Optimization of multi-tip-shaped field emitters with bilayer protective coatings

The calculations needed to optimize the ordered multi-tip-shaped silicon field emitters with the two-layer protective metal-fullerene coatings intended for use in high voltage electronic devices operating in technical vacuum have been performed. The calculations are fulfilled using the COMSOL program. The influence of the morphology of the surface on the emission characteristics of the emitters is determined, including the needles height and radius of their vertices, and also the distance between needles. It has been shown that the emitters with an area of 0.2 cm², operating under the conditions of partial mutual screening, can provide currents of several hundred milliamps for fairly high voltages.     

Tip field emitters coated with fullerenes

Formation and characteristics of fullerene coatings on the surface of tungsten tip field emitters and emitters with ribbed crystals formed on their surface are studied. It is found that electric fields and heat treatments affect the structure and emission characteristics of the fullerene coatings. Methods of creating microprotusions on the surface of the coatings that considerably enhance the electric field have been developed and tested, and emitters with a single microprotrusion yielding emission current densities up to 10⁶–10⁷ A/cm² are demonstrated. Emitters with fullerene coatings in the form of a distributed microcluster structure can yield currents in excess of 100 μA from a single micron-sized tip in a stationary regime.     

Annular Multi-Tip Field Emitters with Metal–Fullerene Protective Coatings

Technical Physics - A technology of creation of annular silicon field emitters with bilayer metal–fullerene coating has been developed and their performance has been studied. It has been...     

Use of ion processing to improve the quality of fullerene-coated field emitters

The efficiency of tip field emitters covered by activated fullerene coatings is studied in a wide range of emission currents and residual gas pressures. Main mechanisms behind the influence of the gaseous medium and ion bombardment on the emitter efficiency are determined. The feasibility of improving the homogeneity of the fullerene coating by potassium ion bombardment is demonstrated. From data on the emitter performance in a technical vacuum, a previously unknown effect is discovered: the structure of activated fullerene coatings is reproduced under intense ion bombardment. It is found that intense bombardment by residual gas ions increases a limiting current extracted from fullerene-coated tip field emitters.     

Potassium-induced activation of field emitters with fullerene coating

The influence of potassium deposition on the emission characteristics of field tip emitters with fullerene coatings is studied. It is shown that a three-to fourfold reduction of the typical voltage U ₁ required for the given emission current can be attained by rapid deposition of potassium layer with a thickness exceeding a monolayer. The deactivation of emitters at room temperature in the absence of electric field is observed and studied. Presumably, the deactivation is caused by potassium redistribution within the coating and/or the formation of bonds between potassium atoms and fullerene molecules. Deactivation of this type actually comes to an end in one or two days. The deposition of potassium on fullerene coating results in an appreciable (up to 50%) decrease in U ₁ of the field emitters even after their long-term (about five days) deactivation.     

Deposition of silicon–carbon coatings from the plasma of a non-self-sustained arc discharge with a heated cathode

Amorphous hydrogenated carbon doped with silicon oxide (a-C:H:Si:O), which is referred to as silicon–carbon coatings in this work, consists of thin amorphous films, which are used as commercial solid lubricants due to their higher stability under extreme environmental conditions as compared to amorphous hydrogenated carbon. The deposition of silicon–carbon coatings from the plasma of a non-self-sustained arc discharge with a heated cathode is considered. Silicon–carbon coatings are deposited using polyphenul methylsiloxane as a precursor at a flow rate of 0.05 mL/min in an argon atmosphere at a pressure of 0.1 Pa. A high-frequency power supply is used to apply a high-frequency bias voltage to a substrate during deposition. After deposition, the mechanical properties of the coatings are studied. The maximum hardness of the coating is 20 GPa at a minimum friction coefficient of 0.16 and a wear rate of 1.3 × 10^–5 mm³ N^–1 m^–1. Energy dispersive analysis shows that the coatings contain a significant content of carbon and oxygen (about 80 and 15%, respectively) and a low content of silicon (about 5%).     

Submicrosecond Pulsed Electron Beam Formation in Electron Sources and Accelerators with Plasma Emitters

The most popular methods for submicrosecond electron beam generation and physical processes underlying electron extraction from plasma in plasma emitters are considered. Electron sources and accelerators developed on the basis of plasma emitters allow pulsed beams with currents from tens to 10³ A and current densities of several amperes per square centimeter, pulse durations of hundreds of nanoseconds, and high repetition rates to be generated.     

Operation of activated-fullerene-coated field emitters in technical vacuum

The operation of tungsten tip field emitters coated by activated fullerenes in technical vacuum is studied. Ways of emitter training to provide the self-reproducibility of the coatings and their long service life under intense ion bombardment in wide ranges of pressures, from 2 × 10^?8 to (5–7) × 10^?7 Torr, and emission currents, from (1.5–2.0) to (10–20) μA, are developed.     

Activation of fullerene coatings on field emitters by potassium atom and ion fluxes

The activation of tip field emitters with a fullerene coating by the atomic and ionic fluxes of potassium is studied. The deposition of atomic potassium decreases characteristic voltage U ₁ generating fixed fieldemission current I by a factor of 3.5–4.0. However, field emitters activated by potassium atoms are rapidly deactivated and the resulting decrease in U ₁ after storage in a vacuum does not exceed 25–30%. A stable approximately twofold decrease in the characteristic voltage can be reached if the fullerene coating is exposed to a potassium ion flux. The enhanced efficiency of emitter activation by a potassium ion flux is explained by the formation of KC ₆₀ endohedral and/or C₆₀ K exohedral molecules in the fullerene coating.     

Thermal desorption states of C<Subscript>60</Subscript> fullerene molecules in polymer matrices

Polymer-C₆₀ fullerene composite coatings are studied using thermal desorption mass spectrometry. It is found that thermal desorption spectra of C₆₀ fullerene molecules can exhibit several resolved peaks (at a specified heating rate) corresponding to thermal desorption states. The relative intensity of the thermal desorption peaks depends on the procedure used for preparing the composite coatings, in particular, on the time of sedimentation of the polymer-fullerene suspension. The occurrence of different stages in thermally stimulated desorption of C₆₀ fullerene molecules is explained by the fact that the fullerene molecules can exist in several phase states characterized by different densities and degrees of ordering in the polymer matrix.     

Thermally stimulated desorption of C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerenes from rigid-chain polyimide films

Polyimide-fullerene composite thin coatings are investigated using thermal desorption mass spectrometry in the temperature range 20–800°C. It is found that, at temperatures below the temperature of decom-position of the polymer matrix, thermally stimulated desorption of fullerene molecules is limited by the diffusion of fullerene molecules in the matrix. The diffusion coefficients and activation energies of diffusion of C₆₀ and C₇₀ fullerene molecules are determined from the experimental data on thermally stimulated desorption in the framework of several approaches. It is revealed that the diffusion of C₇₀ molecules in the polyimide matrix is more hindered than the diffusion of C₆₀ molecules in the same matrix.     

Few-bubble luminescence in the acoustic field of a spherical resonator in aqueous solutions of sodium and terbium compounds

Stabilization and the luminescence mode during slight motion around the equilibrium position of a few (two to eight) bubbles in 2–6 mol/L aqueous solutions of NaCl, NaOH, TbCl saturated with argon were achieved in a device for monitoring single-bubble sonoluminescence in a spherical resonator. Examples are presented of this variety of multibubble sonoluminescence illustrating various spatial-spectral distributions of cavitation bubbles, which contain either emitters comprising only the solvent continuum or also metal emitters (Na*, Tb³⁺*). Stabilization of bubbles in the form of closely (0.5–1 mm) located pairs of bubbles is of particular interest, in one of which only the solvent luminesces, and in the other, a metal.     

Formation on field emitters coated with fullerenes of microformations producing ordered emission images

Field emission projector studies of fullerene coatings deposited on tungsten tip field emitters reveal specific ordered patterns in the form of doublets, quadruplets, rings, disks, and other forms in the emitter images. The ways in which these types of ordered emission patterns arise and their relation to C₆₀ microformations have been established. Possible causes of the emergence of the ordered emission images are analyzed on the basis of published data and experimental results obtained. A modification of the model of field emission from the surface of microformations taking into account internal reflection of the electronic waves from the formation boundaries has been proposed.     

Analysis of the composition of Ti-based thin films deposited on silicon by means of self-ion assisted deposition

The composition of Ti-based thin films deposited on silicon using a self-ion assisted deposition (SIAD) method was investigated by utilising the Rutherford backscattering spectrometry technique and RUMP simulation code. The hydrogen affinity of the coatings produced by means of SIAD was investigated using the ¹H(¹⁵N, αγ)¹²C nuclear resonance reaction. The titanium–based films on silicon were found to have a high content of oxygen, carbon, hydrogen and substantial concentration of the substrate. Near 10% H content enrichment was found at the surface of coatings but no hydrogen enrichment at the coating–substrate interfaces was observed.     

Study of hydrogenated AlN as an anti‐reflective coating and for the effective surface passivation of silicon

Stacks of aluminum oxide and silicon nitride are frequently used in silicon photovoltaics. In this Letter, we demonstrate that hydrogenated aluminum nitride can be an alternative to this dual‐layer stack. Deposited on 1 Ω cm p‐type FZ silicon, very low effective surface recombination velocities of 8 cm/s could be reached after firing at 820 °C. This excellent passivation is traced back to a high density of fixed charges at the interface of approximately –1 × 10¹² cm^–2 and a very low interface defect density below 5 × 10¹⁰ eV^–1 cm^–2. Furthermore, spectral ellipsometry measurements reveal that these aluminum nitride layers have ideal optical properties for use as anti‐reflective coatings. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tracing locations of new coating material during spark anodizing of titanium

The growth of anodic coatings on titanium, under sparking conditions, is investigated in tracer experiments, using alkaline silicate and phosphate electrolytes. Coatings are formed sequentially in each electrolyte, with phosphorus and silicon located by energy-dispersive X-ray analysis and glow discharge optical emission spectroscopy. The coatings, containing anatase, rutile and amorphous oxide, with incorporated phosphorus and silicon species, are shown to grow by discrete thickening at sites of dielectric breakdown. New material is found near the metal, within the coating bulk and at the coating surface. Approximately 10–30% of the new material is located near to the coating surface and about 40–60% near to the metal. The findings are attributed to the formation of breakdown channels allowing access of electrolyte species to the inner parts of the coating and to subsequent rapid formation of coating material, under high temperatures, associated with increased local current density, and high pressures, associated with volume constraints on oxide growth and gas generation.     

Effect of bismuth nanolayers on the oriented growth of fullerene C<Subscript>60</Subscript> on an amorphous substrate

The effect of a bismuth sublayer with an effective thickness of 0.5 to 4 nm on the structure of C₆₀ fullerene films grown on amorphous substrates (silicon covered with a natural oxide layer; glass) using the quasi-closed-volume method is studied. An x-ray diffraction study of fullerene films showed that the intensity ratio between the (220) and (111) peaks depends nonmonotonically on the sublayer thickness. In the bismuth sublayer thickness range 0.5–2.0 nm, fullerene films are found to exhibit a growth texture with the 〈110〉 axis; the average crystallite size was ～20 µm. The quality of the texture can be improved by varying the fullerene growth temperature.     

Fullerene–ferrocene dyad linked by rigid bilinkage: synthesis,photophysical properties and application as copper ion sensor

A novel fullerene–ferrocene based donor–bridge–acceptor dyad was synthesized and characterized by elemental analysis, FT‐IR, ¹H NMR, ¹³C NMR and FAB‐MS. The dyad with a bilinker comprising of azomethine and ester group was studied for its photo physical properties using absorption spectra and steady‐state fluorescence spectra as a function of dielectric constant of the medium. Fluorescence spectra of the dyad studied with excitation at 449 nm showed a weak emission at 742 nm, which got weaker on increasing the dielectric constant of the medium, indicating efficient electron transfer from ferrocene to fullerene. By designing a bilinked structure between the two redox moieties, we obtained a chelating structure which was found to coordinate copper ion efficiently and hence found application as a metal ion sensor. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of a fullerene C60 addition on the strength properties of nanocrystalline copper and aluminum under shock-wave loading

The Hugoniot elastic limit and the spall strength of aluminum and copper samples pressed from a mixture of a metallic powder and 2–5 wt % C₆₀ fullerene powder are measured under a shock loading pressure up to 6 GPa and a strain rate of 10⁵ s^?1 by recording and analyzing full wave profiles using a VISAR laser interferometer. It is shown that a 5% C₆₀ fullerene addition to an initial aluminum sample leads to an increase in its Hugoniot elastic limit by an order of magnitude. Mixture copper samples with 2% fullerene also exhibit a multiple increase in the elastic limit as compared to commercial-grade copper. The elastic limits calculated from the wave profiles are 0.82–1.56 GPa for aluminum samples and 1.35–3.46 GPa for copper samples depending on the sample porosity. The spall strength of both aluminum and copper samples with fullerene additions decreases approximately threefold because of the effect of high-hardness fullerene particles, which serve as tensile stress concentrators in a material under dynamic fracture.     

Single-photon emitters in van der Waals materials

Solid-state sources of single-photon emitters are highly desired for scalable quantum photonic applications, such as quantum communication, optical quantum information processing, and metrology. In the past year, great strides have been made in the characterization of single defects in wide-bandgap materials, such as silicon carbide and diamond, as well as single molecules, quantum dots, and carbon nanotubes. More recently, single-photon emitters in layered van der Waals materials attracted tremendous attention, because the two-dimensional(2 D)lattice allows for high photon extraction efficiency and easy integration into photonic circuits. In this review, we discuss recent advances in mastering single-photon emitters in 2 D materials, electrical generation pathways,detuning, and resonator coupling towards use as quantum light sources. Finally, we discuss the remaining challenges and the outlooks for layered material-based quantum photonic sources.