Nanostructured SiC as a promising material for the cold electron emitters

In this paper, the novel cold electron emitters based on nanostructured SiC layers covering the Si(001) substrate have been proposed. Their main advantage is an extremely simple and cost-effective manufacturing process based on the standard microelectronics-grade silicon wafers with no ultra-high vacuum required and no complicated chemical deposition processes or toxic chemicals involved. It integrates within a single technological step both the SiC growth and nanostructuring the surface in the form of nanosized protrusions, which is extremely beneficial for cathode applications. A simple mathematical model predicts field emission current densities and turn-on electric fields, which would allow practical device applications. According to our estimations, emission currents in the milli-Amp range can be harvested from one square centimeter of the cathode surface with electric field close to 107 V/m. So, the nanostructured SiC can be the promising material for the cold electron emitters.

Spectral Characteristics of the Double-Folded Slot Antennas with Cold-Electron Bolometers for the 220/240 GHz Channels of the LSPE Instrument

We present the results of the experimental and theoretical study of the resonant properties and noise of a single cell of a receiving system based on cold-electron bolometers (CEB) with a double-folded slot antenna and coplanar lines. The system was designed to receive signals at 220/240 GHz frequencies with a 5% bandwidth. In measurements, we used the samples of the double-folded slot antennas with slot lengths of 162 um and coplanar line lengths from 185 to 360 um. Measurements of the resonance properties of CEB located at 0.3 K cryostat plate were carried out using a generator based on a high-temperature YBCO Josephson junction located inside the same cryostat at 4 K plate. This arrangement made it possible to obtain smooth amplitude-frequency characteristics with a clearly defined peak of a 15–21 GHz bandwidth at different frequencies. Based on these results, 2-D array of double-folded slot antennas with CEBs as 220/240 GHz LSPE channel prototype was calculated.The absorption efficiency of the array has reached 81% and 77% for 220 and 240 GHz channels, respectively.

Forming a cold electron population at a weakly outgassing comet

<p>The Rosetta Mission rendezvoused with comet 67P/Churyumov-Gerasimenko in August 2014 and escorted it for two years along its orbit. The Rosetta Plasma Consortium (RPC) was a suite of instruments, which observed the plasma environment at the spacecraft throughout the escort phase. The Mutual Impedance Probe (RPC/MIP; Wattieaux et al, 2020; Gilet et al., 2020) and Langmuir Probe (RPC/LAP; Engelhardt et al., 2018), both part of RPC, measured the presence of a cold electron population within the coma.</p> <p>Newly born electrons, generated by ionisation of the neutral gas, form a warm population within the coma at ~10eV. Ionisation is either through absorption of extreme ultraviolet photons or through collisions of energetic electrons with the neutral molecules. The cold electron population is formed by cooling the newly born, warm electrons via electron-neutral collisions. Assuming the radial outflow of electrons, the cold population was only expected at comet 67P close to perihelion, where outgassing rate from the nucleus was at its highest (Q > 10<sup>28</sup> s<sup>-1</sup>). However, cold electrons were observed until the end of the Rosetta mission at 3.8au when the outgassing was weak (Q<10<sup>26</sup> s<sup>-1</sup>). Under the radial outflow assumption, there should not have been sufficient neutral gas to efficiently degrade the electron energies.</p> <p>We have developed the first 3D collision model of electrons at a comet. Self-consistently calculated electric and magnetic fields from a collisionless and fully-kinetic Particle-in-Cell model (Deca et al., 2017; 2019) are used as a stationary input for the test particle simulations. We model the neutral coma as a spherically symmetric cloud of pure water, which follows 1/r<sup>2</sup> in cometocentric distance. Electron-neutral collisions are treated as a stochastic process using cross sections from Itikawa and Mason (2005). The model incorporates elastic scattering of electrons and a variety of inelastic collisions, including excitation and ionization of the water molecules.</p> <p>We show that the radial outflow of electrons from the coma is insufficient to generate a cold electron population under weak outgassing conditions. Using our original test particle model, we demonstrate the trapping of electrons in the inner coma by an ambipolar electric field and how this increases the efficiency of the electron cooling.  We also show that, at low outgassing rates, electron-neutral collisions significantly cool electrons within the coma and can lead to the formation of a cold population.</p> <p> </p>

Responsivity and Noise Equivalent Power of a Single Cold-Electron Bolometer

We have developed a single-pixel capacitively coupled Cold-Electron Bolometer (CEB) and characterized it in the current-biased regime. The most attractive feature of the CEB is effective electron self-cooling of the absorber, which leads to a lower bolometer noise and higher dynamic range. The bolometer responsivity was measured by determining the voltage response to an applied power through the absorber from a heating current, modulated at frequencies from 35 Hz to 2 kHz. The optimum responsivity of 1.5 × 1010 V/W was measured at a modulation frequency of 35 Hz. The noise equivalent power (NEP) was subsequently obtained from the estimated bolometer noise voltage with respect to the measured bolometer responsivity. The NEP of better 2 × 10−18 W/Hz1/2 was obtained for modulation frequencies greater than 100 Hz. The background power and the bolometer time constant were also estimated from the experimental results. The photon-noise-limited operation of CEB will dominate for a signal power of 10 fW and higher at frequency 80 GHz and higher.

A Distributed Terahertz Metasurface with Cold-Electron Bolometers for Cosmology Missions

We developed and tested a 2D periodic array of cold-electron bolometers arranged into a wideband frequency selective metasurface that absorbs more than 70% of the incident power in the frequency range 100–800 GHz. The array had 10 × 10 unit cells, each containing four bolometers incorporated into a ring. The chip with bolometers was mounted on the back side of the silicon lens without a back-reflector. Preliminary experiments demonstrated voltage responsivity as high as 109 V/W for the current-biased series array. Simulation of the noise performance shows realization of background noise-limited performance with NEPtot < NEPphot for the optical power load P0 > 15 pW. Results of numerical simulation made for the unit cell of the array are presented together with the equivalent diagram based on lumped network elements. The unit cell also was developed numerically to operate in two radiation modes.

Electron cooling at a weakly outgassing comet

&lt;p&gt;The Rosetta spacecraft arrived at comet 67P in August 2014 and then escorted it for 2 years along its orbit. Throughout this escort phase, two plasma instruments (Mutual Impedance Probe, MIP; and Langmuir Probe, LAP) measured a population of cold electrons (&lt; 1 eV) within the coma of 67P (Engelhardt et al., 2018; Wattieaux et al, 2020; Gilet et al., 2020). These cold electrons are understood to be formed by cooling warm electrons through collisions with the neutral gas. The warm electrons are primarily newly-born and produced at roughly 10eV within the coma through ionisation. While it was no surprise that cold electrons would form near perihelion given the high density of the neutral coma, the persistence of the cold electrons up to a heliocentric distance of 3.8 au was highly unexpected. With the low outgassing rates observed at such large heliocentric distances (Q &lt; 10&lt;sup&gt;26&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;), there should not be enough neutral molecules to cool the warm electrons efficiently before they ballistically escape the coma.&lt;/p&gt;&lt;p&gt;We use a collisional test particle model to examine the formation of the cold electron population at a weakly outgassing comet. The electrons are subject to stochastic collisions with the neutral coma which can either scatter or cool the electrons. Multiple electron neutral collision processes are included such that the electrons can undergo elastic scattering as well as collisions inducing excitation and ionisation of the neutral species. The inputted electric and magnetic fields, which act on the test particles, are taken from a 3D fully-kinetic, collisionless Particle-in-Cell (PiC) model of the solar wind and cometary ionosphere (Deca et al., 2017; 2019), with the same neutral coma as used in our model. We use a pure water coma with spherical symmetry and a 1/r&lt;sup&gt;2&lt;/sup&gt; dependence in the neutral number density to drive the production of cometary electrons and the electron-neutral collisions.&lt;/p&gt;&lt;p&gt;We first demonstrate the trapping of electrons in a potential well around the comet nucleus, formed by an ambipolar field. We show how this electron-trapping process can lead to more efficient cooling of electrons and the subsequent formation of a cold electron population, even at low outgassing rates.&lt;/p&gt;