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A novel explosive-emission cathode capable to produce high-current nanosecond electron bunches and enable tuning in terms of size is proposed and demonstrated to performance fit the particular problem. The record parameters, average diode current 6.5 kA and voltage 410 kV, are achieved by covering a conventional, planar copper cathode with a carbon film being composed of graphitic pyrolytic carbon (GrPyC). The demonstrated plasma expansion velocity and current density are comparable with those obtained with conventional graphitic cathodes. However, in contrast to purely graphite cathodes, the shape, size and surface profile of the proposed hybrid GrPyC/Cu cathodes can be readily adjusted allowing adjustments to fit requirements of a variety of high-current electronic applications.

Polyethylene (PE) based composites with segregated carbon nanotubes (CNTs) network was successfully prepared by hot compressing of a mechanical mixture of PE and CNT powders. Through comparison with a composite comprising randomly distributed carbon nanotubes of the same concentration, we prove that namely the segregated CNT network is responsible for the excellent electrical properties, i.e. 10&minus, 1 S/m at 0.5&ndash, 1% and 10 S/m at 6&ndash, 12% of CNT. The investigation of the complex impedance in the frequency range 1 kHz&ndash, 2 MHz shows that the sign of real part of the dielectric permittivity changes from positive to negative in electrically percolated composites indicating metal-like behavior of CNT segregated network. The obtained negative permittivity and AC conductivity behavior versus frequency for high CNT content (3%&ndash, 12%) are described by the Drude model. At the same time, in contrast to reflective metals, high electromagnetic shielding efficiency of fabricated PE composites in the frequency range 40&ndash, 60 GHz, i.e. close to 100% at 1 mm thick sample, was due to absorption coursed by multiple reflection on every PE-CNT segregated network interface followed by electromagnetic radiation absorbed in each isolated PE granule surrounded by conductive CNT shells.

The ability of graphene and other nm-thin carbon films including pyrolytic carbon (PyC) and pyrolyzed photoresist (PPF) to absorb microwave radiation is discussed. We show that being deposited on a properly chosen optically transparent dielectric substrate these films can provide more than 20 dB electromagnetic interference (EMI) shielding efficiency (SE).

International audience; Epoxy matrix-based composite materials filled with various carbon additives, such as natural, artificial and exfoliated graphites (EGs), activated carbons, and thick graphene, were fabricated. Results of their broadband dielectric spectroscopy in wide frequency range, from a few hertz to a few terahertz are reported. The lowest percolation threshold (below 1.5 wt. %) as well as the highest electromagnetic interference (EMI) shielding capacity are observed for composites containing EG. Using an original random resistor-capacitor-diode network model, we proved theoretically that 2 wt.% of EG in the epoxy host is an optimal composition, as it provides high EMI shielding efficiency at the level of 17 dB for a 1.4-mm-thick polymer slice, and at the same time, does not lead to a significant decrease of other important physical properties of epoxy.

The ability of thin conductive films, including graphene, pyrolytic carbon (PyC), graphitic PyC (GrPyC), graphene with graphitic islands (GrI), glassy carbon (GC), and sandwich structures made of all these materials separated by polymer slabs to absorb electromagnetic radiation in microwave-THz frequency range, is discussed. The main physical principles making a basis for high absorption ability of these heterostructures are explained both in the language of electromagnetic theory and using representation of equivalent electrical circuits. The idea of using carbonaceous thin films as the main working elements of passive radiofrequency (RF) devices, such as shields, filters, polarizers, collimators, is proposed theoretically and proved experimentally. The important advantage of PyC, GrI, GrPyC, and GC is that, in contrast to graphene, they either can be easily deposited onto a dielectric substrate or are strong enough to allow their transfer from the catalytic substrate without a shuttle polymer layer. This opens a new avenue toward the development of a scalable protocol for cost-efficient production of ultralight electromagnetic shields that can be transferred to commercial applications. A robust design via finite-element method and design of experiment for RF devices based on carbon/graphene films and sandwiches is also discussed in the context of virtual prototyping.