Previous experiments have demonstrated that carbon nanoisland films (or disordered quantum-dot arrays) deposited on silicon wafers may possess the property of low-field electron emission. This paper presents our new work on comparative characterization of emitting and nonemitting thin carbon films. The experimental results acquired by Auger spectroscopy, electron energy loss spectroscopy, Anderson's technique for workfunction measurement, and secondary-emission techniques confirmed that the emitting films are discontinuous and consist of carbon in sp2-hybridization state, while their workfunction is relatively high (>4 eV). These experimental data clearly contradict the commonly accepted Fowler–Nordheim theory of field emission and suggest that the observed emission phenomenon has a different nature. A novel model is proposed as a development of the well-known hot-electron emission mechanism supplemented with nanoscale-related features of thermoelectric phenomena.

The electronic structure of island carbon films on silicon, which are capable of low-voltage field electron emission (at the mean electric-field strength above several hundreds of V/mm), have been investigated. It has been shown by tunnel spectroscopy that islands of these coatings are characterized by a continuous spectrum of the allowed delocalized states near the Fermi level, i.e., they contain carbon in the sp² state. The photoconductivity of the coatings under study has been observed. Based on the current and spectral characteristics of this phenomenon, it has been shown that islands are separated from each other by tunnel barriers and from the substrate by a Schottky barrier.

Influence of fabrication technology on field electron emission properties of nanoporous carbon (NPC) was investigated. Samples of NPC derived from different carbides via chlorination at different temperatures demonstrated similar low‐field emission ability with threshold electric field 2‐3 V/μm. This property correlated with presence of nanopores with characteristic size 0.5–1.2 nm, determining high values of specific surface area (>800 m²/g) of the material. In most cases, current characteristics of emission were approximately linear in Fowler‐Nordheim coordinates (excluding a low‐current part near the emission threshold), but the plots’ slope angles were in notable disagreement with the known material morphology and electronic properties, unexplainable within the frames of the classical emission theory. We suggest that the actual emission mechanism for NPC involves generation of hot electrons at internal boundaries and that emission centers may be associated with relatively large (20–100 nm) onion‐like particles observed in many microscopic images. Such particles can serve two functions: to provide additional “internal” enhancement of the electric field and to inhibit relaxation of hot charge carriers due to the “phonon bottleneck” effect.

The dynamic characteristics of field emission from nanocarbon films subjected to microsecond electric field pulses are studied. The emission curves exhibit hysteresis the parameters of which are...

Methods of gyrotron electron beam diagnostics developed at St. Petersburg Polytechnic University are reviewed. Bremsstrahlung X-rays produced at the collector can be used for definition of electron energy distribution in the spent beam. This possibility has been tested at two megawatt-power-level gyrotrons at the Karlsruhe Institute of Technology. Analysis of propagation of gigahertz-frequency signals in a slow-wave structure coupled with the beam can be used for the determination of velocity characteristics upstream from the microwave cavity. Numerical simulations performed with CST Particle Studio confirmed that data on axial component of electron velocities can be derived from frequency dependences of the slow-wave gain. Control of electron beam quality via tuning of the electric and magnetic field distributions provides a promising instrument for gyrotron efficiency enhancement.