Vacuum Nanoelectronics Research Articles

Analytical Model of Optical-Field-Driven Subcycle Electron Tunneling Pulses from Two-Dimensional Materials.

We develop analytical models of optical-field-driven electron tunneling from the edge and surface of free-standing two-dimensional (2D) materials. We discover a universal scaling between the tunneling current density (J) and the electric field near the barrier (F): In(J/|F|β) ∝ 1/|F| with β values of 3/2 and 1 for edge emission and vertical surface emission, respectively. At ultrahigh values of F, the current density exhibits an unexpected high-field saturation effect due to the reduced dimensionality of the 2D material, which is absent in the traditional bulk material. Our calculation reveals the dc bias as an efficient method for modulating the optical-field tunneling subcycle emission characteristics. Importantly, our model is in excellent agreement with a recent experiment on graphene. Our results offer a useful framework for understanding optical-field tunneling emission from 2D materials, which are helpful for the development of optoelectronics and emerging petahertz vacuum nanoelectronics.

All-carbon heterostructures self-assembly during field electron emission from diamond nanotip

In this study we demonstrate formation of all-carbon heterostructures induced by field electron emission from diamond needle-shaped crystallites with nanoscale tips. We show that at certain experimental conditions a carbon nanoprotrusion can be formed at the apex of a diamond emitter. Staircase-like current-voltage curves observed for such emitters indicated the presence of the Coulomb blockade effect in the self-assembled all-carbon heterostructures. The mechanism of nanoprotrusion formation via the field-induced surface diffusion of carbon atoms is revealed by observing the structural transformation of the emitter material using transmission electron microscopy. We also explore how the properties of the formed heterostructures evolve with the field emission current, and show that the characteristic size of the formed nanoprotrusion depends on the dimensions of the diamond nanotip. The developed approach offers a way to reproducible fabrication of heterostructured emitters which can be applied as coherent single-electron sources in vacuum nanoelectronics and electron quantum optics.

Reducing and tuning the work function of field emission nanocomposite CNT/NiO cathodes by modifying the chemical composition of the oxide.

This work presents for the first time the possibility of reducing and tuning the work function of field emission cathodes coated with metal oxides by changing the chemical composition of oxide coatings using an example of heat-treated CNT/NiO nanocomposite structures. These cathodes are formulated using carbon nanotube (CNT) arrays that are coated with ultrathin layers of nickel oxide (CNT/NiO) by atomic layer deposition (ALD). It was found that NiO at thicknesses of several nanometers grown on CNTs heat treated at a temperature of 350 °C can change its stoichiometric composition towards the formation of oxygen vacancies, since the Ni3+/Ni2+ peak area ratio increases and the position of the Ni-O peak binding energies shifts as observed using X-ray photoelectron spectroscopy (XPS). According to the secondary electron cut-off, the work function was 4.95 for pristine CNTs and it was found that the work function of deposited NiO layers on CNTs decreased after heat treatment. The decrease in work function occurs as a result of changes in the chemical composition of the oxide film. For the heat-treated CNT/NiO composites, the work function was 4.30 eV with a NiO layer thickness of 7.6 nm, which was less than that for a NiO thin film close to the stoichiometric composition, which had a work function of 4.48 eV. The field emission current-voltage characteristics showed that the fields for producing an emission current density of 10 μA cm-2 were 5.54 V μm-1 for pure nanotubes and 4.32 V μm-1 and 4.19 V μm-1 for NiO-coated CNTs (3.8 and 7.6 nm), respectively. The present study has shown that heat treatment of deposited thin NiO layers on field cathodes is a promising approach to improve the efficiency of field emission cathodes and is a new approach in vacuum nanoelectronics that allows tuning the work function of field emission cathodes.

Universal model for electron thermal-field emission from two-dimensional semimetals

We present the theory of out-of-plane (or vertical) electron thermal-field emission from two-dimensional (2D) semimetals. We show that the current–voltage–temperature characteristic is well captured by a universal scaling relation applicable for broad classes of 2D semimetals, including graphene and its few-layer, nodal point semimetal, Dirac semimetal at the verge of topological phase transition, and nodal line semimetal. Here, an important consequence of the universal emission behavior is revealed: In contrast to the common expectation that band topology shall manifest differently in the physical observables, band topologies in two spatial dimension are indistinguishable from each other and bear no special signature in electron emission characteristics. Our findings represent the quantum extension of the universal semiclassical thermionic emission scaling law in 2D materials and provide theoretical foundations for the understanding of electron emission from cathode and charge interface transport for the design of 2D-material-based vacuum nanoelectronics.

Structure Optimization of Planar Nanoscale Vacuum Channel Transistor

Due to its unique structure, discoveries in nanoscale vacuum channel transistors (NVCTs) have demonstrated novel vacuum nanoelectronics. In this paper, the structural parameters of planar-type NVCTs were simulated, which illustrated the influence of emitter tip morphology on emission performance. Based on simulations, we successfully fabricated back-gate and side-gate NVCTs, respectively. Furthermore, the electric properties of NVCTs were investigated, showing the potential to realize the high integration of vacuum transistors.

Titanium Trisulfide Nanosheets and Nanoribbons for Field Emission-Based Nanodevices

The field emission (FE) properties of TiS3 nanosheets and nanoribbons, synthesized by direct sulfuration of bulk titanium, are investigated. The nanosheets show an enhanced FE behavior with a low turn-on field of ∼0.3 V/μm, required for drawing an emission current density of ∼10 μA/cm2. Interestingly, the TiS3 nanosheet emitter delivered a large emission current density of ∼0.9 mA/cm2 at a relatively low applied electric field of ∼0.4 V/μm. We have estimated the values of the field enhancement factor (β), which are found to be ∼5 × 104 for the TiS3 nanosheet emitter and ∼4 × 103 for the nanoribbon emitter. We attribute the superior FE performance to the presence of atomically sharp edges and the reduced thickness of TiS3, as reflected in the high value of β. In fact, the nanosheet sample presents a higher density of ultrathin layers (∼12 nm-thick), and thus, they have a larger edge to volume ratio than the nanoribbon samples (which are ∼19 nm-thick). The superior FE behavior of TiS3 nanosheets over nanoribbons makes them a propitious field emitter and can be utilized for various FE-based applications, demanding large emission currents and lower operational voltages. Moreover, the FE current stability recorded on these samples confirms their promising performance. Thus, the present investigation brings out a great promise of TiS3 nanosheets and nanoribbons as field emitters for vacuum nanoelectronics devices.

Vacuum Nanoelectronics Based on Semiconductor Field-Emission Structures: Current State and Development Prospects. Review

Vacuum Nanoelectronics Based on Semiconductor Field-Emission Structures: Current State and Development Prospects. Review

Electron Emission Regimes of Planar Nano Vacuum Emitters

Recent advancements in nanofabrication have enabled the creation of vacuum electronic devices with nanoscale free-space gaps. These nanoelectronic devices promise the benefits of cold-field emission and transport through free space, such as high nonlinearity and relative insensitivity to temperature and ionizing radiation, all while drastically reducing the footprint, increasing the operating bandwidth, and reducing the power consumption of each device. Furthermore, planarized vacuum nanoelectronics could easily be integrated at scale similar to typical microscale and nanoscale semiconductor electronics. However, the interplay between different electron emission mechanisms from these devices is not well understood, and inconsistencies with pure Fowler–Nordheim (FN) emission have been noted by others. In this work, we systematically study the current–voltage characteristics of planar vacuum nanodevices having few-nanometer radii of curvature and free-space gaps between the emitter and the collector. By investigating the current–voltage characteristics of nearly identical devices fabricated from two different materials and under various environmental conditions, such as temperature and atmospheric pressure, we are able to clearly isolate three distinct emission regimes within a single device: Schottky, FN, and saturation. Our work will enable robust and accurate modeling of vacuum nanoelectronics, which will be critical for future applications requiring high-speed and low-power electronics capable of operation in extreme conditions.

SnO2 Nanofibers Network for Cold Cathode Applications in Vacuum Nanoelectronics

AbstractField‐emission cold cathodes are the key components of vacuum nanoelectronics that offer great advantages over other electron sources based on the thermionic or photoelectric effects. In the effort to realize new electron sources, a systematic investigation of the field emission (FE) properties of SnO2 nanofiber networks is performed. High‐purity SnO2 nanofibers, confirmed by X‐ray photoelectron spectroscopy, are prepared by electrospinning technique and then uniformly distributed over Si wafer. Field emission properties are investigated using a nanomanipulated tip‐shaped anode, inside a scanning electron microscope, for fine tuning the anode‐cathode separation distance. A field‐emission current is observed with an applied electric field as low as 25 V μm−1. Performance parameters such as turn‐on field and field enhancement factor are evaluated within the theoretical Fowler–Nordheim framework as a function of the anode–cathode separation distance, demonstrating that a maximum enhancement factor of about 150 is obtained at a separation of 200 nm. The emission from a single nanofiber is characterized by a current saturation at high voltages that can be explained in terms of electron supply limitation within conduction band. No evidence of field emission current contribution by electron tunneling from the valence band is observed in the experimental data.

(Invited) III-Nitrides for Vacuum Nanoelectronics

Vacuum Field Effect Transistors (VFETs) are explored using wide-bandgap (III-Nitrides), VFETs avoid high power consumption caused by cathode heating in thermionic emission devices and have small turn-on voltage with potential for millimeter-wave operation. Special attention is placed on emitter design, growth of high-quality materials and evaluation of thermal propertiesProgress in Si- and III-V-based electronic devices allowed operation at high-frequencies extending well into the millimeter-wave range. Device performance is limited by carrier transport properties and parasitics which have been addressed using different semiconductor materials, shrinking of device dimensions and advanced design approaches, permitting in this way to achieve operation at several hundred GHz. Further performance advances continue to be reported but start reaching a limit. The advances made in nanotechnology together with the possibility of utilizing field- rather than thermionic-emission offer, however, the possibility of revisiting the principle of vacuum tubes. Nanoelectronic devices utilizing such approaches offer the possibility of operating at millimeter-wave frequencies. Materials used for their realization are semiconductors i.e. II-Nitrides that can be processed using well-developed technologies and nanofabrication techniques, providing therefore ways of shrinking dimensions in critical parts of the device such as for example the gap between the emitter and cathode.The paper addresses device approaches for vacuum nanoelectronics using wide-bandgap i.e. III-Nitride semiconductors. The studies rely on appropriate emitter design, growth of high-quality materials and evaluation of thermal properties that can play a critical role in device performance.

Ultralow Voltage GaN Vacuum Nanodiodes in Air.

The III-nitride semiconductors have many attractive properties for field-emission vacuum electronics, including high thermal and chemical stability, low electron affinity, and high breakdown fields. Here, we report top-down fabricated gallium nitride (GaN)-based nanoscale vacuum electron diodes operable in air, with record ultralow turn-on voltages down to ∼0.24 V and stable high field-emission currents, tested up to several microamps for single-emitter devices. We leverage a scalable, top-down GaN nanofabrication method leading to damage-free and smooth surfaces. Gap-dependent and pressure-dependent studies provide new insights into the design of future, integrated nanogap vacuum electron devices. The results show promise for a new class of high-performance and robust, on-chip, III-nitride-based vacuum nanoelectronics operable in air or reduced vacuum.

Алмазные фотокатоды как полевые катоды для вакуумной микроэлектроники

The use of diamond photocathodes and electron flow amplifiers in high-frequency vacuum micro and nanoelectronics is analyzed. The main devices are a vacuum microtriode and an electron gun for an integral traveling wave tube.

Fabrication of vertically well-aligned NiSi2 nanoneedle arrays with enhanced field emission properties

In this study, we demonstrated the controllable fabrication of periodic arrays of vertically well-aligned, fully-silicided NiSi2 nanoneedles with sharp nanotips on (100)Si substrates. The new approach proposed here eliminates the need for complicated and costly photolithographic processes and the use of toxic chemicals. All the produced vertical Si and NiSi2 nanoneedles were identified to be single crystalline and with the same geometric morphology and the same axial orientation of [100]. Additionally, the produced tapered NiSi2 nanoneedle array possessed excellent electron emission properties with a very low turn-on field of 0.85 V/μm, which is superior to many reported one-dimensional metal silicide nanostructures. Such an enhancement in the field emission can be attributed to the lower effective work function, sharp nanotips, single-crystalline structure, and good vertical alignment. The combination of the facile approach proposed here and superior electron emission performances make the well-ordered vertical NiSi2 nanoneedles promising candidates for vacuum nanoelectronics and field emission display applications.

Stable electron field emission from graphene/hexagonal boron nitride hybrid structure

Graphene/h-BN hybrid structure is constructed using simple and efficient solution process and the field emission properties of the hybrid structure are examined. It is found that the hybrid structure exhibits much more stable electron field emission properties compared to the pure graphene films. A Significantly higher maximum emission current density is obtained from the hybrid structure. In addition, the hybrid structure displays much better emission stability, whose current fluctuation is less than 4.5%. These results indicate that the graphene/h-BN hybrid structure is a promising candidate of reliable electron emission source in vacuum nanoelectronics devices.

Analytic model of electron transport through and over non-linear barriers

Tunneling barriers are an essential component of electron sources, sensors, detectors, and vacuum nanoelectronics and a pivotal factor in their performance, but the barriers themselves routinely depart from the analytic models used to model their behavior. A new formalism is developed to analytically and accurately model emission through and over barriers associated with depletion layers, nanotip barriers, and metal–insulator–metal (MIM) structures. The transmission probability for depletion layers and MIM and metal–oxide–semiconductor (MOS) barriers is accurately modeled as the electron energy exceeds the barrier height using approaches designed for rapid implementation demanded by simulation codes and extensible to general barriers. The models supersede conventional thermal and field models in depletion and MIM/MOS barrier studies. Thermal-field methods are used to treat the transmission probability and shape factor methods to treat the tunneling factor. Analytic formulas for current density are obtained. The methods ease device simulation and characterization of current–voltage relations for emerging technologically interesting barriers with better accuracy.

Investigation of local ion-stimulated carbon deposition to create vacuum field emission diodes

This paper presents the results of experimental studies of the influence of the technological parameters of a focused ion beam (FIB) on the process of local ion-stimulated deposition of carbon and tungsten when creating elements of vacuum nanoelectronics. The dependences are obtained illustrating the influence of the time of the FIB exposure at a point on the geometric parameters of the structures. Experimental samples of vacuum field-emission diodes based on semiconductor-metal-dielectric structures were fabricated by ion-stimulated carbon deposition. A technological process for creating field-emission diodes has been developed. The prospects of applying the FIB method for creating structures of vacuum field emission nanoelectronics are demonstrated.

First-principles insights on the electronic and field emission properties of Ga and Al doped germanium nanocones

Density functional theory (DFT) simulations have been performed to study the field emission characteristics of pristine, Ga, and Al substituted germanium nanocone (Ge-NC). The influence due to the substitution of group-III elements on Ge-NC is studied using the density of states (DOS) spectrum and electron density. As a matter of fact, from the molecular electrostatic potential surface, it is noticed that the impurity substitution at the apex of Ge-NC leads to increase in the field emission properties due to delocalization of electron by the charge transfer at the apex of nanocone. In addition, the Mulliken charge transfer, work function and current density of the emitted electron were calculated for the pristine and Ga and Al-doped Ge-NC. The results suggest that the substitution of group-III impurity along the apex of Ge-NC leads to the improved field emission, which can be used for the assembly of vacuum electronics and nanoelectronics.

AN ANTHOLOGY OF THE DISTINGUISHED ACHIEVEMENTS IN SCIENCE AND TECHNIQUE. PART 42: ELECTRONICS: RETROSPECTIVE VIEW, SUCCESSES AND PROSPECTS OF ITS DEVELOPMENT

Purpose. Preparation of brief scientific and technical review about sources, retrospective view, basic stages, achievements, problems, trends and prospects of development of world electronics for period of 20th-21st centuries. Methodology. Known scientific methods of collection, analysis and analytical treatment of the opened scientific and technical information of world level in area of a vacuum electronics, semiconductor electronics, vacuum microelectronics and nanoelectronics, and also optical electronics. Results. A brief analytical scientific and technical review is resulted about the primary and present states, achievements, trends and prospects of development of electronics in the developed countries of the world. From positions of approach of the systems advantages and lacks of semiconductor microelectronics are described as compared to a vacuum electronics. Considerable progress is marked in development of semiconductor element base (microtransistors, microprocessors, microcontrollers and other) for creation of different electronic devices and computing engineering. Information, touching the determining deposit of electronic companies of the «Silicon Valley» in the USA in providing of technological breach in area of modern microelectronics, production of computers and their microprocessors, software and creation of devices of mobile communication development, is resulted. The basic problems of space microelectronics are affected. The possible ways of further development are indicated in the world of electronics, including vacuum microelectronics and nanoelectronics, and also optical electronics. The special attention is turned for urgent development of high-efficiency protective facilities specialists against cyber attacks hackers on the computer systems. In a review an accent is done on the sharp necessity of acceptance the proper services of drastic measures for a fight with cyber terrorism. Originality. Systematization of the scientific and technical materials touching world history of development and creation of modern element base of a vacuum electronics and semiconductor microelectronics known from the sources opened in outer informative space is executed. Possible new perspective directions of development in the modern world of microelectronics are formulated. Practical value. Popularization and deepening for students, engineer and technical| specialists and research workers of front-rank scientific and technical knowledge in the topical area of development, creation and application in the modern technique of the different setting of high-computer-integrated electronic devices, extending their scientific range of interests and further development of scientific and technical progress in society.

Thermionic electron emission from single carbon nanostructures and its applications in vacuum nanoelectronics

Abstract

Electronic Scattering of Graphene Plasmons in the Terahertz Nonlinear Regime

Graphene possesses large Kerr nonlinearities that enabled the realization of energy-efficient nonlinear optical devices. At the same time, electronic scattering of graphene plasmons shows very high energy transfer efficiencies at very low beam energies due to its extremely large plasmon wave vector. We have tapped into these two unique optical properties of graphene to study the potential of an energy-efficient optoelectronic light source and all-optical modulator. We found that 2π-phase shift and 94% loss modulation is achievable with just a 25.6-V electron beam passing 10 nm above a graphene waveguide with a Fermi level of 0.1 eV. This also enables nonlinear optical devices to utilize in situ generated plasmons without the need of external optics, which could herald the return of vacuum nanoelectronics.