With the continual miniaturization of electronic devices, there is an urgent need to understand the electron emission and the mechanism of electrical breakdown at nanoscale. For a nanogap, the complete process of the electrical breakdown includes the nano-protrusion growth, electron emission and thermal runaway of the nano-protrusion, and plasma formation. This review summarizes recent theories, experiments, and advanced atomistic simulation related to this breakdown process. First, the electron emission mechanisms in nanogaps and their transitions between different mechanisms are emphatically discussed, such as the effects of image potential (of different electrode's configurations), anode screening, electron space-charge potential, and electron exchange-correlation potential. The corresponding experimental results on electron emission and electrical breakdown are discussed for fixed nanogaps on substrate and adjustable nanogaps, including space-charge effects, electrode deformation, and electrical breakdown characteristics. Advanced atomistic simulations about the nano-protrusion growth and the nanoelectrode or nano-protrusion thermal runaway under high electric field are discussed. Finally, we conclude and outline the key challenges for and perspectives on future theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes.

Nanoprotrusion (NP) on metal surface and its inevitable contamination layer under high electric field is often considered as the primary precursor that leads to vacuum breakdown, which plays an extremely detrimental effect for high energy physics equipment and many other devices. Yet, the NP growth has never been experimentally observed. Here, we conduct field emission (FE) measurements along with in situ transmission electron microscopy (TEM) imaging of an amorphous-carbon ($a\text{−}\mathrm{C}$) coated tungsten nanotip at various nanoscale vacuum gap distances. We find that under certain conditions, the FE current-voltage ($I\text{−}V$) curves switch abruptly into an enhanced-current state, implying the growth of an NP. We then run field emission simulations, demonstrating that the temporary enhanced-current $I\text{−}V$ is perfectly consistent with the hypothesis that a NP has grown at the apex of the tip. This hypothesis is also confirmed by the repeatable in situ observation of such a nanoprotrusion and its continued growth during successive FE measurements in TEM. We tentatively attribute this phenomenon to field-induced biased diffusion of surface $a\text{−}\mathrm{C}$ atoms, after performing a finite element analysis that excludes the alternative possibility of field-induced plastic deformation.

Field electron emission is a key mechanism in nanoelectronics with nanogaps, offering advantages such as high electron velocity and fast switching speeds. However, nanoscale field emission, affected by geometric asymmetry including quantum tunneling near to the emitter, and quantum space charge effects, remains largely unexplored in experimental studies. Here, we in situ investigated field emission characteristics of pure tungsten nanotips across vacuum nanogaps. We revealed a widely applicable scaling behavior between field emission characteristics and the ratio of apex radius to gap length (R/d), and demonstrated that the effects of quantum tunnelling due to emitter shape are the predominant influence. We further proposed a modified field emission equation, incorporating an empirical formula for the apex shape factor, k_MG (k_MG = f(R/d) = 1.680 × (R/d + 0.468)^−1.066), valid for R/d = 0.04 to 48. These findings provide fundamental insights into the optimization of nanoelectronic device design and the advancement of future technologies.

Polymethylsilsesquioxane (PMSQ) has become a kind of widely studied filler used in the electronic circuit board substrates due to its organic–inorganic hybrid structure, low dielectric constant, and good thermal stability, among other factors. Herein, the PMSQ microspheres were prepared by a two-step acid–base-catalyzed sol–gel method; the influences of reaction conditions including the ratio of water/methyltrimethoxysilane (MTMS), reaction temperature, concentration of the catalyst, and stirring time were systematically investigated; and the optimized reaction condition was then obtained towards a narrow particle size distribution and good sphericity. The microstructure of PMSQ microspheres was analyzed by the infrared spectrum and X-ray diffraction (XRD), which indicated that the as-prepared PMSQ had a ladder-dominant structure. The thermogravimetric analysis (TGA) demonstrated an excellent thermal stability of as-prepared PMSQ microspheres. More specifically, the dielectric constants at high frequency (1~20 GHz) of as-prepared PMSQ microspheres were measured to be about 3.7, which turned out a lower dielectric constant compared to SiO₂ powder (≈4.0). This study paves the way to further improve the performance of the electronic circuit board substrates for the application of high-frequency electronic packaging.

Electric-field-induced effects severely impact the long-term stability and reliability of nanoelectronic devices with nanogaps, such as field emission nanodiodes, field-effect nanotransistors and ultrafast switches. However, the damage mechanisms behind nanostructured electrode under high electric fields remain unclear. Here, we investigate deformation behaviors of tungsten nanotips, a typical nanostructured electrode, under an external electric field ( ~ 10 V/nm) using an in situ transmission electron microscopy (TEM), presenting the direct observation of both surface morphological evolution and dislocation dynamics. We find that electron wind effects and nanoscale effects dramatically reduce the atom evaporation threshold to 10-13 V/nm, which is approximately one-fourth to one-fifth of the previously reported values of 40-60 V/nm. Furthermore, we identify a field-induced deformation mechanism where strong electric fields and emission currents generate substantial, size-dependent structural changes closely governed by crystallographic orientation (Wulff shape) without external heating, occurring primarily through field-assisted evaporation rather than conventionally assumed field-induced surface atom diffusion. These findings enhance the understanding of electric-field-induced damage and are crucial for nanoelectronic devices optimization, reliability, and lifetime evaluation.

Microplasma at atmospheric pressure has been widely used in many fields due to the lower power consumption, higher plasma density, as well as better uniformity and stability. In this work, the microplasma characteristics of direct current atmospheric pressure glow discharge, including discharge morphology and electrical properties have been investigated with various interelectrode gaps (10–600 μm) and discharge currents (1–6 mA), and simultaneously, a finite element simulation has been conducted to obtain the distribution of the electric field and particle density. The evolution of cathode layer, anode layer and Faraday dark space at this scale was captured with a higher spatial resolution (∼1 μm) for the first time, demonstrating that the cathode layer, especially the cathode sheath rather than the positive column, plays a dominant role in the transition of the microplasma. As the gap shrinks to a size less than cathode layer (∼40 μm), the cathode sheath with a high electric field is compressed, leading to a rapid decrease of the discharge voltage. The discharge voltage remains basically unchanged regardless of the discharge current, because the electric field in the cathode sheath is limited by the accumulated space charge. The experimental results are well verified and explained by the simulation results. This study provides an in-depth understanding of the glow discharge mechanism at microscale, and of the stability of glow discharge at atmospheric pressure, and benefits to future research on the atmospheric pressure large-area microplasma and its related application.