to shorten the switching time of IGBT. Benefit from this, the field emission IGBT (FE-IGBT) was capable of operating over a broad frequency range from DC to 100 kHz. The static and dynamic characteristics of the device were reported, including a blocking voltage of 800 V, a maximum output current of 0.5 A. This work presented a new route to bloom the performance of IGBT and also created a feasibility to connect vacuum electronics device with solid-state semiconductor devices.

Carbon nanotube fibers (CNTFs) have emerged as promising field emission material and demonstrated excellent field emission characteristics. The collective field emission behavior at the fiber tip, especially the nanoscale dynamic morphological evolution is key to its high current density field emission performance. In this study, we perform in-situ transmission electron microscopy (TEM) to directly visualize the morphological evolution of clustered CNTs at the CNTF tip during field emission. Following cap removal and height reduction, the emission current increased markedly from 865 nA to 15,030 nA in a single CNTF. Fowler-Nordheim analysis reveals a 3fold decrease in field enhancement factor, accompanied by a 322-fold increase in effective emission area. It is attributed to a transition from tip-dominated to collective emission, driven by electric field homogenization which also suppressed the hotspot and enhanced the temperature distribution uniformity. These findings provide crucial insights into the dynamic collective behavior of clustered CNTs and offer guidance for carbon-based cold cathodes and CNT assemblies.

Facing the precising X-ray imaging applications such as medical and integrated circuit industry, high resolution micro-focal spot X-ray source is in urgent need. In this work, a novel carbon nanotube fiber (CNTF) was introduced as the microscale cold cathode for the X-ray source. The precising fabrication and field emission characteristics of CNTF cathode were carried out. The apex of the CNTF exhibited a cone-like structure with a diameter of 3.2 mu m, which gives an extremely high current density of 3632.6 A/cm2, high reduced brightness of 1.14 x 1010 A m- 2 center dot sr- 1 center dot V-1, low semi-angle of divergence of 11.3 degrees, and low current fluctuation of 0.97 %. Benefit from the microscale CNTF cathode, a transmission type micro-focal spot X-ray source was assembled using a simple electrooptical structure. The measured X-ray FSS was 15.6 mu m and the imaging resolution of 8.0 lp/mm was achieved at the anode voltage of 45 kV and anode current of 31.8 mu A. The results demonstrated that the CNTF cold cathode based micro-focal spot X-ray source is a convenient and low-cost device solution which have a great potential in the applications of microscale object and biological tissue imaging.

Monitoring of physicochemical factors in the pore microenvironment is of great significance for early risk warning. Minimally invasive monitoring the dynamic changes of chloride ion in the pore microenvironment of building materials and their aquatic environment is crucial for predicting and early detection of the corrosion of building materials. Herein, we developed an electrochemical device with fishbone-like fully-integrated microelectrodes, which were directly embedded inside the building material and in the coastal sediments, detecting internal corrosion tendency and the dynamic change of chloride ion concentration with minimal invasiveness. The prepared fishbone-like fully-integrated microelectrodes were based on a potentiometric signal output method with good immunity to interference, reversibility and stability. Meanwhile, the effects of pH, temperature, interference ions and fouling on the chloride ion response of the sensor were systematically investigated. Furthermore, the fishbone-like fully-integrated microelectrodes showed better signal stability compared to the non-integrated electrodes. Finally, fishbone-like fully-integrated microelectrodes were embedded in three typical building materials (concrete, mortar, and cement slurry) and they were placed in the coastal area to monitor the chloride ion penetration process. The fishbone-like fully-integrated microelectrodes provided accurate chloride ion concentration level data in building materials and coastal areas, enabling large-scale permeation monitoring in coastal structures.

Abstract Cold-cathode ultrafast electron source is a key component for probing ultrafast dynamics behavior in materials, as well as developing high-frequency and high-power electromagnetic radiation devices. Developing large-current, high-brightness and tunable ultrafast electron sources by leveraging the intrinsic properties of nanomaterials is significant. In this study, we report the in-situ assembly of a double-walled carbon nanotube (DWCNT) cold-cathode based on a tungsten (W) tip via nanotransfer manipulation within a SEM chamber, enabled by electron-beam-induced carbon deposition. The resulting ultrafast electron emission exhibits excellent performance under dual-regime modulation by multiphoton photoemission (MPP) and optical field emission (OFE). Under co-excitation by 800 nm femtosecond laser pulses and a static electric field, the DWCNT cold-cathode demonstrates significantly enhanced emission in both regimes with a maximum peak current of ~65 A and corresponding brightness of 4.98 × 1018 A m-2 sr-1 V-1, and its optical excitation threshold reduces by an order of magnitude compared to the conventional metallic W tip cathode at equivalent emission current levels. Comprehensive material characterizations combined with density functional theory (DFT) calculations reveal that the semiconducting nature of the DWCNT emitter, along with its favorable electronic density of states and correspondingly lower effective work function, provides distinct advantages over metallic CNT and W for ultrafast electron emission. Furthermore, quantitative models are developed for both MPP- and OFE-dominated regimes, which elucidate polarization-dependent electron emission behavior and its underlying physical mechanisms. This work presents a promising semiconducting DWCNT cold-cathode for high-performance ultrafast electron sources, and provides a path for investigating ultrafast electron emission dynamics from multiple perspectives.

The construction of multifunctional aerogels with optimized stealth performance remains challenging due to unbalanced dielectric-magnetic properties and limited tunability of porous structures. Herein, we report polymer-based EVA-Fe3O4-GO (EFG) aerogels via a direct heated cross-linking process and pores modulation engineering. The obtained porous EFG hybrid aerogels construct discontinuous dielectric matrix and optimize dielectric-magnetic synergism, achieving efficient electromagnetic wave absorption. The pores modulation engineering enables precise control over porosity, where regulating NaCl template content modifies pore sizes and densities, forming a hierarchical porous architecture. EFG aerogels exhibit a minimum reflection loss (RLmin) of -34.3 dB at 2.0 mm and a broad effective absorption bandwidth (EAB) of 4.56 GHz in high-frequency bands. The synergistic combination of Fe3O4 nanoparticles and GO sheets enhances magnetic-dielectric loss, while the porous structure promotes multiple microwave scattering. Additionally, the EFG aerogels demonstrate excellent infrared stealth and thermal insulation performance, maintaining surface temperatures below 40 degrees C under continuous heating. The EFG aerogels show promising potential for electromagnetic wave absorption and infrared stealth applications in aerospace and defense sectors, offering a facile strategy for high-performance multifunctional aerogel design.

Spin-polarized field emission electron sources (SP-FEES) have significant applications in high-energy physics and surface analysis. Traditional approaches for calculating electron spin polarization (ESP), which rely on multidimensional wavefunction expansions, tend to be computationally intensive and struggle with convergence issues. This paper proposes a novel method for calculating ESP by incorporating the density of states as a global parameter into the Fowler-Nordheim (FN) theory formula; it enables efficient computation of electron emission current density and ESP. The ESP of the Fe/W structure calculated using this novel method is in good agreement with the experimental results, proving the feasibility of the method. The composite structures of low work function lanthanum hexaboride (LaB6) materials with atomically thin Fe magnetic layers on their surfaces were designed for SP-FEES. The influence of the overall structural evolution of Fe/LaB6 composite structures with a 1 : 1 Fe/LaB6 layer ratio on spin polarization and electron emission properties was investigated using the proposed method. Even-layered structures demonstrate higher ESP than odd-layered ones due to quantum size effects. 1- and 2-layer Fe/LaB6 structures exhibit further enhanced ESP influenced by the superposition of quantum confinement effects at the limiting thickness. Notably, the 2-layer Fe/LaB6 structure exhibits the optimal combination of performance parameters, achieving the highest ESP of -50.40%, the lowest energy spread of 0.136 eV, and a high reduced brightness of 1.71 × 1013 A (m2 sr V)-1. This study presents a computationally straightforward and physically transparent method for calculating polarizations and demonstrates the material advantages of LaB6 in realizing low energy spread and high ESP, which facilitate the design of spin-polarized electron sources.

SmB6 is a promising cold-cathode material due to their abundant surface electron states, low electron affinity and high electrical conductivity. To improve the field emission (FE) performances of SmB6 for practical applications, gadolinium-doped samarium hexaboride (Gd-doped SmB ${ }_{6}$) nanowire films as successfully synthesized on silicon (Si) substrates sing chemical vapor deposition (CVD) way. FE measurements demonstrate that the $\mathbf{1. 6} \mathbf{a t. \%}$ Gd-doped SmB. nanowire film has a low turn-on field of $2.53 \mathrm{~V} / \mu \mathrm{m}$ (at $10 \mu \mathrm{~A} / \mathrm{cm}^{2}$) and achieves a maximum emission current density of up to $271.67 \mu \mathrm{~A} / \mathrm{cm}^{2}$, which is much better than the undoped $\operatorname{SmB}_{6}$ nanowire film. These experimental results reveal that the Gd dopants can effectively improve the FE characteristics of SmB6 nanowire film, originating from the augment of the electrical conductivity, the increase of the aspect ratio and the decrease of surface work function. This work may give some helpful references to enhance the FE performances of cold-cathode nanodevices.

Active modulation of ultrafast electron pulses is essential for tunable terahertz sources and high-resolution imaging. Here, we demonstrate a polarization-tuned ultrafast pulsed electron source using a vertical few-layer graphene (vFLGs) cold cathode. Excited by a linearly polarized femtosecond laser, the vFLGs yield high optical switching ratios of 277 at 0° and 235 at 90° under a 400 V vacuum gap voltage. The emission current exhibits a distinct periodic polarization dependence, evolving from a cosine trend (0°–30°) to a sine trend (30°–90°). This tunable conversion between the multiphoton photoemission (MPP) and photoassisted thermionic emission (PTE) mechanisms provides a vital foundation for the construction of carbon-based ultrafast coherent electron sources.

Due to the large aspect ratio, excellent thermal and mechanical conductivities, the field emission characteristics of carbon nanotubes have been widely studied. As an allotrope, the linear carbon chain in double-walled carbon nanotubes (LCC-DWCNTs) has the potential to be a good field emitter. However, the field emission measurement of LCC-DWCNT is rarely reported. In this work, we demonstrate a stable field emission electron source under ~100 μA composed of LCC-DWCNTs. The bundle-like LCC-DWCNTs field emission electron source exhibits a low turn-on field of 0.245 V/μm at 1 μA, a large current of 1.75 mA, and a stable emission with fluctuation of 0.7%/5 hours@0.9 mA, which overcomes the rapid decay of current in contrast to the DWCNTs. Our results provide a stable field emission electron source, allowing operation even in a low vacuum.

Cold cathode electron guns have demonstrated significant advantages of high resolution and high brightness in vacuum electronic devices. However, the tradeoff between electron transmittance and focal spot size (FSS) is a big challenge. This article proposes a scheme of using a sharp cathode and a suppressor electrode to achieve a small FSS and high transmittance in a cold cathode electron gun simultaneously. Through initial finite-element simulations of an electron beam, the electron gun with a sharp cathode shows much localized electric field and induces an original convergent electron beam. The electron gun with suppressor electrode reduces the electric field gradient on the cathode surface and generates a much focused beam combined with the gate electrode. The influence of the suppressor electrode and the cathode curvature radius on the electron transmittance and electron FSS is measured. The results show that after introducing the suppressor electrode structure and using a cathode with a smaller radius of curvature, the electron beam FSS has decreased by 53.8%, and the electron transmittance has increased by 12.2%. At present, the electron gun with a sharp tungsten field emitter of tip radius of 10 nm and suppressor electrode shows an electron beam FSS of 88 -m and an electron transmittance of 42.7% under an acceleration voltage of 20 kV. The results provide a feasible solution for achieving high electron transmission and small FSS of cold cathode guns.

Field emission (FE) electron sources are made close to atomic-scale to reach the highest spatial resolution as well as stable emission for electron microscopy, electron beam inspection and lithography. At present, no single agreed method exists of using FE current-voltage data to extract the apparent emission area, which is needed for predicting some beam properties. The 1956 theory of Murphy and Good (MG) is better physics than the 1920s theory of Fowler and Nordheim (FN) and colleagues, but many researchers use simplified FN theory to analyse experimental data. The present paper reports an experimental method of finding apparent emission area, based on using field ion and field electron microscopes (FIM-FEM). The discrepancy of emission area between the FIM-FEM method and MG-based analysis is a factor of 7.4, while that with simplified FN-based analysis is about 25, confirming MG theory is better for FE data analysis. The result allows deduction of key indicators, including source energy spread, reduced brightness and emission efficiency. A downloadable program is made available to help analysis. Our work provides a new experimental method of characterizing FE electron sources, especially the atomic-scale cold cathode, for which existing plot-based data-analysis methods are not suitable.

Thermionic cathodes are widely used in applications ranging from electron microscopes and x-ray tubes to microwave power tubes. However, their short lifetime remains a significant limitation that urgently needs to be addressed. In this report, a lanthanum hexaboride (LaB6) thermionic cathode with severe surface poisoning was measured and an abnormal phenomenon was observed: as the temperature increased, the emission current first increased and then decreased, exhibiting current suppression at high temperatures. This behavior contradicts Richardson's law of thermionic emission. After a large emission current self-flashing process, the current suppression phenomenon disappeared. It is proposed that, at high temperatures, the accumulation of electronic charge within the oxide layer on the LaB6 cathode surface generates a reversed electric field, which in turn suppresses the emission current. This proposal has been verified by measuring the electron emission characteristics of a tungsten thermionic cathode equipped with a metal suppression shell under different degrees of charge accumulation. Furthermore, the quantitative electronic charge accumulation was resolved through temperature and electric field simulations combined with theoretical calculations. These findings contribute to understanding the failure mechanism of LaB6 thermionic cathodes and open up a new route for extending their lifetime.

Hafnium-doped InZnO (HIZO) thin film transistors (TFTs) were successfully fabricated via plasma-enhanced atomic layer deposition (PEALD) at low temperature (180 degrees C) for the first time, omitting the annealing process. Concretely, we adjusted the device performance by modulating the doping concentration of hafnium (Hf) cations and the oxygen vacancy content. The optimal 6.25 % doping content was determined. Based on this optimization, the HIZO TFTs exhibited an excellent field-effect mobility (mu(FE)) of 21.7 cm(2)/Vs, a low threshold voltage (V-th) of similar to 0.1 V, a minimum subthreshold swing (SS) of 69 mV/decade and a fantastic I-on/I-off of exceeding 10(8) utilizing the hafnium oxide (HfO2) dielectric, which was one of the state-of-the-art performances among HIZO TFTs reported to date. Meanwhile, an excellent bias stability under both positive and negative bias stress was achieved. The favorable performance can be attributed to the effective suppression of overabundant oxygen vacancies and the passivation of defects at the channel-dielectric interface by Hf doping. The Hall effect measurement and X-ray photoelectron spectroscopy (XPS) further corroborate the ability to inhibit carrier concentration by Hf addition. This study presents a novel strategy for achieving excellent HIZO TFTs, holding promise for the next-generation high-performance display domain.

Creating novel electromagnetic (EM) attenuation (meta)structures by multi-scale engineering is an effective strategy to achieve ultra-broad (≥30 GHz) effective absorption bandwidth (EAB). However, most studies, especially concerning ceramic based EM metamaterials, rely on traditional structures, such as woodpile (0°-90°) scaffolds, honeycomb and so on, making the improving of the EM performance challenging. In this work, ceramic-based hierarchical hybrid metamaterials with different structures (e.g., trapezoidal, stepped and honeycomb) were innovatively established on the basis of polymer-derived defect-rich pyrolytic carbon modified SiOC (PyC/SiOC) ceramic scaffold. The intrinsic EM attenuation capability of ingredient PyC/SiOC ceramic scaffolds was maximized by optimizing the volume infill rate and EM attenuation multi-loss mechanisms. EM multi-loss capability, including conductive loss and defects-induced polarization loss, was maximized by controlling the defects populations in the PyC absorbents. The results demonstrate that the synergistic effect of multi-loss mechanisms and hierarchical hybrid metastructural engineering significantly enhances EM absorption performance. Benefiting from these advantageous multi-scale structures, a simulated ultra-broad EAB of 36.8 GHz over the range of 3.2-40 GHz was achieved. This work provides novel insights and new ideas for the design of broadband EM absorbers.

Oxide-semiconductor thin-film transistors (TFTs) with low-voltage operation have attracted considerable attention owing to their promising prospects in portable and wearable electronics. However, maintaining high device performance under low voltages is challenging. Herein, the ITZO/IAO heterojunction TFTs with low-voltage operation were fabricated utilizing atomic layer deposition (ALD). The correlation between the composition of ITZO thin films and the device performance was investigated. When the In:Sn:Zn cycle ratio was 3:1:1, the ITZO/IAO heterojunction TFTs achieved a remarkable field-effect mobility ( mu(FE)) of 97.86 cm(2)/V & sdot; s, a fantastic I-on/I-off of 10(8) and an outstanding subthreshold swing (SS) of 65 mV/dec, which is a competitive performance among low-voltage oxide-semiconductor TFTs. The energy diagram analysis corroborated that the ultrahigh mu(FE )might be attributed to electron accumulation at the ITZO/IAO interface due to band bending. Furthermore, the threshold voltage shift ( Delta V-th) under positive gate bias stress (PBS) of 10(4 )s was only -21 mV, exhibiting excellent device stability. This work offers a feasible strategy for realizing high-performance oxide-semiconductor TFTs with low-voltage operation.

Nowadays, two theoretical approaches, based on elementary field electron emission (FE) theory and Murphy-Good (MG) FE theory are widely employed to analyze FE data. However, emission areas extracted by these two methods can differ by factors of more than 100. Thus, it is important to have an independent experimental method to verify which theory is more reliable. In this study, a new method using field ion and field electron microscopes (FIM-FEM) is introduced to measure emission area. This confirms MG FE theory as more accurate. A dedicated software package implementing the M-G theoretical framework was developed. The software enables extraction of electron source parameters such as current density, emission area and brightness directly from current-voltage (I-V) curve inputs, eliminating complex manual calculations. Freely available software provides researchers with a convenient and reliable method for characterizing cold FE cathodes, thereby facilitating the design and optimization of advanced electron source devices.

Driven by the miniaturization of vacuum electronic devices, electron sources are also evolving toward planar on-chip structures. Carbon nanotube (CNT) cold cathodes are highly advantageous for future applications in vacuum electronic devices due to their excellent field emission properties, high current density, and compatibility with microfabrication processes. We proposed an on-chip CNT field emission electron source with a 50 μm thick integrated silicon gate, which enables a simple deposition fabrication of the insulating and self-focusing layers, thereby overcoming the difficult wafer thinning process of the submicron self-focusing layer in our previous work. However, increased gate thickness enhances electron interception, leading to reduced gate transparency. The emission aperture, self-focusing layer thickness, and gate sidewall inclination angle are key factors and optimized through simulations to achieve high emission current while maintaining high gate transparency. As a result, an emission aperture diameter of 8 μm, a self-focusing layer thickness of 1 μm, and a 90° vertical gate sidewall are the optimized structure parameters. The field emission simulation showed that the emission current reached 3.67 μA at 150 V, with a gate electron transmission ratio of 97%. The result offers a viable strategy for the structural design and fabrication of planar gated cold cathode electron sources.

Sheet electron beam is the optimal type for electron gun of terahertz vacuum electronic devices, as it can effectively mitigate space charge effects at sub-millimeter scales and significantly enhance the electromagnetic coupling efficiency with planar high-frequency structures. To address the requirements for high power and miniaturization in terahertz backward wave oscillators (BWOs), this paper proposes a sheet beam electron gun based on a carbon nanotube (CNT) cold cathode. The aim is achieving both a high emission current and high current density by compressing the electron beam emitted from a large-area cathode, thereby meeting the operational demands of a 220 GHz BWO. To overcome the challenge of asymmetric beam divergence during strong compression which is caused by the mismatch of space charge forces in the transverse and longitudinal directions, an asymmetric focusing electrode structure is introduced. By independently optimizing the height of the focusing electrode along the wide side and narrow side of the cathode, differential compensation of space charge forces in the two dimensions can be well modulated. The initial electron beam cross-section is 3 mm×1 mm, with a cathode voltage of -15700 V, focusing electrode voltage of -15700 V, anode voltage of 0 V, and a cathode-anode gap of 5 mm. Results show that the electron gun successfully compresses the beam cross-section to 0.6 mm×0.15 mm, achieving an area compression ratio of approximately 33.3. The beam waist is stabilized at 11.5 mm, with an emission current of about 65 mA and the current density of about 72.2 A/cm2. The results provide a theoretical basis and technical solution for the engineering application of CNT cold cathode electron gun for terahertz BWOs.