Hysteresis of pulsed characteristics of field emission from nanocarbon materials

Journal of Nanomaterials

Davydov

Gabdullin

et al. 2014

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.

Section: Discussionmentioning

confidence: 71%

“…(ii) hysteresis of emission from NPC in pulsed field (at sub-s and even s time scale) described in previous publications [40];…”

Section: Discussionmentioning

confidence: 75%

Field‐Induced Electron Emission from Nanoporous Carbons

Journal of Nanomaterials

Davydov

Gabdullin

et al. 2014

“…A description of experimental set-up and techniques was given previously in (6,7). In another paper presented at the 9 th Int.…”

Section: Introductionmentioning

confidence: 99%

On Possible Structure of Field-Induced Electron Emission Centers of Nanoporous Carbon

Fullerenes, Nanotubes and Carbon Nanostructures

Gabdullin

Mishin

2010

Self Cite

Analysis of emission characteristics of a nanostructured porous carbon material measured in pulsed electric field demonstrated that their hysteresis complies with two-barrier emission model in the additional assumption that electron transport through the internal barrier is controlled by electric charging of the surface. Quantitative parameters of emission centers were derived from emission I-V plots. These parameters comply with the model of emission center as a single onion-like particle at the emitter surface connected with the rest of emitter via a tunnel junction.

“…This phenomenon can be explained by the dynamic properties of field emission from such materials (including emission efficiency boosting in a rapidly decreasing electric field) investigated in our previous works. 8,9 …”

Section: Experiments With the Gauge Prototypementioning

confidence: 98%

Carbon‐film field‐emission cathodes in a compact orbitron‐type ionization vacuum sensor

Alexandrov

Surface & Interface Analysis

Mishin

et al. 2007

Self Cite

A possibility to using large-area field-emission cathodes as electron sources in ionic vacuum sensors was investigated. In the specially developed electron-optic scheme, electrons are extracted from a box-shaped cathode by the field of two anode strings. For a large part of the cathode, trajectories of emitted electrons are infinite (in theory), thus high efficiency of gas ionization and overall gauge sensitivity can be achieved. Experimental testing of a sensor prototype has demonstrated general viability of the proposed principle. For a residual gas pressure of about 10 −5 Torr and a cathode emission current 10 µA, the current of collected ions had value of about 1 nA. PROJECT BACKGROUND AND OBJECTIVEThe principle of operation of the most popular highvacuum sensors involves the measurement of ionic current originating from interaction of residual gas with a flow of electrons. Subclasses of ionic vacuum gauges 1 differ in the type of electron source used. Traditionally, the choice was between thermionic cathodes and forms of self-maintained discharge (magnetron, Penning, etc.). Rapid progress in technologies of nanostructured carbon materials 2 -4 suggests new promising solutions for these devices. Carbon-film distributed-field electron emitters combine advantageous features, such as low energy consumption, durability to poor vacuum, zero start-up time, simple design, small weight and no need for magnets. These features potentially make them more competitive in comparison with thermionic and discharge electron sources. The principal objective of the work reported here was the development and testing of ion vacuum sensor designs adapted for operation with carbonfilm field-emitters, in such a way as to realize their inherent advantages. GAUGE ELECTRON-OPTICAL SYSTEM DESIGNThe electron-optical system (EOS) of the developed vacuum sensor (Fig. 1) and their acceleration, emission current control and electron flow confinement and direction of the generated ions to the collector. The anode consists of two thin (50-100 µm) tungsten wires fixed through spring holders to ceramic insulators. The cathode has a 6 ð 6 mm cross-section and a length of 50 mm, and consists of two components: the foil emitter with an active carbon layer and the mesh electrode separating the diode from the ion collector volume. For these dimensions, the macroscopic electric field strength needed at the cathode for field electron emission (E D 0.3-3 V/µm) is achieved for applied voltages U D 1-10 kV.Electrode shapes and positions were optimized by digital simulation of the electron motion to achieve maximum trajectory length for particles emitted from different parts of the cathode. As shown in Fig. 2, for approximately 20% of the cathode area in the optimized EOS configuration, the particles are emitted into a 2D trap and can leave the system only in the axial direction under the influence of the comparatively weak axial electric field component. This enables efficient utilization of the electron energy for the purpose of ionizing residual gas m...