Nanoscale Vacuum Electronic Devices

High-speed electronic devices rely on short carrier transport times, which are usually achieved by decreasing the channel length and/or increasing the carrier velocity. Ideally, the carriers enter into a ballistic transport regime in which they are not scattered. However, it is difficult to achieve ballistic transport in a solid-state medium because the high electric fields used to increase the carrier velocity also increase scattering. Vacuum is an ideal medium for ballistic transport, but vacuum electronic devices commonly suffer from low emission currents and high operating voltages. We have developed a low-voltage field-effect transistor with a vertical vacuum channel (channel length of ∼20 nm) etched into a metal–oxide–semiconductor substrate. We measure a transconductance of 20 nS µm–1, an on/off ratio of 500 and a turn-on gate voltage of 0.5 V under ambient conditions. Coulombic repulsion in the two-dimensional electron system at the interface between the oxide and the metal or the semiconductor reduces the energy barrier to electron emission, leading to a high emission current density (∼1×105 A cm–2) under a bias of only 1 V. The emission of two-dimensional electron systems into vacuum channels could enable a new class of low-power, high-speed transistors. Harboring a two-dimensional electronic system, graphene can be highly conductive in in-plane transport while being transmissive to impinging electrons. Based on these in- and out-of-plane interaction properties, a suspended graphene membrane is promising as an ideal gate (grid) to control electron transport in nanoscale vacuum electronic devices. We have measured capture and transmission efficiencies of very low energy (< 3 eV) electrons impinging upon a suspended graphene anode that is placed on top of a nanoscale void channel formed in a SiO2/Si substrate. Electron capture efficiency of 0.1 % (transmission efficiency of 99.9 %) is observed at 1 V bias. Presence of suspended graphene is also found to significantly enhance electron emission at cathode beyond the level of Child-Langmuir’s space-charge-limited emission. Photocarrier multiplication, the process of generating two or more electron-hole pairs from a single absorbed photon, can occur in semiconductor quantum dots or nanocrystals. Translating this carrier-level performance into a device-level improvement in sensing or converting photon energy, however, remains challenging. We have developed a graphene/SiO2/Si photodetector with a nanoscale void channel that demonstrates internal quantum efficiency of 115-175% measured with photocurrent in UV-Vis range. The self-induced electric field in 2D electron gas of a graphene/oxide/Si structure enables photocarrier multiplication

Atmospheric Cold Plasma via Fringe Field Enhanced Corona Discharge on Single Dielectric Barrier for Large-volume Applications

AbstractThis paper is to design and discuss on homogenous atmospheric cold plasma technique. Instead of using the needle tip with a small radius of curvature, this work utilized the twin tips with the sharp edge that can concentrate electric field around the edge of tips, allowing micro-discharge plasma at low power consumption. Our design structure shows a uniform atmospheric-air cold plasma for large-scale surface treatment applications. Furthermore, the designed large-scale atmospheric cold plasmas also provide a great benefit to environmental utilization

Hybrid Graphene–Si-Based Nanoscale Vacuum Field Effect Phototransistors

Two-dimensional (2D) hybrid nanoelectronic devices stem from the combination of 2D systems or a mixture of 2D materials themselves, such as graphene, with other well-defined nanostructures interacting with each other in the quantum regime and enabling exceptional characteristics. Here, this paper presents a hybrid photodetection platform consisting of a graphene/Si (Gr/Si) heterojunction in conjunction with nanoscale vacuum electronics based on a graphene/SiO₂/Si (GrOS) field effect device. The responsivity of the hybrid platforms based on p-Si and n-Si is fully and finely tunable up to 1.2 and 0.45 A/W, respectively, which correspond to external (internal) quantum efficiencies of 235% (350%) and 88% (132%), respectively. The multiplication gain in the proposed hybrid device originates from the impact ionization initiated by photoinduced carrier injection into the self-induced localized electric field (up to ∼10⁶ V/cm) distributed in a 2DEG region in Si. The electrons travel from the Si edge to graphene via nanoscale air channels. The ON/OFF ratios are in the range of ∼10²–10⁵. Therefore, this hybrid photodetection platform is architecturally Si-compatible and thus highly promising for ultrafast, low-power, and tunable optoelectronic applications. Moreover, the overall results demonstrate the impacts of nanoscale spacing air gap (∼100 nm) between graphene and Si that may affect the traditional graphene–Si Schottky characteristic, and the localized graphene work function at the Gr/Si interface of a hybrid device is determined mainly by the graphene work function of the GrOS field effect structure

Electrohydraulic Discharge Induced Gas-Liquid Interface Plasma for Seed Priming in Hydroponics

Seed priming is a vital process in agriculture, improving germination and uniformity. This study presents an innovative seed priming approach using electrohydraulic discharge plasma (EHDP) techniques, inducing gas-liquid interface plasma on wet seeds&#x2014;EHDP-wet seed surface priming&#x2014;and on seeds submerged in water&#x2014;EHDP-immersed seed priming. These techniques were applied to green oak leaf lettuce (Lactuca sativa L.) seeds. The results show that EHDP-immersed seed priming significantly enhances germination rate (98.3&#x0025;, compared to a control of &#x007E;80&#x0025;), germination uniformity (&#x007E;5 hrs compared to a control of &#x007E;15 hrs), and the Mean Germination Time (MGT) (&#x007E;1.87 days compared to a control of &#x007E;2.5 days). The presented method exploits three primary plasma formation regions, each generating distinct reactive oxygen and nitrogen species (RONS) and ions that interact differently with the seeds. RONS, particularly hydrogen peroxide (H2O2), nitrate (NO $_{3}^{-}$ ), and nitrite (NO $_{2}^{-}$ ), play crucial roles in germination, vigor, nutrient uptake, and hormonal regulation, thereby effectively breaking seed dormancy. Potential plasma treatment damages were addressed, revealing no significant variations in plant height, root length, leaf diameter, leaf thickness, or leaf numbers between control and plasma-primed groups, affirming EHDP plasma priming&#x2019;s safety. This study underscores the EHDP plasma priming&#x2019;s potential to enhance seed germination and early plant growth, while also reducing contamination risks without negatively impacting plant health and development, indicating its transformative potential for the agricultural industry

Rice (<i>Oryza sativa</i> L.) Seed Sterilization and Germination Enhancement via Atmospheric Hybrid Nonthermal Discharge Plasma

We designed a system to produce atmospheric hybrid cold-discharge plasma (HCP) based on microcorona discharge on a single dielectric barrier and applied it to inactivate microorganisms that commonly attach the rice seed husk. The cold-plasma treatment modified the surface of the rice seeds, resulting in accelerated germination and enhanced water imbibition. The treatment can operate under air-based ambient conditions without the need for a vacuum. The cold-plasma treatment completely inactivated pathogenic fungi and other microorganisms, enhancing the germination percentage and seedling quality. The final germination percentage of the treated rice seeds was ∼98%, whereas that of the nontreated seeds was ∼90%. Microcorona discharge on a single dielectric barrier provides a nonaggressive cold plasma that can be applied to organic materials without causing thermal and electrical damage. The hybrid nonthermal plasma is cost effective and consumes relatively little power, making it suitable for the surface sterilization and disinfection of organic and biological materials with large-scale compatibility